identification of the kuroshio extension its bifurcation and northern branch from altimetry and hydrographic data during october 1992 august 1999 spatial and temporal variability a methodology is proposed using altimter derived upper layer thickness and baroclinic transport to identify the kuroshio extension the bifurcation point and the northern branch by combining topex poseidon altimeter and climatological data within a two layer reduced gravity model results obtained from the japanese coast to 175 w show that the location of the bifurcation point presents interannual variability that is related with upstream conditions the longitude of the bifurcation point ranged from 147 to 160 e estimates of baroclinic transport at the kuroshio extension and its northern branch decrease steadily to the east trough the region of study from 35 to 11 and from 10 to 3 sv respectively

late quaternary variations in water mass in the shatsky rise area northwest pacific ocean abstract oxygen isotope analysis of planktonic and benthic foraminifera in piston core s 2 collected from the shatsky rise 33 21 75n 159 07 70e water depth 3107 m provides a paleoceanographic record for the last 540 000 years in the northwestern pacific ocean although peaks in the abundance of sinistral neogloboquadrina pachyderma occur during marine isotope stage 2 and particularly 6 and 12 the southward shifting of the subarctic front did not reach the core site during these glacial periods however mass accumulation rates of total organic carbon biogenic opal and terrigenous matter contents indicate that surface productivity increased during cold periods in addition the c n ratio analyzed in organic matter reached values of up to 10 during glacial periods these results imply that delivery of eolian dust to this site was enhanced by strengthened westerly winds during glacial periods down core fluctuations in 13c values of globigerinoides ruber and globorotalia inflata nearly overlap particularly during the period from 540 to 260 ka this latter trend suggest that the subtropical surface water mass prevailed at the core site throughout that period based upon the very small vertical 13c gradient through water column in modern kuroshio current water

dynamical response of equatorial indian ocean to intraseasonal winds zonal flow nonlinear and linear 4 layer ocean models are used to explore the dynamics of intraseasonal 20 90 day periods zonal flow in the equatorial indian ocean the model simulations suggest that the observed 40 60 day zonal surface current is forced primarily by wind associated with the madden julian oscillation mjo which peaks at 40 60 days the strongest spectral peak of zonal flow however occurs at 90 day period in the model and a corresponding 90 day peak appears in the observed sea level data the 90 day current results from the preferential excitation of kelvin and rossby waves by the lower frequency component of intraseasonal wind and from the enhancement by rossby waves reflected from the eastern ocean boundary

origins and dynamics of the 90 day and 30 60 day variations in the equatorial indian ocean abstract sea level observations in the equatorial indian ocean show a dominant spectral peak at 90 days and secondary peaks at 30 60 days over an intraseasonal period 20 90 days a detailed investigation of the origins and dynamics of these variations is carried out using an ocean general circulation model namely the hybrid coordinate ocean model hycom two parallel experiments are performed in the tropical indian ocean basin for the period 1988 2001 one is forced by ncep 3 day mean forcing fields together with the climate prediction center cpc merged analysis of precipitation cmap pentad precipitation and the other is forced by monthly mean fields to help to understand the role played by the wind driven equatorial wave dynamics a linear continuously stratified ocean model is also used both the observed and modeled 90 day sea level anomaly fields and hycom surface current clearly show equatorial kelvin and first meridional mode rossby wave structures that are forced by the 90 day winds the

sea surface temperature history of the low latitude western pacific during the last 5 3 million years abstract the late neogene was a time of cryosphere development in the northern hemisphere the present study was carried out to estimate the sea surface temperature sst change during this period based on the quantitative planktonic foraminiferal data of 8 dsdp sites in the western pacific target factor analysis has been applied to the conventional transfer function approach to overcome the no analog conditions caused by evolutionary faunal changes by applying this technique through a combination of time slice and time series studies the sst history of the last 5 3 ma has been reconstructed for the low latitude western pacific although the present data set is close to the statistical limits of factor analysis the clear presence of sensible variations in individual sst time series suggests the feasibility and reliability of this method in paleoceanographic studies the estimated sst curves display the general trend of the temperature fluctuations and reveal three major cool periods in the late neogene i e the early pliocene 4 7 3 5 ma the late pliocene 3 1 2 7 ma and the latest pliocene to early pleistocene 2 2 1 0 ma cool events are reflected in the increase of seasonality and meridional sst gradient in the subtropical area the latest pliocene to early pleistocene cooling is most important in the late neogene climatic evolution it differs from the previous cool events in its irreversible steplike change in sst which established the glacial climate characteristic of the late pleistocene the winter and summer sst decreased by 3 3 5 4 c and 1 0 2 1 c in the subtropics by 0 9 c and 0 6 c in the equatorial region and showed little or no cooling in the tropics moreover this cooling event occurred as a gradual sst decrease during 2 2 1 0 ma at the warmer subtropical sites while that at cooler subtropical site was an abrupt sst drop at 2 2 ma in contrast equatorial and tropical western pacific experienced only minor sst change in the entire late neogene in general subtropics was much more sensitive to climatic forcing than tropics and the cooling events were most extensive in the cooler subtropics the early pliocene cool periods can be correlated to the antarctic ice volume fluctuation and the latest pliocene early pleistocene cooling reflects the climatic evolution during the cryosphere development of the northern hemisphere

a linear stratified ocean model of the coastal undercurrent the linear stratified ocean model of mccreary 1981 is used to study the wind driven response of the ocean near an eastern coast the model can be regarded as an extension of the inviscid models of lighthill 1969 and of gill clarke 1974 that allows the vertical diffusion of heat and momentum into the deep ocean solutions are still found as expansions of vertical normal modes vertical mixing affects each mode as a linear drag with a drag coefficient that increases rapidly with mode number n a zonally uniform band of steady equatorward winds forces the ocean and the resulting flow field has many features in common with observations at eastern boundaries there is a surface equatorward jet and a poleward coastal undercurrent confined within 10 20 km of the coast both currents extend well poleward of the wind band upwelling does not reach great depths but occurs only above the core of the undercurrent weak downwelling occurs at greater depths there is offshore ekman drift in the surface mixed layer and return flow at a depth slightly above the core of the undercurrent the baroclinic alongshore pressure gradient field and the vertical mixing of heat and momentum are essential elements of the model dynamics but the beta and horizontal mixing are not low order vertical modes n 6 tend toward a two dimensional balance they generate the transverse circulation pattern associated with coastal ekman pumping

origins of wind driven intraseasonal sea level variations in the north indian ocean coastal waveguide 1 in this paper we show that a linear continuously stratified ocean model reproduces observed wind driven intraseasonal sea level variability in the coastal waveguide of the northern indian ocean nio sensitivity experiments with intraseasonal wind forcing selectively applied in the equatorial region bay of bengal and arabian sea show that a large part of the basin scale sea level variations are driven by zonal wind fluctuations along the equator within the nio coastal waveguide the contribution of remote equatorial forcing decreases from 80 90 in the andaman sea to 50 northeast of sri lanka and then increases to 60 70 along the west coast of india during the southwest monsoon intraseasonal wind variations become stronger over the nio resulting in a larger contribution of local wind forcing to sea level variability along the west up to 60 and east up to 40 coasts of india

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

intraseasonal to semiannual variability of sea surface height in the astern equatorial indian ocean and southern bay of bengal intraseasonal to semiannual variability of sea surface height ssh in the eastern equatorial indian ocean eeio and southern bay of bengal bob is investigated using altimetric data and solutions to 1 layer first baroclinic mode and linear continuously stratified lcs multi baroclinic mode models the amplitude and dominant period of ssh variability differ regionally large amplitude variability is found along the west coast of sumatra in a zonal band across the bob centered along 5 n east of sri lanka and in the northwestern bob respectively along the sumatran west coast ssh variability peaks at 30 60 days 90 days and 180 days along 5 n and east of sri lanka the 30 60 day variability is dominant sensitivity experiments using a nonlinear version of the 1 layer model forced by realistic winds reproduce the observed patterns of intraseasonal variability in the southern bob at 30 60 days the solutions show that eddies nonlinear rossby waves propagating from the east rather than local wind forcing account for most of the variance east of sri lanka furthermore they demonstrate that the variance is significantly enhanced by the nonlinear transfer of 90 120 day energy into the intraseasonal band of 30 60 days the lcs solutions show that the first two baroclinic modes explain most of the ssh variance at 90 180 days the second baroclinic mode dominates the ssh variance at 180 days a consequence of basin resonance and strong wind forcing

seasonal variations in planktonic foraminifera at three sediment traps in the subarctic transition and subtropical zones of the central north pacific ocean the distribution and flux of planktonic foraminifera in the north pacific ocean were studied for a 1 year period beginning in july 1993 using time series samples collected in three sediment traps deployed in a north south transect along 175 e longitude sediment trap locations allowed monitoring of faunas within the subarctic transition and subtropical water masses in this region seasonally high foraminiferal flux rates were recorded at the subarctic site during periods of intense stratification of surface water accompanied by high fluxes of organic matter and biogenic opal contents faunal composition dominated by sinistral forms of neogloboquadrina pachyderma and globigerina umbilicata at the latter site characterized the subarctic water mass feature data collected at the transitional and subtropical sites illustrate differences in seasonal flux rates and in relation to those recorded at the subarctic site faunal composition at the transitional water mass site was dominated by dextral phenotypes of n pachyderma whereas this taxon was absent at the subtropical site also during the period of warmest surface temperature october globigerinoides ruber became dominant at the transitional water mass site in contrast to the subtropical water mass site where globigerinoides sacculifer became dominant while associated with common occurrences of globigerinoides tenellus and globorotalia tumida much lower fluxes of planktonic foraminifera organic matter and biogenic opal also marked subtropical water the distinctive differences in faunal composition and flux rates at the transitional and subtropical sites suggest that little if any exchange of surface water occurred between these two sites and in particular in the area representing the distal kuroshio extension

long wave resonance in tropical oceans and implications on climate the atlantic ocean based on the well established importance of long non dispersive baroclinic kelvin and rossby waves a resonance of tropical planetary waves is demonstrated three main basin modes are highlighted through joint wavelet analyses of sea surface height ssh and surface current velocity scv scale averaged over relevant bands to address the co variability of variables 1 a 1 year period quasi stationary wave qsw formed from gravest mode baroclinic planetary waves which consists of a northern an equatorial and a southern antinode and a major node off the south american coast that straddles the north equatorial current nec and the north equatorial counter current necc 2 a half a year period harmonic 3 an 8 year sub harmonic contrary to what is commonly accepted the 1 year period qsw is not composed of wind generated kelvin and rossby beams but results from the excitation of a tuned basin mode trade winds sustain a free tropical basin mode the natural frequency of which is tuned to synchronize the excitation and the ridge of the qsws the functioning of the 1 year period basin mode is confirmed by solving the momentum equations expanding in terms of fourier series both the coefficients and the forcing terms the terms of fourier series have singularities highlighting resonances and the relation between the resonance frequency and the wavenumbers this ill posed problem is regularized by considering rayleigh friction the waves are supposed to be semi infinite i e they do not reflect at the western and eastern boundaries of the basin which would assume the waves vanish at these boundaries at the western boundary the equatorial rossby wave is deflected towards the northern antinode while forming the necc that induces a positive doppler shifted wavenumber at the eastern boundary the kelvin wave splits into coastal kelvin waves that flow mainly southward to leave the gulf of guinea in turn off tropical waves extend as an equatorially trapped kelvin wave being deflected off the western boundary the succession of warm and cold waters transferred by baroclinic waves during a cycle leaves the tropical ocean by radiation and contributes to western boundary currents the main manifestation of the basin modes concerns the variability of the necc of the branch of the south equatorial current sec along the equator of the western boundary currents as well as the formation of remote resonances as will be presented in a future work remote resonances occur at midlatitudes the role of which is suspected of being crucial in the functioning of subtropical gyres and in climate variability

salinity changes in the north west pacific ocean during the late pliocene early quaternary from 2 73 ma to 2 52 ma recent research has increasingly advocated a role for the north pacific ocean in modulating global climatic changes over both the last glacial cycle and further back into the geological record here a diatom 18o record is presented from ocean drilling program site 882 over the pliocene quaternary boundary from 2 73 ma to 2 52 ma mis g6 mis 99 large changes in 18odiatom of c 4 from 2 73 ma onwards are documented to occur on a timeframe broadly coinciding with glacial interglacial cycles these changes are primarily attributed to large scale inputs of meltwater from glacials surrounding the north pacific basin and the bering sea despite these inputs and associated change in surface water salinity on the basis of existing opal and uk37 temperature data and new modelled water column densities no evidence exists to suggests a removal of the halocline stratification or a resumption of the high productivity system similar to that which prevailed prior to 2 73 ma the permanence of the halocline suggests that the region played a key role in driving global climatic changes over the early glacial interglacial cycles that followed the onset of major northern hemisphere glaciation by inhibiting deep water upwelling and ventilation of co2 to the atmosphere

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

late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments the modern indian ocean summer monsoon is driven by differential heating between the asian continent and the indian ocean to the south this differential heating produces a strong pressure gradient which drives southwest monsoon winds during june july and august satellite and meteorological observations aerosol measurements sediment trap studies and mineralogical studies indicate an atmospheric mode of transport for modern lithogenic sediments in the northwest arabian sea analyses of lithogenic grain size and mass accumulation rate mar records from the owen ridge indicate that eolian transport has been the primary mode of transport for the past 370 kyr visual inspection shows that the mar record is positively correlated with global ice volume as indicated by the marine 18o record in contrast the grain size record varies at a much higher frequency showing little correlation to either the mar or the 18o records spectral analyses confirm these relationships indicating that the lithogenic grain size and mar records are coherent only over the precession band whereby the grain size leads the mar by 124 8 kyr we conclude that an eolian transport mechanism is the only mechanism that allows for this phase difference and at the same time is supported by comparison of the grain size and mar with independent eolian records we use lithogenic grain size as a paleoclimatic indicator of summer monsoon wind strength and lithogenic mar as a paleoclimatic indicator of source area aridity these interpretations are supported by comparison of the lithogenic records to independent indicators of wind strength globigerina bulloides upwelling record and aridity a loess record from central china such comparisons indicate high coherence and zero phase relationships our work supports the findings of previous studies which have documented the link between monsoon strength and the earth s axial precession cycles both the lithogenic mar and the grain size records have high coherency with precessional insolation maximum lithogenic mar source area aridity is in phase with 18o global ice volume and leads maximum precessional insolation by 88 6 kyr we attribute this lead to the influence of glacial conditions on the aridity and therefore the deflation potential of the source areas maximum lithogenic grain size summer monsoon wind strength lags maximum precession by 148 9 kyr we attribute this lag both to the influence of global and or local ice volume and to the availability of latent heat from the southern hemisphere indian ocean the two of which combine to determine the strength of the indian ocean monsoon

what is the timing of orbital scale monsoon changes abstract a major but little noted divergence of opinion has developed among climate scientists over the orbital scale periodicity and phasing of tropical monsoon variations kutzbach 1981 monsoon climate of the early holocene climate experiment with earth s orbital parameters for 9000 years ago science 214 59 61 proposed that monsoons are driven by northern summer insolation at the precession period but clemens and prell 1990 late pleistocene variability of arabian sea summer monsoon winds and continental aridity eolian records from the lithogenic component of deep sea sediments paleoceanography 5 109 145 2003 a 350 000 year summer monsoon multi proxy stack from the owen ridge northern arabian sea marine geology 201 35 51 inferred a more complicated response tied to latent heat transfer from the southern hemisphere because tropical monsoons affect climate over a vast area resolving this divergence is an important task for the climate community the purpose of this note is to highlight definitive evidence from high resolution dating of speleothem calcite that provides unambiguous support for the kutzbach hypothesis

deep sea temperature and ice volume changes across the pliocene pleistocene climate transitions earth has undergone profound changes since the late pliocene which led to the development 2 7 million years ago ma and intensification 0 9 ma of large scale northern hemisphere ice sheets recorded as transitions in the benthic foraminiferal oxygen isotope 18ob record here we present an orbitally resolved record of deep ocean temperature derived from benthic foraminiferal magnesium calcium ratios from the north atlantic which shows that temperature variations are a substantial portion of the global 18ob signal the record shows two distinct cooling events associated with the late pliocene lpt 2 5 to 3 ma and mid pleistocene mpt 1 2 to 0 85 ma climate transitions whereas the lpt increase in ice volume is attributed directly to global cooling the shift to 100 000 year cycles at the mpt is more likely to be a response to an additional change in ice sheet dynamics

impact of atmospheric intraseasonal oscillations on the indian ocean dipole during the 1990s abstract effects of atmospheric intraseasonal oscillations isos on the indian ocean zonal dipole mode iozdm are investigated by analyzing available observations and a suite of solutions to an ocean general circulation model namely the hybrid coordinate ocean model hycom data and model solutions for the period 1991 2000 are analyzed a period that includes two strong iozdm events during 1994 and 1997 and a weak one in 1991 both the data analysis and model results suggest that atmospheric isos play a significant role in causing irregularity of the two strong iozdm events and the premature termination of the weak one of particular interest is a basinwide wind driven oceanic resonance with a period near 90 days involving the propagation of equatorial kelvin and first meridional mode rossby waves across the basin before the onset of the strong 1997 dipole wind variability had significant power near 90 days and the resonance was strongly excited associated with the resonance was a deepened t

forward modeling of carbonate proxy data from planktonic foraminifera using oxygen isotope tracers in a global ocean model the distribution and variation of oxygen isotopes in seawater are calculated using the goddard institute for space studies global ocean model simple ecological models are used to estimate the planktonic foraminiferal abundance as a function of depth column temperature season light intensity and density stratification these models are combined to forward model isotopic signals recorded in calcareous ocean sediment the sensitivity of the results to the changes in foraminiferal ecology secondary calcification and dissolution are also examined simulated present day isotopic values for ecology relevant for multiple species compare well with core top data hindcasts of sea surface temperature and salinity are made from time series of the modeled carbonate isotope values as the model climate changes paleoclimatic inferences from these carbonate isotope records are strongly affected by erroneous assumptions concerning the covariations of temperature salinity and 18ow habitat imposed biases are less important although errors due to temperature dependent abundances can be significant

receiver function images of the distorted philippine sea slab contact with the continental crust implications for generation of the 1891 nobi earthquake mj 8 0 abstract the 28 october 1891 nobi earthquake was one of the largest intraplate earthquakes in japan with an estimated magnitude of 8 0 determined by the japan meteorological agency it occurred in central japan on the eurasian plate beneath which the young philippine sea plate is subducting the geometry of this plate is not smooth rather beneath western japan it appears distorted over a relatively short lateral distance beneath the kinki region of central japan the subduction angle is approximately horizontal and the nobi earthquake occurred just above the horizontal section of the philippine sea slab temporary seismic stations were deployed in this area to investigate local seismic structure and its possible relationship to the cause of the earthquake crustal structure was investigated using receiver function analysis with a spatially dense temporary seismic network a clear image of the subducted philippine sea slab was resolved with ridge like structures beneath the epicentral area of the nobi earthquake the ridge like structure is in contact with the continental crust and the fault plane of the nobi earthquake is located at the edge of one such structure i e in the contact area the unique structure of the area is inferred to cause stress concentration and strain accumulation on local faults which resulted in the large size of the nobi earthquake

permanent el nino like conditions during the pliocene warm period during the warm early pliocene 4 5 to 3 0 million years ago the most recent interval with a climate warmer than today the eastern pacific thermocline was deep and the average west to east sea surface temperature difference across the equatorial pacific was only 1 5 0 9 c much like it is during a modern el nino event thus the modern strong sea surface temperature gradient across the equatorial pacific is not a stable and permanent feature sustained el nino like conditions including relatively weak zonal atmospheric walker circulation could be a consequence of and play an important role in determining global warmth

simulation of north atlantic decadal multidecadal winter sst anomalies driven by basin scale atmospheric circulation anomalies the north atlantic winter sea surface temperature anomaly tsa response to anomalous surface atmospheric circulation anomalies that vary over decadal and short term inter decadal periods is simulated for 1950 through 1992 anomalous ocean variability is driven by adding monthly coads derived anomalous fields of vector wind stress and wind speed to the climatological annual cycle forcing a simple model is derived relating winter tsa to the integrated atmospheric forcing present earlier in time that is responsible for its existence the basinscale structure of forced winter tsa patterns depends on the structure of the atmospheric forcing along with regional differences in the dominant mixed layer processes that generate tsa for example when the atmospheric subtropical high and subpolar low pressure systems are simultaneously strong enhanced flow around and baroclinic adjustments within the subtropical gyre results in anomalously warm water in the gulf stream region off the u s east coast at the same time however the open ocean generally cools because the westerlies and trades are anomalously strong by analyzing tsa variability not driven by the atmosphere an anomalously cold decade is identified characterized by rapid onset and termination that both occur within one year the onset during 1968 coincides with the appearance of the great salinity anomaly while the termination during 1977 coincides with an abrupt northern hemisphere climate shift that is particularly evident in the pacific

basin resonances in the equatorial indian ocean abstractprevious studies have investigated how second baroclinic mode n 2 kelvin and rossby waves in the equatorial indian ocean io interact to form basin resonances at the semiannual 180 day and 90 day periods this paper examines unresolved issues about these resonances including the reason the 90 day resonance is concentrated in the eastern ocean the time scale for their establishment and the impact of complex basin geometry a hierarchy of ocean models is used an idealized one dimensional 1d model a linear continuously stratified ocean model lcsm and an ocean general circulation model ogcm forced by quick scatterometer quikscat wind during 2000 08 results indicate that the eastern basin concentration of the 90 day resonance happens because the westward propagating rossby wave is slower and thus is damped more than the eastward propagating kelvin wave results also indicate that superposition with other baroclinic modes further enhances the eastern maximum and weakens sea level

establishment of the western pacific warm pool during the pliocene evidence from planktic foraminifera oxygen isotopes and mg ca ratios abstract this study presents new evidence of when and how the western pacific warm pool wpwp was established in its present form we analyzed planktic foraminifera oxygen isotopes and mg ca ratios in upper miocene through pleistocene sediments collected at deep sea drilling program dsdp site 292 these data were then compared with those reported from ocean drilling program odp site 806 both drilling sites are located in the western pacific ocean dsdp site 292 is located in the northern margin of the modern wpwp and odp site 806 near the center of the wpwp three stages of development in surface water conditions are identified in the region using planktic foraminferal data during the initial stage from 8 5 to 4 4 ma site 806 was overlain by warm surface water but site 292 was not as indicated by the differences in faunal compositions and sea surface temperature sst between the two sites in addition the vertical thermal gradient at site 292 was weak during this period as indicated by the small differences in the 18 o values between globigerinoides sacculifer and pulleniatina spp during stage two from 4 4 to 3 6 ma the sst at site 292 rapidly increased to 27 c but the vertical thermal gradient had not yet be strengthened as shown by mg ca ratios and the presence of both mixed layer dwellers and thermocline dwellers finally a warm mixed layer with a high sst ca 28 c and a strong vertical thermal gradient were established at site 292 by 3 6 ma this event is marked by the dominance of mixed layer dwellers a high and stable sst and a larger differences in the 18 o values between g sacculifer and pulleniatina spp thus evidence of surface water evolution in the western pacific suggests that site 292 came under the influence of the wpwp at 3 6 ma the northward expansion of the wpwp from 4 4 to 3 6 ma and the establishment of the modern wpwp by 3 6 ma appear to be closely related to the closure of the indonesian and central american seaways

an updated astronomical timescale for the plio pleistocene deposits from south china sea and new insights into asian monsoon evolution abstract here we present an improved astronomical timescale since 5 ma as recorded in the odp site 1143 in the southern south china sea using a recently published asian summer monsoon record hematite to goethite content ratio hm gt and a parallel benthic 18o record correlation of the benthic 18o record to the stack of 57 globally distributed benthic 18o records lr04 stack and the hm gt curve to the 65 n summer insolation curve is a particularly useful approach to obtain refined timescales hence it constitutes the basis for our effort our proposed modifications result in a more accurate and robust chronology than the existing astronomical timescale for the odp site 1143 this updated timescale further enables a detailed study of the orbital variability of low latitude asian summer monsoon throughout the plio pleistocene comparison of the hm gt record with the 18o record from the same core reveals that the oscillations of low latitude asian summer monsoon over orbital scales differed considerably from the glacial interglacial climate cycles the popular view that summer monsoon intensifies during interglacial stages and weakens during glacial stages appears to be too simplistic for low latitude asia in low latitude asia some strong summer monsoon intervals appear to have also occurred during glacial stages in addition to their increased occurrence during interglacial stages vice versa some notably weak summer monsoon intervals have also occurred during interglacial stages next to their anticipated occurrence during glacial stages the well known mid pleistocene transition mpt is only identified in the benthic 18o record but not in the hm gt record from the same core this suggests that the mpt may be a feature of high and middle latitude climates possibly determined by high latitude ice sheet dynamics for low latitude monsoonal climate its orbital scale variations respond more directly to insolation and are little influenced by high latitude processes thus the mpt is likely not recorded in addition the hm gt record suggests that low latitude asian summer monsoon intensity has a long term decreasing trend since 2 8 ma with increased oscillation amplitude this long term variability is presumably linked to the northern hemisphere glaciation since then

persistent suborbital climate variability in marine isotope stage 5 and termination ii new surface water records from two high sedimentation rate sites located in the western subtropical north atlantic near the axis of the gulf stream provide clear evidence of suborbital climate variations through marine isotope stage mis 5 persisting even into the warm peak of the interglaciation substage 5e we found that the amplitude of suborbital climate oscillations did not vary significantly for the whole of mis 5 implying that ice volume has little or no influence on the amplitude of suborbital climate variability in this region although some records suggest that longer suborbital variations 4 10 kyr during mis 5 are linked to deepwater changes none of the existing records is of sufficient resolution to assess if a linkage occurred for oscillations shorter than 4 kyr however when examined in conjunction with published data from the norwegian sea new evidence from the subpolar north atlantic suggests that coupled surface deepwater oscillations occurred during the penultimate deglaciation this supports the hypothesis that during glacial and deglacial times ocean ice interactions and deepwater variability amplify suborbital climate change at higher latitudes we suggest that during the penultimate deglaciation the north atlantic deepwater source varied between nordic sea and open north atlantic locations in parallel with surface temperature oscillations

satellite altimeter monitoring the kuroshio transport south of japan in 1993 1995 we carried out observations of the kuroshio south of japan including direct current measurements and repeated hydrographic surveys along a satellite track of the topex poseidon altimeter the velocity field of the kuroshio is determined by geostrophic calculation using the repeated hydrographic survey data referenced to velocities observed at mid and abyssal depths the volume transport of the kuroshio is estimated from this velocity field the estimated transports of the kuroshio have a high correlation with sea surface height differences across the kuroshio having this relationship and using the altimeter data we obtained a time series of the kuroshio transport over seven years at ten day intervals the kuroshio transport excluding contributions by local recirculations is estimated to be 42 106 m sec on average the correlation between sea surface height difference and transport provides a practical method of long term monitoring of the kuroshio transport using satellite altimetry

isotopic signals in two morphotypes of globigerinoides ruber white from the south china sea implications for monsoon climate change during the last glacial cycle abstract based on the study of surface and downcore sediment samples from the south china sea scs two morphotypes of globigerinoides ruber white have been differentiated by taxonomic criteria at species and or subspecies level and also by their stable isotopic compositions of oxygen and carbon the two morphotypes g ruber sensu stricto s s and g ruber sensu lato s l represent two groups with different depth habitats with g ruber s s living in the upper 30 m of the water column and g ruber s l living at depths below 30 m the different depth habitats are indicated by the comparison between the present oceanographic data and isotopic signals of the two morphotypes in the surface sediment from the scs application of this information to a hemipelagic sediment core in the northern scs shows that drastic changes existed in the morphotypes isotopic records during the last glacial cycle the isotope difference between the two morphotypes diminished during 18 o stage 2 especially during the last glacial maximum it is inferred that this is the result of intensified monsoon winds which caused mixing of the upper layer of the water column during stage 2 the proportion of g ruber s l increased which is interpreted as a result of the increased productivity due to mixing of the subsurface nutrient rich water into the surface layer

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

sea surface temperature variability and deep water reorganisation in the subtropical north atlantic during isotope stage 2 4 abstract two sediment cores from a high accumulation sediment drift at 3000 m water depth in the western north atlantic are investigated in order to examine possible linkages between subtropical surface and bottom water properties and global climate oscillations during the last glacial interglacial cycle planktonic foraminiferal assemblages and the 18 o of globigerinoides ruber both document large sea surface temperature oscillations 3 4 c that appear to co vary with greenland ice core records short episodes of sea surface cooling as far south as the blake outer ridge at 33 n are inferred from increased abundance of the polar species neogloboquadrina pachyderma sinistral during the ice core stadials events nutrient proxy records suggest that the deep waters flooding the site alternated between a northern north atlantic deep water and a southern southern ocean water source in most cases warm surface water conditions interstadials were accompanied by a strong north atlantic deep water component in the bottom water circulation however the transitions into interstadial 14 and 12 seem to be marked by a 1500 yr lag between surface water warming and the deep water circulation shift as recorded by caco 3 and 13 c of benthonic foraminifera

role of tropics in changing the response to milankovich forcing some three million years ago appeared in regions that today have intense oceanic upwelling the eastern equatorial pacific and the coastal zones of southwestern africa and california there was furthermore a significant change in the earth s response to milankovich forcing obliquity signals became large but those associated with precession and eccentricity remained the same the latter change in the earth s response can be explained by hypothesizing that the global cooling during the cenozoic affected the thermal structure of the ocean it caused a gradual shoaling of the thermocline around 3 ma the thermocline was sufficiently shallow for the winds to bring cold water from below the thermocline to the surface in certain upwelling regions this brought into play feedbacks involving

pliocene pleistocene evolution of eastern tropical pacific surface water circulation and thermocline depth we evaluated the response of eastern equatorial pacific upper water column hydrography to the panama seaway closure and the initiation of large scale northern hemisphere glaciation the 18o gradient between globorotalia tumida and globigerinoides sacculifer indicates a general shoaling of the thermocline between 4 2 and 3 0 ma which may be related to a recorded decrease in southeast trade wind strength the 13c gradients suggest that surface water nutrient concentrations have increased during the last 5 myr and that upwelling intermediate waters began to change sources at 3 2 ma changes in the trans pacific east west temperature and nutrient gradients at 4 0 and 1 5 ma are coincident with the seaway closure and a major phase of northern hemisphere glaciation changes in the sensitivity of surface circulation to milankovitch forcing 18o records linearly related to orbital variations only after 3 2 ma are associated with the seaway closure pleistocene initiation of 100 and 41 kyr cycles in the thermocline depth proxy may suggest that the hydrographic response to milankovitch forcing is enhanced by air sea interactions which maintain the relatively steep pleistocene trans pacific gradients the 13c records are dominated by the 41 kyr period and are usually coherent with high latitude climate suggesting that associated changes in the global carbon reservoir dominate the tropical 13c signals

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

intraseasonal variability of sea surface height in the bay of bengal intraseasonal variability isv of sea surface height ssh over the bay of bengal bob is studied using altimetry data and an eddy resolving ocean model in both the model hindcast and satellite observations large ssh isv is found along the eastern and northern coasts of the bob in the western bob and in a zonal band across the bay centered near 5 degrees n the isv displays a clear seasonality in the western bob it reaches its annual maximum in spring whereas it does so in summer and autumn southeast of sri lanka driven by equatorial intraseasonal winds equatorial kelvin waves propagate eastward reach the western coast of sumatra and reflect there to propagate around the perimeter of the bob as coastally trapped waves two distinct bands of high eddy activity are detected in the western and central bob respectively in both bands isolated eddies propagate southwestward eddy formation in the eddy train in the central bay is linked to the coastal wave as it bends around the corner of the irrawaddy delta off myanmar eddy activity contributes to the high isv in the central bay to some extent an energetics analysis indicates that high total eddy energy in the western bob is due to barotropic baroclinic instability of the mean current citation cheng x s p xie j p mccreary y qi and y du 2013 intraseasonal variability of sea surface height in the bay of bengal j geophys res oceans 118 816 830 doi 10 1002 jgrc 20075

late pliocene equatorial pacific 1 late pliocene foraminiferal mg ca and 18o records from ocean drilling program hole 806b in the western equatorial pacific wep reveal warm pool climate evolution during the onset of northern hemisphere glaciation 3 1 2 3 myr b p mg ca data indicate an average late pliocene sea surface temperature sst of 27 8 c a small long term cooling of 0 3 c between 3 1 and 2 3 ma and a glacial interglacial g i sst range of 2 c throughout this time interval for comparison pleistocene ssts at this site over the last 0 9 myr average 27 7 c with a g i range of 3 c orbital scale variability in hole 806b ssts during the late pliocene occurs predominantly at 100 ka in contrast to foraminiferal 18o records which show a dominant 41 kyr period variability at a 41 kyr period out of phase with local annual insolation changes driven by obliquity is also observed in the new wep sst record the wep sst record suggests that an 3 c equatorial pacific sst zonal gradient prevailed during the late pliocene compatible with a weaker walker circulation adjustment of hole 806b ssts for past changes in seawater mg ca suggests that ssts higher than 30 c prevailed at 3 myr b p followed by a progressive cooling of the warm pool through the late pliocene the characteristics of late pliocene tropical climate evolution suggest that atmospheric greenhouse gas forcing played a major role in driving the observed g i sst changes

filtering of milankovitch cycles by earth s geography abstract earth s land sea distribution modifies the temperature response to orbitally induced perturbations of the seasonal insolation we examine this modification in the frequency domain by generating 800 000 yr time series of maximum summer temperature in selected regions with a linear two dimensional seasonal energy balance climate model previous studies have demonstrated that this model has a sensitivity comparable to general circulation models for the seasonal temperature response to orbital forcing on land although the observed response in the geologic record is sometimes significantly different than modeled here differences attributable to model limitations and feedbacks involving the ocean atmosphere cryosphere system there are several results of significance 1 in mid latitude land areas the orbital signal is translated linearly into a large 10 c seasonal temperature response 2 although the modeled seasonal response to orbital forcing on antarctica is 6 c the annual mean temperature effect

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

impact of atmospheric intraseasonal variability in the indian ocean low frequency rectification in equatorial surface current and transport an ocean general circulation model ogcm is used to investigate the low frequency period longer than 90 days rectification of atmospheric intraseasonal variability 10 90 day periods in zonal surface current and transport of the equatorial indian ocean a hierarchy of ogcm solutions is found in an actual tropical indian ocean basin for the period of 1988 2001 to help to identify and isolate nonlinear processes a linear continuously stratified model and a 4 layer intermediate ocean model are also used results from the ogcm solutions suggest 1 2 that intraseasonal atmospheric forcing acts to weaken the equatorial seasonal surface currents amplitudes of the spring and autumn eastward surface jets the wyrtki jets wj and the westward surface current during january march are reduced by as much as 15 25 cm s21 by intraseasonal atmospheric forcing and strengths of the rectification exhibit a significant interannual variability important processes that cause the low frequency rectification are asymmetric response of mixed layer depth to easterly and westerly winds entrainment and upwelling of momentum during spring and autumn the westerly easterly phase of an intraseasonal event enhances weakens or even reverses the seasonal westerly winds increases decreases equatorial convergence and entrainment and thus deepens thins the mixed layer a net westward current is generated over an event mean because easterly wind acts on a thinner surface mixed layer whereas westerly wind acts on a thicker one in contrast during january march when the seasonal winds are equatorial easterlies surface currents are westward and equatorial undercurrents euc develop the rectified surface currents are eastward which reduces the westward surface flow this eastward rectification results largely from the vertical advection and entrainment of the euc the seasonal to interannual variability of the rectified surface flow is determined primarily from the seasonal cycle and interannual variability of the background state seasonal to interannual variability of the intraseasonal wind forcing also contributes the rectified low frequency zonal volume heat transports integrated over the entire water column along the indian ocean equator are persistently eastward with an amplitude of 0 15 3 106 m3 s 21 0 1 2 pw this is because westerly winds generate equatorial downwelling advecting the surface eastward momentum downward and giving an eastward subsurface current easterly winds cause equatorial upwelling and produce an eastward pressure gradient force that drives an eastward subsurface current this eastward subsurface current is advected upward by upwelling the mean effect over an intraseasonal event at the equator is to increase the eastward transport in the water column in the layers above the thermocline the rectified zonal volume heat transports are in the same direction as the rectified surface currents results from this paper may have important implications for understanding climate variability because modification of wj strength and transports can affect the sst and heat storage in the equatorial indian ocean warm pool

a 370 ka paleoceanographic record from the hess rise central north pacific ocean and an indistinct kuroshio extension abstract a 5 m long core np36 collected from the hess rise in the central north pacific ocean 34 11 7 n 179 15 4 e water depth 2664 m was analyzed for benthic and planktonic foraminifera this core yields a continuous record for the last ca 370 000 years according to the oxygen isotope stratigraphy cross spectral analysis of down core variations in planktonic 18o values correlates well with the specmap reference scale allowing recognition of marine isotope stages mis down to mis 10 and the 18o variations coincide well with the changes in sea surface temperature derived using the modern analogue technique time series analyses of mass accumulation rates mar of planktonic and benthic foraminifera were also performed along with analysis of variations in faunal composition mar of planktonic foraminifera display maxima during glacial periods which together with coincident changes in lightness l of sediment measured with the spectrophotometer strongly suggests increasing flux of eolian dust to the hess rise due to strengthened westerly winds however mar of benthic foraminifera including epistominella exigua a common typical phytodetritus feeder also display highest increases during some interglacial periods i e mis 5 and 7 the benthic mar maxima are thought to reflect variations in consumption patterns between benthic and planktonic species a proposed hypothesis that vigorous grazing of phytoplanktons occurred during glacial periods reducing the flux of phytodetritus to the sea floor in turn impacting and limiting production of benthic foraminifera with the opposite effect prevailing during interglacial periods down core variations in right coiling neogloboquadrina pachyderma abundance and the composition of planktonic foraminiferal faunas indicate the subarctic front did not shift southward over the study site during the past 370 000 years alternatively variations in faunal composition indicate that subtropical water prevailed in the study area throughout this period no clear faunal evidence of the presence of the kuroshio extension was found in core np36 reflecting the loss of heat and tropical faunal elements from this water mass as it flowed eastward during late quaternary climatic maxima and minima

monsoon climate of the early holocene climate experiment with the earth s orbital parameters for 9000 years ago values for the precession and obliquity of the earth 9000 years ago indicate that the global average solar radiation for july 9000 years ago was 7 percent greater than at present when the estimated solar radiation values are used in a low resulation climate model the model simulates an intensified continent scale monsoon circulation this result agrees with paleoclimatic evidence from africa arabia and india that monsoon rains were stronger between 10 000 and 5000 years ago than they are today

numerical simulation of the observed near surface east india coastal current on the continental slope we simulate the east india coastal current eicc using two numerical models resolution 0 1 circ times 0 1 circ an oceanic general circulation model ogcm called modular ocean model and a simpler linear continuously stratified lcs model and compare the simulated current with observations from moorings equipped with acoustic doppler current profilers deployed on the continental slope in the western bay of bengal bob we also carry out numerical experiments to analyse the processes both models simulate well the annual cycle of the eicc but the performance degrades for the intra annual and intraseasonal components in a model resolution experiment both models run at a coarser resolution of 0 25 circ times 0 25 circ simulate well the currents in the equatorial indian ocean eio but the performance of the high resolution lcs model as well as the coarse resolution ogcm which is good in the eicc regime degrades in the eastern and northern bob an experiment on forcing mechanisms shows that the annual eicc is largely forced by the local alongshore winds in the western bob and remote forcing due to ekman pumping over the bob but forcing from the eio has a strong impact on the intra annual eicc at intraseasonal periods local equatorial forcing dominates in the south north because the kelvin wave propagates equatorward in the western bob a stratification experiment with the lcs model shows that changing the background stratification from eio to bob leads to a stronger surface eicc owing to strong coupling of higher order vertical modes with wind forcing for the bob profiles these high order modes which lead to energy propagating down into the ocean in the form of beams are important only for the current and do not contribute significantly to the sea level

roles of equatorial waves and western boundary reflection in the seasonal circulation of the equatorial indian ocean an ocean general circulation model ogcm is used to study the roles of equatorial waves and western boundary reflection in the seasonal circulation of the equatorial indian ocean the western boundary reflection is defined as the total kelvin waves leaving the western boundary which include the reflection of the equatorial rossby waves as well as the effects of alongshore winds off equatorial rossby waves and nonlinear processes near the western boundary the evaluation of the reflection is based on a wave decomposition of the ogcm results and experiments with linear models it is found that the alongshore winds along the east coast of africa and the rossby waves in the off equatorial areas contribute significantly to the annual harmonics of the equatorial kelvin waves at the western boundary the semiannual harmonics of the kelvin waves on the other hand originate primarily from a linear reflection of the equatorial rossby waves the dynamics of a dominant annual oscillation of sea level coexisting with the dominant semiannual oscillations of surface zonal currents in the central equatorial indian ocean are investigated these sea level and zonal current patterns are found to be closely related to the linear reflections of the semiannual harmonics at the meridional boundaries because of the reflections the second baroclinic mode resonates with the semiannual wind forcing that is the semiannual zonal currents carried by the reflected waves enhance the wind forced currents at the central basin because of the different behavior of the zonal current and sea level during the reflections the semiannual sea levels of the directly forced and reflected waves cancel each other significantly at the central basin in the meantime the annual harmonic of the sea level remains large producing a dominant annual oscillation of sea level in the central equatorial indian ocean the linear reflection causes the semiannual harmonics of the incoming and reflected sea levels to enhance each other at the meridional boundaries in addition the weak annual harmonics of sea level in the western basin resulting from a combined effect of the western boundary reflection and the equatorial zonal wind forcing facilitate the dominance by the semiannual harmonics near the western boundary despite the strong local wind forcing at the annual period the rossby waves are found to have a much larger contribution to the observed equatorial semiannual oscillations of surface zonal currents than the kelvin waves the westward progressive reversal of seasonal surface zonal currents along the equator in the observations is primarily due to the rossby wave propagation

annual and interannual variability in the kuroshio current system abstract individual seasonal 300 m temperature maps were constructed over the kuroshio current system from 130 e to 170 w for a 4 year period from summer 1976 through spring 1980 using transpac xbt data and jodc temperature depth data quasi stationary meanders in the kuroshic current system occurred at 137 c i e kuroshio meander at 144 e and 150 e i e lee wave meanders and near 160 e i e meander over the shatsky rise a composite of the paths of the kuroshio i e the 12 c isotherm from the individual seasonal maps and the total variance map finds nodes i e minima and anti nodes i e maxima of variability to have existed along the mean kuroshio path the anti nodes coincided with the location of the quasi stationary meanders the nodes in between zonal propagation of temperature anomalies accounted for 20 30 of the total interannual variance these temperature anomalies propagated eastward at 0 5 1 5 cm s 1 in the region 140 155 e and westward at 1 to 2 cm s 1 in the re

small latitudinal shift in the kuroshio extension central pacific during glacial times evidence from pollen transport the mid latitude area of the central pacific is sensitive to ocean environmental change because latitudinal fluctuation in a transition zone between subtropical and subarctic waters has played an important role in climatic change in east asia the north pacific and north america higher amounts of pollen and spores were found in core h3571 on the hess rise during the glacials than during the interglacials pollen originating from broadleaf deciduous forest in warm and humid environments as well as from boreal conifers and tundra park tundra in cold and wet environments occurred during the glacials the boreal conifer pollen such as tsuga picea and haploxylon could originate from the central japanese archipelago that ephedra was supplied from the asian continent and that the main source regions for the rest of the pollen and spores were from the southern japanese archipelago to the area around the east china sea therefore ocean current transportation was important for the transportation of pollen and spores to the hess rise this evidence demonstrates a small southward shift in the kuroshio extension during the glacials it also suggests that terrestrial organic matter om deposited in the open sea may also be transported by ocean currents reflecting coastal terrestrial environments although it is widely believed that terrestrial om in open sea sediments is of aerosol origin

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

role of equatorial basin mode resonance for the seasonal variability of the angola current at 11 s abstractmultiyear moored velocity observations of the angola current near 11 s reveal a weak southward mean flow superimposed by substantial intraseasonal to seasonal variability including annual and semiannual cycles with distinct baroclinic structures in the equatorial atlantic these oscillations are associated with basin mode resonances of the fourth and second baroclinic modes respectively here the role of basin mode resonance and local forcing for the angola current seasonality is investigated a suite of linear shallow water models for the tropical atlantic is employed each model representing a single baroclinic mode forced at a specific period the annually and semiannually oscillating forcing is given by 1 an idealized zonally uniform zonal forcing restricted to the equatorial band corresponding to a remote equatorial forcing or 2 realistic spatially varying fourier components of wind stress data that include local forcing off angola particularly alongshore winds model computed modal am

seasonal to interannual time scale dynamics of the equatorial undercurrent in the indian ocean abstractthis paper investigates the structure and dynamics of the equatorial undercurrent euc of the indian ocean by analyzing in situ observations and reanalysis data and performing ocean model experiments using an ocean general circulation model and a linear continuously stratified ocean model the results show that the euc regularly occurs in each boreal winter and spring particularly during february and april consistent with existing studies the euc generally has a core depth near the 20 c isotherm and can be present across the equatorial basin the euc reappears during summer fall of most years with core depth located at different longitudes and depths in the western basin the euc results primarily from equatorial kelvin and rossby waves directly forced by equatorial easterly winds in the central and eastern basin however reflected rossby waves from the eastern boundary play a crucial role while the first two baroclinic modes make the largest contribution intermediate modes 3 8 are also

reconstruction of glaciation over the past 6 myr from ice borne deposits in the norwegian sea it is well known that a significant intensification of northern hemisphere glaciation occurred 2 5 myr ago in contrast to the much earlier onset 35 myr of glaciation in antarctica1 3 much less is known about the behaviour of the climate before 2 5 myr and it has remained unclear when sizeable glaciers first started to develop in the northern hemisphere here we deduce the history of high northern latitude glaciation over the past 6 myr from records of ice borne deposits in deep sea sediments of the norwegian sea we find that glaciers large enough to reach sea level were present in the norwegian sea area as early as 5 5 myr three million years before the intensification of glaciation at 2 5 myr fluctuations in ice volume can be deduced from the oxygen isotope record but this provides only a global average which may not reflect the history of ice sheet growth in specific regions from a comparison of the oxygen isotope records with the record of ice rafted material we derive an estimate of the relative contributions of southern and northern hemisphere glaciation to global variations in ice volume

surface water hydrography of the kuroshio extension during the pliocene pleistocene climate transition abstract the pliocene pleistocene climate transition offers an opportunity to study the effect of glaciation on the ocean climate system we present a globigerinoides ruber 18 o record from ocean drilling program site 1208 kuroshio current extension kce this exclusively sub tropical foraminifer a summer fall mixed layer dweller at the kce affords the first long 3 0 ma to 1 8 ma orbital scale 2 5 kyr time step account of the sea surface in this area the section s temperature corrected benthic foraminiferal 18 o record constrains global changes in ice volume yielding a 18 o record that primarily reflects summer fall kce hydrography temperature and salinity a 0 3 decrease in 18 o values at 2 7 ma coincides with the onset of northern hemisphere glaciation indicating as much as 1 5 c warming during the summer fall to suggest that the subtropical north pacific sea surface provided heat and moisture for expanding ice sheets on the orbital scale the 41 kyr cycle that dominates high latitude climate is absent from the 18 o record indicating a stable surface water hydrographic regime on this time scale rather the 18 o record varies at and is coherent with the 19 kyr precessional component of the regional insolation curve supporting a direct response to subtropical insolation and insensitivity to extra regional forcing factors such as ice sheets

annual and semiannual cycle of equatorial atlantic circulation associated with basin mode resonance seasonal variability of the tropical atlantic circulation is dominated by the annual cycle but semi annual variability is also pronounced despite weak forcing at that period here we use multi year full depth velocity measurements from the central equatorial atlantic to analyze the vertical structure of annual and semi annual variations of zonal velocity a baroclinic modal decomposition finds that the annual cycle is dominated by the 4th mode and the semi annual cycle by the 2nd mode similar local behavior is found in a high resolution general circulation model this simulation reveals that the annual and semi annual cycles of the respective dominant baroclinic modes are associated with characteristic basin wide structures using an idealized linear reduced gravity model to simulate the dynamics of individual baroclinic modes it is shown that the observed circulation variability can be explained by resonant equatorial basin modes corollary simulations of the reduced gravity model with varying basin geometry i e square basin versus realistic coastlines or forcing i e spatially uniform versus spatially variable wind show a structural robustness of the simulated basin modes a main focus of this study is the seasonal variability of the equatorial undercurrent euc as identified in recent observational studies main characteristics of the observed euc including seasonal variability of transport core depth and maximum core velocity can be explained by the linear superposition of the dominant equatorial basin modes as obtained from the reduced gravity model

strong intraseasonal variability of meridional currents near 5 n in the eastern indian ocean characteristics and causes abstractthis paper reports on strong intraseasonal upper ocean meridional currents observed in the indian ocean between the bay of bengal bob and the equator and elucidates the underlying physical processes responsible for them in situ measurements from a subsurface mooring at 5 n 90 5 e reveal strong intraseasonal variability of the meridional current with an amplitude of 0 4 m s 1 and a typical period of 30 50 days in the upper 150 m which by far exceeds the magnitudes of the mean flow and seasonal cycle such prominent intraseasonal variability is however not seen in zonal current at the same location further analysis suggests that the observed intraseasonal flows are closely associated with westward propagating eddylike sea surface height anomalies sshas along 5 n the eddylike sshas are largely manifestations of symmetric rossby waves which result primarily from intraseasonal wind stress forcing in the equatorial waveguide and reflection of the equatorial kelvin waves at the eastern bou

the 41 kyr world milankovitch s other unsolved mystery 1 for most of the northern hemisphere ice ages from 3 0 to 0 8 m y global ice volume varied predominantly at the 41 000 year period of earth s orbital obliquity however summer or summer caloric half year insolation at high latitudes which is widely believed to be the major influence on high latitude climate and ice volume is dominated by the 23 000 year precessional period thus the geologic record poses a challenge to our understanding of climate dynamics here we propose that variations in the insolation gradient between high and low latitudes control high latitude climate and ice volume during the late pliocene and early pleistocene the differential heating between high and low latitudes driven by obliquity controls the atmospheric meridional flux of heat moisture and latent energy which may exert the dominant control on high latitude climate on milankovitch timescales in the two dimensional zonal energy balance models typically used to study the long term evolution of climate the meridional atmospheric moisture flux is usually kept fixed the hypothesis that insolation gradients control the poleward energy fluxes precipitation and ice volume at high latitudes has never been directly examined within the context of an ice sheet model in light of what we know about modern energy fluxes and their relative influence on high latitude climate this possibility should be examined

the first glacial maximum in north america despite marine evidence for at least 50 pliocene pleistocene ice sheet advances only the most recent one has been accurately reconstructed from terrestrial evidence because there are few techniques for dating older glacial deposits here we show that the cosmic ray produced nuclides beryllium 10 and aluminum 26 can be used to date tills that overlie paleosols

evolution of millennial scale climate variability during the mid pleistocene 1 we use the oxygen isotopic composition of planktonic foraminifera globigerinoides ruber white from ocean drilling program site 1058 in the subtropical northwestern atlantic to construct a high resolution 800 year climate record spanning the mid pleistocene climate transition 410 ka to 1350 ka we investigate whether or not millennial scale instabilities in the proxy record are associated with the extent of continental glaciation g ruber 18o values display high frequency fluctuations throughout the record but the amplitude about mean glacial and interglacial 18o values increases at marine isotope stage mis 22 880 ka and is highest during mis 12 these observations support that millennial scale climate instabilities are associated with ice sheet size time series analysis illustrates that these variations have significant concentration of spectral power centered on periods of 10 12 ka and 5 ka the timing of these fluctuations agrees well or coincides with the periodicities of the second and fourth harmonics respectively of precessional forcing at the equator an insolation based origin of the millennial scale instabilities would be independent of ice volume and explains the presence of these fluctuations before the mid pleistocene climate transition as well as during interglacial intervals e g mis 37 and 17 because the amplitude of the millennial scale variations increases during the mid pleistocene transition feedback mechanisms associated with the growth of large 100 ka paced polar ice sheets may be important amplifiers of regional surface water hydrographic changes

stable isotope stratigraphy of the pliocene pleistocene climate transition in the northwestern subtropical pacific abstract from ocean drilling program odp site 1208 on shatsky rise below the kuroshio current extension we present the north pacific s first orbital scale benthic foraminiferal 18o and 13c time series to span the pliocene pleistocene climate transition excellent agreement between the site 1208 18o record and the global 18o stack of lisiecki and raymo 2005 provides orbital scale age control and confirms continuous stratigraphy from 3 7 to 1 8 ma at the single hole site cross spectral analysis of the 18o and 13c time series reveals that these are coherent to 80 confidence at the 41 kyr obliquity band prior to 3 3 ma glacial isotope stage m2 and increase to the 95 level thereafter throughout 18o cycles consistently lead 13c cycles by 3 kyr this suggests that global ocean 13c variations as produced by terrestrial marine 12c transfers were responsive to obliquity induced climate changes before the northern hemisphere glaciations nhg reached mid latitudes at 2 7 ma in contrast 41 kyr carbonate sedimentation as derived from sediment reflectance cycles maxima tightly coupled to 95 confidence and in phase with minima in the 18o record do not emerge until 2 7 ma foraminiferal fragmentation counts indicate that carbonate preservation is not the primary process behind enhanced carbonate deposition during interglacials thus we surmise that hydrography related changes in biogenic opal and carbonate production in surface water best explain glacial interglacial carbonate cycles beginning with significant nhg firm establishment of orbital scale age control on the stratigraphically complete site 1208 section now provides a platform for high resolution paleoceanographic reconstruction of the relatively understudied north pacific