south indian countercurrent and associated fronts a striking feature of the south indian ocean circulation is the presence of the eastward south indian countercurrent sicc that flows in a direction opposite to that predicted by the classical theories of wind driven circulation several authors suggest that the sicc resembles the subtropical countercurrents stccs observed in other oceans which are defined as narrow eastward jets on the equatorward side of subtropical gyres where the depth integrated flow is westward these jets are associated with subsurface thermal fronts at thermocline depths by the thermal wind relation however the subsurface thermal front associated with the sicc has not been described to date other studies conjecture an important role for salinity in controlling the sicc in the present work we analyze three argo based atlases and data from six hydrographic cruises to investigate whether the sicc is accompanied by permanent thermal and density fronts including salinity effects the seasonal cycle of these fronts in relation to the sicc strength is also investigated we find that the sicc is better described as composed of three distinct jets which we name the northern central and southern sicc we find that the southern sicc around 26 s has an associated thermal front at subsurface depths around 100 200 m with salinity being of secondary importance the southern branch strength is related to mode waters poleward of the front similar to a stcc like current however the sicc multiple jet structure seems to be better described as resulting from pv staircases

influence of the tropics and southern westerlies on glacial interhemispheric asymmetry latitudinal variations in the location of the southern westerly wind belt have been associated with millennial scale climate variations during the last glacial period a reconstruction of sea surface temperatures off the southern coast of australia suggests that these climate variations also drove changes in the location of the oceanic subtropical front

a reexamination of northeast atlantic sea surface temperature and salinity over the last 16 kyr we present a 15 kyr sea surface temperature sst record for a high sedimentation rate core knr51 29ggc from the feni drift off of ireland based on an organic geochemical technique for paleotemperature estimation u37k we compare the u37k temperature record to planktonic foraminiferal 18o and foraminiferal assemblage sst estimates from the same sample horizons u37k gives sst estimates of 13 c for the early deglacial and 18 c for the holocene and recent whereas assemblages give estimates of 9 c and 13 c respectively as in nearby core v23 81 we find ash zone 1 the younger dryas increase in neogloboquadrina pachyderma sinistral abundance and maximum abundance of this species during glaciation n pachyderma dextral oxygen isotopic analyses have a late glacial to interglacial range of 1 5 a reduction of about 1 in 18o occurred at about 12 ka whereas u37k and the foraminiferal fauna indicate a 2 c warming this implies a 0 9 salinity effect on 18o which we attribute to meltwater freshening all three parameters indicate cooling during the younger dryas u37k sst estimates show that the major shift from deglacial to interglacial temperatures occurred after the younger dryas in termination 1b in contrast to the assemblage data which show this jump in sst at the end of the glaciation during termination ia differences between the two sst estimators which may result from their different floral versus faunal sources are more pronounced between transitions ia and ib this may reflect different habitats under the unusual sea surface conditions of the deglaciation

application of the topographic datuming operator to a data setfrom the eastern arabian peninsula we apply a redatuming methodology designed to handle rugged topography and the presence of high velocity layers near the acquisition surface to a 2d land seismic data set acquired in saudi arabia this methodology is based on a recently developed prestack operator which we call the topographic datuming operator tdo the tdo unlike static corrections allows for the movement of reflections laterally with respect to their true locations corresponding to the new datum level thus it mitigates mispositioning of events and velocity bias introduced by the assumption of surface consistency and the time invariant time shifts brought about by static corrections using the shallow velocities estimated from refracted events the tdo provides a superior continuity of reflections and better focusing than that obtained from conventional static corrections in most parts of the processed 2d line the computational cost of applying the tdo is only slightly higher than static corrections the marginal additional computational cost and the possibility of estimating after tdo redatuming stacking velocities that are not affected by a spurious positive bias as in the case of static corrections are further advantages of the proposed methodology the likelihood of strong heterogeneities in the most complex part of the line limits the applicability of any approach based upon geometrical optics however the tdo produces results that are slightly better than those obtained from static corrections because of its ability to partially collapse diffractions generated in the near surface

a diatom and benthic foraminiferal record from the south tasman rise southeastern indian ocean implications for palaeoceanographic changes for the last 200 000 years abstract the last two glacial interglacial cycles represented in core md88 779 in the southeastern indian ocean over the south tasman rise 47 50 69 s 146 32 75 e 2260 m water depth have been analysed an oceanographic reconstruction for this region is presented based principally on the recovery of benthic foraminiferal and diatom assemblages the most striking feature of the microfossil record from core md88 779 is the lack of diatoms during glacials despite evidence of high oceanic productivity benthic foraminiferal data suggest significant increases in ocean surface productivity during glacial periods and in particular during isotopic stages 2 late 3 and 6 for these periods of elevated surface productivity substantial and at times total dissolution of diatom frustules occurred we propose that increased influx of aeolian dust and especially associated iron during glacial periods may have reduced the intake of silica in diatoms thus resulting in less silicified diatoms additionally winnowing is suggested to have removed remaining frustules from the sedimentary record increased productivity at the sea surface is indicative that both the subtropical front and the subantarctic front may have shifted northward during glacial periods and that the subantarctic front was near the coring site on the south tasman rise for these periods we also postulate based on diatom floral evidence that southward moving eddies generated by the subtropical east australian current may have intermittently reached the coring site even during glacial periods

deep oceanic zonal jets constrained by fine scale wind stress curls in the south pacific ocean a high resolution coupled gcm study 1 oceanic alternating zonal jets at depth have been detected ubiquitously in observations and ocean general circulation models gcms such oceanic jets are generally considered as being generated by purely oceanic processes here we explore a possible air sea interaction induced by surface signatures of the deep zonal jets using an eddy permitting coupled atmosphere ocean gcm cgcm the 23 year cgcm integration reproduces bands of latitudinally narrow alternating jets in the southeast pacific they extend from the sea surface to well below the main thermocline and are embedded in the large scale westward flowing south equatorial current the latter mostly confined above the thermocline these jets generate fine scale sea surface temperature sst anomalies through the advection of zonal temperature gradients the atmospheric boundary layer appears to respond thermally to this fine scale sst field which induces fine scale wind stress anomaly through atmospheric pressure adjustment as indicated by a good spatial correlation between the sst laplacian field and the fine scale wind stress curl a sverdrup calculation on the wind stress field of the cgcm predicts fine scale zonal currents driven by the meridional gradient of the fine scale wind stress curl the positions of these sverdrup currents are generally coincident with those of the original zonal jets and the sverdrup prediction explains roughly half of the amplitudes of the jets while the original cause of the deep zonal jets simulated in our cgcm is unidentified this analysis suggests that there is likely a positive air sea feedback the jets generate fine scale wind stress curl that reinforces themselves through the sverdrup dynamics

physical controls on biogeochemical zonation in the southern ocean the primary control on the n s zonation of the southern ocean is the wind induced transport of the antarctic circumpolar current acc the acc divides the southern ocean into three major zones the subantarctic zone saz north of the acc the acc transport zone and the zone south of the acc saccz the zone of acc transport is most often subdivided into two zones the polar frontal zone pfz and the antarctic zone aaz but it may be appropriate to define more subzones or indeed only one at some longitudes to maintain geostrophic balance isopycnals must slope upwards to the south across the acc thus raising nutrient rich deep water closer to the surface as one goes polewards in addition silicate concentrations increase polewards along isopycnals because of diapycnic mixing with silicate rich bottom water surface silicate concentrations therefore decrease northwards from high levels in the saccz to low levels in the saz within the saz and pfz and even in the northern part of the aaz silicate levels may drop to limiting levels for siliceous phytoplankton production during summer nitrate concentrations also decrease northwards but only become limiting in the subtropical zone north of the saz the second circumpolar control is the changing balance of stratification with temperature dominating near surface stratification in the saz and salinity dominating further south because of fresh water input to the surface from melting ice this results in circumpolar features such as the subsurface 2 c temperature minimum and the subduction of the salinity minimum of antarctic intermediate water which are often but not always associated with frontal jets and large transports the transport of the acc is dynamically constrained into narrow bands the number and latitudinal location of which are controlled by the bathymetry and so vary with longitude thus it is not the fronts that are circumpolar but the total acc transport and scalar properties of the salinity and temperature fields evidence of summer silicate and nitrate uptake in all zones saz pfz and aaz shows that there is productivity despite their high nutrient low chlorophyll status blooms covering large areas say 400 km across in the pfz and aaz are found in the vicinity of submarine plateaux which suggest benthic iron fertilizatio

eddy forcing of the mean flow in the southern ocean we examine the force or acceleration exerted by eddies on the mean flow of the southern ocean using mapped sea surface height anomalies derived from satellite altimeter measurements we compare this with the position of jets in the mean flow indicated by regions of increased gradient in the mean sea surface temperature the eddy force itself is not of primary importance rather the curl of that force affects the mean flow so the irrotational force due to the gradient of eddy kinetic energy can be ignored leaving a remainder that can be interpreted in terms of the eddy vorticity flux unlike previous modeling and altimetric studies we find that the eddies act to decelerate some of the strongest jets and act as vorticity sources for others the strongest jets are clearly not accelerated by eddies a problem of interpretation does remain however since it is not clear how sea surface temperatures are related to the mean flow this ambiguity can only be completely resolved by measurement of the mean flow requiring a geoid that is accurate at length scales of order 100 km

southern ocean fronts controlled by wind or topography 1 the location of fronts has a direct influence on both the physical and biological processes in the southern ocean here we explore the relative importance of bottom topography and winds for the location of southern ocean fronts using 100 years of a control and climate change simulation from the high resolution coupled climate model higem topography has primary control on the number and intensity of fronts at each longitude however there is no strong relationship between the position or spacing of jets and underlying topographic gradients because of the effects of upstream and downstream topography the southern hemisphere westerlies intensify and shift south by 1 3 in the climate change simulation but there is no comparable meridional displacement of the antarctic circumpolar current s acc path or the fronts within its boundaries even over flat topography instead the current contracts meridionally and weakens north of the acc the subtropical front stf shifts south gradually even over steep topographic ridges we suggest the stf reacts more strongly to the wind shift because it is strongly surface intensified in contrast fronts within the acc are more barotropic and are therefore more sensitive to the underlying topography an assessment of different methods for identifying jets reveals that maxima of gradients in the sea surface height field are the most reliable approximating the position of fronts using sea surface temperature gradients is ineffective at high latitudes while using sea surface height contours can give misleading results when studying the temporal variability of front locations

southern ocean seasonal temperature and subtropical front movement on the south tasman rise in the late quaternary 1 the subtropical front stf marking the northern boundary of the southern ocean has a steep gradient in sea surface temperature sst of approximately 4c over 0 5 of latitude presently in the region south of tasmania the stf lies nominally at 47s in the summer and 45s in the winter we present here sst reconstructions in a latitudinal transect of cores across the south tasman rise southeast of australia during the late quaternary sst reconstructions are based on two paleotemperature proxies alkenones and faunal assemblages which are used to assess past changes in sst in spring and summer the north south alignment in core locations allows reconstruction of movement of the stf over the last 100 ka surface water temperatures during the last glaciation in this region were 4c colder than today additional temperature changes greater in magnitude than 4c seen in individual cores can be attributed to changes in the water mass overlying the core site caused by the movement of the front across that location during the penultimate interglacial sst was 2c warmer and the stf was largely positioned south of 47s movement of the stf to the north occurred during cool climate periods such as the last marine isotope stages 3 and 4 in the last glaciation the front was at its farthest north position becoming pinned against the tasmanian landmass it moved south by 4 latitude to 47s in summer during the deglaciation but remained north of 45s in spring throughout the early deglaciation after 11 ka b p inferred invigoration of the east australia current appears to have pushed the stf seasonally south of the east tasman plateau until after 6 ka b p when it achieved its present configuration

estimates of sea surface temperature in the coral sea at the last glacial maximum the climap 1981 reconstruction of the coral sea found relatively little cooling 2 c in the low latitudes 10 s but a warming off australia at about 25 s the small low latitude changes are of interest because terrestrial pollen and snowline data from the new guinea highlands imply that surface temperatures may have been 6 to 9 c colder at the last glacial maximum lgm the purpose of this paper is to evaluate these conclusions on the basis of additional core sites new oxygen isotope stratigraphy and new sea surface temperature sst estimates using the modern analog technique mat in the northern coral sea planktonic foraminifer assemblages consist of tropical subtropical species that show little change over the past 20 kyr quantitative estimates of sst using the modern analog technique mat confirm the climap 1981 conclusion that little or no temperature change occurred in this tropical region at the lgm thus reinforcing the conflict with terrestrial evidence in the southern region 25 s two cores indicate that foraminifer faunas became more subtropical at the lgm the mat estimates for the lgm are 3 to 4 c colder than modern producing a steeper thermal gradient in the southern coral sea these data remove the warm sst anomaly along the eastern coast of australia and indicate that during the lgm cool high latitude waters were displaced northward along the coast of australia into the southern coral sea

status of alkenone paleothermometer calibration report from working group 3 1 the alkenone unsaturation index u37k has now proven its worth as a tool for paleothermometry u37k measured in most modern sediments throughout the world ocean can be translated using established calibrations into realistic seemingly reliable estimates of mean annual temperature at the sea surface sst however it remains mysterious why water temperature estimates based on this biotic index correspond to mean annual sst and whether such estimates apply back in geological time solving these mysteries is imperative and will require thoughtful concerted research effort by the biological chemical and geological oceanographic community this report summarizes what is now known about alkenones in particular their use in estimating the growth temperature of specific haptophyte algae that synthesize and export these compounds to the marine sediment record it highlights future field and laboratory research directions that should be taken to clarify and bolster utility of alkenones as a generally valued paleoceanographic tool

340 000 year centennial scale marine record of southern hemisphere climatic oscillation in order to investigate rapid climatic changes at mid southern latitudes we have developed centennial scale paleoceanographic records from the southwest pacific that enable detailed comparison with antarctic ice core records these records suggest close coupling of mid southern latitudes with antarctic climate during deglacial and interglacial periods glacial sections display higher variability than is seen in antarctic ice cores which implies climatic decoupling between mid and high southern latitudes due to enhanced circum antarctic circulation structural and temporal similarity with the greenland ice core record is evident in glacial sections and suggests a degree of interhemispheric synchroneity not predicted from bipolar ice core correlations

on the variability of antarctic circumpolar current fronts inferred from 1992 2011 altimetry abstractantarctic circumpolar current acc fronts defined as water mass boundaries have been known to respond to large scale atmospheric variabilities especially the southern hemisphere annular mode sam and el nino southern oscillation enso distinct patterns of localized variability in meridional front displacements during 1992 2011 are derived from the analysis of satellite sea surface height data major basin scale differences are found between the southeast pacific 150 90 w and the southeast indian 75 150 e sectors of the acc frontal positions in the southeast pacific show large year to year meridional fluctuations attributed mostly to enso and in part sam and no apparent seasonal cycles or long term trends in contrast summer winter frontal locations in the southeast indian extend farther to the south north of their long term mean distribution a southward drift of acc fronts is indicated over the indian sector during the past two decades this long term shift is not directly re

changes in the position of the subtropical front south of new zealand since the last glacial period this study fills an important gap in our understanding of past changes in the southern subtropical front s stf in the southwest pacific ocean paleo sea surface temperatures sst were estimated from planktic foraminiferal census counts from cores straddling the modern s stf in the solander trough south of new zealand the estimated sst were compared for 6 time slices glacial period 25 21 ka last glacial maximum lgm 21 18 ka early deglaciation 18 16 ka late deglacial early holocene period 14 8 ka mid holocene period 8 4 ka and late holocene period 4 0 ka the position of the s stf was determined by two methods 1 the location of the 10 degrees c isotherm and 2 the location of the highest sst gradients these new results suggest that the s stf was not continuous between east and west of new zealand during the glacial period steep sst gradients indicate that a strong s stf rapidly shifted south during the lgm and early deglaciation during the late deglacial and holocene periods the position of the s stf differs between the two methods with reduced sst gradients suggesting amore diffuse s stf in the solander trough at this time the glacial sst data suggest that the s stf shifted north to the west of new zealand while to the east there was a stronger sst gradient across the front this was possibly the result of an increased wind stress curl which could have been caused by stronger or more northerly southern hemisphere westerly winds shww or a merging of the shww split jet in this region

brazil malvinas frontal system as seen from 9 years of advanced very high resolution radiometer data 1 surface thermal fronts in the southwestern atlantic swa ocean are examined using 9 years 1987 1995 of advanced very high resolution radiometer data fronts are detected considering a gradient based edge detector sea surface temperature gradients are calculated from 4 km resolution 5 day composite images covering the western argentine basin south of 30 s variability in the position and intensity of the fronts from seasonal to interannual timescales is characterized in six regions including different parts of the brazil current front bcf and the subantarctic front saf shelf break brazil sb b brazil malvinas collision bm c brazil current overshoot bc o shelf break malvinas sb m malvinas return flow mrf and falkland escarpment fe fronts in the sb b sb m mrf and fe regions are controlled by the bathymetry in the bm c region the bcf and saf appear to merge as a single front this front does not present large seasonal north south excursions as previously described though it pivots seasonally around a fixed point located approximately at 39 5 s 53 5 w changing its orientation from n s in winter to nw se in summer consequently on average the front intersects the 1000 m isobath at 38 30 s in summer and north of 37 s in winter in the bc o region the bcf has a u shape centered at 53 w the intensity of the fronts in each region except in the fe region presents large seasonal variability in the sb b bm c and bc o regions the frontal intensity is highest 0 35 c km during austral winter the annual components explain 83 67 and 71 of the total variance respectively in the sb m and mrf regions the saf is most intense 0 25 c km in summer and fall the annual component of the intensity fluctuations explains 29 and 38 of the total variance respectively in the fe region the annual component of frontal intensity explains only 17 of the variability in the six regions important interannual variability is found the zapiola rise centered at 45 s 43 w appears as a gradient free region closed planetary potential vorticity contours in this area suggest it is dynamically isolated

southern ocean jets and how to find them improving and comparing common jet detection methods this study undertakes a detailed comparison of different methods used for detecting and tracking oceanic jets in the southern ocean the methods under consideration are the gradient thresholding method the probability density function pdf method and the contour method some weaknesses of the gradient thresholding method are discussed and an enhancement the whose method based on techniques from signal processing is proposed the whose method is then compared to the other three methods quantitative comparison is undertaken using synthetic sea surface height fields the whose method and the contour method are found to perform well even in the presence of a strong eddy field in contrast the standard gradient thresholding and pdf methods only perform well in high signal to noise ratio situations the whose pdf and the contour methods are then applied to data from the eddy resolving ocean general circulation model for the earth simulator while the three methods are in broad agreement on the location of the main acc jets the nature of the jet fields they produce differ in particular the whose method reveals a fine scale jet field with complex braiding behavior it is argued that this fine scale jet field may affect the calculation of eddy diffusivities finally recommendations based on this study are made the whose and gradient thresholding methods are more suitable for the study of jets as localized strong currents useful for studies of tracer fluxes the contour and pdf methods are recommended for studies linking jets to hydrographic fronts

solving the complex near surface problem using 3d data driven near surface layer replacement abstract in many land seismic situations the complex seismic wave propagation effects in the near surface area due to its unconsolidated character deteriorate the image quality although several methods have been proposed to address this problem the negative impact of 3d complex near surface structures is still unsolved to a large extent this paper presents a complete 3d data driven solution for the near surface problem based on 3d one way traveltime operators which extends our previous attempts that were limited to a 2d situation our solution is composed of four steps 1 seismic wave propagation from the surface to a suitable datum reflector is described by parametrized one way propagation operators with all the parameters estimated by a new genetic algorithm the self adjustable input genetic algorithm in an automatic and purely data driven way 2 surface consistent residual static corrections are estimated to accommodate the fast variations in the near surface area 3 a replacement velocity model based on the traveltime operators in the good data area without the near surface problem is estimated 4 data interpolation and surface layer replacement based on the estimated traveltime operators and the replacement velocity model are carried out in an interweaved manner in order to both remove the near surface imprints in the original data and keep the valuable geological information above the datum our method is demonstrated on a subset of a 3d field data set from the middle east yielding encouraging results

quasi zonal jets in 3 d argo data of the northeast atlantic 1 time mean zonal velocities estimated from argo float trajectories and density profiles are systematically examined for quasi zonal jets or striations with the use of a simple search algorithm a comparison to altimeter data combined with an independent estimate of the mean dynamic topography shows that the jets in the 2004 2006 period examined are persistent and stationary the jets have a typical meridional width of 100 to 200 km and a median transport of 4 sverdrups the jets tilt at approximately 6 from southwest to northeast in the horizontal plane but show no significant tilt in the vertical plane velocities and the cross stream width are similar for the westward and eastward jets

sea surface temperature fronts in the midlatitude south atlantic revealed by using microwave satellite data 1 the subtropical convergence or frontal zone has been little studied in the central south atlantic ocean despite limited data some work has suggested that this feature exists continuously across the south atlantic here satellite microwave sensed sea surface temperature sst data available from june 2002 are analysed for the existence of frontal gradients in the subtropical to subpolar south atlantic with focus on the central to eastern region the frontal locations and sst gradients in the southwest south atlantic and in the agulhas current retroflection region obtained from this satellite data are consistent with those estimated previously from hydrographic observations evident in the satellite data is pronounced mesoscale variability in subtropical frontal features particularly south of africa and extending west from the agulhas current retroflection to at least the greenwich meridian and in the southwest south atlantic over the central to eastern part of the basin the analysis suggests that there is substantial interannual variability in the strength and latitudinal location of the northern and southern subtropical front as defined by belkin and gordon 1996 some of this variability may be related to shifts in the winds including that in the latitude of the strongest wind stress curl on seasonal scales this central to eastern region is also characterised by variations in the frontal intensity but shifts in the position of regions of strong gradients are less obvious thus the data indicate that there is no continuous subtropical frontal feature across the basin in terms of surface temperature

jets and topography jet transitions and the impact on transport in the antarctic circumpolar current the southern ocean s antarctic circumpolar current acc naturally lends itself to interpretations using a zonally averaged framework yet navigation around steep and complicated bathymetric obstacles suggests that local dynamics may be far removed from those described by zonally symmetric models in this study both observational and numerical results indicate that zonal asymmetries in the form of topography impact global flow structure and transport properties the conclusions are based on a suite of more than 1 5 million virtual drifter trajectories advected using a satellite altimetry derived surface velocity field spanning 17 years the focus is on sites of cross front transport as defined by movement across selected sea surface height contours that correspond to jets along most of the acc cross front exchange is localized in the lee of bathymetric features with more than 75 of crossing events occurring in regions corresponding to only 20 of the acc s zonal extent these observations motivate a series of numerical experiments using a two layer quasigeostrophic model with simple zonally asymmetric topography which often produces transitions in the front structure along the channel significantly regimes occur where the equilibrated number of coherent jets is a function of longitude and transport barriers are not periodic jet reorganization is carried out by eddy flux divergences acting to both accelerate and decelerate the mean flow of the jets eddy kinetic energy is amplified downstream of topography due to increased baroclinicity related to topographic steering the combination of high eddy kinetic energy and recirculation features enhances particle exchange these results stress the complications in developing consistent circumpolar definitions of the acc fronts

high latitude forcing of diatom productivity in the southern agulhas plateau during the past 350 kyr the hydrography of the indian atlantic ocean gateway has been connected to high latitude climate dynamics by oceanic and atmospheric teleconnections on orbital and suborbital timescales a wealth of sedimentary records aiming at reconstructing the late pleistocene paleoceanography around the southern african continent has been devoted to understanding these linkages most of the records are however clustered close to the southern south african tip with comparatively less attention devoted to areas under the direct influence of frontal zones of the southern ocean south atlantic here we present data of the composition and concentration of the diatom assemblage together with bulk biogenic content and the alkenone based sea surface temperature sst variations for the past 350 kyr in the marine sediment core md02 2588 approximately 41 s 26 e recovered from the southern agulhas plateau variations in biosiliceous productivity show a varying degree of coupling with southern hemisphere paleoclimate records following a glacial interglacial cyclicity ecologically well constrained groups of diatoms record the glacial interglacial changes in water masses dynamics nutrient availability and stratification of the upper ocean the good match between the glacial maxima of total diatoms concentration chaetoceros spores abundance and opal content with the maximum seasonal cover of antarctic ice and the atmospheric dust records points to a dominant southern hemisphere forcing of diatom production suborbital variability of sst suggests rapid latitudinal migrations of the subtropical front and associated water masses over the southern agulhas plateau following millennial contractions and expansions of the subtropical gyres warmings of the upper ocean over site md02 2588 during terminations iv to i occurred earlier than that in the antarctic vostok which is indicative of a northern hemisphere lead our multiparameter reconstruction highlights how high latitude atmospheric and hydrographic processes modulated orbital highs and lows in primary production and sst as triggered by northward transport of si eolian dust input and latitudinal migrations of frontal zones

an integrated latest quaternary stage 3 to present paleoclimatic and paleoceanographic record from offshore northern new zealand abstract paleoceanographic and onshore paleoclimatic changes during the last 59 000 yr are established from three deep sea sediment cores off northeast new zealand using an integrated log of sediment texture caco3 content palynology and planktonic and benthic foraminiferal 18o and 13c data together with dated silicic tephras these records from the isotopic stage 4 3 boundary to the present record northern new zealand vegetation history changes in a subsidiary equatorward flow of circumpolar deep water and sea surface temperatures ssts for subtropical water stw between latitudes 36 42 and 35 51 s relative to the holocene isotopically derived ssts record average changes of 2 c 2 c and 2 c for the 59 000 43 000 43 000 24 000 and 24 000 12 000 yr time slices respectively the apparent 2 c warming for the 59 000 43 000 yr period is interpreted to reflect changes in the dominant depth habitat of globigerina bulloides in response to upwelling a 2 c cooling of ssts during isotope stage 2 is interpreted in part to reflect upwelling of cool subsurface water resulting from strong and persistent westerly airflow across new zealand with the concomitant enhanced surface water production of caco3 onshore vegetation consistent with these changes are recorded with full conifer hardwood forest prior to 43 000 yr followed by a change to vegetation implying cooler and drier conditions between 43 000 and 12 000 yr and a subsequent return to full forest during the holocene the sequence of biopelagic and hemipelagic sedimentation observed within these cores reflect oscillation of sea level about a threshold eustatic level that controls the transport of terrigenous detritus offshore local variations and interplay of the regional oceanography and morphology and tectonism of the continental shelf will dictate that relative to present sea level this threshold eustatic sea level will vary in depth and hence age along a continental margin data from the new zealand region reveal an extremely steep meridional thermal gradient across the southern and central new zealand region during the last glaciation with minor cooling of stw to the north apart from localized nearshore upwelling zones but pronounced cooling of subantarctic water to the south of the subtropical convergence zone

is there a continuous subtropical front south of africa a 14 3 year series of weekly absolute sea surface height ssh and associated geostrophic velocities is used for a study of the subtropical to subantarctic frontal system in the region south of africa detecting the fronts from surface velocity maxima confirms a two stepped transition in both the southeastern atlantic ocean the northern and southern subtropical fronts nstf sstf and southwestern indian ocean the agulhas front and sstf as proposed previously from hydrographic data an additional front associated with westward flow north of the nstf is indicative of a partial eastern closure of the south atlantic subtropical gyre between 11 e and 17 5 e the role of northwestward propagating agulhas rings in connecting the two fronts explains the varying location the sstf which marks the southern limit of subtropical waters is found continuous from the atlantic to the indian ocean in the time averaged ssh field in the weekly fields however the velocity maximum criterion defining the front is often met at the southern flanks of agulhas rings or agulhas eddies at 12 e 23 e indicating front disruptions such discontinuities suggest that no south atlantic central water is directly advected into the indian ocean instead the eastward limb of the indo atlantic super gyre encompassing the subtropical gyres of both oceans would rest at these longitudes on diffusive processes at the upper levels and possibly be enhanced at depth a schematic diagram of the fronts and their relations to agulhas rings and eddies is proposed

comparison of alkenone estimates with other paleotemperature proxies 1 to a certain degree all sea surface temperature sst proxies suffer from uncertainty due to signal preservation problems and to perturbations by other environmental variables however a multiproxy reconstruction is justified because most biases should in principle cancel out as they are specific to the biological groups and or to the analyzed chemical species such a multiproxy strategy has proven crucial for calibrating these proxies and is also useful in assessing downcore profiles until now there have been only a dozen deep sea cores where it is possible to compare directly alkenone based ssts with other paleotemperature records from this still limited data set the broad picture is of general agreement for the amplitude of changes at low and middle latitudes the few observed discrepancies suggest that alkenone based temperatures are more comparable to those based on mg ca ratios than those obtained through statistical analysis of the foraminiferal distribution more systematic differences are noted at higher latitudes where alkenones indicate warmer temperatures during the glacial period than transfer functions based on foraminifera or diatoms several reasons have been invoked to resolve the mismatch but more ground truthing work is needed before deciding which temperature changes are the most accurate

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

last glacial maximum sea surface temperature and sea ice extent in the pacific sector of the southern ocean sea surface temperatures and sea ice extent are most critical variables to evaluate the southern ocean paleoceanographic evolution in relation to the development of the global carbon cycle atmospheric co2 and ocean atmosphere circulation here we present diatom transfer function based summer sea surface temperature ssst and winter sea ice wsi estimates from the pacific sector of the southern ocean to bridge a gap in information that has to date hampered a well established reconstruction of the last glacial southern ocean at circum antarctic scale we studied the last glacial maximum lgm at the epilog time slice 19 000e23 000 calendar years before present in 17 cores and consolidated our lgm picture of the pacific sector taking into account published data from its warmer regions our data display a distinct east west differentiation with a rather stable wsi edge north of the pacific antarctic ridge in the ross sea sector and a more variable wsi extent over the amundsen abyssal plain the zone of maximum cooling 4 k during the lgm is in the present subantarctic zone and bounded to its south by the 4 c isotherm the isotherm is in the ssst range prevailing at the modern antarctic polar front representing a circum antarctic feature and marks the northern edge of the glacial antarctic circum polar current acc the northward deflection of colder than modern surface waters along the south american continent led to a significant cooling of the glacial humboldt current surface waters 4e8 k which affected the temperature regimes as far north as tropical latitudes the glacial reduction of acc temperatures may also have resulted in significant cooling in the atlantic and indian southern ocean thus enhancing thermal differentiation of the southern ocean and antarctic continental cooling the comparison with numerical temperature and sea ice simulations yields discrepancies especially con cerning the estimates of the sea ice fields but some simulations reproduce well our proxy based tem perature data

properties of the subantarctic front and polar front from the skewness of sea level anomaly author s shao ae gille st mecking s thompson l abstract 2015 american geophysical union all rights reserved the region of the southern ocean that encompasses the subantarctic front saf to the north and the polar front pf to the south contains most of the transport of the antarctic circumpolar current here skewness of sea level anomaly sla from 1992 to 2013 is coupled with a meandering gaussian jetw model to estimate the mean position meridional width and the percent variance that each front contributes to total sla variability the saf and pf have comparable widths 85 km in the circumpolar average but their widths differ significantly in the east pacific basin 85 and 60 km respectively interannual variability in the positions of the saf and pf are also estimated using annual subsets of the sla data from 1993 to 2012 the pf position has enhanced variability near strong topographic features such as the kerguelen plateau the campbell plateau east of new zealand and downstream of drake passage neither the saf nor the pf showed a robust meridional trend over the 20 year period the southern annular mode was significantly correlated with basin averaged saf and pf positions in the east pacific and with the pf south of australia a correlation between the pf and the basin scale wind stress curl anomaly was also found in the western extratropical pacific but not in other basins

the south atlantic current in this paper we use the historical hydrographic data base for the south atlantic ocean to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the sub tropical front stf and ii the southern current band of the gyre which is called the south atlantic current sac the stf begins in the west in the brazil falkland malvinas confluence zone but at locations at and west of 45 w this front is often coincident with the brazil current front east of 45 w the stf appears to be a distinct feature to at least the region south of africa whereupon it continues into the indian ocean the associated current band of increased zonal speed is the sac which except for one instance is found at or north of the surface stf until indian ocean water from the agulhas retroflection is reached a reversal of baroclinicity in the stf is observed south of a highly saline agulhas ring causing the sac to separate from the stf and turn north into the benguela current zonal flow south of the stf is generally weak and serves to separate the south atlantic and circumpolar currents in the argentine basin the sac has a typical volume transport of 30 sv 1 sv 106m3s 1 in the upper 1000 m relative to a deep potential density surface 4 45 87 kg m 3 and can be as high as 37 sv it is thus comparable to or stronger than the brazil current in the cape basin the transport of the sac is reduced to about 15 sy before it turns north to feed the benguela current in late 1983 this flow was joined by about 8 sv of water from the agulhas current

the south pacific current the southern hemisphere subtropical front stf is a narrow zone of transition between upper level subtropical waters to the north and subantarctic waters to the south it is found near 40 degrees s across the south atlantic and south indian oceans and is associated with an eastward geostrophic current band the current band in each basin is found at or just north of the surface front except near the eastern boundaries where most of the subtropical waters turn north into the eastern limbs of the subtropical gyres the bands associated with the stf are thus distinct features separated from the strong zonal flows of the antarctic circumpolar current farther south the authors have referred to the current bands in the two respective oceans as the south atlantic current and the south indian ocean current in this paper the authors use the historical database from the south pacific ocean to investigate the geostrophic flow associated with the stf there the stf extends across the southern tasman sea from south of tasmania to southern new zealand and a weak eastward flow appears to be associated with it the transport amounts to only about 3 sv 1sv 10 6 m 3 s 1 little of which passes south of new zealand mixing within the eddy rich tasman sea may account for this weakness while also setting up another more significant front in the northern tasman sea the tasman front it branches off from the east australian current toward the north of new zealand along which moves a flow of about 14 sv after passing north of new zealand a portion of this current flows east to contribute to a current band near 30 degrees s while another portion turns south as the east auckland current and meets with subantarctic waters near chatham rise 44 degrees s thus reestablishing the stf an enhanced eastward current band is associated with the front there one that extends across the remainder of the south pacific and is referred to as the south pacific current in comparison with its counterparts in the other basins which typically begin by carrying 30 sv atlantic to 60 sv indian in the upper 1000 m in their western portions before weakening to 10 15 sv in the east the south pacific current is weak near chatham rise it starts with a transport of approximately 5 sv and it remains near this strength as it shifts gradually north across the basin toward south america the current appears to split into two smaller bands in the region of 115 degrees 85 degrees w while near 28 degrees 5 83 degrees w it begins to turn more strongly north and becomes shallower and weaker potential vorticity distributions indicate that this current acts as an impediment toward the northward spreading of antarctic intermediate water but why the south pacific current east of new zealand should be so much weaker than its counterparts in the other basins is not particularly clear it may be due to the presence of new zealand and other topographic barriers to deep now east of australia to the axis of the subtropical gyre in the south pacific shifting more rapidly southward with depth than those elsewhere thus causing greater reductions in the underlying zonal velocities and to strong poleward eddy heat and salt fluxes in the other two basins leading to smaller cross stf gradients in the pacific

a basal ceratopsid centrosaurinae nasutoceratopsini from the oldman formation campanian of alberta canada a partial skull cmn 8804 of a ceratopsid from the upper unit of the campanian oldman formation of alberta is the first canadian example of the newly established nasutoceratopsini a new subclade of centrosaurinae defined as the stem based clade of centrosaurine ceratopsids more closely related to nasutoceratops titusi than to centrosaurus apertus the new clade is diagnosed in part by having a parietosquamosal frill lacking modified epimarginals a small nasal horncore large rostrolaterally directed postorbital horncores and a relatively short deep face although the cmn 8804 taxon closely resembles nasutoceratops its phylogenetic position within nasutoceratopsini is unresolved the cmn 8804 taxon would have been contemporaneous with dinosaurs from the lower portion of the dinosaur park formation 200 km to the northwest in dinosaur provincial park the presence of the cmn 8804 taxon in alberta and the approximately contemporaneous nasutoceratops in utah indicates that the nasutoceratopsins pers

pleistocene variability of the subtropical convergence at east tasman plateau evidence from planktonic foraminiferal mg ca odp site 1172a combined measurements of mg ca and stable oxygen isotopes in tests of the planktonic foraminifer g bulloides from ocean drilling program odp site 1172a east tasman plateau allowed us to reconstruct sea surface temperature sstmg ca sea surface salinity sss and hence variations in the subtropical convergence stc in the southwestern tasman sea over the last four major glacial interglacial changes during interglacials the commonly enhanced sstmg ca and sss correspond to a lowered marine productivity and a lowered terrigenous flux implying that the stc separating cool high nutrient subantarctic surface water from warm saline oligotrophic subtropical surface water and hence the band of zonal westerlies responsible for the eolian dust flux were located south of east tasman plateau the warm east australian current was well established during warm periods and propagated far south during glacial times sstmg ca and sss were lower while both marine productivity and eolian flux increased such conditions prevailed during glacial marine isotope stages mis 12 mis 10 and to a lesser degree mis 6 and implied the extended northward influence of subantarctic surfacewater and a shift of the stc to 44 s the overall climatic signal at site 1172a appears to be largely attenuated when compared to published climate records from comparable latitudes to the west and to the east sstmg ca amplitudes were more pronounced in the subantarctic indian ocean and at chatham rise they exhibit a consistent pattern suggesting that latitudinal shifts of the stc occurred synchronously in the subantarctic indian ocean and at chatham rise but were largely damped at east tasman plateau due to the influence of the east australian current

the two step shape and timing of the last deglaciation in antarctica the two step character of the last deglaciation is well recognized in western europe in greenland and in the north atlantic for example in greenland a gradual temperature decrease started at the bolling b around 14 5 ky bp spanned through the allerod a and was followed by the cold younger dryas yd event which terminated abruptly around 11 5 ky bp recent results suggest that this ba yd sequence may have extended throughout all the northern hemisphere but the evidence of a late transition cooling is still poor for the southern hemisphere here we present a detailed isotopic record analyzed in a new ice core drilled at dome b in east antarctica that fully demonstrates the existence of an antarctic cold reversal acr these results suggest that the two step shape of the last deglaciation has a worldwide character but they also point to noticeable interhemispheric differences thus the coldest part of the acr which shows a temperature drop about three times weaker than that recorded during the yd in greenland may have preceded the yd antarctica did not experienced abrupt changes and the two warming periods started there before they started in greenland the links between southern and northern hemisphere climates throughout this period are discussed in the light of additional information derived from the antarctic dust record

phase relationships between millennial scale events 64 000 24 000 years ago a core recovered on the iberian margin off southern portugal can be correlated with greenland ice cores using oxygen isotope variability in planktonic foraminifera which closely matches the ice core records of temperature over greenland our age model identifies the base of every interstadial between 64 000 and 24 000 years ago and uses the greenland ice core project grip timescale the oxygen isotope signal in benthic foraminifera on this grip based timescale is quite different from the planktonic record and resembles the temperature record over antarctica when this is synchronized with greenland using the record of methane in the atmospheric air in the polar ice cores we interpret the benthic record as indicating significant fluctuations in ice volume during millennial events and we suggest that antarctic temperature changed as a function of ice volume

seasonal patterns of alkenone production in the subtropical oligotrophic north pacific 1 seasonal alkenone concentrations production rates and unsaturation patterns u37k were measured at station aloha in the oligotrophic subtropical north pacific highest alkenone concentration and production rates were found in winter and fall or just below summer the surface mixed layer lowest alkenone concentration and production rates were found within the deep chlorophyll maximum layer dcml in the dcml which occurs at 80 120 m throughout the year u37k temperatures overestimated water temperatures by 2 4 c this result probably reflected the effect of light limitation on the physiology of alkenone producing algae at the depth of maximum alkenone production u37k temperatures underestimated water temperature by 2 4 c in summer and fall but overestimated in situ temperatures by 1 2 c in winter the underestimate of measured water temperature in summer and fall most likely reflected a physiological response to limited nutrient availability the u37k temperature overestimate in winter was best explained by a change in the ecology of alkenone producing algae

taphonomy of jack s birthday site a diverse dinosaur bonebed from the upper cretaceous two medicine formation of montana jack s birthday site is a diverse vertebrate assemblage from the upper two medicine formation of western montana age is roughly 74 ma the site covers roughly 3000 m2 and excavations over 140 m2 a large bone sample 1600 skeletal elements allowed statistical evaluation of the preservational and compositional variation within the site evidence including sedimentary facies plant and invertebrate fossils and bone orientation and condition indicates jack s birthday site represents part of a small shallow floodplain lake lithologies and fossil preservation vary from northwest to southeast over a distance of 50 m this variation represents a transition from lake through shoreline to marginal shoreline floodplain environments containing ten dinosaur taxa and a variety of non dinosaurs jack s birthday site provides one of the best single faunal samples of the region the vertebrate assemblage includes two taphonomic fractions the first consisting of attritional predominantly isolated and allochthonous elements represents a time averaged assemblage the other consists of associated parautochthonous remains restricted to a single horizon taxa represented by associated remains include three iguanodontoids hypacrosaurus prosaurolophus and gryposaurus and the theropod troodon associated individuals of these taxa have non random distributions within the site fisher s exact test p 0 01 and observed taxonomic clustering may reflect group behavior and or event mortality the four or more troodon represent the first described multi individual troodontid occurrence the diversity and spatial complexity of the parautochthonous fraction of the birthday site assemblage is difficult to explain discussion of possible event mortality mechanisms focuses on three drought botulism and cyanobacterial toxicosis these share an ability to act over an ecologically significant period of time affect a variety of species and concentrate mortality along water sources aspects that may have been important in generating the birthday site assemblage evidence at the site favors drought or perhaps a drought botulism hypothesis however taxonomic clusters could represent completely separate events with a variety of causes

physiological impacts on alkenone paleothermometry we conducted isothermal 15 c batch culture experiments with the coccolithophorid emiliania huxleyi strain nepcc 55a to evaluate the extent to which nutrient and light stress contribute to variability in the alkenone unsaturation index u37k alkenone content and composition were constant throughout exponential growth in both experiments when nutrients nitrate and orthophosphate were replete stationary phase nutrient starved cells continued to produce alkenones amassing concentrations alk 3 times higher than those dividing exponentially 1 5 2 pg cell 1 and the u37k of excess alkenone dropped by 0 11 units in contrast 5 days of continuous darkness resulted in a 75 decrease in cellular alk and a significant u37k increase 0 11 units given an established 0 034 unit c response for exponentially growing cells of this strain the observed range of u37k variability at 15 c corresponds to an uncertainty of 3 2 c in predicted growth temperature this level of variability matches that of the global u37k annual mean sea surface temperature calibration for surface marine sediments begging the question what is the physiological condition of alkenone producing cells exported to marine sediments comparison of our laboratory results for a strain of e huxleyi isolated from the subarctic pacific ocean with depth profiles for alkenones in surface waters from two contrasting sites in the northeast pacific ocean suggests that the answer to this question depends on the ocean regime considered a possibility with significant bearing on how stratigraphic u37k records in marine sediments are to be interpreted paleoceanographically

marine transgressions and the evolution of cretaceous dinosaurs fluctuations transgressions and regressions of intercon tinental sea ways during the mesozoic era affected the habitat area of coastal plains by alternately restricting the space during transgressive phases and expanding the space during regressive phases in western north america a coastal plain stretched along the eastern front of the young rocky mountains during most of the late cretaceous here we report results of a six year field study of the sediments and dinosaur remains from this coastal plain in montana that provide evidence that anagenesis characterized dinosaur evolution at this time and that the evolutionary pulse coincided with a marine transgression

multiple jets of the antarctic circumpolar current south of australia abstract maps of the gradient of sea surface height ssh and sea surface temperature sst reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments the braided and patchy nature of the gradient fields seems at odds with the traditional view derived from hydrographic sections that the acc is made up of three continuous circumpolar fronts by applying a nonlinear fitting procedure to 638 weekly maps of ssh gradient ssh it is shown that the distribution of maxima in ssh i e fronts is strongly peaked at particular values of absolute ssh i e streamlines the association between the jets and particular streamlines persists despite strong topographic and eddy mean flow interactions which cause the jets to merge diverge and fluctuate in intensity along their path the ssh values corresponding to each frontal branch are nearly constant over the sector of the southern ocean between 100 e and 180 the front positions inferred from ssh agree closely with

dinosaur biostratigraphy of the edmonton group upper cretaceous alberta canada evidence for climate influence a high resolution biostratigraphic analysis of 287 dinosaurian macrofossils and 138 bonebeds in the edmonton group upper cretaceous of southern alberta provides evidence for at least three dinosa

an integrated method for resolving the seismic complex near surface problem we describe an integrated method for solving the complex near surface problem in land seismic imaging this solution is based on an imaging approach and is obtained without deriving a complex near surface velocity model we start by obtaining from the data the kinematics of the one way focusing operators i e time reversed green s functions that describe propagation between the acquisition surface and a chosen datum reflector using the common focus point technology the conventional statics solutions obtained from prior information about the near surface are integrated in the initial estimates of the focusing operators the focusing operators are updated iteratively until the imaging principle of equal traveltime is fulfilled for each subsurface gridpoint of the datum reflector therefore the seismic data is left intact without any application of time shifts which makes this method an uncommitted statics solution the focusing operators can be used directly for wave equation redatuming to the respective reflector or for prestack imaging if determined for multiple reflecting boundaries the underlying velocity model is determined by tomographic inversion of the focusing operators while also integrating any hard prior information e g well information this velocity model can be used to perform prestack depth imaging or to calculate the depth of the new datum level we demonstrate this approach on 2d seismic data acquired in saudi arabia in an area characterized by rugged topography and complex near surface geology

alkenone sea surface temperature in the southern ocean for the last two deglaciations a piston core taken from the tasman plateau in the southern ocean has been studied for organic compounds to reconstruct the late pleistocene marine environments here we report paleo sea surface temperature sst for the last two deglaciations using the unsaturation degree of alkenones u k 37 preserved in the marine sediments the u k 37 record indicates that the sst was at least 4 c lower than the present sst at the last glacial maximum lgm and the amplitude of paleo sst is at most 5 2 c from the penultimate glacial mis 6 to the last interglacial warm period the eemian our results also demonstrate that the eemian warm period in the southern ocean lasted only 3 000 years followed by a sharp cooling at around 120 kyr bp the sharp cooling in the southern ocean seemed to occur a few millennia 2 3 kyrs before the beginning of continental ice sheet growth

faunal and alkenone reconstructions of subtropical north atlantic surface hydrography and paleotemperature over the last 28 kyr two techniques for estimating past variations in sea surface temperature sst have been used to investigate climatic change in biogeochemical oceanic flux study bofs core 31k 19 n 20 w from the eastern subtropical atlantic high resolution sst records for the last 28 kyr have been produced using planktonic foraminiferal assemblages based on the imbrie kipp transfer function technique and the uk 37 index derived from abundances of c37 alkenones biosynthesized by prymnesiophyte algae modern observations suggest that these indices reflect particular hydrographic conditions in the upper ocean the uk 37 index corresponds to the temperature at the time of maximum coccolith productivity typically late spring early summer in the study area today whereas the faunal transfer function is calibrated for seasonal maximum and minimum temperatures in general the faunal and biomarker paleotemperature records display comparable sst variations during the last glacial and deglacial but although the overall trends are similar differences exist in the magnitude and timing of these temperature changes most notably the faunal twarm and uk 37 sst estimates diverge by 3 c between 8 ka and 6 ka and this offset persists through the late holocene this difference cannot be adequately explained by uncertainties associated with either the calibration data sets or fluctuating preservation levels we therefore propose that the deviation in sst estimates is linked to a switch in the seasonal timing of maximum coccolith production from the summer in the glacial ocean to the late spring early summer in the modern ocean our results suggest that a dual approach to sst estimation based on faunal and biomarker proxies can provide a valuable means of evaluating mixed layer and productivity changes associated with the movement of oceanographic frontal zones during the late quaternary

glacial interglacial sea surface temperature changes across the subtropical front east of new zealand based on alkenone unsaturation ratios and foraminiferal assemblages 0 are compared to those derived from foraminiferal assemblages using the modern analog technique in two of these cores reconstructions of sst in core tops and holocene sediments agree well with modern average summer temperatures of 18 c in subtropical waters and 14 c in subpolar waters with a 4 5 c gradient across the front down core u37 k 0 sst estimates indicate that the regional summer sst was 4 5 c cooler during the last glaciation with an sst of 10 c in subpolar waters and an sst of 14 c in subtropical waters temperature reconstructions from foraminiferal assemblages agree with those derived from alkenones for the holocene in subtropical waters reconstructions also agree with a glacial cooling of 4 to 14 c in contrast reconstructions for subantarctic pre holocene waters indicate a cooling of 8 c with glacial age warm season water temperatures of 6 c thus the alkenones suggest the glacial temperature gradient across the front was the same or reduced slightly to 3 5 4 c whereas foraminiferal reconstructions suggest it doubled to 8 c our results support previous work indicating that the stf remained fixed over the chatham rise during the last glacial maximum however the differing results from the two techniques require additional explanation a change in euphotic zone temperature profiles seasonality of growth or preferred growth depth must have affected the temperatures recorded by these biologically based proxies regardless of the specific reason a differential response to the environmental changes between the two climate regimes by the organisms on which the estimates are based suggests increased upwelling associated with increased winds and or a shallowing of the thermocline associated with increased stratification of the surface layer in the last glaciation index terms 4267 oceanography general paleoceanography 4850 oceanography biological and chemical organic marine chemistry 1050 geochemistry marine geochemistry 4835 4850 1055 geochemistry organic geochemistry keywords paleoceanography sea surface temperature alkenones southern ocean last glacial maximum

contrasting multiproxy reconstructions of surface ocean hydrography in the agulhas corridor and implications for the agulhas leakage during the last 345 000 years planktonic 18o and mg ca derived sea surface temperature sst records from the agulhas corridor off south africa display a progressive increase of sst during glacial periods of the last three climatic cycles the sst increases of up to 4 c coincide with increased abundance of subtropical planktonic foraminiferal marker species which indicates a progressive warming due to an increased influence of subtropical waters at the core sites mg ca derived sst maximizes during glacial maxima and glacial terminations to values about 2 5 c above full interglacial sst the paired planktonic 18o and mg ca derived sst records yield glacial seawater 18o anomalies of up to 0 8 indicating measurably higher surface salinities during these periods the sst pattern along our record is markedly different from a u37k derived sst record at a nearby core location in the agulhas corridor that displays sst maxima only during glacial terminations possible explanations are lateral alkenone advection by the vigorous regional ocean currents or the development of sst contrasts during glacials in association with seasonal changes of agulhas water transports and lateral shifts of the agulhas retroflection the different sst reconstructions derived from u37k and mg ca pose a significant challenge to the interpretation of the proxy records and demonstrate that the reconstruction of the agulhas current and interocean salt leakage is not as straightforward as previously suggested

stationary mesoscale jet like features in the ocean 1 xbt and float data of the world ocean database 2005 are used to validate new stationary jet like features striations recently found in the high resolution mean dynamic ocean topography mdot two study areas were selected in the eastern parts of the north and south pacific subtropical gyres free of any strong currents appropriate horizontal high pass filtering applied to the ensemble mean temperature at 100 m depth revealed the striation signal coherent with mdot the features are also distinct in the data of depth of 12 c isotherm lying close to the thermocline the striations are oriented nearly zonally and coherent vertically at least through 700 m depth their wavelength is approximately 400 km and the azimuth of wavevector is 13 9 in the northern southern domains correspondence between the striations in observations and ofes ogcm for the earth simulator model as well as the nature of the striations are discussed

estimation and application of near surface full waveform redatuming operators abstract land seismic data quality can be severely affected by near surface anomalies the imprint of a complex near surface can be removed by redatuming the data to a level below the surface from where the subsurface structures are assumed to be relatively smooth however to derive a velocity depth model that explains the propagation effects of the near surface is a non trivial task therefore an alternative approach has been proposed where the redatuming operators are obtained in a data driven manner from the reflection event related to the datum in the current implementation the estimation of these redatuming operators is done in terms of traveltimes only based on a high frequency approximation the accompanying amplitudes are usually derived from a local homogeneous medium which is obviously a simplification of reality such parametrization has produced encouraging results in the past but cannot completely remove the near surface complexities leaving artefacts in the redatumed results in this paper we propose a method that estimates the redatuming operators directly from the data i e without using a velocity model in a full waveform manner such that detailed amplitude and phase variations are included the method directly outputs the inverse propagation operators that are needed for true amplitude redatuming based on 2d synthetic data it is demonstrated that the resulting redatuming quality is improved and artefacts are reduced

the control of the southern hemisphere westerlies on the position of the subtropical front in recent years the latitudinal position of the subtropical front stf has emerged as a key parameter in the global climate a poleward positioned front is thought to allow a greater salt flux from the indian to the atlantic ocean and so drive a stronger atlantic meridional overturning circulation here the common view that the stf aligns with the zero wind stress curl wsc is challenged based on the stf climatologies of orsi et al 1995 belkin and gordon 1996 graham and de boer 2013 and on satellite scatterometry winds we find that the zero wsc contour lies on average approximate to 10 degrees approximate to 8 degrees and approximate to 5 degrees poleward of the front for the three climatologies respectively the circulation in the region between the subtropical gyres and the zero wsc contour is not forced by the wsc but rather by the strong bottom pressure torque that is a result of the interaction of the antarctic circumpolar current with the ocean floor topography the actual control of the position of the stf is crucially dependent on whether the front is regarded as simply a surface water mass boundary or a dynamical front for the agulhas leakage problem the southern boundary of the so called super gyre may be the most relevant property but this cannot easily be identified in observations

quantitative interpretation of fossil pollen spectra dissimilarity coefficients and the method of modern analogs abstract dissimilarity coefficients measure the difference between multivariate samples and provide a quantitative aid to the identification of modern analogs for fossil pollen samples how eight coefficients responded to differences among modern pollen samples from eastern north america was tested these coefficients represent three different classes 1 unweighted coefficients that are most strongly influenced by large valued pollen types 2 equal weight coefficients that weight all pollen types equally but can be too sensitive to variations among rare types and 3 signal0to noise coefficients that are intermediate in their weighting of pollen types the studies with modern pollen allowed definition of critical values for each coefficient which when not exceeded indicate that two pollen samples originate from the same vegetation region dissimilarity coefficients were used to compare modern and fossil pollen samples and modern samples so similar to fossil samples were found that most of three late quaternary pollen diagrams could be reconstructed by substituting modern samples for fossil samples when the coefficients indicated that the fossil spectra had no modern analogs then the reconstructed diagrams did not match all aspects of the originals no modern analogs existed for samples from before 9300 yr b p at kirchner marsh minnesota and from before 11 000 yr b p at wintergreen lake michigan but modern analogs existed for almost all holocene samples from these two sites and brandreth bog new york

variability of surface ocean radiocarbon and stable isotopes in the southwestern pacific we present high precision radiocarbon 14c results and stable isotope 18o and 13c records for a coral from heron island 23 s 152 e and new stable isotope 18o and 13c records for annual coral bands from abraham reef 22 s 153 e in the southern great barrier reef studied earlier druffel and griffin 1993 these tracers provide unique information on the regional water mass history and together these data allow us to constrain the variability of circulation in the upper pacific over the past four centuries first we observe decreases in 18o of coral from abraham reef and heron island indicating an increase in sea surface temperature and or a decrease in surface salinity since 1850 second the small suess effect value 14c decrease from 1880 to 1955 due mostly to fossil fuel co2 observed previously at abraham reef druffel and griffin 1993 is confirmed in the measurements reported here from the heron island coral this value is low compared to those observed in other areas of the ocean druffel 1997 druffel and linick 1978 nozaki et al 1978 between 1880 and 1955 third we report alterations in the correlation between el nino events and the occurrence of low 14c which is indicative of long term change s in circulation in the sw pacific the 14c shifts reported here are not large but even small temporal changes in prebomb 14c suggest that important changes in the large scale state of the ocean have occurred such as a temporal change in circulation

the dynamical subtropical front 1 the southern ocean subtropical front stf is thought to play a key role in the global climate system theory suggests that the latitude of the stf regulates the volume of saline agulhas leakage into the atlantic ocean from the indian here we use satellite sea surface temperature sst and sea surface height ssh data to study the physical characteristics of the stf water mass boundary we find that the strong currents in this region do not align with the surface water mass boundary therefore we provide a new climatology for these currents which we define as the dynamical stf dstf the dstf is the eastward extension of the western boundary current in each basin and is characterized by strong sst and ssh gradients and no seasonal cycle at the center of each basin it merges with the sub antarctic front on the eastern side of basins the stf surface water mass boundary coincides with a separate region of multiple sst fronts we call this the subtropical frontal zone stfz the fronts in the stfz have a large seasonal cycle and no ssh signature despite lying close to the same water mass boundary the dstf and stfz are completely unrelated we therefore suggest the term stf only be used when referring to the surface water mass boundary when studying the strong currents on the western side of basins the term dstf is more relevant and similarly the term stfz better describes the region of enhanced sst gradients towards the east

response of surface water masses and circulation to late quaternary climate change east of new zealand a series of cores from east of new zealand have been examined to determine the paleoceanographic history of the late quaternary in the sw pacific using planktonic foraminiferal data distinct shifts of species can be seen between glacial and interglacial times especially south of chatham rise east of south island foraminiferal fragmentation ratios and benthic planktonic foraminiferal ratios both show increased dissolution during glacials especially isotope stage 2 to the south of chatham rise the present day subtropical convergence appears to be tied to the chatham rise at 44 s but during glacial times this rise separated cold water to the south from much warmer water to the north with an associated strong thermal gradient across the rise we estimate that this gradient could have presented as much as an 8 c temperature change across 4 of latitude during the maximum of the last ice age there is only weak evidence of the younger dryas cool event but there is a clear climatic optimum between 8 and 6 4 ka with temperatures 1 2 c higher than the present day the marine changes compare well with vegetational changes on both south and north island

terrestrial and marine records of the last glaciation from western tasmania do they agree abstract no neoglacial or late glacial readvances of ice are known from tasmania the main phase of glaciation occurred after 25 ka bp and attained a maximum slightly before 19 ka bp most ice had decayed by 14 ka bp but some may have survived at high altitude to 10 ka bp an early phase of ice advance prior to 47 ka bp is identified in the upper king valley pollen records of vegetation history show that herbaceous and alpine subalpine shrub vegetation communities were widespread in the lowlands during the late glacial stage and indicate a cold climate the middle last glacial stage vegetation was comprised mainly of subalpine shrub and woodland vegetation that suggests cool moist interstadial climatic conditions a marine pollen record from core so36 7sl suggests herbaceous and scrub vegetation development during isotope stage 4 preceded by wet forest at the end of stage 5

the thermohaline modes of the global ocean abstractthe first 2000 m of the global thermohaline structure of the ocean are statistically decomposed into vertical thermohaline modes using a multivariate functional principal component analysi

observational evidence for a southern hemisphere oceanic supergyre 1 a high resolution hydrographic atlas resolves the narrow boundary flow of the western pacific gyre and its pathway around tasmania southern australia and into the indian ocean basin this confirms recent model descriptions of a southern hemisphere supergyre a nested system of subtropical gyres the observations show that the gyre flow is squeezed into a narrow band between tasmania and the antarctic circumpolar current the residue of east australian current transport turns westward around tasmania and leaks into the indian ocean while there is also a limited form of gyre connection between the indian and atlantic systems south of africa with a mean outflow of agulhas current water into the atlantic basin these gyre circulations remain far more discrete the gyre coupling and the east australian current in particular provide the mechanism by which sub antarctic mode water and antarctic intermediate water are distributed between the ocean basins

alkenones and alkenes in surface waters and sediments of the southern ocean implications for paleotemperature estimation in polar regions abstract the concentration of c37 c39 long chain alkenones and alkenes were determined in surface water and surface sediment samples from the subpolar waters of the southern ocean distributions of these compounds were similar in both sample sets indicating little differential degradation between or within compound classes the relative amounts of the tri to tetra unsaturated c37 alkenones increased with increasing temperature for temperatures below 6 c similar to the di and tri unsaturated c37 alkenones the c37 di tri and tetra unsaturated methyl alkenones are used in paleotemperature calculations via the u37k and the u37k ratios in these datasets the relative abundances of the c37 2 and the c37 3 alkenones as a proportion of the total c37 alkenones were opposite and strongly related to temperature the latter with more scatter but the abundance of the c37 4 alkenone showed no relationship with temperature the original definition of u37k includes the abundance of 37 4 in both the numerator and denominator and thus it is perhaps not surprising that there is considerable scatter in the values obtained for u37k at low temperatures of the two we suggest that u37k is the better parameter for use in paleotemperature estimations even in cold locations u37k values in the sediments fall on virtually the same regression line obtained for the water column samples of sikes and volkman 1993 indicating that their calibration is suitable for use in southern ocean sediments the comparison of water column data with sedimentary temperature estimates suggests that the alkenone distributions are dominated by contributions from the summer when the biomass of emiliania huxleyi and presumably flux to the sediment is expected to be high

velocity independent redatuming a new approach to the near surface problem in land seismic data processing it is well known that a complex near surface encountered in areas such as desert mountainous and glacial till environments can significantly distort primary reflections from deeper horizons of interest this has been and remains a major problem in seismic data processing

circumpolar structure and distribution of the antarctic circumpolar current fronts 1 mean circumpolar paths 1 high resolution hydrographic sections and maps of the gradient of sea surface height ssh reveal that the antarctic circumpolar current acc consists of multiple jets or frontal filaments here we use a 15 year time series of ssh observations to determine the circumpolar structure and distribution of the acc fronts the jets are consistently aligned with particular streamlines along the entire circumpolar path confirming and extending the results of an earlier study restricted to the region south of australia the intensity of the fronts as measured by the cross front gradient of ssh varies along the fronts and the individual branches merge and diverge often in response to interactions with bathymetry maps of absolute velocity at 1000 m depth derived from argo trajectories confirm the existence of multiple current cores throughout the southern ocean high resolution hydrographic sections and profiles of temperature and salinity from argo floats are used to show that the front locations derived from fitting ssh contours to maps of ssh gradient are consistent with locations inferred from the traditional criteria based on water mass properties suitably modified to account for multiple frontal branches three regions are examined in detail the crozet plateau the kerguelen plateau and the scotia sea these examples show how recognition of the multiple jets of the acc can help resolve discrepancies between previous studies of acc fronts

the first radiometric ages from the judith river formation upper cretaceous hill county montana a new isotopic age of ca 78 ma was obtained by the conventional k ar method and by laser fusion 40ar 39ar analysis of biotite and sanidine crystals from two bentonites in the judith river formation of kennedy coulee hill county montana the 40ar 39ar analyses yielded weighted mean ages of 78 2 0 2 ma biotite and 78 2 0 2 ma sanidine for sample 84mg8 3 4 and 79 5 0 2 ma biotite and 78 5 0 2 ma sanidine for sample 85mg7 16 1 these are the first isotopic age determinations from the judith river formation the dated bentonites in kennedy coulee bracket two significant judithian age mammal localities ucmp v77083 and v81234 the radioisotopic age of ca 78 ma for the hill county local faunas and correlations of other judithian local faunas with marine units suggest that the duration of the judithian was at least 5 ma judithian local faunas are probably correlative with the late campanian of the western interior similarities in the principal judithian mammalian faunas from alberta monta

lateglacial landscape and vegetation change and the younger dryas climatic oscillation in new zealand abstract lateglacial sequences in new zealand show progressive afforestation and landscape stabilization reflecting a warming climate between 14 500 bp and 11 500 bp afforestation and landscape stability was achieved throughout most of the north island and the northwest sector of the south island in the south island scrub and tree ferns were replacing previous grasslands in the east by 11 000 bp and broadleaved forest was spreading in the west no significant reversals of these trends occurred and afforestation was complete by 9500 bp glaciers of the high central part of the southern alps made a series of advances between 14 000 and 9000 bp most of these advances are poorly dated but two moraines are of younger dryas age glacial advances in the face of the general lateglacial warming trend may have been driven by stronger westerly winds increasing snowfall on high altitude neves and by reduced ablation as a consequence of moist cloudy low insolation summers the cause of the northern hemisphere younger dryas cooling is still uncertain and expected southern hemisphere responses may differ according to the mechanism proposed for the cooling poor chronological resolution and apparent conflict between the various types of evidence for climatic change make detection of an unambiguous younger dryas in new zealand problematical

glacial to interglacial changes in non carbonate and carbonate accumulation in the sw pacific ocean new zealand abstract fluxes of carbonate and non carbonate terrigenous biogenic siliceous sediment back to a maximum of marine isotope stage mis 6 were determined for 54 cores from off eastern new zealand mass accumulation rates mars were derived using dry bulk densities measured directly from fresh cores or in the case of dry archived samples on estimates from a density carbonate relationship mars exhibit wide spatial and temporal variability in response to i the location of cores relative to the terrigenous source of new zealand current pathways and local oceanographic features and ii palaeoclimatic change for mis 1 2 non carbonate accumulated at a high rate between 27 and 18 ka calendar years due to an influx of waterborne and aeolian terrigenous detritus together with localised production of biogenic silica under a northward intrusion of subantarctic waters and an increase in wind induced upwelling by 18 12 ka non carbonate mars reduced as winds ameliorated and sea level rose to confine some of the terrigenous load to the continental shelf the holocene transgression was accompanied by warmer sea surface temperatures the formation of coastal and lacustrine sediment traps and more widespread terrestrial vegetation these conditions further reduced the deep oceanic non carbonate flux to levels about half those of glacial periods in contrast carbonate mars were lower in cold periods reflecting lower productivity increased dissolution and in the case of the generally productive waters of chatham rise to redistribution by bottom currents however off central new zealand carbonate production was higher on the continental margin possibly because of enhanced upwelling under the strong wind regime of mis 2 such localised effects produced glacial carbonate mars higher than interglacial mis 1 values for the rest of the region carbonate fluxes increased to an early to middle mis 1 maximum before generally declining in recent times

spatial and temporal offsets between proxy records in a sediment drift chronologies for late quaternary marine sediment records are usually based on radiocarbon ages of planktonic foraminifera signals carried by other sedimentary components measured in parallel can provide complementary paleoclimate information a key premise is that microfossils and other indicators within a given sediment horizon are of equal age we show here that haptophyte derived alkenones isolated from bermuda rise drift sediments are up to 7000 years older than coexisting planktonic foraminifera this temporal offset which is apparently due to lateral transport of alkenones on fine grained particles from the nova scotian margin markedly influences molecular estimates of sea surface temperatures more broadly the observation raises questions about both the temporal and the geographic fidelity of paleoenvironmental records encoded by readily transported components of sediments

late quaternary caco3 production and preservation in the southern ocean implications for oceanic and atmospheric carbon cycling recent geochemical models invoke ocean alkalinity changes particularly in the surface southern ocean to explain glacial age pco2 reduction in such models alkalinity increases in glacial periods are driven by reductions in north atlantic deep water nadw supply which lead to increases in deep water nutrients and dissolution of carbonate sediments and to increased alkalinity of circumpolar deep water upwelling in the surface southern ocean we use cores from the southeast indian ridge and from the deep cape basin in the south atlantic to show that carbonate dissolution was enhanced during glacial stages in areas now bathed by circumpolar deep water this suggests that deep southern ocean carbonate ion concentrations were lower in glacial stages than in interglacials rather than higher as suggested by the polar alkalinity model broecker and peng 1989 our observations show that changes in southern ocean caco3 preservation are coherent with changes in the relative flux of nadw suggesting that southern ocean carbonate chemistry is closely linked to changes in deepwater circulation the pattern of enhanced dissolution in glacials is consistent with a reduction in the supply of nutrient depleted water nadw to the southern ocean and with an increase of nutrients in deep water masses carbonate mass accumulation rates on the southeast indian ridge 3200 3800 m and in relatively shallow cores 3000 m from the kerguelen plateau and the south pacific were significantly reduced during glacial stages by about 50 the reduced carbonate mass accumulation rates and enhanced dissolution during glacials may be partly due to decreases in caco3 corg flux ratios acting as another mechanism which would raise the alkalinity of southern ocean surface waters the polar alkalinity model assumes that the ratio of organic carbon to carbonate production on surface alkalinity is constant even if overall productivity in the southern ocean were held constant a decrease in the caco3 corg ratio would result in increased alkalinity and reduced pco2 in southern ocean surface waters during glacials this ecologically driven surface alkalinity change may enhance deepwater mediated changes in alkalinity and amplify rapid changes in pco2

southern hemisphere westerly wind changes during the last glacial maximum paleo data synthesis changes in the strength and position of southern hemisphere westerly winds during the last glacial cycle have been invoked to explain both millennial and glacial interglacial climate fluctuations however neither paleo models nor paleodata agree on the magnitude or even the sign of the change in wind strength and latitude during the most studied glacial period the last glacial maximum lgm compared to the recent past this paper synthesizes paleo environmental data that have been used to infer changes in lgm winds data compilations are provided for changes in terrestrial moisture dust deposition sea surface temperatures and ocean fronts and ocean productivity and existing data on southern hemisphere ocean circulation changes during the lgm are summarized we find that any hypothesis of lgm wind and climate change needs to provide a plausible explanation for increased moisture on the west coast of continents cooler temperatures and higher productivity in the subantarctic zone and reductions in agulhas leakage around southern africa our comparison suggests that an overall strengthening an equatorward displacement or no change at all in winds could all be interpreted as consistent with observations if a single cause related to the southern westerlies is sought for all the evidence presented then an equatorward displacement or strengthening of the winds would be consistent with the largest proportion of the observations however other processes such as weakening or poleward shifts in winds a weakened hydrological cycle extended sea ice cover and changed buoyancy fluxes cannot be ruled out as potential explanations of observed changes in moisture surface temperature and productivity we contend that resolving the position and strength of westerly winds during the lgm remains elusive based on data reconstructions alone however we believe that these data reconstructions of environmental conditions can be used in conjunction with model simulations to identify which processes best represent westerly wind conditions during the lgm

rapid southern ocean front transitions in an eddy resolving ocean gcm the formation of persistent multiple fronts is an established feature of the antarctic circumpolar current acc front strength and location are closely linked to eddy properties and therefore have important implications for the eddy driven closure of the southern ocean meridional overturning circulation acc front structure is analyzed here by calculating regional probability density functions pdfs of potential vorticity diagnosed in an eddy resolving ocean general circulation model rapid spatial transitions in the number of fronts and in the density classes over which they occur are found front transitions are associated with the major topographic obstacles kerguelen island campbell plateau and drake passage multiple fronts are preferentially found downstream of these features these findings highlight the significant departure from zonal symmetry of the acc front structure and emphasize the importance of local dynamics on large scale southern ocean properties

planktonic foraminiferal flux seasonality in subantarctic sediment traps a test for paleoclimate reconstructions sediment trap moorings deployed during 1997 and 1998 in the subantarctic to polar frontal regions of the southern ocean reveal distinct seasonality in foraminiferal flux foraminiferal assemblages vary between each site yet major species exhibit very similar patterns of seasonal succession which can be associated with changes in mixed layer depth enhanced foraminiferal productivity is also associated with periods of high biogenic silica and particulate organic carbon flux on a broader scale foraminiferal assemblages are strongly delineated by temperature temperature estimates derived from the assemblages using the modern analog technique mat are mostly within 2 5 c of the satellite advanced very high resolution radiometer temperatures observed during the deployment period this indicates that core top sediments included in the mat database do reflect modern observed conditions at the sea surface providing a robust technique for estimating past temperature change from foraminiferal assemblages in southern ocean environments

glacial interglacial changes in the east australian current the east australian current eac is the western boundary current of the south pacific gyre transporting warm tropical waters to higher southern latitudes recent modelling shows that the partial separation of the eac 32 s and the coupled formation of the tasman front 34 s are caused by a steep gradient in the zonally integrated wind stress curl analysis of oxygen isotope ratios 18o in the planktonic foraminifer globigerinoides ruber from sediment cores from the coral sea and tasman sea indicates that the eac separation shifted northward to between 23 and 26 s during the last glacial we suggest these results indicate a significant change in the pacific wind stress curl during the glacial given recent evidence for el nino like conditions in the pacific during the last glacial with a reduction in the east west sea surface temperature sst gradient we suggest that weaker trade winds combined with more northerly stronger westerlies were associated with a change to the wind stress curl which repositioned the eac separation and tasman front in contrast by 11 ka bp the eac separation was forced south of 26 s this southward shift was synchronous with a rapid warming of tropical ssts and the onset of a la nina like sst configuration across the tropical pacific it appears that the south pacific trade winds strengthened accordingly causing the eac to readjust its flow this readjustment of the eac marks the onset of modern surface ocean circulation in the southwest pacific but the present eac transport was only achieved in the late holocene after 5 ka bp

planktic foraminiferal and sea surface temperature record during the last 1 myr across the subtropical front southwest pacific planktic foraminiferal faunas and modern analogue technique estimates of sea surface temperature sst for the last 1 million years myr are compared between core sites to the north odp 1125 178 faunas and south dsdp 594 374 faunas of the present location of the subtropical front stf east of new zealand faunas beneath cool subtropical water stw north of the stf are dominated by dextral neogloboquadrina pachyderma globorotalia inflata and globigerina bulloides whereas faunas to the south are strongly dominated by sinistral n pachyderma 80 95 in glacials with increased g bulloides 20 50 and dextral n pachyderma 15 50 in interglacials beneath subantarctic water or saw canonical correspondence analysis indicates that at both sites sst and related factors were the most important environmental influences on faunal composition greater climate related faunal fluctuations occur in the south significant faunal changes occur through time at both sites particularly towards the end of the mid pleistocene climate transition mis18 15 e g decline of globorotalia crassula in stw disappearance of globorotalia puncticulata in saw and during mis8 5 interglacial sst estimates in the north are similar to the present day throughout the last 1 myr to the south interglacial ssts are more variable with peaks 4 7 c cooler than present through much of the early and middle pleistocene but in mis11 mis5 5 and early mis1 peaks are estimated to have been 2 4 c warmer than present these high temperatures are attributed to southward spread of the stf across the submarine chatham rise along which the stf appears to have been dynamically positioned throughout most of the last 1 myr for much of the last 1 myr glacial sst estimates in the north were only 1 2 c cooler than the present interglacial except in mis16 mis8 mis6 and mis4 2 when estimates are 4 7 c cooler these cooler temperatures are attributed to jetting of saw through the mernoo saddle across the chatham rise and or waning of the stw current to the south glacial sst estimates were consistently 10 11 c cooler than present similar to temperatures and faunas currently found in the vicinity of the polar front one interpretation is that these cold temperatures reflect thermocline changes and increased circumpolar surface water spinning off the subantarctic front as an enhanced bounty gyre along the south side of the chatham rise for most of the last 1 myr the temperature gradient across the stf has been considerably greater than the present 4 c during glacial episodes the stf in this region did not migrate northwards but instead there was an intensification of the temperature gradient across it interglacials 4 11 c glacials 8 14 c

the south indian ocean current in this paper the historical hydrographic database for the south indian ocean is used to investigate i the hydrographic boundary between the subtropical gyre and the antarctic circumpolar current acc the subtropical front stf and especially ii the southern current band of the gyre a current band of increased zonal speeds in the upper 1000 m is found just north of the stf in the west near south africa and at the surface stf in the open indian ocean until the waters off the coast of australia are reached as neither any other investigation of this current nor a name for it are known the flow has been called the south indian ocean current sioc this name is anologous to the same current band in the south atlantic ocean the south atlantic current the stf is located in the entire south indian ocean near 40 degrees s the associated current band of increased zonal speeds is the sioc which is found at or north of the stf east of 100 degrees e the sioc separates from the stf and continues to the northeast the zonal flow south of the stf is normally weak and serves to separate the south indian ocean and circumpolar currents near africa the sioc has a typical volume transport of 60 sv 1 sv 10 6 m3 s 1 in the upper 1000 m relative to deep potential density surfaces of sigma 4 45 87 kg m 3 2800 3500 m or sigma 2 36 94 kg m 3 1500 2500 m near western australia the sioc is reduced to about 10 sv as it turns to the northeast