Shifting winter atmospheric teleconnections to the North Pacific reconcile Younger-Dryas and Holocene δ^18O signals

Domain: neuroscience
Published: 2026-02-06
Editorial outcome: major_revision

Abstract
Using Alaskan lake sediment oxygen isotope records (δ18O), which trace the δ18O of precipitation, we establish that abrupt atmospheric shifts occurred during the last deglacial period in the North Pacific-Arctic. The robust lake δ18O chronologies confidently correlate Younger-Dryas (YD) atmospheric adjustments in Alaska with Greenland ice-core records and their seasonal sensitivity are consistent with cooling during winter. In contrast, abrupt δ18O decreases during the late Holocene observed in our records, of similar magnitude as the YD, are best explained by atmospheric modes involving long-distance transport of sub-tropical Pacific moisture. Our sediment cores are among the most reliably dated records yet produced in the circum-Arctic and show that similar decreases in δ18O of winter precipitation during the YD and late Holocene were driven by different atmospheric teleconnections. These results underscore major roles for seasonality and atmospheric patterns in the conceptual understanding of global scale climate oscillations, both past and future.

Introduction
Understanding the geographic extent of reorganizations in atmospheric circulation recognized in the Greenland ice core and other North Atlantic records during stadial and interstadial periods is essential for improving our conceptual models of atmospheric teleconnections with far-reaching impacts on regional climate systems across the globe. However, key uncertainties persist regarding the nature and timing of deglacial climate changes in the North Pacific-Arctic sector, and how they are related to forcing from the North Atlantic. For example, during the Younger Dryas (YD), cooling in Greenland, driven by ice-sheet meltwater discharge and weakened North Atlantic Deep Water (NADW) formation, is expected to have triggered synchronous changes in the North Pacific-Arctic driven by an intensified jet stream and expanded polar front1,2. However, this connection has yet to be confidently demonstrated3. Here, we present precisely dated records on the oxygen isotopes of Alaska precipitation (δ18O p) that are comparable with Greenland ice-core records, which enhances understanding of deglacial and Holocene atmospheric adjustments across the Northern Hemisphere.

We hypothesize that winter cooling during the YD would result in synchronous and abrupt decreases in δ18O p in both the North Atlantic and North Pacific regions due to temperature of condensation-related Rayleigh distillation. In contrast, changes in the δ18O of Alaskan records that do not follow variations observed in the North Atlantic require a different climatic mechanism. Here we explore the idea that different winter atmospheric teleconnections to the North Pacific during two contrasting time intervals (e.g., deglacial and late Holocene) can result in similar decreases in δ18O values in Alaska. We postulate that as ice sheets melted and Alaska’s climate became increasingly maritime, its atmospheric connection to the North Atlantic weakened and became more strongly influenced by the sub-tropical North Pacific as the intensity and frequency of El Niño Southern Oscillation (ENSO) increased in response to orbital precession4–7. Testing our hypotheses of shifts in winter atmospheric teleconnections requires winter sensitive proxies, which are typically underrepresented in proxy records, but are the focus of this study. Our work builds on the strengths of existing records8–13 by improved record chronology, continuity, and temporal resolution provided by thick authigenic carbonate sediment packages within marl lakes in Upper Cook Inlet, that formed within glacial deposits following ice retreat within the Matanuska and Susitna Valley (MatSu; Fig. 1) by ~16.4 ka14 (calibrated kiloyears before present). High rates of lake sediment accumulation mediated by biological productivity were dated by several methods to provide strong age-depth certainty, including radiogenic lead-210 (210Pb), radiocarbon dating of terrestrial macrofossils, and tephrochronology (see Methods and Supplementary Fig. 5 and Supplementary Table 7). The closely sampled bulk carbonate oxygen isotopes (δ18O c) provide high temporal resolution at multi-annual to centennial scales (see Methods and Supplementary Fig. 3 and Supplementary Table 6). The robust bulk sediment carbonate isotope proxy, consistently of authigenic origin (i.e., carbonate formed within lake), records the δ18O of lake water (see Methods and Supplementary Fig. 2 and Supplementary Table 4).

Detailed hydrogeologic studies established that MatSu lakes are sourced by regional groundwater that is dominantly recharged by snowmelt originating as winter precipitation in the surrounding mountains of the ~1500 km2 area15 (Fig. 1). Accordingly, this baseline groundwater δ18O signal is a proxy for winter δ18O p that is transmitted to all MatSu lakes, which in turn have different open and closed hydrologic controls that generate lake-water-δ18O variations more sensitive to winter or summer conditions16 (see Methods and Supplementary Fig. 1 and Supplementary Table 1). We selected hydrologically open and closed lakes for our sediment δ18O reconstruction to provide unique perspectives on changes in seasonality through time. Our open study lakes, April Fools Lake and Neklason Lake, have records of lake-water δ18O sensitive to winter δ18O p. Their combined sediment δ18O records overlap with the modern range of δ18O p between −15 to −19‰17 (Fig. 2c, see Methods and Supplementary Fig. 7). Our closed study lake, Finger Lake, has lake-water δ18O sensitive to summer evaporation resulting from long lake-water-residence times that lead to 18O-enrichment, overprinting the winter δ18O p 16. Thus, the higher δ18O c values in Finger Lake, between −10 to −15‰, relative to our open lake records, reflect summer temperature and aridity conditions that vary independently from winter17.

The regional source of precipitation and prevailing winds in south-central Alaska today is southerly (~75%) modulated by the Aleutian Low (AL) semi-permanent pressure system that intensifies during winter. Surrounding mountain ranges (>4000 m elevation) control spatial precipitation patterns by orographic uplift18 and coastal topographic barriers orient upper-level geostrophic flow; a process that was maintained by continental ice sheet barriers during past glacial periods19,20. Observations have shown that relatively low δ18O p values are linked to stronger frontal boundary interactions, which enhance topographic rainout and mountain snowfall21. Strong frontal boundaries are most commonly driven by meridional flow patterns that transport warm moist air from lower latitudes in the Pacific Ocean resulting in long-distance rainout during vapor transport. Meridional patterns are associated with an intensified or eastward positioned AL that facilitates northward moisture transport during Pacific climate modes, such as the positive modes of the Pacific North America pattern (+PNA), the Pacific Decadal Oscillation (+PDO), and the El Niño Southern Oscillation (El Niño)22,23. In contrast, relatively high δ18O p values are linked with zonal flow patterns and negative Pacific modes (-PNA, -PDO, and La Niña). Zonal patterns are characterized by a weakened or westward positioned AL wherein moisture is more frequently derived from cooler northern ocean sources, including the Bering Sea. Less rainout across shorter vapor transport distances combined with cooler air masses also results in less mountain snowfall16.

Temporal changes in contemporary δ18O p in southern Alaska reflect strong relationships with winter atmospheric circulation patterns, weakly related to average temperature16,17,24. These observations are confirmed in our records by an abrupt δ18O c decrease at April Fools Lake during the positive PDO shift during the winter of 1976–77 which contributed to winter warming and increased precipitation in south-central Alaska (Fig. 2)25,26. At our closed lake, a strong summer evaporation signal resulted in a muted δ18O c response to the atmospheric circulation shift16. Previous proxy studies over the Holocene of North Pacific δ18O p support atmospheric circulation controls and show weak correlations with instrumental temperature records or paleo-temperature reconstructions27–29. For example, higher δ18O p in the Mt. Logan ice core during the Little Ice Age compared to the 20th century would suggest warmer conditions if driven by temperature, which is inconsistent with the cold period13. A more likely explanation for higher δ18O p values is a northward shift in moisture source and shorter vapor transport pathways30.

In this study, we identify similar winter δ18O p anomalies in the North Pacific region during the Younger Dryas and the late Holocene in spite of different global boundary conditions. To reconcile these observations we attribute a shift in dominant winter atmospheric teleconnections from the North Atlantic to the sub-tropical Pacific. This reorganization likely reflects changes in large-scale circulation patterns, including the Aleutian Low and polar jet, which modulate moisture transport into the North Pacific. By providing continuous records from the last glaciation to present for the North Pacific-Arctic region, our Alaskan lake sediment δ18O data allow for confident chronological assessment of seasonal climatic mechanisms with implications for understanding the sensitivity of the North Pacific to shifts in ocean-atmosphere dynamics and global linkages.

Results
North Atlantic controls on Alaska δ18O p during the Younger-Dryas
During regional deglaciation, our lake sediment records indicate early lake development within the Bølling-Allerød (BA) chronozone and intermediate δ18O c values with respect to their range over the full record (Fig. 2). Beginning ~12.8 ka, a sharp decrease in δ18O c is synchronous with onset of the YD chronozone documented in Greenland ice cores within the uncertainty of the lake age models (see Supplementary Fig. 5 and Supplementary Table 6). During the YD chronozone, Alaska δ18O c values were continuously at the lowest levels of the deglacial transition, followed by an abrupt increase of +2‰ at ~11.7 ka. This simultaneous δ18O variation in sediment cores from Alaskan lakes and Greenland ice substantiates an atmospheric temperature teleconnection between Alaska with the North Atlantic driven by variations in Atlantic Meridional Overturning Circulation (AMOC).

A temperature-based interpretation of the decrease of δ18O p in Alaska during this period is supported by (1) global boundary conditions that shifted the polar jet stream southward31; (2) atmospheric circulation characterized by zonal flow over colder Gulf of Alaska sea surface temperatures32,33, expanded Bering Sea ice cover34 and a weakened AL35; and (3) reconstructions indicating dampened ENSO activity during deglaciation by contracted sub-tropical zonal sea surface temperature gradients4. We estimate air temperature declines in Alaska during the YD ranged from ~4 to 8 °C based on the combined effects of δ18O temperature fractionation effects during water vapor condensation and by lake calcite formation11 and considering the influence of sea surface temperature variations on the δ18O value of moisture source vapor36. In summary, these factors at this time would allow cooling in the North Atlantic to result in atmospheric cooling throughout the circum-Arctic.

Because lakes in the MatSu are maintained by groundwater recharged by snowmelt (see Methods and Supplementary Fig. 1), it is most likely that the decreases in δ18O p during the YD reflect colder winter temperatures8,9. In contrast, summer-sensitive proxy evidence from our lakes builds upon existing studies that indicate relatively warm YD summer conditions37–40, or inconsistent temperature trends lacking abrupt changes associated with the YD12. Evidence for warm summer conditions at our lakes during the YD includes high biological productivity and continuation of shallow water marl accumulation, minor changes in terrestrial vegetation, and evaporative enrichment of lake water δ18O (see Supplementary Figs. 3 and 6). The best explanation to account for mild and relatively dry summer indicators, and the negative δ18O excursions in both open and closed lakes during the YD, is significantly colder winters and relatively minor changes in summer41.

Cooling during the YD is not obvious in most proxy records of ecosystem change, or in temperature sensitive glaciers and ground ice in the North Pacific-Arctic sector3. Rather, we suggest that seasonally cold temperatures during winter in Alaska occurred during the YD, similar in timing and structure with those in Greenland, without strongly affecting proxies sensitive to summer conditions, analogous to seasonally sensitive records from the North Atlantic region that also show winter cooling and relatively warm summers41–43. Enhanced seasonality during the deglacial period may have resulted from precession driven summer warming, which accelerated ice-sheet meltwater discharge and weakened NADW, which in turn favored sea-ice growth and greater continentality, and subsequently colder winters43.

The early Holocene atmospheric transition
During and following the YD termination, ca. 11.7 to 11.5 ka, winter δ18O p and summer evaporation reach maximum values, suggesting a brief period of unprecedented warming during summer and winter (Figs. 3 and 4). Higher δ18O p values could also occur due to an increase in rainfall relative to snowfall and/or increased Bering Sea moisture sources related to melting sea ice, which are both also consistent with winter warming. Subsequently, as Bering Sea sea-ice coverage declined and Alaska’s shoreline moved inland with rising sea levels, the resulting loss of continental area led to a more maritime climate which is documented by rising lake-levels during this period44,45. Climate models indicate that seasonal temperatures were sensitive to these changes in Alaska, with cooler summers in coastal areas and warmer winters in the interior that would have shifted the seasonal precipitation balance towards rainfall46. After ~11 ka, decreases in winter δ18O p (Fig. 3a) are interpreted to reflect increased contributions from southerly moisture sources, possibly in response to Bering Strait flooding47. Opening of the Bering Strait led to increased freshwater export from the Arctic Ocean into the North Atlantic known to weaken AMOC48 as tropical Pacific Ocean temperatures were rising4 (Fig. 2) and the AL was strengthening46, which would have favored northward moisture transport. As discussed previously, this leads to lower δ18O p values in Alaska16,17.

These hydrologic changes in Alaska promoted thermokarst49, which increased intra-permafrost groundwater flow and hydrologic connectivity50,51 and accelerated peatland expansion52,53. As respiration of organic matter in soils increases pCO2 and lowers the δ13C values of dissolved inorganic carbon in groundwater recharge, changes in this input to lakes can be recorded by the δ13C of sedimentary organic matter. Thus, increasing surface runoff and groundwater recharge flux to lakes will impact carbon pools and their isotopic signatures by resulting in decreases in the δ13C of aquatic plants and sedimentary organic matter (see Methods and Supplementary Figs. 8–10).

The April Fools Lake organic δ13C record shows high values during the YD, with a significant decrease at the end of the YD-early Holocene transition (Fig. 3b). Observations from additional lake records across interior Alaska show similar trends during this period (Figs. 1, 3c and Supplementary Fig. 8). Significantly, carbon to nitrogen ratios of organic matter in these lakes remained relatively low and invariant, and organic matter content varied little, indicating predominantly aquatic plant carbon sources and little change in productivity that could otherwise impact δ13C (Supplementary Fig. 9). This data supports the idea that precipitation increased regionally after the end of the YD, resulting in higher groundwater fluxes through newly forming permafrost-affected soils54, creating similar patterns of δ13C variations among a wide variety of lakes. During the YD, elevated δ13C suggests drier conditions consistent with greater summer evaporation that is documented by elevated Finger Lake δ18O c (Fig. 4), though moisture remained sufficient to support lake formation. Declining δ13C during the early Holocene corresponds with moisture rising to levels higher than previously recorded. In contrast, some later Holocene δ13C differences among the lakes reflect unique lake development trajectories related to bathymetric setting during later stages of lake ontogeny and terrestrial vegetation change (see Supplementary Fig. 10).

North Pacific controls on Alaska δ18O p during the Holocene
After the early Holocene transition, our records indicate relatively stable winter δ18O p and reduced summer evaporation effects, a previously recognized trend associated with AL intensification and increased supply of moisture from the subtropical Pacific Ocean55 (Fig. 4). The period from ~10 to 4 ka was wetter than previously recorded and experienced low magnitude δ18O variance (±0.5‰) around mean values similar to modern. These controls on δ18O p in Alaska during this period contrasts with that in the Greenland record, which is interpreted to reflect temperature sensitivity to AMOC56. Also, unlike Greenland, Alaskan lake δ18O records show no anomalous climate signals at 8.2 ka in line with weakened connections to North Atlantic forcing (Fig. 4), or at 4.2 ka.

By the late Holocene, both the magnitude, and absolute decreases of winter δ18O p variations in our records intensified, with some events after ~2 ka having values more negative than recorded during the YD (Fig. 4b). This winter trend is best explained by intensified meridional circulation patterns (in contrast to zonal flow) driven by ENSO/PDO6,57, the frequency of which increased during the late Holocene (Fig. 2d) and as discussed results in significant 18O-depletion16. This trend is also consistent with increased variance and high magnitude negative δ18O excursions found in other records across the margin of western North America4–7,58–62. The long-term trend in δ18O in summer-sensitive Finger Lake, also shows higher magnitude variations and the lowest δ18O values of the entire record (Fig. 4a). However, the timing of many of the multi-decadal scale variations do not appear to coincide, which likely illustrates how open and closed lakes reflect different seasons of the same climate. Critically, summer climate reflects circulation patterns when the AL is not the dominant control and therefore differs from winter16,17,21.

The significance of winter climate shifts
Wintertime circulation patterns are well recognized in driving basin-wide patterns in land and ocean temperatures and precipitation, ocean productivity, and marine fish abundance63,64. This long-term context helps frame more recent disruptions of highly variable atmosphere-ocean systems that clearly undergoes shifts in drivers through time65,66. For example, our records document greater extremes in pre-historic baselines that help evaluate recent marine heat waves and associated sea bird and fish die-offs67,68. In the terrestrial realm, independent evaluations of long-term baselines in regional carbon dynamics, including biogeochemical changes associated with permafrost and hydrologic connectivity, may be compared in light of the seasonally complex and highly variable hydroclimatic history provided here69,70.

Our Alaskan lake δ18O records, which provide seasonal information with solid chronological control, verify the existence of a YD signal transmitted to Alaska by the atmospheric during winter. This is a particularly important discovery in the North Pacific-Arctic as identifying this event and determining its linkage with the North Atlantic has previously been difficult, creating uncertainty about the interplay of Atlantic and Pacific teleconnections through time. We confirm severe YD winter cooling with modest reductions in moisture and mild summer conditions. This accounts for the absence of glacial moraine evidence for advances during the YD chron37 and conflicting proxy records that largely reflect summer conditions in terrestrial (i.e., pollen), and marine environments (e.g., Gulf of Alaska alkenones which also reflect warm seasons)71.

Following deglaciation, major sea-level rise, and the opening of the Bering Strait, we document a weakened North Atlantic teleconnection and greater control originating from North Pacific subtropics, which continues to have global influence today. This shift may represent the effects of changing orbital precession on expanding latitudinal ENSO gradients5, which are best assessed by winter proxy records within the North Pacific region and are currently scarce72. Moving forward, thorough examinations of shifting global climate influences over time will clearly be strengthened by well-dated, high-resolution terrestrial paleoclimatic data sensitive to winter.

Our records illustrate the role of seasonality and circulation patterns with regard to understanding abrupt climate change and isotope systematics. The data show that similar decreases in lake sediment records of winter precipitation δ18O can be forced by different mechanisms. Such results provide constraints for isotope enabled climate model simulations that commonly miss the dual role of seasonal moisture and temperature in high latitudes73. The shifting dominance between Atlantic and Pacific influences on Arctic environments identified here emphasize the need to better represent Pacific dynamics in climate models, particularly given their broad hydrologic and ecological impacts. Our data documents the major roles of seasonality and shifting atmospheric patterns into our conceptual understanding of linkages between regional and global scale climate oscillations and rapid climate change, past, ongoing, and future.

Methods
Study lakes, hydrology and climate
All study lakes are biologically productive, fed by alkaline, calcium-rich groundwater. This contributes to the formation of shoreline marl benches, which are composed of well-preserved authigenic carbonate sediments (see Supplementary Table 1 and Supplementary Table 2). April Fools Lake (informal name: 61.49°N, 150.0°W, 41 m a.s.l.) is our western-most study lake, near the terminus of the regional groundwater flow path15. The lake is maintained by several artesian springs along the northeast shoreline and has a surface outlet. Neklason Lake (61.63°N, 149.3°W, 128 m a.s.l.) and Finger Lake (61.60°N, 149.3°W, 103 m a.s.l) are to the east, nearer to the upland groundwater recharge area. Neklason Lake has a surface outlet and is maintained by a surface stream from an upstream lake sourced by springs. Finger Lake has no surface inflow or outflow and is maintained by groundwater.

We developed a lake water isotope dataset for April Fools Lake and compiled existing water isotope data for the MatSu Valley including precipitation, springs, groundwater, Neklason Lake, Finger Lake, and other lakes74 (see Supplementary Fig. 1). The data show variations in the δ18O of groundwater by 2–3‰ that reflect an integrated multi-year δ18O signal of precipitation, which varies seasonally up to ~9‰15,17. Regional trends in lake water δ2H and δ18O define a local evaporation line (LEL) with a slope of ~4. Hydrologically open lakes like April Fools Lake and Neklason Lake have relatively low δ2H and δ18O values that indicate they are good representatives of regional groundwater δ18O values and thus δ18O of precipitation. Hydrologically closed lakes, such as Finger Lake, have relatively high δ2H and δ18O values due to summer evaporation effects which are clearly distinguishable from δ18O of precipitation and groundwater15,17.

The climate of the MatSu Valley is a transition zone between maritime and continental climates with an average seasonal temperature range between −12 and 21 °C. Average total precipitation is 38.8 cm in the valley increasing with elevation to ~90 cm in the local headwaters of the Talkeetna Mountain foothills (~2000 m)15 and to substantially higher amounts at elevations of ~4000 m. Within the contributing alpine watersheds that recharge the groundwater aquifer, the majority of annual precipitation is snowfall between October and April. This results in groundwater fed MatSu lake-water δ18O values strongly weighted towards controls by winter atmospheric circulation, moisture origin, and transport pathways17, which proxy evidence also show during the Holocene16.

Lake sediment lithology and carbonate isotopes
Sediment cores were retrieved from lake ice, or a securely anchored floating platform, with a modified Livingstone piston corer (Supplementary Table 2). Cores with an undisturbed sediment water interface were obtained using a customized polycarbonate tube fit with a piston and extruded in the field at 0.5-cm increments. At the coring sites of our study lakes, the water environments are clear and quiet (Secchi disk depths >3 m), which promotes the precipitation of calcium carbonate within surface waters by photosynthetical alterations of bicarbonate equilibrium (e.g., bio-induced carbonate precipitation)75. The geomorphic and hydrologic configurations of the small low-relief watersheds (<50 m elevation) within wetlands strongly limits watershed transport of allochthonous (i.e., detrital) carbonate sediment. Regional aeolian loess is mainly composed of quartz, plagioclase, mica, amphibole and chlorite, and is low in carbonates76.

We developed a suite of sedimentary analyses that document changes in paleolimnology that help to evaluate controls on the sediment carbonate isotope data. They include dry bulk density, magnetic susceptibility, and percent organic matter and carbonate by loss on ignition (see Supplementary methods and Supplementary Fig. 3). The similar lithology for all of the cores overlying basal deglacial deposits is dominated by two authigenic components, olive to light gray bedded marl or dark brown marly gyttja to green brown gyttja. The only exceptions are two volcanic tephra that are easily identified, either visually by abrupt changes in color, density and texture and by sharp increase in magnetic susceptibility.

All cores have similar light and dark sediment bedded structure which reflect changes in the relative proportions of preserved organic carbon and calcium carbonate. The residual mineral content is typically <10% of sediment weight and comprised of mixtures of biogenic silica and non-carbonate minerals. The carbonate contents of shallow water sediments from April Fools Lake and Neklason Lake is often high (~80 to 90% carbonate; see Supplementary Fig. 3a and Supplementary Fig. 3c and d) and dominated by micrite. Finger Lake shallow water sediments are comprised of pure micrite in the basal unit, marly to highly organic gyttja in the middle unit, and marly gyttja in upper unit (see Supplementary Fig. 3e). April Fools Lake sediments from water depths below the thermocline are predominantly composed of marly gyttja and gyttja due to reduced carbonate preservation caused by dissolution within the water column; our analyses of a core from this region (A15) focused on organic carbon and nitrogen (see Fig. 3 and Supplementary Fig 3b).

An authigenic origin of the bulk sediment carbonates was verified by good agreement between surface sediment oxygen isotope composition and that calculated for isotopic equilibrium between carbonate and lake water (see Supplementary methods and Supplementary Table 4 and Supplementary Fig. 4). Samples for carbonate isotope analyses were taken at contiguous 0.5-to-1-cm sample increments, although in some core sections carbonate contents were found to be too low for analysis (see Supplementary Fig. 3). To facilitate separation of bulk authigenic carbonates for isotope analyses from other larger carbonate particles of biological origin (e.g., ostracode valves, gastropods, and bivalve shells and their fragments) and allochthonous processes (i.e., terrestrial plant macrofossils), samples were wet sieved through nested screens (250, 125, 63, 32 µm), collected separately and freeze-dried. The finest fraction (<32 µm) was analyzed for most samples. For a few samples (<1%), the <32 µm size was combined with the 32 to 63 µm sizes to obtain sufficient mass for analysis because insignificant δ18O difference was found among smaller grain sizes (see Supplementary methods and Supplementary Table 3).

Age data and age-depth models
Sediment core age data are based on 210Pb analyses, two prominent tephras identified as sourced from Mount Hayes, and AMS 14C measurements on macrofossils of terrestrial origin (see Supplementary methods and Supplementary Figs. 3–5 and Supplementary Tables 5–7). Bayesian age-depth modeling provide average 95% certainty bounds of <±200 years among all of the records (see Supplementary Table 6). Carbonate sedimentation rates provide sub-decadal to multi-decadal resolution from present until ~8 ka and multi-decadal to centennial scale resolution between ~8 and 14.5 ka. For the δ13C records in Fig. 3, we employed the available age models for Arolik Lake and Dune Lake. The existing radiocarbon-based age models for Birch Lake, Little Harding Lake, and Eightmile Lake were refined with additional radiocarbon ages and recalibrated using the IntCal20 radiocarbon calibration curve.

The April Fools Lake core A15 δ18O chronology is based on 210Pb, two tephra layers, and 5 radiocarbon ages of terrestrial macrofossils (see Supplementary methods and Supplementary Fig. 3a and Supplementary Fig. 5a). The Neklason Lake core B16 chronology is based on 18 radiocarbon ages of terrestrial macrofossils (see Supplementary Figs. 3c and 5b). A second core from Neklason (A16) reproduced similar δ18O variations across the YD in the lower section (see Supplementary Fig. 5b). To optimize the high-resolution portions of the April Fools Lake and Neklason Lake records, their δ18O stratigraphies were merged into a single high-resolution stable isotope record (see Supplementary Fig. 7). The independent chronologies were spliced together at 7.6 ka with no scaling or adjustment of the isotope scales and verified by the stratigraphically ordered ages. Two cores obtained from Finger Lake were stratigraphically correlated to develop a composite stratigraphy (core A16/23) and the chronology is based on 210Pb, two tephra layers and 22 radiocarbon ages of terrestrial material (see Supplementary Figs. 3e and 5c). The Bayesian age-depth models for each of our lake δ18O record shows correlation during the YD to Greenland within 95% confidence limits.

Lake sediment carbon and nitrogen of organic matter
The percent organic content and its C/N ratios can be used to assess factors that may influence the δ13C of organic matter in lake sediments internal and external to lakes (see Supplementary methods). The records indicate low and relatively invariable C/N between 9 and 13 ka, suggesting an aquatic source material throughout the period (see Supplementary Fig. 8 and Supplementary Fig. 9). Minor variations in organic carbon content suggests limited changes in productivity across the interval. If driven by lake productivity, the sediment decreases in δ13C would infer a chronic productivity decline, which is not observed in the records. Atmospheric pCO2 and its δ13C were relatively constant during this period, suggestion minimal influence from atmospheric exchange processes. While water temperature affects the solubility of CO2, if the observed δ13C decreases were due to temperature change, this would imply a significant decline in temperature during this period, which is not supported by paleoenvironmental data. Thus, we conclude that the δ13C decrease during the interval between 9 and 13 ka most likely reflects a major regional increase in hydrologic input to lakes50.

Data availability
The data generated by this study have been deposited in the U.S. National Oceanic and Atmospheric Administration (NOAA) National Center for Environmental Information (NCEI) under the accession code https://doi.org/10.25921/jvs7-8f93.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "In this manuscript, the authors present high-resolution oxygen isotope records from several lakes in Alaska to investigate climate oscillations during the last deglaciation and compare with the late Holocene. They show that the YD mostly represents winter cooling and is closely tied to Atlantic Ocean influences, supporting the existence of strong connections between North Pacific and North Atlantic during the last deglaciation. On the other hand, rapid climate oscillations during the late Holocene were mostly triggered by Pacific Ocean influences, showing no evidence of influence from North Atlantic. They also discuss the implications of the study for recent and ongoing climate changes in North Pacific region. This is an important study addressing a long-standing paleoclimate question, not only about the connection between North Atlantic and North Pacific, but also the variable nature of this connection. The isotope records presented are valuable and high quality. The interpretations are balanced and robust, supported by the data and arguments. The study design of using lakes with contrasting hydrology and the interpretations of organic d13C records for groundwater flux and moisture conditions are creative and novel. The manuscript is well organized. My only major comment is about presentations of dating controls. It is well known that lacustrine sediment records are very difficult to data from lakes in Alaska and Arctic in general, as suitable terrestrial plant materials are hard to find. The authors should be commended for such a large set of radiocarbon dates from these study lakes as presented in SI Table 1. That being said, dating and chronology are critical for the interpretations and conclusions presented in this study, so I suggest that the authors show explicitly the dating control points on the records shown in figures (comment below as well) and discuss any uncertainties accordingly. That way, readers would have a visual appreciation of the robustness of chronology. Specific comments: Abstract: mention lake records to make the abstract more informative L64: change “guided” to “modulated”? L82-83: Refer Fig. 2b for Neklason Lake record, and d18O from April Fools Lake is not in Fig. 2, but in Fig. 4. Also, should refer Fig. 2a after mentioning Finger Lake here. L89: age models: need cite Suppl Figures? L93: Change superscript 15 to “ref. 15” L96: “from ~4 to 8 C”. Negative signs have been taken care of by “decline” in the sentence, so not needed here. L95-97: unclear. Temperature decline is inferred/estimated from d18O change based on calcite-water fractionation, but what is the role of SS temperature variation here. The former was used for temperature inference/estimate, while the latter is for interpretations. Do I miss anything here? Clarity. L98: perhaps compare d18O values of winter precipitation/groundwater at the sites and lake-water d18O values calculated from calcite d18O measurements using calcite-water d18O fractionation factor L101: change to “…sensitivity; however, ….” L111-115: add dating control points near curves on figures to support/refute the YD timing discussion here L115-116: good point! The fact of calcite precipitation suggests that summer water temperature is high enough. L121: “meteoric precipitation” to avoid possible confusion with calcite precipitation? L134-143: this paragraph needs to refer to Fig. 3, perhaps different panels according to various descriptions, including to April Fools Lake (Fig. 3b) and synthesis records (Fig. 3c). That would greatly increase clarity and readability. L155-157: refer Fig. 3 for MWP mention L171-172: Be mindful here. Finger and especially Neklason records have different sampling resolution, so potentially artifact for variability/magnitude. But indeed, April Fools record is a strong proof that variability/magnitude shift around 2 ka. L180-183: very good statements/examples about implications of this study. Well done. Figure 2: add dating control points on the figure, perhaps on the top with different colors (such as downward triangles) for Finger and Neklason records, even for composite records. Fig. 2c: vertical axis label: change to superscript in m2 L235: change to “Greenland ice-core” L244: Fig. 3 caption: indicate the number of organic d13C records (n= )? L251: a stray bracket “)” L258-259: Livingstone corer can hardly recover sediment-water interface. Either you use a plastic piston corer, or delete the mention as it is not essential for the study. L260: we use “endogenic” to describe carbonate, not d18Ocarbonate, right? rephrase. L290: an extra “”” Supplementary Information: L52, 59, 67: Bayesian SI Fig. 3b. vertical axis label “d13C” SI Fig. 4: n=6 for d13C records need to mention in the main text/figure SI Figs. 5 and 6 are apparently not mentioned in the text, It would be good to do so, when describing the nature/source of organic matter for d13C interpretations. SI Table 1: 3rd column heading: 14C Date (not age here, but “Calibrated Age”) 4th column heading: “…Date (14C yr BP)” , not “years” L116: “informal name”. Hopefully next time when the lake was cored again on July 4th, it wont be named “Independence Lake”:)) L120: “at two locations” L292: why don’t make it a formal SI Table and formatted as such? The table heading needs proof read, as they are incomplete/inaccurate: such as “Horizons dated”, basal age need “Cal yr BP”? Sampling resolution: “cm” can be moved to heading (should cm be converted to years, as you have age model already?) Reviewed by Professor Zicheng Yu", "reviewer_2": "Review on Anderson et al. submissions to Nature Communications This paper presents new isotope results for lakes in Alaska that span the Younger Dryas to Late Holocene, providing interesting high-resolution records that are presented nicely in the figures and may eventually advance our knowledge about the Pacific-Atlantic/Arctic teleconnections. As detailed below, while the topic and dataset are promising, the manuscript requires a substantial revision and reorganization to clarify its framing, improve methodological transparency, and provide a more balanced interpretation of the results. 1. General Comments 1) Chronology and lake reservoir corrections The age-depth model is central to the paper’s conclusions. However, it lacks sufficient justification and statistical rigor during chronology establishments. I do agree with the idea using the tephra layers with absolute dates to correct the lake reservoir effects. However, I also believe that more details are needed for better clarity: a. How the tephrochronology was established for those cores? The authors claim that the tephra correlation is established “Based on similarities” (Line 217 in SI). However, it’s not very clear to the readers what does “similarities” represent. Have you run the geochemical analysis on tephra shards? Which is the routine way for tephra layer correlations. I would suggest the authors provide more robust information for tephrochronology correlation, either other evidence to clearly show the “similarity” or geochemical analyses results on tephra shards. This will directly influence the reliability of lake reservoir effects estimation and following age-depth modelling for lake April Fools. b. Reasons for the rejection of some radiocarbon dates should be given or detailed. This study presents a massive amount of radiocarbon dating on those cores (which is good) but they also rejected some of those radiocarbon dates but give very little discussion why they did this. Taking core April Fools A15 as an example, the authors rejected more than half of the radiocarbon dates (including the lake reservoir corrected aquatic herb-based dates), but the reason were not given/detailed. 2) On the interpretations of stable oxygen isotope (δ18O) of the carbonates. a. Why is your proposed driver the most likely? Lake carbonates δ18O signals are influenced by multiple factors, including temperature, evaporation, seasonality of temperature/precipitation, and hydrological conditions. While the authors try to classify these three lakes into two groups, namely Precipitation-type and Moisture-type (Lines 53-62), to simplify the interpretation of δ18O signals, the manuscript does not convincingly justify why those particular factors are the dominant control as claimed (even without reference supporting their classification)? b. Problem with mixing carbonate types. The manuscript does not clarify the type of carbonates being analysed. From the method section, it seems that the fine fraction (<32 μm) was used for isotopic works. However, this fine fraction seems to be a mixture to me, and this carbonate source ambiguity raises concerns about the geochemical integrity of the proxy signal. For example, what is the proportion of biogenic, inorganic, or even detrital carbonate in the finest fraction (<32 μm)? Are there sedimentary or geochemical indicators that confirm the origin of the carbonates? c. There is currently no discussion of possible isotopic offsets between different carbonate fractions. This is a crucial omission, as differences between, for example, biologically precipitated carbonate and inorganic calcite can introduce systematic biases. Is there any isotopic offset between different grain-sized fractions, between fractions <32 μm and 32-63 μm? Change in the carbonate source can influence the isotopic signals of the carbonates, which is independent of climate change. I would recommend: i. Consider running modern calibration studies on modern water or carbonates samples to enhance the interpretation of the isotopic signals of carbonates (e.g., comparing δ18O of precipitation, lake water, and carbonates with climate parameters). ii. If only bulk carbonates were analysed, the potential impact of this choice on the paleoclimate interpretation should be clearly discussed and acknowledged as a limitation. 3) On the interpretations of bulk organic stable carbon isotope (δ13Corg) The authors interpret the δ13C values of bulk organic matter primarily as a proxy for precipitation variability. However, this interpretation appears overstated and does not adequately consider alternative influences. The C/N ratios reported (generally <15) suggest that the primary source of lake organic matter is aquatic algae. This implies that δ13C variations likely reflect lake-internal productivity processes rather than external hydrological inputs, at least not only external processes. Aquatic algae assimilate dissolved CO2, and the isotopic signature of that carbon pool is influenced by lake water pCO2, which itself is affected by temperature, biological activity, and CO2 exchange with the atmosphere. These internal carbon cycle dynamics can significantly modulate the δ13C signal, making it problematic to directly attribute isotopic shifts to precipitation changes alone. In its current form, the manuscript risks overinterpreting δ13C as a direct climate signal, and I recommend the authors reconsider this conclusion and broaden their interpretive framework. 4) Mismatch between the paper's stated goals and its actual contributions. While the manuscript presents interesting datasets from multiple lake records, I find that it ultimately does not achieve the stated goals outlined in the introduction or title. The authors claim to resolve key questions about climate connections between the Pacific and Arctic/Atlantic, yet the evidence presented-particularly regarding the δ13C and δ18O interpretations —remains ambiguous and open to alternative explanations that are not adequately explored. This ambiguity in the climatic significance of the proxy signals, combined with uneven methodological transparency (e.g., tephrochronology, lake reservoir corrections, unseparated carbonate fractions), undermines the strength of the conclusions. As a result, the study does not convincingly advance our understanding of teleconnections between Pacific and Arctic/Atlantic in the way it aspires to. More supporting evidence is needed to back up that the lakes reflect winter conditions (references are not given in several places), and the authors often argue that changes reflect temperature, without explaining why precipitation source and atmospheric circulation is discounted. Furthermore, the lake records show very different variations during the late Holocene, but rather than acknowledge this and explain why this might be (and give a reasonable explanation of why they still have a climate signal) the authors discuss the high variability as being significant. Finally, at some points in the paper the reader is left behind because the links between ideas are not explained fully. In parts the text requires reorganisation and rewriting, as comparisons with other records or supporting evidence is spread over several paragraphs. 2. Moderate comments Line 53-62 – there is just one reference provided for the interpretations in this paragraph, do the interpretations all come from here? Are there modern observations or data to support this? References or data are needed particularly to support the interpretation of these being open/closed basins and the water residence times, which are the basis for the interpretation about seasonality. Line 67-68 – ‘Contemporary 18O precipitation reflects seasonal air temperatures and shifting moisture sources in addition to topographic rain-out effects’. This sentence sums up some of my concerns later in the paper where changes in the isotopic records are interpreted in certain ways, such as temperature, without considering the other possible causes given here. Line 77 – ‘resolving past seasonal changes’. In the next section you explain why the lakes reflect winter changes but that is not explained well here. I think add to the end of this section more detail and references supporting how you know it reflects winter season changes. Line 81-106 – These two paragraphs could be reorganised – it is quite confusing currently having comparisons with existing records spread over two paragraphs, and the statement about the YD being a winter phenomenon here only makes sense with the evidence shown in the following paragraph Line 98-100 – ‘Our YD delta 18O carbonate records largely reflect winter season cooling’. How do you know it reflects cooling, could winter season circulation changes also have had an effect? Line 102 – ‘Our new data substantiate that the YD in Alaska was most sensitive to wintertime cooling,’ The phrasing of this could be improved as currently the YD is sensitive, rather than the YD being a time period and the climate or winter season climate being sensitive. The references given later for the YD summer being warm should also be put here (currently down at line 112) as should the evidence from the lakes themselves (high productivity and marl accumulation) currently at line 115. This would strengthen the argument that the record is reflecting the winter rather than summer. Consider also my point for line 98 about the interpretation of this as cooling rather than atmospheric circulation, how do you know this? Line 126-129 – references are needed here to support this interpretation Line 143 - I am not sure if moisture shifts is the right term here for what you describe – a shift would suggest to me a change in the distribution of moisture across the area (so maybe some areas having more and others less). But as they are all changing together, are they not just experiencing enhanced moisture? Line 146-148 – ‘both lake types indicate the warmest year-round temperatures and possibly the greatest aridity of the records’. In the Main section above when describing the causes of oxygen isotope changes the atmospheric circulation paths are described – how do you know therefore that the oxygen isotope changes are due to temperature changes and not changes in atmospheric circulation? Both types of lake are influenced by the precipitation, so this seems more likely to be causing shared changes? Line 148 – ‘However, with winter experiencing the most significant warming, high delta 18O…’ Is this based on the cold YD temperatures? How do you know this? Line 146-159 – In this paragraph I feel like a few steps are missed in the explanation – I think you explicitly need to mention that it is thought that freshwater export may have weakened the AMOC (if this is what the references here say) and say how that would have caused warming/zonal circulation in Alaska. And was it the Bering Strait flooding or AMOC changes that you think caused the changes in Alaska? If you don’t know say more clearly that there are a few potential explanations, or different causes at different times (as suggested by figure 3). Line 163-164 – ‘This contrasts with Greenland, which experienced continuous temperature sensitivity to AMOC’. A reference is needed for this. Paragraph starting 174 – here you change the interpretation from oxygen isotope variations being caused by temperature (during the deglacial) to atmospheric circulation. This interpretation is given very certainly, but without many references or explanation of why this change would occur. Furthermore, why are the records all showing different patterns if they reflect atmospheric circulation that would be the same across the area? Line 180 – ‘For example, our records document greater extremes in pre-historic baselines that help evaluate recent marine heat waves and associated sea bird, and fish die-offs.’ This is a rather general statement – do you mean greater extremes than the 20th century variations? Greater using which variable? If you are able to say this then it should be supported by an example of how your results can be used to evaluate these impacts, or at least how modern observations of oxygen isotope values compare with the late Holocene range. Line 197-199 – the links with precession and global changes should probably be introduced before the conclusion section. Without more explanation I don’t understand what is meant by this sentence, or how you have come to this conclusion. This is also discussing the late Holocene changes, which as I mention above are not consistent between your records, which I think is problematic for then making conclusions about the late Holocene climate. Line 206-207 – ‘records show Late Holocene climate shifts comparable to those of the YD’ – you interpret that the isotope changes during the YD are caused by temperature, and during the late Holocene by circulation changes. So I am not sure you can then say they are comparable – it implies YD-scale temperature fluctuations were occurring in the late Holocene. 3. Minor Comments Line 3, the title is concise and readable, but it does not fully capture the scope or key findings of the study. Line 39 – ‘inform abrupt climate change’ – the word inform doesn’t fit here, perhaps ‘inform our understanding of abrupt…’ would work better Line 52 – ‘unresolved timing’, this could be better phrased as ‘uncertain chronologies’. Unresolved timing requires more detail about what the timing is related to. Line 66 – ‘oriented by coastal topographic barriers that were continental ice sheets during past glacial periods’, this phrasing is confusing. Do you mean the topographic barriers were shaped by the ice sheets? Or the barriers are currently topographic but there were ice sheet barriers in the past? Line 73 and 74 – The use of the word ‘reflect’ here I think is unusual but perhaps ok. I would consider ‘cause’ instead Line 74-76 – references needed here Line 107 – add ‘timing and nature’ or something similar, as most of the discussion here is about the character of the YD rather than the timing. Line 123 – ‘with a strong consensus for there having been an Early’ Line 210-211 – reference needed SI Lines 292-293, Lake water pH or conductivity are needed. Lake water pH or conductivity measurements should be presented as geographical setting or background information. It can be useful for the interpretation of the carbonates δ18O signals as disequilibrium offset increases at high alkalinity.", "reviewer_3": "I co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is part of the Nature Communications initiative to facilitate training in peer review and to provide appropriate recognition for Early Career Researchers who co-review manuscripts.", "reviewer_4": "This is a nice paper that presents three new detailed carbonate δ18O lake sediment records from Alaska. They records are of high quality and important for understanding regional paleoclimatic variations, and their potential links to abrupt climate changes in the North Atlantic ocean over the deglacial period. The major comment I have for this paper is that, while great records and important, I don’t see what new discoveries were made about climate dynamics in the North Pacific. Some of the statements about the variability in the Holocene (after the more clear B/A and YD intervals) were not fully reasoned out, and their differences to the Mt. Logan ice core were not explained. I can certainly see why insolation might be a control, as suggested, but I don’t see the reasoning that supports such an interpretation, or why the Late Holocene δ18O record should be interpreted differently than earlier periods. In summary, this is a solid regional-level characterization of south central Alaskan Holocene paleoclimate from lake sediment records. The time series are of high quality and will be an important contribution to our understanding of regional paleoclimate. But the manuscript doesn’t yet make a convincing case on the hemispheric or global forcings of the paleoclimatic changes, or why they are significant for our understanding of north Pacific climate dynamics. Minor points I don't think the authors need to redefine open and closed basin lakes as “precipitation-type” and “moisture-type”. Just the description of open and closed and their relative sensitivities to precipitation δ18O would suffice. I presumed in the introduction that the authors would come back to the Pacific climate modes and show some linkages between proxies for those and the lake sediment records. The lake sediment oxygen isotope records were only qualitatively linked to these to these Pacific Ocean climate modes, without any conclusive evidence of them being important forcings. The authors can describe the source of the carbonate in the lakes up front. Are they measuring authigenic calcite, shells, or something else? In line 174, the authors did not provide their evidence that late Holocene oxygen isotope values would have a different interpretation than during the deglacial period. Further, Rayleigh distillation is happening in all cases across all time intervals, and therefore is not unique to the Late Holocene, so further evidence needs to be provided to support the authors reasoning. Similarly, the manuscript would benefit (in line 198) a better description as to why orbital precession is now an important control over the Holocene. Is this backed up by model runs? And are the authors referring to local summer, winter, or other season for insolation? In figure 2 the authors show the Mount Logan ice core record, which spans the entire time interval covered by the lake sediment records. So, what do the new lake sediment records provide for our understanding of deglaciation paleo climate that was not apparent in the Mount Logan ice core record? There are some obvious differences, with the Mt. Logan δ18O record having a relatively non-trending Holocene, whereas the lake records show more change. What would explain the discrepancy?"}, "author_response": "Below, we have copied all comments from the reviewers (black, italics) followed by our\nresponses (blue text). We provide tracked changes in the revised manuscript accordingly and\nprovide revised line numbers (RL).\nReviewer #1:\nIn this manuscript, the authors present high-resolution oxygen isotope records from several lakes\nin Alaska to investigate climate oscillations during the last deglaciation and compare with the\nlate Holocene. They show that the YD mostly represents winter cooling and is closely tied to\nAtlantic Ocean influences, supporting the existence of strong connections between North Pacific\nand North Atlantic during the last deglaciation. On the other hand, rapid climate oscillations\nduring the late Holocene were mostly triggered by Pacific Ocean influences, showing no\nevidence of influence from North Atlantic. They also discuss the implications of the study for\nrecent and ongoing climate changes in North Pacific region.\nThis is an important study addressing a long-standing paleoclimate question, not only about the\nconnection between North Atlantic and North Pacific, but also the variable nature of this\nconnection. The isotope records presented are valuable and high quality. The interpretations are\nbalanced and robust, supported by the data and arguments. The study design of using lakes with\ncontrasting hydrology and the interpretations of organic d13C records for groundwater flux and\nmoisture conditions are creative and novel. The manuscript is well organized.\nResponse: We sincerely thank Reviewer #1 for their insightful evaluation. We deeply appreciate\nyour assessment of this study’s importance, including recognition of our data quality and the\ncontribution of our creative and original study design. Thank you for guiding improvements of\nthe revised manuscript.\nMy only major comment is about presentations of dating controls. It is well known that\nlacustrine sediment records are very difficult to data from lakes in Alaska and Arctic in general,\nas suitable terrestrial plant materials are hard to find. The authors should be commended for such\na large set of radiocarbon dates from these study lakes as presented in SI Table 1. That\nbeing said, dating and chronology are critical for the interpretations and conclusions presented in this\nstudy, so I suggest that the authors show explicitly the dating control points on the records shown\nin figures (comment below as well) and discuss any uncertainties accordingly. That way, readers\nwould have a visual appreciation of the robustness of chronology.\nResponse: We deeply appreciate the recognitions of the extensive collection of dating control\npoints. We agree that dating and chronology are critical and that explicitly showing the age\ncontrol points in figures provides a visual appreciation of the chronological quality. We have\nadded age points to Figures 1 and 4. Furthermore, we have added a new Supplementary Fig. 3,\nwhich shows stratigraphic data on depths scales, including age points so that readers can evaluate\nage control relative to isotope variations and sampling interval, and lithology (RL 53, 366, 378,\n383, 391, 435). We have added text to Methods titled ‘Age data and age-depth models’ that\ndiscusses the interpretations and uncertainties and also references the age-depth models shown in\nSupplementary Fig 5. (RL 360-415)\nSpecific comments:\nAbstract: mention lake records to make the abstract more informative\nThank you. We substantially revised the abstract and now lake sediment oxygen isotope records\nis mentioned in the first sentence. (RL 20)\nThank you, we took this good suggestion (RL 62)\nL82-83: Refer Fig. 2b for Neklason Lake record, and d18O from April Fools Lake is not in Fig.\n2, but in Fig. 4. Also, should refer Fig. 2a after mentioning Finger Lake here.\nThank you for your detailed review. We have revised the figure references throughout to include\nlettered panels.\nL89: age models: need cite Suppl Figures?\nThank you for identifying this need. We have added specific citations throughout the text to\nguide readers to the relevant figures in the substantially revised and expanded Supplementary\nmaterial.\nL93: Change superscript 15 to “ref. 15” Thank your detailed review of the figure captions. We\nhave deleted ‘from ref.’ and moved the superscript citation to the record name. (RL 155-163).\nL96: “from ~4 to 8 C”. Negative signs have been taken care of by “decline” in the sentence, so\nnot needed here.\nThank you, corrected.\nL95-97: unclear. Temperature decline is inferred/estimated from d18O change based on calcite-\nwater fractionation, but what is the role of SS temperature variation here. The former was used\nfor temperature inference/estimate, while the latter is for interpretations. Do I miss anything\nhere? Clarity.\nThank you for pointing out the need to clarify this sentence. We revised to clarify that SST\nvariations were considered in our estimates because of their influence on the 18O value of\nmoisture source vapor. (RL 132-134).\nL98: perhaps compare d18O values of winter precipitation/groundwater at the sites and lake-\nwater d18O values calculated from calcite d18O measurements using calcite-water d18O\nfractionation factor\nThank you for suggestion. In response to this comment and concerns raised by Reviewer #2 we\nhave substantially revised the text and supplementary material to highlight the comparison\nbetween measured lake water and calculated lake water values based on equilibrium calcite\nfractionation factor. The results are shown in Supplementary Table 4 and Supplementary Fig. 2,\nwhich are now referred to in the main text (RL 46 and 352)\nL101: change to “…sensitivity; however, ….” This sentence was substantially revised (RL 38-40)\nL111-115: add dating control points near curves on figures to support/refute the YD timing\ndiscussion here\nDone! See detailed response above for additions to Figures 2 and 4.\nL115-116: good point! The fact of calcite precipitation suggests that summer water temperature\nis high enough.\nL121: “meteoric precipitation” to avoid possible confusion with calcite precipitation?\nYes, easily misunderstood, good point. However, this section was substantially revised and this\nsentence removed (RL 175-176).\nL134-143: this paragraph needs to refer to Fig. 3, perhaps different panels according to various\ndescriptions, including to April Fools Lake (Fig. 3b) and synthesis records (Fig. 3c). That would\ngreatly increase clarity and readability.\nThank you for this helpful suggestion, which we have addressed (RL184, 188)\nL155-157: refer Fig. 3 for MWP mention\nThank you, done (RL 173).\nL171-172: Be mindful here. Finger and especially Neklason records have different sampling\nresolution, so potentially artifact for variability/magnitude. But indeed, April Fools record is a\nstrong proof that variability/magnitude shift around 2 ka.\nThank you for this very helpful observation that helped guide us to thoroughly reevaluate how to\nimprove the presentation of all our lake 18O records. First, we recognized the value of focusing\nthe presentation of our precipitation 18O records from April Fools and Neklason with Greenland\nin Figure 2 and removed Finger Lake. Second, we recognized the value in merging the high-\nresolution sections of the two records into a composite 18O stratigraphy that is now presented in\nFig. 1 and 4 and discussed in the Methods and shown in Supplementary Fig. 7. Lastly, we re-\nconceived Figure 4 to emphasize the comparison between Finger Lake and the April Fools-\nNeklason composite, including statistical comparison by box plots for time periods to objectively\ncompare means and extremes. Furthermore, sampling intervals for the isotope records are now\nprovided in Supplementary Fig. 3.\nL180-183: very good statements/examples about implications of this study. Well done.\nWe sincerely appreciate your recognition of these examples to explain implications. (RL 221-\n227)\nFigure 2: add dating control points on the figure, perhaps on the top with different colors (such\nas downward triangles) for Finger and Neklason records, even for composite records.\nDone! We used colored circles that match the color of the records in Fig. 2 and 4.\nFig. 2c: vertical axis label: change to superscript in m2\nYes, on the insolation panel – thank you for your good eye!\nL235: change to “Greenland ice-core”\nThank you! A hyphen was added between ‘ice’ and ‘core’ when used as a compound adjective\nthroughout the manuscript.\nL244: Fig. 3 caption: indicate the number of organic d13C records (n= )?\nL251: a stray bracket “)”\nThis figure was substantially revised, and this panel was removed.\nL258-259: Livingstone corer can hardly recover sediment-water interface. Either you use a\nplastic piston corer, or delete the mention as it is not essential for the study.\nYes, thank you for catching this oversight. We revised the sentence to clarify how we collected\nhigh-quality surface sediments. (RL 345-346)\nL260: we use “endogenic” to describe carbonate, not d18Ocarbonate, right? rephrase.\nThank you for pointing out this distinction. We made substantial revisions to the sections about\ncarbonate in response to Reviewer #2 throughout the manuscript using the term ‘authigenic’ and\nthis sentence was removed.\nL290: an extra “””\nThank you for your keen eye! We removed stray quotes throughout references.\nSupplementary Information:\nL52, 59, 67: Bayesian\nYes, capitalized.\nSI Fig. 3b. vertical axis label “d13C”\nYes, for Arolik, thank you, corrected.\nSI Fig. 4: n=6 for d13C records need to mention in the main text/figure\nYes, but n=5, Arolik and Dune not used (low resolution) and added a note to caption indicating\nthat.\nSI Figs. 5 and 6 are apparently not mentioned in the text, It would be good to do so, when\ndescribing the nature/source of organic matter for d13C interpretations.\nYes, thank you for this suggestion that helped guide our revisions in response to concerns by\nReviewer #2’s about source characterization. We have substantially revised the Methods and\nSupplementary material with specific figure citations placed in the main text.\nSI Table 1:\n3rd column heading: 14C Date (not age here, but “Calibrated Age”)\n4th column heading: “…Date (14C yr BP)” , not “years”\nThank you for catching these oversights!\nL116: “informal name”. Hopefully next time when the lake was cored again on July 4th, it wont\nbe named “Independence Lake”:))\nWe appreciate your good humor!\nL120: “at two locations”\nL292: why don’t make it a formal SI Table and formatted as such? The table heading needs proof\nread, as they are incomplete/inaccurate: such as “Horizons dated”, basal age need “Cal yr\nBP”? Sampling resolution: “cm” can be moved to heading (should cm be converted to years, as\nyou have age model already?)\nThank you for these very helpful suggestions – all corrections made. We made this\nSupplementary Table 6 (RL 367).\nReviewer #2:\nThis paper presents new isotope results for lakes in Alaska that span the Younger Dryas to Late\nHolocene, providing interesting high-resolution records that are presented nicely in the figures\nand may eventually advance our knowledge about the Pacific-Atlantic/Arctic teleconnections. As\ndetailed below, while the topic and dataset are promising, the manuscript requires a substantial\nrevision and reorganization to clarify its framing, improve methodological transparency, and\nprovide a more balanced interpretation of the results.\nResponse: We are deeply grateful to Reviewer #2 for their thorough evaluation of our manuscript\nand their recognition of the value of our high-resolution records and figure presentations. We\nsincerely appreciate the feedback about the promise of our manuscript and have implemented\nsubstantial revisions to reach its potential that are outlined below. We have carefully reconsidered\norganization, framing, methods, and interpretation following the reviewer’s suggestions that has\nelevated the manuscript. We believe the revisions will advances knowledge about winter\nteleconnection to the North Pacific-Arctic and Northern Hemisphere atmospheric circulation\nvariations. We sincerely thank the reviewer for guiding these improvements.\n1. General Comments\n1) Chronology and lake reservoir corrections\nThe age-depth model is central to the paper’s conclusions. However, it lacks sufficient\njustification and statistical rigor during chronology establishments. I do agree with the idea\nusing the tephra layers with absolute dates to correct the lake reservoir effects. However, I also\nbelieve that more details are needed for better\nclarity:\nResponse: Thank you for the reviewer’s emphasis on the chronological establishments, which we\nagree are central to this study. We have a new Methods section for the main manuscript and\nsignificantly expanded the Supplementary material to provide additional details and justification\nthat are now cited throughout the main text and described in detail below. The revised text\nexpands on how tephra was used, and the lake reservoir correction (which applied to one of the\nthree lakes), as discussed further below.\na. How the tephrochronology was established for those cores? The authors claim that the tephra\ncorrelation is established “Based on similarities” (Line 217 in SI). However, it’s not very clear\nto the readers what does “similarities” represent. Have you run the geochemical analysis on\ntephra shards? Which is the routine way for tephra layer correlations. I would suggest the\nauthors provide more robust information for tephrochronology correlation, either other evidence\nto clearly show the “similarity” or geochemical analyses results on tephra shards. This will\ndirectly influence the reliability of lake reservoir effects estimation and following age-depth\nmodelling for lake April Fools.\nWe sincerely appreciate the reviewer for these excellent questions that guided our revisions to\nclarify our tephra identification and correlations. Detailed text on tephra identification and\njustification, which is fairly well known for this region, is provided in Methods. The stratigraphic\npositions of tephra in each core are now shown in new Supplementary Fig. 3 and the correlations\namong the cores are shown in Supplementary Fig. 4. We sincerely thank the reviewer for\nprompting these additions which has improved the paper through inclusion of detailed\nstratigraphic and chronological evidence. (RL 371-383)\nb. Reasons for the rejection of some radiocarbon dates should be given or detailed. This study\npresents a massive amount of radiocarbon dating on those cores (which is good ) but they also\nrejected some of those radiocarbon dates but give very little discussion why they did this. Taking\ncore April Fools A15 as an example, the authors rejected more than half of the radiocarbon\ndates (including the lake reservoir corrected aquatic herb-based dates), but the reason were not\ngiven/detailed.\nWe sincerely appreciate the reviewer’s recognition of the detailed dating that we conducted,\nwhich along with the high-resolution data distinguishes our records from existing data in the\nregion. We acknowledge that additional discussion is needed and helpful. We now have detailed\ndiscussion in Methods sub-section “Age data and age-depth models” that includes explanation of\nage rejection of a few ages from the Bayesian age-depth models. This includes clarification that\nthe reservoir corrected aquatic samples in April Fools core A15 were not rejected as ‘age points’\nbut rather explains why they were not used in the Bayesian age-depth models. Their inclusion\ndid not improve the uncertainty of the model based on terrestrial ages and tephra but verify its\naccuracy. Because of uncertainty in the temporal variability of the reservoir effect, we take a\ncautious approach to ensure robust results and limit their use as cross-check for the age-depth\nmodel. The ages are now shown in Supplementary Fig. 5a with explanation in the caption. This\ndiscussion also explicitly discusses the higher uncertainty in the lower sections of Finger Lake\nand justification for applying the minimum modeled ages within the 95% uncertainty range now\nshown in Fig. 4. In response to Reviewer #1’s suggestion, ‘age points’ are now shown in Fig. 2\nand 4 and in new Supplementary Fig 7. Furthermore, the stratigraphic position of every age is\nnow shown in Supplementary Figs. 3 in addition to the table of radiocarbon data, Supplementary\nTable 7. Thank you for your guidance in improving our data presentation and clarity of the\nchronologies. (RL 384-395)\n2) On the interpretations of stable oxygen isotope (δ18O) of the carbonates.\na. Why is your proposed driver the most likely? Lake carbonates δ18O signals are influenced by\nmultiple factors, including temperature, evaporation, seasonality of temperature/precipitation,\nand hydrological conditions. While the authors try to classify these three lakes into two groups,\nnamely Precipitation-type and Moisture-type (Lines 53-62), to simplify the interpretation of\nδ18O signals, the manuscript does not convincingly justify why those particular factors are the\ndominant control as claimed (even without reference supporting their classification)?\nexpanded the main text, methods and supplementary material to explicitly evaluate drivers for\ndifferent lakes and time periods. The revisions also focus on the hydrogeologic mechanisms that\nemphasize winter climate controls on our groundwater lake water systems primarily recharged\nby mountain snowpack. We follow reviewer #4’s suggestion to used open and closed hydrology\nterms and refer to our comprehensive regional isotope hydrology framework in Supplementary\nFig. 1. In addition to substantial revisions of the introduction and a new “Conceptual\nFramework”, we expanded the Methods in a new subsection “Regional climate and precipitation\nisotopes controls”. (RL 34-113, 282-311).\nb. Problem with mixing carbonate types. The manuscript does not clarify the type of carbonates\nbeing analysed. From the method section, it seems that the fine fraction (<32 μm) was used for\nisotopic works. However, this fine fraction seems to be a mixture to me, and this carbonate\nsource ambiguity raises concerns about the geochemical integrity of the proxy signal. For\nexample, what is the proportion of biogenic, inorganic, or even detrital carbonate in the finest\nfraction (<32 μm)? Are there sedimentary or geochemical indicators that confirm the origin of\nthe carbonates?\nThank you for pointing out the need to better clarify our methods and validate the geochemical\nintegrity of the proxy signal. We acknowledge the importance of this concept and have rephrased\nseveral sentences in the introduction to clarify our analysis of bulk inorganic carbonate of\nauthigenic origin (i.e., formed where they found – in this instance, each lake). We expanded the\nMethods with a new section “Lake sediment lithology and carbonate isotopes” and the\nSupplementary material to show sedimentary and geochemical evidence for no significant\ndetrital contribution or changes in sedimentary processes that would affect the purity or isotopic\ncomposition of bio-induced bulk carbonates. In addition to assessing carbonate grain appearance\nby microscopic observations they include 1) pH, alkalinity, biological productivity, and lake\nwater temperatures that support carbonate precipitation caused by pCO during photosynthesis,\n2\nsummarized in new Supplementary Table 1, 2) verification by isotopic equilibrium experiments\ndescribed in Methods and shown in new Supplementary Table 4, 3) stratigraphic profiles that\nshow non-authigenic sedimentary components comprise a minor fraction of total sediment\ncomposition, in new Supplementary Fig. 3, and 4) no evidence for detrital carbonate sources or\nmechanism of delivery to our lakes. We thank the reviewer for guiding these important\nimprovements to the manuscript (RL 39, 50-52, 312-359)\nc. There is currently no discussion of possible isotopic offsets between different carbonate\nfractions. This is a crucial omission, as differences between, for example, biologically\nprecipitated carbonate and inorganic calcite can introduce systematic biases. Is there any\nisotopic offset between different grain-sized fractions, between fractions <32 μm and 32-63 μm?\nChange in the carbonate source can influence the isotopic signals of the carbonates, which is\nindependent of climate change.\nWe appreciate the constructive suggestion and address it fully in the revision. We have expanded\nMethods and Supplementary material to explicitly address our precautions to avoid mixing\nauthigenic bulk carbonates of inorganic or bio-induced origin from biogenic carbonates (e.g.,\ngastropods, ostracodes, Psidium). The revisions clarify that large particles of biogenic carbonates\nwere separated by sieving and that we analyzed the finest fraction to minimize their potential\neffects. The finest fraction is then shown to be in isotopic equilibrium with lake water (as\n7\ndiscussed in the previous response), and we clarify that the need to mix small size fractions in\norder to achieve adequate samples was required for <1% of all samples measured. Further, we\nconducted a series of bulk carbonate size fraction tests and in no instance is a significant\ndeviation of isotopic values for fine grained size fractions observed, now shown in\nSupplementary Table 3. We are grateful to the reviewer’s comments that have guided our method\nclarifications which strengthen our climatic interpretation of our lake carbonate isotope signals.\n(RL 345-359)\nI would recommend:\ni. Consider running modern calibration studies on modern water or carbonates samples to\nenhance the interpretation of the isotopic signals of carbonates (e.g., comparing δ18O of\nprecipitation, lake water, and carbonates with climate parameters).\nWe agree with this excellent suggestion and appreciate the opportunity to clarify that these\ncalibration studies had been conducted. We acknowledge their presentation required\nimprovements as described in our response to the previous comments above. We thank the\nreviewer for guiding these improvements.\nii. If only bulk carbonates were analysed, the potential impact of this choice on the paleoclimate\ninterpretation should be clearly discussed and acknowledged as a limitation.\nWe appreciate this concern. As discussed above, the main factors that can adversely affect\nclimate signals recorded by bulk carbonates have been evaluated and determined to be of minor\nimpact in our systems. Following the reviewer’s suggestion, we take the opportunity to explicitly\nstate that in this hydrogeologic setting, authigenic bulk fine-grained carbonate 18O from\ngroundwater lakes provides exceptional continuous representation of lake water 18O that can be\nwell dated and thereby provide climatic records of unprecedented temporal resolution. (RL 40-\n48)\n3) On the interpretations of bulk organic stable carbon isotope (δ13Corg)\nThe authors interpret the δ13C values of bulk organic matter primarily as a proxy for\nprecipitation variability. However, this interpretation appears overstated and does not\nadequately consider alternative influences. The C/N ratios reported (generally <15) suggest that\nthe primary source of lake organic matter is aquatic algae. This implies that δ13C variations\nlikely reflect lake-internal productivity processes rather than external hydrological inputs, at\nleast not only external processes. Aquatic algae assimilate dissolved CO2, and the isotopic\nsignature of that carbon pool is influenced by lake water pCO2, which itself is affected by\ntemperature, biological activity, and CO2 exchange with the atmosphere. These internal carbon\ncycle dynamics can significantly modulate the δ13C signal, making it problematic to directly\nattribute isotopic shifts to precipitation changes alone.\nThank you for pointing out the need to better explain our consideration of all alternatives in more\ndetail. According to the reviewer’s suggestion we have expanded Methods with a section titled\n“Lake sediment carbon and nitrogen organic matter” and revised Supplementary material and\nFig. 3 to show that during the period of 13C decline and lake level rise, for which we have\ndetermined using C:N that the organic material is of aquatic origin, the resulting interpretation\nboils down to productivity or hydrology. Supplementary Fig. 9 now shows a measure of\nproductivity (e.g., organic content as determined by % LOI-550˚C) in addition to C/N ratios,\n8\nwith either no trend or an increasing trend, which would result in either no change in 13C, or\nchange in the opposite direction (increase) than the data show. The revisions now explain how\nwe ruled out this alternative explanation for this time period when all lakes respond with 13C\ndeclines. However, subsequent Holocene changes diverged among the lakes, likely due to these\ninternal productivity processes, which is acknowledged. In summary, our data show that during\nthis specific time of major hydrologic change, external hydrologic processes were more\nsignificant than internal carbon source or productivity processes. (RL 177-196, 416-447)\nIn its current form, the manuscript risks overinterpreting δ13C as a direct climate signal, and I\nrecommend the authors reconsider this conclusion and broaden their interpretive framework.\nWe deeply appreciate the reviewer’s thoughtful comments that have helped to significantly\nimprove our explanations of the full scope of alternatives strengthening support for our\narguments in favor of the proposed interpretation (see discussion in above comment and\nassociated revisions to text and supplementary material).\n4) Mismatch between the paper's stated goals and its actual contributions.\nWhile the manuscript presents interesting datasets from multiple lake records, I find that it\nultimately does not achieve the stated goals outlined in the introduction or title. The authors\nclaim to resolve key questions about climate connections between the Pacific and Arctic/Atlantic,\nyet the evidence presented-particularly regarding the δ13C and δ18O interpretations—remains\nambiguous and open to alternative explanations that are not adequately explored. This\nambiguity in the climatic significance of the proxy signals, combined with uneven\nmethodological transparency (e.g., tephrochronology, lake reservoir corrections, unseparated\ncarbonate fractions), undermines the strength of the conclusions. As a result, the study does not\nconvincingly advance our understanding of teleconnections between Pacific and Arctic/Atlantic\nin the way it aspires to.\nThank you for pointing out the need for clearer methodological transparency, and greater\nevaluations of alternative explanations. According to the reviewer’s suggestion, the revisions\nhave clarified our chronological methods and the basis for our interpretations of carbonate source\nand isotopic signal. Expanded discussion of alternative explanations of our evidence strengthens\nconfidence of the hydroclimatic interpretations based on robust independent age chronologies,\nallowing confident comparisons between North Pacific variations with those in the North\nAtlantic based on the Greenland Ice core. While our work builds on previous studies, it\nsignificantly improves chronological control, record continuity, and temporal resolution based on\nthe robust bulk sediment carbonate isotope proxy. We have expanded the text to include a\n“Contextual Framework” where we specifically explain our hypotheses that we believe advance\nunderstanding of seasonal atmospheric teleconnections and their relationship to 18O signals\nthrough time. (RL 95-113)\nMore supporting evidence is needed to back up that the lakes reflect winter conditions\n(references are not given in several places), and the authors often argue that changes reflect\ntemperature, without explaining why precipitation source and atmospheric circulation is\ndiscounted. Furthermore, the lake records show very different variations during the late\nHolocene, but rather than acknowledge this and explain why this might be (and give a\n9\nreasonable explanation of why they still have a climate signal) the authors discuss the high\nvariability as being significant.\nWe sincerely appreciate this insightful review and have accordingly substantially revised the\norganization and data presentation to support our conclusions regarding the role of North Atlantic\nforced temperature during the deglacial in contrast to atmospheric circulation during the late\nHolocene. As described above, we have expanded the Methods and Supplementary material to\nclarify and substantiate that our groundwater lakes have sensitivity to winter precipitation 18O\nand revised Fig. 1 to focus on the Greenland comparison with our composite records of April\nFools Lake and Neklason Lakes, now described in Methods and illustrated in Supplementary\nFig. 7. We now present a conceptual framework that discusses how hypotheses regarding\ntemperature and atmospheric circulation changes can be tested using 18O records and\nreorganized other sub-sections accordingly. We revised Fig. 4 to focus on the comparison\nbetween our record of winter precipitation 18O and summer evaporation from Finger lake with\nadditional statistical analyses by box plots to emphasize the comparison between means and\nextremes for the YD and late Holocene. Reviewer #4 raised similar concerns that we address\nfurther in detail below.\nFinally, at some points in the paper the reader is left behind because the links between ideas are\nnot explained fully. In parts the text requires reorganisation and rewriting, as comparisons with\nother records or supporting evidence is spread over several paragraphs.\nThank you for your valuable feedback about the need to carefully evaluate and revise the links b\netween ideas t hroughout the paper. W e substantially reorganized and rewrote the main tex t and e\\xpanded the Methods to i mprove the l ogi cal flow o f ideas and make the concep ts and explanatio\ns easier to follow.\n2. Moderate comments\nMain section:\nLine 53-62 – there is just one reference provided for the interpretations in this paragraph, do the\ninterpretations all come from here? Are there modern observations or data to support this?\nReferences or data are needed particularly to support the interpretation of these being\nopen/closed basins and the water residence times, which are the basis for the interpretation\nabout seasonality.\nThank you for the opportunity to explain that this reference by Kikuchi (2013) is an exhaustive\nU.S. Geological Survey hydrogeologic investigation of our study region that provides modern\nclimate, hydrology, and isotope observations, data, geologic framework and hydrologic modeling\nin support of our hydrologic interpretation of the study lakes (in addition to our data). The report\nshows strong linkages between lake water isotopes and groundwater with related hydrologic\nsetting and climate. The information in this report is specific to our study area as is the work by\nBailey et al. (2019) who analyzed weekly 18O of precipitation 2005-2018. The major\nconclusions from these studies are summarized in the main text and expanded Methods to the\nextent allowed by length limitations. (RL 49-60, 261-281).\nLine 67-68 – ‘Contemporary 18O precipitation reflects seasonal air temperatures and shifting\nmoisture sources in addition to topographic rain-out effects’. This sentence sums up some of my\nconcerns later in the paper where changes in the isotopic records are interpreted in certain ways,\nsuch as temperature, without considering the other possible causes given here.\nwith respect to multiple controls on precipitation 18O, which we have addressed throughout the\nrevised text. By using the combined lake datasets by comparison to North Atlantic records, we\nidentify changes in winter atmospheric teleconnections that best resolve 18O signals through\ntime by different controls. For this region, as this conceptual framework explains, modern\ncontrols are primary moisture source and atmospheric circulation by teleconnection related to\nNorth pacific ocean atmospheric dynamics, as demonstrated by several published studies we\nhave referenced. Such signals are not recorded in ice-core records from Greenland. However, this\nmechanism is a highly unlikely for the YD, because we show correlative signals in both regions\nduring this period. This leads to our conclusion that the most parsimonious climate driver\ninvolves and teleconnection resulting from North Atlantic ocean dynamics by causing colder\nhemispheric high-latitude atmospheric temperatures. Ultimately, we argue that similar signals in\nprecipitation isotopes can result from condensation fractionation effects through either high-\nlatitude cooling or long-distance meridional vapor transport, and that these processes can be\ndistinguished by similarities and differences in records from different regions and hydrologic\nsensitivity. This explanation is now reflected in the revised text. (RL 95-11, 116-152, 213-228,\n239-257).\nLine 77 – ‘resolving past seasonal changes’. In the next section you explain why the lakes reflect\nwinter changes but that is not explained well here. I think add to the end of this section more\ndetail and references supporting how you know it reflects winter season changes.\nAs described above, we expanded the text, Methods and Supplementary material to explain why\nthe lakes reflect winter changes and this sentence was rewritten.\nLine 81-106 – These two paragraphs could be reorganised – it is quite confusing currently having\ncomparisons with existing records spread over two paragraphs, and the statement about the YD\nbeing a winter phenomenon here only makes sense with the evidence shown in the following\nparagraph\nYes, thank you, these two paragraphs have been rewritten as described above we have\nreorganized and expanded the main text to improve the logical flow of ideas and better link\nconcepts.\nLine 98-100 – ‘Our YD delta 18O carbonate records largely reflect winter season cooling’. How\ndo you know it reflects cooling, could winter season circulation changes also have had an effect?\nThank you for your insightful question. We revised the text to include these alternatives and\nsuggest that both can be true if changes in winter circulation led to colder conditions. (RL 99-\n103)\nLine 102– ‘Our new data substantiate that the YD in Alaska was most sensitive to wintertime\ncooling,’ The phrasing of this could be improved as currently the YD is sensitive, rather than the\nYD being a time period and the climate or winter season climate being sensitive. The references\ngiven later for the YD summer being warm should also be put here (currently down at line 112)\nas should the evidence from the lakes themselves (high productivity and marl accumulation)\ncurrently at line 115. This would strengthen the argument that the record is reflecting the winter\nrather than summer. Consider also my point for line 98 about the interpretation of this as cooling\nrather than atmospheric circulation, how do you know this?\nsection on YD, including the text and references about summer conditions that strengthen the\narguments that our records record winter precipitation 18O. (RL 117-152)\nLine 126 -129 – references are needed here to support this interpretation\nThank you, references added to Methods to support our interpretation (RL 463-496)\nLine 143 - I am not sure if moisture shifts is the right term here for what you describe – a shift\nwould suggest to me a change in the distribution of moisture across the area (so maybe some\nareas having more and others less). But as they are all changing together, are they not just\nexperiencing enhanced moisture?\nThank you for your thoughtful consideration of accurate terminology. We agree and re-wrote this\nsection using specific terms such as precipitation, surface runoff, groundwater flux etc. (RL 177-\n182)\nLine 146 -148 – ‘both lake types indicate the warmest year-round temperatures and possibly the\ngreatest aridity of the records’. In the Main section above when describing the causes of oxygen\nisotope changes the atmospheric circulation paths are described – how do you know therefore\nthat the oxygen isotope changes are due to temperature changes and not changes in atmospheric\ncirculation? Both types of lake are influenced by the precipitation, so this seems more likely to be\ncausing shared changes?\nWe sincerely appreciate your thoughtful insight. We agree that both lakes share common changes\nin the 18O of precipitation. We re-wrote this section to clarify that at Finger Lake positive\nextrema due to evaporation during the summer in response to warm temperatures. For Nekalson,\npositive extreme could be shift in rain/snow balance to rain, also in response to warmer winter\ntemperatures. (RL 166-168)\nLine 148 – ‘However, with winter experiencing the most significant warming, high delta 18O…’\nIs this based on the cold YD temperatures? How do you know this?\nYes. Based on the winter sensitivity of the groundwater lake 18O proxy, we interpret the rapid\nincrease during the YD to reflect increased winter temperature although we now consider\nalternative interpretations such as a higher ratio of rain to snow or increased moisture sources\nfrom the Bering Sea related to melting sea ice, which are both consistent with winter warming.\n(RL 166-168)\nLine 146 -159 – In this paragraph I feel like a few steps are missed in the explanation – I think\nyou explicitly need to mention that it is thought that freshwater export may have weakened the\nAMOC (if this is what the references here say) and say how that would have caused\nwarming/zonal circulation in Alaska. And was it the Bering Strait flooding or AMOC changes\nthat you think caused the changes in Alaska? If you don’t know say more clearly that there are a\nfew potential explanations, or different causes at different times (as suggested by figure 3).\nThank you for this suggestion which helped our conceptual framework and revisions of Fig. 3 for\nthis complex period of change. We rewrote this text to link the steps within the explanation of\nhow weakened AMOC and opening of the Bering Strait led to warming in Alaska. (RL 172-176,\n194).\nsensitivity to AMOC’. A reference is needed for this.\nThank you, reference added.\nParagraph starting 174– here you change the interpretation from oxygen isotope variations\nbeing caused by temperature (during the deglacial) to atmospheric circulation. This\ninterpretation is given very certainly, but without many references or explanation of why this\nchange would occur. Furthermore, why are the records all showing different patterns if they\nreflect atmospheric circulation that would be the same across the area?\nThank you for your suggestion to better explain our interpretations. The revision now clarifies\nhow changes in temperature and atmospheric circulation affect oxygen isotopes of precipitation\nin the contextual framework and considers alternative explanations, which has strengthened our\ninterpretive arguments. Our focus in this paper is on broad late Holocene trends in comparison to\nthe deglacial. Because of the complexities in regional expression in response to atmospheric\ncirculation shifts in this topographically varied region, detailed examination of late Holocene\nvariation is beyond the scope of this manuscript. We hope this will be the topic of future papers.\nLine 180– ‘For example, our records document greater extremes in pre-historic baselines that\nhelp evaluate recent marine heat waves and associated sea bird, and fish die-offs.’ This is a\nrather general statement – do you mean greater extremes than the 20th century variations?\nGreater using which variable? If you are able to say this then it should be supported by an\nexample of how your results can be used to evaluate these impacts, or at least how modern\nobservations of oxygen isotope values compare with the late Holocene range.\nThank you for these suggestions and we appreciate the suggestion to be more specific. We have\nrevised the text to explain that we mean greater extremes in 18O as a proxy for ENSO-PDO and\nhow modern variability compares with that during the Holocene. We also identify the 1976 PDO\nshift in Fig. 2 and 4. (RL 85-88)\nLine 197 -199 – the links with precession and global changes should probably be introduced\nbefore the conclusion section. Without more explanation I don’t understand what is meant by this\nsentence, or how you have come to this conclusion. This is also discussing the late Holocene\nchanges, which as I mention above are not consistent between your records, which I think is\nproblematic for then making conclusions about the late Holocene climate.\nThank you for pointing out the need for more explanation. The links between ENSO and\ninsolation are now explained in the conceptual framework with links to the concept of latitudinal\ngradients (RL 106-108, 247)\nLine 206 -207 – ‘records show Late Holocene climate shifts comparable to those of the YD’ –\nyou interpret that the isotope changes during the YD are caused by temperature, and during the\nlate Holocene by circulation changes. So I am not sure you can then say they are comparable – it\nimplies YD-scale temperature fluctuations were occurring in the late Holocene.\nWe rewrote these statements to clarify that the magnitude of 18O changes are comparable, and\nnot temperature. (RL 24, 234)\n3. Minor Comments\nthe study.\nThank you and we agree. The title has been substantially modified to better reflect the study\nscope and key findings\nLine 39 – ‘inform abrupt climate change’ – the word inform doesn’t fit here, perhaps ‘inform\nour understanding of abrupt…’ would work better\nThank you, we rewrote this sentence. (RL 257)\nLine 52 – ‘unresolved timing’, this could be better phrased as ‘uncertain chronologies’.\nUnresolved timing requires more detail about what the timing is related to.\nWe rewrote this sentence. (RL 38-40)\nLine 66 – ‘oriented by coastal topographic barriers that were continental ice sheets during past\nglacial periods’, this phrasing is confusing. Do you mean the topographic barriers were shaped\nby the ice sheets? Or the barriers are currently topographic but there were ice sheet barriers in the\npast?\nWe rewrote this sentence (RL 63-65)\nLine 73 and 74 – The use of the word ‘reflect’ here I think is unusual but perhaps ok. I would\nconsider ‘cause’ instead\nWe rewrote this sentence without using this term (RL 78)\nLine 74-76– references needed here\nAdded ENSO-PDO references (RL 81)\nLine 107– add ‘timing and nature’ or something similar, as most of the discussion here is about\nthe character of the YD rather than the timing.\nAgreed (RL 34)\nLine 123 – ‘with a strong consensus for there having been an Early’\nWe rewrote this sentence (RL175-176)\nLine 210 -211 – reference needed\nWe rewrote this section and removed this sentence.\nSI Lines 292-293, Lake water pH or conductivity are needed. Lake water pH or conductivity\nmeasurements should be presented as geographical setting or background information. It can be\nuseful for the interpretation of the carbonates δ18O signals as disequilibrium offset increases at\nhigh alkalinity.\nThank you. This information is now shown in Supplementary Table 1.\nReviewer #3\npart of the Nature Communications initiative to facilitate training in peer review and to provide\nappropriate recognition for Early Career Researchers who co-review manuscripts.\nWe sincerely thank Reviewer #3 for their time and efforts contribution to this review.\nReviewer #4\nThis is a nice paper that presents three new detailed carbonate δ18O lake sediment records from\nAlaska. They records are of high quality and important for understanding regional paleoclimatic\nvariations, and their potential links to abrupt climate changes in the North Atlantic ocean over\nthe deglacial period.\nResponse: We deeply appreciate Reviewer #4’s positive assessment of our paper and recognition\nof its contribution to determining linkages to abrupt climate changes in the North Atlantic.\nThe major comment I have for this paper is that, while great records and important, I don’t see\nwhat new discoveries were made about climate dynamics in the North Pacific. Some of the\nstatements about the variability in the Holocene (after the more clear B/A and YD intervals) were\nnot fully reasoned out, and their differences to the Mt. Logan ice core were not explained. I can\ncertainly see why insolation might be a control, as suggested, but I don’t see the reasoning that\nsupports such an interpretation, or why the Late Holocene δ18O record should be interpreted\ndifferently than earlier periods.\nThank you for pointing out the need to better explain our reasoning about the role of North\nPacific climate dynamics and its influence on the isotopic records. We appreciate the opportunity\nto clarify late Holocene 18O signals in contrast to the deglacial. To clarify this important distincti\non, we reorganized the introduction and refocused the sub-sections in the results. We also r evised\nthe title of the paper and re-conceived the figures to better clarify how our records build upon pre\nvious work. Our substantial revisions clarify that the Mount Logan record estab lished the importa\nce of late Holocene moisture source and atmospheric circulation variations. However, the uncert\\ain deglacial chronology beyond AD 800 (e.g., correlated to Greenland by sulfate peak clusters) s\\everely lim its any interpretation of t he deglacial record. Our data, b y providing exce llent indepen\\dent chronological control for mul tiple lake cores verifies the existence of an atmospheric YD sig\nal in Alaska that we propose is best explained by winter temperature. This is a particularly impo\rtant discovery in t he North Pacific-Arctic (Alaska ) since iden tifying th is event and determining i\ts linkage with the Atlantic has previousl y been difficu lt to determine, creat ing uncertainty about\nthe interplay of Atlan tic and Pacific telecon nections through time. We have also clarified our reas\\oning for an insolation control within our new framework paragraph. This explains how summer i\nsolatio n is a known dr iver of ENSO/ PDO dynamics – this is shown by modeling and exten sive n\\umber o f proxy datasets. Furthermore, shifting seasonal inso lation trends during the Late Holocen\\e is also u nderstood as a driving m echanism for the global neoglacial period, as reflected by glaci\\er mass balance in Alaska and our isotopic records. We hope these clarifications an d discussion a\\ddress the reviewer’s questions.\nIn summary, this is a solid regional-level characterization of south central Alaskan Holocene\npaleoclimate from lake sediment records. The time series are of high quality and will be an\nimportant contribution to our understanding of regional paleoclimate. But the manuscript\n15\ndoesn’t yet make a convincing case on the hemispheric or global forcings of the paleoclimatic\nchanges, or why they are significant for our understanding of north Pacific climate dynamics.\nWe sincerely appreciate the reviewer’s recognition of the quality and importance of our data and\nthank the reviewer for helping to guide the improvements in making our case in new and revised\ntex. We have focused the revised manuscript on clarifying how the records show a shift in\nteleconnections by different hemispheric and global forcing mechanisms through time and the\nimplications for understanding isotope systematics and the role of seasonality and circulation\npatterns with regards to abrupt climate change. Furthermore, we emphasize that climate\nvariations in this region have significant and broader implications, as changes in the Aleutian\nLow and ENSO that influence terrestrial and marine ecosystems over much of North America\nand the entire North Pacific basin.\nMinor points\nI don't think the authors need to redefine open and closed basin lakes as “precipitation-type”\nand “moisture-type”. Just the description of open and closed and their relative sensitivities to\nprecipitation δ18O would suffice.\nThank you, we agree and revised to open and closed terms. (RL 52, 56)\nI presumed in the introduction that the authors would come back to the Pacific climate modes\nand show some linkages between proxies for those and the lake sediment records. The lake\nsediment oxygen isotope records were only qualitatively linked to these to these Pacific Ocean\nclimate modes, without any conclusive evidence of them being important forcings.\nThank you for pointing out the need to explain that these mechanisms have been well\ndocumented by numerous previous studies of lake sediment carbonate oxygen isotopes, as well,\nas Mount Logan and throughout western North America. We have re-written the introduction and\nincluded several of these citations. We have added discussion of the April Fools data which\nprovides conclusive evidence for the importance of North Pacific forcing during the most\nextreme PDO-regime shift (e.g.1976) of the historic period by recording a coincident large\nnegative excursion now shown in Fig. 2 and reconceived Fig. 4 to focus on the seasonal\ninformation provided by our records and broad-scale millennial patterns. Detailed analysis of the\ncomplex topic of late Holocene event-scale analysis is beyond our space limitations here and is\nthe subject of future paper in progress. (RL 78-92)\nThe authors can describe the source of the carbonate In the lakes up front. Are they measuring\nauthigenic calcite, shells, or something else?\nWe thank the reviewer for emphasizing this need that was also brought up by Reviewer #2\nabove, where our detailed response of revisions made to the Methods and Supplementary\nmaterial is provided.\nIn line 174, the authors did not provide their evidence that late Holocene oxygen isotope values\nwould have a different interpretation than during the deglacial period.\nThank you for pointing out the need for a better organized and clear explanation of the evidence\nfor the different interpretation of late Holocene oxygen isotopes values from those of the\ndeglacial. The revised the introduction, conceptual framework, and methods have been designed\n16\nto clearly explain our evidence for different isotopic controls (e.g., winter temperature versus\nmoisture source and atmospheric circulation)\nFurther, Rayleigh distillation is happening in all cases across all time intervals, and therefore is\nnot unique to the Late Holocene, so further evidence needs to be provided to support the authors\nreasoning.\nThank you, yes, we agree. We revised our use of the term Rayleigh distillation to include by\nwhat mechanisms driving negative isotope excursions, either by temperature of vapor\ncondensation related to colder atmospheric temperature or by increased long-distance northward\nsub-tropical vapor transport during meridional circulation patterns related to North Pacific ocean\nmodes. (RL 103, 300, 306)\nSimilarly, the manuscript would benefit (in line 198) a better description as to why orbital\nprecession is now an important control over the Holocene. Is this backed up by model runs?\nAnd are the authors referring to local summer, winter, or other season for insolation?\nThank you for guiding our revisions to clarify the roles of precession during the Holocene and its\ninfluence on North Pacific modes that we addressed above with respect to insolation. (RL 110,\n150).\nIn figure 2 the authors show the Mount Logan ice core record, which spans the entire time\ninterval covered by the lake sediment records. So, what do the new lake sediment records provide\nfor our understanding of deglaciation paleo climate that was not apparent in the Mount Logan\nice core record? There are some obvious differences, with the Mt. Logan δ18O record having a\nrelatively non-trending Holocene, whereas the lake records show more change. What would\nexplain the discrepancy?\nWe thank the reviewer for pointing out the need to clarify the strengths and chronological\nlimitations of the Mount Logan ice core record. Beyond AD 800, its chronology is highly\nuncertain, and across the deglacial interval it is based on similarity of sulfate peak clusters with\nthose in Greenland (Fisher et al., 2008). Thus, our new lakes records substantially build upon the\nstrengths of the Mount Logan record with improved independently dated records that can now\nconfidently correlate deglacial climate shifts to Greenland. The differences in Logan’s Holocene\ntrends are related to unique features of the high elevation ice-core that is the subject of several\nprevious publications cited, and while beyond the scope of this paper is a planned subject of\nfuture work. Thank you for your comments that guided our improvements of the data\npresentation and explanations.\nNCOMMS-25-12495A to Nature Communications\nTitle: Shifting Winter Atmospheric Teleconnections to the North Pacific reconcile Younger-Dryas\nand Holocene d18O signals\nBelow, we have copied all comments from the reviewers (black, italics) followed by our\nresponses (blue text). We provide tracked changes in the revised manuscript accordingly and\nprovide revised line numbers (RL).\nReviewer 1:\nThe authors have carefully addressed my concerns on the earlier version of the manuscript and\nhave significantly revised and improved the manuscript. I have no major comments.\nWe sincerely thank Reviewer #1 for their supportive evaluation and detailed editorial\nsuggestions.\nI have some editorial suggestions:\nFigure 3: Axis label “Age” should be “Age (cal yr BP)”? Thank you, done.\nRef. 51 and 83 are the same reference. Thank you for catching this error, corrected.\nSupplementary file:\nTable S1: Upper cases and lower cases are inconsistent. For example, “Temperature range”,\n“Specific Conductance”, “Dissolved oxygen”, etc., etc. (similar U/L cases issues with other\ntables as well) All are corrected to U/L format and all tables have been checked for consistency.\nTable S5: Change “210Pb Age AD” to “210Pb Year AD” or equivalence (2015.2 is not age (yr\nold), but date) Thank you, done.\nTable S6: “Dated horizons”? Thank you, done.\nFig. S6: Pollen concentration needs unit Thank you, grains/cm2/yr, done.\nReviewer 2:\nThe manuscript has been improved substantially by the changes made by the authors and it\nreads better than it did previously. The revision has increased the transparency of the\nmethodology and strengthened the justification for its robustness. The findings related to the YD\nand Early Holocene are convincing and interesting, and well presented in the figures. The study\nis strengthened by the additional analyses or reorganization of the manuscript, and the work has\nthe potential to be impactful.\nThat said, I am remain unconvinced about the significance of the variations for the late\nHolocene, which is a section of the manuscript that either requires better justification or for the\nconclusions to be altered.\nAnother concern is about the organization and narrative flow of the revision. The overall\norganization of the manuscript is still challenging to follow, especially for readers not familiar\nwith the study area. While the manuscript has been improved, it still requires some sentences or\nparagraphs to be rephrased for clarity or to provide more explicit explanation of the points that\nare being made.\nWe are sincerely grateful to Reviewer #2 for their recognition of the improvements in\norganization, transparency, justification and for their positive assessment of the findings and\n1\npotential impact. We appreciate their feedback and have carefully reconsidered the justification\nfor the late Holocene variations. Following this feedback, we have also improved the overall\nclarity of the paper, addressed through reorganization of the introduction and including more\nexplicit explanations of points of interpretation. We are very grateful to the reviewer for guiding\nthese important improvements that facilitate understanding the main points of this research by a\nbroad spectrum of readers.\nMajor point:\n1. Although the authors have substantially revised the structure and flow in response to my\nprevious comments, I remain concerned that the manuscript’s organization is still not optimal.\nThe introduction does not follow the general structure expected in a Nature Communication\nmanuscript, which should clearly present the significance of the topic and the central knowledge\ngap. Given the text constraints, there may not be space for an extensive review of prior work, but\nit remains unclear what the main knowledge gap is and how this study addresses it. I recommend\na sharper framing and restructuring of the introduction to highlight both the novelty of the work\nand its broader significance. For example, in Lines 35–48, the introduction begins by\nemphasizing the novelty of the research and technical details, which is not an effective way to\nstart.\nWe appreciate this excellent feedback and agree the framing can be sharpened by following the\nsuggested structure. We have substantially revised and reorganized the introduction to more\nclearly present the topic in the expected order starting with significance, followed the central\nknowledge gap, how this study addresses it highlighting the novelty, and broader significance.\nOverall, the revised introduction begins generally and continues with greater specificity and\ncircles back to broader significance.\n2. Following the Introduction, there is a section titled ‘Conceptual Framework.’ Its purpose is\nnot entirely clear, and the content appears to be more introductory than what is currently\npresented in the Introduction. I recommend merging the ‘Introduction’ and ‘Conceptual\nFramework’ into a single, stronger Introduction, unless the journal requires them to remain\nseparate.\nThank you for this very helpful observation. We merged the conceptual framework with the\nintroduction as suggested which has we believe has significantly strengthened the reorganized\nintroduction. We thank the reviewer for guiding these important changes.\n3. In the previous review I questioned why the records differ for the late Holocene section if they\nare reflecting regional climate and atmospheric circulation, and this has not been explained. I\ndon’t think this has been addressed by inclusion of the ranges in figure 4 or the additional\nconceptual framework (you state at L105 ‘Within Alaskan records, differences in timing and\nmagnitude of delta18O changes imply variability in both temperature and precipitation resulting\nfrom atmospheric circulation patterns’ – but across a relatively small region such as this\nchanges in temperature and precipitation would be the same surely?). I cannot find anywhere\nelse this has been discussed. Perhaps a comparison of the records showing just the late\nHolocene section in the supplementary file would show that they co-vary but have different\nmagnitudes, it is hard to see if this is the case from the figure, which could be explained by local\nfactors. Otherwise I don’t see how you can conclude that the lake records are reflecting late\nin a similar way at all the lakes.\nWe sincerely appreciate the reviewers excellent questions that guided our revisions. We now\nclarify this issue by noting that d18O variations may differ between nearby open and closed lakes\nbecause they reflect different seasons (RL 202-203, 247-250). The revisions better illustrate our\nobjective to utilize differences between the open and closed records to evaluate changes in\nseasonality through time and explains that the sensitivity of closed and open lakes varies with\nregard to summer and winter climatic conditions, respectively. In addition, the revised\nintroduction explains the rational for selecting open and closed lakes as a way to specifically\nexplore independent summer and winter climatic variations that may have differences (RL 66-\n79). Finally, we revised the Fig. 4 annotations and caption to emphasize the winter and summer\nseasons.\n4. The revisions have introduced valuable new text, data, and figures (primarily in the\nSupporting Information), which strengthen the manuscript scientifically. At the same time, this\nrestructuring has created some clarity issues that were not present in the original submission.\nI would encourage the authors to emphasize the central findings more prominently in the main text\nand streamline the methodological details into the Supporting Information, while ensuring a\nclear and logical flow. This adjustment would help the manuscript become more concise and\naccessible to a broad readership, and ultimately enhance its impact and visibility.\nThank you for the recognition that the revised Supplemental Information strengthens the\nmanuscript and for these suggestions that help to further enhance impact. We have revised the\nmain text to more prominently emphasize our central findings. Our revisions of the introduction\nincluded streamlining methodological details to better emphasize important strengths of the data\n(chronology, resolution, continuity, seasonal sensitivity) and to explain why late Holocene\nvariations may differ between open and closed lakes (as described above).\n5. Results and discussion structure. The results section currently contains extensive commentary\nthat reads more like discussion (For example, Lines 126-134). Conversely, the discussion section\nis largely a continuation of further discussion. I would recommend merge results and discussion\ninto a single, well-structured section. Thank you for pointing out this discrepancy and we have\nchanged this heading to “Results and Discussion” as suggested. It is one single section structured\ninto three sub-sections that are logically organized by time-period (deglacial, transition and\nHolocene). We thank the reviewer for this very helpful suggestion.\nModerate/minor points:\nLines 26-28 – this is not a clear sentence, consider rephrasing\nWe revised this sentence to better highlight our findings and their significance to “Our new\nrecords are among the most reliably dated records yet produced in the circum-Arctic and show\nthat similar decreases in d18O of winter precipitation during the Younger-Dryas and late\nHolocene were driven by different atmospheric teleconnections” (RL 26-28)\nLines 52-53 – the c and p on the delta18O could be explained using brackets here\nThe 'c' is defined on line 44 (RL 62) and the 'p' is defined on line 35 (RL 41).\nThis has been revised into several sentences to clarify the intended meaning (RL 86-95)\nLine 77 – ‘associated with intensified’ – often words like an, or the, are missing through the\nmain text. Please check this here and elsewhere.\nAdded ‘an’ and checked for similar missing words throughout.\nLine 87-89 – references needed for the previous proxy studies\nAdded references (RL103)\nLine 90 – ‘would imply unrealistic higher temperatures’ is it unrealistic in magnitude? or just\nthat you expect the LIA to be colder?\nRevised to clarify that we mean warmer temperatures would be inconsistent with the broad\nknowledge that this is a relatively cold period (RL 104-105)\nLine 98, I don’t think “YD is the most recent stadial period”\nThis phrase has been deleted.\nLine 104 – ‘that are not observed in the’ – change to something like: ‘that don't follow variations\nobserved in North Atlantic records require...’\nThank you, we made this suggested change (RL 46-47)\nLine 109, 119, I recommend avoiding the term ‘decline’ here, as it may oversimplify the isotopic\nvariations. Consider more precise alternatives like ‘decrease’ if you want say going to more\n“negative” isotopic values.\nAs suggested, we have changed this terminology to decrease here, and in other similar instances.\n(RL 125)\nLine 126-127 – ‘amplified the influence of zonal Atlantic northern hemispheric drivers of high-\nlatitude isotope relationships’ – the use of zonal, atlantic, northern hemisphere and high latitude\nin this sentence make it unclear what is being said, it should be rephrased to improve clarity.\nThank you. We rephrased this sentence and specifically simplified this phrase to “…that shifted\nthe polar jet stream southward.” (RL 133-136)\nLine 128 – replace first ‘and’ with a comma\nDone (RL 136)\nLine 167, avoid using “exceptional aridity” that can sound subjective or emotive.\nChanged to unprecedented (RL 173).\nLine 168-170 – I am lost here at what sea level change has to do with the climate- perhaps more\nexplicitly link with winter temperatures and summer precipitation\nThank you. We revised this paragraph in response to this suggestion (RL 174-181)\nLine 170 – ‘declines in delta18O correspond with rapid sea-level rise associated with meltwater\n4\npulse 1b… which led to increased freshwater export from the Arctic Ocean into the North\nAtlantic known to influence AMOC stability’ – here again you should be more explicit about\nwhat you mean. Did the changes in SL and AMOC cause the delta18O decline? And if so how?\nThis was a comment raised in my previous review which has not been improved by the re-write.\nThank you. We revised this paragraph in response to this suggestion to explicitly explain the\nrelationship between d18O declines and sea level (RL 182-186)\nLine 181 – I would combine this paragraph with the one above, where no results are mentioned\ncurrently\nThank you. We have significantly revised these paragraphs (RL187-208).\nLine 217- ‘are understood to reflect winter precipitation due to groundwater processes’ –\nunderstood by who? A reference may be needed here. It is not clear why this interpretation is\ndiscounted\nThank you, we significantly revised this paragraph to clarify our interpretation of the Late\nHolocene data (RL 240-250).\nLine 219 – ‘which also result in significant isotope depletion’ – I think references are needed\nhere\nReferences added (RL 244)\nLine 220 – ‘circulation patterns are well recognized in driving basin-wide patterns in land and\nocean temperatures’ – if this is the case, why do the late Holocene changes differ from each\nother?\nThank you for pointing out the need for better explaining this concept. We have revised this\nparagraph to explain that open and closed lake records that reflect sensitivity to winter and\nsummer conditions, respectively, may differ in the same regions (see also our response to Major\npoint #3, above). (RL 246-250)\nLine 241 – ‘weak evidence’ – why is this data weak? if it is not reliable then it should be not used\nto argue for warm summers, as you do here.\nThank you, we revised this phrase to \"the absence of glacial moraine evidence for advances\nduring the YD chron” (RL266)\nLine 387-389, “a fortuitous aquatic macrofossil…” I would suggest remove the “fortuitous” in\ncase some readers interpret it as “lucky” or “fortunate”.\nWe deleted ‘fortuitous’ and this discussion was moved to the Supplementary section where we\ndiscuss the reservoir corrections for aquatic macrofossils.\nThe reference list is not fully formatted according to submission guidance. Please ensure\nconsistency in reference style (e.g., author names, journal abbreviations, use of italics) and\nverify that all references are complete and correctly formatted. In addition, there are\ntypographical errors: extra quotation marks at Lines 517, 576, and 583, and a line break issue\nat Line 533.\nThank you, we carefully revised the reference list following these observations.\nI co-reviewed this manuscript with one of the reviewers who provided the listed reports. This is\npart of the Nature Communications initiative to facilitate training in peer review and to provide\nappropriate recognition for Early Career Researchers who co-review manuscripts.\nWe thank Reviewer #3 for their co-review.\nReviewer #4\nThe authors have provided a revised version of their manuscript which shows that similar\ndecreases in d18O values in two contrasting time intervals (the Younger Dryas and the Late\nHolocene) can be explained by different climatic mechanisms. In the former case, it is\nsynchronization of Alaska with the North Atlantic Ocean, and in the latter attribution to changes\nin Pacific Ocean basin atmospheric circulation.\nThe conclusions remain plausible, and are important results.\nI do feel that the manuscript makes a solid contribution to the potential causes of Holocene\nprecipitation d18O variations, but I don't feel that the manuscript conclusively demonstrated the\nattribution of the Late Holocene variations, and I was left feeling a little underwhelmed with the\nfinal conclusions.\nThe records themselves are really high quality and the paper could even emphasize more\nstrongly (as the authors did in the response to reviewers) that these new records are among the\nmost securely-dated in the circum-Arctic.\nWe are sincerely grateful to Reviewer #4 for their recognition of our findings, their quality, and\ntheir importance. We appreciate their excellent observations and have revised the data\npresentation to more conclusively demonstrate late Holocene attributions and more strongly\nemphasize the strengths of our data, including the final conclusions, described in detail below.\nWe thank the reviewer for helping to guide these important improvements.\nMinor comments:\nThere are a lot of typos in the manuscript. I didn't try to correct them all.\nThank you, we apologize. We have conscientiously reviewed the revised manuscript for typos.\nThe stable isotope terminology in several cases is incorrect, i.e., it is not possible to have\n\"depleted isotopes\". See Table 2.1 of Sharpe's Stable Isotope Geochemistry book for\nrecommendations on proper terminology. \"Absolute depletion of d18Op variations\" also doesn't\nmake sense. A sample can be depleted in 18O, or depleted in 16O, but it can't be deplete\ngenerally. There are other instances where improvement would help the manuscripts\npresentation.\nThank you, we agree, and have corrected every instance of stable isotope terminology according\nto the correct conventions.\nFigure S2 is not legible, and several of the other Supp figures are of low to poor quality.\nThank you for identifying this problem. We have re-inserted all figures as .PNG images at\n600dpi and hopefully this improves the resolution.\nthe Late Holocene could produce the very negative d18O anomalies. But I'm still not sure about\nthe attribution. What forced the change? The authors suggested PDO/ENSO type variations,\nwhich are plausible sources of the anomalies, but I didn't see a strong conclusion, i.e., a link to a\nproxy record of PDO or ENSO that can convincingly show a correlation.\nWe deeply thank the reviewer for this suggestion, and we have accordingly revised Fig. 2 to\nshow proxy reconstructions of ENSO and eastern equatorial Pacific SSTs. The combined ENSO\nrecords make a simpler and stronger visual comparison that convincingly shows a deglacial\ncorrelation between the North Pacific with Greenland and a late Holocene correlation with the\nEquatorial Pacific. We appreciate the reviewer for guiding this important improvement.\nL35: I wouldn't state that lake carbonate and ice d18O are directly comparable, isotopically\nspeaking. One is an indirect precipitation proxy, the other direct.\nThank you, ‘directly’ has been deleted (RL 43)\nL39: delete \"drift\", an outdated term.\nThank you, this sentence has been deleted.\nL46-7, i think you mean Supp Fig 2? I have no problems with the authors *interpreting*\nthe\ncalcite d18O as a proxy for the d18O of the lake water, which reflects the d18O of winter\nprecipitation. That is well supported. But whether the calcite is truly at equilibrium and has\nremained so \"faithfully\" is not so clear.\nThank you – we have corrected this to Supplementary Fig 2. We have removed the word\n“faithfully“ to acknowledge that equilibrium stability is difficult, or perhaps impossible, to prove.\nHowever, our multi-proxy data also shows no clear evidence for a large change in productivity\nacross intervals of large d18O shifts, which the literature suggests are possible drivers of\nequilibrium instability (RL 64-66)\nL48: How large is the region?\nAdded area of ~1500km2 (RL 69)\nL241: What does \"weak evidence in glacial moraines\" mean?\nThank you, we revised to ‘the absence of glacial moraine evidence for YD advances” (RL 266)\nL246: do you mean \"Attribution of such shifts\"?\nThank you, we revised this sentence for a different emphasis (RL 271)\nL251: This sentence should be rewritten to something like \"Our data show that similar decreases\nin lake sediment d18O during the YD and Late Holocene can be forced by different\nmechanisms.\" As written it doesn't make any sense, because fractionation is not what is being\ninvestigated here.\nThank you for this helpful clarification. We made this change in the conclusion (RL 277-278)\nand revised the abstract (RL 26-28). We thank the reviewer for guiding important improvements.\nReviewer #4 (Remarks to the Author):\nThe authors have done a nice job of improving the paper!\nThank you!\nI am satisfied with the revisions and feel the manuscript is ready for publication, after\none small change:\nThe references to d18Op when referring to the lake sediment records is incorrect. They\nshould be d18Oc, which certainly tracks past changes in d18Op, but with a time-varying\ntemperature-dependent fractionation offset and whatever lake-specific isotopic effects\nare happening. It is ok to use d18Op when talking about inferences about changes in\nthe d18O of past precipitation, but not when referring to the sediments.\nWe take your point and have revised the d18O subscripts of 'c' and 'p' in the main text\nfollowing this suggestion. Changes were made on Lines 64, 66, 90, 93, 108, 113, and\n178."}]

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