weakening and strengthening of the indian monsoon during heinrich events and dansgaard oeschger oscillations the dansgaard oeschger oscillations and heinrich events described in north atlantic sediments and greenland ice are expressed in the climate of the tropics for example as documented in arabian sea sediments given the strength of this teleconnection we seek to reconstruct its range of environmental impacts we present geochemical and sedimentological data from core so130 289kl from the indus submarine slope spanning the last similar to 80 kyr elemental and grain size analyses consistently indicate that interstadials are characterized by an increased contribution of fluvial suspension from the indus river in contrast stadials are characterized by an increased contribution of aeolian dust from the arabian peninsula decadal scale shifts at climate transitions such as onsets of interstadials were coeval with changes in productivity related proxies heinrich events stand out as especially dry and dusty events indicating a dramatically weakened indian summer monsoon potentially increased winter monsoon circulation and increased aridity on the arabian peninsula this finding is consistent with other paleoclimate evidence for continental aridity in the northern tropics during these events our results strengthen the evidence that circum north atlantic temperature variations translate to hydrological shifts in the tropics with major impacts on regional environmental conditions such as rainfall river discharge aeolian dust transport and ocean margin anoxia key points intensity of indian monsoon is traced with geochemical and grain size analyses of sediments fluvial versus aeolian sediment input to arabian sea mimics do oscillations during heinrich events the indian monsoon weakened distinctly

monsoonal variability in the northeastern arabian sea during the past 5000years geochemical evidence from laminated sediments abstract a high resolution laminated sediment record from the oxygen minimum zone in the northeastern arabian sea off pakistan was studied to reconstruct climatic variations to infer the monsoon driven moisture history in the northeastern arabian sea during the past 5000 years we have used three types of independant proxies 1 varve thickness 2 stable isotope ratios of planktic foraminifera and 3 inorganic geochemical composition on the basis of these proxies we have subdivided the sedimentary record into five intervals the first time interval from 5000 to 3900 yr bp period i is dominated by summer monsoon activity deduced from ti al zr al k al and sr ca ratios and oxygen isotope data of planktonic foraminifera slightly enhanced winter monsoon conditions can be inferred for the period from 3900 to about 3000 yr bp period ii maximum precipitation during enhanced winter monsoon activity at about 3100 yr bp was followed by an onset of aridification at 3000 yr bp which continued until about 2000 2200 yr bp period iii the textural mineralogical and geochemical data suggest that this aridification was a gradual century scale process rather than an abrupt event comparison to late holocene records in nw and sw india the near east and tropical africa supports our interpretation that period iii from 3000 to 2000 yr bp is characterized by a gradual change in the atmospherical moisture budget over much of this area reduced monsoonal rainfall may be linked to variations of eurasian snow cover as deduced from varve thickness and element to al ratios period iv from 2000 to about 1500 yr bp is characterized by a summer monsoon dominated sequence with higher precipitation than during period iii the 18o record shows an abrupt shift at 2000 yr bp coinciding with an increase of varve thickness which suggests a cooling of surface waters in the northern arabian sea present day conditions in the makran area were established at 1500 yr bp period v based on inorganic geochemical data and meteorological records at several stations in the makran we conclude that period v is dominated by precipitation during the winter season here declined rainfall associated with the summer monsoon may be related to a less northward position of the intertropical convergence zone itcz during summer and a stronger influence of winter monsoon linked phenomenona

marine derived 14c calibration and activity record for the past 50 000 years updated from the cariaco basin abstract an expanded cariaco basin 14c chronology is tied to 230th dated hulu cave speleothem records in order to provide detailed marine based 14c calibration for the past 50 000 years the revised high resolution cariaco 14c calibration record agrees well with data from 230th dated fossil corals back to 33 ka with continued agreement despite increased scatter back to 50 ka suggesting that the record provides accurate calibration back to the limits of radiocarbon dating the calibration data document highly elevated 14c during the glacial period carbon cycle box model simulations show that the majority of observed 14c change can be explained by increased 14c production however from 45 to 15 ka 14c remains anomalously high indicating that the distribution of radiocarbon between surface and deep ocean reservoirs was different than it is today additional observations of the magnitude spatial extent and timing of deep ocean 14c shifts are critical for a complete understanding of observed glacial 14c variability

chronostratigraphy of the 600 000 year old continental record of lake van turkey lake van sediment cores from the ahlat ridge and northern basin drill sites of the icdp project paleovan contain a wealth of information about past environmental processes the sedimentary sequence was dated using climatostratigraphic alignment varve chronology tephrostratigraphy argon argon single crystal dating radiocarbon dating magnetostratigraphy and cosmogenic nuclides based on the lithostratigraphic framework the different age constraints are compiled and a robust and precise chronology of the 600 000 year old lake van record is constructed proxy records of total organic carbon content and sediment color together with the calcium potassium ratios and arboreal pollen percentages of the 174 meter long ahlat ridge record mimic the greenland isotope stratotype ngrip therefore the proxy records are systematically aligned to the onsets of interstadials reflected in the ngrip or synthesized greenland ice core stratigraphy the chronology is constructed using 27 age control points derived from visual synchronization with the gicc05 timescale an absolutely dated speleothem record e g hulu sanbao linzhu cave and the epica dome c timescale in addition the uppermost part of the sequence is complemented with four ages from holocene varve chronology and two calibrated radiocarbon ages furthermore nine argon argon ages and a comparison of the relative paleointensity record of the magnetic field with reference curve piso 1500 confirm the accuracy of the age model also the identification of the laschamp event via measurements of 10be in the sediment confirms the presented age model the chronology of the ahlat ridge record is transferred to the 79 meter long event corrected composite record from the northern basin and supplemented by additional radiocarbon dating on organic marco remains the basal age of the northern basin record is estimated at 90 ka the variations of the time series of total organic carbon content the ca k ratio and the arboreal pollen percentages illustrate that the presented chronology and paleoclimate data are suited for reconstructions and modeling of the quaternary and pleistocene climate evolution in the near east at millennial timescales furthermore the chronology of the last 250 kyr can be used to test other dating techniques

high resolution records of climate change in arid eastern central asia during mis 3 51 600 25 300 cal a bp from wulungu lake north western china detailed records of climate change during the last glaciation in arid central asia are scarce here we present a sedimentological and geochemical record from wulungu lake in north western china providing the first high resolution continuous sedimentary records in this region covering marine isotope stage mis 3 51 600 25 300 cal a bp high lake power end member 2 values and bioproductivity concurrent with low terrigenous clastic input unanimously indicate high lake water levels during 46 180 39 770 31 680 30 080 and 27 780 26 540 cal a bp and moderately wet conditions during 51 600 46 180 and 39 770 31 680 cal a bp the lake attained its lowest water levels after 30 080 cal a bp few dry events characterized by high pool power end member 3 values and terrigenous input are documented for the studied interval and three of them are correlative with heinrich events 5 3 our study supports the hypothesis for a positive northern hemisphere july insolation anomaly which increased the temperature gradient between low and high latitudes increasing the strength of westerlies and increasing sea surface temperatures in the north atlantic resulting in more moisture transported to arid central asian by westerlies

multi proxy evidence of millennial climate variability from multiple bahamian speleothems abstract northern hemisphere tropical paleoclimate records support significant changes associated with dansgaard oeschger d o events and heinrich stadials 1 to 6 during the last 64 000 years however few absolutely dated terrestrial records from the western atlantic span the last six heinrich stadials here we present geochemical results from three new stalagmites collected from a cave in the bahamas which encompass heinrich stadials 1 to 6 we build on a previous study of the 13 c and 18 o values of the calcite and 18 o value of fluid inclusions from a single stalagmite from the same cave spanning the last three heinrich stadials absolute geochronometry using u th equilibrium series demonstrates that the stalagmites formed between 63 8 and 13 8 kyr bp the 13 c and 18 o values of the calcite show higher values associated with heinrich stadials 1 6 and lower values during the d o interstadial events the sr ca ratios of the calcite are shown to be relatively invariant while in two of the samples the mg ca ratios track the 13 c values increases in the 18 o values across heinrich stadials 1 6 are interpreted as being driven by lower temperatures the two deeper occurring stalagmites demonstrate increased mg ca ratios and 13 c values during heinrich stadials 1 and 2 which are interpreted as a signal of reduced flow rates in the epikarst and increased water rock interactions as a result of increased aridity which potentially occurred across all six heinrich stadials the observed reductions in mean annual temperature and amount of precipitation across heinrich stadials are proposed to be driven by a reduction in sea surface temperatures in the north atlantic and an expanded bermuda high during d o interstadials the bahamas cave records likely indicate warmer and or wetter climate however the isotopic shifts are not as significant as the isotopic excursions associated with heinrich stadials

lacustrine lignin biomarker record reveals a severe drought during the late younger dryas in southern taiwan abstract the younger dryas yd event which punctuated the last glacial holocene transition period and had a profound impact on global climate is the most well studied millennial scale climate event although the triggering mechanism remains debate weakened asian summer monsoon during the yd is recorded in oxygen isotopes of stalagmite from mainland china however lacustrine climate record of the yd event has not been reported from the subtropical land ocean boundary of the asian continent near the pacific warm pool we provide a lignin biomarker record covering the last deglaciation and early holocene 17 9 ka bp from the dongyuan lake southern taiwan located at the frontal zone of typhoon invasion the lignin phenol ratio s v shows that the vegetation in the catchments had shifted from gymnosperm dominant to angiosperm dominant plants since 12 2 ka bp significantly decreased lignin concentrations tlp and 8 and elevated lignin degradation parameters ad al v p v s dhba v in combination with other organic proxies toc 13corg during the late yd suggest a severe drought had occurred in southern taiwan during this specific period changes in the lignin proxies from the dongyuan lake lagged the climate changes registered in stalagmite records by around 500 800 years suggesting a slow response of vegetation and soil processes to rapid climate changes

reconstruction of the east asian summer monsoon rainfall distribution at centennial scale during the last glacial maximum abstract the last glacial maximum lgm defined as the period between 23 and 19 ka is considered a key climatic period with conditions in great contrast to the present study of this period may reveal aspects of global ice sheet sensitivity to regional and global climate change which is critical in understanding climate teleconnections and feedback mechanisms a stalagmite record from linglong cave central china in combination with other high resolution stalagmite records from southwest china and east china existing on the same moisture transport pathway allows a reconstruction of rainfall patterns during the lgm by making use of the 18o differences between stalagmite records the rainfall around both southwest and central east china show a prominent change centered at 24 ka corresponding to the h2 event one of the heinrich events related to north atlantic ice rafting also in central east china around the periods at 22 and 20 ka the rainfall is lower than the average during the whole lgm while around 23 21 and 19 ka the rainfall is higher than the average which is opposite to the rainfall variation in southwest china this apparent dipole rainfall pattern during the lgm is similar to the modern east asian summer monsoon easm rainfall distribution observed during weak monsoon periods suggesting a much weaker easm with its front moving less far north during the lgm than at present which may link to north atlantic climate and shifting of the intertropical convergence zone itcz power spectral analysis reveals that the rainfall variations in southwest china are mainly controlled by a cycle of 1000 yr while in central east china it is mainly controlled by cycles of 1800 yr and 1300 yr which are all possible solar activity cycles suggesting that the easm rainfall on long term scales is dominated by external forces

rapid subtropical north atlantic salinity oscillations across dansgaard oeschger cycles geochemical and sedimentological evidence suggest that the rapid climate warming oscillations of the last ice age the dansgaard oeschger cycles were coupled to fluctuations in north atlantic meridional overturning circulation through its regulation of poleward heat flux the balance between cold meltwater from the north and warm salty subtropical gyre waters from the south influenced the strength and location of north atlantic overturning circulation during this period of highly variable climate here we investigate how rapid reorganizations of the ocean atmosphere system across these cycles are linked to salinity changes in the subtropical north atlantic gyre we combine mg ca palaeothermometry and oxygen isotope ratio measurements on planktonic foraminifera across four dansgaard oeschger cycles spanning 45 9 59 2 kyr ago to generate a seawater salinity proxy record from a subtropical gyre deep sea sediment core we show that north atlantic gyre surface salinities oscillated rapidly between saltier stadial conditions and fresher interstadials covarying with inferred shifts in the tropical atlantic hydrologic cycle and north atlantic overturning circulation these salinity oscillations suggest a reduction in precipitation into the north atlantic and or reduced export of deep salty thermohaline waters during stadials we hypothesize that increased stadial salinities preconditioned the north atlantic ocean for a rapid return to deep overturning circulation and high latitude warming by contributing to increased north atlantic surface water density on interstadial transitions

the sensitivity of the climate response to the magnitude and location of freshwater forcing last glacial maximum experiments abstract proxy records indicate that the locations and magnitudes of freshwater forcing to the atlantic ocean basin as iceberg discharges into the high latitude north atlantic laurentide meltwater input to the gulf of mexico or meltwater diversion to the north atlantic via the st lawrence river and other eastern outlets may have influenced the north atlantic thermohaline circulation and global climate we have performed last glacial maximum lgm simulations with the ncar community climate system model ccsm3 in which the magnitude of the freshwater forcing has been varied from 0 1 to 1 sv and inserted either into the subpolar north atlantic ocean or the gulf of mexico in these glacial freshening experiments the less dense freshwater provides a lid on the ocean water below suppressing ocean convection and interaction with the atmosphere above and reducing the atlantic meridional overturning circulation amoc this is the case whether the freshwater is added directly to the area of convection south of greenland or transported there by the subtropical and subpolar gyres when added to the gulf of mexico the amoc reduction is less for the smaller freshwater forcings but is not linear with the size of the freshwater perturbation the recovery of the amoc from a slow state is 200 years for the 0 1 sv experiment and 500 years for the 1 sv experiment for glacial climates with large northern hemisphere ice sheets and reduced greenhouse gases the cold subpolar north atlantic is primed to respond rapidly and dramatically to freshwater that is either directly dumped into this region or after being advected from the gulf of mexico greenland temperatures cool by 6 8 c in all the experiments with little sensitivity to the magnitude location or duration of the freshwater forcing but exhibiting large seasonality sea ice is important for explaining the responses the northern hemisphere high latitudes are slow to recover antarctica and the southern ocean show a bipolar response with warming and reduced sea ice this warming continues after the cessation of the freshwater forcing and shows a dependence on the duration of the freshwater forcing equatorward of the expanded sea ice the simulated temperature and salinity anomalies are sensitive to the amount of colder and fresher waters that are advected out of the subpolar north atlantic in the tropical atlantic the recovery of the intertropical convergence zone itcz from its more southerly position during the freshwater forcing is much more rapid than the recovery of the amoc and is more related to the recovery of low latitude surface temperatures than greenland temperature or sea ice these results have implications for using proxy records as indirect measures of the amoc

response and feedback of the indian summer monsoon and the southern westerly winds to a temperature contrast between the hemispheres during the last glacial interglacial transitional period abstract the hypothesis that an interhemispheric thermal gradient or a temperature contrast between the hemispheres tcbh drives shifts in the latitudinal position of the intertropical convergence zone itcz and the southern westerly winds sww is considered one of the most important climate change mechanisms proposed in the last few decades however the controversy over the shifting magnitude and direction of the itcz and the sww brings uncertainty to the hypothesis here we further examine the shifting characteristics of the itcz and its relationship with the intensity variation of the indian summer monsoon ism based on synthesis and summary of previously published literature data in particular we evaluate regional distribution patterns of the dry and wet climatic changes in southern south america during the last glacial interglacial transitional period including the heinrich event 1 the antarctic cold reversal and the younger dryas the results show that in response to the northern hemisphere wide cooling and the southern hemisphere wide warming the northern hemisphere wide warming and the southern hemisphere wide cooling during the period the itcz over the asian and northern south american continents and the sww shift poleward equatorward while the intensity of the ism decreases increases however the shifting characteristics of the itcz over the vast pacific ocean remain unclear which implies that the relationship between the tcbh and the el nino southern oscillation in the tropical pacific ocean needs to be studied in addition there may be a relatively stable core region in the sww this core region is located in central patagonia at approximately 47 s where the local climate is wetter during the all transition period showing the continuous influence of the sww on this region the position shift of the sww in response to the tcbh phase changes seems to behave as a swing process with an axis of approximately 47 s the poleward swing of the sww may trigger the self repairing process of the global climate system after the catastrophic impacts of the meltwater including the pulling effect of the enhanced upwelling on the atlantic meridional overturning circulation the influence of co2 released from the deep sea and the impact of the gradual strengthening of the ism these results support and reinforce the hypothesis that the tcbh drives global climate change highlight the global teleconnection characteristics of the key physical processes in the earth s climate system and the important role of the sww in this teleconnection and provide a basis for further simulating the climate connections in the two hemispheres especially the impact of the sww on the global climate change

response of the amazon rainforest to late pleistocene climate variability abstract variations in amazonian hydrology and forest cover have major consequences for the global carbon and hydrological cycles as well as for biodiversity yet the climate and vegetation history of the lowland amazon basin and its effect on biogeography remain debated due to the scarcity of suitable high resolution paleoclimate records here we use the isotopic composition d and 13 c of plant waxes from a high resolution marine sediment core collected offshore the amazon river to reconstruct the climate and vegetation history of the integrated lowland amazon basin for the period from 50 000 to 12 800 yr before present our results show that d values from the last glacial maximum were more enriched than those from marine isotope stage mis 3 and the present day we interpret this trend to reflect long term changes in precipitation and atmospheric circulation with overall drier conditions during the last glacial maximum our results thus suggest a dominant glacial forcing of the climate in lowland amazonia in addition to previously suggested thermodynamic mechanisms of precipitation change which are directly related to temperature we conclude that changes in atmospheric circulation are crucial to explain the temporal evolution of amazonian rainfall variations as demonstrated in climate model experiments our vegetation reconstruction based on 13 c values shows that the amazon rainforest was affected by intrusions of savannah or more open vegetation types in its northern sector during heinrich stadials while it was resilient to glacial drying this suggests that biogeographic patterns in tropical south america were affected by heinrich stadials in addition to glacial interglacial climate variability

precisely dated multidecadally resolved asian summer monsoon dynamics 113 5 86 6 thousand years ago abstract we present a new 230th dated absolute chronology of asian summer monsoon asm variability from 113 5 to 86 6 kyr bp before 1950 ad this integrated multidecadally resolved record based on 1435 oxygen isotope data and 46 230th dates with 2 sigma errors as low as 0 3 kyr from three stalagmites collected in sanxing cave southwestern china can be a new reference for calibrating paleoclimate proxy sequences the sanxing 18o record follows the 23 kyr precessional cycle of insolation and is punctuated by prominent millennial scale oscillations of the chinese interstadials cis 25 to 22 corresponding to greenland interstadials gis 25 to 22 the onset of cis 25 24 23 and 22 is dated to 113 1 0 4 108 1 0 3 103 7 0 3 and 91 4 0 6 kyr bp in the sanxing record respectively the end of cis 24 and cis 22 is constrained to 105 5 0 4 and 87 7 0 3 kyr bp respectively a centennial scale precursor event at 104 1 0 3 kyr bp preceding cis 23 is clearly registered these events in the sanxing record are synchronous with those identified in stalagmites from the european alps nalps except for the onset of gis 25 and the end of gis 22 and differ by up to 2 3 kyr from the corresponding ones in greenland ice core records the high degree of similarity of the 18o records between sanxing cave and greenland supports a northern hemisphere forcing of the asm the anti phase relationship of 18o records between sanxing stalagmites and antarctic ice cores suggests an additional asm linkage to the southern hemisphere

evolution of the indian summer monsoon during the interval 32 7 11 4 cal ka bp evidence from the baoxiu peat yunnan southwest china abstract there have been few investigations of the phase relationship between the indian summer monsoon ism and the east asian summer monsoon easm during the last glacial period we present multi proxy mineralogical and geochemical records from a peat core taken from the baoxiu basin central yunnan southwest china to investigate changes in chemical weathering and climate associated with the ism in southwest china spanning the interval 32 7 11 4 ka bp the results suggest that the lgm period 23 18 ka bp was characterized by cold and dry climatic conditions a comparison of proxy data from baoxiu peat with other related proxy climate records reveals that broadly synchronous variations in the ism and easm on orbital timescales can be attributed to solar radiation forcing in the northern hemisphere in addition four synchronous weak millennial scale monsoonal events coincide well with cooling events recorded in the ngrip ice core corresponding to the younger dryas and heinrich events h1 h2 and h3 significantly the strengths of the two asian monsoons show an inverse relationship during the interval 23 19 ka bp probably resulting from el nino like conditions in the tropical pacific

four climate cycles of recurring deep and surface water destabilizations on the iberian margin centennial climate variability over the last ice age exhibits clear bipolar behavior high resolution analyses of marine sediment cores from the iberian margin trace a number of associated changes simultaneously proxies of sea surface temperature and water mass distribution as well as relative biomarker content demonstrate that this typical north south coupling was pervasive for the cold phases of climate during the past 420 000 years cold episodes after relatively warm and largely ice free periods occurred when the predominance of deep water formation changed from northern to southern sources these results reinforce the connection between rapid climate changes at mediterranean latitudes and century to millennial variability in northern and southern polar regions

sub decadally resolved asian monsoon dynamics during chinese interstadial 21 in response to northern high latitude climate abstract greenland interstadial 21 gis 21 one of the longest warm episodes during the last glacial period occurred at the transition from marine isotope stage mis 5a to 4 precise determination of the timing and duration of this interstadial can improve our understanding of the hydroclimatic connection between low and high latitudes across this mis boundary 18o records of two stalagmites from sanxing cave southwest china provide a sub decadally resolved record of asian summer monsoon asm evolution from 79 0 0 2 to 75 7 0 2 thousand years before present kyr bp before 1950 ce revealing the detailed structure of the chinese interstadial 21 cis 21 the replicate sanxing record for the first time captures three centennial scale intervals of strong monsoon and a 700 yr long weak monsoon period within the cis 21 rebound type event concurrent with its counterpart gis 21 this synchronicity between sw china and greenland suggests a rapid atmospheric teleconnection between the north atlantic and the asm region marked by 400 yr long decrease in asm cis 21 ended at 76 8 0 2 kyr bp which is 0 5 1 0 kyr younger than the corresponding termination of gis 21 on aicc2012 and gicc05modelext timescales given its high accuracy and precision the sanxing stalagmite chronology can serve as a benchmark for chronological refinements for ice core records

paleohydrology of the santiaguillo basin mexico since late last glacial and climate variation in southern part of western subtropical north america abstract stratigraphy geochemistry and radiocarbon dating of a succession of sediment in the santiaguillo basin central northern mexico help reconstruct the millennial scale dynamics of hydrological variability that occurred in the southern part of western subtropical north america since the late last glacial runoff was generally above average during the late last glacial from 27 to 18 ka following this interval runoff decreased and deposition of authigenic carbonate and aeolian transported sediment increased until 4 ka heinrich 1 and 2 and younger dryas were intervals of reduced runoff and increased aeolian activity the wetter climate of central northern mexico and arid conditions in north northwestern mexico during the late last glacial were probably related to formation of tropical cyclones in the eastern north pacific during the autumn with restricted rainfall swaths and an absent weaker north american monsoon enhanced north american monsoon and tropical cyclones with expanded rainfall swaths brought more summer and autumn precipitation to a broader region extending from the central northern mexico to the continental interiors of southwestern us during the early holocene

prolonged warming of the brazil current precedes deglaciations abstract paleoceanographic reconstructions from the brazil current are scarce and lack the required temporal resolution to appropriately represent its variability during key periods of the last glacial interglacial cycles here we present the first high temporal resolution multiproxy reconstruction of the brazil current at 24 s covering the last 185 ka during the last and penultimate glacial periods our mg ca derived sea surface temperature sst record shows a strong cooling at ca 47 and ca 156 ka respectively that is followed by a warming trend from late marine isotope stage mis 3 to mis 1 and from late mis 6 to mis5e respectively importantly the brazil current warmed uninterruptedly towards termination i ii after the low sst at ca 47 and ca 156 ka with no sst minima during the last glacial maximum or penultimate glacial maximum the reason for the strong cooling and the warming trend during late mis 3 and late mis 6 could reside in the favorable obliquity configuration however this mechanism is not sufficient to sustain the warming observed for the rest of the last and penultimate glacial periods we propose that the change in the atlantic meridional overturning circulation amoc as described in the literature from a warm to a cold mode for mis 2 and mis 6 is responsible for the accumulation of warm waters in the subtropical western south atlantic preventing sst minima during the last and penultimate glacial maxima in the region change in benthic 13 c corroborates that a fundamental modification in the amoc mode might have triggered the heat accumulation our data also show a sudden increase in sst and surface salinity during the last glacial descent mis 4 indicating that the western portion of the subtropical gyres may have acted as a heat and salt reservoir while higher latitude climates transited to a glacial background our findings imply that the amoc cold mode induces heat storage in the subtropical western south atlantic and because of that the last two regional sst minima occurred out of phase with the glacial maxima of higher latitudes

holocene climate change in central eastern brazil reconstructed using pollen and geochemical records of pau de fruta mire serra do espinhaco meridional minas gerais abstract studies dealing with the reconstruction of holocene climate change of tropical areas are scarce of these multi proxy investigations using peatlands are still absent in this paper we present the holocene record of environmental changes in central eastern brazil reconstructed from a core sampled in pau de fruta mire serra do espinhaco meridional brazil we combined palynological and geochemical analyses supported by core stratigraphy 14 c dating and multivariate statistics the location of the mire is ideal because it is in an area which is directly associated with the south atlantic convergence zone sacz six main phases of change suggested by vegetation and local and regional landscape dynamics were described in phase i 10 000 7360 cal yr bp the climate was very wet and cold and was accompanied by soil instability in the mire catchment severe local erosion and the 8 2 ka event was easily recognizable by a large increase in the deposition of regional dust phase ii 7360 4200 cal yr bp was characterized by wet and warm conditions catchment soil stability and enhanced deposition of regional dust in phase iii 4200 2200 cal yr bp climate was dry and warm and soil erosion in the catchment increased again in phase iv 2200 1160 cal yr bp dry and punctuated cooling was reconstructed together with enhanced deposition of regional dust phase v 1160 400 cal yr bp reflects sub humid climatic conditions like the current climate the lowest inputs of local and regional dust and the largest accumulation of peat in the mire while in phase vi

two phase structure of tropical hydroclimate during heinrich stadial 1 and its global implications abstract previous studies have proposed that the two phase structure of heinrich stadial 1 hs1 is a ubiquitous feature however few studies have focused on the internal structure of hs1 over a tropical domain thus the interhemispheric ocean atmosphere teleconnections during hs1 are poorly defined here we present high resolution sedimentological geochemical and palaeoceanographic records from the core cg2 in the southern south china sea scs off the northern sunda shelf the core continuously spans 9 0 22 0 ky bp the records suggest two episodes of increased monsoon rainfall during the pre hs1 19 0 18 0 ky bp and in the early hs1 17 5 16 1 ky bp along with a weaker monsoon rainfall during the late hs1 16 1 14 7 ky bp in contrast a lower precipitation over the flores sea occurred during the early hs1 off the southern sunda shelf followed by an enhanced precipitation runoff during the late hs1 muller et al 2012 notably these two different precipitation phases characterise a southward intertropical convergence zone itcz shift over the sunda shelf during hs1 these changes are also consistent with other monsoon records as well as other available data from the tropical to high latitudes of both hemispheres supporting the global scope of the twofold hs1 we propose that the two episodes of intense monsoon rainfall over the northern sunda shelf during the pre hs1 and the early hs1 observed in our study are closely linked to two different melting events associated with european ice sheet eis retreat we further propose that the subsequent maximum atlantic meridional overturning circulation amoc reduction and the migration of the itcz to its southernmost position during the late hs1 are tightly connected with the destabilization of the marine terminating ice streams of the laurentide ice sheet lis in the north atlantic tropical positive feedbacks during hs1 in turn should have played an important role in sustaining the amoc reduction and northern hemisphere nh stadial conditions by continuously lowering the salinity of the low latitude currents in the atlantic ocean in addition the tropical itcz appears to have been a key bridge in promoting interhemispheric climate connections by which north atlantic cooling was rapidly linked to increased southern ocean surface westerlies this in turn drove upwelling and co2 ventilation from the southern ocean and thereby facilitated deglacial warming finally these findings show that tropical climate variation is an important component of deglacial climate changes understanding how it responds to millennial events like hs1 may help us better understand global teleconnections

millennial to orbital scale variations of drought intensity in the eastern mediterranean abstract millennial to orbital scale rainfall changes in the mediterranean region and corresponding variations in vegetation patterns were the result of large scale atmospheric reorganizations in spite of recent efforts to reconstruct this variability using a range of proxy archives the underlying physical mechanisms have remained elusive through the analysis of a new high resolution sedimentary section from lake van turkey along with climate modeling experiments we identify massive droughts in the eastern mediterranean for the past four glacial cycles which have a pervasive link with known intervals of enhanced north atlantic glacial iceberg calving weaker atlantic meridional overturning circulation and dansgaard oeschger cold conditions on orbital timescales the topographic effect of large northern hemisphere ice sheets and periods with minimum insolation seasonality further exacerbated drought intensities by suppressing both summer and winter precipitation

the tectonic and climatic evolution of the arabian sea region over long periods of time the tectonic evolution of the solid earth has been recognized as the major control on the development of the global climate system tectonic activity acts in one of two different ways to influence regional and global climate i through the opening and closing of oceanic gateways and its effect on the circulation patterns in the global ocean ii through the growth and erosion of orogenic belts resulting in changes in oceanic chemistry and disruption of atmospheric circulation the arabian sea region has several features that make it the best area for studies of climate and palaeoceanographic responses to tectonic activity most notably in the context of the south asian monsoon and its relationship to the growth of high topography in the adjacent himalayas and tibet the tectonic and climatic evolution of the arabian sea region brings together a collection of recent studies on the area from a wide group of international contributors the paper range from high resolution holocene palaeoceanographic studies of the pakistan margin to regional tectonic reconstructions of the ocean basin and surrounding margins throughout the cenozoic marine geophysics stratigraphy isotope chemistry and neotectonics come together in a multidisciplinary approach to the study of interactions of land and sea while much work remains to be done to understand fully the tectonic and climatic evolution of the arabian sea a great deal has been achieved since the last major review as detailed in the 26 contributions this volume is essential reading for palaeoceanographers sedimentologists and geophysicists it will also be interest to structural geologists and those working in the petroleum industry

atlantic ocean circulation changes preceded millennial tropical south america rainfall events during the last glacial during the last glacial period greenland s climate shifted between cold stadial and warm interstadial phases that were accompanied by ocean circulation changes characterized by reduced atlantic meridional overturning circulation amoc during stadials here we present new data from the western tropical atlantic demonstrating that amoc slowdowns preceded some of the large south american rainfall events that took place during stadials based on 231pa 230th and ti ca measurements in the same sediment core we determine that the amoc started to slowdown 1420 250 and 690 180 1 years before the onset of two large precipitation events associated with heinrich stadials our results bring unprecedented evidence that amoc changes could be at the origin of the large precipitation events observed in tropical south america during heinrich stadials in addition we propose a mechanism explaining the differences in the extent and timing of amoc slowdowns associated with shorter and longer stadials

glacial fluctuations in tropical africa during the last glacial termination and implications for tropical climate following the last glacial maximum abstract the tropics are a dynamic component of the global climate system and exert a profound influence on modern climate variability yet the role of the tropics in past climate changes for example during the last glacial termination is uncertain this uncertainty is due in part to the relative paucity of terrestrial temperature records from the tropics which hinders efforts to understand the mechanisms that influenced deglacial warming and abrupt climate events tropical glaciers are sensitive to changes in climate and mapping and dating past tropical glacial fluctuations provides a valuable record of terrestrial climate changes in the low latitudes we report a chronology of past glacial extents in the rwenzori mountains of uganda 0 3 n 29 9 e based on 51 beryllium 10 10be surface exposure ages from three separate glacial catchments results indicate that rwenzori glaciers retreated considerably during heinrich stadial 1 the rate of net glacial recession slowed between 15 and 11 ka although glaciers continued to retreat during this period rwenzori glaciers then retreated more rapidly during the early holocene the rwenzori glacial chronology is broadly similar to glacial chronologies reconstructed elsewhere in east africa and in tropical south america we suggest that this similarity may reflect coherent tropics wide temperature fluctuations during the last deglaciation the rwenzori glacial chronology provides crucial information on the global footprint of deglacial warming and abrupt climate events and thus the potential mechanisms that influenced tropical climate during the last glacial termination

punctuated asm strengthening in late heinrich stadial from speleothem records southern china the dynamical adjustment process dap is a requisite for climate system to arrange for a new equilibrium state to evaluate the detailed structure of dap during heinrich stadial hs high resolution speleothem based asian summer monsoon asm variability was reconstructed separately covering hss 5 to 1 in these calcite 18o records a gradual increase of asm intensity is evident in each mid hs followed by a centennial scale asm stability lasting on average 590 years during late hs at this time 18o values decrease by 1 about 50 of the total hs compared with maximum values in early hs this structure of monsoonal hs in speleothem records is not reflected in temperature variations at the greenland but is well mirrored in middle to low latitudes within the northern hemisphere and even southern oceanic records it suggests that southern and low latitude climate conditions are likely important for the termination of hs thus a dap of about 400 600 years is a precondition for the asm sub system to prepare for a new equilibrium

a high resolution temporal record of environmental changes in the eastern caribbean guadeloupe from 40 to 10 ka bp abstract in neotropical regions fossil bat guano accumulated over time as laminated layers in caves hence providing a high resolution temporal record of terrestrial environmental changes additionally cave settings have the property to preserve such organic sediments from processes triggered by winds deflation abrasion and sandblasting and intense rainfall leaching away this study reports both stable carbon and nitrogen isotope compositions of frugivorous bat guano deposited in a well preserved stratigraphic succession of blanchard cave on marie galante guadeloupe these isotopic data are discussed with regard to climate changes and its specific impact on eastern caribbean vegetation during the late pleistocene from 40 to 10 ka cal bp guano 13 c values are higher than modern ones suggesting noticeable vegetation changes this provides also evidence for overall drier environmental conditions during the pleistocene compared to today meanwhile within this generally drier climate shifts between wetter and drier conditions can be observed large temporal amplitudes in both 13 c and 15 n variations reaching up to 5 9 and 16 8 respectively also indicate these oceanic tropical environments have been highly sensitive to regional or global climatic forcing stable isotope compositions of bat guano deposited from 40 to 35 ka bp the last glacial maximum and the younger dryas reveal relatively wet environmental conditions whereas at least from the end of the heinrich event 1 and the bolling period the region experienced drier environmental conditions nevertheless when considering uncertainties in the model age the isotopic record of blanchard cave show relatively similar variations with known proxy records from the northern south america and central america suggesting thus that the blanchard cave record is a robust proxy of past itcz migration teleconnections through global atmospheric pattern suggest that islands of the eastern caribbean basin could be also under the influence of a bipolar temperature gradients that impact the mean location of the itcz with a southern hemisphere imprint during the glacial period and a more significant role of northern hemisphere during the last deglaciation

brief interstadial events in the santa barbara basin ne pacific during the past 60 kyr the instability of the northern hemisphere glacial climate over the past 100 kyr has been revealed by at least 20 brief warm interstadial episodes called dansgaard oeschger events recorded in greenland ice cores1 3 and in north atlantic sedimentary records4 5 a few of these events have been recognized elsewhere6 8 here we describe a record of ocean oxygenation and circulation from the santa barbara basin in the northeast pacific ocean which correlates well with the greenland ice core records we see 19 of the 20 dansgaard oeschger events in the form of laminated sediments deposited under anoxic conditions and we can correlate at least 16 of these with the 17 ice core interstadials of the past 60 kyr thus these short term events were not restricted to the north atlantic region the events had substantial ecological and oceanographic effects in the santa barbara basin including changes in benthic faunal populations and in the age and composition of bottom waters similar ventilation changes have been seen in the gulf of california9 10 suggesting that these changes may have been widespread and synchronous along the northeast pacific margin these results suggest sensitivity of broad areas of the ocean atmosphere cryosphere system to short term climate change

atlantic ocean modulated hydroclimate of the subtropical northeastern mexico since the last glacial maximum and comparison with the southern us abstract proxy records generated from chemical composition and radiocarbon dating of a sediment sequence collected from the el potosi basin provide information about variable hydroclimate of the subtropical northeastern mexico since the last glacial maximum lgm minimal amounts of runoff and more carbonate deposition during 19 ka represent the lgm the deglaciation was wetter compared to the lgm and enhanced runoff during 19 12 ka transported more ti bearing clastics from a relatively humid watershed over the deglaciation the basin received more runoff during the bolling allerod compared to the heinrich stadial 1 and younger dryas reduction in the amount of runoff during 10 1 ka and deposition of unweathered si bearing clastics during 4 1 ka suggest that the holocene was drier compared to the deglaciation hydroclimates of the northeastern mexico and southern us were synchronous during the lgm as well as deglaciation change from the drier lgm to wetter bolling allerod occurred as the gulf of mexico became warmer and the region received more summer precipitation however the dissimilarities observed in regional hydroclimates of the holocene need further evaluation

monsoons itczs and the concept of the global monsoon earth s tropical and subtropical rainbands such as intertropical convergence zones itczs and monsoons are complex systems governed by both large scale constraints on the atmospheric general circulation and regional interactions with continents and orography and coupled to the ocean monsoons have historically been considered as regional large scale sea breeze circulations driven by land sea contrast more recently a perspective has emerged of a global monsoon a global scale solstitial mode that dominates the annual variation of tropical and subtropical precipitation this results from the seasonal variation of the global tropical atmospheric overturning and migration of the associated convergence zone regional subsystems are embedded in this global monsoon localized by surface boundary conditions parallel with this much theoretical progress has been made on the fundamental dynamics of the seasonal hadley cells and convergence zones via the use of hierarchical modeling approaches including aquaplanets here we review the theoretical progress made and explore the extent to which these advances can help synthesize theory with observations to better understand differing characteristics of regional monsoons and their responses to certain forcings after summarizing the dynamical and energetic balances that distinguish an itcz from a monsoon we show that this theoretical framework provides strong support for the migrating convergence zone picture and allows constraints on the circulation to be identified via the momentum and energy budgets limitations of current theories are discussed including the need for a better understanding of the influence of zonal asymmetries and transients on the large scale tropical circulation

coherent resonant millennial scale climate oscillations triggered by massive meltwater pulses the role of mean and stochastic freshwater forcing on the generation of millennial scale climate variability in the north atlantic is studied using a low order coupled atmosphere ocean sea ice model it is shown that millennial scale oscillations can be excited stochastically when the north atlantic ocean is fresh enough this finding is used in order to interpret the aftermath of massive iceberg surges heinrich events in the glacial north atlantic which are characterized by an excitation of dansgaard oeschger events based on model results it is hypothesized that heinrich events trigger dansgaard oeschger cycles and that furthermore the occurrence of heinrich events is dependent on the accumulated climatic effect of a series of dansgaard oeschger events this scenario leads to a coupled ocean ice sheet oscillation that shares many similarities with the bond cycle further sensitivity experiments reveal that the timescale of the oscillations can be decomposed into stochastic linear and nonlinear deterministic components a schematic bifurcation diagram is used to compare theoretical results with paleoclimatic data

variation of the asian summer monsoon since the last glacial interglacial recorded in a stalagmite from southwest china abstract a number of studies proposed a close link between the climate changes in the asian summer monsoon asm the southern hemisphere sh and high latitudes of the northern hemisphere nh but the mechanisms is still an open question although speleothems 18o records have displayed excellent values in the reconstruction of paleoclimate change at centennial millennial to orbital timescales the significance of speleothems 18o and 13c is still debatable here a high precise 230th dated stalagmite from southwestern china was used to reconstruct the changes of asm and regional hydrological conditions since the last interglacial 3 6 118 1 ka bp by the coupled 18o and 13c we found 1 the easm and ism are synchronous changing on the orbital timescale responding to the change of north hemisphere summer insolation nhsi and high latitude climate change there is a teleconnection between antarctic temperature change and asm through the mascarene high and the somali jet 2 during mis 5d the stalagmite 18o in yangzi cave is nearly 1 5 higher than that in mis 2 the maximum of last glacial this should be attributed to the different isotopic compositions in moisture source of ism and easm and the dynamic changes of monsoon circulations 3 from mis 3 to mis 2 the asm showed a stepped pattern in weakening consistent with the decreasing nhsi and increasing global ice volume 4 the changes in stalagmite 13c indicated the changes of local hydrological conditions and closely correlated with climate changes revealed by stalagmite 18o the effective humidity which determined by temperature evaporation and precipitation dominated the regional hydrological conditions the change of effective humidity recorded in stalagmite 13c by influencing surface biomass and soil co2 production

caribbean hydroclimate and vegetation history across the last glacial period abstract we present a new speleothem trace element and stable isotope record which extends previous paleoclimate evidence from cuban speleothems to the last 96 ka multiple proxies were used to reconstruct caribbean hydroclimate and vegetation variability on orbital to millennial timescales in particular our proxies indicate a shift to more abundant c4 compared to c3 vegetation and or reduced soil activity during the last glacial maximum our results confirm the close link of caribbean precipitation to north atlantic climate variability insolation and the strength of the amoc the associated variations in caribbean ssts and the shift of the itcz led to substantial changes of the hydrological cycle during heinrich stadials and the younger dryas climatic conditions in cuba were comparably cool and or dry in contrast warm dansgaard oeschger cycles were accompanied by wetter conditions this is in agreement with previous evidence for the holocene when north atlantic cold warm events coincided with drier wetter conditions in cuba however our record suggests that this connection was less dominant during mis 4 to 2 displayed by a weaker response of cuban precipitation proxies to north atlantic climatic shifts than during mis 5 in particular we hypothesize that this weaker connection was mediated by the southerly shifted itcz inducing a weakening of the northern branch of the caribbean low level jet which usually transports moisture into the northern caribbean this is strikingly evident during the deglacial when driest and or coolest conditions prevailed in western cuba from hs 1 into the younger dryas including the bolling allerod interstadial

varve microfacies and varve preservation record of climate change and human impact for the last 6000 years at lake tiefer see ne germany the holocene sediment record of lake tiefer see exhibits striking alternations between well varved and non varved intervals here we present a high resolution multi proxy record for the past 6000

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

a 0 6 million year record of millennial scale climate variability in the tropics a 600 kyr long scanning x ray fluorescence record of redox variability from the cariaco basin venezuela provides insight into rapid climate change in the tropics over the past five glacial interglacial cycles variations in the sediment accumulation of the redox sensitive element molybdenum mo can be linked to changes in intertropical convergence zone migration and reveal that millennial scale variability is a persistent feature of tropical climate over the past 600 kyr including during periods of interglacial warmth this new record supports the idea that high frequency tropical climate variability is not controlled solely by ice volume changes with implications for the role of high latitude forcing of intertropical convergence zone position and tropical hydrology on millennial timescales

spatial temporal differentiation of eolian sediments in the yarlung tsangpo catchment tibetan plateau and response to global climate change since the last glaciation abstract eolian sediments an important paleoenvironmental archive are widespread in the yarlung tsangpo river ytr valley of the southern tibetan plateau tp but their chronology and spatial temporal differentiation are poorly understood and it is not clear whether eolian accumulation is controlled by global climate changes or local paleoenvironment or both in this study we applied quartz osl dating to 30 eolian sediment samples sandy loess and eolian sand from eight profiles in the ytr catchment our new dates were combined with 72 previously published eolian sediment ages osl tl and 14c for the ytr catchment to analyze the response of eolian accumulation to paleoenvironmental changes the overall dataset has eolian accumulation spanning the period from the last interglacial through to the little ice age ranging from 84 6 8 7 ka bp possibly as old as 118 11 ka bp to 0 4 0 1 ka bp with most occurring since the late glacial period 15 ka bp which suggests that the preservation of eolian deposits is controlled by geologic recirculation probability density function distributions pdfs of eolian ages from different parts of the ytr catchment show different age clusters suggesting that factors controlling eolian accumulation vary across the catchment so that spatial temporal disparities are inherent in the system to investigate the effect of regional and global paleoclimate since the last glacial maximum lgm on eolian deposition processes in the ytr we compared the pdf of ages from the combined dataset with a range of paleoclimate proxies the pdf shows significant fluctuations since the lgm including the younger dryas cold event there is no consistent eolian sediment response to changes of the 30 n summer insolation asian summer monsoon and westerlies phases of strong eolian sediment accumulation in the ytr basin do not show a simple correspondence with the classical global climate curve suggesting that eolian processes in the alpine valley environment may be modified by local responses to these changes

can north atlantic sea ice anomalies account for dansgaard oeschger climate signals abstract north atlantic sea ice anomalies are thought to play an important role in the abrupt dansgaard oeschger d o cycles of the last glacial period this model study investigates the impacts of changes in north atlantic sea ice extent in glacial climates to help provide geographical constraints on their involvement in d o cycles based on a coupled climate model simulation of the last glacial maximum 21 ka the nordic seas and western north atlantic broadly south of greenland are identified as two plausible regions for large and persistent displacements of the sea ice edge in the glacial north atlantic sea ice retreat scenarios targeting these regions are designed to represent ice cover changes associated with the cold to warm stadial to interstadial transitions of d o cycles the atmospheric responses to sea ice retreat in the nordic seas and in the western north atlantic are tested individually and together using an atmospheric general circulation model the nordic seas ice retreat causes 1

timing and duration of the east asian summer monsoon maximum during the holocene based on stalagmite data from north china we present a continuous c o isotope series that shows the detailed variability of east asian summer monsoon easm since 11 0 ka bp the series is based on two stalagmites namely dsy1 and lm2 wh

three phased heinrich stadial 4 recorded in ne brazil stalagmites abstract the growth intervals of stalagmites from northeast ne brazil provide precise information on the timing of pluvial periods associated with the southward shift of the intertropical convergence zone itcz during heinrich stadials hs using 230th dating and annual band counting we constrained the timing of the pluvial period associated with hs4 to occur between 40 06 0 11 and 38 38 0 10 thousand years before present kyr b p coinciding with the interval between the end of greenland interstadial gis chinese interstadial cis 9 and gis cis 8 oxygen isotope analysis shows a close anti correlation between ne brazil wet periods and east asian monsoon intensity recorded in hulu cave supporting the hypothesis of a southerly migration of the global itcz during hs4 the pluvial anomaly can be divided into three phases starting with a precursor less intense pluvial interval phase 1 between 40 06 0 11 and 39 59 0 10 kyr b p likely correlative to the cool phase of the north atlantic immediately before the partial collapse of the laurentide ice sheet lis this phase ends abruptly

high resolution greenland ice core data show abrupt climate change happens in few years the last two abrupt warmings at the onset of our present warm interglacial period interrupted by the younger dryas cooling event were investigated at high temporal resolution from the north greenland ice core project ice core the deuterium excess a proxy of greenland precipitation moisture source switched mode within 1 to 3 years over these transitions and initiated a more gradual change over 50 years of the greenland air temperature as recorded by stable water isotopes the onsets of both abrupt greenland warmings were slightly preceded by decreasing greenland dust deposition reflecting the wetting of asian deserts a northern shift of the intertropical convergence zone could be the trigger of these abrupt shifts of northern hemisphere atmospheric circulation resulting in changes of 2 to 4 kelvin in greenland moisture source temperature from one year to the next

hydrology and climatology at laguna la gaiba lowland bolivia complex responses to climatic forcings over the last 25 000 years diatom geochemical and isotopic data provide a record of environmental change in laguna la gaiba lowland bolivia 17 45 s 57 35 w over the last ca 25 000 years high resolution diatom analysis around the last glacial interglacial transition provides new insights into this period of change the full and late glacial lake was generally quite shallow but with evidence of periodic flooding at about 13 100 cal a bp just before the start of the younger dryas chronozone the diatoms indicate shallower water conditions but there is a marked change at about 12 200 cal a bp indicating the onset of a period of high variability with rising water levels punctuated by periodic drying from ca 11 800 to 10 000 cal a bp stable deeper water conditions persisted there is evidence for drying in the early to middle holocene but not as pronounced as that reported from elsewhere in the southern hemisphere tropics of south america this was followed by the onset of wetter conditions in the late holocene consistent with insolation forcing conditions very similar to present were established about 2100 cal a bp a complex response to both insolation forcing and millennial scale events originating in the north atlantic is noted

near collapse of the meridional sst gradient in the eastern equatorial pacific during heinrich stadial 1 1 sea surface temperatures sst and inorganic continental input over the last 25 000 years 25 ka are reconstructed in the far eastern equatorial pacific eep based on three cores stretching from the equatorial front 0 01 n me0005 24jc into the cold tongue region 3 6 s tr163 31p and v19 30 we revisit previously published alkenone derived sst records for these sites and present a revised chronology for v19 30 inorganic continental input is quantified at all three sites based on 230th normalized fluxes of the long lived continental isotope thorium 232 and interpreted to be largely dust our data show a very weak meridional cross equatorial sst gradient during heinrich stadial 1 hs1 18 15 ka b p and high dust input along with peak export production at and north of the equator these findings are corroborated by an earth system model experiment for hs1 that simulates intensified northeasterly trade winds in the eep stronger equatorial upwelling and surface cooling furthermore the related southward shift of the intertropical convergence zone itcz during hs1 is also indicative of drier conditions in the typical source regions for dust

hemispherically asymmetric trade wind changes as signatures of past itcz shifts abstract the atmospheric hadley cells which meet at the intertropical convergence zone itcz play critical roles in transporting heat driving ocean circulation and supplying precipitation to the most heavily populated regions of the globe paleo reconstructions can provide concrete evidence of how these major features of the atmospheric circulation can change in response to climate perturbations while most such reconstructions have focused on itcz related rainfall here we show that trade wind proxies can document dynamical aspects of meridional itcz shifts theoretical expectations based on angular momentum constraints and results from freshwater hosing simulations with two different climate models predict that itcz shifts due to anomalous cooling of one hemisphere would be accompanied by a strengthening of the hadley cell and trade winds in the colder hemisphere with an opposite response in the warmer hemisphere this expectation of hemispherically asymmetric trade wind changes is confirmed by proxy data of coastal upwelling and windblown dust from the atlantic basin during heinrich stadials showing trade wind strengthening in the northern hemisphere and weakening in the southern hemisphere subtropics in concert with southward itcz shifts data from other basins show broadly similar patterns though improved constraints on past trade wind changes are needed outside the atlantic basin the asymmetric trade wind changes identified here suggest that itcz shifts are also marked by intensification of the ocean s wind driven subtropical cells in the cooler hemisphere and a weakening in the warmer hemisphere which induces cross equatorial oceanic heat transport into the colder hemisphere this response would be expected to prevent extreme meridional itcz shifts in response to asymmetric heating or cooling understanding trade wind changes and their coupling to cross equatorial ocean cells is key to better constraining itcz shifts and ocean and atmosphere dynamical changes in the past especially for regions and time periods for which few paleodata exist and also improves our understanding of what changes may occur in the future

tropical rainforest dynamics and palaeoclimate implications since the late pleistocene nilgiris india a multiproxy study involving sedimentology palynology radiocarbon dating stable isotopes and geochemistry was carried out on the parsons valley lake deposit nilgiris india to determine palaeoclimatic fluctuations and their possible impact on vegetation since the late pleistocene the 72 cm deep sediment core that was retrieved reveals five distinct palaeoclimatic phases 1 warm and humid conditions with a high lake stand before the last glacial maximum lgm 29 800 cal yr bp subsequently changing to a relatively cool and dry phase during the lgm 2 considerable dry conditions and lower precipitation occurred between 16 300 and 9500 cal yr bp during this period the vegetation shrank and perhaps was confined to moister pockets or was a riparian forest cover 3 an outbreak in the shift of monsoonal precipitation was witnessed in the beginning of the mid holocene around 8400 cal yr bp implying alteration in the shift toward warm and humid conditions resulting in relatively high pollen abundance for evergreen taxa 4 this phase exhibits a shift to heavier 13 c values around 1850 cal yr bp with an emergence of moist deciduous plants pointing to drier conditions 5 human activities contributed to the exceedingly high percentage of acacia and pinus pollen during the little ice age

east asian hydroclimate modulated by the position of the westerlies during termination i speleothem oxygen isotope records have revolutionized our understanding of the paleo east asian monsoon yet there is fundamental disagreement on what they represent in terms of the hydroclimate changes we report a multiproxy speleothem record of monsoon evolution during the last deglaciation from the middle yangtze region which indicates a wetter central eastern china during north atlantic cooling episodes despite the oxygen isotopic record suggesting a weaker monsoon we show that this apparent contradiction can be resolved if the changes are interpreted as a lengthening of the meiyu rains and shortened post meiyu stage in accordance with a recent hypothesis model simulations support this interpretation and further reveal the role of the westerlies in communicating the north atlantic influence to the east asian climate

a 3000 yr annually laminated stalagmite record of the last glacial maximum from hulu cave china abstract a high resolution annual layer counted and 230 th dated multi proxy record is constructed from a stalagmite in hulu cave china these proxies including 18 o annual layer thickness alt gray level gl and sr ca cover a time span of 3000 yr from 21 to 24 ka the physical proxies alt and gl and the geochemical index sr ca all primarily reflecting karst hydrological processes vary in concert and their coherence is supported by wavelet analyses variations in the 18 o data agree with fluctuations in the alt and sr ca records on multi decadal to centennial scales suggesting that the hulu 18 o signal is strongly associated with varying local rainfall amounts on short timescales a monsoon failure event at 22 2 ka correlates with a decrease in tropical rainfall a reduction in global ch 4 and an ice rafted event in the north atlantic this correlation highlights roles of the asian monsoon and tropical hydrological cycle in modulating global ch 4 because the high latitude emission was inhibited during the last glacial maximum lgm spectral analysis of the 18 o record displays peaks at periodicities of 139 59 53 43 30 23 and 19 15 yr the absence of typical centennial solar cycles may be related to muted changes in ocean circulation during the lgm

oceanic link between abrupt changes in the north atlantic ocean and the african monsoon abrupt changes in the african monsoon which have been recorded throughout the late pleistocene and early holocene epochs tend to coincide with changes in north atlantic thermohaline circulation a numerical simulation shows that the interaction between thermohaline circulation in the north atlantic ocean and wind driven currents in the topical atlantic ocean contributes to the rapidity of african monsoon transitions during abrupt climate change events

warm pool hydrological and terrestrial variability near southern papua new guinea over the past 50k here we presenta 50k archiveof u37 seasurface temperature sst planktic foraminifera oxygen isotopes and terrestrial input indicators including branched and isoprenoid tetraether bit biomarkers 232 th activity and non biogenic sediment components recorded in core md052928 from the wpwp near southern papua new guinea png the planktic foraminifer oxygen isotopes in the core show millennial scale changes indicating fresher seawater during the nh cold periods i e heinrich events hes and suggesting hydrological changes that are most likely linked to the strength of the boreal winter asian australian monsoon aam our observations are corroborated by evidence from the same core that indicates increased terrestrial input caused by higher precipitation on land and more river runoff from southern png during the cold periods consistent with other nearby hydrological records from land our study indicates persistent millennial scale hydrological changes within the past 50k in the western tropical pacific and southeast asia the timing of the millennial scale changes appears to have been determined by the latitudinal displacement of the intertropical convergencezone itcz thatreflectsahistoryofheattrans

organic matter enrichment and hydrocarbon accumulation models of the marlstone in the shulu sag bohai bay basin northern china abstract hybrid unconventional systems are composed of juxtaposed organic rich and organic lean intervals organic matter enrichment hydrocarbon migration and the spatial relationship of source rocks and reservoirs have important influences on differential hydrocarbon accumulation within the system most studies have ignored the complexity of hydrocarbon accumulation in unconventional oil reservoirs a typical hybrid lithology system with a combination of marlstone and rudstone has been discovered in the lower part of the third member of the shahejie formation of the shulu sag bohai bay basin northern china the basin showcases a strong heterogeneity in unconventional hydrocarbon production and is an appropriate case to study hydrocarbon accumulation within hybrid unconventional systems however relevant work in the study area was scarce a study of the mechanisms of organic matter enrichment and hydrocarbon accumulation was required to understand the heterogeneity of the oil reservoirs nine units in ascending order namely il iu iil iiu iiil iiiu iv vl and vu were proposed in this study a detailed geochemical analysis was carried out to distinguish the organic matter sources and preservation conditions among the different units and assess the migration patterns of the hydrocarbons the results show that unit iil has the highest total organic carbon toc content unit iil has a higher quantity of aquatic sourced organic matter with relatively high abundance of short chain n alkanes c27 c29 sterane and 4 methyl steranes based on the low ratios of pristane to phytane the varve like lamination structure of the lithology and suitable salinity we can speculate that good organic matter preservation conditions existed in unit iil maturity of the source rocks increases with depth biomarkers indicate that hydrocarbons within the marlstones were retained in situ whereas hydrocarbons within the rudstones were derived from source rocks via short or long distance migrations fractures can act as effective pathways for hydrocarbon migration organic matter sources preservation conditions maturity and hydrocarbon migration ways jointly controlled the formation of oil reservoirs in the shulu sag the results of this study provide a better understanding of organic matter enrichment and hydrocarbon accumulation and guide further exploration in the basin

a compilation of western european terrestrial records 60 8 ka bp towards an understanding of latitudinal climatic gradients terrestrial records of past climatic conditions such as lake sediments and speleothems provide data of great importance for understanding environmental changes however unlike marine and ice core records terrestrial palaeodata are often not available in databases or in a format that is easily accessible to the non specialist as a consequence many excellent terrestrial records are unknown to the broader palaeoclimate community and are not included in compilations comparisons or modelling exercises here we present a compilation of western european terrestrial palaeo records covering entirely or partially the 60 8 ka intimate time period the compilation contains 56 natural archives including lake records speleothems ice cores and terrestrial proxies in marine records the compilation is limited to include records of high temporal resolution and or records that provide climate proxies or quantitative reconstructions of environmental parameters such as temperature or precipitation and that are of relevance and interest to a broader community we briefly review the different types of terrestrial archives their respective proxies their interpretation and their application for palaeoclimatic reconstructions we also discuss the importance of independent chronologies and the issue of record synchronization the aim of this exercise is to provide the wider palaeo community with a consistent compilation of high quality terrestrial records to facilitate model data comparisons and to identify key areas of interest for future investigations we use the compilation to investigate western european latitudinal climate gradients during the deglacial period and despite of poorly constrained chronologies for the older records we summarize the main results obtained from nw and sw european terrestrial records before the lgm

thermal response of the western tropical atlantic to slowdown of the atlantic meridional overturning circulation abstract the western tropical atlantic plays an important role in the interhemispheric redistribution of heat during millennial scale changes in the strength of the atlantic meridional overturning circulation amoc the proper evaluation of this role depends on a clear understanding of sea surface temperature sst variations during amoc slowdown periods like heinrich stadials hs in the western tropical atlantic however published sst records from the western tropical atlantic between ca 4 s and 7 n show inconsistencies that are apparently related to the employed temperature proxy i e mg ca versus alkenone unsaturation index u 37 k in general while mg ca values indicate warming during heinrich stadials u 37 k values show cooling to assess this issue we sampled core geob16224 1 retrieved off french guiana i e 6 39 38 n and reconstructed water temperatures at high resolution using mg ca on the foraminifera species globigerinoides ruber u 37 k tex86 and modern analogue technique mat transfer functions using planktonic foraminifera assemblages calibrated for 50 m water depth our results show that mg ca and tex86 values recorded an increase in sst related to amoc slowdown conversely u 37 k and mat values registered a decrease in temperatures during hs3 and hs1 our u 37 k and mg ca results thus confirm the previously reported inconsistency for the period between 48 13 cal ka bp we suggest that several non thermal physiological effects probably imparted a negative temperature bias on the u 37 k temperatures during heinrich stadials however mat based temperatures show similar variability with u 37 k based temperatures hence we also suggest that during severe slowdown periods of the amoc a steeper meridional temperature gradient together with a southward shift of the intertropical convergent zone produced not only an increase in sst but also a stronger upper water column stratification and a shoaling of the thermocline decreasing subsurface temperatures our new high resolution temperature records allow a better characterization of the thermal response of the upper water column in the tropical western atlantic to slowdown events of the amoc reconciling previously discrepant records

tropical air sea interactions accelerate the recovery of the atlantic meridional overturning circulation after a major shutdown abstract using a coupled ocean sea ice atmosphere model of intermediate complexity the authors study the influence of air sea interactions on the stability of the atlantic meridional overturning circulation amoc mimicking glacial heinrich events a complete shutdown of the amoc is triggered by the delivery of anomalous freshwater forcing to the northern north atlantic analysis of fully and partially coupled freshwater perturbation experiments under glacial conditions shows that associated changes of the heat transport in the north atlantic lead to a cooling north of the thermal equator and an associated strengthening of the northeasterly trade winds because of advection of cold air and an intensification of the trade winds the intertropical convergence zone itcz is shifted southward changes of the accumulated precipitation lead to the generation of a positive salinity anomaly in the northern tropical atlantic and a negative anomaly in the southern tropical atlantic during the shutdown phase of

abrupt climate change an alternative view hypotheses and inferences concerning the nature of abrupt climate change exemplified by the dansgaard oeschger d o events are reviewed there is little concrete evidence that these events are more than a regional greenland phenomenon the partial coherence of ice core y 18 o and ch4 is a possible exception claims however of d o presence in most remote locations cannot be distinguished from the hypothesis that many regions are just exhibiting temporal variability in climate proxies with approximately similar frequency content further suggestions that d o events in greenland are generated by shifts in the north atlantic ocean circulation seem highly implausible given the weak contribution of the high latitude ocean to the meridional flux of heat a more likely scenario is that changes in the ocean circulation are a consequence of wind shifts the disappearance of d o events in the holocene coincides with the disappearance also of the laurentide and fennoscandian ice sheets it is thus suggested that d o events are a consequence of interactions of the windfield with the continental ice sheets and that better understanding of the wind field in the glacial periods is the highest priority wind fields are capable of great volatility and very rapid global scale teleconnections and they are efficient generators of oceanic circulation changes and more speculatively of multiple states relative to great ice sheets connection of d o events to the possibility of modern abrupt climate change rests on a very weak chain of assumptions

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

the southern glacial maximum 65 000 years ago and its unfinished termination abstract glacial maxima and their terminations provide key insights into inter hemispheric climate dynamics and the coupling of atmosphere surface and deep ocean hydrology and cryosphere which is fundamental for evaluating the robustness of earth s climate in view of ongoing climate change the last glacial maximum lgm 26 19 ka ago is widely seen as the global cold peak during the last glacial cycle and its transition to the holocene interglacial dubbed termination 1 t1 as the most dramatic climate reorganization during this interval climate records show that over the last 800 ka ice ages peaked and terminated on average every 100 ka 100 ka world however the mechanisms pacing glacial interglacial transitions remain controversial and in particular the hemispheric manifestations and underlying orbital to regional driving forces of glacial maxima and subsequent terminations remain poorly understood here we show evidence for a full glacial maximum in the southern hemisphere 65 1 2 7 ka ago and its unfinished termination our 10 be chronology combined with a model simulation demonstrates that new zealand s glaciers reached their maximum position of the last glacial cycle during marine isotope stage 4 mis 4 southern ocean and greenhouse gas records indicate coeval peak glacial conditions making the case for the southern glacial maximum about halfway through the last glacial cycle and only 15 ka after the last warm period mis 5a we present the hypothesis that subsequently driven by boreal summer insolation forcing a termination began but remained unfinished possibly because the northern ice sheets were only moderately large and could not supply enough meltwater to the north atlantic through heinrich stadial 6 to drive a full termination yet the unfinished termination left behind substantial ice on the northern continents about 50 of the full lgm ice volume and after another 45 ka of cooling and ice sheet growth the earth was at inter hemispheric last glacial maximum configuration when similar orbital forcing hit maximum size northern ice sheets and ushered in t1 and thus the ongoing interglacial this argument highlights the critical role of full glacial conditions in both hemispheres for terminations and implies that the southern hemisphere climate could transition from interglacial to full glacial conditions in about 15 000 years while the northern hemisphere and its continental ice sheets required half a glacial cycle

a stratigraphic framework for abrupt climatic changes during the last glacial period based on three synchronized greenland ice core records refining and extending the intimate event stratigraphy due to their outstanding resolution and well constrained chronologies greenland ice core records provide a master record of past climatic changes throughout the last interglacial glacial cycle in the north atlantic region as part of the intimate integration of ice core marine and terrestrial records project protocols have been proposed to ensure consistent and robust correlation between different records of past climate a key element of these protocols has been the formal definition and ordinal numbering of the sequence of greenland stadials gs and greenland interstadials gi within the most recent glacial period the gs and gi periods are the greenland expressions of the characteristic dansgaard oeschger events that represent cold and warm phases of the north atlantic region respectively we present here a more detailed and extended gs gi template for the whole of the last glacial period it is based on a synchronization of the ngrip grip and gisp2 ice core records that allows the parallel analysis of all three records on a common time scale the boundaries of the gs and gi periods are defined based on a combination of stable oxygen isotope ratios of the ice 18o reflecting mainly local temperature and calcium ion concentrations reflecting mainly atmospheric dust loading measured in the ice the data not only resolve the well known sequence of dansgaard oeschger events that were first defined and numbered in the ice core records more than two decades ago but also better resolve a number of short lived climatic oscillations some defined here for the first time using this revised scheme we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the last glacial period that are represented in the greenland ice records the final product constitutes an extended and better resolved greenland stratotype sequence against which other proxy records can be compared and correlated it also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations

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

indian summer monsoon variations and competing influences between hemispheres since 35 ka recorded in tengchongqinghai lake southwestern china abstract the southwestern yunnan province of china which is located at the southeastern margin of the tibetan plateau and close to bay of bengal is significantly influenced by the indian summer monsoon ism in this study we reconstruct proxies for the ism from 35 to 1 ka through detailed analysis of grain size distribution geochemical composition and environmental magnetism from a 7 96 m sediment core from tengchongqinghai lake yunnan province china globally recognized abrupt climatic events including heinrich events 0 3 h0 h3 and the bolling allerod b a warm period are identified in most of our proxies and the long term trend is consistent with other published records such as stalagmite oxygen isotopes 18o from sangxing cave northern hemisphere nh temperature which is influenced by nh solar insolation is commonly suggested to play a dominant role in controlling the ism a comparison of our record with the 18o variations of ice cores from greenland and antarctica a sea surface temperature sst record from the bay of bengal and summer solar insolation at 25 n latitude demonstrates that the general pattern of ism change does follow variations in summer insolation however the ism lags summer insolation by thousands of years while the ism fluctuations are highly correlated with nh temperature on shorter timescales centennial millennial the gradually weakened ism from 22 5 ka until the last glacial maximum lgm indicates a close relationship with the rise of southern hemisphere sh temperature and the relatively cold background of the sh our record expands on the findings of ism records from heqing paleolake basin in southwestern china and the arabian sea sediments suggesting that the nh and sh have a competitive influence on ism by controlling the cross equatorial pressure gradient this relationship means that when nh temperatures are relatively high it has a stronger influence on the ism than sh influences in contrast when the sh temperature is relatively low it has a dominant influence on ism in addition we speculate that the change of sh temperature not only influences the cross equatorial pressure gradient directly but also likely modulates the circulation system of ocean energy by influencing the atlantic meridional overturning circulation amoc

different precipitation patterns across tropical south america during heinrich and dansgaard oeschger stadials abstract detailed knowledge about tropical south american precipitation patterns during heinrich h and dansgaard oeschger do stadials provides relevant insights into the possible evolution of amazonian hydroclimate under future climate change sediment core geob16224 1 ca 7 n raised from a site in the continental slope off french guiana in western equatorial atlantic under the influence of the amazon river discharge documents the impacts of h and do stadials on both inorganic i e fe ca record and organic i e alkenone c37 concentration and c37 c38 ratio geochemistry between 41 and 13 ka bp our results show millennial scale covariations of increased fe ca values with decreased c37 concentration and c37 c38 ratios during h and do stadials comparing our high temporal resolution data with previously published records from ca 17 n to 4 s we are able to differentiate the influence of h and do stadials upon tropical south american precipitation we find that records under the influence of the south american summer monsoon e g western amazon and the northern edge of the intertropical convergence zone itcz e g northernmost south america exhibit strong climate shifts during both h and do stadials but regions under the influence of the southern edge of the itcz e g northeastern brazil experience a weaker reaction during do stadials than during h stadials

quantification of factors impacting seawater and calcite δ18o during heinrich stadials 1 and 4 we perform idealized experiments of a heinrich stadial using an oxygen isotope enabled earth system climate model our results compare relatively well with the planktic and benthic 18o records of heinrich stadials 1 and 4 we find that changes in surface 18oc can be equally attributed to the temperature effect due to fractionation during calcification the circulation and climate effect due to changes in circulation precipitation and evaporation and the meltwater effect due to the addition and subsequent advection of depleted fresh water from continental ice sheets in contrast the meltwater effect and circulation and climate effect have only a small impact on benthic 18oc during the cessation of the atlantic meridional overturning circulation amoc significant temperature changes simulated in both the deep atlantic and pacific oceans substantially influence benthic 18oc during that time during the amoc recovery however anomalously low 18ow surface waters are advected to the deep atlantic thus generating a large 0 5 18oc decrease in the deep north atlantic this is in contrast to a hypothesis that links such depletion seen in atlantic sediment cores during the last glacial stadials to deepwater formation caused by brine rejection and sea ice formation

links between tropical rainfall and north atlantic climate during the last glacial period the last glacial period was marked by dramatic climate fluctuations sediment records from the cariaco basin and the arabian sea suggest that cooling in the north atlantic region was tightly coupled with a southward displacement of the intertropical convergence zone and a weakening of the indian summer monsoon

hydrological and ecosystem response to abrupt changes in the indian monsoon during the last glacial as recorded by sediments from xingyun lake yunnan china abstract the indian summer monsoon ism is the major moisture source of precipitation in southwest china and plays an important role in regional environmental change and in economic and social development since abrupt changes of the ism can cause crop failures and flooding that impact the livelihood of a large population however with the exception of speleothem records abrupt changes of the ism during the last glacial are not well documented in terrestrial records here we present a sediment record from xingyun lake in yunnan province southwest china spanning the interval 36 4 ka bp to 13 4 ka bp 1 ka 1000 cal a which documents the occurrence of a series of millennial scale episodes which may reflect the abrupt weakening of the ism seven ams 14c dates from terrestrial wood fragments provide a robust chronology the results demonstrate that increases in the coarse sediment fraction 30 m correspond to increases in the concentration of pediastrum the grain size of magnetic minerals carbonate content and c n ratios which together indicate episodes of low lake level in addition pollen analysis indicates that quercus oak increased and that ferns decreased during intervals of abrupt weakening of the ism indicating a drier environment nine abrupt shifts to a low lake level are documented for the studied interval and three of them are correlative with heinrich events 1 to 3 our study supports the hypothesis that in response to the cold events in the north atlantic associated with massive iceberg influxes and the corresponding slowing down of atlantic meridional overturning circulation the mean latitudinal extent of the itcz shifted southwards as a result of an atmospheric teleconnection there was a corresponding decrease in precipitation associated with ism precipitation which caused reduced fluvial runoff in yunnan

millennial scale variability during the last glacial the ice core record the oxygen isotope records from greenland ice cores show a very strong reproducible pattern of alternation between warm greenland interstadials gi and cold greenland stadials gs at millennial scale during the last glacial period here we summarise what is known about this variability from ice core records the typical cycle has a sawtooth pattern with a very rapid warming event occurring in a few decades a slow cooling trend and then a final fast cooling 25 such events have been numbered in the last glacial the recent gicc05 age scale provides the best available age scale that can be directly applied to this stratigraphy and we summarise the timing of the warming events and the length and strength of each event the greenland stratigraphy can be transferred to other records if we make assumptions about the contemporaneous nature of rapid events in different archives other parameters such as the snow accumulation rate and the concentration of terrestrial dust and sea salt recorded in the greenland cores also show a strong contrasting pattern between gi and gs methane concentrations are generally high during gi and lower during gs with the increase from gs to gi occurring within a century antarctic ice cores show a different pattern each gi has an antarctic counterpart but antarctica appears to warm while greenland is in a gs and cool during gi these changes are consistent with a mechanism involving ocean heat transport but the rapid nature of warmings poses a challenge for modellers while the rapid methane changes pose questions about the pattern of land biosphere emissions during the glacial that are also relevant for understanding glacial interglacial methane variability

stratigraphic simulation of sedimentary basins concepts and calibration a two dimensional stratigraphic simulation program based on semiempirical algorithms has been successfully applied to clastic carbonate and mixed clastic carbonate depositional regimes the program may be used to predict reservoir distribution to constrain interpretations of well and seismic data to test exploration scenarios in frontier basins and to evaluate the fundamental controls on basin stratigraphy applications to seismic and well log data sets from main pass u s gulf coast offshore sarawak malaysia and the baltimore canyon u s east coast demonstrate that the program simulates stratigraphy on a basin wide scale as well as on the scale of individual prospects the main pass section is an offlapping sequence of neogene clastics the model simulates 17 m y of geologic history at a 200 000 yr resolution and reproduces gross basin geometry major sequence boundaries depth and location of nearshore marine sands intervals of sediment bypass into deep water shelf margin positions and paleobathymetry three neogene carbonate buildups of central luconia offshore sarawak malaysia were simulated using a sea level history optimized to reproduce the carbonate growth anatomy the model reproduced observed seismic reflection geometries and transgressive aggradational progradational retrogradational and subaerial exposure phases the program has also simulated jurassic pleistocene basin and stratigraphic sequence geometries and mixed clastic carbonate facies distribution along a 300 km regional dip line of the baltimore canyon trough modeled features of interest include a progradational middle jurassic carbonate margin punctuated by clastic deposition during sea level lowstands and a late jurassic early cretaceous aggradational carbonate margin culminating in the development and subsequent drowning of isolated carbonate buildups simulated bathymetries facies relations and subaerial exposure surfaces for the early cretaceous aggradation margin are consistent with detailed petrographic paleontologic and seismic stratigraphic interpretations

relative paleointensity rpi in the latest pleistocene 10 45 ka and implications for deglacial atmospheric radiocarbon abstract we report magnetic properties and relative paleointensity rpi proxies from a suite of 10 conventional piston cores and kasten cores from the sw iberian margin collected during cruise jc089 of the rss james cook in august 2013 mean sedimentation rates are in the 10 20 cm kyr range age models were acquired by correlation of ca ti and zr sr xrf core scanning data to l reflectance from the cariaco basin that is in turn tied to the greenland ice core chronology the natural remanent magnetization nrm is represented by a single magnetization component carried by a low coercivity mineral magnetite although reflectance and bulk magnetic properties indicate the presence of a high coercivity hematitic magnetic phase possibly from eolian dust the presence of fine grained hematite means that the sediments are not ideal for rpi studies however the detrital hematite does not appear to contribute to the nrm or anhysteretic remanent magnetization arm in order to test the usefulness of the rpi data we construct a stack of 12 rpi records from the sw iberian margin for the 0 45 ka interval and compare it with a stack of 12 globally distributed marine and lake records chosen on the basis of mean sedimentation rates 15 cm kyr and superior age models the two stacks are similar but different from published rpi stacks particularly for the 10 30 ka interval and imply a virtual axial dipole moment vadm high at 15 18 ka followed by a drop in field strength from 15 to 13 ka a revised vadm estimate calculated from greenland 10be ice core flux using a contemporary age model is remarkably consistent with the new overall rpi stack based on iberian margin and global rpi records the elevated atmospheric 14c levels of the last ice age cannot however be fully explained by this rpi stack although relative changes such as the long term drop in atmospheric 14c from 30 to 15 ka are reproduced supporting the hypothesis of a combined influence of production rate and ocean ventilation on 14c during the last ice age

south american monsoon response to iceberg discharge in the north atlantic heinrich stadials significantly affected tropical precipitation through changes in the interhemispheric temperature gradient as a result of abrupt cooling in the north atlantic here we focus on changes in south american monsoon precipitation during heinrich stadials using a suite of speleothem records covering the last 85 ky b p from eastern south america we document the response of south american monsoon precipitation to episodes of extensive iceberg discharge which is distinct from the response to the cooling episodes that precede the main phase of ice rafted detritus deposition our results demonstrate that iceberg discharge in the western subtropical north atlantic led to an abrupt increase in monsoon precipitation over eastern south america our findings of an enhanced southern hemisphere monsoon coeval with the iceberg discharge into the north atlantic are consistent with the observed abrupt increase in atmospheric methane concentrations during heinrich stadials

hydrographic changes in the tropical and extratropical pacific during the last deglaciation fine scale paired mg ca 18o profiles globigerinoides ruber white sensu lato from the san lazaro basin slb at 25 n in the northeast pacific reveal a transition from a predominant presence of tropical subtropical waters during the last glacial termination t1 to an increasing influence of fresh and cold california current waters toward the holocene changing atmospheric circulation patterns over the northeast pacific in step with the demise of the northern hemisphere ice sheets and or with a shift from el nino to la nina like conditions toward the holocene are prime candidates to explain this water mass change 18osw ivc increases of 0 5 0 7 during the younger dryas yd and heinrich stadial 1 hs1 at the slb are observed in a number of 18osw ivc records from the tropical pacific more directly influenced by changes in the position of the intertropical convergence zone itcz conditioning by itcz migration of the tropical pacific ocean towards salinity increase during yd and hs1 and the subsequent advection of those water masses as far north as 25 n likely accounted for the reconstructed hydrographical changes at the slb a larger influence of tropical water masses as far north as 25 n plausibly contributed to changes in the atmospheric moisture transports to western north america and affected the regional hydrological cycle across t1 finally the fine scale resolution of our 18osw ivc record allows pinpointing a shift from relative salty to fresh surface conditions at 16 2 ka signaling that the two phase structure of hs1 is plausibly a ubiquitous feature of the northern tropical to extratropical ocean atmosphere dynamics