global teleconnections in response to a shutdown of the atlantic meridional overturning circulation abstract the global response to a shutdown of the atlantic meridional overturning circulation amoc is investigated by conducting a water hosing experiment with a coupled ocean atmosphere general circulation model in the model the addition of freshwater in the subpolar north atlantic shuts off the amoc the intense cooling in the extratropical north atlantic induces a widespread response over the global ocean in the tropical atlantic a sea surface temperature sst dipole forms with cooling north and warming on and south of the equator this tropical dipole is most pronounced in june december displacing the atlantic intertropical convergence zone southward in the tropical pacific a sst dipole forms in boreal spring in response to the intensified northeast trades across central america and triggering the development of an el nino like warming that peaks on the equator in boreal fall in the extratropical north pacific a basinwide cooling of 1 c takes place with a general westward increase in in

a planktic foraminiferal transfer function for the southern south atlantic ocean abstract quantitative analysis of planktic foraminiferal assemblages in 81 surface sediment samples from 20 s subtropical gyre to 55 s antarctic zone in the south atlantic ocean documents a close relationship between species distribution and austral summer surface water temperature a data set including the abundance pattern of 25 taxa and morphotypes was used to establish a transfer function based on the definition of five factors altogether these factors account for 97 of the total variance of the original data and their geographic distribution is closely linked to sea surface temperatures the transfer function f81 25 5 allows reconstruction of late quaternary summer surface water temperatures in the boundary region between the antarctic cold and subtropical warm water realm 0 5 to 26 0 c the statistical error for modern data is 1 3 c

the turbulent oscillator a mechanism of low frequency variability of the wind driven ocean gyres intrinsic low frequency variability is studied in the idealized quasigeostrophic midlatitude wind driven ocean gyres operating at large reynolds number a robust decadal variability mode driven by the transient mesoscale eddies is found and analyzed the variability is a turbulent phenomenon which is driven by the competition between the eddy rectification process and the potential vorticity anomalies induced by changes of the intergyre transport

biogenic silica dissolution in sediments of the southern ocean i solubility abstract a stirred flow through reactor technique was used to determine silica solubilities in sediments collected with a multicorer in the indian sector of the southern ocean antares i cruise the results show that the apparent silica solubility in the cores may decrease increase or remain constant with depth the silica solubility profiles are best explained by the early diagenetic interactions between biogenic silica and soluble aluminum derived from detrital material by combining the solubility data with measured dissolved silica profiles it is shown that the variable asymptotic pore water silica levels in the cores cannot be explained solely by differences in silica solubility in sediments that experience a significant detrital input the simultaneous reprecipitation of dissolved aluminum and dissolved silica prevents water silicic acid from reaching saturation with the dissolving biogenic silica the principal oceanographic control on pore water silica build up in the cores studied is the ratio of the deposition fluxes of biogenic silica and detrital material solubility differences inherited from the biomineralization process in the surface waters do not appear to have a significant effect on the observed pore water silica levels

the transient atmospheric circulation response to north atlantic sst and sea ice anomalies abstract the objective of this study is to investigate the transient evolution of the wintertime atmospheric circulation response to imposed patterns of sst and sea ice extent anomalies in the north atlantic sector using a large ensemble of experiments with the ncar community climate model version 3 ccm3 the initial adjustment of the atmospheric circulation is characterized by an out of phase relationship between geopotential height anomalies in the lower and upper troposphere localized to the vicinity of the forcing this initial baroclinic response reaches a maximum amplitude in 5 10 days and persists for 2 3 weeks diagnostic results with a linear primitive equation model indicate that this initial response is forced by diabatic heating anomalies in the lower troposphere associated with surface heat flux anomalies generated by the imposed thermal forcing following the initial baroclinic stage of adjustment the response becomes progressively more barotropic and increases in both spatial extent an

surface lithofacies biofacies and diatom diversity patterns as models for delineation of climatic change in the southeast atlantic ocean abstract distribution of diatom species in surface sediments of the southeast atlantic ocean is regulated by present day oceanographic and hydrodynamic processes five assemblages vectors defined by factor vector analysis reflect different environments and conditions assemblage a is a high diversity flora associated with the nutrient rich relatively cold waters south of the polar front in the diatom ooze belt occurrence of this flora on maud rise and vicinity may reflect periodic occurrence of a polynya in that area assemblage b is a reworked assemblage that dominates the southern portion of the study area productivity there is low reflecting sea ice cover during most of the year the area north of the polar front is dominated by assemblage c whose characteristic species reflect the relatively warm subantarctic surface water winnowing and frustule breakage have altered assemblage d found in three isolated samples by removing relatively delicate forms leaving lag deposits of more robust species assemblage e is a low diversity stress flora reflecting unstable unpredictable environments along the polar front antarctic slope and the northern boundary of winter sea ice these sites are characterized by the sinking of cold water downcore analysis of cores lying adjacent to the polar front and the diatom ooze pelagic clay boundary show evidence for past climatic variation the low trophic level occupied by diatoms and the subsequent sensitivity of these organisms to abiotic environmental parameters such as light quality make relative diatom abundance a useful tool for monitoring fluctuations of winter sea ice and the temperature changes responsible for these fluctuations the position of the polar front has migrated at least three times within the last 0 015 m y b p within the last 0 3 m y b p warm maxima have occurred at approximately 0 0 0 015 0 125 and 0 3 m y b p

circumglobal teleconnections the jet stream waveguide and the north atlantic oscillation abstract monthly and seasonally averaged upper tropospheric northern hemisphere winter fields are examined to determine whether the waveguiding effect of the time averaged tropospheric jets on low frequency disturbances that is predicted by theory does affect the behavior of these disturbances it is found that indeed disturbances in the vicinity of the mean jets particularly the jet that stretches across south asia are fundamentally different from those that reside in regions where the mean winds have weaker meridional gradients like the mid pacific patterns of variability in the jets tend to be smaller scale and to consist of zonally oriented chains of anomalies while variability in the mid pacific is composed of patterns with distinct meridional orientation because they are meridionally trapped and zonally elongated patterns associated with the jet stream waveguide connect activity at points that are much farther apart than do patterns in other regions of the globe within the south asian waveg

kuroshio extension variability and forcing of the pacific decadal oscillations responses and potential feedback abstract a forcing mechanism is sought for the large scale circulation changes in the kuroshio extension region of the western north pacific ocean as inferred by topex poseidon sea surface height ssh data the low frequency signal of the kuroshio extension over the last decade was characterized by a modulation in its zonal mean flow intensity the mean kuroshio extension jet weakened progressively from 1993 to 1996 and this trend reversed after 1997 the ability to simulate the major trends in the observed ssh signals with linear vorticity dynamics leads the authors to conclude that the modulation in the zonal mean jet was remotely forced by wind stress curl anomalies in the eastern north pacific ocean related to the pacific decadal oscillations pdos to be specific the weakening strengthening trend in 1993 96 1997 2001 was caused by westward expansions of negative positive ssh anomalies south of the kuroshio extension and positive negative ssh anomalies north of the kuroshio extension emerg

heat budget in the kuroshio extension region 1993 99 abstract processes responsible for the seasonal and interannual variations of the sea surface temperature as well as of the heat content of the upper ocean 0 400 m in the kuroshio extension region are examined from a 3d advection diffusion model in finite elements with an embedded bulk mixed layer the geostrophic velocity is specified externally from topex poseidon altimeter data and ekman velocity is specified from ncep wind stress the thermal field from the model shows good agreement with observations while both atmospheric and oceanic processes are required to explain observed nonseasonal sst changes the interannual heat storage rate is dominated by horizontal advection in particular the transition between an elongated and a contracted state of the kuroshio caused by geostrophic advection has a clear signature in the sst there is an indication that this process is accompanied by consistent changes in nonseasonal entrainment when the kuroshio is in an elongated state and warmer waters are pr

paleodepth determination from antarctic benthic diatom assemblages abstract analysis of modern surface sediments from fjords in the vestfold hills antarctica indicates that 58 of the variation in benthic diatom assemblages can be attributed to changes in environmental parameters with water depth attenuation of light through the water column is suggested to account for 45 of the variation and the decrease in substrate grain size with depth possibly accounts for a further 13 cluster analysis and principal component analysis were used to objectively circumscribe five floral zones between the surface and 35 m depth the depth distribution of the benthic diatoms was then used to interpret the paleodepth of relict fjord holocene sediments exposed around deep lake in the death valley vestfold hills paleodepths measured from the sea ice bench around deep lake combined with data from grain size analysis indicate that the relict fjord sediments have no analogue amongst the modern fjord sediments sampled in the vestfold hills without a comparable modern habitat on which to model the diatom depth zones however this study was unable to accurately determine the paleowater depth at deep lake using diatoms paleodepth determination will be possible using grain size analysis and diatom data when the substrate and light requirements of benthic diatoms are understood

surface water temperature changes in the high latitudes of the southern hemisphere over the last glacial interglacial cycle a set of numerical equations is developed to estimate past sea surface temperatures sst from fossil antarctic diatoms these equations take into account both the biogeographic distribution and experimentally derived silica dissolution the data represent a revision and expansion of a floral data base used previously and includes samples resulting from progressive opal dissolution experiments factor analysis of 166 samples 124 holocene core top and 42 artificial samples resolved four factors three of these factors depend on the water mass distribution one subantarctic and two antarctic assemblages factor 4 corresponds to a dissolution assemblage inclusion of this factor in the data analysis minimizes the effect of opal dissolution on the assemblages and gives accurate estimates of sst over a wide range of biosiliceous dissolution a transfer function dtf 166 34 4 is derived from the distribution of these factors versus summer sst its standard error is 1 c in the 1 to 10 c summer temperature range this transfer function is used to estimate sst changes in two southern ocean cores 43 s and 55 s which cover the last climatic cycle the time scale is derived from the changes in foraminiferal oxygen and carbon isotopic ratios the reconstructed sst records present strong analogies with the air temperature record over antarctica at the vostok site derived from changes in the isotopic ratio of the ice this similarity may be used to compare the oceanic isotope stratigraphy and the vostok time scale derived from ice flow model the oceanic time scale if taken at face value would indicate that large changes in ice accumulation rates occurred between warm and cold periods

teleconnections in the geopotential height field during the northern hemisphere winter abstract contemporaneous correlations between geopotential heights on a given pressure surface at widely separated points on earth referred to as teleconnections in this paper are studied in an attempt to identify and document recurrent spatial patterns which might be indicative of standing oscillations in the planetary waves during the northern hemisphere winter with time scales on the order of a month or longer a review of existing literature on the subject reveals the existence of at least four such patterns the north atlantic and north pacific oscillations identified by walker and bliss 1932 a zonally symmetric seesaw between sea level pressures in polar and temperature latitudes first noted by lorenz 1951 and what we will refer to as the pacific north american pattern which has been known to operational long range forecasters in this country since the 1950 s a data set consisting of nmc monthly mean sea level pressure and 500 mb height analyses for a 15 year period is used as a basis fo

interdecadal thermocline variability in the north pacific for 1958 97 a gcm simulation an ocean general circulation model is forced with the ncep reanalysis wind stress for 1958 97 to understand mechanisms of ocean subsurface variability with relatively high horizontal 1 83 18 and vertical 41 levels resolutions the model produces mode waters on a range of density surfaces in the western central and eastern north pacific in qualitative agreement with observations these mode waters appear as a thermostad or a region of weak stratification in the upper thermocline as they flow southward from their formation regions in the kuroshio and its extension in the model subsurface temperature variability in the central subtropical gyre reaches a maximum within the thermostad in contrast to what might be expected from the linear baroclinic rossby wave theory this variance maximum is associated with the longitudinal shift in the path of mode waters in particular deepened mixed layer and accelerated eastward currents in the kuroshio extension by wind changes in the mid 1970s act cooperatively to move the central mode waters toward the east causing large subsurface temperature anomalies besides the local maximum in the central north pacific subtropical gyre two additional maxima of the subsurface anomaly are identified in the northwestern and southern parts of the gyre respectively among these subsurface anomaly centers the one in the northwestern north pacific has a strong effect on the model sea surface temperature suggesting that the kuroshio and its extension are a key region to decadal interdecadal ocean atmosphere interaction finally possible effects of atmospheric thermal forcing are discussed

relationships between atmospheric internal variability and the responses to an extratropical sst anomaly abstract the january and february responses of a gcm to an imposed extratropical pacific sst anomaly are compared with the patterns of the model s internal variability relevant patterns of internal variability are diagnosed from ensembles of model control runs by regressing monthly mean geopotentials and temperatures against low level temperatures in the vicinity of the sst anomaly and by eof analysis these patterns are found to play a significant role in determining the local and the remote responses to the sst anomaly different responses to the sst anomaly in the gcm s january and february climates are largely explained by the differences in the regression patterns and in the leading eof the gcm response may be considered as comprising a direct linear response to low level heating that is local to the forcing and baroclinic and an eddy forced component that closely resembles patterns of the model s internal variability it is equivalent barotropic and extends over the entire hemisphere the results

the modeled atmospheric response to midlatitude sst anomalies and its dependence on background circulation states abstract the atmospheric response to a midlatitude sst anomaly in the north pacific and its dependence on background flow are examined in a gcm experiments are conducted using the same warm sst anomalies but two different model states perpetual january and perpetual february the atmospheric responses to the sst anomalies are statistically significant in both january and february but are completely different the anomalous circulation in january is characterized by a trough decaying with height immediately downstream of the sst anomalies in february the anomalous circulation is dominated by a downstream ridge growing with height the patterns of the anomalous heights in the two months are nearly orthogonal vorticity and thermodynamic budgets are diagnosed to illustrate how the anomalous circulations are maintained over the sst anomalies low level convergence and ascent are observed in both months in january the anomalous convergence is balanced by a residual due primarily to the forcing by submont

diatom distribution and paleoceanographic reconstruction in the southern ocean present and last glacial maximum abstract diatom assemblage and preservational data are used to reconstruct paleoceanographic conditions at the last glacial maximum 18 000 yrs bp in the southern ocean from these data the following points can be made about the last glacial maximum in this region 1 contraction and slight northern shift of the belt of well preserved diatoms appears to be related to the northward shift of late spring early summer sea ice cover 2 presence of open ocean though poorly preserved diatom assemblages to the south of this belt strongly suggest that during many summers large areas of the southern ocean were ice free 3 the distribution of thenitzschia kerguelensis factor both in surface sediments and at the last glacial maximum indicates that the gyre systems particularly the weddell gyre were intensified during glacial times 4 although data are sparse in the higher latitude south atlantic there is an indication that the weddell polynya also existed during glacial times although it was shifted a few degrees northward

the response of the itcz to extratropical thermal forcing idealized slab ocean experiments with a gcm using a comprehensive atmospheric gcm coupled to a slab mixed layer ocean experiments are performed to study the mechanism by which displacements of the intertropical convergence zone itcz are forced from the extratropics the northern extratropics are cooled and the southern extratropics are warmed by an imposed cross equatorial flux beneath the mixed layer forcing a southward shift in the itcz the itcz displacement can be understood in terms of the degree of compensation between the imposed oceanic flux and the resulting response in the atmospheric energy transport in the tropics the magnitude of the itcz displacement is very sensitive to a parameter in the convection scheme that limits the entrainment into convective plumes the change in the convection scheme affects the extratropical tropical interactions in the model primarily by modifying the cloud response the results raise the possibility that the response of tropical precipitation to extratropical thermal forcing important for a variety of problems in climate dynamics such as the response of the tropics to the northern hemisphere ice sheets during glacial maxima or to variations in the atlantic meridional overturning circulation may be strongly dependent on cloud feedback the model configuration described here is suggested as a useful benchmark helping to quantify extratropical tropical interactions in atmospheric models

the effects of north atlantic sst and sea ice anomalies on the winter circulation in ccm3 part ii direct and indirect components of the response the wintertime atmospheric circulation responses to observed patterns of north atlantic sea surface temperature and sea ice cover trends in recent decades are studied by means of experiments with an atmospheric general circulation model here the relationship between the forced responses and the dominant pattern of internally generated atmospheric variability is focused on the total response is partioned into a portion that projects onto the leading mode of internal variability the indirect response and a portion that is the residual from that projection the direct response this empirical decomposition yields physically meaningful patterns whose distinctive horizontal and vertical structures imply different governing mechanisms the indirect response which dominates the total geopotential height response is hemispheric in scale with resemblance to the north atlantic oscillation or northern hemisphere annular mode and equivalent barotropic in the vertical from the surface to the tropopause in contrast the direct response is localized to the vicinity of the surface thermal anomaly sst or sea ice and exhibits a baroclinic structure in the vertical with a surface trough and upper level ridge in the case of a positive heating anomaly consistent with theoretical models of the linear baroclinic response to extratropical thermal forcing both components of the response scale linearly with respect to the amplitude of the forcing but nonlinearly with respect to the polarity of the forcing the deeper vertical penetration of anomalous heating compared to cooling is suggested to play a role in the nonlinearity of the response to sst forcing

north atlantic decadal variability air sea coupling oceanic memory and potential northern hemisphere resonance in this paper the causes and mechanisms of north atlantic decadal variability are explored in a series of coupled ocean atmosphere simulations the model captures the major features of the observed north atlantic decadal variability the north atlantic sst anomalies in the model control simulation exhibit a prominent decadal cycle of 12 16 yr and a coherent propagation from the western subtropical atlantic to the subpolar region a series of additional modeling experiments are conducted in which the air sea coupling is systematically modified in order to evaluate the importance of air sea coupling for the north atlantic decadal variability being studied this shall be referred to as modeling surgery the results suggest the critical role of ocean atmosphere coupling in sustaining the north atlantic decadal oscillation at selected time scales the coupling in the north atlantic is characterized by a robust north atlantic oscillation nao like atmospheric response to the sst tripole anomaly which tends to intensify the sst anomaly and meanwhile also provide a delayed negative feedback this delayed negative feedback is predominantly associated with the adjustment of the subtropical gyre in response to the anomalous wind stress curl in the subtropical atlantic atmospheric stochastic forcing can drive sst patterns similar to those in the fully coupled ocean atmosphere system but fails to generate any preferred decadal time scales the simulated north atlantic decadal variability therefore can be viewed as a coupled ocean atmosphere mode under the influence of stochastic forcing this modeling study also suggests some potential resonance between the pacific and the north atlantic decadal fluctuations mediated by the atmosphere the modeling surgery indicates that the pacific climate although not a necessary precondition can impact the north atlantic climate variability substantially

wind driven shifts in the latitude of the kuroshio oyashio extension and generation of sst anomalies on decadal timescales abstract the causes of decadal variations of north pacific sea surface temperatures ssts are examined using a hindcast performed with an ocean general circulation model thermodynamically coupled to an atmospheric mixed layer model ogcm aml model and forced by the time history of observed surface winds the shift in north pacific ocean climate that occurred around 1976 77 is focused on since this is the best observed example available after the 1976 77 shift the aleutian low deepened and moved to the southeast of its previous position this placed anomalous cyclonic flow over the north pacific the sst response as simulated by the ocean model consisted of two components a fast and local part and a delayed and remote part in the central pacific stronger westerlies cool the ocean by increased equatorward ekman drift here the dynamical cooling is sufficiently large that the surface fluxes damp the sst anomaly this ekman response is fast and local and cools the ssts beginning in 1977 and persistin

northern hemisphere winter atmospheric transient eddy heat fluxes and the gulf stream and kuroshio oyashio extension variability abstractspatial and temporal covariability between the atmospheric transient eddy heat fluxes i e t and q in the northern hemisphere winter january march and the paths of the gulf stream gs kuroshio extension ke and oyashio extension oe are examined based on an atmospheric reanalyses and ocean observations for 1979 2009 for the climatological winter mean the northward heat fluxes by the synoptic 2 8 days transient eddies exhibit canonical storm tracks with their maxima collocated with the gs and ke oe the intraseasonal 8 days 3 months counterpart while having overall similar amplitude shows a spatial pattern with more localized maxima near the major orography and blocking regions lateral heat flux divergence by transient eddies as the sum of the two frequency bands exhibits very close coupling with the exact locations of the ocean fronts linear regression is used to examine the lead lag relationship between interannual changes in the northward heat fluxes by the transient

response of the atmosphere ocean mixed layer system to anomalous ocean heat flux convergence we investigate the role of the extratropical oceans in climate variability rather than following the traditional approach of studying the atmospheric response to prescribed sea surface temperature sst anomalies we focus on the role of anomalous ocean heat transport we employ an atmosphere model coupled to a fixed depth slab ocean mixed layer model forced by a field of ocean heat flux convergence ohfc we study the response of this coupled atmosphere ocean mixed layer system to an idealized ohfc anomaly we find that the ohfc forcing is mainly balanced by anomalous surface latent heat flux i e enhanced evaporation notably the anomalous sst is not co located with the forcing nor with the anomalous air sea flux nor with the anomalous diabatic heating contrary to conventional wisdom in our experiment the influence of the extratropical ocean on the atmosphere is not manifest primarily in an sst signature the anomalous diabatic heating is associated with a downstream surface low pressure anomaly in line with the simple theory of the steady response to extratropical heating transient eddy anomalies play only a minor role the principal sst anomaly appears to be a passive response to this anomalous atmospheric flow our results suggest that the traditional narrow focus on sst as the key variable involved in ocean atmosphere interaction may offer only a limited perhaps even misleading guide to the influence of the extratropical oceans on climate variability copyright 2002 royal meteorological society

comparison of foraminiferal coccolithophorid and radiolarian paleotemperature equations assemblage coherency and estimate concordancy the imbrie kipp method of paleotemperature estimation is rigorously tested by comparing atlantic temperature equations independently derived from the microfossils of three biotic groups the foraminifera coccolithophorida and radiolaria this method consists of two steps factor analysis of the modern sea bed data of the individual groups which resolves discrete biogeographic assemblages and regression analysis of the modern assemblage data with observed sea surface temperature data to obtain paleotemperature equations assemblage biogeography shows a simple subdivision into warm low latitude and cold high latitude for all biotic groups between biotic groups there is greater similarity among high latitude assemblages than low latitude ones correlating the assemblage data with observed sea surface temperatures to produce temperature distribution patterns shows differences of less than 2 c in their optimum and critical temperatures regression analysis produced accurate temperature equations for each biotic group all with standard errors of estimate of less than or equal to 2 c multiple correlation coefficients were all greater than 0 970 applying these equations to two multiple biotic data sets the modern and ice age sea bed data and comparing their temperature estimates using the standard error pooled shows over 87 concordancy for both data sets unlike the modern data the discordancy among temperature estimates of the ice age data shows a distinct geographic distribution its cause is believed to be oceanographic a difference in the water mass structure between the modern and ice age ocean

mechanisms determining the atmospheric response to midlatitude sst anomalies abstract previous gcm experiments demonstrated that a model atmosphere produces two different responses to a midlatitude warm sst anomaly over the pacific under perpetual january and february conditions to elucidate the mechanisms responsible for the different gcm responses and their dependence on the background flow experiments with two idealized models are conducted experiments with a linear baroclinic model reveal that the gcm responses at equilibrium are primarily maintained by the anomalous eddy forcing the anomalous flow induced directly by an idealized initial heat source exhibits little sensitivity to the background flow eddy feedbacks on the heating induced anomalous flow are examined using a linear storm track model the anomalous eddy forcing produced by the storm track model is sensitive to the basic state the eddy forcing in january acts to shift the heating induced upper level ridge toward the northeast of the gulf of alaska while in february it acts to reinforce the ridge this sugge

north pacific climate response to freshwater forcing in the subarctic north atlantic oceanic and atmospheric pathways abstract sudden changes of the atlantic meridional overturning circulation amoc are believed to have caused large abrupt climate changes over many parts of the globe during the last glacial and deglacial period this study investigates the mechanisms by which a large freshwater input to the subarctic north atlantic and an attendant rapid weakening of the amoc influence north pacific climate by analyzing four different ocean atmosphere coupled general circulation models gcms under present day or preindustrial boundary conditions when the coupled gcms are forced with a 1 sv sv 106 m3 s 1 freshwater flux anomaly in the subarctic north atlantic the amoc nearly shuts down and the north atlantic cools significantly the south atlantic warms slightly shifting the atlantic intertropical convergence zone southward in addition to this atlantic ocean atmosphere response all of the models exhibit cooling of the north pacific especially along the oceanic frontal zone consistent with paleoclimate recons

fast teleconnections to the tropical atlantic sector from atlantic thermohaline adjustment 1 we examine the first decade of adjustment of the north atlantic climate following an abrupt freshening of the high north atlantic and resulting slowdown of the atlantic meridional overturning circulation amoc in a coupled model with reference to previously proposed teleconnection mechanisms after an initial ocean driven cooling at the subtropical subpolar gyre boundary subsequent equatorward progression is dominated by an atmosphere surface ocean mechanism driving evaporative cooling in the tropical north atlantic and resulting in an anomalous southward itcz displacement by year 2 the tropical cooling is countered by fast ocean baroclinic adjustment to the reduced overturning that increases the volume of tropical surface waters as well as ocean circulation changes to the increased northeasterly trades however it is the atmosphere surface ocean teleconnection that explains the hemispheric asymmetric nature of the tropical atlantic surface climate impact to amoc slowdown underlining its crucial importance in high to low latitude teleconnections

melting history of antarctica during the past 60 000 years marked changes in the surface water hydrology of the southern ocean during the past 60 kyr are revealed by a detailed comparison of the oxygen isotopic composition of planktonic and benthic foraminifera from sediment cores and the surface water temperature estimated by a transfer function derived from the distribution of diatoms in the same sediments from 35 to 17 kyr bp the southern ocean polar front was covered by a melt water lid containing a significant contribution from melting icebergs calved from antarctic ice shelves these icebergs may have originated from a succession of surges of the ice shelves

influence of the meridional shifts of the kuroshio and the oyashio extensions on the atmospheric circulation abstract the meridional shifts of the oyashio extension oe and of the kuroshio extension ke as derived from high resolution monthly sea surface temperature sst anomalies in 1982 2008 and historical temperature profiles in 1979 2007 respectively are shown based on lagged regression analysis to significantly influence the large scale atmospheric circulation the signals are independent from the enso teleconnections which were removed by seasonally varying asymmetric regression onto the first three principal components of the tropical pacific sst anomalies the response to the meridional shifts of the oe front is equivalent barotropic and broadly resembles the north pacific oscillation western pacific pattern in a positive phase for a northward frontal displacement the response may reach 35 m at 250 hpa for a typical oe shift a strong sensitivity since the associated sst anomaly is 0 5 k however the amplitude but not the pattern or statistical significance strongly depends on the lag and an

a simple model of the decadal response of the ocean to stochastic wind forcing abstract a simple linear model is used to estimate the decadal response of the extratropical ocean to wind stress forcing assuming a flat bottom a mean state at rest and no dissipation the barotropic fields are governed by a time dependent sverdrup balance the baroclinic ones by the long rossby wave equation the ocean is bounded by a coast in the east and a radiation condition is used in the west at each frequency the baroclinic response consists of a forced response plus a rossby wave generated at the eastern boundary for zonally independent forcing the response propagates westward at twice the rossby phase speed the wind stress is assumed to be stochastic with a white frequency spectrum so the model represents the continuous excitation of the ocean interior by the weather fluctuations the model predicts the shape and level of the frequency spectra of the oceanic pressure field and their variation with longitude and latitude the baroclinic response is spread over a continuum of frequencies

observed influence of north pacific sst anomalies on the atmospheric circulation abstract a lagged maximum covariance analysis mca of monthly anomaly data from the ncep ncar reanalysis shows significant relations between the large scale atmospheric circulation in two seasons and prior north pacific sea surface temperature sst anomalies independent from the teleconnections associated with the enso phenomenon regression analysis based on the sst anomaly centers of action confirms these findings in late summer a hemispheric atmospheric signal that is primarily equivalent barotropic except over the western subtropical pacific is significantly correlated with an sst anomaly mode up to at least 5 months earlier although the relation is most significant in the upper troposphere significant temperature anomalies are found in the lower troposphere over north america the north atlantic europe and asia the sst anomaly is largest in the kuroshio extension region and along the subtropical frontal zone resembling the main mode of north pacific sst anomaly variability in late winter

the sedimentary record of pelagic biogeography abstract sedimentary remains of fossilizable marine organisms chiefly microplanktonic ones coccolithophorids silicoflagellates diatoms dinoflagellates radiolarians foraminifers have long been used for biogeographic surveys usually with the aim of unravelling paleoenvironmental settings utilization of bottom deposits rather than plankton samples has some advantages for this purpose thanatocoenoses require smaller sample sizes materials are more readily available and they eliminate the small time scale variability which obscures long term trends on the other hand the sedimentary imprint of planktonic distributional patterns is often severely distorted by fragmentation and dissolution of the biogenic remains reworking of sediments winnowing and lateral advection of shells especially toward lower latitudes seasonally and interannually variable output rates and the integration of vertically heterogeneous assemblages the biases derived from these processes are reviewed and the need for more information on selective dissolution vertical distribution patterns and planktonic reproduction and output rates is stressed given the assumptions used in paleoenvironmental studies distributional information drawn from sediment samples is less prone to yielding biased information when applied to these surveys than to bio or paleobiogeographic investigations albeit the former can also be significantly affected as a result of changes in the traits that govern the formation of biogenic sediments

late quaternary sea surface conditions at dsdp hole 594 in the southwest pacific ocean based on dinoflagellate cyst assemblages investigation of organic walled dinoflagellate cyst distribution in 118 surface sediments from the southern ocean documents the relatively high diversity of cyst taxa 46 species and distinct cyst assemblages in relation to surface water masses and temperature gradient the antarctic water is characterised by the dominance of selenopemphix antarctica accompanied by brigantedinium spp and impagidinium pallidum the subantarctic water association consists mainly of nematosphaeropsis labyrinthus impagidinium paradoxum and impagidinium sphaericum whereas the subtropical water association is dominated by operculodinium centrocarpum and spiniferites membranaceus multivariate analyses non metric multidimensional scaling demonstrate the relationships with sea surface conditions and enable the application of the best analogue method on the southern ocean dinoflagellate cyst data base for reconstructing past sea surface conditions the dinoflagellate cyst record from dsdp 594 45 31 41 s 174 56 88 e 1204 m southern margin of the chatham rise shows important fluctuations in species composition from glacial to interglacial over the last 140 000 yr reconstruction of winter and summer ssts reveals much lower temperature than present by 6 to 10 c during marine oxygen isotope stages 6 4 and 2 and higher temperature by 2 3 c during substage 5e copyright 2001 john wiley sons ltd journal of quaternary science

enso like interdecadal variability 1900 93 a number of recent studies have reported an enso like eof mode in the global sea surface temperature sst field whose time variability is marked by an abrupt change toward a warmer tropical eastern pacific and a colder extratropical central north pacific in 1976 77 the present study compares this pattern with the structure of the interannual variability associated with the enso cycle and documents its time history back to 1900 the analysis is primarily based on the leading eofs of the sst anomaly and anomaly deviation fields in various domains and the associated expansion coefficient or principal component time series which are used to construct global regression maps of sst sea level pressure slp and a number of related variables the use of anomaly deviations i e departures of local sst anomalies from the concurrent global mean sst anomaly reduces the influence of global mean sst trends upon the structure of the eofs and their expansion coefficient time series an important auxiliary time series used in this study is a southern oscillation index based on marine surface observations by means of several different analysis techniques the time variability of the leading eof of the global sst field is separated into two components one identified with the enso cycle related variability on the interannual timescale and the other a linearly independent residual comprising all the interdecadal variability in the record the two components exhibit rather similar spatial signatures in the global sst slp and wind stress fields the sst signature in the residual variability is less equatorially confined in the eastern pacific and it is relatively more prominent over the extratropical north pacific the corresponding slp signature is also stronger over the extratropical north pacific and its counterpart in the cold season 500 mb height field more closely resembles the pna pattern the amplitude time series of the enso like pattern in the residual variability reflects the above mentioned shift in 1976 77 as well as a number of other prominent features including a shift of opposite polarity during the 1940s

the forcing of the pacific decadal oscillation the pacific decadal oscillation pdo defined as the leading empirical orthogonal function of north pacific sea surface temperature anomalies is a widely used index for decadal variability it is shown that the pdo can be recovered from a reconstruction of north pacific sea surface temperature anomalies based on a first order autoregressive model and forcing by variability of the aleutian low el nino southern oscillation enso and oceanic zonal advection anomalies in the kuroshio oyashio extension the latter results from oceanic rossby waves that are forced by north pacific ekman pumping the sst response patterns to these processes are not orthogonal and they determine the spatial characteristics of the pdo the importance of the different forcing processes is frequency dependent at interannual time scales forcing from enso and the aleutian low determines the response in equal parts at decadal time scales zonal advection in the kuroshio oyashio extension enso and anomalies of the aleutian low each account for similar amounts of the pdo variance these results support the hypothesis that the pdo is not a dynamical mode but arises from the superposition of sea surface temperature fluctuations with different dynamical origins

evidence for a wind driven intensification of the kuroshio current extension from the 1970s to the 1980s the spatial and temporal characteristics of oceanic thermal variations in the mixed layer and main thermocline of the midlatitude north pacific are distinctive suggesting different physical origins within the main thermocline 400 m depth the variability is dominated by a westward intensified pattern of decadal scale indicative of enhanced eastward geostrophic flow along the southern flank of the kuroshio current extension during the 1980s relative to the 1970s the authors argue that the decadal scale change in the strength of the kuroshio extension was a result of the dynamical adjustment of the oceanic circulation to a decadal variation in wind stress curl according to sverdrup theory four times daily wind stress fields from the national center for atmospheric research national centers for environmental prediction reanalysis project are used to compute the decadal change in sverdrup transport associated with the 1976 77 climate transition it is shown that the decadal changes in sverdrup transport inferred from the wind stress curl field and in observed geostrophic flow inferred from the upper ocean thermal field are consistent both in terms of spatial pattern and magnitude the decadal change in depth averaged geostrophic transport along the kuroshio extension referenced to 1 km is 11 6 sv similar to the sverdrup transport change 11 5 13 9 sv the decadal scale thermocline variation along the western boundary between 308 and 408n exhibits a lag of approximately 4 5 yr relative to the decadal variation in the basin wide wind stress curl pattern this delay may be indicative of the transient adjustment of the gyre scale circulation to a change in wind stress curl via long baroclinic rossby waves

transfer functions between diatom assemblages and surface hydrology in the southern ocean interpretation of the distribution of 31 marine diatom species and two silicoflagellate genera in 28 core tops from the atlantic and west indian sectors of the southern ocean by q mode factor analysis allows definition of three significantly different floral assemblages one associated with subantarctic and two with antarctic waters these three areas are clearly delineated by prominent oceanographic limits the antarctic convergence and the maximum retreat of sea ice during the summer season a set of palaeoecological transfer functions is derived by comparison between the distribution of these associations and surface water hydrological parameters using these equations estimated summer temperatures from core top floral assemblages range from 12 c in the north of the study area to 2 0 c near the southernmost cores the standard errors of estimate are 1 1 c for summer temperatures 1 5 months year for sea ice cover 0 2 mg atp l for sea surface phosphate concentrations numerical tests of these paleoecological equations demonstrate their usefulness to reconstruct the evolution of the surface oceanography of the austral ocean at different periods of the last climatic cycle

predicting western north pacific ocean climate abstract it is shown that wintertime sea surface temperature anomalies in the confluence region of the kuroshio oyashio currents in the western north pacific can be skillfully predicted at lead times of up to 3 yr the predictions are based on the history of the wind stress over the north pacific and oceanic rossby wave dynamics the predictions may be exploitable in fisheries research and other ecological applications

north pacific decadal variability in the community climate system model version 2 abstract north pacific decadal oceanic and atmospheric variability is examined from a 650 yr control integration of the community climate system model version 2 the dominant pattern of winter sea surface temperature sst variability is similar to the observed pacific decadal oscillation with maximum amplitude along the kuroshio extension sst anomalies in this region exhibit significant spectral peaks at approximately 16 and 40 yr lateral geostrophic heat flux divergence caused by a meridional shift of the kuroshio extension forced by basin scale wind stress curl anomalies 3 5 yr earlier is responsible for the decadal sst variability local surface heat flux and ekman heat flux divergence act as a damping and positive feedback respectively a simple linear rossby wave model is invoked to explicitly demonstrate the link between the wind stress curl forcing and decadal variability in the kuroshio extension the rossby wave model not only successfully reproduces the two decadal spectral peaks but a

a mechanism for the recurrence of wintertime midlatitude sst anomalies abstract in the early 1970s namias and born speculated that ocean temperature anomalies created over the deep mixed layer in winter could be preserved in the summer thermocline and reappear at the surface in the following fall or winter this hypothesis is examined using upper ocean temperature observations and simulations with a mixed layer model the data were collected at six ocean weather stations in the north atlantic and north pacific concurrent and lead lag correlations are used to investigate temperature variations associated with the seasonal cycle in both the observations and the model simulations concurrent correlations between the surface and subsurface temperature anomalies in both the data and the model indicate that the penetration of temperature anomalies into the ocean is closely tied to the seasonal cycle in mixed layer depth high correlations extend to relatively deep shallow depths in winter summer lead lag correlations in both the data and the model at some of the stations

coupled atmosphere mixed layer ocean response to ocean heat flux convergence along the kuroshio current extension the winter response of the coupled atmosphere ocean mixed layer system to anomalous geostrophic ocean heat flux convergence in the kuroshio extension is investigated by means of experiments with an atmospheric general circulation model coupled to an entraining ocean mixed layer model in the extra tropics the direct response consists of positive sst anomalies along the kuroshio extension and a baroclinic low level trough and upper level ridge circulation anomaly over the north pacific the low level component of this atmospheric circulation response is weaker in the case without coupling to an extratropical ocean mixed layer especially in late winter the inclusion of an interactive mixed layer in the tropics modifies the direct coupled atmospheric response due to a northward displacement of the pacific inter tropical convergence zone which drives an equivalent barotropic anomalous ridge over the north pacific although the tropically driven component of the north pacific atmospheric circulation response is comparable to the direct response in terms of sea level pressure amplitude it is less important in terms of wind stress curl amplitude due to the mitigating effect of the relatively broad spatial scale of the tropically forced atmospheric teleconnection

interannual variability of the kuroshio extension system and its impact on the wintertime sst field altimetry data from the first 7 yr topex poseidon t p mission october 1992 september 1999 are analyzed to investigate the interannual variability in regions of the kuroshio extension and its southern recirculation gyre large scale interannual changes of the kuroshio extension system are characterized by the oscillation between an elongated state and a contracted state in the elongated state the kuroshio extension has a larger eastward surface transport a greater zonal penetration and a more northerly zonal mean path all these characteristics are closely connected to the presence of an intense zonally elongated southern recirculation gyre in its contracted state the kuroshio extension has a smaller eastward surface transport a more southerly mean path and is accompanied by a weaker southern recirculation gyre during the t p period the kuroshio extension changed from the elongated state in 1992 93 to the contracted state in 1996 97 and back to the elongated state since late 1997 in addition to these large scale changes the mesoscale eddy field also exhibited prominent interannual changes in the kuroshio extension region in the upstream region between the izu ridge and the shatsky rise the eddy kinetic energy level was generally low while the kuroshio extension was in its elongated state and high while in the contracted state downstream of the shatsky rise on the other hand the eke level was high low when the kuroshio extension was in the elongated contracted state the large scale interannual changes in the kuroshio extension system have a significant impact on the regional wintertime sst anomaly field the warm cold wintertime sst anomalies tend to persist in years when the kuroshio extension is in its elongated contracted state a diagnostic analysis of the surface ocean heat balance indicates that the nonseasonal geostrophic advection by the ocean circulation works to reduce increase the wintertime sst anomalies when the kuroshio extension changes from an elongated contracted state to a contracted elongated state the sst anomalies associated with the large scale changes of the kuroshio extension have an area averaged peak topeak amplitude of 18c and appear independent of the interannual sst changes in the tropical pacific ocean

a comparison of radiolarian and foraminiferal paleoecology in the southern indian ocean new evidence for the interhemispheric timing of climatic change the deglacial transition between oxygen isotope stages 6 and 5e about 127 000 yr b p is marked by both oxygen isotopic depletion and estimated sea surface temperature sst increase in two subantarctic indian ocean cores the data show synchroneity between warming of foraminifera based sst estimates and depletion of 18o but an earlier warming trend on the basis of radiolarian sst estimates these data have been previously interpreted to indicate that the high latitude southern ocean warms prior to significant melting of glacial age ice sheets comparison of core top assemblages with surface and subsurface conditions in the southern indian ocean reveals that 1 a three part foraminiferal zonation reflects the surface hydrographic regime with abrupt faunal transitions at two major fronts the subtropical convergence stc and the antarctic polar front apf and 2 a two part radiolarian zonation coincides with a two part subsurface hydrographic regime with an abrupt faunal transition corresponding to the southern terminus of subtropical lower water stlw between the stc and the apf it is suggested that shifts of these surface and subsurface regimes are recorded by these foraminiferal and radiolarian assemblages in this interpretation the observed lead of radiolarian sst with respect to 18o indicates an early response to a southward shift of stlw while the later foraminiferal sst warming indicates a southward shift of the stc thus the origin of the southern hemisphere sst lead may be related to stlw which emanates from the subtropical gyres rather than the polar regions

seasonal evolutions of atmospheric response to decadal sst anomalies in the north pacific subarctic frontal zone observations and a coupled model simulation abstractpotential impacts of pronounced decadal scale variations in the north pacific sea surface temperature sst that tend to be confined to the subarctic frontal zone safz upon seasonally varying atmospheric states are investigated by using 48 yr observational data and a 120 yr simulation with an ocean atmosphere coupled general circulation model cgcm sst fields based on in situ observations and the ocean component of the cgcm have horizontal resolutions of 2 0 and 0 5 respectively which can reasonably resolve frontal sst gradient across the safz both the observations and cgcm simulation provide a consistent picture between sst anomalies in the safz yielded by its decadal scale meridional displacement and their association with atmospheric anomalies correlated with sst anomalies persistent in the safz from fall to winter a coherent decadal scale signal in the wintertime atmospheric circulation over the north pacific starts emerging in november and develops into an equivalent barotropic an

quantification of the biogenic silica dissolution in southern ocean sediments abstract a transfer function has been established to quantify the dissolution of diatom silica in southern ocean sediments the relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box core tops each representative of a modern diatom species sediment assemblage the amount of dissolved silica was measured for each experiment the resulting data set of species abundances 42 samples containing 32 diatom species and 2 silicoflagellate genera was added to the modern data base of diatom species distributed over the southern ocean 124 core tops q mode factor analysis individualizes four factors explaining 83 of the variance the first three factors are controlled by surface water properties mostly temperature the fourth factor is the only one correlated with loss of silica in the reference samples r 0 900 we quantified the dissolution factor using this correlation superficial sediments of the southeast indian ocean are characterized from low to high latitudes by a decrease in silica loss by dissolution from 50 to 10 from the subantarctic zone 40 s to around 55 s followed by an increase of silica loss to values larger than 60 between 63 and 68 s application of the dissolution factor in two cores from the southern ocean 44 and 55 s shows enhanced opal dissolution during the last glaciation particularly during emiliani s stage 3 from 40 000 to 30 000 yr b p