organic geochemical proxies of paleoceanographic paleolimnologic and paleoclimatic processes abstract organic matter constitutes a minor fraction of marine and freshwater sediments yet its important contribution to the sedimentary record can be used to reconstruct marine and continental paleoenvironments the organic matter content of sediments is the residue of past biota the amounts and types of organic matter present in sediments consequently reflect environmental conditions that impacted ecosystems at different past times general sources of the organic matter are inferred from bulk properties such as elemental compositions carbon and nitrogen stable isotope ratios rock eval pyrolysis data and organic petrography details of organic matter origins are refined by analyses of biomarker molecular compositions source changes are proxies for fluctuations in sea level oceanic surface currents and continental climates algal paleoproductivity rates are indicated by organic carbon mass accumulation rates and carbon and nitrogen stable isotopic compositions these parameters record past availability of nutrients and therefore are proxies of surface mixing in the oceans and amount of land runoff to lakes sea surface paleotemperatures are recorded by the number of carbon carbon double bonds in lipid biomarkers produced by marine algae larger proportions of the double bonds are proxies for the cooler surface waters that accompanied periods of global glaciation and intervals of enhanced upwelling the 13c and d values of plant organic matter record past concentrations of carbon dioxide in the atmosphere and changes in delivery of atmospheric moisture respectively diagenesis which causes the concentration and composition of organic matter in sedimentary settings to differ from those of the original biologically synthesized materials can bias organic geochemical paleoenvironmental records the magnitude of this potential source of misinformation must always be considered and evaluated comparison of multiple organic geochemical proxies of past conditions helps to compensate for the effects of diagenetic alterations and thereby to improve interpretations of paleoenvironmental change

variability of the arctic front during the last climatic cycle application of a novel molecular proxy in the nordic seas the arctic front af marks the boundary between the waters of the north atlantic drift norwegian current and those of the arctic domain long or short term shifts in the position of the af may affect climate conditions in the northern hemisphere arctic water masses are also the loci of modern open ocean convection hence defining these areas in the past is important for reconstructing and modelling ocean circulation and its variability c37 alkenones are biomarkers for some algae of the class prymnesiophyceae e g coccolitho phorids such as emiliania huxleyi these alga occur in most parts of the oceans in ice free conditions and are found nowadays throughout the nordic seas we have related the sedimentary abundance of the tetraunsaturated c37 alkenone c37 4 to two types of water masses in the nordic seas in locations affected by atlantic water masses percentages of c37 4 are less than 5 whereas in arctic type water masses these increase to more than 5 we propose that this observation can be used as a modern analogue to reconstruct the position of the af in north atlantic quaternary sediments using this novel molecular proxy we can infer that the southward migration of the af in the ne atlantic reached 50 n during the last glacial maximum lgm but perhaps only 60 n during the younger dryas and that ocean conditions free of sea ice prevailed throughout the northern north atlantic in summer

bulk organic δ13c and c n ratios as palaeosalinity indicators within a scottish isolation basin microfossils in isolation basin sediments are frequently used to reconstruct sea level change but preservation problems and non analogue situations can limit their usefulness here we investigate the potential of stable carbon isotopes 13c and c n ratios from bulk organic matter as an alternative proxy of salinity within isolation basin sediments from a basin in northwest scotland within the holocene sediment 13c and c n are determined largely by the mean weighted values of the predominant source of the organic material analysis of modern materials and comparison with the diatom record shows that the marine parts of the sequence are dominated by high 13c and variable c n in the fresh water sequences the organic material is a mixture of both freshwater aquatic and terrestrial plant input that have relatively low 13c and high c n the application of 13c and c n ratios in the studied basin in general follow the environmental change recorded by the diatoms and shows the potential of bulk organic matter in the investigation of salinity change in isolation basins copyright 2005 john wiley sons ltd

alkenones alkenoates and organic matter in coastal environments of nw scotland assessment of potential application for sea level reconstruction reconstruction of late quaternary sea level history in areas of glacioisostatic uplift often relies on sediment archives from coastal isolation basins natural coastal rock depressions previously isolated from or connected to the sea at different times proxy indicators for marine brackish or lacustrine conditions combined with precise dating can constrain the time when the sea crossed the sill threshold and isolated or connected the basin the utility of isolation basins in investigations of sea level change is well known but investigations have been mostly limited to microfossil proxies the application of which can be limited by preservation and nonanalog problems here we investigate the potential of long chain alkenones alkenoates and bulk organic parameters toc corg n for reconstructing past sea level changes in isolation basins in nw scotland we analyze organic biomarkers and bulk parameters from both modern basins at different stages of isolation from the sea and fossil basins with sea level histories reconstructed from established proxies logit regression analysis was employed to find which of the biomarker metrics or bulk organic measurements could reliably characterize the sediment samples in terms of a marine brackish or isolated lacustrine origin the results suggested a good efficiency for the alkenone index c37 4 at predicting the depositional origin of the sediments this study suggests that alkenones could be used as a novel proxy for sea level change in fossil isolation basins especially when microfossil preservation is poor

long chain alkenones and alkyl alkenoates and the fossil coccolith record of marine sediments long chain n c37 c39 alkenones and alkyl alkenoates are biological markers for sediment inputs of algae from the class prymnesiophyceae which includes the coccolithophorids these compounds have been recognized in many recent and ancient marine sediments but in only a few living algal species notably the ubiquitous coccolithophorid emiliania huxleyi the proven value of long chain alkenones in palaeotemperature assessment prompts an evaluation of their sedimentary record especially their correspondence with coccolithophorid fossils in ancient marine sediments synthesis of available micropalaeontological and molecular data suggests that morphologically related species of the genera crenalithus dictyococcites emiliania gephyrocapsa pseudoemiliania and reticulofenestra all belonging to the family gephyrocapsaceae were potential biological sources of alkenones and alkyl alkenoates in marine sediments deposited since the eocene 45 ma the occurrence of alkenones in cenomanian and albian sediments devoid of nannofossils may be presumed to reflect contributions from ancestors of the gephyrocapsaceae although an investigation of cretaceous samples containing both coccoliths and alkenones would provide further evidence of this proposed correspondence the combination of palaeontological and molecular chemotaxonomic information offers a novel approach to the evaluation of the phylogenetic lineages that link living and extinct algae

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

palaeoecology of two lake basins from disko west greenland the macrofossils lithology and chronology of two lake basins on disko in central west greenland have been investigated both lakes were isolated from the sea in the mid holocene as a result of relative land uplift a marine brackish limnic sequence was recovered from the qivittut lake the marine fauna is unusually diverse whereas the brackish water fauna consists only of few species immediately after isolation the lake passed through a short lived eutrophic phase after which stable mesotrophic conditions were established from the second lake basin the fortunebay lake only limnic sediments were recovered this lake record demonstrates that rather stable conditions have persisted since mid holocene times both lakes show anomalously high accumulation rates

modifications of the c37 alkenone and alkenoate composition in the water column and sediment possible implications for sea surface temperature estimates in paleoceanography 1 the literature pertaining to c37 alkenone and c37 and c38 alkenoate production and diagenesis has been reviewed and evaluated for issues that might jeopardize their usefulness in paleotemperature estimation we also examined the use of the c37 alkenones as paleoproductivity indicators the stability of their 13c isotopic compositions and their incorporation into the nonsolvent extractable organic matter fraction biological transformation of organic matter by bacteria and zooplankton does not appear to cause significant changes to the ratio of c37 2 and c37 3 alkenones but there are major alterations in the relative composition of alkenoates studies of water column processes and postdepositional sedimentary changes indicate overall stability in the c37 2 c37 2 c37 3 ratio leading to effective preservation of the paleotemperature signal this is not the case for alkenoates and there also appear to be some doubts about the dependence between sea surface temperature and the sedimentary abundance of the c37 4 alkenone c37 alkenones may provide useful qualitative estimates of marine paleoproductivity although these compounds are apparently only derived from haptophycea changes in their quantitative composition might reflect changes in nutrient availability that on sedimentary timescales should also be generally significant of other algal species one caveat is that in highly productive upwelling systems productivity may be expressed mostly in diatom growth and thus not measurable by the c37 alkenones no changes in 13c c37 alkenone composition are observed upon zooplankton ingestion although this is expected from a theoretical perspective further studies are encouraged in order to fully assess the stability of the isotopic signal during c37 alkenone diagenesis finally alkenones bound in the nonextractable fraction of sedimentary organics have not been adequately studied and further work is required to clarify any possible correspondence with a temperature signal

long chain alkenones in qinghai lake sediments abstract long chain methyl and ethyl alkenones c 37 c 40 containing two to four double bonds have been detected in sediments from qinghai lake china this is the first report of the alkenones in lake sediments deposited under a variety of salinity conditions where the lake has not encountered any marine incursions the presence of the alkenones suggests the presence of prymnesiophyceae in the lake which may have reached the lake via eolian transportation or seabirds sediment samples from the more saline areas of the lake contained higher concentrations of the more highly unsaturated compounds widespread use of these compounds as paleotemperature indicators in marine sediments introduces the possibility of extrapolating this approach to lacustrine environments if appropriate calibrations can be undertaken

distributions of long chain alkenones and alkyl alkenoates in marine surface sediments from the north east atlantic abstract the abundances of long chain alkenones and alkyl alkenoates are reported for a suite of surface sediments from the ne atlantic 0 75 n despite the differing conditions of their biologies and differing extents of water column degradation and of early diagenesis in the sediments the degree of unsaturation of the alkenones e g the u 37 k parameter and the relative proportion of alkyl alkenoates to alkenones display linear correlations with average temperature for surface waters warmer than 5 c there is evidence that the chain length distribution of the alkenones and of the ratio between the ethyl and methyl c 38 alkenones are species dependent which would enable their use as chemotaxonomic tools

late glacial sea level and ocean margin environmental changes interpreted from biostratigraphic and lithostratigraphic studies of isolation basins in northwest scotland

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

significance of high c n ratios in organic carbon rich neogene sediments under the benguela current upwelling system corganic ntotal values change from 5 in middle miocene sediments deposited under the benguela current upwelling system to 15 in latest miocene and pliocene sediments although the change appears to record a larger proportion of land derived material in younger sediments bulk 13corg values indicate a predominance of marine origin for organic matter throughout the sequence marine paleoproductivity as represented by mass accumulation rates of caco3 and organic carbon increased over this time interval we postulate that the larger corganic ntotal values record a shift towards greater recycling rates of nitrogen rich relative to carbon rich organic matter components as the flux of total organic matter to the seafloor increased furthermore we propose that high corganic ntotal values may record enhanced paleoproductivity in other sedimentary sequences dominated by marine organic matter

variability of unusual distributions of alkenones in the surface waters of the nordic seas 1 samples of filtered particulate organic matter pom were obtained during the summers of 1999 and 2000 from the surface waters of the nordic seas to monitor the spatial distribution of long chain alkenones the aim of the study was to appraise existing alkenone based climatic proxies in northern high latitudes unusually high percentages of the tetraunsaturated alkenone were measured in the polar waters of the east greenland current with c37 4 of up to 77 in 80 of sea ice cover values of percent c37 4 across the nordic seas showed a strong association with water mass type analysis of coccoliths in filters indicated that calcified emiliania huxleyi could not be discounted as the biological precursor of alkenones in all the water masses a combined data set of 69 samples of pom revealed a stronger correlation of percent c37 4 to sea surface salinity sss r2 0 72 than to sea surface temperature sst r2 0 50 values of percent c37 4 in sea surface pom were much higher than those in surficial sediments of the northern north atlantic to explain the discrepancy in sedimentary and surface water column percent c37 4 we propose that the alkenone contents in surface sediments underlying arctic and polar waters are a combination of autochthonous and allochthonous inputs of alkenones our results show that percent c37 4 can be used to reconstruct the relative extension of arctic polar water masses in the north atlantic however the results prevent confirmation of percent c37 4 as a paleo sss proxy in the nordic seas given its multivariate nature in our data set and the decoupling between its range of values in surface waters and sediments

evidence for differential degradation of alkenones under contrasting bottom water oxygen conditions implication for paleotemperature reconstruction abstract the successful reconstruction of sea surface temperatures using alkenone paleothermometry u37k has relied on the premise that there is no significant differential degradation of alkenones with different states of unsaturation during diagenetic processes to test this assumption we conducted a comparative study of contemporary sediments in oxic and anoxic bottom waters from the santa monica basin offshore california long chain alkenones were quantified and sea surface temperature were calculated using the calibrated u37k t relationship of prahl et al 1988 our results show that temperature record from the oxic sediments is higher by as much as 4 c compared to those from time equivalent anoxic sediments as a result of differential degradation of long chain unsaturated alkenones and bioturbation mixing in the oxic sediments the differential degradation of c37 3 vs c37 2 alone could account for up to 2 5 c difference between these two records this finding has significant implication in the interpretation of paleo sea surface temperature data using alkenone paleothermometry

sea surface paleotemperature errors in uk 37 estimation due to alkenone measurements near the limit of detection major errors 0 5 c are produced in paleotemperature estimation with the c37 alkenone method when the amount of the diunsaturated or triunsaturated species c37 2 and c37 3 respectively approaches the limit of detection these errors are more commonly encountered with c37 3 because of its higher adsorption to gas chromatographic gc columns they are particularly relevant at low sedimentary c37 alkenone concentrations and may easily increase to temperature differences of 2 4 c depending on the uk 37 values and the ratio between the c37 3 signal and limit of detection mathematical expressions for the description of the analytical constraints derived from this detection limit problem are given a quality assurance guideline based on sample dilution three times and calculation of the sea surface temperature error is proposed for assessment of reliable measurements reevaluation of literature data in the light of the equations reported in the present study suggest that some previously reported alkenone geochemical effects such as variation in uk 37 temperatures due to postdepositional oxidation may reflect deviations in the gc measurements due to changes in c37 alkenone concentration

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

noble metal enrichment processes in the merensky reef bushveld complex we have analysed sulphides silicates and chromites of the merensky introduction reef for platinum group elements pges re and au using laser the enrichment of noble metals in layered gabbroic ablation inductively coupled plasma mass spectrometry and synthetic intrusions to form stratiform merensky type ore horizons pyrrhotite standards annealed with known quantities of noble metals is an extremely efficient yet poorly understood process os ir and ru reside in solid solution in pyrrhotite and pentlandite metal enrichment must be related to the formation of rh and part of the reef s pd in pentlandite whereas pt au re magmatic layering as the ore horizons form an integral and some pd form discrete phases olivine and chromite often part of the magmatic stratigraphies of their host insuspected to carry os ir and ru are pge free all phases analysed trusions metal concentration is also related to the prescontain noble metals as discrete micro inclusions with diameters ence of magmatic sulphides because the noble metals are either dissolved in base metal sulphides or occur as typically 100 nm inclusions in sulphides commonly have the discrete noble mineral phases intergrown with sulphides element combinations os ir pt and pt pd au inclusions in vermaak hendriks 1976 ballhaus ryan 1995 olivine and chromite are dominated by pt au pd few inclusion ballhaus ulmer 1995 spectra can be related to discrete noble metal phases and few there is considerable controversy as to where the inclusions have formed by sub solidus exsolution rather some metals came from and how metal enrichment worked pge inclusions notably those in olivine and chromite are earlyfor a stratiform platinum group element pge deposit magmatic nuggets trapped when their host phases crystallized we inside the magmatic stratigraphy of a layered intrusion suggest that the silicate melt layer that preceded the merensky reef there are two possibilities either the metals were derived was pge oversaturated at early cumulus times experiments from the melt column above the ore horizon or they came combined with available sulphide silicate partition coefficients sugfrom the magma equivalent to the cumulate package gest that a silicate melt in equilibrium with a sulphide melt underlying the ore owing to the large density contrast containing the pge spectrum of the merensky ore would indeed be between silicate and sulphide melt a popular view is that oversaturated with respect to the least soluble noble metals sulphide the metals were enriched by gravitational settling of melt apparently played little role in enriching the noble metals in sulphide melt i e out of the magma column above the the merensky reef rather its role was to immobilize a pre existing ore campbell et al 1983 barnes naldrett 1985 in situ stratiform pge anomaly in the liquid stratified magma naldrett et al 1987 on the other hand it is well chamber established that gravitational crystal settling plays little role in producing magmatic layering and magmatic stratigraphies mcbirney noyes 1979 morse 1986 campbell 1987 and this cannot remain without consequence for stratiform noble metal deposits a third alternative is noble metal enrichment by late

isolation basin stratigraphy and holocene relative sea level change on arveprinsen ejland disko bugt west greenland this paper presents the results of an investigation into holocene relative sea level rsl change isostatic rebound and ice sheet dynamics in disko bugt west greenland data collected from nine isolation basins on arveprinsen ejland east disko bugt show that mean sea level fell continuously from ca 70 m at 9 9 ka cal yr bp 8 9 ka 14c yr bp to reach a minimum of ca 5 m at 2 8 ka cal yr bp 2 5 ka 14c yr bp before rising to the present day a west east gradient in isostatic uplift across disko bugt is confirmed with reduced rebound observed in east disko bugt however rsl differences up to 20 m at 7 8 ka to 6 8 ka cal yr bp 7 ka to 6 ka 14c yr bp also exist within east disko bugt suggesting a significant north south component to the area s isostatic history the observed magnitude and timing of late holocene rsl rise is not compatible with regional forebulge collapse instead rsl rise began first in the eastern part of the bay as might be expected under a scenario of crustal subsidence caused by neoglacial ice sheet readvance the results of this study demonstrate the potential of isolation basin data for local and regional rsl studies in greenland and the importance of avoiding data compilations from areas where the isobase orientation is uncertain copyright 1999 john wiley sons ltd

evidence of continuous asian summer monsoon weakening as a response to global cooling over the last 8 ma abstract the asian summer monsoon asm is the dominant climate system of south and east asia however the history of monsoon intensification and the driving forces behind it are controversial wind blown sediments in mid latitude east asia and fluvial derived sediments in the northern south china sea imply contrasting asm patterns during the late cenozoic here we use pollen records from the southwest south china sea international ocean discovery program iodp site u1433 to reconstruct the asm evolution in low latitude southeast asia a slow increase in herbaceous plants since 8 ma indicates a persistent weakening of precipitation in indochina which is dominated by the asm this signal is closely associated with a consistent coniferous plant record indicating a continuous cooling trend that correlates well with sea surface temperature sst decrease in the west pacific ocean we propose that the monsoon weakening resulted in as much as a 25 reduction in precipitation over the past 8 ma in response to the northern hemisphere glaciation global cooling with some of the increase in conifers being linked to uplift of the vietnamese central highland and the se flank of the tibetan plateau in yunnan and northern vietnam

unusual distributions of long chain alkenones and tetrahymanol from the highly alkaline lake van turkey long chain c37 to c40 alkenones with di tri and tetra unsaturation are very abundant in sediment trap material and holocene to late pleistocene core samples from the earth s largest soda lake lake van turkey thus the known distribution range of these typical biomarkers for haptophyte microalgae is extended to highly alkaline environments the observed unsaturation patterns differ strikingly from those found in open marine haptophytes and sediments by an enhanced relative abundance of the tetra unsaturated compounds especially the c37 4 methyl ketone their preponderance is suggested to be a facies marker pattern for lacustrine and marginal marine areas of sedimentation using published u37k calibrations no reliable absolute temperatures were obtained for the lake van samples accordingly marine sea surface temperature determinations based on long chain alkenones should be applied with caution when a contribution of these compounds from coastal or nonmarine sources can not be excluded the presence of tetrahymanol and gammacer 3 one in the lake van materials is attributed to organic matter contributions of ciliates the relative abundance of long chain alkenones and of tetrahymanol gammacer 3 one is considered to reflect changes in the environmental conditions in particular in the hydrological setting we suggest that times of pronounced stagnation are recognised by very high tetrahymanol gammacer 3 one concentrations together with drastically increased stanol stenol ratios and intervals of enhanced convection or of high freshwater input are characterised by high alkenone contributions

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