diatoms as hydrographic tracers example from bering sea sediments variations in the distribution of diatom species in surface sediments mirror distinct hydrographic regimes on the bering shelf spring salinity fronts divide the water column into four zones with different vertical structures and different productivity patterns four assemblages of diatoms can be distinguished in sediments underlying the zones

itrf2008 plate motion model 1 the itrf2008 velocity field is demonstrated to be of higher quality and more precise than past itrf solutions we estimated an absolute tectonic plate motion model made up of 14 major plates using velocities of 206 sites of high geodetic quality far from plate boundaries deformation zones and glacial isostatic adjustment gia regions derived from and consistent with itrf2008 the precision of the estimated model is evaluated to be at the level of 0 3 mm a wrms no gia corrections were applied to site velocities prior to estimating plate rotation poles as our selected sites are outside the fennoscandia regions where the gia models we tested are performing reasonably well and far from gia areas where the models would degrade the fit antarctica and north america our selected velocity field has small origin rate bias components following the three axis x y z respectively 0 41 0 54 0 22 0 64 and 0 41 0 60 95 per cent confidence limits comparing our model to nnr nuvel 1a and the newly available nnr morvel56 we found better agreement with nnr morvel56 than with nnr nuvel 1a for all plates except for australia where we observe an average residual rotation rate of 4 mm a using our selection of sites we found large global x rotation rates between the two models 0 016 ma and between our model and nnr morvel56 of 0 023 ma equivalent to 2 5 mm a at the earth surface

paleoceanographic evolution of north pacific surface water off japan during the past 150 000years abstract hydrographic variability in the mixed water region of the northwest pacific ocean at latitudes 35 40 n between the kuroshio extension and oyashio front causes complex upwelling leading to large primary productivity and thus great fishery resources we reconstructed the periodicity of the variability in north pacific intermediate water upwelling and surface ocean hydrography based on the high resolution analysis of diatom assemblages in seven cores representing the last 150 000 years we derived annual sea surface temperatures ssts through a diatom based proxy td the td derived annual ssts c are controlled by orbital forcing and show a reversed saw tooth in southern cores in contrast to a normal saw tooth pattern in the northern cores oceanic diatom abundances along the northern margin of the mixed water region are twice times as high as beneath the axis of the kuroshio extension and fluctuated in a revised saw tooth pattern with higher overall abundances interglacials after the last deglaciation annual ssts declined markedly during heinrich and bond events in the northern north atlantic when ice rafted detritus transported by icebergs was abundant wavelet analyses of the record of oceanic diatom abundances show significant variability at 2 0 kyr 2 to 5 6 kyr and 3 2 to 9 6 kyr periods wavelet analyses of the annual sst records show significant periodicity at 1 4 to 2 6 kyr 3 3 to 4 0 kyr 7 2 to 12 8 kyr cycles

vertical and horizontal surface displacements near jakobshavn isbrae driven by melt induced and dynamic ice loss 1 we analyze global positioning system gps time series of relative vertical and horizontal surface displacements from 2006 to 2012 at four gps sites located between 5 and 150 km from the front of jakobshavn isbrae ji in west greenland horizontal displacements during 2006 2010 at kaga ilul and qeqe relative to the site aasi are directed toward north west suggesting that the main mass loss signal is located near the frontal portion of ji the directions of the observed displacements are supported by modeled displacements derived from nasa s airborne topographic mapper atm surveys of surface elevations from 2006 2009 and 2010 however horizontal displacements during 2010 2012 at kaga and ilul are directed more towards the west suggesting a change in the spatial distribution of the ice mass loss in addition we observe an increase in the uplift rate during 2010 2012 as compared to 2006 2010 the sudden change in vertical and horizontal displacements is due to enhanced melt induced ice loss in 2010 and 2012

interglacial hydroclimate in the tropical west pacific through the late pleistocene records of atmospheric carbon dioxide concentration pco 2 and antarctic temperature have revealed an intriguing change in the magnitude of interglacial warmth and pco 2 at around 430 000 years ago 430 ka but the global climate repercussions of this change remain elusive here we present a stalagmite based reconstruction of tropical west pacific hydroclimate from 570 to 210 ka the results suggest similar regional precipitation amounts across the four interglacials contained in the record implying that tropical hydroclimate was insensitive to interglacial differences in pco 2 and high latitude temperature in contrast during glacial terminations drying in the tropical west pacific accompanied cooling events in northern high latitudes therefore the tropical convective heat engine can either stabilize or amplify global climate change depending on the nature of the climate forcing

evolution of the eastern tropical pacific through plio pleistocene glaciation a tropical pacific climate state resembling that of a permanent el nino is hypothesized to have ended as a result of a reorganization of the ocean heat budget 3 million years ago a time when large ice sheets appeared in the high latitudes of the northern hemisphere we report a high resolution alkenone reconstruction of conditions in the heart of the eastern equatorial pacific eep cold tongue that reflects the combined influences of changes in the equatorial thermocline the properties of the thermocline s source waters atmospheric greenhouse gas content and orbital variations on sea surface temperature sst and biological productivity over the past 5 million years our data indicate that the intensification of northern hemisphere glaciation 3 million years ago did not interrupt an almost monotonic cooling of the eep during the plio pleistocene sst and productivity in the eastern tropical pacific varied in phase with global ice volume changes at a dominant 41 000 year obliquity frequency throughout this time changes in the southern hemisphere most likely modulated most of the changes observed

the evolution of pleistocene climate a time series approach abstract in the later part of the pleistocene variations in global ice volume have been dominated by an approximate 100 000 year cycle analysis of 2 myr long oxygen isotope record from an equatorial pacific core indicates that this is true only for the last 900 000 years prior to this time the amplitude of the 100 000 year cycle is much reduced as is the variance of all oscillations with periods greater than 60 000 years based on results of time series analysis of this 2 myr long record the pleistocene glacial cycles can be divided into three sections 1 the late pleistocene 0 900 kyr b p where the variations in the isotope record are dominated by the 100 000 year cycle 2 the middle pleistocene 900 1450 kyr b p in which low frequency components are not as important as in the later period of the pleistocene and 3 the early pleistocene late pliocene 1450 2000 kyr b p where general reductions of importance at all frequencies is seen as compared to the later intervals recent modeling efforts which describe variations in global ice volume show that the dominant low frequency component observed in the late pleistocene can result from different time constants for the rate of glacial growth and decay in response to variations in the earth s orbital parameters it is hypothesized that during the early pleistocene the rate of growth and decay of glaciers were more similar and that continental erosion by successive glacial advances lowered the land surface in areas of ice cap formation to below sea level when the ice caps became marine based more rapid decay of the ice became possible

geodetic measurements of postglacial adjustments in greenland 1 we analyze data from seven continuous global positioning system gps receivers and one tide gauge all located along the edge of the greenland ice sheet to determine vertical uplift rates we compare our results with predictions based on the ice 5g deglaciation model of peltier 2004 results from the gps receiver at kellyville 1 2 1 1 mm a and from the tide gauge at nuuk 2 2 1 3 mm a indicate that ice 5g overestimates the subsidence rates at those locations by 2 1 and 1 1 mm a respectively kellyville and nuuk are located along the southwestern margin of the greenland ice sheet and the observed negative uplift rates are consistent with independent evidence that the ice margin along the southwestern edge readvanced during the last 8 ka to its current position the ice 5g glaciation deglaciation history includes a readvance between the latitudes of 62 n and 72 n the gps measurements suggest the ice 5g readvance may be too large or mistimed our gps results at qaqortoq located at the southern tip of greenland suggest a secular subsidence rate of 0 3 1 1 mm a while ice 5g predicts an uplift rate of 1 0 mm a ice 5g assumes no ice sheet readvance in south greenland including no readvance of the qassimiut lobe the difference of 1 3 1 1 mm a can tentatively be explained as due to a 33 km readvance of the qassimiut lobe during the last 3 ka for the other gps sites the observed predicted uplift rates are 3 6 1 1 0 1 mm a at thule 0 0 1 1 2 0 mm a at scoresbysund and 0 4 1 1 1 7 mm a at kulusuk for thule kulusuk and scoresbysund the differences between the observed and predicted rates are on the order of 1 3 3 7 mm a though with opposite signs and indicate that ice 5g does not exactly reproduce the correct rebound signal at those locations

late miocene decoupling of oceanic warmth and atmospheric carbon dioxide forcing measurements from several ocean cores reveal that ocean warmth persisted throughout the late miocene epoch despite co2 levels of only 200 350 p p m v probably driven by a deep thermocline that isolated climate responses from co2 variations geological records of past climate provide the only opportunity to investigate earth s response to large variations in atmospheric carbon dioxide concentrations during the late miocene between 12 million and 5 million years ago atmospheric co2 levels of only 200 to 350 parts per million by volume were accompanied by almost ice free conditions in the northern hemisphere and the continents were warmer than they are at present raising questions about the persistence of co2 climate couplings using measurements from several ocean cores lariviere et al show that ocean warmth persisted throughout the late miocene probably driven by a thick thermocline that isolated climate responses from co2 variations as the depth of the thermocline declined during the late miocene the more familiar relationship between co2 and climate was established deep time palaeoclimate studies are vitally important for developing a complete understanding of climate responses to changes in the atmospheric carbon dioxide concentration that is the atmospheric partial pressure of co2 1 although past studies have explored these responses during portions of the cenozoic era the most recent 65 5 million years myr of earth history comparatively little is known about the climate of the late miocene 12 5 myr ago an interval with values of only 200 350 parts per million by volume but nearly ice free conditions in the northern hemisphere2 3 and warmer than modern temperatures on the continents4 here we present quantitative geochemical sea surface temperature estimates from the miocene mid latitude north pacific ocean and show that oceanic warmth persisted throughout the interval of low 12 5 myr ago we also present new stable isotope measurements from the western equatorial pacific that in conjunction with previously published data5 6 7 8 9 10 reveal a long term trend of thermocline shoaling in the equatorial pacific since 13 myr ago we propose that a relatively deep global thermocline reductions in low latitude gradients in sea surface temperature and cloud and water vapour feedbacks may help to explain the warmth of the late miocene additional shoaling of the thermocline after 5 myr ago probably explains the stronger coupling between sea surface temperatures and climate that is characteristic of the more recent pliocene and pleistocene epochs11 12

timing and structure of the mid pleistocene transition records from the loess deposits of northern china abstract the mid pleistocene transition mpt from obliquity to eccentricity forced climate variations has been extensively documented within the oceanic realm using a collection of orbitally tuned records of palaeoclimatic change from the loess sequences of northern china we have analysed terrestrial palaeomonsoon behaviour since 1 5 ma and characterised the structure of the mpt wavelet analysis of a stacked magnetic susceptibility record from the loess sequences indicates that the onset of 100 kyr cyclicity was synchronous in both global ice volume and the east asian monsoon system however analysis in the time domain reveals that during the mpt interim period the east asian winter monsoon appears to have weakened whilst global ice volume was increasing indicating that the palaeomonsoon was not the primary forcing mechanism responsible for driving the global climatic change

expansion of subarctic water masses in the north atlantic and pacific oceans and implications for mid pleistocene ice sheet growth 1 past surface ocean circulation changes associated with the mid pleistocene transition 0 9 0 6 ma were reconstructed in the northern north atlantic odp 983 and the northwest pacific odp 882 using proxies for subarctic subpolar water mass distributions c37 4 alkenone and sea surface temperature u37 both sites experienced a secular expansion of subarctic waters from 1 15 ma spanning both glacial and interglacial intervals after 0 9 ma low c37 4 at site 983 records a northward retreat of subarctic waters during interglacials in the atlantic while continued high glacial c37 4 indicate extensive subarctic waters during glacial maxima associated with the development of the larger late pleistocene ice sheets in contrast a secular decline in c37 4 occurred at site 882 from 0 9 to 0 5 ma marking a more gradual retreat of subarctic conditions in the pacific it is proposed that the expansion of subarctic waters between 1 15 and 0 9 ma exerted negative feedbacks to the moisture supply to the ice sheet source regions and may account for the apparent delayed ice sheet response to atmosphere ocean circulation changes associated with the mid pleistocene transition that began as early as 1 2 ma

horizontal motion in elastic response to seasonal loading of rain water in the amazon basin and monsoon water in southeast asia observed by gps and inferred from grace 1 we find seasonal horizontal crustal motions observed by gps positioning in elastic response to heavy rainfall in the amazon basin and to monsoons in southeast asia to be consistent with those inferred from gravity recovery and climate experiment grace gravity observations of water mass loading solid earth moves toward the amazon during heavy spring rainfall and toward southeast asia during summer monsoons and back away from these areas 6 months later when the water load is minimum vertical oscillations observed by gps and inferred from grace are 2 to 3 times larger than horizontal oscillation near the margins of the areas of large mass loading some discrepancies between gps and grace are probably caused by local effects that influence gps measurements because the gps sites that show significant discrepancies also do not match nearby gps sites however when the load is short wavelength the limited spatial resolution of grace can cause systematic misfits

elastic uplift in southeast greenland due to rapid ice mass loss this is the publisher s version also available electronically from http onlinelibrary wiley com

constraints on the greenland ice sheet since the last glacial maximum from sea level observations and glacial rebound models abstract geomorphological descriptions of changes in the extent of the greenland ice sheet gis have been combined with glacial isostatic adjustment models to reproduce the sea level history of greenland since the last glacial maximum lgm the contribution to past sea level change around greenland due to ice load changes outside of that region has been considerable 10 s of meters while still contributing a rise of several mm yr 1 today the isostatic contribution to relative sea level around greenland from changes in the gis is found by iteratively perturbing preliminary ice models with different lgm extents and deglaciation starting times the resulting first order model that provides the best agreement between observed and predicted sea level contributes 3 1 and 1 9 m water equivalent of additional ice relative to present day ice volumes at the lgm and younger dryas respectively the gis in most areas does not appear to have extended far onto the continental shelf the exceptions being southern most southwest greenland and northern east greenland as well as at the coalescence of the northwest greenland and innuitian ice sheets changes in ice thickness since the lgm were 500 m along the present day outer coast and 1500 m along some parts of the present day ice margin the observed mid to late holocene fall in sea level to below the present day level and the subsequent transgression seen in some areas implies that the gis retreated behind the present day margin by distances of the order of 40 km before readvancing

observed increases in bering strait oceanic fluxes from the pacific to the arctic from 2001 to 2011 and their impacts on the arctic ocean water column 1 mooring data indicate the bering strait throughflow increases 50 from 2001 0 7 sv to 2011 1 1 sv driving heat and freshwater flux increases increase in the pacific arctic pressure head explains two thirds of the change the rest being attributable to weaker local winds the 2011 heat flux 5 1020j approaches the previous record high 2007 due to transport increases and warmer lower layer ll temperatures despite surface temperature sst cooling in the last decade warmer ll waters arrive earlier 1 6 1 1 days yr though winds and sst are typical for recent decades maximum summer salinities likely set in the bering sea remain remarkably constant 33 1 psu over the decade elucidating the stable salinity of the western arctic cold halocline despite this freshwater flux variability strongly driven by transport exceeds variability in other arctic freshwater sources remote data winds sst prove insufficient for quantifying variability indicating interannual change can still only be assessed by in situ year round measurements

north pacific seasonality and the glaciation of north america 2 7 million years ago in the context of gradual cenozoic cooling the timing of the onset of significant northern hemisphere glaciation 2 7 million years ago is consistent with milankovitch s orbital theory which posited that ice sheets grow when polar summertime insolation and temperature are low however the role of moisture supply in the initiation of large northern hemisphere ice sheets has remained unclear the subarctic pacific ocean represents a significant source of water vapour to boreal north america but it has been largely overlooked in efforts to explain northern hemisphere glaciation here we present alkenone unsaturation ratios and diatom oxygen isotope ratios from a sediment core in the western subarctic pacific ocean indicating that 2 7 million years ago late summer sea surface temperatures in this ocean region rose in response to an increase in stratification at the same time winter sea surface temperatures cooled winter floating ice became more abundant and global climate descended into glacial conditions we suggest that the observed summer warming extended into the autumn providing water vapour to northern north america where it precipitated and accumulated as snow and thus allowed the initiation of northern hemisphere glaciation

response of planktic foraminiferal size to late quaternary climate change 1 geographical size distribution within entire holocene foraminiferal assemblages is related to global environmental gradients such as temperature primary productivity and environmental variability this study demonstrates that these correlations are also recognizable in late quaternary assemblages from three locations in the south atlantic on temporal and latitudinal scales the size response to temporal paleoenvironmental changes during glacial interglacial cycles mimics the geographic holocene size variability the amplitude of size variability is directly related to the amplitude of the climatic fluctuations as shown by the stable size temperature relationship over time the documented changes in the assemblage size are caused by species replacement and intraspecific size variability the relative importance of these processes depends on the environmental setting species have been shown to reach their maximum size and abundance under certain optimum conditions and decrease in size if environmental conditions differ from these optima we confirm that late quaternary species sizes were largest at paleotemperatures identical to holocene ones

warm upwelling regions in the pliocene warm period 1 given the importance of upwelling processes to coastal productivity and regional climate it is critical to study the role of upwelling regions within the context of global climate change we generated sea surface temperature sst records for the last 5 million years in three important upwelling regions the eastern equatorial pacific the california margin and the peru margin prior to 3 0 ma ssts at all sites were significantly warmer than today by 3 9 c indicating that cold upwelling regions that characterize the modern pacific ocean did not exist in the early pliocene warm period 4 6 to 3 1 ma earth s most recent period of sustained global warmth alkenone phosphorus and organic carbon mass accumulation rate records indicate that changes in productivity and sst were decoupled and that upwelling of nutrient enriched water occurred even when ssts were warm during the early pliocene thus the long term trends in sst are likely explained by changes in the temperature of upwelled water rather than in the strength of upwelling favorable winds alone the fact that gradual cooling of upwelling regions began before the onset of significant northern hemisphere glaciation provides further evidence that the growth of ice sheets and their influence on atmospheric winds alone can not explain the cooling of upwelling regions our results suggest that the long term average ssts of upwelling regions are influenced by global changes in the depth and or temperature of the ventilated thermocline

the importance of the inelastic and elastic structures of the crust in constraining glacial density mass change and isostatic adjustment from geodetic observations in southeast alaska

recent arctic marine diatom assemblages from bottom sediments in baffin bay and davis strait abstract this study investigates the present geographical boundaries and environmental limits of the diatom flora in the baffin bay and davis strait area seventy four sea floor surface samples were examined the raw data were analyzed with the cabfac factor analysis program five factor assemblages explaining 87 of the observed variance emerged from this test the statistically most important assemblage is the baffin current assemblage composed ofthalassiosira gravida spores the second assemblage is the summer pack ice assemblage consisting ofactinocyclus curvatulus with a lesser contribution ofthalassiosira trifulta a third assemblage dominated bythalassiosira hyalina is located along the southwest coast of greenland indicating low ice concentration the fourth assemblage consists ofporosira sp spores and indicates fast ice conditions the fifth assemblage is dominated bythalassionema nitzschioides andporosira glacialis vegetative cells and indicates the coastal environment diatoms found in the sediment belong to discrete assemblages which reflect differences in water masses such as salinity and ice conditions these findings should assist in the interpretation of paleoceanographic conditions in the region when diatom assemblages are studied in piston core sediments

greenland uplift and regional sea level changes from icesat observations and gia modelling we study the implications of a recently published mass balance of the greenland ice sheet gris derived from repeated surface elevation measurements from nasa s ice cloud and land elevation satellite icesat for the time period between 2003 and 2008 to characterize the effects of this new high resolution gris mass balance we study the time variations of various geophysical quantities in response to the current mass loss they include vertical uplift and subsidence geoid height variations global patterns of sea level change or fingerprints and regional sea level variations along the coasts of greenland long wavelength uplifts and gravity variations in response to current or past ice thickness variations are obtained solving the sea level equation which accounts for both the elastic and the viscoelastic components of deformation to capture the short wavelength components of vertical uplift in response to current ice mass loss which is not resolved by satellite gravity observations we have specifically developed a high resolution regional elastic rebound er model the elastic component of vertical uplift is combined with estimates of the viscoelastic displacement fields associated with the process of glacial isostatic adjustment gia according to a set of published ice chronologies and associated mantle rheological profiles we compare the sensitivity of global positioning system gps observations along the coasts of greenland to the ongoing er and gia in notable contrast with past reports we show that vertical velocities obtained by gps data from five stations with sufficiently long records and from one tide gauge at the gris margins can be reconciled with model predictions based on the ice 5g deglaciation model and the er associated with the new icesat derived mass balance

on the structure and origin of major glaciation cycles 2 the 100 000 year cycle climate over the past million years has been dominated by glaciation cycles with periods near 23 000 41 000 and 100 000 years in a linear version of the milankovitch theory the two shorter cycles can be explained as responses to insolation cycles driven by precession and obliquity but the 100 000 year radiation cycle arising from eccentricity variation is much too small in amplitude and too late in phase to produce the corresponding climate cycle by direct forcing we present phase observations showing that the geographic progression of local responses over the 100 000 year cycle is similar to the progression in the other two cycles implying that a similar set of internal climatic mechanisms operates in all three but the phase sequence in the 100 000 year cycle requires a source of climatic inertia having a time constant similar to 15 000 years much larger than the other cycles similar to 5 000 years our conceptual model identifies massive northern hemisphere ice sheets as this larger inertial source when these ice sheets forced by precession and obliquity exceed a critical size they cease responding as linear milankovitch slaves and drive atmospheric and oceanic responses that mimic the externally forced responses in our model the coupled system acts as a nonlinear amplifier that is particularly sensitive to eccentricity driven modulations in the 23 000 year sea level cycle during an interval when sea level is forced upward from a major low stand by a milankovitch response acting either alone or in combination with an internally driven higher frequency process ice sheets grounded on continental shelves become unstable mass wasting accelerates and the resulting deglaciation sets the phase of one wave in the train of 100 000 year oscillations whether a glacier or ice sheet influences the climate depends very much on the scale the interesting aspect is that an effect on the local climate can still make an ice mass grow larger and larger thereby gradually increasing its radius of influence

present day vertical crustal deformations in west greenland from repeated gps observations summary a gps network consisting of 10 sites was established in the ice free area of west greenland and was observed for the first time in 1995 in 2002 a complete re observation was carried out these repeated gps observations served as a basis for the determination of vertical crustal deformations the data analysis was performed using the bernese software version 5 0 for the central site kangerlussuaq a negative uplift rate subsidence of 3 1 1 1 mm yr 1 was obtained related to the reference frame igb00 the regional pattern is characterized by an east west gradient of up to 4 mm yr 1 between the outer coast and the subsiding area along the present ice margin which can be explained to a great extent as a result of the late holocene re advance of the greenland ice sheet relative sea level changes could be calculated taking the present eustatic sea level rise into account the present day sea level rises at the outer coast between maniitsoq and paamiut and in the large fjords with increasing rates of more than 4m m yr 1 in their innermost parts these findings are in agreement with the general picture obtained from geomorphological and archaeological research for sisimiut and the disko bay area the present sea level change is almost zero whereas the crustal uplift rate for ilulissat was observed to be 1 6 mm yr 1 w econclude that this present vertical uplift rate in ilulissat is affected by the retreat of the ice margin during the last 150 yr and the present negative mass balance of the jakobshavn isbrae and its drainage basin

the explosive diversification of the diatom genus chaetoceros across the eocene oligocene and oligocene miocene boundaries in the norwegian sea abstract eocene to middle miocene stratigraphic changes in species richness abundance and valve size of chaetoceros resting spores in the norwegian sea dsdp site 338 were investigated in order to understand past productivity and paleoenvironmental changes in upwelling regions as a result drastic resting spore events were recognized in a 6 myr interval across the eocene oligocene boundary eo event the oligocene miocene boundary om event and in the early middle miocene emm event the eo event was characterized by explosive diversification at both the morpho generic and specific levels an increase in abundance and a decrease in valve size from the upper eocene through the lowest oligocene the om event was defined by a two fold increase in species richness during the emm event spore abundance decreased rapidly and species richness and valve size decreased gradually these changes may indicate changes in the nutrient supply especially in upwelling regions the increased species richness suggests a change from a stable water column with a constant nutrient supply in the eocene to an unstable one with a sporadic nutrient supply by increased vertical mixing in the oligocene based on evaluation of the ecologic differences between dinoflagellate cysts and chaetoceros resting spores the role of main primary producer might have switched from dinoflagellates and or nannoplankton in the eocene to diatoms especially chaetoceros in the oligocene in the norwegian sea increased resting spore species richness during the om event may show that environmental changes such as global cooling and nutrient mixing led to a diversification of the spore producing genus chaetoceros the emm event might have been affected by changes in paleoceanographic conditions perhaps a decrease in nutrient supply this study presents the first paleoceanographic analysis using not only the total resting spore abundance but also the abundances of individual species and establishes the value of spore taxonomy and diatom analysis including spores

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

pliocene pleistocene evolution of the north pacific ocean atmosphere system interpreted from fossil diatoms the relative abundance of diatom taxa in 216 core tops has been quantified and compared using cluster analysis with assemblages in six cores located beneath different water masses of the north pacific ocean all but one sequence span at least 1 5 m y early pleistocene to holocene and one extends to 2 6 ma the quantitative abundance of each taxon and the space time occurrence of each cluster are interpreted as tracers of oceanographic conditions in addition to high frequency glacial interglacial oscillations the records display rapid steplike changes at 2 4 ma 1 6 1 5 ma 1 0 ma 0 8 0 7 ma and 0 35 ma two secondary transitions recorded only in the northwestern cores occur at 2 0 ma and 1 1 ma we conclude that both the high frequency oscillations and the stepwise transitions reflect variations in extent of subarctic water masses under the influence of the siberian high pressure and aleutian low pressure atmospheric cells we further conclude that 1 the subarctic water mass has developed progressively and attained its modern structure only in the late pleistocene 2 some stages of this evolution may have occurred earlier in the eastern subarctic 3 the holocene is an atypical warm extreme so that the present is not a very good key to the past 4 there were several glaciations between 2 4 and 2 0 ma and 5 the subtropical gyre is more conservative than the subarctic gyre and major changes in the region have been due to forcing from the north we propose a conceptual model of oscillating metastable climatic modes maintained by internal feedback and suggest that steplike changes may occur when one set of boundary conditions is temporarily exceeded

the influence of decadal to millennial scale ice mass changes on present day vertical land motion in greenland implications for the interpretation of gps observations 1 we show predictions of present day vertical land motion in greenland using a recently developed glacial isostatic adjustment gia model calibrated using both relative sea level rsl observations and geomorphological constraints on ice extent predictions from our gia model are in agreement with the relatively small number of gps measurements of absolute vertical motion from south and southwest greenland this suggests that our model of ice sheet evolution over the holocene period is reasonably accurate the uplift predictions are highly sensitive to variations of upper mantle viscosity thus depending on the earth model adopted different periods of ice loading change dominate the present day response in particular regions of greenland we also consider the possible influence of more recent changes in the ice sheet by applying a second ice model specifically a surface mass balance smb model which covers the period 1866 to 2005 predictions from this model suggest that decadal scale smb changes over the past 140 years play only a small role in determining the present day viscous response at the sub mm yr level in most locations for a range of earth model parameters high rates of peripheral thinning from 1995 to 2005 predicted using the smb model produce large elastic uplift rates 6 mm yr in west and southwest greenland this suggests that in some areas close to the ice margin modern surface mass balance changes have a dominant control on present day vertical land motion

bedrock displacements in greenland manifest ice mass variations climate cycles and climate change the greenland gps network gnet uses the global positioning system gps to measure the displacement of bedrock exposed near the margins of the greenland ice sheet the entire network is uplifting in response to past and present day changes in ice mass crustal displacement is largely accounted for by an annual oscillation superimposed on a sustained trend the oscillation is driven by earth s elastic response to seasonal variations in ice mass and air mass i e atmospheric pressure observed vertical velocities are higher and often much higher than predicted rates of postglacial rebound pgr implying that uplift is usually dominated by the solid earth s instantaneous elastic response to contemporary losses in ice mass rather than pgr superimposed on longer term trends an anomalous pulse of uplift accumulated at many gnet stations during an approximate six month period in 2010 this anomalous uplift is spatially correlated with the 2010 melting day anomaly

biogenic opal production changes during the mid pleistocene transition in the bering sea iodp expedition 323 site u1343 abstract biogenic opal content and mass accumulation rate mar at iodp expedition 323 site u1343 were found to fluctuate consistently generally being high under warm conditions and low under cold conditions during the last 2 4 ma continuous wavelet transform analysis of the normalized biogenic opal content indicates that export production in the bering sea varied predominantly at 41 ka periodicity before 1 25 ma and shifted to 100 ka periodicity at the onset of the mid pleistocene transition mpt 1 25 0 7 ma the 100 ka cycles dominated until the holocene export production in the bering sea decreased markedly in the bering sea two times during the mpt the first occurred at the beginning of the mpt 1 25 ma and the second in the middle of the mpt 0 9 ma these decreases coincided with both increases in the relative abundance of sea ice diatoms and decreases in the warm water diatom species neodenticula seminae indicating that reductions in export production in the bering sea during the mpt were associated with climate cooling decreases in export production in the bering sea during the mpt were most likely associated with the increased influence of polar arctic domains on the high latitude north pacific

changes in biogenic opal productivity with milankovitch cycles during the last 1 3 ma at iodp expedition 323 sites u1341 u1343 and u1345 in the bering sea abstract sediments from three sites u1341 u1343 and u1345 of iodp expedition 323 located in the bering sea were analyzed for variation of biogenic opal representing surface water paleoproductivity initial age models of three sites bottom age u1341 4 3 ma u1343 2 4 ma u1345 0 5 ma were established onboard by biostratigraphic and paleomagnetic investigations the initial age models were tuned by 18 o stratigraphy which was established on shore biogenic opal contents of sediments were analyzed for the interval of 1 3 ma to the present generally the biogenic opal values at site u1341 bowers ridge were significantly higher than those at the beringian slope sites u1343 and u1345 higher natural gamma radiation ngr counts and magnetic susceptibility ms at the beringian slope sites suggested a greater contribution of lithogenic matter than at site u1341 on bowers ridge the percentages of sea ice diatoms at the beringian slope sites are also higher than those at bowers ridge sites this is primarily attributed to the fact that the sediments from the beringian slope area were significantly diluted by lithogenic matter derived from the alaskan continent and were largely affected by sea ice cover the cyclicity of biogenic opal accumulation rates at site u1341 is determined to be about 160 40 and 30 ky whereas that at site u1343 is determined to be about 330 100 40 and 20 ky if these had been reflecting a global climate change the cyclicity of biogenic opal contents at all sites would be consistently the same however the results do not show such a consistency obliquity is observed at both sites of the bowers ridge and beringian slope a strong eccentricity was observed only at u1343 but no signature for eccentricity was detected at u1341 therefore the milankovitch cycle with 100 ky periodicity was only observed at the beringian slope area the results suggest that the biogenic opal at site u1341 indicated a local characteristic for biogenic productivity changes thus the absence of the 100 ky cycle of biogenic opal at site u1341 seems to be due to local phenomena such as water circulation although the changes in biogenic opal productivity at site u1341 are attributed to summer insolation

decay and expansion of the early aftershock activity following the 2011 mw9 0 tohoku earthquake the 2011 m w9 0 tohoku earthquake was followed by an abundant amount of seismicity providing a unique opportunity to analyze the triggering mechanism of great earthquakes although the tohoku earthquake occurred close to a dense seismic network many aftershocks that occurred in the first few hours after the mainshock are not recorded in the earthquake catalogs here we use a template waveform approach to recover as many as possible missing events in the first 12 hours following the tohoku mainshock our analysis is able to detect about 1 4 times more events than those listed in the high sensitivity seismograph hi net earthquake catalog combining our new dataset with earthquakes that occurred at latter times we are able to observe a continuous decay of the aftershock rate and along strike expansion of aftershock area we relate the latter observation to the occurrence of post seismic slip over the deep interface

gps measurements of crustal uplift near jakobshavn isbrae due to glacial ice mass loss 1 we analyze 2006 2009 data from four continuous global positioning system gps receivers located between 5 and 150 km from the glacier jakobshavn isbrae west greenland the gps stations were established on bedrock to determine the vertical crustal motion due to the unloading of ice from jakobshavn isbrae all stations experienced uplift but the uplift rate at kangia north only 5 km from the glacier front was about 10 mm yr 1 larger than the rate at ilulissat located only 45 km further away this suggests that most of the uplift is due to the unloading of the earth s surface as jakobshavn thins and loses mass our estimate of jakobshavn s contribution to uplift rates at kangia north and ilulissat are 14 6 1 7 mm yr 1 and 4 9 1 1 mm yr 1 respectively the observed rates are consistent with a glacier thinning model based on repeat altimeter surveys from nasa s airborne topographic mapper atm which shows that jakobshavn lost mass at an average rate of 22 2 km3 yr 1 between 2006 and 2009 at kangia north and ilulissat the predicted uplift rates computed using thinning estimates from the atm laser altimetry are 12 1 0 9 mm yr 1 and 3 2 0 3 mm yr 1 respectively the observed rates are slightly larger than the predicted rates the fact that the gps uplift rates are much larger closer to jakobshavn than further away and are consistent with rates inferred using the atm based glacier thinning model shows that gps measurements of crustal motion are a potentially useful method for assessing ice mass change models

troposphere mapping functions for gps and very long baseline interferometry from european centre for medium range weather forecasts operational analysis data 1 in the analyses of geodetic very long baseline interferometry vlbi and gps data the analytic form used for mapping of the atmosphere delay from zenith to the line of site is most often a three parameter continued fraction in 1 sin elevation using the 40 years reanalysis era 40 data of the european centre for medium range weather forecasts for the year 2001 the b and c coefficients of the continued fraction form for the hydrostatic mapping functions have been redetermined unlike previous mapping functions based on data from numerical weather models isobaric mapping functions niell 2000 and vienna mapping functions vmf boehm and schuh 2004 the new c coefficients are dependent on the day of the year and unlike the niell mapping functions niell 1996 they are no longer symmetric with respect to the equator apart from the opposite phase for the two hemispheres compared to vmf this causes an effect on the vlbi or gps station heights that is constant and as large as 2 mm at the equator and that varies seasonally between 4 mm and 0 mm at the poles the updated vmf based on these new coefficients and called vmf1 hereinafter yields slightly better baseline length repeatabilities for vlbi data the hydrostatic and wet mapping functions are applied in various combinations with different kinds of a priori zenith delays in the analyses of all vlbi international vlbi service for geodesy and astrometry ivs r1 and ivs r4 24 hour sessions of 2002 and 2003 the investigations concentrate on baseline length repeatabilities as well as on absolute changes of station heights

a benchmark study for glacial isostatic adjustment codes the study of glacial isostatic adjustment gia is gaining an increasingly im portant role within the geophysical community understanding the response of the earth to loading is crucial in various contexts ranging from the the interpretation of modern satellite geodetic measurements e g grace and goce to the projections of future sea level trends in response to climate change modern modeling approaches to gia are based on various techniques that range from purely analytical formulations to fully numerical methods despite various teams independently investigating gia we do not have a suitably large set of explicitly validated numerical results through which they may be validated a community benchmark data set would clearly be valuable following the example of the mantle convection community here we present for the first time the results of a benchmark study of codes designed to model gia the approaches benchmarked are based on significantly different codes and different techniques this effort is performed within the working group 4 wg4 of the esf cost action es0701 improved constraints on models of glacial isostatic adjustment our aims are i testing the codes currently in use by the various teams ii establish a sufficiently large set of agreed results iii correct possible systematic errors embedded in the various physical formulations or computer implementations and iv facilitate the dissemination of numerical tools for surface loading studies to the community and to young scientists the test computations are mainly based on models with spherical symmetry and maxwell rheology and include inputs from various different methods and solution techniques viscoelastic normal modes spectral finite elements and finite elements the tests involve the loading and tidal love numbers and their relaxation spectra the deformation and gravity variations driven by surface loads characterized by simple geometry and time history and the rotational fluctuations in response to glacial unloading in spite of the significant differences in the numerical methods employed the test computations show a satisfactory agreement between the results provided by the participants most of the existing misfits have been addressed during the preparation of the manuscript some others are currently the subject of analysis within the wg4 community

calibration of radiocarbon results pertaining to related archaeological events with the advent of the high precision radiocarbon calibration curve there is an increasing demand from archaeologists for results previously reported on the radiocarbon scale to be expressed on the calendar scale furthermore there is a general realization within the archaeological community that much more information can be derived from radiocarbon dating if the samples are taken from coherent well chosen contexts and if any available substantive archaeological information is included in the data analysis this paper describes how the bayesian approach to statistical data analysis can be used for the calibration of groups of radiocarbon results in situations where archaeological information is available a priori about the relationships between the contexts being dated recent innovations in the implementation of the bayesian paradigm are used and the methodology is illustrated by the analysis of data arising from two archaeological excavations

diatom silicoflagellate and ebridian biostratigraphy and paleoceanography in iodp 323 hole u1343e at the bering slope site abstract integrated ocean drilling program iodp expedition 323 was dedicated to reconstruct the details of the pliocene pleistocene paleoenvironmental conditions of the bering sea in this study fossil diatom assemblages from hole u1343e were investigated to define diatom biostratigraphy and reveal paleoceanography of the bering slope region throughout pleistocene as the results four diatom zones with neogene north pacific diatom zone codes npd were determined from the neodenticula seminae zone npd 12 to the n koizumii zone npd 9 diatom biohorizons defined in this study closely correspond with onboard data but the distinct difference is recognized at the top of the n koizumii additional four biostratigraphic zones estimated by three silicoflagellate and one ebridian datums suggest the core sediment age younger than 2 5 ma the fluctuations of several paleoenvironmental diatom indicators show that cold conditions with sea ice existed throughout the duration of the interval studied as well as sea ice expansion occurred at ca 1 9 ma and ca 0 9 ma moreover increases of neritic diatom species reveal a drop in sea level neodenticula seminae is the diatom tracer of the aleutian current and hence the decrease of this taxon suggests decrease in inflow of the north pacific water mass although the sea levels must have been dropped during the cold time interval the consistent occurrences of n seminae indicate that the surface water circulation in the bering sea was significantly influenced by the alaskan stream at ca 1 9 ma on the other hand during the other cooling event at ca 0 9 ma which corresponds to the mid pleistocene transition mpt event an increase of neritic diatom species and decrease of n seminae were observed this suggests that coastal environmental conditions accompanied the sea level drop and that the inflow from the north pacific was weakened the increases of sea ice and neritic diatom species suggest that the sea ice and coastal conditions were developed after the cooling at 0 9 ma the ages at remarkable changes of silicoflagellate assemblages correspond to the ages of global climate shifts at ca 1 4 ma 1 25 ma and 0 8 0 9 ma the unusual alternate dominances of distephanus medianoctisol in glacial and dictyocha species in interglacial periods during the 1 25 0 8 ma interval suggest the north south migration of water masses between the bering sea and the subarctic north pacific

calibrating a glaciological model of the greenland ice sheet from the last glacial maximum to present day using field observations of relative sea level and ice extent we constrain a three dimensional thermomechanical model of greenland ice sheet gris evolution from the last glacial maximum lgm 21 ka bp to the present day using primarily observations of relative sea level rsl as well as field data on past ice extent our new model huy2 fits a majority of the observations and is characterised by a number of key features i the ice sheet had an excess volume relative to present of 4 1 m ice equivalent sea level at the lgm which increased to reach a maximum value of 4 6 m at 16 5 ka bp ii retreat from the continental shelf was not continuous around the entire margin as there was a younger dryas readvance in some areas the final episode of marine retreat was rapid and relatively late c 12 ka bp leaving the ice sheet land based by 10 ka bp iii in response to the holocene thermal maximum htm the ice margin retreated behind its present day position by up to 80 km in the southwest 20 km in the south and 80 km in a small area of the northeast as a result of this retreat the modelled ice sheet reaches a minimum extent between 5 and 4 ka bp which corresponds to a deficit volume relative to present of 0 17 m ice equivalent sea level our results suggest that remaining discrepancies between the model and the observations are likely associated with non greenland ice load differences between modelled and observed present day ice elevation around the margin lateral variations in earth structure and or the pattern of ice margin retreat

upwelling intensification as part of the pliocene pleistocene climate transition a deep sea sediment core underlying the benguela upwelling system off southwest africa provides a continuous time series of sea surface temperature sst for the past 4 5 million years our results indicate that temperatures in the region have declined by about 10 c since 3 2 million years ago records of paleoproductivity suggest that this cooling was associated with an increase in wind driven upwelling tied to a shift from relatively stable global warmth during the mid pliocene to the high amplitude glacial interglacial cycles of the late quaternary these observations imply that atlantic ocean surface water circulation was radically different during the mid pliocene

effects of el nino southern oscillation and north pacific weather patterns on interannual variability in the subarctic bering sea extraordinary interannual variability in ice cover air and sea surface temperatures sst and surface winds in the eastern bering sea have been observed over recent years to investigate the causes of this interannual variability long term 20 30 years time series of air ocean and ice parameters from the bering sea were cross correlated with the southern oscillation index soi an index of el nino southern oscillation enso events in the tropical southern hemisphere as well as with an index of pacific north american pna events in the north pacific five to thirty percent of the interannual variability linear regression with various smoothing in the bering sea data sets with the exception of surface winds is explained by the soi when the bering sea data lags the soi for comparison 29 52 of the variability in the sst off south america can be explained by the soi the signs of the correlations all suggest that warming in the bering sea follows negative anomalies in the soi that is enso events positive anomalies in the soi which tend to precede el nino events were found to precede cooling in the bering sea significant correlation persists for 18 20 months higher order polynomial regressions between the soi and bering sea data can explain up to 40 of the bering sea variability the mechanism for the connection between enso events and bering sea interannual variability appears to be of atmospheric nature and is associated with the winter position and intensity of the aleutian low the aleutian low is intensified and eastward of normal in association with el nino i e warm events but is weaker and westward of normal during cool events it is the regional winds associated with the variable position of the aleutian low that cause the regional warming and cooling events this seesaw in the aleutian low is also used to explain the out of phase ice conditions between the bering sea and the sea of okhotsk pna events are also associated with an intensified aleutian low as well as 700 mbar ridging over northwestern north america causing southerly flow over alaska however while correlation between enso events and pna was significant the correlation between the bering sea and pna was marginal except for surface winds here surface winds from the north were significantly correlated with the pna this apparent inconsistency as well as the lack of correlation of surface winds with the soi is explained by the lack of preferred site of the aleutian low during enso events this lack of preferred site helps explain why the major el nino event of 1982 1983 had little apparent effect on the bering sea

pliocene pleistocene variability of upwelling activity productivity and nutrient cycling in the benguela region in this study we present combined high resolution records of sea surface temperature sst phytoplankton productivity and nutrient cycling in the benguela upwelling system bus for the past 3 5 ma the sst record provided evidence that upwelling activity off namibia mainly intensified ca 2 4 2 0 ma ago in response to the cooling of the southern ocean and the resultant strengthening of trade winds as revealed by productivity related proxies bus intensification led to a major transition in regional biological productivity when considering the termination of the matuyama diatom maximum a diatom high production event major oceanic reorganization in the benguela was accompanied by nutrient source changes as indicated by a new nitrogen isotopic delta n 15 record that revealed a stepwise increase at ca 2 4 and ca 1 5 ma ago the change in source region likely resulted from significant changes in intermediate water formation tied to the reorganization of oceanic conditions in the southern ocean which may have in turn mainly controlled the global ocean n cycle and therefore the n isotopic composition of nutrients since 3 5 ma ago

the response of the bering sea gateway during the mid pleistocene transition abstract the mid pleistocene transition and the response of sea ice in the subarctic north pacific are examined using a diatom record from the north eastern bering sea slope iodp core u1344a high percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions thalassiosira antarctica var borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0 9 to1 2 ma after which it dominates the assemblage until 0 6 ma the decline of neodenticula seminae indicative of alaskan stream water inflow is in agreement with neighbouring core u1343e confirming the reduction of bering sea circulation after 0 9 ma we propose that during the mpt a stepped advancement of sea ice occurs in the bering sea as a response to increased moisture delivery to the high latitudes an extended period of diatom productivity between 0 75 and 0 65 ma marks major deglacial conditions towards the end of the mpt by 0 6 0 55 ma the work highlights the important role played by sea ice and supports the contention of a colder mpt in the subarctic pacific

anisotropic shear wave velocity structure of the earth s mantle a global model 1 we combine a new large data set of surface wave phase anomalies long period waveforms and body wave travel times to construct a three dimensional model of the anisotropic shear wave velocity in the earth s mantle our modeling approach is improved and more comprehensive compared to our earlier studies and involves the development and implementation of a new spherically symmetric reference model simultaneous inversion for velocity and anisotropy as well as discontinuity topographies and implementation of nonlinear crustal corrections for waveforms a comparison of our new three dimensional model s362ani with two other models derived from comparable data sets but using different techniques reveals persistent features 1 strong 200 km thick high velocity anomalies beneath cratons likely representing the continental lithosphere underlain by weaker fast anomalies extending below 250 km which may represent continental roots 2 weak velocity heterogeneity between 250 and 400 km depths 3 fast anomalies extending horizontally up to 2000 3000 km in the mantle transition zone beneath subduction zones 4 lack of strong long wavelength heterogeneity below 650 km suggesting inhibiting character of the upper mantle lower mantle boundary and 5 slow velocity superplumes beneath the pacific and africa the shear wave radial anisotropy is strongest at 120 km depth in particular beneath the central pacific lateral anisotropic variations appreciably improve the fit to data that are predominantly sensitive to the uppermost and lowermost mantle but not to the waveforms that control the transition zone and midmantle depths tradeoffs between lateral variations in velocity and anisotropy are negligible in the uppermost mantle but noticeable at the bottom of the mantle

increasing rates of ice mass loss from the greenland and antarctic ice sheets revealed by grace 1 we use monthly measurements of time variable gravity from the grace gravity recovery and climate experiment satellite gravity mission to determine the ice mass loss for the greenland and antarctic ice sheets during the period between april 2002 and february 2009 we find that during this time period the mass loss of the ice sheets is not a constant but accelerating with time i e that the grace observations are better represented by a quadratic trend than by a linear one implying that the ice sheets contribution to sea level becomes larger with time in greenland the mass loss increased from 137 gt yr in 2002 2003 to 286 gt yr in 2007 2009 i e an acceleration of 30 11 gt yr2 in 2002 2009 in antarctica the mass loss increased from 104 gt yr in 2002 2006 to 246 gt yr in 2006 2009 i e an acceleration of 26 14 gt yr2 in 2002 2009 the observed acceleration in ice sheet mass loss helps reconcile grace ice mass estimates obtained for different time periods

drastic change in the late pliocene subarctic pacific diatom community associated with the onset of the northern hemisphere glaciation abstract to date there is scarcely clear understanding of the detailed responses of the subarctic pacific phytoplankton communities to the significant climate transition across the initiation of the northern hemisphere glaciation nhg approximately 2 7 million years ago we present more highly resolved evidence of the rapid and drastic change in the phytoplankton biosphere using diatom as a tracer of environmental changes and based on quantitative assemblage analysis of two marine cores from oceanic regions of the north pacific subarctic gyre in the late pliocene subarctic pacific coscinodiscus marginatus and neodenticula kamtschatica were widely dominant but the flora rapidly and drastically shifted to one rich in neodenticula complex n koizumii n seminae at the onset of nhg perhaps due to intense changes in paleoceanographic conditions such as cooling and or a collapse of the previously nutrient regime in the region we also suggest that vertical pumping of biogenic matter by diatoms may have been more efficient in this region earlier than the onset of nhg after the nhg intensification the major primary productivity role in the subarctic pacific shifted from the c marginatus rich flora to the neodenticula complex the drastic decrease of biogenic opaline accumulation reportedly associated with the initiation of nhg would have resulted from not only a decrease of primary production but also from the change in diatom assemblages and consequent effects on their principal role in export flux

satellite and hydrographic observations of the bering sea green belt abstract green belt is the aptly named region of high productivity occurring principally along and above the shelf slope boundary in the bering sea topex altimeter measurements of sea surface topography seawifs imagery of chlorophyll a concentration and shipboard measurements of salinity and fluorescence are used to describe the surface structure of the green belt and its relationship to the bering slope current eddy field during the 2000 2001 and 2002 spring blooms during spring 2000 high surface chlorophyll a concentrations 10 mg m 3 were observed within a 200 km wide band adjacent to and seaward of the shelf break in the northwest bering sea this high concentration chlorophyll band was associated with an anticyclonic eddy group that propagated along isobaths above the continental slope and entrained chlorophyll from the shelf slope front during spring 2001 anticyclonic eddies in the northwest bering sea had propagated off slope prior to the onset of the spring bloom and were too far from the shelf slope front to entrain frontal chlorophyll during the bloom a second chlorophyll front associated with the leading edge of the off slope eddies was observed between these two fronts was a region of relatively low chlorophyll a concentration 1 mg m 3 the eddy field during the 2002 spring bloom was observed to propagate northwestward adjacent to the shelf break and entrain chlorophyll from the shelf slope region in a manner similar to what was observed during the 2000 spring bloom these observations suggest that eddies are important if not the principal agents that cause variability in the distribution of chlorophyll during the spring bloom in the central bering sea

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

a sea ice free summer arctic within 30 years an update from cmip5 models interpreted as sea ice extent less than 1 0 million km 2 w e consider this estimate to be still valid based on projections of updated climate models cmip5 and observational data similar to previous models cmip3 cmip5 still shows a wide spread in hindcast and projected sea ice loss among different models further there is no consensus in the scientific literature for the cause of such a spread in results for cmip3 and cmip5 while cmip5 model mean sea ice extents are closer to observations than cmip3 the rates of sea ice reduction in most model runs are slow relative to recent observations all cmip5 models do show loss of sea ice due to increased anthropogenic forcing relative to preindustrial control runs applying the same technique of model selection and extrapolation approach to cmip5 as we used in our previous paper the interval range for a nearly sea ice free arctic is 14 to 36 years with a median value of 28 years relative to a 2007 baseline this suggests a nearly sea ice free arctic in the 2030s citation wang m and j e overland 2012 a sea ice free summer arctic within 30 years an update from cmip5 models geophys res lett 39 l18501

seasonal dynamic thinning at helheim glacier a b s t r a c t we investigate three annual mass balance cycles on helheim glacier in south east greenland using tandem x interferometric digital elevation models dems bedrock gps measurements and ice velocity from feature tracking the dems exhibit seasonal surface elevation cycles at elevations up to 800 m a s l with amplitudes of up to 19 m from a maximum in july to a minimum in october or november concentrated on the fast flowing areas of the glacier indicating that the elevation changes have a mostly dynamic origin by modelling the detrended bedrock loading unloading signal we estimate a mean density for the loss of 671 70 kg m 3 and calculate that total water equivalent volume loss from the active part of the glacier surface flow speeds 1m day 1 ranges from 0 5 km 3 in 2011 to 1 6 km 3

micro and macronutrients in the southeastern bering sea insight into iron replete and iron depleted regimes abstract surface transects and vertical profiles of macronutrients dissolved iron d fe and dissolved manganese d mn were investigated during august 2003 in the southeastern bering sea we observed iron limited hnlc surface waters in the deep basin of the bering sea 15 20 mol kg nitrate 0 07 nmol kg d fe and 1 0 nmol kg d mn nitrate limited iron replete surface waters over the shelf

mass transport waves amplified by intense greenland melt and detected in solid earth deformation the annual cycle and secular trend of greenland mass loading are well recorded in measurements of solid earth deformation horizontal crustal displacements can potentially track the spatiotemporal detail of mass changes with great fidelity our analysis of greenland crustal motion data reveals that a significant excitation of horizontal amplitudes occurs during the intense melt years we discover that solitary seasonal waves of substantial mass transport 1 67 0 54 gt month traveled at an average speed of 7 1 km month through rink glacier in 2012 we deduce that intense surface melting enhanced either basal lubrication or softening of shear margins or both causing the glacier to thin dynamically in summer the newly routed upstream subglacial water was likely to be both retarded and inefficient thus providing a causal mechanism for the prolonged ice transport to continue well into the winter months as the climate continues to produce increasingly warmer spring and summer amplified seasonal waves of mass transport may become ever more present with important ramifications for the future sea level rise

diatoms as paleoenvironmental proxies for seasonal productivity sea ice and surface circulation in the bering sea during the late quaternary abstract diatom assemblages in suspended particulate matter spm surface sediments and piston core samples in the southern bering sea and the western subarctic pacific were examined the distribution of diatom assemblages in the southern bering sea shows not only differences in species composition between the spm and surface sediment samples but also preferential dissolution of different species in the upper water column or surface sediments furthermore we present the downcore profiles of selected diatom taxa for four piston cores to indicate changes in paleoceanographic conditions e g seasonal productivity sea ice and surface water circulation of the glacial and deglaciation periods during the late quaternary in particular we propose five models for the annual cycling of the water masses in the western subarctic pacific and the southern bering sea during the late quaternary significant regional differences in diatom accumulation rates and taxonomic composition between the southern bering sea and the western subarctic pacific reflect spatial shifts in water masses caused by the variable extent of sea ice cover and cold low salinity surface waters in these regions

sea level and deep sea temperature variability over the past 5 3 million years ice volume and hence sea level and deep sea temperature are key measures of global climate change sea level has been documented using several independent methods over the past 0 5 million years myr older periods however lack such independent validation all existing records are related to deep sea oxygen isotope 18o data that are influenced by processes unrelated to sea level for deep sea temperature only one continuous high resolution mg ca based record exists with related sea level estimates spanning the past 1 5 myr here we present a novel sea level reconstruction with associated estimates of deep sea temperature which independently validates the previous 0 1 5 myr reconstruction and extends it back to 5 3 myr ago we find that deep sea temperature and sea level generally decreased through time but distinctly out of synchrony which is remarkable given the importance of ice albedo feedbacks on the radiative forcing of climate in particular we observe a large temporal offset during the onset of plio pleistocene ice ages between a marked cooling step at 2 73 myr ago and the first major glaciation at 2 15 myr ago last we tentatively infer that ice sheets may have grown largest during glacials with more modest reductions in deep sea temperature a novel approach to the estimation of sea level and deep sea temperature has been used to determine these quantities over the past 5 3 million years this approach based on oxygen isotope records from the eastern mediterranean shows that temperature and sea level histories are broadly correlated but also show intriguing temporal offsets most records of past sea level variation and associated changes in ocean temperature rely on variations in oxygen isotopes recorded in deep sea marine microorganisms these signals unfortunately are confounded by other influences making it difficult to extract a clear climate related signal eelco rohling and colleagues now present a novel approach to estimating sea level and deep sea temperature variations for the past 5 3 million years the record based on oxygen isotope variations from the eastern mediterranean avoids the issues of the deep sea approach and generally corresponds to an independent record of the past 1 6 million years as expected temperature and sea level are broadly correlated but also show intriguing temporal discontinuities as at the initiation of plio pleistocene ice ages when a major sea level drop lagged a sharp temperature decline by several hundred thousand years

sea ice impacts on spring bloom dynamics and net primary production in the eastern bering sea 1 in the eastern bering sea changes in sea ice have been implicated in recent major upper trophic level shifts however the underlying relationships between sea ice and primary producers have not been well tested here we combine data from multiple satellite platforms reanalysis model results and biophysical moorings to explore the dynamics of spring and summer primary production in relation to sea ice conditions in the northern bering sea sea ice consistently retreated in late spring leading to ice edge phytoplankton blooms in cold 0 1 c waters however in the southeastern bering sea sea ice retreat was far more irregular although this did not significantly alter bloom timing late retreat led to blooms at the ice edge while early retreat led to blooms in open waters that were warmer 5 4 c and 70 more productive early sea ice retreat also led to higher productivity in summer likely due to weaker thermal stratification overall annual net primary production during warm years of early sea ice retreat was enhanced by 40 50 compared to years with late sea ice retreat in the southeastern bering sea these findings suggest the potential for future sea ice loss to enhance overall carrying capacity of the southeastern bering sea ecosystem consistently warm blooms in the future may also channel more energy flow toward the pelagic rather than benthic environment to date however neither sea ice extent nor the timing of its retreat have undergone long term changes in the eastern bering sea

modelling west antarctic ice sheet growth and collapse through the past five million years changes in earth s orbit are known to influence climate shifts from cold glacials to warm interglacials how the vast west antarctic ice sheet responds to these fluctuations is uncertain but because its collapse could raise sea levels by about 5 metres of great interest naish et al have analysed the and 1b ocean sediment core extracted from beneath the ross ice shelf as part of the andrill drilling project and find evidence that the ice sheet collapsed periodically during the early pliocene 3 5 million years ago when atmospheric co2 levels were similar to or slightly higher than today s the pattern of collapse suggests an influence of approximately 40 000 year cycles in the tilt of earth s rotational axis obliquity also in this issue of nature in a numerical modelling study focused on the past 5 million years in antarctica david pollard and robert deconto combine ice sheet land supported and ice shelf water supported modelling approaches to simulate the movement of the grounding line the border between land and sea ice their results show that over the past 5 million years the west antarctic ice sheet transitioned between full intermediate and collapsed states in just a few thousand years this means that the ice sheet is likely to disintegrate if ocean temperatures in the area rise by 5 c if the west antarctic ice sheet wais melted sea levels would rise by about 5 m such changes are thought to have occurred in the past but could not be simulated by models pollard and deconto combine ice sheet with ice shelf modelling and show that over the past 5 million years the wais transitioned among full intermediate and collapsed states in only a few thousand years suggesting possible disintegration of the wais if ocean temperatures in the area rise by 5 c the west antarctic ice sheet wais with ice volume equivalent to 5 m of sea level1 has long been considered capable of past and future catastrophic collapse2 3 4 today the ice sheet is fringed by vulnerable floating ice shelves that buttress the fast flow of inland ice streams grounding lines are several hundred metres below sea level and the bed deepens upstream raising the prospect of runaway retreat3 5 projections of future wais behaviour have been hampered by limited understanding of past variations and their underlying forcing mechanisms6 7 its variation since the last glacial maximum is best known with grounding lines advancing to the continental shelf edges around 15 kyr ago before retreating to near modern locations by 3 kyr ago8 prior collapses during the warmth of the early pliocene epoch9 and some pleistocene interglacials have been suggested indirectly from records of sea level and deep sea core isotopes and by the discovery of open ocean diatoms in subglacial sediments10 until now11 however little direct evidence of such behaviour has been available here we use a combined ice sheet ice shelf model12 capable of high resolution nesting with a new treatment of grounding line dynamics and ice shelf buttressing5 to simulate antarctic ice sheet variations over the past five million years modelled wais variations range from full glacial extents with grounding lines near the continental shelf break intermediate states similar to modern and brief but dramatic retreats leaving only small isolated ice caps on west antarctic islands transitions between glacial intermediate and collapsed states are relatively rapid taking one to several thousand years our simulation is in good agreement with a new sediment record andrill and 1b recovered from the western ross sea11 indicating a long term trend from more frequently collapsed to more glaciated states dominant 40 kyr cyclicity in the pliocene and major retreats at marine isotope stage 31 1 07 myr ago and other super interglacials

pronounced warmth during early middle pleistocene interglacials investigating the mid brunhes event in the british terrestrial sequence the mid brunhes event mbe is a climatic transition occurring between mis 13 and 11 that separates two climatic modes 1 early middle pleistocene interglacials 780 450 ka that are characterised by only moderate warmth and 2 middle and late pleistocene interglacials occurring after 450 ka that are characterised by greater warmth consistent with or warmer than the holocene this event is observable within a variety of long climate records such as specmap and epica but its effect on terrestrial systems is poorly understood the impact of this event is examined in the british terrestrial sequence by comparing the occurrence of a range of thermophilous plant and animal species and climate reconstructions derived from assemblages containing them from interglacials of the early middle pleistocene with those from the late middle and late pleistocene this comparison reveals that interglacial climates during the early middle pleistocene in britain were as warm as and in some cases warmer than those that occurred during the late middle and late pleistocene this interpretation is supported by sea surface temperature records in the north atlantic which show that temperatures during early middle pleistocene interglacials were at least as warm as those experienced during the holocene there is therefore no evidence in climate records of britain and the north atlantic for a mid brunhes event this suggests that the mbe is not a global climatic transition but is restricted to specific regions in particular the higher latitudes of the southern hemisphere further work is needed to understand the regional variability and cause of the mbe

diatom stratigraphy of the late pleistocene brunhes subarctic pacific sancetta c and silvestri s m 1984 diatom stratigraphy of the late pleistocene brunhes subarctic pacific mar micropaleontol 9 263 274 three piston cores in the subarctic region of the north pacific show consistent changes in relative abundance of diatom species throughout the brunhes magnetic epoch these events can be used both as stratigraphic markers to subdivide the interval and as indicators of oceanographic conditions the stratigraphic record shows an acme for a ochotensis from about 625 350 kyr isotope stages 15 10 a marked increase in amplitude of abundance fluctuations for r hebetata 300 0 kyr stages 8 1 the extinction of r curvirostris at 276 kyr stage 8 and abundance fluctuations of d seminae roughly in phase with the global oxygen isotope record from 450 0 kyr stages 12 1 in the subarctic pacific an abrupt change in species abundance is not a reliable indicator of hiatus occurrence although details are not clear there appears to have been a fundamental change of the subarctic gyre during the middle brunhes stages 10 8 time with more intense glacial intervals and stronger glacial interglacial contrast occurring after that time coarse clastic detritus is not restricted to glacial intervals suggesting that ice rafting has occurred throughout the brunhes interval peak levels of ice rafting may occur during ice growth and decay as well as during short intervals within a stage

holocene marine 14c reservoir age variability evidence from 230th dated corals in the south china sea the south china sea scs is well connected with the western pacific and influenced by the east asian monsoon we have examined temporal variations in radiocarbon marine reservoir ages r and regional marine reservoir corrections delta r of the scs during the holocene using paired measurements of ams c 14 and tims th 230 on 20 pristine corals the results show large fluctuations in both r and delta r values over the past 7500 years yrs with two distinct plateaus during 7 5 5 6 and 3 5 2 5 thousand calendar years before present cal ka bp the respective weighted mean delta r values of these plateaus are 151 85 and 89 59 yrs which are significantly higher than its modern value of 23 52 yrs this suggests that using a constant modern delta r value to calibrate c 14 dates of the scs marine samples will introduce additional errors to the calibrated ages our results provide the first database for the holocene r and delta r values of the scs for improved radiocarbon calibration of marine samples we interpret the two delta r plateaus as being related to two intervals with weakened el nino southern oscillation enso and intensified east asian summer monsoon easm this is because the c 14 content of the scs surface water is controlled by both the c 14 concentration of the pacific north equatorial current nec which is in turn influenced by enso induced upwelling along the pacific equator and vertical upwelling within the scs as a result of moisture transportation to midlatitude region to supply the easm rainfall

contribution of seasonal hydrological loading in the variation of seismicity and geodetic deformation in garhwal region of northwest himalaya abstract the study interprets the effect of seasonal pre co and post monsoon hydrological loading due to the ganga river basin over the seismicity and geodetic deformation in the garhwal himalayan region geodetic data from six cgps sites are used three sites out of six are established in the himalayan region one is located in the ganga basin and two sites are located in the indian shield first we estimated the average seasonal variation in grace derived tws of entire india for the period of 2002 2016 it is observed the seasonal effect over tws terrestrial water storage due to hydrological fluctuations in the indo gangetic plain igp it has also been noticed that the geodetic velocities for both the north and east components are more in pre monsoon than post monsoonal season whereas the vertical component in cgps sites of himalaya dehr and mand agrees to the hypothesis of upliftment during post monsoon and subsidence in pre monsoon tws mass change is detected high during the co monsoon 2 32 104 km3 and it is observed low 2 22 104 km3 in pre and 8 13 103 km3 in post monsoon seasons respectively gps measured horizontal displacement agrees with seasonal loading but it contains some anomalous behaviour which may be the result of surface hydrological mass movement or the effect of the gorkha earthquake 2015 however an inverse relation between vertical geodetic displacement and loading have been observed the average strain rate values over cgps sites during 2016 2018 are more negative in post monsoon than in pre monsoon which means that plate movement is highly compressional we have also inferred a significant role of loading over the seismicity and linear strain rate which increases with decreasing hydrological loading in the ganga river basin and vice versa

planktonic foraminiferal biostratigraphy and assemblages in the bering sea during the pliocene and pleistocene iodp sites u1340 and u1343 abstract iodp site u1340 and site u1343 in the bering sea have been investigated with regard to planktonic foraminifers and fragmentation the base of site u1340 dates back to the early pliocene and the base of site u1343 to the early pleistocene site u1340 is situated at bowers ridge the southern bering sea site u1343 is situated near the gateway to the arctic ocean in the northern bering sea at both sites there are none or very few planktonic foraminifers during the pliocene and early pleistocene after 1 3 1 4 ma the planktonic foraminifers are continuously present for most of the samples examined three stratigraphic events have been identified in this study the first occurrence fo of neogloboquadrina inglei is observed at 1 4 1 5 ma although this event may be affected by poor preservation of foraminifers in older sediments the observed age of the change in the coiling ratio of neogloboquadrina pachyderma from right to left at 1 2 ma agrees with the dating of the same event at the californian margin the age of the last occurrence lo of n inglei also seems to match the same event from the californian margin at 0 7 ma this implies that these events are robust regional events for the entire northern pacific multivariate analyses of the quantitative planktonic foraminifer data show three main faunal assemblages the oldest assemblage from 1 3 1 4 ma to 1 2 ma is dominated by n pachyderma s l dex together with globigerina bulloides other species in this fauna are n inglei n pachyderma s l sin globigerina umbilicata and turborotalita quinqueloba after 1 2 ma the faunal assemblage is dominated by n pachyderma s l sin but the remaining species are the same as before at 0 7 ma n inglei disappears whilst the remaining fauna assemblage stays the same with n pachyderma s l sin still dominating reflecting subpolar polar conditions prior to 1 4 1 3 ma there are very few or no planktonic foraminifers low shell fragmentation and lower toc suggest that the lack of planktonic foraminifers in these sediments cannot be explained either by a shoaling of the carbonate compensation depth or by enhanced supralysoclinal dissolution instead we argue that the appearance of abundant foraminifers in the sediment reflects the same evolutionary adaption of n pachyderma sin to cold conditions to have occurred after 1 1 1 0 ma as in the north atlantic

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

last glacial maximum to holocene sea surface conditions at umnak plateau bering sea as inferred from diatom alkenone and stable isotope records 1 the bering sea gateway between the pacific and arctic oceans impacts global climate when glacial interglacial shifts in shore line position and ice coverage change regional albedo previous work has shown that during the last glacial termination and into the holocene sea level rises and sea ice coverage diminishes from perennial to absent yet existing work has not quantified sea ice duration or sea surface temperatures sst during this transition here we combine diatom assemblages with the first alkenone record from the bering sea to provide a semiquantitative record of sea ice duration sst and productivity change since the last glacial maximum lgm during the lgm diatom assemblages indicate that sea ice covered the southeastern bering sea perennially at 15 1 cal ka b p the diatom assemblage shifts to one more characteristic of seasonal sea ice and alkenones occur in the sediments in low concentrations deglaciation is characterized by laminated intervals with highly productive and diverse diatom assemblages and inferred high coccolithophorid production at 11 3 cal ka b p the diatom assemblage shifts from one dominated by sea ice species to one dominated by a warmer water north pacific species simultaneously the sst increases by 3 c and the southeastern bering sea becomes ice free year round productivity and temperature proxies are positively correlated with independently dated records from elsewhere in the bering sea the sea of okhotsk and the north pacific indicating that productivity and sst changes are coeval across the region

holocene paleoclimate change in the antarctic peninsula evidence from the diatom sedimentary and geochemical record abstract holocene marine deposition in lallemand fjord antarctic peninsula is reinterpreted using statistical analyses cluster analysis analysis of variance nonmetric multidimensional scaling and multiple regression to compare diatom assemblages and the primary sedimentological proxies the assemblages have been deposited in a variable sea ice zone over the last ca 10 500 yr bp in response to a climate change in the late pleistocene early holocene 10 580 7890 yr bp a sea ice diatom assemblage was deposited in the presence of a retreating ice shelf at the head of the fjord in the mid holocene 7890 3850 yr bp an open water assemblage was deposited and sea ice cover was at a minimum we associate the assemblage with climatic warming which characterizes much of the antarctic peninsula during this time a second sea ice assemblage different from that deposited in the early holocene has been deposited in lallemand fjord since the late holocene

impact of skeletal dissolution and secondary aragonite on trace element and isotopic climate proxies in porites corals restricted zones of recent dissolution and secondary aragonite infilling were identified in a coral core collected in 1986 from a living massive porites colony from the central great barrier reef australia secondary aragonite needles 20 m long cover skeletal surfaces deposited from 1972 to late 1974 and increase bulk density by 10 dissolution is observed above this zone whereas older skeleton is pristine we investigate the impact of both types of early marine diagenesis on skeletal geochemistry and coral paleoclimate reconstructions by comparison with similar records from eight contemporary porites colonies collected at nearby reefs secondary aragonite overgrowth causes anomalies in skeletal density mg ca sr ca u ca o and c the secondary aragonite is consistently associated with a cool temperature anomaly for each of the sea surface temperature sst proxies o sst 1 6 c sr ca sst 1 7 c mg ca sst 1 9 c u ca sst 2 8 c dissolution through incongruent leaching also causes cool sst artifacts but only for trace element ratios mg ca sst 1 2 c sr ca sst 1 2 c u ca sst 2 1 c the sequence of preference with respect to dissolution of coral skeleton in seawater is mg ca sr u rigorous screening of coral material for paleoclimate reconstructions is therefore necessary to detect both dissolution and the presence of secondary minerals the excellent agreement between apparent sst anomalies generated by different modes of diagenesis means that replication of tracers within a single coral cannot be used to validate climate proxy interpretations poor replication of records between different coral colonies however provides a strong indication of nonclimatic artifacts such as dissolution and secondary aragonite copyright 2007 by the american geophysical union

astronomical timescale and palaeoclimatic implication of stacked 3 6 myr monsoon records from the chinese loess plateau abstract magnetic susceptibility and grain size records from two continuous red clay and loess palaeosol sequences on the chinese loess plateau have been generated to investigate the evolution and variability of the east asian monsoon eam during the late pliocene and pleistocene tuning the grain size records to orbital obliquity and precession yields an improved astronomical timescale for the loess palaeosol sequence 0 2 6 ma and an extended age model for the upper red clay formation 2 6 3 6 ma this timescale indicates older ages for a number of the magnetic polarity boundaries consistent with lock in depth offsets in loess sequences good site to site correlation enables generation of stacked grain size and susceptibility records spanning the last 3 6 myr these records indicate that monsoon evolution since the late pliocene can be subdivided into three phases 0 1 25 1 25 2 72 and 2 72 3 4 ma each phase is characterized by unique amplitude and frequency characteristics for both summer monsoon magnetic susceptibility and winter monsoon grain size spectral analyses of the stacked monsoon proxies indicate that characteristics of both the summer and winter monsoons are dominated mainly by variance in the eccentricity 410 and 100 kyr obliquity 41 kyr and precession 23 and 19 kyr bands over the past 3 4 myr implying a non linear response of the long term eam evolution to orbital and glacial forcing

glacial southern ocean freshening at the onset of the middle pleistocene climate transition changes in southern ocean hydrography may have played an important role in the middle pleistocene transition mpt particularly through their impact on ocean circulation and atmospheric co2 concentrations here we present foraminiferal mg ca and 18o results for the subsurface dwelling planktonic foraminifer neogloboquadrina pachyderma sinistral at the ocean drilling program odp site 1090 results are used to reconstruct upper ocean temperatures and derive seawater 18o in the subantarctic atlantic ocean during the mpt the new records indicate that starting at 1250 ka glacial temperatures and local ice volume corrected seawater 18o in the upper water column of the subantarctic atlantic ocean decreased pointing to cooler 2 c and fresher 0 4 conditions than in the preceding glacial stages these upper ocean hydrographic changes broadly coincide with the increase in the power of the 100 ky glacial interglacial cycle in both records and with a shift towards decreased deep ventilation in the glacial southern ocean our finding suggests that an increase in southern ocean stratification driven by the observed freshening of the upper water column may have reduced the exchange of carbon between the deep southern ocean and the atmosphere during glacial stages this process may have contributed in combination with other mechanisms to lower glacial atmospheric co2 concentrations during the mpt

mid pliocene warmth stronger greenhouse and stronger conveyor abstract three million years ago prior to the onset of northern hemisphere glaciation global mean temperatures may have been as much as 3 5 c warmer than at present we present evidence based on the carbon isotopic composition of marine organic matter that atmospheric co2 levels at this time were on average only about 35 higher than the preindustrial value of 280 ppm we also present carbon isotopic evidence for stronger thermohaline circulation in the atlantic ocean during the warmest intervals and propose that the north atlantic conveyor belt may act as a positive feedback to global warming by enhancing sea ice retreat and decreasing high latitude albedo based on our results it seems unlikely that the mid pliocene warm period was a doubled co2 world

aleutian basin of the bering sea thermohaline oxygen nutrient and current structure in july 1993 an overview is given of the surface to bottom thermohaline oxygen nutrient and baroclinic flow structures in the aleutian basin of the bering sea and the adjacent north pacific based on high resolution field measurements in july 1993 a basic four layer vertical structure is observed in the upper 1500 m the 30 m top layer is warm low in salinity and nutrients and high in oxygen beneath it a 100 to 150 m thick temperature minimum layer is found believed to be a remnant of winter convection this is followed by a 300 m thick warm layer in which the main halocline oxycline and nutricline are located below it lies a layer of minimum oxygens and maximum nitrates and phosphates centered at a depth of 900 m in the bering sea but rising to 400 m south of the aleutians this basic structure is disrupted in the vicinity of amchitka pass due to strong tidal mixing the deep and abyssal waters of the aleutian basin differ substantially from those at comparable depth in the adjacent pacific by being warmer 0 1 c less saline 0 01 less dense 0 01 kg m3 poorer in oxygen 50 mol kg and richer in silicates 80 mol kg nitrates 1 0 mol kg and phosphates 0 3 mol kg the highest silicate concentrations 240 mol kg occur at the foot of the bering shelf unusual hydrographic conditions exist in an isolated tidal mixing basin in amchitka pass where the bottom mixed layer is 600 m thick 0 7 c warmer 0 14 less saline and 21 mol kg less oxygenated than at comparable depths outside baroclinic currents indicate strong deep jetlike flows on both sides of the aleutian ridge weak shallow eddies in the middle of the aleutian basin and somehat enhanced flows near the bering shelf edge the alaska stream in july 1993 was 100 km wide had a double core with a top speed of 0 54 m s and had a westward volume transport of 38 sv with 14 sv below 1000 dbar the north aleutian current had a speed of 0 2 m s and an eastward transport of 10 sv with 4 sv below 1000 dbar off the bering slope both eastward and westward flows were observed with volume transports near 7 sv

evolution of ocean temperature and ice volume through the mid pleistocene climate transition earth s climate underwent a fundamental change between 1250 and 700 thousand years ago the mid pleistocene transition mpt when the dominant periodicity of climate cycles changed from 41 thousand to 100 thousand years in the absence of substantial change in orbital forcing over this time an increase occurred in the amplitude of change of deep ocean foraminiferal oxygen isotopic ratios traditionally interpreted as defining the main rhythm of ice ages although containing large effects of changes in deep ocean temperature we have separated the effects of decreasing temperature and increasing global ice volume on oxygen isotope ratios our results suggest that the mpt was initiated by an abrupt increase in antarctic ice volume 900 thousand years ago we see no evidence of a pattern of gradual cooling but near freezing temperatures occur at every glacial maximum

origin of the middle pleistocene transition by ice sheet erosion of regolith the transition in the middle pleistocene 0 9 ma seen in 18o deep sea core records from relatively low amplitude high frequency 41 kyr to high amplitude low frequency 100 kyr ice volume variations under essentially the same orbital forcing can be attributed to a change from an all soft bedded to a mixed hard soft bedded laurentide ice sheet through glacial erosion of a thick regolith and resulting exposure of unweathered crystalline bedrock a one dimensional ice sheet and bedrock model which includes transport of sediment and ice by subglacial sediment deformation demonstrates that a widespread deforming sediment layer maintains thin ice sheets before the transition which respond linearly to the dominant 23 and 41 kyr orbital forcing progressive removal of the sediment layer eventually causes a transition to thicker ice sheets whose dominant timescale of change 100 kyr reflects nonlinear deglaciation processes in model simulations over the last 3 ma initialized with no ice and a uniform 50 m sediment layer the time series of ice volume and extent agree in several important aspects with the observed records

subpolar link to the emergence of the modern equatorial pacific cold tongue the cold upwelling tongue of the eastern equatorial pacific is a central energetic feature of the ocean dominating both the mean state and temporal variability of climate in the tropics and beyond recent evidence for the development of the modern cold tongue during the pliocene pleistocene transition has been explained as the result of extratropical cooling that drove a shoaling of the thermocline we have found that the sub antarctic and sub arctic regions underwent substantial cooling nearly synchronous to the cold tongue development thereby providing support for this hypothesis in addition we show that sub antarctic climate changed in its response to earth s orbital variations from a subtropical to a subpolar pattern as expected if cooling shrank the warm water sphere of the ocean and thus contracted the subtropical gyres

mass loss on himalayan glacier endangers water resources 1 ice cores drilled from glaciers around the world generally contain horizons with elevated levels of beta radioactivity including 36 cl and 3 h associated with atmospheric thermonuclear bomb testing in the 1950s and 1960s ice cores collected in 2006 from naimona nyi glacier in the himalaya tibet lack these distinctive marker horizons suggesting no net accumulation of mass ice since at least 1950 naimona nyi is the highest glacier 6050 masl documented to be losing mass annually suggesting the possibility of similar mass loss on other high elevation glaciers in low and mid latitudes under a warmer earth scenario if climatic conditions dominating the mass balance of naimona nyi extend to other glaciers in the region the implications for water resources could be serious as these glaciers feed the headwaters of the indus ganges and brahmaputra rivers that sustain one of the world s most populous regions

geodetic measurements reveal short term changes of glacial mass near jakobshavn isbrae greenland from 2007 to 2017 abstract the global positioning system gps and gravity recovery and climate experiment grace provide important geodetic datasets to study glacial mass change applying the multichannel singular spectral analysis to the gps measured vertical and horizonal crustal displacement and grace derived vertical displacement near jakobshavn isbrae ji in western greenland from 2007 to 2017 we reconstruct the short term loading displacements due to ice mass changes both the vertical and east displacements show strong seasonal variability they also reveal three episodes of transient displacements downward and eastward motion from late 2007 to around 2010 sustained upward and westward motion from 2010 to early 2013 and downward and eastward motion till late 2016 we also forward model the seasonal and transient displacements caused by surface mass balance smb and glacier dynamics our model agrees well with the geodetic observations and provides quantitative insights into the contribution from smb and ice dynamics to the ice mass changes we find that smb is the dominant contributor to the seasonal and transient displacements at three out of four gps sites aasi ilul and qeqe while at the fourth gps site kaga that is closest to the glacier the contributions to the transient displacements from smb and glacier dynamics are comparable the forward modeling also suggests that the dynamic mass change in the ji catchment underwent strong seasonal variations and these variations correlated more with the seasonal retreat and advance of the calving front than with the changes of glacial velocities our altimetry results reveal that the frontal portion of ji catchment lost 34 gt in 2012 and this loss of ice declined to only 11 gt in 2016 due to widespread thickening along the main flowline

intensification of the walker and hadley atmospheric circulations during the pliocene pleistocene climate transition when comparing new sea surface temperature sst records between the western and eastern equatorial pacific spanning the last 3 2 ma we found that the zonal temperature gradient over the entire tropical pacific irreversibly increased by 3 to 4 degrees c from 2 2 to 2 0 ma here we suggest a pronounced increase in atmospheric circulation from a weak to a strong zonal walker circulation wc during the early pleistocene evidence from other oceanic areas also suggests a strengthening in the meridional hadley circulation hc during the same time period therefore we also suggest that the invigoration of both atmospheric circulation patterns was intimately coupled during the plio pleistocene transition and likely linked to a shrinkage in the zonal extension of the tropical to subtropical warm sphere associated with a prominent increase in the pole to equator temperature gradient our conclusion refutes assumptions that the intensification of atmospheric circulation in the tropics and subtropics significantly contributed to the initiation of continental ice sheet formation at high latitudes since the onset of extensive northern hemisphere glaciation nhg occurred similar to 2 75 ma ago in the late pliocene instead the development of a stronger atmospheric circulation similar to 2 2 2 0 ma ago could have significantly contributed to the plio pleistocene climate cooling c 2010 elsevier b v all rights reserved

crustal uplift due to ice mass variability on upernavik isstrom west greenland abstract we estimate the mass loss rate of upernavik isstrom ui using surface elevation changes between a spot 5 digital elevation model dem from 2008 and nasa s airborne topographic mapper atm data from 2010 to assess the validity of our mass loss estimate we analyze gps data between 2007 and 2011 from two continuous receivers upvk and srmp which are established on bedrock and located 65 and 2 km from the front of ui respectively we construct along track elevation changes on ui for several time intervals during 2005 2011 based on atm spot 5 and ice cloud and land elevation satellite icesat data to assess temporal changes of ui we estimate a mass loss rate of 6 7 4 2 gt yr over an area of 1600 km 2 the ice mass loss occurs primarily over the northern glacier of ui this pattern is also observed 40 km upstream where we observe glacier thinning at a rate of 1 6 0 3 m yr across the northern portion of ui and 0 5 0 1 m yr across the southern portion gps measurements suggest bedrock uplift rates of 7 6 0 6 mm yr upvk and 16 2 0 6 mm yr srmp the modeled ice mass loss of ui causes bedrock uplift rates of 1 3 0 6 mm yr upvk and 8 3 4 2 mm yr srmp including additional contributions from ice mass changes outside ui and from glacial isostatic adjustment gia we obtain total modeled uplift rates of 4 7 0 6 mm yr upvk and 13 8 4 2 mm yr srmp the modeled uplift rates from our ui ice mass loss are substantially lower indicating that additional mass loss is taking place outside of ui we obtain a difference of 0 6 mm yr between the modeled and observed relative uplift rates srmp relative to upvk suggesting that the mass loss of ui is well captured in the model we observe elevation changes from 15 to 40 m yr near the front during the period 2005 2011 indicating that ui undergoes large variations in thinning pattern over short time spans

tropical ocean temperatures over the past 3 5 million years determining the timing and amplitude of tropical sea surface temperature sst change is an important part of solving the puzzle of the plio pleistocene ice ages alkenone based tropical sst records from the major ocean basins show coherent glacial interglacial temperature changes of 1 to 3 c that align with but slightly lead global changes in ice volume and deep ocean temperature over the past 3 5 million years tropical temperatures became tightly coupled with benthic 18o and orbital forcing after 2 7 million years we interpret the similarity of tropical sst changes in dynamically dissimilar regions to reflect top down forcing through the atmosphere the inception of a strong carbon dioxide greenhouse gas feedback and amplification of orbital forcing at 2 7 million years ago connected the fate of northern hemisphere ice sheets with global ocean temperatures since that time

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

global glacial isostasy and the surface of the ice age earth the ice 5g vm2 model and grace abstract the 100 kyr quasiperiodic variation of continental ice cover which has been a persistent feature of climate system evolution throughout the most recent 900 kyr of earth history has occurred as a consequence of changes in the seasonal insolation regime forced by the influence of gravitational n body effects in the solar system on the geometry of earth s orbit around the sun the impacts of the changing surface ice load upon both earth s shape and gravitational field as well as upon sea level history have come to be measurable using a variety of geological and geophysical techniques these observations are invertible to obtain useful information on both the internal viscoelastic structure of the solid earth and on the detailed spatiotemporal characteristics of glaciation history this review focuses upon the most recent advances that have been achieved in each of these areas advances that have proven to be central to the construction of the refined model of the global process of glacial isos