resolving sea ice dynamics in the north western ross sea during the last 2 6 ka from seasonal to millennial timescales abstract time series analyses of satellite images reveal that sea ice extent in the ross sea has experienced significant changes over the last 40 years likely triggered by large scale atmospheric anomalies however resolving how sea ice in the ross sea has changed over longer timeframes has until now remained more elusive here we used a laminated sediment piston core 14 6 m collected from the edisto inlet western ross sea to reconstruct fast ice dynamics over the last 2 6 ka our goal was to first understand the climate expression of selected well defined sediment laminae and then use these characteristics for reconstructing past sea ice behaviour across the whole sedimentary sequence we used the recently established sea ice diatom biomarker proxy ipso25 in combination with diatom census counts and bulk analyses analyses performed on a suite of discrete laminae revealed statistically significant differences between dark and light laminae reflecting different depositional conditions based on their respective biogeochemical fingerprints we infer that dark laminae accumulated during sea ice thaws in early summer under these conditions laminae contain relatively high concentrations of ipso25 and display an enriched 13c composition for the bulk organic matter om while diatom assemblages in dark laminae are relatively homogenous as the thaw continues later in the summer corethron pennatum becomes the dominant diatom species resulting in the formation of light laminae characterized by low ipso25 concentrations since c pennatum can migrate vertically through the water column to uptake nutrients and avoid competition in oligotrophic waters its high concentration likely reflects stratified and ice free surface waters typical of late summer down core trends show that the correlation between sediment brightness and geochemical fingerprint i e ipso25 and 13c holds throughout the record based on the knowledge gained at lamina level our down core high resolution reconstruction shows that the summer fast ice coverage changed dramatically during the late holocene specifically we conclude that the edisto inlet experienced regular early summer opening between 2 6 ka and ca 0 7 ka after which coastal fast ice persisted during summer months and ice free conditions became less frequent comparison with previous regional ice core data suggests that the sudden cooling recorded over the victoria land coast region since 0 7 ka might potentially explain our observation of persistent summer fast ice in the western ross sea our study has shown that multi proxy data derived from laminated sediments can provide hitherto unknown detail regarding past summer sea ice dynamics in coastal antarctic regions

biological forcing of hemipelagic sedimentary laminae evidence from odp site 893 santa barbara basin california core observation x radiography and scanning electron microanalysis of distinctly laminated indistinctly laminated and nonlaminated sediments from odp site 893 show that laminated as well as nonlaminated i e massive hemipelagic sediments can form in the absence of bioturbation this view contrasts with conventional sedimentological interpretations equating laminated hemipelagic sediments with anoxic water masses i e absence of bioturbation and nonlaminated sedimentary intervals exclusively with oxygenation episodes that permitted infaunal colonization we conclude that heterogeneities in the texture and or composition of sediment supply are necessary for the production of laminated sediments the absence of hydraulic and biological reworking permits their preservation laminae at site 893 have two prominent components biosilica and terrigenous detritus compositional contrasts between adjacent laminae in x radiographs reflect short term seasonal and subseasonal heterogeneities in sediment flux core intervals with large contrasts in density and or composition between adjacent laminae are termed as having high bimodality hb hb couplets produce distinctly laminated sediments that intergrade vertically with indistinctly laminated and nonlaminated sediments adjacent laminae in indistinctly laminated sediments possess minimal contrasts in bulk density and composition nonlaminated sediments are compositionally and texturally homogeneous many biosiliceous laminae responsible for distinctly laminated hb couplets record mass flocculation and sedimentation of ungrazed diatom frustules formed during discrete bloom events ecological interpretation of diatomite laminae suggests that many were effectively self sedimenting i e the production of gelatinous exudates by phytoplankton facilitated their aggregation and rapid sedimentation the results indicate that lamination style preserves meaningful ocean climate data concerning episodicity heterogeneity and export efficiency of biologically mediated sedimentary flux in upwelling dominated coastal ecosystems

glacial morphology and sediment formation in the mertz trough east antarctica abstract the nathaniel b palmer 01 01 cruise produced a seabeam map showing unprecedented detail of the bathymetry in the mertz trough of east antarctica in addition seismic reflection surveys and sediment core collection were completed in the region the morphology of the mertz trough is combined with core data to interpret the sequence of events that occurred in this area since the last glacial maximum these complementary data indicate that an ice sheet once covered the mertz trough which deposited diamicton and formed mega scale glacial lineations during glacial maximal conditions and grounding line wedges during recession an erosional feature caused by subglacial meltwater breaching at least one of the grounding line deposits is also recognized along with a fan of sediment deposited seaward of the breach sediment cores from the mertz trough consist of two distinct units the diamicton deposited subglacially and a diatom mud and ooze deposited after the ice retreated the latter unit has been preferentially deposited in deeper areas of the trough as a hemipelagic drape and shows that a change in the nature of the diatom unit occurred about 3300 14c yr bp

an experimental study of the partitioning of copper between pyrrhotite and a high silica rhyolitic melt the partitioning of copper has been investigated experimentally between a natural pyrrhotite and a natural high silica rhyolitic melt under water saturated conditions at 800 degrees c 1 kbar and two oxygen fugacities the partition coefficients d super po melt cu defined as the ratio of the concentrations of copper in pyrrhotite to copper in melt are 910 or 436 1sigma at the c ch 4 buffer and 554 or 220 1sigma at one half of a log unit above nno the mean value for all determinations is 773 or 400 1sigma although the experimental results show wide scatter at test indicates that the partition coefficients at the two oxygen fugacities may be considered significantly different at the 88 percent confidence level the results are consistent with hypothetical chemical potential equilibria and with previous field and experimental data estimates obtained through mathematical modeling suggest that such partition coefficients may result in sequestration of 98 percent of the copper by pyrrhotite in a relatively s rich and h 2 o poor magma whereas 24 percent of the copper may be sequestered by pyrrhotite in a relatively low sulfur magma in which water saturation and evolution of an aqueous fluid occur early the results may provide significant constraints in interpretation of the behavior of cu in felsic magmatic systems and in application of the orthomagmatic hydrothermal hypothesis to geologic processes associated with porphyry type copper deposits

pollen evidence for variations in the southern margin of the westerly winds in sw patagonia over the last 12 600 years we report pollen and charcoal records from vega nandu 51 0 s 72 45 w a small mire located near the modern forest steppe ecotone in torres del paine national park southern chile the record shows an open landscape dominated by low shrubs and herbs between 12 600 and 10 800 cal yr bp under cold and relatively humid conditions nothofagus experienced frequent large amplitude oscillations between 10 800 and 6800 cal yr bp indicating recurrent transitions between shrubland parkland environments under warm and highly variable moisture conditions a sustained increase in nothofagus started at 6800 cal yr bp punctuated by step wise increases at 5100 and 2400 cal yr bp implying further increases in precipitation we interpret these results as indicative of variations in the amount of precipitation of westerly origin with prominent increases at 6800 5100 and 2400 cal yr bp these pulses led to peak precipitation regimes during the last two millennia in this part of sw patagonia our data suggest variations in the position and or strength of the southern margin of the westerlies most likely linked to variations in the extent and or persistence of sea ice and sea surface temperature anomalies in the southern ocean over the last two centuries the record shows a forest decline and expansion of rumex acetosella an exotic species indicative of european disturbance 2007 university of washington all rights reserved

seismic stratigraphy of palmer deep a fault bounded late quaternary sediment trap on the inner continental shelf antarctic peninsula pacific margin abstract the palmer deep is an enclosed bathymetric depression on the inner portion of the antarctic peninsula continental shelf about 30 km southwest of anvers island three sub basins separated by bathymetric sills comprise the palmer deep basin i basin ii and basin iii deep tow boomer seismic reflection data reveal thick 50 m sediment sections in each basin consisting of holocene diatomaceous mud the boomer records proved fine scale resolution of decimetre thick sediment layers within the uppermost holocene seismic unit deeper penetration gi and small airgun records obtained in 1997 provide insight into the structural and depositional history of the basins which extends clearly back in time before the holocene unit imaged by the boomer records the palmer deep contains a sediment infill estimated at about 270 m thick arranged in a complex five unit internal stratigraphy unusual for the inner continental shelf of antarctica combined use of the boomer and airgun sources allows complementary resolution of both deep and shallow stratigraphy with some reflectors common in both records such as the middle basin reflector at 45 ms twt below seafloor the middle basin reflector most likely is of latest pleistocene age isotopic stage 2 and therefore 80 of the basin fill pre dates the classic last glacial maximum the palmer deep is bounded by active extensional faults as evidenced by offset and stratigraphic growth within holocene sections to accommodate shelf wide glaciation on the pacific margin of the antarctic peninsula we suggest a subglacial and subaqueous origin for much of the palmer deep basin fill hence the palmer deep basins were the locus of subglacial lakes beneath the ice sheet at times of glacial maximum

sea ice and wind variability during the holocene in east antarctica insight on middle high latitude coupling abstract micropaleontological and biomarker data from two high accumulation marine sites from the coastal and continental shelf zone ccsz off east antarctica adelie land at 140 e and eastern prydz bay at 77 e are used to reconstruct holocene changes in sea ice and wind stress at the basin wide scale these data demonstrate congruent increase in sea ice concentration persistence and wind stress related sea surface turbulence in the two regions since 7 cal ka bp with a particularly strong signal since 4 5 3 5 cal ka bp comparison of these high latitude records with sea ice and turbulence records from the southern mid latitudes highlights distinctive climatic evolutions according to the different latitudinal bands sea ice persistence and turbulence increase in east antarctica ccsz are opposite to sea surface warming and sea ice retreat recorded after 4 5 3 5 cal ka bp in the east atlantic and indian sector between 55 and 45 s at the same period paleodata suggest sst cooling in all major coastal upwelling systems of the southern hemisphere caused by the northward transport of subpolar surface waters as a response to southern westerlies reinforcement we therefore propose as suggested for the northern hemisphere that holocene changes in the latitudinal insolation gradient primarily forced by obliquity and precession and amplified by sea ice and glacial ice expansions in the antarctic realm are responsible for the observed contrasted latitudinal patterns of southern latitudes

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

high resolution holocene climate record from maxwell bay south shetland islands antarctica the highest resolution holocene sediment core from the antarctic peninsula to date was collected during the first shaldril cruise nbp0502 drilling yielded a 108 2 m long core 87 recovery site nbp0502 1b from maxwell bay south shetland islands this high resolution sediment record comes from a region that is currently experiencing dramatic climate change and associated glacial retreat such records can help to constrain the nature of past climate change and causal mechanisms and to provide a context for evaluating current climate change and its impacts the base of the drill site sampled till and or proximal glacimarine sediments resting directly on bedrock glacimarine suspension deposits composed of dark greenish gray silty mud with variable diatom abundance and scattered very fine sand laminations make up the majority of the sedimentary section detailed sedimentological and geochemical analyses including magnetic susceptibility total organic carbon toc content carbon and nitrogen isotopic composition pebble content and biogenic silica content allow subdivision of the glacimarine section into nine units and seismic facies analyses resulted in the identification of six distinct seismic units we used 29 radiocarbon ages to construct an age model and calculate sedimentation rates that vary by two orders of magnitude from 0 7 mm a to 30 mm a radiocarbon ages from glacimarine sediments just above the till date back to between 14 1 and 14 8 ka thus ice was grounded in the fjord during the last glacial maximum and eroded older sediments from the fjord following initial retreat of grounded ice from maxwell bay the fjord was covered by a permanent floating ice canopy probably an ice tongue the highest sedimentation rate corresponds to an interval that contains abundant sand laminations and gravelly mud intervals and likely represents a melt out phase or period of rapid glacial retreat from 10 1 ka to 8 2 ka there is no evidence for an early holocene climatic reversal as recorded farther south at the palmer deep drill site minimum sea ice cover and warm water conditions occurred between 8 2 and 5 9 ka from 5 9 to 2 6 ka there was a gradual cooling and more extensive sea ice cover in the bay after 2 6 ka the climate varied slightly causing only subtle variation in glacier grounding lines there is no compelling evidence for a little ice age readvance in maxwell bay the current warming and associated glacial response in the northern antarctic peninsula appears to be unprecedented in its synchroneity and widespread impact

deglacial seasonal and sub seasonal diatom record from palmer deep antarctica the antarctic peninsula is one of the most sensitive regions of antarctica to climate change here ecological and cryospheric systems respond rapidly to climate fluctuations a 4 4m thick laminated diatom ooze deposited during the last deglaciation is examined from a marine sediment core odp site 1098 recovered from basin i palmer deep western antarctic peninsula this deglacial laminated interval was deposited directly over a glaciomarine diamict hence during a globally recognised period of rapid climate change the ultra high resolution deglacial record is analysed using sem backscattered electron imagery and secondary electron imagery laminated to thinly bedded orange brown diatom ooze near monogeneric hyalochaete chaetoceros spp resting spores alternates with blue grey terrigenous sediments open water diatom species these discrete laminae are interpreted as austral spring and summer signals respectively with negligible winter deposition sub seasonal sub laminae are observed repeatedly through the summer laminae suggesting variations in shelf waters throughout the summer tidal cycles high storm intensities and or intrusion of circumpolar deep water onto the continental shelf introduced conditions which enhanced specific species productivity through the season

subglacial morphology and glacial evolution of the palmer deep outlet system antarctic peninsula abstract the palmer deep is an erosional inner shelf trough located at the convergence of ice flow from three distinct accumulation centers it served as a funnel for ice flow out across the continental shelf of the antarctic peninsula swath mapping of 1440 km 2 of seafloor in and adjacent to the palmer deep basin defines a large paleo ice stream that flowed 230 km across the antarctic peninsula continental shelf during the last glacial maximum mis 2 the unique perspective and detail of the palmer deep physiography allow us to recognize several phases of erosion and deposition in the outlet basin these events are uniquely constrained by two odp drill cores sites 1099 and 1098 that together recovered over 150 m of latest pleistocene and holocene sediment we divide this region of the continental shelf into three zones based upon mega to meso scale bathymetric features and emphasize that all three were part of one glacial outlet during the most recent period of glaciation these zones include from inner shelf to outer shelf the palmer deep basin the palmer deep outlet sill and the hugo island trough specific seafloor features associated with these zones include relict terraces sub glacial lake deltas channels and levees debris slopes spindle and out bed forms mega scale glacial lineations morainal banks and bank breach points the origin of many of these features can be linked to the development of a sub glacial lake basin within the palmer deep during or prior to mis 2 its subsequent drainage and recession of the palmer deep ice stream system this sub glacial lake system is reconstructed at the head of a major paleo ice stream

age assignment of a diatomaceous ooze deposited in the western amundsen sea embayment after the last glacial maximum reliable dating of glaciomarine sediments deposited on the antarctic shelf since the last glacial maximum lgm is challenging because of the rarity of calcareous micro fossils and the recycling of fossil organic matter consequently radiocarbon 14 c ages of the acid insoluble organic fraction aio of the sediments bear uncertainties that are difficult to quantify here we present the results of three different methods to date a sedimentary unit consisting of diatomaceous ooze and diatomaceous mud that was deposited following the last deglaciation at five core sites on the inner shelf in the westernamundsen sea west antarctica in three coresconventional 14 c dating of the aio in bulk samples yielded age reversals down core but at all sites the aio 14 c ages obtained from diatomaceous ooze within the diatom rich unit yielded similar uncorrected 14 c ages between 13517 56 and 11543 47 years before present a bp correction of these ages by subtracting the core top ages which probably reflect present day deposition as indicated by 210 pb dating of the sediment surface at one core site yielded ages between ca 10500 and 8400 cal a bp correction of the aio ages of the diatomaceous ooze by only subtracting the marine reservoir effect mre of 1300 a indicated deposition of the diatom rich sediments between 14100 and 11900 cal a bp most of these ages are consistent with age constraints between 13 0 and 8 0ka for the diatom rich unit which we obtained by correlating the relative palaeomagnetic intensity rpi records of three of the sediment cores with global and regional reference curves as a third dating technique we applied conventional radiocarbon dating of the aio included in acid cleaned diatom hard parts extracted from the diatomaceous ooze this method yielded uncorrected 14 c ages of only 5111 38 and 5106 38 a bp respectively we reject these young ages because they are likely to be overprinted by the adsorption of modern atmospheric carbon dioxide onto the surfaces of the diatom hard parts prior to sample graphitisation and combustion for 14 c dating the deposition of the diatom rich unit in the western amundsen sea suggests deglaciation of the inner shelf before ca 13ka bp the deposition of diatomaceous oozes elsewhere on the antarctic shelf around the same time however seems to be coincidental rather than directly related copyright 2009 john wiley sons ltd

late quaternary glacial history of george vi sound area west antarctica during the last glacial maximum in west antarctica separate ice caps developed on alexander island and on palmer land became confluent in george vi sound and discharged northward from latitude 72 s radiocarbon 32 000 yr and amino acid approximately 120 000 yr age determinations on shell fragments hiatella solida found in basal till suggest a wisconsin age for the glaciation that incorporated them the pattern of ice flow differed from that deduced for this area in the climap reconstruction following the maximum stage there was a stadial event when outlet valley glaciers flowed from smaller ice caps into george vi sound more widespread recession permitted the george vi ice shelf to deposit palmer land erratics on eastern alexander island before isostatic recovery raised them to final elevations of about 82 m the ice shelf may have been absent at about 6500 yr b p when large barnacles bathylasma corolliforme were living in the sound small glaciers readvanced to form at least two terminal moraines before the ice shelf re formed and incorporated the barnacle shells into its moraine on alexander island the shells gave a 14c age corrected for antarctic conditions of about 6500 yr b p and an amino acid ratio consistent with a holocene age valley glaciers readvanced over the ice shelf moraine before oscillations of both valley glaciers and the ice shelf led to the formation of the present sequence of contiguous ice cored moraines probably during the little ice age such oscillations may represent a climatic control not yet observed in the dry valleys of victoria land the only other part of antarctica studied in detail for glacier fluctuations

the fall dump a new perspective on the role of a shade flora in the annual cycle of diatom production and export flux investigations of diatom fluxes recorded in laminated sediments using scanning electron microscope techniques together with evidence from sediment trap studies have contributed to a reappraisal of the annual cycle of diatom production and export flux we propose that where there is a strong seasonal thermocline and nutricline a number of diatoms hitherto regarded as typical sparse summer flora characteristic of oligotrophic waters are able to generate substantial production at depth these species including rhizosolenia spp stephanopyxis palmeriana thalassiothrix spp and some coscinodiscus spp may represent a shade flora that have adapted to grow in low light conditions and or to regulate their buoyancy to move between a deep nutrient source and the euphotic zone although rates of growth and primary production are substantially lower than species characteristic of spring bloom or upwelling conditions the total primary production integrated over the several month period of summer stratification may be as significant as the spring bloom or greater the term fall or autumn bloom as a counterpart of the spring bloom is therefore a misnomer whereas the spring bloom involves a rapid burst of reproduction and sedimentation the fall dump is the sedimentation of a long lived episode of production lasting the duration of the seasonal thermocline and triggered by the fall winter mixing that breaks down stratification the fall dump may produce as much or in some cases more export production than the spring bloom the results of this study suggest that a reorientation of thinking on diatom ecology and palaeoecology may be required

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

millennial to decadal scale paleoenvironmental change during the holocene in the palmer deep antarctica as recorded by particle size analysis 1 a record of holocene paleoenvironmental variability from the antarctic peninsula has been produced using sediment cores from site 1098 gathered on ocean drilling project leg 178 the results provide an accurate and continuous record of biotic and sedimentologic responses to holocene environmental change holes 1098b and 1098c were used to produce the first ultrahigh resolution record of grain size variability for the past 13 000 years we utilized samples every 2 5 cm at 3 5 yr cm 1 which involved the analysis of 1466 samples from two holes at the site particle size was measured on uniform suspensions of dispersed particles using a laser diffraction method the particles are mainly grains of silt 65 85 and clay 15 35 size the analyses revealed that in most intervals biotic particles in the form of diatom frustules mostly spores dominate the silt component which is inversely reflected by magnetic susceptibility ms in intervals of the core that deviate from this relationship it was found that the ms signal correlated with medium to fine or coarse silt that was dominated by terrigenous rather than a biogenic diatom component spectral analyses of the variability in clay and medium fine silt content over the last 9000 calendar years reveal cycles of 1800 400 200 100 70 60 and 50 years the analyses revealed that particle size specifically medium fine silt is an excellent proxy for environmental change in the palmer deep region such changes may be forced by solar variability the 200 and 400 year cycles lunar tidal changes the 1800 year cycles and an as yet undetermined multidecadal forcing phenomena that operates in the se pacific sector of the southern ocean

the role of sex in the sedimentation of a marine diatom bloom a longitudinal transect in the atlantic sector of the southern ocean extending from the ice covered weddell sea across the antarctic circumpolar current and into the polar frontal zone was studied repeatedly during the austral spring the centric diatom corethron criophilum was found at most stations in variable numbers but in the polar frontal zone i encountered a large bloom undergoing a mass sexual phase this event apparently triggered downward transport of empty diatom cell walls in numbers that suggest the phenomenon is significant for the vertical silica flux and the formation of monospecific layers of this important diatom species in southern ocean sediments comparison of the cell wall dimensions of such a monospecific layer with those in the plankton in the sexual phase reveals a characteristic signature that may indicate the provenance of these layers

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

silica cycling and isotopic composition in northern marguerite bay on the rapidly warming western antarctic peninsula the southern ocean is a key region for silica si cycling and the isotopic signatures established here influence the rest of the world s oceans the climate and ecosystem of the southern ocean are changing rapidly with the potential to impact si cycling and isotope dynamics this study examines high resolution time series dataset of dissolved si concentrations and isotopic signatures particulate si concentrations and diatom speciation at a coastal site on the western antarctic peninsula wap in order to characterise changes in si cycling with respect to changes occurring in productivity and diatom assemblages dissolved and particulate si phases reflect the dominant control of biological uptake and combined with isotopic fractionation were consistent with a season of low intermediate productivity biogenic si is tightly coupled to both chlorophyll and particulate organic carbon at the sampling site consistent with diatom dominated phytoplankton assemblages along the wap variability in diatom speciation has a negligible impact on the isotopic signature of dissolved si in surface waters although this is unlikely to hold for sediments due to differential dissolution of diatom species a continued decline in diatom productivity along the wap would likely result in an increasing unused si inventory which can potentially feed back into si limited areas promoting diatom growth and carbon drawdown further afield

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

productivity cycles of 200 300 years in the antarctic peninsula region understanding linkages among the sun atmosphere oceans sea ice and biota compared to the rest of the world9s oceans high resolution late holocene paleoclimatic data from the southern ocean are still rare we present a multiproxy record from a sediment core retrieved from a deep basin on the western side of the antarctic peninsula that reveals a dramatic perspective on paleoclimatic changes over the past 3700 yr analyses completed include measurement of magnetic susceptibility and granulometry bed thickness particle size percent organic carbon bulk density and microscopic evaluation of diatom and benthic foraminiferal assemblages and abundances downcore variability of these parameters demonstrates the significance of both short term cycles which recur approximately every 200 yr and longer term events 2500 yr cycles that are most likely related to global climatic fluctuations in the upper 600 cm of the core lower values of magnetic susceptibility ms are correlated with lower bulk density the presence of thinly laminated units specific diatom assemblages and generally higher total organic carbon content below 600 cm magnetic susceptibility is uniformly low though variability in other parameters continues the magnetic susceptibility signal is controlled primarily by dilution of ferromagnetic phases with biosiliceous material this signal may be enhanced further by dissolution of magnetite in the magnetic susceptibility lows high total organic carbon the role of variable primary productivity and its relationship to paleoclimate is assessed through the diatom data in particular magnetic susceptibility lows are characterized by higher than normal abundances of chaetoceros resting spores corethron criophilum and or rhizosolenia spp also are found as is a higher ratio of the most common species of fragilariopsis versus species of thalassiosira these assemblages are indicative of periods of high primary productivity driven by the presence of a meltwater stabilized water column the 200 yr cyclicity noted in other paleoclimatic records around the world suggests a global forcing mechanism possibly solar variability in addition to the cyclic changes in productivity overall elevated productivity is noted below 600 cm or prior to ca 2500 yr b p this increased productivity may represent the tail end of a holocene climatic optimum which is widely recognized in other parts of the world but as yet is poorly documented in antarctica

late holocene glacial advance and ice shelf growth in barilari bay graham land west antarctic peninsula three marine sediment cores were collected along the length of the fjord axis of barilari bay graham land west antarctic peninsula 65 55 s 64 43 w multi proxy analytical results constrained by high resolution geochronological methods 210 pb radiocarbon 137 cs in concert with historical observations capture a record of holocene paleoenvironmental variability our results suggest early and middle holocene 7022 2815 cal calibrated yr b p retreated glacial positions and seasonally open marine conditions with increased primary productivity climatic cooling increased sea ice coverage and decreased primary productivity during the neoglacial 2815 to cal 730 cal yr b p this climatic cooling culminated with glacial advance to maximum holocene positions and expansion of a fjord wide ice shelf during the little ice age lia ca 730 82 cal yr b p seasonally open marine conditions were achieved and remnant ice shelves decayed within the context of recent rapid regional warming 82 cal yr b p to present our findings agree with previously observed late holocene cooling and glacial advance across the antarctic peninsula suggesting that the lia was a regionally significant event with few disparities in timing and magnitude comparison of the lia antarctic peninsula record to the rest of the southern hemisphere demonstrates close synchronicity in the southeast pacific and southern most atlantic region but less coherence for the southwest pacific and indian oceans comparisons with the northern hemisphere demonstrate that the lia antarctic peninsula record was contemporaneous with pre lia cooling and sea ice expansion in the north atlantic arctic suggesting a global reach for these events

late pleistocene paleoceanographic changes in the ross sea glacial interglacial variations in paleoproductivity nutrient utilization and deep water formation abstract the outer ross sea continental shelf has experienced large variations in ice sheet extent over the pleistocene that are theorized to be largely driven by changes in the westward flowing antarctic slope current asc at the continental shelf break this current regulates southward incursions of warm modified circumpolar water and it is thought to have triggered past marine ice sheet retreat additionally expansions of grounded ice sheets on the continental shelf have fundamentally altered the ross sea water mass formation processes influencing surface water salinity sea ice cover nutrient utilization deep water ventilation and primary productivity here we report the geochemical physical properties grain size bulk 15n and diatom records during the late pleistocene from two sediment cores from the iselin bank on the outermost continental shelf in the ross sea these core sites were not overridden by grounded ice sheets during the late pleistocene glacial interglacial cycles allowing for a continuous archive of glacimarine environments that were influenced by the asc interglacial periods are typically characterized by high surface water productivity and nutrient utilization with chaetoceros resting spores indicating nutrient limitation under open ocean conditions and glacial periods are typically characterized by low surface water productivity and nutrient utilization with sea ice diatoms and planktonic foraminifers indicating light limitation under extensive sea ice ice margin proximal conditions a grain size analysis indicates coarse skewed distributions and winnowing in the iselin bank region during cold periods the winnowing may be related to enhanced asc flow instead of density driven shelf water outflow

oceanographic and physiographic controls on modern sedimentation within antarctic fjords physical oceanographic data and modern surface sediments were collected from eleven fjords along the western side of the antarctic peninsula and south shetland islands surface sediment samples 62 were analyzed for texture and total organic carbon content the distribution of biogenic and terrigenous facies within the fjords is controlled by bay geometry and oceanographic regime climate plays a secondary role but along with ice drainage basin size controls the rate of terrigenous supply to the glacial marine environment specifically fjords along the danco coast and palmer archipelago with a high length to width ratio tend to have bottom sediments that are arenaceous where ice rafted sediment is released preferentially at the head of the fjord biogenic facies are favored where the bay geometry is complex where such complexity exists separate oceanographic regimes develop that lead to separation of terrigenous and biogenic sediments processes of interflow mid and deep water turbid cold tongues and coriolis deflection produce terrigenous facies along the inner fjord and western edges of a fjord system warm outer bay waters tend to develop a stable eddy circulation pattern that favors the productivity of phytoplankton in the surface layers outer bays are therefore floored with organic rich siliceous muds and ice rafted material only in the south shetland islands is melt water input significant enough to generate estuarine circulation within the fjord but here strong bottom currents result in arenaceous bottom sediments with no biogenic facies ice rafted diamictons are produced proximal to the edges of small tide water glaciers in the south shetlands the facies relationships established in this study provide a strong reference for paleoclimatic studies that utilize downcore measurements of texture and organic carbon

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

holocene sediment records from the continental shelf of mac robertson land east antarctica geochemical records are presented for five sediment cores from basins on the continental shelf of mac robertson land east antarctica the cores contain 2 4 m thick sequences of hemipelagic siliceous mud and ooze smo deposited under seasonally open marine conditions the inner and middle shelf smo sequences are massive dark olive green material whereas the outer shelf smo sequences are dark olive material interspersed with light olive green layers 1 10 cm thick the biogenic material is dominated by marine diatoms including fragilariopsis curta fragilariopsis cylindrus and chaetoceros spp in the dark colored smo and corethron criophilum in the light colored layers radiocarbon dates suggest that the cores provide continuous accumulation records extending from 1 kyr before present b p back as far as 4 15 kyr b p with estimated accumulation rates of 0 07 5 mm yr 1 the three core records from the middle and outer shelf suggest six episodes of increased accumulation of biogenic material at 5 5 kyr b p all three cores 1 2 and 6 2 kyr b p two of the three cores and 3 8 and 10 8 kyr b p one core most of which coincide with corethron layers we interpret these features as the result of enhanced diatom production over the outer shelf possibly related to climatic warm periods the absence of such features in the inner shelf core records is thought to reflect a relatively constant level of seasonal diatom production in adjacent waters maintained by a coastal polynya

laminations from the palmer deep a diatom based interpretation 1 highly laminated holocene age diatomaceous sediments are characteristic of the palmer deep western antarctic peninsula ocean drilling program odp leg 178 site 1098 from 10 000 years b p to the present laminations are comprised of several groups of diatoms chaetoceros resting spores the dominant laminae former result from intense spring blooms rhizosolenia proboscia thalassiothrix and corethron are common also the consequence of summer production marked by a well stratified water column each lamination represents a single productivity event but laminations are not necessarily annual high concentrations of a subpolar form of eucampia antarctica in laminations between 9000 and 6700 years b p suggest early holocene warmth a consequence of southward intrusion of more subpolar waters the glacial interglacial transition is distinguished by pairs of laminae most likely deposited annually laminations with an overwhelming dominance of chaetoceros resting spores alternate with more terrigenous laminae representing alternation of intense spring blooms with more mixed deposition during the summer proximity to retreating glacial ice results in the supply of silt and sand that provides a marker bed between successive blooms

holocene glacier and deep water dynamics adelie land region east antarctica abstract this study presents a high resolution multi proxy investigation of sediment core md03 2601 and documents major glacier oscillations and deep water activity during the holocene in the adelie land region east antarctica a comparison with surface ocean conditions reveals synchronous changes of glaciers sea ice and deep water formation at milankovitch and sub milankovitch time scales we report 1 a deglaciation of the adelie land continental shelf from 11 to 8 5 cal ka bp which occurred in two phases of effective glacier grounding line retreat at 10 6 and 9 cal ka bp associated with active deep water formation 2 a rapid glacier and sea ice readvance centred around 7 7 cal ka bp and 3 five rapid expansions of the glacier sea ice systems during the mid to late holocene associated to a long term increase of deep water formation at milankovich time scales we show that the precessionnal component of insolation at high and low latitudes explains the major trend of the glacier sea ice ocean system throughout the holocene in the adelie land region in addition the orbitally forced seasonality seems to control the coastal deep water formation via the sea ice ocean coupling which could lead to opposite patterns between north and south high latitudes during the mid to late holocene at sub milankovitch time scales there are eight events of glacier sea ice retreat and expansion that occurred during atmospheric cooling events over east antarctica comparisons of our results with other peri antarctic records and model simulations from high southern latitudes may suggest that our interpretation on glacier sea ice ocean interactions and their holocene evolutions reflect a more global antarctic holocene pattern

comparison of contemporary and fossil diatom assemblages from the western antarctic peninsula shelf during the past ten years the antarctic peninsula has been identified as the most rapidly warming region of the southern hemisphere and it is important to place this warming in the context of the natural climate and oceanographic variability of the recent geological past many biological proxies such as marine diatom assemblages have been used to determine southern ocean palaeoceanographic conditions during the late quaternary however few investigations have attempted to link observations of modern floras with the fossil record in this study we examine a suite of modern austral spring december 2003 and summer february 2002 surface water samples from along the western antarctic peninsula wap continental shelf and compare these to core top surface sediment samples using detrended correspondence analysis dca and principal component analysis pca of diatom abundance data we investigate the relationship of contemporary diatom floras with the fossil record this multivariate analysis reveals that our modern assemblages can be divided into three groups summer southern wap sites summer northern wap sites and spring wap sites sea surface temperature sst is an important environmental variable for explaining seasonal differences in diatom assemblages between spring and summer but sea surface salinity sss is more important for understanding temporally equivalent regional variations in assemblage our summer diatom samples are more reminiscent of early season assemblages reflecting the unusually late sea ice retreat from the region that year when the modern assemblages are compared to the fossil record it is clear that most of the important diatoms from the summer assemblage are not preserved into the sediments and that the fossil record more closely reflects spring assemblages this observation is important for any future attempts to quantitatively reconstruct palaeoceanographic conditions along the wap during the late quaternary and highlights the need for many more such studies in order to address longer timescales such as interannual variability in the context of the fossil record

a record of holocene glacial and oceanographic variability in neny fjord antarctic peninsula analyses of a 12 m marine sediment core from neny fjord marguerite bay antarctic peninsula 68 2571 s 66 9617 w yield a high resolution record of holocene climate variability the sediments preserve signals of past glacial and marine environments and offer a unique insight into atmospheric and oceanic forcings on the western antarctic peninsula climate dating of basal material reveals that deglaciation of the fjord occurred prior to 9040 cal yr bp and provides a minimum constraint on the timing of deglaciation close to the southern antarctic peninsula ice divide continuous deposition of ice distal sediments and seasonally open water diatoms indicates that the site has not been over ridden by glacier ice during the holocene a facies of sand rich material offers the only evidence of a localized glacier advance during the mid holocene statistical analysis of diatom assemblage data reveals several climatic episodes of varying magnitude and duration these include an early holocene warm period 9000 and 7000 cal yr bp potentially associated with influx of circumpolar deep water onto the continental shelf and coinciding with widespread glacial retreat and holocene collapse of the george vi ice shelf the mid holocene 7000 to 2800 cal yr bp sediments are characterized by diatom assemblages indicative of less pervasive sea ice cover and prolonged growing seasons with evidence of increased meltwater discharge from 4000 cal yr bp the youngest sediments 2800 cal yr bp to present contain a record that is consistent with the widely documented neoglacial period followed by an abrupt reversal and climate amelioration from sometime after 200 cal yr bp

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

holocene glacial history and sea level changes on james ross island antarctic peninsula a reconstruction of deglaciation and associated sea level changes on northern james ross island antarctic peninsula based on lithostratigraphical and geomorphological studies shows that the initial deglaciation of presently ice free areas occurred slightly before 7400 14 c yr bp sea level in connection with the deglaciation was around 30 m a s l a glacier readvance in brandy bay of at least 7 km with the initial 3 km over land reached a position off the present coast at ca 4600 yr bp the culmination of the advance was of short duration and by 4300 yr bp the coastal lowlands again were ice free a distinct marine level at 16 18 m a s l was contemporaneous with or slightly post dates the brandy bay advance thus indicating the relative sea level around 4600 4500 yr bp our results from james ross island confirm that over large areas in this part of antarctica the last deglaciation occurred late 1997 by john wiley sons ltd

marine record of holocene climate ocean and cryosphere interactions herbert sound james ross island antarctica abstract the sediment record offshore james ross island northeast antarctic peninsula presents an unparalleled opportunity to directly compare marine and terrestrial climate records spanning the holocene in maritime antarctica an 11 m drill core was collected between herbert sound and croft bay as part of the shaldril nbp 0502 initiative and produced the southernmost sediment record from the eastern side of the ap thirty eight radiocarbon ages are used to construct an age model of centennial scale resolution multi proxy records including magnetic susceptibility pebble content particle size total organic carbon and diatom assemblages were interrogated in the context of nearby holocene age ice core lake and drift records from james ross island differences in the timing and expression of holocene events reflect marine controls on tidewater glaciers such as water mass configurations and sea ice glacial behavior mimics ice core paleotemperatures during the holocene with the exception of distinct ocean warming events herbert sound was fully occupied by grounded ice during the last glacial maximum and experienced rapid lift off followed by a floating ice phase the canopy of floating ice receded by 10 2 4 cal kyr bp presumably in response to early holocene warming herbert sound and croft bay fully deglaciated by 7 2 cal kyr bp when the mid holocene hypsithermal commenced and the sound became open and productive an extreme peak in productivity 6 1 cal kyr bp indicates an oceanic warming event that is not reflected in atmospheric temperature or lacustrine sediment records increase in sea ice cover and ice rafting mark the onset of the neoglacial 2 5 cal kyr bp when pronounced atmospheric cooling is documented in the james ross island ice core our comparison facilitates more holistic understanding of atmosphere ocean cryosphere interactions that may aid predictions of glacial response to future warming and sea level scenarios

pliocene glacial cyclicity in a deep sea sediment drift antarctic peninsula pacific margin abstract giant deep sea sediment drifts are widespread features along the continental rise of the west antarctic peninsula representing the most proximal continuous sedimentary recorders for west antarctic ice events and glacial interglacial cyclicity sediment physical geochemical records and x ray images derived from odp leg 178 site 1095 sediment drift 7 show characteristics in glacial interglacial cyclicity and associated sedimentary processes during early pliocene two boundary types dividing half cycles have been recognized 1 interglacial to glacial transitions that are distinct and characterized by a sharp boundary and abrupt change in lithology 2 glacial to interglacial transitions that are diffuse and characterized by a gradual decline of sediment physical and geochemical values with a marked reduction in sedimentation rates the boundaries defined in conjunction with magneto and biostratigraphic tie points form the framework for the calculation of relative sedimentation and accumulation rates used for reconstructing early pliocene paleoproductivity and terrigenous flux to the drift warm early pliocene climate conditions for west antarctic peninsula region are indicated by open ocean conditions in glacials short residence times of the grounded ice sheet at the shelf edge with sporadic fluctuations as well as periodic collapses of the ice sheet front we propose a 5 phase drift sedimentation model for the early pliocene and postulate a highly dynamic ice sheet likely reduced in thickness resulting in oscillations which lie closer to the shelf edge than was the case during the late quaternary

biogenic facies in the antarctic glacimarine environment basis for a polar glacimarine summary abstract the association of glacial deposits diamicts or tillites with biogenic and or chemically derived sedimentary rocks in the ancient record is one which continues to challenge interpretation an analogous association can be found on portions of the east antarctic continental shelf where relict glacial and glacimarine diamictons are overlain by a varied and complex suite of modern biogenic deposits carbonate bioclastic material can be found in two distinct zones and its deposition may have been contemporaneous with partial glacial expansion onto the shelf a nearshore carbonate facies consists of in situ and partially reworked barnacles bryozoans ostracods pelycepods gastropods planktonic and benthonic foraminifera a siliceous biogenic component is intermixed within the shallow water 500 m siliceous facies of pelagic hemipelagic and sediment gravity flow origin is found within inner shelf depressions and consists predominantly of diatom frustules and radiolaria these accumulations of siliceous ooze and mud clearly post date glacial recession from the shelf and contain laminated cross laminated and massive interbeds which are accumulating at rates of 0 3 cm yr the extreme polar climate inhibits meltwater production and terrigenous influx into marine basins this allows for the accumulation of biogenic rich material which is also favored by the high seasonal productivity inherent in the south polar oceans ancient analogs to these modern deposits exist and their association with glacimarine strata could be used to infer polar climatic settings and glacial retreat that is related to eustatic sea level rather than regional warming

sea ice seasonality during the holocene adelie land east antarctica abstract thin sections of laminated cores from different antarctic coastal areas have demonstrated the potential of diatom species to document climate change at the seasonal scale here we present the relative abundances of four diatom species and species groups fragilariopsis curta group as a proxy for yearly sea ice cover f kerguelensis as a proxy for summer sea surface temperature chaetoceros hyalochaete resting spores as a proxy for spring sea ice melting and the thalassiosira antarctica group as a proxy for autumn sea ice formation in core md03 2601 retrieved off adelie land on the antarctic continental shelf these abundances were compared to surface temperatures and sea ice cover modelled over the last 9000 years both the marine records and the simulated climate demonstrated a cooler early holocene 9000 7700 years bp a warmer mid holocene 7700 4000 years bp and a colder late holocene 4000 1000 years bp yearly sea ice cover followed an inverse pattern to temperatures with less sea ice during the mid holocene hypsithermal than during the late holocene neoglacial however diatom census counts and model output indicate that sea ice spring melting happened earlier in the season as expected but that autumn sea ice formation also occurred earlier in the season during the hypsithermal than during the colder neoglacial thereby following seasonal changes in local insolation

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

benthic foraminiferal record of holocene deep water evolution in the palmer deep western antarctic peninsula benthic foraminiferal data from ocean drilling program site 1098 indicate significant changes in deep water conditions of the palmer deep western antarctic peninsula margin throughout the holocene 13 ka to present the earliest holocene represents a period of transition from the last glacial maximum lgm cold bottom waters similar to saline shelf water ssw dominated the middle holocene the late holocene in the palmer deep has been characterized by alternating dominance of circumpolar deep water cdw and saline shelf water these changes have global oceanographic and climatic implications we suggest that the middle holocene bottom water record in the absence of circumpolar deep water on the western antarctic peninsula shelf indicates high saline shelf water production and or weakened circumpolar deep water production during the middle holocene climatic optimum the late holocene benthic foraminiferal record indicates rapidly fluctuating sea ice conditions and may indicate a teleconnection between the south pacific and southern ocean thus having implications related to the southern oscillation index

holocene paleoceanography of bigo bay west antarctic peninsula connections between surface water productivity and nutrient utilization and its implication for surface deep water mass exchange abstract paleoceanographic changes in response to holocene climate variability in bigo bay west antarctic peninsula wap were reconstructed through geochemical isotopic sedimentological and microfossil analysis core wap13 gc47 is composed of 4 lithologic units unit 4 was deposited under ice shelf settings unit 3 represents the mid holocene open marine conditions unit 2 indicates lateral sediment transport by a glacier advance during the neoglacial period the chronological contrast between the timing of open marine conditions at core wap13 gc47 ca 7060 cal yr bp at 540 cm and the ages of calcareous shell fragments ca 8500 cal yr bp in unit 2b suggests sediment reworking during the neoglacial period unit 1 was deposited during the medieval warm period mwp and the little ice age lia surface water productivity represented by biogenic opal and total organic carbon toc concentrations increased and bulk 15n nitrate utilization decreased during the warmer early to middle holocene and the mwp in contrast surface water productivity decreased with increased bulk 15n during the colder neoglacial period and lia in bigo bay the nitrate utilization was enhanced during cold periods in association with strong surface water stratification resulting from increased sea ice meltwater discharge or proximity to an ice shelf calving front in bigo bay reduced nitrate utilization during warm periods is related to weak stratification induced by less sea ice meltwater input and stronger circumpolar deep water influence

mg ca temperature calibration of polar benthic foraminifera species for reconstruction of bottom water temperatures on the antarctic shelf benthic foraminifera mg ca is a well established bottom water temperature bwt proxy used in paleoclimate studies the relationship between mg ca and bwt for numerous species has been determined using core top and culturing studies however the scarcity of calcareous microfossils in antarctic shelf sediments and poorly defined calibrations at low temperatures has limited the use of the foraminiferal mg ca paleothermometer in ice proximal antarctic sediments here we present paired ocean temperature and modern benthic foraminifera mg ca data for three species trifarina angulosa bulimina aculeata and globocassidulina subglobosa but with a particular focus on trifarina angulosa the core top data from several antarctic sectors span a bwt range of 1 7 to 1 2 c and constrain the relationship between mg ca and cold temperatures we compare our results to published lower latitude core top data for species in the same or related genera and in the case of trifarina angulosa produce a regional calibration the resulting regional equation for trifarina angulosa is temperature c mg ca 1 14 0 035 0 069 0 033 addition of our trifarina angulosa data to the previously published uvigerina spp dataset provides and alternative global calibration although some data points appear to be offset from this relationship and are discussed mg temperature relationships for bulimina aculeata and globocassidulina subglobosa are also combined with previously published data to produce calibration equations of temperature c mg ca 1 04 0 07 0 099 0 01 and temperature c mg ca 0 99 0 03 0 087 0 01 respectively these refined calibrations highlight the potential utility of benthic foraminifera mg ca paleothermometry for reconstructing past bwt in antarctic margin settings although further work is required before they are routinely used

sediment chronology in antarctic deglacial sediments reconciling organic carbon 14c ages to carbonate 14c ages using ramped pyrox we present the first study which directly compares carbonate radiocarbon 14c dates with the ramped pyrox rp radiocarbon dating technique within a single sediment core and we confirm the utilit

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

self sedimentation of phytoplankton blooms in the geologic record abstract understanding the formation of laminated organic rich sediments is an essential topic for researchers interested in fossil fuels biogeochemical cycles earth s environmental history and global change biologists have very recently demonstrated that some marine phytoplankton blooms actively govern their own sedimentation by the formation of sticky transparent gels that facilitate rapid aggregation accelerated sinking and efficient export flux here we present fossil evidence of unfragmented low diversity phytoplankton assemblages preserved as sedimentary laminae and irregular flocs that are attributable to a similar phytoplankton driven sedimentary mechanism we term self sedimentation the geological evidence suggests that self sedimentation precludes significant heterotrophic grazing propels the formation of some conspicuous hemipelagic sedimentary laminae and results in efficient carbon and opal flux to the sediments we suggest that the self sedimentation phenomenon may have broad implications for the geological history of biogeochemical cycling oceanic ecological dynamics and abrupt atmospheric environmental change broader recognition of the self sedimentation phenomenon as explicitly defined here is a prerequisite to testing these unconventional hypotheses

postglacial marine diatom record of the palmer deep antarctic peninsula odp leg 178 site 1098 2 diatom assemblages 1 the distribution of late pleistocene to holocene diatom assemblages from ocean drilling program odp leg 178 site 1098 palmer deep is described and compared using multivariate statistical methods cluster analysis and analysis of variance five assemblages are identified from site 1098 which are correlated with the climatic zones identified previously in the palmer deep domack et al 2001 a thalassiosira diatom assemblage characterizes the deglaciation phase 13 2 11 0 ka and was deposited during glacial retreat at the end of the regional last glacial maximum a well preserved rhizosolenia assemblage was deposited during a climatic reversal 11 0 9 0 ka and indicates periods of seasonally open water with diatom blooms an open water fragilariopsis kerguelensis assemblage characterizes the mid holocene climatic optimum 9 0 3 7 ka in the neoglacial late holocene 3 7 ka climatic cooling increased sea ice cover and increased wind are inferred from a cocconeis assemblage during the climatic optimum neoglacial transition 4 4 1 8 ka laminae characterized by corethron criophilum were preserved it is uncertain whether the laminae represent short lived interannual bloom events with high settling rates or have been deposited over longer time periods

early holocene decadal scale ocean variability recorded in gulf of california laminated sediments scanning electron microscope examination of holocene laminated sediment from guaymas basin gulf of california resolves up to five depositional events per year each lamina sublamina of an early holocene section of continuously laminated sediment was recorded from backscattered electron imagery photomosaic analysis diatom mat laminae composed predominantly of thalassiothrix longissima are associated with early winter mixed diatom flora laminae mats are probably brought into the gulf with pacific water during the summer concentrated at the surface or at the pycnocline and then rapidly deposited in the early winter as water column stratification breaks down time series analysis of one 300 year section from piston core jpc56 revealed significant periodicities in the deposition of mat laminae at 50 years 11 years and 22 24 years an 50 year cycle in fish populations has been related to changing north pacific ocean atmosphere circulation these pacific wide changes in circulation affect the currents dominant at the mouth of the gulf when the california current is dominant fewer diatom mats are imported into the gulf and when the north equatorial pacific gyre is dominant more are imported the 11 year 22 to 24 year and 50 year cycles are all suggested to be influenced by solar cycles

rapid deglaciation of marguerite bay western antarctic peninsula in the early holocene glacial geological evidence of rapid ice stream retreat is important for the potential insight it can bring to understanding of contemporary rapid ice sheet change here we report new chronological constraints on the deglacial history of the marguerite trough ice stream which formerly drained part of the western margin of the antarctic peninsula this ice stream has been previously identified on geomorphological grounds as an example of an outlet that underwent rapid retreat following the last glacial maximum but the precise timing of this retreat has not been conclusively determined we obtained cosmogenic surface exposure dates on erratic boulders that record the thinning history of ice flowing into the ice stream these dates show that the ice stream underwent 270 m of thinning very rapidly at 9 6 ka bp the timing of ice stream thinning agrees closely with previously published data on ice shelf retreat the age of the first post glacial beaches and minimum constraining ages for the onset of lacustrine sedimentation and post glacial sedimentation in inner shelf fjords we compare the timing of retreat to the similarly sized anvers trough ice stream further north and find that retreat in marguerite bay was more rapid and earlier than in the anvers trough we argue that the intrusion of circumpolar deep water is the most likely forcing mechanism for retreat in marguerite bay a key finding of this study is that rapid retreat occurred in deep water with reverse continent dipping slope but also in relatively shallow water with a positive slope this may have implications for understanding of oceanographically forced ice sheet change in other parts of west antarctica

diatom assemblages in surface sediments of the northwestern weddell sea antarctic peninsula a study of 42 surface sediment samples from the northwestern weddell sea documents the relationship between the modern distribution of diatom assemblages and present oceanographic conditions in the region three diatom assemblages were identified using r mode principal components analysis and cluster analysis while q mode cluster analysis was used to distinguish two geographically distinct biofacies based on the relative abundance of diatom species the biofacies of the former larsen a ice shelf lais is more closely associated with a sea ice diatom assemblage while the biofacies of the prince gustav channel northern peninsula pgc np is associated with two open coastal diatom assemblages this division is consistent with variance observed in the current oceanographic setting whereby the lais is generally characterized by a longer seasonal duration of sea ice coverage and lower primary productivity relative to the pgc np which is marked by a shorter seasonal duration of sea ice coverage and greater surface water productivity this relationship is further reflected in the distribution of the paleoenvironmentally significant diatom species fragilariopsis curta thalassiosira antarctica and chaetoceros subg hyalochaete spp as well as in absolute abundance data specifically f curta and the morphological form t antarctica t1 are representative of greater seasonal duration of sea ice coverage and lower productivity chaetoceros subg hyalochaete spp and the morphological form t antarctica t2 are associated with decreased seasonal duration of sea ice cover and greater surface water productivity a setting that is further reflected in high absolute diatom abundances these findings provide a basis for future paleoceanographic work in the region especially as studies of surface sediment diatom assemblages are vital to establishing a link between downcore diatom assemblages and those presently found in the water column

a 13 200 year history of century to millennial scale paleoenvironmental change magnetically recorded in the palmer deep western antarctic peninsula abstract a 13 200 yr record of magnetic parameters from the palmer deep western antarctic peninsula records a sequence of five distinct shifts in glacimarine sedimentation coupled with century scale variations in paleoproductivity the five major shifts are manifested as abrupt order of magnitude changes in low field magnetic susceptibility accompanied by changes in magnetic particle size and mineralogy the late holocene 3 4 0 ka the early holocene 11 5 9 ka and the last glacial maximum prior to 13 2 ka are intervals of strong low field magnetic susceptibility and are characterized by multi domain md magnetite md magnetite is associated with zones of abundant gravel grains and is interpreted here as an indicator of material transported as ice rafted debris deglaciation 13 2 11 5 ka and the middle holocene 9 3 4 ka were times of enhanced productivity the middle holocene marks the onset of century scale productivity cycles seen in high field magnetic susceptibility which is responding to variations in biogenic silica deglaciation and the middle holocene interval contain pseudo single domain magnetite and titanomagnetite respectively these observations are surprising given the abundance of coarse md magnetite available in local source rocks the magnetic mineral assemblage in the deglaciation interval however can be explained by density sorting in meltwater plumes during the middle holocene the magnetic mineral assemblage suggests the reduction or cessation of locally derived terrigenous sediment and by inference the reduction or cessation of iceberg generation the early holocene middle holocene shift in terrigenous sedimentation may be responding in part to sea level which controls the position of the grounding line the palmer deep late holocene interval coincides with the neoglacial period a time of glacier re advances worldwide

oceanographic variability on the west antarctic peninsula during the holocene and the influence of upper circumpolar deep water recent intensification of wind driven upwelling of warm upper circumpolar deep water ucdw has been linked to accelerated melting of west antarctic ice shelves and glaciers to better assess the long term relationship between ucdw upwelling and the stability of the west antarctic ice sheet we present a multi proxy reconstruction of surface and bottom water conditions in marguerite bay west antarctic peninsula wap through the holocene a combination of sedimentological diatom and foraminiferal records are for the first time presented together to infer a decline in ucdw influence within marguerite bay through the early to mid holocene and the dominance of cyclic forcing in the late holocene extensive glacial melt limited sea ice and enhanced primary productivity between 9 7 and 7 0 ka bp is considered to be most consistent with persistent incursions of ucdw through marguerite trough from 7 0 ka bp sea ice seasons increased and productivity decreased suggesting that ucdw influence within marguerite bay waned coincident with the equatorward migration of the southern hemisphere westerly winds sww ucdw influence continued through the mid holocene and by 4 2 ka bp lengthy sea ice seasons persisted within marguerite bay intermittent melting and reforming of this sea ice within the late holocene may be indicative of episodic incursions of ucdw into marguerite bay during this period the cyclical changes in the oceanography within marguerite bay during the late holocene is consistent with enhanced sensitively to enso forcing as opposed to the sww forcing that appears to have dominated the early to mid holocene current measurements of the oceanography of the wap continental shelf suggest that the system has now returned to the early holocene like oceanographic configuration reported here which in both cases has been associated with rapid deglaciation

sediment delivery and depositional patterns off adelie land east antarctica in relation to late quaternary climatic cycles article i nfo this study focuses on the understanding of depositional patterns over late quaternary glacial interglacial cycles and of the influence of diagenesis on geochemical sedimentary records from the continental margin off adelie land east antarctica we provide a complete analysis of the 30 m long sediment core md03 2603 collected on a deep sea sediment mound deposit the lr04 benthic oxygen isotope stack vs down core records of ba al and ba ti atomic ratios reflectance data and micropaleontological evidence allow to determine a detailed chronology back to 490 ka bp long lived uranium and thorium 238 u 234 u 232 th and 230 th provide an assessment of lateral vs vertical sediment advection by constraining the sediment focusing factor is high in most glacial intervals when mostly detrital material was transported down slope and focused to the core area interglacials display highs in ba al and ba ti coupled to low values related to stronger contour current flow biogenic fractions are more abundant during interglacials and more diluted by detrital fractions during glacials the diatom assemblage is dominated by the open ocean species fragilariopsis kerguelensis but glacial intervals display an increase of sea ice related and coastal species the integrated approach high resolution record of major and minor elements uauth 15 n norg 13 c and corg provides key insights into how redox conditions affect glacial interglacial sedimentation processes our evidence shows that diagenetic effects due to development of reducing conditions and consequent higher preservation of organic matter may overprint the paleoclimatic significance of some proxies involved into a sequence of diagenetic remineralization pathways comparison of the marine record to ice core data epica dome c edc allows to extend the information to the whole east antarctic margin sediment proxies of increased burial of biogenic material or increased preservation of organic matter are linked to climatic amelioration on the continent highs in edc dust flux correlate with high mn al and mo al ratios within the sediment record confirming that establishment of colder conditions on the continent triggered changes in sedimentation rates at the glacial interglacial transition which in turn affected the development of reducing redox fronts within the sediment

chronology of the palmer deep site antarctic peninsula a holocene palaeoenvironmental reference for the circum antarctic palmer deep sediment cores are used to produce the first high resolution continuous late pleistocene to holocene time series from the antarctic marine system the sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite fifty four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka bp reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error i e 50 years in addition surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the antarctic peninsula spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400 200 and 50 70 year frequency bands similar to other high resolution records from the holocene but so far unique f

mechanisms of holocene palaeoenvironmental change in the antarctic peninsula region the antarctic peninsula is one of the three fastest warming regions on earth here we review holocene proxy records of marine and terrestrial palaeoclimate in the region and discuss possible forcing mechanisms underlying past change with a specific focus on past warm periods our aim is to critically evaluate the mechanisms by which palaeoclimate changes might have occurred in order to provide a longer term context for assessing the drivers of recent warming two warm events are well recorded in the holocene palaeoclimate record namely the early holocene warm period and the mid holocene hypsithermal mhh whereas there are fewer proxy data for the mediaeval warm period mwp and the recent rapid regional rrr warming we show that the early holocene warm period and mhh might be explained by relatively abrupt shifts in position of the southern westerlies superimposed on slower solar insolation changes a key finding of our synthesis is that the marine and terrestrial records in the ap appear to show markedly different behaviour during the mhh this might be partly explained by contrasts in the seasonal insolation forcing between these records circumpolar deep water cdw has been implicated in several of the prominent changes through the holocene but there are still differences in interpretation of the proxy record that make its influence difficult to assess further work is required to investigate contrasts between marine and terrestrial proxy records east west contrasts in palaeoclimate the history of cdw to retrieve a long onshore high resolution record of the holocene and determine the role of sea ice in driving or modulating palaeoclimate change along with further efforts to study the proxy record of the rrr and the mwp

diatoms in the gulf of california seasonal flux patterns and the sediment record for the last 15 000 years flux and taxonomic composition of the diatom assemblage was determined for biweekly sediment traps in the central gulf of california over a 2 year period fluxes and relative abundance of taxa are not significantly different in traps from the eastern side of the guaymas basin and the western side of the carmen basin indicating that patterns of diatom production are uniform across the central gulf at all seasons of the year the annual maximum in diatom flux occurred during the winter season of both years either as a sustained event over many weeks 1990 or as a series of short blooms 1991 1992 of the most abundant taxa only hyalochaete chaetoceros species showed a clear seasonal cycle with a flux maximum in the spring of both years factor analysis defines five assemblages representing 1 summer and fall conditions of surface stratification and nutrient limitation 2 winter bloom triggered by onset of strong northwesterly winds 3 late spring to summer production probably related to sporadic events during periods of weak southeasterly winds 4 spring 1991 inferred to reflect the distal edge of a coastal upwelling phase 5 lateral advection of resuspended sediments from the continental shelf possibly resulting from trapped coastal waves during summer hurricanes and from storms during the 1991 1992 el nino southern oscillation enso the diatom data support the inference that subtropical pacific water penetrates deeper into the gulf during enso events in order to compare the sediment trap record to a sediment core a second factor analysis was done using only the taxa which are preserved in the sediment and omitting the most abundant taxa which showed little downcore variation this produces five factors representing 1 summer fall low production 2 early winter bloom 3 late winter spring upwelling 4 enso conditions and 5 a late spring summer assemblage of uncertain significance variation of species characterisic of each factor was examined in piston core atlantis ii 125 8 56jpc taken from the oxygen minimum zone in guaymas basin correlation to nearby deep sea drilling project hole 480 indicates that the core penetrates to about 15 ka with laminated sediments in the holocene 0 10 ka and late deglacial 11 13 ka and massive nonlaminated sediments around younger dryas time 10 11 ka and before 13 ka downcore variations in the diatom assemblage do not correspond directly to presence of laminations implying that the processes controlling bottom water oxygen content are not determined by conditions of surface water production presence of calcareous nannofossils downcore correlates inversely with two diatom assemblages enso and winter bloom indicators and not with occurrence of laminations suggesting that occurrence of calcareous nannofossils in the sediment is at least partly a function of surface water production prior to 12 ka production was lower than at present during all seasons implying weaker winds throughout the year subtropical waters extended to the midgulf as they do today during enso events between 11 and 12 ka conditions were similar to those of the present with relatively high winter and spring production resulting from northwesterly winds enso events were still common although less so than during the preceding period younger dryas time was one of transition with intermediate conditions a slackening of winter spring northwesterly winds and reduction of total annual production and increased occurrence of enso conditions in the early to middle holocene winter northwesterlies increased to a maximum resulting in very high production but apparently did not persist into spring subtropical waters mostly disappeared from the gulf in the late holocene northwesterly winds have supported high production during both winter and spring seasons

the significance of diatoms in the formation of laminated sediments of the shaban deep northern red sea laminated sediments spanning the last 20 000 years though not continuously in the shaban deep a brine filled basin in the northern red sea were analyzed microscopically and with backscattered electron imagery in order to determine laminae composition with emphasis on the diatomaceous component based on this detailed study we present schematic models to propose paleoflux scenarios for laminae formation at different time slices the investigated core geob 5836 2 26 12 61 n 35 21 56 e water depth 1475 m shows light and dark alternating laminae that are easily distinguishable in the mid holocene and at the end of the deglaciation 13 15 ka period light layers are mainly composed of coccoliths terrigenous material and diatom fragments while dark layers consist almost exclusively of diatom frustules monospecific or mixed assemblages the regularity in the occurrence of coccolith diatom couplets points to an annual deposition cycle where contrasting seasons and associated plankton blooms are represented diatoms fall winter deposition coccoliths summer signal we propose that for the past 15 000 years the laminations represent two season annual varves strong dissolution of carbonate with the concomitant loss of the coccolith rich layer in sediments older than 15 ka prevents us from presenting a schematic model of annual deposition however the diatomaceous component reveals a marked switch in species composition between last glacial maximum lgm sediments dominated by chaetoceros resting spores and sediments somewhat younger 18 19 ka dominated by rhizosolenia we propose that different diatom assemblages reflect changing conditions in stratification in the northern red sea strong stratification conditions such as during two meltwater pulses at 14 5 and 11 4 ka are reflected in the sediment by rhizosolenia layers while chaetoceros dominated assemblages represent deep convection conditions

post glacial seasonal diatom record of the mertz glacier polynya east antarctica an ultra high resolution post glacial laminated sediment record from mertz ninnis trough east antarctic margin eam has been analysed using sem backscattered electron imagery secondary electron imagery and quantitative diatom abundance laminations are classified using visually dominant diatom species and terrigenous content four biogenic diatom ooze laminae types one diatom bearing terrigenous lamina type and one diatom bearing terrigenous sub lamina type have been identified diatom ooze lamina types comprise near monogeneric hyalochaete chaetoceros spp resting spore laminae laminae characterised by corethron pennatum laminae characterised by rhizosolenia spp and mixed diatom assemblage laminae diatom bearing terrigenous lamina and sub lamina types comprise mixed diatom assemblage terrigenous laminae and sub laminae characterised by porosira glacialis resting spores formation of each of these lamina types is controlled by seasonal changes in nutrients oceanographic regimes and the mertz glacier polynya dynamics

paleoceanographic changes in the southern ocean off elephant island since the last glacial period links between surface water productivity nutrient utilization bottom water currents and ice rafted debris abstract to understand past changes in ocean cryosphere interactions in the southern ocean off the antarctic peninsula multi proxy analyses of three sediment cores located off elephant island were used to reconstruct changes in paleoproductivity nutrient utilization bottom current intensity and iceberg calving since the last glacial period the glacial period was characterized by low surface water productivity with high nutrient utilization indicating surface water stratification during the deglaciation surface water productivity increased with decreasing nutrient utilization implying that the increase is associated with increased nutrient supply from the subsurface water by enhancing antarctic circumpolar current acc influence as fronts migrate southward with warming abundant occurrence of grains 1 mm during the deglacial period indicates rapid ice sheet retreat with large scale melting and calving during the glacial period however coarse silt fine sand sized fraction represented ice rafted debris ird the different ird grain size characteristics are thought to be related to the ird source material characteristics regardless of ird input the running downcore correlation 5 to 9 point between sortable silt mean grain size and percentage showed that sediments are well sorted by bottom current however the cross plot of them showed different temporal relationships sediments were sorted by the acc and southwestward flowing bottom current along with southward migration of fronts and the acc southwestward flowing bottom current influence diminished whereas the acc influence increased particularly from 7 ka our results indicate that the sedimentary processes in the scotia sea largely depend on the regional interactions between the ocean and the cryosphere

bi polar ocean linkages evidence from late holocene antarctic marine and greenland ice core records a continuous 14c dated palaeoenvironmental 4000 year proxy from the antarctic peninsula glacial marine record demonstrates pronounced cycles of elevated palaeoproductivity warm events that rec

authigenic ferrimagnetic iron sulfide preservation due to nonsteady state diagenesis a perspective from perseverance drift northwestern weddell sea we document magnetic mineral diagenesis with high resolution magnetic susceptibility hysteresis isothermal remanent magnetization and other rock magnetic measurements through a shallow sulfate m