deep sea ostracoda from the eastern equatorial pacific odp site 1238 over the last 460 ka abstract core top and near surface core catcher samples from eight drill sites in the eastern tropical pacific were investigated for ostracod assemblage composition integrated ocean drilling program iodp sites u1337 and u1338 4200 4463 m water depth are almost devoid of ostracoda ocean drilling program odp sites 1237 1238 1239 1240 1241 and 1242 depth range of 1400 3200 m exhibit a similar taxonomic composition with a predominance of krithe spp site 1238 located 200 km west of ecuador at a water depth of 2203 m had the highest total abundance and was selected for the downcore assemblage study of glacial interglacial variations over the last 460 ka a total of three different assemblages were distinguished glacial interglacial and background the glacial assemblage is characterized by higher total ostracod abundance ostracod valve accumulation rates and species diversity the typical glacial taxa are krithe spp legitimocythere castanea bradleya mesembrina cytheropteron spp and fallacihowella sol interglacial intervals are characterized by low abundance and diversity and the characteristic taxa are pseudobosquetina mucronalata bradleya sp 1 agrenocythere hazelae and poseidonamicus major a background assemblage is found throughout the entire record and consists of parakrithe sp ambocythere cf sturgio and rugocythereis sp during glacial intervals marine isotope stages mis 6 8 10 12 site 1238 was more strongly influenced by the colder higher oxygenated circum polar deep water interglacial intervals mis 7 9 11 were characterized by climate warming increased bottom water corrosiveness and decrease in dissolved oxygen the upper part of the record at site 1238 mis 1 5 is characterized by increased biogenic sedimentation rates and possible intensification of upwelling

benthic ostracoda and foraminifera from the north adriatic sea italy mediterranean sea a proxy for the depositional characterisation of river influenced shelves abstract we investigated the distribution of ostracoda and benthic foraminifera from the shallow 20 m diversified meiofaunal assemblages occur with ostracoda discriminating sediment starved areas enriched in sand our results demonstrate that the combined use of ostracoda and benthic foraminifera represents a powerful tool for the depositional characterisation of river influenced shelves and to achieve detailed palaeogeographical reconstructions from shallow marine successions

paleomagnetism and 40ar 39ar chronology of lavas from meseta del lago buenos aires patagonia 1 as part of a larger project investigating paleosecular variation in south america 36 paleomagnetic and geochronology sites were sampled on meseta del lago buenos aires 47 s 289 e 200 km east of the active plate boundary in southern patagonia basaltic lavas sampled range from late miocene to late pleistocene yet most of the individual lavas are younger than 3 3 ma thirty eight isochron ages determined via 40ar 39ar incremental heating experiments frame a detailed stratigraphy the isochron ages range from 66 9 4 1 ka for scoria cones and a youthful lava flow in the rio pinturas valley to 10 12 1 35 ma for thick plateau forming lavas exposed along the se edge of the meseta the last 3 3 myr is characterized by seven episodes of volcanism at ca 3 2 3 0 ma 2 4 ma 1 7 ma 1 35 ma 1 0 ma 750 ka 430 330 ka and 110 ka the bulk of lavas forming the surface of the meseta erupted in the last 1 7 my all sites have stable magnetization and after step demagnetization using either thermal or alternating field techniques yield characteristic directions held by magnetite and or titanomagnetite ten sites have distinct transitional directions defined by pole latitudes 55 and associated ages indicate possible connections to known reversals within the matuyama chron including the onset of the jaramillo subchron 1 016 0 01 ma the cobb mountain subchron 1 25 0 03 ma the ontong java 1 event 1 37 0 03 ma and the termination of the olduvai subchron 1 72 0 02 ma remaining sites are divided into normal 14 sites and reversed polarity 12 sites at 95 confidence mean normal and reversed directions overlap the mean direction for 26 sites is i 63 0 d 3 4 95 5 4 which is indistinguishable from the expected geocentric axial dipole paleosecular variation measured by the dispersion of virtual geomagnetic poles about the rotation axis is higher than expected at 20 0 model g using data for the past 5 myr predicts a dispersion of 17 this discrepancy may be due to true dispersion of the field in southern south america or it may be an artifact of inadequate sampling

enhanced ventilation of the north atlantic subtropical gyre thermocline during the last glaciation the ocean s intermediate1 6 and deep7 8 circulation are both known to have differed during the last glaciation from those of today but little is known about the history of the subtropical gyres variations in gyre processes should be closely linked to variations in global climate as gyre circulation is driven by air sea interactions and reflects the climate at the ocean surface the gyres are also a significant reservoir of carbon and nutrients so that gyre processes affect the distribution of carbon and nutrients in the oceans and thus atmospheric co2 here we use measurements of 13c and 18o in foraminifera from the bahamas to produce a detailed reconstruction of nutrient and temperature profiles in the thermocline during the last glaciation the thermocline of the glacial north atlantic subtropical gyre lacked the oxygen minimum that is characteristic of the modern ocean and was depleted in nutrients indicating greater more uniform thermocline ventilation at that time thus not only intermediate waters1 5 but the entire upper water column within the glacial north atlantic was depleted of nutrients moreover glacial thermocline waters were cooler had a steeper temperature gradient and a shallower base both the ventilation and the thermal structure of the glacial thermocline are consistent with what is known of the glacial climate9 14

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

north atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles variations in the ratio of magnesium to calcium mg ca in fossil ostracodes from deep sea drilling project site 607 in the deep north atlantic show that the change in bottom water temperature during late pliocene 41 000 year obliquity cycles averaged 1 5 c between 3 2 and 2 8 million years ago ma and increased to 2 3 c between 2 8 and 2 3 ma coincidentally with the intensification of northern hemisphere glaciation during the last two 100 000 year glacial to interglacial climatic cycles of the quaternary bottom water temperatures changed by 4 5 c these results show that glacial deepwater cooling has intensified since 3 2 ma most likely as the result of progressively diminished deepwater production in the north atlantic and of the greater influence of antarctic bottom water in the north atlantic during glacial periods the ostracode mg ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from site 607 as well as derivation of a hypothetical sea level curve for the late pliocene and late quaternary the effects of dissolution on the mg ca ratios of ostracode shells appear to have been minimal

deep sea ostracode species diversity response to late quaternary climate change late quaternary ostracode assemblages from the north atlantic ocean were studied to establish the effect of climatic changes of the past 210 000 yr marine oxygen isotope stages 7 1 on deep sea benthic biodiversity and faunal composition two hundred and twenty five samples from thechain 82 24 core 4pc 41o43 0 n 32o51 0 w 3427 m water depth on the western mid atlantic ridge revealed high amplitude fluctuations in ostracode abundance and diversity coincident with orbital and suborbital scale climate oscillations measured by several paleoceanographic proxy records during the past 210 000 yr ostracode biodiversity as measured by species number s and the shannon weaver index h s oscillated from h s d 0 4 during glacial periods marine isotope stages 6 5d 5b 4 and 2 to h s d 1 1 during interglacial and interstadial periods stages 7 5e 5c 5a 3 and 1 a total of 23 diversity peaks could be recognized eleven of these signify major periods of high diversity h s 0 8 sd 10 21 occurring every 15 20 ka twelve were minor peaks which may represent millennial scale diversity oscillations the composition of ostracode assemblages varies with krithe dominated assemblages characterizing glacial intervals and argilloecia cytheropteroncharacterizing deglacials and trachyleberid genera poseidonamicus echinocythereis henryhowella oxycythereis abundant during interglacials diversity and faunal composition changes can be matched to independent deep sea paleoceanographic tracers such as benthic foraminiferal carbon isotopes krithe trace elements mg ca ratios and to north atlantic region climate records such as greenland ice cores when interpreted in light of ostracode species ecology these faunal and diversity patterns provide evidence that deep sea benthic ecosystems experience significant reorganization in response to climate changes over orbital to millennial timescales published by elsevier science b v

an early to mid pleistocene deep arctic ocean ostracode fauna with north atlantic affinities abstract an early to middle pleistocene ostracode fauna was discovered in sediment core p1 93 ar 23 p23 76 95 n 155 07 w from 951 meter water depth from the northwind ridge western arctic ocean piston core p23 yielded more than 30 000 specimens and a total of about 30 species several early to mid pleistocene species in the genera krithe echinocythereis pterygocythereis and arcacythere are now extinct in the arctic and show taxonomic affinities to north atlantic ocean species our results suggest that there was a major ostracode faunal turnover during the global climate transitions known as the mid pleistocene transition mpt 1 2 to 0 7 ma and the mid brunhes event mbe 400 ka reflecting the development of perennial sea ice during interglacial periods and large ice shelves during glacial periods over the last 400 000 years

the little ice age and medieval warm period in the sargasso sea sea surface temperature sst salinity and flux of terrigenous material oscillated on millennial time scales in the pleistocene north atlantic but there are few records of holocene variability because of high rates of sediment accumulation holocene oscillations are well documented in the northern sargasso sea results from a radiocarbondated box core show that sst was approximately 1 degree c cooler than today approximately 400 years ago the little ice age and 1700 years ago and approximately 1 degree c warmer than today 1000 years ago the medieval warm period thus at least some of the warming since the little ice age appears to be part of a natural oscillation 39 refs 4 figs 1 tab

postglacial patagonian mass movement from rotational slides and spreads to earthflows abstract many of the volcanic plateau margins of the eastern formerly glaciated foreland of the patagonian andes are undermined by giant landslides 108 m3 one cluster of such landslides extends along the margin of the meseta del lago buenos aires mlba plateau that is formed mainly by neogene quaternary basalts the dry climate is at odds with numerous 2 km long earthflows nested within older and larger compound landslides we present a hydrological analysis a detailed geomorphic map interpretations of exposed landslide interiors and radiocarbon dating of the el mirador landslide which is one of the largest and morphologically most representative landslide we find that the presence of lakes on top of the plateau representing low infiltration rates correlates negatively with the abundance of earthflows on landslide debris along the plateau margins field outcrops show that the pattern of landslides and earthflows is likely controlled by groundwater seepage at the contact between the basalts and underlying soft miocene molasse numerous peat bogs store water and sediment and are more abundant in earthflow affected areas than in their contributing catchment areas radiocarbon dates indicate that these earthflows displaced metre thick layers of peat in the late holocene

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

effects of seasonality forced by orbital insolation cycles on offshore molluscan faunal change during rapid warming in the sea of japan during oxygen isotope stages 50 to 26 an offshore environment that was unsuitable for both cold and warm water molluscs may have temporarily prevailed in the southern sea of japan this inner to outer shelf environment existed with a lateral scale of a few kilometers and a vertical scale of a few tens of meters during at least three transitions from oxygen isotope stages 48 to 47 44 to 43 and 32 to 31 these deglaciation periods coincided with the three highest peaks of july solar insolation at 65 n 495 493 and 500 w m2 between oxygen isotope stages 50 and 26 this implies that anomalously high seasonality induced by orbital insolation cycles is likely to have played an important role in establishing non analog benthic communities with a very low density and diversity of molluscs in the early pleistocene sea of japan

the northern guests and other palaeoclimatic ostracod proxies in the late quaternary of the basque basin s bay of biscay abstract the analysis of the ostracod assemblages from three cores obtained from the middle and outer shelves of the basque basin allows us to evidence the influence of different water masses on the basque shelf during late quaternary mis 3 the present during pre holocene the dominance of krithe spp and cytherella lata marks the input of cold costa edwardsii and palmoconcha guttata evidences the presence of warm waters 11 17 c however the abundance of krithe spp c lata and cytherella alvearium in the eastern outer shelf shows the input of colder waters by upwelling currents from deeper areas of the southern bay of biscay and their restricted influence to the eastern margin in the middle shelf despite the affectation of warm waters dominance of c edwardsii during the early holocene c 8 8 6 8 ka cal bp the values of 18 o bull neogloboquadrina pachyderma sin and northern guests acanthocythereis dunelmensis and trachyleberis sp percentages point to the entrance of colder polar surface and bottom waters during the mid holocene c 6 8 4 3 ka cal bp which came from the west of the study area as upwelling currents during the late holocene c 4 3 ka cal bp to the present these circumpolar waters retreated from the middle shelf and the bottom waters suffered a relative warming besides some cold climatic events such as heinrich event he 3 c 31 3 ka cal bp have been characterized in the basque shelf by the presence of northern guests a dunelmensis cytheropteron testudo and trachyleberis sp which defines the occasional input of cold 0 8 c bottom waters coming from the circumpolar area of the north atlantic ocean into the basque shelf during late quaternary

glacial interglacial differences in circulation and carbon cycling within the upper western north atlantic we investigated glacial interglacial changes in the circulation and carbon cycling in the western north atlantic subtropical gyre using hydrographic data and downcore records of the stable isotopic compositions of individual shells of bahamian benthic foraminifera potential temperature salinity depth relations show that modern thermocline 200 1000 m and deep 1000 2000 m waters in the providence channels bahamas originate in the sargasso sea and are typical of the subtropical gyre gradients in the stable isotopic compositions of late holocene planulina and cibicidoides species from the bank margins 400 to 1500 m depth reflect temperature nutrient and isotopic gradients of modern subtropical gyre waters the difference between the 18o of glacial maximum and late holocene foraminifera is 2 1 for the upper 900 m of the water column and 1 6 for deeper waters indicating that these waters were 4 c and 2 c cooler respectively during glacial time the glacial temperature gradient dt dz was similar to today while the base of the thermocline was 100 m shallower these results differ significantly from our earlier results from multiple shell 18o analyses which implied upper thermocline waters were only 1 c cooler and dt dz was greater during the glacial maximum the difference occurs because bioturbation adversely affects multiple shell analyses of glacial aged samples from shallow water depths at all depths above 1500 m foraminiferal 13c are greater during the glacial maximum than the late holocene by at least 0 1 to 0 2 as much as 0 6 in the lower thermocline indicating that nutrient concentrations throughout the thermocline were reduced and there was no oxygen minimum zone during the glacial maximum this suggests greater more uniform ventilation of the thermocline results of single and multiple shell 13c analyses of glacial age foraminifera compare favorably because samples most affected by mixing correspond to water depths where the glacial interglacial change of 13c was small cooler upper ocean waters during the glacial maximum reflect cooler temperatures at the ocean surface where isopycnal surfaces outcrop including large areas of the subtropical ocean a shallower thermocline base is consistent with southward migration of the northern edge of the subtropical gyre or increased mode water production enhanced thermocline ventilation is consistent with more vigorous winds and all isopycnal surfaces outcropping in the area of ekman downwelling

okhotsk sea ostracods in surface sediments depth distribution of cryophilic species relative to oceanic environment abstract the depth distribution of benthic ostracods in surface sediments of the southern okhotsk sea in the marginal northwestern pacific reflects environmental factors such as water depth water mass properties and sea ice transport ostracods are much more abundant on the continental shelf than on the continental slope with only a few specimens present on the lower slope many species in this study area are identical to cryophilic species in the northern japan sea which lies adjacent to the southern okhotsk sea comparison of the depth distribution patterns of shallow water e g johnnealella nopporensis and munseyella hatatatensis and deep water e g argilloecia toyamaensis species in the northern japan sea reveals two relationships 1 the depth distribution range of j nopporensis m hatatatensis and other species in the okhotsk sea upper shelf to upper continental slope 50 500 m is greater than in the japan sea upper to middle shelf 40 120 m 2 the abundances of a toyamaensis and other species on the continental slope of the okhotsk sea are lower than on the japan sea slope the presence of a few shallow water species such as m hatatatensis on the upper continental slope of the okhotsk sea is probably the result of ice rafting the low abundance of a toyamaensis and other species in the okhotsk sea reflects both lower dissolved oxygen values compared to the northern japan sea and the shallow depth of soya strait that connects the two seas

the gisp2 δ18o climate record of the past 16 500 years and the role of the sun ocean and volcanoes measured 18o 16o ratios from the greenland ice sheet project 2 gisp2 ice core extending back to 16 500 cal yr b p provide a continuous record of climate change since the last glaciation high resolution annual 18o 16o results were obtained for most of the current millennium a d 818 1985 and record the medieval warm period the little ice age and a distinct 11 yr 18o 16o cycle volcanic aerosols depress central greenland annual temperature 1 5 c maximally and annual 18o 16o for about 4 yr after each major eruptive event on a bidecadal to millennial time scale the contribution of solar variability to holocene greenlandic temperature change is 0 4 c the role of thermohaline circulation change on climate problematic during the holocene is more distinct for the 16 500 10 000 cal yr b p interval analogous to 14c age calibration terminology we express time in calibrated cal yr b p a d 1950 0 cal yr b p the oldest dryas bolling older dryas allerod younger dryas sequence appears in great detail bidecadal variance in 18o 16o but not necessarily in temperature is enhanced during the last phase of lateglacial time and the younger dryas interval suggesting switches of air mass transport between jet stream branches the branched system is nearly instantaneously replaced at the beginning of the bolling and holocene at 14 670 and 11 650 cal yr b p respectively by an atmospheric circulation system in which 18o 16o and annual accumulation initially track each other closely thermodynamic considerations of the accumulation rate temperature relationship can be used to evaluate the 18 o 16o temperature relationship the gisp2 ice layer count years of major gisp2 climate transitions also support the use of coral 14c ages for age calibration

western north atlantic evidence for millennial scale changes in ocean circulation and climate two late quaternary series of high resolution percent carbonate data from western north atlantic sediment drifts bermuda rise and bahama outer ridge show millennial scale oscillations superimposed on the familiar longer period oscillations of orbital origin the dominant high frequency oscillation in these records has a quasi period of about 4000 years these percent caco3 changes most likely result from the influence of climate change on the flux of terrigenous material from eastern canada the resuspension of continental margin sediment by deep eddy kinetic energy and carbonate dissolution sediment is transported to the bermuda rise by deep recirculating gyres and to the bahama outer ridge by the deep western boundary current system stable isotope results on foraminifera across several of these oscillations from interstadial climate conditions and from a glacial inception display variability similar to that of percent caco3 oxygen isotope ratios of planktonic foraminifera suggest large variations in near surface temperature and or salinity and carbon isotope ratios of benthic foraminifera indicate that there were significant oscillations in the flux of north atlantic deep water nadw these data support models which couple surface ocean conditions in the north atlantic production of nadw north atlantic heat flux and evidence for temperature oscillations in ice cores

ostracode mg ca paleothermometry in the north atlantic and arctic oceans evaluation of a carbonate ion effect 1 the reconstruction of deep sea bottom water temperature bwt is important to assess the ocean s response to and role in orbital and millennial scale climate change deep sea paleothermometry employs magnesium to calcium mg ca ratios in calcitic benthic microfaunas foraminifera ostracodes as a primary proxy method mg ca paleothermometry may however be complicated by bottom water carbonate ion chemistry which might affect mg ca ratios in shells to address temperature and carbonate ion influence on mg ca ratios we studied mg ca ratios in the benthic ostracode genus krithe in the north atlantic and arctic oceans using a 686 specimen core top collection including 412 previously unpublished analyses mg ca ratios are positively correlated to temperature in multiple species from the north atlantic bwt 0 885 mg ca 5 69 r2 0 73 and for k glacialis in the arctic ocean and nordic seas bwt 0 439 mg ca 5 14 r2 0 50 consistent with previously published calibrations we found no evidence for a relationship between krithe mg ca and carbonate ion saturation in the north atlantic ocean nordic seas and arctic ocean supporting the use of krithe mg ca for reconstructing past bwt

response of deep ocean circulation to initiation of northern hemisphere glaciation 3 2 ma carbon isotopic records from benthic foraminifera are used to map patterns of deep ocean circulation between 3 and 2 million years ago the interval when significant northern hemisphere glaciation began the 18o and 13c data from four atlantic sites 552 607 610 and 704 and one pacific site 677 show that global cooling over this interval was associated with increased suppression of north atlantic deep water nadw formation however the relative strength of nadw production was always greater than is observed during late pleistocene glaciations when extreme decreases in nadw are observed in the deep north atlantic our data indicate that an increase in the equator to pole temperature gradient associated with the onset of northern hemisphere glaciation did not intensify deepwater production in the north atlantic but rather the opposite occurred this is not unexpected as it is the warm high salinity characteristic rather than the low temperature of thermocline waters that is critical to the deepwater formation process in this region today

deep sea ostracode turnovers through the paleocene eocene thermal maximum in dsdp site 401 bay of biscay north atlantic abstract previous low resolution studies suggest that ostracodes in contrast with deep sea foraminifera largely survived the massive environmental changes of the paleocene eocene thermal maximum petm in a new high resolution study from the continental slope 1800 m paleodepth ne atlantic we also find extensive survivorship of ostracode faunas but this is accompanied by a temporary drop in species diversity and ecological diversity during the petm there are 12 common ostracode species before the petm that are reduced to only two species at the same time as the benthic foraminiferal extinction event all but three species reappear in the later parts of the petm and statistical analysis suggests that most of the apparent lazarus species might be found with sufficient sampling of petm faunas we find no evidence for an excursion fauna of ostracodes as has been detected in calcareous nannofossils planktic foraminifera and benthic foraminifera however the ostracode assemblages changed from a relatively diverse ecological assemblage before and after the petm to one dominated by infaunal species typical of low oxygen conditions during the petm the absence of major extinction and the temporary nature of species disappearances are comparable to turnovers in shallow marine ostracodes and stands in sharp contrast to the 50 species level extinction in benthic foraminifers

suborbital timescale variability of north atlantic deep water during the past 200 000 years we generated 200 kyr long proxy records of surface and deepwater variability from a subpolar north atlantic core v29 202 enabling us to assess the linkage between surface and deepwater changes on suborbital timescales in particular we used a benthic 13c record to evaluate the deep water response to dansgaard oeschger temperature oscillations and to heinrich events times of massive iceberg delivery to the north atlantic we found that the reduction of north atlantic deep water nadw production was generally associated with cold or dropping sea surface temperatures ssts as indicated by planktonic foraminiferal assemblages the nadw contribution to the site did not drop appreciably during heinrich events h4 through h2 probably because these events followed intervals of prolonged surface cooling already characterized by low rates of nadw production by contrast nadw reduction appears to have been synchronous with h5 sst rise associated with both dansgaard oeschger oscillations and heinrich events was usually accompanied by increasing nadw strength in a few cases the nadw recovery appeared to lag the sst rise however the apparent delay is most likely an artefact of the sedimentary record low concentrations of benthic foraminifera as a result of low benthic foraminiferal abundances during stage 6 the stage 6 benthic foraminiferal 13c record is of lower resolution than the younger part of the record the stage 6 proxy records for surface hydrography nevertheless reveal millennial scale oscillations similar to those seen in stage 3 the available 13c data suggest that nadw weakened in association with the cold portions of stage 6 sst oscillations we also sought to confirm a recent study which concluded that there was little nadw variability during the peak of the last interglaciation marine oxygen isotope substage 5e eemian isotope stage 5 was marked by a trend of increasing benthic 13c in v29 202 rising 13c through isotope stage 5 is also seen in tropical surface water records and at some deep atlantic sites and may reflect the common derivation of these water masses variations of 0 5 superimposed on this rising 13c trend within substage 5e in v29 202 are so far not evident in tropical feed waters and may therefore indicate that nadw production was weaker during the late than mid eemian an electronic supplement of this material may be obtained on a diskette or anonymous ftp from kosmos agu org login to agu s ftp account using anonymous as the username and guest as the password go to the right directory by typing cd apend type ls to see what files are available type get and the name of the file to get it finally type quit to leave the system paper 95pa02089 suborbital timescale variability of north atlantic deep water during the past 200 000 years by d w oppo and s j lehman diskette may be ordered from american geophysical union 2000 florida avenue n w washington dc 20009 15 00 payment must accompany order

simulation of abrupt climate change induced by freshwater input to the north atlantic ocean temperature records from greenland ice cores1 2 suggest that large and abrupt changes of north atlantic climate occurred frequently during both glacial and postglacial periods one example is the younger dryas cold event broecker3 speculated that these changes result from rapid changes in the thermohaline circulation of the atlantic ocean which were caused by the release of large amounts of melt water from continental ice sheets here we describe an attempt to explore this intriguing phenomenon using a coupled ocean atmosphere model in response to a massive surface flux of fresh water to the northern north atlantic of the model the thermohaline circulation weakens abruptly intensifies and weakens again followed by a gradual recovery generating episodes that resemble the abrupt changes of the ocean atmosphere system recorded in ice and deep sea cores4 the associated change of surface air temperature is particularly large in the northern north atlantic ocean and its neighbourhood but is relatively small in the rest of the world

quaternary glacial and deglacial ostracoda in the thermocline of the little bahama bank nw atlantic palaeoceanographic implications abstract we determined faunal and oceanographic changes during the last glacial and deglacial in the providence channel little bahama bank lbb using modern ocean from lbb florida hatteras slope and blake plateau western north atlantic and late quaternary lbb distributions of the benthic ostracode genus krithe from the mid depth 300 1600 m subtropical north atlantic ocean nine species of krithe are limited in their bathymetric distribution by warm bottom water temperatures or a temperature related parameter in the thermocline of the modern atlantic during the last glacial interval in the northwest providence channel of the little bahama bank five species of krithe k aequabilis k dolichodeira k gr minima k reversa and k trinidadensis migrated upslope conversely during the deglaciation most krithe species migrated downslope re occupying their deeper niches these vertical species migrations are attributed to decreased glacial bottom water temperatures and perhaps increased dissolved oxygen during the last glacial and warmer water temperatures during the deglacial based upon thermal values of recent depth ranges of selected species of krithe we estimate that glacial waters cooled about 4 c shallower than 900 m and about 2 c deeper than 900 m and deglacial waters warmed about the same values in shallow and mid depth water masses comparing to modern temperatures the discovery of common halocypris a mesopelagic ostracode in little bahama bank glacial and deglacial sediments also suggests greater oxygenation relative to the late holocene

40ar 39ar and k ar chronology of pleistocene glaciations in patagonia during the pleistocene east of lago buenos aires argentina at 46 5 s at least 19 terminal moraines were deposited as piedmont glaciers from the patagonian ice cap advanced onto the semi arid high plains adjacent to the southern andes exceptional preservation of these deposits offers a rare opportunity to document ice cap fluctuations during the last 1 2 m y 4 0 ar 3 9 ar incremental heating and unspiked k ar experiments on four basaltic lava flows interbedded with the moraines provide a chronologic framework for the entire glacial sequence the 4 0 ar 3 9 ar isochron ages of three lavas that overlie till 90 km east of the cordillera at lago buenos aires and another 120 km from the andes along rio gallegos at 51 8 s that underlies till strongly suggest that the ice cap reached its greatest eastward extent ca 1100 ka at least six moraines were deposited within the 256 k y period bracketed by basaltic eruptions at 1016 10 ka and 760 14 ka similarly six younger more proximal moraines were deposited during an 651 k y period bracketed by an underlying 760 14 ka basalt and the 109 3 ka cerro volcan basalt flow that buried all six moraines coupled with in situ cosmogenic surface exposure ages of moraine boulders the 109 ka age of cerro volcan implies that moraines deposited during the penultimate local glaciation correspond to marine oxygen isotope stage 6 further westward toward lago buenos aires six additional moraines younger than the cerro volcan basalt flow occur surface exposure dating of boulders on these moraines combined with the 1 4 c age of overlying varved lacustrine sediment indicates deposition during the last glacial maximum lgm 23 16 ka although antarctic dust records signal an important patagonian glaciation at 60 40 ka moraines corresponding to marine oxygen isotope stage 4 are not preserved at lago buenos aires apparently these were overrun and obliterated by the younger ice advance at 23 ka notwithstanding the overall pattern of glaciation in patagonia is one of diminishing eastward extent of ice during successive glacial advances over the past 1 m y we hypothesize that tectonically driven uplift of the patagonian andes which began in the pliocene yet continued into the quaternary in part due to subduction of the chile rise spreading center during the past 2 m y maximized the ice accumulation area and ice extent by 1 1 ma subsequent deep glacial erosion has reduced the accumulation area resulting in less extensive glaciers over time

natural hazards versus climate change and their potential impacts in the dry northern himalayas focus on the upper kali gandaki mustang district nepal in the himalayas the consequences of climate change are a fairly debated issue mainly questioning the availability of water resources to the lowland population north of the monsoon himalayas a semi arid continental climate prevails and settlements rely economically mostly on irrigated crops high altitude rangelands trade and tourism the upper kali gandaki mustang is situated in this area with sharp contrasts between valley bottoms 3 000 m and high glaciated peaks up to 8 000 m the impacts of climate change may appear in different ways gullying is common and might increase with greater climate variability increased ground instabilities earthflows and occasional debris flows affecting extensive shale marly substrates are also expected linked to changes in snow cover and seasonality similarly the combination of higher snowfall and rapid melting may favour the occurrence of flash floods the possibility of glacial outburst floods is less probable because of the present limited glaciation eventually permafrost melting may induce rock avalanches down the steepest cliffs and might impact the adjacent valley floors collectively these hazards will affect irrigation canals and fields new infrastructures and the associated growing settlements water availability in the near future is more difficult to predict however any change in the amount and nature of precipitation may affect groundwater reserves hence spring discharge and runoff with consequences for agricultural products eventually the overall potential increase in natural hazards may jeopardize the development of small markets and the good connection of these upper valleys to the main urban centres of nepal a country with a very low economic and social capacity to adjust

pliocene 3 2 2 4 ma ostracode faunal cycles and deep ocean circulation north atlantic ocean ostracode assemblages from deep sea drilling project sites 607 western mid atlantic ridge and 610 southeast rockall plateau show rapid systematic shifts during late pliocene glacial interglacial cycles that reflect deep sea environmental change progressive decreases in north atlantic deep water taxa and increases in southern ocean taxa occur from 3 4 to 2 4 ma and high amplitude faunal cycles begin near 2 8 ma four ostracode assemblages each with a characteristic phase relative to 41 k y obliquity glacial interglacial 18 o cycles characterize the benthic faunal record at site 607 cross spectral analysis shows that the site 607 glacial assemblage has a 41 k y periodicity significant at the 95 level other assemblages show a less significant but still obvious concentration of variance at 41 k y faunal patterns suggest climatically controlled reorganization of deep sea benthic communities during glacial interglacial cycles due to oscillating deep sea environments

cenozoic bathyal and abyssal ostracods beneath the oligotrophic south pacific gyre iodp expedition 329 sites u1367 u1368 and u1370 abstract this study reports on paleocene through pleistocene deep sea ostracod assemblages from carbonate sequences recovered at integrated ocean drilling program iodp sites u1367 u1368 and u1370 during expedition 329 to the south pacific gyre spg the spg has the lowest surface primary productivity in the world oceans and the sedimentary system beneath it has the lowest rates of organic matter flux to the seafloor in the ocean results show that this oligotrophic oceanic environment supported abundant and diverse ostracod faunas during the oligocene and the middle miocene suggesting that ostracods are capable of exploiting low levels of food availability in the deep ocean the spg records revealed ostracod assemblages following major global climatic transitions the cretaceous paleocene 65 5 ma and the eocene oligocene 33 5 ma transitions and the middle miocene climatic optimum 14 ma the danian ostracod assemblage is scarce and characterized by paraphysocythere spp and anebocythereis hostizea high faunal turnover by the early oligocene gives rise to an assemblage predominantly characterized by typical lower bathyal and abyssal genera krithe poseidonamicus argilloecia and cytheropteron that are indicative of cold moderately oxygenated conditions and signal the cooling of the deep ocean after the e o transition an increase in abundance of robust epifaunal taxa bradleya henryhowella dutoitella pennyella and rugocythereis and a pronounced decrease argilloecia and cytheropteron characterize the middle miocene and pleistocene assemblages and indicate the presence of more corrosive bottom waters and enhanced oligotrophic conditions in the spg however low variability in the ostracod assemblage taxonomic composition and stratigraphic distribution at sites u1367 and u1368 suggest that mostly stable paleoceanographic conditions existed in the south pacific gyre during the early to the late oligocene and from the middle to late miocene u1368 declines in ostracod abundances toward the top of the sedimentary sequences at these sites are synchronous with the late oligocene warming and the late miocene carbonate crash in the equatorial pacific but they seem to also overlap the time when the site locations subsided below the calcium carbonate compensation depth ccd as they moved away from the east pacific rise

a morphotectonic analysis of central patagonian cordillera negative inversion of the andean belt over a buried spreading center 1 we use digital elevation models and satellite imagery data completed with field observations to develop an integrated morphotectonic analysis of the anomalous topography of the central cordillera of patagonia between 46 s and 48 s in a region overlying subducted segments of the chile spreading ridge this region shows a number of peculiar features not expected in a normal subduction related belt located away from a buried spreading center first it is characterized by overall short wavelength topography and highly contrasted reliefs typical of deeply incised young mountain belts but surprisingly also by an average very low elevation of 900 m second the cordillera lacks central high reliefs instead there is a central depressed domain with average low slope gradients including the deepest point of the study area 300 m below sea level in the bottom of lake general carrera buenos aires this depressed area is flanked by western and eastern regions of higher elevation having opposite general slope dips to the east the central patagonian cordillera is now separated from the flat plains of the pampean domain representing its former piedmont and several elevated basaltic plateaus mesetas by 160 n 180 n trending morphotectonic corridors and the western border scarps of the mesetas these scarps correspond to neotectonic features controlled by recent vertical faults mostly active after 3 ma remnants of a former peneplain the avellanos surface are widespread within the entire cordilleran region from geological evidence this peneplain formed between 15 and 4 ma and was connected originally with the mesetas domain and now is dissected by these corridors it is shown that a negative inversion related to extensional and strike slip faulting occurred in the frontal region of the cordillera at 3 ma synchronously with the emplacement of magmatic products timing of the extensional deformation in central patagonia is concomitant with the migration at depth of different segments of the south chile ridge which entered the trench at 6 and 3 ma respectively and the consequent opening of a slab window allows asthenospheric hot mantle to reach lithospheric regions finally migration of segments of the chile spreading ridge since 6 ma triggered regional uplift of the cordillera followed by limited extension in relation with increased thermal weakening of the crust

late quaternary paleoceanography of the eurasian basin arctic ocean we reconstructed late quaternary deep 3000 4100 m and intermediate depth 1000 2500 m paleoceanographic history of the eurasian basin arctic ocean from ostracode assemblages in cores from the lomonosov ridge gakkel ridge yermak plateau morris jesup rise and amundsen and makarov basins obtained during the 1991 polarstern cruise modern assemblages on ridges and plateaus between 1000 and 1500 m are characterized by abundant relatively species rich benthic ostracode assemblages in part reflecting the influence of high organic productivity and inflowing atlantic water in contrast deep arctic eurasian basin assemblages have low abundance and low diversity and are dominated by krithe and cytheropteron reflecting faunal exchange with the greenland sea via the fram strait major faunal changes occurred in the arctic during the last glacial interglacial transition and the holocene low abundance low diversity assemblages from the lomonosov and gakkel ridges in the eurasian basin from the last glacial period have modern analogs in cold low salinity low nutrient greenland sea deep water glacial assemblages from the deep nansen and amundsen basins have modern analogs in the deep canada basin during termination 1 at intermediate depths diversity and abundance increased coincident with increased biogenic sediment reflecting increased organic productivity reduced sea ice and enhanced inflowing north atlantic water during deglaciation deep nansen basin assemblages were similar to those living today in the deep greenland sea perhaps reflecting deepwater exchange via the fram strait in the central arctic early holocene faunas indicate weaker north atlantic water inflow at middepths immediately following termination 1 about 8500 7000 year b p followed by a period of strong canada basin water overflow across the lomonosov ridge into the morris jesup rise area and central arctic ocean modern perennial sea ice cover evolved over the last 4000 5000 years late quaternary faunal changes reflect benthic habitat changes most likely caused by changes in the import of cold deepwater of greenland sea origin and warmer and middepth atlantic water to the eurasian basin through the fram strait and export of arctic ocean deepwater

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

biotic response of tethyan bathyal ostracodes through the eocene oligocene transition the composite faunal record from the massicore and massignano global stratotype section and point east central italy abstract the eocene oligocene transition eot is marked by a double stepped positive 18 o excursion of 1 3 and a deepening of the calcium compensation depth ccd interpreted to represent marked antarctic glaciation and global ocean atmosphere cooling i e oi 1 event a 0 5 m 55 70 kyr resolution ostracode faunal study of the massicore drilled up section from the italian massignano quarry containing the eocene oligocene global stratotype section and point gssp revealed a relative increase in krithe and decreases in faunal evenness and shannon index correlative to the oi 1 event these transient faunal changes may reflect local water column changes e g export production or intensified thermohaline flow of cooler deep waters through the paleotethyan seaway comparison of these massicore ostracode faunal data to previously published massignano quarry ostracode faunal data reveals similar relative abundances among common taxa where the study intervals overlap and thereby provide a more complete tethyan ostracode record spanning all of c13n and the broader eot at the gssp locality

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

late quaternary deep sea ostracodes in the polar and subpolar north atlantic paleoecological and paleoenvironmental implications two sediment cores from the northern north atlantic one from the iceland plateau and one from the rockall plateau were investigated in order to examine the response of deep sea benthic ostracodes to climate related environmental changes since marine isotope stage mis 7 ostracode fauna was divided into three factor assemblages by using q mode factor analyses and diversity was calculated using the shannon wiener index the iceland plateau revealed an interglacial assemblage dominated by henryhowella a transitional assemblage dominated by eucythere and a background assemblage that consists of the common taxa krithe and cytheropteron the presence of henryhowella is linked to conditions that prevailed during the peak interglacial periods mis 5e and 1 characterized by increased food supply well oxygenated bottom water and lateral advection the presence of eucythere mainly during the interstadial periods appears to be related to slightly increased food supply whereas the background assemblage is considered to be opportunistic and able to cope with decreased food supply as interpreted for glacial times on the rockall plateau the opportunistic background assemblage consisting mainly of krithe argilloecia and cytheropteron shows no obvious relation to climate changes the interglacial assemblage consists of several taxa dominated by pelecocythere but as on the iceland plateau it also contains henryhowella the third assemblage is the glacial assemblage that consists of a variety of taxa several of which are known from the modern arctic ocean and the greenland sea shelf thus this assemblage indicates glacial conditions on the rockall plateau that are comparable to those found in the present day arctic ocean diversity calculations revealed higher ostracode diversities in glacial than in interglacial episodes in both cores and particularly high diversities during periods of increased input of iceberg rafted debris ird in the rockall plateau core both cores reveal lower surface water productivity during the glacial compared to the interglacial periods and particularly low productivity during the ird events as inferred from carbonate contents we assume therefore that ostracode diversity in the study areas is negatively correlated with food flux

impacts of post glacial rebound on landslide spatial distribution at a regional scale in northern iceland skagafjorður in de glaciated areas para glaciation i e the conditioning of landscapes by prior glaciation has often been considered a major predisposing factor in landslide occurrence its consequences have been particularly well identified at a fine scale especially on bedrock jointing hitherto the relative impacts of para glaciation on hillslope dynamics at a regional scale had nevertheless not been quantified statistically we examine skagafjor ur area northern iceland where landslides are widespread at least 108 were mapped in an area of c 3000km2 we compare the role of para glaciation debuttressing influence of post glacial rebound with that of classic factors topography lithology etc in landslide occurrence and location using a spatial analysis based on a chi square test on the one hand the results highlight that landslides are over represented in areas where post glacial rebound was at its maximum with a stronger concentration of landslides in the northern part of the fjord on the other hand the distribution of landslides did not show any clear relationship with the pattern of glacial debuttressing tschuprow coefficient highlights that the influence of post glacial rebound on landslide location is higher than the combined influence of slope gradient curvature or geological structure this result is supported by our initial evidence for the timing of landslides in the area most landslides occurred during the first half of the holocene and a period of hillslope instability was initiated when the post glacial uplift was at its maximum finally the mechanisms that link post glacial rebound and landsliding as well as the geomorphic impacts of landslides are discussed

species composition and glacial interglacial variations in the ostracode fauna of the northeast atlantic during the past 200 000 years sediment core m23414 from the rockall plateau north atlantic covering the last two climatic cycles marine isotope stages mis 7 to 1 was investigated for glacial interglacial variations in the deep sea benthic ostracode fauna a highly diversified ostracode fauna including 98 species was found two climate related assemblages were identified associated with interglacial and peak glacial periods respectively the interglacial group occurs during the end of mis 7 5 and 1 and is composed of the genera henryhowella pelecocythere echinocythereis cytherella bradleya aversovalva and eucytherura the glacial group consists of the genera acetabulastoma which is known as sea ice indicator in the modern arctic ocean polycope bythoceratina rhombobythere and some species possibly belonging to the genus pseudocythere and is found during mis 6 4 and 2 these longer term variations within the ostracode fauna seem related to the particular glacial and interglacial climate conditions that affected both deep water production as well as primary production in the surface waters however a detailed comparison of ostracode abundances with the occurrence of events marked by increased ice rafted debris reveals also much shorter term climate related changes in the ostracode fauna thus the temporal fluctuations within ostracode assemblages reflect long and short term alterations of the deep sea environment that are clearly linked to climate changes

changes in north atlantic deep sea temperature during climatic fluctuations of the last 25 000 years based on ostracode mg ca ratios 1 we reconstructed three time series of last glacial to present deep sea temperature from deep and intermediate water sediment cores from the western north atlantic using mg ca ratios of benthic ostracode shells although the mg ca data show considerable variability scatter that is common to single shell chemical analyses comparisons between cores between core top shells and modern bottom water temperatures bwt and comparison to other paleo bwt proxies among other factors suggest that multiple shell average mg ca ratios provide reliable estimates of bwt history at these sites the bwt records show not only glacial to interglacial variations but also indicate bwt changes during the deglacial and within the holocene interglacial stage at the deeper sites 4500 and 3400 m water depth bwt decreased during the last glacial maximum lgm the late holocene and possibly during the younger dryas maximum deep sea warming occurred during the latest deglacial and early holocene when bwt exceeded modern values by as much as 2 5 c this warming was apparently most intense around 3000 m the depth of the modern day core of north atlantic deep water nadw the bwt variations at the deeper water sites are consistent with changes in thermohaline circulation warmer bwt signifies enhanced nadw influence relative to antarctic bottom water aabw thus maximum nadw production and associated heat flux likely occurred during the early holocene and decreased abruptly around 6500 years b p a finding that is largely consistent with paleonutrient studies in the deep north atlantic bwt changes in intermediate waters 1000 m water depth of the subtropical gyre roughly parallel the deep bwt variations including dramatic mid holocene cooling of around 4 c joint consideration of the mg ca based bwt estimates and benthic oxygen isotopes suggests that the cooling was accompanied by a decrease in salinity at this site subsequently intermediate waters warmed to modern values that match those of the early holocene maximum of 7 c intermediate water bwt changes must also be driven by changes in ocean circulation these results thus provide independent evidence that supports the hypothesis that deep ocean circulation is closely linked to climate change over a range of timescales regardless of the mean climate state more generally the results further demonstrate the potential of benthic mg ca ratios as a tool for reconstructing past ocean and climate conditions

irregular glacial interstadials recorded in a new greenland ice core the greenland ice sheet offers the most favourable conditions in the northern hemisphere for obtaining high resolution continuous time series of climate related parameters profiles of 18o 16o ratio along three previous deep greenland ice cores1 3 seemed to reveal irregular but well defined episodes of relatively mild climate conditions interstadials during the mid and late parts of the last glaciation but there has been some doubt as to whether the shifts in oxygen isotope ratio were genuine representations of changes in climate rather than artefacts due to disturbed stratification here we present results from a new deep ice core drilled at the summit of the greenland ice sheet where the depositional environ ment and the flow pattern of the ice are close to ideal for core recovery and analysis the results reproduce the previous findings to such a degree that the existence of the interstadial episodes can no longer be in doubt according to a preliminary timescale based on stratigraphic studies the interstadials lasted from 500 to 2 000 years and their irregular occurrence suggests complexity in the behaviour of the north atlantic ocean circulation

palaeoenvironmental reconstruction of lacustrine source rocks in the lower 1st member of the shahejie formation in the raoyang sag and the baxian sag bohai bay basin eastern china abstract the lower 1st member es1l of the oligocene shahejie formation is the most important source rock interval in the raoyang sag and the baxian sag to reveal the controlling factors that affected the distribution of organic rich source rocks we analyzed the lower es1 es1l samples collected from the raoyang sag and the baxian sag using sedimentological and geochemical techniques to reconstruct the lacustrine palaeoenvironmental conditions most of the samples had chemical index of alteration cia values between 70 and 75 which reflect a stable and moderately weathered source under a transitional climate the distribution of depocenters and palaeo water depths indicated that the main catchment area was concentrated in the raoyang sag with a maximum palaeo water depth of 14 m and a wave base depth of 7 5 m stable isotope data from carbonates 18ocarb and 13ccarb showed that the lakes with long residence times in the raoyang sag had a positive correlation and that the lakes with short residence times in the baxian sag had no isotopic covariance during the deposition of the lower es1 the p al and p ti ratios ptotal and carbon isotope values of the organic matter 13corg in the two sags illustrated stable palaeoproductivity without much fluctuation the enrichments of mo u and ratios of c p org b ga and sr ba further indicated saline and anoxic bottom water conditions associated with stable water column stratification in well xi63 and brackish and less anoxic bottom water conditions in well nd1 during the deposition of the main source rock of the lower es1 moreover the plots of mo and u enrichment versus toc and hydrogen index values versus 13c i e the difference between the 13c values of carbonates and organic matter corroborated the inference that the preservation of organic matter was the main factor controlling the formation of organic rich source rocks in the raoyang sag and the baxian sag during the deposition of the lower es1

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

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

sudden changes in north atlantic circulation during the last deglaciation sudden changes in the flow of warm atlantic surface waters into the norwegian sea occurred frequently during the last deglaciation typically involving shifts in sea surface temperature of 5 c in fewer than 40 years these led to equally large and rapid changes in atmospheric temperatures and to shifts in atlantic deep thermo haline circulation and ice sheet melting rates

evidence for general instability of past climate from a 250 kyr ice core record recent results1 2 from two ice cores drilled in central greenland have revealed large abrupt climate changes of at least regional extent during the late stages of the last glaciation suggesting that climate in the north atlantic region is able to reorganize itself rapidly perhaps even within a few decades here we present a detailed stable isotope record for the full length of the greenland ice core project summit ice core extending over the past 250 kyr according to a calculated timescale we find that climate instability was not confined to the last glaciation but appears also to have been marked during the last interglacial as explored more fully in a companion paper3 and during the previous saale holstein glacial cycle this is in contrast with the extreme stability of the holocene suggesting that recent climate stability may be the exception rather than the rule the last interglacial seems to have lasted longer than is implied by the deep sea specmap record4 in agreement with other land based observations5 6 we suggest that climate instability in the early part of the last interglacial may have delayed the melting of the saalean ice sheets in america and eurasia perhaps accounting for this discrepancy

ecological analysis of benthic ostracods in the northern japan sea based on water properties of modern habitats and late cenozoic fossil records abstract the ecology of ostracods in the northern japan sea is well documented these ostracods can be grouped in two assemblages 1 the tsushima warm current surface water assemblage twsa northern which lives in an environment where summer temperatures reach up to about 20 c winter temperatures up to about 5 c several species in this assemblage e g loxoconcha optima and pontocythere subjaponica tolerate seasonally low temperatures and lived in the region since the early pleistocene 2 the japan sea intermediate proper water assemblage jsi pa which lives at greater depths lower shelf to upper slope this assemblage lives under stable conditions with a small annual range in temperature 0 5 c the assemblage has a relatively low diversity contains species such as acanthocythereis dunelmensis and robertsonites spp and has been present in the area since the pliocene these data indicate that the presently living species either tolerate seasonally low temperatures twsa northern or tolerate stable but very low temperatures near 0 c and therefore they could survive the pleistocene environmental fluctuations in the japan sea caused by glacio eustatic changes in sea level our data document the survival of ostracod species during past climate change and thus can be used to speculate on the effect of possible future climate change on the faunas we predict that some of the cryophilic species in the japan sea cannot be expected to survive global warming for more than 2 centuries

pleistocene deep sea ostracods from the bering sea iodp expedition 323 abstract the study presents the first pleistocene 0 1 9 ma record of deep sea ostracods from the bering sea derived primarily from integrated ocean drilling program expedition 323 site u1344 59 3 0 n 179 12 2 w 3171 m of water depth deep sea ostracod abundances in the bering sea sediments are some of the lowest that have been recorded in bathyal and abyssal marine environments

movement of deep sea coral populations on climatic timescales during the past 40 000 years global climate has moved into and out of a full glacial period with the deglaciation marked by several millennial scale rapid climate change events here we investigate the ecological response of deep sea coral communities to both glaciation and these rapid climate change events we find that the deep sea coral populations of desmophyllum dianthus in both the north atlantic and the tasmanian seamounts expand at times of rapid climate change however during the more stable last glacial maximum the coral population globally retreats to a more restricted depth range holocene populations show regional patterns that provide some insight into what causes these dramatic changes in population structure the most important factors are likely responses to climatically driven changes in productivity o 2 and co 3 2

abrupt climate change and collapse of deep sea ecosystems we investigated the deep sea fossil record of benthic ostracodes during periods of rapid climate and oceanographic change over the past 20 000 years in a core from intermediate depth in the northwestern atlantic results show that deep sea benthic community collapses occur with faunal turnover of up to 50 during major climatically driven oceanographic changes species diversity as measured by the shannon wiener index falls from 3 to as low as 1 6 during these events major disruptions in the benthic communities commenced with heinrich event 1 the inter allerod cold period iacp 13 1 ka the younger dryas yd 12 9 11 5 ka and several holocene bond events when changes in deep water circulation occurred the largest collapse is associated with the yd iacp and is characterized by an abrupt two step decrease in both the upper north atlantic deep water assemblage and species diversity at 13 1 ka and at 12 2 ka the ostracode fauna at this site did not fully recover until 8 ka with the establishment of labrador sea water ventilation ecologically opportunistic slope species prospered during this community collapse other abrupt community collapses during the past 20 ka generally correspond to millennial climate events these results indicate that deep sea ecosystems are not immune to the effects of rapid climate changes occurring over centuries or less

quaternary paleoceanography of the deep arctic ocean based on quantitative analysis of ostracoda abstract ostracodes were studied from deep arctic ocean cores obtained during the arctic 91 expedition of the polarstern to the nansen amundsen and makarov basins the lomonosov ridge morris jesup rise and yermak plateau in order to investigate their distribution in arctic ocean deep water aodw and apply these data to paleoceanographic reconstruction of bottom water masses during the quaternary analyses of coretop assemblages from arctic 91 boxcores indicate the following ostracodes are common at all depths between 1000 and 4500 m and species distribution is strongly influenced by water mass characteristics and bathymetry quantitative analyses comparing eurasian and canada basin assemblages indicate that distinct assemblages inhabit regions east and west of the lomonosov ridge a barrier especially important to species living in lower aodw deep eurasian basin assemblages are more similar to those living in greenland sea deep water gsdw than those in canada basin deep water two upper aodw assemblages were recognized throughout the arctic ocean one living between 1000 and 1500 m and the other having high species diversity at 1500 3000 m downcore quantitative analyses of species abundances and the squared chord distance coefficient of similarity reveals a distinct series of abundance peaks in key indicator taxa interpreted to signify the following late quaternary deep water history of the eurasian basin during the last glacial maximum lgm a gsdw aodw assemblage characteristic of cold well oxygenated deep water 3000 m today inhabited the lomonosov ridge to depths as shallow as 1000 m perhaps indicating the influence of gsdw at mid depths in the central arctic ocean during termination 1 a period of high organic productivity associated with a strong inflowing warm north atlantic layer occurred during the mid holocene several key faunal events indicate a period of warming and or enhanced flow between the canada and eurasian basins a long term record of ostracode assemblages from kastenlot core ps2200 5 1073 m water depth from the morris jesup rise indicates a quasi cyclic pattern of water mass changes during the last 300 kyr interglacial ostracode assemblages corresponding to oxygen isotope stages 1 5 and 7 indicate rapid changes in dissolved oxygen and productivity during glacial interglacial transitions

levantine intermediate water hydrodynamic and bottom water ventilation in the northern tyrrhenian sea over the past 56 000 years new insights from benthic foraminifera and ostracods abstract foraminifera and ostracods have been quantitatively studied in core md01 2472 from the upper continental slope at water depth of 501 m to evaluate their relationship with bottom water condition variability and decipher the control of the levantine intermediate water liw current on benthic faunas the occurrence of reworked ostracod species originating from the continental shelf and the presence of shallow water elphidium ammonia benthic foraminifera are used to estimate the degree of along slope transport at the core site this has revealed two intervals of along slope transport also associated with coarse grained contourite deposits deposited during the yd and hs2 episodes planktonic benthic foraminiferal and ostracod assemblages reflect climate oscillations peaks of the polar planktonic neogloboquadrina pachyderma left coiling s may be used to identify heinrich events interstadials are marked by abundant ostracod species such as paracypris sp argilloecia acuminata and cytheropteron alatum and the presence of benthic foraminifera like bulimina marginata bulimina costata and gyroidina altiformis the b a and holocene are characterized by abundant warm water species of planktonic foraminifera and by the ostracod species polycope sp we hypothesize that there is relationship between liw intensification during cold rapid climate events and benthic fauna assemblage variations due to changes in 1 bottom water ventilation and 2 the export of nutrients and or sediment particles by bottom currents

glacial interglacial variability in deep sea ostracod assemblage composition at iodp site u1314 in the subpolar north atlantic abstract we present a detailed study of glacial interglacial deep sea benthic ostracod assemblage variability at iodp site u1314 subpolar north atlantic in relation to the history of ice rafting events and changes in deep ocean circulation over the past 170 ky our records of ostracod diversity abundance and dissolution and sediment properties ird and caco 3 show an excellent correspondence to high amplitude orbital and millennial variability observed in the climate records 13 c and 18 o from neighboring deep water sites suggesting that the benthic meiofauna fluctuates synchronously with the prevailing oceanographic conditions surface ocean conditions deep ocean circulation and water temperature and food flux krithe dominant argilloecia and cytheropteron are the most abundant and diverse genera in association with rockallia enigmatica three ostracod assemblages are recognized the genera pennyella argilloecia pelecocythere ambocythere pseudobosquetina bradleya and nannocythere are associated with interglacials and interstadials and possibly reflect increased flux of food to the sediments and more vigorous nadw formation a transitional assemblage composed of species of cytheropteron xestoleberis and eucythere is restricted to climatic transitions and indicate moderate environmental conditions and seasonal productivity a glacial stadial assemblage is characterized by a temporal predominance of either intermediate depth and shallow water arctic subarctic species belonging to cytheropteron polycope pedicythere swainocythere cluthia heterocyprideis elofsonella and finmarchinella or abyssal north atlantic ostracods bythocythere dutoitella bathycythere and bythocypris the influx of high latitude taxa can be partially explained by ice rafting but may also represent a shift of the location of intermediate and deep water convection to the area south of iceland therefore the combination of species characteristic of different watermasses during glacials may reflect shifts in the influence of high nutrient southern source water e g aabw vs low nutrient gnaiw during glacials

orbital and suborbital variability in north atlantic bottom water temperature obtained from deep sea ostracod mg ca ratios abstract magnesium calcium mg ca ratios were measured in the deep sea ostracod crustacea genus krithe from chain core 82 24 4pc from the western mid atlantic ridge 3427 m in order to estimate ocean circulation and bottom water temperature bwt variability over the past 200 000 years mg ca ratios have been used as a paleothermometer because the ratios are controlled primarily by ambient water temperatures at the time the organism secretes its adult carapace over the past two glacial interglacial cycles mg ca values oscillated between about 7 mmol mol and 12 mmol mol equivalent to a bwt range of 0 to 3 5 c the lowest values were obtained on specimens from glacial marine isotope stages miss 2 4 and 6 the highest values were obtained from specimens from the early part of the holocene interglacial mis 1 and also from miss 5 and 7 these trends suggest that bwts in the north atlantic ocean fluctuate over orbital time scales suborbital variability in mg ca ratios and bwt was also observed for the past 100 000 years ratios rose from 8 mmol mol to 10 mmol mol implying a bwt increase of 1 to 3 c during 14 mg ca excursions the highest ratios were found in krithe dated at approximately 32 36 38 43 48 73 85 and 93 ka although the age model for the chain 82 24 4pc and temporal resolution do not allow precise correlation some of these deep sea bottom temperature excursions appear to correspond to heinrich events recorded in other regions of the north atlantic and perhaps dansgaard oeschger interstadial events recorded in greenland ice cores if confirmed this would support the hypothesis that millennial scale oscillations of climate in the north atlantic are capable of affecting global climate via thermohaline circulation changes

inland variability of carbon nitrogen concentrations and δ13c in amazon floodplain varzea vegetation and sediment we analysed carbon nitrogen and 13c values in sediment sampled in the amazon floodplains the surface sediment samples were collected along inland transects divided according to their vegetation cover a forest where the dominant vegetation was inundation forests b grass where the dominant vegetation was grasses mainly from echnochloa polystachya c mixed where the vegetation changed from grasses near the river bank to forest inland the average sediment carbon and nitrogen concentrations were significantly higher in forest samples c 0 99 n 0 12 than in grass samples c 0 84 n 0 10 the average sediment 13c was significantly heavier in grass 26 7 than in forest samples 28 6 reflecting the isotopically heavier c4 grasses carbon in the forest and mixed transects inland increases in the carbon and nitrogen concentrations were observed at approximately 50 to 60 m from the riverbank the concentration of carbon and nitrogen became similar to the river particulate organic carbon poc concentration which is the primary floodplain sediment source we hypothesized that this trend is caused by the deposition of carbon and nitrogen depleted sand size particles in the first few metres of the floodplain whereas the more enriched silt clay particles are preferentially deposited far inland in contrast to inland trends no significant downriver trend was observed in the carbon and nitrogen concentrations however a downriver 13c increase was observed for sediment in grass covered areas based on 13c values in different varzea environments we estimated the relative contribution of riverine poc and vegetation material present in the varzea sediments under different vegetation covers for forest sediment samples we estimated that 60 of the carbon was derived from the riverine poc and the forests provided the remaining 40 for open areas covered with grasses we estimated that only 10 was derived from these plants and 90 was derived from riverine poc copyright 2003 john wiley sons ltd

the effects of glacio eustatic sea level change on pleistocene cold water ostracod assemblages from the japan sea abstract the pleistocene palaeo habitats and the extinction history of cold water ostracods in the japan sea are recorded in its coastal strata the presence of now extinct species in the omma formation of central japan 1 5 ma indicates that such species predominated in a shallow open sea environment the tolerance ranges of these species as to water temperature and salinity are inferred to have been narrower than those of most extant cold water species in the same families that live in shallow open water as well as in brackish inner bays the horizons in the omma formation with peak relative abundances of now extinct species differ from the horizons with peak abundances of living japan sea species we therefore suggest that the now extinct species were adapted to optimum temperature and salinity conditions that differ from those in the modern japan sea the observation that few now extinct species survived after 0 4 ma may be explained by the hypothesis that physicochemical properties of the water masses changed we argue that during the glacial periods with increased amplitude 0 9 0 4 ma the salinity decreased as the result of glacio eustatic changes and the closure of shallow straits owing to low sea levels causing the extinctions