rapid vegetation change during the early holocene in the faroe islands detected in terrestrial and aquatic ecosystems high resolution pollen plant macrofossil and sedimentary analyses from early holocene lacustrine sediments on the faroe islands have detected a significant vegetation perturbation sug gesting a rapid change in climate between ca 10 380 cal yr bp and the saksunarvatn ash 10 240 60 cal yr bp this episode may be synchronous with the decline in 18 o values in the greenland ice cores it also correlates with a short cold event detected in marine cores from the north atlantic that has been ascribed to a weakening of thermohaline circulation associated with the sudden drainage of lake agassiz into the northwest atlantic or alternatively a period with dis tinctly decreased solar forcing the vegetation sequence begins at ca 10 500 cal yr bp with a succession from tundra to shrub tundra and increasing lake productivity rapid population increases of aquatic plants suggest high summer temperatures between 10 450 and 10 380 cal yr bp high pollen percentages concentra tions and influx of betula juniperus and salix together with macrofossil leaves indicate shrub growth around the site during the initial phases of vegetation colonisation unstable conditions followed ca 10 380 cal yr bp that changed both the upland vegetation and the aquatic plant communities a decrease in percentage values of shrub pollen is recorded with replacement of both aquatics and herbaceous plants by pioneer plant communities an increase in total pollen accumulation rates not seen in the concentration data suggests increased sediment delivery the catchment changes are consistent with less seasonal moister conditions subsequent climatic amelioration reinitiated a warmth driven succession and catchment stabilisation but retained high precipitation levels influ encing the composition of the post event communities copyright 2003 john wiley sons ltd

a study of cleaning procedures used for foraminiferal mg ca paleothermometry the various cleaning steps required for preparation of foraminiferal samples for mg ca and sr ca analysis are evaluated for their relative importance and effects on measured elemental ratios it is shown that the removal of silicate contamination is the most important step for the measurement of mg ca ratios in an example bulk sample mg ca decreases from 10 5 to 2 5 mmol mol 1 during clay removal oxidation of organic material causes a lowering of sample mg ca in the order of 10 or approximately 1 c when converted to temperature use of dilute acid leaching to remove adsorbed contaminants causes partial dissolution of the sample carbonate and a corresponding decrease in mg ca reductive treatment also causes dissolution of the sample and a decrease in the mg ca ratio of up to 10 15 sample preparation for sr ca analysis does not require the same degree of rigor as is necessary for mg ca work the within run reproducibility of the method described here for g ruber in a core top sample from the arabian sea was 1 8 mean sample ratio was 4 72 mmol mol 1 when converted to temperature this becomes 28 0 2 c the equivalent result for sr ca was 0 5 mean ratio 1 44 mmol mol 1

late quaternary diatom assemblages from prydz bay eastern antarctica abstract the paleo depositional environment of inner prydz bay east antarctica has been reconstructed for the past 21 320 14c yr b p using diatom assemblages and sediment facies from a short 352 cm long gravity core between 21 320 and 11 650 14c yr b p compact tillite and diamicton are present in the core and diatom frustules are rare to absent these data suggest that an ice sheet grounded over the site during the last glacial maximum following glacial retreat siliceous muddy ooze was deposited from 11 650 to 2600 14c yr b p in an open marine setting during this stage diatom frustules are abundant and well preserved and thalassiosira antarctica resting spores and fragilariopsis curta dominate the assemblage this assemblage suggests open marine deposition in an environment where the spatial and temporal distribution of sea ice is less than today since 2600 14c yr b p sea ice and ice edge diatom species have become more abundant and neoglacial cooling is inferred the assemblage is similar to that forming currently in prydz bay where sea ice is absent

kerguelen plateau quaternary late pliocene palaeoenvironments from diatom silicoflagellate and sedimentological data abstract gravity cores from the south kerguelen plateau contain sections representing two quaternary intervals 1

reconstruction of the last deglaciation deconvolved records of δ18o profiles micropaleontological variations and accelerator mass spectrometric14c dating bioturbation acts as a low pass filter in displacing and reducing the amplitudes of stratigraphic signals this often leads to a loss of high frequency events in the stratigraphic record in addition when considering an isotopic signal 18o 14c measured in stratigraphic carriers such as foraminifera bioturbation and carrier abundance changes can create artifacts which may be falsely interpreted as leads or lags in the paleoclimatic record

late pleistocene holocene marine conditions in the ross sea antarctica evidence from the diatom record statistical analyses of diatom assemblages from radiocarbon dated sediment cores were used to reconstruct changing palaeoceanographic conditions in the western and west central ross sea antarctica from c 12 14c kyr bp to the present data from three kasten cores support a north to south time transgressive glacial interglacial transition assemblages at the base of each core suggest that glacial processes affecting frustule preservation were significant during the late pleistocene increasing biogenic silic and decreasing per centages of reworked species suggest that upper water column productivity instead of preservational processes increasingly dominates diatom assemblages during grounding line recession c 12to c 6 14c kyr bp a warm ing during the middle to late holocene c 6to c 3 14c kyr bp may have resulted in a spring sea ice melting prior to the annual inception of the ross sea polynya in the west central ross sea and b increased plateletice delivery due to increased melting beneath t

paleo sea surface temperature calculations in the equatorial east atlantic from mg ca ratios in planktic foraminifera a comparison to sea surface temperature estimates from u37k oxygen isotopes and foraminiferal transfer function we present two 270 kyr paleo sea surface temperature sst records from the equatorial divergence and the south equatorial current derived from mg ca ratios in the planktic foraminifer globigerinoides sacculifer the present study suggests that the magnesium signature of g sacculifer provides a seasonal sst estimate from the upper 50 m of the water column generated during upwelling in austral low latitude fall winter common to both down core records is a glacial interglacial amplitude of 3 3 5 c for the last climatic changes and lower holocene and glacial oxygen isotope stage 2 temperatures compared with interglacial stage 5 5 and glacial stage 6 temperatures respectively the comparison to published sst estimates from alkenones oxygen isotopes and foraminiferal transfer function from the same core material pinpoints discrepancies and conformities between methods

sea surface temperature and productivity records for the past 240 kyr in the arabian sea abstract deep sea sediments of two cores from the western ty93 929 p and the southeastern md900963 arabian sea were used to study the variations of the indian monsoon during previous climatic cycles core ty93 929 p was located between the sw monsoon driven upwelling centres off somalia and oman which are characterized by large seasonal sea surface temperature sst and particle flux changes by contrast core md900963 was situated near the maldives platform an equatorial ocean site with a rather small sst seasonality less than 2 c for both cores we have reconstructed sst variations by means of the unsaturation ratio of c37 alkenones which is compared with the 18o records established on planktonic foraminifera in general the sst records follow the 18o variations with an sst maximum during oxygen isotope stage 5 5 the last interglacial at about 120 130 kyr and a broad sst minimum during isotope stage 4 and 3 3 approximately 40 50 kyr the sst difference between the holocene and the last glacial maximum lgm is of the order of 2 c in both cores the ssts during isotope stage 6 are distinctly higher by 1 2 c than the cold sst minima during the last glacial cycle lgm and stage 3 to reconstruct qualitatively the past productivity variations for the two cores we used the concentrations and fluxes of alkenones and organic carbon together with a productivity index based on coccolith species florisphaera profunda relative abundance within each core there is a general agreement between the different palaeoproductivity proxies in the southeastern arabian sea core md900963 glacial stages correspond to relatively high productivity whereas warm interstadials coincide with low productivity all time series of productivity proxies are dominated by a cyclicity of about 21 23 kyr which corresponds to the insolation precessional cycle a hypothesis could be that the ne monsoon winds were stronger during the glacial stages which induced deepening of the surface mixed layer and injection of nutrients to the euphotic zone by contrast the records are more complicated in the upwelling region of the western arabian sea core ty93 929 p this is partly due to large changes in the sedimentation rates which were higher during specific periods isotope stages 6 5 4 5 2 3 and 2 unlike core md900963 no simple relationship emerges from the comparison between the 18o stratigraphy and productivity records the greater complexity observed for core ty93 929 p could be the result of the superimposition of different patterns of productivity fluctuations for the two monsoon seasons the sw monsoon being enhanced during interglacial periods whereas the ne monsoon was increased during glacial intervals a similar line of reasoning also could help explain the sst records by the superimposition of variations of three components global atmospheric temperature and sw and ne monsoon dynamics

eastern pacific sea surface temperature since 1600 a d the δ18o record of climate variability in galapagos corals we measured stable oxygen isotope ratios and skeletal growth rates in the massive corals pavona clavus and p gigantea from the west coast of isabela island galapagos to assess interannual to decadal climate variability in the eastern pacific comparisons of instrumental data sets show that sea surface temperatures sst in the galapagos region are representative of a broad portion of the eastern equatorial pacific the site is especially well suited for long term studies of the el nino southern oscillation enso phenomenon as it lies within the eastern pacific center of action for thermal anomalies associated with enso the p gigantea isotope record is nearly monthly in resolution spans the period 1961 1982 and shows strong correlation with a galapagos instrumental sst record r 0 90 for annual averages cross spectral analysis shows that sst can explain greater than 80 of the variance in 18o at both the annual cycle and within the high frequency portion of the enso band 3 5 years the p clavus record is annual in resolution extends from 1587 to 1953 a d and was obtained from a 10 m diameter colony preserved within the urvina bay uplift because seawater 18o variations in the region are very small we interpret the urvina bay coral 18o record in terms of annual average sst the isotopic record appears to be a very good but not perfect indicator of enso events and shows good correspondence with the historical enso reconstruction of quinn et al 1987 a number of low 18o excursions that we observe during the 17th and 18th centuries very likely represent enso events that are missing from the historical tabulations most interannual 18o variations between 1607 and 1953 a d represent annual average temperature excursions of 1 to 2 5 c during the little ice age the annual 18o series correlates well with many north american tree ring records and shows low temperatures during the early 1600s and early 1800s and relatively warmer conditions during the 1700s unlike most northern hemisphere tree ring and instrumental records we see no evidence at this site for warming between 1880 and 1940 but rather observe a slight cooling 28 of the total variance the main enso mode is centered at 4 6 years and accounts for 12 of the total variance additional significant oscillations occur at periods of 3 3 6 8 11 17 22 and 34 years both annual growth rate and 18o show variance at periods equivalent to the solar and solar magnetic periods e g 11 and 22 years respectively in addition the amplitude of the 11 year 18o cycle generally varies with the amplitude of the solar cycle supporting previous suggestions that the solar cycle may modulate interannual to decadal climate variability in the tropics the dominant oscillatory modes both within the enso and interdecadal frequency bands shift to shorter periods from the early to middle 1700s and again from the middle to late 1800s this may reflect major reorganizations within the tropical ocean atmosphere system and suggests that tropical pacific climate variability is linked across timescales ranging from years to decades

western arabian sea sst during the penultimate interglacial a comparison of u37k and mg ca paleothermometry millennial scale records of planktonic foraminiferal mg ca bulk sediment u37 k and planktonic foraminiferal 18o are presented across the last two deglaciations in sediment core niop929 from the arabian sea mg ca derived temperature variability during the penultimate and last deglacial periods falls within the range of modern day arabian sea temperatures which are influenced by monsoon driven upwelling the u37 k derived temperatures in mis 5e are similar to modern intermonsoon values and are on average 3 5 c higher than the mg ca temperatures in the same period mis 5e u37 k and mg ca temperatures are 1 5 c warmer than during the holocene while the u37 k mg ca temperature difference was about twice as large during mis 5e this is surprising as nowadays both proxy carriers have a very similar seasonal and depth distribution partial explanations for the mis 5e u37 k mg ca temperature offset include carbonate dissolution the change in dominant alkenone producing species and possibly lateral advection of alkenone bearing material and a change in seasonal or depth distribution of proxy carriers our findings suggest that 1 mg ca of g ruber documents seawater temperature in the same way during both studied deglaciations as in the present with respect to e g season and depth and 2 u37 k based temperatures from mis 5 or older represent neither upwelling sst nor annual average sst as it does in the present and the holocene but a higher temperature despite alkenone production mainly occurring in the upwelling season further we report that at the onset of the deglacial warming the mg ca record leads the u37 k record by 4 ka of which a maximum of 2 ka may be explained by postdepositional processes deglacial warming in both temperature records leads the deglacial decrease in the 18o profile and mg ca based temperature returns to lower values before 18o has reached minimum interglacial values this indicates a substantial lead in arabian sea warming relative to global ice melting

quantifying carbonate dissolution and calibration of foraminiferal dissolution indices in the somali basin two sediment traps moored off somalia in 1992 1993 collected similar settling fluxes of carbonate and siliceous shells formed by various plankton groups planktic foraminifera showed large seasonal variations with more than 74 of the total planktic foraminifera flux collected during the sw monsoon summer upwelling when globigerina bulloides was dominating along with globigerinita glutinata and neogloboquadrina dutertrei the intermonsoon and ne monsoon assemblages were dominated by globigerinoides ruber we used the trap records as our no dissolution reference for comparison with three boxcore recorders in order to quantify the carbonate dissolution along a depth transect dissolution increases downslope from station 905 to 907 and 915 at depths of 1567 m 2807 m and 4035 m respectively the carbonate fraction of the sediment at station 915 which is located near the ccd is the most affected by dissolution with more than 97 of the planktic foraminifera dissolved here the planktic foraminifera assemblage is strongly modified with thick walled species such as n dutertrei globorotalia tumida and pulleniatina obliquiloculata as the most resistant it is not representative of the settling assemblage the planktic foraminiferal assemblages of the sediment surface at stations 905 and 907 remain similar to the trap assemblages and the foraminifera are well preserved although only 25 of foraminifera are apparently preserved at station 905 and 8 at station 907 those numbers are surprisingly low and infer that only a small fraction of the foraminiferal carbonate production is buried and removed from the carbon cycle this discrepancy between the export and buried flux is partly be due to bio mechanical destruction by benthic processes and to supralysoclinal dissolution due to metabolic co2 generated by the benthic organisms another important factor is the interannual variability of the productivity well known in the arabian sea the calibration of commonly used foraminiferal dissolution indices percentage of foraminiferal fragments percentage of resistant species foraminiferal dissolution index fdx to our data only shows reliable results for high dissolution levels 97 off somalia the most accurate of the proxies is the percentage of foraminiferal fragments compared to the other methods tested i e fdx planktic foraminiferal loss l percentage of radiolarians and diatoms percentage of benthic foraminifera the species assemblage appears to be not significantly modified by dissolution unless the estimated shell loss is high 92 of the arriving shells in our samples this level is expressed in the percentage of fragmentation the percentage of radiolarians and diatoms the percentage of resistant foraminifera species and fdx as 80 35 25 and 1 8 respectively the relative abundance of globigerina bulloides is a valid sw monsoon upwelling proxy only when dissolution is moderate 92 globigerina bulloides and globigerinoides ruber have similar burial efficiencies and susceptibilities to dissolution thus the ratio g bulloides g ruber is a valid proxy for past changes in the intensity of the sw monsoon even in the strongly dissolved samples in our sediment record the ratio g bulloides g ruber indicates that the sw monsoon was stronger in the recent past than in 1992 93

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

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

evolution of a supercooled ice shelf water plume with an actively growing subice platelet matrix we use new observations in western mcmurdo sound combined with longitudinal hydrographic transects of the sound to identify a northward flowing ice shelf water isw plume exiting the cavity of the mcmurdo ross ice shelf we estimate the plume s net northward transport at 0 4 0 1 sv carving out a corridor approximately 35 km wide aligned with the victoria land coast basal topography of the mcmurdo ice shelf is such that the plume is delivered to the surface without mixing with overlying warmer water and is therefore able to remain below the surface freezing temperature at the point of observation beneath first year ice thus the upper ocean was supercooled by up to 50 mk at the surface due to pressure relief from recent rapid ascent of the steep basal slope the 70 m thick supercooled layer supports the growth and maintenance of a thick semirigid and porous matrix of platelet ice which is trapped by buoyancy at the ice ocean interface continued growth of individual platelets in supercooled water creates significant brine rejection at the top of the water column which resulted in convection over the upper 200 m thick homogeneous layer by examining the diffusive nature of the intermediate water between layers of isw and high salinity shelf water we conclude that the isw plume must have originated beneath the ross ice shelf and demonstrate that it is likely to expand eastward across mcmurdo sound with the progression of winter

evidence from diatoms for holocene climate fluctuation along the east antarctic margin diatom assemblages in two holocene sediment cores gc1 and gc2 from the mac robertson shelf east antarctica are compared with modern sedimentary diatom assemblages from the same area open marine deposition commenced in iceberg alley gc1 on the outer continental shelf 10 7 adj 14 c kyr bp

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

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

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

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

calibration of the planktonic foraminiferal mg ca paleothermometer sediment trap results from the guaymas basin gulf of california 1 the mg ca ratio has been measured in two surface dwelling species of planktonic foraminifera globigerinoides ruber and globigerina bulloides from biweekly sediment trap samples collected in guaymas basin gulf of california between august 1992 and november 1997 the guaymas basin experiences significant seasonal changes in sea surface temperature sst 16 33 c and thus is an ideal location for testing the temperature dependence of mg incorporation into foraminiferal calcite the planktonic foraminiferal mg ca ratios are directly compared with concurrent temperature measurements from the study site the results from the sediment trap study reveal a strong positive correlation between sst and the mg ca ratio in both g ruber r2 0 86 and g bulloides r2 0 90 the mg ca ratio increases exponentially by 7 per 1 c change in temperature for g ruber and by 6 for g bulloides these results indicate that the mg ca ratio in g ruber and g bulloides accurately records the measured seasonal surface temperature cycle and interannual variability in the guaymas basin within 1 c the greatest deviation between mg ca estimated sst and observed sst occurs in the spring and fall for both species this variability is attributed to rapidly changing hydrographic conditions and possible offset between the time of calcification and the temperature measurements in addition g ruber and g bulloides exhibit very high mg ca ratios during the strong el nino southern oscillation years of 1992 and 1997 verifying their potential to record sst up to 33 c and 28 c respectively the trace metal data are compared with foraminiferal oxygen isotope and alkenone measurements made on the same suite of sediment trap samples to assess the internal consistency of these temperature proxies strong correlations exist between the 18o and mg ca for g ruber r2 0 86 and g bulloides r2 0 79 similarly sea surface temperature estimates from mg ca ratios are in good agreement with alkenone derived temperature estimates r2 0 89 for g ruber and r2 0 81 for g bulloides

an organic geochemical assessment of oceanographic conditions at manop site c over the past 26 000 years eleven sediment samples taken downcore and representing the past 26 kyr of deposition at manop site c 0 57 2 n 138 57 3 w were analyzed for lipid biomarker composition biomarkers of both terrestrial and marine sources of organic carbon were identified in general concentration profiles for these biomarkers and for total organic carbon toc displayed three common stratigraphic features in the time series 1 a maximum within the surface sediment mixed layer 4 ka 2 a broad minimum extending throughout the interglacial deposit and 3 a deep pronounced maximum within the glacial deposit using the biomarker records a simple binary mixing model is described that assesses the proportion of terrestrial to marine toc in these sediments best estimates from this model suggest that 20 of the toc is land derived introduced by long range eolian transport and the remainder is derived from marine productivity the direct correlation between the records for terrestrial and marine toc with depth in this core fits an interpretation that primary productivity at site c has been controlled by wind driven upwelling at least over the last glacial interglacial cycle the biomarker records place the greatest wind strength and highest primary productivity within the time frame of 18 to 22 kyr b p diagenetic effects limit our ability to ascertain directly from the biomarker records the absolute magnitude that different types of primary productivity have changed at this ocean location over the past 26 kyr

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

interhemispheric synchrony of the last deglaciation inferred from alkenone palaeothermometry the relative timings of the last deglacial warming in the southern and northern hemispheres are not well constrained but are a crucial component in understanding the mechanisms of deglaciation1 a clearer picture of the degree of interhemispheric synchrony has been obscured by a dearth of high resolution temperature records that can be tied to the absolute calendar timescale moreover the quantification of tropical temperatures during the last glacial cycle is controversial2 8 here we apply the alkenone method of sea surface temperature reconstruction9 10 to several high resolution sediment cores recovered from the tropical indian ocean between 20 n and 20 s the inferred initial sea surface temperature warming 15 000 calendar years ago at 20 s is in phase with northern hemisphere sea this study and air11 temperature changes but lags antarctic warming12 14 by several millennia this finding along with the results of recent modelling studies15 16 provides strong support for the idea that changes in the ocean s global thermohaline circulation were not the only cause of interhemispheric climate teleconnection during the last deglaciation

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

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

nine centuries of microparticle deposition at the south pole abstract the analysis of microparticles in a 101 m core from amundsen scott south pole station antarctica has revealed a substantial increase in total particle concentration between approximately 1450 and 1850 a d a period encompassing the latest neoglacial interval or little ice age it is likely that this reflects a simultaneous increase in the concentration of particulate material in the antarctic atmosphere this is important climatologically for the antarctic atmosphere may represent the closest approximation to the natural background aerosol thus cores from east antarctica may contain long and detailed records of the natural global background aerosol such records are unavailable from any other medium additionally a cyclical variation which appears to be annual has been detected in the south pole particle record these features allow construction of a relative time scale for ice cores older than 100 yr from regions of low accumulation 1 where many traditional techniques are not applicable this is especially significant as the comparison of climatic data extracted from ice cores with other records of proxy data depends upon the ability to assign an accurate time scale to the ice core an estimated nine century record of net annual accumulation at the south pole has been compiled and the calculated error in the time scale is 90 yr

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

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

late quaternary insolation forcing on total organic carbon and c37 alkenone variations in the arabian sea we here present records of total organic carbon toc and c37 alkenones used as indicators for past primary productivity from the western was and eastern arabian sea eas new data from an open ocean site of the was upwelling area are compared with similar records from ocean drilling program odp site 723 from the continental margin off oman and md 900963 from the eas these records together with other proxies used to reconstruct upwelling intensity indicate periods of high productivity in tune with precessional forcing on the basis of their phase relationship to boreal summer insolation they can be divided into three groups in the was differences between monsoonal proxies 1 and productivity 2 document a combined signal of moderate sw monsoon winds and of strengthened and prolonged ne monsoon winds whereas in the eas phasing indicates maximum productivity 3 at times of stronger ne monsoon winds associated with precession related maxima in ice volume

a convective model for the weddell polynya abstract mechanisms are considered which may induct the large over 105 km2 area of open water or polynya which frequently occurs within the weddell sea winter sea ice we propose that when surface cooling and ice formation decrease the temperature and increase the salinity of the surface water the latter by salt rejection during ice formation in a preconditioned area static instability with intense vertical mixing can occur the upwelled warm salty deep water can then supply enough heat to melt the ice or prohibit its formation even in the middle of winter a simple two level model is derived to test this theory and is found to agree well with observations the process is found to be irregular due to different times of ice onset from one year to the next and to a lesser extent from variations in surface heating and cooling further it is shown that unless the freshwater input exactly balances the increased salinity from the overturn each year the system will either gain or lose salt yearly an

precision of the current methods to measure the alkenone proxy u 37 k and absolute alkenone abundance in sediments results of an interlaboratory comparison study measurements of the u 37 k index and the absolute abundance of alkenones in marine sediments are increasingly used in paleoceanographic research as proxies of past sea surface temperature and haptophyte mainly coccolith bearing species primary productivity respectively an important aspect of these studies is to be able to compare reliably data obtained by different laboratories from a wide variety of locations hence the intercomparability of data produced by the research community is essential here we report results from an anonymous interlaboratory comparison study involving 24 of the leading laboratories that carry out alkenone measurements worldwide the majority of laboratories produce data that are intercomparable within the considered confidence limits for the measurement of alkenone concentrations however there are systematic biases between laboratories which might be related to the techniques employed to quantify the components the maximum difference between any two laboratories for any two single measurements of u 37 k in sediments is estimated with a probability of 95 to be c in addition the overall within laboratory precision for the u 37 k temperature estimates is estimated to be c 95 probability similarly from the analyses of alkenone concentrations the interlaboratory reproducibility is estimated at 32 and the repeatability is estimated at 24 the former is compared to a theoretical estimate of reproducibility and found to be excessively high hence there is certainly scope and a demonstrable need to improve reproducibility and repeatability of u 37 k and especially alkenone quantification data across the community of scientists involved in alkenone research

depth and seasonality of alkenone production along the california margin inferred from a core top transect alkenone unsaturation indices uk 37 of marine sediment could prove particularly useful on organic rich continental margins where carbonate dissolution hampers the use of other paleoclimatic proxies mccaffrey et al 1990 kennedy and brassell 1992 forty core top samples of recent sediment from a latitudinal transect 23 40 n along the california margin yield uk 37 values that correlate linearly with modern mean annual sea surface temperatures ssts in the range of 12 23 c reproducibility of the unsaturation value in closely spaced cores is near analytical error uk 37 data define a relationship to temperature nearly identical to the prahl et al 1988 laboratory cultures of emiliania huxleyi the close agreement is particularly significant in light of the nannofossil composition of the sediments where the abundance of the coccolith taxon gephyrocapsa oceanica known to synthesize alkenones equals or exceeds that of e huxleyi comparison with seasonal temperature variations at different depths indicates that little if any alkenone production occurs at depths 30 m along the continental margin water depths 2 km sediments in more pelagic locations exhibit small but consistent biases toward winter and or subsurface production similar to previously reported sediment trap and core top data from the oregon margin prahl et al 1993 doose et al 1997

antarctic records of precession paced insolation driven warming during early pleistocene marine isotope stage 31 precisely dated antarctic continental margin and southern ocean geological records show that the early pleistocene interglacial marine isotope stage 31 mis 31 was characterized by warmer than present surface waters with reduced sea ice and enhanced high latitude marine carbonate production micropaleontologic isotopic and paleomagnetic evidence from drill cores at 77 s cape roberts project 1 and 53 s odp site 1094 indicate circumantarctic changes in sea surface temperature and water mass stratification that are in phase with high southern latitude insolation changes during mis 31 these changes imply a significant though as yet unquantifiable reduction in antarctic ice volume this study supports the hypothesis that the interhemispheric antiphased relationship of the precession cycle attenuates a potentially significant antarctic ice volume signal in the deep sea oxygen isotope record the implications are that antarctic marine ice sheets may be more susceptible to warming and high insolation driven retreat than has been widely recognized

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

bioaccumulation record and paleoclimatic significance in the western bransfield strait the last 2000 years abstract two gravity cores a 3 and a 6 from the western basin of the bransfield strait antarctica were recovered during the bio hesperides expedition fruela 96 both cores consist mainly of hemipelagic and laminated muds with black layers rich in sand sized volcanic ash geochemical analyses toc and opal radiometric dating techniques ams 14 c and 210 pb and micropaleontological analyses diatoms were performed on both cores ams analyses on toc yielded 14 c ages older than expected 3960 50 yr bp for the core top of a 3 and 3410 50 yr bp for a 6 210 pb analyses revealed that core top age for both gravity cores could be estimated to be about 100 15 yr bp the results of diatom analyses were related to the sequence of neoglacial events that have occurred over the last two millennia the abundance patterns of chaetoceros rs the biogenic silica content and the abundance of diatom valves agree with the high productivity values previously reported for the bransfield strait waters the significant recent reduction in resting spores of the diatom chaetoceros suggests as a reduction in surface productivity trend differences between chaetoceros resting spore abundance and toc contents are explained in terms of organic matter preservation diatom communities from the bransfield strait did not play an important role in the global co 2 cycle during cold periods bio and geochemical changes have an overprinted high frequency cyclicity at about 200 300 yr which might be related to the 200 yr solar cycle

calibration of mg ca thermometry in planktonic foraminifera from a sediment trap time series 1 paired mg ca and 18o measurements on planktonic foraminiferal species g ruber white g ruber pink g sacculifer g conglobatus g aequilateralis o universa n dutertrei p obliquiloculata g inflata g truncatulinoides g hirsuta and g crassaformis from a 6 year sediment trap time series in the sargasso sea were used to define the sensitivity of foraminiferal mg ca to calcification temperature habitat depths and calcification temperatures were estimated from comparison of 18o of foraminifera with equilibrium calcite based on historical temperature and salinity data when considered together mg ca mmol mol of all species except two show a significant r 0 93 relationship with temperature t c of the form mg ca 0 38 0 02 exp 0 090 0 003 t equivalent to a 9 0 0 3 change in mg ca for a 1 c change in temperature small differences exist in calibrations between species and between different size fractions of the same species o universa and g aequilateralis have higher mg ca than other species and in general data can be best described with the same temperature sensitivity for all species and pre exponential constants in the sequence o universa g aequilateralis g bulloides g ruber g sacculifer other species this approach gives an accuracy of 1 2 c in the estimation of calcification temperature the 9 sensitivity to temperature is similar to published studies from culture and core top calibrations but differences exist from some literature values of pre exponential constants different cleaning methodologies and artefacts of core top dissolution are probably implicated and perhaps environmental factors yet understood planktonic foraminiferal mg ca temperature estimates can be used for reconstructing surface temperatures and mixed and thermocline temperatures using g ruber pink g ruber white g sacculifer n dutertrei p obliquiloculata etc the existence of a single mg thermometry equation is valuable for extinct species although use of species specific equations will where statistically significant provide more accurate evaluation of mg ca paleotemperature

alkenones as paleoceanographic proxies 1 alkenone derived estimates of temperature and co2 are contributing to our understanding of earth s climate history in order to increase confidence in alkenone based climate proxies we recommend the following actions first the sedimentary component or fraction containing alkenones should be identified in order to assess the impact of horizontal advection and vertical mixing on alkenone derived temperature and co2 estimates second differential mixing rates of alkenone containing particles and sand sized foraminifera should be quantified by independent dating of the two phases until that is accomplished apparent temporal offsets of climate proxies in the two phases should be interpreted cautiously third the stability of the unsaturation ratio and carbon isotopic compositions of alkenones during all phases of diagenesis should be confirmed both field and laboratory observations are required fourth future alkenone investigations should be coupled with other paleoclimate proxy measurements at high deposition rate sites in a variety of oceanographic settings in upwelling regions and in the vicinity of river plumes salinity and nutrient proxies should be measured since changes in these parameters may affect alkenone biosynthesis

coccolithophore fluxes from sediment traps in the northeastern arabian sea off pakistan abstract we investigated coccolithophore fluxes from four sediment traps located in the northeastern arabian sea at the continental slope of pakistan two moorings wpt and ept western isastern pakomin trap consisting of one and two sediment traps were deployed at water depths of about 500 m and 1500 m they collected settling particles from october 1993 to february 1994 and from may 1995 to february 1996 at intervals of 22 and 24 days respectively a longer sampling was prevented probably due to high sedimentation events which occluded the trap cones both areas were characterised by a strong seasonality in coccolith fluxes high fluxes were recorded with up to 2000 10 6 coccoliths m 2 d 1 in the early sw summer monsoon and up to 5400 10 6 coccoliths m 2 d 1 in the early ne winter monsoon generally coccosphere fluxes exhibited a similar trend but were some orders of magnitude lower than coccolith fluxes twenty seven taxa were identified in this study all well to moderately well preserved and with a small range of diversity the species composition was dominated by gephyrocapsa oceanica florisphaera profunda and emiliania huxleyi making up about 70 of the assemblages during the sw summer monsoon high productivity in the surface waters of the eastern arabian sea may be linked to the upwelling system off oman apparently nutrient rich surface water derived from the southwestern upwelling areas off oman with high standing stocks were carried into this area by northeast flowing currents in contrast during the ne winter monsoon the locally observed high coccolithophore production is hypothesised to respond to local injections of nutrient rich deep water into the surface water due to sea surface cooling leading to convection consequently fluxes during the winter monsoon were in the same range as during the summer monsoon

holocene climate variability in antarctica based on 11 ice core isotopic records a comparison is made of the holocene records obtained from water isotope measurements along 11 ice cores from coastal and central sites in east antarctica vostok dome b plateau remote komsomolskaia dome c taylor dome dominion range d47 km105 and law dome and west antarctica byrd with temporal resolution from 20 to 50 yr the long term trends possibly reflect local ice sheet elevation fluctuations superimposed on common climatic fluctuations all the records confirm the widespread antarctic early holocene optimum between 11 500 and 9000 yr in the ross sea sector a secondary optimum is identified between 7000 and 5000 yr whereas all eastern antarctic sites show a late optimum between 6000 and 3000 yr superimposed on the long time trend all the records exhibit 9 aperiodic millennial scale oscillations climatic optima show a reduced pacing between warm events typically 800 yr whereas cooler periods are associated with less frequent warm events pacing 1200 yr

eight centuries of volcanic signal and climate change at talos dome east antarctica 1 during the 1996 programma nazionale di ricerche in antartide international trans antarctic scientific expedition traverse two firn cores were retrieved from the talos dome area east antarctica at elevations of 2316 m td 89 m long and 2246 m st556 19 m long cores were dated by using seasonal variations in non sea salt nss so42 concentrations coupled with the recognition of tritium marker level 1965 1966 and nss so42 spikes due to the most important volcanic events in the past pinatubo 1991 agung 1963 krakatoa 1883 tambora 1815 kuwae 1452 unknown 1259 the number of annual layers recognized in the td and st556 cores was 779 and 97 respectively the d record obtained from the td core has been compared with other east antarctic isotope ice core records dome c epica south pole taylor dome these records suggest cooler climate conditions between the middle of 16th and the beginning of 19th centuries which might be related to the little ice age lia cold period because of the high degree of geographical variability the strongest lia cooling was not temporally synchronous over east antarctica and the analyzed records do not provide a coherent picture for east antarctica the accumulation rate record presented for the td core shows a decrease during part of the lia followed by an increment of about 11 in accumulation during the 20th century at the st556 site the accumulation rate observed during the 20th century was quite stable

the evolution of ace lake antarctica determined from sedimentary diatom assemblages abstract the sediments in ace lake in the vestfold hills east antarctica contain a continuous sequence of diatom frustules that record the lake s history since its formation during the retreat of continental ice more than 9200 years ago frustules from six indicator groups pinnularia microstauron nitzschia cylindrus nitzschia curta eucampia antarctica a freshwater stauroneis species and several centric species in a sediment core were used to determine the sequence of the lake s evolution the history of the lake falls into five stages ace lake began as a marine inlet influenced by dynamic mixing of ocean and meltwater inputs as the ice sheet retreated isostatic uplift isolated the lake allowing it to be flushed by meltwater input from the retreating ice sheet over the course of 800 years 9200 8400 14c yr b p the lake became meromictic supporting a freshwater diatom assemblage approximately 6700 years ago coinciding with antarctic sea level maxima diatom assemblages indicate that seawater flooded over the sill into ace lake disturbing the freshwater meromixis the sediments in this period were laminated and contained elemental sulphur suggesting that the marine input was limited in extent and energy approximately 5500 years ago this marine input ceased and the lake again became a meromictic basin which stabilised over 1700 years to become the lake that it is today and has been with little change for about the past 4000 years

biogeochemistry and microbial diversity in the marine cavity beneath the mcmurdo ice shelf antarctica ice shelves surround 75 of antarctica s coastline and are highly sensitive to climate change several have recently collapsed and others are predicted to in the near future marine waters beneath ice shelves harbor active ecosystems while adjacent seas can be important areas of bottom water formation despite their oceanographic significance logistical constraints have resulted in few opportunities to directly sample sub ice shelf cavities here we present the first data on microbial diversity and biogeochemistry beneath the mcmurdo ice shelf mis near ross island antarctica physicochemical profiles obtained via a 56 m deep borehole through the mis revealed three vertically layered water masses antarctic surface water aasw ice shelf water isw and modified high salinity shelf water mhssw metabolically active moderately diverse shannon diversity from 2 06 to 5 74 microbial communities were detected in the aasw and mhssw heterotrophic bacterial production and dissolved organic matter concentrations were higher 12 37 and 24 respectively in mhssw relative to aasw chemoautotrophic production was 5 3 nmol c l 1 d 1 and 6 0 nmol c l 1 d 1 in the aasw and mhssw respectively phytoplankton cells were more abundant and larger in the mhssw sample relative to the aasw which indicates sinking of phytoplankton produced in surface waters and together with southerly flowing currents 0 09 0 16 m s 1 horizontal advection of phytoplankton from mcmurdo sound advected phytoplankton carbon together with in situ chemoautotrophic production provide important sources of organic matter and other reduced compounds to support ecosystem processes in the dark waters in the ice shelf cavity

an evaluation of lohmann s foraminifera weight dissolution index down water column traverses of core top weights for three planktonic species confirm lohmann s 1995 relationship between foraminifera shell weight loss and bottom water carbonate ion content however they also suggest that the initial shell thickness varies with growth habitat and that the offset between bottom water and pore water carbonate ion concentration varies even on small space scales

fluxes of planktic foraminifera in response to monsoonal upwelling on the somalia basin margin abstract sediment trap samples collected off somalia bi weekly from early june 1992 through mid february 1993 show large seasonal variations in the shell flux and species composition of planktic foraminifera these variations mirror the monsoon driven circulation which resulted in massive upwelling and offshore eddy transport in summer during the sw monsoon june september and accounted for nearly 90 of the estimated annual shell flux of planktic foraminifera g bulloides dominated the sw monsoon along with g glutinata t quinqueloba n dutertrei and t iota in a fauna rich species but with a low diversity and equitability during the autumn intermonsoon november december the ocean became stratified and the nutrient exhausted whereas during the ne monsoon january march a warm surface mixed layer developed with the nutrients entrained by deep wind mixing it was dominated by g ruber in association with g tenella g aequilateralis g trilobus g sacculifer and g menardii in a fauna poorer in species but with a higher diversity and equitability consequently the ratio in the abundance of g bulloides and g ruber follows the monsoonal cycle closely as both species persist throughout the year only the rare g theyeri seems to be restricted to the sw monsoon in october at the end of the sw monsoon the trap at 265 m above the bottom intercepted massive amounts of fine grained carbonate m resuspended from the shelf and upper slope it contained extreme fluxes of bioclastic fragments benthic foraminifera and benthic ostracods as well as enhanced fluxes of small sized planktic foraminifera m notably g rubescens integrated over the year the species composition intercepted by the trap shows a very good match with the shell fauna in a core top sediment from the same site apparently the year estimated monsoonal record of planktic foraminifera which is strongly dominated by the sw monsoon production survives burial intact consequently the species composition of planktic foraminifera and measures such as the bulloides ruber ratio can be applied as a proxy for past changes in the intensity of the sw monsoon off somalia compared to the modern condition

ecological and environmental factors affecting alkenone distributions in seawater and sediments 1 the use of alkenones to estimate past sea surface temperatures has gained wide acceptance but there are still some issues that need to be resolved before alkenone proxies can be used confidently in all environmental settings a particular concern is defining what seawater temperature is recorded by the alkenone distributions preserved in sediments does it for example reflect a seasonal average or a snapshot of bloom conditions or some other combination of environmental effects this paper reviews some of the environmental and ecological factors that might affect alkenone distributions and in particular the influence of depth and seasonality on alkenone production in the water column

accurate estimation of sea surface temperatures using dissolution corrected calibrations for mg ca paleothermometry 1 paired 18o and mg ca measurements on the same foraminiferal shells offer the ability to independently estimate sea surface temperature sst changes and assess their temporal relationship to the growth and decay of continental ice sheets the accuracy of this method is confounded however by the absence of a quantitative method to correct mg ca records for alteration by dissolution here we describe dissolution corrected calibrations for mg ca paleothermometry in which the preexponent constant is a function of size normalized shell weight 1 for g ruber 212 300 m mg ca ruber 0 025 wt 0 11 e0 095t and b for g sacculifer 355 425 m mg ca sacc 0 0032 wt 0 181 e0 095t the new calibrations improve the accuracy of sst estimates and are globally applicable with this correction eastern equatorial atlantic sst during the last glacial maximum is estimated to be 2 9 0 4 c colder than today

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

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

a detailed comparison of the uk 37 and coccolith records over the past 290 kyears implications to the alkenone paleotemperature method the uk 37 record and the coccolithophorid remains in a sediment core from the north atlantic ocean have been compared to assess the possible influence of changes in alkenone producing coccolithophorids on the uk 37 sea surface temperature relationship we have determined three major reversals in the populations of noelaerhabdaceae gephyrocapsa and emiliania species in the central north atlantic over the last 290 kyears 245 260 170 and 40 50 kyears bp a detailed comparison of the uk 37 and coccolithophorid records revealed the absence of significant changes in the uk 37 values despite major changes in coccolithophorid assemblages the data indicate that changes in alkenone producing organisms in the past do not involve significant changes in the uk 37 temperature relationship and that the succession did not primarily depend on climatic change it also supports the fact that the uk 37 derived sst differences observed between glacial stages 2 4 6 and 8 are not related to the succession of coccolithophorid species

cold conditions in antarctica during the little ice age implications for abrupt climate change mechanisms abstract the little ice age lia is one of the most prominent climate shifts in the past 5000 yrs it has been suggested that the lia might be the most recent of the dansgaard oeschger events which are better known as abrupt large scale climate oscillations during the last glacial period if the case then according to broecker 2000a 2000b antarctica should have warmed during the lia when the northern hemisphere was cold here we present new data from the ross sea antarctica that indicates surface temperatures were 2 c colder during the lia with colder sea surface temperatures in the southern ocean and or increased sea ice extent stronger katabatic winds and decreased snow accumulation whilst we find there was large spatial and temporal variability overall antarctica was cooler and stormier during the lia although temperatures have warmed since the termination of the lia atmospheric circulation strength has remained at the same elevated level we conclude that the lia was either caused by alternative forcings or that the sea saw mechanism operates differently during warm periods

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

oceanographic mechanisms and penguin population increases during the little ice age in the southern ross sea antarctica abstract the adelie penguin is a well known indicator for climate and environmental changes exploring how large scale climate variability affects penguin ecology in the past is essential for understanding the responses of southern ocean ecosystems to future global change using ornithogenic sediments at cape bird ross island antarctica we inferred relative population changes of adelie penguins in the southern ross sea over the past 500 yr and observed an increase in penguin populations during the little ice age lia 1500 1850 ad we used cadmium content in ancient penguin guano as a proxy of ocean upwelling and identified a close linkage between penguin dynamics and atmospheric circulation and oceanic conditions during the cold period of 1600 1825 ad a deepened amundsen sea low asl led to stronger winds intensified ocean upwelling enlarged ross sea and mcmurdo sound polynyas and thus higher food abundance and penguin populations we propose a mechanism linking antarctic marine ecology and atmospheric oceanic dynamics which can help explain and predict responses of antarctic high latitudes ecosystems to climate change

the little ice age as recorded in the stratigraphy of the tropical quelccaya ice cap the analyses of two ice cores from a southern tropical ice cap provide a record of climatic conditions over 1000 years for a region where other proxy records are nearly absent annual variations in visible dust layers oxygen isotopes microparticle concentrations conductivity and identification of the historical a d 1600 huaynaputina ash permit accurate dating and time scale verification the fact that the little ice age about a d 1500 to 1900 stands out as a significant climatic event in the oxygen isotope and electrical conductivity records confirms the worldwide character of this event

foraminiferal assemblages from ice proximal paleo settings in the whales deep basin eastern ross sea antarctica abstract reconstructions of ross sea paleoenvironments based on foraminifera are hindered by the dearth of actualistic data especially from below the ross ice shelf to fill this gap we used a recently developed well resolved deglaciation record from the whales deep basin of the eastern ross sea to understand the ecological affinities of different foraminiferal assemblages during open water conditions similar to the present two benthic foraminiferal communities are strongly dominated by agglutinated species however in the underlying sediments that represent sub ice shelf and grounding zone proximal settings on the outer continental shelf we identified five different assemblages of calcareous foraminifera by antarctic margin standards these calcareous assemblages are periodically truly abundant along with assemblages dominated by benthic calcareous species that are well known from many antarctic settings i e globocassidulina biora trifarina earlandi and astrononion echolsi two important assemblages are dominated by a heretofore undescribed pustulose morphotype of g biora and poorly known spinose morphotype of t earlandi based on our correlations to the deglacial record these two assemblages live near the grounding line or in environments with especially intense bottom water currents as grounded and floating ice retreated south to the middle continental shelf these later sub ice shelf and grounding zone proximal settings were largely devoid of calcareous foraminifera and instead were inhabited by agglutinated taxa this improved understanding of foraminiferal assemblage distributions from a variety of environments within the eastern ross sea may contribute to better use of foraminiferal data to investigate the evolution of environmental changes in grounding line proximal environments

temporal variability of microparticle properties in polar ice sheets abstract four recent ice core studies reveal a consistently recurring temporal correlation between increased microparticle concentrations and lower global temperatures more negative 13 o 16 o ratios a continuous 900 year record of particle deposition from the 101 m south pole core was obtained by analyzing 6218 samples the concentration of insoluble particles with diameters 0 63 m increases substantially between a d 1450 and 1850 a period of slightly reduced global temperatures encompassing the latest neoglacial or little ice age there is evidence suggesting that some of the additional material may be volcanic although further substantiation is required the microparticle analyses of selected sections from three deep cores coupled with the respective 18 o measurements reveal that in all three cores the last glacial or late wisconsin ice contained great quantities of microparticles the ratio of the average microparticle concentration in wisconsin sections to that in holocene sections is 6 for the 905 m dome c antarctica core 3 for the 2164 m byrd station antarctica core and 12 for the 1387 m camp century greenland core microparticle increases of this magnitude can not be accounted for merely by a reduction in net accumulation these data suggest that the global atmosphere was heavily laden with suspended particulates near the end of the last major glaciation

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 surface windfield over the antarctic ice sheets the intense radiative cooling of air over the ice slopes of antarctica generates a surface wind regime that is strongly controlled by topography and plays a key role in determining the behaviour of the atmosphere and ocean in high southern latitudes1 7 resultant surface winds are intimately linked to the orientation of the ice terrain fig 1 and display the highest degree of persistence found on earth the close coupling between wind and topography allows estimation of the former if the latter is known with some precision here we report on time averaged near surface airflow over the antarctic continent during winter diagnosed from a recent accurate synthesis of terrain slopes and from estimates of the lower atmospheric temperature structure the simulated drainage pat tern exhibits strong spatial variability with the airflow concentrated into several zones near the coastal margin these confluence regions are responsible for strong persistent katabatic winds over downstream coastal stretches and are indicative of zones of greatest katabatic potential

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

review of alkenone calibrations culture water column and sediments 1 i review the status of alkenone unsaturation parameters as proxies for growth temperature and the potential for pco2 estimates using the carbon isotopic composition of alkenones culture studies allow investigators to manipulate parameters that could influence the relative proportions of c37 and c38 ketones in producing organisms and to assess the possible influence of genetic variability on the calibration of unsaturation to growth temperature culture studies suggest large variability in the relation of unsaturation indices to growth temperature and hint that growth rate may play a role along with temperature in controlling unsaturation water column studies match the unsaturation index measured in particulate matter to ambient temperature providing a snapshot of unsaturation temperature relationship in comparison to culture work assemblages of regional water column data sets give more consistent relations of the unsaturation index to temperature although the argument can be made for regional rather than basin wide or global calibrations a much simpler picture emerges from analyzing a global array of core top sediments regressions show that the sedimentary unsaturation indices follow a linear trend that is best correlated to mean annual temperature in the upper 10 m of the overlying water column the regression is indistinguishable from the original prahl et al 1988 culture calibration of the u37k index to growth temperature exceptions occur at high latitudes where the effects of highly seasonal production and the possible influence of salinity may affect the unsaturation index in sediments core top analyses also fail to reveal the variability of other alkenone parameters for example the ratio of c37 to c38 ketones which have been found in culture studies much of the variance that appears in culture and water column calibrations is thus apparently removed in sediments perhaps by temporal averaging the promising paleo pco2 approach based on the isotopic composition of alkenones awaits the arrival of a significant number of core top and stratigraphic studies that will determine the extent to which physiological factors compromise the alkenone paleobarometer

reevaluation of the oxygen isotopic composition of planktonic foraminifera experimental results and revised paleotemperature equations cultured planktonic foraminifera orbulina universa symbiotic and globigerina bulloides nonsymbiotic are used to reexamine temperature 18o relationships at 15 25 c relationships for both species can be described by linear equations equations for o universa grown under low light ll and high light hl share a slope of 4 80 0 21 c 1 with a hl ll offset of 0 33 due to symbiont photosynthetic activity the effect of co32 on o universa is 0 002 mol 1 kg 1 and is insensitive to temperature for g bulloides ontogenetic effects produce size related trends in temperature 18o whereby larger shells are enriched in 18o relative to smaller specimens the o universa temperature 18o relationships are more accurate than previously published equations for describing plankton tow data our equations do not explain planktonic core top data with the same precision but provide a good fit to benthic cibicidoides data below 10 c temperature 18o relationships for g bulloides provide good agreement with field data for this species from the northeast pacific

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

biostratigraphic characterization and quaternary microfossil palaeoecology in sediment drifts west of the antarctic peninsula implications for cyclic glacial interglacial deposition abstract the sedano project recovered 19 gravity cores on sediment drifts from the pacific continental margin of the antarctic peninsula camerlenghi et al 1997a high resolution terrigenous sedimentary record of the sediment drifts on the antarctic peninsula pacific margin in ricci c a ed the antarctic region museo nazionale dell antartide siena pp 705 710 fifteen cores were sampled with the aim of developing an integrated biostratigraphy and palaeoecology based on calcareous nannofossils diatoms planktonic and benthic foraminifera framed in a depositional process reconstruction barren gray laminated and brown bioturbated hemipelagic sediments characterize glacial and interglacial cycles respectively analyses from both intervals allow comparison between microfossil occurrence in glacial and interglacial cycles the unit boundaries were drawn more accurately by means of the microfossil distribution on the basis of micropalaeontological and sedimentological evidence interglacial unit c is correlated to oxygen isotope stage 5 thus dating the unit boundaries at 127 and 70 ka peaks in diatom abundance correlate well with interglacial units and indicate high productivity and an open ocean environment a calcareous nannofossil cold taxa association is present in most cores examined and its consistent distribution within interglacial unit c indicates key environmental relationships the occurrence of calcareous nannofossils has been related to temperature tolerance sea ice cover reduction nutrient availability and factors limiting primary productivity our results confirm that coccolithophorids occurred at southern high latitudes in the western marginal basins of the antarctic peninsula during short periods of the late quaternary a foraminiferal assemblage made up of sinistral neogloboquadrina pachyderma and few benthics occurs only in interglacial units correlation of microfossil occurrences with climatic cycles adds information on their palaeoecology and palaeoproductivity in the southern high latitudes

effects of seawater carbonate ion concentration and temperature on shell u mg and sr in cultured planktonic foraminifera we investigate the sensitivity of u ca mg ca and sr ca to changes in seawater co3 and temperature in calcite produced by the two planktonic foraminifera species orbulina universa and globige rina bulloides in laboratory culture experiments our results demonstrate that at constant temperature u ca in o universa decreases by 25 7 per 100 mol co3 k g 1 as seawater co3 increases from 110 to 470 mol kg 1 results from g bulloides suggest a similar relationship but u ca is consistently offset by 40 at the same environmental co3 in o universa u ca is insensitive to temperature between 15 c and 25 c applying the o universa relationship to three u ca records from a related species globigerinoides sacculifer we estimate that caribbean and tropical atlantic co3 was 110 70 mol kg 1 and 80 40 mol kg 1 higher respectively during the last glacial period relative to the holocene this result is consistent with estimates of the glacial interglacial change in surface water co3 based on both modeling and on boron isotope ph estimates in settings where the addition of u by diagenetic processes is not a factor down core records of foraminiferal u ca have potential to provide information about changes in the ocean s carbonate concentration below ambient ph ph 8 2 mg ca decreased by 7 5 o universa t o 16 6 g bulloides per 0 1 unit increase in ph above ambient ph the change in mg ca was not significant for either species this result suggests that mg ca based paleotemperature estimates for the quaternary during which surface ocean ph has been at or above modern levels have not been biased by variations in surface water ph sr ca increased linearly by 1 6 0 4 per 0 1 unit increase in ph shell mg ca increased exponentially with temperature in o universa where mg ca 0 85 exp 0 096 t whereas the change in sr ca with temperature was within the reproducibility of replicate measurements copyright 2004 elsevier ltd

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

glacial contourites on the antarctic peninsula margin insight for palaeoenvironmental and palaeoclimatic conditions deep sea finely laminated and barren glacial sediments occur in the sediment drift field offshore the pacific margin of the antarctic peninsula where a weak contour current flows at present to the sw atypical sedimentary facies were related to the coexistence and interaction of different sedimentary processes three end members of radiograph facies were defined to represent the sedimentary sequences controlled by a dominant process as follows 1 direct influence of turbidity currents on sedimentation is observed in the area surrounding the alexander channel system with silty layers interbedded with laminated mud free of ice rafted debris ird 2 distal meltwater turbid flows dominate the more proximal area of the top plateau with structureless and coarser grained sediments containing ird 3 along the crest of the drift persistent weak bottom currents control the deposition of fine grained sediments conveyed into the system through other processes these laminated sediments contain ird and are atypically not bioturbated because of unusual climatically related environmental conditions of suppressed primary productivity and oxygen reduced deep waters these glacial contourites were observed on most of the antarctic margin with the exception of the areas in which polynyas were maintained during the glacial stages glacial contourites can be used as a proxy to define temporal and spatial extension of the antarctic sea ice deep sea sediments of the sediment drifts offshore the pacific margin of the antarctic peninsula were investigated within the sedano sediment drifts of the antarctic offshore and mogam morphology and geology of antarctic margins antarctic peninsula and wilkes land projects of the italian programma nazionale di ricerche in antartide fig 1 the continental shelf of the pacific margin of the antarctic peninsula is dissected by a number of modern u shaped troughs that reflect the neogene path of large ice streams rebesco et al 1998 2002 sediments across the continental shelf were transported mainly by ice streams and delivered to the continental slope and rise during the periods of maximum glacial expansion the continental rise hosts a number of large sediment drifts separated by dendritic deep sea channel systems that originated on the lower continental slope in alignment with the reaches of each glacial trough amblas et al 2006 rebesco et al 2007 two main alternating lithologies related to climatic changes were initially distinguished pudsey camerlenghi 1998 pudsey 2000 interglacial brown bioturbated mud containing sparse icerafted debris ird and glacial grey laminated mud further detailed studies consisting of over 1000 sedimentological compositional and biostratigraphic analyses diatoms foraminifers and nannofossils allowed lucchi et al 2002a to distinguish four distinctive sets of sedimentary facies connected to a sequence of four climatic stages each characterized by the onset of typical sedimentary processes fig 2 as follows 1 strongly bioturbated mud with abundant ird and aeolian sediment input was produced during the interglacial phase fig 2a the increased bioactivity is matched by insignificant downand along slope processes negligible suspended load and sediment transport by the southwesterly flowing bottom currents is occurring at present on the continental rise giorgetti et al 2003 2 terrigenous structureless mud including a series of close spaced ird layers was produced during the deglaciation transition from glacial to interglacial conditions by the disintegration of the retreating grounded ice sheet fig 2b the absence of calcareous microfossils is related to strong carbonate dissolution and rise of the carbonate compensation depth ccd as a result of major meltwater discharge which in turn caused water stratification with less oxygenated and nutrient enriched conditions at the sea bottom 3 a large variety of from viana a r rebesco m eds economic and palaeoceanographic significance of contourite deposits geological society london special publications 276 111 127 0305 8719 07 15 00 the geological society of london 2007

an intensity ratio calibration method for the accurate determination of mg ca and sr ca of marine carbonates by icp aes an inductively coupled plasma atomic emission spectroscopy icp aes method for the accurate and precise simultaneous measurement of the mg ca and sr ca content of carbonates was established while a precision of 0 3 1 standard deviation sd is easily obtainable for both mg ca and sr ca analysis a ca matrix effect complicates achieving similar levels of accuracy with conventional calibration procedures an alternative ratio calibration procedure is proposed which overcomes the ca matrix effects and ensures the accuracy of the mg ca and sr ca analysis of marine carbonates to 0 3 almost an order of magnitude better than conventional calibration methods the longer term precision is 0 1 if the batch run average values are corrected for longer term drift the method is suitable for analysis of foraminiferal calcite and coral aragonite and can easily be adjusted for the analysis of other carbonates or microsamples

the organic geochemistry of peru margin surface sediments i a comparison of the c37 alkenone and historical el nino records abstract the alkenone u k 37 paleothermometer has potential as a sedimentary marker for el nino southern oscillation enso events in the peru upwelling regime we assessed this potential by comparing the historical enso record with detailed u k 37 profiles for 210 pb dated cores from the peru margin oxygen minimum zone omz sediments with the greatest potential for holding a sedimentary u k 37 record of el nino events are sediments from the center of the omz sectioned at intervals the yearly sedimentation rate the u k 37 signals of individual el nino events were substantially attenuated in the sediments we examined and periods of frequent enso activity e g 1870 1891 were more readily identified than isolated enso events in periods of less frequent enso activity detailed depth profiles of the c 37 alkenones in a core from 253 m o 2 k 37 values for the five 2 mm sections from 0 1 cm suggests that the u k 37 may be unaffected by the alkenone loss correlation between the c 37 alkenone concentration profiles in two cores from 15 s collected nine years apart are consistent with the use of these compounds for molecular stratigraphy

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

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

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

controls on alkenone unsaturation ratios along the salinity gradient between the open ocean and the baltic sea abstract alkenone unsaturation ratios of sedimentary lipids are used as a geochemical proxy for sea surface temperatures and interest is growing in their potential as indicators of different water masses and possibly of salinity we analyzed the abundance of unsaturated c37 to c38 ketones in lipid extracts of 57 surface sediment 0 1 cm samples along a salinity gradient from 8 to 33 psu in the transition from the skagerrak to the baltic sea nw europe in addition to surface sediments we analyzed alkenones in suspended particulate matter at 13 stations over a gradient in salinity from 25 to 33 psu during a bloom of the coccolithophore emiliania huxleyi alkenones were detected in all samples suspended matter and sediment with variable contributions of the tetra unsaturated c37 alkenone compound c37 4 range from 2 to 10 of total c37 alkenone content comparing the alkenone unsaturation index u37k and c37 4 data to climatological sea surface temperature and sea surface salinity data sets revealed that sst estimated from u37k of saline end members samples from the skagerrak is in the general range of modern sst during bloom periods of haptophytes at salinities below 30 psu c37 4 increases to above 5 and the unsaturation ratios cease to be related to climatological annual or seasonal sea surface temperatures on the other hand the c37 4 appears to be inversely and significantly correlated to salinity highest c37 4 proportions in the inner baltic sea are caused by an unidentified organism but in the transition area at salinities down to 10 psu the producer apparently is e huxleyi the suspended matter data together with those from the water column support the hypothesis of changing biosynthesis of alkenones under salt stress by the coccolithophore e huxleyi but constrain the maximum of c37 4 attributable to salt stress to 10 of all c37 alkenones

unstable climate oscillations during the late holocene in the eastern bransfield basin antarctic peninsula core a9 eb2 from the eastern bransfield basin antarctic peninsula consists of pelagic diatom ooze clay couplets and bioturbated diatom ooze and hemipelagic bioturbated mud sediments interbedded with turbidites homogeneous mud and silt clay couplets the cyclic and laminated nature of these pelagic sediments represents alternation between the deposition of diatom rich biogenic sediments and of terrigenous sediments sediment properties and geochemical data explain the contrasting lamination with light layers being finer grained and relatively rich in total organic carbon and biogenic silica content also the high resolution magnetic susceptibility ms variations highlight distinct features high ms values coincide with clastic rich sections and low ms values correspond to biogenic sections the chronology developed for core a9 eb2 accounts for anomalous ages associated with turbidites and shows a linear sedimentation rate of approximately 87 cm 103 yr which is supported by an accumulation rate of 80 cm 103 yr calculated from 210pb activity the late holocene records clearly identify neoglacial events of the little ice age lia and medieval warm period mwp other unexplained climatic events comparable in duration and amplitude to the lia and mwp events also appear in the ms record suggesting intrinsically unstable climatic conditions during the late holocene in the bransfield basin of antarctic peninsula

high resolution diatom stratigraphy of quaternary sediments from the scotia sea upper quaternary pelagic and hemipelagic sediments from the scotia sea and south scotia ridge range from diatom ooze to diatom bearing mud diatom content increases northwards and at most sites diatom rich and diatom poor sediments alternate downcore on a scale of metres a local stratigraphy is based on relative abundance of six prominent diatom taxa eucampia antarctica rhizosolenia spp thalassiosira spp chaetoceros spores nitzschia kerguelensis and othernitzschia species and one silicoflagellate species distephanus speculum these stratigraphic units defined using diatoms are correlated with radiolarian abundance stratigraphy cycladophora davisiana and with palaeomagnetic stratigraphy information from modern environments phytoplankton and sediment trap studies indicates that changes in diatom species composition are related to n s movement of the winter ice edge and of the antarctic convergence

microfossil distributions in modern amundsen sea sediments abstract acquisition of 20 piston cores from the amundsen sea continental shelf provides material for the first determinations of modern and paleo distributions of microfossils including planktonic and benthic foraminifera diatoms and radiolaria in this region microfossil analyses of filtered sea water and sea ice samples allow comparisons of the biocoenosis with the thanatocoenosis in the sediments in all three biotic provinces are distinguished 1 the outer shelf region north of thurston island is characterized by high abundances of planktonic and calcareous benthic foraminifera low diatom abundances in sediments here despite high abundances in the sea ice may reflect prevention of deposition by ocean currents 2 the southernmost province in pine island bay is marked by very low abundances of all microfossil groups possibly because the floating terminus of pine island glacier has retreated from this area only during the last 100 years in that case the polynya that exists today in this region during some austral summers is so recent a feature that little or no biogenic sediment has had an opportunity to accumulate beneath it 3 the eastern margin province situated between the pine island bay and outer margin provinces along the eastern coast of the amundsen sea is characterized by high abundances of diatoms and arenaceous benthic foraminifera which probably record the presence of the amundsen sea polynya in this area during the last 1000 to 2500 years dominance of the benthic fauna in this area by arenaceous foraminifera is a function of the great depth from which most cores in this area were retrieved 500 924 m below the ccd

primary signal ecological and environmental factors report from working group 2 alkenone based proxies are routinely used for paleoceanographic and climatologic reconstructions despite the fact that their calibration to environmental parameters is still a matter of debate significant differences are observed among culture calibrations using different strains of alkenone producers between regional field calibrations within the euphotic zone and between water column and core top based calibrations the reasons for these discrepancies are not well understood and call for further evaluation the possibility is raised that several aspects of genetics physiology and ecology of alkenone producing haptophytes may be responsible and suggestions of future research are proposed

molecular record of secular sea surface temperature changes on 100 year timescales for glacial terminations i ii and iv high resolution palaeoclimate records based on oxygen isotope data have provided important insights into climate variability and rates of natural climate change on about a thousand year timescale1 3 little is known4 however about the variation of climate and of palaeoceanographic conditions throughout the quaternary on timescales of less than 1 000 years at frequencies far greater than those of the milankovitch orbital cycles here we show that such high time resolution is possible from molecular stratigraphic studies based on biomarker organic molecules alkenones we have sampled alkenone stratigraphic records at 70 to 200 yr intervals across glacial terminations i ii and iv in sediment cores from oop site 658 off northwest africa5 sea surface temperatures ssts derived from the alkenone uk37 index6 8vary rapidly beyond the range of analytical noise by up to 2 5 c in 300 yr showing hitherto unknown cycles with about 600 yr periodicities some of the changes parallel similar events in the oxygen isotope stratigraphy sst oscillations may be linked in part to abrupt breakdowns in atlantic deep water ventilation resulting from meltwater events of quaternary glacial terminations3 9 10

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