sea level estimates during the last deglaciation based on δ18o and accelerator mass spectrometry 14c ages measured in globigerina bulloides coupled measurements of 18o and accelerator mass spectrometry ams 14c in a particular species of planktonic foraminifera may be used to calculate sea level estimates for the last deglaciation of critical importance for this type of study is a knowledge of the seasonality of foraminiferal growth which can be provided by 18o measurements of modern shells core tops plankton tows isotopic 18o ams 14c dating and faunal records transfer function sea surface temperature were obtained from two cores in the north atlantic at about 37 n the locations were chosen to obtain high sedimentation rate records removed from the major ice melt discharge areas of the last deglaciation based upon globigerina bulloides data four 18o based sea level estimates were calculated 67 7 m at 12 200 yr b p and 24 8 m at about 8200 yr b p for core su 81 18 83 10 m at 12 200 yr b p and 13 11 m at about 8500 yr b p for core su 81 14 using a second working hypothesis concerning the seasonability of g bulloides growth it is suggested that the sea level rose by about 40 m during the millennium which followed 14 500 yr b p

history of laurentide meltwater flow to the gulf of mexico during the last deglaciation as revealed by reworked calcareous nannofossils the history of meltwater flow from the laurentide ice sheet to the gulf of mexico during the last deglaciation which holds possible implications for the cause of the younger dryas cold episode is not well understood we propose a new chronology based on using the percentage of reworked calcareous nannofossils in orca basin sediments as a proxy for erosion the period of greatest meltwater flow to the gulf was between 12 7 and 12 1 ka during the bolling warm interval and flow remained high until the beginning of the younger dryas cold episode at 11 3 ka this corresponds to meltwater pulse ia a sharp meltwater decrease at 12 2 ka may represent the older dryas glacial readvance little or no meltwater is inferred to have flowed to the gulf from 10 to 9 ka which is the time of the second major meltwater pulse ib therefore meltwater must have been permanently diverted away from the gulf of mexico at the beginning of the younger dryas

response of planktonic foraminifera to glacial cycles mid pleistocene change in the southern south china sea a high resolution study 2 ka of planktonic foraminifers in 997 samples from odp site 1143 9821 72vn 113817 11ve water depth 2772 m in the southern south china sea scs reveals faunal response to glacial cycles in the last 2 1 ma most distinctive is the contrasting variations in the abundance of two tropical subtropical species that exhibit similar resistance to dissolution in modern oceans the relative and absolute abundances of globorotalia menardii are high in interglacials and low in glacials and covary with d 18 o fluctuations over the studied interval pulleniatina obliquiloculata however follow oxygen isotopes only before the mid pleistocene revolution mpr showing high abundances during glacials and low during interglacials after 850 ka three abundance maxima of p obliquiloculata are observed corresponding to three major glacial episodes marine isotope stages mis 2 12 and 16 respectively this change in abundance patterns of p obliquiloculata appears to be unique to the southern scs as in late pleistocene records from other western pacific regions including the okinawa trough and the northern scs all show co varying patterns with d 18 oa sg menardii does cross spectral analyses performed between percentages of globorotalia menardii and d 18 o records show high coherency at 41 ka obliquity and then at 100 ka eccentricity bands we suggest that the high abundances of g menardii during interglacials in the past 2 1 ma reflect warmer temperatures percentages of pulleniatina obliquiloculata vs oxygen isotope records show quite large phase difference at 41 ka obliquity band before the mpr as a contrast there are negligible phase differences in the vicinity of 100 and 41 ka after the mpr which means reverse trend between percentages of p obliquiloculata and d 18 o fluctuations the differences of p obliquiloculata from g menardii in abundance and orbital forcings are interpreted as resulting from a profound change in the regional upper ocean structure during the mpr time probably relating to a final glacial cut off of the southern scs from the indian water at 850 ka and to higher salinity during glacial times after 850 ka we speculate that this change is related to the decreased connection between the pacific and indian ocean d 2004 elsevier b v all rights reserved

paleoceanography of surface waters in the gulf of mexico during the late quaternary abstract late quaternary paleotemperatures and paleosalinities of surface waters of the gulf of mexico were estimated using a multivariate statistical analysis of census data of planktonic foraminifera two climatic extremes were selected for detailed basinwide study the climatic optimum 125 000 yr ago and the glacial maximum 18 000 yr ago in addition patterns of climatic change were examined in seven piston cores from 127 000 yr ago to the present day during the climatic optimum 125 000 yr ago temperature distributions in surface waters were similar to those of the present the 22 c winter isotherm trended northeastward across the central basin and paleotemperatures decreased northward summer distributions were nearly homogeneous and ranged between 28 and 29 c winter salinities were 1 fresher than present values in the northmost gulf and 0 4 fresher in the central basin summer salinities were similar during both times in contrast during the last glacial maximum temperatures were 1 to 2 c cooler in winter and 1 c cooler in summer and isotherms formed a circular pattern in the gulf during both seasons salinity was 0 3 fresher in winter than at present but 0 6 saltier in summer conditions deteriorated from the climatic optimum to the glacial maximum in the mexico basin winter temperatures were 2 c cooler from 75 000 to 45 000 yr ago y6 to y3 subzones summer temperatures reached a minimum 3 c cooler 32 000 yr ago y2 y3 boundary and seasonality reached minimal values 5 c from 45 000 to 15 000 yr ago all three parameters became similar in value to those in the straits of florida from 45 000 to 15 000 yr ago suggesting that the exchange of surface waters was enhanced at this time between the two regions summer salinities remained similar to present conditions in the mexico basin whereas winter salinities increased 2 by 32 000 yr ago and then fell 0 5 until the glacial maximum ended the westerlies may have migrated southward over the mexico basin in winter from 32 000 to 15 000 yr ago

biotic and geochemical δ 18 o δ 13 c mg ca ba ca responses of globigerinoides ruber morphotypes to upper water column variations during the last deglaciation gulf of mexico abstract within the gulf of mexico gom the bryant canyon is exceptional in that rapid sedimentation sustained by high rates of terrigenous sediment delivery and surface marine productivity make this basin an excellent recorder of paleoenvironmental and paleoclimatic conditions we present a new 21 kyr record of sea surface temperature sst and local salinity changes from the nw gom core jpc 26 approximated from combined globigerinoides ruber morphotype specific 18 o and mg ca as well as ba ca which reflect the subtropical gom hydrographic dynamics and their relationship to both mississippi river discharges and climate evolution during the last deglaciation overall the reconstructed sst and sss related patterns reveal notable variations in amplitude between the analyzed morphotypes adding valuable insights to previously published g ruber w mixed gom records especially during the deglaciation bryant canyon meltwater flooding events bcdfs and associated sea surface freshening seem to be more pronounced than the sst reduction our mg ca derived sst records of both morphotypes g ruber sensu stricto s s and g ruber sensu lato s l show comparable general trends but with important sst differences t we interpret down core t as a record of changing upper water column hydrography with particular influence from the deglacial meltwater bcdfs or holocene bchfs flooding events during the warm intervals the deeper thicker and probably more seasonally persistent mixed layer led to more uniform thermal conditions for both g ruber morphotypes and therefore to a minimum t on the contrary during the cold and low salinity periods the shallower mixed layer favored more habitat divergence and caused a maximum thermal gradient in the well stratified upper water column overall this supports the notion that g ruber s s is consistently calcifying in warmer waters than g ruber s l either due to a shallower depth habitat or to a more summer weighted seasonal distribution moreover intra specific paired 13 c and ba ca differences show that g ruber s l is more sensitive to river water influence than g ruber s s due to its ability to change its depth habitat and therefore exploit optimal temperature salinity productivity stratification conditions during the low salinity events overall our observations support the current practice of treating the two g ruber morphotypes separately and further illustrate the necessity to map both their spatial and temporal distribution

the last glacial maximum to holocene environment changes in the southern okinawa trough presented here are the oxygen and carbon isotope records of two epipelagic planktonic foraminiferal species globigerinoides sacculifer and neogloboquadrina dutertrei from a sediment core which was collected from the southern okinawa trough these isotope records provide an opportunity to understand the paleoceanographic evolution of the okinawa trough since the last deglaciation the younger dryas cooling event in the okinawa trough is reported for the first time in this paper these data also record meltwater spikes during the younger dryas interval and the entry of the kuroshio current into the okinawa trough the oxygen isotope sequence also records the warm and or humid climate conditions around east asia at about 5 6 ka and the evolution of the kuroshio current during the late holocene

paleoenvironmental changes and glacial stades of the last 50 000 years in the cordillera central colombia using data from glacial geomorphology tephra soil stratigraphy and mineralogy palynology and radiocarbon dating a sequence of glacial and bioclimatic stades and interstades has been identified for the past ca 50 000 yr in the ruiz tolima massif cordillera central six cold stades separated by warmer interstades occurred before 48 000 between 48 000 and 33 000 between 28 000 and 21 000 from 16 000 to ca 14 000 ca 13 000 12 400 and ca 11 000 10 000 yr b p although the radiocarbon ages are minimum limiting ages obtained from tephra layers on top of tills the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections two minor moraine stages likely reflect glacier pauses during cold intervals ca 7400 yr b p and slightly earlier finally glaciers readvanced between the 17th and 19th centuries in contrast to the glacier cover ca 34 km2 on volcanoes of the massif during the last glacial maximum lgm the ice cover expanded to 1200 km2and was still 800 km2during late glacial time lgt glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude ela by ca 1100 m during the lgm and 500 600 m during lgt relative to the modern ela which lies at ca 5100 m in the cordillera central glaciers in this region apparently reached their greatest extent when the climate was cold and moist e g during stades corresponding to marine isotope stage 3 glaciers were still expanding during the lgm ca 28 000 21 000 yr b p but they shrank considerably after 21 000 yr b p because of greatly reduced precipitation

relationships between anoxia glacial meltwater and microfossil preservation in the orca basin gulf of mexico abstract the isotopic and microfossil records from piston core en32 pc6 from the orca basin gulf of mexico reveal that various factors have moderated the sediment composition of the basin during the last 29 000 yrs 29 ka b p coincident with the introduction of isotopically depleted glacial meltwater into the gulf approximately 16 ka b p anoxic conditions commenced within the intraslope basin as evidenced by sedimentary laminations and improved microfossil pteropod planktonic foraminifera and radiolaria preservation the increased delivery of terrigenous organic matter with the glacial meltwater may have been responsible for inducing the anoxia also at this time the water of the orca basin was most likely somewhat stratified due to elevated salinities and the increased supply of organic matter onto the continental slope from the continent would have depleted the oxygen supply of the orca basin by oxidative consumption about 13 ka b p oxygenated conditions resumed and microfossil abundance preservation decreased when meltwater input diminished at 8 5 ka b p the orca basin again became anoxic due to the development of the orca basin brine

a reconstruction of sea surface temperature variability in the southeastern gulf of mexico from 1734 to 2008 c e using cross dated sr ca records from the coral siderastrea siderea this study uses skeletal variations in coral sr ca from three siderastrea siderea coral colonies within the dry tortugas national park in the southeastern gulf of mexico 24 42 n 82 48 w to reconstruct monthly sea surface temperature sst variations from 1734 to 2008 common era c e calibration and verification of the replicated coral sr ca sst reconstruction with local regional and historical temperature records reveals that this proxy temperature relationship is stable back to 1879 c e the coral sst reconstruction contains robust interannual 2 0 c and multidecadal variability 1 5 c for the past 274 years the latter of which does not covary with the atlantic multidecadal oscillation winter sst extremes are more variable than summer sst extremes 2 2 c versus 1 6 c 2 suggesting that loop current transport in the winter dominates variability on interannual and longer time scales summer sst maxima are increasing 1 0 c for 274 years mc 0 5 c 2 whereas winter sst minima contain no significant trend colder decades 1 5 c during the little ice age lia do not coincide with decades of sunspot minima the coral sst reconstruction contains similar variability to temperature reconstructions from the northern gulf of mexico planktic foraminifer mg ca and the caribbean sea coral sr ca suggesting areal reductions in the western hemisphere warm pool during the lia mean summer coral sst extremes post 1985 c e 29 9 c exceeds the long term summer average 29 2 c for 1734 2008 c e yet the warming trend after 1985 c e 0 04 c for 24 years mc 0 5 2 is not significant whereas caribbean coral sr ca studies contain a warming trend for this interval

deglacial climatic oscillations in the gulf of california a high resolution accelerator radiocarbon dated climate record of the interval 8 000 18 000 years b p from deep sea drilling project site 480 guaymas basin gulf of california shows geochemical and lithological oscillations of oceanographic and climatic significance during deglaciation nonlaminated sediments are associated with cooler climatic conditions during the late glacial up to 13 000 years b p and from 10 300 to 10 800 years b p equivalent to the younger dryas event of the north atlantic region we propose that the changes from laminated varved to nonlaminated sediments resulted from increased oxygen content in pacific intermediate waters during the glacial and the younger dryas episodes and that the forcing for the latter event was global in scope prominent events of low 18o are recorded in benthic foraminifera from 8 000 to 10 000 and at 12 000 years b p evidence for an earlier event between 13 500 and 15 000 years b p is weaker maximum 18o is found to have occurred 10 500 13 500 and 15 000 years ago and beyond oxygen isotopic variability most likely reflects changing temperature and salinity characteristics of pacific waters of intermediate depth during deglaciation or environmental changes within the gulf of california region several lines of evidence suggest that during deglaciation the climate of the american southwest was marked by increased precipitation that could have lowered salinity in the gulf of california recent modelling studies show that cooling of the gulf of mexico due to glacial meltwater injection which is believed to have occurred at least twice during deglaciation would have resulted in increased precipitation with respect to evaporation in the american southwest during summertime the timing of deglacial events in the gulf of mexico and the gulf of california supports such an atmospheric teleconnection

the deglaciation over laurentian fan history of diatoms ird ice and fresh water abstract a high resolution diatom census coupled with other proxy data from laurentian fan lf provides a detailed description of the last deglaciation bringing new insight to that period by revealing directly the timing of sea ice formation and melting cold events heinrich event 1 h1 and the younger dryas yd were multiphase events h1 16 8 15 7 cal kyr bp was defined by a two pulse release of icebergs promoting sea ice formation melting of sea ice after h1 corresponds to a cold and fresh anomaly that may have kept the bolling colder than the allerod at 13 6 cal kyr bp a cooling trend culminated with sea ice formation marking the yd onset 12 8 cal kyr bp the decrease in sea ice 12 2 cal kyr bp led to a yd second phase characterized by very cold winters however the contribution of warm water diatoms tends to increase at the same time and the yd gradual end 11 6 cal kyr bp contrasts with its abrupt end in greenland ice cores the yd cannot be regarded as an event triggered by a fresh water input through the laurentian channel since only one weak brief input nearly 1000 yrs after its onset is recorded very cold and cool conditions without ice mark the following preboreal a northward heat flux between 10 8 and 10 2 cal kyr bp was interrupted by the increased influence of coastal waters likely fed by inland melting there was no further development of sea ice or ice drift then

orbital and internal forcing of climate on the yucatan peninsula for the past ca 36 ka abstract a 19 6 m sedimentary sequence from lake quexil guatemala is presented as a proxy record of climatic change on the low lying yucatan peninsula over the last ca 36 ka long term climatic fluctuations are attributed to orbital forcing of insolation while abrupt changes during the late glacial period are the result of internal forcing mechanisms that remain imperfectly modelled gcms simulating meltwater cooling of the gulf of mexico may predict some but not all climatic responses in the circum caribbean lake quexil did not experience greater aridity than predicted by orbital forcing during late glacial zones q lg 1 and 2 which were drier only in comparison with holocene conditions q lg 1 appears to have been colder than expected based on insolation alone and is contemporary with the younger dryas event between meltwater pulses 1a and 1b thus other feedbacks also may have cooled surface temperatures in the gulf of mexico such as unique late glacial circulation patterns increased albedo for the florida and yucatan peninsulas or surface temperatures on the north american continent additional terrestrial sequences are needed to improve the chronology and confirm the distribution of sub regional climatic variability in the circum caribbean

changes in planktic foraminiferal faunas temperature and salinity in the gulf stream during the last 30 000 years influence of meltwater via the mississippi river abstract variations in the distribution of planktic foraminiferal faunas temperature and salinity in the surface water of the gulf stream during the last 30 000 years have been reconstructed based on a sediment core from the blake ridge subtropical western atlantic ocean temperatures and salinities were calculated using planktic foraminiferal transfer functions and previously published oxygen isotope values productivity was estimated using the 106 m size fraction of planktic foraminifera the reconstructed values show that temperature variations have been small during the investigated period with a total range of only 3 c the highest temperatures about 1 5 c above the present temperature in the area occurred during the late glacial heinrich event 1 and the mid holocene time periods the lowest temperatures about 1 5 c below the present temperatures occurred during the bolling interstadial the early holocene period was relatively cool the low temperatures during the bolling interstadial and during the early holocene are in contrast to the northeastern atlantic where the bolling interstadial was the warmest period of the deglaciation and the early holocene the warmest during the holocene we attribute the lower temperatures during the bolling and early holocene periods to colder meltwater from the laurentide ice sheet flowing into the gulf of mexico through the mississippi river system and carried to the blake ridge via the gulf stream

geomorphic expression of abrupt climate change in southwestern north america at the glacial termination eolian and subaqueous landforms composed of gypsum sand provide geomorphic evidence for a wet episode at the termination of glacial climate in southwestern north america drying of pluvial lake estancia central new mexico occurred after ca 12 000 14c yr b p thereafter eolian landforms on the old lake floor constructed of gypsum sand were overridden by rising lake water modified by subaqueous processes and organized into beach ridges along the lake s eastern shore preservation of preexisting eolian landforms in the shallow lake suggests abupt changes in lake level and climate available radiocarbon ages suggest that the final highstand recorded by beach ridges may have developed during the younger dryas yd stade the beach ridges provide information about lake surface area which was 45 of the lake area reached during the maximum highstands of the late pleistocene a similar proportional response has been reported for yd climate changes outside the north atlantic region

volume and routing of late glacial runoff from the southern laurentide ice sheet melting of the laurentide ice sheet during the last deglaciation added large volumes of water to many rivers and lakes of north america and to the world s oceans the volume and routing of this meltwater not only helped shape the land s surface but also played a role in the evolution of late glacial climate a computerized model was prepared to quantify meltwater generation from seven drainage areas along the southern side of the laurentide ice sheet at 500 yr time slices between 14 000 and 8000 yr b p nearly all waters reaching the oceans flowed through the st lawrence hudson or mississippi river valleys discharge through the mississippi river to the gulf of mexico during late glacial time varied by more than a factor of 5 ranging between 17 400 m3 sec 1 550 km3 yr 1 and 98 200 m3 sec 1 3200 km3 yr 1 discharge entering the north atlantic ocean through the st lawrence and hudson valleys ranged between 20 300 m3 sec 1 640 km3 yr 1 and 65 300 m3 sec 1 2060 km3 yr 1 with very abrupt twofold changes at about 11 000 10 000 and 9500 yr b p as a result of the rerouting of water from the lake agassiz basin as the areal extent and mass of the laurentide ice sheet diminished the total volume of meltwater plus runoff due to precipitation from its southern side declined from 3800 km3 yr 1 at about 14 000 yr b p to 2100 to 2600 km3 yr 1 between 11 500 and 8000 yr b p no meltwater entered the gulf of mexico after 9500 yr b p after the demise of the ice sheet over hudson bay about 8000 yr b p the modern continental drainage network was established and flows through the st lawrence declined to modern values of about 320 km3 yr 1

hydrocarbon gas hydrates in sediments of the mississippi canyon area northern gulf of mexico the gulf of mexico hydrates research consortium has begun installing a seafloor observatory to monitor gas hydrate outcrops and the hydrate stability zone in mississippi canyon area lease block 118 relevant background information concerning the mississippi canyon area and gas hydrate occurrences in the northern gulf of mexico is presented microbial influences and possible scenarios of hydrate accumulation are considered the design of the observatory was based on field data recorded in the mississippi canyon area principally lease block 118 mc118 and the vicinity of lease block 798 mc798 swath bathymetry by autonomous underwater vehicle played a large part as did seismic imaging within the hydrate stability zone and core sampling these data and the results of their analyses are discussed in detail discussion and interim conclusions are presented in an effort to expand the information base on how natural gas hydrates form in sediments and how they affect seafloor stability the university of mississippi organized the gulf of mexico hydrates research consortium in 1999 its principal goal is to develop and install a seafloor observatory capable of monitoring a hydrate outcrop and its environment more or less continuously for a period of 5 10 years in 2006 the consortium included researchers from more than 30 universities and corporations a board of scientific advisers oversees project management site selection geochemical aspects microbial aspects seismoacoustic aspects data quality control and data archiving a summary of project history an overview of observatory design and a list of organizations that participate in the scientific board is given by mcgee 2006 a number of possible sites for the observatory were considered by the site selection committee data presented here were collected in the vicinity of two sites of known hydrate occurrence in the mississippi canyon area sites lease block 118 mc118 and lease block 798 mc798 a lease block in the northern gulf of mexico comprises a square of sides 3 statute miles 5 km consortium members voted in october 2004 to select a prominent seafloor mound located in mc118 as the observatory site the minerals management service mms of the us department of interior reserved the vicinity of the mound exclusively for consortium activities pre installation studies began in january 2005 and the first monitoring components were installed during may of the same year additional components were scheduled for deployment during the following september but the aftermath of hurricane katrina forced a delay until june 2006 in addition to information on regional contexts this contribution includes early results and tentative conclusions produced by consortium activities prior to the resumption of the installation quaternary geology of the mississippi

isotopic and rock magnetic expression of environmental change at the pleistocene holocene transition in the central great plains abstract in a region too dry for the effective use of the traditional palynological approach loess deposits of the central great plains offer a source of proxy information for the reconstruction of past climates the brady soil a ubiquitous feature developed within the uppermost late pleistocene peoria loess recorded the character of vegetation change associated with climate shifts during the pleistocene holocene transition stable carbon isotope ratio analysis and two room temperature magnetic parameters were used to examine the nature of the change during this period 13 c values derived from soil organic matter indicate that in the late pleistocene minor populations of drought tolerant c4 plants were interspersed among the dominant cool season grasses c3 in the west while c3 grasses were accompanied by trees in the east by the early holocene c4 grasses were the dominant vegetation in the west and contributed substantially to the 13 c signal in the east magnitude of the 13 c shift suggests an increase in july mean daily temperature of 8 10 c according to existing models magnetic susceptibility and frequency dependence signal the cessation of loess deposition and development of the brady soil and indicate a spatial pattern in the intensity of weathering across the region

glacial meltwater cooling of the gulf of mexico gcm implications for holocene and present day climates an atmospheric general circulation model the ncar ccm has been used to investigate the possible effects that reduced gulf of mexico sea surface temperatures sst could have on regional and hemispheric climates 18o records and terrestrial evidence indicate at least two major glacial meltwater discharges into the gulf of mexico subsequent to the last glacial maximum it is probable that these discharges reduced gulf of mexico sst we have conducted three numerical experiments with imposed gulf wide sst coolings of 3 c 6 c and 12 c and find in all three experiments significant reductions in the north atlantic storm track intensity along with a strong decrease in transient eddy water vapor transport out of the gulf of mexico surface pressures are higher over the north atlantic indicating a reduction of the climatological icelandic low the region is generally cooler and drier with a reduction in precipitation that agrees well with evidence from greenland ice cores other statistically significant changes occur across the northern hemisphere but vary between the three experiments in particular warmer wetter conditions are found over europe for both the 6 c and 12 c sst reductions but cooler conditions are found for the 3 c reduction this indicates a dependence in both the sign and magnitude of the model response on the magnitude of the imposed sst anomaly the results suggest that the present day north atlantic storm track is dependent on warm gulf of mexico sst for much of its intensity they also suggest that meltwater induced coolings may help account in part for some of the climatic oscillations that occurred during the last glacial interglacial transition

evidence of the younger dryas in central america abstract three sites provide records that address whether the younger dryas was manifest in central america marine records from barbados and the cariaco basin are discussed as well as possible climatic forcing mechanisms sequences from montane la chonta bog costa rica and lowland lake quexil guatemala record a temperature decline of 1 5 2 5 c dated between 11 070 10 400 14c years bp and ca 12 000 10 300 14c years bp respectively the record from lake la yeguada panama does not include cooling although significant reorganization of local communities occurred during the younger dryas chronozone colder tropical ssts throughout deglaciation contributed to sub regional climatic variation more intense monsoonal activity and cooler air temperatures however the temperature reversals are not associated with the coldest tropical ssts which occurred during meltwater pulses the temperature reversals appear to be a response to extra tropical conditions presumably in the north atlantic which suggests that younger dryas cooling extended as far south as costa rica in panama monsoonal conditions may have blocked cooler temperatures precipitation continued to increase throughout deglaciation due to strong forcing by seasonal solar insolation in central america while desiccation events occurred to the north and south

a reevaluation of the evidence for a younger dryas climatic reversal in the tropical andes abstract a review of the evidence for a younger dryas equivalent climatic reversal in the tropical andes shows that a number of hypotheses need to be reassessed assumptions of the el abra cold and humid phase in colombia are compromised by insufficient dating control periods of glacier advance in peru and bolivia lack sufficient dating control to be correlated with the european younger dryas only glaciers on the quelccaya ice cap in peru may have advanced shortly before the onset of the european climatic reversal but even there a correlation is questionable a late glacial advance in the chimborazo area in ecuador is considerably older than previously suggested the same glacier advance has been dated to earlier than 12 000 bp in other areas of ecuador the emerging picture suggests two phases of glacier advances in the tropical andes 13 000 12 000 bp and 9000 10 000 bp both may have been caused by increasing precipitation unequivocal evidence for a cold younger dryas event in the tropical andes has yet to emerge

younger dryas sea level and meltwater pulse 1b recorded in barbados reef crest coral acropora palmata the younger dryas climate event occurred during the middle of the last deglacial cycle and is marked by an abrupt shift in the north atlantic polar front almost to its former glacial position trending east to west using high precision and high accuracy u th dated barbados reef crest coral acropora palmata we generate a detailed sea level record from 13 9 to 9000 years before present kyr b p and reconstruct the ice volume response to the younger dryas cooling from the mid allerod 13 9 kyr b p to the end of the younger dryas 11 65 kyr b p rates of sea level rise decreased smoothly from 20 mm yr 1 to 4 mm yr 1 culminating in a 400 year slow stand before accelerating into meltwater pulse 1b mwp 1b the mwp 1b event at barbados is better constrained as beginning by 11 45 kyr b p and ending at 11 1 kyr b p during which time sea level rose 14 2 m and rates of sea level rise reached 40 mm yr 1 we propose that mwp 1b is the direct albeit lagged response of the northern hemisphere ice sheets to the rapid warming marking the end of the younger dryas coinciding with rapid warming in the circum north atlantic region and the polar front shift from its zonal to meridional position 11 65 kyr b p as predicted by glaciological models the ice sheet response to rapid north atlantic warming was lagged by 400 years due to the thermal inertia of large ice sheets the regional circum north atlantic younger dryas climate event is elevated to a global response through sea level changes starting with the global slowdown in sea level rise during the younger dryas and culminating with mwp 1b no meltwater pulses are evident at the initiation of the younger dryas climate event as is often speculated

provenance of freshwater pulses in the gulf of mexico during the last deglaciation during the last deglaciation the decaying laurentide ice sheet lis delivered huge volumes of meltwater toward the gulf of mexico the present investigation of clay mineralogy and grain size characteristics of terrigenous sediments deposited in the orca basin gulf of mexico offers a unique opportunity to link the marine record of these meltwater floods with the reconstructed continental glacial history and the modeled drainage patterns five peculiar sedimentary levels characterized by high smectite content and low caco3 content were identified and occurred simultaneously with major meltwater floods according to recently published clay mineral distribution maps for north america these results help to pinpoint the southwestern margin of the lis as a main contributor to most of the meltwater discharges in addition the peculiar mineralogical composition illite and chlorite rich of the sediments characterizing the meltwater episode associated with heinrich event 1 suggests a provenance from the great lakes area supporting the interpretation of destabilization of the lis southeastern margin during this event decreased terrigenous contribution associated with changing provenance of sediments after 12 9 cal ka bp suggests strong modifications of the continental hydrography in relation to lake agassiz history and changes in the morphology of mississippi delta due to rising sea level

a high resolution speleothem record of climatic variability at the allerod younger dryas transition in missouri central united states stable isotopic analysis and 234 u 230 th mass spectrometry dating of a single calcite stalagmite from onondaga cave east central missouri reveal climatic variability between 13 200 and 12 400 yr bp coincident with the aller d younger dryas transition in the gisp2 greenland ice cores n 18 o values of speleothem calcite mark decreasing temperatures between 13 200 and 13 000 yr bp while more rapidly decreasing n 13 c values record a sharp shift toward c3 vegetation at approximately 13 100 yr bp because of uncertainties in the chronological control of both this speleothem and the gisp2 record and the brevity of this speleothem record v800 years direct comparison of the two sequences is difficult the interval preserved by this speleothem may span the inter aller d cold period iacp alone both the iacp and the start of the younger dryas or only the first half of the younger dryas in any case these data demonstrate that the climate of the north american interior deteriorated significantly and rapidly during the interval associated with the aller d younger dryas transition fl 2001 elsevier science b v all rights reserved

isotopic evolution of glacial lake agassiz new insights from cellulose and porewater isotopic archives abstract significantly differing estimates of the oxygen isotope composition of lake agassiz have been obtained from two co existing isotopic archives within a sediment core originating from montcalm manitoba in the southern basin of the ancient proglacial lake oxygen isotope analysis of cellulose extracted from the sediments which originated during the lockhart phase 11 700 11 000 14 c yr bp suggests that phytoplankton lived in surface waters having 18 o around 18 1 vsmow substantially enriched relative to connate porewaters in the same core which indicate bottom waters had much lower values of around 24 5 0 5 vsmow this difference may be attributable to seasonal isotopic stratification of the upper part of the water column in the 250 m deep lake modern observations from analogous environments in northern canada suggest that inflow of evaporatively enriched runoff from the large area of deglaciated terrain contributing to lake agassiz possibly enhanced by evaporation from the surface of the lake itself could readily account for sufficient seasonal 18 o enrichment in the epilimnion sediment porewaters in contrast have preserved the isotopic signature of hypolimnion waters supplied by a mixture of glacial meltwater and precipitation derived runoff from the laurentide ice sheet and lack discernable isotopic alteration by evaporation these new estimates are combined with inferred lake water compositions from other isotopic archives to develop a speculative framework for the isotopic evolution of the lake providing improved constraints on the probable isotopic composition of lake agassiz outflow over time which has important implications for efforts to trace and model its changing discharge

deglacial abrupt climate change in the atlantic warm pool a gulf of mexico perspective 1 during the last deglaciation greenland ice core and north atlantic sediment records exhibit multiple abrupt climate events including the younger dryas cold episode 12 9 11 7 ka however evidence for the presence of the younger dryas in the gulf of mexico gom and the relationship between gom sea surface temperature sst and high latitude climate change is less clear we present new mg ca sst records from two varieties of the planktonic foraminifer globigerinoides ruber white and pink to assess northern gom sst history from approximately 18 4 10 8 ka thirty five accelerator mass spectrometry ams 14c dates from orca basin core md02 2550 provide excellent age control and document high sedimentation rates 40 cm kyr g ruber white and pink mg ca sst data exhibit increases 4 6 0 6 c and 2 2 0 5 c respectively from at least 17 8 16 6 ka with nearly decadal resolution that are early relative to the onset of the bolling allerod interstadial moreover g ruber white sst decreases at 16 0 14 7 ka 1 0 0 5 c and 12 8 11 6 ka 2 4 0 6 c correlate to the oldest and younger dryas in greenland and cariaco basin the g ruber pink sst record which reflects differences in seasonality and or depth habitat is often not in phase with g ruber white and closely resembles antarctic air temperature records overall it appears that orca basin sst records follow antarctic air temperature early in the deglacial sequence and exhibit enhanced seasonality during greenland stadials

marine evidence for episodic holocene megafloods in north america and the northern gulf of mexico hemipelagic muds deposited during the past 5 3 cal kyr in the northern gulf of mexico orca basin contain seven intervals punctuated by relatively coarse siliciclastic grain size peaks planktonic faunal turnovers and negative 13c excursions we believe these episodes represent megaflood deposits reflecting historically unprecedented outfall of north american floodwater and terrigenous mud plumes into the gulf resulting in collapse of the open ocean pelagic ecosystem the deposits record multidecadal episodes of high continental precipitation and large mississippi river floods at 4 7 3 5 3 0 2 5 2 0 1 2 and 0 3 cal ka 500 1200 year recurrence interval variations in tropical plankton frequencies define submillenial warming intervals that culminate in these fluvial episodes strengthened tropical currents in the gulf at these times appear to have increased sea surface temperatures and associated flow of moist gulf air to the midwest terrestrial paleohydrologic records support the marine evidence for millennial scale changes in recurrence of large midwest flood episodes

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

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

paleo sea surface salinities in the low latitude atlantic the δ18o record of globigerinoides ruber white on the basis of the comparison of 18o values of globigerinoides ruber white 18og ruber from modern sediments and measured sea surface temperatures sst and salinity sss 18og ruber values most clearly record summer sst and sss of the uppermost 50 m of water in the low latitude atlantic a new transfer equation is presented for estimating local summer paleo sss at 0 50 m depth using 18og ruber paleo sst and the global 18o ice effect of sea water with the standard error reaching 0 72 0 77 sss the equation was applied to a 35 kyr long 18og ruber record and paleo sst estimates based on planktonic foraminiferal assemblages to reconstruct the paleo sss changes along the east atlantic margin off the northwest sahara the resulting local sss show a general increase by 0 3 1 4 during the last glacial maximum lgm and large parts of glacial termination i suggesting a general increase in the upwelling of the highly saline north atlantic central water and or a reduced lateral advection of less saline canary current water two short salinity lows up to 0 35 less than today during and after the lgm are coeval with the heinrich meltwater events 1 and 2 in the north atlantic indicating the breakdown of coastal upwelling and meltwater advection from the north both events are followed by an extreme sss maximum 38 15 along with the restoration of the salinity conveyor belt at 9 0 5 5 ka the salinity minimum up to 0 65 less than today reflects the continental runoff linked to the phase of strong north saharan humidity during the early holocene climatic optimum

evidence for seasonal low salinity surface waters in the gulf of mexico over the last 16 000 years oxygen isotopic analyses of individual orbulina universa from orca basin core en32 pc6 document the presence of low salinity surface waters in the northern gulf of mexico over the past 16 kyr isotopic data from an interval immediately following the younger dryas event indicate the rapid decrease in 18o values at the conclusion of the younger dryas was due to a year round return of meltwater to the gulf of mexico data indicate periodic or seasonal low salinity waters existed over the region of the orca basin prior to the initiation of the meltwater spike estimates suggest o universa grew its shell in salinities at least 4 5 below ambient since o universa may have calcified deep in the mixed layer during periods of low salinity surface salinities could have been even lower comparison of the average of individual o universa oxygen isotopic values with data from multiple shell samples of white gs ruber from the same core samples demonstrates that the two species record similar values during the late holocene in contrast o universa records lower oxygen isotopic values during the late glacial deglacial intervals possibly due to differences in seasonal distribution or shell ontogeny between the two species

routing of meltwater from the laurentide ice sheet during the younger dryas cold episode rooth1 proposed that the younger dryas cold episode which chilled the north atlantic region from 11 000 to 10 000 yr bp was initiated by a diversion of meltwater from the mississippi drainage to the st lawrence drainage system the link between these events is postulated to be a turnoff during the younger dryas cold episode of the north atlantic s conveyor belt circulation system which currently supplies an enormous amount of heat to the atmosphere over the north atlantic region2 this turnoff is attributed to a reduction in surface water salinity and hence also in density of the waters in the region where north atlantic deep water nadw now forms here we present oxygen isotope and accelerator radiocarbon measurements on planktonic foraminifera from orca basin core en32 pc4 which reveal a significant reduction in meltwater flow through the mississippi river to the gulf of mexico from about 11 200 to 10 000 radiocarbon years ago this finding is consistent with the record for lake agassiz which indicates that the meltwater from the southwestern margin of the laurentide ice sheet was diverted to the northern atlantic ocean through the st lawrence valley during the interval from 11 000 to 10 000 years before present yr bp

sedimentary evidence of deglacial megafloods in the northern gulf of mexico pigmy basin abstract cored sediments from the pigmy basin northern gulf of mexico were analyzed in order to better constrain late deglacial and early holocene paleoenvironmental and sedimentary changes in response to north american climate evolution mineralogical and geochemical proxies indicate the succession of two sedimentary regimes dominantly detrital during the deglaciation 15 12 9 cal ka bp whereas biogenic contribution relatively increased later on during the younger dryas and early holocene 12 9 and 10 cal ka bp geochemical data reveal that the deglacial record mainly reflects variations of terrigenous supply via the mississippi river rather than modifications of redox conditions in the basin specific variations of almost all the parameters measured in this paper are synchronous with the main deglacial meltwater episode meltwater spike described or modeled in previous marine or continental studies during this episode most parameters display stair step like pattern variations highlighting three successive steps within the main meltwater flow variations in grain size and clay mineral assemblage recorded in the pigmy basin indicate that the erosional regime was very strong on land during the first part of the meltwater spike and then milder inducing more subtle modifications in the sedimentary regime in this part of the gulf specific geochemical and mineralogical signatures notably clay minerals and trace metal geochemistry pinpoint a dominant origin from nw north america for detrital particles reflecting meltwater outflow from the south western laurentide ice sheet lis margin during the most intense freshwater discharge the observed decrease of the sedimentation rate from about 200 to 25 cm ka at ca 12 9 ka evidenced a drastic decrease of erosional processes during late phase of discharge consistently with the hypotheses of major reduction of meltwater flow the major modification at 12 9 cal ka bp is interpreted to result from both modifications of the main mississippi fluvial regime due to eastward and northward rerouting of meltwater flow at the onset of the younger dryas and the increase of sea surface temperature linked to insolation finally slight grain size modifications suggest that some freshwater discharges may have episodically reached the gulf of mexico after the younger dryas reflecting possible small adjustments of the postglacial hydrological regime

geology and tsunamigenic potential of submarine landslides in santa barbara channel southern california abstract a large submarine landslide complex and four small landslides developed under the santa barbara channel suggesting a potential hazard from landslide generated tsunamis we integrate offshore stratigraphy and geologic structure multibeam bathymetric information and several kinds of seismic reflection data to understand how and when the submarine landslides formed seismic reflection data show that mass failure along the slope began at least 200 ka ago landslides appear as zones of poor reflectivity having an irregular upper surface and these zones alternate vertically with strong parallel reflections the emplacement ages of two of the three main landslide lobes are well established at 8 and 10 ka the source material for the youngest part of the landslide complex was sediment of probable late pleistocene and holocene age that accumulated in a shelf edge delta directly under this delta growth of faults and anticlines was particularly intense and tended to oversteepen the deltaic deposits these active structures also formed migration pathways and reservoirs for aqueous and hydrocarbon fluids from the deep basin tsunami deposits have been described from a low lying area near santa barbara and numerical modeling of tsunamis generated by hypothetical landslides in santa barbara channel indicates a moderate to severe threat borrero j c dolan j f and synolakis c e 2001 tsunamis within the eastern santa barbara channel geophys res lett 28 4 643 646 involving wave runups of 2 20 m for a range of assumed landslide volumes inundation from these waves however is expected to be highly focused so that only narrow 10 km sections of the shoreline would be affected

unusual magnetic properties of sedimentary pyrrhotite in methane seepage sediments comparison with metamorphic pyrrhotite and sedimentary greigite

accelerator mass spectrometer ages for late glacial events at ballybetagh ireland abstract although the character of late glacial vegetation development in ireland is well known the dating is weak for a number of reasons we report six accelerator mass spectrometer ams 14 c dates of hand picked organic material from ballybetagh several of the dates are based on terrestrial plant remains thus eliminating the commonly encountered problem associated with irish sites of errors due to the hard water effect the two most significant indicate that 1 the rumex salix zone which represents the initial establishment of vegetation following deglaciation began about 12 600 yr b p and 2 the classic younger dryas began at 10 600 yr b p somewhat younger than the traditionally accepted age of 11 000 yr b p

c4 plant productivity and climate co2 variations in south central texas during the late quaternary abstract a continuous record of organic carbon 13c from a buried soil sequence in south central texas demonstrates 1 strong coupling between marine and adjacent continental ecosystems in the late pleistocene as a result of glacial meltwater entering the gulf of mexico and 2 ecosystem decoupling in the holocene associated with a reduction of meltwater and a shift in global circulation patterns in the late pleistocene reduction in c4 plant productivity correlates with two well documented glacial meltwater pulses 15 000 and 12 000 14c yr b p indicating a cooler than present adjacent continental environment increased c4 production between 11 000 and 10 000 14c yr b p suggests that the younger dryas was a warm interval responding to the diversion of glacial meltwater away from the mississippi river with waning meltwater flow c4 productivity generally increased throughout the holocene culminating in peak warm intervals at 5000 and 2000 14c yr b p shifts in the abundances of c3 c4 plants through the late quaternary show no correlation to ecophysiological responses to atmospheric co2 concentration

glacial to holocene terrigenous organic matter input to sediments from orca basin gulf of mexico a combined optical and biomarker approach in this study we assessed changes in the contribution of terrigenous organic matter om to the gulf of mexico over the course of the last deglaciation the last 25 kyr to this end we combined optical kerogen analyses with bulk sedimentary biomarker and compound specific carbon isotope analyses samples were obtained from core md02 2550 from orca basin 2249 m water depth at 26 56 77n 91 20 74w with temporal resolution ranging from multi decadal to millennial scale depending on the proxy all proxies confirmed larger terrigenous input during glacial times compared to the holocene in addition the kerogen analyses suggest that much of the glacial om is reworked at least 50 of spores and pollen grains and 40 of dinoflagellate cysts the holocene sediments in contrast contain mainly marine om which is exceptionally well preserved during the deglaciation terrigenous input was generally high due to large meltwater fluxes whereby discrepancies between different proxies call for additional influences such as the change in distance to the river mouth local productivity changes and hydrodynamic particle sorting it is possible that kerogen particles and the terrigenous biomarkers studied here represent distinct pools of land derived om with inputs varying independently

the abrupt termination of the younger dryas climate event previous studies on two deep greenland ice cores have shown that a long series of climate oscillations characterized the late weichselian glaciation in the north atlantic region1 and that the last glacial cold period the younger dryas ended abruptly 10 700 years ago2 here we further focus on this epoch defining event and present detailed heavy isotope and dust concentration profiles which suggest that in less than 20 years the climate in the north atlantic region turned into a milder and less stormy regime as a consequence of a rapid retreat of the sea ice cover a warming of 7 c in south greenland was completed in about 50 years

meltwater and precipitation runoff to the north atlantic arctic and gulf of mexico from the laurentide ice sheet and adjacent regions during the younger dryas runoff from north america may have played a significant role in ocean circulation and climate change during the last deglaciation because the driving force behind such changes may have been related to salinity of the north flowing atlantic ocean conveyor circulation it is critical to know the volume timing and location of fresh water entering the north atlantic from the melting laurentide ice sheet during the younger dryas cold episode 11 000 10 000 years b p there was a two fold increase in the volume of meltwater plus precipitation runoff to more than 1700 km yr 1 flowing through the st lawrence valley to the north atlantic mainly because retreating ice allowed the glacial lake agassiz basin to drain eastward into the great lakes at this time there was a corresponding decline in discharge from lake agassiz through the mississippi river to the gulf of mexico runoff to the arctic ocean also increased at about the beginning of the younger dryas from 740 to 900 km yr 1 because of the capture of what is now the headwater region of the mackenzie river watershed this in combination with rising sea level and warming climate may have increased the amount of pack ice reaching the north atlantic through the norwegian sea from the arctic ocean at 10 000 years b p eastward overflow from the western interior of north america was blocked by advancing ice again forcing overflow to the gulf of mexico and possibly to the northwest into the arctic ocean although total runoff to the oceans from all regions draining from the laurentide ice sheet did not vary substantially between 12 000 and 9000 years b p if discharge to the gulf of mexico is excluded fresh water reaching the north atlantic averaged 4000 km yr 1 during the younger dryas in contrast to 2870 km yr 1 just before this cold episode and 3440 km yr 1 just after it

laurentide ice sheet meltwater and abrupt climate change during the last glaciation 1 a leading hypothesis to explain abrupt climate change during the last glacial cycle calls on fluctuations in the margin of the north american laurentide ice sheet lis which may have routed fresh water between the gulf of mexico gom and the north atlantic affecting north atlantic deep water variability and regional climate paired measurements of 18o and mg ca of foraminiferal calcite from gom sediments reveal five episodes of lis meltwater input from 28 to 45 thousand years ago ka that do not match the millennial scale dansgaard oeschger warmings recorded in greenland ice we suggest that summer melting of the lis may occur during antarctic warming and likely contributed to sea level variability during marine isotope stage 3

the oxygen isotope composition of tropical ocean surface water during the last deglaciation evidence of abrupt climate change in each of the tropical oceans can be found in high deposition rate sediments from the continental margins new ams 14 c dated sediments from the arabian sea reveal a two step depletion of surface ocean 18 o 16 o during the last deglaciation with a return to more enriched values approximately 10 5 ka bp the two step depletion can be correlated among isotope records derived from foraminifer calcite in the arabian sea the gulf of mexico the sulu sea and gulf of california confirming the existence of the two step depletion and 18 o enriched event at 10 5 ka bp in at least three tropical sites outside the north atlantic to determine whether the isotopic enrichment at 10 5 ka bp was caused by local cooling of the surface ocean we estimated sea surface temperatures over this interval using quantitative paleo ecological techniques there is no evidence for cooling in the arabian sea sulu sea or gulf of mexico consistent with the hypothesis that the enrichment at 10 5 ka bp is related to a change in the isotopic composition of the tropical surface ocean and not change in the temperature of calcification we conclude that the cooling at higher latitudes that occurred at 10 5 ka bp did not extend southward to the tropical ocean more cores from high sedimentation rate sites in the tropics are needed to identify the cause and extent of the 18 o signal however these preliminary results are consistent with two meltwater pulses during the deglaciation that distributed isotopically depleted water into each of the tropical oceans with a slow down in meltwater flux at 10 5 ka bp the most likely transport route for the isotopically depleted water from the melting northern hemisphere ice sheets to these isolated tropical ocean basins is via the relatively fast circulation of the atmosphere although other pathways are possible

northeastern atlantic benthic foraminifera during the last 45 000 years changes in productivity seen from the bottom up we studied benthic foraminifera from the last 45 kyr in the 63 mu m size fraction in biogeochemical ocean flux studies bofs cores 5k 50 degrees 41 3 n 21 degrees 51 9 w depth 3547 m and 14k 58 degrees 37 2 n 19 degrees 26 2 w depth 1756 m at a time resolution of several hundreds to a thousand years the deepest site showed the largest fluctuations in faunal composition species richness and benthic foraminiferal accumulation rates the fluctuations resulted from changes in abundance of epistominella exigua and alabaminella weddellensis in the present oceans these species bloom opportunistically when a spring plankton bloom results in seasonal deposition of phytodetritus on the seafloor the phytodetritus species had very low relative abundances and accumulation rates during the last glacial maximum a strong increase in absolute and relative abundance of e exigua and a weddellensis during deglaciation paralleled the decrease in abundance of the polar planktonic foraminifer neogloboquadrina pachyderma s and the increase in abundance of warmer water planktonic species such as globigerina bulloides this strong increase in relative abundance of the phytodetritus species and the coeval increase in benthic foraminiferal accumulation rate were thus probably caused by an increase in the deposition of phytodetritus to the seafloor and thus probably of surface productivity when the polar front retreated to higher latitudes the abundance of phytodetritus species decreased during the younger dryas but not to the low levels of fully glacial conditions during heinrich events periods of excessive melt water formation and ice rafting benthic accumulation rates were very low as were the absolute and relative abundances of the phytodetritus species supporting suggestions that surface productivity was very low during these events in both cores pullenia and cassidulina species were common during isotope stages 2 3 and 4 as were bolivinid buliminid and uvigerinid species high relative abundances of these species have been interpreted as indicative either of sluggish deep water circulation or of high organic carbon fluxes to the seafloor in our cores relative abundances of these species are negatively correlated with benthic foraminiferal accumulation rates and we can thus not interpret them as indicative of increased productivity during glacials the percentage of these low oxygen species calculated on a phytodetritus species free basis decreased slightly at deglaciation at 5k but not at 14k this suggests that decreased production of north atlantic deep water during the last glacial might have slightly affected benthic foraminiferal faunas in the eastern north atlantic at 3547 m depth but not at 1756 m in conclusion major changes in deep sea benthic foraminiferal faunas over the last 45 000 years in our cores from the northeastern atlantic were the result of changes in surface water productivity not of changes in deep water circulation productivity was lower during the glacial probably because of extensive ice cover

glacier readvances in the andes at 12 500 10 000 yr bp implications for mechanism of late glacial climatic change radiocarbon dates from two sites in the andes ecuador and peru confirm that glaciers culminated a readvance after 11 000 yr bp a moraine stage equivalent in altitude and position relative to existing glaciers is present in most glacierized ranges but its age is equivocal broadly limiting dates from colombia and peru suggest that the stage may be late glacial as it is younger than 12100 yr bp but formed before the early holocene in southern chile a comparable moraine stage is older than ca 9100 yr bp andean glaciers appear to have advanced at least twice during the late glacial interval glacier reconstruction from these moraine limits suggests depression of the equilibrium line altitude by at least 300 400 m in the northern and north central andes and possibly less than this farther south late glacial climatic change occurred globally and possibly reflects north atlantic temperature and circulation changes forced by deglaciation of the northern ice sheets migrations north and south of the atlantic polar front and the switching off and on of a dust pump in low midlatitudes

the oak ridge fault system and the 1994 northridge earthquake the 17 january 1994 northridge earthquake moment magnitude m w 6 7 in the san fernando valley in southern california illuminated a hitherto unrecognized blind reverse fault with a moderate southward dip 1 this fault lies beneath the active north dipping santa susana fault system and uplifted both the footwall and the hanging wall of the santa susana fault during the earthquake1 here we argue that footwall uplift on the santa susana fault before the earthquake could have been used to identify the northridge blind thrust as an active fault moreover we propose that the northridge earthquake occurred on a continuation of the oak ridge fault system which reaches the surface in the ventura basin to the west slip rates on the western part of this fault system 2 3 are nearly three times larger than on the northridge blind thrust 4 increasing the probability of a n or t bridge sized earthquake in the heavily populated ventura basin

meltwater cooling of the gulf of mexico a gcm simulation of climatic conditions at 12 ka marine and terrestrial evidence indicate that at least two major glacial meltwater discharges into the gulf of mexico occurred during the last deglaciation based on radiocarbon dates the time interval between these two meltwater events appears to coincide with the younger dryas roughly 10 11 ka we have used an atmospheric general circulation model the national center for atmospheric research community climate model version 1 ncar ccm1 to investigate possible effects of reduced gulf of mexico sea surface temperatures sst assumed due to the meltwater discharges on regional and hemispheric climates we conducted six numerical experiments 1 perpetual january wintertime and 2 july summertime sensitivity experiments using present day boundary conditions except for an imposed gulfwide sst cooling of 6 c 3 perpetual january and 4 july control simulations using 12 ka boundary conditions for continental ice sea surface temperature no reduction due to meltwater cooling sea ice and radiative forcing and 5 perpetual january and 6 july 12 ka simulations with a 6 c sst cooling of the gulf of mexico in both of the january simulations with a cooled gulf of mexico a significant reduction in the north atlantic storm track intensity occurred with higher surface pressures over the north atlantic indicating a reduction of the icelandic low in the january 12 ka control there are large changes in surface pressure over the atlantic ocean and greenland relative to the present day control however these changes are almost completely offset when the gulf of mexico is cooled in the july simulations with a cool gulf of mexico the atlantic subtropical high is strengthened and expanded to the west this results in stronger trade winds across the caribbean and southwest atlantic there is also an enhanced monsoonal flow of moisture over northwest mexico and the american southwest and rocky mountain regions leading to increased precipitation unlike the winter situation in summer the gulf of mexico cooling serves to enhance the effects of the other 12 ka boundary conditions

calibration of the c 14 timescale over the past 30 000 years using mass spectrometric u th ages from barbados corals uranium thorium ages obtained by mass spectrometry from corals raised off the island of barbados confirm the high precision of this technique over at least the past 30 000 years comparison of the u th ages with 14c ages obtained on the holocene samples shows that the u th ages are accurate because they accord with the dendrochronological calibration before 9 000 yr bp the 14c ages are systematically younger than the u th ages with a maximum difference of 3 500 yr at 20 000 yrbp the u th technique thus provides a way of calibrating the radiocarbon timescale beyond the range of dendrochronological calibration

phasing of deglacial warming and laurentide ice sheet meltwater in the gulf of mexico evidence is emerging that the tropical climate system played a major role in global climate change during the last deglaciation however existing studies show that deglacial warming was asyn chronous across the tropical band complicating the identification of causal mechanisms the orca basin in the northern gulf of mexico is ideally located to record subtropical atlantic sea surface temperature sst warming in relation to meltwater input from the laurentide ice sheet paired d 18 o and mg ca data on the planktonic foraminifer globigerinoides ruber from core en32 pc6 are used to separate deglacial changes in sst and d 18 o of sea water sst as calculated from mg ca data increased by 3 8c from ca 17 2 to 15 5 ka in association with heinrich event 1 and was not in phase with greenland air temperature subtracting tem perature effects from d 18 o values in g ruber reveals two excur sions representing laurentide meltwater input to the gulf of mex ico one of 1 5 from ca 16 1 to 15 6 ka and a second major spike of 2 5 from ca 15 2 to 13 0 ka that encompassed melt water pulse 1a and peaked ca 13 8 ka during the bolling allerod conversion to salinity through the use of a laurentide meltwater end member of 225 indicates that near surface salinity de creased by 2 4 during these spikes these results suggest that gulf of mexico sst warming preceded peak laurentide ice sheet decay and the bolling allerod interval by 2 k y and that heat was retained in the subtropical atlantic during heinrich event 1 consistent with modulation of deglacial climate by thermohaline circulation

the mode and mechanism of the last deglaciation oceanic evidence changes in ocean temperature carbonate productivity and ice rafted detritus in the north atlantic suggest that half of the northern hemisphere ice volume at the last glacial maximum had disappeared by 13 000 yr b p despite the still extensive limits of the ice sheets this early thinning of the ice sheets occurred during a time when summer insolation values were slowly rising but when pollen evidence south of the ice margins indicates cold dry air masses we infer that this rapid early ice disintegration 16 000 13 000 yr b p was caused by oceanic mechanisms 1 rising sea level causing increased calving along ice margins 2 the chilling of the sea surface by icebergs and meltwater reducing moisture extraction by the atmosphere and transport to the ice sheets and 3 winter freezing of the low salinity meltwater layer suppressing local moisture extraction and the regional influx of moisture bearing storms from lower latitudes in winter and hence starving the ice sheets these oceanic feedback mechanisms were strongest from 16 000 to 13 000 yr b p and weaker but still active from that date until the end of deglaciation at 6000 yr b p

climate induced variations in productivity and planktonic ecosystem structure from the younger dryas to holocene in the cariaco basin venezuela a high resolution molecular organic geochemical study of sediments in the anoxic cariaco basin indicates significant changes in primary productivity and planktonic community structure associated with the transition from the younger dryas to the holocene variations in climate conditions over the past 12 14c kyr have induced large scale changes in upwelling intensity which directly affected levels of primary productivity as reflected in accumulation rates of bulk productivity proxies concentrations and accumulation rates of sterol and alkenone biomarkers have been used to identify how productivity changes affected the structure of the planktonic ecosystem a shift in the dominant primary producer from diatoms younger dryas to coccolithophores holocene is identified if productivity and ecosystem variations like those identified in the tropical upwelling zone of the cariaco basin region occur throughout the tropical oceans they have the potential to affect global climate through perturbations in the biogeochemical cycle of carbon

differential response of vegetation to postglacial climate in the lower salmon river canyon idaho late pleistocene to holocene terrestrial climate and vegetation records in the lower salmon river canyon of idaho are interpreted from the stable isotopic composition of soil carbonates and from aeolian sedimentation frequencies carbonate and sediment samples from six sections were processed and analyzed with the resulting isotopic and grainsize data organized in relation to a normalized time series developed from an associated radiocarbon chronology this record is interpreted in regards to changes in aridity temperature and wind speed during the late quaternary and is further compared with regional paleoenvironmental records lowered n 18 o and n 13 c concentrations before 20 000 yr bp are interpreted as reflecting late wisconsinan cold conditions after 18 000 yr bp climatic conditions show warmer periods punctuated by sharp returns to colder temperatures and increased c3 flora by 12 000 yr bp higher resolution data show very unstable climatic conditions across the pleistocene holocene boundary reflected in wide variations in n 18 o and n 13 c and aeolian sand deposition during the period between 12 000 and 9000 yr bp the lower salmon river canyon is thought to have experienced marked seasonality with summers and winters respectively warmer and colder than today this climatic scenario was accompanied by an initial instability in canyon vegetation following the establishment of a low energy floodplain in the canyon after 10 000 yr bp a pattern of c3 dominant riparian flora appears during the middle holocene climatic and vegetative variability is much reduced from the preceding period after 4000 yr bp soil carbonate isotopes reflect a trend toward cooler climate conditions and more mesic vegetation populations 2002 elsevier science b v all rights reserved

climatic effects of glacial lake agassiz in the midwestern united states during the last deglaciation stable isotope and pollen analyses of a sediment core from deep lake minnesota provide new information on the climatic effects of glacial lake agassiz in minnesota and insights into the cause of the prominent picea recurrence during the younger dryas in the southern great lakes region bulk carbonate 18o exhibited large fluctuations between 12 0 and 9 1 ka dates are in calendar years throughout this paper unless indicated otherwise probably reflecting the effects of glacial lake agassiz superimposed on climatic warming related to large scale climatic controls in particular a 3 decrease in 18o 11 2 10 2 ka interrupted the 18o enrichment of 1 from 12 0 to 11 2 ka and 3 5 from 10 2 to 9 1 ka this 18o decrease coincided with the expansion of lake agassiz we interpret this decrease as a result of decreased summer temperature and increased precipitation derived from the cold and isotopically light meltwaters of lake agassiz during this 18o decline pinus pollen continued to increase at the expense of picea pollen at deep lake as at other minnesota sites providing evidence that climatic cooling induced by lake agassiz did not cause a reversal to a picea dominated vegetation the absence of such a vegetational response implies that the prominent picea recurrence during the younger dryas in the southern great lakes region was not caused solely by climatic cooling due to increased flux of meltwater from lake agassiz into the great lakes instead the picea recurrence might have been driven primarily by the westward penetration of the younger dryas cooling

late quaternary glacial stades in the cordillera central colombia based on glacial geomorphology tephra soil stratigraphy palynology and radiocarbon dating using data from glacial geomorphology tephra soil stratigraphy and mineralogy palynology and radiocarbon dating a sequence of glacial and bioclimatic stades and interstades has been identified for the last ca 50000 yr in the ruiz tolima massif cordillera central colombia six pleistocene cold stades separated by warmer interstades occurred before 48000 between 48000 and 33000 between 28000 and 21000 from 16000 to ca 14000 ca 13000 12400 and ca 11000 10000 yr bp although these radiocarbon ages are minimum limiting ages obtained from tephra layers on top of tills the tills are not significantly older because most are bracketed by dated tephra sets in measured stratigraphic sections two minor moraine stages likely reflect glacier standstill during cold intervals ca 7400 yr bp and slightly earlier finally glaciers readvanced between the seventeenth and nineteenth centuries in contrast to the ice clad volcanoes of the massif ca 34 km2 in area above an altitude of ca 4800 m the ice cover expanded to 1200 km2 during the last glacial maximum lgm and was still 800 km2 during late glacial time lgt glacier reconstructions based on the moraines suggest depression of the equilibrium line altitude ela by ca 1100 m during the lgm and 500 600 m during lgt relative to the modern ela which lies at ca 5100 m in the cordillera central glaciers in this region apparently reached their greatest extent when the climate was cold and wet e g during stades corresponding to oxygen isotope stage 3 glaciers were still expanding during the lgm ca 28000 21000 yr bp but they shrank considerably after 21000 yr bp because of greatly reduced precipitation 1997 john wiley sons ltd

deglacial paleoceanographic history of the bay of plenty new zealand 1 we present sea surface temperature sst records with centennial scale resolution from the bay of plenty north of new zealand foraminiferal assemblage based paleo sst estimates provide a deglacial record of sst since 16 5 14c ka average holocene ssts are 15 6 c for winter and 20 3 c for summer whereas average glacial values were 14 2 c for winter and 19 5 c for summer compared to modern time cooling of ssts at the last glacial maximum lgm was 0 9 c in winter and 1 5 c in summer the shift from glacial to holocene temperatures began at 14 25 14c ka warming by 2 c until 12 85 14c ka when temperatures dipped back to glacial values at 11 65 14c ka the timing of this return to glacial like sst correlates well with the antarctic cold reversal acr rather than the younger dryas and documents that the influence of the acr extended into the subtropics of the southern hemisphere at least in this region of the southwest pacific by 10 55 14c ka an sst maximum in summer ssts of up to 3 c warmer than modern occurred 24 c after which sst dropped remaining at present day temperatures since 9 3 14c ka this early holocene climatic optimum has been widely noted in the southern ocean and this record indicates that this phenomenon also extended into the subtropics to the north of new zealand

climate change in the circum north atlantic region during the last deglaciation a survey of new and published palaeoclimate data indicates that both the high and low latitude north atlantic regions were characterized by at least three synchronous periods of abrupt climate change during the last glacial to interglacial transi tion climate model results suggest that changes in the melting history of the laurentide ice sheet may explain much of this nonlinear response of the climate system to astronomical milankovitch forcing

stratigraphy and paleolimnologic record of lower holocene sediments in northern lake huron and georgian bay seismic reflection profiling and piston coring identified seismic reflectors in northern lake huron and georgian bay linked with unconformities caused by at least six reductions in lake level in ascending stratigraphic order these lowstands occurred at about 11 200 bp associated with the kirkfield outlet from early lake algonquin 10 200 9900 bp associated with the post algonquin lake level fall 9800 9050 bp the most extreme lowstand associated with the main stanley hough draw down and 7800 7450 bp the concomitant highstands are lake algonquin from about 11 200 10 200 bp early lake mattawa between 9600 and 9350 bp the main mattawa phase 9050 7800 bp and the nipissing highstand at about 4700 bp isotopic and paleoecological data show that all of the lowstands are characterized by cold dilute and isotopically very light 20 waters from the melting laurentian ice cap highstands on the other hand are characterized by higher dissolved solid concentrations and a much smaller

millennial to century scale variability in gulf of mexico holocene climate records of the intertropical convergence zone itcz related to orbital forcing the d 18 o of the surface dwelling planktic foraminifer globigerinoides ruber show negative excursions between 14 and 10 2 ka radiocarbon years that reflect influx of meltwater into the western gom during melting of the laurentide ice sheet the relative abundance of the planktic foraminifer globigerinoides sacculifer is related to transport of caribbean water into the gom maximum transport of caribbean surface waters and moisture into the gom associated with a northward migration of the average position of the itcz occurs between about 6 5 and 4 5 ka in addition abundance variations of g sacculifer show century scale variability throughout most of the holocene the gom record is consistent with records from other areas suggesting that century scale variability is a pervasive feature of holocene climate the frequency of several cycles in the climate records is similar to cycles identified in proxy records of solar variability indicating that at least some of the century scale climate variability during the holocene is due to external solar forcing index terms 4267 oceanography general paleoceanography 9604 information related to geologic time cenozoic 3030 marine geology and geophysics micropaleontology

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

stratigraphy of the younger dryas chronozone and paleoenvironmental implications central and southern great plains abstract the great plains of the united states was the setting for some of the earliest research in north america into patterns and changes in the character of late pleistocene environments and their effects on contemporary human populations many localities in the region have well stratified records of terminal pleistocene and early holocene human paleoindian activity and past environments these have proven important in debates over the character of the younger dryas chronozone ydc 11 000 10 000 14c bp 12 900 11 700 cal bp in the continental interior this paper reviews the lithostratigraphic record of the ydc on the central and southern great plains and summarizes paleobiological records largely isotopic the goal is to determine if there is any uniformity in the timing character direction and or magnitude of changes in depositional environments or broader geomorphic systems before during or after the ydc in order to address the question of the character of environments through this time the stratigraphic records of the late pleistocene to early holocene transition and in particular the stratigraphic records of the ydc vary through time and space the data clearly show that a host of geomorphic processes produced the terminal pleistocene and early holocene stratigraphic records of the great plains moreover the ydc is not necessarily manifest as a distinct lithostratigraphic or biostratigraphic entity in these different types of deposits and soils the various geomorphic systems of the great plains did not behave synchronously in response to any common climate driver these stratigraphic records reflect local environmental conditions and probably a complex response to the reorganization of mid latitude climates in the terminal pleistocene and early holocene

a revised holocene geochronology for the lower mississippi valley data from two locations 1 a hydrodam site at the old river diversion structure south of the latitude of natchez ms and 2 eight water wells from the latitude of baton rouge la are the basis for a revised holocene geochronology of the lower mississippi river floodplain based on 84 radiocarbon dates analyses of 64 borehole logs and 75 grain size analyses which together provide major insight into questions concerning the complexity of meander belt movement the influence of the younger dryas on the lower valley and on the pleistocene holocene interface following the younger dryas the early holocene was characterized by periodic flooding and deposition separated by times of little or no deposition

mid to late wisconsin pollen record of san felipe basin baja california abstract a lacustrine sequence from laguna seca san felipe baja california in the southwestern sonoran desert provides the first record of mid to late wisconsin vegetation in one of the driest regions of north america pollen analysis was performed in the intermediate part of the sequence from ca 44 000 to ca 13 000 14 c yr b p according to six 14 c radiocarbon dates sedimentation of eolian sands prior to 44 000 14 c yr b p indicates dry conditions high pollen concentration of montane and chaparral species in the pollen assemblages contrast with the modern desert vegetation sixty four pollen types were identified the source of mid to late wisconsin sedimentation must have been the plant communities in the surrounding highlands of the basin mid wisconsin pollen assemblages dominated by pines junipers and artemisia reflect humid conditions in the area by late wisconsin time a significant increment in junipers indicates a lowering in the altitudinal ranges of woodlands chaparral pollen from wind pollinated species is abundant while desert plants specifically animal or insect pollinated species are poorly represented the san felipe record does not identify the last glacial maximum as the time of greatest effective moisture as suggested by pluvial lake levels and other paleoclimatic evidence in the soutwestern united states

the younger dryas cool episode in the gulf of mexico data are presented from orca basin piston core en32 pc4 in the gulf of mexico that confirm the existence of surface water cooling during the younger dry as chronozone 11 10 ka late glacial planktonic foraminiferal species made a reappearance between 11 4 and 9 8 ka an episode also marked by distinctly higher oxygen isotopic values derived from the planktonic foraminifer globigerinoides ruber the presence of the younger dryas event in the gulf at 27 n demonstrates that surface water cooling extended to mid latitude regions in the north atlantic the cool surface water interval is bracketed by rapid shifts in 18o related to changes in the influx of meltwater to the gulf of mexico a chronology based upon seven accelerator radiocarbon dates indicates that cooling commenced over a 500 year period and ended in less than 200 years these results are among the first deep sea sediment data documenting the climatic transitions bracketing the younger dryas with a rapidity observed in ice core records a rapid decrease in 18o values measured in the white form of gs ruber at 10 2 ka is explained by significant meltwater influx into the gulf and rapid increase in sea surface temperatures surprisingly a similar decrease is not observed in the pink form of gs ruber a summer surface water dweller in the gulf this discrepancy may be explained by continued meltwater influx throughout the younger dryas during the summers only such that there was no change in the 18o of the pink form at the end of the episode an additional possibility is that warming at the end of the younger dryas raised year average temperatures and summer temperatures remained constant the coincidence of rapid shifts in 18o with the younger dryas strongly suggests a dynamic causal relationship and therefore supports a model for the cause of the younger dryas cooling based on changes in the routing of laurentide glacial meltwater

the chronology of the last deglaciation implications to the cause of the younger dryas event it has long been recognized that the transition from the last glacial to the present interglacial was punctuated by a brief and intense return to cold conditions this extraordinary event referred to by european palynologists as the younger dryas was centered in the northern atlantic basin evidence is accumulating that it may have been initiated and terminated by changes in the mode of operation of the northern atlantic ocean further it appears that these mode changes may have been triggered by diversions of glacial meltwater between the mississippi river and the st lawrence river drainage systems we report here accelerator mass spectrometry ams radiocarbon results on two strategically located deep sea cores one provides a chronology for surface water temperatures in the northern atlantic and the other for the meltwater discharge from the mississippi river our objective in obtaining these results was to strengthen our ability to correlate the air temperature history for the northern atlantic basin with the meltwater history for the laurentian ice sheet

geoarchaeology and paleoecology of the deeply stratified richard beene site medina river valley south central texas usa abstract a geoarchaeological investigation that included soil stratigraphic and paleoecological analyses was conducted at richard beene a deeply stratified open air site associated with an alluvial terrace of the medina river in south central texas the sequence of cultural and alluvial deposits at the site is one of the most complete records of holocene human occupation and sedimentation documented in north america and is very important to the interpretation of the cultural history of the inner gulf coastal plain and adjacent areas of the southern plains the most salient ecological characteristics of the site are its riparian setting and location in the ecotone between north america s western grasslands and eastern woodlands the cultural record spans the past 10 000 years and is buried in 14 m of fine grained flood deposits with multiple buried paleosols excavations totaling 730 m2 sampled 20 stratigraphically distinct archaeological components in valley fill beneath the applewhite terrace yielding more than 80 000 artifacts including flakes tools bones mussel shells and fire cracked rocks left by archaic and late pre columbian hunter gatherers seven primary stratigraphic units and five laterally traceable buried paleosols were identified at the site the oldest stratigraphic unit consists of coarse grained channel deposits that accumulated soon before 33 000 14c yr b p most of the units however consist of fine grained alluvium that accumulated between ca 10 000 and 1000 14c yr b p the 13c values of organic matter from the site s soil stratigraphic sequence indicate increased c4 production during the younger dryas 11 000 10 000 14c yr b p and c4 productivity generally increased throughout the holocene culminating in peak warm intervals at ca 5000 and 2000 14c yr b p although during relatively dry periods grasses expanded at the expense of trees a mosaic of trees and grasses i e a savannah typical of a grassland forest ecotone prevailed at the site throughout the holocene such a food rich environment characterized by an abundance of deer and geophytes as well as mussels from the medina river accounts for repetitive human occupation spanning at least 10 000 years

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

a 50 000 year record of climate oscillations from florida and its temporal correlation with the heinrich events oscillations of pinus pine pollen in a 50 000 year sequence from lake tulane florida indicate that there were major vegetation shifts during the last glacial cycle episodes of abundant pinus populations indicate a climate that was more wet than intervening phases dominated by quercus oak and ambrosia type ragweed and marsh elder the pinus episodes seem to be temporally correlated with the north atlantic heinrich events which were massive periodic advances of ice streams from the eastern margin of the laurentide ice sheet possible links between the tulane pinus and heinrich events include hemispheric cooling the influences of mississippi meltwater on sea surface temperatures in the gulf of mexico and the effects of north atlantic thermohaline circulation on currents in the gulf