tropical indo pacific hydroclimate response to north atlantic forcing during the last deglaciation as recorded by a speleothem from sumatra indonesia abstract abrupt changes in atlantic meridional overturning circulation are known to have affected the strength of the indian and asian monsoons during glacial and deglacial climate states however there is still much uncertainty around the hydroclimate response of the indo pacific warm pool ipwp region to abrupt climate changes in the north atlantic many studies suggest a mean southward shift in the intertropical convergence zone itcz in the ipwp region during phases of reduced atlantic meridional overturning however existing proxies have seasonal biases and conflicting responses making it difficult to determine the true extent of north atlantic forcing in this climatically important region here we present a precisely dated high resolution record of eastern indian ocean hydroclimate variability spanning the last 16 ky thousand years from 18 o measurements in an aragonite calcite speleothem from central sumatra this represents the western most speleothem record from the ipwp region precipitation arrives year round at this site with the majority sourced from the local tropical eastern indian ocean and two additional long range seasonal sources associated with the boreal and austral summer monsoons the sumatran speleothem demonstrates a clear deglacial structure that includes 18o enrichment during the younger dryas and 18o depletion during the bolling allerod similar to the pattern seen in speleothems of the asian and indian monsoon realms the speleothem 18 o changes at this site are best explained by changes in rainfall amount and changes in the contributions from different moisture pathways reduced rainfall in sumatra during the younger dryas is most likely driven by reductions in moisture transport along the northern or southern monsoon transport pathways to sumatra considered with other regional proxies the record from sumatra suggests the response of the ipwp to north atlantic freshwater forcing is not solely driven by southward shifts of the itcz but also a reduction in moisture transport along both monsoon pathways

links between southwestern tropical indian ocean sst and precipitation over southeastern africa over the last 17 kyr abstract time series of mg ca ba ca and 18o analyzed in tests of surface dwelling planktonic foraminifer globigerinoides ruber from two marine sediment cores recovered in the mozambique channel off the zambezi river southwestern tropical indian ocean reveal climate variability over the last 17 kyr analysis of samples collected from the water column of the mozambique channel validates that mg ca in g ruber reflects calcification temperatures at 0 30 m water depth and that the surface water of the southwestern indian ocean is very sensitive to dissolved ba input from adjacent rivers foraminiferal ba ca and mg ca time series are used to reconstruct hydrological and thermal changes over southeastern african and southwestern tropical oceans the mg ca based sea surface temperature sst estimates indicate that the thermal evolution of the tropical southwestern indian ocean followed within age model uncertainties climate changes over antarctica the trend of the sst record is marked by a gradual warming from 24 7 0 6 c at 17 0 0 2 kyr bp to 26 4 0 3 c at 10 11 kyr bp interrupted by two prominent coolings of 1 5 0 2 c and 1 c centered at 15 0 1 kyr bp and 13 4 0 2 kyr bp respectively declining ssts in the early holocene reach their minimum 25 c at 8 7 0 2 kyr bp and give way to stable thermal conditions over the middle and late holocene the ba ca record indicates that the zambezi basin experienced relatively wet conditions during the early phase of the last deglaciation bolling allerod and the early holocene these wet phases coincide with an increase of sst in the mozambique channel in contrast relatively dry conditions throughout the middle and late holocene epoch are accompanied by relatively cold mozambique channel surface water these shifts likely reflect a response to meridional shifts of the austral westerlies and subtropical front these hypothesized shifts would have modulated the advection of cold southern ocean water into the mozambique channel changes in sst in the mozambique channel and possible resultant changes in the zonal gradient in the tropical indian ocean in turn had a strong impact on the precipitation over southeastern africa

variability of el nino southern oscillation activity at millennial timescales during the holocene epoch the variability of el nino southern oscillation enso during the holocene epoch in particular on millennial timescales is poorly understood palaeoclimate studies have documented enso variability for selected intervals in the holocene but most records are either too short or insufficiently resolved to investigate variability on millennial scales1 2 3 here we present a record of sedimentation in laguna pallcacocha southern ecuador which is strongly influenced by enso variability and covers the past 12 000 years continuously we find that changes on a timescale of 2 8 years which we attribute to warm enso events become more frequent over the holocene until about 1 200 years ago and then decline towards the present periods of relatively high and low enso activity alternating at a timescale of about 2 000 years are superimposed on this long term trend we attribute the long term trend to orbitally induced changes in insolation and suggest internal enso dynamics as a possible cause of the millennial variability however the millennial oscillation will need to be confirmed in other enso proxy records

abrupt mid holocene decline in the indian summer monsoon caused by tropical indian ocean cooling the evolution of the indian summer monsoon ism has been widely investigated and traditionally interpreted as consequences of orbital forcing change and the migration of the intertropical convergent zone itcz the potential influence of sea surface temperature sst on ism variation at millennial time scales has been progressively proposed in recent studies towards a better understanding of holocene evolution of ism especially the potential response to variations in sst a 643 cm continuous sediment sequence covering the past 11 1 ka was recovered from beihai wetland in western yunnan plateau fossil pollen analysis revealed that evergreen broadleaved forest dominated the regional vegetation in the early holocene which represented a warm and humid period associated with strong ism expansions of deciduous broadleaved forest and grassland from 5 2 cal ka bp to the present together with the appearance of abundant plant remains indicate the formation of the wetland system ordination analysis of the pollen assemblages further confirmed the abrupt vegetation turnover at ca 5 2 cal ka bp which is consistent with the abrupt decline in reconstructed mean annual precipitation pann from ca 1400 to 1100 mm and indicates an abrupt decline in the summer monsoon we performed a climate regime shift test on various records from the ism domain and eastern africa and found this phenomenon as well which could not be explained by changes in solar insolation or the migration of the itcz a mid holocene cooling was detected from the indian ocean especially a decreased sst in the tropical indian ocean ca 5 5 cal ka bp cooling of the tropical indian ocean possibly caused the abrupt retreat of the summer monsoon by restraining the duration of the monsoonal season and the convergent process which was supported by an abrupt monsoon decline based on results from a minimal concept model

mid holocene el nino southern oscillation enso attenuation revealed by individual foraminifera in eastern tropical pacific sediments holocene reconstructions of the el nino southern oscillation enso provide valuable perspective on its recent evolution and can be important for assessing its future optimal assessment of past enso variability requires observations from its center of action in the eastern equatorial pacific but these are limited due to paucity of high resolution paleoceanographic archives e g corals here we use a new approach to quantify past enso variance based on the oxygen isotopic composition 18 o of individual foraminifera globigerinoides ruber from deep sea sediments in the enso source region individual g ruber foraminifera behave as monthly recorders of sea surface conditions including enso extremes circumventing the lack of annual resolution in the sediments intrapopulation 18 o distributions derived with this method from a core near the galapagos islands reveal mid holocene reductions in variance of 50 requiring drastic attenuation of the enso amplitude furthermore mg ca thermometry indicates that mid holocene background conditions were accompanied by a stronger zonal temperature gradient that coincided with a northward displaced intertropical convergence zone itcz the results suggest that the position of the itcz is an important factor in the low frequency modulation of enso and could influence its future evolution

pacific ocean heat content during the past 10 000 years observed increases in ocean heat content ohc and temperature are robust indicators of global warming during the past several decades we used high resolution proxy records from sediment cores to extend these observations in the pacific 10 000 years beyond the instrumental record we show that water masses linked to north pacific and antarctic intermediate waters were warmer by 2 1 0 4 c and 1 5 0 4 c respectively during the middle holocene thermal maximum than over the past century both water masses were 0 9 c warmer during the medieval warm period than during the little ice age and 0 65 warmer than in recent decades although documented changes in global surface temperatures during the holocene and common era are relatively small the concomitant changes in ohc are large

patterns of deglacial warming in the pacific ocean a review with emphasis on the time interval of heinrich event 1 abstract based on a compilation of currently available records of past sea surface temperature sst variability estimated from a variety of different proxies the regional scale deglacial sst development in the pacific ocean is tentatively classified into four endmember types the subtropical and tropical pacific is characterized by a continuous deglacial warming without marked interruption during the time interval of heinrich event 1 h1 whereas the subarctic north pacific exhibits centennial scale warm cold oscillations during this time interval sst records from marginal seas of the pacific show a deglacial warming interrupted by a cooling event coeval with h1 followed by a marked bolling sst increase a single sst record from the southwestern subantarctic pacific displays a continuous deglacial warming across h1 followed by an antarctic cold reversal type cooling during the allerod thus in contrast to the deglacial sst development in the atlantic which has been inferred to be overwhelmingly driven by the redistribution of heat through changes in the meridional overturning circulation moc none of the open oceanic pacific sst records reviewed here displays any obvious and or dominant response to the reduction of the moc and or the reorganization of atmospheric circulation during h1 within the limits of absolute chronologies all tropical and subtropical pacific sst records show an onset of deglacial warming at 19 1 ka coeval with the onset of the deglacial rise in sea level

a simple evaluation of cleaning procedures on fossil benthic foraminiferal mg ca 1 recent studies suggest that benthic foraminiferal mg ca may be useful in reconstructing deep water temperature changes during the quaternary and on longer timescales rosenthal et al 1997 lear et al 2000 martin et al 2002 because changes in deep water temperature may be small sample preparation could play an important role in reconstructing accurate temperatures from shell mg ca a simple examination of changes in measured shell chemistry of benthic foraminifera from two intervals subjected to increasingly rigorous cleaning reveals that fossil benthic foraminiferal samples cleaned by oxidation yield lower mg ca values than samples only rinsed and weak acid leached reductive cleaning further lowered the shell mg ca of one of the two benthic species examined lower mg ca values following oxidation and reduction appear to reflect removal of contaminant mg associated with remnant organic matter and adsorbed phases

holocene sea level changes in the indo pacific holocene sea level reconstructions exist from many locations in the indo pacific region despite being a large geographical region the nature of holocene sea level change is broadly similar in all locations differences do exist however in the timing and magnitude of the mid holocene high stand mhhs and the nature of late holocene sea level fall across the region when the indo pacific is subdivided into smaller regions these discrepancies do not disappear and in some cases the discrepancies are large within a single coastline it is clear from this analysis that the fundamental criteria to produce accurate local relative sea level curves are hardly ever met there are serious problems associated with the correct interpretation of sea level indicators and their relationship to mean sea level and with the quality of age determinations a consistent methodology throughout the indo pacific for the analysis of sea level data is lacking future sea level analysis from far field locations must involve the application of a consistent methodology in order to allow meaningful comparison between studies this should help to resolve the ongoing debate about the magnitude and timing of the mid holocene high stand and the nature of late holocene sea level fall across the region

holocene glacier activity at the southwestern part of hardangerjokulen central southern norway evidence from lacustrine sediments lacustrine sediments from lake isdalsvatn downstream from the southwestern margin of the plateau glacier hardangerjokulen central southern norway show that the lake received glacial meltwater until 7890 95 bp a thin bluish grey minerogenic silt layer probably reflects a short glacial re advance between 7005 90 and 6835 150bp after the latter date inflow of glacial meltwater ceased indicating that small or more probably no glaciers existed on the southwestern hard angerjokulen plateau a drop in organic content and a slight increase in detrital content inferred from magnetic susceptibility at 120cm depth in the core may indicate some glacier activity in the catchment from about 3400 bp textural changes at 50cm depth indicate increased neoglacial activity in the upper catchment area from 2265 80 bp differences in glacier chronologies between the southern and northern sectors of hardangerjokulen may be explained partly by different glacier responses to the precipitation and wind distribu

indo pacific warm pool variability during the holocene and last glacial maximum we measured oxygen isotopes and mg ca ratios in the surface dwelling planktonic foraminifer globigerinoides ruber white s s and the thermocline dweller pulleniatina obliquiloculata to investigate upper ocean spatial variability in the indo pacific warm pool ipwp we focused on three critical time intervals the last glacial maximum lgm 18 21 5 ka the early holocene 8 9 ka and the late holocene 0 2 ka our records from 24 stations in the south china sea timor sea indonesian seas and western pacific indicate overall dry and cool conditions in the ipwp during the lgm with a low thermal gradient between surface and thermocline waters during the early holocene sea surface temperatures increased by similar to 3 degrees c over the entire region indicating intensification of the ipwp however in the eastern indian ocean timor sea the thermocline gradually shoaled from the lgm to early holocene reflecting intensification of the subsurface indonesian throughflow itf increased surface salinity in the south china sea during the holocene appears related to northward displacement of the monsoonal rain belt over the asian continent together with enhanced influx of saltier pacific surface water through the luzon strait and freshwater export through the java sea opening of the freshwater portal through the java sea in the early holocene led to a change in the vertical structure of the itf from surface to thermocline dominated flow and to substantial freshening of timor sea thermocline waters

cleaning method impact on the mg ca of three planktonic foraminifer species a downcore study along a depth transect abstract we performed a downcore comparison of mg ca ratios obtained using reductive and non reductive cleaning methods applied to globigerinoides ruber pulleniatina obliquiloculata and globorotalia menardii picked along two nearby sediment cores retrieved at 2100 m and 3875 m in the eastern equatorial indian ocean at the shallower site our results show statistically significant discrepancies in averaged relative mg ca loss induced by the reductive cleaning compared to non reductive cleaning g menardii 8 5 g ruber 6 2 p obliquiloculata 4 4 suggesting that reductive cleaning impact on relative mg ca loss is species specific at the deeper site differences between the relative mg ca losses for the three species are smaller g menardii 3 7 g ruber 4 1 and p obliquiloculata 6 3 suggesting the clear impact of in situ preservation state on the cleaning related mg ca loss the mg ca loss in both relative and absolute mmol mol value of species g ruber and g menardii are significantly smaller at the deeper site than the shallower site implying that these two species which have experienced intense dissolution on the sea floor are less prone to lose further mg during the reductive cleaning p obliquiloculata however show non significant difference in mg ca loss between the two sites indicating that the cleaning related mg ca loss in this species is somewhat insensitive to the preservation state at our two sites our data reveal that mg ca loss results from partial dissolution induced by the reductive step we conclude that the non reductive cleaning approach should be preferred for building inter laboratory homogeneous datasets of mg ca derived temperatures whereas the reductive step should be only included when severe oxide coating is observed

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

the early holocene sea level rise the causes anatomy and consequences of the early holocene sea level rise ehslr are reviewed the rise of ca 60m took place over most of the earth as the volume of the oceans increased during deglaciation and is dated at 11 650 7000 cal bp the ehslr was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams the patterns of ice sheet decay and the evidence for meltwater pulses are reviewed and it is argued that the ehslr was a factor in the ca 8470 bp flood from lake agassiz ojibway patterns of relative sea level changes are examined and it is argued that in addition to regional variations temporal changes are indicated the impact of the ehslr on climate is reviewed and it is maintained that the event was a factor in the 8200 bp cooling event as well as in changes in ocean current patterns and their resultant effects the ehslr may also have enhanced volcanic activity but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated the rise probably influenced rates and patterns of human migrations and cultural changes it is concluded that the ehslr was a major event of global significance knowledge of which is relevant to an understanding of the impacts of global climate change in the future

scandinavian glacial and climatic fluctuations during the holocene abstract historical documents and lichenometric studies give a detailed picture of the little ice age in scandinavia there was a large advance in norway which has been dated at a few places to 1750 small readvances during the retreat occurred around a d 1780 1810 1840 1850 1850 1870 1890 1910 and 1930 in sweden most of these advances have been recognized and in addition extensive advances are dated by lichenometry to around a d 1600 1650 and 1700 1720 soils buried beneath moraines often yield radiocarbon dates that are much too old methods dependent on these must therefore be used with care evidence for pre little ice age advances are often considered equivocal the most reliable information is probably provided by studies of lacustrine sediments combining information from all sources the most significant pre little ice age glacier advances most likely occurred in 7 5 5 1 4 5 3 2 2 8 2 2 1 9 and 1 5 1 1 radiocarbon ka bp advances that were less extensive or for which there is less evidence occurred around 6300 5600 2500 940 600 560 and 380 bp

determination of element ca ratios in foraminifera and corals using cold and hot plasma techniques in inductively coupled plasma sector field mass spectrometry abstract we have developed a rapid and precise procedure for measuring multiple elements in foraminifera and corals by inductively coupled plasma sector field mass spectrometry icp sf ms with both cold 800 w radio frequency rf power and hot 1200 w rf power plasma techniques our quality control program includes careful subsampling protocols contamination free workbench spaces and refined plastic ware cleaning process element ca ratios are calculated directly from ion beam intensities of 24mg 27al 43ca 55mn 57fe 86sr and 138ba using a standard bracketing method a routine measurement time is 3 5 min per dissolved sample the matrix effects of nitric acid and ca and sr levels are carefully quantified and overcome there is no significant difference between data determined by cold and hot plasma methods but the techniques have different advantages the cold plasma technique offers a more stable plasma condition and better reproducibility for ppm level elements long term 2 sigma relative standard deviations 2 rsd for repeat measurements of an in house coral standard are 0 32 for mg ca and 0 43 for sr ca by cold plasma icp sf ms and 0 69 for mg ca and 0 51 for sr ca by hot plasma icp sf ms the higher sensitivity and enhanced measurement precision of the hot plasma procedure yields 2 rsd precision for mol mol trace elements of 0 60 mg ca 9 9 al ca 0 68 mn ca 2 7 fe ca 0 50 sr ca and 0 84 ba ca for an in house foraminiferal standard our refined icp sf ms technique which has the advantages of small sample size 2 4 g carbonate consumed and fast sample throughput 5 8 samples hour should open the way to the production of high precision and high resolution geochemical records for natural carbonate materials

orbitally paced paleoproductivity variations in the timor sea and indonesian throughflow variability during the last 460 kyr 1 a high resolution 1 2 kyr multiproxy record from the timor sea in the easternmost indian ocean international marine global change images program core md01 2378 latitude 13 04 95 s longitude 121 47 27 e 1783 m water depth closely tracks changes in intermediate water ventilation and paleoproductivity over the last 460 kyr within one of the main outflow passages of the indonesian throughflow spectral analysis of five different flux based productivity proxies indicates spectral power concentrated in the 100 kyr glacial interglacial and the 23 kyr and 19 kyr precessional periods paleoproductivity maxima lead ice volume benthic 18o maxima by 20 to 40 1300 to 2600 years at the precession band the spectral differences in tropical paleoproductivity records from the pacific and indian oceans suggest that local processes wind and circulation patterns driven by insolation are dominant in driving productivity rather than large scale tropical features in the timor sea productivity fluctuations over the last 460 kyr were strongly influenced by monsoonal wind patterns offshore nw australia 23 and 19 kyr and were also modulated by sea level related variations in the intensity of the indonesian throughflow 100 kyr

the last five glacial interglacial transitions a high resolution 450 000 year record from the subantarctic atlantic 1 a submillennial resolution radiolarian based record of summer sea surface temperature sst documents the last five glacial to interglacial transitions at the subtropical front southern atlantic ocean rapid fluctuations occur both during glacial and interglacial intervals and sudden cooling episodes at glacial terminations are recurrent surface hydrography and global ice volume proxies from the same core suggest that summer sst increases prior to terminations lead global ice volume decreases by 4 7 3 7 ka in the eccentricity band 6 9 2 5 ka obliquity and 2 7 0 9 ka precession a comparison between sst and benthic 13c suggests a decoupling in the response of northern subantarctic surface intermediate and deep water masses to cold events in the north atlantic the matching features between our sst record and the one from core md97 2120 southwest pacific suggests that the super regional expression of climatic events is substantially affected by a single climatic agent the subtropical front amplifier and vehicle for the transfer of climatic change the direct correlation between warmer tsite at vostok and warmer sst at odp site 1089 suggests that warmer oceanic atmospheric conditions imply a more southward placed frontal system weaker gradients and therefore stronger agulhas input to the atlantic ocean

timing of meltwater pulse 1a and climate responses to meltwater injections the temporal relationship between meltwater pulse 1a mwp 1a and the climate history of the last deglaciation remains a subject of debate by combining the greenland ice core project d18o ice core record on the new greenland ice core chronology 2005 timescale with the u th dated barbados coral record we conclusively derive that mwp 1a did not coincide with the sharp bolling warming but instead with the abrupt cooling of the older dryas to evaluate whether there is a relationship between meltwater injections north atlantic deep water nadw formation and climate change we present a high resolution record of nadw flow intensity from eirik drift through the last deglaciation it indicates only a relatively minor 200 year weakening of nadw flow coincident with mwp 1a our compilation of records also indicates that during heinrich event 1 and the younger dryas there were no discernible sea level rises and yet these periods were characterized by intense nadw slowdowns shutdowns clearly deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition instead our results emphasize that the location of meltwater pulses may be more important with nadw formation being particularly sensitive to surface freshening in the arctic nordic seas

corroborating ecological depth preferences of planktonic foraminifera in the tropical atlantic with the stable oxygen isotope ratios of core top specimens 1 past variability in upper ocean thermocline depth is commonly estimated from the abundance of different species of planktonic organisms or the difference in oxygen isotopic composition between two species of planktonic foraminifera one that lives in the mixed layer and one that lives in or near the thermocline to test the latter relationships we measured the oxygen isotopic composition of eight species of planktonic foraminifera pink and white varieties of globigerinoides ruber globigerinoides sacculifer without the final chamber orbulina universa pulleniatina obliquiloculata globorotalia menardii neogloborotalia dutertrei and globorotalia tumida in surface sediment samples from 31 tropical atlantic deep sea sediment cores bayesian analysis was used to compare measured oxygen isotopic compositions with their predictions based on modern data sets of annual temperatures and oxygen isotopic composition of ocean water in the upper 500 m at the core sites posterior probability densities for predictive model parameters were computed probability distributions of calcification depth for analyzed species corroborated their ecological preferences inferred from net tow and sediment trap data robustness of the habitat signals in core top specimens suggests that reconstructions of the entire upper ocean temperature profiles not just their thermocline depth or temperature might be possible

the influence of the sunda strait opening on paleoenvironmental changes in the eastern indian ocean abstract with sea level rise in the early holocene the warm and low salinity sea water from the java sea was transported into the eastern indian ocean after the opening of the sunda strait however the impact of this process on sediment provenance and paleoproductivity is rarely known in this study we analyzed the grain size sr nd pb isotopic compositions and biogenic elements of core cj01 185 1538 m water depth in the eastern indian ocean off the sunda strait our new results reveal a large volcanic eruption in the west of java at 2 1 ka and the krakatau eruption at 1883 ce on the basis of the pb isotopic compositions 87 sr 86 sr ratios and e nd values we infer that sediments from core cj01 185 were derived primarily from java island there is a distinct change in sr nd pb isotopic compositions of the sediments from the last glacial period to the holocene indicating less radiogenic nd isotopes from the java sea into the eastern indian ocean after the opening of the sunda strait at 10 ka moreover the sedimentation rate increased significantly from 6 5 cm kyr 1 during the last glacial period to 20 cm kyr 1 in the holocene the input of additional terrigenous nutrients from the java sea induced paleoproductivity with higher toc and tn concentrations after the opening of the sunda strait our results thus suggest that the paleoproductivity was mainly influenced by terrigenous materials input in the holocene other than southeast monsoon or upwelling in the last glacial period

tropical warming in the timor sea led deglacial antarctic warming and atmospheric co2 rise by more than 500 yr on the basis of the radiocarbon c 14 plateau tuning method a new age model for timor sea core md01 2378 was established it revealed a precise centennial scale phasing of climate events in the ocean cryo and atmosphere during the last deglacial and provides important new insights into causal linkages controlling events of global climate change at site md01 2378 reservoir ages of surface waters dropped from 1600 yr prior to 20 cal ka to 250 500 yr after 18 8 cal ka this evidence is crucial for generating a high resolution age model for deglacial events in the indo pacific warm pool sea surface temperatures sst started to change near 18 8 cal ka that is similar to 500 yr after the start of presumably northern hemispheric deglacial melt and sea level rise as shown by the benthic foraminiferal oxygen isotope ratio delta o 18 however the sst rise occurred 500 1000 yr prior to the onset of deglacial antarctic warming and the first major rise in atmospheric carbon dioxide at about 18 ka the increase in sst may partly reflect reduced seasonal upwelling of cold subsurface waters along the eastern margin of the indian ocean which is reflected by a doubling of the thermal gradient between the sea surface and the thermocline a halving of chlorin productivity from 19 to 18 5 cal ka and in particular by the strong decrease in surface water reservoir ages two significant increases in deglacial timor sea surface salinities from 19 to 18 5 and 15 5 to 14 5 cal ka may partly reflect the deglacial increase in the distance of local river mouths partly an inter hemispheric millennial scale see saw in tropical monsoon intensity possibly linked to a deglacial increase in the dominance of pacific el nino regimes over heinrich stadial 1 c 2010 elsevier b v all rights reserved

holocene surface hydroclimate changes in the indo pacific warm pool abstract the indo pacific warm pool ipwp is an area hosting key tropical climate processes such as the el nino southern oscillation enso and indian ocean dipole iod the tropical climate processes via various feedback mechanisms control the surface ocean climate in the indian ocean and its surrounding continents on annual to inter annual timescales however little has been known about how the tropical processes are effective forcing climate mechanism over longer timescales here we presented a reconstruction of the spatiotemporal pattern of sea surface temperature sst with inferred hydroclimate changes since the early holocene 11ka using proxies of planktonic foraminifer shell mg ca organic biomarker tex86 foraminifer oxygen isotopes and a terrigenous bit index measured from a 220 cm long core bs24 2 724041 n 97 010943 e 1015 m water depth which was taken offshore of northwest sumatra in the eastern indian ocean with an age model of 13 ams 14c dating by the uses of planktonic foraminiferal shells from the core the tex86h temperatures of bs24 show as summer weighted and reflect integrated thermal effects from the surface to thermocline water while the mg ca temperature of bs24 better reflects mean annual sst our results along with a regional synthesis of published sst records from the ipwp suggest that the ipwp has migrated eastwardly since the mid holocene 5ka in phase with this eastward migration the ipwp ssts have decreased but the upwelling in the eastern indian ocean appears to have been a persistent feature since the mid holocene our empirical orthogonal function eof analysis on the compiled ipwp sst records indicates two dominant modes of spatio temporal variability of surface hydrographes in the ipwp that are attributed to a combined effect of orbital and solar forcing with expressions analogous to the indian ocean basin wide mode iobm and the indian ocean dipole model iod

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

paleoclimate history of galapagos surface waters over the last 135 000 yr abstract records of planktonic and benthic foraminiferal 18 o and planktonic mg ca from core tr163 22 just northwest of the galapagos islands reveal a detailed 250 450 year resolution climate history of the region over the last 135 thousand years kyr sea surface temperatures ssts reconstructed from g ruber mg ca averaged 24 3 0 4 c during the holocene 22 6 0 6 c during marine isotope stage mis 2 3 and 4 and 26 0 0 9 c during mis 5e changes in sst lead changes in both planktonic and benthic 18 o by an average 3 kyr suggesting that sst changes in this region predated continental ice volume changes changes in sst display clear millennial scale variability especially in marine isotope stage 3 with behavior somewhat similar to antarctic proxy air temperature and south pacific sst records removal of the temperature component from the planktonic 18 o record demonstrates that glacial interglacial 18 o water changes at this site were 1 0 0 2 similar to estimates for mean ocean shifts implying that salinity changes due to regional hydrological variation between the last glacial maximum and holocene in the galapagos region were minimal comparison between the tr163 22 sst record and an sst record from core tr163 19 north of the equatorial front reveals a largely similar broad scale climate history suggesting that changes in the galapagos region were caused by large scale forcing rather than by local or regional dynamical changes changes in atmospheric greenhouse forcing are the most plausible explanation for the observed large scale climate changes in the eastern equatorial pacific

holocene millennial scale summer temperature variability inferred from sediment parameters in a non glacial mountain lake danntjorn jotunheimen central southern norway holocene changes in summer temperature in the jotunheimen area have been inferred from variations in several sediment parameters from a composite combined from two overlapping sediment cores lake core record mean time resolution of 15 years from lake danntjorn a small mountain lake located close to the modern pine tree limit in jotunheimen central southern norway loss on ignition analysis at contiguous 0 5 cm intervals throughout the cores revealed that the variations in residue after ignition of the sediments at 5501c in the upper 260 cm 8500 calendar years were not associated with variations in magnetic susceptibility in the basal deglacial and early holocene sequence of the lake sediments however the two sediment parameters fluctuated mainly in phase in addition the biogenic silica bsi concentration is relatively high thus in the early part of the holocene the variations in the residue were probably primarily driven by input of minerogenic detrital material inwash and or windblown and biological productivity including bsi from diatoms in the lake itself and in the lake surroundings from approximately 8500 calendar years bp variations in the residue probably primarily reflect variations in low minerogenic low magnetic susceptibility with little variations and diatom bsi productivity as demonstrated with analysis of bsi concentration between 260 and 233 cm 8500 7760 calendar years bp the highest residue values probably mainly reflecting high diatom productivity occurred at 7800 7200 7000 6700 6200 5400 5050 4300 2500 1800 1550 900 700 and o100 calendar years bp the most significant o8000 calendar years bp residue minima mainly low diatom productivity were recorded at 7100 6800 6600 6000 5700 5000 4400 4200 3800 3600 3200 3000 2750 2300 1900 1700 1070 740 600 380 and 80 calendar years bp bp ad 2000 the lake record from jotunheimen is discussed in the context of holocene terrestrial and marine records from the north atlantic region and possible natural climate forcing factors r 2004 elsevier ltd all rights reserved

evidence for indonesian throughflow slowdown during heinrich events 3 5 we present sea surface and upper thermocline temperature records 60 100 year temporal resolution spanning marine isotope stage 3 similar to 24 62 ka b p from international marine global change study core md01 2378 121 degrees 47 27 e and 13 degrees 04 95 s 1783 m water depth located in the outflow area of the indonesian throughflow within the timor sea stable isotopes and mg ca of the near surface dwelling planktonic foraminifer globigerinoides ruber white and the upper thermocline dwelling pulleniatina obliquiloculata reveal rapid changes in the thermal structure of the upper ocean during heinrich events thermocline warming and increased delta o 18 seawater p obliquiloculata record during heinrich events 3 4 and 5 reflect weakening of the relatively cool and fresh thermocline flow and reduced export of less saline water from the north pacific and indonesian seas to the tropical indian ocean three main factors influenced indonesian throughflow variability during marine isotope stage 3 1 global slowdown in thermohaline circulation during heinrich events triggered by northern hemisphere cooling 2 increased freshwater export from the java sea into the indonesian throughflow controlled by rising sea level from similar to 60 to 47 ka and 3 insolation related changes in the australasian monsoon with associated migration of hydrological fronts between indian ocean and indonesian throughflow derived water masses at similar to 46 40 ka

deep dwelling foraminifera as thermocline temperature recorders we measured the oxygen isotopic composition of the deep dwelling foraminiferal species g inflata g truncatulinoides dextral and sinistral and p obliquiloculata in 29 modern core tops raised from the north atlantic ocean we compared calculated isotopic temperatures with atlas temperatures and defined ecological models for each species g inflata and g truncatulinoides live preferentially at the base of the seasonal thermocline under temperature stress i e when the base of the seasonal thermocline is warmer than 16 c g inflata and g truncatulinoides live deeper in the main thermocline p obliquiloculata inhabits the seasonal thermocline in warm regions we tested our model using 10 cores along the mauritanian upwelling and show that the comparison of o variations registered by the surficial species g ruber and g bulloides and the deep dwelling species g inflata evidences significant glacial interglacial shifts of the mauritanian upwelling cells

decoupled holocene variability in surface and thermocline water temperatures of the indo pacific warm pool 1 the holocene variability in sea surface and thermocline water temperatures sst and twt in the indo pacific warm pool ipwp has been reconstructed by planktonic foraminiferal mg ca from sediments of the western tropical philippine sea afterward the younger dryas interval yd sst warmed gradually till 10 ka and remained approximately constant afterwards but twt rose more rapidly to a peak between 12 and 10 ka and then declined by 1 5 c through the holocene the trend of twt closely followed the boreal summer insolation and could be correlated to tropical climate changes represented by southward movement of the inter tropical convergence zone itcz and related changes in east asian monsoons

effect of preservation state of planktonic foraminifera tests on the decrease in mg ca due to reductive cleaning and on sample loss during cleaning four species of planktic foraminifera from core tops spanning a depth transect on the ontong java plateau were prepared for mg ca analysis both with cd cleaning and without mg cleaning a reductive cleaning step reductive cleaning caused etching of foraminiferal calcite focused on mg rich inner calcite even on tests which had already been partially dissolved at the seafloor despite corrosion there was no difference in mg ca of pulleniatina obliquiloculata between cleaning methods reductive cleaning decreased mg ca by an average all depths of 4 for globigerinoides ruber white and 10 for neogloboquadrina dutertrei mg ca of globigerinoides sacculifer above the calcite saturation horizon only was 5 lower after reductive cleaning the decrease in mg ca due to reductive cleaning appeared insensitive to preservation state for g ruber n dutertrei and p obliquiloculata mg ca of cd cleaned g sacculifer appeared less sensitive to dissolution than that of mg cleaned mg cleaning is adequate but sem and contaminants al ca fe ca and mn ca show that cd cleaning is more effective for porous species a second aspect of the study addressed sample loss during cleaning lower yield after cd cleaning for g ruber g sacculifer and n dutertrei confirmed this to be the more aggressive method strongest correlations between yield and co32 in core top samples were for cd cleaned g ruber r 0 88 p 0 020 and cd cleaned p obliquiloculata r 0 68 p 0 030 in a down core record wind28k correlation r between yield values 30 and dissolution index xdx was 0 61 p 0 002 where cleaning yield 30 most mg cleaned mg ca values were biased by dissolution

temperature differences between the hemispheres and ice age climate variability 1 the earth became warmer and cooler during the ice ages along with changes in the earth s orbit but the orbital changes themselves are not nearly large enough to explain the magnitude of the warming and cooling atmospheric co2 also rose and fell but again the co2 changes are rather small in relation to the warming and cooling so how did the earth manage to warm and cool by so much here we argue that for the big transitions at least the earth did not warm and cool as a single entity rather the south warmed instead at the expense of a cooler north through massive redistributions of heat that were set off by the orbital forcing oceanic co2 was vented up to the atmosphere by the same redistributions the north then warmed later in response to higher co2 and a reduced albedo from smaller ice sheets this form of north south displacement is actually very familiar as it is readily observed during the younger dryas interval 13 000 years ago and in the various millennial scale events over the last 90 000 years

assessing the effect of dissolution on planktonic foraminiferal mg ca ratios evidence from caribbean core tops in order to assess the dissolution effect on foraminiferal mg ca ratios we analyzed mg ca of seven planktonic foraminiferal species and four of their varieties from caribbean core tops from 900 4700 m water depth depending on the foraminiferal species and variety mg ca start to decline linearly below co32 levels of 18 26 mol kg by 0 04 0 11 mmol mol per 1 mol kg co32 similar to decreases of 0 5 0 8 mmol mol per kilometer below 2500 3000 m water depth above these species specific critical levels mg ca remains stable with higher intraspecific mg ca variability than below we developed routines to correct mg ca from below these critical thresholds for dissolution effects which reduce the overall intraspecific variability by 24 64 and provide dissolution corrected mg ca appropriate to calculate holocene paleotemperatures when taking into account only dissolution unaffected mg ca from 2000 m the systematic succession of foraminiferal species according to their mg ca reflects expected calcification depths

influence of the intertropical convergence zone on the east asian monsoon a palaeoclimate record spanning the past 16 000 years with nearly annual time resolution has been obtained from lake huguang maar in china the magnetic properties and titanium content of the lake sediments are thought to reflect changes in the east asian winter monsoon strength thus providing a complement to palaeoclimate archives that record the strength of the rain bearing summer monsoon the records point to an anti correlation between winter and summer monsoon strength best explained by migration of the intertropical convergence zone itcz a belt of low pressure air at the equator interestingly the decline of china s tang dynasty and the mayan civilization broadly coincide with drought periods recorded in lake huguang maar and cariaco basin sediments respectively did major shifts in the position of the itcz catalyse simultaneous events in civilizations on opposite sides of the pacific ocean the asian australian monsoon is an important component of the earth s climate system that influences the societal and economic activity of roughly half the world s population the past strength of the rain bearing east asian summer monsoon can be reconstructed with archives such as cave deposits1 2 3 but the winter monsoon has no such signature in the hydrological cycle and has thus proved difficult to reconstruct here we present high resolution records of the magnetic properties and the titanium content of the sediments of lake huguang maar in coastal southeast china over the past 16 000 years which we use as proxies for the strength of the winter monsoon winds we find evidence for stronger winter monsoon winds before the bolling allerod warming during the younger dryas episode and during the middle and late holocene when cave stalagmites suggest weaker summer monsoons1 2 3 we conclude that this anticorrelation is best explained by migrations in the intertropical convergence zone similar migrations of the intertropical convergence zone have been observed in central america for the period ad 700 to 900 refs 4 6 suggesting global climatic changes at that time from the coincidence in timing we suggest that these migrations in the tropical rain belt could have contributed to the declines of both the tang dynasty in china and the classic maya in central america

co2 radiative forcing and intertropical convergence zone influences on western pacific warm pool climate over the past 400 ka abstract the western pacific warm pool wpwp is an important heat source for the atmospheric circulation and influences climate conditions worldwide estimating wpwp sensitivity to past radiative forcing perturbations is important for understanding the magnitudes and patterns of current and projected tropical climate change here we present a new mg ca based sea surface temperature sst reconstruction over the past 400 ka from the bismarck sea off papua new guinea along with benthic foraminiferal 18o records and a transient intermediate complexity earth system model simulation the mg ca sst record exhibits a close similarity with atmospheric co2 content for the whole study period our model analysis demonstrates that greenhouse gas forcing is the primary driver for glacial interglacial sst changes in the entire wpwp region mg ca sst in the bismarck sea also includes a weaker precessional component which covaries with reconstructed and simulated local precipitation and simulated surface currents we propose that orbitally driven latitudinal shifts of the intertropical convergence zone and oceanic heat advection are responsible for this residual sst variability on glacial timescales the reconstructed wpwp surface temperature changes over the past 400 ka are highly correlated with east antarctic air temperature variations the strong effect of greenhouse gas forcings on both records and on global mean temperature variability allows us to determine a scaling factor of 1 1 5 between reconstructed wpwp temperature anomalies and estimates of the global mean temperature

assessing millennial scale variability during the holocene a perspective from the western tropical pacific we investigate the relationship between tropical pacific and southern ocean variability during the holocene using the stable oxygen isotope and magnesium calcium records of cooccurring planktonic and benthic foraminifera from a marine sediment core collected in the western equatorial pacific the planktonic record exhibits millennial scale sea surface temperature sst oscillations over the holocene of 0 5 c while the benthic 18oc document 0 10 millennial scale changes of upper circumpolar deep water ucdw a water mass which outcrops in the southern ocean solar forcing as an explanation for millennial scale sst variability requires 1 a large climate sensitivity and 2 a long 400 year delayed response suggesting that if solar forcing is the cause of the variability it would need to be considerably amplified by processes within the climate system at least at the core location we also explore the possibility that sst variability arose from volcanic forcing using a simple red noise model our best estimates of volcanic forcing falls short of reproducing the amplitude of observed sst variations although it produces power at low frequency similar to that observed in the md81 record although we cannot totally discount the volcanic and solar forcing hypotheses we are left to consider that the most plausible source for holocene millennial scale variability lies within the climate system itself in particular ucdw variability coincided with deep north atlantic changes indicating a role for the deep ocean in holocene millennial scale variability

the classic marine isotope substage 5e since its identi cation nearly fty years ago marine iso tope stage 5 mis 5 has been placed onto absolute time scaleson the basis of three independent approaches cesare emiliani who set up the isotope stages emiliani 1955 depended onuranium series dating of the sediments a method that today isregarded as not generally capable of yielding useful precisionor accuracy broecker and van donk 1970 pioneered the ap proach of correlating to radiometrically dated marine coral ter races thishasbeenmuchaidedinrecentyearsbyimprovementsin the precision and accuracy of these age determinations thathave owed from the development of thermal ionization massspectrometry tims for uranium series dating edwards

changes in the thermocline structure of the indonesian outflow during terminations i and ii we present centennial records of sea surface and upper thermocline temperatures in core md01 2378 from the timor sea which provide new insights into the variability of the indonesian outflow across the last two glacial terminations mg ca in globigerinoides ruber white s s indicates an overall increase of 3 2 degrees c in sea surface temperature sst over termination i following an early holocene plateau at 11 3 6 4 ka ssts cooled by 0 6 degrees c during the middle to late holocene 6 4 0 7 ka the early holocene warming occurred in phase with increasing northern hemisphere summer insolation coinciding with northward displacement of the intertropical convergence zone enhanced boreal summer monsoon and expansion of the indo pacific warm pool thermocline temperatures pulleniatina obliquiloculata mg ca gradually decreased from 24 5 to 21 5 degrees c since 10 3 ka reflecting intensification of a cool thermocline throughflow the vertical structure of the upper ocean in the timor sea evolved in similar fashion during the holocene and mis5e although the duration of sst plateaux differed 11 3 to 6 4 ka in termination i and from 129 to 119 ka in termination 11 which was probably due to the more intense northern hemisphere summer insolation during mis 5e during both terminations sst increased simultaneously in the southern high latitudes and the tropical eastern indian ocean suggesting virtually instantaneous atmospheric climate feedbacks between the high and low latitudes c 2008 elsevier b v all rights reserved

on eustatic sea level history last glacial maximum to holocene abstract this paper addresses the question of the magnitude and time dependence of the globally averaged eustatic rise of sea level that occurred subsequent to the time of last glacial maximum lgm at approximately 21 000 calendar years before present through the analysis of relative sea level rsl histories predicted by a realistic mass conserving and gravitationally self consistent theory of postglacial sea level change it is demonstrated that there are preferred oceanic locations at which this eustatic function is well approximated by local sea level history one such location is the island of barbados in the caribbean sea a site from which a coral based record exists that extends from mid holocene to lgm because of the sea level ambiguity that is inherent to coral based records however it is important that the global ice equivalent eustatic sea level curve inferred on the basis of the barbados data be tested against observations at other locations from which similarly extensive records are also available but which are derived on the basis of sea level indicators which are not subject to the ambiguities inherent to corals it is shown that when the eustatic function employed in the global theoretical model is tuned so as to enable the model to fit the barbados observations where the maximum relative sea level rsl depression is assumed to be near 120 m then the theory misfits the record from the sunda shelf in the indonesian archipelago as well as the record from j bonaparte gulf in northern australia both of these recently published records appear to constrain the lgm low stand of rsl to a value above 120 m the implications of these results for interpretation of the long coral derived records from the huon peninsula of papua new guinea and the island of tahiti are also discussed

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

holocene itcz and indian monsoon dynamics recorded in stalagmites from oman and yemen socotra abstract high resolution oxygen isotope 18o profiles of holocene stalagmites from four caves in northern and southern oman and yemen socotra provide detailed information on fluctuations in precipitation along a latitudinal transect from 12 n to 23 n 18o values reflect the amount of precipitation which is primarily controlled by the mean latitudinal position of the itcz and dynamics of the indian summer monsoon ism during the early holocene rapidly decreasing 18o values indicate a rapid northward displacement in the mean latitudinal position of the summer itcz and the associated ism rainfall belt with decadal to centennial scale changes in monsoon precipitation correlating well with high latitude temperature variations recorded in greenland ice cores during the middle to late holocene the summer itcz continuously migrated southward and monsoon precipitation decreased gradually in response to decreasing solar insolation a trend which is also recorded in other monsoon records from the indian and east asian monsoon domains importantly there is no evidence for an abrupt middle holocene weakening in monsoon precipitation although abrupt monsoon events are apparent in all monsoon records they are short lived and clearly superimposed on the long term trend of decreasing monsoon precipitation for the late holocene there is an anti correlation between ism precipitation in oman and inter monsoon spring autumn precipitation on socotra revealing a possible long term change in the duration of the summer monsoon season since at least 4 5 ka bp together with the progressive shortening of the ism season gradual southward retreat of the mean summer itcz and weakening of the ism the total amount of precipitation decreased in those areas located at the northern fringe of the indian and asian monsoon domains but increased in areas closer to the equator

abrupt increase in east indonesian rainfall from flooding of the sunda shelf 9500 years ago we present a precisely dated multi proxy stalagmite record from liang luar cave flores southeast indonesia that reveals a rapid increase in indonesian monsoon rainfall at 9 5 ka a ramp fitting method for detecting statistically significant inflections in a time series was applied to the stalagmite 18o mg ca and sr ca profiles to quantify the precise timing and magnitude of an abrupt increase in monsoon strength over a period of 350 years previously published lake level records from the monsoon affected australian interior show a sudden intensification of the australian monsoon at 14 ka however our records indicate that monsoon intensification in flores occured 4 5 kyr later the timing of the monsoon shift in flores is synchronous with the rapid expansion of rainforest in northeast australia and regional freshening of the southern makassar strait which under present day conditions is sensitive to monsoon variability the freshening of southern makassar was coeval with an abrupt 1 5 c cooling in the upper thermocline of the timor sea 9 5 ka indicative of reduced surface heat transport by the indonesian throughflow itf when the java sea opened during postglacial sea level rise this suggests that the abrupt increase in monsoon rainfall on flores was not due to a change in the itf because a decrease in rainfall would be expected to accompany cooler local sea surface temperatures ssts but rather by the sudden increase in ocean surface area and or temperature in the monsoon source region as the sunda shelf flooded during deglaciation we propose that it was the abrupt intensification of the monsoon through the late deglaciation that maintained the subsequent structure of the itf following the flooding of the sunda shelf at 9 5 ka

el nino southern oscillation extrema in the holocene and last glacial maximum 1 the el nino southern oscillation enso is the largest engine of interannual climate variability on the planet yet its past behavior and potential for future change are poorly understood and vigorously contested reconstructions of past enso are indispensable for testing climate models tasked with predicting future enso activity in a warming world but suitable geologic archives are scarce especially for the last glacial period here we reconstruct mean climate and enso variability in the holocene and last glacial maximum lgm from oxygen isotopic ratios 18o of individual foraminifera retrieved from deep sea sediments our results document coordinated adjustments of the tropical pacific enso system between two diametrically opposite states an amplified enso state in the lgm associated with a reduced zonal temperature gradient and a damped enso state in the mid holocene with enhanced gradient orbital precession provided the switch between these states and acted as the dominant external driver of the tropical pacific enso system in the past 25 000 years the linked response of the mean state and variability to orbital forcing provides an integrated framework for testing enso theory and models

glacial to holocene surface hydrography of the tropical eastern indian ocean quantifying the spatial and temporal sea surface temperature sst and salinity changes of the indo pacific warm pool is essential to understand the role of this region in connection with abrupt climate changes particularly during the last deglaciation in this study we reconstruct sst and seawater delta o 18 of the tropical eastern indian ocean for the past 40 000 years from two sediment cores geob 10029 4 1 degrees 30 s 100 degrees 08 e and geob 10038 4 5 degrees 56 s 103 degrees 15 e retrieved offshore sumatra our results show that annual mean ssts increased about 2 3 degrees c at 19 000 years ago and exhibited southern hemisphere like timing and pattern during the last deglaciation our sst records together with other mg ca based sst reconstructions around indonesia do not track the monsoon variation since the last glacial period as recorded by terrestrial monsoon archives however the spatial sst heterogeneity might be a result of changing monsoon intensity that shifts either the annual mean ssts or the seasonality of g ruber towards the warmer or the cooler season at different locations seawater delta o 18 reconstructions north of the equator suggest fresher surface conditions during the last glacial and track the northern high latitude climate change during the last deglaciation in contrast seawater delta o 18 records south of the equator do not show a significant difference between the last glacial period and the holocene and lack bolling allerod and younger dryas periods suggestive of additional controls on annual mean surface hydrology in this part of the indo pacific warm pool c 2010 elsevier b v all rights reserved

holocene and eemian sea surface temperature trends as revealed by alkenone and mg ca paleothermometry in this study we review a global set of alkenone and foraminiferal mg ca derived sea surface temperatures sst records from the holocene and compare them with a suite of published eemian sst records based on the same approach for the holocene the alkenone sst records belong to the actualized ghost database kim j h schneider r r 2004 ghost global database for alkenone derived holocene sea surface temperature records available from http www pangaea de projects ghost while the mg ca derived sst database represents a new compilation the actualized ghost database not only confirms the sst changes previously described but also documents the holocene temperature evolution in new oceanic regions such as the northwestern atlantic the eastern equatorial pacific and the southern ocean a comparison of holocene sst records stemming front the two commonly applied paleothermometry methods reveals contrasting sometimes divergent sst evolution particularly at low latitudes where sst records are abundant enough to infer systematic discrepancies at a regional scale opposite sst trends at particular locations could be explained by out of phase trends in seasonal insolation during the holocene this hypothesis assumes that a strong contrast in the ecological responses of coccolithophores and planktonic foraminifera to winter and summer oceanographic conditions is the ultimate reason for seasonal differences in the origin of the temperature signal provided by these organisms as a simple test for this hypothesis eemian sst records are considered because the holocene and eemian time periods experienced comparable changes in orbital configurations but had a higher magnitude in insolation variance during the eemian for several regions sst changes during both interglacials were of a similar sign but with higher magnitudes during the eemian as compared to the holocene this observation suggests that the ecological mechanism shaping sst trends during the holocene was comparable during the penultimate interglacial period although this ecology hypothesis fails to explain all of the available results we argue that any other mechanism would fail to satisfactorily explain the observed sst discrepancies among proxies c 2010 elsevier ltd all rights reserved

variations in sea surface hydrology in the southern makassar strait over the past 26 kyr we present centennial scale records of sea surface temperature and oxygen isotopes in a sediment core from mandar bay offshore sulawesi in the southern makassar strait which provide new insights into the variability of indonesian climate over the past 26 kyr the age model for the core is constrained by 17 ams radiocarbon ages with a surface ocean reservoir age correction based on paired wood and foraminiferal samples small holocene reservoir ages of 105 180 years point to intense surface ocean atmosphere interchange linked to increased monsoonal precipitation whereas last glacial maximum and deglacial reservoir ages are significantly higher mg ca derived sea surface temperature reconstructions based on globigerinoides ruber s s white exhibit an extended plateau during the antarctic cold reversal suggesting an atmospheric connection to high latitude southern hemisphere climate and a seasonal bias on g ruber this is in agreement with southern hemisphere sites along the track of the indonesian throughflow and in contrast to northern hemisphere records from the south china sea sulu sea and western pacific off mindanao which exhibit warming during the bolling allerod ice volume corrected delta o 18 seawater delta o 18 sw increased during heinrich stadial 1 and the younger dryas whereas the bolling allerod is characterized by low delta o 18 sw we attribute delta o 18 sw variability in the southern makassar strait during the last glacial maximum and glacial termination to changes in provenance and seasonality of precipitation rather than to variability in the amount of local precipitation and runoff c 2016 elsevier ltd all rights reserved

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

climate impact of late quaternary equatorial pacific sea surface temperature variations magnesium calcium data from planktonic foraminifera in equatorial pacific sediment cores demonstrate that tropical pacific sea surface temperatures ssts were 2 8 0 7 c colder than the present at the last glacial maximum glacial interglacial temperature differences as great as 5 c are observed over the last 450 thousand years changes in sst coincide with changes in antarctic air temperature and precede changes in continental ice volume by about 3 thousand years suggesting that tropical cooling played a major role in driving ice age climate comparison of sst estimates from eastern and western sites indicates that the equatorial pacific zonal sst gradient was similar or somewhat larger during glacial episodes extraction of a salinity proxy from the magnesium calcium and oxygen isotope data indicates that transport of water vapor into the western pacific was enhanced during glacial episodes

biomass burning in indonesia and papua new guinea natural and human induced fire events in the fossil record abstract microscopic charcoal preserved in sediments from ten wetlands in the indonesian and papua new guinea region provide a proxy record of regional fire events during the last 20 000 years two periods of high regional charcoal frequency are encountered during the last glacial transition 17 000 9000 years b p and the middle to late holocene 5000 years b p to the present despite the presence of humans in the region throughout the last 20 000 years there is no suggestion that on a regional spatial scale fire frequencies were solely related to changing subsistence patterns of the human population pollen data from these same sites suggest that during times of high charcoal the rate at which vegetation changes represented by the fossil pollen spectra also increases high climate variability may promote a greater community turnover rate and in turn a more fire susceptible forest community rapid climate change and high variability during the last glacial transition and intensification of el nino related climate variability during the middle to late holocene may have been important mechanisms for promoting fire in rainforest environments and maintaining diversity of tropical rain forests

the amplitude and phasing of climate change during the last deglaciation in the sulu sea western equatorial pacific 1 variations in tropical sea surface temperature patterns and the phasing relative to climate change in higher latitudes provide insight into the mechanisms of climate change on both orbital and shorter time scales here we present well dated high resolution records of planktonic foraminiferal 18o and mg ca based sst spanning the last deglaciation from the sulu sea located in the western equatorial pacific the results indicate that the last glacial maximum was 2 3 0 5 c cooler than present in the sulu sea with a concomitant decrease in sea surface salinity the similarity between variations in surface salinity in the sulu sea the western and eastern equatorial pacific and the greenland ice core record suggests that the observed changes in salinity reflect large scale rearrangement of atmospheric patterns which were coherent and synchronous throughout the northern hemisphere the results suggest that the glacial equatorial pacific climate was strongly influenced by both tropical and extra tropical forcing although it is not clear whether interannual enso variability is a good analogue of glacial interglacial climate change

radiocarbon simulations for the glacial ocean the effects of wind stress southern ocean sea ice and heinrich events simulations of oceanic radiocarbon for the last glacial maximum are presented using a three dimensional global ocean circulation model forced with glacial background states according to various reconstructions we investigate the influence of sea surface temperatures sea ice margins wind stress and antarctic sea ice formation on the glacial tracer distribution and meridional overturning circulation the aim of these sensitivity studies is to reconcile available radiocarbon data from marine sediments with reconstructed sea surface temperatures and estimated sea ice production rates model runs with a modified freshwater balance in the southern ocean mimicking increased brine release due to enhanced divergence of antarctic sea ice arrive at radiocarbon values close to observations these experiments also yield abyssal temperatures and salinities which are consistent with recent inferences in the simulation with the best agreement with radiocarbon observations north atlantic deep water export is reduced by 40 compared to present day while antarctic bottom water flow is intensified to similar strength in the south atlantic transient simulations show that glacial freshwater discharge into the north atlantic can cause abrupt increases of atmospheric radiocarbon as observed during heinrich event 1 however the effect is only significant in scenarios with a massive short time discharge at the beginning which is followed by low level freshwater input for the rest of the event or if it is assumed that the meridional overturning circulation was already in a modern operational mode

radiolarian based paleotemperatures during the last 160 kyr at odp site 1089 southern ocean atlantic sector two cores site 1089 odp leg 177 and ps2821 1 recovered from the same location 40 56 ps 9 54pe at the subtropical front stf in the atlantic sector of the southern ocean provide a high resolution climatic record with an average temporal resolution of less than 600 yr a multi proxy approach was used to produce an age model for core ps2821 1 and to correlate the two cores both cores document the last climatic cycle from marine isotopic stage 6 mis 6 ca 160 kyr bp ka to present summer sea surface temperatures sssts have been estimated with a standard error of ca 8 1 16 c for the down core record by using q mode factor analysis imbrie and kipp method the paleotemperatures show a 7 c warming at termination ii last interglacial transition from mis 6 to mis 5 this transition from glacial to interglacial paleotemperatures with maximum temperatures ca 3 c warmer than present at the core location occurs earlier than the corresponding shift in n 18 o values for benthic foraminifera from the same core this suggests a lead of southern ocean paleotemperature changes compared to the global ice volume changes as indicated by the benthic isotopic record the climatic evolution of the record continues with a progressive temperature deterioration towards mis 2 high frequency millennial scale climatic instability has been documented for mis 3 and part of mis 4 with sudden temperature variations of almost the same magnitude as those observed at the transitions between glacial and interglacial times these changes occur during the same time interval as the dansgaard oeschger cycles recognized in the n 18 oice record of the grip and gisp ice cores from greenland and seem to be connected to rapid changes in the stf position in relation to the core location sudden cooling episodes younger dryas yd type and antarctic cold reversal acr type of events have been recognized for both termination i acr i and yd i events and ii acr ii and yd ii events and imply that our core is located in an optimal position in order to record events triggered by phenomena occurring in both hemispheres spectral analysis of our ssst record displays strong analogies particularly for high sub orbital frequencies to equivalent records from vostok antarctica and from the subtropical north atlantic ocean this implies that the climatic variability of widely separated areas the antarctic continent the subtropical north atlantic and the subantarctic south atlantic can be strongly coupled and co varying at millennial time scales a few to 10 ka periods and eventually induced by the same triggering mechanisms climatic variability has also been documented for supposedly warm and stable interglacial intervals mis 1 and 5 with several cold events which can be correlated to other southern ocean and north atlantic sediment records d 2002 elsevier science b v all rights reserved

reconciling discrepancies between uk37 and mg ca reconstructions of holocene marine temperature variability significant discrepancies exist between the detrended variability of late holocene marine temperatures inferred from mg ca and uk37 proxies with the former showing substantially more centennial scale variation than the latter discrepancies exceed that attributable to differences in location and persist across various calibrations indicating that they are intrinsic to the proxy measurement we demonstrate that these discrepancies can be reconciled using a statistical model that accounts for the effects of bioturbation sampling and measurement noise and aliasing of seasonal variability the smaller number of individual samples incorporated into mg ca measurements relative to uk37 measurements leads to greater aliasing and generally accounts for the differences in the magnitude and distribution of variability an inverse application of the statistical model is also developed and applied in order to estimate the spectrum of marine temperature variability after correcting for proxy distortions the correction method is tested on surrogate data and shown to reliably estimate the spectrum of temperature variance when using high resolution records applying this inverse method to the actual mg ca and uk37 data results in estimates of the spectrum of temperature variance that are consistent this approach provides a basis by which to accurately estimate the distribution of intrinsic marine temperature variability from marine proxy records

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

debris flow dominance of alluvial fans masked by runoff reworking and weathering arid alluvial fan aggradation is highly episodic and fans often comprise active and inactive sectors hence the morphology and texture of fan surfaces are partly determined by secondary processes of weathering and erosion in addition to primary processes of aggradation this introduces considerable uncertainty in the identification of formative processes of terrestrial and martian fans from aerial and satellite imagery the objectives of this study are i to develop a model to describe the sedimentological and morphological evolution of inactive fan surfaces in arid settings and ii to assess the relative importance of primary processes of aggradation and secondary processes of weathering and reworking for surface morphology and sedimentology and for the stratigraphic record we studied an alluvial fan characterized by a recently active sector and a long abandoned inactive sector along the coast of the hyperarid atacama desert here rates of primary geomorphic activity are exceptionally low because of extreme aridity while weathering rates are relatively high because of the effects of coastal fogs long term processes of fan aggradation and reworking were determined through sedimentological facies analysis of stratigraphic sections ground surveys for textural and morphological patterns at the fan surface were integrated with remote sensing by an unmanned airborne vehicle uav discharges and sediment transport capacities were calculated to estimate the efficiency of secondary runoff in reshaping the inactive fan sector stratigraphic sections reveal that the fan was dominantly aggraded by debris flows whereas surface morphology is dominated by debris flow signatures in the active sector and by weathering and runoff on the inactive sector on the latter rapid particle breakdown prevents the formation of a coarse desert pavement furthermore relatively frequent local runoff events erode proximal debris flow channels on the inactive sector to form local lag deposits and accumulate fine sediment in low gradient distal channels forming a well developed drainage pattern that would suggest a runoff origin from aerial images nevertheless reworking is very superficial and barely preserved in the stratigraphic record this implies that fans on earth and mars that formed dominantly by sporadic mass flows may be masked by a surface morphology related to other processes

complexity of holocene climate as reconstructed from a greenland ice core glaciochemical time series developed from summit greenland indicate that the chemical composition of the atmosphere was dynamic during the holocene epoch concentrations of sea salt and terrestrial dusts increased in summit snow during the periods 0 to 600 2400 to 3100 5000 to 6100 7800 to 8800 and more than 11 300 years ago the most recent increase and also the most abrupt coincides with the little ice age these changes imply that either the north polar vortex expanded or the meridional air flow intensified during these periods and that temperatures in the mid to high northern latitudes were potentially the coldest since the younger dryas event

millennial scale trends in west pacific warm pool hydrology since the last glacial maximum models and palaeoclimate data suggest that the tropical pacific climate system plays a key part in the mechanisms underlying orbital scale and abrupt climate change atmospheric convection over the western tropical pacific is a major source of heat and moisture to extratropical regions and may therefore influence the global climate response to a variety of forcing factors the response of tropical pacific convection to changes in global climate boundary conditions abrupt climate changes and radiative forcing remains uncertain however here we present three absolutely dated oxygen isotope records from stalagmites in northern borneo that reflect changes in west pacific warm pool hydrology over the past 27 000 years our results suggest that convection over the western tropical pacific weakened 18 000 20 000 years ago as tropical pacific and antarctic temperatures began to rise during the early stages of deglaciation convective activity as inferred from oxygen isotopes reached a minimum during heinrich event 1 ref 10 when the atlantic meridional overturning circulation was weak pointing to feedbacks between the strength of the overturning circulation and tropical pacific hydrology there is no evidence of the younger dryas event in the stalagmite records however suggesting that different mechanisms operated during these two abrupt deglacial climate events during the holocene epoch convective activity appears to track changes in spring and autumn insolation highlighting the sensitivity of tropical pacific convection to external radiative forcing together these findings demonstrate that the tropical pacific hydrological cycle is sensitive to high latitude climate processes in both hemispheres as well as to external radiative forcing and that it may have a central role in abrupt climate change events

enso related decadal scale climate variability from the indo pacific warm pool the el nino southern oscillation enso is a climatic phenomenon that affects socio economical welfare in vast areas in the world a continuous record of holocene enso related climate variability of the indo pacific warm pool ipwp is constructed on the basis of stable oxygen isotopes in shells of planktic foraminifera from a sediment core in the western pacific ocean at the centennial scale variations in the stable oxygen isotope signal delta o 18 are thought be a representation of enso variability although an imprint of local conditions cannot be entirely excluded the record for the early holocene 10 3 6 ka bp shows in comparison with the mid to late holocene small amplitude variations in the delta o 18 record of up to 0 3 parts per thousand indicating relatively stable and warm sea surface conditions the mid to late holocene 6 2 ka bp exemplified higher variability in delta o 18 and thus in oceanic ipwp conditions climatically we interpret this change 5 5 4 2 ka bp as a phenomenon induced by variability in frequency and or intensity changes of el nino in the period 4 2 2 ka bp we identified several periods centred on 1 9 2 1 2 7 3 3 3 7 and 4 2 ka bp with in general heavy 6180 values during these periods the ipwp was relocated to a more eastward position enhancing the susceptibility for el nino like conditions at the core site over the last 2000 yr precipitation increased in the area as a response to an increase in asian monsoon strength resulting in a freshening of the surface waters this study corroborates previous findings that the present day enso activity started around 5 5 ka bp c 2006 elsevier b v all rights reserved

interlaboratory comparison study of mg ca and sr ca measurements in planktonic foraminifera for paleoceanographic research thirteen laboratories from the usa and europe participated in an intercomparison study of mg ca and sr ca measurements in foraminifera the study included five planktonic species from surface sediments from different geographical regions and water depths each of the laboratories followed their own cleaning and analytical procedures and had no specific information about the samples analysis of solutions of known mg ca and sr ca ratios showed that the intralaboratory instrumental precision is better than 0 5 for both mg ca and sr ca measurements regardless whether icp oes or icp ms is used the interlaboratory precision on the analysis of standard solutions was about 1 5 and 0 9 for mg ca and sr ca measurements respectively these are equivalent to mg ca based temperature repeatability and reproducibility on the analysis of solutions of 0 2 c and 0 5 c respectively the analysis of foraminifera suggests an interlaboratory variance of about 8 rsd for mg ca measurements which translates to reproducibility of about 2 3 c the relatively large range in the reproducibility of foraminiferal analysis is primarily due to relatively poor intralaboratory repeatability about 1 2 c and a bias about 1 c due to the application of different cleaning methods by different laboratories improving the consistency of cleaning methods among laboratories will therefore likely lead to better reproducibility even more importantly the results of this study highlight the need for standards calibration among laboratories as a first step toward improving interlaboratory compatibility

sea level reversal during termination ii the termination of the penultimate glacial period tii shows both similarities and differences to the last termination ti both terminations show significant cold reversals in the postglacial warming trend ti consists of a continuously increasing sea level trend whereas tii may demonstrate a sea level reduction midway through the termination we present a new continuous sea level record for tii derived from red sea 18 o records that supports the existence of the tii sea level reversal the record gives an unprecedented look at the structure of the tii sea level reversal which consists of an early highstand lasting several millennia in duration followed by a 30 12 m to 40 12 m reduction in sea level and a stillstand of several millennia before the final sea level rise to the marine oxygen isotope stage mis 5e interglacial we suggest that there is a link between the sea level reversal and internal millennial scale variability in the climate system

cortex a shipboard xrf scanner for element analyses in split sediment cores abstract the cortex corescanner texel is a non destructive xrf system for the logging of split sediment cores it is a seaworthy instrument that remains active during heavy weather conditions the scanner produces reliable counts for k to sr highly correlated with concentrations measured with atomic absorption spectrometry aas the option to scan al si and elements heavier than sr is in preparation a core section of 1 m can be scanned at 2 cm intervals within an hour a maximum resolution of 1 mm can be achieved at present each region and sedimentary environment requires separate calibration in the nearby future the generator settings will be standardized which may result in the development of a standard calibration procedure because of the high resolution of its semi quantitative records the cortex is a useful tool for detailed time series analysis inter core correlation and shipboard analysis

the holocene environmental changes in southern indonesia reconstructed from highland caldera lake sediment in bali island diatom pollen geomagnetic and geochemical analyses were carried out on a 3 6 m long sediment core taken from lake buyan a highland caldera lake in central bali island to reconstruct the holocene climate changes in equatorial southern indonesia the core represents 8 thousand years sedimentation of organic diatomaceous lake mud constant inclusion of benthic diatom fossils as main components indicated that suspension and inflow of littoral materials were the main sedimentary process the core contained laminated sediments in two distinct intervals at 6 5 5 0 and 3 6 3 1 cal ky bp and multi proxy records showed generally drier climate in these sections especially at 3 6 3 1 cal ky bp lake bottom waters were more reducing condition in these laminated periods probably due to increased lake productivity by prolonged dry season and wind mixing laminae structures were made up of a layer composed of benthic diatoms and amorphous organic materials and a layer made by only planktonic diatom fossils each of which may represent rainy and dry period deposits although southern indonesia shows clear australian monsoon rainfall seasonality at present counting of layer numbers showed interannual cycles of laminae formation prolonged dry seasons could obscured the rainfall seasonality in these periods but precise depositional patterns were elusive unlaminated sections showed homogeneous sediment mixture of benthic planktonic diatoms and more volume of terrigenous materials indicating wetter climate and seasonality similar to the present time this was supported by the higher share of marsh environment pollens reflecting more stable lake level trends the dry climate from 6 5 cal ky bp was in line with the general perception of stronger enso dynamics from the mid holocene due to weaker than before boreal summer insolation but the sporadic appearances of dry periods imply the influence of regional climate forcings such as temporal migrations of inter tropical convergence zone itcz it was however possible that temporal shifts of large climate mode occurred in equatorial pacific and indian oceans wettest climate was inferred from 3 1 cal ky bp to the present and this might reflect increased importance of austral hemisphere atmospheric convection and subsequent southerly position of itcz in austral summer time

el nino like pattern in ice age tropical pacific sea surface temperature sea surface temperatures ssts in the cold tongue of the eastern equatorial pacific exert powerful controls on global atmospheric circulation patterns we examined climate variability in this region from the last glacial maximum lgm to the present using a sst record reconstructed from magnesium calcium ratios in foraminifera from sea floor sediments near the galapagos islands cold tongue sst varied coherently with precession induced changes in seasonality during the past 30 000 years observed lgm cooling of just 1 2 c implies a relaxation of tropical temperature gradients weakened hadley and walker circulation southward shift of the intertropical convergence zone and a persistent el nino like pattern in the tropical pacific this is contrasted with mid holocene cooling suggestive of a la nina like pattern with enhanced sst gradients and strengthened trade winds our results support a potent role for altered tropical pacific sst gradients in global climate variations

southward migration of the intertropical convergence zone through the holocene titanium and iron concentration data from the anoxic cariaco basin off the venezuelan coast can be used to infer variations in the hydrological cycle over northern south america during the past 14 000 years with subdecadal resolution following a dry younger dryas a period of increased precipitation and riverine discharge occurred during the holocene thermal maximum since approximately 5400 years ago a trend toward drier conditions is evident from the data with high amplitude fluctuations and precipitation minima during the time interval 3800 to 2800 years ago and during the little ice age these regional changes in precipitation are best explained by shifts in the mean latitude of the atlantic intertropical convergence zone itcz potentially driven by pacific based climate variability the cariaco basin record exhibits strong correlations with climate records from distant regions including the high latitude northern hemisphere providing evidence for global teleconnections among regional climates

a high resolution study of holocene paleoclimatic and paleoceanographic changes in the nordic seas 1 high resolution records from images core md95 2011 in the eastern norwegian sea provide evidence for relatively large and small scale high latitude climate variability throughout the holocene during the early and mid holocene a situation possibly driven by consistent stronger westerlies increased the eastward influence of arctic intermediate and near surface waters for the late holocene a relaxation of the atmospheric forcing resulted in increased influence of atlantic water the main changes in holocene climate show no obvious connection to changing solar irradiance and spectral analysis reveals no consistent signature for any periodic behavior of holocene climate at millennial or centennial timescales there are however indications of consistent multidecadal variability

a high resolution absolute dated late pleistocene monsoon record from hulu cave china oxygen isotope records of five stalagmites from hulu cave near nanjing bear a remarkable resemblance to oxygen isotope records from greenland ice cores suggesting that east asian monsoon intensity changed in concert with greenland temperature between 11 000 and 75 000 years before the present yr b p between 11 000 and 30 000 yr b p the timing of changes in the monsoon as established with 230th dates generally agrees with the timing of temperature changes from the greenland ice sheet project two gisp2 core which supports gisp2 s chronology in this interval our record links north atlantic climate with the meridional transport of heat and moisture from the warmest part of the ocean where the summer east asian monsoon originates

radiocarbon calibration curve spanning 0 to 50 000 years bp based on paired 230 th 234 u 238 u and 14 c dates on pristine corals abstract radiocarbon dating is the most widely used dating technique in the world recent advances in accelerator mass spectrometry ams and sample preparation techniques have reduced the sample size requirements by a factor of 1000 and decreased the measurement time from weeks to minutes today it is estimated that more than 90 percent of all measurements made on accelerator mass spectrometers are for radiocarbon age dates the production of 14 c in the atmosphere varies through time due to changes in the earth s geomagnetic field intensity and in its concentration which is regulated by the carbon cycle as a result of these two variables a radiocarbon age is not equivalent to a calendar age four decades of joint research by the dendrochronology and radiocarbon communities have produced a radiocarbon calibration data set of remarkable precision and accuracy extending from the present to approximately 12 000 calendar years before present this paper presents high precision paired 230 th 234 u 238 u and 14 c age determinations on pristine coral samples that enable us to extend the radiocarbon calibration curve from 12 000 to 50 000 years before present we developed a statistical model to properly estimate sample age conversion from radiocarbon years to calendar years taking full account of combined errors in input ages and calibration uncertainties our radiocarbon calibration program is publicly accessible at http www radiocarbon ldeo columbia edu along with full documentation of the samples data and our statistical calibration model

superlakes megafloods and abrupt climate change about 8200 years ago the climate of much of the northern hemisphere cooled abruptly for a period of about 200 years in their perspective clarke et al examine the most likely culprit for this cooling an outburst of fresh water from a vast ice dammed glacial lake in north america the superlake had formed when the kilometers thick ice sheet covering much of north america disintegrated when the ice dam became unstable fresh water flooded from the lake into the north atlantic it remains unclear how this fresh water affected ocean circulation or whether the outburst occurred in more than one stage but the timing points strongly to the outburst flood as the trigger of the 8200 year climate event

half precessional cycle of thermocline temperature in the western equatorial pacific and its bihemispheric dynamics the el nino southern oscillation enso which is tightly coupled to the equatorial thermocline in the pacific is the dominant source of interannual climate variability but its long term evolution in response to climate change remains highly uncertain this study uses mg ca in planktonic foraminiferal shells to reconstruct sea surface and thermocline water temperatures sst and twt for the past 142 ky in a western equatorial pacific wep core md01 2386 unlike the dominant 100 ky glacial interglacial cycle recorded by sst and 18o which echoes the pattern seen in other wep sites the upper ocean thermal gradient shows a clear half precessional 9 4 ky or 12 7 ky cycle as indicated by the reconstructed and simulated temperature t and 18o differences between the surface and thermocline waters this phenomenon is attributed to the interplay of subtropical to tropical thermocline anomalies forced by the antiphased meridional insolation gradients in the two hemispheres at the precessional band in particular the twt shows greater variability than sst and dominates the t changes which couple with the west east sst difference in the equatorial pacific at the half precessional band implying a decisive role of the tropical thermocline in orbital scale climate change

deglacial δ18o and hydrologic variability in the tropical pacific and indian oceans abstract evidence from geologic archives suggests that there were large changes in the tropical hydrologic cycle associated with the two prominent northern hemisphere deglacial cooling events heinrich stadial 1 hs1 19 to 15 kyr bp kyr bp 1000 yr before present and the younger dryas 12 9 to 11 7 kyr bp these hydrologic shifts have been alternatively attributed to high and low latitude origin here we present a new record of hydrologic variability based on planktic foraminifera derived 18o of seawater 18osw estimates from a sediment core from the tropical eastern indian ocean and using 12 additional 18osw records construct a single record of the dominant mode of tropical eastern equatorial pacific and indo pacific warm pool ipwp hydrologic variability we show that deglacial hydrologic shifts parallel variations in the reconstructed interhemispheric temperature gradient suggesting a strong response to variations in the atlantic meridional overturning circulation and the attendant heat redistribution a transient model simulation of the last deglaciation suggests that hydrologic changes including a southward shift in the intertropical convergence zone itcz which likely occurred during these northern hemisphere cold events coupled with oceanic advection and mixing resulted in increased salinity in the indonesian region of the ipwp and the eastern tropical pacific which is recorded by the 18osw proxy based on our observations and modeling results we suggest the interhemispheric temperature gradient directly controls the tropical hydrologic cycle on these time scales which in turn mediates poleward atmospheric heat transport

timing duration and transitions of the last interglacial asian monsoon thorium 230 ages and oxygen isotope ratios of stalagmites from dongge cave china characterize the asian monsoon and low latitude precipitation over the past 160 000 years numerous abrupt changes in 18o 16o values result from changes in tropical and subtropical precipitation driven by insolation and millennial scale circulation shifts the last interglacial monsoon lasted 9 7 1 1 thousand years beginning with an abrupt less than 200 years drop in 18o 16o values 129 3 0 9 thousand years ago and ending with an abrupt less than 300 years rise in 18o 16o values 119 6 0 6 thousand years ago the start coincides with insolation rise and measures of full interglacial conditions indicating that insolation triggered the final rise to full interglacial conditions