latest quaternary oceanographic changes in the okhotsk sea based on diatom records abstract the okhotsk sea is a locus of the north pacific intermediate water formation today the formation of the okhotsk intermediate water is linked with seasonal sea ice cover diatom records from the okhotsk sea show the following 1 during the last glacial maximum between 21 000 yr b p and 18 000 yr b p sea ice covered the western side of the sea throughout the whole year but the eastern part was open this permitted more efficient heat exchange with the atmosphere than waters and hence ventilation of the glacial okhotsk sea waters which in turn caused a greater extent of intermediate water formation through the bussol strait 2 the perennial sea ice cover extended northward and sea ice was present throughout the whole year over a great part of the sea except for the eastern part between 18 000 yr b p and 17 000 yr b p 3 the ice free area extended greatly to the south during the interval between 17 000 yr b p and 11 000 yr b p 4 there was no perennial ice cover over the whole sea and the ice free area that appeared as the seasonal ice area began to extend to the western part between 11 000 yr b p and 8 000 yr b p 5 after 8000 yr b p the ice free waters contracted to the present extent

long chain alkenone patterns in the baltic sea an ocean freshwater transition two different patterns of long chain alkenones are found in surficial sediments of the baltic sea which is the largest brackish water body on earth one pattern occurs in surficial sediments from the western baltic sea where surface water salinitiy is in excess of 7 7 psu it corresponds to the pattern produced by the marine coccolithophorid emiliania huxleyi with a suite of c37 di to tetra unsaturated methyl ketones and c38 di and tri unsaturated methyl and ethyl ketones a second pattern resembling that found in lake sediments in lacking c38 methyl ketones and having distinctly higher c37 4 methyl ketone concentrations dominates in surficial sediments of the eastern and northern baltic sea where salinities are lower than 7 7 psu correspondence of sea surface temperature sst estimates from the u37 and u379 indices using marine calibrations with mean sst in the euphotic zone from july august the main haptophyte growth season is poor thus these indices are not applicable as sedimentary thermometers in surficial sediments of the baltic sea the different patterns may either reflect the salinity dependent occurrence of specific alkenone producers or changes in the alkenone biosynthesis due to physiological stress caused by salinity variations furthermore advection of saline and oxygenated north sea water may transport marine algal material characterized by a marine e huxleyi like alkenone pattern into the western baltic sea thus covering the signature of the local alkenone producers with a baltic sea pattern copyright 2000 elsevier science ltd

freshwater impacts recorded in tetraunsaturated alkenones and alkenone sea surface temperatures from the okhotsk sea across millennial scale cycles 1 we present records of phytoplankton produced alkenones down a long piston core which reveal changes of sea surface temperature sst and sea surface salinity sss in the southwestern okhotsk sea over the past 120 ka between 20 and 60 ka b p alkenone derived temperatures typically increased by 6 c 8 c from periods corresponding within a few hundred years to stadials to those corresponding to interstadials recorded in greenland ice cores the abundance of c37 4 alkenone relative to total c37 alkenones percent c37 4 a possible proxy for salinity indicated that during most low sss was associated with high sst the warm freshwater events might be related to 1 a decline in the supply of saline water entering the okhotsk sea through the soya strait 2 strengthening of the freshwater supply from the amur river and precipitation over the okhotsk sea associated mainly with increased asian summer monsoon activity and 3 the effect of melting sea ice these findings increase our understanding of the close linkage between high and low latitudes in relation to climate change and the synchronicity of climate changes within a few centuries between the pacific and the atlantic sides of the northern hemisphere

on the nature of transverse variability in a coastal plain estuary even though estuarine processes are inherently three dimensional most of the previous studies have focused primarily on the axial longitudinal and vertical variabilities recent surveys in the lower delaware bay indicate the presence of significant transverse variability in the salinity distribution and residual circulation pattern conceptual models are developed to examine the mechanisms which might explain the observed transverse structure results indicate that both the gravitational effect and wind forcing are capable of generating substantial transverse structure in drowned river valley estuaries with triangular cross sections

evidence from shark teeth for a brackish arctic ocean in the eocene greenhouse temperatures are rising at an unprecedented rate in the arctic and affecting the sensitive hydrological cycle with increased freshwater inputs to the marine environment a deep time analogue often used to understand and predict the environmental and ecological impacts of global warming is the early middle eocene greenhouse ca 53 38 ma although the terrestrial arctic during this interval is well documented marine records are rare and largely based on one central arctic ocean site at lomonosov ridge here we estimate a mean paleosalinity of 12 7 psu for coastal waters of the western arctic ocean by incorporating 18 o co 3 values of shark teeth with estimates of eocene arctic paleotemperature and freshwater 18 o values into a salinity model this paleosalinity is substantially lower than estimates by others for the eocene central arctic ocean 21 25 psu and today9s arctic ocean 32 35 psu our results provide the first eocene salinity estimate for the western arctic ocean and when considered with prior results from lomonosov ridge suggest a reduced surface salinity but larger salinity gradient 10 psu across the eocene arctic ocean during the early middle eocene greenhouse from an ecologic perspective while today9s lamniform sharks are largely intolerant of low salinity eocene species were abundant in the brackish arctic ocean suggesting that past environmental tolerances were much greater than today

18 o modelling of freshwater inputs in baffin bay and canadian arctic coastal waters 18o salinity modelling of marine environments has been proposed for various areas including some arctic seas the present report concerns arctic coastal waters collected along the west coast of greenland northern baffin bay the arctic archipelago and the north shore of alaska measurements of 18o versus salinity allow the identification of three main components marine standard water continental freshwater and sea ice meltwater continental waters may be represented by either glacial meltwater western greenland land drainage mackenzie areas or both quantitative determinations of the respective parts involved in mixed coastal waters imply a precise knowledge of the isotopic characteristics of the local continental waters these determinations may be achieved either numerically or graphically

relationship of the tetra unsaturated c37 alkenone to salinity and temperature implications for paleoproxy applications 1 this study assesses the relationship to salinity and temperature of the levels of the tetra unsaturated 37 carbon methyl alkenone c37 4 in the surface ocean uk 37 a measure of the relative abundances of the c37 2 and the c37 3 alkenones has a well constrained linear relationship to temperature in the open ocean prahl and wakeham 1987 and is a well established technique for estimating past sea surface temperatures in the sediments e g muller et al 1998 unlike the di and tri unsaturated c37 alkenones the temperature response of the tetra unsaturated c37 alkenone is less certain sikes et al 1997 and recent work has suggested a relationship to salinity instead rosell mele 1998 schulz et al 2000 our study examined 106 surface water and sediment trap samples from the atlantic pacific and southern oceans to assess the relationship of the relative abundance of c37 4 to temperature and salinity we also examined the relative unsaturation of c37 2 and c37 3 the parameter uk 37 to the same parameters to place the c37 4 results in context uk 37 has a strong correlation to salinity in the atlantic but the relationship does not hold worldwide whereas uk 37 shows a strong linear relationship to temperatures in all ocean basins as shown in previous calibrations the salinity response in the atlantic does not confirm cause and effect and interpretation of the broader data set suggests any correlation is an artifact of the strong correlation of salinity to temperature in this basin implying salinity has no effect on the unsaturation of the c37 2 or c37 3 alkenones the c37 4 alkenone shows no discernable relationship to temperature or salinity across the several basins even when correlations are restricted to cooler temperatures where the tetra unsaturated alkenone would be expected to be present these results indicate that c37 4 alkenone levels in the open ocean do not reflect either salinity levels or temperature but respond most strongly to some other environmental variable perhaps changes in growth rate light or nutrient supply as suggested by culture studies

processes controlling the advance and retreat of sea ice in the sea of okhotsk using defense meteorological satellite program dmsp special sensor microwave imager ssm i sea ice data and meteorological data we investigate processes controlling the advance and retreat of sea ice in the sea of okhotsk for this investigation we apply a new algorithm to the ssm i data which is capable of calculating ice concentration and distinguishing sea ice types this algorithm is confirmed by comparison with national oceanic and atmospheric administration noaa advanced very high resolution radiometer avhrr imagery our investigations show that there exists a locality for the areas of new ice formation and the ice formation near the ice edge always occurs as a recovery after sea ice has retreated suddenly we also reveal that the speed of ice edge advance fairly coincides with that predicted by 2 of the geostrophic wind furthermore there exists a good correspondence between the times when the overall advance and retreat of ice cover begin and the decrease and increase of air temperature begin we conclude that the advance of the ice cover in the sea of okhotsk occurs primarily through ice advection by wind and that the interannual variation in the maximum sea ice extent can be interpreted by that in wind and air temperature conditions

oxygen isotopic identity of the delaware coastal current results are presented and discussed from a preliminary study on the oxygen isotopic composition of coastal and inner shelf waters from the middle atlantic bight between the mouths of delaware bay and chesapeake bay the water samples were collected during the spring april may 1993 in conjunction with a detailed hydrographic survey of the delaware coastal current the relationship between salinity and 18o both of which are generally accepted conservative properties of seawater allows identification of the fresh and saline mixing end members for the delaware coastal current the main source of freshwater to the delaware coastal current is a mixture of runoff into delaware bay with an estimated 18os 0 composition of 7 08 the freshwater input is dominated by delaware river discharge with a mean 18o of 8 0 based on previous studies there appears to be a secondary contribution of freshwater that is isotopically heavier from coastal plain drainage the extrapolated 18os 32 35 value 0 93 of the saline component implies exchange with middle atlantic bight shelf water through along shelf and across shelf mixing processes limited data suggest that the oxygen isotopic composition of low salinity water exiting the chesapeake bay mouth is discernible compared with that of the delaware coastal current

environmental controls on the stable isotopic composition of mercenaria mercenaria potential application to paleoenvironmental studies 1 we have investigated the environmental controls of seasonally resolved records of oxygen and carbon isotopes of modern mercenaria mercenaria bivalves collected live from five coastal sites along the east coast of north america seasonal profiles of 18o and 13c obtained by subsampling the incremental growth layers of aragonite were compared with in situ historical records of temperature and salinity we show that m mercenaria 18o profiles track accurately the seasonal variations of water temperature and that variations in growth rates do not affect the shell 18o values growth rates are strongly reduced or interrupted below water temperatures ranging from 8 to 10 c implying that only bivalves sampled in tropical areas track the full amplitude of seasonal variations although further measurements of water 18o and a better understanding of seasonal variations of the water 18o salinity relationships are necessary mercenaria mercenaria bivalves appear to precipitate their shell close to isotopic equilibrium whereas the amplitude of the seasonal profiles of 18o reflects variations in water temperature the annual average 18o decreases with latitude reflecting the trend of rainfall and riverwater 18o with latitude over the northern american continent

glacial holocene environment of the southeastern okhotsk sea evidence from geochemical and palaeontological data abstract environmental conditions and productivity changes in the southeastern okhotsk sea have been reconstructed for the last 20 ka using planktonic and benthic foraminiferal oxygen isotope records and calcium carbonate organic carbon and opal content data from two sediment cores species variability in benthic foraminiferal and diatom assemblages provides additional palaeoceanographic evidence ams radiocarbon dating of the sediments and oxygen isotope stratigraphy serve as the basis for the age models of the cores for the last 20 14 c kyr and for correlation between environmental variations in the okhotsk sea and regional and global climate changes benthic foraminiferal assemblages in the two cores depth 1590 and 1175 m varied with time so that we could recognise seven zones with different species composition changes in the benthic foraminiferal assemblages parallel major environmental and productivity variations during the last glaciation fluxes of organic matter to the sea floor showed strong seasonal variations indicated by the presence of abundant a weddellensis and infaunal uvigerina spp benthic foraminiferal assemblages changed with warming at 12 5 11 and 10 8 14 c kyr bp when productivity blooms and high organic fluxes were coeval with global meltwater pulses 1a and 1b younger dryas cooling caused a decline in productivity 11 10 kyr bp affecting the benthic faunal community subsequent warming triggered intensive diatom production opal accumulation and a strong oxygen deficiency causing significant changes in benthic fauna assemblages from 5 26 4 4 kyr bp to present time

characteristics of alkenones synthesized by a bloom of emiliania huxleyi in the bering sea abstract we investigated the characteristics of the alkenones produced by a bloom of emiliania huxleyi in the eastern bering sea in 2000 alkenones were detected in surface waters between 57 n and 63 n where phosphate concentrations were low and the ammonium nitrate ratio was high the total alkenone content c37 2 c37 3 and c37 4 ranged from 22 0 to 349 g g 1 in suspended particles and from 0 109 to 1 42 g g 1 in surface sediments this suggests that a large proportion of the particulate alkenones synthesized in the surface water rapidly degraded within the water column and or at the water sediment interface of the bering shelf the change in the stable carbon isotopic composition 13c of c37 3 alkenone could not be explained only by variation in co2 aq in the surface water but also depended on the growth rate of e huxleyi the alkenone unsaturation index uk 37 was converted into an alkenone temperature with three equations prahl et al 1988 sikes et al 1997 muller et al 1998 sikes et al s 1997 equation gave the best correlation with the observed sea surface temperature sst in the eastern bering sea however some temperatures estimated by sikes et al s 1997 equation from the uk 37 varied from the observed sst possibly because of the rapidly changing rate of alkenone synthesis in the logarithmic growth stage or the low rate of alkenone synthesis when nutrients were limiting temperatures estimated from uk 37 in the surface sediments 6 8 8 2 c matched the observed sst in september 7 8 c but differed from the annual average sst of 4 to 5 c suggesting that most of the alkenone in the eastern bering sea was synthesized during limited periods for instance in september the relative amounts of c37 4 alkenone as proportions of the total alkenones referred to as c37 4 were high ranging from 18 3 to 41 4 low salinity water

reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr 1 marine and terrestrial derived biomarkers alkenones brassicasterol dinosterol and long chain n alkanes as well as carbonate biogenic opal and ice rafted debris ird were measured in two sediment cores in the sea of okhotsk which is located in the northwestern pacific rim and characterized by high primary productivity down core profiles of phytoplankton markers suggest that primary productivity abruptly increased during the global meltwater pulse events 1a about 14 ka and 1b about 11 ka and stayed high in the holocene spatial and temporal distributions of the phytoplankton productivity were found to be consistent with changes in the reconstructed sea ice distribution on the basis of the ird this demonstrates that the progress and retreat of sea ice regulated primary productivity in the sea of okhotsk with minimum productivity during the glacial period the mass accumulation rates of alkenones caco3 and biogenic opal indicate that the dominant phytoplankton species during deglaciation was the coccolithophorid emiliania huxleyi which was replaced by diatoms in the late holocene such a phytoplankton succession was probably caused by an increase in silicate supply to the euphotic layer possibly associated with a change in surface hydrography and or linked to enhanced upwelling of north pacific deep water index terms 1050 geochemistry marine geochemistry 4835 4850 1055 geochemistry organic geochemistry 4267 oceanography general paleoceanography keywords okhotsk sea paleoproductivity sediment citation seki o m ikehara k kawamura t nakatsuka k ohnishi m wakatsuchi h narita and t sakamoto 2004 reconstruction of paleoproductivity in the sea of okhotsk over the last 30 kyr paleoceanography 19 pa1016

variation of alkenone sea surface temperature in the sea of okhotsk over the last 85 kyrs sea surface temperatures ssts in the sea of okhotsk were reconstructed based on alkenone unsaturation indices in two sediment cores alkenone ssts were found to range from 3 to 9 c over the last 85 kyr with higher sst values in warm periods holocene and the oxygen isotope stage ois 5a in the last glacial periods ois 4 and 3 average alkenone sst was estimated to be 4 c which was 4 c lower than the holocene on average however alkenone ssts around the last glacial maximum lgm are as high as those of the holocene the variation patterns of u k 0 37 in the okhotsk sea were found to be similar to those reported in the sea of japan org chem 32 2001 57 over the last 30 kyr although the ssts were lower in the sea of okhotsk the higher u k

decreased surface salinity in the sea of okhotsk during the last glacial period estimated from alkenones 1 studies of sediment cores from the sea of okhotsk which is characterized by seasonal sea ice have shown a large variability of sea ice indicators during the glacial interglacial cycles in this study we apply the relative abundance of the c37 4 alkenone to total c37 alkenones c37 4 as a molecular indicator of salinity and water masses to further investigate surface oceanographic condition in the sea of okhotsk in the glacial period we found a large fluctuation of c37 4 4 35 with higher values 20 35 during the last glacial period and lower values 8 during warm periods suggesting a decreased surface salinity in the glacial period the variation of c37 4 was found to be consistent with the ice rafted debris ird in the sediment core correlation coefficient r2 between c37 4 and ird 0 72 this suggests that the duration of seasonal sea ice was longer in the glacial period than today the lowered surface salinity in the glacial might also have been seriously affected by the close off of the shallow soya strait which currently transports massive volumes of saline water from the sea of japan to the sea of okhotsk

experiments in taphonomy abstract several long term taphonomic experiments are described with the aim of providing comparative data with which to interpret palaeontological and archaeological sites the study of taphonomy is an adjunct to site interpretation especially the reconstruction of palaeoecology and an understanding of taphonomic processes can only come about through actualistic and laboratory analyses experiments described include the overton down earthworks 32 year old buried bone trampled bone from draycott 17 years old weathered amphibian bone also from draycott 16 years old surface weathered bone from arabia following 10 years exposure bone dispersal weathering burial burning and scavenging in rhulen wales with many skeletons ranging from 1 to 20 years old and finally a series of laboratory experiments set up to test particular processes these included earthworm activity abrasion breakage and predation on small mammals two examples are given at the end to show how the effects of these processes can be identified in the past and how their identification can help to resolve particular issues in two palaeontological sites these are the middle pleistocene deposits at westbury sub mendip somerset and middle miocene deposits at pasalar turkey

variability of unusual distributions of alkenones in the surface waters of the nordic seas 1 samples of filtered particulate organic matter pom were obtained during the summers of 1999 and 2000 from the surface waters of the nordic seas to monitor the spatial distribution of long chain alkenones the aim of the study was to appraise existing alkenone based climatic proxies in northern high latitudes unusually high percentages of the tetraunsaturated alkenone were measured in the polar waters of the east greenland current with c37 4 of up to 77 in 80 of sea ice cover values of percent c37 4 across the nordic seas showed a strong association with water mass type analysis of coccoliths in filters indicated that calcified emiliania huxleyi could not be discounted as the biological precursor of alkenones in all the water masses a combined data set of 69 samples of pom revealed a stronger correlation of percent c37 4 to sea surface salinity sss r2 0 72 than to sea surface temperature sst r2 0 50 values of percent c37 4 in sea surface pom were much higher than those in surficial sediments of the northern north atlantic to explain the discrepancy in sedimentary and surface water column percent c37 4 we propose that the alkenone contents in surface sediments underlying arctic and polar waters are a combination of autochthonous and allochthonous inputs of alkenones our results show that percent c37 4 can be used to reconstruct the relative extension of arctic polar water masses in the north atlantic however the results prevent confirmation of percent c37 4 as a paleo sss proxy in the nordic seas given its multivariate nature in our data set and the decoupling between its range of values in surface waters and sediments

alkenone based reconstruction of late holocene surface temperature and salinity changes in lake qinghai china china the alkenone temperature proxy u k 0 37 indicates up to a 1 c change in mean annual air temperature or a 2 c change in summer lake water temperature during the late holocene oscillating warm and cold periods could be related to the 20th century warm period the little ice age the medieval warm period the dark ages cold period and the roman warm period the relative importance of c37 4 alkenone to total c37 alkenone production c37 4 fluctuated between 15 45 with higher values during warm periods suggesting that lake water was also fresher during these periods the coupled late holocene surface temperature and salinity changes suggest that asian monsoons strongly influenced the climate of the lake qinghai region citation liu z a c g henderson and y huang 2006 alkenone based reconstruction of lateholocene surface temperature and salinity changes in lake qinghai china geophys res lett 33 l09707 doi 10 1029 2006gl026151

alkenone distributions in the north atlantic and nordic sea surface waters 1 the c37 c39 alkenones were quantified in suspended particulate matter obtained from the surface waters of the north atlantic including the nordic seas over a temperature range of 4 20 c u37k values were linearly correlated to temperature over the entire range covered by our data set i e 4 20 c u37k 0 027t 0 036 r2 0 97 the compilation of water column data from the atlantic pacific and southern ocean and mediterranean sea suggests that the linear model may not be the best function for fitting u37k and in situ temperature values it also shows that suspended matter data from warm waters t 20 c are still needed to constrain the equation of the global curve high abundances of c37 4 were found in the coldest polar waters around 4 c c37 4 represented up to 35 a value that dropped to zero at temperatures above 10 c values of c37 4 were linearly correlated to temperature c37 4 3 7t 43 7 r2 0 50 and salinity c37 4 48 1s 1691 r2 0 78 further investigations from other oceanic basins are necessary to confirm these findings

oxygen isotopic composition of bottom seawater and tunicate cellulose used as indicators of water masses in the northern bering and chukchi seas oxygen isotopic composition of bottom seawater and tunicate cellulose were used as short term and long term indicators respectively of water mass characteristics in the northern bering and chukchi seas oxygen isotopic composition of northeastern bering sea waters is influenced by yukon river inflows of sup 18 o depleted continental water mixing with relatively sup 18 o enriched waters contributed by the anadyr current tunicate cellulose sampled under alaska coastal water is more depleted in sup 18 o than that collected under bering shelf and anadyr waters which reflects the oxygen isotopic composition of these waters tunicate cellulose collected under the mixed bering shelf water displays intermediate delta sup 18 o values oxygen isotopic analyses of bottom seawater were used to determine the spatial location and influence of continental and coastal derived precipitation and of sea ice formation on water mass structure on the continental shelf of the northern bering and chukchi seas results indicate that the oxygen isotopic composition of tunicate cellulose averaged over multiple seasons may serve as a long term biochemical indicator of water mass patterns in ice covered polar regions where continuous sampling is impractical

glacial meltwater input to the alaska coastal current evidence from oxygen isotope measurements results of a study of the oxygen isotopic composition of coastal pelagic and fresh waters from the northern gulf of alaska region are presented this study was undertaken to investigate whether isotopic tracers could be of use in determining the important freshwater inputs to the alaska coastal current acc and whether they could confirm the presence of the acc in coastal waters west of kodiak island the alaska coastal current the major coastal circulation feature of the northern gulf of alaska can be distinguished from oceanic waters on the basis of its lower salinity at least as far west as kodiak island this study adds significantly to the small amount of oxygen isotopic information available for the waters of this region the isotopic results suggest that in late summer glacial meltwater may provide a substantial portion of the total freshwater runoff into the acc and that the acc does extend as far to the west as unimak pass

a biomarker approach for assessing marine and terrigenous inputs to the sediments of sea of okhotsk for the last 27 000 years abstract a sediment core taken from the sea of okhotsk which is located in the western north pacific rim with an extensive seasonal sea ice cover was investigated for lipid class compounds total organic carbon total nitrogen and 13 c of bulk organic matter to reconstruct changes in sedimentary regimes of marine and terrestrial organic matter over the last 27 kyrs higher molecular weight n alkanes fatty acids and fatty alcohols showed an increase in terrigenous inputs in glacial and to a greater extent in early deglacial periods the enhanced terrestrial input in the deglaciation stages has for the first time been found and never been reported in the open ocean biomarker profiles together with the coarse grain size distribution in nearby sediment cores suggested that sea ice rafting was the main transport mechanism of continental material to the okhotsk sea sediments however the ice rafting inputs have been weakened from 14 kyrs bp to the holocene probably due to a rapid reduction of the sea ice cover and continental shelf erosion profiles of c 37 alkenones phytol and brassicasterol as well as temporal variation in calcium carbonate and organic carbon contents indicated that the marine inputs were enhanced during the deglaciation the enhanced marine inputs were likely caused by an intensification of the primary production induced by a possibly increased nutrient supply from the continental shelves in early deglaciation and by the deglacial retreat of the sea ice cover at 14 kyrs bp this study demonstrates that biomarkers in the marginal marine sediments had recorded changes in the biogeochemical processes in the sea of okhotsk over the last 27 kyrs which may be significantly affected by changes in the okhotsk water exchange processes such as sea ice activity and sea ice transport of terrigenous materials

diatom record of the late holocene in the okhotsk sea abstract the environmental conditions during the past 7000 cal yr bp in the okhotsk sea can be subdivided into three intervals based on diatom assemblages 1 6600 4650 cal yr bp open ocean sea ice free conditions alternated with sea ice cover 2 4650 1300 cal yr bp open ocean conditions and sea ice cover declined fluctuating with short duration and cold open ocean conditions gradually developed and 3 1300 cal yr bp present when cold open ocean conditions predominated with occasional and rapid warming chronological comparisons between climatic fluctuations and cultural history in hokkaido and okhotsk suggest that deteriorating climate could have affected local culture

abrupt increase in precipitation and weathering of soils in east siberia coincident with the end of the last glaciation 15 cal kyr bp abstract an abrupt increase in the temperature in greenland in the wake of the initiation of the bolling allerod warm phase at ca 15 cal kyr bp was followed after a few decades by a dramatic increase in the concentration of methane in the atmosphere of the earth resulting from an increase in humidity in the tropics j p severinghaus e j brook science 286 1999 930 934 analysis of a sediment core from lake baikal east siberia spanning the end of the last glacial period and the holocene revealed an abrupt stepwise 1 3 3 4 fold decrease in the concentration of several soluble elements such as na k mg ca and si in hot nitric acid extracts of small intervals 3 cm this chemical change appears to have occurred over the same time span based on similarities in the profiles of silica and diatoms found in other 14 c dated cores this suggests that the calcium rich mammoth steppe landscape r d guthrie quat sci rev 20 2001 549 573 of siberia created during the last glaciation underwent a dramatic transformation at the end of this period at the beginning of the bolling allerod warm phase due to an increase in precipitation within a time interval of less than 300 yr

timing of the last glacial maximum from observed sea level minima during the last glacial maximum ice sheets covered large areas in northern latitudes and global temperatures were significantly lower than today but few direct estimates exist of the volume of the ice sheets or the timing and rates of change during their advance and retreat here we analyze four distinct sediment facies in the shallow tectonically stable bonaparte gulf australia each of which is characteristic of a distinct range in sea level to estimate the maximum volume of land based ice during the last glaciation and the timing of the initial melting phase we use faunal assemblages and preservation status of the sediments to distinguish open marine shallow marine marginal marine and brackish conditions and estimate the timing and the mass of the ice sheets using radiocarbon dating and glacio hydroisostatic modelling our results indicate that from at least 22 000 to 19 000 calendar years before present land based ice volume was at its maximum exceeding today s grounded ice sheets by 52 5 x 10 exp 6 cu km a rapid decrease in ice volume by about 10 percent within a few hundred years terminated the last glacial maximum at 19 000 250 years

hydrological impact of heinrich events in the subtropical northeast atlantic reconstructing the impact of heinrich events outside the main belt of ice rafting is crucial to understanding the underlying causes of these abrupt climatic events a high resolution study of a marine sediment core from the iberian margin demonstrates that this midlatitude area was strongly affected both by cooling and advection of low salinity arctic water masses during the last three heinrich events these paleoclimatic time series reveal the internal complexity of each of the last three heinrich events and illustrate the value of parallel studies of the organic and inorganic fractions of the sediments

multiproxy evidence of holocene climate variability from estuarine sediments eastern north america water temperature estimated from ostracode mg ca ratios the results indicate a much drier early holocene in which mean paleosalinity was 28 ppt in the northern bay falling 25 to 20 ppt during the late holocene early holocene mg ca derived temperatures varied in a relatively narrow range of 13 to 16 c with a mean temperature of 14 2 c and excursions above 16 c the late holocene was on average cooler mean temperature of 12 8 c in addition to the large contrast between early and late holocene regional climate conditions multidecadal 20 40 years salinity and temperature variability is an inherent part of the region s climate during both the early and late holocene including the medieval warm period and little ice age these patterns are similar to those observed during the twentieth century caused by nao related processes comparison of the midlatitude chesapeake bay salinity record with tropical climate records of intertropical convergence zone fluctuations inferred from the cariaco basin titanium record suggests an anticorrelation between precipitation in the two regions at both millennial and centennial timescales

climatic and oceanographic variations on the california continental margin during the last 160 kyr organic matter in sediment samples from three odp sites ocean drilling program leg 167 that form a south north transect was investigated to reconstruct the paleoclimatic and oceanographic conditions on the california continental margin during the last 160 kyr alkenone derived paleosea surface temperatures sst are 3 to 6 c colder in glacial stages and reveal a clear relationship with global climate changes the differences are greater in the north latitudinal sst comparison exhibits water mixing of the colder california current with warmer waters from the south particularly in the southern central california borderland area organic matter accumulation on the california continental margin indicates an interplay between climatic and atmospheric glacial interglacial variations and spatially and temporally changing nutrient availability along the california coastline climatic and atmospheric dependent circulations apparently caused variations in the intensity of coastal upwelling along the southern central california margin and this suggests due to the close connection of the california current to the local wind patterns that the california current was weaker during glacial and stronger during interglacial periods

distribution and formation of okhotsk sea intermediate water an analysis of isopycnal climatological data 1 in order to clarify the distribution and formation of okhotsk sea intermediate water osiw an isopycnal climatological data set based on all of the available historical observations is developed and examined the isopycnal maps clearly show that there are two direct ventilation sources for osiw dense shelf water dsw with cold and fresh properties influenced by sea ice formation in the northwest shelf region and forerunner of soya warm current water fscw which has warm and saline properties originating in the japan sea the cold and fresh water extends southward from the northwest shelf to the shelf slope off sakhalin island it suggests that dsw is transported southward by the east sakhalin current the dsw enters the kuril basin and mixes with fscw and western subarctic water wsaw originating from the north pacific to form osiw the annual mean production rate of dsw estimated from the total volume of dsw over the shelf in spring and summer is 0 67 sv 1 sv 106 m3 s the annual mean volume transport of fscw is estimated to be 0 08 sv on the basis of its cross section area and the current speed assumption of isopycnal mixing yields a mixing ratio of 1 1 0 1 among dsw wsaw and fscw to form osiw we estimate the annual production rate of osiw to be 1 4 sv the corresponding osiw s renewal time is 7 years continued assumption of isopycnal mixing yields a mixing ratio of 0 6 0 4 between wsaw and osiw to form oyashio intermediate water oyiw

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

interhemispheric appraisal of the value of alkenone indices as temperature and salinity proxies in high latitude locations alkenone sediment data from the nordic seas and north atlantic are compared to those from sikes et al 1997 for the southern ocean to evaluate further uk37 and uk37 as proxies to estimate cold temperatures 10 c and the effect of salinity and temperature in the relative abundance of 37 4 to the total abundance of c37 alkenones 37 4 uk37 and uk37 are found to be equally viable as proxies but there are significant regional differences in their cold temperature dependence the measurement of 37 4 in cores from the north atlantic region can be used to identify situations when uk37 is not a reliable paleothermometer variations in salinity are probably responsible for changes in the sedimentary record of 37 4 and a preliminary calibration has been obtained for 37 4 f salinity this new relationship should be further confirmed through field or laboratory experiments but it paves the way to derive a molecular proxy to reconstruct paleosalinity in surface waters