last abundant appearance datum of hemidiscus karstenii driven by climate change abstract the last abundant appearance datum of the endemic southern ocean diatom hemisdiscus karstenii jouse is dated at around 190 000 years before present which provides a robust and convenient biostratigraphic marker to late pleistocene paleoceanographic studies however no prior studies have sought to understand what processes may have driven h karstenii to extinction we here present the first morphometric investigation of h karstenii over marine isotope stage mis 10 to 6 355 000 years to 150 000 years the combination of these data to records of h karstenii absolute abundances fragilariopsis kerguelensis biometry and absolute abundances and southern high latitude air and ocean temperatures over the past 355 000 years suggests that h karstenii populations reduced their mean size and productivity in response to the rapid drop in temperatures across the mis 7 to mis 6 glacial inception this prolonged cooling event may have pushed h karstenii to its adaptive limit until it could not sustain physiological viability the repetitive occurrence of very cold events during the early mis 6 may have additionally prevented surviving populations of h karstenii from re establishing abundant communities leading to extinction late in mis 6

silicic acid dynamics in the glacial sub antarctic implications for the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh purports that changes in silicon and nitrogen depletion ratios in the glacial antarctic created a large pool of unused silicic acid that was transported to lower latitudes in subantarctic mode water samw where it enhanced diatom productivity lowering atmospheric pco2 however increased opal accumulation beneath the sub antarctic during glacial times implies significant consumption of silicic acid in subantarctic surface waters that may have significantly diminished or eliminated si leakage to test how nutrient dynamics in the sub antarctic affected the si oh 4 content of samw during the last glacial period we produced 30si opal records for cores from the subantarctic and subtropical zones of the indian ocean spanning the last 50 000 years comparison with diatom bound 15n records shows that subantarctic surface waters were enriched in si relative to n during the last glaciation consistent with the salh the record from the subtropics does not show this enrichment in si during the last glacial period suggesting that subantarctic surface waters were mainly incorporated into samw rather than being transported across the subtropical front isotope mass balance calculations were used to test for si leakage from the sub antarctic the results show that silicic acid concentration in samw would more than double during the last glaciation if upwelling and northward ekman drift in the antarctic were similar to the present day circulation calculations that assume increased stratification in the glacial antarctic eliminate si leakage but they do not produce the known increase in opal burial in the glacial sub antarctic reconciling the isotope data and opal burial records with a highly stratified antarctic requires the addition of a large local source of silicic acid in the glacial sub antarctic that is inconsistent with present day circulation and nutrient distributions including such a source in our calculations results in significant opal burial in the sub antarctic but it does not enhance si leakage over that occurring in the holocene resolving past changes in the circulation of the southern ocean is clearly vital to future tests of the salh

glacial valve size variation of the southern ocean diatom fragilariopsis kerguelensis preserved in the benguela upwelling system southeastern atlantic abstract the valve size variations of the southern ocean so diatom fragilariopsis kerguelensis from the sediments of antarctic polar front and subantarctic front were shown to be strongly correlated with iron availability at the glacial interglacial timescale however recent evidence from the subtropical region of the so has suggested sea surface temperature to be a key controlling factor by mediating silica uptake other than the iron availability we present here the first record of f kerguelensis size variation in core geob3606 1 collected in the benguela upwelling system bus se atlantic 25 28 s 13 05 e where f kerguelensis valves were preserved during the glacial period 68 30 ka as a consequence of silicic acid leakage from polar to mid latitudes our study presents the first record of diatom morphology variations of f kerguelensis from a mid latitude core location to test the previous hypotheses proposed for so our results demonstrate that f kerguelensis valves at geob3606 1 were almost half of the mean size of specimens compared to the so downcore records further f kerguelensis valves were smaller and more abundant during early marine isotope stage mis 3 and conversely larger and less abundant during mis4 and late mis3 however such patterns are not supported by the linear regression analyses suggesting that iron availability could have mediated the size changes of f kerguelensis rather than the species productivity during 68 30 ka these findings agree with the recently gained knowledge on the life cycle patterns of f kerguelensis related to reproduction strategies cell size range and formation of initial cells

eocene stratigraphy of southeastern tierra del fuego island argentina recognizing folded and thrusted eocene foreland strata of the oil producing austral basin provides new insights on the paleogene evolution of tierra del fuego island and the adjacent atlantic shelf field mapping and petrographic and micropaleontologic studies at the punta torcida anticline depict an eocene composite section about 1600 m thick assigned to the la despedida group this group is divided into three formations punta torcida 215 m leticia 520 m and cerro colorado 855 m these formations are subdivided into informal members in the punta torcida formation the lower member is composed of dark gray mudstones with thin sandstone beds the middle member of the punta torcida contains mudstones with small sandstone lenses both the lower and middle members have a high radiolarian content the upper member contains mudstones lithologic succession presence of pyrite and a well preserved benthic assemblage having little diversification suggest a regressive sequence formed in shelf settings with a dysaerobic to anoxic bottom planktonic foraminifera indicate a ypresian age equivalent to upper zone p6 to basal zone p9 tropical planktonic zones in the leticia formation the lower and upper members are glauconite rich highly bioturbated sandstones in the middle member rich in pyrite and carbonized plant material the glauconite is rare or absent large channels filled with cross stratified sandstone lenses and having a general absence of planktonic foraminifera suggest estuarine restricted marine settings planktonic foraminifera indicate a late middle eocene age basal zone p12 to middle of zone p14 indicating a hiatus with the underlying punta torcida formation the cerro colorado formation a coarsening and thickening upward succession of mudstones and sandstones is a major shelfal transgressive regressive sequence punctuated by minor deepening and shallowing its four members record different benthic assemblages that reflect cooling waters the uppermost member bears abundant radiolarians and planktonic foraminifera typical of an oxygen minimum habitat and indicating a late eocene age upper zone p15 to upper zone p16 the microfauna and stratigraphic position of the lower three members are consistent with a latest middle eocene age middle of zone p14 to lower zone p15 in preliminary observations on the outcrop area of late cretaceous paleogene strata between cabo san pablo and bahia thetis two important angular unconformities were recorded one at the contact between the estratos de policarpo and the rio bueno la despedida group and the other at the contact between the la despedida group and the cabo pena rio leona formations

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

glacial interglacial variability in diatom abundance and valve size implications for southern ocean paleoceanography antarctic sea ice extent along with southern ocean biological productivity varied considerably during glacial interglacial periods and both are known to have played a considerable role in regulating atmospheric co2 variations in the past here we present data on diatom absolute abundance valves g of sediment and size over the past 42 ka b p and how they link to glacial interglacial changes in antarctic sea ice extent southern ocean frontal systems and aeolian dust flux our records of sea ice and permanent open ocean zone diatom abundances suggest a shift in the antarctic winter sea ice limit and polar front respectively up to the modern day polar frontal zone during marine isotopic stages mis 2 and late mis 3 in addition to glacial shifts in the polar front diatom assemblages also recorded a plausible northward shifts in polar front during few intervals of mis 1 glacial periods north of the polar front in the indian sector of the southern ocean were characterized by higher total diatom abundance larger fragilariopsis kerguelensis apical length and thalassiosira lentiginosa radius this is probably a consequence of 1 a northward expansion of the opal belt a region characterized by high production and export of biogenic silica 2 an increase in terrigenous input via erosion of crozet islands and 3 the alleviation of iron deficit by high input of fe bearing dust the larger and highly silicified diatoms such as f kerguelensis and t lentiginosa may have mainly contributed in transporting biogenic silica and organic carbon to the seabed for the last 42 ka in the northern polar frontal zone of the indian sector of the southern ocean

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

calcium carbonate as ikaite crystals in antarctic sea ice 1 we report on the discovery of the mineral ikaite caco3 6h2o in sea ice from the southern ocean the precipitation of caco3 during the freezing of seawater has previously been predicted from thermodynamic modelling indirect measurements and has been documented in artificial sea ice during laboratory experiments but has not been reported for natural sea ice it is assumed that caco3 formation in sea ice may be important for a sea ice driven carbon pump in ice covered oceanic waters without direct evidence of caco3 precipitation in sea ice its role in this and other processes has remained speculative the discovery of caco3 6h2o crystals in natural sea ice provides the necessary evidence for the evaluation of previous assumptions and lays the foundation for further studies to help elucidate the role of ikaite in the carbon cycle of the seasonally sea ice covered regions

the southern ocean s biological pump during the last glacial maximum ice core records from antarctica show large 80 ppm and regular climate related changes in atmospheric co2 with minimum values during glacial periods and maximum values during peak interglacials the suggested role of the southern ocean in driving these changes is based on either the potential for increased utilization of surface nutrients or the potential for decreased ventilation of deep waters during glacial times several recent studies have invoked increased stratification of the southern ocean to explain lower glacial atmospheric co2 levels in terms of reduced exchange of co2 between the deep sea and the atmosphere a northward displacement and or substantial weakening of the westerly winds during glacial periods are implicit in the scenarios that invoke enhanced stratification however both circulation models and proxy results argue against a weakening of the westerlies in fact the mean flow of the antarctic circumpolar current and wind driven upwelling during the last glacial maximum lgm are thought to be at least as vigorous as those which exist today given these boundary conditions we offer two competing scenarios for ecosystem structure and export production of the glacial southern ocean the first scenario satisfies all proxy records for nutrient utilization and phytoplankton growth rate and requires increased relative to today nitrate utilization south of the antarctic polar front apf by phytoplankton other than diatoms together with a shift in the zone of maximum diatom growth from south interglacials to north glacials of the apf the second scenario has reduced growth of all phytoplankton species south of the apf during glacials and a shift in the zone of maximum export production to the north of the polar front the principal weakness of the first scenario is that there is little sedimentary evidence to support the increased export of particulate organic carbon required by the inferred increase in nitrate utilization south of the apf the principal weakness of the second scenario is that it requires a change in the isotopic fractionation of nitrogen by phytoplankton growing south of the polar front for reasons presently unknown the southern ocean s biological pump at the lgm has yet to be characterized unequivocally

modelled atmospheric temperatures and global sea levels over the past million years the climate has passed through a series of glacials and interglacials over the past million years but the nature of this cyclicity in terms of temperature ice volume and sea level and the underlying causes are not well known bintanja et al use a new method to deduce a one million year time series of these variables the reconstructed records are much longer than other methods have provided for any of these variables individually the most intense glacial stages were 17 c colder than today and most of the continental ice was present in north america strong cooling in the beginning of glacials was found to precede ice sheet build up these findings may shed light on the causes of ice age cycles marine records of sediment oxygen isotope compositions show that the earth s climate has gone through a succession of glacial and interglacial periods during the past million years but the interpretation of the oxygen isotope records is complicated because both isotope storage in ice sheets and deep water temperature affect the recorded isotopic composition1 2 3 4 5 separating these two effects would require long records of either sea level or deep ocean temperature which are currently not available here we use a coupled model of the northern hemisphere ice sheets6 and ocean temperatures forced to match an oxygen isotope record for the past million years compiled from 57 globally distributed sediment cores to quantify both contributions simultaneously we find that the ice sheet contribution to the variability in oxygen isotope composition varied from ten per cent in the beginning of glacial periods to sixty per cent at glacial maxima suggesting that strong ocean cooling preceded slow ice sheet build up the model yields mutually consistent time series of continental mean surface temperatures between 40 and 80 n ice volume and global sea level we find that during extreme glacial stages air temperatures were 17 1 8 c lower than present with a 120 10 m sea level equivalent of continental ice present

nutrient cycling in the indian sector of the southern ocean over the last 50 000 years most high southern latitude records of carbon and nitrogen isotopic ratios and elemental ratios are from the antarctic and polar front zones thus hindering a comprehensive view of nutrient cycling in the southern ocean we present for the first time two records from the subantarctic zone and the southern subtropical zone of the indian ocean these records provide a latitudinal transect covering the main oceanographic systems of the southern ocean carbon and nitrogen content of the diatom bound organic matter increases during the last glacial in the antarctic and subantarctic zones but does not show a clear climate related signal in the subtropical zone comparison of these records with sea surface temperatures reconstructed at the core locations and record of dust deposition over antarctica suggests that eolian iron input possibly switched diatom physiology toward higher carbon to silica and nitrogen to silica uptake and storage south of the subantarctic front due to the dependency of photosynthesis on iron concentration levels conversely the northernmost core was too remote from any iron source over the last 50 000 years antarctic diatoms therefore have the sole potential to change the nutrient content of the waters escaping from the southern ocean hence providing partial support to the silicic leakage hypothesis as a potential cause of lower glacial atmospheric co 2

variations of the acc cdw during mis3 traced by magnetic grain deposition in midlatitude south indian ocean cores connections with the northern hemisphere and with central antarctica we examine the magnetic mineral deposition in three cores located at midlatitude sites in the south indian ocean in an area where sediment eroded from the kerguelen crozet plateau and transported by the marine currents principally the antarctic circum current accumulates at a high sedimentation rate we focus on marine isotopic stage 3 characterized by large climatic fluctuations at northern latitudes and compare the obtained records to the climatic records at byrd antarctica and summit gisp2 greenland and to the north atlantic deep water variations in the north atlantic magnetic mineral deposition at the studied sites exhibits a profile with maxima at the time of heinrich events h4 and h5 which suggests a strong antarctic circum current when the north atlantic deep water was reduced at northern latitude during these events we show that an interhemispheric seesaw characterized by temporary surface warmings in the southern hemisphere is also marked by a strong antarctic circum current at the time of the northern heinrich events the rapid dansgaard oeschger oscillations evidenced in the northern records after interstadials is12 and is8 are not visible suggesting a limited counterpart of these events in the midlatitude southern indian ocean

an integrated crustal velocity field for the central andes 1 we present an integrated velocity field for the central andes derived from gps observations collected between january 1993 and march 2001 that eliminates the velocity bias between the south america nazca plate project snapp and central andes gps project cap velocity fields published by norabuena et al 1998 and bevis et al 1999 the reference frame is realized by minimizing the motion of eight continuous gps stations and one rover gps station located in the stable core of the south american plate the rms horizontal motion of these stations is just 1 1 mm yr the amplitude of these residual motions is roughly compatible with expected levels of measurement error in our new solution five of the six snapp stations located just outside the orogenic belt are effectively stationary and the velocities for adjacent cap and snapp stations now agree at a level consistent with their formal uncertainties

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

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

southern ocean sea ice and frontal changes during the late quaternary and their linkages to asian summer monsoon abstract the present study documents the interactions between southern hemisphere high latitude antarctica southern ocean southern indian ocean subtropics agulhas leakage and asian summer monsoon the study uses sst and sea ice reconstructions along with diatom absolute abundances and diatom biometry from two sediment cores located at the subantarctic front saf and antarctic polar front apf in the southwest indian sector of the southern ocean sea ice records suggest the presence of the mean winter sea ice limit at around the modern apf location during mis 2 and mis 4 and episodic and unconsolidated winter sea ice far north as 43 s during lgm when the ssts were lowest higher diatom productivity and larger mean sizes of f kerguelensis and t lentiginosa recorded at the northern core site during the glacial stages suggest a northward shift of the apf a decrease in diatom productivity and sizes at the southern core site highlights stratified permanent open ocean zone pooz surface waters in response to longer sea ice presence during the glacial stages the comparative study between the records of southern hemisphere high latitude and asian summer monsoon climate variability revealed that the asian summer monsoon variability could have been more likely forced by low latitude insolation gradient changes and supported by antarctic climate changes via meridional shifts of the fronts and sea ice the past changes in the intensity of asian summer monsoon along with the southern ocean frontal variation might have influenced the southern indian ocean surface circulation by changing the agulhas leakage intensity

iron deficiency limits phytoplankton growth in antarctic waters enrichment experiments were performed in the ross sea to test the hypothesis that iron deficiency is responsible for the phytoplankton s failure to use up the luxuriant major nutrient supplies found in these and all other offshore antarctic ocean waters nitrate uptake rates in the controls without added trace elements ranged from 0 58 to 1 22 mol kg 1 d 1 the addition of 1 to 5 nmol of unchelated fe per liter resulted in rates that were 2 to 10 times higher 2 54 to 6 00 mol no3 kg 1 d 1 rates in bottles with 2 nmol mn added were identical to those in the controls 0 57 to 1 04 mol no3 kg 1 d 1 total decreases in no3 were balanced by increases in particulate organic n these results suggest that fe deficiency is the primary reason that the present day southern ocean biological pump is shut off in contrast iron was 50 times more abundant during the last glacial maximum greater fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric c02 these results also imply that large scale southern ocean fe fertilization is feasible at least in terms of the total amounts of fe required i e 100 000 to 500 000 tons yr 1

appraisal of groundwater resource in holocene soil deposits by resistivity hydrochemical and granulomerial studies in the gulf of mannar coast from southern india this article is aimed to delineate groundwater sources in holocene deposits area in the gulf of mannar coast from southern india for this purpose 2 d electrical resistivity tomography ert hydrochemical and granulomerical studies were carried out and integrated to identify hydrogeological structures and portable groundwater resource in shallow depths which in general appears in the coastal tracts the 2 d ert was used to determine the two dimensional subsurface geological formations by multicore cable with wenner array low resistivity of 1 5 omega m for saline water appeared due to calcite at the depth of about 5 m below the ground level bgl sea water intrusion was observed around the maximum resistivity as 5 omega m at the 8 m depth bgl in the calcite environs but the calcareous sandstone layer shows around 15 64 omega m at the 6 m depth bgl the hydrochemical variation of tds hco3 cl na k ca2 and mg2 concentrations was observed for the saline and sea water intrusion in the groundwater system the granulometic analysis shows that the study area was under the sea between 5400 and 3000 year ago the events of ice melting an unnatural ice stone rain hail among 5000 4000 years ago resulted in the inundation of sea over the area and deposits of late holocene marine transgression formation up to puthukottai quartzite region for a stretch of around 17 km

last glacial sea surface temperatures and sea ice extent in the southern ocean atlantic indian sector a multiproxy approach 1 on the basis of the quantitative study of diatom radiolarian and planktic foraminiferal assemblages we estimated summer sea surface temperature ssst and sea ice extent at 50 sediment core localities in the atlantic and western indian sector of the southern ocean to reconstruct the last glacial environment at the glamap 18 to 15 ka equal to 21 500 to 18 000 calendar cal years bp and epilog 19 5 to 16 0 ka equal to 23 000 to 19 000 cal years bp time slices stratigraphic identification of the time slices was accomplished by a combination of ams 14c measurements benthic isotope and siliceous microfossil abundance records while the ssst estimates reveal greater surface water cooling than reconstructed by climap 1981 reaching a maximum in the area of the present subantarctic zone the sea ice reconstruction indicates that climap overestimated the expansion of the antarctic sea ice field especially for austral summer during winter the sea ice field was expanded by 60 70 compared to the present last glacial summer sea surface isotherms indicate a northward shift of the zonal bands of the antarctic circumpolar current and a relative expansion of the cold water realm south of the subantarctic front by 5 in latitude this coincides with a northward displacement of the zone of enhanced biogenic silica deposition and iceberg occurrence as a result of northward expansion of antarctic cold waters and a relatively small displacement of the subtropical front thermal gradients were steepened during the last glacial in the area of the present subtropical front the northward displacement of antarctic cold waters and the related deflection of southern ocean waters along the eastern boundary of south america may have resulted in a weakened cold water route across the drake passage in contrast the transport of warm and salty surface water from the indian into the atlantic ocean via the warm water route was not blocked allowing continuous but reduced import of heat into the south atlantic

morphometric variability in the diatom fragilariopsis kerguelensis implications for southern ocean paleoceanography abstract diatoms play a central role in the ecosystem of the southern ocean where they represent the main producers and carriers of organic carbon and dissolved silicon towards the deep ocean variability in space and time of the size of the most abundant species fragilariopsis kerguelensis may directly impact the way this ecosystem functions and also affect the nutrient balance of the global ocean as important water masses e g the antarctic intermediate water get their nutrient signature in this area we used a biometric approach and analyzed the size variability of f kerguelensis valves in sixty four surface sediment samples from the southern ocean in sediment trap samples from a mooring site pf3 at the antarctic polar front apf and along a nearby piston core ps1654 2 the average length and valve area of f kerguelensis displayed a distinct increase in the proximity of the apf and lower values to the north and south of it and also changed markedly over seasonal cycles as diatom blooms and nutrient availability waxe and wane the last glacial to interglacial transition also witnesses important changes in the general shape and valve size of f kerguelensis with specimens from glacial intervals being ca 30 larger than their interglacial counterparts 195 versus 150 m 2 valve area a sharp peak in average area and a very specific valve morphology correspond to the first signs of deglaciation and concurring sst sea surface temperature increase and sea ice retreat the latter together with melting icebergs may have contributed dissolved iron to surface waters the highest average sizes during glacial intervals are higher than what found anywhere in the southern ocean today the newly proposed proxy valve area and shape of f kerguelensis may thus prove useful for the reconstruction of the past position and nutrient characteristics of the apf and opal belt a region characterized by high production and export of biogenic silica in a particularly sensitive and dynamic area such as the southern ocean

holocene migration of oceanic front systems over the conrad rise in the indian sector of the southern ocean there has been limited previous research about holocene climate variability in the indian sector of the southern ocean here we examine centennial scale changes in diatom assemblages and stable isotopic ratios since 10 000 cal a bp in a high accumulation rate sediment core from the conrad rise although abundances of dominant diatom taxa fragilariopsis kerguelensis and thalassiothrix antarctica are comparatively constant relative abun dances of secondary taxa fluctuate before c 9900 cal a bp winter sea ice and cold water covered the conrad rise following deglaciation the sea ice retreated from the conrad rise lagging that of the atlantic and eastern indian sectors by about 1500 a the polar front moved southward during the early holocene optimum and north antarctic zone waters covered the conrad rise for about 650 a after 9300 cal a bp solar insolation strongly influenced sea surface temperature and primary productivity in the southern ocean in the high latitude indian sector productivity increased 1500 a after the onset of late holocene neoglaciation periodic d 18 o and cold water diatom taxa spikes at intervals of 200 and 300 500 a respectively occurred after 9300 cal a bp probably associated with solar activity fluctuations in short term sea surface temperature and cold water taxa are synchronous with changes in dd observed in an east antarctic ice core copyright 2011 john wiley sons ltd

late quaternary sea ice history in the indian sector of the southern ocean as recorded by diatom assemblages abstract a modern analog technique mat5201 31 has been applied to fossil diatom assemblages to provide down core estimates of february sea surface temperatures ssts and of sea ice duration over the past 220 000 years at 56 40 s 160 14 e at the core location sea ice progression lagged the sst drop by 1 ka at interglacial glacial transitions and sea ice retreat was almost synchronous to the sst increase at glacial interglacial terminations sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times although ssts were almost constant during glacials this indicates that ssts are the major parameter determining the advance and retreat of sea ice at transitions but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo air temperature and meridional wind stress the strong correlation r 0 75 between sea ice duration at the core location and the vostok co2 record argues for a control of antarctic sea ice extent on atmospheric co2 concentration via the modification of the ocean to atmosphere gas balance

accumulation of biogenic and lithogenic material in the pacific sector of the southern ocean during the past 40 000 years the 230th normalization technique was applied to surface sediments and down core records from the pacific sector of the southern ocean between 120 w and 170 w in order to reconstruct vertical rain rates corrected for lateral redistribution of sediment preserved rain rates of opal organic carbon and biogenic ba all indicate that biological productivity south of the antarctic polar front apf was much lower than today during the last glacial maximum lgm probably in response to increased ice cover however by analogy with modern opal fluxes south of the acc we show that year round ice cover is not a prerequisite for very low rates of opal accumulation available records from north of the apf indicate little to no change in opal export in contrast to records from the indian and atlantic sectors which show enhanced opal export north of the apf during the lgm glacial records from north of 66 s in the pacific all show lithogenic fluxes that were greater than today but significantly lower than lithogenic fluxes in the glacial atlantic and indian sectors together these new records from the pacific sector show that during the lgm the three basins of the southern ocean were significantly more differentiated than today the observed inter basin distribution of lithogenic fluxes and opal burial and the presumed geographical distribution of increased dust input to the southern ocean during the lgm are consistent with an atlantic indian pacific gradient in the degree of iron stimulated diatom productivity within the zone lying between the apf and the subantarctic front previous studies which focused primarily on the atlantic sector may have overestimated the glacial increase in the strength of the biological pump in the southern ocean

diatom distribution in southern ocean surface sediments atlantic sector implications for paleoenvironmental reconstructions abstract a study of 230 surface sediment samples collected in the atlantic sector of the southern ocean between the southernmost weddell sea and the subtropical zone documents the modern distribution of diatoms revealing patterns of paleoenvironmental significance estimations of diatom valves per gram dry sediment display numbers of 50 200 106 in the zone of high opal burial located between the mean position of the winter sea ice edge and the polar front and maximum values of greater than 200 106 in the near shore sedimentary basins off the antarctic peninsula lowest diatom concentrations and assemblages strongly affected by dissolution were encountered in the weddell basin despite alteration of the diatom assemblages prior to their incorporation into the sediment record the biogeographic distribution and the abundance pattern of most of the 35 studied diatom species shows a close relationship with the surface hydrography water temperature these relationships can be used to estimate past surface water temperatures based on statistical treatments of the assemblages or on simple relations of species occurrences in the geological record another close link occurs between the distribution of sea ice and sea ice related diatoms

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

global plate velocities from the global positioning system we have analyzed 204 days of global positioning system gps data from the global gps network spanning january 1991 through march 1996 on the basis of these gps coordinate solutions we have estimated velocities for 38 sites mostly located on the interiors of the africa antarctica australia eurasia nazca north america pacific and south america plates the uncertainties of the horizontal velocity components range from 1 2 to 5 0 mm yr with the exception of sites on the pacific and nazca plates the gps velocities agree with absolute plate model predictions within 95 confidence for most of the sites in north america antarctica and eurasia the agreement is better than 2 mm yr we find no persuasive evidence for significant vertical motions 3 standard deviations except at four sites three of these four were sites constrained to geodetic reference frame velocities the gps velocities were then used to estimate angular velocities for eight tectonic plates absolute angular velocities derived from the gps data agree with the no net rotation nnr nuvel 1a model within 95 confidence except for the pacific plate our pole of rotation for the pacific plate lies 11 5 west of the nnr nuvel 1a pole with an angular speed 10 faster our relative angular velocities agree with nuvel 1a except for some involving the pacific plate while our pacific north america angular velocity differs significantly from nuvel 1a our model and nuvel 1a predict very small differences in relative motion along the pacific north america plate boundary itself our pacific australia and pacific eurasia angular velocities are significantly faster than nuvel 1a predicting more rapid convergence at these two plate boundaries along the east pacific rise our pacific nazca angular velocity agrees in both rate and azimuth with nuvel 1a

climate mediated size variability of diatom fragilariopsis kerguelensis in the southern ocean abstract fragilariopsis kerguelensis o meara hustedt is the most abundant open ocean diatom species in southern ocean sediments and its average valve area has recently been used to infer glacial interglacial paleoceanographic conditions studies from the atlantic sector of the southern ocean demonstrated how larger average valve area of f kerguelensis during the last glacial compared to the interglacial possibly relate to greater availability of iron through wider sea ice coverage and higher eolian dust input we present here data on average valve area of f kerguelensis from three sediment cores covering the last 42 cal ka bp from different zones of the southern ocean our records confirm previous results from the atlantic sector but highlight a different pattern from the indian sector where the largest valves of f kerguelensis are encountered during the holocene fragilariopsis kerguelensis average valve area variations in the antarctic polar front apf of the atlantic sector and subantarctic front of the indian sector are in phase with records of opal burial while this correlation does not hold for the apf of the indian sector variations in circum polar upwelling were suggested as the main controlling factor of opal production during the last 20 000 years we here hypothesize that high nutrient input from the antarctic peninsula during the last deglaciation may have exerted a stronger control on f kerguelensis average valve area and opal export in the atlantic sector of the southern ocean than inferred changes in circum polar upwelling

late quaternary changes in biogenic opal fluxes in the southern indian ocean abstract late quaternary sedimentary and paleoenvironmental conditions in the southern indian ocean have been reconstructed from radioisotope and proxy element profiles biogenic opal and organic carbon measured on five sediment cores taken along a transect across the indian sector of the antarctic circumpolar current dissolution corrected opal rain rates were used to reconstruct past changes of opal productivity for this region records from these five cores indicate that opal productivity during glacial periods was lower than presently recorded south of the antarctic polar front apf probably due to increased ice cover north of apf opal productivity was slightly greater during glacial periods than during the holocene probably in response to 1 the northward migration of the apf by approximately 5 latitude 2 a northward transport of si from the antarctic zone and 3 an increase of fe necessary for opal producing organisms via upwelling and the erosion of the kerguelen plateau we also invoke a decoupling between opal burial and organic carbon flux to the seabed to explain the variation in buried si c ratio between glacial and interglacial sediment this decoupling is principally explained by better organic carbon preservation in the glacial sediments due to strong sediment focussing an increase in glacial export paleoproductivity is not supported by the data implying that bioproductivity variations in the southern indian ocean are unlikely to have contributed to the glacial drawdown of atmospheric co 2 inferred from ice core data

coastal zone color scanner pigment concentrations in the southern ocean and relationships to geophysical surface features the spatial and seasonal distributions of phytoplankton pigment concentration over the entire southern ocean have been studied for the first time using the coastal zone color scanner historical data set from october 1978 through june 1986 enhanced pigment concentrations are observed between 35 s and 55 s throughout the year with such enhanced regions being more confined to the south in the austral summer and extending further north in the winter north and south of the polar front phytoplankton blooms 1 mg m3 are not uniformly distributed around the circumpolar region instead blooms appear to be located in regions of ice retreat or high melt areas such as the scotia sea and the ross sea in relatively shallow areas e g the patagonian and the new zealand shelves in some regions of ekman upwelling like the tasman sea and near areas of high eddy kinetic energy such as the agulhas retroflection among all features examined by regression analysis bathymetry appears to be the one most consistently correlated with pigments correlation coefficient being about 0 3 for the entire region the cause of negative correlation with bathymetry is unknown but is consistent with the observed abundance of iron in shallow areas in the antarctic region it is also consistent with resuspension of phytoplankton cells by wind induced mixing especially in shallow waters on the other hand in the deep ocean especially at latitudes 30 in average pigment concentration over the entire region during different seasons indicates possible influence of time dependent parameters

application of gis and hydrogeochemistry of groundwater pollution status of nagapattinam district of tamil nadu india this study evaluated groundwater quality of the coastal aquifer in nagapattinam district with intensive agricultural activities in the southern part of india chemical components such as ph ec tds major cations and anions were used to identify seawater intrusion fifty two groundwater samples were collected from dug and bore wells in this region during summer and monsoon seasons 2011 ec tds na and cl were higher in summer than in monsoon the correlation and two way joining cluster analyses clearly show that groundwater quality is mainly controlled by seawater intrusion and other anthropogenic sources modified hill piper exhibits that most of the samples belong to water contaminated with gypsum sector the interpretation of gibbs plot represents the groundwater samples that fall in evaporation and rock weathering zone and other samples are affiliated to various anthropogenic activities based on na sar chloride hardness and wilcox classification the groundwater is moderately suitable for agriculture this region is vulnerable to seawater intrusion during summer due to the severe pumping of groundwater in groundwater quality maps produced by inverse distance weighting of arcgis some good and medium patches could be used for agriculture to a certain extent the northern southern and central parts of the study area fell in poor quality regions because of seawater intrusion and infiltration of irrigation water contaminated with pesticides and fertilizers

morphometry of the diatom fragilariopsis kerguelensis from southern ocean sediment high throughput measurements show second morphotype occurring during glacials abstract fragilariopsis kerguelensis is one of the most abundant diatoms in the sediments of the southern ocean its morphometric features have been proposed as proxies based on links with for example iron availability sea surface temperature and glacial interglacial conditions we investigated morphometric changes in f kerguelensis valves in a well studied sediment core record focusing on transition periods between glacials and interglacials by applying a high throughput diatom imaging and morphometry workflow we found two clearly distinct morphotypes which were differentiated by their rectangularity one of them occurred preferentially in glacial samples whilst the other persisted throughout this indicates that their relative abundances depend on environmental conditions and thereby points to the possibility that paleo proxies based on f kerguelensis valve morphometric features might in the future benefit from differentiating these two morphotypes as an initial exploration of this idea we show that the abundance ratio of both morphotypes correlates well with paleo temperatures which had been reconstructed using independent data from the same core distinguishing between the two morphotypes only became possible by image analysis for precisely measuring diatom valve outlines and area highlighting the potential of such methods for diatom analyses

application of modern analog technique to marine antarctic diatoms reconstruction of maximum sea ice extent at the last glacial maximum modern analog technique mat applied to antarctic diatoms is a new approach for quantitative sea ice paleoreconstructions in the southern ocean in a first step we show that mat is a better approach than the imbrie and kipp method to reconstruct the modern sea ice pattern we then use this approach to reconstruct sea ice presence in number of months per year during the last glacial maximum lgm at this time sea ice presence was greater than today leading to a shorter diatom growing season the maximum sea ice extent inferred from quantitative values of sea ice presence was located 5 8 north of its actual position leading to double the surface of modern winter sea ice this greater sea ice extent may have played a significant role on atmospheric and surface oceanic circulations and therefore on southern mid latitude and high latitude climates it may also have reduced the amount of heat moisture and co2 from the ocean to the atmosphere thus participating in the lowering of atmospheric co2 during the lgm

geodetic determination of relative plate motion and crustal deformation across the scotia south america plate boundary in eastern tierra del fuego 1 global positioning system gps measurements provide the first direct measurement of plate motion and crustal deformation across the scotia south america transform plate boundary in tierra del fuego this plate boundary accommodates a part of the overall motion between south america and antarctica the subaerial section of the plate boundary in tierra del fuego about 160 km in length is modeled as a two dimensional strike slip plate boundary with east west strike along the magallanes fagnano fault system the principal fault of this portion of the plate boundary relative plate motion is left lateral strike slip on a vertical fault at 6 6 1 3 mm year based on an assumed locking depth of 15 km the site velocities on the scotia plate side are faster than the relative velocity by an additional 1 2 mm yr suggesting there may be a wider region of diffuse left lateral deformation in southern patagonia the north south components of the velocities however do not support the existence of active large scale transpression or transtension between the south america and scotia plates along this section of the plate boundary

variations of the antarctic circumpolar current intensity during the past 500 ka 1 we examine the past variations of the antarctic circumpolar current acc by using variations in size and abundance of the magnetic grains deposited by this current at a site east the kerguelen crozet plateau core md00 2375g was taken at a midlatitude site during the antaus cruise conducted in 2000 by the french r v marion dufresne marine isotope stages mis down to mis 13 are identified and an age model is derived from a correlation to the ice core isotopic record obtained from epica in antarctica continuous records of abundance and size of the magnetic grains were obtained using environmental magnetism methods results show a strong modulation of the acc flow intensity in response to glacial and interglacial cycles the low abundance and the small size of magnetic grains indicate that the acc was weak during warm stages and strong during glacial epochs a large modulation is also observed at the sub stage scale during the interglacials a minimum in concentration and grain size occurs at the onset of mis 11 at the mis 6 5 10 9 and possibly 12 11 transitions observed variations suggest a mechanism involving both rapid and progressive variations of the acc flow at deglaciations

the reconstruction of late quaternary antarctic sea ice distribution the use of diatoms as a proxy for sea ice the study of annual diatom transfer from the southern ocean surface to the sea floor using time series sediment traps combined with the mapping of diatom assemblages from surface sediments results in the definition of a proxy for past variations of sea ice extent the application and robustness of the proposed proxy are demonstrated by the study of late pleistocene sediment cores recovered from different environmental regimes in the southern ocean relative amounts of the sea ice indicator diatoms fragilariopsis cylindrus and fragilariopsis curta of 3 in diatom assemblages preserved in sediments are representative of the presence of seasonal winter sea ice summer sea ice occurrence is signalled by a distinct drop in biogenic sedimentation rate as a result of strongly reduced biogenic export in the presence 3 of diatom assemblage of the deep temperature diatom fragilariopsis obliquecostata the spatial and temporal distribution pattern of the sea ice proxy indicates significant sea ice variations during marine isotope stages 1 and 5 in the present antarctic zone of the southern ocean during glacial maxima the antarctic winter sea ice was extended into the present polar front zone while the antarctic summer sea ice was most probably expanded into the area of the present winter sea ice edge during the short climatic optima at the onset of interglacial periods the winter sea ice extent was distinctly reduced

mid brunhes century scale diatom sea surface temperature and sea ice records from the atlantic sector of the southern ocean odp leg 177 sites 1093 1094 and core ps2089 2 abstract diatom assemblages from odp leg 177 sites 1093 1094 and core ps2089 2 from the present antarctic sea ice free zone and close to the polar front were analyzed in order to reconstruct the climate development around the mid brunhes event 400 000 yr ago as reflected by summer sea surface temperature ssst and sea ice distribution dense sample spacing allows a mean temporal resolution during marine isotope stage mis 11 423 362 ka of 300 400 yr ssst values were estimated from diatom assemblages using a transfer function technique the distribution pattern of sea ice diatoms indicates that the present day ice free antarctic zone was seasonally covered by sea ice during the cold mis 12 and mis 10 these glacial periods are characterized by sea ice fluctuations with a periodicity of 3 and 1 85 kyr suggesting the occurrence of dansgaard oeschger style millennial scale oscillations in the atlantic sector of the southern ocean during the glacial stages mis 12 and mis 10 termination v mis 12 11 is characterized by a distinct temperature increase of 4 6 c intersected especially at the southern site 1094 and core ps2089 2 by two distinct cooling events reminiscent of the younger dryas which are associated with a northward shift of the winter sea ice edge in the antarctic zone the ssst record is characterized by distinct temperature intervals bounded by stepwise rapid changes maximum temperatures were reached during termination v and the early mis 11 exceeding modern values by 2 c over a period of 8 kyr this pattern indicates a very early response of the southern ocean to global climate on milankovitch driven climate variability the ssst optimum is marked by millennial scale temperature oscillations with an amplitude of ca 1 c and periodicities of ca 1 85 and 1 47 kyr probably reflecting changes in the ocean circulation system the sssts during the mis 11 temperature optimum do not exceed values obtained from other interglacial optima such as the early periods of mis 5 or mis 1 from the antarctic zone however the total duration of the warmest period was distinctly longer than observed from other interglacials the comparison of the south atlantic climate record with a high resolution record from odp leg 162 site 980 from the north atlantic shows a strong conformity in the climate development during the studied time interval

gis based evaluation of water quality index of groundwater resources around tuticorin coastal city south india groundwater is a vital source of water for industrial domestic and agricultural activities in tuticorin city due to lack of surface water resources groundwater quality and its suitability for drinking usage were evaluated a total of 72 groundwater samples were collected from open wells and boreholes during pre and post monsoon period samples were analyzed for physico chemical properties major cation and major anions in the laboratory using the standard methods given by the american public health association the geographic information system based spatial distribution map of different major elements has been prepared using arcgis 9 2 these maps are classified as desirable maximum permissible and the values that exceed maximum permissible limit are termed as not permissible prescribed by the who 2004 from the piper plot which gives the cation chemistry the concentration of the alkalies na and k exceeds the alkaline earths ca2 and mg2 and those of strong acids exceeds weak acids in the case of anions during the two periods strong acid shows dominance over weak acid and hco3 and cl have influences almost equal to na which indicate the saltwater intrusion into the freshwater aquifer of the study area a canadian council of ministers for the environment water quality index ccme wqi map was also generated with the gis technique to better understand the water portability over space the categories of water quality evaluated by ccme wqi values of major part of the study area fall under fair category during prm and good category during the pom period the ccme wqi is a very useful and an efficient tool to summarize and to report on the monitoring data to the decision makers in order to understand the status of the groundwater quality finally the study concludes that the groundwater quality is impaired by man made activities and proper management plan is necessary to protect valuable groundwater resources in tuticorin city

current rates of convergence across the central andes estimates from continuous gps observations we present velocity solutions for 16 continuous gps cgps stations located in south america in a geodetic reference frame that nominally fixes the craton or stable core of this continent the rms horizontal velocity of 8 stations located within the craton is 1 3 mm yr three cgps stations located in chile between about 33 s and 20 s have velocities in the range 19 24 mm yr these motions manifest current rates of convergence across the southern limb of the central andes the igs station in arequipa peru at 16 5 s in the northern limb of the orocline however has a velocity of just 10 mm yr

dissolved iron in the vicinity of the crozet islands southern ocean the annual phytoplankton bloom occurring north of the crozet plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high nutrient low chlorophyll hnlc conditions normally associated with the southern ocean therefore during crozet natural iron bloom and export experiment crozex a large multidisciplinary study performed between november 2004 and january 2005 measurements of total dissolved iron dfe0 2 m were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples dfe concentrations were determined by flow injection analysis with n n dimethyl p phenylenediamine dihydrochloride dpd catalytic spectrophotometric detection dfe concentrations varied between 0 086 and 2 48 nm with low values in surface waters enrichment of dissolved iron 1 nm at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron waters farther north also appear to be affected by this input of coastal and shelf origin although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of 0 07 nm km 1 at the time of sampling using lateral and vertical diffusion coefficients derived from ra isotope profiles and also estimates of atmospheric inputs it was then possible to estimate a dfe concentration of 0 55 nm to the north of the islands prior to the bloom event which is sufficient to initiate the bloom the lateral island source being the largest component a similar situation is observed for other sub antarctic islands such as kerguelen south georgia that supply dissolved iron to their surrounding waters thus enhancing chlorophyll concentrations

glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls 1 the valve area of fragilariopsis kerguelensis the most abundant diatom species in the southern ocean strongly changes in size in response to varying conditions in the surface ocean we examined the link both in two iron fertilization experiments and in sediment samples covering several glacial terminations between size variability in this species and environmental conditions across the antarctic polar front including sea ice extent sea surface temperature and the input of eolian dust the iron fertilization experiments show valve area to be positively correlated with iron concentrations in ambient waters which suggests the possibility of a causal relation between valve size of fragilariopsis kerguelensis and ambient surface water iron concentration larger valves are usually found during glacial times and thus seem to be related to lower sea surface temperature and wider sea ice coverage moreover our results indicate that there usually is a strong correlation between larger valve size and increased input of eolian dust to the southern ocean however this correlation obvious for the fertilization experiments and for glacial terminations i ii iii and v does not seem to be valid for termination vi where size appears to be inversely correlated to dust input citation cortese g r gersonde k maschner and p medley 2012 glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls paleoceanography 27 pa1208 doi 10 1029 2011pa002187

hydrogeochemical characterization and quality assessment of groundwater in parts of southern gangetic plain a comprehensive assessment of groundwater is carried out in parts of the southern gangetic plain to identify the hydrogeochemical processes influencing groundwater geochemistry and to ascertain the suitability of groundwater for drinking and irrigational uses results of detailed chemical analysis reveal that groundwater of the study area is slightly acidic ph values from 6 2 to 7 37 during post monsoon with dominant concentrations of na and ca2 cations and hco3 and cl anions groundwater chemistry is largely controlled by rock weathering and ion exchange processes with secondary contribution from anthropogenic sources in particular values of ec total hardness and concentrations of na and hco3 exceed the prescribed limits of indian and who water quality standards suitability of groundwater for irrigation purposes are evaluated on the basis of sodium adsorption ratio sodium percent na magnesium hazard residual sodium carbonate and kelley s index in this regard nearly 40 50 of the groundwater in the study area is found to be of excellent to good quality in addition principal component analysis performed to identify the dominant geochemical processes shows that the first three components are together account for 80 84 and 78 85 of the total variance in the dataset for post monsoon and pre monsoon periods respectively this analysis also reveals key contributions from hydrogeochemical processes like mineral dissolution silicate and carbonate weathering alongside anthropogenic activities like leaching of fertilizers from agricultural lands

shifting frontal regimes and its influence on bioproductivity variations during the late quaternary in the indian sector of southern ocean abstract reconstruction of palaeoproductivity from southern ocean is crucial for understanding the functioning of the southern ocean biological pump in the past high resolution records of multi proxy parameters calcium carbonate opal total organic carbon biogenic barium and planktonic carbon isotope ratios 13 c were investigated in two well dated sediment cores sk200 22a and sk200 27 from the indian sector of southern ocean situated to the north and south of antarctic polar front apf respectively the palaeoproductivity records extending 95 ka bp sk200 22a and 75 ka bp sk200 27 revealed inverse relationships between the calcite and opal productivity indicating the influence of shifting nutrient regimes at core sk200 22a reduced calcite productivity during marine isotope stage mis 2 4 and part of mis 3 suggest an equatorward migration of the frontal regimes during glacial intervals compared to this the region south of the apf core sk200 27 was characterized by the near absence of calcite content during the last glacial period and increased opal productivity during mis 1 and mis 3 supporting a southward migration of apf during warmer intervals ba bio records exhibit good correlation with opal records in both the cores and also correlate with that of calcite record at sk200 22a indicating that ba is influenced by the combined opal and calcite productivity the enhanced opal productivity during the glacial periods north of the apf is attributed to the northward shifting of oceanic fronts and associated transfer of nutrients diatom productivity records of sk200 22a reveal significant similarities with the dust records from the antarctic and southern ocean but showed no significant relationships with the diatom record of sk200 27 it is proposed that the dust derived fe input had apparently influenced the palaeoproductivity north of the modern apf but had a minor influence on opal productivity south of the apf comparison with the ice core climate records from antarctica and greenland revealed that bioproductivity peaks in the study region are nearly synchronous with the millennial antarctic warming events remarkably the calcite and opal productivity records at sk200 22a responded differently to the antarctic warming events with opal productivity lagging behind the calcite productivity peaks by 1 2 ka

southern ocean dust climate coupling over the past four million years dust plays a central part in ocean biogeochemical cycles by supplying iron and other essential micronutrients to regions where marine productivity is limited by the availability of iron martinez garcia et al present a marine record of dust and iron supply to the southern ocean during the past four million years the data derived from leaf waxes establish that previous records of dust flux from antarctic ice cores are broadly representative of a larger area importantly the dust and iron supply rose sharply 1 25 million years ago suggesting that increased dust supply may be a major influence on the more severe swings between the glacial and interglacial climate of the late pleistocene dust has the potential to modify global climate by influencing the radiative balance of the atmosphere and by supplying iron and other essential limiting micronutrients to the ocean1 2 indeed dust supply to the southern ocean increases during ice ages and iron fertilization of the subantarctic zone may have contributed up to 40 parts per million by volume p p m v of the decrease 80 100 p p m v in atmospheric carbon dioxide observed during late pleistocene glacial cycles3 4 5 6 7 so far however the magnitude of southern ocean dust deposition in earlier times and its role in the development and evolution of pleistocene glacial cycles have remained unclear here we report a high resolution record of dust and iron supply to the southern ocean over the past four million years derived from the analysis of marine sediments from odp site 1090 located in the atlantic sector of the subantarctic zone the close correspondence of our dust and iron deposition records with antarctic ice core reconstructions of dust flux covering the past 800 000 years refs 8 9 indicates that both of these archives record large scale deposition changes that should apply to most of the southern ocean validating previous interpretations of the ice core data the extension of the record beyond the interval covered by the antarctic ice cores reveals that in contrast to the relatively gradual intensification of glacial cycles over the past three million years southern ocean dust and iron flux rose sharply at the mid pleistocene climatic transition around 1 25 million years ago this finding complements previous observations over late pleistocene glacial cycles5 8 9 providing new evidence of a tight connection between high dust input to the southern ocean and the emergence of the deep glaciations that characterize the past one million years of earth history

large scale circulation around the crozet plateau controls an annual phytoplankton bloom in the crozet basin the circulation in the vicinity of the crozet plateau in the southwest indian ocean sector of the southern ocean is examined using hydrographic sections argo floats surface drifters and satellite altimetry all four techniques confirm that a major branch of the antarctic circumpolar current the subantarctic front saf flows anticyclonically round the del cano rise west of the crozet plateau i e eastward to the south of the del cano rise then northward and sometimes northwestward into the crozet basin before turning back eastward in a combined front with the agulhas return current and the subtropical front this s bend in the saf is a permanent feature controlled by the bathymetry as has been inferred previously by pollard and read pollard r t read j f 2001 circulation pathways and transports of the southern ocean in the vicinity of the southwest indian ridge journal of geophysical research 106 c2 2881 2898 similar but much weaker anticyclonic flow is found round the crozet plateau itself with no more than 5 10 106 m3 s 1 turning north to the east of the crozet islands circulation north of the crozet plateau between the plateau and the s bend of the saf is extremely weak fed only by anticyclonic meanders breaking off the saf into the area from the west or north and occasional input from the northward partially wind driven i e ekman flow south and east of the islands in consequence of the weak circulation dissolved iron from the land or sediments of the crozet plateau and islands can build up during the winter in the polar frontal zone between crozet and the saf which gives rise to an annual bloom in this area biological evidence from satellite images and from phytoplankton and zooplankton distributions supports the circulation pattern we develop this pattern confirms that patchiness of productivity in the bloom area results from close juxtaposition of water that has entered the area from the west from the saf and from the south and east after flowing past the islands flow from the south and east has had a chance to entrain iron from the islands and sediments whereas flow from the west has not

modeling broadscale deformation in northern california and nevada from plate motions and elastic strain accumulation we present a first order method for modeling broadscale deformation consistent with both plate tectonic motions and elastic strain accumulation on plate boundary faults interseismic deformation is assumed to be a superposition of long term rigid body motions between faults defined by angular velocities of spherical plates and backslip on shallow locked portions of faults in an elastic half space this method is applied to 1993 2000 continuous gps data from 35 sites in a profile from the san francisco bay area northern california to eastern nevada deformation is consistent within the 1 mm yr 1 uncertainties of the estimated site velocities with a simple 10 parameter model using 6 rigid plates and 3 locked san andreas system faults