the salinity temperature and δ18o of the glacial deep ocean we use pore fluid measurements of the chloride concentration and the oxygen isotopic composition from ocean drilling program cores to reconstruct salinity and temperature of the deep ocean during the last glacial maximum lgm our data show that the temperatures of the deep pacific southern and atlantic oceans during the lgm were relatively homogeneous and within error of the freezing point of seawater at the ocean s surface our chloride data show that the glacial stratification was dominated by salinity variations in contrast with the modern ocean for which temperature plays a primary role during the lgm the southern ocean contained the saltiest water in the deep ocean this reversal of the modern salinity contrast between the north and south atlantic implies that the freshwater budget at the poles must have been quite different a strict conversion of mean salinity at the lgm to equivalent sea level change yields a value in excess of 140 meters however the storage of fresh water in ice shelves and or groundwater reserves implies that glacial salinity is a poor predictor of mean sea level

isotope data from ice station weddell implications for deep water formation in the weddell sea helium isotope data 3he 4he ratios and 4he concentrations and h218o h216o ratios obtained from stations occupied during the drift of ice station weddell february to june 1992 are used together with hydrographic data to study formation of deep and bottom water in the western weddell sea the data indicate deep and bottom water formation along the entire track of the ice station 71 4 to 65 8 s 53 w ice shelf water isw seems to contribute significantly to the formation of weddell sea deep water wsdw and weddell sea bottom water wsbw in the southern part of the drift track toward the north the fraction of isw contained in wsdw wsbw decreases this trend is overlaid by high isw fractions in the deep and bottom waters found in the vicinity of the larsen ice shelf the fraction of western shelf water wsw in wsbw shows the opposite trend increasing from south to north the combined fraction of isw and wsw in waters with potential temperatures below 0 c is about 20 corresponding to a roughly 200 m thick layer overall wsw seems to contribute approximately 2 to 3 times more water than isw to the water column below the 0 c isotherm using the estimated flow of isw over the sill north of the filchner depression of 1 sv foldvik et al 1985a together with the ratio of wsw plus winter water ww to isw we calculate a value of about 5 sv for the formation rate of wsbw with a potential temperature of 0 7 c about one third of this flux represents near surface waters wsw ww which have recently been equilibrated with the atmosphere whereas pure isw contributes about 10

the timing of deglacial circulation changes in the atlantic 1 well dated benthic foraminifer oxygen isotopic records 18o from different water depths and locations within the atlantic ocean exhibit distinct patterns and significant differences in timing over the last deglaciation this has two implications on the one hand it confirms that benthic 18o cannot be used as a global correlation tool with millennial scale precision but on the other hand the combination of benthic isotopic records with independent dating provides a wealth of information on past circulation changes comparing new south atlantic benthic isotopic data with published benthic isotopic records we show that 1 circulation changes first affected benthic 18o in the 1000 2200 m range with marked decreases in benthic 18o taking place at 17 5 cal kyr b p ka due to the southward propagation of brine waters generated in the nordic seas during heinrich stadial 1 hs1 cold period 2 the arrival of 18o depleted deglacial meltwater took place later at deeper north atlantic sites 3 hydrographic changes recorded in north atlantic cores below 3000 m during hs1 do not correspond to simple alternations between northern and southern sourced water but likely reflect instead the incursion of brine generated deep water of northern as well as southern origin and 4 south atlantic waters at 44 s and 3800 m depth remained isolated from better ventilated northern sourced water masses until after the resumption of north atlantic deep water nadw formation at the onset of the bolling allerod which led to the propagation of nadw into the south atlantic

water mass properties and exchange between the nordic seas and the northern north atlantic during the period 23 6 ka benthic oxygen isotopic evidence 1 twenty benthic oxygen isotope records from different water depths in the nordic seas and the north atlantic are compared during the last glacial maximum brine formation on continental shelves produced brine shelf water bsw sinking below 1500 m in the nordic seas open ocean convection in the nordic seas produced glacial north atlantic intermediate water gnaiw gnaiw overflowed the greenland scotland ridge and entrained depths above and at least partly below 2000 m in the north atlantic during the early deglaciation bsw enriched intermediate water masses in the nordic seas were formed these overflowed the greenland scotland ridge and influenced the north atlantic intermediate and deepwater masses in the bolling allerod ba open ocean convection increased and produced intermediate water in the nordic seas with outflow to the north atlantic however deep water with modern characteristics did not entrain water below 2000 m in the north atlantic in similar amounts as during the holocene a new period of brine formation during the younger dryas transported bsw to intermediate water masses in the norwegian sea there was also open ocean convection and meridional overturning in the nordic seas but it was probably reduced compared to the ba in the early holocene and mid holocene meridional overturning appears similar to that of today potential locations for large scale formation of bsw might have been broad and shallow 200 m areas of the north sea northeast of greenland and north of east siberia these settings should be favorable for bsw formation during cold periods

intensified deep pacific inflow and ventilation in pleistocene glacial times the production of cold deep waters in the southern ocean is an important factor in the earth s heat budget1 the supply of deep water to the pacific ocean is presently dominated by a single source the deep western boundary current east of new zealand here we use sediment records deposited under the influence of this deep western boundary current to reconstruct deep water properties and speed changes during the pleistocene epoch in physical and isotope proxies we find evidence for intensified deep pacific ocean inflow and ventilation during the glacial periods of the past 1 2 million years the changes in throughflow may be directly related to an increased production of antarctic bottom water during glacial times possible causes for such an increased bottom water production include increasing wind strengths in the southern ocean or an increase in annual sea ice formation leaving dense water after brine rejection and thereby enhancing deep convection we infer also that the global thermohaline circulation was perturbed significantly during the mid pleistocene climate transition between 0 86 and 0 45 million years ago

local and regional trends in plio pleistocene δ18o records from benthic foraminifera we present new orbital resolution pliocene pleistocene benthic stable oxygen isotope 18ob records from ocean drilling program sites 1264 and 1267 from walvis ridge in the southeast atlantic we compare long term 250 kyr interbasin 18ob gradients between pacific and north atlantic regional stacks as well as intra and interbasin gradients from the perspective of walvis ridge the 18ob values from sites 1264 and 1267 are almost always higher than deep north atlantic and pacific sites with large gradients 0 5 emerging abruptly at 2 4 ma and persisting until 1 3 ma from this we infer the presence of a new water mass which resulted from the influence of dense 18o enriched nordic sea overflow waters via the abyssal east atlantic meanwhile long term average 18ob values in the north atlantic appear to have remained within 0 0 25 lower than in the pacific however the magnitude of this difference is sensitive to the inclusion of records from the equatorial west atlantic these results together with constraints based on temperature salinity and density suggest an influence of the seawater 18o 18osw versus salinity relationship of source waters on 18ob values within the atlantic in particular the abrupt emergence at 2 4 ma of higher 18ob values at sites 1264 and 1267 relative to north atlantic records appears to require a low latitude surface water 18osw signal this implies a connection between northward heat transport and deep water export into the abyssal east atlantic hence our results have implications for the interpretation of 18ob records and highlight the potential for 18ob to constrain deep atlantic water mass sources and pathways during the plio pleistocene

impact of sea ice variability on the oxygen isotope content of seawater under glacial and interglacial conditions records of temporal variability in the oxygen isotopic composition of biogenic carbonates 18oc from ocean sediment cores inform our understanding of past continental ice volume and ocean temperatures interpretation of 18ocvariability typically neglects changes due to factors other than ice volume and temperature here we investigate whether glacial interglacial changes in sea ice which fractionates seawater during its formation could shift the isotopic value of seawater in the deep ocean affecting benthic foraminiferal 18oc and thereby potentially impacting oxygen isotope based sea level reconstructions or in surface waters affecting planktic foraminiferal 18oc we simulate glacial and interglacial states with the isotope enabled university of victoria earth system climate model and perform a global analysis distinct patterns of sea ice production emerge for the glacial versus interglacial states we find no substantive shift in 18ow in model deep or bottom waters due to the simulated interglacial glacial sea ice variability small isotopic shifts due to sea ice variability are concentrated in the model s surface waters of the northern hemisphere specifically in the labrador sea and northeastern north atlantic

north atlantic nordic seas exchanges abstract the northeastern part of the north atlantic is unique in the sense that it is much warmer in the surface than other ocean areas at similar latitudes the main reason for this is the large northward transport of heat that extends to high latitudes and crosses the greenland scotland ridge to enter the nordic seas and the arctic there the warm atlantic water is converted to colder water masses that return southwards over the ridge partly as surface outflows and partly as overflows through the deep passages across the ridge in this paper the state of knowledge on the exchanges especially across the eastern part of the greenland scotland ridge is reviewed based on results from the ices nansen north atlantic norwegian sea exchanges project from the nordic woce project and from other sources the accumulated evidence allows us to describe the exchanges in fair detail the origins of the waters the patterns of their flow towards and over the ridge and their ultimate fate there is also increasing information on temporal variations of the exchanges although dynamical changes are still not well understood quantitative estimates for the volume transport of most of the overflow branches seem reasonably well established and transport measurements of the atlantic inflows to the nordic seas are approaching acceptable levels of confidence which allows preliminary budgets to be presented the deep overflows are driven by pressure gradients set up by the formation of deep and intermediate water the dominance of deep overflows over surface outflows in the water budget argues that this thermohaline forcing also dominates over direct wind stress and estuarine forcing in driving the atlantic water inflow across the greenland scotland ridge while wind stress seems to influence the characteristics and distribution of the atlantic water north of the ridge

transient nature of the earth s climate and the implications for the interpretation of benthic δ18 o records abstract from the marine benthic 18 o records it is known that the earth s climate has experienced significant variability over the past 40 million years in general a number of assumptions are often needed to disentangle the benthic 18 o data into its temperature and ice volume contributions in this study a transient 1 d ice sheet model is used which overcomes these shortcomings by relating temperature to the benthic 18 o data leading to a self consistent and continuous record of 18 o temperature and sea level the contribution of land ice to benthic 18 o is examined with a set of sensitivity experiments varying the mean 18 o of the ice for different ice sheets it is shown that the scaling factor of sea water 18 o w to sea level is not constant over the long time scales however our sensitivity experiments do show that over the long time scale the general assumed 1 0 1 1 per 100 m of sea level is in reasonable agreement with our model results moreover the sea level ice volume response to temperature s t is shown to vary through time with the largest response found when variations in antarctic ice volume dominates the sea level variations during the oligocene to early miocene furthermore this response is quite large compared to the individual response of ice sheets during the plio pleistocene whereas the combined s t in this period is comparable to that during the oligocene accordingly the transient behaviour is very important for the interpretation of data records with respect to climate sensitivity and climate change during the past 40 million years

on the structure and origin of major glaciation cycles 1 linear responses to milankovitch forcing time series of ocean properties provide a measure of global ice volume and monitor key features of the wind driven and density driven circulations over the past 400 000 years cycles with periods near 23 000 41 000 and 100 000 years dominate this climatic narrative when the narrative is examined in a geographic array of time series the phase of each climatic oscillation is seen to progress through the system in essentially the same geographic sequence in all three cycles we argue that the 23 000 and 41 000 year cycles of glaciation are continuous linear responses to orbitally driven changes in the arctic radiation budget and we use the phase progression in each climatic cycle to identify the main pathways along which the initial local responses to radiation are propagated by the atmosphere and ocean early in this progression deep waters of the southern ocean appear to act as a carbon trap to stimulate new observations and modeling efforts we offer a process model that gives a synoptic view of climate at the four end member states needed to describe the system s evolution and we propose a dynamic system model that explains the phase progression along causal pathways by specifying inertial constants in a chain of four subsystems solutions to problems involving systems of such complexity are not born full grown like athena from the head of zeus rather they evolve slowly in stages each of which requires a pause to examine data at great lengths in order to guarantee a sure footing and to properly choose the next step victor p starr

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

low frequency source for long offset sub basalt and deep crustal penetration a seismic source rich in low frequencies is essential for deep crustal imaging using wide angle and long offset 6 km recording to construct a good whole crustal velocity model for use in structural interpretation and as a starting model for waveform inversion when ocean bottom seismometers obs are used to record data at large distances the offset and hence the depth of penetration of the seismic energy is limited only by the low frequency output of the seismic source data from a 48 element 9324 in3 air gun source have been recorded to offsets of 400 km and compare favorably with 200 kg explosive sources staples et al 1999 where thick basalt flows are present as on volcanic rifted margins such as those of the north and south atlantic they strongly scatter the high frequencies produce strong reverberations and make imaging of deeper structures difficult deep crustal arrivals such as diving waves in the upper mantle are often observed only at long offsets typically 50 km in continental crust in this paper we investigate the effectiveness of low frequency sources in providing good quality long offset sub basalt and deep crustal penetration

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

recent benthic foraminifera from the eastern south atlantic ocean dependence on food supply and water masses abstract sixty surface sediment samples from the eastern south atlantic ocean including the walvis ridge the angola and cape basins and the southwest african continental margin were analysed for their benthic foraminiferal content to unravel faunal distribution patterns and ecological preferences live stained with rose bengal and dead faunas were counted separately and then each grouped by q mode principal component analysis into seven principal faunal end members then multiple regression technique was used to correlate recent assemblages with available environmental variables and to finally differentiate between four principal groups of environmental agents acting upon the generation of benthic foraminiferal assemblages 1 seasonality of food supply and organic carbon flux rates together with oxygen content in the pore and bottom waters 2 lateral advection of deep water masses 3 bottom water carbonate corrosiveness and 4 energetic state at the benthic boundary layer and grain size composition of the substrate food supply and corresponding dissolved oxygen contents in the pore and bottom waters turned out to be the most important factors which control the distribution pattern of the recent benthic foraminifera at the continental margin in the zone of coastal upwelling and its mixing area benthic foraminiferal assemblages are dominated by stenobathic high productivity faunas characterized by elevated standing stocks low diversities and a large number of endobenthic living species at the continental shelf and upper continental slope the live assemblages are characterized by rectuvigerina cylindrica uvigerina peregrina s 1 uvigerina auberiana and rhizammina spp while the dead assemblages are characterized by cassidulina laevigata bolivina dilatata bulimina costata and b mexicana at the lower continental slope strong influence of high organic matter fluxes on the species composition is restricted to the area off the cunene river mouth where the live assemblage is dominated by uvigerina peregrina s 1 the corresponding dead assemblage by melonis barleeanum and m zaandamae in the adjacent areas of the lower continental slope the biocoenosis is characterized by reophax bilocularis and epistominella exigua which becomes dominant in the corresponding dead assemblage at the walvis ridge and in the abyssal angola and cape basins where organic matter fluxes are low and highly seasonal benthic foraminiferal assemblages reflect both the oligotrophic situation and the deep and bottom water mass configuration the top and flanks of the walvis ridge are inhabited by the rhizammina psammosphaera and r bilocularis live assemblages the corresponding dead assemblages are dominated by g subglobosa on the ridge top and e exigua on the flanks within the highly diverse e exigua dead assemblage several associated epibenthic species coincide with the core of nadw between about 1600 and 3700 m water depth these species include osangularia culter cibicidoides kullenbergi melonis pompilioides bolivinita pseudothalmanni and bulimina alazanensis the assemblages of the abyssal cape and angola basins are characterized by nuttallides umbonifer and a high proportion of agglutinated species these species are adapted to very low organic matter fluxes and a carbonate corrosive environment

north atlantic intermediate waters in the late pliocene to early pleistocene we generated benthic isotope records from ocean drilling program odp site 981 on the feni drift 2173 m water depth and from odp site 983 on the gardar drift 1983 m water depth to examine the interaction between north atlantic deep water nadw and glacial north atlantic intermediate water gnaiw formation from 2 0 to 1 4 ma we find nadw at both sites during interglacial periods and a mix of nadw and southern ocean water at the feini drift during most glacial periods prior to 1 7 ma we find no evidence ofr gnaiw at the gardar drift site instead glacial gardar drift 13c values are as low or lower than values for all other sites in the north atlantic and reflect continued glacial overflow from the nordic seas after 1 7 ma gardar drift 13c values increase and suggest that there was gnaiw at the gardar drift site during some glacial intervals overall we find that nadw and gnaiw production changed around 1 7 ma in concert with changes in sea surface temperature and salinity and in the earth s obliquity cycle

pore fluid constraints on the temperature and oxygen isotopic composition of the glacial ocean pore fluids from the upper 60 meters of sediment 3000 meters below the surface of the tropical atlantic indicate that the oxygen isotopic composition 18 o of seawater at this site during the last glacial maximum was 0 8 0 1 per mil higher than it is today combined with the 18 o change in benthic foraminifera from this region the elevated ratio indicates that the temperature of deep water in the tropical atlantic ocean was 4 c colder during the last glacial maximum extrapolation from this site to a global average suggests that the ice volume contribution to the change in 18 o of foraminifera is 1 0 per mil which partially reconciles the foraminiferal oxygen isotope record of tropical sea surface temperatures with estimates from barbados corals and terrestrial climate proxies

comment on deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions sosdian and rosenthal reports 17 july 2009 p 306 used magnesium calcium ratios in benthic foraminifera from the north atlantic to reconstruct past bottom water temperatures they suggested that both ice volume change and ice sheet dynamics played important roles during the late pliocene and mid pleistocene climate transitions we present evidence that their record of deep ocean temperature is not reliable thus raising doubts about their conclusions

probing slow earthquakes with deep learning slow earthquakes may trigger failure on neighboring locked faults that are stressed sufficiently to break and slow slip patterns may evolve before a nearby great earthquake however even in the clearest cases such as cascadia slow earthquakes and associated tremor have only been observed in intermittent and discrete bursts by training a convolutional neural network to detect known tremor on a single seismic station in cascadia we isolate and identify tremor and slip preceding and following known larger slow events the deep neural network can be used for the detection of quasi continuous tremor providing a proxy that quantifies the slow slip rate furthermore the model trained in cascadia recognizes tremor in other subduction zones and also along the san andreas fault at parkfield suggesting a universality of waveform characteristics and source processes as posited from experiments and theory

north atlantic intermediate to deep water circulation and chemical stratification during the past 1 myr benthic foraminiferal carbon isotope records from a suite of drill sites in the north atlantic are used to trace variations in the relative strengths of lower north atlantic deep water lnadw upper north atlantic deep water unadw and southern ocean water sow over the past 1 myr during glacial intervals significant increases in intermediate to deep 13c gradients commonly reaching 1 2 are consistent with changes in deep water circulation and associated chemical stratification bathymetric 13c gradients covary with benthic foraminiferal 18o and covary inversely with vostok co2 in agreement with chemical stratification as a driver of atmospheric co2 changes three deep circulation indices based on 13c show a phasing similar to north atlantic sea surface temperatures consistent with a northern hemisphere control of nadw sow variations however lags in the precession band indicate that factors other than deep water circulation control ice volume variations at least in this band

new evidence for changes in plio pleistocene deep water circulation from southern ocean odp leg 177 site 1090 abstract changes in atlantic deep water circulation were reconstructed by comparing the benthic foraminiferal 13c record at odp site 1090 in the south atlantic with similar records from the north atlantic sites 982 607 925 929 and deep pacific site 849 oceans important deep water circulation changes occurred in the early pleistocene at 1 55 myr and during the mid pleistocene transition at 0 9 myr at 1 55 myr glacial 13c values in the southern ocean became significantly lower than those in the deep pacific establishing a pattern that persisted throughout the late pleistocene we propose that the lowering of 13c values of southern component water scw at this time resulted from expansion of sea ice and reduced ventilation of deep water during glacial periods after marine isotope stage 52 accompanying this change in southern ocean deep water circulation was enhanced interhemispheric coupling between the north and south atlantic after 1 55 myr at 0 9 myr the magnitude of glacial to interglacial variability in 13c increased and shifted to a longer frequency 100 kyr along with oceanic 18o ice volume calculation of percent northern component water ncw using site 1090 as the scw end member yielded 20 30 less reduction of ncw during glacial periods of the late pleistocene also a trend toward reduced glacial suppression of ncw during the past 400 kyr is not evident the apparent decoupling of ice volume and deep water circulation reported previously may be an artifact of using a pacific rather than a southern ocean carbon isotopic record to calculate past mixing ratios of ncw and scw

late neogene history of deepwater ventilation in the southern ocean we compiled carbon isotope records from the north atlantic south atlantic and pacific oceans to estimate changes in vertical and interbasinal 13c gradients for the last 9 myr benthic 13c values of deep water in the south atlantic decreased in a series of steps at 7 2 75 and 1 55 ma away from the north atlantic and toward the pacific the benthic 13c of intermediate water in the south atlantic evolved differently from deep waters resulting in an increase in the intermediate to deep 13c gradient 13cid the 13cid increased in steps at 2 75 and 1 55 ma marking the development and intensification of a chemical divide in the atlantic ocean between well ventilated intermediate water and poorly ventilated deep water we suggest these changes in interbasinal and vertical gradients resulted from decreasing northern component water and reduced ventilation of southern component water scw the latter was caused by several interrelated processes in antarctic sources areas including increased sea ice cover enhanced surface water stratification decreased ekman induced upwelling and reduced vertical mixing across the thermocline because antarctic surface water processes and deepwater ventilation rates ultimately influence atmospheric co2 concentration these processes may have acted as a positive feedback that contributed to the major cooling steps in late neogene climate

the effect of chemical pretreatment of sediment upon foraminiferal based proxies 1 paleoceanographic studies routinely combine different foraminiferal proxies i e weight abundance trace metal and stable isotope measurements into a cohesive narrative the application of chemical treatment to disaggregate ocean sediments in the most efficient way to isolate the fossils of foraminifera from the other sediment components is dictated by the time available and the material used yet few studies have aimed to test both the physical and geochemical effects associated with such practices in this study we use samples with different sedimentological characteristics i e varying percentages of caco3 and of terrigenous material to test the impact upon these proxies of three processing methods and a control 1 no chemicals contol run 2 soaking in sodium hexametaphosphate calgon 3 soaking in hydrogen peroxide and 4 soaking in a sodium pyrophosphate the samples were analyzed for faunal abundance shell weight stable isotope 18o 13c and trace metal mg ca geochemistry for four species of planktonic foraminifera globigerina bulloides globigerinoides ruber globorotalia inflata and globorotalia menardii results show that apart from the calgon solution the values of faunal abundance shell weight mg ca and stable isotopes are similar irrespective of the cleaning treatment utilised and therefore warrant cross comparison of results obtained with different preparation techniques the use of calgon in pretreatment shows statistically different values for only foraminiferal shell weight

paleosalinity and δ18o a critical assessment in paleoceanography a traditional application of oxygen isotope ratios in fossil carbonate from deep sea cores concerns the reconstruction of paleotemperatures recently isotopic data have been increasingly employed in the reconstruction of paleosalinities as well this application involves a number of basic assumptions a critical review of which is presented here as the calculation of paleosalinity from 18o residuals assumes constant and linear surface water salinity s 18o relationships we investigate this basic assumption for areas with important and variable freshwater budget and or sea ice influences we show that it is particularly unwarranted to assume such temporally invariant linearity in temperate and subpolar seas because of the effects of freezing and melting more critically we argue that the determinant of many regions s 18o is advection not the local water balance so that the basic 18o of seawater in many regions of the world ocean would likely have changed in a manner somewhat different from that expected from the ice volume record although the differences may not be significant for the gross reconstruction of such features as past sea level we believe they do potentially bias paleosalinity reconstructions mostly toward high salinities to fully exploit the potential of oxygen isotope records as quantitative paleosalinity indicators both the spatial and temporal variabilities need to be constrained hence we recommend that 1 for any time slice of specific interest to paleoceanographic and paleoclimatological studies a coupled ocean atmosphere isotope model or at least an ocean isotope model driven by a paleoclimate isotope model should be used to define the distribution of the base mixing end member 18o of sea water 2 much further regional scale research is needed on flux rates and isotopic compositions of the various terms in the freshwater budget as well as on the variability in the various advective terms the latter variability may be assessed from reconstructions of past seaice distributions and of volume fluxes isotopic compositions of outflow from marginal seas and through sea straits passages

abrupt climate events 500 000 to 340 000 years ago evidence from subpolar north atlantic sediments subpolar north atlantic proxy records document millennial scale climate variations 500 000 to 340 000 years ago the cycles have an approximately constant pacing that is similar to that documented for the last glacial cycle these findings suggest that such climate variations are inherent to the late pleistocene regardless of glacial state sea surface temperature during the warm peak of marine isotope stage 11 mis 11 varied by 0 5 to 1 c less than the 4 to 4 5 c estimated during times of ice growth and the 3 c estimated for glacial maxima coherent deep ocean circulation changes were associated with glacial oscillations in sea surface temperature

changes in east atlantic deepwater circulation over the last 30 000 years eight time slice reconstructions using 95 epibenthic 13c records eight time slices were reconstructed to trace the distribution of east atlantic deepwater and intermediate water masses over the last 30 000 years our results show that there have been three distinct modes of deepwater circulation near the stage 3 2 boundary the origin of north atlantic deep water nadw was similar to today mode 1 however after late stage 3 the source region of the nadw end member shifted from the norwegian greenland sea to areas south of iceland mode 2 a reduced nadw flow persisted during the last glacial maximum with constant preformed 13c values the nutrient content of nadw increased markedly near the azores fracture zone from north to south probably because of the mixing of upwelled antarctic bottom water aabw from below which then advected with much higher flux rates into the northeast atlantic later the spread of glacial meltwater over the north atlantic led to a marked short term ventilation minimum below 1800 m about 13 500 14c years ago mode 3 the formation of nadw recommenced abruptly north of iceland 12 800 12 500 years ago and reached a volume approaching that of the holocene in the younger dryas 10 800 10 350 years b p another short term shutdown of deepwater formation followed between 10 200 and 9 600 years b p linked to a further major meltwater pulse into the atlantic each renewal of deepwater formation led to a marked release of fossil co2 from the ocean the likely cause of the contemporaneous 14c plateaus over the last 9000 years deepwater circulation varied little from today apart from a slight increase in aabw about 7000 14c years ago it is also shown that the oxygenated mediterranean outflow varied largely independent of the variations in deepwater circulation over the last 30 000 years

carbonate ion effect on mg ca sr ca and stable isotopes on the benthic foraminifera oridorsalis umbonatus off namibia abstract we investigate the influence of carbonate system parameters carbonate ion concentration co32 carbonate ion saturation co32 on the trace element and stable isotope ratios in the endobenthic foraminifera oridorsalis umbonatus data from modern core top samples from the namibian continental slope suggest that the shell composition of this species is influenced by the chemistry of the pore water for these organic rich sediments the impact of ocean bottom water properties on both pore water and shell chemistry is surprisingly small sr ca correlates positively with co32 and to a lesser extent with co32 which is opposed to previous results a co32 decrease of 10 mol kg leads to an increase of 0 05 mmol mol in sr ca we observe a correlation between shell 18o corrected for temperature and 18o seawater and co32 however the variability of the corrected 18o is close to the analytical limit no clear dependences were observed for 13c and mg ca

oxygen 18 and helium as tracers of ice shelf water and water ice interaction in the weddell sea oxygen 18 and helium isotope data from stations located in the filchner depression on the continental slope of the southern weddell sea and in the central weddell sea are presented and discussed the 18o and 4he signals imprinted on the water circulating under the filchner ronne ice shelf ice shelf water or isw due to melting of glacial ice at the base of the ice shelf are traced across the sill separating the filchner depression from the weddell sea low 18o values are correlated with high 4he concentrations in the isw found in the filchner depression minimum 18o values 0 8 maximum 4he concentrations about 4 7 10 8 cm3 stp g 1 the fraction of glacial meltwater contained in the isw found in the filchner depression is estimated to about 6 to 7 the 18o and helium isotope data from the overflowing shelf water component observed on the continental slope confirm the hypothesis that isw contributes significantly to the weddell sea bottom water wsbw on the basis of a inultiparameter water mass analysis it is discussed which fraction of the wsbw originates from isw and which other shelf waters potentially could contribute to wsbw

stable isotope stratigraphy of the pliocene pleistocene climate transition in the northwestern subtropical pacific abstract from ocean drilling program odp site 1208 on shatsky rise below the kuroshio current extension we present the north pacific s first orbital scale benthic foraminiferal 18o and 13c time series to span the pliocene pleistocene climate transition excellent agreement between the site 1208 18o record and the global 18o stack of lisiecki and raymo 2005 provides orbital scale age control and confirms continuous stratigraphy from 3 7 to 1 8 ma at the single hole site cross spectral analysis of the 18o and 13c time series reveals that these are coherent to 80 confidence at the 41 kyr obliquity band prior to 3 3 ma glacial isotope stage m2 and increase to the 95 level thereafter throughout 18o cycles consistently lead 13c cycles by 3 kyr this suggests that global ocean 13c variations as produced by terrestrial marine 12c transfers were responsive to obliquity induced climate changes before the northern hemisphere glaciations nhg reached mid latitudes at 2 7 ma in contrast 41 kyr carbonate sedimentation as derived from sediment reflectance cycles maxima tightly coupled to 95 confidence and in phase with minima in the 18o record do not emerge until 2 7 ma foraminiferal fragmentation counts indicate that carbonate preservation is not the primary process behind enhanced carbonate deposition during interglacials thus we surmise that hydrography related changes in biogenic opal and carbonate production in surface water best explain glacial interglacial carbonate cycles beginning with significant nhg firm establishment of orbital scale age control on the stratigraphically complete site 1208 section now provides a platform for high resolution paleoceanographic reconstruction of the relatively understudied north pacific

the mid pliocene 4 3 2 6 ma benthic stable isotope record of the southern ocean odp sites 1092 and 704 meteor rise abstract we present mid pliocene 4 3 2 6 ma benthic stable oxygen and carbon isotope data from ocean drilling program site 1092 odp leg 177 drilled in the sub antarctic sector of the southern ocean the results are compared with the stable isotope results from nearby site 704 odp leg 114 oxygen isotope data show that minimum values are about 0 5 less than those of the holocene which is consistent with the results from site 704 indicating only minor deglaciation of antarctica during the studied interval oxygen isotope data from both site 1092 and site 704 are slightly higher relative to pacific values during several intervals which could be related to the contribution of warm saline north atlantic deep water nadw comparisons of benthic carbon isotope gradients between sites located in the north atlantic sub antarctic sector of the southern ocean and pacific indicate that at times the gradient between the southern ocean and the pacific evolved differently than the atlantic pacific gradient this suggests that variations in nadw strength alone might not be responsible for the observed carbon isotope values in the southern ocean