environmental responses of the northeast antarctic peninsula to the holocene climate variability in this study we present a unique high resolution holocene record of oceanographic and climatic change based on analyses of diatom assemblages combined with biomarker data from a sediment core collected from the vega drift eastern antarctic peninsula eap these data add to the climate framework already established by high resolution marine sedimentary records from the palmer deep western antarctic peninsula wap heavy sea ice conditions and reduced primary productivity were observed prior to 7 4 ka b p in relation with the proximity of the glacial ice melt and calving subsequent holocene oceanographic conditions were controlled by the interactions between the westerlies antarctic circumpolar current acc weddell gyre dynamics a warm period characterized by short seasonal sea ice duration associated with a southern shift of both acc and westerlies field persisted until 5 ka b p this warm episode was then followed by climate deterioration during the middle to late holocene 5 to 1 9 ka b p with a gradual increase in annual sea ice duration triggered by the expansion of the weddell gyre and a strong oceanic connection from the eap to the wap increase of benthic diatom species during this period was indicative of more summer autumn storms which was consistent with changes in synoptic atmospheric circulation and the establishment of low to high latitude teleconnections finally the multicentennial scale variability of the weddell gyre intensity and storm frequency during the late holocene appeared to be associated with the increased el nino southern oscillation frequency

the link between climate warming and break up of ice shelves in the antarctic peninsula a review of in situ and remote sensing data covering the ice shelves of the antarctic peninsula provides a series of characteristics closely associated with rapid shelf retreat deeply embayed ice fronts calving of myriad small elongate bergs in punctuated events increasing flow speed and the presence of melt ponds on the ice shelf surface in the vicinity of the break ups as climate has warmed in the antarctic peninsula region melt season duration and the extent of ponding have increased most break up events have occurred during longer melt seasons suggesting that meltwater itself not just warming is responsible regions that show melting without pond formation are relatively unchanged melt ponds thus appear to be a robust harbinger of ice shelf retreat we use these observations to guide a model of ice shelf flow and the effects of meltwater crevasses present in a region of surface ponding will likely fill to the brim with water we hypothesize building on weertman 1973 hughes 1983 and van der veen 1998 that crevasse propagation by meltwater is the main mechanism by which ice shelves weaken and retreat a thermodynamic finite element model is used to evaluate ice flow and the strain field and simple extensions of this model are used to investigate crack propagation by meltwater the model results support the hypothesis

rapid disintegration of the wordie ice shelf in response to atmospheric warming the breaking up of ice shelves around the antarctic peninsula has been cited1 as a sign that a dangerous warming is beginning in antarctica here we present satellite images showing the disintegration of the wordie ice shelf which lies off the west coast of the antarctic peninsula fig 1 fracture either in the form of surface crevasses or rifts extending to the bottom of the ice shelf has been responsible for iceberg calving and weakening the central region of the ice shelf these fracture processes which led to retreat of the ice front were apparently enhanced by the presence of increased amounts of melt water resulting from a warming trend recorded in mean annual air temperatures in marguerite bay if this warming trend continues other nearby ice shelves on the antarctic peninsula may be at risk but substantial additional warming would be required before similar processes could initiate breakup of the ross and filchner ronne ice shelves which help stabilize the west antarctic ice sheet

calcite dolomite geothermometry in the system caco3 mgco3 feco3 an experimental study an experimental study of the system caco3 mgco3 feco3 was undertaken in order to calibrate the iron correction to the calcite dolomite geothermometer which is based on the solubility of magnesium in calcite in the assemblage calcite dolomite the experiments at 450 c and lower temperatures resulted in products with a very small grain size and incomplete equilibration however application of a carefully devised automatic data processing algorithm to analyses of the phases in experimental charges combined with a thermodynamic analysis results in geothermometer diagrams which should be preferred to previous theoretical predictions

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

sea ice atmosphere and upper ocean variability in the weddell sea antarctica a frequency domain singular value decomposition is performed on 20 years 1979 1998 of monthly sea ice concentration sea ice drift and sea level pressure data in the weddell sea antarctica interannual oscillations with periods of around 3 4 years are found to dominate the variability in this region anomalous atmospheric patterns periodically reach the weddell sea from the west and perturb the sea ice circulation and distribution in the weddell gyre through changes in the intensity and direction of the climatological winds sea ice accumulates in the southeastern weddell sea every 3 4 years owing to two atmospherically driven processes 1 weak ice export to the north due to a weak northward branch of the gyre driven by weak southerly winds and 2 large ice import from the east due to a strong east wind drift driven by strong easterly winds along the coast the opposite situation gives rise to a depletion of sea ice in the same region half a cycle later sea ice anomalies are then advected north northeastward before turning eastward in the gyre circulation the eastward propagation of ice anomalies along the ice margin accounts for the passage of the antarctic circumpolar wave through the atlantic sector of the southern ocean a low frequency signal is also detected in the weddell sea variations albeit rather speculatively in this 20 year long record sea ice variability on this timescale appears to be associated with a change in the shape and characteristics of the weddell gyre circulation around 1990 this mode of variability implicates feedbacks between the gyre and weddell deep water temperature variations whose impact is observed near the maud rise topographic feature

holocene glacial and climate history of prince gustav channel northeastern antarctic peninsula the antarctic peninsula is one of the most rapidly warming regions on earth as evidenced by a recent increase in the intensity and duration of summer melting the recession of glaciers and the retreat and collapse of ice shelves despite this only a limited number of well dated near shore marine and lake sediment based palaeoenvironmental records exist from this region so our understanding of the longer term context of this rapid climate change is limited here we provide new well dated constraints on the deglaciation history and changes in sea ice and climate based on analyses of sedimentological proxies diatoms and fossil pigments in a sediment core collected from an isolation basin on beak island in prince gustav channel ne antarctic peninsula 63 36 s 57 20 w twenty two radiocarbon dates provided a chronology for the core including a minimum modelled age for deglaciation of 10 602 cal yr bp following the onset of marine sedimentation conditions remained cold and perennial sea ice persisted in this part of prince gustav channel until c 9372 cal yr bp this was followed by a seasonally open marine environment until at least 6988 cal yr bp corresponding with the early retreat and disintegration of the ice shelf in southern prince gustav channel following isolation of the basin from 6988 cal yr bp a relatively cold climate persisted until 3169 cal yr bp a mid late holocene climate optimum occurred between 3169 and 2120 cal yr bp inferred from multiple indicators of increased biological production this postdates the onset of the mid late holocene climate optimum in the south shetland islands 4380 cal yr bp and the south orkney islands 3800 cal yr bp suggesting that cooler climate systems of the weddell sea gyre to the east of the peninsula may have buffered the onset of warming climate deterioration is inferred from c 2120 cal yr bp until 543 cal yr bp this was followed by warming superimposed on this warming trend the instrumental record of recent warming at nearby hope bay is mirrored by a recent increase in the lake s primary production and a shift in the diatom communities in the uppermost 3 cm of sediments suggesting that this is amongst the first records to show an ecological response to recent rapid temperature increase these new constraints on glaciological and climate events in prince gustav channel are reviewed in the context of wider changes in the antarctic region

sedimentation associated with antarctic peninsula ice shelves implications for palaeoenvironmental reconstructions of glacimarine sediments abstract recent disintegration of a number of antarctic peninsula ice shelves has given us a unique opportunity to investigate sub ice shelf sediments we characterize three sediment facies associations of two antarctic peninsula ice shelves larsen a and larsen inlet subglacial facies consist mainly of basal till diamicton with high shear strengths deposited under a grounded ice sheet progressive upward decrease in shear strength reflects a gradual decrease in the confining vertical effective pressure of grounded ice during till deposition proximal ice shelf glacimarine facies diamicton gravel rich and sand rich facies gravelly mud dropstone mud and sandy muds were deposited by sub ice shelf rain out bottom current activity and sediment gravity flows following decoupling of grounded ice from the sea floor distal ice shelf glacimarine and or open marine facies comprise terrigenous and diatom bearing bioturbated muds and gravelly muds that contain limited ice rafted debris these accumulated after recession of the grounding line to the coast with coarse grained surface sediments possibly documenting most recent ice shelf break up antarctic peninsula ice shelf sediments are more heterogeneous than ice shelf facies deposited elsewhere in antarctica cold polar antarctic ice shelves can be differentiated from temperate and sub polar marine terminated glacial sedimentary systems by the dominance of coarse grained proximal ice shelf glacimarine facies and an absence of subaqueous outwash meltwater sediment facies

late holocene oceanographic and climatic variability recorded by the perseverance drift northwestern weddell sea based on benthic foraminifera and diatoms abstract the perseverance drift located in the joinville d urville trough northwestern weddell sea records changes in ocean and sea ice conditions throughout the middle to late holocene with a record extending back to ca 3400 yr bp the 2562 cm composite record collected from a water depth of 806 m documents the uppermost section of the 90 m thick sediment drift spring blooming diatoms chaetoceros subg hyalochaete are abundant through the sedimentary record the greater proportion of chaetoceros vegetative valves compared to resting spores indicates that the marine environment is highly productive and nutrients generally are not limiting epiphytic diatoms dominated by cocconeis spp are observed throughout jkc36 suggesting transport of algal detritus from shallower regions to the benthos three foraminiferal assemblages fas miliammina spp globocassidulina spp and paratrochammina bartami paratrochammina lepida portatrochammina antarctica characterize the benthic foraminiferal fauna and reflect affinities with water masses circulating across the perseverance drift and tolerance to corrosive bottom waters the interval 3400 1800 yr bp is marked by high abundances of globocassidulina spp indicating incursions of weddell sea transitional water over the drift site this interval implies a period of freshening of the water column coinciding with an open marine or seasonally open marine environment during the middle to late holocene climatic optimum the interval 1800 yr bp to the present displays characteristics of slightly colder conditions as indicated by the absence of the calcareous globocassidulina spp fa and the pronounced presence of agglutinated p bartami p lepida p antarctica fa along with other agglutinated species that are indicative of the presence of sea ice therefore this interval is interpreted to represent the onset of neoglaciation at the northeastern tip of the antarctic peninsula the consistent presence of miliammina spp fa corroborates that the sedimentary record represents a productive open marine setting with seasonally variable sea ice extent the drift is a unique geologic archive that provides an excellent target for future coring based on the preservation of abundant carbonate material for radiocarbon dating and the potential to develop a multi proxy data set that could offer a robust understanding of the holocene depositional and paleoclimatic conditions of the northwestern weddell sea

factors influencing the distribution of diatoms and other algae in the ross sea quantitative microscopic analyses of sediment trap samples collected in the ross sea between january 1990 and february 1992 reveal striking temporal and spatial differences in algal bloom composition and size trap samples from the southwestern ross sea site a 76 30 s 167 30 e were dominated by the diatom fragilariopsis curia maximum of 92 a species associated with both sea ice and the retreating ice edge in the ross sea this species was probably seeded by melting congelation ice highest flux of diatom valves to both upper and lower traps in the 1991 1992 season occurred as a distinct event in mid february 1991 after which flux decreased by 1 to 3 orders of magnitude as overall flux decreased an increase in relative abundance of chaetoceros resting spores and the open water species thalassiosira antarctica was observed in the lower trap suggesting some localized lateral advection in the south central ross sea site b 76 30 s 175 w algal diversity was much higher with a greater contribution of nondiatom material the prymnesiophyte phaeocystis antarctica dinoflagellates and cysts of unknown affinity were much more common than at site a as were the diatoms fragilariopsis cylindrus fragilariopsis kerguelensis and thalassiosira gracilis highest diatom flux occurred later february 20 to march 6 1991 at this site and was an order of magnitude lower as compared to maximum flux at site a distinct differences in bloom size and composition between sites a and b may be a function of upper water column structure differences in the amount of sea ice melting and the type of sea ice present at the time of ice breakout congelation versus pack ice despite rich surface productivities lower silica flux to the seafloor at site b results from the higher proportion of nonsiliceous algae at site c 72 30 s 172 30 e in the northwestern ross sea diatoms again dominated algal flux however assemblage composition differed from that observed at both sites a and b relative abundance of f curta was lower averaging 60 70 while the remainder of the assemblage was made up of f cylindrus other more robust species of fragilariopsis and chaetoceros resting spores algal flux at site c is intermediate in style between sites a and b significantly spatial differences in diatom assemblages noted above appear to be reflected in seafloor surface sediments suggesting that downcore diatom data provide an interpretable record of paleoproductivity in the ross sea

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

a recent sea ice retreat west of the antarctic peninsula satellite passive microwave data show a record decrease in sea ice extent in the bellingshausen sea from mid 1988 through early 1991 the change coincides with more southerly surface winds increased cyclonic activity and rising surface air temperatures which reached historic highs along the west coast of the antarctic peninsula in 1989 preceded by high ice cover in 1986 87 the retreat was most evident during summer in the formerly perennial sea ice field over the continental shelf ocean heat storage probably contributed to the persistence and coastal propagation of this anomaly

deglacial ocean and climate seasonality in laminated diatom sediments mac robertson shelf antarctica the palaeoceanography and climate history of the east antarctic margin eam are less well understood than those of west antarctica yet the eam plays an important role in deep ocean circulation and the global ocean system and has likely done so in the past deglacial age marine sediments from the eam provide clues about its past role during this critical period of rapid climate change several deep basins across the eam such as iceberg alley 67 s 63 e on the mac robertson shelf mrs accommodate thick marine sequences that archive the deglaciation in the form of diatom rich continuously laminated varved sediments these laminated sediments are pristinely preserved and contain seasonal and long term information on the cryospheric and palaeoceanographic changes associated with the rapid retreat of the glacial ice sheet across the mrs we present results of microfabric analysis of the lower 2 m of deglacial varves from jumbo piston core jpc43b iceberg alley backscattered electron imagery bsei of polished thin sections and scanning electron microscope secondary electron imagery sei of lamina parallel fracture surfaces are used to analyze the varves one hundred and ninety two laminations are investigated and their nature and temporal significance are discussed in terms of seasonal deposition and cyclicity of diatom species our high resolution palaeodata record exceptionally high diatom production and silica flux associated with the retreat of the east antarctic ice sheet and seasonal sea ice changes along the eam this information is invaluable for assessing cryospheric oceanographic variation and therefore the local and regional response to this period of rapid climate change varves are made up of lamina couplets comprising i thickly laminated to thinly bedded orange orange brown very pure diatom ooze dominated by hyalochaete chaetoceros spp vegetative cells and resting spores and ii brown blue grey terrigenous angular quartz sand silt and clay with an abundant mixed diatom flora the colour variation between these two types of lamination is striking using floristic and textural information we interpret the diatom oozes as spring flux and the terrigenous laminae as summer flux each couplet pair represents one annual cycle and reflects seasonal changes in nutrient availability and stratification associated with the cyclical advance and retreat of seasonal sea ice the diatom oozes can reach up to 7 5 cm in thickness indicating enormous silica flux to the sea floor associated with ice sheet retreat

modern distribution of diatoms in sediments from the george v coast antarctica abstract currently little information exists concerning high frequency climate change in the antarctic data that are essential to gaining a more complete understanding of global climate change sediments from the george v coast continental margin potentially contain a high resolution record of the late holocene the relatively high rate of sedimentation 3 mm year and the presence of laminated intervals which contain undisturbed sequences make these sediments valuable for future downcore work in order to utilize diatom assemblages as proxies of paleoclimatic and paleoceanographic parameters a preliminary study of the surface sediment distribution of diatoms from the george v coast continental margin was completed nitzschia curta van heurck hasle and nitzschia kerguelensis o meara hasle present great potential for tracking the holocene retreat of ice across the continental shelf of this region concentrations of n curta an ice related form decreases in an offshore direction whereas n kerguelensis an oceanic species associated with circumpolar flow displays an increase in sediments offshore the genus thalassiosira cleve displays a clear association with areas of open water primary production as has been noted in others parts of the antarctic downcore variability in relative abundance of this genus will be useful in understanding the history of sea ice versus open water production on the george v coast shelf in contrast the distribution of chaetoceros ehrenberg resting spores appears to be more complex but may be related to the position of the stationary ice edge associated with the annual minimal extent of sea ice finally an understanding of the downcore variability of thalassiothrix antarctica schimper ex karsten a species which is very abundant in the laminated sections of the sediment cores will have to rely on studies of its distribution in other areas of the antarctic as it is sparsely distributed along the george v coast today

spring distributions of density nutrients and phytoplankton biomass in the ice edge zone of the weddell scotia sea we collected data on temperature salinity nutrient concentrations nitrate nitrite phosphate and silicic acid and phytoplankton biomass chlorophyll a particulate carbon nitrogen and biogenic silica in the upper 150 m in the marginal ice zone of the eastern scotia sea and northwestern weddell sea during november and early december of 1983 a distinct hydrographic front separating drake passage water from weddell and scotia sea surface waters was located at approximately 59 s and was the site of a consistent maximum in phytoplankton biomass in addition there was a pronounced phytoplankton biomass maximum associated with a surface salinity minimum near the northern limit of pack ice in the waters of the weddell scotia confluence that characterized the western portion of the study area in the eastern half of the study area characterized by largely unmodified weddell sea surface water the phytoplankton biomass near the ice edge was 2 5 times lower than that in the weddell scotia confluence but was increasing with time the water column structure nutrient fields and phytoplankton biomass distribution all suggest that the high phytoplankton biomass in the ice edge zone of the weddell scotia confluence and the lower but temporally increasing biomass near the ice edge in unmodified weddell sea water reflect ice edge phytoplankton blooms in different stages of their seasonal development a bloom had become well established in the waters of the weddell scotia confluence by mid november but the ice free vertically stable near surface water column necessary for enhanced phytoplankton growth had apparently not been present long enough for high biomass levels to develop within the weddell sea proper

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

ice retreat in the eastern antarctic peninsula region the application of diatoms for understanding climate change abstract climate driven retreat of ice shelves on the eastern side of the antarctic peninsula has opened up new coastal marine environments enabling the development of primary productivity diatom assemblages in surface sediment samples from the eastern side of the antarctic peninsula were analyzed to investigate the use of diatoms as paleoenvironmental indicators of changes in glacial and sea ice extent here we present surface sediment diatom assemblage data from samples taken on 5 cruises between 2000 2012 from the northeastern most tip of the antarctic peninsula prince gustav channel larsen a and larsen b embayments and a single sample from just east of larsen c ice shelf absolute diatom abundance increases to the northeast reflecting greater contribution of diatom valves originating from surface waters that are ice free for a longer period of time this trend is mirrored by the relative abundance of chaetoceros subg hyalochaete a spring bloom indicator group the genus fragilariopsis is dominated by sea ice associated species including fragilariopsis curta fragilariopsis cylindrus fragilariopsis obliquecostata fragilariopsis sublinearis and fragilariopsis vanheurckii fragilariopsis spp relative abundance varies inversely with chaetoceros subg hyalochaete distributions of thalassiosira antarctica t1 and thalassiosira antarctica t2 interpreted as a cooler and warmer forms respectively while generally inverse to one another with the t antarctica t2 more common to the northeast are not straightforward with a pocket of high relative abundance in larsen b embayment these diatom data and their comparison to modern oceanography of the eastern antarctic peninsula provide a basis for further paleoceanographic work in the region

holocene paleoclimate change in the antarctic peninsula evidence from the diatom sedimentary and geochemical record abstract holocene marine deposition in lallemand fjord antarctic peninsula is reinterpreted using statistical analyses cluster analysis analysis of variance nonmetric multidimensional scaling and multiple regression to compare diatom assemblages and the primary sedimentological proxies the assemblages have been deposited in a variable sea ice zone over the last ca 10 500 yr bp in response to a climate change in the late pleistocene early holocene 10 580 7890 yr bp a sea ice diatom assemblage was deposited in the presence of a retreating ice shelf at the head of the fjord in the mid holocene 7890 3850 yr bp an open water assemblage was deposited and sea ice cover was at a minimum we associate the assemblage with climatic warming which characterizes much of the antarctic peninsula during this time a second sea ice assemblage different from that deposited in the early holocene has been deposited in lallemand fjord since the late holocene

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

peristerite compositions in quartzofeldspathic schists franz josef fox glacier area new zealand plagioclase compositions vary from an0 1 2 5 to an32 with increasing grade in chlorite zone to oligoclase zone quartzofeldspathic schists franz josef fox glacier area southern alps new zealand this change is interrupted by the peristerite composition gap in rocks transitional between greenschist and amphibolite facies grade oligoclase an20 24 and albite an0 1 0 5 are found in biotite zone schists below the garnet isograd with increasing grade the plagioclase compositions outline the peristerite gap which is asymmetric and narrows to compositions of an12 and an6 near the top of the garnet zone in any one sample oligoclase is the stable mineral in mica rich layers above the garnet isograd whereas albite and oligoclase exist in apparent textural equilibrium in adjacent quartz plagioclase layers the initial appearance of oligoclase in both layers results from the breakdown of epidote and possibly sphene carbonate is restricted to the quartz plagioclase rich layers and probably accounts for the more sodic composition of oligoclase in these layers the formation of more ca rich albite and more na rich oligoclase near the upper limit of the garnet zone coincides with the disappearance of carbonate and closure of the peristerite gap garnet appears to have only a localized effect on ca enrichment of plagioclase in mica rich layers within the garnet zone the na content of white mica increases sympathetically with increasing ca content of oligoclase and metamorphic grade comparison of the peristerite gap in the franz josef fox glacier schists and schists of the same bulk composition in the haast river area 80 km to the s indicates that oligoclase appears and epidote disappears at lower temperatures and that the composition gap between coexisting albite and oligoclase is narrower in the franz josef fox glacier area it is suggested that a higher thermal gradient 38 40 c km and variations in si al ordering during growth of the plagioclases between the two areas may account for these differences in the alpine schists the peristerite gap exists over a temperature and pressure interval of about 370 515 c and 5 5 7 kbar 550 700 mpa ph2o

cambrian and late precambrian basaltic igneous activity in the scottish dalradian a review in the evolution of the scottish dalradian basin the climax of widespread tholeiitic magmatism pre dated or coincided with major basement faulting and the onset of deep marine sedimentation in lower cambrian times earlier basin deepening and precursory igneous activity had already occurred major and trace element chemistry of low grade metabasites indicates their affinity with basalts from ocean spreading centres or transition to within plate types geological evidence favours a tectonic setting for this igneous suite and the highland border series on the nw margin of an actively evolving lower cambrian ocean basin possibly a marginal basin to the iapetus ocean system

geothermometry geobarometry and the al2sio5 triple point at mt moosilauke new hampshire the distribution of aluminum silicate minerals in pelitic schists constrains pressure and temperature conditions during the acadian orogeny to have been approximately those of the al 2 sio 5 invariant point thus providing an excellent opportunity to evaluate the internal consistency of a variety of published geothermometers and geobarometers with the al 2 sio 5 invariant point of holdaway 1971 four fluid independent equilibria yield p t estimates consistent with holdaway 1971 two fluid dependent equilibria yield internally consistent but unrealistically high temperatures our data are consistent with the conclusions that 1 only pyrope grossular mixing in the quaternary garnet system is significantly non ideal and 2 the activity coefficient for the anorthite component in plagioclase is approximately 2 at triple point p t conditions modified journal abstract

decadal timescale links between antarctic peninsula ice core oxygen 18 deuterium and temperature the antarctic peninsula region has exprienced a long term warming trend over the twentieth century with the 1971 90 mean at faraday being 1 9 c warmer than the mean over 1903 41 based on expedition reports for the period prior to 1900 there is conflicting evidence from different data sources an initial interpretation of isotopic data from ice cores suggests that the nineteenth century was warmer than the twentieth century in contrast snow accumulation rate data for the nineteenth century from the same ice cores suggest lower temperatures here we investigate these facts by studying the links between atmospheric temperature over the antarctic peninsula circulation parameters and isotopic data over the period of instrumental records we show that the relationships between these variables are complex and highly spatially variable in particular the correlations between temperature and 18o and d are generally of the order r 0 5 or less on timescales of one to five years conflicts between evidenc

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

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

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

cymrite new occurrence and stability the rare mineral cymrite baal2si2o8 h2o was discovered in nevada in a cambrian bedded barite sequence that exhibits low grade metamorphism the mineral occurs exclusively in thin bedded siliceous rock containing anhedral pyrite crystals up to 1 cm cymrite forms rectangular grains ca 40 m across distributed throughout the chalcedonic quartz matrix an sem image of one such blocky grain shows that it is filled by tiny aggregates instead of a single crystal of cymrite this cymrite may have replaced a pre existing rectangular mineral most likely barite the nevada occurrence of cymrite prompted a restudy of its stability relations conventional hydrothermal techniques were adopted in the experimental work with run durations up to 7 months the univariant curve for the dehydration reaction baa12si2o8 h2o baa12si2o8 h2o passes the following reversed brackets 300 315 c at 3 kbar 290 300 c at a 2 kbar 270 285 c at 1 kbar and 240 270 c at 0 5 kbar these results indicate that cymrite can be stable at much lower pressures than those previously reported the replacement of barite by cymrite was experimentally demonstrated with an alkaline solution as depicted by the reaction baso4 2oh a12o3 2sio2 baa12si2o8 h2o so 4 2

rain events in an arid environment their distribution and ionic and isotopic composition patterns makhtesh ramon basin israel abstract forty six individual rain events and successive fractions of these events were studied with a network of instruments in the arid makhtesh ramon basin southern israel during 1981 1983 annual rainfall varied from 47 to 107 mm number of rain events varied from 8 to 20 per year start of the rainy season varied from september to january termination of the rainy season varied from march to may and length of the rainy season varied from 4 to 9 months about 85 of the rain events were recorded at more than one station indicating an aerial distribution exceeding 20 km a cliff amount effect was observed the rain on the cliff 800 m was 73 more than the rain at the bottom of the makhtesh 500 m dust samples revealed the following soluble ions in equivalents ca 2 mg 2 na k and hco 3 cl so 2 4 the dust also contained cacl 2 rain composition of 61 analyzed samples revealed in equivalents ca 2 na mg 2 k and hco 3 cl so 2 4 neutral ph of 7 1 7 6 and presence of cacl 2 a similar pattern was observed in 54 samples collected during the same period at sde boker 30 km north of the ramon thus typifying the negev heights two distinct sources of dissolved ions were inferred dust providing mainly ca hco 3 2 and cloud borne sea spray providing mainly na mg 2 cl and so 2 4 a chemical and isotopic effect was observed the rain of the rainier year contained 34 less dissolved ions and was isotopically lighter in 18 o by 54 than the rain of the less rainy year a chemical and isotopic front effect was observed the first fraction of the individual rain events contained more dissolved ions 32 69 and was enriched by more 18 o 31 than the subsequent rain fractions the observed rain distribution and chemical isotopic effects are discussed in terms of input sources evaporation processes and altitude effects the obtained data define rain and salt inputs into the hydrological systems

diatom flux in mcmurdo sound antarctica abstract quantitative floral analyses have been performed on sea ice sediment trap and surface sediment samples collected from six sites in mcmurdo sound antarctica although diatom abundances in the sea ice reach 108 109 cells m 2 maximum diatom fluxes between october december 1984 as measured in the sediment trap samples are only 105 107 individuals m 2 day 1 the cumulative flux of diatoms for this three month period is approximately 107 109 individuals m 2 possibly an order of magnitude less than the sea ice abundances implying that diatom and opal flux must significantly increase when the sea ice melts and releases those particles previously trapped in the ice five species dominate the sea ice assemblage amphiprora sp pleurosigma sp nitzschia stellata pinnularia quadratarea andnitzschia curta these species are also common in the water column along withthalassiosira spp a genus rarely found within the sea ice within the upper 250 m of the water column at a site in granite harbor diatom flux decreases between 47 79 from 34 to 220 m opal flux however decreases by only 13 40 over this same interval indicating that dissolution of thinly silicified diatom frustules has occurred at mid water depths increases in absolute diatom flux of two species in particular nitzschia curta andthalassiosira spp may indicate their transport from other areas at all sites the greatest increase in diatom flux occurs just above the sea floor resuspension of diatom tests and or lateral advection creates a near bottom nepheloid layer in which significant modification of the diatom assemblage occurs a combination of preferential dissolution of those forms which dominate the sea ice and dilution of the assemblage with resuspended and or advected diatoms representative of many year averages of the flora may be responsible for the production of a sediment assemblage primarily made up ofthalassiosira spp nitzschia curta and other robust forms ofnitzschia

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

carbon export associated with free drifting icebergs in the southern ocean abstract enrichment of the pelagic ecosystem associated with the proliferation of free drifting icebergs prompts questions about increased productivity and the export flux of organic carbon to the deep ocean with continued climate warming lagrangian sediment traps lst were deployed autonomously beneath a large tabular free drifting iceberg c 18a in the nw weddell sea during march and april 2009 to collect sinking particles at a depth of 600 m three lst deployments associated with c 18a within a 30 km radius collected sinking diatom frustules dominated by corethron pennatum and fragilariopsis nana euphausiid fragments crustacean and fish fecal material detrital aggregates and mineral grains one lst deployment at a control site 74 km away in open water devoid of icebergs collected diatom frustules euphausiid molts crustacean fecal material and detrital aggregates phytoplankton abundance microbial abundance and biomass were significantly higher in the lst samples than in open water collections at 500 m depth the mean mass flux and organic carbon flux associated with iceberg c 18a were twice as high 124 mg m 2 d 1 and 5 6 mg corg m 2 d 1 respectively than at the control site a similar trend was observed in corg 234th activity being highest near c 18a and lowest at the control site extrapolation of the area of enrichment to 30 km radius around c 18a 2826 km2 produces an estimated mass flux of 350 tons d 1 and carbon flux of 15 8 tons corg d 1 five similar sized icebergs to c 18a were identified in satellite images in a surrounding 47 636 km2 area at the same time of sampling assuming a 30 km radius as the area of influence around each of these five icebergs 46 of the total area would be enhanced with an export flux at 600 m of 122 4 tons corg d 1 the large numbers of smaller icebergs identified visually in this area would only increase this area of influence icebergs serve as areas of local enrichment and with increased proliferation must be considered in the cycling of carbon in the southern ocean

silicate and sulphide thermobarometry of low to medium grade metamorphic rocks from holkham bay south east alaska the western metamorphic belt of the coast plutonic complex south east alaska and adjacent british columbia contains strongly deformed rocks and a prominent topographic low the coast range megalineament near holkham bay south east alaska the lineament separates the western metamorphic belt into a western low grade greenschist facies terrane and an eastern medium grade amphibolite facies terrane sphalerite compositions of grains in direct contact with pyrite and pyrrhotite in chlorite muscovite zone rocks in the low grade terrane give pressures of about 8 kbar compatible with pressures of 8 10 kbar at 500 c calculated from plagioclase biotite garnet muscovite assemblages adjacent to the windham bay pluton about 15 km away a pressure of 4 8 0 7 kbar was calculated from sphalerite compositions in staurolite zone rocks east of the coast range megalineament this is indistinguishable from pressures of 4 8 1 kbar at 585 c and 5 1 1 kbar at 680 c plagioclase garnet aluminum silicate quartz equilibria and 4 1 1 kbar at 585 c plagioclase biotite garnet muscovite equilibrium determined for the medium grade terrane an identical pressure of 4 8 0 7 kbar was calculated from sphalerite compositions in biotite zone rocks adjacent to the lineament this is considerably higher than a pressure of 3 1 1 kbar at 525 c obtained using plagioclase biotite garnet muscovite geobarometry from shear zones within the lineament the discrepancy may be explained by later equilibration of mineral phases within the shear zones the geothermobarometry suggests relatively low temperatures and high pressures for the low grade terrane 6 10 kbar and intermediate temperatures and pressures for the medium grade terrane to the east 4 6 kbar comparison of the barometers indicate that sphalerite can be used to estimate metamorphic pressures similar to those estimated from silicate mineral chemistry when pyrrhotite sphalerite pyrite assemblages are used

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

rapid collapse of northern larsen ice shelf antarctica in january 1995 4200 square kilometers of the northern larsen ice shelf antarctic peninsula broke away radar images from the ers 1 satellite complemented by field observations showed that the two northernmost sections of the ice shelf fractured and disintegrated almost completely within a few days this breakup followed a period of steady retreat that coincided with a regional trend of atmospheric warming the observations imply that after an ice shelf retreats beyond a critical limit it may collapse rapidly as a result of perturbated mass balance

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

high resolution reconstruction of southwest atlantic sea ice and its role in the carbon cycle during marine isotope stages 3 and 2 1 recent modeling suggests that changes in southern ocean sea ice extent potentially regulated the exchange of co2release between the ocean and atmosphere during glacials unfortunately a lack of high resolution sea ice records from the southern ocean has prevented detailed testing of these model based hypotheses with field data here we present high resolution records of southern ocean sea ice for the period 35 15 cal ka bp derived from diatom assemblages measured in three glacial sediment cores forming an 8 transect across the scotia sea southwest atlantic chronological control was achieved through a novel combination of diatom abundance stratigraphy relative geomagnetic paleointensity data and down core magnetic susceptibility and ice core dust correlation results showed that the winter sea ice edge reached its maximum northward extent of 53 s at least 3 north of its modern limit between 25 and 23 5 cal ka bp predating the last glacial maximum lgm maximum northward expansion of the summer sea ice edge also pre dated the lgm advancing to at least 61 s and possibly as far north as 55 s between 31 and 23 5 cal ka bp a 12 advance from its modern position a clear shift in the seasonal sea ice zone is evident following summer sea ice edge retreat at 23 5 cal ka bp potentially related to austral insolation forcing this resulted in an expanded seasonal sea ice zone between 22 5 cal ka bp and deglaciation our field data confirm that southern ocean sea ice had the physical potential to influence the carbon cycle both as a physical barrier and more importantly through the suppression of vertical mixing and cycling of pre formed nutrients our data indicates that southern ocean sea ice was most effective as a physical barrier between 31 and 23 5 cal ka bp and as a mechanism capable of reducing vertical mixing between 22 5 cal ka bp and deglaciation however poor correlations with atmospheric co2 variability recorded in ice cores particularly the lack of a co2response during a rapid sea ice meltback event recorded at our study sites at the same time as antarctic isotopic maximum 2 suggest that southern ocean sea ice in the scotia sea did not play a controlling role in atmospheric co2 variation during the glacial

distribution of diatoms in surface sediments of prydz bay antarctica abstract four diatom assemblages are identified from the surface sediments of prydz bay and the mac robertson shelf using multivariate analysis a coastal assemblage is characterised by the sea ice diatoms fragilariopsis curta f angulata f cylindrus and pseudonitzschia turgiduloides a continental shelf assemblage is characterised by sea ice and ice edge diatoms and an oceanic assemblage is characterised by the open water diatoms fragilariopsis kerguelensis thalassiosira lentiginosa t gracilis var expecta and trichotoxin reinboldii the cape darnley assemblage contains both sea ice and open water diatoms but all are characteristically large and heavily silicified multiple regression has been used to identify the relationships between the diatom assemblages and known environmental variables there are strong correlations between the coastal shelf and oceanic assemblages and ecological conditions including latitude sea ice distribution and ocean currents the cape darnley assemblage is thought to represent an assemblage from which the smaller and more lightly silicified species have been removed by current winnowing

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

rapid bottom melting widespread near antarctic ice sheet grounding lines as continental ice from antarctica reaches the grounding line and begins to float its underside melts into the ocean results obtained with satellite radar interferometry reveal that bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed the melting rate is positively correlated with thermal forcing increasing by 1 meter per year for each 0 1 c rise in ocean temperature where deep water has direct access to grounding lines glaciers and ice shelves are vulnerable to ongoing increases in ocean temperature

geothermometry and geobarometry of inverted metamorphic zones in the w central scottish dalradian the attitude of the garnet isograd surface in the balquhidder region of the scottish dalradian is such that the metamophic zones must be inverted higher grade rocks overlying lower grade rocks textural and structural information indicates that peak barrovian metamorphism post dates emplacement of the tay nappe as post metamorphic folds are open and upright no tectonic means of overturning the isograd surface can be invoked metamorphism must have occurred in a negative thermal gradient the metamorphic temperature at the garnet isograd is about 500 c and increases along a negative metamorphic gradient perpendicular to the isograd surface of about 27 c km metamorphic pressure is about 9 kbar the initial temperature inversion was probably caused by emplacement of the tay nappe it is unlikely that subsequent conductive thermal relaxation alone would have caused inverted metamorphic zonation however the relaxative process may have been sufficiently modified by convective transfer of heat by fluid evolved from metamorphic reactions for this to occur

polymetamorphism in the dalradian of the central scottish highlands systematic variations in both timing and conditions of metamorphism are observed in the dalradian rocks of central perthshire scotland early d2 d3 and syn d3 relatively low pressure metamorphism 550 c 7 kb occurs in the flat belt rocks of the tay nappe to the south and later post d3 higher pressure conditions 550 c 9 kb dominate the steep belt to the north the latter appear to be superimposed on earlier low pressure assemblages chloritoid biotite with the pressure increase probably relating to formation of the tummel steep belt possibly near 460 ma this polymetamorphism in addition to the generally high pressures of barrovian metamorphism throughout perthshire may account for the poor development of the metamorphic zonal pattern in this region compared to the eastern dalradian

abundant sulphate in the neoproterozoic ocean implications of constant δ34s of barite in the aberfeldy sedex deposits scottish dalradian the timing and extent of ocean oxygenation is controversial proterozoic sulphur isotope datasets often show marked fluctuations over small stratigraphic intervals suggesting that oceanic sulphate concentrations were much lower than modern values a large accumulation of neoproterozoic sulphate 8 million tonnes preserved as stratiform barite rock is located in the grampian highlands near aberfeldy diagenetic metamorphic alteration has caused pronounced 34s variations near bed margins this aside barite throughout the deposits shows a narrow range in 34s mean 36 1 5 we infer that this is representative of contemporaneous seawater sulphate and that 34sseawater was constant during deposition of a stratigraphical thickness 250m of mostly fine grained clastic sediments uniformity of 34sseawater during barite precipitation even in thick 10m beds and with the co occurrence of abundant sulphides incorporating bacteriogenically reduced sulphur implies no limit to availability of seawater sulphate during hydrothermal exhalative events our data combined with previous 34s research on dalradian metasediments suggest a stability abundance and constancy of ocean sulphate in the neoproterozoic this contrasts with isotopic data using trace sulphate in limestones it appears that around the time of the marinoan glaciation c 635 ma the ocean although stratified at least locally comprised a substantial reservoir of sulphate bearing oxygenated seawater

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

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

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

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

paleoenvironmental analyses of surface sediments from the bohai sea china using diatoms and silicoflagellates diatom and silicoflagellate fossils from surface sediments were analyzed at 63 sites in the bohai sea their spatial variations of the fossils were indicative of past environmental conditions hydrodynamics and the interaction of the yellow sea intrusion and yellow river discharge into the bohai sea in total 162 taxa were identified higher species diversity and lower abundance occurred near the mouth of the yellow river and laizhou bay while lower species diversity and higher abundance occurred in the central bohai sea and bohai strait the spatial differences between fossil diversity and abundance are strongly related to the freshwater and sediment inputs from the yellow river lower salinity provides a diverse habitat for brackish and marine species while a higher deposition rate can dilute the fossil concentrations three distinct biofacies representing the laizhou bay central bohai sea and bohai strait were classified after principal component analysis the dominant species along the salinity gradient shifted from paralia sulcata in the bohai strait to cyclotella stylorum and dictyocha messanensis in the laizhou bay while a mixing zone existed in the central bohai sea the canonical correspondence analysis between major species and environmental factors indicated a relationship between p sulcata and the yellow sea intrusion with significant positive correlations being observed between salinity gradient water depth and autumn temperature in comparison c stylorum and d messanensis were related to the discharge of the yellow river having significant positive correlations with the low salinity and nutrient rich environment c 2014 elsevier b v all rights reserved

recent atmospheric warming and retreat of ice shelves on the antarctic peninsula in 1978 mercer1 discussed the probable effects of climate warming on the antarctic ice sheet predicting that one sign of a warming trend in this region would be the retreat of ice shelves on the antarctic peninsula analyses of 50 year meteorological records have since revealed atmospheric warming on the antarctic peninsula2 3 and a number of ice shelves have retreated4 8 here we present time series of observations of the areal extent of nine ice shelves on the antarctic peninsula showing that five northerly ones have retreated dramatically in the past fifty years while those further south show no clear trend comparison with airtemperature data shows that the pattern and magnitude of ice shelf retreat is consistent with the existence of an abrupt thermal limit on iceshelf viability the isotherm associated with this limit having been driven south by the atmospheric warming ice shelves therefore appear to be sensitive indicators of climate change

extensive phytoplankton blooms in the atlantic sector of the glacial southern ocean 1 the sources and sinks of atmospheric carbon dioxide over glacial interglacial cycles are under debate variation in productivity of the antarctic circumpolar current acc could potentially play a significant role but current interpretations of sedimentary geochemical proxies suggest that glacial productivity was not higher than today we present areal and down core distribution patterns of previously overlooked diatom resting spores that indicate the occurrence of extensive phytoplankton blooms across the entire atlantic sector of the acc particularly in the seasonal ice zone siz linked to higher iron input during the last glacial sea ice acts as an effective transporter of iron and enhances its bioavailability the dominance of the deep living radiolarian cyladophora davisiana in glacial siz sediments indicates that organic carbon export to mesopelagic depths was at least tenfold higher than today

recent diatom record of mcmurdo sound antarctica implications for history of sea ice extent analyses of diatom assemblages within surface sediments from mcmurdo sound antarctica document the regional circulation patterns in this large embayment in the southwestern ross sea thalassiosira spp indicative of water column primary productivity is most common in eastern and portions of northwestern mcmurdo sound as a result of its advection into these regions from areas of open water primary productivity surface sediments from southwestern mcmurdo sound are composed mainly of nitzschia curta a small pennate form commonly found both as a member of the sea ice microbial community as well as a dominant component in ice edge blooms in the ross sea the northward advection of oligotrophic water into the western sound from beneath the mcmurdo ice shelf results in the dominance of an autochthonous flora in the southwestern sound sediments deposited during the past 500 years also have been dominated by thalassiosira spp and nitzschia curta thalassiosira spp concentrations reached a maximum between 1600 and 1875 a d corresponding to the time of the little ice age more persistent winds may have been responsible for more prevalent polynyas at that time resulting in greater amounts of open water primary productivity and subsequent higher percentages of thalassiosira spp increased areal extent and or duration of coastal polynyas during the little ice age suggests that within the southwestern ross sea the production of high salinity shelf water and hence antarctic bottom water may have been greater at that time

the biogeography of major diatom taxa in southern ocean surface sediments 3 tropical subtropical species abstract this paper gives a modern circumscription of tropical subtropical diatoms regarding their relationship with sea surface temperatures sst and sea ice cover diatoms from 228 core top sediment samples collected from the southern ocean were studied to determine the geographic distribution of eight major diatom species taxa preserved in surface sediments generally located north of the subantarctic front the comparison of the relative contribution of diatom species with modern february sst and sea ice cover reveals species specific sedimentary distributions regulated both by water temperatures and sea ice conditions although selective preservation might have played some role their presence in surface and downcore sediments from the southern ocean are reliable indicators of high sst and poleward transport of waters from the tropical subtropical atlantic our work supports the use of diatom remains to reconstruct past variations of these environmental parameters via qualitative and transfer function approaches

biogenic silica and diatom thanatocoenosis in surface sediments below the peru chile current controlling mechanisms and relationship with productivity of surface waters abstract based on 76 surface sediment samples collected between ca 22 and 44 s along the chilean coast in the southeast pacific ocean we report on the north south distribution of opal content and diatom concentration and the quantitative and qualitative composition of the preserved diatom community latitudinal differences in the siliceous signal reflect the influence of two main mechanisms of surface water production coastal upwelling off northern and central chile till ca 38 s and nutrient enrichment by the input of cold southern non upwelling associated waters south of ca 38 s the poleward increase in biogenic opal and diatom values parallels well the north south increase of pigment concentration in surface waters as recorded by satellites between 22 and 33 s where low pigment concentrations are measured opal content and diatom concentration are mostly low except at 22 23 s in contrast both higher opal and diatom values at 34 38 s and 41 42 s correspond well with higher pigment estimations preserved diatom populations document the present day dominant hydrographical conditions nutrient enrichment of surface waters due to coastal upwelling results in intensive production of diatoms off northern and central chile reflected by the predominance of the richly composed association of chaetoceros spores north of ca 38 s the diatom association shows that the area between 35 and 38 s is transitional the abrupt decrease of chaetoceros spores south of 38 s off chile coupled with the enhanced contribution of thalassiosira spp representatives of high productivity low temperature waters points to the presumed high nutrient supply by the iron limited nutrient rich antarctic circumpolar water the contribution of benthic diatoms reflects some lateral transport from the near shore area into deeper positions south of 38 s

diatom assemblages from coastal settings of west antarctica abstract diatom assemblages from 33 core tops collected along a 2500 km transect of the northern antarctic peninsula and pine island bay areas were examined for their use as paleoenvironmental proxies environmental affinities of assemblages were interpreted within a broad geographical context and a wide range of ecological conditions four major assemblages were identified three pelagic assemblages related to different sea ice duration sst and other conditions affecting primary production and one benthic and epiphytic dominated assemblage typical of near shore shallow water habitats chaetoceros resting spores are an important component of diatom assemblages their high concentrations may reflect increased primary production and are associated with low total assemblage diversities the lowest diversities are observed at sites with increased resting spore percentages along the nw coast of the antarctic peninsula sedimentation rates strongly influence total diatom concentrations by contrast relative abundances of chaetoceros resting spores remain mostly unaffected by terrigenous flux and may serve as a reliable proxy for primary production this broad sampling of antarctic coastal environments fills a gap in our knowledge of phytoplankton communities in polar regions and helps establish the framework for reconstructing paleoenvironments from the paleorecord

metamorphic conditions and uplift history in central perthshire evidence from mineral equilibria in the foss celsian barite sulphide deposit aberfeldy interlayered lithologies of diverse mineralogy enclosing the middle dalradian syngenetic ba zn pb deposit at foss s of loch tummel in perthshire allow estimates of the p t conditions of metamorphism using several new geothermometers and geobarometers temperatures of 500 560 c are derived from calcite dolomite geothermometry and from data on mg fe partitioning within garnet hornblende and garnet biotite pairs plagioclase biotite garnet muscovite and biotite muscovite chlorite equilibria indicate peak metamorphic pressures of 8 10 kbar which are in agreement with the results of sphalerite geobarometry textural evidence indicates that the rare platy mineral cymrite baa1 2 si 2 o 8 h 2 o was widespread in mineralized lithologies during penetrative deformation and has since largely been replaced by celsian the p t location of the experimentally determined reaction line cymrite ss celsian ss h 2 o places further constraints on the peak metamorphic conditions and suggests that the final episode of penetrative deformation d 3 was followed by a period of near isothermal uplift during which celsian became stable the cymrite field appears to have been re entered during late brittle deformation peak metamorphic conditions recorded by mineral equilibria at foss differ from those of areas 10 km to the n and s

models for the tectonothermal evolution of the eastern dalradian of scotland the preserved array of pressures in the eastern dalradian indicates that considerable syn to post metamorphic differential uplift has occurred this inferred differential uplift suggests that buchan sillimanite zone rocks originally lay at higher structural levels than presently adjacent cooler kyanite zone rocks to the west a number of features are believed to coincide with the western margin of the sillimanite zone these are a maximum in temperature sharp thermal features a high strain zone and a train of metabasites these features are explained by invoking syn metamorphic movement between the buchan sillimanite zone and the kyanite zone to its west involving some horizontal component of movement it is suggested that the lateral now eroded equivalents of the buchan area once provided part of the required tectonic thickening for other parts of the dalradian areas surrounding the buchan area suffered tectonic burial followed by metamorphism during uplift relative to the buchan area

thermohaline stratification below the southern ocean sea ice the end of winter stratification within the cold cyclonic trough of the weddell gyre near 60 s between 5 e and the greenwich meridian is resolved with the mikhail somov data set the temperature maximum of the weddell deep water wdw is for the most part less than 0 5 c but warmer cells of wdw are found these warm wdw cells have temperature salinity and oxygen properties similar to the wdw characteristic of the weddell gyre inflow which is situated to the southeast of the mikhail somov study region the warm wdw cells are accompanied by domes in the pycnocline of 40 m amplitude over the surrounding pycnocline while deeper isopycnals are depressed anticyclonic shear below the 27 83 isopycnal within the warm wdw cells is compensated by the cyclonic shear associated with the pycnocline dome the pycnocline domes are exposed to about 50 greater entrainment by the turbulently active winter mixed layer relative to the regional entrainment rate this entrainment can significantly erode the warm cells in a single winter season introducing excess heat and salt into the mixed layer while the heat is lost to the atmosphere the excess salt is not necessarily compensated by increased fresh water introduction it is hypothesized that the warm wdw cells within the weddell gyre trough are derived from instability within the frontal zone which extends from maud rise to the northeast separating the weddell warm regime from the cold regime greater than normal injection of warm wdw cells into the weddell gyre trough would increase the surface salinity which would tend to destabilize the pycnocline increasing the probability of deep convection and polynya events

sphalerite geobarometry in the cu fe zn s system phase relations have been determined among sphalerite pyrite pyrrhotite and intermediate solid solution iss from 439 degrees to 725 degrees c at 1 bar and 353 degrees to 760 degrees c at 5 kb the extents of solid solution in the four phase assemblage are described as functions of temperature in kelvins by the following equations log mole zns in iss 1 bar 2 795 1 632 t super 1 log mole zns in iss 5 kb 2 659 1 608 t super 1 log mole cus in pyrrhotite 1 bar 2 546 1 866 t super 1 log mole cus in sphalerite 1 bar 4 202 3 755 t super 1 and log mole cus in sphalerite 5 kb 4 084 3 791 t super 1 the pressure dependence in kb of the composition of sphalerite in equilibrium with pyrite and pyrrhotite with or without iss can be expressed for the temperature independent portion of the sphalerite geobarometer as p 42 30 32 10 log mole fes because of the low solubility of copper in sphalerite in the four phase assemblage below 650 degrees c the presence of chalcopyrite in natural ores should be of no consequence to sphalerite geobarometry over its temperature independent portion nevertheless sphalerites which are inhomogeneous in fes and which contain abundant blebs of chalcopyrite in excess of the amount that can be reasonably accounted for by an equilibrium process of solubility and subsequent exsolution are a common feature of many sulfide ores such sphalerite grains should be avoided in applying the geobarometer the chalcopyrite blebs may be a product of a premetamorphic sphalerite chalcopyrite intergrowth or represent true exsolution from sphalerite in any one of 1 a former sphalerite pyrrhotite iss equilibrium 2 a stable four phase assemblage at temperatures above the temperature independent portion of the geobarometer or 3 a metastable four phase assemblage in which pyrite was inert use of the sphalerite geobarometer requires a thorough understanding of the textural relationships and discrimination of equilibrium from disequilibrium or low temperature reequilibrated assemblages

southern ocean winter mixed layer austral winter 1986 observations from the polarstern along the greenwich meridian from the ice edge to the antarctic margin show the mixed layer beneath the winter sea ice cover to be significantly depressed in oxygen saturation incorporation of weddell deep water wdw into the winter mixed layer responsible for this undersaturation also introduces heat and salinity into the surface layer which strongly influences the mixed layer sea air exchanges and sea ice formation processes the total wdw transfer into the mixed layer averages 45 myr 1 implying a residence time for the surface water of 2 5 years the associated winter heat flux is 41 w m 2 which limits ice thickness to about 0 55 m agreeing quite well with observations the air temperatures during the cruise are just sufficient to remove the wdw heat input in the presence of observed ice thickness and concentration this suggests that the sea ice cover and wdw heat input into the mixed layer are in approximate balance by midwinter the annual heat flux from wdw to the surface layer and hence into the atmosphere is estimated as 16 w m 2 extrapolation of the greenwich meridian wdw entrainment value to the full circumpolar 60 70 s belt yields total up welling of 24 106 m3 s 1 similar extrapolation of the heat flux value gives a circumpolar total of 2 8 1014 w as a consequence of circulation topography interaction the maud rise water column stands out as an anomaly relative to the surrounding region with a significantly more saline and dense mixed layer below the mixed layer the water column over the crest of the rise is identical to that over the flanks if the latter water column is upwelled by 400 m this uplifting is believed to be a response of the upstream flow encountering the rise increased upstream flow would be expected to increase maud rise upwelling and the dependent salinity density of the mixed layer slight increases in the mixed layer density could trigger a convective mode and generation of a polynya it is hypothesized that spin up of the weddell gyre s barotropic circulation induced by an increase of the regional wind stress curl would enhance the probability of polynya development over maud rise

uplift patterns and orogenic evolution in the scottish dalradian rb sr and k ar mineral ages from the dalradian rocks of angus and perthshire indicate considerable diachronism of cooling following the caledonian regional metamorphism the oldest mineral ages 515 ma are similar to the independent estimates of peak metamorphic age and hence indicate very rapid cooling they occur in the highest grade samples of the angus region and are associated with localized uplift regional rapid uplift events at 460 440 ma and 410 390 ma may also be recognized and correlated with structural and igneous activity and metamorphic age dates within the scottish highlands thermal models show the importance of localized and discontinuous uplift in determining both the timing of metamorphism and the shape of the p t paths they suggest that the major diachronous metamorphism and granite production in the scottish highlands is depth controlled rather than representing major lateral diachronism of thickening or heat sources localized uplift may exercise considerable control on mineral facies variation within orogenic belts the local uplift in angus introduces hot high pressure tarfside nappe rocks into higher level tay nappe rocks thus the uniform block uplift models frequently used in the interpretation of metamorphic and structural phenomena in orogenic belts are an oversimplification of the real events

a new geobarometer for the assemblage biotite muscovite chlorite quartz the equilibrium thermodynamics of the reaction 4kmga1si40 o oh mg5a1 si30 o oh muscovlte chlorite muscovite biotite ka13si 0 oh 3kmg3aisi 0 0 oh 7si0 4h o quartz fluid can be formulated as a geobarometer thermo dynamic data for the mg a1 celadonite end member of muscovite is derived from the reversed mineral equilibria experiments of velde i 965 using the calculation method of powell 1978 giving afh 1298 5823 5 kj s 1298 0 3060kjk v 1298 13 8kjkbar

cymrite and celsian in manganese rich metamorphic rocks from andros island greece manganese rich rocks from the island of andros cyclades greece contain cymrite baal2si2o8 h2o and celsian the textural relationships indicate replacement of celsian by cymrite several microprobe analyses of cymrites show a solid solution of 0 7 6 1 mole kalsi3o8 h2o the relic celsians have similar k contents thus the described rocks from andros represent the first natural example for the reaction celsian water cymrite the rocks from andros underwent an eocene high pressure metamorphism lateron the high pressure parageneses were nearly effaced by a late oligocene barrovian type metamorphism it is assumed that both cymrite and celsian were formed at conditions near the reaction curve celsianss water cymritess during the barrovian type event

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 response of the bering sea gateway during the mid pleistocene transition abstract the mid pleistocene transition and the response of sea ice in the subarctic north pacific are examined using a diatom record from the north eastern bering sea slope iodp core u1344a high percentages of diatom sea ice species in the assemblage foster the development of groupings specific to differing ice conditions thalassiosira antarctica var borealis emerges as a key diatom species that delineates the development of thick multiannual sea ice and marks a series of advancements from 0 9 to1 2 ma after which it dominates the assemblage until 0 6 ma the decline of neodenticula seminae indicative of alaskan stream water inflow is in agreement with neighbouring core u1343e confirming the reduction of bering sea circulation after 0 9 ma we propose that during the mpt a stepped advancement of sea ice occurs in the bering sea as a response to increased moisture delivery to the high latitudes an extended period of diatom productivity between 0 75 and 0 65 ma marks major deglacial conditions towards the end of the mpt by 0 6 0 55 ma the work highlights the important role played by sea ice and supports the contention of a colder mpt in the subarctic pacific

observations on the relationship between the antarctic coastal diatoms thalassiosira antarctica comber and porosira glacialis grunow jorgensen and sea ice concentrations during the late quaternary the available ecological and palaeoecological information for two sea ice related marine diatoms bacillariophyceae thalassiosira antarctica comber and porosira glacialis grunow jorgensen suggests that these two species have similar sea surface temperature sst sea surface salinity sss and sea ice proximity preferences from phytoplankton observations both are described as summer or autumn bloom species commonly found in low sst waters associated with sea ice although rarely within the ice both species form resting spores rs as irradiance decreases sst falls and sss increases in response to freezing ice in autumn recent work analysing late quaternary seasonally laminated diatom ooze from coastal antarctic sites has revealed that sub laminae dominated either by t antarctica rs or by p glacialis rs are nearly always deposited as the last sediment increment of the year interpreted as representing autumn flux in this study we focus on sites from the east antarctic margin and show that there is a spatial and temporal separation in whether t antarctica rs or p glacialis rs form the autumnal sub laminae for instance in deglacial sediments from the mertz ninnis trough george v coast p glacialis rs form the sub laminae whereas in similar age sediments from iceberg alley mac robertson shelf t antarctica rs dominate the autumn sub lamina in the dumont d urville trough adelie land mid holocene hypsithermal warm period autumnal sub laminae are dominated by t antarctica rs whereas late holocene neoglacial cool period sub laminae are dominated by p glacialis rs these observations from late quaternary seasonally laminated sediments would appear to indicate that p glacialis prefers slightly cooler ocean climate conditions than t antarctica we test this relationship against two down core holocene quantitative diatom abundance records from dumont d urville trough and svenner channel princess elizabeth land and compare the results with sst and sea ice concentration results of an antarctic and southern ocean holocene climate simulation that used a coupled atmosphere sea ice vegation model forced with orbital parameters and greenhouse gas concentrations we find that abundance of p glacialis rs is favoured by higher winter and spring sea ice concentrations and that a climatically sensitive threshold exists between the abundance of p glacialis rs and t antarctica rs in the sediments an increase to 0 1 for the ratio of p glacialis rs t antarctica rs indicates a change to increased winter sea ice concentration to 80 concentration cooler spring seasons with increased sea ice slightly warmer autumn seasons with less sea ice and a change from 7 5 months annual sea ice cover at a site to much greater than 7 5 months in the east antarctic sediment record an increase in the ratio from 0 1 to above 0 1 occurs at the transition from the warmer hypsithermal climate into the cooler neoglacial climate 4 cal kyr indicating that the ratio between these two diatoms has the potential to be used as a semi quantitative climate proxy

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

holocene history of the larsen a ice shelf constrained by geomagnetic paleointensity dating a sedimentary record collected from beneath the former lar sen a ice shelf reveals the holocene history of the larsen a re gion the record begins with the transition from grounded ice to a floating ice shelf completed by 10 7 6 0 5 ka and ends with the modern recession the record contains several late holocene dia tomaceous ooze layers that suggest proximity to productive open water events radiocarbon ages obtained from these sediments were complicated by the presence of detrital and reworked carbon we have eliminated these complications and constructed a chro nology for the larsen a ice shelf history via tuning of the geo magnetic field paleointensity record with a reference curve this approach provides chronological control to sediment sequences that lack appropriate material for radiocarbon dating geomag netic paleointensity features with wavelengths of 2 3 k y can be recognized and interhemispherically correlated illustrating the po tential to use geomagnetic paleointensity variations as a global cor relation and dating tool at sub milankovitch time scales

biogenic and abiogenic components of laminated hemipelagic sediments in the central gulf of california abstract alternating light and dark submillimeter to millimeter thick layered sediments rhythmites are found along the slopes of the central and southern gulf of california where a strong oxygen minimum zone intersects the sediment water interface two short intervals of distinct alternations were sampled lamina by lamina from two cores in the central gulf both cores are from the slope of the guaymas basin one core is from the mainland side the other core is from the baja side each lamina sample was analyzed for its opal micro floral assemblage textural character trace metal and bulk chemical cu mn fe ni zn ca k al sio2 and c org content and mineralogy on both sides of the gulf the light laminae contain more diatom frustules up to 90 and less terrigenous and organic material than the dark laminae the sediment is predominantly silt sized the dark laminae contain more terrigenous material which is primarily clay size on both sides of the gulf the light laminae apparently represent sedimentation during the dry winter season of northwesterly winds whereas the dark laminae represent the wet summer season of southeasterly winds

sea surface temperatures in disko bay during the little ice age caution needs to be exercised before assigning thalassiosira kushirensis resting spore as a warm water indicator in palaeoceanographic studies