high precision isotopic characterization of usgs reference materials by tims and mc icp ms the pacific centre for isotopic and geochemical research pcigr at the university of british columbia has undertaken a systematic analysis of the isotopic sr nd and pb compositions and concentrations of a broad compositional range of u s geological survey usgs reference materials including basalt bcr 1 2 bhvo 1 2 andesite agv 1 2 rhyolite rgm 1 2 syenite stm 1 2 granodiorite gsp 2 and granite g 2 3 usgs rock reference materials are geochemically well characterized but there is neither a systematic methodology nor a database for radiogenic isotopic compositions even for the widely used bcr 1 this investigation represents the first comprehensive systematic analysis of the isotopic composition and concentration of usgs reference materials and provides an important database for the isotopic community in addition the range of equipment at the pcigr including a nu instruments plasma mc icp ms a thermo finnigan triton tims and a thermo finnigan element2 hr icp ms permits an assessment and comparison of the precision and accuracy of isotopic analyses determined by both the tims and mc icp ms methods e g nd isotopic compositions for each of the reference materials 5 to 10 complete replicate analyses provide coherent isotopic results all with external precision below 30 ppm 2 sd for sr and nd isotopic compositions 27 and 24 ppm for tims and mc icp ms respectively our results also show that the first and second generation usgs reference materials have homogeneous sr and nd isotopic compositions nd isotopic compositions by mc icp ms and tims agree to within 15 ppm for all reference materials interlaboratory mc icp ms comparisons show excellent agreement for pb isotopic compositions however the reproducibility is not as good as for sr and nd a careful sequential leaching experiment of three first and second generation reference materials bcr bhvo agv indicates that the heterogeneity in pb isotopic compositions and concentrations could be directly related to contamination by the steel mortar pestle used to process the materials contamination also accounts for the high concentrations of certain other trace elements e g li mo cd sn sb w in various usgs reference materials

a revised calendar age for the last reconnection of the black sea to the global ocean abstract during the last decade a debate arose regarding the timing and pattern of the last reconnection of the black sea lake with the global ocean on a geochemical basis the radiocarbon age of black sea lake surface water during the time of reconnection was determined to be 8400 14c a bp despite the potential bias induced by the hard water effect in lakes the reconnection age was calibrated without any reservoir age correction which led to an estimate of 9400 cal a bp since knowledge for the actual calendar age has important hydrologic implications that would provide new insights regarding the mechanism of reconnection determining the actual calendar age for the last reconnection remains important based upon modeling experiments and micropaleontological reconstructions the black sea lake reconnection occurred in two steps as follows 1 initial marine inflow imi followed by 2 a period of increasing basin salinity that led to the disappearance of lacustrine species dls in order to better define the actual calendar age for the last reconnection a review of the sedimentary expressions of the imi and dls boundaries was performed in order to correlate them throughout the black sea sedimentary environments this correlation reconciles the apparent inconsistency in the published radiocarbon dataset and provides the atmospheric radiocarbon age of the last reconnection which represents the reference for reservoir age calculations and which can be directly calibrated we determine reservoir ages for the water column as well as the reconnection calendar age to be 9000 cal a bp at the reconnection with the global ocean black sea lake reservoir ages were non negligible and water depth dependent consistent with a weak water column stratification during the early holocene the calibrated age of initial marine inflow 9000 cal a bp implies that the former bosphorus sill was shallower by 10 m than is commonly assumed in the literature compared to the sedimentary context of the sakarya coastal plain this result suggests that the level of the isolated black sea was below the former bosphorus sill depth at the time of the last reconnection furthermore a lag of 900 yr between initial marine inflow and the disappearance of lacustrine species indicates that approximately ten centuries were needed to establish the currently observed two way flow exchange with the global ocean

khvalynian transgression of the caspian sea was not a result of water overflow from the siberian proglacial lakes nor a prototype of the noachian flood abstract the paper presents a critical review of the hypothesis that the khvalynian transgression resulted from abundant inflow of meltwater from siberian proglacial lakes through the aral sea and along the uzboi channel into the caspian sea had a catastrophic character and could be considered as a prototype of the biblical noachian flood a thorough analysis of evidence cited by the proponent of the hypothesis revealed the lack of factual substantiation 1 there are no data indicative of aral drainage 2 there is no evidence that siberian proglacial water was inflowing into the caspian sea 3 taxonomic and spatial distribution of molluscs in khvalynian sediments do not indicate that transgression was essentially influenced by thawing of ice sheets on the russian plain 4 there is no evidence that the khvalynian transgression was catastrophic sea level rose by few centimeters per year over several thousands of years 5 there are no data indicating that khvalynian water overflowing through the manych spillway into the neoeuxinian lake was significant inflow could increase the level and salinity of the lake by 30 m and 5 respectively thus there is no evidence that the khvalynain transgression could serve as a reliable source for the biblical noachian flood

pleistocene chronostratigraphy in estonia southeastern sector of the scandinavian glaciation abstract pleistocene chronostratigraphy in estonia is based on 29 studied sites sections the dating of which covers a span from approximately 200 ka bp to the pleistocene holocene chronostratigraphic boundary and a local varved clay chronology for eastern estonia which enables tentative correlation of lateglacial lg events to finnish and swedish varve chronologies analysis of existing and unpublished data was used to review the current pleistocene chronostratigraphy and particularly the history of weichselian cold stage in estonia osl ages from fluvial deposits that included the korvekula holsteinian or rongu eemian continental interglacial deposits revealed that the pre weichselian interglacial deposits were glacially dislocated during the weichselian available osl tl and 14 c dates and new 14 c ams ages of mammoth bones indicate ice free conditions between 105 and 68 ka bp and a comparatively mild middle weichselian between 43 and 22 ka bp the lg chronology indicates in general rapid average 110 m yr deglaciation of the territory between ca 14 7 and 12 7 ka bp the duration of the late weichselian glaciation in estonia ranged between 7 3 and 9 3 ka

glacial hydrologic conditions in the black sea reconstructed using geochemical pore water profiles abstract chloride and 18 o compositions of interstitial water extracted from a long sediment core retrieved from the nw coast of the black sea allowed us to constrain the main hydrologic changes of the back sea during the late pleistocene and holocene prior to its reconnection with the mediterranean sea through the marmara sea at approximately 9000 calendar yr before present 9 ka cal bp the black sea has evolved as a fresh to brackish water lake at the time of reconnection hydrologic changes were drastic bottom water salinities changed from a few psu practical salinity unit to 22 psu since solutes in the interstitial water column within sediments are advected and diffused the measured concentrations do not reflect those of past bottom waters in order to reconstruct these former concentrations we used an advection diffusion model different scenarios of bottom water chloride and 18 o variations were accounted for in this model in order to simulate present day vertical profiles for concentrations of interstitial water in order to compare them to measured ones the comparison suggests that the glacial black sea was a homogeneous freshwater lake with a 18 o of 10 and a salinity of 1 psu modern hydrologic conditions would only have been reached at 2 ka cal bp concomitant with the onset of coccolith rich thin layers that characterize modern basin sediments such delayed salinization over 7000 yr in the basin may have been due to higher precipitation during the early holocene we also simulated the impact of a catastrophic reconnection and a smoother reconnection both salinity scenarios lead to undistinguishable modelled present day profiles indicating that the precise impact of the last reconnection was lost due to the advection diffusion processes

the co evolution of black sea level and composition through the last deglaciation and its paleoclimatic significance abstract the black sea was an inland lake during the last ice age and its sediments are an excellent potential source of information on eurasian climate change showing linkages between regionally and globally recognized millennial scale climate events of the last deglaciation here we detail changes from the last glacial maximum lgm through the transition to an anoxic marginal sea using isotopic strontium and oxygen and trace element sr ca ratios in carbonate shells which record changing input sources and hydrologic conditions in the basin and surrounding region sr isotope records show two prominent peaks between 18 and 16 ka bp cal reflecting anomalous sedimentation associated with meltwater from disintegrating eurasian ice sheets that brought black sea level to its spill point following a sharp drop in sr isotope ratios back toward glacial values two stages of inorganic calcite precipitation accompanied increasing oxygen isotope ratios and steady sr isotope ratios these calcite peaks are separated by an interval in which the geochemical proxies trend back toward glacial values the observed changes reflect negative water balance and lake level decline during relatively warm periods bolling allerod and preboreal and increasing river input less evaporation resulting in higher lake levels during the intervening cold period the younger dryas a final shift to marine values in sr and oxygen isotope ratios at 9 4 ka bp cal corresponds to connection with the global ocean and marks the onset of sedimentation on the black sea continental shelf this date for the marine incursion is earlier than previously suggested based on the appearance of euryhaline fauna and the onset of sapropel formation in the deep basin

abrupt changes of temperature and water chemistry in the late pleistocene and early holocene black sea new mg ca sr ca and published stable oxygen isotope and 87sr 86sr data obtained on ostracods from gravity cores located on the northwestern black sea slope were used to infer changes in the black sea hydrology and water chemistry for the period between 30 to 8 ka b p calibrated radiocarbon years the period prior to 16 5 ka b p was characterized by stable conditions in all records until a distinct drop in 18o values combined with a sharp increase in 87sr 86sr occurred between 16 5 and 14 8 ka b p this event is attributed to an increased runoff from the northern drainage area of the black sea between heinrich event 1 and the onset of the bolling warm period while the mg ca and sr ca records remained rather unaffected by this inflow they show an abrupt rise with the onset of the bolling allerod warm period this rise was caused by calcite precipitation in the surface water which led to a sudden increase of the sr ca and mg ca ratios of the black sea water the stable oxygen isotopes also start to increase around 15 ka b p although in a more gradual manner due to isotopically enriched meteoric precipitation while sr ca remains constant during the following interval of the younger dryas cold period a decrease in the mg ca ratio implies that the intermediate water masses of the black sea temporarily cooled by 1 2 c during the younger dryas the 87sr 86sr values drop after the cessation of the water inflow at 15 ka b p to a lower level until the younger dryas where they reach values similar to those observed during the last glacial maximum this might point to a potential outflow to the mediterranean sea via the sea of marmara during this period the inflow of mediterranean water started around 9 3 ka b p which is clearly detectable in the abruptly increasing mg ca sr ca and 87sr 86sr values the accompanying increase in the 18o record is less pronounced and would fit to an inflow lasting 100 a

kinematic constraints on glacier contributions to 21st century sea level rise on the basis of climate modeling and analogies with past conditions the potential for multimeter increases in sea level by the end of the 21st century has been proposed we consider glaciological conditions required for large sea level rise to occur by 2100 and conclude that increases in excess of 2 meters are physically untenable we find that a total sea level rise of about 2 meters by 2100 could occur under physically possible glaciological conditions but only if all variables are quickly accelerated to extremely high limits more plausible but still accelerated conditions lead to total sea level rise by 2100 of about 0 8 meter these roughly constrained scenarios provide a most likely starting point for refinements in sea level forecasts that include ice flow dynamics

high frequency palaeoceanographic changes during the past 140 000 yr recorded by the organic matter in sediments of the iberian margin abstract biogenic records of the marine palaeoproductivity carbonates organic carbon and c 37 alkenones and the molecular stratigraphy of past sea surface temperatures ssts u 37 k were studied at high resolution in two cores of the iberian margin the comparison of these records indicates that the oceanographic conditions switched abruptly during the past 160 kyr between three kinds of regimes a first regime with high 17 22 c sst and low productivity typifies the interglacial periods marine isotopic stages mis 5 and 1 several periods during mis 6 2 and the terminations ii and i are characterised by about 4 5 c colder sst and a higher organic matter accumulation both of which define the second regime this anticorrelation between sst and marine productivity suggests that these variations are related to the intensity of the coastal upwelling by contrast with this upwelling behaviour extremely low biological productivity and very cold sst 6 12 c occurred during short phases of glacial mis 6 4 and 2 and as abrupt events 1 kyr or less during mis 3 the three oceanographic regimes are consistent with micropalaeontological changes in the same cores based on foraminifera and diatoms the general trend of these hydrologic changes follows the long term glacial interglacial cycle but the millennium scale variability is clearly related to heinrich events and dansgaard oeschger cycles strengthening of the upwelling corresponds probably to an intensification of the subtropical atmospheric circulation over the north atlantic which was influenced by the presence of continental ice sheets however extreme glacial conditions due to massive discharges of icebergs interrupted the upwelling interestingly both terminations ii and i coincided with strong but transient intensification of the upwelling

a novel proxy for terrestrial organic matter in sediments based on branched and isoprenoid tetraether lipids we propose a novel tracer for terrestrial organic carbon in sediments based on the analysis of tetraether lipids using high performance liquid chromatography mass spectrometry hplc ms analysis of terrestrial soil and peats shows that branched tetraether lipids are predominant in terrestrial environments in contrast to crenarchaeol the characteristic membrane lipid of non thermophilic crenarchaeota which is especially abundant in the marine and lacustrine environment based on these findings an index was developed the so called branched and isoprenoid tetraether bit index based on the relative abundance of terrestrially derived tetraether lipids versus crenarchaeol this bit index was applied to surface sediments from the angola basin where it was shown to trace the outflow of the congo river furthermore analyses of particulate organic matter from the north sea showed relatively higher bit indices in water column particulate organic matter near large river inputs a survey of globally distributed marine and lacustrine surface sediments shows that the bit index in these environments correlates with the relative fluvial input of terrestrial organic material making this index generally applicable the new proxy allows the rapid assessment of the fluvial input of terrestrial organic material in immature sediments up to 100 ma old

a precise search for drastic temperature shifts of the past 40 000 years in southeastern europe 1 climatic models simulate abrupt oscillations that are associated in the north atlantic with dansgaard oeschger and heinrich events however the geographic extension of temperature anomalies is largely uncontrolled due to the scarcity of quantitative records of sufficient time resolution on the european continent here we propose based on a recently developed temperature proxy tex86 a reconstruction of millennial scale temperature variations in a black sea sediment archive for the last 40 000 years prior to any paleoclimatological interpretations the effects of potential bias such as seasonality and depth of maximum export production on temperature reconstructions are considered for the black sea based on previous work a tentative method for temperature corrections taking into account varying terrigenous inputs is further proposed reconstructed temperatures for black sea core md042790 were remarkably stable during the last glacial however significant shifts toward lower temperatures of 2 c occurred during heinrich events 2 and 3 the deglaciation displayed a temperature increase of 10 c consistent with neighboring european reconstructions a younger dryas cooling of approximately 5 6 c was clearly expressed in the reconstruction in notable contrast to observations from nearby archives heinrich events imprinted our glacial temperature record consistent with a strong reorganization of oceanic circulation and a large spreading of the temperature anomaly from the north atlantic toward the southeast furthermore in contrast to high latitude records our black sea record lacks the signatures of dansgaard oeschger interstadials suggesting a decreasing temperature gradient away from the north atlantic

hf and nd isotopes in marine sediments constraints on global silicate weathering the combined use of lu hf and sm nd isotope systems potentially offers a unique perspective for investigating continental erosion but little is known about whether and to what extent the hf nd isotope composition of sediments is related to silicate weathering intensity in this study hf and nd elemental and isotope data are reported for marine muds leached fe oxide fractions and zircon rich turbidite sands collected off the congo river mouth and from other parts of the se atlantic ocean all studied samples from the congo fan muds fe hydroxides sands exhibit indistinguishable nd isotopic composition end 16 indicating that fe hydroxides leached from these sediments correspond to continental oxides precipitated within the congo basin in marked contrast hf isotope compositions for the same samples exhibit significant variations leached fe hydroxide fractions are characterized by ehf values from 1 1 to 1 3 far more radiogenic than associated sediments from 7 1 to 12 0 and turbidite sands from 27 2 to 31 6 ehf values for congo fan sediments correlate very well with al k i e a well known index for the intensity of chemical weathering in central africa taken together these results indicate that 1 silicate weathering on continents leads to erosion products having very distinctive hf isotope signatures and 2 a direct relationship exists between ehf of secondary clay minerals and chemical weathering intensity these results combined with data from the literature have global implications for understanding the hf nd isotope variability in marine precipitates and sediments leached fe hydroxides from congo fan sediments plot remarkably well on an extension of the seawater array i e the correlation defined by deep sea fe mn precipitates providing additional support to the suggestion that the ocean hf budget is dominated by continental inputs fine grained sediments define a diffuse trend between that for igneous rocks and the seawater array which we refer to as the zircon free sediment array ehf 0 91 end 3 10 finally we show that the hf nd arrays for seawater unweathered igneous rocks zircon free and zircon bearing sediments ehf 1 80 end 2 35 can all be reconciled using monte carlo simulations with a simple weathering model of the continental crust

ice dammed lakes and rerouting of the drainage of northern eurasia during the last glaciation during the quaternary period ice sheets centred over the barents and kara seas expanded several times onto mainland russia and blocked northflowing rivers such as the yenissei ob pechora and mezen large ice dammed lakes with reversed outlets e g toward the caspian sea formed south of these ice sheets some lakes are reconstructed from shorelines and lacustrine sediments others mainly from ice sheet configuration ice dammed lakes considerably larger than any lake on earth today are reconstructed for the periods 90 80 and 60 50 ka the ages are based on numerous optically stimulated luminescence osl dates during the global last glacial maximum lgm about 20 ka the barents kara ice sheet was too small to block these eastern rivers although in contrast to the 90 80 and 60 50 ka maxima the scandinavian ice sheet grew large enough to divert rivers and meltwater across the drainage divide from the baltic basin to the river volga and that way to the caspian sea climate modelling shows that the lakes caused lower summer temperatures on the continent and on the lower parts of the ice sheet the final drainage of the best mapped lake is modelled and it is concluded that it probably emptied within few months we predict that this catastrophic outburst had considerable impact on sea ice formation in the arctic ocean and on the climate of a much larger area c 2003 elsevier ltd all rights reserved less

continental scale transport of sediments by the baltic ice stream elucidated by coupled grain size and nd provenance analyses abstract we introduce a methodology for determining the transport distance of subglacially comminuted and entrained sediments we pilot this method on sediments from the terminal margin of the baltic ice stream the largest ice stream of the fennoscandian ice sheet during the last glacial maximum a strong correlation r2 0 83 between the end and latitudes of circum baltic river sediments enables us to use end as a calibrated measure of distance the proportion of subglacially transported sediments in a sample is estimated from grain size ratios in the silt fraction

late glacial to holocene climate and sedimentation history in the nw black sea abstract gravity cores from the continental slope in the northwestern black sea were studied using high resolution stable isotope grain size and xrf scanning data the measurements provide a 30 000 years ams 14c dated record of variations in the hydrological regime of the black sea and give insight into changing paleoenvironments in the surrounding areas stable climatic conditions during the last glacial maximum were followed by a series of meltwater pulses most likely originating from the scandinavian ice sheet between 18 000 and 15 500 yr bp 1 this meltwater input rose the level of the caspian sea to a point that caspian water could spill into the black sea via the manych depression north of the caucasian mountains high frequency oscillations in the xrf data during this period suggest a probable link to the arctic climate regime later during the bolling allerod and the early holocene prevailing high temperatures led to authigenic calcite precipitation through increased phytoplankton activity interrupted by the younger dryas and the 8200 yr bp cold event with dominant clastic sedimentation

late glacial to holocene paleoenvironmental evolution of the black sea reconstructed with stable oxygen isotope records obtained on ostracod shells high resolution stable oxygen isotope d 18 o on ostracod shells xrf scanning and bulk grain size data obtained on a transect of 6 gravity cores from the continental slope in the northwestern black sea give new insight into the hydrological evolution of the black sea since the last glacial maximum lgm stable climatic conditions during the lgm were followed by a series of meltwater pulses between 18 and 15 5 kyr bp that resulted in temporary isotopic depletion of the black sea waters subsequently steadily increasing d 18 o values in all cores are mainly caused by isotopically enriched precipitation at the onset of the allerod bolling warm period a comparison of the major trends in d 18 o at different water depths suggests evaporation driven deep water formation since 14 5 kyr bp while the two shallowest cores from 168 and 465 m water depth were under the influence of increased warming in the upper water column since 14 5 and 12 5 kyr bp respectively the core from 168 m depth seems to be additionally influenced by freshwater input of the danube this core provides a high resolution record from the younger dryas allerod boundary and suggests that a nao like climate mode was governing the interannual variability in the run off of the danube which implies that this climate mode has been a persistent climatic feature over central europe the inflow of saline mediterranean waters occurs between 9 and 8 kyr bp where a merging of all d 18 o records signals an initial homogenisation of the water column

the first estimation of fleuve manche palaeoriver discharge during the last deglaciation evidence for fennoscandian ice sheet meltwater flow in the english channel ca 20 18 ka ago the fleuve manche english channel palaeoriver represents the largest river system that drained the european continent during pleistocene lowstands particularly during the elsterian marine isotope stage 12 and saalian drenthe mis 6 glaciations when extensive ice advances into the north sea area forced the central european rivers to flow southwards to the bay of biscay ne atlantic numerous long piston cores and high resolution acoustic data from the northern bay of biscay have been correlated using a well constrained chronostratigraphical framework and for the first time allow the estimation of the discharge of the fleuve manche palaeoriver at the end of the last glacial period i e weichselian our results discussed in the light of relationships between river loads and drainage area characteristics strongly suggest that the bay of biscay collected sediment laden meltwater from the northern european lowlands and the southern part of the fennoscandian ice sheet at the end of the last glacial period and particularly during the paroxysmal phase of the european deglaciation ca 20 18 ka ago this demonstrates that the fleuve manche drainage area at that time was equivalent to those dating from the major elsterian and saalian drenthe glaciations based on our data we propose a revision of the palaeogeographical and palaeoglaciological evolution of the north sea area while showing that the british and fennoscandian ice sheets entered the north sea basin until ca 18 ka initiating isostatic adjustment of the basin this allowed the north sea fluvial system to flow southwards through the dover strait finally we discuss the fleuve manche freshwater discharge during the maximum european ice sheet retreat ca 18 ka the estimated discharge at this time appears important and sufficiently sustained to possibly contribute to the profound destabilisation of the thermohaline circulation recognised in the north atlantic from ca 18 to 16 ka

an abrupt drowning of the black sea shelf abstract during latest quaternary glaciation the black sea became a giant freshwater lake the surface of this lake drew down to levels more than 100 m below its outlet when the mediterranean rose to the bosporus sill at 7 150 yr bp 1 saltwater poured through this spillway to refill the lake and submerge catastrophically more than 100 000 km2 of its exposed continental shelf the permanent drowning of a vast terrestrial landscape may possibly have accelerated the dispersal of early neolithic foragers and farmers into the interior of europe at that time

subglacial hydrology in north western germany during the last glaciation groundwater flow tunnel valleys and hydrological cycles abstract numerical modelling of groundwater dynamics in an overpressured system of subglacial aquifers and aquitards under the marginal portion of the scandinavian ice sheet in northwestern germany has been coupled with calculations of basal meltwater production rates and with field evidence of meltwater erosional features largely fine grained subglacial sediments with relatively low hydraulic conductivities had a capacity to drain only about 25 of all basal meltwater produced in the relevant subglacial catchment area the rest of the meltwater was evacuated through tunnel valleys in spontaneous outburst events subglacial drainage cycles are proposed in which each cycle begins with meltwater drainage through the substratum groundwater flow followed by water ponding at the ice bed interface and ends in catastrophic meltwater releases through tunnel valleys

stabilization of glaciers terminating in closed water bodies evidence and broader implications 1 the behavior of glaciers terminating in deep water is determined by the interaction of buoyancy iceberg production and the sensitivity of ice flow to subtle changes in resistance at the glacier bed modeling efforts assume rapid evacuation of icebergs but some glaciers terminate in closed basins where icebergs may accumulate multibeam bathymetric survey of a glacial lake in iceland that received outlet glaciers during the little ice age document near parallel flow of narrow ice fingers that extended up to 1 km beyond the grounding line these previously unseen features apparently occurred when iceberg production exceeded iceberg melt resulting in iceberg buttressing of the ice margin similar stabilization of ice flow may resolve long standing debates about past continental ice sheet behavior including the rapid readvance of the laurentide ice sheet into lake superior ca 11 ka and the genesis of glacial flutes observed in the central arctic ocean basin

geometrical force balance in glaciology 1 the analytical force balance traditionally used in glaciology relates gravitational forcing to ice surface slope for sheet flow and to ice basal buoyancy for shelf flow it is unable to represent stream flow as a transition from sheet flow to shelf flow by having gravitational forcing gradually passing from being driven by surface slope to being driven by basal buoyancy downslope along the length of an ice steam this is a serious defect because ice streams discharge up to 90 of ice from ice sheets into the sea the defect is overcome by using a geometrical force balance that includes basal buoyancy represented by the ratio of basal water pressure to ice overburden pressure as a source of gravitational forcing when combined with the mass balance the geometrical force balance provides a holistic approach to ice flow in which resistance to gravitational flow must be summed upstream from the calving front of an ice shelf this is not done in the analytical force balance and it provides the ice thinning rate required by gravitational collapse of ice sheets as interior ice is downdrawn by ice streams

ice melange dynamics and implications for terminus stability jakobshavn isbrae greenland 1 we used time lapse imagery seismic and audio recordings iceberg and glacier velocities ocean wave measurements and simple theoretical considerations to investigate the interactions between jakobshavn isbrae and its proglacial ice melange the melange behaves as a weak granular ice shelf whose rheology varies seasonally sea ice growth in winter stiffens the melange matrix by binding iceberg clasts together ultimately preventing the calving of full glacier thickness icebergs the dominant style of calving and enabling a several kilometer terminus advance each summer the melange weakens and the terminus retreats the melange remains strong enough however to be largely unaffected by ocean currents except during calving events and to influence the timing and sequence of calving events furthermore motion of the melange is highly episodic between calving events including the entire winter it is pushed down fjord by the advancing terminus at 40 m d 1 whereas during calving events it can move in excess of 50 103 m d 1 for more than 10 min by influencing the timing of calving events the melange contributes to the glacier s several kilometer seasonal advance and retreat the associated geometric changes of the terminus area affect glacier flow furthermore a force balance analysis shows that large scale calving is only possible from a terminus that is near floatation especially in the presence of a resistive ice melange the net annual retreat of the glacier is therefore limited by its proximity to floatation potentially providing a physical mechanism for a previously described near floatation criterion for calving

late quaternary ice sheet history of northern eurasia the maximum limits of the eurasian ice sheets during four glaciations have been reconstructed 1 the late saalian 140 ka 2 the early weichselian 100 80 ka 3 the middle weichselian 60 50 ka and 4 the late weichselian 25 15 ka the reconstructed ice limits are based on satellite data and aerial photographs combined with geological field investigations in russia and siberia and with marine seismic and sediment core data the barents kara ice sheet got progressively smaller during each glaciation whereas the dimensions of the scandinavian ice sheet increased during the last ice age the barents kara ice sheet attained its maximum size as early as 90 80 000 years ago when the ice front reached far onto the continent a regrowth of the ice sheets occurred during the early middle weichselian culminating about 60 50 000 years ago during the late weichselian the barents kara ice sheet did not reach the mainland east of the kanin peninsula with the exception of the nw fringe of taimyr a numerical ice sheet model forced by global sea level and solar changes was run through the full weichselian glacial cycle the modeling results are roughly compatible with the geological record of ice growth but the model underpredicts the glaciations in the eurasian arctic during the early and middle weichselian one reason for this is that the climate in the eurasian arctic was not as dry then as during the late weichselian glacial maximum

interhemispheric atlantic seesaw response during the last deglaciation the asynchronous relationship between millennial scale temperature changes over greenland and antarctica during the last glacial period has led to the notion of a bipolar seesaw which acts to redistribute heat depending on the state of meridional overturning circulation within the atlantic ocean here we present new records from the south atlantic that show rapid changes during the last deglaciation that were instantaneous within dating uncertainty and of opposite sign to those observed in the north atlantic our results demonstrate a direct link between the abrupt changes associated with variations in the atlantic meridional overturning circulation and the more gradual adjustments characteristic of the southern ocean these results emphasize the importance of the southern ocean for the development and transmission of millennial scale climate variability and highlight its role in deglacial climate change and the associated rise in atmospheric carbon dioxide

age verification of the lake gribben forest bed and the younger dryas advance of the laurentide ice sheet analysis of nine wood samples from the lake gribben forest bed near lake gribben michigan yielded a combined age of 10 025 100 14c years bp which confirms and refines prior age estimates for the bed the stratigraphic position of these samples below a prograding ice contact fan indicates the time that a glacial margin reached the southern edge of the lake superior basin geomorphic tracing and correlation of associated deposits indicate that a contemporaneous margin extended almost 1000 km from duluth minnesota across the lake superior basin to north bay ontario along the southern shore of lake superior ice margin expansion began during and ended at the close of the younger dryas a surging glacier system would not produce a nearly linear moraine system across both a major basin lake superior and a major upland abitibi upland therefore we attribute this advance of the laurentide ice sheet to climatic forcing of the younger dryas event

an interlaboratory study of tex86 and bit analysis using high performance liquid chromatography mass spectrometry recently two new proxies based on the distribution of glycerol dialkyl glycerol tetraethers gdgts were proposed i e the tex86 proxy for sea surface temperature reconstructions and the bit index for reconstructing soil organic matter input to the ocean in this study fifteen laboratories participated in a round robin study of two sediment extracts with a range of tex86 and bit values to test the analytical reproducibility and repeatability in analyzing these proxies for tex86 the repeatability indicating intralaboratory variation was 0 028 and 0 017 for the two sediment extracts or 1 2 c when translated to temperature the reproducibility indicating among laboratory variation of tex86 measurements was substantially higher i e 0 050 and 0 067 or 3 4 c when translated to temperature the latter values are higher than those obtained in round robin studies of mg ca and u37 k paleothermometers suggesting the need to primarily improve compatibility between labs the repeatability of bit measurements for the sediment with substantial amounts of soil organic matter input was relatively small 0 029 but reproducibility was large 0 410 this large variance could not be attributed to specific equipment used or a particular data treatment we suggest that this may be caused by the large difference in the molecular weight in the gdgts used in the bit index i e crenarchaeol versus the branched gdgts potentially this difference gives rise to variable responses in the different mass spectrometers used calibration using authentic standards is needed to establish compatibility between labs performing bit measurements

high resolution record of northern hemisphere climate extending into the last interglacial period high resolution record of northern hemisphere climate extending into the last interglacial period

seasonal speedup of a greenland marine terminating outlet glacier forced by surface melt induced changes in subglacial hydrology we present subdaily ice flow measurements at four gps sites between 36 and 72 km from the margin of a marine terminating greenland outlet glacier spanning the 2009 melt season our data show that 35 km from the margin seasonal and shorter time scale ice flow variations are controlled by surface melt induced changes in subglacial hydrology following the onset of melting at each site ice motion increased above background for up to 2 months with resultant up glacier migration of both the onset and peak of acceleration later in our survey ice flow at all sites decreased to below background multiple 1 to 15 day speedups increased ice motion by up to 40 above background these events were typically accompanied by uplift and coincided with enhanced surface melt or lake drainage our results indicate that the subglacial drainage system evolved through the season with efficient drainage extending to at least 48 km inland during the melt season while we can explain our observations with reference to evolution of the glacier drainage system the net effect of the summer speed variations on annual motion is small 1 this in part is because the speedups are compensated for by slowdowns beneath background associated with the establishment of an efficient subglacial drainage system in addition the speedups are less pronounced in comparison to land terminating systems our results reveal similarities between the inland ice flow response of greenland marine and land terminating outlet glaciers

danube river sediment input and its interaction with the north western black sea abstract the influence of the river danube is determinant to the sedimentation of the north western and western black sea area after 1970 following the building of the iron gates dam the danube river sediment discharge diminished to 30 40 of its previous value after a 12 000 year evolution marked by active progradation the danube delta has become mainly inactive over the last few decades partly due to interventions of man made origin the deficit of sediment influx has led to the intense erosional processes of the deltaic littoral on the black sea north western shelf two main areas with contrasting sedimentary processes have been identified the internal danube sediment fed shelf and the external sediment starved shelf the modern highstand sedimentary history of the north western black sea deep area is marked by the cessation of the danube deep sea fan active development the main depositional units within the north western black sea are described

near synchronous interhemispheric termination of the last glacial maximum in mid latitudes isotopic records from polar ice cores imply globally asynchronous warming at the end of the last glaciation however 10be exposure dates show that large scale retreat of mid latitude last glacial maximum glaciers commenced at about the same time in both hemispheres the timing of retreat is consistent with the onset of temperature and atmospheric co2 increases in antarctic ice cores we suggest that a global trend of rising summer temperatures at the end of the last glacial maximum was obscured in north atlantic regions by hypercold winters associated with unusually extensive winter sea ice

a review of molecular organic proxies for examining modern and ancient lacustrine environments molecular organic geochemical proxies are increasingly being utilized to reconstruct past environmental conditions as new tools continue to be discovered and developed to date organic geochemical proxies have been developed mainly for use in marine systems and are widely used in paleoceanography in contrast organic proxies have been less commonly used on lacustrine sedimentary records one reason for this is that the wide range in the physical and chemical properties of lakes complicates application of some organic geochemical proxies in lacustrine settings furthermore in comparison to marine studies presently only a small number of studies have conducted or are currently conducting fundamental research aimed at developing organic geochemical proxies for use in lacustrine settings despite this an increasing number of paleo limnological studies are currently applying organic geochemical techniques to examine present and past environmental conditions in this manuscript we review the use of a number of commonly utilized organic geochemical and isotopic proxies and discuss their potential for environmental reconstruction in quaternary lacustrine deposits

surface melt induced acceleration of greenland ice sheet flow ice flow at a location in the equilibrium zone of the west central greenland ice sheet accelerates above the midwinter average rate during periods of summer melting the near coincidence of the ice acceleration with the duration of surface melting followed by deceleration after the melting ceases indicates that glacial sliding is enhanced by rapid migration of surface meltwater to the ice bedrock interface interannual variations in the ice acceleration are correlated with variations in the intensity of the surface melting with larger increases accompanying higher amounts of summer melting the indicated coupling between surface melting and ice sheet flow provides a mechanism for rapid large scale dynamic responses of ice sheets to climate warming

constraints on black sea outflow to the sea of marmara during the last glacial interglacial transition new cores from the upper continental slope off romania in the western black sea provide a continuous high resolution record of sedimentation rates clay mineralogy calcium carbonate content and stable isotopes of oxygen and carbon over the last 20 000 yr in the western black sea these records all indicate major changes occurring at 15 000 12 800 8400 and 7100 yr before present these results are interpreted to reflect an evolving balance between water supplied by melting glacial ice and other river runoff and water removed by evaporation and outflow the marked retreat of the fennoscandian and alpine ice between 15 000 and 14 000 yr is recorded by an increase in clays indicative of northern provenance in black sea sediments a short return toward glacial values in all the measured series occurs during the younger dryas cold period the timing of the first marine inflow to the black sea is dependent on the sill depths of the bosporus and dardanelles channels the depth of the latter is known to be 80 5 m which is consistent with first evidence of marine inundation in the sea of marmara around 12 000 yr the bedrock gorge of the bosporus reaches depths in excess of 100 m relative to present sea level though it is now filled with sediments to depths as shallow as 32 m two scenarios are developed for the connection of the black sea with the sea of marmara one is based on a deep bosporus sill depth effectively equivalent to the dardanelles and the other is based on a shallow bosporus sill less than 35 m in the deep sill scenario the black sea s surface rises in tandem with the sea of marmara once the latter connected with the aegean sea and black sea outflow remains continuous with inflowing marine water gradually displacing the freshwater in the deep basin the increase in the 18 o of mollusk shells at 12 800 yr and the simultaneous appearance of inorganic calcite with low 18 o is compatible with such an early marine water influx causing periodic weak stratification of the water column in the shallow sill scenario the black sea level is decoupled from world sea level and experiences rise and fall depending on the regional water budget until water from the rising sea of marmara breaches the shallow sill in this case the oxygen isotope trend and the inorganic calcite precipitation is caused by increased evaporation in the basin and the other changes in sediment properties reflect climate driven river runoff variations within the black sea watershed the presence of saline ponds on the black sea shelf circa 9600 yr support such evaporative drawdown but a sensitive geochemical indicator of marine water one that is not subject to temperature salinity or biological fractionation is required to resolve whether the sill was deep or shallow

vegetation and environmental responses to climate forcing during the last glacial maximum and deglaciation in the east carpathians attenuated response to maximum cooling and increased biomass burning the carpathian mountains were one of the main mountain reserves of the boreal and cool temperate flora during the last glacial maximum lgm in east central europe previous studies demonstrated lateglacial vegetation dynamics in this area however our knowledge on the lgm vegetation compo sition is very limited due to the scarcity of suitable sedimentary archives here we present a new record of vegetation fire and lacustrine sedimentation from the youngest volcanic crater of the carpathians lake st anne lacul sf ana szent anna tto examine environmental change in this region during the lgm and the subsequent deglaciation our record indicates the persistence of boreal forest steppe vegetation with pinus betula salix populus and picea in the foreland and low mountain zone of the east carpathians and juniperus shrubland at higher elevation we demonstrate attenuated response of the regional vegetation to maximum global cooling between 22 870 and 19 150 cal yr bp we find increased regional biomass burning that is antagonistic with the global trend increased regional fire activity suggests extreme continentality likely with relatively warm and dry summers we also demonstrate xerophytic steppe expansion directly after the lgm from 19 150 cal yr bp and regional increase in boreal woodland cover with pinus and betula from 16 300 cal yr bp plant macrofossils indicate local 950 m a s l establishment of betula nana and betula pubescens at 15 150 cal yr bp pinus sylvestris at 14 700 cal yr bp and larix decidua at 12 870 cal yr bp pollen data furthermore support population genetic inferences regarding the regional presence of some temperate deciduous trees during the lgm fagus sylvatica corylus avellana fraxinus excelsior our sedimentological data also demonstrate intensified aeolian dust accumulation between 26 000 and 20 000 cal yr bp

new insights into the last deglaciation of the south eastern flank of the scandinavian ice sheet abstract the existing glaciodynamic paradigm used to explain the dynamics morphogenesis and deglaciation of the last scandinavian ice sheet sis does not satisfactorily reflect all the nuances of ice sheet dynamics formation of particular forms of glacial relief and details of deglaciation significant problems are to be found in the explanations proposed for the processes of deglaciation therefore a new theory for the deglaciation of the last sis based on new geochronological geological and geomorphological data has been developed and is presented here it is suggested that along the south eastern perimeter of the sis with the exception of the salpausselka moraine ridges there is no evidence anywhere for re advances of the sis during deglaciation apart from the salpausselka moraine ridges the evidence for so called stadial or phasial recessional events is interpreted as the result of sis surges that occurred at different times and positions along the ice sheet margin this new theory also proposes that deglaciation of the south eastern flank of the sis was dominated by surface thinning rather than marginal retreat characteristic landforms such as kame terraces located on the distal slopes of recessional marginal ridges and plateau like glaciolacustrine kames were developed during deglaciation probably due to the interaction of active ice lobes surges and masses of dead ice that persisting beyond the ice margin

morphology of river channels and surface runoff in the volga river basin east european plain during the late glacial period abstract morphology of the large palaeochannels over the entire periglacial belt of the northern hemisphere shows distinct evidence of high surface runoff at the late glacial time channel width and meander wavelength of 73 well preserved fragments of large palaeochannels were measured in the volga river basin east european plain palynological studies of palaeo moskva river alluvium make it possible to locate the climatic and hydrological region analogues of the late glacial landscapes these analogues allowed reconstruction of the former surface runoff of the late glacial rivers as well as the total volume of flow to the caspian sea using the transform functions these reconstructions support the climatic hypothesis of the khvalyn transgression of the caspian sea and explain high water levels during this transgression without melt water inflow from the receding scandinavian ice sheet

influence of early diagenesis on geotechnical properties of clay sediments romania black sea abstract the geotechnical properties of clay sediments were investigated using laboratory and in situ measurements as part of the geohazard assessment in the romanian sector of the black sea affected by landslides and seafloor deformation features the sediments were characterized as predominantly high plastic silty clay of high compressibility low undrained shear strength low cohesion and moderate sensitivity a shallow increase in shear strength exceeding the general trend could have been reconciled with evidence for the precipitation of iron sulfides and calcium carbonates related to early diagenetic reactions of sulfate reduction e g cryptic sulfur cycle and anaerobic oxidation of methane comparison of the compression behaviour of natural and reconstituted samples indicated that precipitation of these materials at particle contacts produced cementation the analysis of deeper sediments sharing similar geochemical properties illustrated that the early precipitation of even low quantity of sulfur and carbonate cements allowed clays to develop sufficient strength to preserve an abnormal high water content even under tens of meters burial depth because this cementation process was observed to be associated with an enhanced sensitivity and a strain softening response to undrained shearing it was concluded that such early diagenesis should be considered as a key environmental factor leading to weak layer formation that may influence the susceptibility of seafloor to failure

slip generated patterns of swarm microearthquakes from west bohemia vogtland central europe evidence of their triggering mechanism 1 we investigated space time relations between consecutive events of west bohemian 2000 swarm and their association with the coulomb stress changes induced on a fault plane by prior swarm events a few thousand m 3 3 strike slip swarm earthquakes clustered along a fault plane at depths 6 5 10 5 km and showed common rake angle of 30 in order to disclose earthquake interaction we investigated the space time relations between consecutive earthquakes we determined relative position vectors for each consecutive event pair the prior event and the immediate aftershock ia and we measured time lags between them the resulting cluster of relative position vectors shows a high density of aftershocks near the origin which decays with distance it points out a triggering effect of the prior event upon subsequent aftershocks the spatial distribution of the relative positions disclosed dominance of aftershocks in the slip parallel directions which is manifested by pronounced elongation of the cluster of the relative positions and of the angular dependence of the rate of ias the temporal distribution of the relative positions indicates that some aftershocks prove high interevent velocities and occur systematically at greater distances suggesting the existence of two distinct triggering mechanisms acting at large and small timescales we evaluated the complete coulomb stress change upon the fault plane due to the prior event and showed that the observed space time distribution of the relative positions can be explained by a common effect of both static and dynamic stress changes which act on different distance and timescale

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

late pleistocene glacial chronology of the pietrele valley retezat mountains southern carpathians constrained by 10be exposure ages and pedological investigations abstract the southern carpathians are located in the transition zone between mediterranean and continental climates and constituted the major areas of ice accumulation in the carpathians during pleistocene glaciations an absolute glacial chronology had not yet been established in this study we constrain the glacial history of the pietrele valley in the retezat mountains located in the southern carpathians and find that the timing of the late wurmian glacial advance is asynchronous to global climate records likely reflecting changes in moisture availability in the area the former ice extent of two major glacial advances m1 or lolaia glacial advance and m2 or capra judele glacial advance in the valley was reconstructed based on mapping and surveying of glacial features field relations and different pedological weathering indicators of till imply that the m1 glacial advance occurred well before the global last glacial maximum lgm its deposition during the penultimate glaciation is unlikely no boulders suitable for exposure dating were found on m1 moraines seventeen exposure ages show that the moraines of the maximum late wurmian m2 glacial advance were abandoned around 16 1 1 6 ka another late glacial advance m3 or stevia advance occurred during the younger dryas chron as constrained by two exposure ages we suggest that the glacial advance that occurred during the time of the global lgm was less extensive than the m2 glacial advance and the deposits were overrun by the lateglacial m2 glacier as we found no field evidence of glacial deposits between the m1 and the m2 moraines we explain this obvious asynchronity of the local late wurmian ice extent with that of global records of ice accumulation with increased aridity in the carpathians during the global lgm due to a lower sea level the reconstructed late pleistocene equilibrium line altitude ela shows a distinct increase in the trend from the alps and the bavarian forest to the carpathians in comparison to the modern ela this finding supports the high aridity in the study area during the late pleistocene two distinct lateglacial moraines were deposited during times of reported colder and wetter climatic conditions around the north atlantic heinrich events h0 and h1

isotopic compositions of diagenetic dolomites in the tortonian marls of the western mediterranean margins evidence of past gas hydrate formation and dissociation abstract previous studies in the lorca basin s e spain sediment geol 2002 have shown that the diagenetic dolomitic concretions from the tortonian marls are related to the past occurrence of gas hydrates which were rapidly dissociated when the sea level dropped during the messinian salinity crisis these conclusions were based on the oxygen and carbon isotopic compositions of these dolomites which indicated that the carbonate diagenesis occurred either in 13 c rich 18 o poor solutions as it is typical in gas hydrate systems or in 13 c poor 18 o rich solutions generated during gas hydrate decomposition we have recently discovered similar dolomitic nodules in other tortonian marly successions from s e spain and northern morocco the oxygen and carbon isotopic compositions of the diagenetic dolomites from these areas in spain and morocco are very similar to those from the lorca basin this demonstrates that the dolomitic nodules from the tortonian marls of the betic and rifian basins were all related to the same diagenetic environments where pore fluids were modified by gas hydrate formation dissociation processes these overall observations in s e spain and northern morocco suggest that the dissociation of gas hydrates during the messinian salinity crisis was not a local phenomenon but corresponded to a major event which affected both sides of the western mediterranean margins it might have been initiated during the first major restriction step that started around 6 7 ma in the mediterranean sea and probably climaxed at 5 9 ma when the mediterranean sea level dropped by more than 1000 m during the salt deposition stage

black sea lake reservoir age evolution since the last glacial hydrologic and climatic implications abstract chronologies of sediments that document the last glacial history of the black sea lake are hampered by issues relating to reservoir age regulated by basin hydrology reservoir ages represent a tool that could potentially be used to better understand the response of black sea lake hydrology to climate change therefore deciphering reservoir age evolution is crucial both for better constraining the basin chronological framework and for providing new insights into our understanding of black sea lake hydrology by tuning a meaningful new high resolution geochemical dataset obtained from core md04 2790 to a climate reference record here we propose a reliable chronology spanning the last 32 kyr bp the chronology is compared to a large ams radiocarbon dataset n 51 pairs of calendar and radiocarbon ages allowed us to compute reservoir ages and to then reconstruct a high resolution quantitative reservoir age record for the last glacial history of the black sea lake the main factor controlling reservoir ages in lakes is the hard water effect hwe which is regulated by basin hydrology therefore changes in the reconstructed reservoir age record have been qualitatively interpreted in terms of the hydrologic responses of the black sea lake to climate change our results allowed us to determine periods of complete isolation or outflow for the black sea lake during heinrich event 2 he2 and during the last glacial maximum lgm the basin was strictly isolated whereas prior to he2 and during he1 it outflowed into the marmara sea following the onset of the bolling allerod factors other than the hwe are thought to have influenced the reservoir age preventing conclusive interpretations we also determined an undocumented to date phase of black sea lake stratification during the full glacial he2 and lgm our results indicate that reservoir age is a powerful tool for investigating and better understanding past hydrologic changes in lakes and inland seas

deep sea ecosystem variability of the aegean sea during the past 22 kyr as revealed by benthic foraminifera abstract specific responses of the regional deep sea ecosystems to climatic and oceanographic processes during the last 22 kyr are revealed by benthic foraminiferal faunas from two cores in the northern and southern aegean sea under glacial boundary conditions high diversity benthic foraminiferal faunas and elevated benthic foraminiferal numbers indicate enhanced organic matter availability and well ventilated deep water masses in the whole aegean sea the glacial termination is accompanied by significant fluctuations in productivity and deep water ventilation in the northern aegean sea meltwater inflow from mountain glaciers during the bolling allerod warm period resulted in a restriction of local deep water formation as mirrored by a dominance of bolivinids during the deposition of sapropel s1 drops in benthic foraminiferal number and diversity are more significant in the southern aegean sea when compared to the north this suggests the persistence of local deep water formation in the northern aegean sea during s1 deposition in addition faunal fluctuations within s1 at both sites suggest the repeated influence of short term cooling events on the re ventilation and re colonization of aegean deep sea ecosystems during the middle and late holocene benthic foraminiferal faunas document the establishment of oligotrophic and well ventilated conditions in the southern aegean sea the corresponding faunas from the northern aegean sea reflect generally mesotrophic conditions and variable deep water oxygenation during the entire holocene the deep sea ecosystems of this region responded very sensitively to short term changes in humidity and temperature these abrupt climate changes controlled the inflow of nutrients from rivers and the black sea and the formation of local deep water masses

early reactivation of european rivers during the last deglaciation during the last glacial maximum the sea level lowstand combined with the large extent of the fennoscandian and british ice sheets led to the funneling of european continental runoff resulting in the largest river system that ever drained the european continent here we show an abrupt and early reactivation of the european hydrological cycle at the onset of the last deglaciation leading to intense discharge of the channel river into the bay of biscay this freshwater influx probably combined with inputs from proglacial or ice dammed lakes dramatically affected the hydrology of the region both on land and in the ocean

asian provenance of glacial dust stage 2 in the greenland ice sheet project 2 ice core summit greenland samples of dust from the greenland ice sheet project 2 gisp2 ice core summit greenland dated within marine isotope stage 2 between 23 340 and 26 180 calendar years b p around the time of the coldest local last glacial temperatures have been analyzed to determine their provenance to accomplish this we have compared them with approximately coeval aeolian sediments mostly loesses sampled in possible source areas psas from around the northern hemisphere the 5 m grain size fraction of these samples was analyzed on the basis that it corresponds to the atmospheric dust component of that time and locale which was sufficiently fine grained to be transported over long distances on the basis of comparison of the clay mineralogy and sr nd and pb isotope composition with ice dust and psas and assuming that we have sampled the most important psas we have determined that the probable source area of these gisp2 dusts was in eastern asia the dust was not derived from either the midcontinental united states or the sahara two more proximal areas that have been suggested as potential sources based on atmospheric circulation modeling except for a brief period during an interstadial when dust transport was exceptionally low for glacial times and had a mineralogical composition indicative of a slightly more southern provenance the source area of the dust did not change significantly during times of variably higher fluxes of dust with larger mean grain size or lower fluxes of dust with smaller mean grain size this includes the high dust period that correlates with the heinrich 2 period of major iceberg discharge into the north atlantic variable wind strengths must therefore be invoked to account for these abrupt and significant changes in dust flux and grain size

hydrology in the sea of marmara during the last 23 ka implications for timing of black sea connections and sapropel deposition 1 sediments deposited under lacustrine and marine conditions in the sea of marmara hold a late quaternary record for water exchange between the black sea and the mediterranean sea here we report a multiproxy data set based on oxygen and strontium isotope results obtained from carbonate shells major and trace elements and specific organic biomarker measurements as well as a micropaleontological study from a 14c dated sediment core retrieved from the sea of marmara pronounced changes occurred in 18o and 87sr 86sr values at the fresh and marine water transition providing additional information in relation to micropaleontological data organic biomarker concentrations documented the marine origin of the sapropelic layer while changes in n alkane concentrations clearly indicated an enhanced contribution for organic matter of terrestrial origin before and after the event when compared with the black sea record the results suggest that the black sea was outflowing to the sea of marmara from the last glacial maximum until the warmer bolling allerod the first marine incursion in the sea of marmara occurred at 14 7 cal ka b p however salinification of the basin was gradual indicating that black sea freshwaters were still contributing to the marmara seawater budget after the younger dryas which is associated with a high input of organic matter of terrestrial origin both basins were disconnected resulting in a salinity increase in the sea of marmara the deposition of organic rich sapropel that followed was mainly related to enhanced primary productivity characterized by a reorganization of the phytoplankton population

the wandering of the volga delta a response to rapid caspian sea level change due to its very low gradient and absence of tide and surf the volga delta is an even more extreme example of the fluvially dominated type than the mississippi delta however it differs from all other large delta systems in that it borders a closed basin the caspian sea now at 26 m below global sea level caspian sea level is much more dynamic than that of the world oceans and rises at present about 1 5 cm yr a hundred time the eustatic rate within the quatemary sea level oscillations of at least 5 orders of magnitudes have been distinguished which seem grossly out of phase with eustatic sea level between the weichselian early khvalyn highstand of 50 m and the early holocene mangyshlak lowstand at 80 m the apex of the volga delta has wandered over 700 km alongstream the present day volga delta is not a highstand deposit but probably represents a minor transgression in a major regressional stage the delta does not show a coarsening upwards sedimentary sequence but consists of a weichselian transgressional fining upwards sequence topped by eolian deposits in which the delta distributary channels have been incised present day sedimentation is limited to a narrow fringe along the delta front and to deeper waters over 200 km offshore sea level changes outpaced aggradation to such an extent that volga sediment is spread over the whole north caspian plain sequence stratigraphical principles are difficult to apply because sea level cycles of five orders of magnitude are superimposed and because there is not enough sediment loading or tectonic subsidence to create sufficient accommodation space

the provenance and crustal residence ages of british sediments in relation to palaeogeographic reconstructions 24 smnd isotope analyses of fine grained phanerozoic and modern clastic sediments from britain and quebec are presented in combination with published data they have been used to calculate crustal residence ages tcr and to assess the provenance of the british sedimentary mass sediments now preserved on either side of the suture formed by the closure of the iapetus ocean ca 400 ma ago were derived from isotopically distinct source regions sediments north of the suture are characterised by1 7 tcr 2 8 ga whereas those to the south exhibit a smaller range and an average value of 1 6 ga the northern and southern source regions were most probably laurentia and gondwana respectively it seems likely that a third source perhaps baltica provided the lower palaeozoic southern uplands succession sediments deposited in southern britain after the closure of iapetus were derived mainly from the recycling of older sediments the tectonic rearrangements which occurred during the phanerozoic are not reflected in the smnd isotopic structure of the southern british sedimentary mass suggesting that the caledonian and hercynian orogenies and even the grenville orogeny involved minimal accretion of new mantle derived material into the british and adjacent continental crust smnd analyses of fine grained clastic sediments provide a powerful sedimentological tool for elucidating palaeogeography clastic source areas sediment recycling and maturity and some aspects of sediment transport

seismic stratigraphy of late quaternary deposits from the southwestern black sea shelf evidence for non catastrophic variations in sea level during the last 10 000 yr abstract detailed interpretation of single channel seismic reflection and huntec deep tow boomer and sparker profiles demonstrates that the southwestern black sea shelf formed by a protracted shelf edge progradation since the miocene pliocene five seismic stratigraphic units are recognized unit 1 represents the last phase of the progradational history and was deposited during the last glacial lowstand and holocene it is divided into four subunits subunit 1a is interpreted as a lowstand systems tract 1b and 1c are interpreted as a transgressive systems tract and subunit 1d is interpreted as a highstand systems tract the lowstand systems tract deposits consist of overlapping and seaward prograding shelf edge wedges deposited during the lowstand and the subsequent initial rise of sea level these shelf edge wedges are best developed along the westernmost and easternmost segments of the study area off the mouths of rivers the transgressive systems tract deposits consist of a set of shingled shore parallel back stepping parasequences deposited during a phase of relatively rapid sea level rise and include a number of prograded sediment bodies including barrier islands beach deposits and thin veneers of seismically transparent muds showing onlap onto the flanks of older sedimentary features a number of radiocarbon dates from gravity cores show that the sedimentary architecture of unit 1 contain a detailed sedimentary record for the post glacial sea level rise along the southwestern black sea shelf these data do not support the catastrophic refilling of the black sea by waters from the mediterranean sea at 7 1 ka postulated by ryan pitman major shimkus maskalenko jones dimitrov gorur sakinc yuce mar geol 138 1997 119 126 ryan pitman touchstone book 1999 319 pp and ballard coleman rosenberg mar geol 170 2000 253 261

the last deglaciation of the southeastern sector of the scandinavian ice sheet the scandinavian ice sheet sis was an important component of the global ice sheet system during the last glaciation but the timing of its growth to or retreat from its maximum extent remains poorly known we used 115 cosmogenic beryllium 10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice margin fluctuations of the sis between 25 000 and 12 000 years before the present the age of initial deglaciation indicates that the sis may have contributed to an abrupt rise in global sea level subsequent ice margin fluctuations identify opposite mass balance responses to north atlantic climate change indicating differing ice sheet sensitivities to mean climate state

catastrophic flooding of the black sea abstract decades of seabed mapping reflection profiling and seabed sampling reveal that throughout the past two million years the black sea was predominantly a freshwater lake interrupted only briefly by saltwater invasions coincident with global sea level highstand when the exterior ocean lay below the relatively shallow sill of the bosporus outlet the black sea operated in two modes as in the neighboring caspian sea a cold climate mode corresponded with an expanded lake and a warm climate mode with a shrunken lake thus during much of the cold glacial quaternary the expanded black sea s lake spilled into to the marmara sea and from there to the mediterranean however in the warm climate mode after receiving a vast volume of ice sheet meltwater the shoreline of the shrinking lake contracted to the outer shelf and on a few occasions even beyond the shelf edge if the confluence of a falling interior lake and a rising global ocean persisted to the moment when the rising ocean penetrated across

abrupt drainage cycles of the fennoscandian ice sheet continental ice sheets are a key component of the earth s climate system but their internal dynamics need to be further studied since the last deglaciation the northern eurasian fennoscandian ice sheet fis has been connected to the black sea bs watershed making this basin a suitable location to investigate former ice sheet dynamics here from a core retrieved in the bs we combine the use of neodymium isotopes high resolution elemental analysis and biomarkers to trace changes in sediment provenance and river runoff we reveal cyclic releases of meltwater originating from lake disna a proglacial lake linked to the fis during heinrich stadial 1 regional interactions within the climate lake fis system linked to changes in the availability of subglacial water led to abrupt drainage cycles of the fis into the bs watershed this phenomenon raised the bs water level by 100 m until the sill of the bosphorus strait was reached flooding the vast northwestern bs shelf and deeply affecting the hydrology and circulation of the bs and probably of the marmara and aegean seas

mass balance for nd in the mediterranean sea abstract the mass balance for nd in the mediterranean sea has been assessed through the measurement of nd isotope ratios in particulates from rivers entering the mediterranean sea floor clays and ferromanganese crusts and samples of atmospheric dusts nd values for the po and rhone rivers respectively are 10 8 and 9 7 whereas the nile seyhan and tarsus have 3 3 6 2 and 6 3 sea floor clays and ferromanganese crusts range from 2 0 to 10 1 and dust samples vary from 8 2 to 11 0 the relatively radiogenic nd isotope composition of the mediterranean seawater ed 6 to 7 compared to the atlantic nd 12 reflects partial equilibration of the particulate input into the basin rather than merely the dissolved input

the role of seasonality in abrupt climate change abstract a case is made that seasonality switches dominated by wintertime were instrumental in abrupt climate changes in the north atlantic region during the last glaciation and into the holocene the primary evidence comes from mismatches between mean annual temperatures from greenland ice cores in comparison with snowline changes in east greenland northern europe and north america the most likely explanation is a shutdown or reduction in strength of the conveyor this allows the spread of winter sea ice across the north atlantic thus causing the northern region to experience much colder winters because they mimic the greenland temperature rather than the snowline signal changes in the atlantic intertropical convergence zone and the asian monsoon may also share a winter linkage with greenland thus the paleoclimate record is consistent with the notion that a huge continental sector of the northern hemisphere stretching from greenland to asia was close to an extreme winter threshold during much of the last glaciation winter climate crossed this threshold repeatedly with marked changes in seasonality that may well have amplified and propagated a signal of abrupt change throughout the hemisphere and into the tropics

recent contributions of glaciers and ice caps to sea level rise satellite measurements of earth s gravity field show that the mass loss of glaciers and ice caps contributed to sea level rise by approximately 0 4 millimetres per year between 2003 and 2010 the extent to which mass loss from ice covered land areas contributes to sea level rise is not known accurately in part because previous global estimates use different techniques for glaciers ice caps and ice sheets the gravity recovery and climate experiment grace satellite has provided monthly measurements of the global gravity field since 2002 using grace data jacob et al assess regional mass loss between 2003 and 2010 and conclude that mass loss from ice covered land areas contributed almost 1 5 mm per year to the sea level rise estimated mass loss from the high mountains of asia was negligible in contrast to some other reports glaciers and ice caps gics are important contributors to present day global mean sea level rise1 2 3 4 most previous global mass balance estimates for gics rely on extrapolation of sparse mass balance measurements1 2 4 representing only a small fraction of the gic area leaving their overall contribution to sea level rise unclear here we show that gics excluding the greenland and antarctic peripheral gics lost mass at a rate of 148 30 gt yr 1 from january 2003 to december 2010 contributing 0 41 0 08 mm yr 1 to sea level rise our results are based on a global simultaneous inversion of monthly grace derived satellite gravity fields from which we calculate the mass change over all ice covered regions greater in area than 100 km2 the gic rate for 2003 2010 is about 30 per cent smaller than the previous mass balance estimate that most closely matches our study period2 the high mountains of asia in particular show a mass loss of only 4 20 gt yr 1 for 2003 2010 compared with 47 55 gt yr 1 in previously published estimates2 5 for completeness we also estimate that the greenland and antarctic ice sheets including their peripheral gics contributed 1 06 0 19 mm yr 1 to sea level rise over the same time period the total contribution to sea level rise from all ice covered regions is thus 1 48 0 26 mm 1 which agrees well with independent estimates of sea level rise originating from land ice loss and other terrestrial sources6

seasonal evolution of subglacial drainage and acceleration in a greenland outlet glacier an acceleration of ice mass loss has been observed near the margin of the greenland ice sheet partly as a result of faster ice motion observations by gps receivers reveal high seasonal variability in ice motion with summer motion up to 220 higher than winter background levels the greenland ice sheet contains enough water to raise sea levels by 7 m however its present mass balance and future contribution to sea level rise is poorly understood1 accelerated mass loss has been observed near the ice sheet margin partly as a result of faster ice motion2 3 4 surface melt waters can reach the base of the ice sheet and enhance basal ice motion5 6 however the response of ice motion to seasonal variations in meltwater supply is poorly constrained both in space and time here we present ice motion data obtained with global positioning system receivers located along a 35 km transect at the western margin of the greenland ice sheet throughout a summer melt season our measurements reveal substantial increases in ice velocity during summer up to 220 above winter background values these speed up events migrate up the glacier over the course of the summer the relationship between melt and ice motion varies both at each site throughout the melt season and between sites we suggest that these patterns can be explained by the seasonal evolution of the subglacial drainage system similar to hydraulic forcing mechanisms for ice dynamics that have been observed at smaller glaciers

climatic forcing of eastern mediterranean deep water formation and benthic ecosystems during the past 22 000 years abstract lateglacial and holocene faunal and stable isotope records from benthic foraminifers in the eastern mediterranean sea ems suggest a high spatiotemporal variability of deep water oxygenation and biogeochemical processes at the sea floor during that time changes in the oxygenation and food availability of the deep sea ecosystems are closely linked to the hydrology of the ems borderlands they reflect orbital and suborbital climate variations of the high northern latitudes and the african monsoon system during the last glacial maximum cool surface waters and high evaporation resulted in maximum convection and oxic deep waters in all sub basins strong wind induced mixing fostered surface water production with seasonal phytodetritus fluxes during the glacial termination and the holocene oxygenation and food availability of deep sea benthic ecosystems were characterized by a pronounced regional differentiation local deep water formation and trophic conditions were particularly variable in the northern aegean sea as a response to changes in riverine runoff and black sea outflow during the interval of sapropel s1 formation in the early holocene average oxygen levels decreased exponentially with increasing water depth suggesting a basin wide shallowing of vertical convection superimposed by local signals in the northernmost aegean sea deep water ventilation persisted during the early period of s1 formation owing to temperature driven local convection and the absence of low salinity black sea outflow at the same time severe temporary anoxia occurred in the eastern levantine basin at water depths as shallow as 900 m this area was likely influenced by enhanced nutrient input of the nile river that resulted in high organic matter fluxes and related high oxygen consumption rates in the water column in the southern aegean and levantine seas we observe a gradual increase in deep water residence times preceding s1 formation by approximately 1 1 5 kyr once oxygen levels fell below a critical threshold the benthic ecosystems collapsed almost synchronously with the onset of s1 deposition the recovery of benthic ecosystems during the terminal phase of s1 formation is controlled by subsequently deeper convection and re ventilation over a period of approximately 1500 years after the re ventilation of the various sub basins had been completed during the middle and late holocene deep water renewal was more or less similar to recent rates during that time deep sea ecosystem variability was driven by short term changes in food quantity and quality as well as in seasonality all of which are linked to millennial scale changes in riverine runoff and associated nutrient input

north atlantic control on precipitation pattern in the eastern mediterranean black sea region during the last glacial based on proxy records from western black sea cores we provide a comprehensive study of climate change during the last glacial maximum and late glacial period in the black sea region for the first time we present a record of relative changes in precipitation for nw anatolia based on variations in the terrigenous supply expressed as detrital carbonate concentration the good correspondence between reconstructed rainfall intensity in nw anatolia and past western mediterranean sea surface temperatures ssts implies that during the glacial period the precipitation variability was controlled like today by mediterranean cyclonic disturbances periods of reduced precipitation correlate well with low ssts in the mediterranean related to heinrich events h1 and h2 stable oxygen isotopes and lithological and mineralogical data point to a significant modification in the dominant freshwater sediment source concomitant to the meltwater inflow after 16 4 cal ka bp this change implies intensification of the northern sediment source and with other records from the mediterranean region consistently suggests a reorganization of the atmospheric circulation pattern affecting the hydrology of the european continent the early deglacial northward retreat of both atmospheric and oceanic polar fronts was responsible for the warming in the mediterranean region leading simultaneously to more humid conditions in central and northern europe

the khvalynian transgressions and early human settlement in the caspian basin abstract radiocarbon dates for both lower and upper khavalynian transgressions fall in the timespan between 10 and 17 ka bp with 13 6 11 8 ka bp as the most probable age this transgression supposedly proceeded as a rapid succession of sea level fluctuations the initial emergence of mousterian industries in the caspian basin as indicated by the volgograd site might be correlated with a mild interval preceding the atelian regression which was broadly contemporaneous with the last glacial maximum 25 18 ka bp the subsequent expansion of mousterian sites was largely coeval with the khvalynian transgression supposedly specific environments that arose in the caspian basin favoured a prolonged conservation of the mousterian technique and possibly a survival of neanderthal populations a possible factor is a cascade of eurasian basins that included the caspian black sea spillway which effectively isolated the caucasian central asian area