geochemical cycling of redox sensitive metals in sediments from lake malawi a diagnostic paleotracer for episodic changes in mixing depth changes in heat balance wind stress and lake level can affect the efficiency of mixing and depth of oxygen penetration in deep tropical lakes this study examines how transient changes in these parameters as reflected by the redox state of bottom waters are recorded in the sedimentary record of lake malawi we measured concentration profiles of redox sensitive metals across a layer of oxidized sediment deposited within a sequence composed of reduced sediments in a core taken at 298 m water depth 100 m below the present day chemocline by examining a range of metals that exhibit different geochemical behaviors mobilization under reducing fe mn versus oxidizing u conditions formation of insoluble sulfides cd mo pb zn susceptibility to scavenging onto fe or mn oxyhydroxide precipitates co mo pb v zn we are able to outline a sequence of events consistent with the formation of this feature 1 at some time before 11 ky bp there was an episode of penetration of oxygenated waters to depths close to or greater than that of this core i e substantially deeper in the lake basin than at present at this time diagenetically remobilized fe and mn were oxidized and precipitated in a near surface sediment horizon 2 fe and mn oxyhydroxides that precipitated from the water column as metal rich anoxic waters were mixed upward into oxygenated waters were deposited in an immediately overlying layer of the sediment such material continued to accumulate in surface sediments for a few hundred years until oxic conditions no longer prevailed in overlying waters 3 as the depth of the chemocline rose relative to the present day lake surface this authigenic material was in turn overlain by reducing sediments 4 subsequent diagenetic remobilization at the top and bottom of this redox sandwich resulted in formation of horizons enriched in u mo and sulfide forming metals notably cd along the redox gradients both above and to a lesser extent below the layer of oxidized sediment these enrichments immobilized under reducing conditions will remain as permanent markers of the episode of deepening of the chemocline even after reduction and remobilization of the oxidized fe and mn solids in addition such markers may be useful in determining whether observed episodic interruptions in deposition of varved sediments in the deep anoxic basins of lake malawi are due to bioturbation brought on by episodes of deeper oxygen penetration in the water column

metal diagenesis in oxic marine sediments the metal nutrient relationships observed for nickel and cadmium in the deep ocean are continued at the interface between seawater and oxidizing pore water this continuum results in pore water concentrations of these metals which are only slightly greater than near bottom seawater levels manganese concentrations in these oxidizing pore waters are also extremely low less than three times bottom water in contrast release in the boundary layer produces a maximum of dissolved copper which is 10 40 times ambient seawater assuming these pore waters are at steady state flux estimates based on these measurements suggest that the manganese in todorokite rich nodules of the central equatorial pacific was not supplied by upward diffusion through pore waters below the interface most nodular nickel is precipitated with manganese while nodular copper is supplied by diffusion

early diagenesis in differing depositional environments the response of transition metals in pore water the cycling of fe mn ni co cu cr v and mo during early diagenesis was investigated in sediments from five different depositional environments in the california borderland dissolved o2 no3 no2 and so4 were also measured at each site to establish the position of redox boundaries pertinent to this study sites were chosen to allow the comparison of several parameters of potential importance to the cycling of these metals bottom water o2 concentration sediment redox conditions cycling of metal oxide carrier phases and the relative contribution of biogenic and terrigenous material to the detrital metal flux at 10 m oxygen and above the sequence of terminal electron acceptor utilization was typical of pelagic sediments differing only in scale under these conditions the recycling of mn oxides resulted in an enriched layer near the interface at bottom water 02 concentrations 5 m mn oxides are not recycled under these conditions fe oxides and so42 are important oxidants the depth of the zone of manganese oxidation with respect to the interface affects the efficiency of metal scavenging by manganese oxides trapping and recycling of ni and co with mn oxides results in remobilization from reducing sediments and enrichment in oxic sediments scavenging of these metals is favored by a deep oxic zone in the sediments in contrast cr v and mo appear to be transported to the sediments as reduced species and are released from the sediments by oxidation the source of the reduced species is assumed to be biogenic material the accumulation of these metals is favored by reducing conditions in the sediments cu is enriched in the sediments by transport with detrital biogenic material followed by adsorption onto sediment solids cu is released at the interface and rapidly removed onto the solids at all sites except the one pelagic site at the base of the slope the magnitude of cu released in the slowly accumulating pelagic sediment exceeds the cu binding capacity of the solids resulting in pore water cu concentrations in excess of 100 nm in general metal cycling associated with the early diagenesis of sediments was observed to decouple transport processes from burial processes for the transition metals measured in this study

analogue modeling of overlapping spreading centers insights into their propagation and coalescence abstract the propagation and segmentation of mid ocean ridges is studied using centrifuged analogue models built with non linear materials the deformation of the brittle ductile model is controlled by diapiric uprise of buoyant analogous asthenospheric material induced by a centrifugal body force this linear upwelling laterally stretches the model mantle that in turn induces failure in the upper layer simulating the brittle crust arrays of fractures initiate within zones of high stress concentration above the diapir fractures propagate laterally in a direction perpendicular to the maximum tensile the minimum principal stress secondary tension cracks initiate in the vicinity of parent fracture tips through going fractures that crosscut the model surface develop by short fractures propagating toward each other and coalescing in different types of patterns the overlap overstep and inclination of fractures developed at the initial stage of extension control their subsequent growth and coalescence non overlapping sub parallel fractures propagate along nearly straight paths and coalesce to produce a single planar fracture if overlapping fractures are parallel they propagate towards each other along curved paths that enclose an intervening elliptical core of intact material fracture curvature in this case results from crack crack interaction and is similar to that of overlapping spreading centers oscs observed along mid ocean ridges overlapping non parallel fractures tend to coalesce by one of their tips propagating sub parallel to the spreading direction toward the other fracture such offsets can serve as models for the development of the orthogonal ridge transform fault patterns common along mid ocean ridges

the last glaciation in central magellan strait southernmost chile abstract glacial landforms and drift stratigraphy in central magellan strait southernmost chile document repeated fluctuations during the last glacial cycle of outlet lobes from an ice cap centered over the southern andes the lobes developed comparatively low gradient profiles because of low basal shear stresses over soft deformable beds and this made them sensitive to even small scale changes in the mass balance such low profiles and rapid calving in deep proglacial lakes during deglaciation may have made the magellan ice lobe particularly responsive to climatic fluctuations during the last glacial cycle and to advance and retreat over considerable distances study of the glacial landforms and drift stratigraphy has led to the identification of at least five glacier advances to limits at and south of the segunda angostura fragments of mollusc shells contained in basal till indicate marine incursions between some advances thus documenting extensive deglaciation a partial chronology based on amino acid studies and radiocarbon dating suggests that five of these advances occurred during the last glacial cycle the most extensive advances may have culminated during substages of marine isotope stage 5 substage 5b or 5d and or during stage 4 slightly less extensive advances occurred between ca 28 000 and 14 000 yr b p

postglacial vegetation fire and climate dynamics at central chilean patagonia lake shaman 44 s a 19 cal ka bp pollen and charcoal record from lake shaman 44 s 71 w chile was analyzed to establish vegetation fire and climate dynamics of the forest steppe ecotone in central chilean patagonia lake shaman record indicates that the upper rio cisnes valley was free of ice at around 19 cal ka bp from this date and until 14 8 cal ka bp a grass steppe with high proportions of shrubs associated to colder and drier conditions than present developed in this area a continuous increase of nothofagus accompanied by a decline in the steppe shrubs and sudden dominance of paludal over aquatic plants from 11 cal ka bp was associated to effective moisture increase but still under modern values the replacement of the cold dry grass shrub steppe by a similar than present forest steppe ecotone suggests an increase in temperature indicating the onset of the holocene at the same time moderate fire activity suggested by the charcoal record could be related to major fuel availability as consequence of nothofagus forest expansion between 8 and 3 cal ka bp the record indicates the easternmost position of the forest steppe ecotone suggesting the highest effective moisture with the establishment of seasonality between 5 and 3 cal ka bp from 3 cal ka bp the record indicates a retraction of the forest steppe ecotone accompanied by a high pollen record variability and an increased fire activity these late changes suggest decreased effective moisture associated with a high climatic variability at regional and extra regional scale climatic changes at lake shaman s record are mostly associated to changes latitudinal shifts and or strengthening weakening of past southern westerlies that were previously recorded along patagonia from the lateglacial to the mid holocene during the late holocene a regional pattern characterized by high record variability emerges throughout central chilean patagonia this variability would be related to 1 low magnitude southern westerlies changes probably associated to enso and or sam or 2 the complex relationships between vegetation fire and human occupations during the last 3 cal ka

sediment cd and mo accumulation in the oxygen minimum zone off western baja california linked to global climate over the past 52 kyr 1 concentrations of organic carbon orgc cadmium cd and molybdenum mo were measured in two sediment cores raised from depths of 430 and 700 m within the oxygen minimum zone omz off southern baja california at a temporal resolution of 0 5 kyr over the past 52 kyr these records are supplemented with diffuse spectral reflectance dsr measurements obtained on board ship soon after collection at a resolution of 0 05 kyr in the core from 700 m depth a component extracted from the dsr data and the three geochemical proxies generally vary in concert with each other and over a wide range 4 22 orgc 1 40 mg kg cd 5 120 mg kg mo intervals of increased orgc cd and mo accumulation generally correspond to warm periods recorded in the oxygen isotopic composition of greenland ice with the exception of the bolling allerod which is only weakly expressed off baja california concentrations of the biogenic proxies are higher in the core from 430 m depth but erratic sediment accumulation before 15 ka precludes dating of the older intervals that are laminated and contain elevated orgc cd and mo concentrations the new data provide further evidence of an intimate teleconnection between global climate and the intensity of the omz and or productivity along the western margin of north america on the basis of a comparison with cd and mo records collected elsewhere in the region we conclude that productivity may actually have varied off southern baja california by no more than a factor of 2 over the past 52 kyr

the evolution of the patagonian ice sheet from 35 ka to the present day patice abstract we present patice a gis database of patagonian glacial geomorphology and recalibrated chronological data patice includes 58 823 landforms and 1 669 geochronological ages and extends from 38 s to 55 s in southern south america we use these data to generate new empirical reconstructions of the patagonian ice sheet pis and subsequent ice masses and ice dammed palaeolakes at 35 ka 30 ka 25 ka 20 ka 15 ka 13 ka synchronous with the antarctic cold reversal 10 ka 5 ka 0 2 ka and 2011 ad at 35 ka the pis covered of 492 6 x103 km2 had a sea level equivalent of 1 496 mm was 350 km wide and 2090 km long and was grounded on the pacific continental shelf edge outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams the pis reached its maximum extent by 33 28 ka from 38 s to 48 s and earlier around 47 ka from 48 s southwards net retreat from maximum positions began by 25 ka with ice marginal stabilisation then at 21 18 ka which was then followed by rapid irreversible deglaciation by 15 ka the pis had separated into disparate ice masses draining into large ice dammed lakes along the eastern margin which strongly influenced rates of recession glacial readvances or stabilisations occurred at least at 14 13 ka 11 ka 6 5 ka 2 1 ka and 0 5 0 2 ka we suggest that 20th century glacial recession a 1 is occurring faster than at any time documented during the holocene

ocean chemistry during glacial time abstract measurements of co2 to air ratios in the gas trapped in bubbles in ice of glacial age suggest that the co2 content of the atmosphere was considerably lower during peak glacial time than during holocene time the purpose of this paper is to show that such a change must in all likelihood be the result of alterations in the nutrient element chemistry of sea water two possible scenarios are presented one involves alternate storage and erosion of phosphorous leaving residues from shelf sediments the other involves changes in the c p ratio in the organic debris falling to the deep sea means of verifying the nutrient cycle hypothesis are also given it is shown that the 13c record as we know it in planktonic and benthic foraminifera the oxygen record as inferred from benthic foraminifera species distributions and the early post glacial caco3 preservation event as recorded by aragonitic pteropods are consistent with both of the hypotheses presented only if an early post glacial spike in the 13c record for planktonic shells could be found would it be possible to eliminate one of these hypotheses i e that involving shelf storage the implications of these nutrient hypotheses to climate theory are as follows if shelf storage is responsible for the glacial to interglacial co2 increase then the co2 change must be considered an amplifier of some primary cause the reason is that sea level changes are needed to drive deposition on and erosion from the shelves on the other hand if changes in the c p ratio for falling debris are responsible then the co2 change could either be an amplifier or a primary cause for the major glacial to interglacial climatic cycle the latter is possible as self sustained oscillations in ocean chemistry might be driven by interactions between ocean ecology and ocean nutrient chemistry

the magnitude and rapidity of the climate change marking the end of the pleistocene in the mid latitudes of south america abstract the chi squared test of independence and cluster analysis of otsuka similarity coefficients of fossil beetle assemblages from the chilean lake region in the mid latitudes of south america support the following conclusions 1 the mean summer temperature of the glacial climate was 4 5 c lower than today s climate 2 the climatic change from glacial to interglacial mode was in a single step centered on about 14 000 yr b p 3 the climatic change was rapid and within 1500 years the biota of a moorland had been completely replaced by a biota of a rain forest 4 by 12 500 yr b p the low elevation beetle fauna of the chilean lake region was similar in composition to that of the present day and 5 no reversal in the postglacial warming trend equivalent in age to the younger dryas stade was detected

a holocene record of environmental change from rio zeballos central patagonia there are few continuous palaeoenvironmental records spanning the holocene in andean southern patagonia near the northern patagonian ice field 47 s insights into the environmental context for h

cadmium isotopic evidence for increasing primary productivity during the late permian anoxic event abstract earth s most extreme extinction event near the end of the late permian decimated more than 90 of all extant marine species widespread and intensive oceanic anoxia almost certainly contributed to the catastrophe though the driving mechanisms that sustained such conditions are still debated of particular interest is whether water column anoxia was a consequence of a stagnant ocean or if it was controlled by increases in nutrient supply primary productivity and subsequent heterotrophic respiration testing these competing hypotheses requires deconvolving sedimentary bottom water redox conditions from changes in surface water productivity in marine sediments we address this issue by studying marine shales from east greenland and the mid norwegian shelf and combining sedimentary redox proxies with cadmium isotopic analyses sedimentary nitrogen isotopic data pyrite framboid analyses and organic and inorganic shale geochemistry reveal sulfidic conditions with vigorous upwelling and increasingly anoxic conditions with a strengthening upwelling in the greenland and norwegian sections respectively detailed analysis of sedimentary metal budgets illustrates that cd is primarily associated with organic carbon and records primary geochemical signatures thus enabling reconstruction of surface water nutrient utilization cadmium isotopic analyses of the authigenic shale fraction released by inverse aqua regia digestion yield an average cd 114 110 of 0 15 0 01 2 se n 12 rel nist srm 3108 indicative of incomplete surface water nutrient utilization up section the constant degree of nutrient utilization combined with strong upwelling requires increasing primary productivity and not oceanic stagnation to balance the larger nutrient fluxes to both study sites during the development of the late permian water column anoxia overall our data illustrate that if bottom water redox and upwelling can be adequately constrained cd isotopic analyses of organic rich sediments can be used to provide valuable information on nutrient utilization and therefore past productivity

three late quaternary pollen diagrams from southern patagonia and their palaeoecological implications abstract diagrams of fossil pollen in three deposits postdating glacial recession of the last ice age provide an account of late glacial and holocene vegetation and palaeoclimate in southern patagonia sites are mires located along the estrecho de magallanes at punta arenas 53 09 s 70 57 w and puerto del hambre 53 36 s 70 55 w and an intermittent lake some 300 km to the north at torres del paine 50 59 s 72 40 w chronostratigraphy is controlled by 20 radiocarbon dates the oldest site puerto del hambre covering close to 16 000 years charcoal from the sites and carbonate torres del paine as well as tephra layers and an instance of marine incursion puerto del hambre supply additional data of interpretive value accompanying the fossil pollen records is a reference survey of modern pollen fallout from 43 surface sample localities late glacial vegetation during deglaciation consisted mostly of tundra dominated by communities of empetrum acaena gunnera and tubuliflorae compositae under a relatively cold dry climate nothofagus although present in numbers initially at puerto del hambre did not expand until the close of the late glacial at punta arenas expansion of nothofagus was episodic occurring during apparent warmer intervals of the last three millennia of steppe tundra holocene vegetation is depicted at first as a patchwork of nothofagus woodland and steppe subject to climate of relative warmth and limited moisture except at torres del paine where moisture levels were apparently higher than at sites to the south closed nothofagus forest communities subsequently are best developed in the late holocene under a climate with generally cooler wetter parameters fire believed to be caused mostly by palaeoindians has had an important role in shaping vegetation sequences in the holocene formidable however in the development of vegetation are the latitudinal displacements variable intensities of atmospheric conditions caused by shifting storm tracks of the southern westerlies

influence of diagenetic processes in thau lagoon on cadmium behavior and benthic fluxes dgt diffusive gradient in thin films and det diffusive equilibration in thin films combined probes were used in thau lagoon sediments to describe variations of dissolved concentrations of metals such as cadmium manganese and iron through the sediment water interface two contrasted stations regarding organic carbon fluxes were studied from december 2001 to may 2003 during four field campaigns station c4 in the middle of the lagoon and station c5 in a shellfish farming zone laboratory experiments and field deployments in such environment showed that dgt sampled pore water labile cadmium whereas iron and manganese concentrations were underestimated these results suggest that no steady state in the flux of metals onto the gel was established for fe and mn kinetics of metal sulfide dissolution precipitation may control metal fluxes onto the gel probe in marine sedimentary environments analysis of sediment and water column samples showed cadmium concentrations above natural background 3 3 and 7 6 nmol kg 1 for station c4 and station c5 sediments respectively between 40 and 800 pmol l 1 for the water column suggesting contamination spatial and temporal patterns of cadmium behavior were observed the sediment at station c4 was generally a source of cadmium whereas at station c5 it was a sink the vertical extension of the diagenetic series was more important at station c4 with deeper oxygen penetration and lack of dissolved sulfide whereas station c5 showed steep h2s gradients at the same depths the data suggested that cadmium source was more likely organic matter cadmium mobility was probably controlled by aerobic mineralization at station c4 and by dissolution precipitation of sulfides at station c5 seasonal variations were observed in the depth of oxygen penetration and sulfide diffusion generating important remobilization of cadmium during december 2001 conversely in may 2003 at station c5 bottom water suboxic conditions i e o2 60 enhanced reductive conditions in the sediment favoring uptake of cadmium by the sediment from the water column

the last glacial interglacial transition in patagonia argentina the stable isotope record of bulk sedimentary organic matter from laguna potrok aike abstract an investigation of stable isotope 13 c toc and 15 n tn and elemental parameters toc tn contents and toc tn ratios of bulk organic matter 13 c toc values toc tn contents and toc tn ratios indicate that the lake approached a new state with reduced primary productivity probably induced by unfavourable growing conditions for primary producers like strengthened winds and reduced nutrient availability the steady increase in 15 n tn values presumably suggests limitation of nitrate supply for growth of primary producers resulting from a nutrient shortage after the preceding phase with high productivity nitrate limitation and consequent decreased lacustrine primary productivity continued into the early holocene 10 970 8400 cal years bp as reflected by isotopic and elemental values

trace metals in metalliferous sediments manop site m interfacial pore water profiles we present data showing enrichments of metals mn cu v cr cd and ni and dissolved organic matter dom in surficial pore waters depths 1 cm at a metalliferous sediment site in the pacific we also present a model of metal release during particulate organic carbon poc oxidation and opal dissolution at the sediment seawater interface a comparison of measured interfacial metal concentrations with those predicted from the model suggest that cd ni and cr are released during oxidation of poc at the sediment seawater interface however for v cu and mn additional source s and or processes are required to account for the measured interfacial concentrations for cu recycling via interfacial remineralization and release to bottom waters with subsequent scavenging out of bottom waters by particulates probably provides the major additional source for v we suggest that in addition to some contribution from a benthic flux bottom water scavenging scenario complexation with dom at the interface serves as a trap to accumulate v released from particulates in the zone of oxygen reduction for manganese we suggest that most of the interfacial pore water content is produced from reduction of sedimentary mn iv by reactions with dom at the sediment seawater interface the calculated benthic flux of manganese as a result of this reaction may account for a large fraction of the particulate manganese rain that is apparently not preserved in the sediment at this site

cadmium chemical tracer of deepwater paleoceanography the oceanic distribution of cadmium resembles that of phosphorus because the cadmium content of foraminiferal shells is governed by the cadmium content of seawater planktonic and benthic fossil shells can be used to infer nutrient distributions within ancient oceans empirical studies demonstrate that cadmium in benthic foraminiferal shells is related to the bottom water composition through a proportionality constant d 2 9 this constant is the same for each of the species studied cibicidoides wuellerstorfi cibicidoides kullenbergi nuttallides umbonifera and uvigerina spp downcore cadmium data from high quality pacific and atlantic sediment cores suggest that the cadmium inventory of the ocean did not change significantly between the most recent glacial maximum and the present hence changes in the cadmium content of fossils at a site directly reflect changes in nutrient distributions due to altered oceanic circulation patterns studies of cadmium in pleistocene sediments show that deep ocean circulation patterns were significantly different during the most recent glacial maximum in the western north atlantic ocean the nutrient content of waters from 2500 to 3500 m was twice as high during glacials as during interglacial periods signifying an increase in the proportion of waters of antarctic origin in this depth interval and a decrease but not a cessation in the flux of north atlantic deep waters through this depth range below 3500 m the nutrient increase was greater indicating a higher proportion of antarctic bottom water above 2500 m the nutrient content was lower during glacial periods than it has been during interglacial times the cd content of high latitude north atlantic and southern ocean surface waters does not show a significant glacial interglacial change which argues against theories for changes atmospheric carbon dioxide that require changes in high latitude nutrient concentrations

the relationship between pore water carbon isotopic composition and bottom water oxygen concentration abstract we present pore water 13c profiles from the western north atlantic and the eastern pacific oceans and interpret them using a stoichiometric model of the relationship between carbon isotopic composition and oxygen concentration pore water 13c at the depth in the sediments where oxygen approaches zero is largely determined by the oxygen concentration of the overlying bottom water although sulfate reduction adds a significant amount of isotopically light carbon at some locations the 13c difference between bottom water and pore water at o2 0 13c increases from 1 in sediments of three low bottom water oxygen basins in the southern california borderlands to 4 in sediments underlying well oxygenated water in the western north atlantic we suggest that the relationship between bottom water oxygen and 13c could form the basis for a new way to use the benthic foraminifera 13c record to estimate bottom water oxygen concentration paleo oxygen values derived from a pair of benthic foraminifera species which record the bottom water pore water o2 0 13c difference will be independent of the preformed 13c of the deep water mass

δ13c values of miocene pacific benthic foraminifera correlations with sea level and biological productivity 13 c 12 c ratios of miocene benthic foraminifera from 22 pacific ocean sites vary with time but are similar at almost all sites in any restricted interval 13 c values are correlated with sea levels inferred from onlap offlap curves reflecting the deposition of greater amounts of organic matter on the continental shelves during transgressions differences in 13 c between sites are correlated with local differences in biological productivity in the overlying surface waters 13 c 12 c values of benthic foraminifera show promise as indicators of marine paleoproductivity

comparison of atlantic and pacific paleochemical records for the last 215 000 years changes in deep ocean circulation and chemical inventories abstract detailed cd ca and 13 c data have been obtained for benthic foraminifera from western north atlantic and equatorial pacific sediment cores in the modern ocean both tracers are closely linked to nutrient distributions the sedimentary records for both tracers indicate that bottom waters overlying the atlantic site have been nutrient depleted relative to those at the pacific site over the last 215 000 years from this evidence it is reasonable to infer that there has been a continuous net flux of nutrient depleted water from the western north atlantic into the pacific this exchange has undergone significant fluctuations with the export of nutrient depleted atlantic water diminishing by about a factor of two relative to the inflow from southern ocean sources over the last 215 000 years carbon isotope fluctuations in both regions are dominated by variable storage of isotopically light carbon on continents with a lesser contribution from these deep ocean circulation changes the cadmium signal in the north atlantic is dominated by changes in deep ocean circulation patterns cadmium shows less variability in the pacific which may reflect changes in the global average cadmium content or minor changes in deep pacific circulation patterns using these records to estimate global averages it appears that glacial ocean water had 22 more cd and 0 46 less 13 c than the modern ocean these numbers are estimates which may be revised as more data become available although they are not likely to be as much as 20 in error for cd or 0 2 for 13 c relative north atlantic deep water nadw formation rates are modulated with a significant 41 kyr periodicity linked to obliquity induced variations in high latitude insolation nadw lags 8 2 kyr behind insolation however

caco3 dissolution in california continental margin sediments the influence of organic matter remineralization in situ benthic flux chamber and oxygen microelectrode and shipboard porewater results have been used to quantify sea floor dissolution of caco3 on the continental rise adjacent to central california usa the porewater distributions and benthic fluxes of o2 no3 ta ca2 13c and tic are interpreted using a numerical simulation of organic matter remineralization and caco3 dissolution in marine sediments the processes considered in the simulation include organic matter oxidation by o2 no3 and so42 caco3 dissolution and precipitation hs and nh4 oxidation and sediment mixing and sediment accumulation calculated benthic fluxes of o2 no3 ta tic 13c and ca2 porewater concentrations of o2 no3 and nh4 and sediment distributions of organic carbon caco3 excess 210pb and 14c agree well with the measurements benthic fluxes of alkalinity and inferred caco3 dissolution rates cannot be explained on the basis of dissolution driven solely by bottom water undersaturation if the influence of metabolically produced co2 is included benthic fluxes are fully reconciled however this is in agreement with benthic chamber ca2 and 13c results that independently imply substantial caco3 dissolution in these sediments the above observations are in contrast to those reported by jahnke et al 1994 for the west african continental rise and the western equatorial pacific where 1 g diagenetic models predict dissolution fluxes larger than observed with benthic flux chambers we conclude that the extent of metabolic caco3 dissolution may vary regionally numerous factors such as the depth of metabolic co2 production and caco3 dissolution kinetics are known or predicted to influence metabolic dissolution among the factors that should be considered in reconciling these observations are l the extent to which sulfate reduction and reoxidation reactions may influence acid base properties in surface sediments and 2 the total sedimentary caco3 content of the sites that may influence porewater acidity through surface exchange reactions at the mineral surface

porewater cadmium geochemistry and the porewater cadmium δ13c relationship results from two continental margin cores collected off pt sur california make possible a direct determination of the relationship between dissolved cadmium and the carbon isotopic composition of dissolved inorganic carbon in the interstitial water of suboxic marine sediments the 13c values of dissolved inorganic carbon decrease nearly 1 in the top 0 5 cm of the sediments and display a more gradual decrease through the top 20 cm of the sediments dissolved cadmium concentrations increase by 0 6 to 1 5 nmol kg in the top 0 5 cm of the sediments and then rapidly decrease to values of approximately 0 12 nmol kg between 5 and 10 cm into the sediments apparently as a result of scavenging onto iron oxide surfaces this pattern contrasts with porewater cadmium profiles previously reported for pelagic sediments which show no evidence of cadmium scavenging by the sediments however porewater cadmium concentrations are poorly correlated with porewater 13c values in both oxic and suboxic sediments these results suggest that the cadmiumcalcium ratios and 13c values of infaunal benthic foraminifera need not be tightly linked and that the relationship between these two aspects of foraminiferal shell chemistry may vary in response to changes in sediment geochemistry

the influence of microhabitats on the carbon isotopic composition of deep sea benthic foraminifera we report 13c and 18o values for rose bengal stained benthic foraminifera from a set of box cores from continental margin environments in the atlantic and pacific oceans these isotopic results are compared with foraminiferal distribution data and pore water 13c profiles to evaluate the importance of environmental microhabitat effects on the carbon isotopic composition of benthic foraminifera the 13c values of infaunal taxa are consistently lower than those of epifaunal taxa suggesting that microhabitat effects on test composition do exist the 13c differences between foraminiferal carbonate and bottom water dissolved inorganic carbon are not correlated with the 18o differences between benthic foraminifera tests and equilibrium calcite but they do correlate with variations in the chemistry of sediment pore waters however interspecific 18o differences as well as 13c differences between species with similar vertical distributions in the sediments indicate that taxon specific vital effects also influence test composition

the chronology of the last glacial maximum and deglacial events in central argentine patagonia this paper evaluates the chronology of the last glacial cycle and deglaciation in the lago pueyrredon valley of central patagonia 47 5 s argentina the valley was a major outlet of the former patagonian ice sheet and the moraines that record its fluctuations are an important proxy record of climate change in southern south america such moraines are well preserved in the lago pueyrredon valley owing in part to the semi arid environment east of the mountain front here we provide the first direct chronology for the age of the rio blanco moraine system by utilizing cosmogenic nuclide surface exposure ages boulders on the moraines give 10be exposure ages that indicate the last glacial maximum lgm maximum extent occurred by 27 25 ka subsequent advances occurred at 23 22 ka 20 18 ka and ca 18 17 ka initial deglaciation began after ca 18 17 ka and was interrupted as evidenced by the lago columna moraines up valley subsequently the outlet glaciers occupying both the lago pueyrredon basin chilean name lago cochrane and the lago buenos aires basin chilean name lago general carrera to the north rapidly retreated more than 80 km at around 16 5 15 ka the timing of the lgm maximum extent and the onset of deglaciation occurred broadly synchronously throughout patagonia deglaciation resulted in a series of interconnected glacier dammed lakes in the region that initially drained toward the atlantic ocean and later drained to the pacific ocean as a consequence of disintegrating ice in the andes

sedimentary redox conditions in continental margin sediments n e pacific influence on the accumulation of redox sensitive trace metals redox conditions in near surface sediments from the continental margin off western canada were characterized to determine how they influence the accumulation of redox sensitive trace metals despite the development of suboxic conditions within millimeters of the sediment water interface there is little enrichment of re u cd or mo in the upper 10 to 15 cm of the sediment column this observation is consistent with the low extractible solid mn concentrations but high i corg ratios that imply that near surface sediment redox conditions are poised between mn and i reduction in contrast below 15 cm re and to a lesser extent cd and u are enriched e g up to 65 ng g re but only in those cores collected from within and below the oxygen minimum zone molybdenum concentrations remain low b1 5 g g in all cores indicating that these near surface sediments never became fully anoxic

glacial enrichments of authigenic cd and u in subantarctic sediments a climatic control on the elements oceanic budget we examine the possibility that glacial increase in the areal extent of reducing sediments might have changed the oceanic cd inventory thereby decoupling cd from po4 we suggest that the precipitation of cd sulfide in suboxic sediments is the single largest sink in the oceanic cd budget and that the accumulation of authigenic cd and u is tightly coupled to the organic carbon flux into the seafloor sediments from the subantarctic ocean and the cape basin south atlantic where oxic conditions currently prevail show high accumulation rates of authigenic cd and u during glacial intervals associated with increased accumulation of organic carbon these elemental enrichments attest to more reducing conditions in glacial sediments in response to an increased flux of organic carbon a third core overlain by circumpolar deep water cpdw as are the other two cores but located south of the antarctic polar front shows an approximately inverse pattern to the subantarctic record the contrasting patterns to the north and south of the antarctic polar front suggest that higher accumulation rates of cd and u in subantarctic sediments were driven primarily by increased productivity this proposal is consistent with the hypothesis of glacial stage northward migration of the antarctic polar front and its associated belt of high siliceous productivity however the increase in authigenic cd and u glacial accumulation rates is higher than expected simply from a northward shift of the polar fronts suggesting greater partitioning of organic carbon into the sediments during glacial intervals lower oxygen content of cpdw and higher organic carbon to biogenic silica rain rate ratio during glacial stages are possible causes higher glacial productivity in the cape basin record very likely reflects enhanced coastal up welling in response to increased wind speeds we suggest that higher productivity might have doubled the areal extent of suboxic sediments during the last glacial maximum however our calculations suggest low sensitivity of seawater cd concentrations to glacial doubling of the extent of reducing sediments the model suggests that during the last 250 kyr seawater cd concentrations fluctuated only slightly between high levels about 0 66 nmol kg 1 on glacial initiations and reaching lowest values about 0 57 nmol kg 1 during glacial maxima the estimated 5 lower cd content at the last glacial maximum relative to modern levels 0 60 nmol kg 1 cannot explain the discordance between cd and 13c such as observed in the southern ocean this low sensitivity is consistent with foraminiferal data suggesting minimal change in the glacial cd mean oceanic content

paired carbon isotope and cadmium data from benthic foraminifera implications for changes in oceanic phosphorus oceanic circulation and atmospheric carbon dioxide abstract the carbon isotope and cadmium content of foraminiferal shells from oceanic sediments provides information on past chemical distributions in the ocean starting from reasonable assumptions it can be shown that paired data on both tracers provides more information than does either separately the slope of paired isochronous 13c and cd ca data from fossil benthic foraminifera depends on oceanic p cd and gd 13c p ratios the zero cd ca intercept of this line depends on mean oceanic 13c p and the 13c p ratio given data sufficient to define oceanic mean 13c and cd contents it is possible to place quantitative constraints on the product of the c p redfield ratio and mean oceanic phosphorus and to estimate a circulation parameter which is independent of changes in ocean chemical inventories with the limited available data no significant changes in oceanic p cd can be detected between the holocene and most recent glacial maximum if this data is taken to be representative of the whole ocean then the p and cd contents of the ocean were about 17 higher during the last glacial maximum than at present ocean box models indicate that this change in oceanic p and a 2 c deep ocean cooling during glacials would cause a 47 ppmv reduction in atmospheric pco2 during glacial intervals

climatic inferences from glacial and palaeoecological evidence at the last glacial termination southern south america there is uncertainty about the interhemispheric timing of climatic changes during the last glacial interglacial transition different hypotheses relying on different lines of evidence point variously to the northern hemisphere leading the southern hemisphere and vice versa or to synchrony between the hemispheres southern south america is well placed to test the various alternatives using both glacial and palaeoecological evidence we argue here from a synthesis of key proxy records that there was a sudden rise in temperature that initiated deglaciation sychronously over 16 of latitude at 14 600 14 300 14 c yr bp 17 500 17 150 cal yr there was a second step of warming in the chilean lake district at 13 000 12 700 14 cy r bp 15 650 15 350 cal yr which saw temperatures rise to close to modern values a third warming step particularly clear in the south occurred at ca 10 000 14 c yr bp 11 400 cal yr the latter achieving holocene levels of warmth following the initial warming there was a lagged response in precipitation as the westerlies after a delay of ca 1600 yr migrated from their northern glacial location to their present latitude which was attained by 12 300 14 cy r bp 14 300 cal yr the latitudinal contrasts in the timing of maximum precipitation are reflected in regional contrasts in vegetation change and in glacier behaviour the large scale of a 80 km glacier advance in the strait of magellan at 12 700 10 300 14 c yr bp 15 350 12 250 cal yr which spans the antarctic cold reversal and the younger dryas was influenced by the return of the westerlies to southern latitudes the delay in the migration of the westerlies coincides with the heinrich 1 iceberg event in the north atlantic the suppressed global thermohaline circulation at the time may have affected sea surface temperatures in the south pacific and the return of the westerlies to their present southerly latitude only followed ocean reorganisation to its present interglacial mode copyright 2000 john wiley sons ltd

late glacial ice advances in the strait of magellan southern chile abstract during the last glacial cycle low gradient glaciers repeatedly drained north eastward into the strait of magellan and dammed extensive proglacial lakes in the central section of the strait this paper focuses on the two most recent glacial advances in the strait culminating over 150 and 80 km from the present ice limits the timing of the first of the two advances has up to now been ambiguous and depended on the interpretation of anomously older dates of 16 590 15 800 yr bp for deglaciation at puerto del hambre here we show there is evidence from seismic data and truncated shorelines that the puerto del hambre basin has been tectonically displaced and that the dates do not represent minimums for deglaciation several other dates show that the advance occurred sometime before 14 260 yr bp the timing of the second advance has been investigated using a refined tephrochronology for the region which has also enabled a palaeoshoreline and glaciolacustrine sediments to be linked to a moraine limit 14c dating of peat and a key tephra layer above and below the glaciolacustrine deposits respectively suggest that the advance culminated in the strait of magellan between 12 010 and 10 050 yr bp

trace metal enrichments in lake tanganyika sediments controls on trace metal burial in lacustrine systems abstract we investigate the distributions of several key diagenetic reactants c s fe and redox sensitive trace metals mo cd re u in sediments from lake tanganyika east africa this study includes modern sediments from a chemocline transect which spans oxygenated shallow waters to sulfidic conditions at depth as well as ancient sediments from a longer core 2 m taken at 900 m water depth modern sediments from depths spanning 70 335 m are generally characterized by increasing enrichments of c s mo cd and u with increasing water depth but static fe distributions it appears that the sedimentary enrichments of these elements are to varying degrees influenced by a combination of organic carbon cycling and sulfur cycling these modern lake characteristics contrast with a period of high total organic carbon corg total sulfur stot and trace metal concentrations observed in the 900 m core a period which follows the most recent deglaciation 18 11 ky this interval is followed abruptly by an interval 11 6 ky that is characterized by lower c s u and mo consistent with other work we suspect that the low concentrations of s mo and u may indicate a period of intense lake mixing during which time the lake may have been less productive and less reducing as compared to the present an alternative but not mutually exclusive hypothesis is that changes in the lake s chemical inventory driven by significant hydrological changes could be influencing the distribution of sedimentary trace elements through time

controls on trace metal authigenic enrichment in reducing sediments insights from modern oxygen deficient settings any effort to reconstruct earth history using variations in authigenic enrichments of redox sensitive and biogeochemically important trace metals must rest on a fundamental understanding of their modern oceanic and sedimentary geochemistry further unravelling the multiple controls on sedimentary enrichments requires a multi element approach of the range of metals studied most is known about the behavior of fe mn and mo in this study we compare the authigenic enrichment patterns of these elements with a group whose behavior is not as well defined cd cu zn and ni in three oxygen poor settings the black sea the cariaco basin venezuela and the peru margin these three settings span a range of biogeochemical environments allowing us to isolate the different controls on sedimentary enrichment our approach relying on the covariation of elemental enrichment factors ef defined for element x as efx x al sample x al lithogenic has previously been applied to mo and u to elucidate paleoenvironmental information on for example benthic redox conditions the particulate shuttle and the evolution of water mass chemistry we find two key controls on trace metal enrichment first the concentration of an element in the lithogenic background sediment used in calculating efx controls the magnitude of potential enrichment maximum enrichment factors of 376 and 800 are calculated for mo 1 ppm in detrital sediments and cd 0 3 ppm respectively compared to values not greater than 17 in any setting for the other five metals 45 ppm to 4 5 wt in detrital sediments second there is a relationship between the aqueous concentration of the element in overlying seawater and its degree of enrichment in the sediment we further identify four important processes for delivery of trace metals to the sediment these are 1 cellular uptake especially important for zn and cd 2 interaction co precipitation with sulfide mo cu and cd 3 passive scavenging via the traditional particulate shuttle mo ni and cu and 4 an association with the benthic fe redox shuttle mn ni finally we summarize the oceanic mass balance of cd and mo and place the first constraints on the contribution of reducing sediments to the oceanic mass balance of cu zn and ni we show that reducing sediments are the ultimate repository for up to half the total output flux of these elements from the oceanic dissolved pool

thin tephra layers in peat revealed by x radiography x radiography has been found to provide a rapid economical non destructive method of locating very thin fine grained tephra of icelandic origin in scottish peats tephra layers form time parallel marker horizons or isochrones that are of great archaeological significance because they cover large areas offer precise chronological control for associated material and occur at times of significant cultural and environmental changes not all of the discrete deposits of recent volcanic fallout in scotland are sufficiently dense to show clearly on x radiographs but those which do provide particularly clear easily located marker horizons with many applications in palaeoenvironmental studies the tephra layer in caithness produced by fallout from a c 4000 by eruption of hekla provides a particularly good example of the use of x radiography to locate volcanic ash the method also reveals other structures of archaeological and palaeoenvironmental significance butler 1992 journal of archaeological science 19 151 161

palaeoenvironmental changes during the last 1600 years inferred from the sediment record of a cirque lake in southern patagonia laguna las vizcachas argentina abstract laguna las vizcachas is a cirque lake located at the margin of an extra andean volcanic plateau in southern patagonia argentina within the area of steppe and semi desert east of the andes the number of paleoenvironmental records is still limited in this region sediments of this lake were studied in order to obtain multi proxy information about the paleoenvironmental history of this site for the medieval climate anomaly and the little ice age chronozones in combination with results from other sites across southern patagonia our data enhance the understanding of spatial patterns of past hydrological changes and contribute to distinguishing between the signals of temperature and precipitation as laguna las vizcachas is situated at 1100 m a s l in a cool mountain climate the lake system is more sensitive to changes of temperature and winter ice cover than other sites from lower elevations in this region our interpretation of the multi proxy dataset is based on signals of clastic sediment input lake productivity organic matter sources and preservation dilution effects and early diagenetic overprint the record reveals a period of enhanced fluvial runoff resulting from higher precipitation from the 12th until the end of the 14th century as inferred from high concentrations of ti ca and from magnetic susceptibility this may coincide with higher wind intensities as suggested by higher proportions of epiphytic diatoms which point to an enhanced lateral transport from their littoral habitat towards the coring position at the center of the lake in comparison with other records from southern patagonia the results from laguna las vizcachas suggest opposite precipitation regimes between the western and eastern parts of patagonia during that time which corresponds partly to the medieval climate anomaly chronozone however this proposal is compromised by the chronological uncertainties of the different records under consideration the diatom record of laguna las vizcachas indicates temperature changes highest proportions of benthic diatoms point to coldest conditions from the mid 15th until the mid 17th century followed by relatively warm conditions until the mid 18th century as suggested by a decrease of benthic taxa and a conspicuous rise of the planktonic non planktonic diatom ratio that can be used as an indicator for the length or presence absence of winter ice cover

trace element indicators of increased primary production and decreased water column ventilation during deposition of latest pliocene sapropels at five locations across the mediterranean sea abstract compositions of productivity and redox sensitive trace metals in two upper pliocene sapropel sequences from western mediterranean odp sites 974 and 975 and eastern mediterranean sites 964 969 and 967 provide information about the conditions leading to sapropel deposition except at site 975 closest to the atlantic ocean all sapropels display elevated element al ratios for ba re cd mo u cr cu v and zn high total organic carbon toc concentrations and ba al ratios point to increased primary productivity during sapropel deposition enrichments of redox sensitive trace elements and elevated re mo ratios indicate water column oxygen depletion during sapropel formation anoxia likely was caused by increased fluxes of organic matter to the seafloor that would have enhanced oxygen demand at depth one of the sapropel sequences investigated in this study insolation cycle 178 contains a zone having low toc low ba al ratios and low trace metal contents these features identify this interval as an interruption of the increased productivity associated with sapropels and of the sub oxic anoxic conditions that are fully developed in the upper half of this sapropel layer significant differences in trace metal enrichments between the eastern and western mediterranean indicate that the eastern basin was a focal point for sapropel initiation in contrast site 975 appears to have been heavily influenced by the atlantic ocean during i cycles 178 and 180 and was not strongly influenced by the paleoceanographic changes affecting the rest of the mediterranean

redox sensitive element uptake in north east atlantic ocean sediments benthic boundary layer experiment sites regularly increasing radiocarbon age depth profiles and near constant sediment composition with depth have demonstrated that sediment accumulation has been relatively constant during the late holocene at two north east atlantic sites on rockall bank and feni drift uk benthic boundary layer experiment sites in such a quasi steady state situation the geochemical responses to early diagenesis of the redox sensitive elements cd mn mo re se and u are readily discerned through changes in element concentrations with depth collectively a colour change in the sediments surficial mnox enriched layers and 210pbexcess profiles allow an estimate of the mean position of the oxic post oxic boundary in the sediments at both sites this boundary is situated deeper than the 210pbexcess surface mixed layer but shallower than the 14c surface mixed layer which represent mixing on 102 and 103 year time scales respectively this implies that the well defined surface mnox enrichment and its associated 226ra and mo fractions must have been efficiently recycled first by downwards mixing into anoxic conditions and then by subsequent reduction and diffusive migration back up into oxic conditions this occurs in 40 years at the feni drift site and in 103 years at the rockall bank site authigenic enrichments of se cd and u are evident immediately below the oxic post oxic boundary although re enrichment does not occur until a few centimetres deeper the long term fluxes of authigenic se cd u and re uptake are evaluated with steady state assumptions while diffusion from bottom waters can supply sufficient se u and re an additional source likely corg is required for cd

integrated reconstruction of holocene millennial scale environmental changes in tierra del fuego southernmost south america abstract this study presents new paleoenvironmental data obtained from sedimentary cores from lago fagnano an elongated lake located at 54 s in southernmost south america data from palynomorphs pollen spores and algae and associated palynofacies as well as from diatom taxa retrieved from these cores compared with other regional proxies contribute to evaluate the similarities and differences in the climate patterns based on different proxies from southernmost patagonia the pollen analysis reveals that a grass steppe environment existed during the early holocene 11 300 8000 cal a bp followed by a major vegetation change characterized by development of forest steppe ecotone communities between 8000 and 6500 cal a bp under more humid conditions between 6500 and 4000 cal a bp expansion and colonization by nothofagus forests reflect an increase in effective moisture levels while openness in the forest communities characterizes the region after 1100 cal a bp the palynological organic matter combined with the algal content reflects hydrological changes occurring in the lake and its nutrient status probably in close relation with past climate oscillations all these past ecological changes are closely related to oscillations in precipitation and temperature as a response to the variations in the latitudinal position and or strength of the southern westerlies wind belt during the holocene

glacial geomorphology of the torres del paine region southern patagonia implications for glaciation deglaciation and paleolake history abstract the processes affecting paleoclimate variability and pleistocene glacial landscape development in the southern mid latitudes remain poorly understood in part because of the scarcity of comprehensive well studied records glacial landforms are invaluable for reconstructing past ice sheet climate and associated environmental changes along the southern andes but there are significant spatial and temporal gaps in existing data in this paper we present new geomorphic and sedimentologic analyses including surficial maps for the torres del paine region 51 s 73 w southern south america our findings provide a new framework for understanding changes in the regional glacier history and pleistocene landscape development glacial extent during the local last glacial maximum lgm remains unknown but new chronological data supported by geomorphic evidence afford evidence for a larger ice sheet at torres del paine than previously assumed deglaciation from the local lgm was underway by 17 400 200 1 cal yr bp as opposed to previous suggestions we have found that most of the moraines fringing the lakes in the torres del paine national park were deposited during a late glacial expansion that occurred between 14 100 and 12 500 cal yr bp late glacial advances also have been documented recently for the ultima esperanza and lago argentino basins to the south and north of torres del paine respectively suggesting an overall regional ice response to a climate signal the tehuelche paleolake accompanied each of the ice sheet fluctuations in torres del paine new data document at least three main phases of this paleolake which drained eastward to the atlantic ocean while the andes gaps were blocked with ice during the late phase of glacial lake formation when water levels reached 125 155 m a s l the lake likely merged with paleolake consuelo in the ultima esperanza area at the end of the last glaciation lake tehuelche in torres del paine had drained into the pacific ocean by the late glacial period suggesting that ice southwest of torres del paine may have retreated back into the mountains by this time

on the distribution of copper nickel and cadmium in the surface waters of the north atlantic and north pacific ocean concentrations of copper nickel and cadmium have been determined for about 250 surface water samples nonupwelling open ocean concentrations of these metals are cu 0 5 1 4 nmol kg ni 1 2 nmol kg and cd less than 10 pmol kg in the equatorial pacific upwelling zone concentrations of ni 3 nmol kg and cd 80 pmol kg are higher than in the open ocean but cu 0 9 nmol kg is not significantly enriched metal concentrations are higher in cool nutrient rich eastern boundary currents cu 1 5 nmol kg ni 3 5 nmol kg and cd 30 50 pmol kg copper is distinctly higher in the coastal waters of the gulf of panama 3 4 nmol kg and also higher in the shelf waters north of the gulf stream 2 5 nmol kg these copper enrichments may be caused by copper remobilized from mildly reducing shelf sediments and maintained by a coastal nutrient trap in the open ocean events of high cu water 1 5 3 5 nmol kg are seen on scales up to 60 km presumably these are due to the advection of coastal water into the oceanic interior the lowest copper concentrations in the north pacific central gyre 0 5 nmol kg bruland 1980 are lower than in the sargasso sea 1 3 nmol kg while for nickel the lowest concentrations are 2 nmol kg in both the north pacific and the north atlantic nickel and cadmium while generally correlated with the nutrients in surface waters show distinct regional changes in their element nutrient correlations the residual concentrations of trace metals in the surface waters of the ocean can be explained if biological discrimination against trace metals relative to phosphorus increases as productivity decreases

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

pore waters of the central pacific ocean nutrient results interstitial waters from the manop siliceous and calcareous ooze sites in the central pacific ocean were recovered by shipboard squeezing and centrifuging techniques and an in situ harpoon sampler the pore waters were analyzed for nutrients carbonate system species mn 2 ca 2 total alkaline earth metals and dissolved oxygen siliceous ooze site only in calcareous sediments the co 2 alkalinity po 4 3 and ca 2 results obtained from shipboard techniques are significantly different than those recovered in situ the other species measured as well as all of the data from the siliceous ooze site reveal no significant dependence on the method used to sample the pore water the relative changes in o 2 no 3 mn 2 alkalinity and co 2 indicate that respiration using o 2 no 3 and mno 2 as electron acceptors is the dominant reaction affecting the pore water species we develop a model which simulates the fate of pore water oxygen and nitrate and particulate organic carbon in sediments this model includes the effects of pore water diffusion oxygen and nitrate respiration sediment accumulation sediment mixing and changes in sediment porosity we observe that factor of 2 variations in the rates of sediment mixing and accumulation have only a minor effect on the pore water profiles the major factor controlling the pore water profiles is the flux of organic carbon across the sediment water interface we conclude that the large intra site variability observed in the interstitial water nitrate profiles is probably caused by small scale variations in the flux of organic material

ventilation changes in the northeast pacific during the last deglaciation under present climate conditions convection at high latitudes of the north pacific is restricted to shallower depths than in the north atlantic to what extent this asymmetry between the two ocean basins was maintained over the past 20 kyr is poorly known because there are few unambiguous proxy records of ventilation from the north pacific we present new data for two sediment cores from the california margin at 800 and 1600 m depth to argue that the depth of ventilation shifted repeatedly in the northeast pacific over the course of deglaciation the evidence includes benthic foraminiferal cd ca 18o 16o and 13c 12c data as well as radiocarbon age differences between benthic and planktonic foraminifera a number of features in the shallower of the two cores including an interval of laminated sediments are consistent with changes in ventilation over the past 20 kyr suggested by alternations between laminated and bioturbated sediments in the santa barbara basin and the gulf of california keigwin and jones 1990 kennett and ingram 1995 behl and kennett 1996 data from the deeper of the two california margin cores suggest that during times of reduced ventilation at 800 m ventilation was enhanced at 1600 m depth and vice versa this pronounced depth dependence of ventilation needs to be taken into account when exploring potential teleconnections between the north pacific and the north atlantic

holocene sea level changes along the strait of magellan and beagle channel southernmost south america abstract radiocarbon dated marine sediments from five coastal sites along the strait of magellan and beagle channel in southernmost chile permit construction of a curve of relative sea level fluctuations during the holocene morphologic and stratigraphic data point to coastal submergence during the early holocene as the sea rose to a maximum level at least 3 5 m higher than present about 5000 yr ago progressive emergence then followed during the late holocene data from widely separated localities define a smooth curve the form of which is explainable in terms of isostatic and hydroisostatic deformation of the crust resulting from changing ice and water loads apparently anomalous data from one site located more than 100 km behind the outer limit of the last glaciation may reflect isostatic response to deglaciation the sea level curve resembles one derived by clark and bloom 1979 in proceedings of the 1978 international symposium on coastal evolution in the quaternary sao paulo brasil pp 41 60 sao paulo using a spherical earth model both in amplitude and in the timing of the maximum submergence

fluctuations of the ultima esperanza ice lobe 52 s chilean patagonia during the last glacial maximum and termination 1 abstract we present a new record from the ultima esperanza region 51 25 52 25 s southwestern patagonia to unravel the timing and structure of glacial fluctuations during the last glacial termination t1 this sector of southern south america represents the only windward facing continental landmass in the southern hemisphere that intersects the core of the southern westerly wind belt geomorphic stratigraphic and geochronological evidence indicate the following stages during and since the last glacial maximum lgm i deposition of prominent moraine complexes during at least two advances dated between 39 and 17 5 ka ii development of an ice dammed proglacial lake glacial lake puerto consuelo accompanying ice recession iii active deposition of moraine complexes at intermediate positions followed by recession at 15 2 ka iv lake level drop and subsequent stabilization between 15 2 12 8 ka v a glacial readvance in glacial lake puerto consuelo between 14 8 12 8 ka vi ice recession stabilization and lake level lowering between 12 8 10 3 ka and vii glacial withdrawal and disappearance of glacial lake puerto consuelo prior to 10 3 ka by comparing our results with the chronologies from neighboring regions we explore whether there was a consistent temporal geographic pattern of glacial fluctuations during the lgm and t1 and examine their implications at regional hemispheric and global scales the correspondence of these variations with key paleoclimate events recorded in the southern and the northern hemispheres suggest a common forcing that most likely propagated through the atmosphere regional heterogeneities at millennial timescales probably reflect the influence of processes related to deep ocean circulation and changes in the position intensity of the antarctic polar front and southern westerly winds

deglacial palaeoclimate at puerto del hambre subantarctic patagonia chile the primary objective of this study is to further substantiate multistep climatic forcing of late glacial vegetation in southern south america a secondary objective is to establish the age of deglaciation in estrecho de magallanes bahia inutil pollen assemblages at 2 cm intervals in a core of the mire at puerto del hambre 53 36 21 s 70 55 53 w provide the basis for reconstructing the vegetation and a detailed account of palaeoclimate in subantarctic patagonia chronology over the 262 cm length of core is regulated by 20 ams radiocarbon dates between 14 455 and 10 089 14c yr bp of 13 pollen assemblage zones the earliest representing the oldest dryas chronozone 14 455 13 000 14c yr bp records impoverished steppe with decreasing frequencies and loss of southern beech nothofagus successive 100 yr long episodes of grass herbs and of heath empetrum ericaceae before 14 000 14c yr bp infer deglacial successional communities under a climate of increased continentality prior to the establishment of grass dominated steppe the bolling allerod 13 000 11 000 14c yr bp is characterised by mesic grassland under moderating climate that with abrupt change to heath dominance after 12 000 14c yr bp was warmer and not as humid at the time of the younger dryas 11 000 10 000 14c yr bp grass steppe expanded with a return of colder more humid climate later with gradual warming communities were invaded by southern beech the puerto del hambre record parallels multistep deglacial palaeoclimatic sequences reported elsewhere in the southern andes and at taylor dome in antarctica deglaciation of estrecho de magallanes bahia inutil is dated close to 14 455 14c yr bp invalidating earlier dates of between 15 800 and 16 590 14c yr bp copyright 2000 john wiley sons ltd

younger dryas in southernmost south america an update abstract high resolution pollen data from a peat section in southern tierra del fuego documents high paleoenvironmental variability between 11 ka and 9 ka detailed analysis of plant macro remains in the same section showed that the repeated high amplitude changes in pollen taxa were related to repeated fire disturbance burning at least once even the surface of the mire in many peat sections from southernmost patagonia and tierra del fuego charcoal particles have been found intermittently since about 13 ka and in great abundance especially after 11 ka this suggests that the environmental changes previously interpreted to imply a return to colder climates comparable to the north atlantic younger dryas event instead are in response to local and regional disturbances by fires

timing and magnitude of holocene sea level changes along the middle and south patagonian atlantic coast derived from beach ridge systems littoral terraces and valley mouth terraces abstract geomorphologic and chronostratigraphic investigations in various coastal localities along the middle and south patagonian atlantic coast from bahia vera 44 s in the north to san julian 49 s in the south confirm a rich sequence of holocene beach ridge systems and littoral and valley mouth terraces beach ridges are present up to 10 m above current highest tide level htw and date to the early mid holocene transgression maximum beach ridge deposits represent high energy wave dominated coastal environments whereas valley mouth terraces and littoral terraces elevations of 5 5 6 5 m above htw developed in wave protected coastal environments the surface elevation of these littoral forms suggest that the middle and south patagonian atlantic coast is likely undergoing a slow glacio isostatic uplift on the order of 0 3 0 4 mm a since the mid holocene the early holocene sea level rise reached the modern coastline by 8100 14 c years ago c 8600 cal bp at the latest sea level at that time was most likely near its present position the holocene transgression maximum lasted from 6900 to at least 6200 14 c bp c 7400 to 6600 cal bp raising relative sea level to about 2 m to a maximum of 3 m above the present level after which sea level declined to the present level two significant sea level falls of at most 1 m occurred a between 6200 and 6000 14 c bp c 6600 to 6400 cal bp and b between 2600 and 2400 14 c bp c 2300 to 2050 cal bp we assume that both significant sea level falls were predominantly driven by eustatic changes of ocean volume whereas both thermo steric changes and changes of tides may also have contributed to these relatively strong sea level drops gravitational changes driven by greenland ice growth sensu mitrovica et al 2001 may also have amplified any eustatic portion of sea level fall the trend of a general sea level decline since the mid holocene transgression maximum seems to be predominantly glacio isostatically driven

authigenic cadmium enrichments in suboxic sediments precipitation and postdepositional mobility the postdepositional mobility of cd and u has been investigated in north atlantic turbidites in order to validate their utility as proxies of paleo organic carbon fluxes in this region pelagic sediments are interspersed with relatively organic rich turbidites following instantaneous emplacement of turbidite units an oxidation front progressively migrated downwards into the suboxic turbidite thereby leading to redistribution of authigenic phases according to their affinity to different redox conditions authigenic cd concentrations show a large peak at the redox boundary and are significantly lower in the oxidized portion than in the deeper unoxidized part of the turbidite this distribution indicates that cd has been continuously remobilized by the oxidation front thereby suggesting high sensitivity of the cd species to the redox state and an efficient immobilization mechanism for cd under reducing conditions we propose the precipitation of cds as a plausible mechanism for removal of cd in reducing sediments rather than adsorption onto mineral surfaces this proposal is consistent with porewater data indicating diffusion of cd toward and uptake by suboxic sediments solubility calculations suggest that precipitation of cds may occur in suboxic sediments in the presence of trace levels of h2s below routine detection limits there is no evidence for release of cd or u back into seawater upon oxidation of reducing sediments the strong coupling between precipitation of authigenic cd and u and the early diagenetic degradation of organic carbon offers the potential of reconstructing paleo productivity using records of cd and u however postdepositional redistribution of authigenic cd and u may significantly alter records of authigenic cd and u thereby rendering paleo productivity reconstructions uncertain we propose that the cd u authigenic ratio may provide a qualitative indicator to assess the relative role of steady state incorporation relative to transient burn down enrichments

microhabitat effects on cd ca and δ 13 c of benthic foraminifera cd ca and 13c were measured on bottom and pore water samples and samples comprising dead individuals of six species of benthic foraminifera including cibicidoides wuellerstorfi uvigerina peregrina and melonis barleeanum from throughout the sediment mixed layer at three well characterised sites in the northeastern atlantic living i e rose bengal stained u peregrina and m barleeanum from one of the three sites were also analysed co existing living and dead foraminifera of the same species from the same site have similar cd ca and 13c and show no significant down core variability therefore comparison of 13c in foraminifera with bottom water and pore waters was used to estimate average calcification depths within the sediment for each species and thereby determine dcd based on the cd concentrations at these depths pore waters are 2 4 times more enriched in cd than bottom waters consequently dcd values are different from estimates based on bottom water cd results give dcd of 1 for all the infaunal species with no significant water depth dependence dcd for c wuellerstorfi based on bottom water cd are 3 2 1 1 at 3600 m water depth and 3 9 1 3 at 1900 m water depth being consistent with dcd estimated from culture experiments the results suggest that the depth dependence of dcd based on bottom water cd may be partly explained by a pore water influence on the test chemistry for infaunal species

vegetation and climate changes during the last 22 000 yr from a marine core near taitao peninsula southern chile high temporal resolution of pollen analyses from marine core md07 3088 46 s documents regional and coastal vegetation changes in the mid latitude of southern chile during the last 22 kyr bp the coastal margin was partly ice free during the last glacial period with the presence of scattered vegetation after 17 6 kyr bp the expansion of nothofagus woodland highlights a warming trend and marks the beginning of the last deglaciation the deglacial forest expansion is interrupted by the development of magellanic moorland simultaneously with the antarctic cold reversal this vegetation change illustrates a pause in the warming trend with an abrupt increase in precipitation which is related to strong intensity of southern westerly winds after 12 8 kyr bp the retreat of magellanic moorland illustrates a second step warming that is strengthened after 11 5 kyr at the onset of the holocene expansion of heliophytic taxa illustrates warmest and driest conditions of the holocene from 11 to 7 4 kyr bp later the decrease of heliophytic taxa shows a return to cooler and wetter conditions illustrated by the presence of the north patagonian rainforest that reaches modern condition after 5 kyr climate changes inferred from the marine pollen record are consistent with geochemical data changes from the same samples and illustrate a clear synchronicity with d variations of epica dome c ice core during the last deglaciation and holocene comparison between vegetation changes from the marine core and regional palaeoclimatic records highlights southward northward shifts of the southern westerly wind belt and supports a close link between southern westerly wind belt and atmospheric co2 variability during the last deglaciation

holocene changes in the position and intensity of the southern westerly wind belt the position and intensity of the southern westerly wind belt varies seasonally as a consequence of changes in sea surface temperature during the austral winter the belt expands northward and the wind intensity in the core decreases conversely during the summer the belt contracts and the intensity within the core is strengthened reconstructions of the westerly winds since the last glacial maximum however have suggested that changes at a single site reflected shifts throughout the entire southern wind belt 1 4 here we use sedimentological and pollen records to reconstruct precipitation patterns over the past 12 500 yr from sites along the windward side of the andes precipitation at the sites located in the present core and northern margin of the westerlies is driven almost entirely by the wind belt 5 and can be used to reconstruct its intensity rather than varying coherently throughout the holocene epoch we find a distinct anti phasing of wind strength between the core and northern margin over multi millennial timescales during the early holocene the core westerlies were strong whereas the northern margin westerlies were weak we observe the opposite pattern in the late holocene as this variation resembles modern seasonal variability we suggest that our observed changes in westerly wind strength can best be explained by variations in sea surface temperature in the eastern south pacific ocean chile is ideally located to reconstruct past variability of the southern westerly wind belt sww as the sww almost entirely controls precipitation on the western side of the andes in southern south america with an extreme northsouth

sensitivity of chemical species to climatic changes in the last 45 kyr as revealed by high resolution dome c east antarctica ice core analysis

cadmium deposition and mobility in the sediments of an acidic oligotrophic lake abstract a dated core from the profoundal zone in a pristine oligotrophic acidic lake was analyzed for cd as well as for al ca fe mg mn pb ti and total carbon and nitrogen overlying water and porewater samples were also obtained on six occasions at the same site and yielded vertical profiles of ph and dissolved cd ca fe mg mn sulfide so 4 2 organic and inorganic carbon concentrations these extensive porewater and sediment geochemical data were used together with information on infaunal benthos to decipher the sedimentary record of cd contamination depth variation of sediment ca concentrations indicate that the lake suffered from progressive acidification starting about 1950 the present day accumulation rate of cd j acc cd 5 4 0 4 10 11 mol cm 2 yr 1 in the sediments is the sum of the flux of cd deposited with settling particles j s cd 3 3 0 2 10 11 mol cm 2 yr 1 and the fluxes of dissolved cd across the sediment water interface due to molecular diffusion j d cd 1 8 0 3 10 11 mol cm 2 yr 1 bioturbation j b cd 1 1 0 2 10 14 mol cm 2 yr 1 and bioirrigation j i cd 0 27 0 05 10 11 mol cm 2 yr 1 biological mixing of the sediments was negligible the shape of the vertical profile of total cd concentration with depth in the sediment appears to be determined more by its input history than by post depositional mobilization and redistribution in the sediment column

suborbital intermediate water variability inferred from paired benthic foraminiferal cd ca and δ13c in the tropical west atlantic and linking with north atlantic climates abstract paired benthic cd ca and 13c records have been generated along core m35003 in the western tropical atlantic decreased glacial water column dissolved cadmium cdw and increased benthic 13c indicate enhanced ventilation with nutrient deplete intermediate waters in line with similar inferences from other north atlantic mid depth records an abrupt early deglacial 13c collapse that is associated with a marked positive cdw anomaly indicates a transient collapse of mid depth ventilation from north atlantic sources conceivably in conjunction with the h1 meltwater anomaly the cdw record displays fine scale fluctuations that mimic the greenland dansgaard oeschger d o cycles and show decreased cdw during stadials this pattern is opposite to cdw variations in a deep water record from bermuda rise that display increased cdw concentrations during stadials the divergent pattern between mid depth and deep water cdw records indicates millennial scale switches between deep and shallow convection in the glacial north atlantic at the pace of the d o climatic cycles several high amplitude anomalies occur in the cdw record that reach levels similar to those observed today in the north pacific while a substantial nutrient increase in the mid depth north atlantic cannot be ruled out during these events changes of pore water chemistry and cd p fractionation during biological uptake offer alternative scenarios to explain the peak cdw maxima

late pleistocene to holocene marine transgression and thermohaline control on sediment transport in the western magellanes fjord system of chile 53 s abstract in the western strait of magellan in southernmost chile marine transgression occurred between 14 500 and 13 500 cal bp this is indicated by strongly increased accumulation of biogenic carbonate and first appearance of foraminifers in sediment records from that time until 11 500 cal bp sedimentation in the western fjords became predominant autochthonous due to higher salinity and clay flocculation and late glacial glacier retreat present day thermohaline zonation pattern extensively representative for the holocene and sedimentation rates indicate that westerlies hampered westward outflow of superficial 0 30 m water depth glacial clay rich freshwater from glaciated areas during the holocene isostatic uplift of the andes overcompensated sea level rise in areas with high glacial glacier loading this led to shallowing fjord sills and restricted exchange with marine water especially since high freshwater inflow produced strong pycnoclines and preserved old saline water in fjord bottoms to the east of the climate divide the seno skyring fjord system shows a year round stable stratification despite a strong wind induced eastward superficial current in the upper 30 50 m of the water column such currents enabled significant late glacial eastward transport of glacial clay sediment cores from this area indicate that east ward sediment flux slowed down during the holocene probably due to less intense westerlies investigated present day thermohaline characteristics of the fjord system across the superhumid climate divide of the southern andes indicate details of the exchange between marine and freshwater which are fundamental for evaluation of sediment transport pathways biogenic productivity and interpretation of paleoclimate records in this area

experimental determination of trace element partition coefficients in cultured benthic foraminifera abstract we present the first trace metal partition coefficients obtained from reproducing cultures of deep sea benthic foraminifera paleoceanographically important species including juvenile bulimina marginata cibicidoides pachyderma and uvigerina peregrina were maintained in sediment microcosms at 10 c 35 psu and ph 8 for 1 3 years juvenile foraminifera were separated cleaned and dissolved under clean conditions for determination of trace metal partition coefficients on recently deposited 1 3 months foraminiferal calcite in addition to the deep sea species we analyzed a shallow water benthic foraminifer ammonia beccarii overlying water samples were collected from the microcosms concurrent to the period of calcification 3 months prior to separation ba ca partition coefficients d ba were measured in replicate for benthic foraminifera species bulimina marginata 0 24 0 07 uvigerina peregrina 0 24 0 06 ammonia beccarii 0 20 0 04 the d ba for bulimina marginata and uvigerina peregrina were found to closely match the range from the ontong java plateau sample size limitations allowed for only one analysis of d ba for cibicidoides pachyderma however our nonreplicated d ba of 0 5 0 1 falls within the accepted range of core top samples 0 37 0 06 we report a d cd for ammonia of 1 0 0 5 for cibicidoides of 4 2 for bulimina of 3 1 and for uvigerina 2 1 which all fall within the ranges reported for core top calibrations the large uncertainties in d cd reflect variation in dissolved cd concentration in the artificial seawater reservoir due to loss and replacement of cd during the course of the experiment the variability between species is probably the result of variability in pore water cd in the sediment culture system and may reflect habitat effects

the vulnerability of the nothofagus forest steppe ecotone to climate change palaeoecological evidence from tierra del fuego 53 s abstract a new late glacial holocene palaeoenvironmental record from near lago lynch 53 54 s 69 26 w tierra del fuego is presented the record was sampled from a mire located within the deciduous nothofagus forest steppe ecotone and pollen and spore analysis suggest a high degree of vulnerability of past vegetation to changes in effective moisture ams radiocarbon dating supplemented by the application of tephrochronology including the geochemical fingerprinting of six visible and cryptotephra layers provides robust age constraint the lago lynch record commences at c 15 6 ka the sequence of vegetation changes between c 15 6 and 14 4 ka reflect a gradual increase in temperature and humidity followed by a colder interval between c 14 4 and 13 3 ka which is broadly coeval with the antarctic cold reversal after c 13 3 ka patches of nothofagus forest appeared suggesting more mesic temperate conditions leading gradually to the establishment of an open canopy nothofagus forest by c 12 5 ka which marks the start of the holocene moderate to strong effective moisture levels dominated during the early holocene until c 11 0 ka followed by a sustained period c 11 0 6 5 ka of drier climatic conditions particularly two arid phases at c 10 5 10 0 ka and 8 5 6 5 ka an eastwards expansion of the forest margin after c 6 5 ka at the site suggests a return to more humid conditions during the late holocene we argue that the periods of increased moisture and aridity inferred from lago lynch closely reflect the extent to which the southern westerly winds swws push eastwards to the drier regions of fuego patagonia during the holocene the longitudinal variations in moisture are driven by the nature and timing of latitudinal shifts in the swws more significantly the vulnerability of the forest steppe ecotone to moisture changes amplifies the ecological impact of relatively small scale shifts in the swws

holocene tephrochronology record of large explosive eruptions in the southernmost patagonian andes for regionally widespread holocene tephra layers in southernmost patagonia correlations based on both chemical and chronological data indicate their derivation from five large volume 1 km3 explosive eruptions of four different volcanoes in the southernmost andes bulk tephra and tephra glass major and trace element chemistry and sr isotopic ratios unambiguously distinguish different source volcanoes and imply that two of the regionally widespread tephra mb1 and mb2 were derived from mt burney 52 s one r1 from reclus 51 s one a1 from aguilera 50 s and one h1 from hudson volcano 46 s the h1 tephra derived from the hudson volcano which is located at the southern end of the andean southern volcanic zone svz 33 46 s contains distinctive greenish andesitic glass with feo 4 5 wt and tio2 1 2 wt in contrast rhyolitic glass in tephra derived from the eruptions of mt burney reclus and aguilera volcanoes which are located in the andean austral volcanic zone avz 49 55 s is clear and transparent and has significantly lower feo and tio2 tephra derived from these three avz volcanoes all contain plagioclase orthopyroxene minor clinopyroxene and amphibole biotite occurs only in the aguilera a1 tephra which also has the highest bulk tephra and tephra glass k2o and rb contents averages of new and published 14c ages determined on organic material in soil and sediment samples above and below these tephra constrain the uncalibrated 14c age of the r1 eruption of reclus volcano to 12 685 260 years bp the mb1 and mb2 eruptions of mt burney to 8 425 500 and 3 830 390 years bp the hudson h1 eruption to 6 850 160 years bp and the a1 eruption of aguilera volcano to 3 000 100 years bp the volume of the largest of these eruptions h1 of the hudson volcano is estimated as 18 km3 the volume of the reclus r1 eruption is estimated at 10 km3 the aguilera a1 eruption at between 4 and 9 km3 and the younger mt burney mb2 eruption at 2 8 km3 the volume of the older mb1 mt burney eruption is the least well constrained but must have been larger than the younger mb2 eruption the data indicate that the frequency of explosive activity of volcanic centers in the avz is lower than in the southern svz

deep circulation of the north atlantic over the last 200 000 years geochemical evidence variations in the cadmium calcium ratio of north atlantic deep water are recorded in the fossil shells of benthic foraminifera the oceanic distribution of cadmium is similar to that of the nutrients hence the cadmium calcium ratio in shells records temporal variations in nutrient distributions data from a north atlantic sediment core show that over the past 200 000 years there has been a continuous supply of nutrient depleted waters into the deep north atlantic the intensity of this source relative to nutrient enriched southern waters diminished by about a factor of 2 during severe glaciations this evidence combined with carbon isotope data indicates that the continental carbon inventory may have been less variable than previously suggested

past human populations and landscapes in the fuegian archipelago southernmost south america this contribution discusses possible relationships between human populations and holocene environmental deterioration phenomena cold arid pulses and volcanic eruptions in the fuegian archipelago south america based on summed probability distributions of archaeological dates paleoenvironmental information geospatial data and archaeological evidence during the first millennia after peopling only the hudson ca 7700 cal yr bp and the first monte burney ca 8600 cal yr bp eruptions might have played a role in human dispersion particularly a more intense human occupation around the beagle channel and long distance interactions are proposed as risk buffer strategies related to the hudson eruption a cooling phase and a demographic growth at ca 5500 cal yr bp might have favored more dispersed spatial occupations and a subsistence diversification in the beagle channel in the northern steppes the second monte burney eruption ca 4300 cal yr bp and an arid episode ca 2600 cal yr bp are proposed as the main triggers for changes in land use patterns long network interactions and subsistence strategies even though occupation changes in the fuegian archipelago coexist with environmental deterioration episodes after 1500 cal yr bp demographic processes and the european colonization most likely explain this trend similarities between the steppe ecotone and forest occupation curves suggest common behavioral patterns across the holocene

north atlantic thermohaline circulation during the past 20 000 years linked to high latitude surface temperature during a surface cooling event 10 000 to 12 000 years ago higher cd ca and lower 13c 12c ratios are observed in benthic foraminifera shells from rapidly accumulating western north atlantic sediments data from sediment cores show that marked nutrient depletion of intermediate waters occurs in association with reduced glacial north atlantic deep water flux it is proposed that cold high latitude sea surface temperatures enhance intermediate water formation at the expense of deep water formation

the geochemistry of redox sensitive trace metals in sediments abstract we analyzed the redox sensitive elements v mo u re and cd in surface sediments from the northwest african margin the u s northwest margin and the arabian sea to determine their response under a range of redox conditions where oxygen penetrates 1 cm or less into the sediments mo and v diffuse to the overlying water as mn is reduced and remobilized authigenic enrichments of u re and cd are evident under these redox conditions with the onset of sulfate reduction all of the metals accumulate authigenically with re being by far the most enriched general trends in authigenic metal accumulation are described by calculating authigenic fluxes for the 3 main redox regimes oxic reducing where oxygen penetrates 1 cm and anoxic conditions using a simple diagenesis model and global estimates of organic carbon rain rate and bottom water oxygen concentrations we calculate the area of sediments below 1000 m water depth in which oxygen penetration is 1 cm to be 4 of the ocean floor we conclude that sediments where oxygen penetrates 1 cm release mn v and mo to seawater at rates of 140 260 60 150 and 5 10 of their respective riverine fluxes using the authigenic metal concentrations and accumulation rates from this work and other literature these sediments are sinks for re cd and u with burial fluxes of 70 140 30 80 and 20 40 respectively of their dissolved riverine inputs we modeled the sensitivity of the response of seawater re cd and v concentrations to changes in the area of reducing sediments where oxygen penetrates 1 cm our analysis suggests a negligible change in seawater re concentration whereas seawater concentrations of cd and v could have decreased and increased respectively by 5 10 over 20 kyr if the area of reducing sediments increased by a factor of 2 and by 10 20 if the area increased by a factor of 3 the concentration variations for a factor of 2 increase in the area of reducing sediments are at about the level of uncertainty of cd ca and v ca ratios observed in foraminifera shells over the last 40 kyr this implies that the area of reducing sediments in the ocean deeper than 1000 m 4 has not been greater than twice the present value in the recent past

late holocene climatic changes in tierra del fuego based on multiproxy analyses of peat deposits a ca 1400 yr record from a raised bog in isla grande tierra del fuego argentina registers climate fluctuations including a medieval warm period although evidence for the little ice age is less clear changes in temperature and or precipitation were inferred from plant macrofossils pollen fungal spores testate amebae and peat humification the chronology was established using a 14c wiggle matching technique that provides improved age control for at least part of the record compared to other sites these new data are presented and compared with other lines of evidence from the southern and northern hemispheres a period of low local water tables occurred in the bog between a d 960 1020 which may correspond to the medieval warm period date range of a d 950 1045 generated from northern hemisphere tree ring data a period of cooler and or wetter conditions was detected between ca a d 1030 and 1100 and a later period of cooler wetter conditions estimated at ca cal a d 1800 1930 which may correspond to a cooling episode inferred from law dome antarctica

expansion of magellanic moorland during the late pleistocene palynological evidence from northern isla de chiloe chile the late quaternary vegetation of northern isla de chiloe is inferred from palynological analysis of a section in the rio negro drainage 42 03 s 73 50 w at ca 30 500 yr b p maxima of astelia and donatia occurred suggesting wetland development from that time until ca 27 000 yr b p steppe indicators such as compositae gramineae dominated suggesting drier conditions after 27 000 yr b p the moorland shrub dacrydium gradually increased reaching a maximum by 18 000 yr b p at this time astelia increased again suggesting development of cushion bog during cold and wet conditions the glacial postglacial transition is characterized by a marked change from peaty sediments to clays a decrease in the cushion bog flora and the prevalence of gramineae compositae and swamp taxa this vegetation prevailed until ca 7000 yr b p when forest taxa became dominant the floristic pattern inferred from the pollen spectra of the rio negro section suggests that the late pleistocene vegetation of chiloe resembled modern magellanic moorland vegetation 52 56 lat s based on climatic conditions presently associated with magellanic moorland its occurrence in chiloe at low elevations during the late pleistocene implies a decrease in average temperature of at least 4 c and an increase in annual precipitation of at least 1500 mm

reduced advection into atlantic ocean deep eastern basins during last glaciation maximum causes of change in deep water 13c can be either global or local in extent global causes include 1 climatically induced changes in the amount of terrestrial biomass which alter the average carbon isotopic composition of the oceanic reservoir1 and 2 erosion and deposition of organic rich continental shelf sediments during sea level fluctuations which change the mean oceanic carbon phosphorus ratio2 regional gradients of 13c are created by remineralization of organic detritus within the deep ocean itself thus reflecting the distribution of water masses and modern thermohaline flow changes in a single geological record of benthic foraminiferal 13c can result from any combination of these global and abyssal circulation effects by sampling a large number of cores collected over a wide bathymetric range yet confined to a small geographical region we have minimized the ambiguity we can assume that each 13c record was equally affected by global causes of 13c variation the differences seen between the 13c records must therefore reflect changes in the distribution of 13c in the deep ocean we interpret these differences in distribution in terms of changes in the ocean s abyssal circulation benthic foraminiferal carbon isotopic evidence from a suite of sierra leone rise cores indicates that the deeper parts of the eastern atlantic basins underwent a reduction in o2 during the maximum of the last glaciation reduced advection of o2 rich deep water through low latitude fracture zones associated with increased delivery of organic matter to the deep ocean lowered the 13c of deep water co2 at all depths below the sill separating the eastern and western atlantic basins 3 this decreased advection into the eastern atlantic ocean coincides with the overall decrease in deep water production in the north atlantic during the last glacial maximum4 7

late and postglacial vegetation and fire history in southern patagonia and tierra del fuego abstract two 17 000 yr old peat bog records from low elevation sites in tierra del fuego harberton 54 54 s and southern patagonia rio rubens 52 4 48 s and one c 14 000 cal yr bp record from the upper treeline in tierra del fuego paso garibaldi 54 43 s were analyzed for pollen charcoal and plant macrofossils to reconstruct changes in regional and local vegetation fire frequency and bog hydrology respectively past environmental changes in both lowland records and in the upper treeline record are interpreted in terms of variations in effective moisture during the late glacial period effective moisture changes at both low and high elevation sites were interpreted from comparable shifts between mesic herb rich grasslands and arid empetrum heath or shrub grassland with abundant disturbance indicators the late glacial effective moisture changes were primarily driven by temperature changes during the early holocene expansion of open nothofagus woodlands in the lowlands in present day areas of dense forest was related to a marked precipitation increase however precipitation must have remained highly variable with century long periods of increased summer drought as evidenced by repeated intervals when bogs dried out and fire frequency was high up slope shifts of the nothofagus forest andean tundra ecotone at 11 000 and 9000 cal yr bp also appear to reflect precipitation increases precipitation variability however must not have affected the upper treeline environments as no fires were recorded and the present day nothofagus forest had become established after 9000 cal yr bp upper treeline apparently was below present from 8000 to 7000 and 2500 to c 400 cal yr bp during those times low elevation environments did not register change which suggests that the upper treeline may have been affected by lower temperatures after c 5000 cal yr bp fires became rare in the lowlands suggesting a shift to an equable precipitation regime with only minor intervals of summer drought no simultaneous change was recorded at the upper treeline thus for the late glacial and early holocene the upper and lower treeline environments apparently responded similarly to primarily moisture changes only during the mid and late holocene environmental changes at high and low elevations differed suggesting responses to different climate signals precipitation in the lowlands and temperature at high elevation

core top evaluation of benthic foraminiferal isotopic ratios for paleo oceanographic interpretations abstract the benthic foraminifera cibicides wuellerstrofi oridforsalis tener and pyrgo rotalaria from twelve core tops in the norwegian greenland sea and c wuellerstorfi o tener and o umbonatus from four core tops on the rio grande rise were analysed for oxygen and carbon isotopes the norwegian greenland sea data yield statistically discrete means for both 18o and 13c for each species the interregional comparison of our data to published data from the east pacific rise shows that c wuellerstorfi 18o and 13c variations reflect oceanographic differences between sites whereas the data on oridorsalis and pyrgo do not we conclude that c wuellerstorfi is a reliable sensor of bottom water conditions whereas other taxa are of unproven utility supportive biological studies and the lack of positive covariance of 18o to 13c among deep sea benthic taxa lead us to reject models calling for incorporation of metabolic co2 to explain the isotopic variation among deep sea benthic foraminifera we propose a within sediment microhabitat hypothesis to explain the 13c variations among taxa

the δ13c in benthic foraminiferal tests of fontbotia wuellerstorfi schwager relative to the δ13c of dissolved inorganic carbon in southern ocean deep water implications for glacial ocean circulation models on a transect between 20 and 70 s in the eastern atlantic ocean and weddell sea water samples from 19 hydrographic stations and bottom water from 55 surface sediment samples taken with a multiple corer were investigated for the stable carbon isotopic composition of the total dissolved inorganic carbon 13c co2 these measurements were compared to 13c values determined on live specimens of the benthic foraminifer fontbotia wuellerstorfi and closely related genera from the same stations in addition at 16 stations the stable carbon isotope composition of sedimentary organic carbon was measured general deepwater and bottom water mass circulation patterns as inferred from the 13c co2 are in close agreement with those known from other nonconservative tracers very low 13c values of upper circumpolar deep water 0 3 pee dee belemnite pdb in the polar front region and the eastern limb of the weddell gyre coincide with nutrient maxima however a significant decoupling of the dissolved phosphate signal from the 13c co2 signal is indicated in the abyssal weddell sea we attribute this to temperature dependent fractionation processes during gas exchange of surface waters with the atmosphere at sites of bottom water formation multiple corer water from the sediment water interface is slightly 13c depleted relative to deepwater and bottom water 13 co2 the surface sediment organic carbon 13c is 3 to 4 lower south of the polar front than north of it and the 13corg in freshly accumulated phytodetritus is 3 to 4 lower than surface sediment organic carbon 13c comparison of live f wuellerstorfi 13c and related genera with bottom water 13c co2 exhibits at most stations between the subtropical front 41 s and the southern boundary of the antarctic circumpolar current 55 s a significant lowering of foraminiferal 13c values compilation of a mean last glacial interglacial 13c amplitude 13c from six published southern ocean cores results in a shift of 0 99 0 13 pdb this shift is greater than that in all other regions however all of these cores are from positions close to recent oceanic fronts thus for these peripheral areas of the southern ocean we suggest about half of the glacial interglacial shift can be explained by varying frontal zone positions and widths accompanied by a change in mode and height of export production

stable carbon isotopes in marine porewaters abstract we present centimeter scale porewater 13 c profiles from four sites in the central equatorial pacific ocean which reveal steep porewater 13 c gradients up to 1 0 cm 1 at the deep sea sediment water interface we describe the processes controlling porewater carbon isotopic composition and incorporate them into a model of the deep sea benthic carbon cycle our measured 13 c profiles are then used to estimate carbon rain rates at two of these sites manop sites c and s the 13 c data yield organic carbon rain rates of 10 mol c cm 2 yr 1 at site c and 3 mol c cm 2 yr 1 at site s these carbon rain rates agree with recent carbon rain estimates based on sediment trap data and porewater nitrate profiles but are a factor of 2 lower than estimates based on millimeter scale porewater oxygen profiles our model results indicate that changes of the same magnitude in organic carbon rain rate and bottom water composition o 2 co 2 and 13 c have comparable effects on the carbon isotopic composition of surficial porewaters this suggests the need to consider the effects of benthic carbon cycling on the stable carbon isotope record preserved in deep sea benthic foraminifera tests

deglacial changes of the southern margin of the southern westerly winds revealed by terrestrial records from sw patagonia 52 s much of the ongoing discussion regarding synchrony or bipolar asynchrony of paleoclimate events has centered on the timing and structure of the last glacial termination in the southern mid latitudes in particular the southwestern patagonian region 50 e55 s its location adjacent to the drake passage and near the southern margin of the southern westerly winds sww allows examining the postulated links between the southern oceanesww coupled system and atmospheric co2 variations through the last glacial termination results from two sites located in the ultima esperanza area 52

covariability of the southern westerlies and atmospheric co2 during the holocene a suite of mechanisms has been proposed to account for natural variations in atmospheric co 2 during the holocene all of which have achieved limited success in reproducing the timing direction and magnitude of change recent modeling studies propose that changes in the latitudinal position and strength of the southern hemisphere westerly winds sww can greatly influence large scale ocean circulation and degassing of the deep ocean via changes in wind driven upwelling in the southern ocean the extent to which the hypothesized sww southern ocean coupled system could account for changes in atmospheric co 2 is uncertain because of a lack of observations on the behavior of the sww in the past the paucity of appropriate records of productivity changes in the southern ocean and our limited understanding of the sensitivity of the southern ocean biological and or physical system to sww forcing here we report a reconstruction of the behavior of the sww during the past 14 k y based on terrestrial ecosystem proxies from western patagonia south america the reconstructed variations in the intensity of zonal flow correspond to the timing and structure of atmospheric co 2 changes and are consistent with the modeled magnitude of co 2 changes induced by varying strengths of the sww the close match between data and models supports the view that the sww southern ocean coupled system underpins multimillennial co 2 variations during the current interglacial and possibly during glacial cycles over the past 800 k y

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

sensitivity of the phosphate cadmium carbon isotope relation in the ocean to cadmium removal by suboxic sediments reconstructions of past deep ocean nutrient concentrations rely largely on the carbon isotopic composition and cadmium content of shells of benthic foraminifera when comparing records of these two paleonutrient tracers a relation similar to the phosphate cadmium carbon isotope relation in the water column today is generally assumed we present new water column sediment and pore water data from the california continental margin which demonstrate that cd accumulation is enhanced in suboxic sediments these results suggest that the oceanic cd inventory is sensitive to changes in the areal extent and redox intensity of suboxic sediments and thus that the phosphate cadmium relation in the ocean could have been different in the past the magnitude of this effect and its evolution through time is presently hard to quantify because the oceanic cd budget is poorly constrained

holocene palaeoclimates of southern patagonia limnological and environmental history of lago cardiel argentina multiproxy palaeoenvironmental and palaeolimnological analyses of two holocene age sediment cores from the margin of lago cardiel a 76 m deep closed basin lake in southern patagonia latitude 49 s provide information on lake level changes that can be related to regional palaeoclimate scenarios sedimentol ogic magnetic susceptibility organic and inorganic carbon content and environmental indicators pollen dia toms ostracodes and stable isotopes on ostracodes show lake levels markedly higher than today during the early holocene following a rapid lake level rise after a desiccation phase prior to 11 000 bp after about 6000 bp lake levels were generally lower but underwent repeated e uctuations these inferred changes support the previously proposed view that the southern westerly stormtracks were focused zonal north of latitude 50 s during the early holocene allowing for antarctic cold fronts to bring easterly moisture to southern patagonia whereas during the late holocene the stormtracks shifted seasonally with an overall more meridional behaviour resulting in less and more variable moisture at these latitudes

glacier modeling and the climate of patagonia during the last glacial maximum ice cap modeling constrained by empirical studies provides an effective way of reconstructing past climates the former patagonian ice sheet is in a climatically significant location since it lies athwart the southern hemisphere westerlies and responds to the latitudinal migration of climatic belts during glacial cycles a numerical model of the patagonian ice cap for the last glacial maximum lgm is developed which is time dependent and driven by changing the mass balance altitude relationship it relies on a vertically integrated continuity model of ice mass solved over a finite difference grid the model is relatively insensitive to ice flow parameters but highly sensitive to mass balance the climatic input is adjusted to produce the best fit with the known limits of the ice cap at the lgm the ice cap extends 1800 km along the andes and has a volume of 440 000 km3 during the lgm the equilibrium line altitude ela was lower than at present by at least 560 m near latitude 40 s 160 m near latitude 50 s and 360 m near latitude 56 s the latitudinal variation in ela depression can be explained by an overall fall in temperature of about 3 0 c and the northward migration of precipitation belts by about 5 latitude annual precipitation totals may have decreased by about 0 7 m at latitude 50 s and increased by about 0 7 m at latitude 40 s the ela rises steeply by up to 4 m per kilometer from west to east as the westerlies cross the andes and this prevents ice growth to the east the limited decrease in temperature during the lgm could be related to the modest migration of the antarctic convergence between south america and the antarctic peninsula

late glacial and holocene palaeoenvironmental change in the central strait of magellan southern patagonia abstract high resolution palaeoenvironmental data for the wisconsin late glacial and early holocene is provided from two sites puerto del hambre and estancia esmeralda ii in the central section of the strait of magellan southern chile palaeoecological and lithostratigraphical evidence is correlated with other palaeoenvironmental data from the magellan region using 14 c dating and tephrochronology the oldest record from puerto del hambre commences at 14 470 14 c yr bp 17 330 cal yr bp following retreat of the magellan glacier climatic warming after that time is indicated by ice retreat from the central section of the strait of magellan and palynological evidence however mean annual temperature continued to be cooler than present until c 10 300 14 c yr bp 12 270 12 110 cal yr bp the magellan environment was relatively humid between c 14 100 and c 12 550 14 c yr bp 16 910 and 15 170 14 410 cal yr bp at c 12 550 14 c yr bp there was a sharp decrease in effective moisture levels of humidity fluctuated but remained relatively low until c 10 300 14 c yr bp this period of cool and drier climate is contemporary with a significant glacier advance dated to between c 12 700 and 10 300 14 c yr bp 15 330 and 12 270 12 110 cal yr bp which would have produced an enhanced rainshadow effect around 10 300 14 c yr bp a shift to warmer conditions occurred between c 10 300 and 8550 14 c yr bp 12 270 12 110 and 9530 cal yr bp an extreme arid phase is recorded which led to an increase in fires at c 8550 14 c yr bp an increase in available moisture allowed the eastward spread of nothofagus forest at 8265 14 c yr bp 9270 9160 cal yr bp there was a relative rise in sea level in the strait of magellan this marine incursion lasted until 3970 14 c yr bp 4420 cal yr bp reaching its maximum around c 6450 14 c yr bp 7420 7340 cal yr bp