biogenic silica accumulation in the ross sea and the importance of antarctic continental shelf deposits in the marine silica budget abstract thirty five box cores were collected from the continental shelf in the ross sea during cruises in january and february 1983 pb 210 and pu 239 240 geochronologies coupled with biogenic silica measurements were used to calculate accumulation rates of biogenic silica sediment in the southern ross sea accumulates at rates ranging from 0 6 to 2 7 mm y with the highest values occurring in the southwestern ross sea biogenic silica content in surface sediments ranges from 2 by weight in sulzberger bay and the eastern ross sea to 41 in the southwestern ross sea biogenic silica accumulation in the southwestern ross sea averages 2 7 10 2 g cm2 y and is comparable to accumulation rates in high productivity upwelling environments from low latitude continental margins e g gulf of california coast of peru the total rate of biogenic silica accumulation in the southern ross sea is approximately 0 2 1014 g y with most of the accumulation occurring in basins 500 1000 m water depth if biogenic silica accumulation in the southern ross sea continental shelf is typical of other basins on the antarctic continental shelf as much as 1 2 1014 g y of silica could be accumulating in these deposits biogenic silica accumulation on the antarctic continental shelf may account for as much as a fourth of the dissolved silica supplied to the world ocean by rivers and hydrothermal vents

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

oceanographic control of diatom abundances and species distributions in surface sediments of the tropical and southeast atlantic abstract this paper is a descriptive account of the diatomaceous component of pelagic sediments from the tropical and southeast atlantic ocean geographic patterns of diatom abundances whole and fragment forms per gram major species relative abundances and diatom assemblages resolved by q mode factor analysis are presented comparisons drawn to sea surface temperature salinity and productivity distributions suggest that i diatom abundances primarily reflect surface productivity with no apparent dissolution effects due to water depth ii relative abundances of major species vary in their ecologic dependence but do reflect major oceanographic features of the surface waters and iii of the five diatom assemblages resolved four finely delineate the complexity of the low latitude oceanography these assemblages in decreasing order of statistical importance are associated with 1 warm waters of moderate to high primary productivity 2 the oceanward margin of the benguela current a region of high primary production with a maximum in austral summer 3 low salinity waters off the mouths of the zaire and niger rivers and 4 subtropical to tropical waters of lower productivity mostly in the western equatorial atlantic the fifth factor represents the equatorward advection of subantarctic to antarctic diatoms by deep ocean currents

differentiation conditions of a basaltic magma from santorini and its bearing on the production of andesite in arc settings santorini volcano in the aegean region greece is characterized by andesitic to silicic dominated explosive activity and caldera forming eruptions sourced from magmatic reservoirs located at various structural levels beneath the volcano there is a good understanding of the silica rich magmatism of the island whereas the andesite dominated volcanism and the petrogenesis of the parental mafic magmas are still poorly understood to fill this gap we have performed crystallization experiments on a representative basalt from santorini with the aim of determining the conditions of differentiation pressure temperature volatile fugacities and the parental magma relationship with the andesitic eruptive rocks experiments were carried out between 975 and 1040 c in the pressure range 100 400 mpa fo2 from qfm to nno 3 5 where qfm is quartz fayalite magnetite and nno is nickel nickel oxide with h2omelt contents varying from saturation to nominally dry conditions the results show that basalt phenocrysts within the basalt crystallized at around 1040 c in a magma storage reservoir located at a depth equivalent to 200 400 mpa pressure with 3 5 wt dissolved h2o and fo2 around qfm comparison with the xenocryst and phenocryst assemblages of the upper scoria 1 andesite shows that andesitic liquids are produced by fractionation of a similar basalt at 1000 c and 400 mpa following 60 80 wt crystallization of an ol cpx plag ti mag opx 6 pig ilm assemblage with melt water contents around 4 6 wt at santorini the andesitic low viscosity and water rich residual liquids produced at these depths segregate from the parent basaltic mush and feed the shallow magma reservoirs eventually erupting upon mixing with resident magma changes in prevailing oxygen fugacity may control the tholeiitic calc alkaline character of santorini magmas explaining the compositional and mineralogical differences observed between the recent thyra and old eruptive products from akrotiri

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

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

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

seasonally resolved diatom δ18o records from the west antarctic peninsula over the last deglaciation understanding the response of the antarctic ice sheets during the rapid climatic change that accompanied the last deglaciation has implications for establishing the susceptibility of these regions to future 21st century warming a unique diatom 18o record derived from a high resolution deglacial seasonally laminated core section off the west antarctic peninsula wap is presented here by extracting and analysing single species samples from individual laminae season specific isotope records were separately generated to show changes in glacial discharge to the coastal margin during spring and summer months as well as documenting significant intra annual seasonal variability during the deglaciation with increased discharge occurring in summer relative to spring further intra seasonal variations are apparent between individual taxa linked to the environment that individual diatom species live in whilst deglacial 18o are typically lower than those for the holocene indicating glacial discharge to the core site peaked at this time inter annual and inter seasonal alternations in excess of 3 suggest significant variability in the magnitude of these inputs these deglacial variations in glacial discharge are considerably greater than those seen in the modern day water column and would have altered both the supply of oceanic warmth to the wap as well as regional marine atmospheric interactions in constraining changes in glacial discharge over the last deglaciation the records provide a future framework for investigating links between annually resolved records of glacial dynamics and ocean climate variability along the wap

seasonal and subseasonal climate changes recorded in laminated diatom ooze sediments adelie land east antarctica a 40 m long sediment core covering the 1000 9600 years bp period was retrieved from the dumont d urville trough off adelie land east antarctica during the md 130 images x cado cruise this sedimentary sequence allows the documentation of changes in climate seasonality during the holocene here we show preliminary results of diatom communities lithic grain distribution and titanium content measured on two 30 cm long sequences of thin sections the two sequences originate from two different climate regimes the colder neoglacial and the warmer hypsithermal proxies were measured at microscale resolution on 25 laminations for the neoglacial and 14 laminations for the hypsithermal the two sequences reveal alternating light green and dark green laminae light laminae result from low terrigenous input and high sea ice edge diatom fluxes and are interpreted to represent the spring season dark laminae result from high terrigenous input mixed with a diversified open ocean diatom flora and are interpreted to represent the summer autumn season the two sequences therefore resolve annual couplets composed of one light plus one dark lamina variations in the relative thickness of laminations and annual couplets associated with diatom assemblage changes are observed in each sequence and between the two sequences giving information on interannual to millennial changes in environmental conditions

diatom evidence for late holocene climatic events in granite harbor antarctica downcore diatom data from a deep basin in granite harbor antarctica provide new high resolution information concerning changes in oceanographic and depositional processes that have occurred during approximately the last 1250 years the influence of global scale climatic change during the time of the medieval warm period and possibly the little ice age is revealed by long term changes in floral assemblages as recorded by changes in the relative concentration of nitzschia cylindrus the diatom data suggest that granite harbor experienced less annual ice and pack ice cover during both these periods possibly because of higher temperatures during the medieval warm period and stronger offshore winds during the little ice age the sedimentary record reveals several distinct short lived events in which nearly monospecific blooms of corethron criophilum and chaetoceros spp occurred possibly the result of strong stabilization of the upper water column and were most likely a response to regional rather than global conditions although short lived these events may play a significant role in the delivery of organic carbon and biogenic silica to the seafloor

the southern ocean surface between marine isotope stages 6 and 5d shape and timing of climate changes summer sea surface temperature ssst and sea ice extent obtained at millennial to centennial resolution are presented for seven cores recovered in the atlantic and western indian antarctic zone from termination ii and the last interglacial s s i e marine isotope substage mis 5e the diatom based ssst estimates show that during the late mis 6 intensified export of cold waters from the weddell sea resulted in sssts close to 0 c in the central and eastern atlantic sector due to northward expansion of the winter sea ice edge by 3 5 latitude the sea ice seasonality was reduced such conditions have great potential for efficient year round reduction in air sea gas exchange and glacial co2 draw down the warming at termination ii started at 132 131 ka marked by rapid retreat of the sea ice edge the ssst increased within a few thousands of years to reach maximum interglacial summer temperatures ranging between 2 5 and 3 5 c in the earliest mis 5e 128 125 ka besides a distinct cold reversal around 129 5 ka the warming was punctuated by short lived temperature rebounds with amplitudes of 1 1 5 c occurring at 200 300 yr frequency thus in the range of the periodicity of solar input increased chaetoceros spp abundance suggests meltwater events as the primary cause of the coolings the ssst optimum characterised by strongly enhanced biogenic sedimentation rates ended at ca 125 ka with the full re establishment of the global conveyor belt and beginning of the northern hemisphere climatic optimum at this time sssts decreased stepwise and stabilised on values slightly warmer than today showing in the following period of mis 5e only low amplitude oscillations during mis 5d a northward expansion of the sea ice field took place but sssts only slightly colder than modern ones and a weakened meridional temperature gradient indicate that the southern ocean did not fall in a true glacial mode the tight correlation between southern ocean ssst and winter sea ice records and vostok atmospheric temperature and co2 records support the idea that the antarctic winter sea ice and southern ocean temperature exert a primary control on the atmospheric ocean co2 exchanges and hence on global climate reduction of the antarctic sea ice field and increase of ssst at the onset of termination ii could have been triggered by precessional changes influencing southern high latitude summer insolation positive feedback mechanisms reduction of surface albedo and release of co2 into the atmosphere and changes in global ocean circulation affected by a collapse or strong reduction in north atlantic deep water nadw production could have induced further reinforcement of the southern ocean warming

climate evolution at the last deglaciation the role of the southern ocean abstract two sediment sequences recovered close to and south of the present polar front 50 53 s in the atlantic sector of the southern ocean were analysed in order to evaluate the environmental evolution of the southern ocean surface over the last deglaciation and the holocene our reconstruction is based on radiocarbon dated records of diatom based sea surface temperature and sea ice proxies and planktic foraminiferal stable isotopes the onset of the deglacial warming and gradual southward retreat of the winter sea ice field between 18 and 17 cal kyr bp occurrence of a thermal reversal centered at ca 13 cal kyr bp antarctic cold reversal or acr and early holocene occurrence of the climatic optimum well correlate with climatic reconstructions available from the indian southern ocean and from antarctic ice cores time correspondence of southern ocean warming and heinrich event 1 in the north atlantic is compatible with the transmission of the climate signal from the northern to the southern hemisphere through the bipolar seesaw our data support modeling results suggesting that the northern hemisphere bolling warming and turn on of the north atlantic deep water formation are triggered by gradual warming and sea ice retreat in the southern ocean meltwater shedding into the southern ocean associated with the acr may maintain northern hemisphere warming during the allerod the development of sea surface warming and sea ice retreat is compatible with a southern ocean control on the atmospheric co2 increase during the deglaciation during the early holocene 9 7 cal kyr bp our southern core records renewed surface ocean cooling and northward readvance of the winter sea ice field such early holocene cooling is common to cores from the high latitude atlantic sector and might be brought about by expansion of the weddell gyre circulation at that time

the biogeography of major diatom taxa in southern ocean sediments 2 open ocean related species diatoms from 228 southern ocean core top sediment samples were examined to determine the geographic distributions of 32 major diatom species taxa preserved in the sediments of three zonally distinct regions sea ice open ocean and the tropical subtropical in the first of three papers 14 species taxa occurring in the region where sea ice covers the ocean surface on an annual basis are geographically documented comparisons are drawn between the diatom abundances on the sea floor sea ice parameters annual duration and concentration in february and september and february sea surface temperature such parameters are commonly used in reconstructing past oceanographic conditions in the sea ice and open ocean zones analysis of the geographic patterns and sea surface parameter correlations reveals species specific distributions regulated primarily by sea ice coverage and sea surface temperature which support the use of diatom remains for the estimation of these past seasurface environmental parameters comparison with reliable accounts of the 14 species from the sediments or plankton also provides the first glimpses into species specific ecology and habitat linkages d 2005 elsevier b v all rights reserved

the fate of diatom valves in the subantarctic and polar frontal zones of the southern ocean sediment trap versus surface sediment assemblages abstract an array of deep ocean sediment traps was initiated in 1997 within the australian sector of the southern ocean and serviced annually for over a decade the subantarctic site is ongoing as part of the southern ocean time series here we expand on previous findings obtained from the shallow traps 1000 m depth in the polar frontal zone pfz and subantarctic zone saz by examining the chemical composition and diatom assemblages collected by sediment traps deployed at bathypelagic depths in the pfz 1500 m depth years 1997 1998 1999 2000 and 2003 2004 and saz 2000 and 3800 m year 1999 2000 additionally the diatom assemblages of the surface sediments below the traps were analyzed to document how the seasonal signal is recorded in the sedimentary record analysis of the changes of the bsi poc ratios with depth at both sites confirms previous work suggesting that the decoupling between si and c cycles in the southern ocean is not different from other biogeochemical provinces of the world s ocean comparison of the seasonal flux pattern registered by the traps indicates that the diatom assemblages in the sediments of the antarctic zone and pfz mainly represent the summer period in contrast the assemblages found in the sediments of the saz are a reflection of the spring and summer months a period characterized by a larger variability in chemical and physical parameters the strong correlation between the poc fluxes and the relative abundance of a group of diatom species mainly pseudo nitzschia and small fragilariopsis in the pfz traps suggest that there is an intimate relationship between the development of these species and the poc pulses to the deepest layers of the water column in this region interestingly analysis of the diatom assemblages in the surface sediments reveals that the strong dissolution in the sediment water interface removed the signal of these carbon sinkers from the sedimentary record leaving the sediment assemblage enriched in heavily silicified species

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

seasonally laminated diatom rich sediments from dumont d urville trough east antarctic margin late holocene neoglacial sea ice conditions laminated sediments are unique archives of palaeoenvironmental and palaeoceanographic conditions recording changes on seasonal and interannual timescales diatom rich laminated marine sediments are examined from dumont d urville trough east antarctic margin to determine changes in environmental conditions on the continental shelf from 1136 to 3122 cal yr bp scanning electron microscope backscattered electron imagery bsei and secondary electron imagery are used to analyse diatom assemblages from laminations and to determine interlamina relationships diatom observations are quantified with conventional assemblage counts laminae are primarily classified according to visually dominant species identified in bsei and secondarily by terrigenous content nine lamina types are identified and are characterized by hyalochaete chaetoceros spp resting spores crs crs and fragilariopsis spp fragilariopsis spp corethron pennatum and rhizosolenia spp c pennatum rhizosolenia spp mixed diatom assemblage stellarima microtrias resting spores rs porosira glacialis rs and coscinodiscus bouvet and p glacialis rs formation of each lamina type is controlled by seasonal changes in sea ice cover nutrient levels and water column stability quantitative diatom assemblage analysis revealed that each lamina type is dominated by crs and fragilariopsis sea ice taxa indicating that sea ice cover was extensive and persistent in the late holocene however the lamina types indicate that the sea ice regime was not consistent throughout this period notably that a relatively warmer period 3100 to 2500 cal yr bp was followed by cooling which resulted in an increase in year round sea ice by 1100 cal yr bp

palaeoceanographic reconstruction of surface ocean changes in the southern norwegian sea for the last 130 000 years based on diatoms and with comparison to foraminiferal records abstract fossil marine diatom assemblages in a sediment core from the central northern faroe slope in the norwegian sea were used to reconstruct palaeoceanographic changes in the surface water mixed layer from the last 130 000 years marine isotope stage mis 6 5 transition to mis 1 including the eemian and holocene interglacials and to compare the results with previously published results on planktic foraminifera representing the subsurface conditions of the thermocline diatom floras from mis 5 of the nordic seas have rarely been studied in detail before and never the entire period from pre eemian to present the composition of diatom species together with maxima in absolute abundance of diatoms indicate two periods of warmer sea surface temperatures correlating with the eemian and holocene interglacials respectively the eemian differs from the holocene in that the iceland faroe front never developed suggesting the cold east icelandic current originating from the east greenland current running north of iceland was reduced or more mixed with atlantic water than during the holocene and that the surface temperature and salinity gradients were weaker the northern faroe slope was in the early weichselian of mis 5d 5a mainly influenced by weaker inflow of atlantic water and stronger influence of the east icelandic current and by seasonal sea ice cover during the later part of the weichselian mis 4 mis 2 cold conditions prevailed with extensive sea ice cover except during the warmer interstadials the diatom floras were more sensitive to climate changes than the planktic foraminifera and indicate longer periods with warm surface conditions and increased influence of the warm atlantic surface water from the faroe current in mis 5 suggesting a shallower and much steeper thermocline during the transitional periods compared to today the diatoms are good indicators for atlantic water inflow and possible convection in the nordic seas not merely reflecting orbital variations in insolation as previously suggested

submillennial variations in ocean conditions during deglaciation based on diatom assemblages from the southwest atlantic we present a high resolution paleoceanographic record of deglaciation based on diatom assemblages from a core located just south of the polar front in the southwest atlantic core kc073 is from a sediment drift at the mouth of the falkland trough and contains sediments from the last glacial maximum lgm to present dated using radiocarbon dates on bulk organic matter and radiolarian stratigraphy the site lies along the path of the antarctic circumpolar current acc and immediately downstream of where north atlantic deep water nadw is entrained into the acc significant variations in ocean conditions are reflected in high amplitude changes in diatom concentrations and assemblage composition the diatom assemblage at the lgm indicates that winter sea ice extent was at least 5 farther north than present until at least 19 0 ka calendar years and summer sea ice may have occasionally extended over the site but for the most part it lay to the south during deglaciation chaetoceros resting spores crs dominate the diatom assemblage with valve concentrations in excess of 500 106 valves per gram submillennial scale variations in the numbers of crs and thalassiosira antarctica occur throughout the late deglacial and dominate the changes in diatom concentration we propose that the influx of crs is controlled by the flow of nadw over the falkland plateau as such our data provide unique evidence that nadw impacted on this sector of the southern ocean during deglaciation during the holocene the sedimentation rate dramatically reduced we suggest that the acc flow increased over the site and inhibited settling and winnowed the surface sediments

last glacial holocene climate variability in the atlantic sector of the southern ocean abstract the southern ocean plays a major role in the glacial interglacial global carbon cycle however there is a substantial lack of information from its antarctic zone south of the polar front pf to understand key climate processes e g sea ice variability productivity changes co2 source region shifts of the southern westerly wind active in this region during the glacial interglacial transition due to the limited high resolution sediment records from this area to close this gap we investigated high resolution diatom records from a series of sediment cores from the atlantic and western indian sectors of the southern ocean between the modern pf and the winter sea ice wsi edge summer sea surface temperature ssst and sea ice information spanning the past 30 thousand years were derived from diatom transfer functions and indicators which augment comprehensive information on past surface ocean conditions and related ocean and atmospheric circulation as well as opal deposition these complementary lines of evidences also provide important environmental boundary conditions for climate simulations understanding the past climate development in the high latitudes southern ocean our reconstructions show that the last glacial lg sssts south of the modern pf are 1 3 c colder than modern conditions wsi expanded to the modern pf our data suggests effective carbon export in the antarctic zone during the lg deglacial two steps of warming support the bipolar seesaw mechanism antarctic zone is an important source region for the co2 deglacial increase the warming was more suppressed towards south due to continuous ice discharge from antarctica the sssts exceeded modern values during the early holocene optimum when wsi extent probably retreated south of its modern position the southern boundary of maximum opal deposition zone may have shifted to south of 55 s in the bouvet island area at this time the mid late holocene cooling with wsi re expanding to the bouvet island area probably related to enhanced cold water export by the weddell gyre from the developing cavity under the west antarctic ice shelf the cooling also suggests a northward shift of the southern westerly wind at least its southern boundary

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 1 total diatom abundance 1 late pleistocene to holocene climate variability in the antarctic peninsula is described from ocean drilling program odp leg 178 site 1098 palmer deep using total diatom abundance valves per gram dry sediment as a paleoproductivity proxy diatom frustules are absent in the diamicton at the base of the core which was deposited prior to age calibrated circa 13 2 ka immediately above the diamicton frustules are in low abundance as rare fragments and become increasingly more abundant and well preserved up core a rapid and major increase in productivity after circa 12 8 ka is evident from distinctly laminated sediments that overlie the diamicton the strongly laminated section was deposited during a deglaciation phase that followed the retreat of grounded ice after the last glacial maximum diatom productivity decreased during a climatic cooling and or change in meltwater supply until circa 9 0 ka between 9 0 and 4 4 ka productivity increased steadily again with diatom abundance maxima reached during a mid holocene climatic optimum the optimum is interrupted by a brief cold event of 1000 years duration 6 0 5 0 ka after 4 4 ka productivity generally decreased and the last 500 years have experienced the lowest diatom productivity of the postglacial period the palmer deep sediment is compared to ice core and lake sediment records from other regions around the antarctic peninsula these diverse data sets confirm that the antarctic peninsula has been a region of rapid and variable climate fluctuation since the last glacial maximum

rare earth element geochemistry of shallow carbonate outcropping strata in saudi arabia application for depositional environments prediction abstract the interpretation of depositional environments provides important information to understand facies distribution and geometry the classical approach to interpret depositional environments principally relies on the analysis of lithofacies biofacies and stratigraphic data among others an alternative method based on geochemical data chemical element data is advantageous because it can simply reproducibly and efficiently interpret and refine the interpretation of the depositional environment of carbonate strata here we geochemically analyze and statistically model carbonate samples n 156 from seven sections of the arab d reservoir outcrop analog of central saudi arabia to determine whether the elemental signatures major trace and rare earth elements rees can be effectively used to predict depositional environments we find that lithofacies associations of the studied outcrop peritidal to open marine depositional environments possess altered ree signatures and that this trend increases stratigraphically from bottom to top which corresponds to an upward shallowing of depositional environments the relationship between rees and major minor and trace elements indicates that contamination by detrital materials is the principal source of rees whereas redox condition marine and diagenetic processes have minimal impact on the relative distribution of rees in the lithofacies in a statistical model factor analysis and logistic regression rees major and trace elements cluster together and serve as markers to differentiate between peritidal and open marine facies and to differentiate between intertidal and subtidal lithofacies within the peritidal facies the results indicate that statistical modelling of the elemental composition of carbonate strata can be used as a quantitative method to predict depositional environments and regional paleogeography the significance of this study lies in offering new assessments of the relationships between lithofacies and geochemical elements by using advanced statistical analysis a method that could be used elsewhere to interpret depositional environment and refine facies models

sedimentation of biogenic siliceous particles in antarctic waters from the atlantic sector abstract sediment traps were deployed in the drake passage bransfield strait and west of south orkney islands powell basin during december 1980 january 1981 december 1983 and between march and december 1983 respectively most of the trapped material is biogenic opal except in the lower half of the water column in bransfield strait where large amounts of resuspended aluminosilicates and quartz grains were present frustules and skeletons of siliceous microorganisms diatoms silicoflagellates radiolarians chrysophycean cysts fragments and moults of crustaceans and tests of foraminifera were found quantitatively diatoms are the dominant constituent of the trapped biogenic material alteration of diatom assemblages in the water column is due to mechanical breakdown by grazing zooplankton it mainly affects large frustules e g corethron criophilum castracane in the uppermost part of the water column dissolution of frustules occurs mostly at the sediment water interface and leads to the enrichment of strongly silicified valves e g nitzschia kerguelensis o meara hasle thalassiosira antarctica comber resting spores at the bransfield strait site a large part of biogenic opal was incorporated into fecal pellets of krill and copepods the bulk of pellet content consists of fragmented diatom frustules 1 10 m in size most intact valves found in the sediments have settled through the water column by means other than fecal pellet transport e g settling as solitary particles or incorporated into or attached to marine snow or large amorphous aggregates

deglacial environments in eastern prydz bay east antarctica abstract a high resolution continuous record of diatom census counts and diatom specific biomarkers in sediment core nbp0101 jpc24 allows assessment of oceanographic and environmental conditions in eastern prydz bay during the deglaciation 11 100 9000 cal yr bp at decadal timescale our study improves previous snapshots investigations based on resin embedded thin sections and presents a new proxy that compliments the diatom census counts our results suggest that the ice sheet retreat over the core site is dated at 11 100 cal yr bp setting the onset of local deglaciation and subsequent open marine conditions the glacial retreat in prydz bay is due to global warming initiated at 18 cal ka bp and the regional development of the prydz bay cyclonic gyre our results further demonstrate that the deglaciation in eastern prydz bay can be separated in four phases the first between 11 100 and 10 900 cal yr bp when the ice shelf was proximal and sea ice was almost perennial the second and the third phases between 10 900 10 400 cal yr bp and 10 400 9900 cal yr bp respectively when the ice shelf retreated and seasonal sea ice cycle consequently developed promoting warmer water to pump into the bay within the gyre which in turn forced the ice shelf recession and the yearly sea ice cycle establishment and the fourth between 9900 and 9000 cal yr bp when holocene condition were set with a recurrent seasonal sea ice cycle and a well established prydz bay gyre

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

diatoms preserved in surface sediments of the northeastern kerguelen plateau abstract an island mass effect was observed from the sedimentary distribution of diatoms on the northeastern kerguelen plateau five new samples placed in context to species distributions previously reported from the permanently open ocean zone pooz revealed a plateau community dominated by three species taxa fragilariopsis kerguelensis thalassionema nitzschioides f nitzschioides and chaetoceros hyalochaete resting spores intermediate abundances of thalassiosira antarctica were unique to the plateau sediment signature as were increased abundances of eucampia antarctica v antarctica the off plateau sediment sample contained typical pooz sediment distributions dominated by f kerguelensis thalassiosira lentiginosa and thalassiothrix antarctica the role of deposition from the surface waters to the sediments was investigated by comparison to the diatom thanatocoenose observed in surface waters these results suggest that the use of sediment abundances of c hyalochaete resting spores and f kerguelensis to determine past productivity events such as wind sourced iron enrichment of the southern ocean at the last glacial maximum is not straightforward the elevated abundance of t nitzschioides f nitzschioides on the plateau did not indicate an iron deplete regime but the converse for the evaluation of paleo productivity hypotheses for the open southern ocean we suggest caution in the use of subantarctic and kerguelen plateau sediment signatures and emphasize that there is a need to also study antarctic coastal and especially sea ice melt water stimulated blooms

quaternary surface water temperature estimations calibration of a diatom transfer function for the southern ocean the quantitative diatom analysis of 218 surface sediment samples recovered in the atlantic and western indian sector of the southern ocean is used to define a base of reference data for paleotemperature estimations from diatom assemblages using the imbrie and kipp transfer function method the criteria which justify the exclusion of samples and species out of the raw data set in order to define a reference database are outlined and discussed sensitivity tests with eight data sets were achieved evaluating the effects of overall dominance of single species different methods of species abundance ranking and no analog conditions e g eucampia antarctica on the estimated paleotemperatures the defined transfer functions were applied on a sediment core from the northern antarctic zone overall dominance of fragilariopsis kerguelensis in the diatom assemblages resulted in a close affinity between paleotemperature curve and relative abundance pattern of this species downcore logarithmic conversion of counting data applied with other ranking methods in order to compensate the dominance of f kerguelensis revealed the best statistical results a reliable diatom transfer function for future paleotemperature estimations is presented

late pliocene sea ice expansion and its influence on diatom species turnover in the southern ocean abstract fossil diatom records from the southern ocean are needed to clarify the detailed conditions under warmer than present global climate in the piacenzian stage 3 60 2 588 ma and to provide direct evidence of simultaneity between changes in environmental conditions and diatom species turnovers in this study fossil diatom records between 3 5 and 2 8 ma were investigated at two sites located along a latitudinal gradient within the indian sector of the southern ocean offshore from prydz bay and south east of the kerguelen plateau paleoceanographic changes were assessed from assemblage changes of extant diatom indicators fluctuations of their relative percentages were compared with those of extinct diatom species the diatom assemblage between 3 5 and 3 1 ma consisted of open ocean species which indicate warmer than present sst notable increases in sea ice associated species were identified at 3 3 ma and 3 1 ma at both sites our results suggest sea ice existence during short intervals of 3 3 ma and 3 1 2 8 ma at the studied area at both sites relative abundances of species which have first occurrences during the piacenzian increased at 3 2 3 1 ma conversely those of species which have last occurrences during the piacenzian decreased at the same period these diatom records show a correlation with cooling at 3 1 ma suggested from extant indicators and compositional changes in fossil diatoms from the southern ocean this comparison can provide insights into the environmental effects on diatom evolutionary acceleration which can help identify ecologies of extinct species

distribution of chaetoceros resting spores in modern peri antarctic sediments abstract one hundred and sixty five surface sediment samples from the southern ocean were examined for distribution and relative abundance of chaetoceros resting spores the contribution of resting spores to the total diatom assemblage ranges from 0 in the subantarctic zone to 95 in the antarctic peninsula sector on the basis of both absolute and relative abundances four biogeographic zones are distinguished 1 the antarctic peninsula sector 2 the embayment systems ross sea and weddell sea 3 the continental shelf zone water depth 2000 m chaetoceros resting spores abundance reaches up to 900 10 6 valves g of dry sediment in the gerlache strait southwest of the antarctic peninsula the hydrology of this region is characterized by an intense stratification of the water column due to sea ice meltwater inputs continental glacial runoffs and thermal warming of the surface water layer the availability of nutrients the lack of vertical mixing in those surface waters having low salinity 2 4 c is thought to be the main pre condition for development of large chaetoceros species blooms we propose that increased relative abundances of chaetoceros resting spores in fossil diatom assemblages from the southern ocean can therefore be used as tracers of water column stratification due to glacial melt water

diatom evidence of hydrographic changes and ice conditions in igaliku fjord south greenland during the past 1500 years biostratigraphic diatom analyses were carried out on two sediment cores from igaliku fjord south greenland in order to reconstruct hydrographic and climatic fluctuations during the late holocene ad 550 to present pronounced differences in hydrographic setting of the coring sites provide palaeoenvironmental information of both local and more regional character five diatom zones were identified from the subfossil diatom records each describing a hydrographic setting two major climate periods the mediaeval warm period ad 800 1250 and the little ice age ad 1580 1850 that were separated by a variable transitional period were recognized prior to these periods a cold and presumably moist climate regime prevailed between ad 500 and 700 cooling events were identified during the mediaeval warm period in the period ad 960 to 1140 the diatom data demonstrate that marked hydrographic changes occurred in the course of a relatively short timespan beginning at about ad 1300 and culminating around

sedimentary processes on the wilkes land continental rise reflect changes in glacial dynamic and bottom water flow four sediment cores were analysed in order to determine the sedimentary processes associated with the channel ridge depositional system that characterise the george v land continental margin on the wilkes land the sedimentary record indicates that the wega channel was a dynamic turbiditic system up to m i s 11 after this time the channel became a lower energy environment with sediments delivered to the channel through high density bottom waters that we identify to be the high salinity shelf waters hssw forming on the shelf area the hssw entrains the fine grained sediments of the shelf area and deliver them to the continental rise the biostratigraphy and facies of the sediments within the wega channel indicate that the hssw down flow was active also during last glacial the change from a turbiditic system to a low energy bottom current system within the wega channel likely reflects a different ice flow pattern with ice sheet reaching the continental shelf edge only within the ice trough ice stream

distribution of diatom surface sediment assemblages within effingham inlet a temperate fjord on the west coast of vancouver island canada abstract twenty nine surface sediment samples from effingham inlet a small fjord on the west coast of vancouver island british columbia were analyzed for diatoms this fjord has been selected for paleoceanographic investigation due to the presence of laminated sediments resulting from the dysoxic to anoxic bottom water conditions in the inner and outer basins of the inlet distributional patterns of the diatom microflora reflected proximity to littoral regions phytoplankton production and marine influence from outside the fjord principal components and cluster analyses of the microflora established four diatom assemblages with a clear separation between the inner and outer basin diatom floras inner basin stations were characterized by elevated absolute abundance with assemblages dominated by spring early summer bloom taxa including skeletonema costatum thalassiosira nordenskioeldii and thalassiosira pacifica chaetoceros spp resting spores were abundant throughout effingham inlet with the exception of the stations closest to the fjord head stations located in the outer basin and towards the fjord mouth had relatively lower absolute abundance yet showed a higher relative and absolute abundance of thalassionema nitzschioides rhizosolenia setigera coscinodiscus radiatus ditylum brightwellii odontella longicruris and paralia sulcata in relation to the inner basin many of these latter taxa are often associated with late summer and autumn conditions in fjords along coastal british columbia oceanographic data for effingham inlet suggest that increased offshore penetration is more likely to occur from summer to early fall with a more restricted offshore influence in the inner basin diatom surface sediment assemblages in effingham inlet appear to reflect incursions of offshore waters into the fjord absolute abundance estimates and the preservation of lightly silicified taxa suggest excellent preservation of fossil material in the sediments of the predominantly anoxic inner basin preservation in the outer basin is reduced reflecting more frequent recharge by oxygenated waters spilling over the outer sill into the basin our findings suggest the inner basin should be an optimal site for reconstruction of diatom production with records from the outer basin providing more consistent information about offshore influence and coastal upwelling conditions over the holocene estimates of diatom abundance within the inner basin sediment may serve as a good proxy of production although proxy tracers of bottom water conditions and sedimentological analyses must be coupled to the diatom record to ensure depositional conditions were not influencing valve preservation or abundance our results suggest that fjords can serve as good environments for paleoceanographic reconstructions of both inshore and offshore conditions although careful site selection and understanding of processes affecting the microfossil record are essential

paleogeography of the sea of azov region in the late holocene reconstruction by diatom and pollen data from marine sediments this paper presents new available high resolution pollen and diatom evidences relief and sedimentation processes during the new azov stage of the sea development as well as the reconstruction of environmental changes in the late holocene according to data obtained from the southern steppe landscapes that are similar to the modern ones were widespread in the area adjacent to the sea of azov during the formation of the new azov layers the last three thousand years however the late holocene trend to climate aridization was interrupted by three phases of cool and more humid conditions late subboreal 3000 2300 cal calendar years bp middle subatlantic 2000 1700 cal bp and the little ice age 600 150 cal bp diatom data suggest that during the first and second phases of cooling the sea of azov was characterized by conditions of shallow waters with relatively high salinity and specific hydrodynamics

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

microfossil and stable isotope evidence for changes in late holocene palaeoproductivity and palaeoceanographic conditions in the prydz bay region of antarctica microfaunal and microfloral data from two gravity cores and stable isotope results from one of these cores taken on fram bank near prydz bay antarctica indicate changes in sea ice patterns and oceanographic conditions which may have been linked to regional and global climate changes that occurred over the past 8000 yr modern diatom assemblages indicative of ice free conditions 1 2 months of the year and dominated by nitzschia species became prevalent some time around 2000 2700 yr b p the occurrence of chaetoceros spp diatom spore dominated assemblages and increased abundances of benthic and planktonic foraminifera ostracods and diatoms coupled with carbon and oxygen isotope changes around 2700 3400 yr b p strongly suggests that this area of the shelf experienced conditions conducive to increased productivity during this time period based on diatom assemblage associations recognized in modern environments the upper water column of fram bank shelf waters was probably stratified during that time due to the presence of low salinity melt water and a very shallow mixed layer protected from storms with sea ice cover for less than 10 months per year the close correspondence of 13c and 18o values from n pachyderma r2 0 74 throughout one core suggests that whatever oceanographic conditions influenced 18o also influenced 13c changes in prydz bay microfossil abundances and isotopes may result from alterations in circulation patterns upwelling conditions or sea ice patterns which significantly affected benthic and planktonic productivity in the area the environmental conditions indicated by older sediments in the cores are less clear but an ice tongue may have been in place 3200 3800 yr b p and minor fluctuations in productivity are indicated around 6000 and 7000 7500 yr b p the lower 100 cm of both cores may not represent in situ deposition but if the corrected ams dates reflect the actual age of the sediments analyzed microfossil and isotope data indicate that productivity and oceanographic conditions were very variable around 8500 8600 yr b p the chronology adopted herein must be regarded as tentative until further study of the area has been undertaken

palaeoclimatic changes in kveithola svalbard during the late pleistocene deglaciation and holocene evidences from microfossil and sedimentary records abstract climate changes are reflected in the arctic ecosystem history over different timescales we use a multi proxy based approach for palaeoenvironmental and palaeoclimatic reconstructions conducted on sediment cores compared with summer insolation and greenland ice core 18o data in order to establish a framework for climate changes from late pleistocene to late holocene our dataset includes the results compiled from a sediment core collected on the middle slope of the kveithola trough mouth fan south of svalbard during the coribar cruise 2013 the studied core presents remarkable lithological and magnetic susceptibility similarities with cores recovered in the same area during the svais 2007 and the ogs eglacom cruise 2008 allowing the construction of the age model the results indicate that during the last 14 5 cal ky bp advances and retreats of the svalbard barents sea ice sheet were strictly linked to the interplay of atlantic and arctic water inflows to the study area during the deglaciation from the last glacial maximum to the onset of the holocene the climate underwent a series of abrupt changes including the bolling allerod warm interstadial and the younger dryas cold event during the early holocene the investigated area was dominated by enhanced warm atlantic water inflow which was concomitant with summer insolation increase characterizing the holocene thermal maximum conversely the late holocene was governed by deteriorating climatic conditions with predominant arctic polar water inflow on the surface water masses off western svalbard possibly associated with summer insolation decline due to orbital forcing