potential analogues for paleoclimatic variations in eastern interior alaska during the past 14 000 yr atmospheric circulation controls of regional temperature and moisture responses the paleoclimatic history of a region can be viewed as a series of surface temperature and moisture anomalies through time the effects of changes in large scale climatic controls e g insolation major circulation controls can be mediated by the influence of smaller scale controls e g topographic barriers coastlines this may result in heterogenous surface climatic responses at the regional and sub regional scale divergent paleoclimatic trajectories between regions may be explainable in terms of such meso scale patterns using modern analogues for paleoclimate we examine how the sequence of climatic variations in eastern interior alaska during the interval 12 000 0 14c yr bp could have been generated by specific atmospheric circulation patterns fossil pollen and lake level records document the long term trends in temperature and effective moisture for the region water balance modelling provides additional estimates of paleoprecipitation synoptic climatological patterns are described using the modern instrumental record of upper level and sea level pressure surface temperature and precipitation at 12 000 14c yr bp eastern interior alaska was cooler and drier than present a situation generated today by a southward displacement of the jet stream conditions warmer and drier than present at 9000 14c yr bp may have been generated by increased ridging north of alaska and a weakened westerly circulation warmer wetter conditions than present possibly prevailed in the late middle holocene these might reflect ridging over alaska and troughing further west cool wet conditions feature enhanced westerly flow into alaska through an eastward shift in the east asian trough and positive pressure anomalies in the north pacific they may be analogous to cold periods of the little ice age the analogues demonstrate how surface conditions in other parts of beringia may sometimes be similar to while at other times different from those in the eastern interior these broader spatial patterns provide hypotheses about past climates that can be tested with paleoclimatological data for example the widespread positive temperature anomalies associated with the warm dry 9000 14c yr bp analogue fit with the expansion northward of the eastern siberian treeline the anomalously cool conditions in northeast siberia associated with the warm wet analogue may explain the continued late middle holocene treeline advance in alaska while there was retreat in siberia

lateglacial and early holocene climate oscillations in the matanuska valley south central alaska abstract here we present multi proxy data from two cores taken from hundred mile lake in the matanuska valley of south central alaska to investigate the climate vegetation and deglaciation history of the last 14 000 years the chronology of the cores was controlled by five ams dates sediment lithology changes from clay at 14 13 ka 1 ka 1000 cal bp through marl at 13 8 ka to gyttja at 8 0 ka the transition from clay to marl probably represents increased productivity of the lake in a stabilizing watershed induced by initial allerod climate warming after ice retreat as calcite precipitation of marl was facilitated by chara photosynthesis under high water temperature in summer the 18o record obtained from bivalve pisidium mollusc shells shows several large shifts between 13 and 8 ka a negative excursion of 2 in 18o at 12 4 11 5 ka is suggestive of a regional expression of the younger dryas gs 1 cooling event a 4 5 negative shift from 10 5 at 13 11 ka to 15 at 10 5 8 ka occurred during the peak carbonate interval around 10 5 ka this surprisingly large negative shift in 18o values during the early holocene thermal maximum has not been documented elsewhere in the region this shift suggests a major change in atmospheric circulation patterns possibly through more frequent easterly flow of warm and dry air masses that are also depleted in 18o pollen results from marl sediments indicate vegetation change from a herb tundra through shrub birch dominated tundra to an alder forest which follows closely with other regional pollen sequences in south central alaska the results from this study suggest that the climatic shift during the early holocene was of greater magnitude than the younger dryas event implying the importance of regional feedback processes in high latitudes in controlling regional climate response to large scale forcing

pacific ocean and cenozoic evolution of climate 1 the pacific ocean has played a major role in climate evolution throughout the cenozoic 65 0 ma it is a fundamental component of global heat transport and circulation the dominant locus of primary productivity and consequently the largest reservoir for carbon exchange between the oceans and the atmosphere a satisfactory understanding of the cenozoic evolutionary history of the pacific and its impact on global climate is currently data limited nevertheless the large dynamic range of cenozoic conditions sets the stage to greatly expand our understanding of global climate and biogeochemical cycles past earth experiments are particularly useful to understand interactions between climate and geosystems under different greenhouse gas loads we highlight in this review four important problems in which the pacific played a major role the effect of changing geographic boundary conditions on ocean circulation interactions between the carbon cycle and climate the pacific ocean s influence on north american climate and its water cycle and the gradual evolution of climate systems

paleodrainage on the chukchi shelf reveals sea level history and meltwater discharge abstract chirp subbottom data collected across the chukchi shelf offshore nw alaska imaged numerous paleochannels and valleys that appear to have been downcut and incised during sea level falls associated with glacial intervals in contrast the two most recent incisions appear to have been formed during the period of sea level rise following the last glacial maximum lgm the architecture and infill associated with these two incisions suggests that they were formed by an increase in discharge these events appear to be unrelated to sea level fluctuations but rather triggered by climatic variations during the most recent deglaciation i e meltwater discharge radiocarbon dates from sediment cores within the southern incised valley suggest that the two episodes of meltwater discharge may correlate with meltwater pulse 1 a 14 000 cal yr bp and evidence of iceberg scouring on outer chukchi shelf 12 000 to 13 000 cal yr bp respectively regional transgression across the interfluves on the middle chukchi shelf appears to postdate the second meltwater discharge and may correlate with meltwater pulse 1 b 11 500 cal yr bp this evidence suggests that in glacially dominated landscapes episodes of large discharge to the shelf might be out of phase with the sea level cycle in addition the presence of glacial meltwater drainage on the shelf implies a greater volume of continental glaciation during the lgm than previously recognized

oriented lake development in the context of late quaternary landscape evolution mckinley bay coastal plain western arctic canada abstract oriented lakes characterized by elongate forms central basins and shallow littoral shelves are common features of circum arctic coastal lowlands the environmental conditions geological processes and chronology associated with the development of oriented lakes however are little known but essential for understanding how such arctic lowlands evolve using combined techniques of field and drill log stratigraphy and sedimentology luminescence and radiocarbon dating methods and geomorphic mapping we reconstruct the landscape evolution leading toward oriented lake formation on the mckinley bay coastal plain of western arctic canada a region with over 900 oriented lakes most lakes with deep central basins are inherited from a preglacial braidplain ca 73 27 ka and alluvial braided channel network that extended beyond the glacial limit ca 18 6 14 3 ka eolian erosion active during the lateglacial and postglacial period ca 12 8 1 9 ka reworked fluvial deposits eolian processes modified existing basins and created other shallow deflationary basins as small barchanoid dunes migrated under cold dry paraglacial conditions between about 12 8 and 10 7 ka vegetation cover developed at the onset of the early holocene climatic optimum ca 10 7 ka and parabolic dunes were active between 9 6 and 4 6 ka thus oriented lakes developed in basins conditioned by fluvial and eolian processes in the absence of much near surface ground ice lateral expansion of deep basin lakes and shallow stabilized deflationary basins predominated during the late holocene through wind induced wave and current processes overall this sequence of oriented lake formation does not support a thaw lake cycle but rather small basin evolution of a periglacial landscape

sediment core profiles of long chain n alkanes in the sea of okhotsk enhanced transport of terrestrial organic matter from the last deglaciation to the early holocene 1 terrestrial plant derived n alkanes c25 c35 w ere measured in three piston cores pc1 pc2 and pc4 in the sea of okhotsk covering the last 30 kyrs down core profiles of the n alkane concentrations and mass accumulation rates mar were characterized by deglacial maxima in particular cores pc2 and pc4 which were collected from the central and western sea of okhotsk respectively show a two step increase around the meltwater pulse events mwp 1a 14 5 13 5 kyr bp and 1b about 10 kyr bp this finding was interpreted by the outflow of terrestrial organic matter from the submerged land shelf to the sea of okhotsk through the east sakhalin current this study demonstrated that the sea level rise forced by global warming in the deglaciation period may have caused the enhanced transport of terrestrial organic matter in marginal seas index terms 3022 marine geology and geophysics marine sediments processes and transport 4267 oceanography general paleoceanography 1055 geochemistry organic geochemistry citation seki o k kawamura t nakatsuka k ohnishi m ikehara and m wakatsuchi sediment core profiles of long chain n alkanes in the sea of okhotsk enhanced transport of terrestrial organic matter from the last deglaciation to the early holocene geophys res lett 30 1 1001 doi 10 1029 2001gl014464 2003

paleogene calcite compensation depth in the eastern subtropical pacific answers and questions 1 ocean drilling program leg 199 drilled a north south transect across the eocene paleoequator in the eastern pacific permitting reconstruction the calcite compensation depth ccd since earliest eocene time the ccd was relatively shallow near the early eocene pacific equator 3200 m and unlike modern latitudinal ccd gradients deepened to the north to 3600 m paleolatitude 10 n at 41 ma the ccd underwent a brief sharp transient deepening of 700 m then remained shallow until the eocene oligocene boundary at the e o boundary the ccd deepened by 1200 m in less than 300 kyr this rapid deepening served to more than double the area of seafloor subject to caco3 deposition sea level fall associated with ice volume buildup and ensuing shelf basin fractionation is unlikely to be the sole cause of the increased deep ocean caco3 burial rather a sudden rapid increase in the amount of ca entering the ocean appears necessary to explain the observations

late quaternary vegetation history of the fishhook bend area porcupine river alaska ped pond is a lake lying in a pleistocene scour channel of the porcupine valley the valley is considered to be a possible path of late quaternary species migrations between interior alaska and northwest canada pollen in the oldest lake sediments ca 13 000 years old indicates that shrub birch and willow probably occurred locally in a sparsely vegetated herb dominated landscape populus juniperus and typha latifolia increased about 10 000 years ago suggesting particularly warm temperatures during the early holocene picea glauca which is presently common in the surrounding forests first arrived near ped pond about 8500 years ago this arrival date together with existing evidence from other sites indicates that spruce expanded rapidly across far eastern beringia 8000 9000 years ago other boreal forest taxa picea mariana betula papyrifera and alnus spp became established locally between 7000 and 8000 years bp a date of ca 7500 years bp at ped pond suggests that the alnus rise in northeast

a 16 000 year record of vegetational change in south western alaska as inferred from plant macrofossils and pollen pollen and macrofossil analyses of a sediment core from beaver pond 60 37 14 n 154 19 w 579 m a s l reveal a record of regional and local postglacial vegetation change in south western alaska the chronology is based on five ams accelerator mass spectrometry 14c ages obtained from terrestrial plant macrofossils pollen and macrofossil records suggest that open herb and shrub tundra with e g poaceae cyperaceae artemisia vaccinium and salix prevailed on the landscape before ca 14 000 cal a bp the shift from herb to shrub dominated tundra salix subsequent betula expansion possibly reflects climatic warming at the beginning of the bolling period at ca 14 700 14 500 and around 13 500 cal a bp vegetation betula shrub tundra remained relatively stable until the early holocene macrofossil influx estimates provide evidence for greater biomass in betula shrub tundra during the early postglacial period than today charcoal accumulation rates suggest tundra fire activity was probably greater from ca 12 500 to 10 500 cal a bp similar to results from elsewhere in alaska the pollen and macrofossil records of beaver pond suggest the prevalence of low shrub tundra shrub betula betula nana vaccinium ledum palustre ericaceae and tall shrub tundra alnus viridis ssp crispa salix between 10 000 and 4000 cal a bp this holocene vegetation type is comparable with that of the modern treeless wet and moist tundra in south western alaska the expansion of picea glauca occurred 4000 cal a bp much later than that of a viridis ssp crispa whereas in central and eastern alaska picea glauca expanded prior to or coincident with alnus viridis at sites located only 200 400 km north east of beaver pond farewell and wien lakes picea glauca and betula forests expanded 8000 6000 cal a bp unfavourable climatic conditions and soil properties may have inhibited the expansion and establishment of picea across south west alaska during the mid and late holocene copyright 2011 john wiley sons ltd

reconstructed summer degree days in central alaska and northwestern canada since 1524 abstract three time series based on precisely dated annual tree ring widths have been used to reconstruct june plus july degree days for the central alaska and northwestern canada region the time series are the longest recently developed chronologies for the area and represent 57 core samples from 27 trees the degree day reconstruction extending back to a d 1524 exhibits much year to year variation and extended warming and cooling trends including a general warming trend from about 1840 to 1960 the reconstruction is in agreement with some subaretic glacial information and with data of percentage melting from arctic ice cores this and similar reconstructions can provide quantitative information to compare with general circulation and energy budget models for longer time periods than are available in recorded meteorological data

stratigraphy and palaeoclimatic significance of late quaternary loess palaeosol sequences of the last interglacial glacial cycle in central alaska abstract loess is one of the most widespread subaerial deposits in alaska and adjacent yukon territory and may have a history that goes back 3 ma based on mineralogy and major and trace element chemistry central alaskan loess has a composition that is distinctive from other loess bodies of the world although it is quartz dominated central alaskan loess was probably derived from a variety of rock types including granites metabasalts and schists detailed stratigraphic data and pedologic criteria indicate that contrary to early studies many palaeosols are present in central alaskan loess sections the buried soils indicate that loess sedimentation was episodic or at least rates of deposition decreased to the point where pedogenesis could keep ahead of aeolian input as in china loess deposition and pedogenesis are likely competing processes and neither stops completely during either phase of the loess soil formation cycle loess deposition in central alaska took place before and probably during the last interglacial period during stadials of the mid wisconsin period during the last glacial period and during the holocene an unexpected result of our geochronological studies is that only moderate loess deposition took place during the last glacial period our studies lead us to conclude that vegetation plays a key role in loess accumulation in alaska factors favouring loess production are enhanced during glacial periods but factors that favour loess accumulation are diminished during glacial periods the most important of these is vegetation boreal forest serves as an effective loess trap but sparsely distributed herb tundra does not thus thick accumulations of loess should not be expected where tundra vegetation was dominant and this is borne out by modern studies near the treeline in central alaska much of the stratigraphic diversity of north american loess including that found in the central lowlands the great plains and alaska is explained by a new model that emphasizes the relative importance of loess production factors versus loess accumulation factors

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

interpreting the ca isotope record of marine biogenic carbonates an 18 million year record of the ca isotopic composition 44 42ca of planktonic foraminiferans from odp site 925 in the atlantic on the ceara rise provides the opportunity for critical analysis of ca isotope based reconstructions of the ca cycle 44 42ca in this record averages 0 37 0 05 1 sd and ranges from 0 21 to 0 52 the record is a good match to previously published neogene ca isotope records based on foraminiferans but is not similar to the record based on bulk carbonates which has values that are as much as 0 25 lower bulk carbonate and planktonic foraminiferans from core tops differ slightly in their 44 42ca i e by 0 06 0 06 n 5 while the difference between bulk carbonate and foraminiferan values further back in time is markedly larger leaving open the question of the cause of the difference modeling the global ca cycle from downcore variations in 44 42ca by assuming fixed values for the isotopic composition of weathering inputs 44 42caw and for isotope fractionation associated with the production of carbonate sediments sed results in unrealistically large variations in the total mass of ca2 in the oceans over the neogene alternatively variations of 0 05 in the ca isotope composition of weathering inputs or in the extent of fractionation of ca isotopes during calcareous sediment formation could entirely account for variations in the ca isotopic composition of marine carbonates ca isotope fractionation during continental weathering such as has been recently observed could easily result in variations in 44 42caw of a few tenths of permil likewise a difference in the fractionation factors associated with aragonite versus calcite formation could drive shifts in sed of tenths of permil with shifts in the relative output of calcite and aragonite from the ocean until better constraints on variations in 44 42caw and sed have been established modeling the ca2 content of seawater from ca isotope curves should be approached cautiously

a deglacial and holocene record of climate variability in south central alaska from stable oxygen isotopes and plant macrofossils in peat we used stable oxygen isotopes derived from bulk peat d 18 otom in conjunction with plant macrofossils and previously published carbon accumulation records in a w14 500 cal yr bp peat core ht fen from the kenai lowlands in south central alaska to reconstruct the climate history of the area we find that patterns are broadly consistent with those from lacustrine records across the region and agree with the interpretation that major shifts in d 18 otom values indicate changes in strength and position of the aleutian low al a semi permanent low pressure cell that delivers winter moisture to the region we find decreased strength or a more westerly position of the al relatively higher d 18 otom values during the bolling allerod holocene thermal maximum htm and late holocene which also correspond to warmer climate regimes these intervals coincide with greater peat preservation and enhanced carbon c accumulation rates at the ht fen and with peatland expansion across alaska the htm in particular may have experienced greater summer precipitation as a result of an enhanced pacific subtropical high a pattern consistent with modern d 18 o values for summer precipitation the combined warm summer temperatures and greater summer precipitation helped promote the observed rapid peat accumulation a strengthened al relatively lower d 18 otom values is most evident during the younger dryas neoglaciation and the little ice age consistent with lower peat preservation and c accumulation at the ht fen suggesting less precipitation reaches the leeward side of the kenai mountains during periods of enhanced al strength the peatlands on the kenai peninsula thrive when the al is weak and the contribution of summer precipitation is higher highlighting the importance of precipitation seasonality in promoting peat accumulation this study demonstrates that d 18 otom values in peat can be applied

reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr 1 marine and terrestrial derived biomarkers alkenones brassicasterol dinosterol and long chain n alkanes as well as carbonate biogenic opal and ice rafted debris ird were measured in two sediment cores in the sea of okhotsk which is located in the northwestern pacific rim and characterized by high primary productivity down core profiles of phytoplankton markers suggest that primary productivity abruptly increased during the global meltwater pulse events 1a about 14 ka and 1b about 11 ka and stayed high in the holocene spatial and temporal distributions of the phytoplankton productivity were found to be consistent with changes in the reconstructed sea ice distribution on the basis of the ird this demonstrates that the progress and retreat of sea ice regulated primary productivity in the sea of okhotsk with minimum productivity during the glacial period the mass accumulation rates of alkenones caco3 and biogenic opal indicate that the dominant phytoplankton species during deglaciation was the coccolithophorid emiliania huxleyi which was replaced by diatoms in the late holocene such a phytoplankton succession was probably caused by an increase in silicate supply to the euphotic layer possibly associated with a change in surface hydrography and or linked to enhanced upwelling of north pacific deep water index terms 1050 geochemistry marine geochemistry 4835 4850 1055 geochemistry organic geochemistry 4267 oceanography general paleoceanography keywords okhotsk sea paleoproductivity sediment citation seki o m ikehara k kawamura t nakatsuka k ohnishi m wakatsuchi h narita and t sakamoto 2004 reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr paleoceanography 19 pa1016

potential role of vegetation feedback in the climate sensitivity of high latitude regions a case study at 6000 years b p previous climate model simulations have shown that the configuration of the earth s orbit during the early to mid holocene approximately 10 5 kyr can account for the generally warmer than present conditions experienced by the high latitudes of the northern hemisphere new simulations for 6 kyr with two atmospheric mixed layer ocean models community climate model version 1 ccm1 and global environmental and ecological simulation of interactive systems version 2 genesis 2 are presented here and compared with results from two previous simulations with genesis 1 that were obtained with and without the albedo feedback due to climate induced poleward expansion of the boreal forest the climate model results are summarized in the form of potential vegetation maps obtained with the global biome model which facilitates visual comparisons both among models and with pollen and plant macrofossil data recording shifts of the forest tundra boundary a preliminary synthesis shows that the forest limit was shifted 100 200 km north in most sectors both ccmi and genesis 2 produced a shift of this magnitude genesis 1 however produced too small a shift except when the boreal forest albedo feedback was included the feedback in this case was estimated to have amplified forest expansion by approximately 50 the forest limit changes also show meridional patterns greatest expansion in central siberia and little or none in alaska and labrador which have yet to be reproduced by models further progress in understanding of the processes involved in the response of climate and vegetation to orbital forcing will require both the deployment of coupled atmosphere biosphere ocean models and the development of more comprehensive observational data sets

seawater calcium isotope ratios across the eocene oligocene transition during the eocene oligocene transition eot ca 34 ma earth s climate cooled significantly from a greenhouse to an icehouse climate while the calcite caco3 compensation depth ccd in the pacific ocean increased rapidly fluctuations in the ccd could result from various processes that create an imbalance between calcium ca sources to and sinks from the ocean e g weathering and caco3 deposition with different effects on the isotopic composition of dissolved ca in the oceans due to differences in the ca isotopic composition of various inputs and outputs we used ca isotope ratios 44 40ca of coeval pelagic marine barite and bulk carbonate to evaluate changes in the marine ca cycle across the eot we show that the permanent deepening of the ccd was not accompanied by a pronounced change in seawater 44 40ca whereas time intervals in the neogene with smaller carbonate depositional changes are characterized by seawater 44 40ca shifts this suggests that the response of seawater 44 40ca to changes in weathering fluxes and to imbalances in the oceanic alkalinity budget depends on the chemical composition of seawater a minor and transient fluctuation in the ca isotope ratio of bulk carbonate may reflect a change in isotopic fractionation associated with caco3 precipitation from seawater due to a combination of factors including changes in temperature and or in the assemblages of calcifying organisms

the role of the global carbonate cycle in the regulation and evolution of the earth system we review one of the most ancient of all the global biogeochemical cycles and one which reflects the profound geochemical and biological changes that have occurred as the earth system has evolved through time that of calcium carbonate caco3 in particular we highlight a mid mesozoic revolution in the nature and location of carbonate deposition in the marine environment driven by the ecological success of calcareous plankton this drove the creation of a responsive deep sea sedimentary sink of caco3 the result is that biologically driven carbonate deposition provides a significant buffering of ocean chemistry and of atmospheric co2 in the modern system however the same calcifying organisms that under pin the deep sea carbonate sink are now threatened by the continued atmospheric release of fossil fuel co2 and increasing acidity of the surface ocean we are not yet in a position to predict what the impact on caco3 production will be or how the uptake of fossil fuel co2 by the ocean will be affected this uncertainty in the future trajectory of atmospheric co2 that comes from incomplete understanding of the marine carbonate cycle is cause for concern

late glacial and holocene δ15n and δ13c variation from a kenai peninsula alaska peatland abstract we use stable carbon and nitrogen isotopes from a kenai peninsula alaska fen spanning the late glacial and holocene to enhance our understanding of peatland hydrology and nutrient cycling we find that isotopic values for carbon and nitrogen are lighter in the late glacial and early holocene 28 to 34 and 0 to 4 respectively than the remainder of the record the light 13 c value corresponds with submerged and emergent aquatic vegetation during the late glacial suggesting high respired carbon input similarly light 15 n values imply that nitrogen is derived from sediment and groundwater sources early holocene 13 values ranging from 30 to 34 infer high recycled carbon uptake from methanogenesis related to the warm climate and the wet swale environment a shift to heavier 15 n and 13 c isotopic values 9600 cal yr bp coincides with a change in the lithology to sphagnum dominated peat indicative of peat accumulation above the water table a shift to lighter values from 5500 to 4200 cal yr bp coincides with a period of glacial recession related to warmer conditions whereas a subsequent period of heavier values is correlative with glacial advance culminating at 3000 cal yr bp suggesting that the hydrology of this peatland is closely linked with the glacial meltwater 15 n remains near 0 relatively close to the atmospheric value of 15 n throughout the holocene suggesting that the fen has been supported by n fixation we propose that groundwater on the kenai lowlands was fed by subglacial meltwater and the warm early holocene summers resulted in high glacial ablation and groundwater recharge sustaining a high swanson fen water table cooler temperatures resulted in a decrease of glacial meltwater input at the close of the early holocene

biological and ecological insights into ca isotopes in planktic foraminifers as a palaeotemperature proxy sea surface temperature sst is a critical variable in the earth s climate system since it influences atmospheric circulation the hydrological cycle and via ocean surface density drives ocean circulation a detailed reconstruction of past sst s is therefore a central goal of palaeoceanographic studies although calcium isotopes in foraminiferal carbonate have been introduced as a new proxy for sst reconstruction there is considerable debate about their robustness and general applicability to resolve some of these questions we have investigated the extent to which other environmental parameters e g the calcification temperature depth stratification growth rates and or environmental adaptation may influence the 44ca values of planktic foraminifers in modern and eocene samples geographically distributed data sets are affected by the exchange of cryptic species i e morphologically similar but genetically distinct species and by a mixing of optimal versus less optimal adaptation thus we have compared species within individual samples to evaluate whether the well documented depth stratification of foraminifers is reflected in their calcium isotopes the eocene data set shows a general agreement between 44ca and 18o derived calcification temperatures which supports a temperature effect on ca isotope incorporation the vertical temperature gradient using the different depth habitats of several foraminiferal species indicates a 44ca temperature dependence of 0 034 c 1 similar to inorganic calcite 0 015 c 1 and cultured o universa 0 019 c 1 the gradient resembles the global sediment 44ca compilation but it is significantly smaller than the temperature calibration of 0 22 0 02 c 1 for cultured g sacculifer the modern data set shows a general correlation between 44ca and depth habitat reflecting a similar temperature gradient to the eocene sample set in contrast the lower absolute 44ca values for the eocene foraminifers suggest a lower seawater isotope composition in situ analyses of individual calcite layers reveal large isotopic differences between the different calcite layers of the foraminifers highlighting the strong biological control on 44ca in foraminiferal calcite that may overprint a potential t relationship

human dispersal into interior alaska antecedent conditions mode of colonization and adaptations abstract in spite of more than a half century of exploration no definitive evidence has yet come to light for human occupation in eastern beringia preceding 12 000 yr bp the oldest dates between 11 500 and 12 000 yr bp are from sites in interior and northern alaska archaeological sites dating to this time period such as the broken mammoth site in the central tanana river valley have yielded evidence of pioneer colonization by groups with relatively little knowledge of lithic resources three possibly older cave sites bluefish caves lime hills caves and trail creek caves have stratigraphic and taphonomic problems that are not easily resolved no sites in the glaciated coastal zone of southern alaska are pleistocene in date and numerous objections can be raised to the viability of the coastal migration hypothesis particularly in the western gulf of alaska region for northern and interior alaska the earliest colonization appears to have been a push pull phenomenon linked to the dissolution of the bering land bridge through a combination of rising sea levels and ameliorating climate the climate of the birch poplar rise in the terminal pleistocene may have forced the extinction of obligate grazers such as mammoth and horse but it seems to have favored other taxa such as bison and elk at least until 9000 yr bp faunal data from the broken mammoth site in the central tanana valley with good organic preservation demonstrate the utilization of a wide diversity of taxa including small game waterfowl and fish faunal and sedimentological data give slight support to a younger dryas reversal but this was dwarfed by the mid holocene period of dry windy conditions during which interior alaska may have been largely abandoned

origin of last glacial loess in the western yukon tanana upland central alaska usa loess is widespread over alaska and its accumulation has traditionally been associated with glacial periods surprisingly loess deposits securely dated to the last glacial period are rare in alaska and paleowind reconstructions for this time period are limited to inferences from dune orientations we report a rare occurrence of loess deposits dating to the last glacial period 19 ka to 12 ka in the yukon tanana upland loess in this area is very coarse grained abundant coarse silt with decreases in particle size moving south of the yukon river implying that the drainage basin of this river was the main source geochemical data show however that the tanana river valley to the south is also a likely distal source the occurrence of last glacial loess with sources to both the south and north is explained by both regional synoptic scale winds from the northeast and opposing katabatic winds that could have developed from expanded glaciers in both the brooks range to the north and the alaska range to the south based on a comparison with recent climate modeling for the last glacial period seasonality of dust transport may also have played a role in bringing about contributions from both northern and southern sources

holocene glacier fluctuations waskey lake northeastern ahklun mountains southwestern alaska lake sediments from waskey lake ahklun mountains southwestern alaska were studied to decipher the history of upvalley glacier e uctuations during the holocene several indicators of glacier activity were measured including magnetic susceptibility organic matter content grain size distribution bulk sediment mineralogy and diatom assemblages seven radiocarbon ages on macrofossils along with cross checks by tephrochronology provide the chronology of the cores the results from core wl 1 indicate that glaciers lingered near waskey lake until 9100 cal yr bp perhaps under conditions of high winter accumulation peak organic matter content occurs at 7400 cal yr bp when precipitation might have shifted to summer the onset of neoglaciation occurred 3100 cal yr bp and glaciers reached their maximum extent 700 cal yr bp this chronology is consistent with the lichenometrically dated moraines from the glacier foree elds although the ages are tentative the youngest and most widespread group of moraines was deposited sometime between 650 and 200 cal yr bp during the little ice age since then glaciers in the waskey lake area have shrunk by 50 and equilibrium line altitudes ela have risen by 35 6 22 m this rise in ela is much less than the 100 to 200 m rise observed elsewhere in alaska and indicates considerable spatial variability in late holocene climatic change

coherent late holocene climate driven shifts in the structure of three rocky mountain lakes large scale atmospheric pressure centers such as the aleutian and icelandic low have a demonstrated relationship with physical lake characteristics in contemporary monitoring studies but the responses to these phenomena are rarely observed in lake records we observe coherent changes in the stratification patterns of three deep 30 m lakes inferred from fossil diatom assemblages as a response to shifts in the location and intensity of the aleutian low and compare these changes with similar long term changes observed in the 18o record from the yukon specifically these records indicate that between 3 2 and 1 4 ka the aleutian low shifted westward resulting in an increased frequency of storm tracks across the pacific northwest during winter and spring this change in atmospheric circulation ultimately produced deeper mixing in the upper waters of these three lake systems enhanced stratification between 4 5 and 3 3 ka and from 1 3 ka to present suggests a strengthened aleutian low and more meridion

holocene development of boreal forests and fire regimes on the kenai lowlands of alaska several studies have noted a relationship between vegetation type and fire frequency yet despite the importance of ecosystem processes such as fire the long term relationships between disturbance climate and vegetation type are incompletely understood we analysed pollen plant macrofossils and sedimentary charcoal from three lakes within the kenai lowlands to determine postglacial relationships between disturbance climate and vegetation for the boreal forest of southwest alaska an herb tundra was established in the lowlands following deglaciation by 13 000 cal bp salix alnus and probably betula kenaica expanded in the area after 10 700 cal bp followed by picea glauca by 8500 cal bp picea mariana became established by 4600 cal bp the early holocene was probably the driest time during the postglacial as determined by aquatic plant macrofossils and climate models lake levels reached near modern conditions by at least 8000 cal bp mean fire intervals mfi were longest during the shrubherb tundra phase 1389 65 yr decreased after expansion of b kenaica salix and populus 779 49 yr and picea glauca 819 41 yr and increased again with the arrival of p mariana 1309 66 yr unlike previous studies our data demonstrate the highest fire frequencies during the early to mid holocene and less frequent fire during the late holocene when p mariana forests dominated the lowlands early holocene forests of p glauca and b kenaica existed in summers that were longer and drier than today while the increasingly wetter and cooler climates of the late holocene probably hindered forest fire around paradox lake perhaps because of less frequent summer drought

responses of an arctic landscape to lateglacial and early holocene climatic changes the importance of moisture many of the physical and biological processes that characterize arctic ecosystems are unique to high latitudes and their sensitivities to climate change are poorly understood stratigraphic records of land surface processes and vegetation change in the arctic foothills of northern alaska reveal how tundra landscapes responded to climatic changes between 13 000 and 8000 14 c yr bp peat deposition began and shrub vegetation became widespread ca 12 500 14 c yr bp probably in response to the advent of warmer and wetter climate increased slope erosion caused rapid alluviation in valleys and populus trees spread northward along braided floodplains before 11 000 14 c yr bp lake levels fell and streams incised their floodplains during the younger dryas yd 11 000 10 000 14 c yr bp a hiatus in records of populus suggest that its geographic range contracted and pollen records of other species suggest a cooler and drier climate during this interval basal peats dating to the yd are rare suggesting that rates of paludification slowed immediately after 10 000 14 c yr bp lake levels rose streams aggraded rapidly again intense solifluction occurred and populus re invaded the area moist acidic tundra vegetation was widespread by 8500 14 c yr bp along with wet organic rich soils most of these landscape scale effects of climatic change involved changes in moisture although low temperature is the most conspicuous feature of arctic climate shifts in effective moisture may be the proximate cause for many of the impacts that climate change has in arctic regions r 2002 elsevier science ltd all rights reserved

late glacial and holocene landscapes of central beringia abstract new palynological and sedimentological data from st lawrence island present a rare view into late glacial and holocene environments of the central bering land bridge the late glaciation was a time of dynamic landscape changes in south central beringia with active thermokarst processes including the formation and drainage of thaw lakes the presence of such a wet unstable substrate if widespread probably would have had an adverse impact on food sources and mobility for many of the large mammal populations the establishment of betula shrub tundra on the island suggests late glacial summers that were warmer than present consistent with regional paleoclimatic interpretations however the increasing proximity to the bering sea as postglacial sea levels rose modified the intensity of warming and prevented the establishment of deciduous forest as found in other areas of beringia at this time the mid to late holocene is marked by more stable land surfaces and development of sphagnum and cyperaceae peat deposits the accumulation of organic deposits decline of shrub betula and decrease in thermokarst disturbance suggest that conditions were cooler than the previous a recent decline in peat accumulation at the study sites may relate to local geomorphology but similar decreases have been noted for other arctic regions

a framework for interpreting paleoclimatic variations in eastern beringia abstract paleoclimatic variations in a particular region can be viewed as the outcome of the superimposition of the effects of a number of large scale controls a framework for understanding paleoclimatic variations in a region can be established by considering the long term history of those controls jointly with climatic modeling results that illustrate how regional climates respond to changes of individual controls the relevant controls of late quaternary paleoclimatic variations in eastern beringia include 1 the size of the ice sheet which influences both atmospheric circulation and temperature 2 insolation which influences mainly temperature and seasonality 3 carbon dioxide concentration in the atmosphere which influences temperature and 4 feedbacks involving sea ice sea surface temperatures and snow cover which reinforce the insolation effects we review the results of a number of paleoclimatic experiments with general circulation models to illustrate the potential response of eastern beringia to the variations of these controls we then present a framework for understanding paleoclimatic variations in eastern beringia by describing the likely responses of the climate of this region to the known variations in the controls in addition we discuss key times during the quaternary when particular combinations of the controls give rise to natural experiments which lend themselves to the testing of particular hypotheses our understanding of the nature of climatic variations at high latitudes should increase through examination of paleoclimatic evidence that documents the response of the region at those key times

possible role of atmosphere biosphere interactions in triggering the last glaciation we coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system at the time of glacial inception 115 000 years ago orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present atmospheric composition oceans biosphere and cryosphere summers were however cold enough to induce major vegetation shifts in high northern latitudes southward migration of the boreal forest tundra limit helped to create favourable conditions for continental ice sheet growth with increasing snow depth and duration in labrador arctic canada and northern western fennoscandia these results support a role for biogeophysical feedback in initiating glaciations

mid miocene paleoproductivity in the atlantic ocean and implications for the global carbon cycle 1 a prominent middle miocene 17 5 13 5 ma carbon isotope excursion ubiquitously recorded in carbonate sediments has been attributed to enhanced marine productivity and sequestration of 13c depleted organic carbon in marine sediments or enhanced carbon burial in peat lignite deposits on land here we test the hypothesis that the marine 13c record reflects a change in productivity with proxy records from three atlantic ocean sites deep sea drilling program site 608 and ocean drilling program sites 925 and 1265 our multiproxy approach is based on benthic foraminiferal accumulation rates elemental ratios ba al and p al the 13c of bulk sedimentary organic matter and dissolution indices we compare these proxies to benthic foraminiferal 13c values measured on the same samples our results indicate that marine paleoproductivity in the atlantic ocean is not related to the benthic foraminiferal 13c excursion a numerical box model confirms that marine productivity cannot account for the 13c maximum the model shows that sequestration of 1 5 1018 mol c in the terrestrial realm over a period of 3 ma leads to a 0 9 13c increase in the deep ocean which is near the observed records therefore an increase in continental organic carbon sequestration is the most plausible way to enrich the ocean s carbon pool with 13c which is consistent with coeval lignite deposits worldwide the 13c values of bulk sedimentary organic matter parallel the 13c of dissolved inorganic carbon as reflected by benthic foraminiferal 13c values suggesting no significant change in atmospheric pco2 levels over the investigated period

land sea linkage of holocene paleoclimate on the southern bering continental shelf detailed diatom records within surface and core sediments from the southern bering continental shelf sbcs reveal that the holocene evolution of sea ice distribution is associated with low pressure patterns holocene sea ice distribution over the sbcs was mainly controlled by the location of the aleutian low the corresponding paleoceanographic and paleoclimate conditions can be divided into three stages 1 the early holocene before 7000 cal yr bp was characterized by extensive sea ice distribution under two low pressure cells which covered the western bering sea and the gulf of alaska respectively 2 between 3000 and 7000 cal yr bp the low pressure system over the gulf of alaska became weak causing total sea ice mass over the sbcs to retreat 3 in the past 3000 years prevailing southwesterly winds over the sbcs due to the developing aleutian low have reduced further sea ice cover on the sbcs these paleoclimatic changes were probably a response to enso variation the timings of water mass exchanges on the sbcs coincided with sea level change along the alaskan peninsula as a result subsequent morphologic alterations have also influenced the paleoceanographic condition of the sbcs the effect of the surface coastal water and bottom marine water on the sbcs intensified about 6000 cal yr bp when sea level increased

holocene climate inferred from oxygen isotope ratios in lake sediments central brooks range alaska analyses of sediment cores from two lakes in the central brooks range provide temperature and moisture balance information for the past 8500 cal yr at century scale resolution two methods of oxygen isotope analysis are used to reconstruct past changes in the effective moisture precipitation minus evaporation and temperature effective moisture is inferred from oxygen isotope ratios in sediment cellulose from meli lake area 0 13 km 2 depth 19 4 m the lake has a low watershed to lake area ratio 7 and significant evaporation relative to input summer temperature shifts are based on oxygen isotope analyses of endogenic calcite from tangled up lake area 0 25 km 2 depth 3 5 m this basin has a larger watershed to lake area ratio 91 and less evaporation relative to input sediment oxygen isotope analyses from the two sites indicate generally more arid conditions than present prior to 6000 cal yr b p subsequently the region became increasingly wet temperature variability is recorded minimally at centennial scale resolution with values that are generally cool for the past 6700 cal yr the timing and direction of climate variability indicated by the oxygen isotope time series from meli and tangled up lakes are consistent with previously established late holocene glacier advances at 5000 cal yr b p in the central brooks range and high lake levels at birch lake since 5500 cal yr b p this unique use of oxygen isotopes reveals both moisture balance and temperature histories at previously undetected high resolution temporal scales for northern alaska during the middle to late holocene c 2001 university of washington

regional atmospheric circulation change in the north pacific during the holocene inferred from lacustrine carbonate oxygen isotopes yukon territory canada analyses of sediment cores from jellybean lake a small evaporation insensitive groundwater fed lake provide a record of changes in north pacific atmospheric circulation for the last 7500 yr at 5 to 30 yr resolution isotope hydrology data from the southern yukon indicate that the oxygen isotope composition of water from jellybean lake reflects the composition of mean annual precipitation 18op recent changes in the 18o of jellybean sedimentary calcite 18oca correspond to changes in the north pacific index npi a measure of the intensity and position of the aleutian low al pressure system this suggests that 18op variability was related to the degree of fractionation during moisture transport from the gulf of alaska across the st elias mountains and that holocene shifts were controlled by the intensity and position of the al following this model between 7500 and 4500 cal yr b p long term trends suggest a predominantly weaker and or westward al between 4500 and 3000 cal yr b p the al shifted eastward or intensified before shifting westward or weakening between 3000 and 2000 cal yr b p rapid shifts eastward and or intensification occurred 1200 and 300 cal yr b p holocene changes in north pacific atmospheric circulation inferred from jellybean lake oxygen isotopes correspond with late holocene glacial advances in the st elias mountains changes in north pacific salmon abundance and shifts in atmospheric circulation over the beaufort sea

a 7600 yr vegetation and fire history from anthony lake northeastern oregon usa with linkages to modern synoptic climate patterns we used pollen and high resolution charcoal analysis of lake sediment to reconstruct a 7600 yr vegetation and fire history from anthony lake located in the blue mountains of northeastern oregon from 7300 to 6300 cal yr bp the forest was composed primarily of populus and fire was common indicating warm dry conditions from 6300 to 3000 cal yr bp populus declined as pinus and picea increased in abundance and fire became less frequent suggesting a shift to cooler wetter conditions from 3000 cal yr bp to present modern day forests composed of pinus and abies developed and from 1650 cal yr bp to present fires increased we utilized the modern climate analogue approach to explain the potential synoptic climatological processes associated with regional fire the results indicate that years with high fire occurrence experience positive 500 mb height anomalies centered over the great basin with anomalous southerly component of flow delivering dry air into the region and with associated sinking motions to further suppress precipitation it is possible that such conditions became more common over the last 1650 cal yr bp supporting an increase in fire despite the shift to more mesic conditions

eocene oligocene ocean de acidification linked to antarctic glaciation by sea level fall one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene boundary some 34 million years ago this climate transition was accompanied by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear merico et al use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition they find that only shelf to deep sea carbonate partitioning can explain the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change during this important climate transition a global biogeochemical box model is used to test competing hypotheses put forward to explain the eocene oligocene transition it is found that only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor this work sheds new light on the mechanisms linking glaciation and ocean acidity change across the climate transition of the cenozoic one of the most dramatic perturbations to the earth system during the past 100 million years was the rapid onset of antarctic glaciation near the eocene oligocene epoch boundary1 2 3 34 million years ago this climate transition was accompanied3 by a deepening of the calcite compensation depth the ocean depth at which the rate of calcium carbonate input from surface waters equals the rate of dissolution changes in the global carbon cycle4 rather than changes in continental configuration5 have recently been proposed as the most likely root cause of antarctic glaciation but the mechanism linking glaciation to the deepening of calcite compensation depth remains unclear here we use a global biogeochemical box model to test competing hypotheses put forward to explain the eocene oligocene transition we find that of the candidate hypotheses only shelf to deep sea carbonate partitioning is capable of explaining the observed changes in both carbon isotope composition and calcium carbonate accumulation at the sea floor in our simulations glacioeustatic sea level fall associated with the growth of antarctic ice sheets permanently reduces global calcium carbonate accumulation on the continental shelves leading to an increase in pelagic burial via permanent deepening of the calcite compensation depth at the same time fresh limestones are exposed to erosion thus temporarily increasing global river inputs of dissolved carbonate and increasing seawater 13c our work sheds new light on the mechanisms linking glaciation and ocean acidity change across arguably the most important climate transition of the cenozoic era

dendroclimatic reconstruction of summer temperatures in northwestern canada since a d 1638 based on age dependent modeling abstract ring widths from five picea glauca stands at the alpine treeline in northwestern canada are used to investigate climate growth responses and to develop a long reconstruction of summer temperatures response function and linear regression analyses indicate that the radial growth response of these trees to climate varies with age and site at most sites the period of significant positive response to growing season temperatures declines with tree age age dependent and standard age independent models are then used to develop two reconstructions of june july temperatures for northwestern canada extending back to a d 1638 calibration statistics were similar for both models but the standard model performed poorly during verification the reconstruction produced using age dependent modeling suggests june july temperatures were cooler than present throughout most of the past 350 years with the exception of the late 18th century particularly cool periods occurred at 1700 and in the mid 19th century in constast the standard model suggests that temperatures were similar to or warmer than present during the last 350 years the age dependent reconstruction compares favorably with other proxy climate records from northern north america age dependent dendroclimatic modeling can provide a sensitive record of recent climatic change that allows the inclusion of previously rejected sites into dendroclimatic analyses

investigating the sensitivity of the atmospheric general circulation model echam 3 to paleoclimatic boundary conditions we present atmospheric simulations of three different time slices of the late quaternary using the echam 3 general circulation model in t42 resolution in this work we describe the results of model runs for the time slices 6000 years bp last climate optimum 21 000 bp last glacial maximum and 115 000 years bp glacial inception although the solar insolation is known for all time slices a complete data set of the other boundary conditions which are necessary for running the atmospheric model exists only for the last glacial maximum in the form of the climap reconstruction for the other two time slices which are interglacial states like the modern climate sea surface temperatures land albedo and ice sheet topography are kept at modern values and only the solar insolation is changed appropriately the response of the model to solar insolation changes is quite reasonable the modelled anomalies are small and roughly opposite in sign for 6000 bp and 115 000 bp respectively in the case of last glacial maximum the glacial ice sheet topography and ice albedo produce a much larger climate anomaly in the model however to enable a real test of model performance under glacial boundary conditions the climap sea surface temperatures which are now known to be partly inaccurate should be replaced by an updated state of the art reconstruction

the cosmochemical behavior of beryllium and boron abstract the chemistry of be and b in the solar nebula is reinvestigated using thermodynamic equilibrium calculations the dominant be gases are monatomic be at high temperatures and the hydroxides beoh and be oh 2 at lower temperatures beryllium condenses as gugiaite ca 2 besi 2 o 7 in solid solution with melilite with a 50 condensation temperature of 1490 k if an ideal solid solution of chrysoberyl beal 2 o 4 into spinel is assumed most of the be condenses into spinel yielding a 50 condensation temperature of 1501 k however the difference in the crystal structures of spinel and chrysoberyl indicates that their solid solution may be non ideal at high temperatures the dominant b gases are bo hbo and hbo 2 while nabo 2 kbo 2 and libo 2 are dominant at lower temperatures boron is less refractory than be and is calculated to condense into solid solution with feldspar the majority of b condenses as danburite cab 2 si 2 o 8 in solid solution with anorthite at lower temperatures when the feldspar composition is more albitic the remaining b condenses as reedmergnerite nabsi 3 o 8 the 50 condensation temperature of b is 964 k the 50 condensation temperature of b is similar to that of na and much higher than that of s therefore normalized b abundances in chondrites are expected to correlate with na abundances be is predicted to be concentrated in melilite a conclusion which is consistent with the few measurements of be concentrations in calcium aluminum rich inclusions cais boron is predicted to be concentrated in feldspar but no analytical data are available to test this prediction

an oxygen isotope record of holocene climate change in the south central brooks range alaska abstract understanding the ecological and socio economic impacts of climatic warming requires knowledge of associated changes in moisture balance reconstructions of holocene moisture balance variation offer indispensible baseline information against which recent changes can be evaluated we analyzed chara stem encrustations in the sediments of takahula lake located in the south central brooks range of alaska for oxygen and carbon isotope composition to infer climatic change over the past 8000 years to help constrain climatic interpretations of the sediment 18 o record we also analyzed water samples from takahula and other lakes in the region for oxygen and hydrogen isotope composition results show that winter precipitation dominates the water balance of these lakes and that post input evaporation is a key control of lake water isotope composition of takahula lake stratigraphic patterns in chara 18 o supplemented by those in 13 c and sediment lithology reveal distinct changes in effective moisture precipitation minus evaporation over the past 8000 years effective moisture was relatively high from 8000 to 5000 cal bp with marked fluctuations between 6800 and 5000 cal bp it then decreased to reach a minimum around 4000 cal bp and increased with fluctuations from 4000 to 2500 cal bp followed by a decreasing trend toward the present that was interrupted by a wet little ice age centered at 400 cal bp aridity during the 20th century was among the highest of the entire 8000 year record at the millennial timescale the temporal patterns of moisture balance shifts at takahula lake are broadly coherent with those inferred from previous paleoclimate records from the region the chara 18 o values around 5600 cal bp and during the little ice age are up to 5 lower than at present and 3 6 lower than that of the modern input water to the lake these exceptionally low values suggest that factors other than effective moisture must have contributed to the pronounced variations in the takahula lake 18 o record increased winter precipitation associated with a westerly aleutian low position may account for 1 of the 18 o decrease other factors leading to the 18 o depletion during these periods probably include decreased temperatures as well as increased lake ice cover and associated reductions in evaporation

spatial variations of holocene climatic change in the yellowstone region abstract the paleoecologic record of the northern rocky mountains shows considerable spatial variability which has been difficult to explain as a unified response to large scale changes in effective moisture or temperature through time comparison of past and present climatic patterns suggests that the spatial heterogeneity in the fossil record arises from a local response to the effects of greater summer solar radiation during the early holocene solar radiation directly determines evapotranspiration and indirectly controls the strength of the summer monsoon and the eastern pacific subtropical high pressure system the yellowstone region provides an example of an area where the indirect effects of solar radiation are manifest by the juxtaposition of two contrasting climatic regimes today and where these regimes were amplified during the early holocene fossil pollen data suggest that central and southern yellowstone the summer dry area became drier in the early holocene while northern yellowstone the summer wet area became wetter the boundary between regimes however is controlled by topography and has not changed significantly in the holocene the spatial variations of holocene vegetation and climatic changes in the northern rocky mountains may therefore be explained as a trade off between strengthened monsoonal circulation and a stronger subtropical high in the early holocene and the relative importance of these precipitation regimes on a topographically complex landscape

late holocene moisture balance variability in the southwest yukon territory canada abstract analyses of sediment cores from marcella lake a small hydrologically closed lake in the semi arid southwest yukon provides effective moisture information for the last 4500 years at century scale resolution water chemistry and oxygen isotope analyses from lakes and precipitation in the region indicate that marcella lake is currently enriched in 18 o by summer evaporation past lake water values are inferred from oxygen isotope analyses of sedimentary endogenic carbonate in the form of algal charophyte stem encrustations a record of the 18 o composition of mean annual precipitation at jellybean lake a nearby evaporation insensitive system provides data of simultaneous 18 o variations related to decade to century scale shifts in aleutian low intensity position the difference between the two isotope records represents 18 o enrichment in marcella lake water caused by summer effective moisture conditions results indicate increased effective moisture between 3000 and 1200 cal bp and two marked shifts toward increased aridity at 1200 and between 300 and 200 cal bp these prominent late holocene changes in effective moisture occurred simultaneously with changes in aleutian low circulation patterns over the gulf of alaska indicated by jellybean lake the reconstructed climate patterns are consistent with the topographically controlled climatic heterogeneity observed in the coastal mountains and interior valleys of the region today

holocene thermal maximum in the western arctic 0 180 w the spatio temporal pattern of peak holocene warmth holocene thermal maximum htm is traced over 140 sites across the western hemisphere of the arctic 0 180 w north of 60 n paleoclimate inferences based on a wide variety of proxy indicators provide clear evidence for warmer than present conditions at 120 of these sites at the 16 terrestrial sites where quantitative estimates have been obtained local htm temperatures primarily summer estimates were on average 1 6 0 8 c higher than present approximate average of the 20th century but the warming was time transgressive across the western arctic as the precession driven summer insolation anomaly peaked 12 10 ka thousands of calendar years ago warming was concentrated in northwest north america while cool conditions lingered in the northeast alaska and northwest canada experienced the htm between ca 11 and 9 ka about 4000 yr prior to the htm in northeast canada the delayed warming in quebec and labrador was linked to the residual laurentide ice sheet which chilled the region through its impact on surface energy balance and ocean circulation the lingering ice also attests to the inherent asymmetry of atmospheric and oceanic circulation that predisposes the region to glaciation and modulates the pattern of climatic change the spatial asymmetry of warming during the htm resembles the pattern of warming observed in the arctic over the last several decades although the two warmings are described at different temporal scales and the htm was additionally affected by the residual laurentide ice the similarities suggest there might be a preferred mode of variability in the atmospheric circulation that generates a recurrent pattern of warming under positive radiative forcing unlike the htm however future warming will not be counterbalanced by the cooling effect of a residual north american ice sheet

european lakes as palaeohydrological and palaeoclimatic indicators abstract lakes in temperate regions have fluctuated in size on annual to millenial time scales changes in water level or depth can be reconstructed by applying geomorphic sedimentological and biostratigraphic methods to transects of sediment cores this systematic field based approach has been used at a number of sites in europe it is illustrated by reconstructions of water level changes in lakes from southern sweden these lakes have shown broadly synchronous changes during the holocene such synchronous changes in water levels at several sites in a region reflect climatic changes inferences about the mechanism of the climatic change depend on identifying both synchronous changes within a region and differences in the direction magnitude and timing of lake level changes between regions continental compilations of lake level data are therefore necessary detailed studies are not available from enough sites but the interpretation of already existing stratigraphic and biostratigraphic data in terms of lake level changes has greatly increased the number of sites available for a continental scale synthesis in europe this eclectic literature based approach is illustrated with examples from southern europe lakes in the mediterranean region were high around the glacial maximum and again somtime during the first half of the holocene in the western mediterranean the peak of late glacial aridity occurred at 15 000 16 000 bp and the lakes were already high again by 12 000 bp in the east maximum late glacial aridity occurred between 13 000 and 11 000 bp and there was a gradual return to wetter climates during the early holocene such that 9000 bp was more arid than 6000 bp most lakes in the mediterranean region were high at 6000 bp the transition to arid conditions after 5000 bp occurred abruptly in the west and more gradually in the east the lakes of southern sweden indicate drier climates in the early holocene ca 9000 bp more effective moisture between 8000 and 6000 bp increased aridity between 5500 and 3500 bp and increased effective moisture again during the last 3000 years the history of lake level changes in southern sweden and the mediterranean region can be partially explained in terms of changes in the direct effects of insolation and in the strength and position of the westerlies and of the subtropical high pressure cell during the late quaternary

the chronostratigraphy of late pleistocene glacial and periglacial aeolian activity in the tuktoyaktuk coastlands nwt canada aeolian periglacial sand deposits are common in the tuktoyaktuk coastlands of western arctic canada regionally extensive and thick aeolian sand sheet deposits have been observed in two major stratigraphic settings within a sand unit characterized by large aeolian dune deposits and interbedded with glaciofluvial outwash from the laurentide ice sheet lis small localized sand sheets have also been observed along the tops of sandy bluffs within sequences of drained thermokarst lakes deposits and as an involuted veneer above buried basal ice of the lis on the basis of radiocarbon and optically stimulated luminescence osl dates from preserved periglacial aeolian sand sheets and dunes a regional chronostratigraphy is presented which indicates that both extensive dunes and sand sheets accumulated mainly between ca 30 and 13 ka a switch to dominantly sand sheet aggradation at ca 14 13 ka with sand sheets forming widely until ca 8 ka is attributed to a surface armouring by glacial deposits associated with the advance of the lis and b amelioration of the climate from cold aridity an absence of osl dates between ca 8 and 1 ka suggests that sand sheets stabilized during much of the holocene local sand sheet aggradation during recent centuries has occurred near sandy bluffs and on the floors of drained thermokarst lakes the osl dates constrain the maximum extent of the lis in the tuktoyaktuk coastlands to marine isotope stage 2

new evidence for high discharge to the chukchi shelf since the last glacial maximum using chirp subbottom profiling across the chukchi shelf offshore nw alaska we observed a large incised valley that measures tens of kilometers in width the valley appears to have been repeatedly excavated during sea level lowering however the two most recent incisions appear to have been downcut during the last sea level rise suggesting an increase in the volume of discharge modern drainage from the northwestern alaskan margin is dominated by small low discharge rivers that do not appear to be large enough to have carved the offshore drainage the renewed downcutting and incision during the deglaciation and consequent base level rise implies there must have been an additional source of discharge paleoprecipitation during deglaciation is predicted to be at least 10 less than modern precipitation and thus cannot account for the higher discharge to the shelf glacial meltwater is the most likely source for the increased discharge

role of orbitally induced changes in tundra area in the onset of glaciation the link between glacial interglacial cycles and changes in insolation due to variations in the earth s orbital parameters is well established1 4 but of the attempts to simulate incipient glaciation using three dimensional general circulation models gcms driven by orbital forcing alone5 10 only one10 has been successful gcm experiments7 11 show that reduced summer insolation 115 000 years ago during an interglacial to glacial climate shift produces sufficient high latitude cooling to cause expansion of tundra at the expense of boreal forest11 which in turn can induce more cooling11 14 here we show using a global climate model that the increase in surface albedo under snow covered conditions that results from a biome model estimate11 of tundra expansion 115 000 years ago is sufficient to induce glaciation over extreme northeastern canada if the additional cooling from this estimated tundra expansion induces further expansion then widespread glaciation occurs at latitudes above 65 n these results suggest that the climate feedback from high latitude tundra expansion might have contributed to the onset of the most recent glaciation

postglacial vegetation and climate change in the northern bristol bay region southwestern alaska pollen analysis of sediment cores from grandfather and ongivinuk lakes reveals a record of postglacial vegetation and climate change in the northern bristol bay region the chronology is based on six conventional 14c dates of bulk organic matter from the grandfather core a mesic herb tundra dominated the landscape 13 000 9800 yr b p betula shrubs probably first appeared in the region 11 300 yr b p but were restricted to favorable microhabitats until 9800 yr b p the later establishment of betula shrubs and relatively low betula pollen abundance in these records compared to other areas of eastern beringia suggest that postglacial warming in southwestern alaska was dampened by regional climatic controls possibly low sea surface temperatures of the north pacific ocean between 10 800 and 9800 yr b p diminished betula shrub cover along with decreased aquatic productivity as recorded by pediastrum cell nets and biogenic silica suggest a brief reversion to colder and drier climatic conditions possibly associated with the younger dryas event around 9800 yr b p betula shrub tundra and meadow communities expanded probably in response to increased temperature and precipitation alnus arrived and formed extensive thickets within the region ca 7400 yr b p the establishment of the modern boreal forest tundra ecotone is marked by the arrival of picea glauca at grandfather lake ca 4000 yr b p and the subsequent increase to present population densities ca 2000 yr b p the unique features of these pollen records emphasize the spatial complexity of late quaternary vegetation and climate history in eastern beringia

late quaternary vegetational change in the kotzebue sound area northwestern alaska abstract two sediment cores from kaiyak and squirrel lakes in northwestern alaska yielded pollen records that date to ca 39 000 and 27 000 yr b p respectively between 39 000 and 14 000 yr b p the vegetation around these lakes was dominated by gramineae and cyperaceae with some salix and possibly betula nana glandulosa forming a local shrub component of the vegetation betula pollen percentages increased about 14 000 yr b p indicating the presence of a birchdominated shrub tundra alnus pollen appeared at both sites between 9000 and 8000yr b p and picea pollen mostly p mariana arrived at squirrel lake about 5000 yr b p the current foresttundra mosaic around squirrel lake was established at this time whereas shrub tundra existed near kaiyak lake throughout the holocene when compared to other pollen records from north western north america these cores 1 represent a meadow component of lowland beringian tundra between 39 000 and 14 000 yr b p 2 demonstrate an early holocene arrival of alnus in northwestern alaska that predates most other alnus horizons in northern alaska or northwestern canada and 3 show an east to west migration of picea across northern alaska from 9000 to 5000 yr b p

late quaternary pollen records from the kobuk and noatak river drainages northwestern alaska abstract pollen diagrams from joe and niliq lakes date to ca 28 000 and 14 000 yr b p respectively mesic shurb tundra grew near joe lake ca 28 000 to 26 000 yr b p with local populus populations prior to ca 27 000 yr b p shrub communities decreased as climate changed with the onset of itkillik ii glaciation 25 000 to 11 500 yr b p and graminoid dominated tundra characterized vegetation ca 18 500 to 13 500 yr b p herb tundra was replaced by shrub betula tundra near both sites ca 13 500 yr b p with local expansion of populus ca 11 000 to 10 000 yr b p and alnus ca 9000 yr b p mixed picea glauca p mariana woodland was established near joe lake ca 6000 yr b p these pollen records when combined with others from northern alaska and northwestern canada indicate 1 mesic tundra was more common in northwestern alaska than in northeastern alaska or northwestern canada during the duvanny yar glacial interval 25 000 to 14 000 yr b p 2 with deglaciation shrub betula expanded rapidly in northwestern alaska but slowly in areas farther east 3 an early postglacial thermal maximum occurred in northwestern alaska but had only limited effect on vegetation and 4 pollen patterns in northern alaska and northwestern canada suggest regional differences in late quaternary climates

calibration of radiocarbon ages and the interpretation of paleoenvironmental records abstract calibration of the radiocarbon timescale of paleoecological records is essential if they are to be explained correctly in terms of their governing ecological or climatological controls the differences between calendar ages and radiocarbon ages that arise from variations in 14c production through time can distort the chronologies of individual records and the interpretations based on them misleading impressions of synchrony or diachrony of events among multiple records can result and estimates of the apparent duration of episodes and rates of sedimentation and local population changes can be biased displays of the temporal patterns of migration or extinction may also be affected spurious correlations may arise between records with radiocarbon controlled chronologies and time series of potential controls that are expressed on a calendar time scale support for particular explanations of features in a paleoecological record may vary depending on whether radiocarbon ages are calibrated or not this situation is illustrated using the eastern beringian populus subzone as an example when the radiocarbon ages that control the timing of the populus subzone are calibrated the contemporaneous decrease in ice volume and increase in summer insolation are implicated as the ultimate controls of the occurrence of the subzone

pleistocene graminoid dominated ecosystems in the arctic abstract we review evidence obtained from analyses of multiple proxies floristics mammal remains paleoinsects pollen macrofossils plant cuticles phytoliths stable isotopes and modeling that elucidate the composition and character of the graminoid dominated ecosystems of the pleistocene arctic the past thirty years have seen a renewed interest in this now extinct biome sometimes referred to as tundra steppe steppe tundra in north american sources while many questions remain converging evidence from many new terrestrial records and proxies coupled with better understanding of paleoclimate dynamics point to the predominance of xeric and cold adapted grassland as the key former vegetation type in the arctic confirming earlier conjectures completed in the 1960s 1980s a variety of still existing species of grasses and forbs played key roles in the species assemblages of the time but their mixtures were not analogous to the tundras of today local mosaics based on topography proximity to the ice sheets and coasts soil heterogeneity animal disturbance and fire regimes were undoubtedly present however inadequate coverage of terrestrial proxies exist to resolve this spatial heterogeneity these past ecosystems were maintained by a combination of dry and cold climate and grazing pressure disturbance by large e g mammoth and horse and small e g ground squirrels mammals some recent studies from eastern beringia alaska suggest that more progress will be possible when analyses of many proxies are combined at local scales

a late quaternary paleotemperature record from hanging lake northern yukon territory eastern beringia abstract the late quaternary paleoclimate of eastern beringia has primarily been studied by drawing qualitative inferences from vegetation shifts to quantitatively reconstruct summer temperatures we analyzed lake sediments for fossil chironomids and additionally we analyzed the sediments for fossil pollen and organic carbon content a comparison with the 18 o record from greenland indicates that the general climatic development of the region throughout the last glaciation holocene transition differed from that of the north atlantic region between 17 and 15 ka mean july air temperature was on average 5 c colder than modern albeit a period of near modern temperature at 16 5 ka total pollen accumulation rates ranged between 180 and 1200 grains cm 2 yr 1 at 15 ka approximately coeval with the bolling interstadial temperatures again reached modern values at 14 ka nearly 1000 yr after warming began betula pollen percentages increased substantially and mark the transition to shrub dominated pollen contributors chironomid based inferences suggest no evidence of the younger dryas stade and only subtle evidence of an early holocene thermal maximum as temperatures from 15 ka to the late holocene were relatively stable the most recognizable climatic oscillation of the holocene occurred from 4 5 to 2 ka

lateglacial and holocene climate disturbance and permafrost peatland dynamics on the seward peninsula western alaska abstract northern peatlands have accumulated large carbon c stocks acting as a long term atmospheric c sink since the last deglaciation how these c rich ecosystems will respond to future climate change however is still poorly understood furthermore many northern peatlands exist in regions underlain by permafrost adding to the challenge of projecting c balance under changing climate and permafrost dynamics in this study we used a paleoecological approach to examine the effect of past climates and local disturbances on vegetation and c accumulation at a peatland complex on the southern seward peninsula alaska over the past 15 ka 1 ka 1000 cal yr bp we analyzed two cores about 30 m apart nl10 1 from a permafrost peat plateau and nl10 2 from an adjacent thermokarst collapse scar bog for peat organic matter om c accumulation rates macrofossil pollen and grain size analysis a wet rich fen occurred during the initial stages of peatland development at the thermokarst site nl10 2 the presence of tree pollen from picea spp and larix laricinia at 13 5 12 1 ka indicates a warm regional climate corresponding with the well documented bolling allerod warm period a cold and dry climate interval at 12 1 11 1 ka is indicated by the disappearance of tree pollen and increase in poaceae pollen and an increase in woody material likely representing a local expression of the younger dryas yd event following the yd the warm holocene thermal maximum htm is characterized by the presence of populus pollen while the presence of sphagnum spp and increased c accumulation rates suggest high peatland productivity under a warm climate toward the end of the htm and throughout the mid holocene a wet climate induced several major flooding disturbance events at 10 ka 8 1 ka 6 ka 5 4 ka and 4 7 ka as evidenced by decreases in om and increases in coarse sand abundance and aquatic fossils algae chara and water fleas daphnia the initial peatland at permafrost site nl10 1 is characterized by rapid c accumulation 66 g c m 2 yr 1 high om content and a peak in sphagnum spp at 5 8 4 6 ka suggesting the lack of permafrost a transition to extremely low c accumulation rates of 6 3 g c m 2 yr 1 after 4 5 ka at this site suggests the onset of permafrost aggradation likely in response to neoglacial climate cooling as documented across the circum arctic region a similar decrease in c accumulation rates also occurred at non permafrost site nl10 2 time weighted c accumulation rates are 21 8 g c m 2 yr 1 for core nl10 1 during the last 6 5 ka and 14 8 g c m 2 yr 1 for core nl10 2 during the last 15 ka evidence from peat core analysis and historical aerial photographs shows an abrupt increase in sphagnum spp and decrease in area of thermokarst lakes over the last century suggesting major changes in hydrology and ecosystem structure likely due to recent climate warming our results show that the thermokarst permafrost complex was much more dynamic with high c accumulation rates under warmer climates in the past while permafrost was stabilized and c accumulation slowed down following the neoglacial cooling in the late holocene furthermore permafrost presence at local scales is controlled by both regional climate and site specific factors highlighting the challenge in projecting responses of permafrost peatlands and their c dynamics to future climate change

biological control of calcium isotopic abundances in the global calcium cycle measurements of 44ca 40ca expressed as 44ca were made on igneous rocks and on shell and bone material from modern organisms to investigate the magnitude and origins of calcium isotopic fractionation in nature the results document a span of 4 in 44ca measured with the double spike technique to a precision of 0 15 volcanic rocks including basalt and rhyolite show little variability and cluster near 44ca 0 0 2 systematic analysis of biological samples indicates that biological processing of calcium discriminates against heavy isotopes and that biological fractionation is the primary generator of calcium isotopic fractionation in nature preliminary data suggest that calcium becomes isotopically lighter as it moves through food chains calcium carbonate shells of marine microorganisms and deep sea carbonate ooze have 44ca about 1 0 lower than seawater this fractionation causes seawater to be enriched in heavy calcium 44ca 0 9 relative to igneous rocks marine organisms consequently are isotopically heavier than their terrestrial counterparts at similar trophic level the calcium isotopic composition of living and fossil organisms may record information on diet and environment

a re evaluation and spatial analysis of evidence for a younger dryas climatic reversal in beringia abstract an objective classification of paleoclimatic proxies from 75 lake and peat records is used to re evaluate data quality and inferred climatic patterns in beringia during the younger dryas mapped data reveal coherent but spatially complex regional patterns suggesting the younger dryas was characterized by 1 cooling in southern alaska eastern siberia and portions of northeastern siberia and 2 uniform to warmer than present conditions through most of central alaska northeastern siberia and possibly the russian far east and northern alaska the beringian patterns correspond to distinctive large scale climatic forcings although in some locations further modified by more local influences such as topography general circulation models and modern synoptic climatology provide a conceptual framework for exploring possible mechanisms responsible for the observed changes forcings and associated climatic responses consistent with the proxy data include 1 lowered sea surface temperatures in the north atlantic and pacific reducing temperature and precipitation in eastern siberia 2 intensified aleutian low and lowered sea surface temperatures causing cooler summers and higher winter precipitation in southern alaska 3 stronger pacific subtropical high and an eastward shift of the east asian trough reducing summer temperatures in southern alaska and causing relative warmth in northeastern siberia and 4 strong high pressure system producing warm dry conditions in interior alaska

late quaternary paleoclimate of western alaska inferred from fossil chironomids and its relation to vegetation histories abstract fossil chironomidae assemblages with a few chaoboridae and ceratopogonidae from zagoskin and burial lakes in western alaska provide quantitative reconstructions of mean july air temperatures for periods of the late middle wisconsin 39 000 34 000 cal yr b p to the present inferred temperatures are compared with previously analyzed pollen data from each site summarized here by indirect ordination paleotemperature trends reveal substantial differences in the timing of climatic warming following the late wisconsin at each site although chronological uncertainty exists zagoskin lake shows early warming beginning at about 21 000 cal yr b p whereas warming at burial lake begins 4000 years later summer climates during the last glacial maximum lgm were on average 3 5 c below the modern temperatures at each site major shifts in vegetation occurred from 19 000 to 10 000 cal yr b p at zagoskin lake and from 17 000 to 10 000 cal yr b p at burial lake vegetation shifts followed climatic warming when temperatures neared modern values both sites provide evidence of an early postglacial thermal maximum at 12 300 cal yr b p these chironomid records combined with other insect based climatic reconstructions from beringia indicate that during the lgm 1 greater continentality likely influenced regions adjacent to the bering land bridge and 2 summer climates were at times not dominated by severe cold

spatial variability of late quaternary paleoclimates in the western united states abstract paleoclimatic interpretation of proxy data is complicated sometimes by the appearance of heterogeneous patterns of climatic responses across networks of sites modern climate analogues for the western united states similar to those patterns of atmospheric circulation of 18 000 and 9000 yr b p were examined in order to explain such patterns of spatial heterogeneity modern analogues were defined by comparing modern atmospheric circulation patterns with those simulated by general circulation models maps of temperature and precipitation anomalies of the modern analogues reveal patterns of spatial heterogeneity which resemble the patterns of effective moisture compiled from paleoclimatic data january 1957 was found to be a reasonable 18 000 yr b p analogue and it features isolated areas of increased wetness in the northern great basin and increased dryness in the northwest interior analogues for 9000 yr b p from a composite of 11 augusts display patterns of spatial heterogeneity of effective moisture over most of the mountainous areas the analogues suggest that spatial heterogeneity of climate is the rule rather than the exception over much of the western united states with the climatic anomalies at any particular time representing the outcome of the mediation of large scale atmospheric circulation controls by smaller scale topographic features

climate and vegetation in northeastern alaska 18 000 yr b p present changing abundances of taxa in the pollen record of northeastern alaska contain a climate signal and may be compared with gcm simulations of paleoclimates cold dry conditions indicated by full glacial pollen spectra are in broad agreement with model simulations successive expansion of betula and salix and later populus during the deglacial period 14 000 11 000 yr b p are likely correlated with the crossing of temperature thresholds determined largely by the size and position of the laurentide ice a degree of asynchroneity between sites probably reflects differential site responses to regional effects plus inaccuracies of radiocarbon dating the early holocene was probably the warmest period of the present interglacial as summer climate was influenced by a strong positive insolation anomaly picea glauca expanded in majorr river valleys ca 9000 yr ago and slightly later at upland sites in the brooks and alaska ranges at some sites a juniperus subzone which suggests particularly warm and dry conditions occurs between ca 10 000 and 8000 yr b p early mid holocene expansions of alnus 8500 7000 yr b p and picea mariana 7500 5000 yr b p suggest the subsequent development of moister conditions which have continued to the present temporal patterns in picea treeline position during the holocene are different in northern alaska northwestern canada and central canada in alaska the treeline is currently at its furthest holocene extent in northwestern canada the treeline has retreated since the mid holocene and in central canada a mid holocene advance and retreat occurred such differences between regions suggest a complex response of this taxon to climatic controls and underscore the need to interpret vegetation changes in relation to regional scale climate phenomena if the pollen chronology is calibrated with reference to u th dates the relationship of vegetational events to the insolation maximum at ca 10 000 yr b p is significantly altered the changed chronology also affects the interpretation of pollen records in relation to gcm simulations which are partly keyed to calendar years