temperature calibration and phylogenetically distinct distributions for freshwater alkenones evidence from northern alaskan lakes abstract alkenones are a class of unsaturated long chain ketone biomarkers that have been used to reconstruct sea surface temperature and more recently continental temperature by way of alkenone unsaturation indices e g u 37 k and u 37 k alkenones are frequently found in brackish and saline lakes however species effects confound temperature reconstructions when multiple alkenone producing species with different temperature responses are present interestingly available genetic data indicate that numerous freshwater lakes host a distinct phylotype of alkenone producing haptophyte algae the group i or greenland phylotype providing evidence that species effects may be diminished in freshwater lakes these findings encourage further investigation of alkenone paleotemperature proxies in freshwater systems here we investigated lakes from northern alaska n 35 and show that alkenones commonly occurred in freshwater lakes where they featured distinct distributions characterized by dominant c37 4 alkenones and a series of tri unsaturated alkenone isomers the distributions were characteristic of group i type alkenone distributions previously identified in greenland and north america our analysis of suspended particulate matter from toolik lake 68 38 n 149 36 w yielded the first in situ freshwater u 37 k calibration u 37 k 0 021 t 0 68 r2 0 85 n 52 rmse 1 37 c we explored the environmental significance of the tri unsaturated isomers using our northern alaskan lakes dataset in conjunction with new data from haptophyte cultures and canadian surface sediments our results show that these temperature sensitive isomers are biomarkers for the group i phylotype and indicators of multiple species effects together these findings highlight freshwater lakes as valuable targets for continental alkenone based paleotemperature reconstructions and demonstrate the significance of the recently discovered tri unsaturated isomers

long chain alkenones in greenland lake sediments low δ13c values and exceptional abundance abstract long chain alkenones lcas are a key class of biomarkers for certain members of the algal class prymnesiophyceae i e prymnesiophytes they are ubiquitous in ocean sediments where they are extensively used for paleotemperature reconstruction but are rare in lake sediments here we report the discovery of lcas c37 c39 throughout a sediment core from one lake and in surface sediments of five lakes located in west greenland lca concentrations in the surface sediments are one to two orders of magnitude greater than those reported for other lacustrine surface sediments around the world the presence of c38 methyl ketones distinguishes greenland lca distributions from those found in other saline lakes in cold regimes lcas are present in five lakes with elevated salinity but absent from five freshwater lakes in the study region using the published temperature calibration for lake sediments alkenone unsaturation indices u 37 k and u 37 k in the surface sediments of the greenland lakes appear to record late spring early summer temperature when algal blooms occur supporting the use of lacustrine alkenones as a paleotemperature proxy the lcas have exceptionally low 13c values ranging from 40 to 42 and are depleted by 3 10 relative to short chain fatty acids and sterols in the same samples these 13c values are the lowest reported for alkenones in a natural setting and have important implications for tracing the alkenone producers in lakes

similarities between planktonic and larger foraminiferal evolutionary trends through paleogene paleoceanographic changes abstract the paleogene evolutionary records of planktonic foraminifera and larger benthic foraminifera show parallel patterns in development that may in part reflect changes in nutrient flux to surface waters following the terminal cretaceous extinctions faunas were dominated by a few cosmopolitan opportunistic species more specialized k strategists in both groups diversified during the paleocene dominating into the early eocene consistent with he globally mild climatic regime and probable limited rates of nutrient flux to surface waters high latitude cooling intensified in the middle eocene promoting diversification of less specialized taxa characteristic of cooler and deeper waters higher latitudes meridional upwelling zones and boundary currents geographic ranges of warm water taxa diminished and fragmented yet many species survived thus global diversities during the middle eocene were the highest in the cenozoic as cooling and increased rates of nutrient flux further intensified in the late eocene extinction rates of warm water planktonic and larger benthic species exceeded origination rates of cooler water and less specialized forms so diversity dropped to intermediate levels where it remained through the late eocene and oligocene previous observations that planktonic foraminiferal faunas dominated by warm water taxa are often replaced by cool water faunas even though oxygen isotopes only recorded relatively minor cooling can be reconciled by the explanation that the biotic communities responded to changes in trophic resources and euphotic habitats that accompany the temperature reduction as well as to temperature change itself

the fate of foramol temperate type carbonate platforms abstract on rimmed shelves of bahamian type characterized by chlorozoan associations and typical of tropical seas carbonate production keeps pace with normal sea level rise except when rapid rise or drastic environmental changes occurs on the other hand open temperate carbonate shelves are characterized by low carbonate production of the foramol association molluscs benthic foraminifera bryozoans coralline algae etc and generally show seaward relict sediments because carbonate production cannot keep pace with normal rate of sea level change several examples of recent drowning foramol carbonate platforms e g large areas of the mediterranean sea eastern northeastern yucatan shelf as well as analogous ancient drowned foramol type carbonate platforms e g early to middle miocene of the southern apennines miami terrace may support the idea that the drowning of many ancient carbonate platforms has been favoured by their biogenic foramol sensu lato constitution because of their typically low rate of growth foramol carbonate platforms are fated to be drowned even if the sea level rise is one with which the normal growth of chlorozoan platforms can keep pace similar conditions may also occur in tropical areas where variations in environmental conditions such as the presence of cold waters changes in salinity and increased nutrients preclude the development of chlorozoan associations

a new approach for reconstructing holocene temperatures from a multi species long chain alkenone record from lake qinghai on the northeastern tibetan plateau abstract the extent of unsaturation in long chain alkenones lcks in lakes has potential for quantitatively indicating paleotemperature in terrigenous environments however the traditional temperature proxies derived from marine lcks may not be able to address the problem related to the prevalent species effect which restricts the application of lcks in lacustrine studies in our lck record from the northeastern tibetan plateau c 37 c 38 differences revealed that the lck producer species in lake qinghai may have changed during the holocene this possible species effect may have caused inconsistency between the u k 37 and u k 37 records therefore we formulated a new proxy u ks 37 with a parameter s to indicate the different exponential response in lck unsaturation to temperature change in multiple species our u ks 37 derived temperature time series resembles the general temperature trends of the northern hemisphere on a millennial scale while exhibiting several apparent cold events especially at ca 9 ka the result shows that the holocene optimum in lake qinghai was interrupted by cold events in the early holocene this could be a result of a weak asia summer monsoon and cold air transmission in the north atlantic

miocene drowning of temperate foramol carbonate platform upper miami terrace oligocene neritic rocks dredged from 350 m on the upper miami terrace exhibit repeated phosphatization as well as a filled void system containing post burdigalian foraminifera during drowning a neritic hardground was subjected to both pelagic deposition infills and repeated marine exposure borings p coatings etc the neritic grainstone packstone contains large benthic foraminifera red algae bryozoans pelecypods ahermatypic corals echinoids and some planktonic foraminifera this composition association is the foramol type characteristic of temperate to subtropical neritic environments such as the present mediterranean brazilian and new zealand shelves these temperate sediments derive from the local biocoenose and accumulate slowly in deep sheets of loose skeletal debris they become relict seaward where they are often bored corroded stained glauconitized and cemented into hardgrounds locally hemipelagic cover might produce a palimpsest sequence recent foramol type platforms are undergoing drowning the miami terrace is compared to very similar miocene foramol type platforms now exposed in the southern apennines both are characterized by neritic sequences passing upward into hemipelagics via a palimpsest interval marked by glauconitic phosphatic iron stained grains often mineralized into hardgrounds the drowning of the miami terrace hence coincided with and the authors suppose was a result of the shift from a rapid oligotrophic tropical accumulationmore to a slow temperate eutrophic carbonate accumulation caused in turn by a temporary paleo oceanographic shift to cooler richer neritic conditions within the history of this now subtropical setting less

platforms of the nicaraguan rise examples of the sensitivity of carbonate sedimentation to excess trophic resources the nicaraguan rise is an active tectonic structure in the western caribbean carbonate accumulation on its platforms has not kept pace with relative holocene sea level rise despite a tropical location remote from terrigenous sedimentation trophic resources apparently exceed levels favoring coral reef development because sponge algal communities dominate the drowning western platforms in contrast to mixed coral algal benthos on pedro bank and well developed coral reefs along the north coast of jamaica concentrations of biotic pigments in sea surface waters show a corresponding west east gradient oceanic waters flowing over the western banks carry nearly twice as much biotic pigment as oceanic waters north of jamaica sources enriching the western caribbean are terrestrial runoff upwelling off northern south america and topographic upwelling over the nicaraguan rise that relatively modest levels of trophic resources can suppress coral reef development holds important implications for understanding carbonate platform drownings in the geologic record

new insights into environmental controls on the occurrence and abundance of group i alkenones and their paleoclimate applications evidence from volcanic lakes of northeastern china abstract the distinctive long chain alkenones lcas produced by group i isochrysidales from freshwater and oligohaline lakes have great potential for quantitative paleotemperature reconstructions the widespread application of sedimentary group i lcas however is hampered by an incomplete understanding of the environmental controls on the occurrence of group i lcas in freshwater lakes the correspondence between group i lca concentrations and ph 6 2 8 5 in northern alaskan freshwater lakes longo et al 2016 suggests that group i isochrysidales may preferentially thrive in freshwater lakes with high ph here we systematically study lca distributions haptophyte specific 18s rdna sequences and concentrations of major ions and trace elements in 18 freshwater volcanic lakes in northeastern china with an extended ph range from 7 17 to 9 99 we find that 11 of the 18 lakes examined contain group i lcas and the corresponding dna sequences of their producers our dna results indicate that the dominant alkenone producer in all 11 lakes is closely related to the group i greenland otu 5 genotype with the exception of two anthropogenically impacted lakes where small numbers of group ii sequences are found statistical analyses indicate that the highest concentrations of group i lcas are found in oligotrophic freshwater lakes with ph ranging from 7 3 to 8 8 we find that elevated concentrations of certain trace elements may lead to the disappearance of group i lcas despite lake water falling within the optimal ph range together with previously published group i lca data from the temperature calibration in northern hemisphere freshwater lakes longo et al 2018 we find for the first time that group i r3b r3b c37 3b c38 3bet c37 3b values are most sensitive to winter temperature changes when mean winter temperature is higher than 20 c our results suggest that the freshwater volcanic lakes in northeastern china are highly valuable targets for paleotemperature reconstructions using group i lcas

characteristics of alkenones synthesized by a bloom of emiliania huxleyi in the bering sea abstract we investigated the characteristics of the alkenones produced by a bloom of emiliania huxleyi in the eastern bering sea in 2000 alkenones were detected in surface waters between 57 n and 63 n where phosphate concentrations were low and the ammonium nitrate ratio was high the total alkenone content c37 2 c37 3 and c37 4 ranged from 22 0 to 349 g g 1 in suspended particles and from 0 109 to 1 42 g g 1 in surface sediments this suggests that a large proportion of the particulate alkenones synthesized in the surface water rapidly degraded within the water column and or at the water sediment interface of the bering shelf the change in the stable carbon isotopic composition 13c of c37 3 alkenone could not be explained only by variation in co2 aq in the surface water but also depended on the growth rate of e huxleyi the alkenone unsaturation index uk 37 was converted into an alkenone temperature with three equations prahl et al 1988 sikes et al 1997 muller et al 1998 sikes et al s 1997 equation gave the best correlation with the observed sea surface temperature sst in the eastern bering sea however some temperatures estimated by sikes et al s 1997 equation from the uk 37 varied from the observed sst possibly because of the rapidly changing rate of alkenone synthesis in the logarithmic growth stage or the low rate of alkenone synthesis when nutrients were limiting temperatures estimated from uk 37 in the surface sediments 6 8 8 2 c matched the observed sst in september 7 8 c but differed from the annual average sst of 4 to 5 c suggesting that most of the alkenone in the eastern bering sea was synthesized during limited periods for instance in september the relative amounts of c37 4 alkenone as proportions of the total alkenones referred to as c37 4 were high ranging from 18 3 to 41 4 low salinity water

temperature dependency of long chain alkenone distributions in recent to fossil limnic sediments and in lake waters distribution patterns of c37 and c38 polyunsaturated long chain alkenones lcas serve as proxies for the determination of paleotemperatures for marine surface waters we studied recent subrecent and late glacial holocene sediments from germany austria russia and the u s to test for a correspondence between lca distribution and surface water temperature in limnic systems previously reports of lca occurrence were restricted to sediments of 6 wide distributed freshwater and alkaline lakes in this study 13 of 27 investigated lakes contained lcas in surface sediments with concentrations varying between 12 to 205 g g toc late glacial to holocene sediment sequences from lake steisslingen and lake wummsee germany lake pichozero russia and brush lake u s a contained abundant lcas with averaged concentrations of 33 to 7536 g g toc for the first time we observed the occurrence of lcas within in the water column of oligotrophic lake stechlin ne germany alkenones were restricted to the zone of maximum chlorophyll concentration within the water column indicating that lcas have a biosynthetic origin and can be attributed to phototrophic micro algae attempts to identify the producing organism however were not successful culture experiments allow various phytoplankton to be excluded as producers alkenone producing algae are evidently of small size hindering microscopical identification lcas commonly occur in high concentrations in late glacial sediments mainly during the cold period of the younger dryas whereas the holocene usually is devoid of polyunsaturated alkenones the episodic occurrence of lcas restricts their utility as proxies for continuous geological records furthermore lack of microscopical verification and the episodic distribution allow for different producers of unsaturated alkenones in recent and late glacial sediments an empirical relationship between lca distribution and temperature was observed in fossil sediments from lake steisslingen there is a good correspondence between uk37 and the temperature controlled 18o isotope ratio of lake chalk comparison of lca patterns obtained from the uppermost centimetres of lake sediments with averaged summer surface water temperatures of the lakes studied demonstrates a trend of covariance r2 uk 37 0 90 uk37 0 67 n 9 hence the same mechanism that causes temperature dependence of lca patterns in marine systems might be effective in limnic settings identification of alkenone producers and their culture under controlled temperature are still mandatory before lcas can be routinely applied as paleotemperature proxy in limnic systems

alkenone distributions and hydrogen isotope ratios show changes in haptophyte species and source water in the holocene baltic sea the baltic sea a dynamic marginal marine basin experienced a number of large changes in salinity during the holocene as a result of fluctuations in global and local sea level related to melting of glacial ice sheets and subsequent isostatic rebound these changes likely had pronounced effects on the species composition of haptophytes a common phytoplankton group found in the baltic sea this dynamic environment provides the ideal setting to study how species change impacts distribution and hydrogen isotope ratios of long chain alkenones h c37 haptophyte specific biomarkers here we analyzed the aforementioned parameters in holocene sediments covering the contrasting hydrological phases of the baltic sea alkenone distributions changed with different baltic sea salinity phases suggesting that species shifts coincide with salinity change h c37 values show two major shifts one in the middle of the freshwater ancylus lake phase 10 6 to 7 7 ka and a second at the transition from the brackish littorina sea phase 7 2 to 3 ka into the fresher modern baltic 3 ka to the present the first shift represents a significant enrichment of 50 which cannot be explained by salinity or species changes only at this time the isotopically depleted ice sheets had melted and only the relatively enriched freshwater source remained the second shift coincident with a change in distribution is likely caused by a change in species composition alone these findings show that hydrogen isotope ratios of long chain alkenones combined with their relative distribution can be used to reconstruct changes in source water

abrupt holocene climate change as an important factor for human migration in west greenland west greenland has had multiple episodes of human colonization and cultural transitions over the past 4 500 y however the explanations for these large scale human migrations are varied including climatic factors resistance to adaptation economic marginalization mercantile exploration and hostile neighborhood interactions evaluating the potential role of climate change is complicated by the lack of quantitative paleoclimate reconstructions near settlement areas and by the relative stability of holocene temperature derived from ice cores atop the greenland ice sheet here we present high resolution records of temperature over the past 5 600 y based on alkenone unsaturation in sediments of two lakes in west greenland we find that major temperature changes in the past 4 500 y occurred abruptly within decades and were coeval in timing with the archaeological records of settlement and abandonment of the saqqaq dorset and norse cultures which suggests that abrupt temperature changes profoundly impacted human civilization in the region temperature variations in west greenland display an antiphased relationship to temperature changes in ireland over centennial to millennial timescales resembling the interannual to multidecadal temperature seesaw associated with the north atlantic oscillation

environmental controls on long chain alkenone occurrence and compositional patterns in lacustrine sediments northwestern china abstract long chain alkenones occur widely in lacustrine settings and their compositions are potential proxies for reconstructing terrestrial paleoclimatological and paleoenvironmental changes however factors influencing their occurrence abundance compositional pattern and unsaturation indices are not well understood here we investigated the alkenones in surface sediments from 19 lakes in northwestern china as well as potential environmental factors of the lakes 12 contain long chain alkenones 3 have the isomeric c 37 3 alkenone and 3 have very low abundance of alkenones our results show that salinity has a substantial influence on the occurrence concentration and compositional pattern most of the compositions are dominated by tri unsaturated compounds with c 38 methyl ketones absent the predominance of c 37 4 and the occurrence of a c 37 3 isomer are suggested to be responses to low salinity as both are only found in the three alkenone containing freshwater lakes the proportion of c 37 4 varies by up to 50 and shows a negative relationship with salinity within the surveyed region an arched relationship of alkenone content and salinity is apparent with no or very low contents of alkenones in freshwater salinity 100 g l environments the u 37 k index is suggested to be a better terrestrial temperature proxy than u 37 k as u 37 k values from lakes containing elevated alkenone content are all within the ranges of published u 37 k temperature calibrations and u 37 k values show a weak positive relationship with salinity

high time resolution alkenone paleotemperature variations in tokyo bay during the meghalayan implications for cold climates and social unrest in japan abstract the regional paleoenvironmental record of tokyo central japan is required to enrich our understanding of climate change in east asia and its impact on japanese civilizations previous studies have generated paleotemperature records based on the analysis of shell mounds along the coast of tokyo bay and pollen from terrestrial borehole cores however a continuous high time resolution quantitative paleotemperature record does not exist a piston core was recovered from tokyo bay from which 22 mollusk shells were extracted an age model for the core determined via accelerator mass spectroscopy ams 14c dating of the shells and a scoria layer from the hoei eruption 1707 ce showed that the core contains continuous record from ca 2400 bce we analyzed the alkenone unsaturation ratios uk 37 to reconstruct the variations in the paleotemperature the temperature during the meghalayan was generally warmer than that at present exhibiting a declining trend which roughly matches the changes in the orbital forcing summer insolation and the millennial scale latitudinal shift of the subarctic front in the northeastern pacific ocean the largest cold period which occurred ca 2300 bce and had a minimum temperature of 19 5 c interrupted the warm conditions this cold period may correspond to the global cooling drying 4 2 ka bp event which marks the boundary between the northgrippian and meghalayan our results also revealed that several cold periods occurred which may have been caused by decreases in solar activity or large volcanic eruptions particularly large decadal to centennial scale cold periods were observed ca 440 bce and 100 ce during the yayoi era ca 900 bce 300 ce the coldest period after the establishment of a centralized system of government ca 300 ce present was recorded ca 1050 ce which may have been caused by the combination of a strong el nino mode and reduced solar activity these climate change events can all be linked and therefore may be the potential causes of significant periods of famine and civil war in japanese history which eventually led to major shifts in japanese social systems

appraisal of alkenone and archaeal ether based salinity indicators in mid latitude asian lakes abstract lake water salinity an important indicator of lake hydrological conditions is critical to deciphering terrestrial paleoclimatic and paleoenvironmental changes the proportion of c37 4 alkenone to total c37 alkenones c37 4 and the relative abundance of archaeol to caldarchaeol ace are promising salinity indices in lacustrine settings developing regional calibrations for both indicators is challenging due to limited datasets and a poor understanding of the factors that influence them here we present c37 4 and ace data collected from 55 lakes in mid latitude asia with a wide salinity range to evaluate how well the two proxies can be correlated with salinity and to infer potential influencing factors the c37 4 values only show a weak negative correlation with salinity from all investigated lakes the occurrence of c37 3 alkenone isomer and abnormal values in the alkenone c37 c38 ratio might signal species shifts or environmental factors that compromise the c37 4 salinity relationship in our data set seasonal bias in alkenone production could further obscure this c37 4 salinity relationship a stronger relationship emerges after removing samples influenced by these factors c37 4 8 56 log 10 salinity 80 6 r 2 0 62 n 37 or c37 4 13 46 log 10 salinity 101 48 with uncertainty in both variables considered the ace values show a strong positive correlation with salinity from all investigated lakes ace 2 27 10 4 salinity 25 4 r 2 0 75 n 68 or ace 1 86 10 4 salinity 38 1 with uncertainty in both variables considered however substantial deviations of the ace values in low salinity range

paleoenvironmental and paleoclimatic variations around lake van eastern turkey recorded by sedimentary source specific biomarkers 250 130 ka mis7 and mis6 abstract paleoclimatic changes during mis7 and mis6 remain poorly described in the near east we quantified source specific biomarkers in lake van sediments during the interglacial glacial cycle mis7 mis6 long chain n alkanes produced by land derived vegetation as well as long chain alkenones and sterols namely brassicasterol and dinosterol produced by aquatic algae were investigated stable hydrogen isotopic measurements 2h on n c29 alkanes were used as a proxy for aridity and revealed three wetter periods interrupted by two drier intervals during mis7 in contrast during the mis6 glaciation a generally drier climate was predominant during the warmer and wetter periods of mis7 a higher input of aquatic organic matter to lake van sediments was recorded by higher concentrations of long chain alkenones dinosterol and brassicasterol long chain alkane abundances do not show a pattern related to aridity and were observed in higher concentrations in wetter as well as drier periods generally in the eastern mediterranean a wetter interglacial interrupted by drier episodes followed by a dry glacial period was the common feature observed during the mis7 mis6 interglacial glacial cycle however in comparison to the last interglacial glacial cycle the extreme dry glacial period registered around lake van from mis5d to mis2 was apparently unique and not equaled by a similar event within the last 250 ka

widespread occurrence of distinct alkenones from group i haptophytes in freshwater lakes implications for paleotemperature and paleoenvironmental reconstructions abstract alkenones are c35 c42 polyunsaturated ketone lipids that are commonly employed to reconstruct changes in sea surface temperature however their use in coastal seas and saline lakes can be hindered by species mixing effects we recently hypothesized that freshwater lakes are immune to species mixing effects because they appear to exclusively host group i haptophyte algae which produce a distinct distribution of alkenones with a relatively consistent response of alkenone unsaturation to temperature to evaluate this hypothesis and explore the geographic extent of group i haptophytes we analyzed alkenones in sediment and suspended particulate matter samples from lakes distributed throughout the mid and high latitudes of the northern hemisphere n 30 our results indicate that group i type alkenone distributions are widespread in freshwater lakes from a range of different climates mean annual air temperature range 17 3 10 9 c mean annual precipitation range 125 1657 mm yr 1 latitude range 40 81 n and are commonly found in neutral to basic lakes ph 7 0 including volcanic lakes and lakes with mafic bedrock we show that these freshwater lakes do not feature alkenone distributions characteristic of group ii lacustrine haptophytes providing support for the hypothesis that freshwater lakes are immune to species mixing effects in lakes that underwent temporal shifts in salinity we observed mixed group i ii alkenone distributions and the alkenone contributions from each group could be quantified with the rik37 index additionally we observed significant correlations of alkenone unsaturation u 37 k with seasonal and mean annual air temperature with this expanded freshwater lakes dataset with the strongest correlation occurring during the spring transitional season u 37 k 0 029 t 0 49 r 2 0 60 p 0 0001 we present new sediment trap data from two lakes in northern alaska toolik lake 68 632 n 149 602 w lake e5 68 643 n 149 458 w that demonstrate the highest sedimentary fluxes of alkenones in the spring transitional season concurrent with the period of lake ice melt and isothermal mixing together these data provide a framework for evaluating lacustrine alkenone distributions and utilizing alkenone unsaturation as a lake temperature proxy

holocene history of landscape instability in iceland can we deconvolve the impacts of climate volcanism and human activity abstract biogeochemical proxy records from icelandic lake sediment track large scale shifts in north atlantic holocene climate and highlight the impact that north atlantic ocean and atmospheric circulation has on iceland s climate and environment following early holocene warmth centennial scale climate change is superimposed on millennial scale cooling culminating in the transition to the little ice age 1300 1900 ce although the long term cooling trend is presumably driven by variations in earth s orbit and the concomitant decline in northern hemisphere nh summer insolation the centennial scale variability has been linked to the strength of the atlantic meridional overturning circulation amoc volcanism coupled with sea ice ocean related feedbacks internal modes of atmospheric variability and plausibly variations in solar irradiance one manifestation of these regional climate changes on iceland is the intensification of soil erosion resulting in the degradation of ecosystems and landscape in recent millennia persistent and severe soil erosion has also been linked to human impact on the environment following the settlement 870 ce rapid population growth introduction of livestock and the poorly consolidated nature of tephra dominated soils lake proxy composite records suggest that although event dominated landscape instability and soil erosion from the early to middle holocene were likely triggered by large volcanic eruptions the landscape was capable of recovering however a threshold was reached 5 ka bp resulting in a state change whereby the icelandic landscape could no longer fully recover from cold events and or tephra fall landscape sensitivity to climate further intensified at 1 5 ka bp as identified by regime shift analysis hence widespread and irreversible soil erosion began several centuries before the acknowledged settlement of iceland with a second acceleration 1250 ce a 2 ka fully coupled climate transient simulation using cesm1 1 shows a 0 5 c reduction in summer temperature around iceland in the first millennium ce consistent with increased landscape instability and soil erosion in iceland a second phase of persistent summer cooling in the model occurs after 1150 ce with stronger cooling after 1450 ce reaching a maximum shortly after 1850 ce 1 c lower than at the start of the simulation our results suggest that natural variations in regional climate and volcanism are likely responsible for soil erosion prior to human impact with intensification of these processes following settlement particularly during the cooling associated with the little ice age given that the conclusions drawn in this review diverge from the standard paradigm of human induced soil erosion history in iceland research should continue to focus on this complex question from multiple disciplines in particular a combination of emerging biogeochemical techniques e g lipid biomarkers and ancient dna may be best poised to test and quantify the relative roles of natural environmental variables and human settlement in the history of soil erosion on iceland

controls on alkenone unsaturation ratios along the salinity gradient between the open ocean and the baltic sea abstract alkenone unsaturation ratios of sedimentary lipids are used as a geochemical proxy for sea surface temperatures and interest is growing in their potential as indicators of different water masses and possibly of salinity we analyzed the abundance of unsaturated c37 to c38 ketones in lipid extracts of 57 surface sediment 0 1 cm samples along a salinity gradient from 8 to 33 psu in the transition from the skagerrak to the baltic sea nw europe in addition to surface sediments we analyzed alkenones in suspended particulate matter at 13 stations over a gradient in salinity from 25 to 33 psu during a bloom of the coccolithophore emiliania huxleyi alkenones were detected in all samples suspended matter and sediment with variable contributions of the tetra unsaturated c37 alkenone compound c37 4 range from 2 to 10 of total c37 alkenone content comparing the alkenone unsaturation index u37k and c37 4 data to climatological sea surface temperature and sea surface salinity data sets revealed that sst estimated from u37k of saline end members samples from the skagerrak is in the general range of modern sst during bloom periods of haptophytes at salinities below 30 psu c37 4 increases to above 5 and the unsaturation ratios cease to be related to climatological annual or seasonal sea surface temperatures on the other hand the c37 4 appears to be inversely and significantly correlated to salinity highest c37 4 proportions in the inner baltic sea are caused by an unidentified organism but in the transition area at salinities down to 10 psu the producer apparently is e huxleyi the suspended matter data together with those from the water column support the hypothesis of changing biosynthesis of alkenones under salt stress by the coccolithophore e huxleyi but constrain the maximum of c37 4 attributable to salt stress to 10 of all c37 alkenones

biogeochemical evidence from ogcp core 2a sediments for environmental changes preceding deposition of tuff ib and climatic transitions in upper bed i of the olduvai basin abstract sediment cores recovered by the olduvai gorge coring project ogcp in 2014 afford the opportunity to examine the coupling of biogeochemical evidence for climatic and environmental change within the context of hominin evolution at this renowned east african locality investigations of elemental total organic carbon toc or corg wt carbon to nitrogen ratio c n molecular source specific biomarkers and isotopic 13corg 2hnc31 compositions of organic matter provide evidence for temporal changes in sedimentary materials derived from terrestrial plants c3 c4 and aquatic producers algae sponges cyanobacteria and in precipitation the 13 kyr record of upper bed i immediately preceding tuff ib extends high resolution stratigraphic profiles of precession scale alternations of wetter and drier conditions to encompass the entire interval from the bed i basalt to tuff ib the second wetter interval designated w2 records local influences on climate and water supply consistent with evidence for discrete sediment sources based its physical properties e g gamma radiation magnetic susceptibility compared with the overall sequence the 13ctoc values for wetter interval w2 reveal two millennial scale 2 5 kyr drier episodes followed by a shift in the dominance of c3 over c4 plants accompanying the transition to a drier climate d3 moreover biogeochemical data for upper bed i show that changes from drier to wetter conditions occur more rapidly 900 yr than wetter to drier transitions 2 6 kyr based on interpolated ages in addition biomarker profiles indicate that aquatic plants primarily algae and macrophytes may have been subject to more profound and faster fluctuations than variations in terrestrial vegetation expressed in terms of the relative proportions of woodland and grassland settings thus environmental and climatic changes not only influenced the availability of resources of food and shelter for hominins within the olduvai region but also led to their variation on centennial to millennial to precessional timescales

phylogenetic diversity and evolutionary relatedness of alkenone producing haptophyte algae in lakes implications for continental paleotemperature reconstructions alkenones have been found in an increasing number of lakes around the world making them a promising new tool for continental paleoclimate reconstruction however individual lakes may harbor different species of haptophyte algae with different sensitivities to temperature variations thus presenting a significant challenge to the use of lacustrine alkenones for paleotemperature reconstructions to explore the extent of lacustrine haptophyte diversity we conducted the first comprehensive phylogenetic and geochemical survey of lacustrine alkenone producers we sampled 15 alkenone containing lake surface sediments from a variety of geographic locales and inferred identities of environmental sequences using 18s ribosomal rna rrna gene based phylogenies for two lakes brayaso in southwest greenland and tso ur on the tibetan plateau we also analyzed both surface and downcore sediments to characterize haptophyte populations through time in parallel with phylogenetic analyses we determined the alkenone distributions including c37 c38 ratios and the presence absence of c38 methyl ketones and c40 compounds in all the samples the resulting alkenone profiles from this study do not all align with traditional marine versus coastal lacustrine alkenone profiles additionally our genetic data indicate the presence of multiple haptophyte species from a single lake sediment sample these distinct haptophyte populations could not be discerned from the alkenone profiles alone these results show that alkenone profiles are not a reliable way to assess the haptophyte algae in lakes and that dna fingerprinting is a preferred approach for species identification although closely related haptophyte species or subspecies may not warrant different temperature calibrations our results emphasize the importance of genetic data for inferring haptophyte identities and eventually selecting alkenone temperature calibrations for paleoclimate reconstructions

combined dna and lipid analyses of sediments reveal changes in holocene haptophyte and diatom populations in an antarctic lake preserved ribosomal dna of planktonic phototrophic algae was recovered from holocene anoxic sediments of ace lake antarctica and the ancient community members were identified based on comparative sequence analysis the similar concentration profiles of dna of haptophytes and their traditional lipid biomarkers alkenones and alkenoates revealed that fossil rdna also served as quantitative biomarkers in this environment the dna data clearly revealed the presence of six novel phylotypes related to known alkenone and alkenoate biosynthesizing haptophytes with isochrysis galbana uio 102 as their closest relative the relative abundance of these phylotypes changed as the lake chemistry particularly salinity evolved over time changes in the alkenone distributions reflect these population changes rather than a physiological response to salinity by a single haptophyte using this novel paleo ecological approach of combining data from lipid biomarkers and preserved dna we showed that the post glacial development of ace lake from freshwater basin to marine inlet and the present day lacustrine saline system caused major qualitative and quantitative changes in the biodiversity of the planktonic populations over time

alkenone producers inferred from well preserved 18s rdna in greenland lake sediments 1 the 18s ribosomal dna rdna sequences of haptophyte algae were successfully amplified using the polymerase chain reaction pcr from water filtrate surface sediments and a late holocene sediment sample 1000 years old from a group of lakes in the sondre stromfjord region of west greenland the dna of the algal primary producer is extremely well preserved in the laminated lake sediments which have been deposited in cold 1 2c anoxic and sulphidic bottom water phylogenetic analyses of the greenland haptophyte rdna sequences suggest that alkenones in the greenland lake sediments are produced by haptophyte algae of the class prymnesiophyceae the 18s rdna sequences from the greenland samples cluster within a distinct phylotype differing from both marine haptophytes and from those reported previously from ace lake antarctica the similarity of haptophyte rdna sequences among all samples in this study suggests a single alkenone based temperature calibration may be applied to these lakes for at least the past 1000 years these sedimentary archives hold great promise for highresolution alkenone based paleotemperature reconstruction of southern west greenland a region sensitive to atmospheric oceanic climate phenomena such as the north atlantic oscillation nao

biogeochemical evidence for environmental changes of pleistocene lake olduvai during the transitional sequence of ogcp core 2a that encompasses tuff ib 1 848 ma abstract olduvai gorge is renowned for discoveries of hominin fossils and tools in a well resolved sedimentary context representing one of the foremost sites in east africa that has afforded critical evidence of hominin evolution in 2014 the olduvai gorge coring project ogcp recovered the first deep sediment cores from this location these cores provide the first opportunity to examine an extensive stratigraphic record from one location and independent of the weathering and related degradation typical of outcrop samples samples from these cores have been correlated to bed i tuffs and basalt marker beds that are well characterized from outcrops within the gorge this study focuses on the biogeochemical investigation of a 10 m segment from ogcp sediment core 2a where age constraints indicate deposition occurred over 50 000 years from 1 8055 0 003 ma to 1 8551 0 013 ma the segment includes tuff ib and if which were deposited at a time that prior research indicates represents marked changes in the paleoenvironment at olduvai with indications that paleolake olduvai may have been completely desiccated by the time tuff if was deposited this environmental change is recorded by the composition of sedimentary organic matter om in terms of bulk organic geochemical properties observed as a decrease in toc and 13corg in addition temporal variations in source specific biomarkers n alkanes phytane steradienes a norsteranes and alkenones reflect a shift from a deeper lake setting with a prevalence of aquatic sourced om combined with input from terrestrial plant waxes to a more shallow perennial lake where evidence of burrows and erosional surfaces is associated with microbially degraded om and intermittent aquatic biomarkers thus variations in biogeochemical proxies complement the sedimentological evidence confirming increased periods of prolonged desiccation of paleolake olduvai beginning around the time of tuff ib deposition

global temperature calibration of the alkenone unsaturation index uk 37 in surface waters and comparison with surface sediments in this paper we compile the current surface seawater c37 alkenone unsaturation uk 37 measurements n 629 1 to 30 c temperature range to derive a global field based calibration of uk 37 with alkenone production temperature a single nonlinear global surface water calibration of uk 37 accurately predicts alkenone production temperatures over the diversity of modern day oceanic environments and alkenone synthesizing populations t 0 957 54 293 uk 37 52 894 uk 37 2 28 321 uk 37 3 r2 0 97 n 567 the mean standard error of estimation is 1 2 c with insignificant bias in estimated production temperature among the different ocean regions sampled an exception to these trends is regions characterized by strong lateral advection and extreme productivity and temperature gradients e g the brazil malvinas confluence in contrast to the surface water data the calibration of uk 37 in surface sediments with overlying annual mean sea surface temperature anno is best fit by a linear model anno 29 876 uk 37 1 334 r2 0 97 n 592 the standard error of estimation 1 1 c is similar to that of the surface water production calibration but a higher degree of bias is observed among the regional data sets the sediment calibration differs significantly from the surface water calibration uk 37 in surface sediments is consistently higher than that predicted from anno and the surface water production temperature calibration and the magnitude of the offset increases as the surface water anno decreases we apply the global production temperature calibration to the coretop uk 37 data to estimate the coretop alkenone integrated production temperature coretop ipt and compare this with the overlying annual mean sea surface temperature anno we use simple models to explore the possible causes of the deviation observed between the coretop temperature signal as estimated by uk 37 and anno our results indicate that the deviation can best be explained if seasonality in production and or thermocline production as well as differential degradation of 37 3 and 37 2 alkenones both affect the sedimentary alkenone signal

sedimentary alkenone distributions reflect salinity changes in the baltic sea over the holocene the baltic sea has had a complex salinity history since the last deglaciation here we show how distributions of alkenones and their d values varied with past fluctuations in salinity in the baltic sea over the holocene by examining a holocene record 11 2 0 1 cal kyr bp from the arkona basin major changes in the alkenone distribution i e changes in the fractional abundance of the c37 4 me alkenone the c38 2 et alkenone and a c36 2 me alkenone the latter which has not been reported in the baltic sea previously correlated with known changes in salinity both alkenone distributions and hydrogen isotopic composition suggest a shift in haptophyte species composition from lacustrine to brackish type haptophytes around 7 7 7 2 cal kyr bp corresponding with a salinity change that occurred when the connection between the basin and the north sea was re established a similar salinity change occurred in the black sea previously published alkenone distributions and their d values from the black sea were used to reconstruct holocene changes in surface water salinity and hence it was shown that the unusual c36 2 alkenone dominates the alkenone distribution at salinities of 2 8 ppt g kg this information was used to corroborate the interpretations made about salinity changes from the data presented for the baltic sea low and variable salinity waters in the baltic sea over the holocene have led to a variable alkenone producing haptophyte community composition including low salinity adapted species hindering the use of the unsaturation ratios of long chain alkenones for sea surface temperature reconstruction however these alkenone based indices are potentially useful for studying variations in salinity regionally as well as in the past

a multiphasic younger dryas cold period recorded in sediments of lake steisslingen sw germany a biomarker perspective abstract the younger dryas 12 680 11 590 yr bp was the last millennial scale cold event of the quaternary when a mean annual temperature decline of 3 5 c impacted severely on the environment whereas pollen distributions document changes in land vegetation details of limnic ecosystem responses to the cooling event and to its recovery are still not well known here we studied the laminated sediments of lake steisslingen sw germany deposited between 13 500 and 11 100 yr bp in order to investigate the evolution of an aquatic ecosystem bulk sediment and organic matter composition mark onset and termination of the younger dryas but remain monotonous through this interval requiring application of organic and isotope geochemical techniques to follow past ecosystem dynamics the younger dryas is characterized by both an abrupt appearance and demise of long chain alkenones indicative for haptophyte algae based on algal and bacterial biomarker distribution the younger dryas can be divided into three stages each characterized by the dominance of a microorganism group the first phase was dominated by nc17 alkanes and hopanoids indicative of cyanophytes and heterotrophic bacteria the second phase shows a proliferation of cold adapted haptophyte algae while in the latest phase highly branched isoprenoids hbi reveal an aquatic community shift towards diatoms heterocyte glycolipids document a moderate change in n2 fixing cyanobacterial community structure over the allerod younger dryas transition but show a marked collapse of the cyanobacteria association at the younger dryas preboreal climate recovery terrigenic wax lipids indicate significant changes in vegetation between the allerod younger dryas and preboreal chronozones but remain homogeneous within the younger dryas

chlorozoan versus foramol lithofacies in upper cretaceous rudist limestones abstract the study of upper cretaceous limestones of the nurra region northwestern sardinia italy that crop out with open shelf rudist rich deposits has shown that during the early senonian coniacian santonian interval sediments characterized by assemblages dominated by molluscs with variable amounts of red algae bryozoa and echinoids replaced sediments including hermatypic corals green algae and variable amounts of non skeletal grains these latter components were largely dominant in the previous carbonate shelf contexts of the nurra during jurassic early cretaceous times becoming less numerous until they disappeared in the transgressive deposits that followed the tectonically induced middle cretaceous emersion phase a rhodalgal association typical of anomalous tropical areas or transitional ones has been recognized in the replacing limestones that may be more generically considered foramol type deposits this seems to document conditions of stress in the waters impinging on the nurra carbonate platform during the coniacian santonian transition the observation that in the late cretaceous a similar evolutionary trend seems to have characterized many shallow neritic successions from many different areas leads us to hypothesize more general causes of stress e g induced upwellings on the marginal sectors of the shelves increased oceanic overturns and hyperproductivity due to terrestrial runoff on post emersive transgressed substrata peculiar oceanic conditions were able to create depositional contexts that were considerably changed with respect to the previous ones such that the more opportunistic forms of the foramol assemblages flourished the change in dominant assemblages resulted in a different organization of the sediment as a response to the different producing communities the resulting temperate type carbonate shelves were characterized by a low growth potentiality essentially due to a higher dispersion rate and this could have facilitated their drowning

molecular stratigraphy a new tool for climatic assessment variations in sea surface temperatures over the past 500 000 years are inferred from the relative abundance behaviour of two organic compounds c37 alkenones over the upper 8 metres of a sediment core from the eastern equatorial atlantic this molecular record ascribed to contributions from prymnesiophyte algae correlates well with the variations in the 18 signal for the calcareous skeletons of certain planktonic foraminifera thus providing the first demonstration of a new stratigraphical technique which may be especially valuable where methods based on carbonate 18 fail

alkenone distribution in lake van sediment over the last 270 ka influence of temperature and haptophyte species composition abstract fossil long chain alkenones have been used for several decades to reconstruct past ocean surface water temperatures and gained recent interest as a paleotemperature proxy for continental lake settings however factors besides temperature can affect alkenone distributions in haptophyte algae and alkenone compositions can differ between haptophyte species alkenone biosynthesizing haptophyte algae are genetically much more diverse in lakes than in the marine realm and species level variations in alkenone compositions could have implications for alkenone paleothermometry here we performed a paired analysis of alkenone distributions and haptophyte species compositions using ancient dna in up to 270 ka old sediments of lake van in turkey to reveal a possible species effect on fossil alkenone distributions and paleotemperature estimates the same predominant haptophyte in lake van today prevailed also since the last 100 ka however a calibration of alkenone paleotemperature especially in the oldest analyzed intervals is complicated due to a more complex haptophyte species composition predominated by a haptophyte lvhap 6 which is phylogenetically different from sequences recovered from currently existing lakes including lake van and from haptophyte species existing in culture the predominance of lvhap 6 coincided with the presence of alkenone mec38 3 and relatively high mec37 3 4 2 4 and mec38 4 5 ratios 3 0 uk37 index values in the sediment core over the last 270 ka reflect relative changes in past temperature and are additionally linked to haptophyte species composition a sustained period of high salinity as indicated by pore water salinity measurements could potentially have triggered the succession of haptophytes as sources of alkenones in lake van

response of bedrock channel width to tectonic forcing insights from a numerical model theoretical considerations and comparison with field data the morphology of bedrock river channels is controlled by climatic and tectonic conditions and substrate properties knowledge of tectonic controls remains scarce this is partly due to slow tectonic rates and long response times of natural channels and partly due to the difficulty in isolating and constraining tectonic forcing conditions in the field to study the effect of tectonic forcing on channel geometry we have developed a numerical model of the cross sectional evolution of a detachment limited channel its predictions are matched by an analytical model based on the assumption of the minimization of potential energy expenditure using these models we illustrate how local tectonics can alter the observed width discharge scaling and discuss published field data in light of our findings except for one case the models fail to correctly describe field observations of well constrained cases this implies that the shear stress stream power family of models is too simple to describe the behavior of natural channels additional complexities such as sediment effects and discharge variability exert a strong control on channel morphology and need to be taken into account in the modeling of channel dynamics and steady state

group i alkenones and isochrysidales in the world s largest maar lakes and their potential paleoclimate applications abstract the espenberg maar lakes on the seward peninsula alaska are the largest volcanic crater lakes in the world and contain the longest known lacustrine sedimentary archives in alaska the lack of glacial aged marine sedimentary archives around the bering land bridge due to exposure of the shelf during sea level low stands makes these lakes highly valuable for understanding the region s past climate and environmental changes located en route to humanity s last colonized american continents the seward peninsula s climate and environments during the last glacial period bear major anthropological significance however a lack of quantitative proxies has so far hampered exploration of these lakes for paleoclimate reconstructions here we report for the first time the discovery of abundant group i alkenones and isochrysidales in surface sediments from three maar lakes white fish north killeak and devil mountain using a combination of lipid biomarker and 18s rrna gene sequencing analyses our discovery adds to the expanding list of oligotrophic freshwater lakes where group i alkenones are found and water chemistry data contribute to the understanding of the environmental controls on group i isochrysidales our results further confirm the use of the u 37 k index of group i alkenones as a proxy for the mean temperature of the spring isotherm mtsi and rik37 as a quantitative measurement for isochrysidales group mixing we also demonstrate the analytical challenges for analyzing alkenones in freshwater lakes and the effectiveness of eliminating coelution using silver thiolate chromatographic material agtcm

late holocene coupled moisture and temperature changes on the northern tibetan plateau the northern tibetan plateau involves complex interactions between the mid latitude westerly circulation and the subtropical asia monsoon circulation acting as a bridge communicating high and low latitude climatic processes previous studies from the region suggest relatively wet conditions in cold periods during the late holocene for instance the little ice age lia however the inference of such temperature moisture association is subject to the large uncertainty in lacustrine 14c chronology due to the particularly large lake reservoir effect in the region here we take a different approach by reconstructing paired temperature and moisture records from the same sediment cores to assess the temperature moisture association independent of chronology uncertainty we use alkenone indices uk 37 and c37 4 to reconstruct high resolution temperature and moisture changes simultaneously from two lakes in the qaidam basin northern tibetan plateau over the last 2500 years characterized by marked climatic variability our paired records confirm the warm dry and cold wet association in arid northwestern china during the late holocene opposite to the warm wet and cold dry association in subtropical asian monsoonal regions our moisture records further suggest substantially drier conditions during the medieval warm period mwp than the current warm period lastly the temperature and moisture changes inferred from our records can be well correlated with solar irradiance changes suggesting a possible link between solar forcing and natural climate variability during the late holocene on the northern tibetan plateau

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters