surface and subsurface seawater temperature reconstruction using mg ca microanalysis of planktonic foraminifera globigerinoides ruber globigerinoides sacculifer and pulleniatina obliquiloculata laser ablation inductively coupled plasma mass spectrometry microanalyses of mg ca across individual final chambers of three planktonic foraminifera species globigerinoides ruber g sacculifer and pulleniatina obliquiloculata reveal significant interspecies differences in test mg concentrations whereas these three species have similar mg ca values at low sea surface temperatures similar to 22 degrees c they diverge markedly at high sea surface temperatures similar to 29 degrees c explanations for these differences in species mg ca values based on detailed comparison of species intratest mg ca distributions suggest that compositional variability within tests cannot account for the observed deviation of species mg ca values in warm water equatorial regions multiple regression modeling and delta o 18 analysis of globigerinoides sacculifer tests indicate that interspecies differences in mg ca values result from different depth habitats the average mg ca values of g ruber final chambers reflect the temperature of the surface mixed layer 0 25 m whereas those of g sacculifer and pulleniatina obliquiloculata correlate best with subsurface temperatures at 50 75 m and 100 125 m water depths respectively mg ca calibration to the temperatures at these depths reveals a similar temperature control on mg test composition in all species combining our results with mg ca values from published culturing experiments we derive a generalized equation for the effect of temperature and seawater salinity on foraminiferal mg ca we also show that the mg ca composition of specific calcite layers within foraminiferal tests including the low mg ca layers of globigerinoides ruber and g sacculifer and the cortex layer of pulleniatina obliquiloculata correlates with seawater temperature and can be used as an additional proxy for seawater temperature

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

340 000 year centennial scale marine record of southern hemisphere climatic oscillation in order to investigate rapid climatic changes at mid southern latitudes we have developed centennial scale paleoceanographic records from the southwest pacific that enable detailed comparison with antarctic ice core records these records suggest close coupling of mid southern latitudes with antarctic climate during deglacial and interglacial periods glacial sections display higher variability than is seen in antarctic ice cores which implies climatic decoupling between mid and high southern latitudes due to enhanced circum antarctic circulation structural and temporal similarity with the greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations

holocene climate changes in southern greenland evidence from lake sediments a holocene lake sediment record is presented from lake n14 situated on angissoq island 15 km off the main coast of southern greenland the palaeoclimatic development has been interpreted on the basis of flux and percentage content of biogenic silica clastic material organic material and sulphur as well as sedimentation rate moss content and magnetic susceptibility a total of 43 radiocarbon dates has ensured a reliable chronology it is argued that varying sediment composition mainly reflects changing precipitation by analogy with the present meteorological conditions in southern greenland holocene climate development is inferred between 11550 and 9300 cal yr bp temperature and precipitation increase markedly but this period is climatically unstable from 9300 yr bp conditions become more stable and a holocene climatic optimum characterised by warm and humid conditions is observed from 8000 to 5000 cal yr bp from 4700 cal yr bp the first signs of a climatic deterioration are observed and from 3700 cal yr bp the climate has become more dry and cold superimposed on the climatic long term trend is climate variability on a centennial time scale that increases in amplitude after 3700 cal yr bp a climatic scenario related to the strength and position of the greenland high pressure cell and the iceland low pressure cell is proposed to explain the holocene centennial climate variability a comparison of the lake n14 record with a terrestrial as well as a marine record from the eastern north atlantic ocean suggests that the centennial climate variability was uniform over large areas at certain times less

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

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

atlantic overturning circulation and agulhas leakage influences on southeast atlantic upper ocean hydrography during marine isotope stage 11 climate dynamics during the marine isotope stage mis 11 interglacial may provide information about how the climate system will evolve under the conditions of low amplitude orbital forcing that are also found during the late holocene new stable isotope and alkenone data are presented from southeast atlantic ocean drilling program site 1085 providing detailed information on interglacial climate evolution and the impacts of atlantic meridional overturning circulation moc and agulhas leakage on the regional upper ocean hydrography the data suggest that although warm surface ocean conditions were maintained at approximate holocene levels for 40 000 years during mis 11 subsurface temperature and salinity recorded by deeper dwelling planktonic foraminifera species were maintained at their highest values for only 7000 8000 years surface water temperature and salinity data suggest that the interocean exchange of warm salty waters into the southeast atlantic ocean was directly related to changes in the activity of the moc during the study interval specifically transient regional warming events during periods of weakened overturning circulation may have been amplified by the continuous interocean exchange of warm salty indian ocean waters that primed the moc for abrupt resumptions into a vigorous mode of operation conversely a peak in interocean exchange at the end of the mis 11 interglacial optimum may reflect enhanced trade wind forcing of surface waters whose export to the north atlantic ocean could have contributed to renewed ice sheet buildup during the mis 11 to 10 glacial inception

incorporation and preservation of mg in globigerinoides sacculifer implications for reconstructing the temperature and 18o 16o of seawater using bathymetric transects of surface sediments underlying similar sea surface temperatures but exposed to increasing dissolution we examined the processes which affect the relationship between foraminiferal mg ca and 18o we found that globigerinoides saccculifer calcifies over a relatively large range of water depth and that this is apparent in their mg content on the seafloor foraminiferal mg ca is substantially altered by dissolution with the degree of alteration increasing with water depth selective dissolution of the chamber calcite formed in surface waters shifts the shell s bulk mg ca and 18o toward the chemistries of the secondary crust acquired in colder thermocline waters the magnitude of this shift depends on both the range of temperatures over which the shell calcified and the degree to which it is subsequently dissolved in spite of this shift the initial relationship between mg ca and 18o determined by their temperature dependence is maintained we conclude that paired measurements of 18o and mg ca can be used for reconstructing 18owater though care must be taken to determine where in the water column the reconstruction applies

paleogene volcanism in central afghanistan possible far field effect of the india eurasia collision abstract a volcanic sedimentary succession of paleogene age is exposed in isolated patches at the southern margin of the tajik block in the ghor province of central afghanistan the volcanic rocks range from basalts and andesites to dacites including adakites they are intercalated with sedimentary rocks deposited in shallow marine environments dated biostratigraphically as paleocene eocene this age corresponds to the age of the asy b d andesites located in the western ghor province estimated by the 40ar 39ar method as 54 ma the magmatism post dates the cimmerian collision between the tajik block including the band e bayan block and the farah rod block located to the south while the investigated volcanic rocks apparently bear geochemical signatures typical to an active continental margin environment it is presumed that the magmatism was related to rifting processes most likely initiated by far field tectonics caused by the terminal collision of the indian plate with eurasia najman et al 2017 this event led to the dextral movement of the farah rod block particularly along hari rod herat fault system resulting in the development of a transtensional regime in the proximal southern margin of the tajik block and giving rise to a rift basin where marine sediments were interbedded with pillow lavas intruded by sheeted dyke series

southern ocean origin for the resumption of atlantic thermohaline circulation during deglaciation during the two most recent deglaciations the southern hemisphere warmed before greenland at the same time the northern atlantic ocean was exposed to meltwater discharge which is generally assumed to reduce the formation of north atlantic deep water yet during deglaciation the atlantic thermohaline circulation became more vigorous in the transition from a weak glacial to a strong interglacial mode here we use a three dimensional ocean circulation model to investigate the impact of southern ocean warming and the associated sea ice retreat on the atlantic thermohaline circulation we find that a gradual warming in the southern ocean during deglaciation induces an abrupt resumption of the interglacial mode of the thermohaline circulation triggered by increased mass transport into the atlantic ocean via the warm indian ocean and cold pacific ocean water route this effect prevails over the influence of meltwater discharge which would oppose a strengthening of the thermohaline circulation a southern ocean trigger for the transition into an interglacial mode of circulation provides a consistent picture of southern and northern hemispheric climate change at times of deglaciation in agreement with the available proxy records

reversed flow of atlantic deep water during the last glacial maximum the meridional overturning circulation moc of the atlantic ocean is considered to be one of the most important components of the climate system this is because its warm surface currents such as the gulf stream redistribute huge amounts of energy from tropical to high latitudes and influence regional weather and climate patterns whereas its lower limb ventilates the deep ocean and affects the storage of carbon in the abyss away from the atmosphere despite its significance for future climate the operation of the moc under contrasting climates of the past remains controversial nutrient based proxies1 2 and recent model simulations3 indicate that during the last glacial maximum the convective activity in the north atlantic ocean was much weaker than at present in contrast rate sensitive radiogenic 231pa 230th isotope ratios from the north atlantic have been interpreted to indicate only minor changes in moc strength4 5 6 here we show that the basin scale abyssal circulation of the atlantic ocean was probably reversed during the last glacial maximum and was dominated by northward water flow from the southern ocean these conclusions are based on new high resolution data from the south atlantic ocean that establish the basin scale north to south gradient in 231pa 230th and thus the direction of the deep ocean circulation our findings are consistent with nutrient based proxies and argue that further analysis of 231pa 230th outside the north atlantic basin will enhance our understanding of past ocean circulation provided that spatial gradients are carefully considered this broader perspective suggests that the modern pattern of the atlantic moc with a prominent southerly flow of deep waters originating in the north atlantic arose only during the holocene epoch

controls on shell mg ca and sr ca in cultured planktonic foraminiferan globigerinoides ruber white mg ca and sr ca ratios were determined on a single species of planktonic foraminiferan globigerinoides ruber white collected from the gulf of eilat and cultured in seawater at five different salinities 32 to 44 five temperatures 18 to 30 c and four ph values 7 9 to 8 4 the mg ca temperature calibration of cultured g ruber with an exponential slope of 8 3 c agrees well with previously published calibrations from core tops and sediment traps however the dependence of mg ca on salinity with an exponential slope of 5 3 psu is also significant and should be included in the calibration equation with this purpose we calculated a calibration equation for g ruber dependent on both temperature and salinity within the 95 confidence limits mg ca mmol mol exp 0 06 0 02 s psu 0 08 0 02 t c 2 8 1 0 r2 0 95 the influence of ph on mg ca ratios is negligible at ambient seawater ph 8 1 to 8 3 however we observe a dominating ph control on shell mg ca when the ph of seawater is lower than 8 0 sr ca in g ruber shows a significant positive correlation with average growth rate presumably part of the variability in shell sr ca in the geological record is linked to changes in growth rates of foraminifera as a response to changing environmental conditions

contrasting multiproxy reconstructions of surface ocean hydrography in the agulhas corridor and implications for the agulhas leakage during the last 345 000 years planktonic 18o and mg ca derived sea surface temperature sst records from the agulhas corridor off south africa display a progressive increase of sst during glacial periods of the last three climatic cycles the sst increases of up to 4 c coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites mg ca derived sst maximizes during glacial maxima and glacial terminations to values about 2 5 c above full interglacial sst the paired planktonic 18o and mg ca derived sst records yield glacial seawater 18o anomalies of up to 0 8 indicating measurably higher surface salinities during these periods the sst pattern along our record is markedly different from a u37k derived sst record at a nearby core location in the agulhas corridor that displays sst maxima only during glacial terminations possible explanations are lateral alkenone advection by the vigorous regional ocean currents or the development of sst contrasts during glacials in association with seasonal changes of agulhas water transports and lateral shifts of the agulhas retroflection the different sst reconstructions derived from u37k and mg ca pose a significant challenge to the interpretation of the proxy records and demonstrate that the reconstruction of the agulhas current and interocean salt leakage is not as straightforward as previously suggested

using species specific paleotemperature equations with foraminifera a case study in the southern california bight abstract species specific paleotemperature equations were used to reconstruct a record of temperature from foraminiferal 18 o values over the last 25 kyr in the southern california bight the equations yield similar temperatures for the 18 o values of globigerina bulloides and neogloboquadrina pachyderma in contrast applying a single paleotemperature equation to g bulloides and n pachyderma 18 o yields different temperatures which has been used to suggest that these species record the surface to thermocline temperature gradient in santa barbara basin an isotopically distinct morphotype of g bulloides dominates during glacial intervals and yields temperatures that appear too cold when using a paleotemperature equation calibrated for the morphotype common today when a more appropriate paleotemperature equation is used for glacial g bulloides we obtain more realistic glacial temperatures glacial interglacial temperature differences g i t calculated in the present study indicate significant cooling 8 10 c throughout the southern california bight during the last glacial maximum lgm the magnitude of glacial cooling varies from 8 c near the middle of the southern california bight tanner basin and san nicolas basin to 9 c in the north santa barbara basin and 9 5 10 c in the south velero basin and no name basin our temperature calculations agree well with previous estimates based on the modern analog technique in contrast studies using n pachyderma coiling ratios u k 37 indices and transfer functions estimate considerably warmer lgm temperatures and smaller g i t

low latitude hydrological cycle and rapid climate changes during the last deglaciation sea surface temperature and oxygen isotopic records from two well dated indian ocean cores covering the last deglaciation show the occurrence of two periods of increased salinity along the route of warm surface water transport from the indian to the atlantic ocean one between 18 and 14 5 ka and the other during the younger dryas our results imply that during these periods salt accumulated in the tropical atlantic creating favorable conditions for an abrupt resumption of the thermohaline circulation and abrupt northern hemisphere warming furthermore we suggest that the observed pattern of millennial climate variability during the last glacial and deglaciation resulted from the interaction between the relatively slow rhythm of expansion and decay of the northern hemisphere ice sheets and el nino southern oscillation variability through changes in the position of the intertropical convergence zone this interaction generated an oscillator with millennial time response that operated at times of sufficient northern hemisphere ice sheets extent

manganese carbonate overgrowths on foraminifera tests below the zone where manganese is remobilized as mn2 aq reductively cleaned foraminifera in deep sea sediments have much higher mnca than those in core tops and sediment traps mnca ranges from less than 20 10 6 in and above the mno2 maximum to as high as 700 10 6 in reducing panama basin sediments the most plausible explanation for this enrichment is that the tests are coated with mn carbonate overgrowths these coatings can account for a significant proportion of the mn in reduced deep sea sediments uptake of manganous ion by carbonate may explain the absence of mn nodules in areas of high carbonate accumulation extreme degrees of overgrowth can alter foram trace element values but this artifact can be avoided by avoiding foraminifera with high mn ca

asynchronous alkenone and foraminifera records from the benguela upwelling system abstract radiocarbon stratigraphy is an essential tool for high resolution paleoceanographic studies age models based on radiocarbon ages of foraminifera are commonly applied to a wide range of geochemical studies including the investigation of temporal leads and lags the critical assumption is that temporal coupling between foraminifera and other sediment constituents including specific molecular organic compounds biomarkers of marine phytoplankton e g alkenones is maintained in the sediments to test this critical assumption in the benguela upwelling area we have determined radiocarbon ages of total c37 c39 alkenones in 20 samples from two gravity cores and three multicorer cores the cores were retrieved from the continental shelf and slope off namibia and samples were taken from holocene deglacial and last glacial maximum core sections the alkenone radiocarbon ages were compared to those of planktic foraminifera total organic carbon fatty acids and fine grained carbonates from the same samples interestingly the ages of alkenones were 1000 to 4500 yr older than those of foraminifera in all samples such age differences may be the result of different processes bioturbation associated with grain size effects lateral advection of recycled material and redeposition of sediment on upper continental slopes due to currents or tidal movement are examples for such processes based on the results of this study the age offsets between foraminifera and alkenones in sediments from the upper continental slope off namibia most probably do not result from particle selective bioturbation processes resuspension of organic particles in response to tidal movement of bottom waters with velocities up to 25 cm s recorded near the core sites is the more likely explanation our results imply that age control established using radiocarbon measurements of foraminifera may be inadequate for the interpretation of alkenone based proxy data observed temporal leads and lags between foraminifera based data and data derived from alkenone measurements may therefore be secondary signals i e the result of processes associated with particle settling and biological activity

foraminiferal mg ca increase in the caribbean during the pliocene western atlantic warm pool formation salinity influence or diagenetic overprint we constructed a high resolution mg ca record on the planktonic foraminifer globigerinoides sacculifer in order to explore the change in sea surface temperature sst due to the shoaling of the isthmus of panama as well as the impact of secondary factors like diagenesis and large salinity fluctuations the study covers the latest miocene and the early pliocene 5 6 3 9 ma and was combined with 18o to isolate changes in sea surface salinity sss before 4 5 ma sstmg ca and sss show moderate fluctuations indicating a free exchange of surface ocean water masses between the pacific and the atlantic the increase in 18o after 4 5 ma represents increasing salinities in the caribbean due to the progressive closure of the panamanian gateway the increase in mg ca toward values of maximum 7 mmol mol suggests that secondary influences have played a significant role evidence of crystalline overgrowths on the foraminiferal tests in correlation with aragonite sr ca and productivity cyclicities indicates a diagenetic overprint on the foraminiferal tests laser ablation inductively coupled plasma mass spectrometry analyses however do not show significantly increased mg ca ratios in the crystalline overgrowths and neither do calculations based on pore water data conclusively result in significantly elevated mg ca ratios in the crystalline overgrowths alternatively the elevated mg ca ratios might have been caused by salinity as the 18o record of site 1000 has been interpreted to represent large fluctuations in sss and cultivating experiments have shown an increase in mg ca with increasing salinity we conclude that the mg ca record 4 5 ma can only reliably be considered for paleoceanographical purposes when the minimum values not showing any evidence of secondary influences are used resulting in a warming of central caribbean surface water masses after 4 5 ma of 2 c

antarctic control on tropical indian ocean sea surface temperature and hydrography 1 we reconstructed the surface hydrography of the south equatorial current in the western indian ocean for the last 65 000 years using a marine sediment core record results show that tropical indian ocean temperatures resemble temperatures from antarctic ice cores with warm and cold fluctuations synchronous with the antarctic cold reversal and the antarctic warm events a1 a4 the most likely thermal link involves subantarctic mode water samw which forms north of the subpolar frontal zone and spreads northward into the indian ocean this subsurface water mass is the prime suspect because of a stronger temperature response in the thermocline recorded by the foraminifer n dutertrei than in surface water g ruber