dynamics of decadal variability in the atlantic subpolar gyre a stochastically forced oscillator internal variability of the atlantic subpolar gyre is investigated in a 600 years control simulation of a comprehensive coupled climate model the subpolar gyre shows irregular oscillations of decadal time scale with most spectral power between 15 and 20 years positive and negative feedback mechanisms act successively on the circulation leading to an internal oscillation this involves periodically enhanced deep convection in the subpolar gyre center and intermittently enhanced air sea thermal coupling as a result anomalies of the large scale atmospheric circulation can be transferred to the ocean on the ocean s intrinsic time scale exciting the oscillator stochastically a detailed understanding of oscillatory mechanisms of the ocean and their sensitivity to atmospheric forcing holds considerable potential for decadal predictions as well as for the interpretation of proxy data records

accelerated lake expansion on the tibetan plateau in the 2000s induced by glacial melting or other processes ccelerated lake expansion in the 2000s has been confirmed by both dramatic lake area increases for 312 lakes larger than 10 km2 derived from optical images and rapid water level rises for 117 lakes with water level data measured by satellite altimetry however the underlying climate causes remain unclear this paper analyzes the relationship between the water level changes of lakes on the plateau and the potential driving factors such as the glacier meltwater supply and a dependency on precipitation and runoff over the whole plateau and in each zone the results show that the rates of change of non glacier fed lakes in the 2000s were as high as those of glacier fed lakes across the whole plateau and the lake level changes were closely associated with the lake supply coefficients the basin lake area ratio the lake variations agreed well with the spatial pattern of precipitation changes however in different zones especially at around 33 n north of the plateau glacier fed lakes did exhibit faster lake level increases than no glacier fed lakes indicating that the presence of a glacier meltwater supply augmented the precipitation driven lake expansions in these areas despite the absence of quantitative modeling due to limited data availability this study provides qualitative support that the lake expansions on the tibetan plateau in the 2000s have been driven primarily by changes in precipitation and evapotranspiration and not solely by the effect of glacier wastage

lake seasonality across the tibetan plateau and their varying relationship with regional mass changes and local hydrology the recent growth and deepening of inland lakes in the tibetan plateau tp may be a salient indicator of the consequences of climate change the seasonal dynamics of these lakes is poorly understood despite this being potentially crucial for disentangling contributions from glacier melt and precipitation which are all sensitive to climate to lake water budget using in situ observations satellite altimetry and gravimetry data we identified two patterns of lake level seasonality in the central northern and northeastern tp lake levels are characterized by considerable increases during warm seasons and decreases during cold seasons which is consistent with regional mass changes related to monsoon precipitation and evaporation in the northwestern tp however lake levels exhibit dramatic increases during both warm and cold seasons which deviate from regional mass changes this appears to be more connected with high spring snowfall and large summer glacier melt the variable lake level response to different drivers indicates heterogeneous sensitivity to climate change between the northwestern tp and other regions

characteristics of δ13cdic in lakes on the tibetan plateau and its implications for the carbon cycle dissolved inorganic carbon isotope 13cdic is an important tool to reveal the carbon cycle in lake systems however there are only few studies focusing on the spatial variation of 13cdic of closed lakes here we analyze the characteristics of 13cdic of 24 sampled lakes mainly closed lakes across the qiangtang plateau qtp and identify the driving factors for its spatial variation the 13cdic value of these observed lakes varies in the range of 15 0 to 3 2 with an average value of 1 2 the 13cdic value of closed lakes is close to the atmospheric isotopic equilibrium value much higher than that in rivers and freshwater lakes reported before the high 13cdic value of closed lakes is mainly attributed to the significant contribution of carbonate weathering in the catchment and the evasion of dissolved co2 induced by the strong evaporation of lake water the 13cdic value of closed lakes has a logarithmic correlation with water chemistry tds dic and pco2 also suggesting that the evapo concentration of lake water can influence the 13cdic value the 13cdic value shows two opposite logarithmic correlations with lake size depending on the 13cdic range this study suggests that the 13c in carbonates in lacustrine sediments can be taken as an indicator of lake volume variation in closed lakes on qtp copyright 2011 john wiley sons ltd

the 8 2 ka event abrupt transition of the subpolar gyre toward a modern north atlantic circulation 1 climate model simulations of the 8 2 ka event show an abrupt strengthening of the atlantic subpolar gyre that allows us to connect two major but apparently contradictory climate events of the early holocene the freshwater outburst from proglacial lakes and the onset of labrador sea water formation the 8 2 ka event is the largest climatic signal of our present interglacial with a widespread cooling in the north atlantic region about 8200 years before present it coincides with a meltwater outburst from north american proglacial lakes that is believed to have weakened the atlantic meridional overturning circulation and northward heat transport followed by a recovery of the deep ocean circulation and rising temperatures after a few centuries marine proxy data however date the onset of deep water formation in labrador sea to the same time the subsequent strengthening of the slope current system created a regional signal recorded as an abrupt and persistent surface temperature decrease although similarities in timing are compelling a mechanism to reconcile these apparently contradictory events was missing our simulations show that an abrupt and persistent strengthening of the atlantic subpolar gyre provides a plausible explanation the intense freshwater pulse triggered a transition of the gyre circulation into a different mode of operation stabilized by internal feedbacks and persistent after the cessation of the perturbation as a direct consequence deep water formation around its center intensifies this corresponds to the modern flow regime and stabilizes the meridional overturning circulation possibly contributing to the holocene s climatic stability

changes in meridional temperature and salinity gradients in the north atlantic ocean 30 72 n during the last interglacial period eight deep sea sediment cores from the north atlantic ocean ranging from 31 to 72 n are studied to reconstruct the meridional gradients in surface hydrographic conditions during the interval of minimum ice volume within the last interglacial period using benthic foraminiferal 18o measurements and estimates of sea surface temperature sst and sea surface salinity sss we show that summer ssts and ssss decreased gradually during the interval of minimum ice volume at high latitude sites 52 72 n whereas they were stable or increased during the same time period at low latitude sites 31 41 n this increase in meridional gradients of ssts and ssss may have been due to changes in the latitudinal distribution of summer and annual average insolation and associated oceanic and atmospheric feedbacks these trends documented for the eemian ice volume minimum period are similar to corresponding changes observed during the holocene and may have had a similar origin

smos sea surface salinity signals of tropical instability waves sea surface salinity sss measurements from the soil moisture and ocean salinity smos mission provide an unprecedented opportunity to observe the salinity structure of tropical instability waves tiws from space especially during the intense 2010 la nina condition in the eastern equatorial pacific ocean smos sss signals correlate well and have similar amplitude to 1 m salinity from the tropical atmosphere ocean tao array at six locations with strong tiw signals at these locations the linear negative relationships between smos sss and ostia sst signals vary from 0 20 c 1 to 0 25 c 1 which are comparable to the ones obtained from tao from june to december 2010 the largest tiw signals and meridional gradients of both sss and sst appear around 2 n west of 100 w they shift southward and cross the equator at 90 w in addition to the large negative correlation band around 2 n a band of negative correlations between sss and sst signals also exists around 8 n west of 110 w for the 33 day signals the peak amplitude of the 33 day smos sss signals west of 135 w is reduced by 40 with respect to values east of 135 w while the reduction for sst is much lower 20 the amplitudes and longitudinal extents of tiw signals and the dominant westward propagation speed of 17 day tiws as detected by smos and aquarius at the equator decrease from 2010 to 2013 associated with the transition from a strong la nina to non la nina conditions

a census of tehuantepec and papagayo eddies in the northeastern tropical pacific 1 we use a 12 year 1992 2004 time series of satellite altimetry to characterize long lived wind generated anticyclonic eddies originating in the gulfs of tehuantepec and papagayo in the northeastern tropical pacific a total of 42 tehuantepec and 26 papagayo eddies were observed eddy merging usually of a tehuantepec papagayo pair was observed on 16 occasions on average the eddy season began in late october and lasted approximately 250 days until early july with 3 5 tehuantepec and 2 2 papagayo eddies formed each year minimum average eddy lifespan was 143 days and 84 days for tehuantepec and papagayo eddies respectively there was considerable interannual variability in eddy activity with greater fewer number of eddies more intense weaker eddies and a longer shorter eddy season during el nino la nina years eddy intensification was consistently observed at the east pacific rise

reversed north atlantic gyre dynamics in present and glacial climates the dynamics of the north atlantic subpolar gyre spg are assessed under present and glacial boundary conditions by investigating the spg sensitivity to surface wind stress changes in a coupled climate model to this end the gyre transport is decomposed in ekman thermohaline and bottom transports surface wind stress variations are found to play an important indirect role in spg dynamics through their effect on water mass densities our results suggest the existence of two dynamically distinct regimes of the spg depending on the absence or presence of deep water formation dwf in the nordic seas and a vigorous greenland scotland ridge gsr overflow in the first regime the gsr overflow is weak and the spg strength increases with wind stress as a result of enhanced outcropping of isopycnals in the centre of the spg as soon as a vigorous gsr overflow is established its associated positive density anomalies on the southern gsr slope reduce the spg strength this has implications for past glacial abrupt climate changes insofar as these can be explained through latitudinal shifts in north atlantic dwf sites and strengthening of the north atlantic current regardless of the ultimate trigger an abrupt shift of dwf into the nordic seas could result both in a drastic reduction of the spg strength and a sudden reversal in its sensitivity to wind stress variations our results could provide insight into changes in the horizontal ocean circulation during abrupt glacial climate changes which have been largely neglected up to now in model studies

satellite observations of mesoscale eddies in the gulfs of tehuantepec and papagayo eastern tropical pacific seawifs high resolution ocean color images and avhrr sea surface temperature were obtained for the period from november 1998 to march 1999 generation of mesoscale eddies was observed for the region between the gulf of tehuantepec and the gulf of papagayo tropical pacific ocean eighteen eddies with diameters ranging between 100 and 450 kmwere identified 14 originated in the gulf of tehuantepec and m ost were cyclonic our results show that the frequency of cyclonic eddy formation is higher than it has been reported and their lifetime can be longer using both ocean color images and daily temporal resolution instead of sea surface temperature alone improved our ability to identify and follow the propagation of these eddies the generation and fate of smaller cyclonic eddies around the periphery of the anticyclonic eddy indicate the importance of the onshore offshore exchange of energy and biological material which has not been considered previously three anticyclonic eddies were generated in the gulf of papagayo these eddies have a common origin and they travel along the main flux of the costa rica coastal current crcc which later turns offshore and joins the north equatorial current this behavior can be seen clearly on seawifs images and suggests that the crcc influences eddy propagation time series of chlorophyll a concentration and sst were obtained fromtwo points at tehuantepec and two at papagayo cross correlation analysis confirms an inverse relationship between these variables showing that a decrease in sst is followed by an increase in chlorophyll a concentration values indicating high growth and primary production rates r 2004 elsevier ltd all rights reserved

sea ice induced changes in ocean circulation during the eemian we argue that arctic sea ice played an important role during early stages of the last glacial inception two simulations of the institut pierre simon laplace coupled model 4 are analyzed one for the time of maximum high latitude summer insolation during the last interglacial the eemian and a second one for the subsequent summer insolation minimum at the last glacial inception during the inception increased arctic freshwater export by sea ice shuts down labrador sea convection and weakens overturning circulation and oceanic heat transport by 27 and 15 respectively a positive feedback of the atlantic subpolar gyre enhances the initial freshening by sea ice the reorganization of the subpolar surface circulation however makes the atlantic inflow more saline and thereby maintains deep convection in the nordic seas these results highlight the importance of an accurate representation of dynamic sea ice for the study of past and future climate changes

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

bistability of the atlantic subpolar gyre in a coarse resolution climate model 1 high resolution models indicate that the dynamics of the nordic seas and the subpolar gyre is crucial for deep water formation and overturning circulation in the atlantic during the last decades significant changes in ocean properties have been observed in this region we show that large scale dynamics as captured by coarse resolution climate models allows for a bistability of the atlantic subpolar gyre we suggest three positive feedbacks which yield the necessary nonlinearity for this behavior transitions between the two states can be triggered by small fluctuations in surface freshwater flux to the nordic seas only slightly larger than natural variability presently observed in the region

satellite observations of the wind jets off the pacific coast of central america part ii regional relationships and dynamical considerations abstract satellite estimates of winds at 10 m above the sea surface by the nasa scatterometer nscat during the 9 month period october 1996 june 1997 are analyzed to investigate the correlations between the three major wind jets along the pacific coast of central america and their relationships to the wind and pressure fields in the inter american seas and eastern tropical pacific comparisons with sea level pressure confirm the conventional view that tehuantepec wind variations are driven by pressure variations in the gulf of mexico associated with north american cold air outbreaks the three jets sometimes developed sequentially from north to south statistically however the papagayo and panama jets were poorly correlated with variations of the tehuantepec jet over the nscat observational period the papagayo and panama jets were significantly correlated with each other and were coupled to coherent variations of the trade winds extending from the caribbean sea to the eastern tropical pacific the det

inception of the northern european ice sheet due to contrasting ocean and insolation forcing about 115 000 yr ago the last interglacial reached its terminus and nucleation of new ice sheet growth was initiated evidence from the northernmost nordic seas indicate that the inception of the last glacial was related to an intensification of the atlantic meridional overturning circulation amoc in its northern limb the enhanced amoc combined with minimum northern hemisphere insolation introduced a strong sea land thermal gradient that together with a strong wintertime latitudinal insolation gradient increased the storminess and moisture transport to the high northern european latitudes at a time when the northern hemisphere summer insolation approached its minimum

simulating arctic climate warmth and icefield retreat in the last interglaciation in the future arctic warming and the melting of polar glaciers will be considerable but the magnitude of both is uncertain we used a global climate model a dynamic ice sheet model and paleoclimatic data to evaluate northern hemisphere high latitude warming and its impact on arctic icefields during the last interglaciation our simulated climate matches paleoclimatic observations of past warming and the combination of physically based climate and ice sheet modeling with ice core constraints indicate that the greenland ice sheet and other circum arctic ice fields likely contributed 2 2 to 3 4 meters of sea level rise during the last interglaciation

the influence of nonlinear mesoscale eddies on near surface oceanic chlorophyll oceanic rossby waves have been widely invoked as a mechanism for large scale variability of chlorophyll chl observed from satellites high resolution satellite altimeter measurements have recently revealed that sea surface height ssh features previously interpreted as linear rossby waves are nonlinear mesoscale coherent structures referred to here as eddies we analyze 10 years of measurements of these ssh fields and concurrent satellite measurements of upper ocean chl to show that these eddies exert a strong influence on the chl field thus requiring reassessment of the mechanism for the observed covariability of ssh and chl on time scales longer than 2 to 3 weeks the dominant mechanism is shown to be eddy induced horizontal advection of chl by the rotational velocities of the eddies

aquarius reveals salinity structure of tropical instability waves 1 sea surface salinity sss measurements from the aquarius sac d satellite during september december 2011 provide the first satellite observations of the salinity structure of tropical instability waves tiws in the pacific the related sss anomaly has a magnitude of approximately 0 5 psu different from sea surface temperature sst and sea surface height anomaly ssha where tiw related propagating signals are stronger a few degrees away from the equator the sss signature of tiws is largest near the equator in the eastern equatorial pacific where salty south pacific water meets the fresher inter tropical convergence zone water the dominant westward propagation speed of sss near the equator is approximately 1 m s this is twice as fast as the 0 5 m s tiw speed widely reported in the literature typically from sst and ssha away from the equator this difference is attributed to the more dominant 17 day tiws near the equator that have a 1 m s dominant phase speed and the stronger 33 day tiws away from the equator that have a 0 5 m s dominant phase speed the results demonstrate the important value of aquarius in studying tiws

geographical variability of the first baroclinic rossby radius of deformation global 1 83 18 climatologies of the first baroclinic gravity wave phase speed c1 and the rossby radius of deformation l1 are computed from climatological average temperature and salinity profiles these new atlases are compared with previously published 5 83 58 coarse resolution maps of l1 for the northern hemisphere and the south atlantic and with a 1 83 18 fine resolution map of c1 for the tropical pacific it is concluded that the methods used in these earlier estimates yield values that are biased systematically low by 5 15 owing to seemingly minor computational errors geographical variations in the new high resolution maps of c1 and l1 are discussed in terms of a wkb approximation that elucidates the effects of earth rotation stratification and water depth on these quantities it is shown that the effects of temporal variations of the stratification can be neglected in the estimation of c1 and l1 at any particular location in the world ocean this is rationalized from consideration of the wkb approximation

interglacials of the last 800 000 years interglacials including the present holocene period are warm low land ice extent high sea level end members of glacial cycles based on a sea level definition we identify eleven interglacials in the last 800 000 years a result that is robust to alternative definitions data compilations suggest that despite spatial heterogeneity marine isotope stages mis 5e last interglacial and 11c 400 ka ago were globally strong warm while mis 13a 500 ka ago was cool at many locations a step change in strength of interglacials at 450 ka is apparent only in atmospheric co2 and in antarctic and deep ocean temperature the onset of an interglacial glacial termination seems to require a reducing precession parameter increasing northern hemisphere summer insolation but this condition alone is insufficient terminations involve rapid nonlinear reactions of ice volume co2 and temperature to external astronomical forcing the precise timing of events may be modulated by millennial scale climate change that can lead to a contrasting timing of maximum interglacial intensity in each hemisphere a variety of temporal trends is observed such that maxima in the main records are observed either early or late in different interglacials the end of an interglacial glacial inception is a slower process involving a global sequence of changes interglacials have been typically 10 30 ka long the combination of minimal reduction in northern summer insolation over the next few orbital cycles owing to low eccentricity and high atmospheric greenhouse gas concentrations implies that the next glacial inception is many tens of millennia in the future

transient simulation of the last glacial inception part ii sensitivity and feedback analysis the sensitivity of the last glacial inception around 115 kyr bp 115 000 years before present to different feedback mechanisms has been analysed by using the earth system model of intermediate complexity climber 2 climber 2 includes dynamic modules of the atmosphere ocean terrestrial biosphere and inland ice the last of which was added recently by utilising the three dimensonal polythermal icesheet model sicopolis we performed a set of transient experiments starting at the middle of the eemiam interglacial and ran the model for 26 000 years with timedependent orbital forcing and observed changes in atmospheric co 2 concentration co2 forcing the role of vegetation and ocean feedback co 2 forcing mineral dust thermohaline circulation and orbital insolation are closely investigated in our model glacial inception as a bifurcation in the climate system appears in nearly all sensitivity runs including a run with constant atmospheric co 2 concentration of 280 ppmv a typical interglacial value and simulations with prescribed present day seasurface temperatures or vegetation cover although the rate of the ice sheets growth is smaller than in the case of the fully in teractive model only if we run the fully interactive model with constant present day insolation and apply present day co 2 forcing does no glacial inception appear at all this implies that within our model the orbital forcing alone is sufficient to trigger the interglacial glacial transition while vegetation ocean and atmospheric co2 concentration only provide additional although important positive feedbacks in addition we found that possible reorganisations of the thermohaline circulation influence the distribution of inland ice

evidence for early warming and cooling in north atlantic surface waters during the last interglacial in depth analysis of planktic foraminiferal census data paired with 18o records of specific indicator species provides new insight into the surface ocean evolution of the northeast atlantic during the previous interglacial warm period oxygen isotope stage ois 5e full interglacial conditions existed at the study site for a maximum of only 8 kyr between 125 and 117 ka highest sea surface temperatures ssts occurred during early ois 5e concomitant with high summer insolation but after the main phase of ice sheet melting of the preceding glaciation saalian this early peak sst interval is marked by the appearance of tropical subtropical species and lasted for 4 kyr until 121 ka as corroborated by a major change in planktic 18o relative stability in global ice volume continued for another 3 4 kyr before ssts dropped further toward the next stadial during early ois 5e the situation of the surface water vertical structure appears to have been different from the early holocene for ois 5e it is therefore suggested that the particular melting history of late saalian ice had a long lasting and profound effect on both postdeglacial surface water mass configuration in the north atlantic and heat moisture transfer into europe

late eemian warming in the nordic seas as seen in proxy data and climate models 1 we analyze a transient simulation of the last glacial inception in a climate model of intermediate complexity focusing on sea ice ocean circulation dynamics in the north atlantic and nordic seas as northern high latitude summer insolation decreases toward the end of the eemian interglacial arctic sea ice export to the north atlantic increases this surface fresh water transport weakens deep water formation in the north atlantic and the near surface circulation of the subpolar gyre as a consequence the relative contribution of subpolar gyre waters to the atlantic inflow into the nordic seas is reduced giving way to more warm and saline subtropical waters from the north atlantic current we thus find an episode of relatively high heat and salt transport into the nordic seas during the last glacial inception between 119 000 and 115 000 years before present this stabilizes deep ocean convection in the region and warms scandinavia during a phase of low insolation these findings are in good agreement with proxy data from the nordic seas and north atlantic at the end of the warm interval sea surface temperature drops by about 3 c marking the onset of large scale glacier growth over scandinavia

spatio temporal variability of the equatorial front in the eastern tropical pacific from remote sensing salinity data 2010 2015 abstract in the eastern pacific the equatorial front ef separates the relatively cold and salty equatorial surface water to the south from the relatively warm and fresh surface tropical water to the north although previous studies have succinctly described the main ef characteristics little is known about its spatial pattern and temporal variability beyond seasonal scale in this study we used 5 years of remote sensing sea surface salinity sss data acquired by smos in a synoptic and continuous manner to describe the spatio temporal variability of the haline ef hef after validating the sss satellite dataset with concomitant in situ data we developed an algorithm based on maximum sss gradients to automatically identify the hef position on every smos sss map this algorithm applied to the 4 day resolution smos sss product allows us to investigate the spatio temporal variability of the hef between 2010 and 2015 seasonally west of the galapagos islands the hef is centered at 2 n and shows relatively weak meridional displacements in contrast east of the galapagos archipelago the hef varies on average between 4 s in spring and 2 n in autumn at intraseasonal scales the hef shows meridional fluctuations of 1 25 around its average position these intraseasonal fluctuations are partly related to kelvin waves which was more noticeable since 2014 over the 5 year studied period the hef position showed a northward trend of 0 3 0 4 latitudinal degrees per year between 2010 and 2015 however the relatively short time series does not permit to investigate whether this low frequency trend is due to long term variability or interdecadal fluctuations

intraseasonal variability of surface salinity in the eastern tropical pacific associated with mesoscale eddies strong variability in sea surface salinity sss in the eastern tropical pacific etpac on intraseasonal to interannual timescales was studied using data from the soil moisture and ocean salinity soil moisture active passive and aquarius satellite missions a zonal wave number frequency spectral analysis of sss reveals a dominant timescale of 50 180days and spatial scale of 8 degrees 20 degrees of longitude with a distinct seasonal cycle and interannual variability this intraseasonal sss signal is detailed in the study of 19 individual etpac eddies over 2010 2016 identified by their sea level anomalies propagating westward at a speed of about 17cm s etpac eddies trap and advect water in their core westward up to 40 degrees of longitude away from the coast the sss signatures of these eddies with an average anomaly of 0 5 pss magnitude difference from ambient values enable the study of their dynamics and the mixing of their core waters with the surroundings three categories of eddies were identified according to the location where they were first tracked 1 in the gulf of tehuantepec 2 in the gulf of papagayo and 3 in the open ocean near 100 degrees w 12 degrees n they all traveled westward near 10 degrees n latitude category 3 is of particular interest as eddies seeded in the gulf of tehuantepec grew substantially in the vicinity of the clipperton fracture zone rise and in a region where the mean zonal currents have anticyclonic shear the evolution of the sss signature associated with the eddies indicates the importance of mixing to their dissipation

surface area changes of glaciers in the tibetan plateau interior area since the 1970s using recent landsat images and historical maps the tibetan plateau interior area tpia often termed the qangtang plateau is distinguished by many dome like mountains higher than 6000 m a s l these mountains provide favourable conditions for the development of ice caps and glaciers of extreme continental subpolar type according to historical topographic maps 1959 80 and recent landsat images 2004 11 continuous retreat was observed and the glacierized part of this area decreased by 9 5 0 27 a 1 with respect to the total glacier area of 8036 4 km 2 in the 1970s glaciers in the zhari namco basin have experienced the highest area shrinkage with a reduction rate of 0 72 a 1 while the smallest reduction occurred in bangong co 0 12 a 1 and dogai coying basins 0 11 a 1 a regional gradient of area loss was found with a larger decrease in the south and a smaller decrease in the north of the plateau comparisons indicate glaciers have experienced smaller shrinkage in the tpia than in surrounding regions glacier shrinkage in the tpia is mainly attributed to an increase in air temperature while precipitation glacier size and positive difference of glaciation also played an important role

global ice volume fluctuations north atlantic ice rafting events and deep ocean circulation changes between 130 and 70 ka multiproxy data from north atlantic deep sea sediment core neap18k provide a detailed record of climate through oxygen isotope stage ois 5 seven distinct large scale episodes of ice rafting c25 c19 were identified between 126 and 70 ka global ice volume reconstructions based on high resolution benthic 18 o records indicate that major ice rafting events were not confined to ice volume maxima at ois 5d and 5b but also occurred during periods of ice sheet growth and disintegration however iceberg discharges were restricted to times when sea levels were 40 65 m below present values ice rafting episode c25 the first large scale cooling of mid atlantic surface waters after the last interglacial occurred during the gradual buildup of continental ice sheets at the ois 5e 5d transition major ice sheet collapses allied to ice rafting events c24 and c21 were associated with rapid sea level increases of 20 and 40 m respectively suborbital climatic fluctuations in the neap18k sedimentary record denoted by prominent 7 5 4 5 and 3 k y cyclicities appear to correlate with both greenland atmospheric temperatures and changes in thermohaline circulation patterns inferred from benthic 13 c values and hence provide clear evidence of a highly interconnected north atlantic climatic regime during ois 5

east pacific ocean eddies and their relationship to subseasonal variability in central american wind jets subseasonal variability in sea surface height ssh over the east pacific warm pool off central america is investigated using satellite observations and an eddy resolving ocean general circulation model ssh variability is organized into two southwest tilted bands on the northwest flank of the tehuantepec and papagayo wind jets and collocated with the thermocline troughs eddy like features of wavelength similar to 600 km propagate southwestward along the high variance bands at a speed of 9 13 cm s wind fluctuations are important for eddy formation in the gulf of tehuantepec with a recurring interval of 40 90 days when forced by satellite wind observations the model reproduces the two high variance bands and the phase propagation of the tehuantepec eddies our observational analysis and model simulation suggest the following evolution of the tehuantepec eddies on the subseasonal timescale in response to the gap wind intensification a coastal anticyclonic eddy forms on the northwest flank of the wind jet and strengthens as it propagates offshore in the following two to three weeks an energetics analysis based on the model simulation indicates that besides wind work barotropic and baroclinic instabilities of the mean flow are important for the eddy growth both observational and model results suggest a re intensification of the anticyclonic eddy in response to the subsequent wind jet event off papagayo ocean eddy formation is not well correlated with local wind jet variability in both the gulfs of tehuantepec and papagayo subseasonal ssh variability is preferentially excited on the northwest flank of the wind jet factors for this asymmetry about the wind jet axis as well as the origins of wind jet variability are discussed

holocene sea subsurface and surface water masses in the fram strait comparisons of temperature and sea ice reconstructions highlights holocene sea subsurface temperatures after husum hald 2012 estimated from planktic foraminifer fauna in e fram strait biomarkers and ip25 derived indices including dip25 indicate surface water variability delayed onset of early holocene conditions in subsurface 10 6 ka compared to surface 11 7 ka water conditions warm atlantic layer likely occupied uppermost 200 m in eastern fram strait between 10 and 9 ka diverging late holocene trends in surface and subsurface conditions linked to presence of strong pycnocline stratification abstract two high resolution sediment cores from eastern fram strait have been investigated for sea subsurface and surface temperature variability during the holocene the past ca 12 000 years the transfer function developed by husum and hald 2012 has been applied to sediment cores in order to reconstruct fluctuations of sea subsurface temperatures throughout the period additional biomarker and foraminiferal proxy data are used to elucidate variability between surface and subsurface water mass conditions and to conclude on the holocene climate and oceanographic variability on the west spitsbergen continental margin results consistently reveal warm sea surface to subsurface temperatures of up to 6 c until ca 5 cal ka bp with maximum seawater temperatures around 10 cal ka bp likely related to maximum july insolation occurring at that time maximum atlantic water aw advection occurred at surface and subsurface between 10 6 and 8 5 cal ka bp based on both foraminiferal and dinocyst temperature reconstructions probably a less stratified ice free nutrient rich surface ocean with strong aw advection prevailed in the eastern fram strait between 10 and 9 cal ka bp weakened aw contribution is found after ca 5 cal ka bp when subsurface temperatures strongly decrease with minimum values between ca 4 and 3 cal ka bp cold late holocene conditions are furthermore supported by high planktic foraminifer shell fragmentation and high 18o values of the subpolar planktic foraminifer species turborotalita quinqueloba while ip25 associated indices as well as dinocyst data suggest a sustained cooling due to a decrease in early summer insolation and consequently sea ice increase since about 7 cal ka bp in surface waters planktic foraminiferal data including stable isotopes indicate a slight return of stronger subsurface aw influx since ca 3 cal ka bp the observed decoupling of surface and subsurface waters during the later holocene is most likely attributed to a strong pycnocline layer separating cold sea ice fed surface waters from enhanced subsurface aw advection this may be related to changes in north atlantic subpolar versus subtropical gyre activity

variability in surface and deep water conditions in the nordic seas during the last interglacial period abstract stable isotope foraminifera and ice rafted detritus ird records covering the last interglacial the eemian from 7 sediment cores in a transect from the norwegian to the greenland sea are presented the percentages of neogloboquadrina pachyderma s and globigerina quinqueloba foraminiferal content and to some extent planktonic stable isotope records demonstrate marked regional changes in surface water conditions importantly the variability in the abundances of subpolar foraminifera and foraminiferal content are not coherent implying that these two types of proxies fluctuated independently of each other and most likely reflect changes in sea surface temperature and surface water carbonate productivity respectively paleoceanographic reconstructions demonstrate significant movements of the oceanographic fronts at the warmest periods the arctic front was located far west of the present day location at least within the iceland sea region at 126 125 ka this was most probably due to a stronger or more westerly located norwegian current within the later warm intervals higher heat flux to the western part of the basin reflects a combination of a stronger irminger current and or a weaker east greenland current during the main cold spell at 124 ka a diffuse arctic front had a more southeasterly location than today and intrusion of atlantic surface waters was probably limited to a narrow corridor in the eastern norwegian sea a general correspondence between minima in sea surface temperatures and light benthic 18o may indicate enhanced influx of freshwater to the basin within the cold events at least in the norwegian sea we find some evidence that the changes in surface water conditions are associated with changes in deep water ventilation the majority of the fluctuations may be related to occasional breakdown or reduction of the thermohaline circulation within the nordic seas in the earliest eemian this could result from meltwater forcing during the remaining part of the last interglacial the fine balance between temperature and salinity which the deep water formation is depending on may have been disturbed by periodic increases in fresh water supply or variable influx of warm atlantic surface waters

deep sea records from the southeast labrador sea ocean circulation changes and ice rafting events during the last 160 000 years 1 results from two deep sea cores from northeast of newfoundland at 1251 and 2527 m water depth respectively indicate that during the time period from 160 000 to 10 000 years bp ice rafting events in the labrador sea were accompanied by rapid variations in deep and surface water circulation twelve ice rafting events occurred each coinciding with high concentrations of detrital carbonate and oxygen isotopic depletion of both surface and bottom waters eleven of these can be correlated with the north atlantic heinrich events h1 h11 the remaining very conspicuous ice rafting event took place early in mis substage 5e at a time when the planktic faunal assemblage suggests marked warming of the sea surface in the shallower core benthic delta 13 c values rise from a minimum during the deglaciation to peak substage 5e values following the last ice rafting event indicating that the ventilation of intermediate depths was renewed after the deglaciation was complete and continued throughout substage 5e the benthic foraminifera suggest that this well ventilated water mass was comparable to the modern labrador sea water lsw the benthic faunas suggest that a relatively warm intermediate water mass entered the se labrador sea during heinrich events generally low benthic delta 13 c values indicate that this water mass was poorly ventilated and rich in inorganic nutrients isotope data and benthic faunal distributions indicate that north atlantic deep water nadw formed in the norwegian greenland sea reached the se labrador sea between the heinrich events

possible role of atmosphere biosphere interactions in triggering the last glaciation we coupled a global biome model iteratively with an atmospheric general circulation model to study the possible role of vegetation in the climate system at the time of glacial inception 115 000 years ago orbital forcing alone was not sufficient to initiate glaciation when other components of the climate system were kept as present atmospheric composition oceans biosphere and cryosphere summers were however cold enough to induce major vegetation shifts in high northern latitudes southward migration of the boreal forest tundra limit helped to create favourable conditions for continental ice sheet growth with increasing snow depth and duration in labrador arctic canada and northern western fennoscandia these results support a role for biogeophysical feedback in initiating glaciations

coherent deep flow variation in the iceland and american basins during the last interglacial the first direct evidence that the deepflow speed of north atlantic deep water nadw in the south iceland and north americanbasins declined dramatically over a period of a few hundred years at about 120 000 years ago is presented the flow rate inferred from silt grain size then rose into the subsequent cool period stage 5d these changes are clear and synchronous in records from both locations these circulation events are recorded less markedly in chemical and isotopic proxies for the nutrient status of water masses the congruence of flowvariation and hydrography at the two separated sites suggests they are primarily controlled by variation in the deep thermohaline circulation

intermediate water links to deep western boundary current variability in the subtropical nw atlantic during marine isotope stages 5 and 4 records from ocean drilling program sites 1057 and 1059 2584 m and 2985 m water depth respectively have been used to reconstruct the behavior of the deep western boundary current dwbc on the blake outer ridge bor from 130 to 60 kyr b p marine isotope stage mis 5 and the 5 4 transition site 1057 lies within labrador sea water lsw but close to the present day boundary with lower north atlantic deep water lnadw while site 1059 lies within lnadw high resolution sortable silt mean inline equation grain size and benthic 13c records were obtained and changes in the dwbc intensity and spatial variability were inferred comparisons are made with similar proxy records generated for the holocene from equivalent depth cores on the bor during mis 5e inline equation evidence at site 1057 suggests slower relative flow speeds consistent with a weakening and a possible shoaling of the lsw sourced shallower limb of the dwbc that occupies these depths today in contrast the paleocurrent record from the deeper site suggests that the fast flowing deep core of the dwbc was located close to its modern depth below 3500 m during this interval the benthic 13c suggests little chemical stratification of the water column and the presence of a near uniform lnadw dominated water mass after 111 kyr b p the inline equation record at site 1057 increases to reach values similar to site 1059 for the rest of mis 5 the strengthening of flow speeds at the shallow site may correspond to the initiation of glacial north atlantic intermediate water formation also suggested by a divergence in the benthic 13c records with site 1057 values increasing to 1 2 coupled suborbital oscillations in dwbc flow variability and paleohydrography persisted throughout mis 5 comparison of these data with planktonic 18o records from the sites and alkenone derived sea surface temperature sst estimates from the nearby bermuda rise suggest a hitherto unrecognized degree of linkage between oscillations in subtropical north atlantic sst and dwbc flow

reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years the record of glacier fluctuations in western scandinavia as reconstructed from continental data has been correlated with records of ice rafted detritus ird from well dated sediment cores from the norwegian sea covering the past 150 000 yr b p the input of ird into the ocean is used as a proxy for ice sheet advances onto the shelf and thus for the calibration of a glaciation curve the marine results generally support land based reconstructions of glacier fluctuations and improve the time control on glacial advances the saalian ice sheet decayed very rapidly approximately 125 000 yr b p in the early weichselian a minor but significant ird maximum indicates the presence of icebergs in isotope substage 5b especially between 95 000 and 83 000 yr b p reduced amounts of calcareous nannofossils indicate that surface waters were influenced by meltwater discharges during isotope substages 5d and 5b an extensive build up of inland ice began again during isotope stage 4 but maximum glaciation was reached only in early stage 3 58 000 53 000 yr b p marine sediments have minimum carbonate content indicating strong dilution by lithogenic ice rafted material generally the ird accumulation rate was considerably higher in stages 4 2 than in stage 5 a marked peak in ird accumulation rates from 47 000 to 43 000 yr b p correlates well with a second middle weichselian ice sheet advance dated by the laschamp olby paleomagnetic event minimum ice extent during the alesund interstade 38 500 32 500 yr b p and several glacial oscillations during the late weichselian are also seen in the ird record of several late weichselian glacial oscillations on the shelf at least four correspond to the north atlantic heinrich events ice sheet behavior was either coupled or linked by external forcing during these events whereas internal ice sheet mechanisms may account for the noncoherent fluctuations

sea level variability in the eastern tropical pacific as observed by topex and tropical ocean global atmosphere tropical atmosphere ocean experiment sea surface height measurements from the topex altimeter and dynamic height from tropical ocean global atmosphere tropical atmosphere ocean toga tao moorings are used to explore sea level variability in the northeastern tropical pacific ocean after the annual harmonic is removed there are two distinct bands of variability one band is centered at 5 n to 7 n and extends from 165 w to 110 w and the other band is centered at 10 n to 12 n and extends from 120 w to the coast of central america the correspondence between the two independent observation data sets at 5 n is excellent with correlations of about 90 the variability at 5 7 n is identified as instability waves formed just south of the north equatorial countercurrent during the months of july through march wave amplitudes are largest in the range of longitudes 160 140 w where they can exceed 10 cm the waves disappear when the equatorial current system weakens during the months of march through may the variability at 11 n in 1993 has the form of anticyclonic eddies these eddies propagate westward at a speed of about 17 cm s 1 consistent with the dispersion characteristics of free rossby waves the eddies are shown to have their origin near the coast of central america during northern fall and winter their formation seems to result from intense wind bursts across the gulfs of tehuantepec and papagayo which generate strong anticyclonic ocean eddies the disappearance of the eddies in the summer of 1993 coincides with the seasonal intensification of equatorial currents thus the variability at 11 n has very little overlap in time with the variability at 5 n

evaluation of glacier changes in high mountain asia based on 10 year grace rl05 models in this paper 10 years of time variable gravity data from the gravity recovery and climate experiment release 05 have been used to evaluate the glacier melting rate in high mountain asia hma using a new computing scheme i e the space domain inverse method we find that in hma area there are three different kinds of signal sources that should be treated together the two generally accepted sources glacier melting and india underground water depletion are estimated to change at the rate of 35 0 5 8 gt yr 0 09 mm yr sea level rising and 30 6 5 0 gt yr respectively the third source is the remarkable positive signal 30 gt yr in the inner tibetan plateau which is challenging to explain further we have found that there is a 5 year undulation in pamir and karakoram which can explain the controversies of the previous studies on the glacier melting rate here this 5 year signal can be explained by the influence of arctic oscillation and el nino southern oscillation

topographic sensitivity studies with a bryan cox type ocean model abstract this paper describes a series of four experiments each run for 10 years at 1 1 resolution on a north atlantic domain designed to illuminate the sensitivity of a bryan cox type ocean model to changes in the representation of the ridges that restrict the flow of dense deep water out of the greenland iceland norway gin basin in reality much of the outflow takes place through narrow sills which are subgrid scale in the model and small changes in the model topography to reflect these sills have a large impact on the outflow and on the compensating inflow of warm north atlantic water the circulation of the gin basin is dramatically changed depending on the amount of this inflow with no inflow the basin cools and freshens as would be expected whereas with too much inflow it becomes warm salty and homogeneous to great depths moreover the small changes in topography have wider implications for the simulation the presence or absence of dense overflows has a great impact on the mixed

last interglacial mis5e hydrographic shifts linked to meltwater discharges from the east greenland margin abstract proximal evidence of the surface ocean response to size reduction of the greenland ice sheet gis during the last interglacial mis5e and preceding glacial termination t2 remains largely elusive using a new sediment record from the western iceland sea the behavior of the northeastern gis and its relation to the subpolar north atlantic surface hydrography is examined extremely light oxygen isotopic 18o values are found off central east greenland during early mis5e and point to enhanced meltwater release potentially from the northeastern sector of the gis data from downstream the cold east greenland current egc and its eastward branches suggest a far reaching effect of this meltwater not only in the nordic seas but also in the se labrador sea in particular whereas an early mis5e warming at 128 5 126 5 ka in the two regions coincided with the relative reduction of meltwater input into the egc the subsequent cooling noted at 126 5 ka followed a renewed major freshwater event off central east greenland our data further indicate persistent freshwater influence from the east greenland margin over the entire mis5e interval and in addition also reveal a late mis5e meltwater event the latter event occurred just prior to the last glacial inception and emphasizes the importance of greenland meltwater as forcing factor on interglacial climates

climate records and changes in deep outflow from the norwegian sea 150 55 ka in order to contribute to our understanding of the linkage between climate and ocean circulation we have studied benthic foraminifera from near the northern end of the faeroe shetland channel covering isotope stages 6 to lower stage 3 150 55 ka our records demonstrate shifts between recurring assemblages which on millennial timescales monitor the outflow history of norwegian sea deep water the records show that the outflow is closely linked to the climate of the region as documented in the greenland ice cores outflow was relatively strong during all major warmer interstadials whereas there was no outflow during the colder stadials during isotope substage 5e outflow was stable for 10 12 kyr with significant changes at the beginning and end only

characteristics of wind generated rings in the eastern tropical pacific ocean eddies are generated in the eastern tropical pacific 3 s 23 n 75 105 w by winds blowing through central american mountain passes from the atlantic we used coastal zone color scanner czcs and advanced very high resolution radiometer avhrr satellite imagery complemented with monthly in situ sea surface temperature and wind series from the comprehensive ocean atmosphere data set coads to study these eddies and their effect on pigment concentrations in the region pigment values in the gulf of tehuantepec generally reach higher values in november march before those in the gulf of papagayo the eddies generated in the gulf of tehuantepec are associated with passages of cold fronts across the gulf of mexico from the north while the eddies off papagayo and panama are associated with increases in trade wind intensity czcs images showed larger numbers of eddies per season than have been previously reported on the basis of in situ and avhrr observations or numerical simulations we counted 13 eddies in 1979 1980 8 in 1984 1985 and 6 in 1985 1986 the eddies transfer both energy and biological constituents from the continental margin to the offshore tropical pacific the eddies frequently moved distances in excess of 1500 km from their point of origin both anticyclonic and cyclonic eddies are generated but in general there are more anticyclones anticyclonic eddies generally moved to the southwest some cyclonic eddies moved to the south and southeast along the central american coast and appeared to be trapped by the cyclonic costa rica thermal dome eddies traveled at speeds varying between 9 and 21 cm s 1 and had diameters of 100 500 km phytoplankton concentrations associated with the eddies varied from 2 to 10 mg m 3 within 70 km of the coast to 1 mg m 3 up to 600 km of the coast between late april and october fewer eddies were observed and phytoplankton concentrations were lower 0 25 mg m 3 and more uniform over the region

observations of the dispersion characteristics and meridional sea level structure of equatorial waves in the pacific ocean spectral techniques applied to altimetry data are used to examine the dispersion relation and meridional sea level structure of wavelike variability with periods of about 20 to 200 days in the equatorial pacific ocean zonal wavenumber frequency power spectra of sea surface height when averaged over about 7 s 7 n exhibit spectral peaks near the theoretical dispersion curves of first baroclinic mode equatorial kelvin and rossby waves there are distinct statistically significant ridges of power near the first and second meridional mode rossby wave dispersion curves sea level variability near the theoretical kelvin wave and first meridional mode rossby wave dispersion curves is dominantly but not perfectly symmetric about the equator while variability near the theoretical second meridional mode rossby wave dispersion curve is dominantly antisymmetric these results are qualitatively consistent with expectations from classical or shear modified theories of equatorial waves the meridional structures of these modes resemble the meridional modes of equatorial wave theory but there are some robust features of the meridional profiles that were not anticipated the meridional sea level structure in the intraseasonal kelvin wave band closely resembles the theoretically expected gaussian profile but sea level variability coherent with that at the equator is detected as far away as 11 75 s possibly as a result of the forced nature of these kelvin waves both first and second meridional mode rossby waves have larger amplitude in the northern hemisphere the meridional sea level structure of tropical instability waves closely resembles that predicted by lyman et al using a model linearized about a realistic equatorial zonal current system

mesoscale variability in the northeastern tropical pacific forcing mechanisms and eddy properties 1 the generation mechanisms and properties of the mesoscale eddies in the northeastern tropical pacific netp are studied using a series of numerical solutions and satellite observations the spatial and temporal resolution of mountain wind jets over the gulfs of tehuantepec and papagayo are essential for an accurate modeling of the regional mesoscale variability three previously proposed eddy generation mechanisms are the local transient wind forcing the combined low frequency wind and boundary forcing and the remote equatorial kelvin wave forcing in our model the transient wind forcing was represented by wind fields with synoptic variability and the remote equatorial kelvin wave forcing by 5 day open boundary conditions with interannual variability solutions with and without high frequency forcings are contrasted to evaluate the contributions of the three mechanisms the combined low frequency wind and boundary forcing is the primary eddy forcing mechanism in the netp in the tehuantepec region the high frequency wind forcing contributes more to the mesoscale variability than the remote equatorial kelvin wave forcing while in the papagayo region their contributions are comparable eddies in the tehuantepec and papagayo regions are larger in both amplitude and size and are more likely to deflect equatorward than eddies in the rest of the netp the maximum temperature anomaly of eddies is at around 50 m depth eddies with lifetimes 6 weeks are more likely anticyclonic while eddies with lifetimes 6 weeks are more likely cyclonic the anticyclone dominance for large amplitude long lived eddies is the combined consequence of wind driven asymmetric dipole spin up and the evolutionary fragility of large amplitude cyclones

signature of mesoscale eddies in satellite sea surface salinity data a persistent signature of coherent mesoscale eddies in sea surface salinity sss is revealed by analyzing the relationship between satellite sss and sea surface height ssh variability in an eddy following reference frame our analysis focuses on mid ocean eddies in two representative regions the southern indian ocean and the north atlantic subtropical gyre the resulting composite averages reveal a clear signature of mesoscale eddies in satellite sss with typical sss anomalies of 0 03 0 05 psu the spatial structure of eddy induced sss perturbations can be characterized as a superposition of a dipole structure arising from horizontal advection of the background sss gradient by eddy velocity field and a monopole structure related to the eddy core the observed relationships between sss and ssh anomalies are used to provide a regional assessment of the role of mesoscale eddies in the ocean freshwater transport in the north atlantic subtropical gyre this article is protected by copyright all rights reserved

relation of subtropical atlantic temperature high latitude ice rafting deep water formation and european climate 130 000 60 000 years ago abstract a new high resolution record of sea surface temperature from the subtropical western north atlantic documents a series of abrupt coolings within marine isotope stage 5 which can be objectively correlated with marine core evidence for increased ice sheet discharge at subpolar latitudes and reduced north atlantic deep water formation these results indicate that ice sheet forcing of deep ocean circulation influenced surface temperatures over much of the north atlantic a proposed correlation to the pollen record of grande pile france indicates that each cold event seen in the pollen sequence has a unique counterpart in the record of subtropical ocean temperature if this correlation is correct it suggests that the warmest part of the european eemian ended suddenly in response to oceanographic changes and that the subsequent post temperate phase of the eemian extended well into the interval of ice sheet growth corresponding to marine isotope substage 5d

simulating the amplification of orbital forcing by ocean feedbacks in the last glaciation according to milankovitch theory the lower summer insolation at high latitudes about 115 000 years ago allowed winter snow to persist throughout summer leading to ice sheet build up and glaciation1 but attempts to simulate the last glaciation using global atmospheric models have failed to produce this outcome when forced by insolation changes only2 3 4 5 these results point towards the importance of feedback effects for example through changes in vegetation or the ocean circulation for the amplification of solar forcing6 7 8 9 here we present a fully coupled ocean atmosphere model of the last glaciation that produces a build up of perennial snow cover at known locations of ice sheets during this period we show that ocean feedbacks lead to a cooling of the high northern latitudes along with an increase in atmospheric moisture transport from the equator to the poles these changes agree with available geological data10 11 12 13 14 15 and together they lead to an increased delivery of snow to high northern latitudes the mechanism we present explains the onset of glaciation which would be amplified by changes in vegetation in response to weak orbital forcing

influence of the atlantic subpolar gyre on the thermohaline circulation during the past decade record high salinities have been observed in the atlantic inflow to the nordic seas and the arctic ocean which feeds the north atlantic thermohaline circulation thc this may counteract the observed long term increase in freshwater supply to the area and tend to stabilize the north atlantic thc here we show that the salinity of the atlantic inflow is tightly linked to the dynamics of the north atlantic subpolar gyre circulation therefore when assessing the future of the north atlantic thc it is essential that the dynamics of the subpolar gyre and its influence on the salinity are taken into account

variation of labrador sea water formation over the last glacial cycle in a climate model of intermediate complexity abstract the variation of north atlantic deep water nadw formation over the last glacial cycle from oxygen isotopic substage 5e ois 5e the eemian to future global warming projections is investigated using the uvic earth system climate model the results are compared with available micropaleontological and stable isotope proxy paleo reconstructions equilibrium simulations for the eemian 125 kyr bp and the last glacial maximum lgm 21 kyr bp both reveal the absence of labrador sea water lsw formation although nadw formation still occurs albeit at a reduced rate relative to the modern times for the eemian the location of convection in the eastern north atlantic is similar to the present although it is generally shallower and less extensive in the case of the lgm deep convection has moved southward to the western coast of europe and is much more localised the inferred inception of a modern like circulation slightly before 7 kyr bp revealed by proxy reconstructions is not captured by the model unless the meltwater forcing from the laurentide ice sheet is applied in a long transient simulation this raises questions concerning the applicability of equilibrium simulations in capturing the early holocene climate in all global warming projections the lsw formation initially ceases as atmospheric co 2 rises but recovers once the level is held fixed in the atmosphere convection in the north extends further into the nordic seas as the sea ice edge retreats in all simulations convection remains active in the eastern north atlantic with its latitude depending on the position of the sea ice edge suggesting that the formation of lower nadw is a robust feature of late quaternary climate as the labrador sea is found to be very sensitive to the freshwater forcing it suggests that this region represents an ideal location for the concentration of observational studies to monitor a possible oceanic response to anthropogenic climate change

comment on reflection of scandinavian ice sheet fluctuations in norwegian sea sediments during the past 150 000 years by karl heinz baumann klas s lackschewitz jan mangerud robert f spielhagen thomas c w wolf welling rudiger henrich and heidemarie kassens

multiproxy fossil comparison reveals contrasting surface ocean conditions in the western iceland sea for the last two interglacials abstract dinoflagellate cyst dinocyst coccolith and planktic foraminiferal assemblages from a core in the western iceland sea were used to reconstruct and compare the surface ocean developments of the holocene and the last interglacial marine isotopic stage or mis 5e while increasing subpolar planktic foraminifers from 10 ka indicate subsurface warming peaking around 7 5 ka the dinocyst data suggest that the uppermost ocean remained dominated by cold waters until 6 5 ka a reduced advection of cold polar waters through the east greenland east icelandic current thereafter entailed warmest and most saline holocene conditions between 6 5 and 5 ka in turn followed by a general cooling trend by contrast both planktic foraminifers and dinocysts show an increased presence of atlantic type waters from 122 ka onward resulting in a mis 5e thermal optimum around 120 5 ka nonetheless occasional freshwater input from melting drift ice created stratified but also seasonally variable conditions during this first half of mis 5e this stratification signature disappeared at 120 ka when a marked repositioning of the oceanographic fronts occurred slightly colder conditions are indicated by both phyto and zooplankton from there on until the end of mis 5e around 117 ka a late mis 5e cooling at the iceland plateau is opposite to a late mis 5e optimum observed in the eastern nordic seas this regional difference is likely explained by various feedback mechanisms following the major reorganisation of the oceanic fronts at 120 ka the holocene and mis 5e interglacial variability is not reflected in the quasi monospecific coccolith assemblages and illustrates the low sensitivity of living coccolithophore communities to subtle temperature changes in the low temperature regions of the nordic seas overall quite different surface water properties appear to have characterised both interglacial intervals with a higher share of warm atlantic elements in the planktic communities during mis 5e this suggests a higher contribution of atlantic waters in the southwestern nordic seas probably due to a more northward expansion of the irminger current under weakened polar east greenland east icelandic currents such a reduced influence of polar waters in the southwestern nordic seas may thus explain other evidence for relatively warm conditions in mis 5e all around southern greenland

north atlantic current and european environments during the declining stage of the last interglacial this paper provides a tentative reconstruction of environmental shifts in europe associated with changes of the north atlantic current and related meridional sea surface temperature sst gradients during most of the eemian interglacial ca 126 115 ka the north atlantic current extended far north into the nordic seas and european environments were comparable to those of the holocene however ca 115 ka an sst drop in the nordic seas marked a southward displacement of the north atlantic current this hydrographic shift was associated with substantial cooling in northern europe and drier conditions in the mediterranean region the polar timberline retreated southward from 69 n in northernmost scandinavia to 52 n in central europe and thermophilous deciduous trees became extinct north of the 48th parallel woodlands persisted in southern europe for another 5 k y well into marine isotope substage 5d these conditions indicate steep vegetation and climate gradients at the inception of the last glacial

modulation of the ganges brahmaputra river plume by the indian ocean dipole and eddies inferred from satellite observations the bay of bengal receives large amounts of freshwater from the ganga brahmaputra gb river during the summer monsoon the resulting upper ocean freshening influences seasonal rainfall cyclones and biological productivity sparse in situ observations and previous modeling studies suggest that the east india coastal current eicc transports these freshwaters southward after the monsoon as an approximately 200 km wide 2 000 km long river in the sea along the east indian coast sea surface salinity sss from the soil moisture active passive smap satellite provides unprecedented views of this peculiar feature from intraseasonal to interannual timescales smap sss has a 0 83 correlation and 0 49 rms difference to 0 5 m in situ measurements smap and in stu data both indicate a sss standard deviation of 0 7 to 1 away from the coast that rises to 2 pss within 100 km of the coast providing a very favorable signal to noise ratio in coastal areas smap also captures the strong northern bob postmonsoon cross shore sss contrasts 10 pss measured along ship transects smap data are also consistent with previous modeling results that suggested a modulation of the eicc gb plume southward extent by the indian ocean dipole iod remote forcing associated with the negative indian ocean dipole in the fall of 2016 indeed caused a stronger eicc and river in the sea that extended by approximately 800 km further south than that in 2015 positive iod year the combination of smap and altimeter data shows eddies stirring the freshwater plume away from the coast

sensitivity of the last glacial inception to initial and surface conditions we investigate the sensitivity of simulations of the last glacial inception lgi with respect to initial size of the greenland ice sheet and surface state of ocean vegetation conditions and two different co2 reconstructions utilizing the climber 2 earth system model we obtain the following results a ice sheet expansion in north america at the end of the eemian can be reduced or even completely suppressed when pre industrial or eemian ocean vegetation is prescribed b a warmer surrounding ocean and in particular a large laurentide ice sheet reduce the size of the greenland ice sheet before and during the lgi c a changing ocean contributes much stronger to the expansion of the laurentide ice sheet when we apply the co2 reconstruction according to barnola et al nature 329 408 414 1987 instead of petit et al nature 399 429 436 1999 d in the fully coupled model the co2 reconstruction used has only a small impact on the simulated ice sheets but it does impact the course of the climatic variables e for the greenland ice sheet two equilibrium states exist under the insolation and co2 forcing at 128 000 years before present 128 kyear bp the one with an ice sheet reduced by about one quarter as compared to its simulated pre industrial size and the other with nearly no inland ice in greenland f even the extreme assumption of no ice sheet in greenland at the beginning of our transient simulations does not alter the simulated expansion of northern hemispheric ice sheets at the lgi

quantifying glacier mass change and its contribution to lake growths in central kunlun during 2000 2015 from multi source remote sensing data abstract joint monitoring of the variations of glaciers and lakes within a basin is essential for an accurate understanding of region wide climate change and the water cycle process the central kunlun kekexili region is an ideal experimental field due to the wide distribution of glaciers and lakes in this study we first investigated the glacier mass balance of 2000 2015 16 for seven major glacier clusters by utilizing high resolution spot 6 7 stereo imagery and the srtm dem the final results revealed an overall mass balance of 0 16 0 05 m w e a for the study region with a total glacier area of 967 km2 secondly icesat glas altimetry data were used to quantify the water level change of 2003 2008 09 for the two largest glacier fed closed lakes i e lexiewudan lake and kekexili lake in this region based on this we applied a strategy which establishes the statistical relationship between the lake area change and the lake water level change for 2003 2008 09 to estimate the specific water level using the corresponding lake area we then further calculated the variation in lake water storage between 2000 and 2015 the results showed that the water storage of lexiewudan lake and kekexili lake increased by 1 82 0 14 km3 and 1 90 0 38 km3 respectively for each lake basin meanwhile the glaciers lost 0 18 0 03 km3 and 0 21 0 04 km3 of water accounting for 9 9 and 11 1 of the increase in lake water storage for lexiewudan lake and kekexili lake respectively our results not only demonstrate that glacier meltwater has only a limited impact on the lake expansion in this region but they also provide new evidence for the warming and wetting process of the climate in the northern part of the qinghai tibet plateau

lake water and glacier mass gains in the northwestern tibetan plateau observed from multi sensor remote sensing data implication of an enhanced hydrological cycle abstract lakes and glaciers are widely distributed in the northwestern tibetan plateau a synchronized examination of lake and glacier mass variations there has not previously been conducted which has limited the understanding of the lake water balance and the hydrologic cycle in the region in this study we comprehensively examine lake area and volume and glacier mass changes using multi sensor satellite data we find that lake expansion in the northwestern tibetan plateau was more robust from 1976 to 2018 when compared to other regions of the plateau especially for the glacier fed and endorheic lakes lake volume changes show that most of the lakes had an increase in water volume particularly in 2000 2018 with a total water storage gain of 28 6 gt by using high resolution kh 9 and tandem x data we observe that the glacier surface elevation of the western kunlun mountains had a slight thinning rate of 0 07 0 16 m yr in 1973 2000 but a positive rate of 0 002 0 003 m yr in 2000 2018 the heterogeneous pattern of glacier elevation changes between the north n and south s slopes are revealed i e 0 02 0 01 m yr n against 0 12 0 03 m yr s in 1973 2000 and 0 05 0 02 m yr n against 0 06 0 02 m yr s in 2000 2018 overall the glaciers trend to a stable state 0 05 m yr in both the south slope of the western kunlun mountains and aru co regions between 2000 and 2018 similar patterns are also found for basin wide examinations of lake storage changes mass gains and glacier mass budgets positive or close to stable the seasonal snow cover area changes derived from cloud free modis snow cover products present a variable and insignificant trend between 2003 and 2017 snow depth derived from passive microwave remote sensing data exhibits a decreasing trend between 1979 and 2015 but the water equivalent could contribute only an insignificant amount to the observed lake changes the lake water gains and almost positive glacier mass balance imply that the hydrological cycle in the northwestern tibetan plateau has become enhanced

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

sea level and deep water temperature changes derived from benthic foraminifera isotopic records we show that robust regressions can be established between relative sea level rsl data and benthic foraminifera oxygen isotopic ratios from the north atlantic and equatorial pacific ocean over the last climatic cycle we then apply these regressions to long benthic isotopic records retrieved at one north atlantic and one equatorial pacific site to build a composite rsl curve as well as the associated confidence interval over the last four climatic cycles our proposed reconstruction of rsl is in good agreement with the sparse rsl data available prior to the last climatic cycle we compute bottom water temperature changes at the two sites and at one southern indian ocean site taking into account potential variations in north atlantic local deep water 18o our results indicate that a last glacial maximum lgm enrichment of the ocean mean oxygen isotopic ratio of 0 95 is the lowest value compatible with unfrozen deep waters in the southern indian ocean if local deep water 18o did not increase during glacials with respect to present such a value of the lgm mean ocean isotopic enrichment would impose a maximum decrease in local bottom water 18o at the north atlantic site of 0 30 during glacials

a decomposition of the atlantic meridional overturning circulation into physical components using its sensitivity to vertical diffusivity abstract the sensitivity of the atlantic ocean meridional overturning circulation to the vertical diffusion coefficient in the global coupled atmosphere ocean sea ice model climber 3 is investigated an important feature of the three dimensional ocean model is its low diffusive tracer advection scheme the strength mmax of the atlantic overturning is decomposed into three components 1 the flow ms exported southward at 30 s 2 the large scale upward flow that balances vertical diffusion in the atlantic and 3 a wind dependent upwelling flux wbound along the atlantic boundaries that is not due to vertical diffusion the export of water at 30 s varies only weakly with but is strongly correlated with the strength of the overflow over the greenland scotland ridge the location of deep convection is found to be mixing dependent such that a shift from the nordic seas to the irminger sea is detected for high values of the ratio r ms mmax gives a measure of the interhemispheric overturning efficienc

evolution and demise of the last interglacial warmth in the subpolar north atlantic detailed faunal isotopic and lithic marine records provide new insight into the stability and climate progression of the last interglacial period marine isotope stage mis 5 which peaked approximately 125 000 years ago in the eastern subpolar north atlantic at the latitude of ireland interglacial warmth of the ice volume minimum of substage 5e mis 5e lasted 10 000 years 10 ka and its demise occurred in two cooling steps the first cooling step marked the end of the climatic optimum which was 2 3 ka long minor ice rafting accompanied each cooling step the second larger step encompassing cold events c26 and c25 was previously identified in the northwestern atlantic approximately 41c of cooling occurred between peak interglacial warmth and c25 and the region experienced an additional temporary cooling of at least 1 21c during c24 a cooling event associated with widespread ice rafting in the north atlantic beginning with c24 mis 5 was characterized by oscillations of at least 1 21c superimposed on a generally cool baseline the results of this study imply that the marine climatic optimum of the last interglacial was shorter than previously thought the finding that the eastern subpolar north atlantic cooled significantly before c24 reconciles terrestrial evidence for progressive climate deterioration at similar and lower latitudes with marine conditions our results also demonstrate a close association between modest ice rafting cooling and deep ocean circulation even during the peak of mis 5e and in the earliest stages of ice growth

quantifying evaporation and its decadal change for lake nam co central tibetan plateau most lakes in the interior tibetan plateau have expanded rapidly since the late 1990s because of a lack of observations lake water balances and their changes are far from well understood evaporation is a component of the lake water balance and this study quantifies its magnitude decadal change and its contribution to the water balance changes in lake nam co one of the largest lakes on the tibetan plateau with an area of approximately 2000 km2 and a mean depth of approximately 40 m the lake temperature and the evaporation are simulated by the flake model the simulation results are validated against observed lake temperature profile from 2013 and moderate resolution imaging spectroradiometer lake surface temperature data from 2000 to 2014 the simulated latent heat flux and sensible heat flux are validated against bowen ratio derived estimates for 2013 based on the validated simulation results the long term mean annual evaporation is approximately 832 69 mm and this value is much less than the potential evaporation estimated using the penman monteith equation the annual evaporation from 1980 to 2014 displays a complex decadal oscillation mainly due to the changes in energy related terms air temperature and radiation the mean lake evaporation since the late 1990s is greater than previous periods thus this change in evaporation has suppressed the recent expansion of nam co

age dating and the orbital theory of the ice ages development of a high resolution 0 to 300 000 year chronostratigraphy using the concept of orbital tuning a continuous high resolution deep sea chronostratigraphy has been developed spanning the last 300 000 yr the chronology is developed using a stacked oxygen isotope stratigraphy and four different orbital tuning approaches each of which is based upon a different assumption concerning the response of the orbital signal recorded in the data each approach yields a separate chronology the error measured by the standard deviation about the average of these four results which represents the best chronology has an average magnitude of only 2500 yr this small value indicates that the chronology produced is insensitive to the specific orbital tuning technique used excellent convergence between chronologies developed using each of five different paleoclimatological indicators from a single core is also obtained the resultant chronology is also insensitive to the specific indicator used the error associated with each tuning approach is estimated independently and propagated through to the average result the resulting error estimate is independent of that associated with the degree of convergence and has an average magnitude of 3500 yr in excellent agreement with the 2500 yr estimate transfer of the final chronology to the stacked record leads to an estimated error of 1500 yr thus the final chronology has an average error of 5000 yr