a reexamination of northeast atlantic sea surface temperature and salinity over the last 16 kyr we present a 15 kyr sea surface temperature sst record for a high sedimentation rate core knr51 29ggc from the feni drift off of ireland based on an organic geochemical technique for paleotemperature estimation u37k we compare the u37k temperature record to planktonic foraminiferal 18o and foraminiferal assemblage sst estimates from the same sample horizons u37k gives sst estimates of 13 c for the early deglacial and 18 c for the holocene and recent whereas assemblages give estimates of 9 c and 13 c respectively as in nearby core v23 81 we find ash zone 1 the younger dryas increase in neogloboquadrina pachyderma sinistral abundance and maximum abundance of this species during glaciation n pachyderma dextral oxygen isotopic analyses have a late glacial to interglacial range of 1 5 a reduction of about 1 in 18o occurred at about 12 ka whereas u37k and the foraminiferal fauna indicate a 2 c warming this implies a 0 9 salinity effect on 18o which we attribute to meltwater freshening all three parameters indicate cooling during the younger dryas u37k sst estimates show that the major shift from deglacial to interglacial temperatures occurred after the younger dryas in termination 1b in contrast to the assemblage data which show this jump in sst at the end of the glaciation during termination ia differences between the two sst estimators which may result from their different floral versus faunal sources are more pronounced between transitions ia and ib this may reflect different habitats under the unusual sea surface conditions of the deglaciation

alkenone molecular stratigraphy in an oceanic environment affected by glacial freshwater events the sedimentary record of a ratio uk37 of long chain c37 unsaturated alkenones is a useful indicator of glacial interglacial climatic change in the late quaternary northern gulf of mexico where a planktonic foraminiferal 18o caco3 record is complicated by meltwater and or fluvial events williams and kohl 1986 application of a laboratory temperature calibration of the uk37 ratio prahl and wakeham 1987 to a pigmy basin hydraulic piston core record deep sea drilling project core 619 suggested that the minimum glacial surface mixed layer sml temperature was 8 1 c colder than the holocene high sml temperature of 25 6 0 5 c this predicted glacial interglacial temperature difference was significantly larger than the differences predicted by either the foraminiferal 18o or foraminiferal assemblage temperature methods 0 8 2 0 c this large difference may be caused by local prymnesiophyte assemblage changes in response to climatically induced hydrographic changes interglacial periods may be dominated by pelagic prymnesiophyte assemblages while glacial periods may be dominated by neritic assemblages a combined mechanism of both climatically varying prymnesiophyte species assemblage and depth of alkenone biosynthesis may account for the large difference between the temperature methods

tropical sea surface temperatures during the last glacial period a view based on alkenones in indian ocean sediments abstract the quantification of tropical temperatures during the last glacial cycle 0 150 kyr bp is a controversial issue since different proxies seem to provide conflicting informations to obtain a complementary point of view we use the alkenone method to estimate sea surface temperatures and focus our work on deep sea sediments recovered from the tropical indian ocean we present alkenone data obtained in two cores which cover in detail the last deglaciation and in about twenty cores distributed between 20 s and 20 n that were chosen to evaluate the temperature contrast of the last glacial interglacial transition our results indicate that indian ocean tropical temperatures remained an average within 1 5 2 5 c of their present values during the last glaciation at 10 n the last deglaciation is characterized by two warming steps which is similar to the classical deglacial chronology observed in the north atlantic area at 20 s the deglacial warming occurred at ca 15 cal kyr bp lagging significantly 5 4 kyr behind the antarctic warming but in phase with northern hemisphere time series

late holocene marine radiocarbon reservoir correction δr for the west coast of south africa in order to calibrate radiocarbon ages based on samples with a marine carbon component it is important to know the marine carbon reservoir correction or r value this study measured the r on both known age pre bomb marine shells and paired marine and terrestrial samples from two regions on the west coast of south africa the southwestern cape and namaqualand pooling the data by region produces r values that are similar enough to use a west coast weighted mean r of 146 85 14c years to correctly calibrate marine shell or mixed marine and terrestrial 14c ages there are however temporal differences in r throughout the holocene which we compare with proxy data for upwelling and sea surface temperatures

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

improving past sea surface temperature estimates based on planktonic fossil faunas a new method of past sea surface temperature sst reconstruction based on the modern analog technique prell 1985 and on the indirect approach bartlein et al 1986 has been developed the revised analog method ram applied to planktonic foraminifera this technique leads to significant improvements in modern sst reconstruction with respect to former methods our estimates are characterized by much lower residuals and a better coverage of the observed sst range moreover the error of ram estimates of past ssts is lower than that associated with former reconstructions particularly at middle and high latitudes in low latitudes cold season ssts reconstructed by ram during glacials are 1 3 c lower than previously estimated our results tend thus to reconcile paleoestimates of glacial temperatures based on planktonic microfossils and on continental data in the tropics

high resolution uk 37 temperature reconstructions in the south china sea over the past 220 kyr past sea surface temperatures sst in the northern and southern areas of the south china sea have been reconstructed for the past 220 kyr using the uk37 alkenone index the sst profiles follow the glacial interglacial pattern exhibiting differences between last glacial maximum and holocene that are 1 3 c larger than those observed at the same latitudes in the atlantic and pacific oceans in termination i both planktonic foraminiferal 18o and sst exhibit well defined bolling allerod and younger dryas events with temperature differences between both periods of 0 8 and 0 4 c in north and south respectively ssts record a constant north south difference of 1 c in the interglacials and nearly 2 5 c in the glacial stages these differences define two distinct climatic and water circulation patterns that correspond with glacial interglacial sea level oscillations which opened and closed water exchange with the tropical indo pacific ocean through the present sunda shelf

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

evidence for a warm last glacial maximum in the nordic seas or an example of shortcomings in uk 37 and uk 37 to estimate low sea surface temperature the occurrence of ice free conditions in the nordic seas during the last glacial maximum has been demonstrated using microfossil and biomarker approaches an accurate picture of the prevailing oceanographic conditions may be more difficult to ascertain thus uncertainties for most proxies increase at the cold extreme of temperature calibrations and glacial sediments contain small amounts of microfossils and biomarkers here we discuss sea surface temperature estimates derived from alkenone indices for the last glacial maximum in the nordic seas that provide a surprising scenario where surface temperatures were warmer than at present we conclude that the uk37 and uk37 estimates may not be interpreted in terms of sea surface temperature as several factors may have conspired to bias the molecular signal however using an alternative index based on the abundance of the c37 4 alkenone we estimate a maximum temperature of 6 c

planktonic foraminiferal and alkenone records of the last deglaciation from the eastern arabian sea the oxygen isotope record of planktonic foraminifera from tropical core md77194 eastern arabian sea exhibits a clear two step deglaciation with a brief 18o transient event in the tropics this 18o maximum could correspond to a cooling or to a change in the 18o content of sea water in this study past sea surface temperature sst and primary production pp are reconstructed from foraminiferal transfer functions and compared to values estimated from alkenone measurements sst and pp records from both proxies indicate a 1 5 2 5 c deglacial warming coupled with a pp decrease and a 0 5 1 c cooling during the younger dryas yd a detailed comparison between independent micropaleontological and geochemical proxies helps us identify potential biases and thus strengthen the paleo reconstructions

assessment of sea surface temperature at 42 n in the california current over the last 30 000 years assessment of changes in surface ocean conditions in particular sea surface temperature sst is essential to understand long term changes in climate especially in regions where continental climate is strongly influenced by oceanographic processes to evaluate changes in sst in the northeast pacific we have analyzed long chain alkenones of prymnesiophyte origin at 38 depths in a piston and associated trigger core collected beneath the contemporary core of the california current system at 42 n 270 km off the coast of oregon california the samples span 30 000 years of deposition at this location unsaturation patterns u37k in the alkenone series display a statistically significant difference p 0 001 between interglacial 0 44 0 02 n 11 and glacial 0 29 0 04 n 20 intervals of the cores detailed examination of other compositional features of the c37 c38 c39 alkenone series and a related c36 alkenoate series measured downcore suggests the published u37k temperature calibration u37k 0 034 t 0 039 defined for cultures of a strain of emiliania huxleyi isolated from the subarctic pacific provides best estimates of winter sst at our study site this inference is purely statistical and does not imply however that the phytoplankton source of these biomarkers is most productive in winter or at the ocean surface the temperature record for u37k implies 1 an 4 c shift occurred in winter sst from 7 5 1 1 c at the last glacial maximum to 11 7 0 7 c in the present interglacial period and 2 this warming trend was confined to the time frame 14 10 ka within the glacial to interglacial transition period these conclusions are corroborated entirely by results from an independent sst transformation of radiolarian species assemblage data obtained from the same core materials

atlantic core top calibration of the u37k index as a sea surface palaeotemperature indicator abstract a field calibration of the uk index with sea surface temperature is discussed through analysis of an extensive suite of surface sediments n 109 from the northeastern atlantic 2 s 75 n values of u 37 k are compared with sea surface temperatures for overlying waters measured at different depths and seasons to obtain a correlation suitable for palaeotemperature reconstructions the best fit is obtained using surface 0 m temperatures corresponding to caloric winter and autumn months however the annual average spring and summer surface temperature equations also have high correlation coefficients and are also appropriate for climatic studies the results further validate the general applicability of the u 37 k as a climatic proxy because the calibration equations are valid over a wide range of surface water temperatures 0 28 c for different algal populations and are representative of the average contribution of alkenones to sediments as found in sediment cores

faunal and alkenone reconstructions of subtropical north atlantic surface hydrography and paleotemperature over the last 28 kyr two techniques for estimating past variations in sea surface temperature sst have been used to investigate climatic change in biogeochemical oceanic flux study bofs core 31k 19 n 20 w from the eastern subtropical atlantic high resolution sst records for the last 28 kyr have been produced using planktonic foraminiferal assemblages based on the imbrie kipp transfer function technique and the uk 37 index derived from abundances of c37 alkenones biosynthesized by prymnesiophyte algae modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean the uk 37 index corresponds to the temperature at the time of maximum coccolith productivity typically late spring early summer in the study area today whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures in general the faunal and biomarker paleotemperature records display comparable sst variations during the last glacial and deglacial but although the overall trends are similar differences exist in the magnitude and timing of these temperature changes most notably the faunal twarm and uk 37 sst estimates diverge by 3 c between 8 ka and 6 ka and this offset persists through the late holocene this difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels we therefore propose that the deviation in sst estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring early summer in the modern ocean our results suggest that a dual approach to sst estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late quaternary

molecular record of secular sea surface temperature changes on 100 year timescales for glacial terminations i ii and iv high resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand year timescale1 3 little is known4 however about the variation of climate and of palaeoceanographic conditions throughout the quaternary on timescales of less than 1 000 years at frequencies far greater than those of the milankovitch orbital cycles here we show that such high time resolution is possible from molecular stratigraphic studies based on biomarker organic molecules alkenones we have sampled alkenone stratigraphic records at 70 to 200 yr intervals across glacial terminations i ii and iv in sediment cores from oop site 658 off northwest africa5 sea surface temperatures ssts derived from the alkenone uk37 index6 8vary rapidly beyond the range of analytical noise by up to 2 5 c in 300 yr showing hitherto unknown cycles with about 600 yr periodicities some of the changes parallel similar events in the oxygen isotope stratigraphy sst oscillations may be linked in part to abrupt breakdowns in atlantic deep water ventilation resulting from meltwater events of quaternary glacial terminations3 9 10

terrestrial conditions at the last glacial maximum and climap sea surface temperature estimates are they consistent climap 1981 seasonal reconstruction of the earth s surface at the last glacial maximum geological society of america map and chart series mc 36 boundary conditions were used as inputs to the giss general circulation model and the last glacial maximum lgm climate was simulated for six model years the simulation was compared with snow line depression and pollen inferred temperature data at low latitudes specifically for hawaii colombia east africa and new guinea the model does not produced as much cooling at low latitudes as is implied by the terrestrial evidence an alternative experiment in which the climap sea surface temperatures were uniformly lowered by 2 c produces a better fit to the land data although in hawaii model temperatures are still too warm the relatively warm climap tropical sea surface temperatures also provide for only a slight decrease in the hydrologic cycle in the model in contrast to both evidence of lgm tropical aridity and the results of the experiment with colder ocean temperatures with the climap sea surface temperatures the lgm global annual mean surface air temperature is 3 6 c colder than at present if the ocean temperatures were allowed to cool in conformity with the model s radiation balance the lgm simulation would be 5 6 c colder than today and in better agreement with the tropical land evidence

combined coccolith foraminiferal and biomarker reconstruction of paleoceanographic conditions over the past 120 kyr in the northern north atlantic 59 n 23 w we present data for north atlantic core biogeochemical ocean flux study bofs 16k 59 n 23 w water depth 2370 m including coccolith flora 18o planktonic foraminiferal sea surface temperatures ssts by fa20 and simmax methods and alkenone based u37k and u37k ssts a good correlation exists between the abundances of cold water coccolith species and foraminifera and a broad correlation exists between coccolith and alkenone abundances except in the holocene reworked cretaceous coccoliths at the last glacial maximum are coincident with warm deviations of the u37k signal assessment of various calibrations of u37k and u37k with paleotemperature shows the inappropriateness of a global correlation we have produced a north atlantic u37k calibration on the basis of north atlantic data alone u37k 0 026t 0 186 which produces sst data for summer season at 0 m water depth comparable to the warm season foraminiferal ssts except during the intervals 26 36 58 65 and 100 120 ka when the alkenones indicate somewhat cooler surface waters

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

simulated influence of carbon dioxide orbital forcing and ice sheets on the climate of the last glacial maximum a coupled atmosphere ocean sea ice model is used to investigate the climate of the last glacial maximum 21 000 years ago and the relative climate forcing effects of atmosphere co2 the earth s orbital parameters and ice sheet albedo tropical temperatures are found to be 2 2 c less than today s slightly colder than indicated by the climap palaeoclimate reconstruction this result is consistent with a low to medium climate sensitivity to radiative perturbations temperatures are colder still in the northern north atlantic region owing to a weakening and shallowing of the thermohaline circulation a sensitivity analysis suggests that changes in ocean circulation since the last glacial maximum have not contributed directly to the global mean temperature change since that time

retreat velocity of the north atlantic polar front during the last deglaciation determined by 14 c accelerator mass spectrometry the glacial oscillations which dominate the quaternary global climate are closely related to changes in incoming solar radiation but the details of palaeoclimatic spectra suggest that other parameters usually referred to as feedback have significantly increased the climatic response to extraterrestrial forcing1 the last deglaciation appears to be one of the more characteristic examples of nonlinearity because its abruptness strongly contrasts with the smooth shape of the associated solar radiation maximum dated at 11 000 yr bp in addition the presence of the younger dryas cold event concomitant with the solar radiation maximum could be interpreted as a transitory phenomenon caused by the rapid meltwater influx linked to the first phase of the ice sheet s disintegration2 3 here using accelerator mass spectrometry we date precisely the movements of the polar front during the whole period of glacial retreat 15 000 8 000 yr bp our results show that the polar front has moved between 35 n and 55 n in 1 000 yr for the earliest retreat 12 500 12 000 bp and moved almost instantaneously that is 400 yr during the two abrupt climatic changes associated with the younger dry as cold event