11 000 yrs of environmental change in the northwest passage a multiproxy core record from central parry channel canadian high arctic article i nfo piston core 97022 004pc 74 48 0 n 97 05 9 w 267 m water depth represents a rare paleoenvironmental archive from the understudied west central canadian arctic archipelago lithological biogeochemical and microfossil dinoflagellate cysts non pollen palynomorphs benthic and planktonic foraminifera character istics in combination with a chronostratigraphy based on seventeen radiocarbon dates show seven promi nent paleoenvironmental episodes since the end of the last regional glaciation the basal diamict zone i records decoupling of previously grounded glacial ice followed by ice proximal conditions zone iia commencing at 10 8 cal ka bp age depth model extrapolation after an interval of pervasive sea ice zone iib ice distal conditions are established zone iic although sparse microfossils are present in glaciomarine sediments zone ii noticeable biological activity with heightened abundances and diversities across all groups begins in the postglacial zone iii 10 3 10 0 cal ka bp when planktonic foraminifera neogloboquadrina pachyderma appear as planktonics are excluded from the study area today due to shal low inter channel sills this likely signals the inflow of relatively warm and saline atlantic derived arctic intermediate water below 250 m presumably facilitated by glacio isostatically enhanced deglacial water depths the subsequent zone iv 10 0 7 0 cal ka bp characterized by heightened biological productivity in both plankton and benthos and reduced seasonal sea ice cover may correspond to a previously proposed holocene thermal maximum this apparent amelioration ends by the mid holocene zone v 7 0 5 7 cal ka bp when arctic intermediate water is excluded from the study area and water depths approach modern values high arctic conditions with seasonal sea ice cover a circulation dominated by arctic ocean surface water and microfossil assemblages similar to modern are found from 5 7 cal ka bp onwards zones vi vii as only minor environmental fluctuations are apparent during the late holocene shorter term climatic episodes e g little ice age are not recognized in this record

quantitative mineralogy of surface sediments on the iceland shelf and application to down core studies of holocene ice rafted sediments abstract quantitative x ray diffraction analyses on the 2 mm sediment fraction from the iceland shelves are reported for subglacial diamictons seafloor surface sediments and the last 2000 cal yr bp from two cores the overall goal of the paper is to characterize the spatial variability of the mineralogy of the present day surface sediments 18 non clay minerals and 7 clay minerals compare that with largely in situ erosional products typified by the composition of subglacial diamictons and finally examine the late holocene temporal variability in mineral composition using multi mineral compositions the subglacial diamictons are dominated in the non clay mineral fraction by the plagioclase feldspars and pyroxene with 36 7 6 1 and 17 9 3 5 wt respectively with smectites being the dominant clay minerals the surface seafloor sediments have similar compositions although there are substantial amounts of calcite plus there is a distinct band of sites from nw to n central iceland that contain 1 6 wt of quartz this latter distribution mimics the modern and historic pattern of drift ice in iceland waters principal component analysis of the transformed wt log ratio non clay minerals is used to compare the subglacial surface and down core mineral compositions fifty eight percent of the variance is explained by the first two axes with dolomite microcline and quartz being important foreign species these analyses indicate that today the nw n central iceland shelf is affected by the import of exotic minerals which are transported and released from drift ice the down core mineralogy indicates that this is a process that has varied over the last 2000 cal yr bp

holocene environmental evolution of the se greenland shelf north and south of the denmark strait irminger and east greenland current interactions abstract holocene climatic and paleoceanographic development of the se greenland shelf is studied from cores md99 2317 and md99 2322 at sites north and south of the denmark strait respectively lithofacies ird counts calcium carbonate percentages benthic and planktic foraminiferal assemblages and oxygen isotope analyses and summer ssts reveal significant climate variations in the holocene driven by declining solar insolation and its interaction with waning continental ice sheets and changing atmospheric pressure patterns large changes in the east greenland and irminger currents and the greenland ice sheet are manifested as a 4 part division of the holocene an early holocene cold interval dominated by melting of the greenland ice sheet and polar front retreat extends from 11 8 to 9 5 cal kyr bp a cold interval from 9 5 to 8 1 cal kyr bp involved episodic cooling of the irminger current resulting from the last phases of laurentide ice sheet deglaciation and delayed the holocene optimum off east greenland by 3 kyr relative to peak summer solar insolation which likely helped to limit the early holocene melting of the greenland ice sheet the period 8 1 3 5 cal kyr bp represents a climatic optimum interval of maximum greenland ice sheet retreat and strong irminger current inflow to the denmark strait between 6 8 and 3 5 cal kyr bp the irminger current penetrated further north into the nordic seas than has been observed in recent decades this signal is consistent with diminished northerly winds a weaker greenland high and contracted subpolar gyre by 5 cal kyr bp periods of increased polar water and decreasing salinity in the irminger current suggest a transition toward expansion of the subpolar gyre and increased polar water in the egc the neoglacial interval from 3 5 to 0 2 cal kyr bp was cold and variable with increased freshwater forcing from the arctic ocean advance of the greenland ice sheet and southward advance of the polar front enhanced northerly winds and a strengthened greenland high are consistent with thicker and more extensive polar water and greatly diminished northward advection of irminger current in the denmark strait

marked decline in atmospheric carbon dioxide concentrations during the paleogene the relation between the partial pressure of atmospheric carbon dioxide pco2 and paleogene climate is poorly resolved we used stable carbon isotopic values of di unsaturated alkenones extracted from deep sea cores to reconstruct pco2 from the middle eocene to the late oligocene approximately 45 to 25 million years ago our results demonstrate that pco2 ranged between 1000 to 1500 parts per million by volume in the middle to late eocene then decreased in several steps during the oligocene and reached modern levels by the latest oligocene the fall in pco2 likely allowed for a critical expansion of ice sheets on antarctica and promoted conditions that forced the onset of terrestrial c4 photosynthesis

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

late holocene ca 4 ka marine and terrestrial environmental change in reykjarfjordur north iceland climate and or settlement core b997 328pc is from the landward side of a 100 m deep basin in reykjarfjordur a small fjord on the north coast of the northwest peninsula of iceland this is an area that can be severely affected by incursions of polar sea ice but has not suffered marked land erosion during the settlement period the core is 422 cm in length and consists principally of fine grained muds with in situ molluscs eleven ams 14c dates on molluscs indicate a constant sediment accumulation rate of ca 1 cm 10 yr 1 for the last 4280 50 yr bp we measured and derived a variety of proxies for indications of changes in the nearshore environment these included physical properties and grain size mass accumulation rates micropalaeontology pollen and foraminifera multivariate analysis and constrained clustering were used to define major changes in the proxies in several parameters the major change in the fjord environment occurred close to 1000 14c yr ago thus approximately coincident with the onset of the settlement of iceland other changes are noted at around 1600 and 3400 14c yr ago betula pollen disappears from the record ca 1500 yr bp and there are peaks in marine productivity occurring ca 2 and 3 4 ka a major decline in carbonate accumulation and a sharp increase in the cold water benthic foraminifer elphidium excavatum forma clavata 400 yr ago represents the local marine signature of the little ice age none of the changes in our data can be explained adequately by a simple call to land use practices and an increase in land to sea transport but both the pollen and foraminiferal records indicate a decrease and even loss of warm elements in both flora and fauna over the past 4 kyr copyright 2001 john wiley sons ltd

late quaternary lithofacies provenance and depositional environments 12 30 cal ka north and south of the denmark strait this paper describes the lithofacies and chronology of cores from north and south of the denmark strait for a period when ice sheets flanked both sides of the strait a wide range of sediments have been recovered indicating a complex of depositional processes jm96 1229ggc1 1047 m water depth is from the base of the nw iceland slope at the southern edge of the blosseville basin whereas jm96 1226ggc4 retrieved sediments south of the sill in 1519 m of water additional information is based on jm96 1220ggc2 and 1221ggc2 which were recovered from the upper w iceland slope at 500 m water depth below the latra moraine of possible last glacial maximum age and upslope of jm96 1226 ams 14c dates indicate that jm96 1226 and 1229 span the last 10 to 27 32 ka bp whereas jm96 1220 and 1221 recovered sediments dated between ca 8 and 18 ka bp closely spaced radiocarbon dates on jm96 1229 indicate an erosional hiatus of 7 ky between 12 and 19 cal ka lithofacies descriptions are based on visual descriptions and x radiographs jm96 1229 consists of fine grained sediments sometimes graded with scattered ice rafted debris whereas jm96 1226 consists largely of beds of matrix supported diamicton provenance indicators mass magnetic susceptibility and geochemistry for jm96 1229 support the delivery of sediments from nw iceland but there is a substantial difference in these properties between sediments from the w iceland upper slope and the sediments in jm96 1226 south of the denmark strait this indicates that the diamictons on the floor of the strait did not derive entirely from the iceland ice sheet and adjacent upper slope the general absence of sediments 12 cal ka on the slopes and floor of the denmark strait indicates that denmark strait overflow waters inhibited sediment accumulation during the holocene between ca 12 and 30 cal ka however a combination of more proximal sediment sources ice sheets and reduced thermohaline activity resulted in the accumulation of sediments on the slopes and basin floors

multi proxy records showing significant holocene environmental variability the inner n iceland shelf hunafloi abstract over the last 50 yr the n iceland margin has seen dramatic changes in temperature and salinity associated with the relative dominance of warm atlantic water versus cold arctic or polar waters we report a study of holocene environmental changes to assess the sensitivity of this area on a longer timescale we present sedimentologic isotopic and biotic coccolith proxies from a 5 5 m piston core b997 330pc that was retrieved from a small basin on the inner n iceland shelf seven ams dates indicate a relatively constant rate of sediment accumulation which averaged 55 cm kyr sampling resolution of our proxies varied between 16 and 90 yr sample our data indicate substantial variability in environmental conditions over the last 10 000 cal yr total carbonate content and coccolith concentrations track each other and indicate that the early holocene was a time of low net carbonate accumulation net accumulation of carbonate reached maximum values in the mid to late holocene 4 2 cal ka but there has since been a substantial decrease with a minima during the little ice age north atlantic drift coccolith species show peaks in accumulation rates at 2 and 8 cal ka and low influx between 3 5 and 6 cal ka reworked neogene coccoliths occur also 8 ka and coincide with light 18 o values in the epifaunal foraminifera cibicides lobatulus principal component analysis indicates considerable covariance between biotic isotopic and sedimentological parameters three axes explain 84 of the variance in the data set and define three groups of interrelated variables a major change occurs ca 5 cal ka after which conditions become more variable with a 1 5 kyr cyclicity

interaction between warm atlantic sourced waters and the east greenland current in northern denmark strait 68 n during the last 10 600 cal a bp changes in the holocene interaction of the i cold fresh east greenland current egc and ii warm saline irminger current ic in northern denmark strait have been reconstructed from benthic and planktic foraminifera assemblages ice rafted debris grain size analyses and quantitative x ray diffraction during the time from c 10 600 to 8000 cal a bp palaeoceanographic reconstructions reveal waning deglacial influence from the receding greenland ice sheet and presence of a strong egc caused low surface water productivity from c 8000 cal a bp a predominant influence of atlantic sourced ic waters on subsurface water conditions became established in northern denmark strait which accompanied low surface water productivity relatively warm surface and subsurface water conditions i e reduced egc and strong ic influence are found from c 6500 to 4500 cal a bp representing holocene optimum like conditions a mid to late holocene egc strengthening caused increased stratification and formation of a distinct halocline however we recognize millennial scale periods of reduced stratification by an enhanced influence of atlantic sourced ic water on surface water conditions i at c 2500 1400 cal a bp the time of the roman warm period and ii at c 300 cal a bp the later part of the little ice age these periods of oceanic warming probably relate to changes in the subpolar gyre dynamics that led to enhanced entrainment of atlantic sourced ic water into northern denmark strait

significant southern ocean warming event in the late middle eocene a prominent middle eocene warming event is identified in southern ocean deep sea cores indicating that long term cooling through the middle and late eocene was not monotonic at sites on maud rise and the kerguelen plateau a distinct negative shift in 1 8 o values 1 0 is observed ca 41 5 ma this excursion is interpreted as primarily a temperature signal with a transient warming of 4 c over 600 k y affecting both surface and middle bathyal deep waters in the indian atlantic region of the southern ocean this isotopic event is designated as the middle eocene climatic optimum and is interpreted to represent a significant climatic reversal in the midst of middle to late eocene deep sea cooling the lack of a significant negative carbon isotope excursion as observed during the paleocene eocene thermal maximum and the gradual rate of high latitude warming suggest that this event was not triggered by methane hydrate dissociation rather a transient rise in pco 2 levels is suspected possibly as a result of metamorphic decarbonation in the himalayan orogen or increased ridge arc volcanism during the late middle eocene

an exploratory method to detect tephras from quantitative xrd scans examples from iceland and east greenland marine sediments tephras mainly from iceland are becoming increasingly important in interpreting leads and lags in the holocene climate system across nw europe here we demonstrate that quantitative phase analysis of x ray diffractograms of the 150 m fraction and identify these same peaks in xrd scans two of these correlate geochemically and chronologically with hekla 1104 and 3 at a distal site to the wnw of iceland on the east greenland margin core md99 2317 the weight of volcanic glass reaches values of 11 at about the time of the saksunarvatn tephra the xrd method identifies the presence of volcanic glass but not its elemental composition hence it will assist in focusing attention on specific sections of sediment cores for subsequent geochemical fingerprinting of tephras

abrupt deep sea warming palaeoceanographic changes and benthic extinctions at the end of the palaeocene a remarkable oxygen and carbon isotope excursion occurred in antarctic waters near the end of the palaeocene 57 33 myr ago indicating rapid global warming and oceanographic changes that caused one of the largest deep sea benthic extinctions of the past 90 million years in contrast the oceanic plankton were largely unaffected implying a decoupling of the deep and shallow ecosystems the data suggest that for a few thousand years ocean circulation underwent fundamental changes producing a transient state that although brief had long term effects on environmental and biotic evolution

late quaternary iceberg rafted detritus events on the denmark strait southeast greenland continental slope 65 n related to north atlantic heinrich events hu93030 007 lcf 65o01 39 0 n and 30o14 81 0 w is a 4 5 m long giant 11 cm diameter piston core from 1800 m water depth on the continental slope south of the denmark strait sill the core sampled acoustically stratified sediments at a site below the kangerlussuaq trough nine ams 14 c dates on planktic foraminifera indicate that the core spans 14 to 28 14 c ka the sediments consists of two principal lithofacies lithofacies i li comprises tan ochre intervals with abundant ice rafted sandstone siltstone clasts larger than 2 mm and with an average thickness of 47 cm it is also associated with peaks in carbonate content and toc lithofacies ii lii consists of fine grained dark gray hemipelagic sediment there are three distinct intervals of li dated between 14 3 and 15 5 lic 20 1 and 21 9 lib 24 7 and 25 8 lia ka the ages suggest that deposition of li is approximately coeval with heinrich events 1 and 2 in the north atlantic whereas lia appears younger than h 3 lithofacies i is derived from far travelled ice bergs from an unknown source but not from the northeastern laurentide ice sheet stable isotope studies on neogloboquadrina pachydermasinistral show little evidence for significant meltwater events associated with li but surprisingly light oxygen isotopic events are present in the benthic foraminiferal analyses cibicidoides wuellerstorfiand melonis zaandamae the ages of the hu93030 007 iceberg rafted detritus ird events are similar to ird peaks in cores north of denmark strait on the east greenland slope hu87033 009 lcf se baffin slope 62o30 99 0 n and 59o26 82 0 w 1437 m wd is situated in a similar position to hu93030 007 but with respect to the laurentide ice sheet its d 18 o record on planktic foraminifera is virtually identical to that of hu93030 007 the timing of ird events is similar in both these cores between 14 and 30 ka h 3 may be present in hu87033 009 as an ird event but in contrast to h 1 and h 2 it is not evident as a discernible detrital carbonate event 1998 elsevier science b v all rights reserved

spatial and temporal patterns of iceberg rafting ird along the east greenland margin ca 68 n over the last 14 cal ka twelve 1 2 m 10 cm diameter gravity cores collected in 1988 and 1991 from the continental shelf and fjords of east greenland near kangerlussuaq fjord trough ca 68 n 32 w have distinct changes in lithofacies and in the quantity of iceberg rafted ird sediments these changes are readily observed in x radiographs of the split cores we quantify the ird contribution through grain size analyses and counting the number of clasts 2 mm from the x radiographs chronological control is provided by acclerated mass spectroscopy 14c dates on foraminifera during deglaciation after 14 cal ka there was one interval of ird accumulation ca 12 13 cal ka followed by a brief return to ird conditions centred at 9 cal ka thereafter a prominent feature of most cores on the shelf is an increase in ird accumulation that started ca 5 6 cal ka and which has increased toward the present indicators of iceberg rafting such as the net sand flux and numbers of clasts 2 mm ka 1 follow a power law distribution when graphed against distance from the present east greenland coast a measure of the position of the glacier margins the form of the relationship indicates that there is a dramatic decrease in the supply of sediment from the fjords to the shelf these relationships are used to estimate changes in the location of the ice margin during the late quaternary based on a site on the east greenland slope denmark strait and to discuss factors that can negate such a simple transfer function 1997 by john wiley sons ltd

influence of sediment source and type on the magnetic susceptibility of fiord and shelf deposits baffin island and baffin bay n w t volume and mass magnetic susceptibility are measured on recent and late quaternary sediments from the fiords and shelf of eastern baffin island baffin bay and the northern labrador sea major changes in hinterland bedrock geology are associated with order of magnitude changes in magnetic susceptibility the fiords that head into the proterozoic foxe fold belt have mass magnetic susceptibilities ms of 2 4 10 7 m3 kg compared with 25 60 10 7 m3 kg in sediments derived from archean gneisses and granites another low ms region is the middle reach of frobisher bay ms studies in cambridge mcbeth and itirbilung fiords included analyses of surface samples and samples from lehigh 3 m and piston 11 m cores lehigh cores had higher ms values on average than the piston cores suggesting a coarsening in texture or an increase in the flux of magnetic minerals during the last 0 3 3 ka an analysis of the ms logs of 17 piston cores indicated that six broad patterns of ms can be recognized based on a

variations in felsic versus mafic sources in the western nordic seas during mis 1 to mis 4 abstract the goal of this paper is to employ quantitative methods to first describe the spatial variations in the quantitative non clay and clay mineral composition of seafloor surface sediments secondly use those data to describe the temporal variations in mineral compositions of nine cores that extend variously between the present day and 85 ka bp and thirdly describe regional variations in the transport of felsic versus mafic rich glacial marine sediments at four sites close to denmark strait k mean clusters of recent seafloor samples n 156 distinguished four mineral facies which characterize a range of mafic to felsic compositions these samples serve as a training set to identify the down core mineral facies in eight cores n 1053 the degree of provenance mixing is measured by fuzzy clustering on an unsupervised cluster analysis classification decision trees validate the mineral facies only 6 misclassified and indicate that variations in the weight of pyroxene are of primary importance in defining cluster membership mineral compositions identify two end member core sites jm07 174gc greenland sea and lo9 18 reykjanes ridge while the cores north and south of the greenland faroes ridge cores ps2644 md99 2274 2280 and 2323 are a mixture of mafic rich and felsic rich mineral facies variations in magnetic susceptibility and quartz wt exhibit coherent runs of values above or below their medians in three of the cores occurred indicating that these cannot be ascribed to random variations p

seeking a holocene drift ice proxy non clay mineral variations from the sw to n central iceland shelf trends regime shifts and periodicities quantitative x ray diffraction analysis of the 2 mm sediment fraction was carried out on 1257 samples from the seafloor and 16 cores from the iceland shelf west of 18 w all but one core b997 347pc were from transects along troughs on the nw to n central shelf an area that in modern and historic times has been affected by drift ice the paper focuses on the non clay mineralogy of the sediments excluding calcite and volcanic glass quartz and potassium feldspars occupy similar positions in an r mode principal component analysis and oligoclase feldspar tracks quartz these minerals are used as a proxy for ice rafted detritus ird accordingly the sum of these largely foreign minerals q k to icelandic bedrock is used as a proxy for drift ice a stacked equi spaced 100 a record is developed which shows both low frequency trends and higher frequency events the detrended stacked record compares well with the flux of quartz mg cm 2 a 1 at md99 2269 off n iceland the multi taper method indicated that there are three significant frequencies at the 95 confidence level with periods of ca 2500 445 and 304 a regime shift analysis pinpoints intervals when there was a statistically significant shift in the average q k weight and identifies four ird rich events separated by intervals with lower inputs there is some association between peaks of ird input less dense surface waters from 18o data on planktonic foraminifera and intervals of moraine building copyright 2009 john wiley sons ltd

holocene climatic instability a prominent widespread event 8200 yr ago the most prominent holocene climatic event in greenland ice core proxies with approximately half the amplitude of the younger dryas occurred 8000 to 8400 yr ago this holocene event affected regions well beyond the north atlantic basin as shown by synchronous increases in windblown chemical indicators together with a significant decrease in methane widespread proxy records from the tropics to the north polar regions show a short lived cool dry or windy event of similar age the spatial pattern of terrestrial and marine changes is similar to that of the younger dryas event suggesting a role for north atlantic thermohaline circulation possible forcings identified thus far for this holocene event are small consistent with recent model results indicating high sensitivity and strong linkages in the climatic system

the east greenland continental margin 65 n since the last deglaciation changes in seafloor properties and ocean circulation nine gravity cores collected on the east greenland continental margin off kangerdlugssuaq fjord reveal a drastic decrease in average sedimentation rates from the cross shelf through the continental slope from 43 2 cm kyrs to 2 2 cm kyrs respectively since the last deglaciation beginning at 2g cm2kyrs at 4000 yrs b p both caco3 and non caco3 accumulation rates became high g cm2kyrs since 3000 yrs b p these rates distinctly decreased melting of glaciers and current activity which drastically changed in space and time controlled the terrigenous sediment input and thus the grain size distribution and the physical properties of sediments across the shelf these observations suggest that current winnowing on sediments is one of the dominant processes at present this is seen in the acoustic reflectivity and in the acoustically hard seafloor particularly at the upper continental slope in addition icebergs transported southward along the continental margin have scoured the sediment surface in water depths 350m

testing the cretaceous greenhouse hypothesis using glassy foraminiferal calcite from the core of the turonian tropics on demerara rise glassy turonian foraminifera preserved in clay rich sediments from the western tropical atlantic yield the warmest equivalent 18o sea surface temperatures ssts yet reported for the entire cretaceous cenozoic we estimate turonian ssts that were at least as warm as conservative mean 30 c to significantly warmer warm mean 33 c than those in the region today however if independent evidence for high middle cretaceous pco2 is reliable and resulted in greater isotopic fractionation between seawater and calcite because of lower sea surface ph our conservative and warm sst estimates would be even higher 32 and 36 c respectively our new tropical ssts help reconcile geologic data with the predictions of general circulation models that incorporate high cretaceous pco2 and lend support to the hypothesis of a cretaceous greenhouse our data also strengthen the case for a turonian age for the cretaceous thermal maximum and highlight a 20 40 m y mismatch between peak cretaceous cenozoic global warmth and peak inferred tectonic co2 production we infer that this mismatch is either an artifact of a hidden turonian pulse in global ocean crust cycling or real evidence of the influence of some other factor on atmospheric co2 and or ssts a hidden pulse in crust cycling would explain the timing of peak cretaceous cenozoic sea level also turonian but other factors are needed to explain high frequency 10 100 k y instability in middle cretaceous ssts reported elsewhere

deep circulation in the late cretaceous oxygen isotope paleotemperatures from inoceramus remains in d s d p cores abstract inoceramus is an epibenthic bivalve which lived in a wide variety of paleoenvironments encompassing a broad range of paleodepths a survey of all cretaceous sediments from deep sea drilling project legs 1 69 and 75 revealed over 500 inoceramus specimens at twenty sites of these 47 well preserved late cretaceous specimens from the south atlantic pacific and indian oceans were analyzed for oxygen and carbon isotopes the specimens exhibit small internal isotopic variability and oxygen isotopic paleotemperatures that are consistent with a deep sea habitat paleotemperatures ranging from 5 to 16 c show that late cretaceous oceans were significantly warmer than the present oceans the data suggest that deep water was formed both by cooling at high latitudes and by evaporation in the subtropics

quaternary tephrachronology on the iceland plateau north of iceland four major ash zones recorded in piston cores raised from the iceland plateau north of iceland are shown to be coincident with the last four interglacial isotopic stages their geochemical composition links the ashes to volcanic events on iceland the occurrence of these ash layers which record events orders of magnitude larger than the normal holocene volcanic eruptions can not be explained by changes in sea ice cover and atmospheric circulation alone it is suggested that these events are related to pressure releases in the magma chambers resulting from major deglaciations of the icelandic ice cap

paleocene to eocene benthic foraminiferal isotopes and assemblages implications for deepwater circulation early paleogene warm climates may have been linked to different modes and sources of deepwater formation warm polar temperatures of the paleocene and eocene may have resulted from either increased atmospheric trace gases or increased heat transport through deep and intermediate waters the possibility of increasing ocean heat transport through the production of warm saline deep waters wsdw in the tethyan region has generated considerable interest in addition general circulation model results indicate that deepwater source regions may be highly sensitive to changing basin configurations to decipher deepwater changes we examined detailed benthic foraminiferal faunal and isotopic records of the late paleocene through the early eocene 60 to 50 ma from two critical regions the north atlantic bay of biscay site 401 and the pacific shatsky rise site 577 these records are compared with published data from the southern ocean maud rise site 690 islas orcadas rise site 702 during the late paleocene similar benthic foraminiferal 18o values were recorded at all four sites this indicates uniform deepwater temperatures consistent with a single source of deep water the highest 13c values were recorded in the southern ocean and were 0 5 more positive than those of the pacific we infer that the southern ocean was proximal to a source of nutrient depleted deep water during the late paleocene upper paleocene reflector ab was cut on the western bermuda rise by cyclonically circulating bottom water also suggesting a vigorous source of bottom water in the southern ocean a dramatic negative excursion in both carbon and oxygen isotopes occurred in the latest paleocene in the southern ocean this is a short term 100 kyr globally synchronous event which also is apparent in both the atlantic and pacific records as a carbon isotopic excursion of approximately 1 faunal analyses from the north atlantic and pacific sites indicate that the largest benthic foraminiferal faunal turnover of the cenozoic was synchronous with the isotopic excursion lending support to the hypothesis that the extinctions were caused by a change in deepwater circulation we speculate that the southern ocean deepwater source was reduced or eliminated at the time of the excursion during the early eocene southern ocean 13c values remained enriched relative to the north atlantic and pacific however the southern ocean was also enriched in 18o relative to these basins we interpret that these patterns indicate that although the southern ocean was proximal to a source of cool nutrient depleted water the intermediate to upper deep water sites of the north atlantic and pacific were ventilated by a different source that probably originated in low latitudes i e wsdw

a high resolution holocene sediment record from hunafloaall n iceland margin centuryto millennial scale varability since the vedde tephra md99 2269 is a 25 m long core from hunafloaall a deep trough which runs northward towards the shelf break from the narrow neck of land which joins the northwest peninsula of iceland with the main land the core was recovered from the thickest part of an elongate shelf sediment body underlain by glacial diainictons with ages 26 ka bp 3 5 khz profiles indicate the presence of a reflector ri which can be traced over long distances twelve ams radiocarbon dates and the presence of the saksunarvatn tephra which is the origin for the ri reflector at 21 m core depth define a linear depth age relation with an accumulation rate of 200 cm ky the date on the core top is modern x radiographs indicate that the sediments are principally massive bioturbated muds the data were measured at resolutions of between 5 and 40 yr sample our primary data represent aspects of a multisensor track measurements b colour c grain size d sediment properties and e sediment magnetic properties principal component analysis pca was used to simplify the analysis of these five data sets and resulted in nine significant axes compared to over 70 original variables the explained variance on the first axes varied between 47 and 96 these time series were reduced to a common 50 yr sample interval which were then also subject to pca using the resulting pc scores we present three primary axes of environmental variability in hunafloaall that have century scale quasi periodicities and demonstrate that these are highly correlated with specific raw variables we focus on variables linked to changes in grain size and productivity and show regional coherence cores b997 321 and 330 in the coercivity grain size measure armj 20 armj 0 which have a close similarity to the detrended 14 c series this provides a potential link to the vigour of the thermohaline circulation to the north of the iceland shelf in the iceland and greenland seas our data indicate increas

holocene sea surface conditions in the western north atlantic spatial and temporal heterogeneities 1 holocene records of sea surface conditions in the western nordic seas were obtained from quantitative reconstructions based on dinoflagellate cyst assemblages two sediment cores from the east greenland and the north iceland shelves provide a detailed account of the long and short term dynamics of the opposing flows of arctic versus atlantic waters both marker species and quantitative reconstructions depict an overall trend toward warmer winter temperatures saltier surface waters and decreased sea ice extent the latter is supported by a close relationship between relative abundances of an atlantic dinocyst species nematosphaeropsis labyrinthus and ice rafted debris ird records we propose that the late holocene increased ird delivery in the denmark strait region was primarily induced by a combination of less extensive sea ice cover under increased atlantic water inflow and sustained iceberg calving tied to the readvance of the greenland ice sheet our records thus suggest diminishing polar water supplies throughout the holocene although the timing of regime changes differs between the western and eastern sides of the denmark strait finally comparison of our records with a core from southern greenland points to very heterogeneous sea surface conditions in the western north atlantic which could be explained by the decoupled dynamics of the two irminger current branches similarities between the southern greenland marine record and a continental record nearby suggest a close coupling with atmospheric processes reminiscent of a north atlantic oscillation like climate pattern

environmental seismology what can we learn from ambient noise environmental seismology consists in studying the coupling between the solid earth and the cryosphere or the hydrosphere the anthropospher in practice we monitor the modifications of the wave propagation due to environmental forcing such as temperature and hydrology using ambient seismic noise that constitute a continuous cheap and relatively reproducible source of vibrations recent developments in data processing 1 together with increasing computational power and sensor concentration have led to original observations that allow for this new field of seismology in this paper we will review how we can track and interpret tiny changes in the subsurface of the earth related to external changes from modifications of the seismic wave propagation with application to geomechanics hydrology and natural hazard 2 we will demonstrate that using ambient noise we can track thermal variations in the subsoil in buildings or in rock columns with application to damage estimation the temporal and spa

latest pleistocene and holocene alpine glacier fluctuations in scandinavia abstract during the early holocene abrupt decadal to centennial scale climate variations caused significant glacier variations in norway increased freshwater inflow to the north atlantic and arctic oceans has been suggested as one of the most likely mechanisms to explain the abrupt and significant lateglacial and early holocene climatic events in nw europe the largest early holocene glacier readvances occurred 11 200 10 500 10 100 9700 9200 and 8400 8000 cal yr bp the studied norwegian glaciers apparently melted away at least once during the early mid holocene the period with the most contracted glaciers in scandinavia was between 6600 and 6000 cal yr bp subsequent to 6000 cal yr bp the glaciers started to advance and the most extensive glaciers existed at about 5600 4400 3300 2300 1600 cal yr bp and during the little ice age times with overall less glacier activity were apparently around 5000 4000 3000 2000 and 1200 cal yr bp it has been proposed that several glacier advances occurred in scandinavia including northern sweden at 8500 7900 7400 7200 6300 6100 5900 5800 5600 5300 5100 4800 4600 4200 3400 3200 3000 2800 2700 2000 1900 1600 1200 1000 and 700 200 cal yr bp glaciers in northern sweden probably reached their greatest little ice age extent between the 17th and the beginning of the 18th centuries evidence for early holocene glacier advances in northern scandinavia however has been questioned by more recent multi disciplinary studies the early to mid holocene glacier episodes in northern sweden may therefore be questioned most norwegian glaciers attained their maximum little ice age extent during the mid 18th century cumulative glacier length variations in southern norway based on marginal moraines dated by lichenometry and historic evidence show an overall retreat from the mid 18th century until the 1930s 40s subsequently most norwegian glaciers retreated significantly maritime outlet glaciers with short frontal time lags 15 20 years continued their retreat to the 1970s and 1980s however maritime glaciers started to advance as a response to higher winter accumulation during the first part of the 1990s after 2000 several of the observed glaciers have retreated remarkably fast annual frontal retreat 100 m mainly due to high summer temperatures the general glacier retreat during the early holocene and the neoglacial advances after 6000 cal yr bp are in line with orbital forcing due to the decrease of northern hemisphere summer solar insolation and the increase in winter insolation in addition regional weather modes such as the north atlantic oscillation nao and the arctic oscillation ao play a significant role with respect to decadal and multi decadal climate variability

holocene variability of the north atlantic irminger current on the south and northwest shelf of iceland abstract the irminger current ic transports heat and nutrients to the icelandic shelf and its fluctuations are strongly linked to variations in the strength of the north atlantic surface flow from the south by using benthic foraminiferal assemblages and their stable isotopic composition in two marine sediment cores located in the pathway of the ic on the west iceland shelf we were able to derive bottom water temperature estimates at a 100 year resolution and define the temperature difference between the core sites throughout the holocene these are the first transfer function bottom water temperatures presented from the icelandic shelf based on benthic foraminiferal assemblages our findings demonstrate a delayed holocene thermal maximum in the marine current system around iceland compared to the northern hemisphere summer insolation receipts the maximum heat transport in the ic occurred between 8 and 4 ka years later than some previous records report a reconstruction of the ambient seawater 18o based on paired samples of c2 transfer function temperature estimates and oxygen isotopic composition indicates repeated freshwater input to the n atlantic inflow in the early holocene impacting the current system before 8 ka two fundamental regime shifts are evident in the paleoceanography and foraminiferal properties during the holocene occurring around 8 ka towards more stable conditions and again around 4 ka towards more unstable conditions increasing fluctuation with similarities to the great salinity anomaly in the 1970s occur after 4 ka

carbon and oxygen isotopic disequilibria of recent deep sea benthic foraminifera abstract the carbon and oxygen isotopic compositions of 149 samples of benthic foraminifera from deep sea core tops indicate that none of the nine species studied secrete calcium carbonate in isotopic equilibrium with ambient bottom water uvigerina pyrgo murrhina and oridorsalis tener are the closest to 18o equilibrium with average deviations about 0 4 while planulina wuellerstorfi and p murrhina are the closest to 13c equilibrium with average deviations about 1 p wuellerstorfi shows the most systematic relationship between 13c and bottom water apparent oxygen utilization the intraspecific variabilities in 18o and 13c suggest that estimates of bottom water paleotemperatures can be made to a precision of 0 7 c while estimates of past apparent oxygen utilization aou can be made to 35 mol kg based on intraspecific comparisons of the recent samples with fossils no temporal changes in the degree of either 18o or 13c disequilibrium have been detected for planulina wuellerstorfi uvigerina oridorsalis tener and globocassidulina subglobosa

the n and w iceland shelf insights into last glacial maximum ice extent and deglaciation based on acoustic stratigraphy and basal radiocarbon ams dates abstract we present 32 ams radiocarbon dates collected from sediments obtained during cruises of css hudson 1993 rv jan mayen 1996 and bjarni saemundsson 1997 the radiocarbon dates were obtained on samples from the basal part of sediment cores collected across an area between 64 and 67 n and 18 29 w core sites were based on 3 5 khz acoustic subbottom surveys the 3 5 khz subbottom profiles indicate that several of the troughs contain 30 m of quaternary sediment at many sites the acoustic surveys suggest the presence of one or more strong reflectors which can be traced over extended areas 100 km of the seafloor these may represent large scale volcanic ash falls such as the vedde ash and its correlatives as well as other regionally significant tephras we report dates from seven areas 1 northern troughs eyjafjardarall hunafloadjup and reykjafjardarall 2 hunafloi area and inner shelf and fjords 3 djupall area 4 isafjardardjup area 5 kolluall 6 western shelf break and slope and 7 jokuldjup the dates range in age from marine isotope stages 3 1 five cores have basal dates 16 ka and thus provide information on the timing and environments during the deglaciation several dates of 12 ka indicate that the inner shelf may have been largely ice free by that time estimates of average sediment accumulation rates vary between 4 and 90 cm kyr with modal estimates of 30 40 cm kyr

abrupt climate change and transient climates during the paleogene a marine perspective detailed investigations of high latitude sequences recently collected by the ocean drilling program odp indicate that periods of rapid climate change often culminated in brief transient climates with more extreme conditions than subsequent long term climates two examples of such events have been identified in the paleogene the first in latest paleocene time in the middle of a warming trend that began several million years earlier the second in earliest oligocene time near the end of a middle eocene to late oligocene global cooling trend superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice sheet on antarctica in both cases the climate extremes were not stable lasting for less than a few hundred thousand years indicating a temporary or transient climate state geochemical and sedimentolog

a simulation of mid cretaceous climate a series of general circulation model experiments utilizing genesis have been completed for the mid cretaceous based on geography variable atmospheric carbon dioxide concentrations 2 to 6 times present day concentrations and variable poleward oceanic heat flux 6 to 1 2 1015 w increased from present day by combining all three major variables co2 geography and oceanic heat flux the distribution of mid cretaceous temperatures can be achieved in the simulations increased co2 is required to promote global warmth and increased oceanic heat flux is required to prevent the tropics from overheating with higher levels of co2 four times present day co2 with 1 2 1015 w provided the best match to the distribution of mid cretaceous data the best match to the cretaceous observations was achieved with a globally averaged surface temperature increase of 6 2 c at the lower end of past estimates of mid cretaceous warmth this value may be a better estimate of mid cretaceous global warming finally the model experiments can be used to provide a paleocalibration of the global warming expected for a doubling of atmospheric carbon dioxide the best estimates for the mid cretaceous appear to be a 2 5 to 4 0 c sensitivity in the mid to upper range of the sensitivity of current climate models used to assess future global change

holocene periodicity in north atlantic climate and deep ocean flow south of iceland climate fluctuations during the past millennium are relatively well documented1 on a longer timescale there is growing evidence of millennial scale variability of holocene climate at periodicities of 2 500 and 950 years possibly caused by changes in solar flux 2 3 and 1 500 years maybe related to an internal oscillation of the climate system 4 5 6 but the involvement of deep water masses in these holocene climate changes has yet to be established here we use sediment grain size data from the iceland basin to reconstruct past changes in the speed of deep water flow the study site is under the influence of iceland scotland overflow water isow the flow of which is an important component of the thermohaline circulation that modulates european climate flow changes coincide with some known climate events the little ice age and the mediaeval warm period and extend over the entire holocene epoch with aquasi periodicity of 1 500 years the grain size data indicate afaster isow flow when the climate of northern europe is warmer however a second mode of operation is observed in the early holocene when warm climate intervals are associated with slower isow flow at that time the melting remnant of land based glacial age ice may have provided a sufficient source of fresh water to the ocean to reduce isow flow south of iceland

late quaternary calcium carbonate sedimentation and terrigenous input along the east greenland continental margin nine large box cores collected in the western greenland iceland norwegian gin sea were analyzed for calcium carbonate content and coarse fraction components stratigraphic control is based on oxygen isotope records performed on four of the cores all cores were correlated using oxygen and carbon isotope data fluctuations in calcium carbonate content coarse terrigenous particle content and volcanic ash beds glacial and interglacial cycles are documented by a number of terrigenous particle events and differentiated calcium carbonate production which can be correlated to major paleoceanographic and paleoclimatic shifts in the older core sections extensive deposition of ice rafted detritus ird persisted until about oxygen isotope stage 9 and document a relatively stable environment in this area strongly influenced by cold surface water masses the following interval was characterized by variations in the general surface water circulation pattern although high amounts of ird are still present in iceland sea sediments pronounced shifts in terrigenous input and pelagic carbonate records were identified close to the oxygen isotope stage full size image 1 k and full size image 1 k boundaries indicating massive melting of icebergs in the western gin sea these enormous inputs of debris were followed by an increase in calcium carbonate production caused by maximum intrusion of warm atlantic surface waters relatively high calcium carbonate contents also show that only little dilution by fine grained material and a minimum of ice melting occurred during these warm phases during oxygen isotope stage 5 conditions were more uniform indicating a less pronounced westward penetration of atlantic waters as compared to the holocene the last glacial stages 4 2 is characterized by the occurrence of heinrich like events although high ird contents were present throughout this interval a distinct contrast between the northernmost cores and the cores in the south is indicative of a rather strong westward penetration of atlantic water in the north and of an area dominated by cold water east of the kolbeinsey ridge during the holocene however conditions west of jan mayen seem to have remained constantly dominated by cold surface waters throughout the whole time investigated

the origin of massive diamicton facies by iceberg rafting and scouring scoresby sund east greenland almost 90 of 39 m of core material recovered from scoresby sund and the adjacent east greenland shelf is massive diamicton interpreted to be formed predominantly by the release of iceberg rafted debris and reworking by iceberg scouring there is also likely to be a contribution from suspension settling of fines derived from glaciofluvial sources model calculations suggest that the 14c derived holocene sedimentation rate of 0 1 0 3 m 1000 yr 1 in scoresby sund can be accounted for mainly by iceberg rafting of debris a further 4 of core material is of gravel or coarse sand lenses interpreted to reflect iceberg dumping of debris intensive iceberg scouring which reworks sea floor sediments is observed on acoustic records from over 30 000 km2 of the scoresby sund fiord system and the adjacent east greenland shelf 69 72 n and 75 n the rate of iceberg production from greenland ice sheet outlet glaciers and iceberg drift tracks on the shelf suggests that iceberg rafting and scouring may be important over a significant proportion of the 500 000 km2 area above the shelf break the relatively extensive modern occurrence of massive diamicton formed by iceberg rafting and scouring together with suspension settling of fines suggests that it may also be a significant facies in the glacier influenced geological record the recognition in the geological record of the massive diamicton facies described above may also indicate the former presence of fast flowing ice sheet outlet glaciers

insights from the paleogene tropical pacific foraminiferal stable isotope and elemental results from site 1209 shatsky rise 1 stable isotope and elemental measurements were conducted on foraminifera from a sequence of calcareous pelagic ooze at ocean drilling program site 1209 to document the thermal evolution of the north pacific water column over shatsky rise and to address long standing questions about the nature of oceanic circulation in the early paleogene a major change in seasonality and water column structure in the early eocene marks a change in tropical pacific climate and circulation just prior to the early eocene climatic optimum subsequent long term cooling is interrupted by a transient positive 18o excursion identified in planktonic and benthic foraminifera during the late early eocene that is interpreted as evidence for ephemeral formation of deep water from a low latitude saline source paired analysis of benthic mg ca and 18o was undertaken to assess the relative contribution of temperature and seawater oxygen isotope composition to the benthic 18o record stratigraphic trends of benthic 18o and mg ca decouple during two intervals in the early eocene and early middle eocene although variable seawater 18o is the most likely candidate to explain decoupling of benthic 18o and mg ca it is difficult to argue for substantial change in continental ice volume during a presumably ice free interval of time

sediment characteristics in iceberg dominated fjords kangerlussuaq region east greenland abstract sediment cores from three east greenland fjords contain sediment lithofacies and depositional processes in an iceberg dominated glacial marine setting three major lithofacies diamicton fine grained mud and sand are deposited by two processes sediment rain out and sediment gravity flows the sediments in kangerlussuaq fjord are predominately fine grained muds deposited by rain out from icebergs and glacier meltwater with sediment gravity flows acting as secondary agents of deposition miki fjord records rain out of fine grained muds from a river plume emanating from a proglacial delta at the fjord head alternating units of diamicton and fine grained mud in nansen fjord are deposited by sediment rain out from icebergs particle size is governed by the oceanographic conditions in the fjord at the time of deposition despite their proximity to each other each fjord is distinguished by a distinct sedimentological signature kangerlussuaq fjord has low total organic carbon contact miki fjord has high mass magnetic susceptibility and nansen fjord has high amounts of ice rafted debris comparison of the east greenland iceberg dominated and alaska glacial meltwater dominated environments indicates few major differences between sediments deposited in these two settings this similarity raises doubt as to how well glacial marine sedimentary sequences can be used to interpret and reconstruct differences between glacial marine environments in the past without knowledge of sediment accumulation rates environmental conditions at the time of sediment deposition and comparable sedimentological data between studies

possible atmospheric co2 extremes of the middle cretaceous late albian turonian 1 atmospheric carbon dioxide co2 estimates for the middle cretaceous mk have a range of 4000 ppm which presents considerable uncertainty in understanding the possible causes of warmth for this interval this paper examines the problem of mk greenhouse forcing from an inverse perspective we estimate upper ocean water temperatures from oxygen isotope measurements of well preserved late albian turonian planktonic foraminifera and compare these against temperatures predicted by general circulation model gcm experiments with co2 concentrations of 500 7500 ppm at least 4500 ppm co2 is required to match maximum temperatures inferred from well preserved planktonic foraminifera approximately 900 ppm co2 produces a good match between the model and the minimum temperature estimates for the mk an ocean model forced by these two extremes in surface conditions brackets nearly all available bottom water temperature estimates for this interval the climate model results support nearly the entire range of mk co2 estimates from proxy data the ocean model suggests possible mk oceanographic changes from deep water formation in the high latitude region of one hemisphere to the other hemisphere in response to changes in atmospheric temperatures and hydrologic cycle strength we suggest that rather than contradicting one another the various proxy co2 techniques especially those with high temporal resolution may capture true variability in co2 concentrations and that mk co2 could have varied by several thousand ppm through this interval

decadal to millennial scale periodicities in north iceland shelf sediments over the last 12 000 cal yr long term north atlantic oceanographic variability and solar forcing giant piston core md99 2269 recovered 25 m of sediment in hunafloaall a deep trough on the north iceland margin fronting the iceland sea and the site of a shelf sediment drift the rate of sediment accumulation is 2 m kyr 5 yr cm the core terminated in the vedde tephra v12 cal ka the sediment was sampled at between 5 and 50 yr sample including rock magnetic grain size and sediment properties data reduction was carried out using principal component analysis two pc axes for the 5 yr sample magnetic data are strongly correlated with measures of coercivity arm20 mt arm and magnetic concentrations karm in turn arm20 mt arm is highly correlated negatively with grain size and the mean size of the sortable silt fraction analyses of the two pc axes with mtm spectral methods indicate a series of significant s 99 periodicities at millennial to multidecadal scales including those at v200 125 and 88 yr which are associated with solar variability we also document a strong correlation between the sediment magnetic properties and the d 18 o on benthic foraminifera on the north iceland inner shelf we hypothesize that the links between variations in grain size magnetic concentrations and solar forcing are controlled by atmospheric and oceanographic changes linked to changes in the relative advection of atlantic and polar waters along the north iceland margin today these changes are associated with variations in the deep convection in the greenland and iceland seas the precise linkages are however presently elusive although a combination of coarser sediments and low d 18 o values define a holocene thermal maximum between v8 and 6 cal ka 2003 elsevier science b v all rights reserved

the sizes frequencies and freeboards of east greenland icebergs observed using ship radar and sextant the scoresby sund fjord system east greenland contains the most productive fast flowing outlet glaciers draining east from the greenland ice sheet calving 18 km3 a 1 of icebergs the sizes frequencies and freeboards of 1900 icebergs were measured from f s polarstern using ship x band radar and sextant radar beam spreading exaggerates iceberg width by 60 m per nautical mile of range beyond the first mile data sets on iceberg size e g that collated for antarctic icebergs collected using ship radars which do not take this effect into account will overestimate iceberg dimensions significantly the location and concentration of icebergs within the fjord complex can be explained by 1 the locations of the principal source glaciers and 2 fjord topography and bathymetry iceberg concentration maximum 0 6 icebergs km 2 declines with distance from the major iceberg sources we found that 69 of icebergs within the fjord system are 1 km in length the largest is 2 7 km long icebergs become spread more evenly over the range of size classes in the outer fjord and shelf modal iceberg keel depth calculated from freeboard measurements is 4 500 m in the inner fjords shifting to lower values in the outer fjords reflecting shallower bathymetry radar measurements of iceberg width cannot be used to infer keel depths accurately because width and keel depth are only weakly correlated comparison between freeboards and keel depths for icebergs from east greenland and the barents sea indicates that the iceberg source i e floating or grounded exerts a fundamental control on iceberg dimensions the drift pattern of icebergs is from the head to the mouth of the fjord system although fjord bifurcations bathymetry and currents provide additional complications the trends in observed iceberg size and frequency and in inferred keel depth in the scoresby sund region are likely to be applicable to other fjords and shelves around greenland

magnetic susceptibility variations in upper pleistocene deep sea sediments of the ne atlantic implications for ice rafting and paleocirculation at the last glacial maximum magnetic susceptibility ms variations are used to intercorrelate 17 upper pleistocene sediment cores taken from the ne atlantic between 40 degrees and 60 degrees n the ms based correlation depends on regionally consistent patterns of variation in the deposition of ice rafted detritus ird in response to pleistocene glaciations and especially to high frequency ice rafting episodes referred to in recent studies as heinrich events the sedimentological and rock magnetic basis for the apparent relationship between the ms signal and ird content of ne atlantic sediments is examined by 1 comparing the ms profiles of selected cores with their records of coarse fraction 150 mu m lithic fragment abundance and neogloboquadrina pachyderma sin percentages and 2 normalizing ms by expressing it both on a carbonate free basis and as a quotient with anhysteretic remanent magnetization a parameter sensitive to magnetic mineral grain size variations these comparisons show that variations in bulk sediment ms are only partly driven by simple carbonate dilution productivity and dissolution effects changes in both the concentration and grain size of magnetic minerals within the lithogenic noncarbonate fraction also impose a significant influence on bulk ms values in particular horizons rich in ird are associated with significant increases in the relative proportion of coarse grained multidomain ferrimagnetic particles in the sediment this is because ice rafting in contrast to most other mechanisms capable of transporting detrital magnetic minerals to pelagic environments has a high potential for delivering large ferrimagnetic grains as components of sand sized polycrystalline lithic fragments this fundamental linkage between the ird content and ms signal of ne atlantic sediments is used to reconstruct the patterns of variation in ird deposition and by inference surface currents of the last glacial maximum lgm similar to 18 19 ka relative to the present day ne atlantic using the time slice mapping approach developed by the climap project group our lgm holocene ms ratio map based on sample pairs from over 80 deep sea cores confirms that there was a weak cyclonic gyre north of the polar front in the lgm north atlantic the gyre comprised a sluggish warm current in the ne atlantic flowing north between latitudes 47 degrees and 62 degrees n partly fed by subtropical waters from south of the polar front and carrying large numbers of icebergs derived from several sources most of which melted between latitudes 45 degrees and 52 degrees n the warm current probably continued its flow into the iceland basin where it fed into a south flowing current which transported melting icebergs from iceland and scandinavia along the western flank of the reykjanes ridge

warm saline bottom water in the ancient ocean considerable isotopic evidence indicates that oceanic bottom water was much warmer in the geological past a simple convection model driven by multiple turbulent buoyant plumes and observations of present deep water formation have led to the development of a theory for the formation of warm saline bottom water it is suggested that changes in the size and configuration of marginal seas in net evaporation zones due to lithospheric plate motions and eustatic sea level change caused these seas to become sources of warm saline bottom water evidence from the palaeotemperature record and palaeogeography during the late cretaceous is used to reinforce the hypothesis climatic and chemical consequences of the formation of warm saline bottom water are discussed

laser vs settling velocity differences in silt grainsize measurements estimation of palaeocurrent vigour the use of grain size distribution of muds for the reconstruction of past deep ocean currents is becoming established and applied in the palaeoceanographic community the methods are also applicable to shallow marine and tidal flat muds with similar inferences concerning the energy of wave and current sorting being drawn fine sediment grain size distributions can be obtained using a variety of instruments based on fundamentally different theoretical principles these machines may give varying sometimes misleading results giving divergent interpretations of flow speed history the new evidence presented here combined with earlier work suggests that of the three most commonly used analytical methods for fine silts with clays settling velocity sedigraph should be the method and instrument of choice with electrical resistance pulse counters e g coulter counter as a suitable alternative the data also show that laser particle sizers should be avoided for palaeocurrent reconstructions because the measured size of platey minerals can be dominated by their large projected area this causes them to be recorded as the same size as larger equant grains although they have much smaller settling velocity and were deposited in aggregates this produces results with a weaker relationship to the dynamics of deposition the central problem is thus that some coarse clay fine silt is recorded as medium to coarse silt the key size in the sortable silt mean size method of inferring changes in flow speed for coarse silts e g loess the laser gives more satisfactory results

late quaternary sedimentation along a fjord to shelf trough transect east greenland c 68 n the east greenland continental margin between c 66 and 68 n consists of a major fjord trough system that extends from kangerdlugssuaq fjord along kangerdlugssuaq trough to denmark strait measurements of the temperature and salinity of the water column along this transect indicates that warm water 0 2 c underlies the surface polar water of the east greenland current a series of short 1 3 m gravity cores along the fjord trough transect have sufficient numbers of foraminifera that a suite of ams 14c dates has been obtained including both basal and core top age estimates rates of sediment accumulation vary through space and time over the last 1 ka estimates vary from c 3 to 0 1 m these dates and measurements of sediment density together with measurements of the percentages by weight of total organic carbon and biogenic silica are used to show graphs of fluxes of the organic and inorganic sediment components over the last 1 14 ka an analysis of the net flux of foraminifera indicates a reduction in numbers during the younger dryas chronozone and a general similarity with data from the renland east greenland ice core data

distinguishing subglacial till and glacial marine diamictons in the western ross sea antarctica implications for a last glacial maximum grounding line analyses of lithology stratigraphy and tephra from marine sediment cores collected from the western ross sea during cruises eltanin 32 and 52 and deep freeze 80 and 87 indicate that subglacial till does not extend to the continental shelf edge subglacial till occurs as the lowest unit in most cores landward south of approximately 74 s while seaward of approximately 74 s the lowest diamicton units are glacial marine diamictons glacial marine diamictons are distinguished from subglacial tills by the presence of higher and more variable total organic carbon content downcore distinct tephra layers stratification higher diatom and foraminifera abundances higher sand content and radiocarbon dates in chronological order downcore sand sized tephra layers from two cores on the outer continental shelf are interpreted as single eruptive events one likely to have been derived from the mount melbourne volcano and the other from the pleiades volcano radiocarbon dates from sediment above and below the tephra layer in one of these cores df87 32 show that deposition indicative of open water conditions occurred between 22 and 26 ka in the western ross sea

holocene variations in mineral and grain size composition along the east greenland glaciated margin ca 67 70 n local versus long distance sediment transport quantitative x ray diffraction qxrd analysis of the 2 mm sediment fraction from surface sea floor samples and marine sediment cores that span the last 10 12 cal ka bp are used to describe spatial and temporal variations in non clay mineral compositions for an area between kangerlussuaq trough and scoresby sund 67 70 n east greenland bedrock consists primarily of an early tertiary alkaline complex with high weight of pyroxene and plagioclase farther inland and to the north the bedrock is dominantly felsic with a high fraction of quartz and potassium feldspars principal component pc analysis of the non clay sediment compositions indicates the importance of quartz and pyroxene as compositional end members with an abrupt shift from quartz and k feldspar dominated sediments north of scoresby sund to sediments rich in pyroxene and plagioclase feldspars offshore from the early tertiary basaltic outcrop coarse 2 mm or 1 mm ice rafted sediments are largely absent from the trough sediments between 8 and 5 cal ka bp but then increase in the last 4 cal ka bp compositional unmixing of the sediments in grivel basin and kangerlussuaq trough indicate the dominance of local over long distance sediment sources with pulses of sediment from tidewater glaciers in kangerlussuaq and nansen fjords reaching the inner shelf during the neoglaciation the change in ird is more dramatic in the sediment grain size proxies than in the quartz wt forty to seventy percent of the variance in the quartz records from either side of denmark strait is explained by low frequency trends but the data from the grivel basin east greenland are distinctly different with an approximate 2500 yr periodicity

eocene oligocene transition in the southern ocean history of water mass circulation and biological productivity high resolution records of carbon and oxygen isotopes and benthic foraminiferal accumulation rates for the eocene oligocene section at ocean drilling program site 689 maud rise weddell sea paleodepth about 1500 m were used to infer variations in paleoproductivity in relation to changes in climate and ventilation of the deeper water column the benthic foraminiferal abundance and isotope records show short term fluctuations at periodicities of 100 and 400 ka implying orbitally driven climatic variations both records suggest that intermediate depth water chemistry and primary productivity changed in response to climate during the eocene productivity increased during cold periods and during cold to warm transitions possibly as a result of increased upwelling of nutrient rich waters in the oligocene in contrast productivity maxima occurred during intervals of low d18o values presumably warmer periods when a proto polar front moved to the south of the location of site 689 this profound transition in climate productivity patterns occurred around 37 ma coeval with rapid changes toward increasing variability of the oxygen and carbon isotope and benthic abundance records and toward larger amplitude d18o fluctuations therefore we infer that at this time temperature fluctuations increased and a proto polar front formed in conjunction with the first distinct pulsations in size of the antarctic ice sheet we speculate that this major change might have resulted from an initial opening of the drake passage at 37 ma at least for surface and intermediate water circulation

preliminary steps toward formation of a generalized budget for cold water carbonates high latitude carbonate sediments were once considered isolated exceptions to the tropical rule they are now being studied throughout the world and preliminary descriptive models have been proposed constituents composition and distribution of cold water carbonate sediments have been described and they are diagnostically different from their tropical counterparts the rates of depositional and post depositional processes may differ as well the present study of the rates of gross production net production and diagenesis was undertaken at shell beach in the gulf of maine 43 45 n 69 45 w a shelly pocket beach surface and subsurface sediments were collected and analyzed for caco3 content assemblage and alteration population density of dominant organisms and the weight of skeletal material in typical adults were determined transport of sediment was observed gross production by dominant organisms was calculated to be 1600 g caco3 m2 y over the area of production net production while less exact was on the order of 13 130 g caco3 m2 y the difference between these is explained by strong destructive diagenesis dominantly biological and at a rate of 80 1300 g caco3 m3 y the large gap between gross and net production seems to be characteristic of cold water carbonate sediments as does the strongly destructive diagenesis the gap must be remembered when assessing fossil cold water populations

unlocking the ice house oligocene miocene oxygen isotopes eustasy and margin erosion oxygen isotope records and glaciomarine sediments indicate at least an intermittent presence of large continental ice sheets on antarctica since the earliest oligocene circa 35 ma the growth and decay of ice sheets during the oligocene to modern ice house world caused glacioeustatic sea level changes the early eocene was an ice free greenhouse world but it is not clear if ice sheets existed during the middle to late eocene doubt house world benthic foraminiferal 18o records place limits on the history of glaciation suggesting the presence of ice sheets at least intermittently since the earliest oligocene the best indicator of ice growth is a coeval increase in global benthic and western equatorial planktonic 18o records although planktonic isotope records from the western equatorial regions are limited subtropical planktonic foraminifera may also record such ice volume changes it is difficult to apply these established principles to the cenozoic 18o record because of the lack of adequate data and problems in stratigraphic correlations that obscure isotope events we improved oligocene to miocene correlations of 18o records and erected eight oxygen isotope zones oi1 oi2 mi1 mi6 benthic foraminiferal 18o increases which are associated with the bases of zones oil circa 35 8 ma oi2 circa 32 5 ma and mil circa 23 5 ma can be linked with 18o increases in subtropical planktonic foraminifera and with intervals of glacial sedimentation on or near antarctica our new correlations of middle miocene benthic and western equatorial planktonic 18o records show remarkable agreement in timing and amplitude we interpret benthic planktonic covariance to reflect substantial ice volume increases near the bases of zones mi2 circa 16 1 ma mi3 circa 13 6 ma and possibly mi5 circa 11 3 ma possible glacioeustatic lowerings are associated with the 18o increases which culminated with the bases of zone mi4 circa 12 6 ma and mi6 circa 9 6 ma although low latitude planktonic 18o records are required to test this these inferred glacioeustatic lowerings can be linked to seismic and rock disconformities for example we link 12 oligocene early late miocene inferred glacioeustatic lowerings with 12 of the sequence boundaries inferred eustatic lowerings of haq et al 1987

surface sea floor and near surface box cores sediment mineralogy in baffin bay as a key to sediment provenance and ice sheet variations to better understand the glacial history of the ice sheets surrounding baffin bay and to provide information on sediment pathways samples from 82 seafloor grabs and core tops and from seven box cores were subjected to quantitative x ray diffraction weight percent wt analysis of the 2000 m all show an abrupt drop in calcite wt post 5 cal ka bp following a major peak in detrital carbonate mainly dolomite this dolomite rich detrital carbonate dc event in jr175bc06 is possibly coeval with the younger dryas cold event four possible glacial sourced end mem bers were employed in a compositional unmixing algorithm to gain insight into down core changes in sediment provenance at the deep central basin estimates of the rates of sediment accumulation in the central basin are only in the range of 2 to 4 cm cal ka surprisingly low given the glaciated nature of the surrounding land

the tephrochronology of iceland and the north atlantic region during the middle and late quaternary a review the tephrochronology of iceland and the north atlantic region is reviewed in order to construct a unified framework for the last 400 kyr bp nearly all of the tephra layers described are also characterised geochemically a number of new tephra layers are analysed for the first time for their geochemical signature and a number of pre holocene tephra layers have been given an informal denotation the tephrostratigraphy of ash zone ii is highlighted where possible the rhyolitic tephra layers found outside iceland have been correlated to known icelandic tephra layers or to the volcanic source area the application of tephra fallout in various depositional environments is described and discussed copyright 2000 john wiley sons ltd

testing the cenozoic multisite composite δ18o and δ13c curves new monospecific eocene records from a single locality demerara rise ocean drilling program leg 207 until recently very few high quality deep ocean sedimentary sections of eocene age have been available consequently our understanding of eocene paleoceanography has become heavily reliant on composite records patched together from multiple sites in different ocean basins and generated using multiple taxa potential sources of local noise in the global signal here we test the reliability of the early to middle eocene composite 18o and 13c stratigraphies zachos et al 2001 by generating new monospecific records in benthic foraminiferal calcite from a single locality demerara rise in the tropical western atlantic ocean drilling program leg 207 we present new stable isotope correction factors for commonly used eocene benthic foraminiferal species we find that interspecies isotopic offsets are constant across the isotopic range supporting the notion that the inconstant intertaxa offsets reported elsewhere result from mixing species within genera in general the 18o stratigraphy from demerara rise supports the validity of the eocene 18o composite while revealing a temporary warming punctuating middle eocene cooling this warming may correspond to the so called middle eocene climatic optimum previously documented in the southern ocean the composite and demerara rise records for 13c differ substantially by removing the intersite and intertaxa sources of uncertainty in 13c we obtain a clearer picture of carbon cycling during the eocene secular change in interocean 13c gradients through the eocene reveals that intervals of climatic warmth especially the early eocene are associated with very small water mass ageing gradients

sea ice and marine climate variability for nw iceland denmark strait over the last 2000 cal yr bp md99 2263 is a 46 cm box core collected from djupall a trough that cuts across the nw iceland shelf and ends above denmark strait we provide a multiproxy record that documents changes in the regional marine climate over the last 1700 yr the depth age model is based on seven calibrated radiocarbon dates on mollusk shells and on 210pb and 137cs sediment accumulation rates were variable 0 2 0 8 mm yr but increased dramatically ad 1500 grain size magnetic properties quantitative mineral composition of the 2 mm sediment fraction benthic foraminiferal composition benthic and planktic 18o ratios and abundances fluxes of the sea ice biomarker ip25 were determined to better compare the various proxies 12 of the critical climate proxies were co ordinated into 100 yr sample time series which were examined by principal component analysis the 1st axis explained 49 of the variance and the 2nd axis explained an additional 17 the variables most strongly associated with the 1st axis were sediment pr

radiaxial calcite alteration product of and petrographic proxy for magnesian calcite marine cement radiaxial calcite is a common and distinctive pore fill in ancient limestones but the origin of this fabric is highly controversial we present data from the late cretaceous equatorial pacific that suggest that radiaxial calcite forms through alteration of early magnesian calcite 7 mol mgco 3 marine cement these data suggest that radiaxial calcites are not straightforward indicators of pore fluid chemistry on the other hand the presence of radiaxial calcite in limestones may provide a distinctive petrographic proxy for earlier magnesian calcite cement and thus a generally warm caco 3 saturated marine environment

reconstructing holocene palaeoclimate and palaeoceanography in isafjarðardjup northwest iceland from two fjord records overprinted by relative sea level and local hydrographic changes we reconstruct palaeoclimate and palaeoceanography of the isafjar ardjup fjord system from two cores one from the inner fjord and one near the fjord mouth while separating the potential overprinting of relative sea level rsl and local fjord hydrographic changes on these records the inner fjord core b997 339 reflects local fjord hydrography the outer fjord core md99 2266 reflects the regional oceanic signal glacial marine conditions ended at ca 10 200 cal a bp indicated by both ice rafted debris records the other proxy records show spatial and temporal variability within the fjord system at the inner fjord site b997 339 foraminiferal assemblages and the 18o record indicate lowered rsl between ca 10 600 and 8900 cal a bp and document the onset of fjord water overturning at ca 8900 cal a bp which obscured the climate record at the fjord mouth md99 2266 mass accumulation rates suggest lowered rsl between ca 10 200 and 5500 cal a bp and local freshwater and or reduced salinities of the irminger current water masses affected the 18o signal between ca 10 200 and 7900 cal a bp at md99 2266 foraminiferal fauna record the holocene thermal maximum between ca 8000 and 5700 cal a bp and the onset of modern oceanic circulation at ca 7000 cal a bp copyright 2010 john wiley sons ltd

early cenozoic benthic foraminiferal isotopes species reliability and interspecies correction factors 1 oxygen and carbon isotope records are important tools used to reconstruct past ocean and climate conditions with those of benthic foraminifera providing information on the deep oceans reconstructions are complicatedby interspecies isotopic offsets that result from microhabitat preferences carbonate precipitation in isotopically distinct environments and vital effects species specific metabolic variation in isotopic fractionation we provide correction factors for early cenozoic benthic foraminifera commonly used for isotopic measurements cibicidoides spp nuttallides truempyi oridorsalis spp stensioina beccariiformis hanzawaia ammophila and bulimina spp showing that most yield reliable isotopic proxies of environmental change the statistical methods and larger data sets used in this study provide more robust correction factors than do previous studies interspecies isotopic offsets appear to have changed through the cenozoic either 1 as a result of evolutionary changes or 2 as an artifact of different statistical methods and data set sizes used to determine the offsets in different studies regardless of the reason the assumption that isotopic offsets have remained constant through the cenozoic has introduced an 1 2 c uncertainty into deep sea paleotemperature calculations in addition we compare multiple species isotopic data from a western north atlantic section that includes the paleocene eocene thermal maximum to determine the most reliable isotopic indicator for this event we propose that oridorsalis spp was the most reliable deepwater isotopic recorder at this location because it was best able to withstand the harsh water conditions that existed at this time it may be the best recorder at other locations and for other extreme events also

holocene sediment properties of the east greenland and iceland continental shelves bordering denmark strait 64 68 n north atlantic the oceanographic polar front separates the east greenland and iceland margins surface water temperatures across denmark strait vary by 8 12 c and represent one of the steepest oceanographic gradients on earth the eastgreenland margin is a polar environment with extensive sea ice cover and calving glacier margins in contrast the iceland shelf is much more temperate and freshwater run off is a key component in land ocean sediment transfers average sediment properties from these two contrasting climate and oceanographic continental shelf environments are compared in the spatial domain at 13 sites the data represent the last 10 000 radiocarbon years of normal marine sedimentation for the two regions the two regions have similar average rates of sediment accumulation around 43 5 cm kyr 1 so that this key variable is factored out in explaining any differences in sediment properties dry sediment density moisture content hygroscopic moisture total organic carbon and carbonate contents mass magnetic susceptibility and the percentages of sand and silt are compared focusing on 1 median values for sediment properties and 2 downcore variability measured by the coefficient of variation cv there are significant differences in all but one hygroscopic moisture of the sediment properties between iceland and east greenland in four cases the sense of the differences was not as predicted in terms of downcore variation cv no difference was found between the two regions nor between the 13 sites whereas there are some significant differences between the variables carbonate and mass magnetic susceptibility have the largest spreads and moisture content and dry sediment density are the least variable protocols are developed to identify the type core in a regional series of sites the results indicate a need to develop a regional perspective on sediment properties both as inputs to models of sedimentary processes in different polar arctic environments and as an indication of which sediment properties might be best suited for palaeoenvironmental downcore time series

new precipitation and accumulation maps for greenland annual total precipitation and the annual accumulation on the greenland ice sheet are evaluated and presented in two maps the maps are based on accumulation measurements of 25 1 pits and cores obtained from the upper accumulation zone and precipitation measurements made at 35 meteorological stations in the coastal region to construct the accumulation map the annual precipitation was split into solid and liquid precipitation components annual total precipitation exceeding 2500 mm w e occurs on the southeastern tip of greenland while the minimum precipitation is estimated to occur on the northeastern slope of the ice sheet the mean annual precipitation for all of greenland is 340 mm w e the largest annual accumulation of about 1500 mm w e is found on the glaciers in the southeastern corner of greenland while the smallest accumulation is found on the northeastern slope of the ice sheet west of danmarkshavn the mean accumulation on the greenland ice sheet is estimated at 310 mm w e the regional difference in accumulation is examined with respect to the 850 hpa m bar level circulation the present surface topography is found to play an important role in determining regional accumulation on the ice sheet

heat transport deep waters and thermal gradients coupled simulation of an eocene greenhouse climate for the first time a coupled general circulation model with interactive and dynamical atmospheric oceanic and sea ice components is used to simulate an eocene 50 ma greenhouse climate we introduce efficient ocean spin up methods for coupled paleoclimate modeling sea surface temperatures ssts and salinities evolve unconstrained producing the first proxy data independent estimates for these eocene climate parameters tropical and extratropical model predicted ssts are warmer than modern values by 3 and 5 c respectively salinity driven deep water formation occurs in the north atlantic and tethys the zonal average overturning circulation is weaker than modern eocene ocean heat transport is 0 6 pw less than modern in the northern hemisphere and 0 4 pw greater in the southern hemisphere the model predicted near modern vertical and meridional eocene temperature gradients imply that the dominant theory for maintaining low gradients increased ocean heat transport is incorrect or incomplete and other mechanisms should be explored

holocene ice rafting and sediment transport from the glaciated margin of east greenland 67 70 n to the n iceland shelves detecting and modelling changing sediment sources abstract we examine variations in the ice rafted sources for sediments in the iceland east greenland offshore marine archives by utilizing a sediment unmixing model and link the results to a coupled iceberg ocean model surface samples from around iceland and along the e ne greenland shelf are used to define potential sediment sources and these are examined within the context of the down core variations in mineralogy in the

an origin for laminated glacimarine sediments through sea ice build up and suppressed iceberg rafting laminated glacimarine sediments are observed in visual core logs and x radiographs from scoresby sund and nansen fjord east greenland they are mostly underlain and overlain by massive or stratified glacimarine diamicton dmm or dms which is a product of iceberg delivery of heterogeneous debris and in scoresby sund reworking by deep drafted iceberg keels the laminated sediments are ams radiocarbon dated to two cold periods since the last late weichselian deglaciation the younger dryas stadial milne land stadial in east greenland and the little ice age during cold climatic events multiyear shorefast sea ice sikussak formed in these fjords and trapped the icebergs fine grained laminated muds fl were deposited in scoresby sund when the flux of icebergs was suppressed but turbid meltwater continued to provide some sediment flux to the fjord systems varying through time to produce laminations in nansen fjord thinner and often massive mud layers fm resulted from shorter intervals of sea ice cover with no ice rafting stratified diamicton layers dms which alternate with mud deposition to produce a laminated unit probably represent intervening times of more open conditions with iceberg rafting in scoresby sund foraminifera are either absent from the laminated unit or begin to appear towards the end of its deposition the absence of both benthic and planktonic foraminifera also suggests that multiyear sea ice was covering the core sites there is no evidence of macrofaunal activity and bioturbation is absent from the laminated sediments satellite data show that multiyear shorefast sea ice is present in several areas of the high arctic today and this traps icebergs calved from interior ice cap drainage basins thus the process of laminated glacimarine sediment formation is likely to be applicable to a number of areas of the modern and quaternary arctic