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

eddy resolving observation of the north pacific subtropical mode water abstracthydrographic data obtained by high resolution shipboard observations and argo profiling floats have been analyzed to study the mesoscale structure and circulation of the north pacific subtropical mode water stmw the float data show that in the late winter of 2008 stmw having a temperature of approximately 18 8 17 7 and 16 6 c formed west of 140 e at 140 150 e and east of 150 e respectively in the recirculation gyre south of the kuroshio extension after spring the newly formed stmw gradually shift southward decreasing in thickness simultaneously the stmws of 16 6 and 17 7 c are gradually stirred and then mixed in terms of properties in late fall they seem to be integrated to form a single group of stmws having a temperature centered at 17 2 c such stmw circulation in 2008 is much more turbulent than that in 2006 which was investigated in a previous study the difference between the two years is attributed to the more variable state of the kuroshio extension in 2008 associate

quantifying lithogenic inputs to the north pacific ocean using the long lived thorium isotopes abstract dissolved 232th is added to the ocean though the partial dissolution of lithogenic materials such as aerosol dust in the same way as other lithogenically sourced and more biologically important trace metals such as fe oceanic 230th on the other hand is sourced primarily from the highly predictable decay of dissolved 234u the rate at which dissolved 232th is released by mineral dissolution can be constrained by a th removal rate derived from 230th 234u disequilibria assuming steady state calculated fluxes of dissolved 232th can in turn be used to estimate fluxes of other lithogenically sourced dissolved metals as well as the original lithogenic supplies such as aerosol dust deposition given the concentration and fractional solubility of th or other metals in the lithogenic material this method is applied to 7 water column profiles from the innovative north pacific experiment inopex cruise of 2009 and 2 sites from the subtropical north pacific the structure of shallow depth profiles suggests rapid scavenging at the surface and at least partial regeneration of dissolved 232th at 100 200 m depth this rapid cycling could involve colloidal th generated during mineral dissolution which may not be subject to the same removal rates as the more truly dissolved 230th an additional deep source of 232th was revealed in deep waters most likely dissolution of seafloor sediments and offers a constraint on dissolved trace element supply due to boundary exchange

decadal variability in the kuroshio oyashio extension simulated in an eddy resolving ogcm abstract through analysis of a hindcast integration of an eddy resolving quasi global ocean general circulation model decadal variability in the kuroshio oyashio extension region is investigated with particular emphasis on that of the subarctic oyashio and the kuroshio extension ke fronts the ke front is deep and is accompanied by a sharp sea surface height ssh gradient with modest sea surface temperature sst gradient in contrast the subarctic front is shallow and is recognized as a zone of tight gradient in sst but not ssh as a decadal scale change from a warm period around 1970 to a cool period in the mid 1980s those fronts in the model migrate southward as observed and the associated pronounced cooling is confined mainly to those frontal zones reflecting the distinctive vertical structure of the fronts the mixed layer cooling is the strongest along the subarctic front whereas the subsurface cooling and the associated salinity changes are most pronounced along the ke front concomitan

on the subsurface cfc maxima in the subtropical north pacific thermocline and their relation to mode waters and oxygen maxima the spatial structure of the subsurface chlorofluorocarbon cfc concentration maxima in the subtropical north pacific is examined using data from the pacific ocean sector of the world ocean circulation experiment woce hydrographic program collected in the period 1991 1994 comparison with potential vorticity pv sections reveals that the cfc maxima coincide with the pv minimum associated with subtropical mode water stmw in the western pacific as suggested by earlier observations warner et al 1996 in the eastern part of the central pacific the cfc maxima appear to be shallower than the central mode water cmw while they are deeper than the eastern subtropical mode water in the eastern pacific a subsurface oxygen maximum also coincides with stmw and the cfc maxima in the west is located between the cfc maxima and cmw in the central pacific and is absent in the east the collocation in the west is explained by the fact that stmw is the densest water to outcrop in the recirculation to the south of the kuroshio and the kuroshio extension while denser water is not directly ventilated in this region data from two post woce cruises and results from a steady state age model indicate that the cfc maxima are transient and are deepening such that the collocation of the cfc maxima and stmw does not persist in the late 1990s model experiments based on a smooth age profile demonstrate that the deepening of the cfc maxima is closely related to changes in the atmospheric cfc growth rates

testing the fossil record sampling proxies and scaling in the british triassic jurassic the quality of the fossil record varies immensely across taxa geographic regions environments and time intervals because much of this variation can be confounded when examining global patterns we present a detailed investigation of the british triassic and jurassic one of the most intensively studied pairs of systems in the world marine jurassic palaeodiversity is at least partly controlled by rock availability and accessibility the terrestrial record is patchier and effects of rock availability are overprinted by a stronger signal of sporadic preservation these results also fit a sea level driven common cause explanation as one would expect to see close correlation between rock availability and palaeodiversity in the marine realm but less so in the terrestrial formation counts and palaeodiversity do not correlate a surprising result given the number of earlier studies that have found close correlations however this study differs from most others in that formation counts and palaeodiversity metrics are derived from independent data sources and so within study redundancy is avoided the study confirms the complexity of rock fossil time series and the likelihood that the fossil record documents a complex mix of potential biological signal common cause signal and rock record and sampling bias it may be impossible to identify a useful simple sampling proxy for the fossil record that captures every bias and sampling error ironically when preservation is good sampling proxies representing rock availability such as outcrop area can be used to predict palaeodiversity but are ineffectual when the fossil record is patchy

shifts in the intertropical convergence zone himalayan exhumation and late cenozoic climate the early miocene ca 23 16 ma was the time of peak himalayan exhumation and postulated mid crustal channel flow in the high himalayas a tectonic configuration not recognized before or after in the range previous models have correlated this rapid exhumation with the onset of the asian monsoon and or suggested that it contributed ultimately to mid miocene global cooling via silicate weathering and or organic carbon burial and consequent atmospheric co 2 drawdown based on published pacific ocean sedimentation records and india eurasia plate reconstructions we compare the position of the intertropical convergence zone itcz with the paleolatitude of the himalayas and show that these converged in the early miocene because the itcz is a zone of high precipitation we suggest that this convergence was an important driver of early miocene high himalayan exhumation and erosion continued northward motion of the indian plate took the himalayas north of the itcz which migrated south through the remainder of the miocene high himalayan exhumation and ductile shearing correspondingly decreased after the early miocene this mechanism for increased himalayan erosion is independent of the timing of the onset or enhancement of the asian monsoon which is debated

ventilation of the subtropical north pacific the shallow salinity minimum abstract the shallow salinity minimum of the subtropical north pacific is shown to be a feature of the ventilated wind driven circulation subduction of low salinity surface water in the northeastern subtropical gyre beneath higher salinity water to the south causes the salinity minimum variation of salinity along surface isopycnals causes variations in density and salinity at the minimum a model of ventilated flow is used to demonstrate how the shallow salinity minimum can arise the model is modified to account for nonzonal realistic winds it is also extended to examine the three dimensional structure of the western shadow zone the boundary between the subtropical and subpolar gyres is given by the zero of the zonal integral of ekman pumping the western shadow zone fills the subtropical gyre at the base of the ventilated layers and decreases in extent with decreasing density for parameters appropriate to the north pacific the eastern shadow zone is of very limited extent observations of salini

frontogenesis subduction and cross front exchange at upper ocean fronts the subduction of water at upper ocean fronts driven by internal instabilities is investigated a simple analytic model which assumes conservation of potential density and potential vorticity is used to characterize the expected structure of subducted parcels as a function of the surface layer depth and the length scale of the parcel parcels subducted from a deep surface layer will be characterized by anomalously low potential vorticity and anticyclonic circulation while shallow surface layers result in subducted parcels with high potential vorticity and cyclonic circulation a nonlinear isopycnal primitive equation model is used to demonstrate how baroclinic instability and the resulting frontogenesis force the subduction of parcels below and across the front frontogenesis generates vertical velocities of 0 30 m d and ageostrophic cross front flows of 3 to 5 cm s the subduction is achieved by the deep ageostrophic flow which carries water from the surface layer below and across the front the subducted parcels quickly develop a circulation through balanced adjustment anticyclonic for deep surface layers and cyclonic for shallow surface layers the characteristics of parcels subducted in winter conditions closely resemble a class of eddies called submesoscale coherent vortices the horizontal and vertical scales of the vortices are determined by the frontogenetic mechanism and the depth of the surface layer the total permanent subduction rate is estimated to be 20 m yr for frontal subduction driven by frontogenesis although local and temporary subduction can be much larger the subducted anticyclonic vortices are often coupled to upper ocean cyclonic vortices thus forming a baroclinic dipole that propagates at approximately 3 5 cm s and is capable of transporting the anomalous water properties far from the region of formation similarities with observations in the north atlantic subtropical convergence zone and near the gulf stream are discussed

locally enhanced wintertime air sea interaction and deep oceanic mixed layer formation associated with the subarctic front in the north pacific 1 satellite derived high resolution air sea flux data and argo float data were analyzed to reveal the fine scale spatial structures of air sea turbulent heat and momentum fluxes and their relationship with the deep oceanic mixed layer around the subarctic front saf in the north pacific an important feature inferred from the satellite derived dataset is the presence of a pair of positive and negative air sea flux anomaly bands with a width of 100 200 km on both sides of the saf such a fine scale structure in air sea fluxes has not been captured in previous datasets the saf plays a significant role in determining the fine scale structure of air sea fluxes the oceanic mixed layer is deeper to the south of the saf and the maximum mixed layer depth is observed near the positive anomaly band in air sea fluxes this study concludes that active air sea interactions due to the presence of the saf enhances upward air sea heat and momentum fluxes to the south of saf and selectively produces a deep oceanic mixed layer where the formation of transition region mode water occurs

paleotemperature and paleosalinity inferences and chemostratigraphy across the aptian albian boundary in the subtropical north atlantic 1 geochemical analyses of extraordinarily well preserved late aptian early albian foraminifera from blake nose ocean drilling program site 1049 reveal rapid shifts of 18o 13c and 87sr 88sr in the subtropical north atlantic that may be linked to a major planktic foraminifer extinction event across the aptian albian boundary the abruptness of the observed geochemical shifts and their coincidence with a sharp lithologic contact is explained as an artifact of a previously undetected hiatus of 0 8 1 4 million years at the boundary contact but the values before and after the hiatus indicate that major oceanographic changes occurred at this time 87sr 88sr increase by 0 000 200 13c values decrease by 1 5 to 2 2 and 18o values decrease by 1 0 planktics to 0 5 benthics across the hiatus further both 87sr 88sr ratios and 18o values during the albian are anomalously high the 87sr 88sr values deviate from known patterns to such a degree that an explanation requires either the presence of inter basin differences in seawater 87sr 88sr during the albian or revision of the seawater curve for 18o planktic values in some aptian samples likely reflect a diagenetic overprint but preservation is excellent in the rest of the section in well preserved material benthic foraminiferal values are largely between 0 5 and 0 0 and planktic samples are largely between 0 0 to 1 0 with a brief excursion to 2 0 during oae 1b using standard assumptions for cretaceous isotopic paleotemperature calculations the 18o values suggest bottom water temperatures at 1000 1500 m of 8 10 c and surface temperatures of 10 14 c which are 4 6 c and 10 16 c cooler respectively than present day conditions at the same latitude the cool subtropical sea surface temperature estimates are especially problematic because other paleoclimate proxy data for the mid cretaceous and climate model predictions suggest that subtropical sea surface temperatures should have been the same as or warmer than at present because of their exquisite preservation whole scale alteration of the analyzed foraminifera is an untenable explanation our proposed solution is a high evaporative fractionation factor in the early albian north atlantic that resulted in surface waters with higher 18o values at elevated salinities than commonly cited in cretaceous studies a high fractionation factor is consistent with high rates of vapor export and a vigorous hydrological cycle and like the sr isotopes implies limited connectivity among the individual basins of the early cretaceous proto atlantic ocean

current and historical perspectives on the completeness of the fossil record of pelycosaurian grade synapsids abstract understanding of the early evolution of tetrapods may have been influenced by the effects of geological and anthropogenic sampling biases as suggested by previous studies here we make a thorough assessment of how these and other biases affect the record of pelycosaurian grade synapsids a group of tetrapods that dominated the terrestrial realm during the late carboniferous and early permian modified versions of the character and skeletal completeness metrics are used to assess the completeness of the known specimens while a recently published supertree of basal synapsids is tested for congruence between the stratigraphic and phylogenetic hypotheses a historical analysis is also applied to the record in order to show how the biases in the study of this group over the past centuries may have influenced the current record the results show that the completeness of basal synapsid specimens shows very little variation throughout the early permian a peak in skeletal and character completeness metric values in the middle permian wordian is attributed to exceptional preservation of the mezen fauna a significant negative correlation is found between the skeletal completeness metric and a taxic diversity curve of pelycosaurs implying a tendency to name many species based on poor material the lack of correlation between the character completeness metric and diversity is attributed to the history of discovery in the group the majority of pelycosaur species were named between the 1930s and 1960s when character based assignments were secondary to size location and stratigraphy a strong correspondence between the phylogeny and stratigraphy implies a reliable phylogenetic hypothesis but the low relative completeness index score suggests that a great deal of the fossil record is missing while the relative completeness index has improved over the past century the rate of improvement has slowed in the last two decades and the slowing rate of discovery of new species suggests that the limit of what the fossil record of pelycosaurs has to offer is being approached a consistent shape of diversity curves over the past century implies that the same biases which affected the record in the past are still affecting it now this study highlights the need for sampling correction methods to be employed in studies of early synapsids

the north pacific oxygen uptake rates over the past half century the transport of dissolved oxygen o2 from the surface ocean into the interior is a critical process sustaining aerobic life in mesopelagic ecosystems but its rates and sensitivity to climate variations are poorly understood using a circulation model constrained to historical variability by assimilation of observations we show that the north pacific thermocline effectively takes up o2 primarily by expanding the area through which o2 rich mixed layer water is detrained into the thermocline the outcrop area during the critical winter season varies in concert with the pacific decadal oscillation pdo when the central north pacific ocean is in a cold phase the winter outcrop window for the central mode water class cmw a neutral density range of 25 6 26 6 expands southward allowing more o2 rich surface water to enter the ocean s interior an increase in volume flux of water to the cmw density class is partly compensated by a reduced supply to the shallower densities of subtropical mode water 24 0 25 5 the thermocline has become better oxygenated since the 1980s due partly to strong o2 uptake positive o2 anomalies appear first near the outcrop and subsequently downstream in the subtropical gyre in contrast to the o2 variations within the ventilated thermocline observed o2 in intermediate water density range of 26 7 27 2 shows a declining trend over the past half century a trend not explained by the open ocean water mass formation rate

the north pacific climatology of winter mixed layer and mode waters abstract a climatology of the winter mixed layer in the north pacific ocean was constructed using hydrographic data from historical archives and recent observational programs including the world ocean circulation experiment the main aim was to provide better knowledge about source areas of upper water masses the authors have endeavored to preserve water properties near the frontal regions by keeping the smoothing scale as small as possible the resulting climatology shows considerable differences in the mixed layer depth and its water properties from those derived from the world ocean atlas woa maps of the potential vorticity field of the north pacific pycnocline are presented using the isopycnally averaged climatology hydrobase three distinct lateral minima of potential vorticity are identified as subtropical mode water stmw central mode water cmw and eastern subtropical mode water estmw in the western central and eastern parts of the subtropical gyre respectively the hydrobase isopy

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

potential vorticity distribution in the north pacific abstract vertical sections and maps of potential vorticity 1f z for the north pacific are presented on shallow isopycnals high potential vorticity is found in the tropics subpolar gyre and along the eastern boundary of the subtropical gyre all associated with ekman upwelling low potential vorticity is found in the western subtropical gyre subtropical mode water in a separate patch near the sea surface in the eastern subtropical gyre and extending around the gyre and near sea surface outcrops in the subpolar gyre the last is analogous to the subpolar mode water of the north atlantic and southern ocean meridional gradients of potential vorticity are high between the subtropical and subpolar gyres at densities which outcrop only in the subpolar gyre lateral gradients of potential vorticity are low in large regions of the subtropical gyre on these isopycnals on slightly denser isopycnals which do not outcrop in the north pacific there are large regions of low potential vorticity gradients

neuropteran insecta palaeodiversity with predictions for the cretaceous fauna of the wealden the wealden group of southern england is a succession of non marine sediments from the lower cretaceous c 141 119 ma which also outcrop in belgium and northwest germany most insect orders are present as fossils including neuroptera one of the most basal holometabolous orders the fossil record of neuroptera is diverse spanning permian recent with all major family radiations having occurred prior to the wealden however wealden neuroptera have received little attention to date with only three families reported and one species described the fossil record in general is notoriously incomplete and palaeoenvironmental reconstructions can facilitate predictions of what other organisms were present in the habitat but which were either not preserved or only occasionally preserved and yet to be found as fossils we examine the wealden palaeohabitat and global neuropteran palaeodiversity and consider these in relation to palaeo biogeography of fossil and extant taxa including habitat preferences we predict that the following families will form components of the cretaceous wealden fauna nymphidae polystoechotidae chrysopidae hemerobiidae and coniopterygidae

differential formation and circulation of north pacific central mode water abstract a repeat hydrographic section along 165 e was analyzed to verify a westward extension of the formation region of the north pacific ocean central mode water cmw suggested by previous synoptic observations and to investigate the relation between the formation region and thermohaline fronts the cmw formation region extends at least as far west as 155 e much farther than recognized in a previous study based on climatology it is located in two interfrontal regions between the kuroshio extension front and the kuroshio bifurcation front kbf and between the kbf and the subarctic front where two types of cmw namely the lighter variety with potential density of 25 8 26 2 kg m 3 and the denser one of 26 3 26 4 kg m 3 are formed how this differential formation of cmw is reflected in its gyrewide distribution was examined using one time sections of the world ocean circulation experiment woce hydrographic program in the north pacific the main circulation paths of the two types of cmw diverge eas

the subarctic frontal zone in the north pacific characteristics of frontal structure from climatological data and synoptic surveys the subarctic front is a thermohaline structure across the north pacific separating colder fresher water to the north from warmer saltier water to the south levitus s 1982 data and 72 conductivity temperature depth salinity temperature depth sections are used to show the spatial and seasonal variations of the climatological frontal zone and the characteristics of the frontal structure in synoptic surveys the temperature gradient in the mean frontal zone is stronger in the western pacific and decreases eastward while the salinity gradient has less variation across the pacific the temperature gradient also has larger seasonal variation with a maximum in spring than the salinity gradient the synoptic surveys show that the frontal zone is narrower and individual fronts tend to be stronger in the western pacific than in the eastern pacific density gradients tend to be more compensated at the strongest salinity fronts than at the strongest temperature fronts a horizontal minimum of vertical stability is found south of the subarctic halocline outcrop the northern boundary of the north pacific intermediate water merges with the frontal zone west of 175 w and is north of the northern boundary of the subarctic frontal zone in the eastern pacific the shallow salinity minima start within the subarctic frontal zone in the eastern pacific

geochemistry and zircon u pb hf isotopic systematics of the ningshan granitoid batholith middle segment of the south qinling belt central china constraints on petrogenesis and geodynamic processes abstract the ningshan granitoid batholith ngb is located in the middle segment of the south qinling belt sqb section of the qinling orogenic belt in shaanxi province china and consists of the laocheng yanzhiba and lanbandeng intrusions the laocheng intrusion is dominated by quartz diorites granodiorites and monzogranites with the yanzhiba intrusion being granodiorite dominated and the lanbandeng intrusion predominantly consisting of two mica monzogranites la icp ms zircon u pb isotopic dating indicates that the ngb formed during two distinct episodes of magmatism with an earlier episode at 222 216 ma and a later episode at 210 ma whole rock geochemistry and geochronology data have allowed us to divide the ngb into three groups with group 1 rocks consisting of laocheng intrusion quartz diorites and granodiorites and yanzhiba intrusion granodiorites that were produced in the early magmatic episode group 1 samples have high k calc alkaline compositions and are characterized by high mg values high sr cr and ni concentrations and high la yb n and sr y ratios but low yb and y concentrations implying that these rocks were formed from a mixed magma derived from melting of neoproterozoic crustal basaltic rocks and magmas sourced from a region of depleted mantle group 2 rocks are composed of the mid k calc alkaline monzogranites in the laocheng intrusion that were formed in the later magmatic episode and are characterized by lower mg values and lower cr ni and co concentrations than the group 1 samples but with high sr concentrations and la yb n and sr y ratios low y and yb concentrations negligible eu anomalies and a significant range in zircon ehf t values the highest zircon ehf t values of the group 2 samples plot close to the depleted mantle evolutionary line indicating that these rocks were derived from a mixed magma with both crustal and mantle derived components group 3 samples consist of high k calc alkaline two mica monzogranites of the lanbandeng intrusion that were formed during the later magmatic episode these rocks are characterized by high sio2 al2o3 and k2o concentrations with low mgo and sr concentrations low la yb n and sr y ratios nb ta p and ti depletions and significantly negative eu anomalies implying that the magmas from which these rocks formed were derived from partial melting of sedimentary rocks and minor amount of basalt the early magmatic episode associated with formation of the ngb occurred in a continental arc environment at 222 216 ma with 210 ma magmatism during a geodynamic transition from syn collisional to post collisional tectonics across the sqb

subtropical countercurrent variations in cooling climates induced by freshwater forcing over the subarctic north atlantic the subtropical countercurrent stcc could affect ocean eddy activity and the atmosphere above how the stcc varied in a cooling scenario such as the stadials during the last deglaciation 19 11 ka ka 1000 years ago is still unclear by 1 sv 1 sv 106 m3 s 1 freshwater hosing over the subpolar north atlantic to suppress the atlantic meridional overturning circulation amoc the stcc variations under pre industrial pi and last glacial maximum lgm 21 ka conditions are analyzed in both hosing experiments the northern hemisphere cools the upper ocean becomes less stratified and the wintertime mixed layer deepens in the kuroshio oyashio extension koe region as a result more mode waters 20 are formed and they become more vertically uniform the enhanced mode waters induce a stronger vertical shear and accelerate the stcc based on thermal wind relationship the strengthened stcc further induces warm ocean temperature and upward air sea heat flux anomalies along it while the stcc strengthens in both hosing experiments the location variations are different in the pi hosing experiment the bering strait is open fresh water enters the north pacific through the bering strait and increases the stratification in the downstream of the koe region the mixed layer front shifts westward and induces a robust westward shift of mode waters and the stcc in the lgm hosing experiment on the contrast there is no obvious location shift because the bering strait is closed

mesozoic echinoid diversity in portugal investigating fossil record quality and environmental constraints on a regional scale several analyses of diversity through geological time use global synoptic databases and this practice often makes it difficult to distinguish true signals in changing diversity from regional scale sampling and or geological artefacts here we investigate how echinoid diversity changed through the mesozoic of the lusitanian basin in portugal based on a comprehensive revised database and seek to distinguish biological signal from geological or environmental constraints the observed diversity pattern is far from having a defined trend showing many fluctuations that appear to be linked with gaps in the geological record this study revealed that independently of the method used whether correlation tests or model fitting the diversity signal is not completely explained by the studied sampling proxies among the different proxies marine facies variation in combination with outcrop area best explains the palaeodiversity curve

determinants of extinction in the fossil record the causes of mass extinctions and the nature of biological selectivity at extinction events are central questions in palaeobiology it has long been recognized however that the amount of sedimentary rock available for sampling may bias perceptions of biodiversity1 2 3 4 5 6 7 and estimates of taxonomic rates of evolution5 6 7 8 this problem has been particularly noted with respect to the principal mass extinctions5 6 7 8 9 10 11 12 here we use a new compilation of the amount of exposed marine sedimentary rock to predict how the observed fossil record of extinction would appear if the time series of true extinction rates were in fact smooth many features of the highly variable record of apparent extinction rates within marine animals can be predicted on the basis of temporal variation in the amount of exposed rock although this result is consistent with the possibility that a common geological cause determines both true extinction rates and the amount of exposed rock it also supports the hypothesis that much of the observed short term volatility in extinction rates is an artefact of variability in the stratigraphic record

subduction of north pacific central mode water associated with subsurface mesoscale eddy 1 during a shipboard high density hydrographic survey carried out in the western north pacific in fall 2008 we observed an anticyclonic eddy with a thickness of 150 dbar and a diameter of 40 km near 500 dbar depth at 27 5 n 145 e this subsurface mesoscale eddy contains the north pacific central mode water cmw which has anomalously low potential vorticity and high dissolved oxygen compared to the climatological cmw properties in the same region profiling float measurements detect similar cmw patches near and south of the kuroshio extension as well as southward cmw migration within the cmw formation region north of the kuroshio extension these observed facts suggest that cmw is subducted into the permanent pycnocline not only through large scale eastward advection near the northern edge of the subtropical gyre but also through southward cross frontal advection associated with the formation and migration of subsurface mesoscale eddies

properties formation and dissipation of the north pacific eastern subtropical mode water and its impact on interannual spiciness anomalies abstract the properties formation and dissipation of the north pacific eastern subtropical mode water estmw their interannual variability and impact on spiciness anomalies in the upper permanent pycnocline were investigated using argo profiling float data in 2005 2015 the core temperature and salinity of estmws were horizontally compensated to a constant density and core potential density concentrates in a range of 24 5 25 2 kg m 3 with two distinct peaks estmws showed different spatial distribution and persistence for its core potential density denser estmws with a potential density of 24 9 25 2 kg m 3 were formed in winter mixed layer depth maximum centered at 30 n 140 w and lighter estmws of 24 5 24 9 kg m 3 were formed south and east of it after formation through shoaling of the winter mixed layer the former persisted until the following autumn and a small part of it subducted in winter while the latter dissipated in summer the formation region of estmw corresponded to the summer sea surface density maximum resulting from its poleward sea surface salinity front sea surface density maximum maintains weak stratification during summer preconditioning the deepening of the winter mixed layer and hence the formation of estmws a relationship between the estmw formation region and the summer sea surface density maximum was also found in the north atlantic and the south pacific implying the importance of sea surface salinity fronts and the associated summer sea surface density maximum to estmw formation interannual variations of estmw reflected that of the winter mixed layer in its formation region and the thickness of estmw was related to the pacific decadal oscillation estmw contributed to the occurrence of spice injection and affected spiciness anomalies in the upper permanent pycnocline through its formation and dissipation

variability of the kuroshio extension jet recirculation gyre and mesoscale eddies on decadal time scales abstract twelve years of sea surface height ssh data from multiple satellite altimeters are used to investigate the low frequency changes and the interconnections of the kuroshio extension ke jet its southern recirculation gyre and their mesoscale eddy field the dominant signal is characterized by the steady weakening of the ke jet recirculation gyre from 1993 to 1996 followed by a gradual strengthening after 1997 during the weakening period of 1993 96 the ke path migrated southward in general and this path migration reversed in direction during the strengthening period of the ke jet and recirculation gyre after 1997 by hindcasting the ssh signals using linear vorticity dynamics it was found that weakening strengthening in the ke jet and recirculation gyre is consistent with westward propagation of negative positive ssh anomalies generating in the eastern north pacific and strengthening during their westward propagation when the ke jet and recirculation gyre were in a weak mode during 19

mesoscale eddies in the northwestern pacific ocean three dimensional eddy structures and heat salt transports the region encompassing the kuroshio extension ke in the northwestern pacific ocean 25 n 45 n and 130 e 180 e is one of the most eddy energetic regions of the global ocean the three dimensional structures and transports of mesoscale eddies in this region are comprehensively investigated by combined use of satellite data and argo profiles with the allocation of argo profiles inside detected eddies the spatial variations of structures of eddy temperature and salinity anomalies are analyzed the results show that eddies predominantly have subsurface near surface intensified temperature and salinity anomalies south north of the ke jet which is related to different background stratifications between these regions a new method based on eddy trajectories and the inferred three dimensional eddy structures is proposed to estimate heat and salt transports by eddy movements in a lagrangian framework spatial distributions of eddy transports are presented over the vicinity of the ke for the first time the magnitude of eddy induced meridional heat freshwater volume transport is on the order of 0 01 pw 103 m3 s the eddy heat transport divergence results in an oceanic heat loss south and heat gain north of the ke thereby reinforcing and counteracting the oceanic heat loss from air sea fluxes south and north of the ke jet respectively it also suggests a poleward heat transport across the ke jet due to eddy propagation

estimating the rock volume bias in paleobiodiversity studies to interpret changes in biodiversity through geological time it is necessary first to correct for biases in sampling effort related to variations in the exposure of rocks and recovery of fossils with age data from new zealand indicate that outcrop area is likely to be a reliable proxy of rock volume in both stable cratonic regions where the paleobiodiversity record is strongly correlated with relative sea level and on tectonically active margins in contrast another potential proxy the number of rock formations is a poor predictor of outcrop area or sampling effort in the new zealand case

upper ocean thermal variations in the north pacific during 1970 1991 abstract a newly available extensive compilation of upper ocean temperature profiles was used to study the vertical structure of thermal anomalies between the surface and 400 m depth in the north pacific during 1970 1991 a prominent decade long perturbation in climate occurred during this time period surface waters cooled by 1 c in the central and western north pacific and warmed by about the same amount along the west coast of north america from late 1976 to 1988 comparison with data from coads suggests that the relatively sparse sampling of the subsurface data is adequate for describing the climate anomaly the vertical structure of seasonal thermal anomalies in the central north pacific shows a series of cold pulses beginning in the fall of 1976 and continuing until late 1988 that appear to originate at the surface and descend with time into the main thermocline to at least 400 m depth individual cold events descend rapidly 100 m yr 1 superimposed upon a slower cooling 15 m yr 1 the inter

subduction of decadal north pacific temperature anomalies observations and dynamics abstract observations of oceanic temperature in the upper 400 m reveal decadal signals that propagate in the thermocline along lines of constant potential vorticity from the ventilation region in the central north pacific to approximately 18 n in the western pacific the propagation path and speed are well described by the geostrophic mean circulation and by a model of the ventilated thermocline the approximate southward speed of the thermal signal of 7 mm s 1 yields a transit time of approximately eight years the thermal anomalies appear to be forced by perturbations of the mixed layer heat budget in the subduction region of the central north pacific east of the date line a warm pulse was generated in the central north pacific by a series of mild winters from 1973 to 1976 and reached 18 n around 1982 after 1978 a succession of colder winters initiated a cold anomaly in the central north pacific that propagated along a similar path and with a similar speed as the warm anomaly then arrived in the west

the first half of tetrapod evolution sampling proxies and fossil record quality abstract the first half of tetrapod evolution witnessed substantial diversification of the clade and several major turnovers and mass extinctions in the time since their origin more than 380 myr ago to the beginning of the middle jurassic 175 myr ago tetrapods apparently diversified fitfully reaching their highest level in the middle permian and showing major diversity declines in the late moscovian early permian wordian lower wuchiapingian end permian lower anisian lower ladinian late triassic lower norian to upper rhaetian end triassic and early jurassic upper sinemurian lower pliensbachian of these diversity drops only the end permian and end triassic correspond to recognised mass extinctions and the late moscovian and early norian drops to other previously identified environmental crises the remainder could be real extinction or turnover events or partially artefacts of biased sampling there are strong correlations between formation counts and tetrapod palaeodiversity suggesting a sampling component in the raw data but the covariation is not uniform through the whole time span being poor from devonian to middle permian and better from late permian to early jurassic there is limited evidence for covariation between the tetrapod palaeodiversity time series and other putative sampling metrics such as specimen completeness numbers of publications map areas gap bounded sedimentary units rock volumes formations and fossil collections modelling by multiple correlations shows that formation count is generally the best explanatory model either on its own or combined with other sampling time series however it is not clear that formation count is independent of the palaeodiversity time series because rises and falls in both signals could reflect variations in original diversity or in preservation or in sampling

marine diversity through the phanerozoic problems and prospects the fossil record provides direct evidence of how diversity has changed over time but cannot be taken at face value diversity curves constructed from counting taxa in the rock record are seriously biased by unevenness of geographical and stratigraphical sampling effort inequality in the rock record available for sampling and inconsistent taxonomic practice sample standardization removes some bias but does not overcome more general incompleteness problems modelling that accounts for potential biases is a newer approach but needs accurate estimates of rock record and consistent taxonomic data uncertainty remains over whether the steep rise in diversity over the last 100 ma is real or reflects sampling bias the repeated rise and fall of marine diversity over time correlates closely with the areal extent of sedimentary deposits and independent estimates of the quality of the fossil record implying a common driving factor namely tectonically mediated sea level change however whether changes in diversity are primarily biological in origin or reflect sampling artefact remains contentious there is a distinct possibility that many of the apparent rises and falls in diversity over the phanerozoic including most of the mass extinctions arise either partially or entirely from rock record bias

palaeotemperatures indicated by upper jurassic kimmeridgian tithonian fossils from mallorca determined by oxygen isotope composition abstract the oxygen and carbon composition of calcite has been determined for belemnites ammonite aptychi and the matrix surrounding these fossils from the kimmeridgian tithonian of mallorca petrography cathodoluminescence and trace element analyses indicate that both ammonite aptychi and matrix has been diagenetically altered whereas the belemnites have been undergone minimal or no modification the belemnites give the heaviest oxygen isotope values of 0 04 to 0 99 pdb and lighter values of 0 71 to 3 98 pdb come from the ammonite aptychi and matrix the carbon isotopic compositions obtained from all the fossils are positive and are similar to those derived from modern marine shallow water skeletons palaeotemperatures calculated on the basis of the oxygen isotopic composition of the belemnites give a range of values from 13 6 to 16 c these results agree with late jurassic palaeotemperatures from similar palaeolatitudes

the spatial distribution and annual cycle of upper ocean thermohaline structure 1 observations of the spatial distribution and persistence of thermohaline structure are presented and show how advection and diffusion affect a passive tracer more than two years of underwater glider observations in the central subtropical north pacific showed thermohaline variability over horizontal scales from 5 to 1300 km thermohaline fluctuations along isopycnals spice fluctuations were elevated in layers throughout the water column with the largest fluctuations near the surface and subtropical frontal regions fluctuations were uncorrelated between the layers but stirred by the same velocity field spice variance had local extrema in the vertical because of differences in source water properties and the influence of neighboring water masses spice variance spanned about three orders of magnitude along deeper isopycnals with larger variance where different water masses met and where velocity and vorticity variance were elevated horizontal wave number spectra of spice had slopes of 2 everywhere in the upper 1000 m submesoscale spice fluctuations had slopes in physical space near the ratio of the coriolis parameter to the buoyancy frequency f n consistent with predictions of quasi geostrophic theory in the mixed layer thermohaline structure had a significant annual cycle with smaller interannual differences thermohaline fluctuations left behind during restratification and isolated from the mixed layer decayed with time because of diffusion along isopycnals horizontal diffusivity estimates in the remnant mixed layer were 0 4 m2 s 1 at 15 28 km wavelengths and 0 9 m2 s 1 at 35 45 km wavelengths

climate variability in the north pacific thermocline diagnosed from oxygen measurements an update based on the u s clivar co2 repeat hydrography cruises 1 new observations of oxygen variability in the north pacific ocean are reported on the basis of comparison of the u s climate variability and predictability and carbon clivar co2 repeat hydrography sections conducted along 30 n 2004 and 152 w 2006 with the earlier world ocean circulation experiment woce data and other cruises along these sections the largest changes in apparent oxygen utilization aou continue to occur as found in earlier north pacific repeat section analyses within the thermocline on 26 6 kg m 3 which is the densest isopycnal to outcrop in the open north pacific in climatological data in the northeastern north pacific along 152 w where a total of five cruises 1980 1984 1991 1997 and 2006 spanning a period of 26 years are available the aou changes correspond to an overall increase in aou on 26 6 kg m 3 from the 1980s early 1990s to 2006 however from 1997 to 2006 a decrease in aou is observed within the boundary region between the subtropical and subpolar gyres at 40 45 n along the center axis of the subtropical gyre at 30 n where two cruises are available 1994 and 2004 aou has also substantially increased on 26 6 kg m 3 from 1994 to 2004 in the eastern part of the section the repeat section data along 152 w and 30 n are consistent with a pattern of decadal scale ventilation anomalies that originate in the northwestern pacific possibly through variability including cessation of the 26 6 kg m 3 outcrop travel eastward along the subtropical subpolar gyre boundary and enter the northern portion of the subtropical gyre along the way for the 152 w aou data within the gyre boundary region 40 45 n good agreement exists with the close by time series data from ocean station p 50 n 145 w where a bidecadal cycle in aou has been observed in contrast a sensible correlation with the pacific decadal oscillation could not be found

observations of the subtropical mode water evolution from the kuroshio extension system study abstract properties and seasonal evolution of north pacific ocean subtropical mode water stmw within and south of the kuroshio extension recirculation gyre are analyzed from profiling float data and additional hydrographic and shipboard adcp measurements taken during 2004 the presence of an enhanced recirculation gyre and relatively low mesoscale eddy variability rendered this year favorable for the formation of stmw within the recirculation gyre stmw formed from late winter convection that reached depths greater than 450 m near the center of the gyre the lower boundary of stmw corresponding to 25 5 kg m 3 was set by the maximum depth of the late winter mixed layer properties within the deep portions of the stmw layer remained largely unchanged as the season progressed in contrast the upper boundary of the stmw layer eroded steadily as the seasonal thermocline deepened from late april to august vertical eddy diffusivity responsible for this erosion was estimated from a budget analysis of

formation and subduction of central mode water based on profiling float data 2003 08 abstract temperature and salinity data from argo profiling floats in the north pacific during 2003 08 have been analyzed to study the structure of winter mixed layer north of the kuroshio extension and the subsurface potential vorticity distribution in the subtropical gyre in relation to the formation and subduction of the central mode water cmw in late winter two zonally elongated bands of deep mixed layer extend at 33 39 and 39 43 n from the east coast of japan to 160 w these correspond to the formation region of the lighter variety of cmw l cmw and that of the denser variety of cmw d cmw and the recently identified transition region mode water trmw respectively in the western part of the l cmw and d cmw trmw formation regions west of 170 e the winter mixed layer becomes deeper and lighter to the east i e to the downstream as a result the formed mode water is reentrained into the mixed layer in the farther east in the following winter and modified to the lighter water and is thus

reemergence areas of winter sea surface temperature anomalies in the world s oceans 1 using datasets of sea surface temperature sst surface heat flux upper ocean thermal data and climatological temperature and salinity profiles we try to detect reemergence areas of winter sst anomalies in the world s oceans and describe characteristics of these areas in terms of mixed layer depth mld annual mean heat flux and properties of waters formed in winter mixed layer eventually seven reemergence areas are found four in the northern hemisphere and three in the southern hemisphere all areas have a large seasonal variation of mld and are the regions where annual mean heat fluxes are relatively small except for two regions in the northern hemisphere in the viewpoint of water properties it is found that these areas correspond to the mode water formation regions subtropical mode waters of the indian ocean south pacific south atlantic north pacific and north atlantic and north pacific central and north atlantic subpolar mode waters

interdecadal variability in dissolved oxygen in the intermediate water layer of the western subarctic gyre and kuril basin okhotsk sea using dissolved oxygen do concentration at isopycnal surfaces we have observed an oscillation in the intermediate water layer of the western subarctic gyre wsg and the kuril basin of the okhotsk sea with a period of about 20 years the interdecadal oscillation in do is strongly correlated with the intensity of the aleutian low pressure cell with a 2 year time lag the interdecadal variations in do in the intermediate water layer of the wsg and the okhotsk sea may be a result of oscillation in the atmospheric forcing leading to variations in the isopycnal fluxes of do at the boundaries of the okhotsk sea western subarctic gyre subtropical region the isopycnal surface replacement in the wsg and in changes in the intermediate water formation rate in the okhotsk sea

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

remote reemergence areas of winter sea surface temperature anomalies in the north pacific 1 taking account of water movement we detect pairs of formation and reemergence areas of winter sea surface temperature sst anomalies in the north pacific by analyzing various kinds of data sets two pairs of formation and reemergence areas are detected one pair is located in the northern subtropical gyre and water properties in both the formation and reemergence areas well correspond to those of north pacific central mode water npcmw another pair is found in the western to central part of the subtropical gyre the formation area corresponds well to that of north pacific subtropical water npstmw but the reemergence area is remote from the formation area examinations on upper ocean current field trace of temperature anomalies in the subsurface and change of water properties from the formation area to the reemergence area clearly indicate that waters with winter sst anomalies move from the formation area to the reemergence area in a year

midlatitude shelf seas in the cenomanian turonian greenhouse world temperature evolution and north atlantic circulation 1 an 8 million year record of subtropical and midlatitude shelf sea temperatures derived from oxygen isotopes of well preserved brachiopods from a variety of european sections demonstrates a long term cenomanian temperature rise 16 20 c midlatitudes that reached its maximum early in the late turonian 23 c midlatitudes superimposed on the long term trend shelf sea temperatures vary at shorter timescales in relation to global carbon cycle perturbations in the mid cenomanian and the late turonian two minor shelf sea cooling events 2 3 c coincide with carbon cycle perturbations and times of high amplitude sea level falls although this evidence supports the hypothesis of potential glacioeustatic effects on cretaceous sea level the occurrence of minimum shelf sea temperatures within transgressive beds argues for regional changes in shelf sea circulation as the most plausible mechanism the major carbon cycle event in the latest cenomanian oceanic anoxic event 2 is accompanied by a substantial increase in shelf sea temperatures 4 5 c that occurred 150 kyr after the commencement of the 13c excursion and is related to the spread of oceanic conditions in western european shelf sea basins our oxygen isotope record and published 18o data of pristinely preserved foraminifera allow the consideration of north atlantic surface water properties in the cenomanian along a transect from the tropics to the midlatitudes on the basis of fossil derived 18o estimated w ranges and modeled salinities temperature salinity density ranges were estimated for tropical subtropical and midlatitude surface waters accordingly the cenomanian temperate shelf seas waters have potentially the highest surface water density and could have contributed to north atlantic intermediate to deep waters in the preopening stage of the equatorial atlantic gateway

features of the water mass front in the northwestern north pacific analysis of the hydrographic data taken in the northern north pacific has revealed a water mass front defined as the abrupt change of mixing rates between the two typical water masses typical water masses are situated above the main thermocline in the subtropical and subpolar gyres this front termed water mass front in the present study can be regarded as the boundary between the subtropical gyre and the subpolar gyre the index for detecting the frontal position from the temperature field is given as the 5 c isotherm at the 300 m level comparisons with data from previous studies are also made and this front appears to correspond to the subarctic front in almost every instance

effects of mesoscale eddies on subduction and distribution of subtropical mode water in an eddy resolving ogcm of the western north pacific abstract the effects of mesoscale eddies on the subduction and distribution of the north pacific subtropical mode water stmw are investigated using an eddy resolving ocean general circulation model ogcm first the subduction rate is calculated and the contribution of eddies to the subduction of stmw is estimated it is found that eddy subduction significantly contributes to the total subduction of stmw second eddy thickness transport and diapycnal flux are directly diagnosed to investigate the large scale eddy induced transport process of stmw the large southward eddy thickness transport in the stmw core density is consistent with eddy subduction the eddy transport on the isopycnal surface of stmw is directed down the thickness gradient and traverses the mean flow the meridional eddy transport streamfunction indicates two eddy circulation cells south of 30 n associated with the circulation of stmw these cells flatten density surfaces similar to the effect of the gent and mcwilliams gm schem

dynamical role of mode water ventilation in decadal variability in the central subtropical gyre of the north pacific abstract decadal variability in the interior subtropical north pacific is examined in the geophysical fluid dynamics laboratory coupled model cm2 1 superimposed on a broad classical subtropical gyre is a narrow jet called the subtropical countercurrent stcc that flows northeastward against the northeast trade winds consistent with observations the stcc is anchored by mode water characterized by its low potential vorticity pv mode water forms in the deep winter mixed layer of the kuroshio oyashio extension koe east of japan and flows southward riding on the subtropical gyre and preserving its low pv characteristic as a thick layer of uniform properties the mode water forces the upper pycnocline to shoal and the associated eastward shear results in the surface intensified stcc on decadal time scales in the central subtropical gyre 15 35 n 170 e 130 w the dominant mode of sea surface height variability is characterized by the strengthening and weakening of the stcc because of variations

formation region of north pacific subtropical mode water in the late winter of 2003 1 the mixed layer structure and properties in the formation region of the north pacific subtropical mode water stmw east of japan in the late winter of 2003 were examined using temperature and salinity data primarily from argo profiling floats the formation region extends south of the kuroshio extension between 30n and 35n and as far east as 175e it is characterized by a mixed layer with depths greater than 200db and meridionally uniform temperature between 16 5c and 18 2c associated with a mixed layer front at its southern edge the mixed layer in the formation region becomes colder fresher and denser toward the east leading to the formation of warmer saltier and lighter stmw in the western part of the region the spatial variation of the mixed layer depth in the formation region corresponds well with the underlying permanent thermocline depth index terms 4223 oceanography general descriptive and regional oceanography 4283 oceanography general water masses 4572 oceanography physical upper ocean processes citation oka e and t suga formation region of north pacific subtropical mode water in the late winter of 2003 geophys res lett 30 23 2205 doi 10 1029 2003gl018581 2003

bathymetric influences upon the character of north pacific fronts 1976 1980 thermal fronts in the north pacific from june 1976 to may 1980 have been mapped at the 300 m level by using temperature data obtained in the region 30 45 n 160 e 160w in the transpac xbt volunteer observing ship program the origins of the paths of the major frontal bands in the study region i e the kuroshio extension the subarctic fronts and the subtropical front appear to be related to the principal bathymetric features of the western mid latitude north pacific i e the shatsky rise the emperor seamount chain and the hess rise in the long term mean the kuroshio extension front at 35 n was observed to have bifurcated at the shatsky rise near 160 e into two bands one band continued northeast along the shatsky rise to 42 n to become the north subarctic front the other band continued zonally eastward where it encountered the emperor seamounts near 36 n 170 e and trifurcated into bands which tracked through passages between the seamounts near 37 n 34 n and 32 n respectively downstream the most northern of these three bands became the south subarctic front near 39 n the middle band continued as the kuroshio extension front at 35 n and the most southern band became the subtropical front near 32 n the middle band tracked north of the hess rise while the most southern band tracked south of the hess rise a near meridional frontal band linked the north and south subarctic fronts in the emperor seamount region near 170 e in the annual mean and individual seasonal mean maps the essential character of topographic influence of the long term mean was observed however the individual frontal bands varied seasonally about the long term mean by 2 of latitude also all four major frontal bands were not always observed and intermittent linkages and additional filaments also occurred

subtropical mode water in the northeast pacific basin a new type of mode water in the upper thermocline of the eastern subtropical north pacific is identified and examined using data from world ocean circulation experiment high resolution repeat expendable bathythermograph xbt section px37 and archives of historical xbt data this water mass labeled eastern subtropical mode water is characterized by a subsurface potential vorticity minimum and is located east of hawaii northeast pacific basin in a density range of 24 25 4 it is a distinct water mass from the classical subtropical mode water stmw of the western pacific eastern stmw is formed as a relatively deep late winter mixed layer associated with the subtropical subpolar water mass boundary near 25 30 n 135 140 w and is capped and subducted into the permanent thermocline along a section between san francisco and honolulu eastern stmw production is seen in every year for which there is adequate data in this section the volume of eastern stmw formed each winter and the temperature of the potential vorticity minimum are similar during the periods 1970 1979 and 1991 1997

cenomanian palaeotemperatures derived from the oxygen isotopic composition of brachiopods and belemnites evaluation of cretaceous palaeotemperature proxies sixty low magnesium calcite samples from cenomanian articulate brachiopods belemnites and oysters from the epicontinental shelf sea of europe were geochemically and microscopically studied in order to evaluate their preservation and potential as carriers of palaeoenvironmental information the sampled localities in northern spain germany and southern england cover the transition between subtropical 25 30 n and temperate 33 38 n climates mean cenomanian salinity adjusted palaeotemperatures of diagenetically unaltered terebratulid and rhynchonellid brachiopods are 25 5 1 3 c in spain and 19 4 1 9 c in southern england the resulting low to mid latitude meridional temperature gradient of 0 7 c per degree latitude is similar to the gradient today and suggests modern heat transport values for cenomanian low latitudes oxygen isotopic composition of unaltered specimens of the upper cenomanian belemnite praeactinocamax plenus mean 0 2 is enriched in 18o by 1 in comparison to brachiopod shells correspondingly upper cenomanian palaeotemperatures derived from belemnite calcite 13 0 1 3 c underestimate modelled mid latitude sea surface temperatures by 6 c since p plenus occurs as boreal pulse fauna during a short interval in the late cenomanian its heavy oxygen isotopic composition can be attributed either to migration from a cooler and or deeper water mass or to unknown vital effects

subtropical countercurrent in an idealized ocean gcm abstract in the north pacific there is a shallow eastward current called the subtropical countercurrent which flows across the central subtropical gyre the present article studies the generation mechanism of the subtropical countercurrent reproduced in an ocean general circulation model gcm with a simple geometry driven by surface wind stress and surface buoyancy forcing in the ocean gcm the deep mixed layer occurs in the northern part of subtropical gyre and shoals abruptly in the central subtropical gyre the mixed layer front the narrow transition zone of the mixed layer depth slants from the western central subtropical gyre to the northeast and the low potential vorticity fluid is formed at the intersection of the mixed layer front and the outcrop line since the surface density is almost zonally uniform and the mixed layer front slants northeastward the minimum potential vorticity fluids on denser isopycnals are formed in the northeastern region while those on lighter isopycnals are form