pedogenic carbonate carbon isotopic constraints on paleoprecipitation evolution of desert in the pacific northwest usa in response to topographic development of the cascade range abstract the cascade range in the northwestern u s acts as an orographic barrier to the easterly movement of humid air masses from the pacific ocean producing a massive rain shadow with arid to semi arid climate conditions on the leeward side of the range pedogenic carbonates formed in the c3 dominated landscapes east of the range have 13ccarbonate that is enriched by approximately 4 relative to carbonates formed in sub tropical c3 dominated ecosystems we measured stable isotopic compositions of pedogenic carbonates preserved in the quaternary and neogene sedimentary rock units in the inland pacific northwest and examined the impact of long term aridification and paleohydrology on their isotopic compositions the determined 13ccarbonate record shows a gradual increase of 5 from approximately 10 in older pedogenic carbonates to 5 in younger ones whereas 18ocarbonate record indicates a decrease of approximately 4 in the late neogene in addition the quaternary 13ccarbonate and 18ocarbonate records indicate the highest 13c and 18o among the samples during the pleistocene and significant fluctuation over the time period the gradual increase in the 13ccarbonate and the decrease in the 18ocarbonate in the late neogene are interpreted by the development of the rain shadow as a result of topographic development of the cascade range changes in the quaternary isotope records suggest a decrease in regional precipitation and isotopically depleted winter precipitation resulting from changes in large scale atmospheric circulation patterns due to advance and retreat of northern hemisphere continental ice sheet the isotope record from pedogenic carbonates provides a direct record of climatic change suggesting that long term carbon isotope data can provide useful constraints on timing and intensity of regional desertification and its associated climate and topographic interaction

seawater ph pco2 and co2 3 variations in the caribbean sea over the last 130 kyr a boron isotope and b ca study of planktic foraminifera abstract here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry mc icpms this new approach is fast 10 samples analysed in duplicate per analytical session and accurate to better than 0 25 at 95 confidence with acceptable sample size requirements 1 3 mg of carbonate a core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by mc icpms and the isotopic composition of b oh 4 in seawater as predicted using the recently measured isotopic equilibrium factor of 1 0272 at the depth of habitat a down core and core top investigation of boron concentration b ca ratio shows that the partition coefficient is influenced by co2 3 complicating the application of this proxy nevertheless it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the caribbean sea odp site 999a over the last 130 kyr this reconstruction shows that during much of the holocene and the last interglacial period surface water at site 999a was in equilibrium with the atmosphere with respect to co2 during the intervening colder periods although the surface water pco2 was lower than the holocene it was a minor to significant source of co2 to the atmosphere possibly due to either an expansion of the eastern equatorial atlantic upwelling zone or a more local expansion of coastal upwelling in the southern caribbean such reorganisation of the oceanic carbonate system in favour of a larger source of co2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric co2 during glacial periods to be more efficient than previously supposed

the distribution of fe in the antarctic circumpolar current abstract the large scale distributions of dissolved and total fe in surface and deep waters of the antarctic circumpolar current exhibit strong relationships with hydrography and biological processes the mean dissolved fe concentrations are low in surface waters of the antarctic circumpolar current 0 31 0 49 nm with a minimum of 0 17 nm and higher averaging 1 11 9 nm in the polar frontal region enhanced dissolved surface water concentrations in the polar frontal region are attributed to input from the continental shelf and coincide with phytoplankton spring blooms of large diatoms the effects of sea ice melting and iceberg melting on the fe concentrations were relatively small dissolved deep water concentrations 400 m in the antarctic circumpolar current ranged from 0 4 to 2 8 nm circumpolar deep water has relatively high dissolved fe concentrations in the polar frontal region 0 4 2 8 nm compared with deep waters further to the south 0 6 1 1 nm similarly total dissolvable unfiltered fe concentrations in the upper circumpolar deep water tend to decrease southward from the polar frontal region in the lower circumpolar deep water total dissolvable fe concentrations are higher than in the upper circumpolar deep water due to the existing nepheloid layer and sources on the mid atlantic ridge dissolved and total dissolvable fe concentrations in the antarctic bottom water are higher than those of other water masses in the antarctic circumpolar current consistent with the nepheloid layer as well as diagenetic input from shelf sediments the high nutrient low chlorophyll areas of the antarctic ocean and northeast pacific ocean have different major fe input sources of similar magnitude in the antarctic circumpolar current upward transport of fe is the main input source whereas in the north pacific ocean aerosols are the dominant source

palaeoceanography tropical ties changes in dust flux export productivity and bottom water oxygenation in the equatorial pacific ocean have been tightly linked with variations in north atlantic climate over the past 100 000 years according to analyses of marine sediments

variations in the zn si record over the last interglacial glacial transition we examined the zinc content of diatom frustules as an indicator of past changes in surface seawater zn2 concentration zn si data of samples from three cores located in the south atlantic sector of the southern ocean spanning the last interglacial glacial transition are presented changes in the zn si record are linked to changes in the surface water zn2 concentration the source of variation in zn2 concentration appears to be via changes in deep water upwelling and circulation we rule out changes in phytoplankton productivity and aeolian dust input as a source of variation in the zn si record likewise the zn si data are not linked to shifts in the diatom species composition of the sediment or sediment preservation effects the zn si results presented do not support the zinc hypothesis there is no link between the uptake of co2 by phytoplankton as inferred from the 13c record and the zn si record

glacial interglacial variability in denitrification in the world s oceans causes and consequences the late quaternary history of water column denitrifcation of the eastern pacific margins and the arabian sea is reconstructed using sedimentary 15n measurements the 15n values in six piston cores raised from these regions show remarkably similar cyclic variations being heavy 9 10 5 during the interglacials and 2 3 lighter during the glacials this implies that denitrification in these regions decreased substantially during the glacial periods the glacial decline in denitrification is attributed to reduced upwelling and flux of organic material through the oxygen minimum zone since water column denitrification in these areas accounts for about half of the fixed nitrogen loss in the modern ocean the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods because nitrate is a limiting nutrient oceanic productivity and attendant changes in co2 may therefore have been modulated on glacial interglacial timescales by variations in the oceanic no3 content

impact of strong deep ocean stratification on the glacial carbon cycle 1 during the last glacial maximum the climate was substantially colder and the carbon cycle was clearly different from the late holocene according to proxy data deep oceanic 13c was very low and the atmospheric co2 concentration also reduced several mechanisms have been proposed to explain these changes but none can fully explain the data especially the very low deep ocean 13c values oceanic core data show that the deep ocean was very cold and salty which would lead to enhanced deep ocean stratification we show that such an enhanced stratification in the coupled climate model climber 2 helps get very low deep oceanic 13c values indeed the simulated 13c reaches values as low as 0 8 in line with proxy data evidences moreover it increases the oceanic carbon reservoir leading to a small yet robust atmospheric co2 drop of approximately 10 ppm

sources and flow patterns of deep ocean waters as deduced from potential temperature salinity and initial phosphate concentration through the deconvolution of ocean chemical data it has been shown that the ratio of o2 utilization to phosphate production in the sea is 175 6 rather than 138 as proposed by redfield et al 1963 we find no evidence that this ratio changes significantly with location or depth in the sea we have used this new ratio to calculate the initial phosphate concentrations for the waters sampled during the geosecs and tto programs the important application of these new results is in constraining the origin and flow patterns of deep waters in the ocean we believe that a strong case can be made that antarctic salinity maximum water i e the common water of montgomery 1958 is produced by the mixing of waters entering the antarctic from mid depths in the indian pacific and atlantic with weddell sea bottom water southern component antarctic common water consists of about 45 weddell sea bottom water 30 intermediate waters from the pacific and indian oceans and 25 deep water originating from the northern atlantic

tracing dust sources and transport patterns using sr nd and pb isotopes continental dust transported through the atmosphere can be a tracer of atmospheric circulation and transport as well as being a source of information about climate in the dust s source area this information about the provenance of dust transported from desert areas and deposited elsewhere on the oceans and continents can be evaluated using several observational techniques satellite imagery has been used to this end in recent decades and air mass back trajectories have been calculated to trace dust deposits back to their source area another method consists of analysis of the concentration and composition of certain tracers in the dust itself and comparing them to soils and sediments from possible source areas this method has the advantage of being useable for paleo atmospheric circulation and paleo dust transport studies whereas satellite imagery and air mass back trajectories are restricted to relatively recent times we review here different kinds of isotopic tracers that have been used to trace dust provenance but special attention is focused on the use of sr nd and pb isotopes we evaluate their use in studies of both spatially as well as temporally varying continental dust source and transport

last glacial interglacial productivity and associated changes in the eastern arabian sea abstract we reconstruct paleo productivity and bottom water oxygenation changes during the past 32 ka from the southeastern arabian sea using absolute abundance of planktic foraminifera relative abundance of globigerina bulloides angular asymmetrical benthic foraminifera aabf measurements of total organic carbon c org caco 3 and globigerinoides ruber 18 o and 13 c the faunal and geochemical proxies suggest that productivity in the southeastern arabian sea was high during mis 3 a distinct decrease in productivity is inferred during the last glacial maximum 19 23 ka lgm bottom water was well oxygenated during mis3 only to become oxygen depleted during the lgm productivity decreased abruptly during heinrich stadial 1 hs 1 but the response to heinrich stadial 2 hs 2 was different low productivity during the early deglaciation is also synchronous with an increase in ice volume corrected 18 o 18 o sw ivc a salinity proxy between 18 9 18 3 18 9 ka bp and 15 9 15 0 16 3 ka bp and a concomitant decrease in 13 c between 18 2 17 5 18 7 ka bp and 16 4 15 3 16 7 ka bp these patterns suggest that the global 13 c minimum event during the last deglaciation was associated with the weak monsoon interval during hs 1 and a drop in productivity in tropical regions a progressive increase in productivity is observed throughout the holocene with a distinct jump at 5 4 3 8 6 3 ka bp we infer that although productivity was higher in the eastern arabian sea during most of the last glacial interval the overall resultant carbon sequestration was confined only to a restricted zone and not large enough to substantially alter atmospheric co 2

southwest pacific deep water carbonate chemistry linked to high southern latitude climate and atmospheric co2 during the last glacial termination abstract a greater amount of co2 was stored in the deep sea during glacial periods likely via greater efficiency of the biologic pump and increased uptake by a more alkaline ocean reconstructing past variations in seawater carbonate ion concentration a major component of alkalinity enables quantification of the relative roles of different oceanic co2 storage mechanisms and also places constraints on the timing magnitude and location of subsequent deep ocean ventilation here we present a record of deep water inorganic carbon chemistry since the last glacial maximum lgm 19 23 ka bp derived from sediment core rr0503 83 raised from 1627 m in new zealand s bay of plenty the core site lies within the upper limit of southern sourced circumpolar deep water cdw just below the lower boundary of antarctic intermediate water aaiw we reconstruct past changes in bottom water inorganic carbon chemistry from the trace element and stable isotopic composition of calcite shells of the epibenthic foraminifer cibicidoides wuellerstorfi a record of co 3 2 co 3 2 co 3 2 i n s i t u co 3 2 saturation derived from the foraminiferal boron to calcium ratio b ca provides evidence for greater ice age storage of respired co2 and reveals abrupt deglacial shifts in co 3 2 i n s i t u of up to 30 mol kg 5 times larger than the difference between average lgm and holocene values the rapidity of these changes suggests the influence of changing water mass structure and atmospheric circulation in addition to a decrease in co2 content of interior waters

complementary constraints from carbon 13c and nitrogen 15n isotopes on the glacial ocean s soft tissue biological pump a three dimensional process based model of the ocean s carbon and nitrogen cycles including 13c and 15n isotopes is used to explore effects of idealized changes in the soft tissue biological pump results are presented from one preindustrial control run pictrl and six simulations of the last glacial maximum lgm with increasing values of the spatially constant maximum phytoplankton growth rate max which accelerates biological nutrient utilization mimicking iron fertilization the default lgm simulation without increasing max and with a shallower and weaker atlantic meridional overturning circulation and increased sea ice cover leads to 280 pg more respired organic carbon corg storage in the deep ocean with respect to pictrl dissolved oxygen concentrations in the colder glacial thermocline increase which reduces water column denitrification and with delay nitrogen fixation thus increasing the ocean s fixed nitrogen inventory and decreasing 15nno3 almost everywhere this simulation already fits sediment reconstructions of carbon and nitrogen isotopes relatively well but it overestimates deep ocean 13cdic and underestimates 15nno3 at high latitudes increasing max enhances corg and lowers deep ocean 13cdic improving the agreement with sediment data in the model s antarctic and north pacific oceans modest increases in max result in higher 15nno3 due to enhanced local nutrient utilization improving the agreement with reconstructions there models with moderately increased max fit both isotope data best whereas large increases in nutrient utilization are inconsistent with nitrogen isotopes although they still fit the carbon isotopes reasonably well the best fitting models reproduce major features of the glacial 13cdic 15n and oxygen reconstructions while simulating increased corg by 510 670 pg compared with the preindustrial ocean these results are consistent with the idea that the soft tissue pump was more efficient during the lgm both circulation and biological nutrient utilization could contribute however these conclusions are preliminary given our idealized experiments which do not consider changes in benthic denitrification and spatially inhomogenous changes in aeolian iron fluxes the analysis illustrates interactions between the carbon and nitrogen cycles as well as the complementary constraints provided by their isotopes whereas carbon isotopes are sensitive to circulation changes and indicate well the three dimensional corg distribution nitrogen isotopes are more sensitive to biological nutrient utilization

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

enhanced carbon dioxide outgassing from the eastern equatorial atlantic during the last glacial biological productivity and carbon export in the equatorial atlantic are thought to have been dramatically higher during the last glacial period than during the holocene here we reconstruct the ph and co2 content of surface waters from the eastern equatorial atlantic ocean over the past 30 k y using the boron isotope composition of globigerinoides ruber a mixed layer dwelling planktic foraminifera our new record combined with previously published data indicates that during the last glacial in contrast to today a strong west to east gradient existed in the extent of air sea equilibrium with respect to pco2 pco2 with the eastern equatorial atlantic acting as a significant source of co2 100 atm while the western atlantic remained close to equilibrium 25 atm this pattern suggests that a fivefold increase in the upwelling rate of deeper waters drove increased atlantic productivity and large scale regional cooling during the last glacial but the higher than modern pco2 in the east indicates that export production did not keep up with enhanced upwelling of nutrients however the downstream decline of pco2 provides evidence that the unused nutrients from the east were eventually used for biologic carbon export thereby effectively negating the impact of changes in upwelling on atmospheric co2 levels our findings indicate that the equatorial atlantic exerted a minimal role in contributing to lower glacial age atmospheric co2

climate and marine carbon cycle response to changes in the strength of the southern hemispheric westerlies 1 it has been previously suggested that changes in the strength and position of the southern hemisphere westerlies could be a key contributor to glacial interglacial atmospheric co2 variations to test this hypothesis we perform a series of sensitivity experiments using an earth system model of intermediate complexity a strengthening of the climatological mean surface winds over the southern ocean induces stronger upwelling and increases the formation of antarctic bottom water enhanced ekman pumping brings more dissolved inorganic carbon dic rich waters to the surface however the stronger upwelling also supplies more nutrients to the surface thereby enhancing marine export production in the southern hemisphere and decreasing the dic content in the euphotic zone the net response is a small atmospheric co2 increase 5 ppmv compared to the full glacial interglacial co2 amplitude of 90 ppmv roughly the opposite results are obtained for a weakening of the southern hemisphere westerly winds

constraint of the co2 rise by new atmospheric carbon isotopic measurements during the last deglaciation 1 the causes of the 80 ppmv increase of atmospheric carbon dioxide co2 during the last glacial interglacial climatic transition remain debated we analyzed the parallel evolution of co2 and its stable carbon isotopic ratio 13co2 in the european project for ice coring in antarctica epica dome c ice core to bring additional constraints agreeing well but largely improving the taylor dome ice core record of lower resolution our 13co2 record is characterized by a w shape with two negative 13co2 excursions of 0 5 during heinrich 1 and younger dryas events bracketing a positive 13co2 peak during the bolling allerod warm period the comparison with marine records and the outputs of two c cycle box models suggest that changes in southern ocean ventilation drove most of the co2 increase with additional contributions from marine productivity changes on the initial co2 rise and 13co2 decline and from rapid vegetation buildup during the co2 plateau of the bolling allerod

contribution of asian dust and volcanic material to the western philippine sea over the last 220 kyr as inferred from grain size and sr nd isotopes asian dust and volcanogenic materials are two major components in the northwestern pacific quantitatively distinguishing them and estimating their mass accumulation rates mars are very important for understanding regional and global climate change here we present the grain size composition of detrital sediments and the radiogenic strontium sr and neodymium nd isotopic compositions of different grain size fractions of detrital sediments that were recovered from the western philippine sea these new records show that the different grain size distributions can be associated with 1 asian dust from the western and central chinese deserts and chinese loess and 2 volcanogenic materials that were derived from the luzon islands the mars of this asian dust and volcanic materials are obtained by using weibull function fitting the mars of asian dust and volcanic materials are coupled with the glacial interglacial cycle these values are found to have been higher and more variable during the glacial period than during the interglacial period we argue that the strengthening aridity of the asian continent which is connected to solar insolation and ice volume variations from orbital eccentricity constitutes an important mechanism that drives the high mars of glacial dust in the western philippine sea the internal positive feedback of dust may be another important mechanism the significant increase in volcanic material during the glacial period was caused by sea level changes which were driven by the ice volume and solar insolation at high latitudes and by strengthened precipitation from the el nino southern oscillation enso which is driven by orbital eccentricity and precession cycles on the luzon islands

opposing authigenic controls on the isotopic signature of dissolved iron in hydrothermal plumes iron is a scarce but essential micronutrient in the oceans that limits primary productivity in many regions of the surface ocean the mechanisms and rates of fe supply to the ocean interior are still poorly understood and quantified iron isotope ratios of different fe pools can potentially be used to trace sources and sinks of the global fe biogeochemical cycle if these boundary fluxes have distinct signatures seafloor hydrothermal vents emit metal rich fluids from mid ocean ridges into the deep ocean iron isotope ratios have the potential to be used to trace the input of hydrothermal dissolved iron to the oceans if the local controls on the fractionation of fe isotopes during plume dispersal in the deep ocean are understood in this study we assess the behaviour of fe isotopes in a southern ocean hydrothermal plume using a sampling program of total dissolvable fe tdfe and dissolved fe dfe we demonstrate that 56fe values of dfe 56dfe within the hydrothermal plume change dramatically during early plume dispersal ranging from 2 39 0 05 to 0 13 0 06 2 sd the isotopic composition of tdfe 56tdfe was consistently heavier than dfe values ranging from 0 31 0 03 to 0 78 0 05 consistent with fe oxyhydroxide precipitation as the plume samples age the dfe present in the hydrothermal plume includes stabilised dfe species with potential to be transported to the deep ocean we estimate that stable dfe exported from the plume will have a 56fe of 0 28 0 17 further we show that the proportion of authigenic iron sulfide and iron oxyhydroxide minerals precipitating in the buoyant plume exert opposing controls on the resultant isotope composition of dissolved fe passed into the neutrally buoyant plume we show that such controls yield variable dissolved fe isotope signatures under the authigenic conditions reported from modern vent sites elsewhere and so ought to be considered during iron isotope reconstructions of past hydrothermalism from ocean sediment records

internal tides and vertical mixing over the kerguelen plateau within the context of the natural iron fertilization study keops time series measurements of ctd and ladcp profiles at a site 50 6 s 72 e 528 m coinciding with an annual phytoplankton bloom over the kerguelen plateau were made during the january february 2005 keops cruise an important activity of highly nonlinear semidiurnal internal tides having peak to peak isopycnal displacements of up to 80 m is identified these internal tides appear to be a principal agent for promoting elevated vertical mixing indispensable for upward transfer of iron within the seasonal thermocline we estimate local vertical eddy diffusivities of the order of 4 10 4 m2 s 1 using a thorpe scale analysis although this estimate is higher by an order of magnitude than the canonical value o 0 1 10 4 m2 s 1 in the open ocean away from boundaries it is consistent with nonlinear internal wave wave interaction theories as verified by independent diffusivity estimates using the vertical wavenumber spectral methods for shear and strain it is also suggested that the general ocean circulation may play an important role in preconditioning the bloom in that the relatively sluggish circulation over the shallow plateau compared to the much more dynamic neighbouring deep ocean may foster the bloom s observed annual recurrence over the plateau

the contrasting biogeochemistry of iron and manganese in the pacific ocean abstract vertical and horizontal distributions of dissolved and suspended particulate fe and mn and vertical fluxes of these metals obtained with sediment traps were determined throughout the pacific ocean in general dissolved fe is low in surface and deep waters 0 1 to 0 7 nmol kg with maxima associated with the intermediate depth oxygen minimum zone 2 0 to 6 6 nmol kg vertical distributions of dissolved mn are similar to previous reports exhibiting a surface maximum a subsurface minimum a mn maximum layer coincident with the oxygen minimum zone and lowest values in deep waters near shore removal processes are more intense for dissolved fe than for dissolved mn dissolved mn in the surface mixed layer remains elevated much farther offshore than dissolved fe elevated near surface dissolved mn concentrations occur in the north pacific equatorial current suggesting transport from the eastern boundary near surface mixed layer dissolved mn concentrations are higher in the north pacific gyre reflecting enhanced northern hemisphere aeolian sources residence time estimates for the settling of refractory paniculate fe and mn from the upper water column are 62 220 days fe and 105 235 days mn in contrast residence times for the scavenging of dissolved fe and mn are 2 13 years fe and 3 74 years mn scavenging residence times for dissolved mn based on horizontal mixing in the surface mixed layer of the northeast pacific are 0 4 years nearshore to 19 years 1000 km offshore there is no evidence for in situ fe redox dissolution within sub oxic waters in the eastern tropical north pacific dissolved fe appeared to be controlled by dissolution from sub oxic sediments with oxidative scavenging in the water column or upper sediment layers however in situ mn dissolution within the oxygen minimum zone was evident

a review of the australian new zealand sector of the southern ocean over the last 30ka aus intimate project the australia new zealand region of the southern ocean is influenced by several of the major global water masses of the oceans and is the prime entry point for cold deep waters into the pacific basin during the last glacial there was increased sea ice extent around antarctica as far north as 55 s as well as increased iceberg presence inferred from ice rafted debris evidence from microfossil assemblages suggests that sea surface temperatures sst were up to 7 c cooler consistent with recent estimates of cooling for new zealand derived from glacier modelling and other terrestrial proxies the subtropical front stf subantarctic front saf and polar front pf had migrated north except where the position of the fronts were controlled bathymetrically despite the potential for iron fertilisation by increased dust input into the ocean during the glacial there is limited evidence for higher total biological productivity in the pacific sector of the southern ocean the altered oceanic circulation during the glacial also decreased nutrients in the surface waters and affected the outgassing of co 2 this contributed to an increased storage of co 2 in the deep waters and lowering of the carbonate lysocline during the deglaciation sea ice retreat and sst increased rapidly at 18 ka roughly synchronous with the reinvigoration of deep water circulation in the southern ocean and the release of co 2 stored in the deep waters the gradient in carbon isotopes 13 o benthic between antarctic intermediate water aaiw and lower circumpolar deep water lcdw was greatest at the start of the deglaciation suggesting that the aaiw ventilation preceded lcdw ventilation or there was a significant change in air sea fractionation of 13 o benthic there was a slight enrichment in 18 o planktic decrease in ssts and a reduction in intermediate and deep water circulation between 14 and 12 5 ka bp during the antarctic cold reversal acr coincident with glacier advances in the new zealand southern alps and other terrestrial records of cooling following the acr there was a second more minor release of deep water co 2 most likely related to reinvigoration of north atlantic deep water nadw from 10 ka onwards the modern intermediate and deep water circulation was established air temperatures and ssts reached a maximum in the early holocene with the stf located at its most southerly position and there was a widespread retreat of antarctic ice sheets to their modern position a decline to modern sst and air temperatures in the mid to late holocene followed while millennial cycles overprinted on the sst and 18 o planktic records may be the result of subtle changes in the position and strength of the westerly winds during the holocene

on the late pleistocene ocean geochemistry and circulation a box model of the atmosphere and ocean was developed to investigate how geochemical distributions extant during the late pleistocene may have come about the model simulates the regional distribution of calcium carbonate dissolution as well as the chemical oceanography and atmospheric co2 13c and radiocarbon if the downward biological flux of particulate carbon increases by a factor of 2 to 3 in the antarctic and if this increase is combined with a relative increase of the atlantic sector antarctic bottom water aabw versus north atlantic deep water nadw source ratio from 1 3 to about 2 1 then the model predicts several changes that seem to be recorded in the sedimentary record as follows 1 a global redistribution of nutrients and 12c from the intermediate to deep water takes place with the atlantic intermediate water phosphate decreasing 0 6 mole kg 1 and the 13c increasing 0 3 to 0 5 2 the dissolved oxygen level of the deep sea is reduced from an average of about 180 to 70 mole kg 1 but the intermediate water oxygen declines only a small amount 3 the decrease in intermediate water nutrient concentration results in lower average organic carbon and calcium carbonate production in the warm surface ocean 4 the atmospheric co2 decreases by 90 to 110 ppm 5 initially a global increase in calcium carbonate dissolution occurs which is followed by a relaxation toward better preservation than exists for the present ocean in the model in this paper the reduction of nadw by itself does not produce these effects rather the nutrient decrease that does occur is found mostly in north pacific intermediate water and the model atmospheric co2 decrease is only 10 to 30 ppm it is observed that 92 of the atmospheric co2 change takes place according to a 200 year time constant in the model this corresponds to the response time of the upper ocean and atmosphere to a change in the stationary state atmospheric pco2 thus according to this model the time lag between the nutrient based cause and the atmospheric co2 response is not expected to be particularly large

deep sea benthic foraminifera and biogenic opal glacial to postglacial productivity changes in the western equatorial pacific the accumulation rate of benthic foraminifera in deep sea sediments is strongly correlated with the productivity of the surface ocean core tops from diverse deep sea settings straddling different export production levels are used in this study for the calibration between the organic carbon flux to the seafloor jsf flux and the benthic foraminifera accumulation rate bfar the correlation can be used to reconstruct organic carbon flux to the seafloor in the past and hence the productivity of past oceans these results are compared with the accumulation rates of carbonate and biogenic opal in the sediments it is found that biogenic opal is more sensitive to productivity changes in the modern ocean than is carbonate the appropriate equations are derived for the equatorial pacific using core material fromeurydice erdc indomed inmd andpleiades plds expeditions these equations are then applied to two selected time horizons in sediments from the ontong java plateau a western equatorial pacific pelagic depth transect the last transition lt and the last glacial lg it is found that productivity was higher during the last glacial relative to the late holocene by a factor between 1 6 and 2 during the last transition productivity was intermediate between glacial and recent values we do not see any corresponding increase in the rates of accumulation of carbonate or biogenic opal during the last glacial this observation questions the importance of ocean productivity as the main controlling factor of carbonate and biogenic opal accumulation rates back through geological time

glacial interglacial co2 change the iron hypothesis several explanations for the 200 to 280 ppm glacial interglacial change in atmospheric co2 concentrations deal with variations in southern ocean phytoplankton productivity and the related use or nonuse of major plant nutrients an hypothesis is presented herein in which arguments are made that new productivity in today s southern ocean 7 4 1013g yr 1 is limited by iron deficiency and hence the phytoplankton are unable to take advantage of the excess surface nitrate phosphate that if used could result in total southern ocean new production of 2 3 1015 g c yr 1 as a consequence of fe limited new productivity holocene interglacial co2 levels preindustrial are as high as they were during the last interglacial 280 ppm in contrast atmospheric dust fe supplies were 50 times higher during the last glacial maximum lgm because of this fe enrichment phytoplankton growth may have been greatly enhanced larger amounts of upwelled nutrients may have been used and the resulting stimulation of new productivity may have contributed to the lgm drawdown of atmospheric co2 to levels of less than 200 ppm background information and arguments in support of this hypothesis are presented

iron isotope composition of the bulk waters and sediments from the amazon river basin abstract the present study provides iron concentrations and isotopic compositions determined by multi collector inductively coupled plasma mass spectrometry mc icp ms along with key chemical mineralogical and physical properties of 35 representative bulk unfiltered waters and bulk sediments from the amazon river basin these samples from the amazon river five of its main tributaries the solimoes negro madeira tapajos and trombetas rivers and four sub tributaries the purus jau ucayali and napo rivers were essentially collected during seven field missions conducted for over two years these encompassed the centennial flood of may 2009 and the exceptional low water stage of september october 2010 thereby providing the most extreme hydrological situations that have been recorded over the last hundred years while the data confirmed massive losses of iron up to 19 000 tons day ca 50 of the amazon river bulk water budget in the solimoes and negro rivers mixing zone the fe isotope signatures of these bulk waters behaved conservatively this property allows the use of bulk water fe isotope signature to track iron sources and explain such isotopic signature in terms of simple mixing unfiltered samples from the organic rich black water rivers present light 57 fe relative to the average continental crust composition this contrasts with the composition of the bulk white waters carrying a high mineral suspended load that have 57 fe values undistinguishable from the crustal isotopic signature 0 1 relative to irmm 14 this observation indicates that the fe isotopic composition represents a reliable direct tracer of the iron speciation and therefore of the host phases of iron in its sources specifically the white water 57 fe most likely trace the signatures of igneous and sedimentary sources as well as of their lateritic soil minerals while the bulk black water 57 fe track a preferential release of fe that has gone through a reduction step in the organic rich horizons of tropical podzols as a result of the biological activity this study shows that the total iron transferred by the amazon river represents between 5 and 30 of the world s ocean fe input by rivers and this amazon bulk water iron displays an isotopic composition indistinguishable from that of the average continental crust

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

global variations of surface ocean productivity in low and mid latitudes influence on co2 reservoirs of the deep ocean and atmosphere during the last 21 000 years based on detailed reconstructions of global distribution patterns both paleoproductivity and the benthic 13c record of co2 which is dissolved in the deep ocean strongly differed between the last glacial maximum and the holocene with the onset of termination i about 15 000 years ago the new export production of low and mid latitude upwelling cells started to decline by more than 2 4 gt carbon year this reduction is regarded as a main factor leading to both the simultaneous rise in atmospheric co2 as recorded in ice cores and with a slight delay of more than 1000 years to a large scale gradual co2 depletion of the deep ocean by about 650 gt c this estimate is based on an average increase in benthic 13c by 0 4 0 5 the decrease in new production also matches a clear 13c depletion of organic matter possibly recording an end of extreme nutrient utilization in upwelling cells as shown by sarnthein et al 1987 the productivity reversal appears to be triggered by a rapid reduction in the strength of meridional trades which in turn was linked via a shrinking extent of sea ice to a massive increase in high latitude insolation i e to orbital forcing as primary cause

origin of basal dolomitic claystone in the marsili basin tyrrhenian sea abstract red brown dolomitic claystones overlay the marsili basin basaltic basement at odp site 650 sequential leaching experiments reveal that most of the elements considered to have a hydrothermal or hydrogenous origin in a marine environment such as fe cu zn pb co ni are present mainly in the aluminosilicate fraction of the dolomitic claystones their vertical distribution content and partitioning chemistry of trace elements and ree patterns suggest enhanced terrigenous input during dolomite formation but no significant hydrothermal influence from the underlying basaltic basement positive correlations in the c and o isotopes in the dolomites reflect complex conditions during the dolomitization the stable isotopes can be controlled in part by temperature variations during the dolomitization majority of the samples however form a trend that is steeper than expected for only temperature control on the c and o isotopes the latter indicates possible isotopic heterogeneity in the proto carbonate that can be related to arid climatic conditions during the formation of the basal dolomitic claystones in addition the dolostones stable isotopic characteristics can be influenced by diagenetic release of heavier 18o from clay dehydration and or alteration of siliciclastic material strontium and pb isotopic data reveal that the non carbonate fraction the dye of the dolomitic claystones is controlled by saharan dust 75 80 and by material with isotopic characteristics similar to the aeolian arc volcanoes 20 25 the non carbonate fraction of the calcareous ooze overlying the dolomitic claystones has a sr and pb isotopic composition identical to that of the dolomitic claystones indicating that no change in the input sources to the sedimentary basin occurred during and after the dolomitization event combination of climato tectonic factors most probably resulted in suitable conditions for dolomitization in the marsili and the nearby vavilov basins the basal dolomitic claystone sequence was formed at the initiation of the opening of the marsili basin 2 ma which coincided with the consecutive glacial stage the glaciation caused arid climate and enhanced evaporation that possibly contributed to the stable isotope variations in the proto carbonate the conductive cooling of the young lithosphere produced high heat flow in the region causing low temperature passive convection of pore waters in the basal calcareous sediment we suggest that this pumping process was the major dolomitization mechanism since it is capable of driving large volumes of seawater the source of mg2 through the sediment the red brown hue of the dolomitic claystones is terrigenous contribution of the glacially induced high eolian influx and was not hydrothermally derived from the underlying basaltic basement the detailed geochemical investigation of the basal dolomitic sequence indicates that the dolomitization was most probably related to complex tectono climatic conditions set by the initial opening stages of the marsili basin and glaciation

sedimentary record of the mid pleistocene climate transition in the southeastern south atlantic odp site 1090 abstract one important goal of leg 177 of the ocean drilling program odp was to explore the nature of the mid pleistocene climate transition mpt on the southern hemisphere a suitable mpt record was encountered at site 1090 in the southeastern south atlantic where a 44 m thick sequence of quaternary diatom bearing foraminiferal muds and oozes was recovered on the agulhas ridge environmental responses to the mpt comprised changes in terrestrial climate biological productivity and regional ocean circulation as inferred from compositional sediment data and clay mineralogy a shift towards more arid conditions occurred between 900 and 800 ka in southern africa changes in palaeoceanography already started earlier since 1150 ka northward displacements of the polar front appeared during glacial periods and shifted the area of dominant diatom deposition towards site 1090 likewise glacial interglacial contrasts in regional conveyor circulation strengthened after 1200 ka and became most severe after 650 ka however while changes in regional conveyor circulation likely responded in tune with global ice volume changes and show the onset of 100 kyr cycles after 1200 ka an unusual 130 kyr pattern characterises the pattern of frontal movements between 1200 ka and 650 ka probably in response to imperfect adaptation of regional climate to the global 100 kyr climate cycles

eolian dust input to the subarctic north pacific eolian dust is a significant source of iron and other nutrients that are essential for the health of marine ecosystems and potentially a controlling factor of the high nutrient low chlorophyll status of the subarctic north pacific we map the spatial distribution of dust input using three different geochemical tracers of eolian dust 4he 232th and rare earth elements in combination with grain size distribution data from a set of core top sediments covering the entire subarctic north pacific using the suite of geochemical proxies to fingerprint different lithogenic components we deconvolve eolian dust input from other lithogenic inputs such as volcanic ash ice rafted debris riverine and hemipelagic input while the open ocean sites far away from the volcanic arcs are dominantly composed of pure eolian dust lithogenic components other than eolian dust play a more crucial role along the arcs in sites dominated by dust eolian dust input appears to be characterized by a nearly uniform grain size mode at 4 m applying the 230th normalization technique our proxies yield a consistent pattern of uniform dust fluxes of 1 2 g m2 yr across the subarctic north pacific elevated eolian dust fluxes of 2 4 g m2 yr characterize the westernmost region off japan and the southern kurile islands south of 45 n and west of 165 e along the main pathway of the westerly winds the core top based dust flux reconstruction is consistent with recent estimates based on dissolved thorium isotope concentrations in seawater from the subarctic north pacific the dust flux pattern compares well with state of the art dust model predictions in the western and central subarctic north pacific but we find that dust fluxes are higher than modeled fluxes by 0 5 1 g m2 yr in the northwest northeast and eastern subarctic north pacific our results provide an important benchmark for biogeochemical models and a robust approach for downcore studies testing dust induced iron fertilization of past changes in biological productivity in the subarctic north pacific

a critical review of marine sedimentaryδ13corg pco2 estimates new palaeorecords from the south china sea and a revisit of other low latitude δ13corg pco2 records in an attempt to understand better the local biogeochemistry of the south china sea scs and to unravel the contribution of this marginal low latitude basin to changes in atmospheric co2 concentrations we analyzed the carbon isotopic composition of organic matter 13corg in four sediment cores from throughout the scs covering the last 220 kyr higher values around 19 5 to 20 5 mark glacial stages while lower values around 21 to 22 5 are characteristic of interglacials following well established procedures the 13corg records are converted to local pco2 estimates on the basis of these and other low latitude 13corg pco2 estimates from the literature we present a critical evaluation of the use of 13c of bulk sedimentary organic matter to hindcast past changes in local co2 aq three crucial pitfalls are identified 1 given the present inability to quantify precisely the time varying amount of terrigenous corg input to marine sediments absolute values of pco2 estimates based on bulk sedimentary corg are questionable 2 none of the low latitude sedimentary 13corg pco2 records shows the expected correlation between temporal changes in upwelling intensity and co2 estimates most likely due to the antagonistic influences of co2 aq and phytoplankton growth rate on 13corg 3 a detailed comparison of marine 13corg pco2 records with the vostok co2 record reveals significant differences in phasing specifically at the end of the last deglaciation and during the oxygen isotope stage 5 4 transition however in areas where equilibrium between oceanic and atmospheric co2 occurs for example the scs and the mediterranean the timing of changes in 13corg should agree with the co2 record from ice cores if 13corg is a reliable proxy for changes in co2 aq taken together the compilation of records presented here cautions the use of 13corg as an unambiguous tracer of dissolved molecular co2 in the surface ocean and calls for a re evaluation of the role of the low latitude ocean on temporal changes in atmospheric co2

the cause of the glacial to interglacial atmospheric co2 change a polar alkalinity hypothesis in an attempt to create a scenario for the cause of the glacial to interglacial co2 change recorded in air trapped in polar ice we call on an increase in the alkalinity of polar surface waters in this way we circumvent a major deficiency of the polar nutrient scenarios of sarmiento and toggweiler 1984 siegenthaler and wenk 1984 and knox and mcelroy 1984 namely our scenario does not require a drop in the nutrient content of polar surface waters in conformity with the demonstration by boyle 1988a b that the cadmium content of planktonic foraminifera from polar regions did not decrease from late glacial to holocene time the rise in alkalinity required by our model is a natural consequence of the demise during glacial time of north atlantic deep water as a major force in ocean circulation and of the nutrient maximum deepening of boyle 1988b rather than being original our hypothesis builds on the concept basic to the polar nutrient hypotheses namely that the co2 partial pressure in polar waters controls that for both the atmosphere and warm surface ocean it also requires the alkalinity increase in surface waters produced by boyle s nutrient deepening

the sequence of events surrounding termination ii and their implications for the cause of glacial interglacial co2 changes events surrounding termination ii as preserved in the vostok ice core provide a number of clues about the mechanisms controlling glacial to interglacial climate change antarctic temperature and the atmosphere s co2 content increased together over a period of 8000 years this increase is bounded by a drop in dust flux at its onset and by a drop in the 18o of trapped air at its finish a similar lag between dust flux and foraminiferal 18o is seen in a southern ocean marine record suggesting that the 18o in air trapped in vostok ice is a valid proxy for ice volume the synchronous change of atmospheric co2 and southern hemisphere temperature thus preceded the melting of the northern hemisphere ice sheets this observation coupled with the fact that nutrient reorganization in the north atlantic occurs with or after the sea level rise eliminates many scenarios proposed to explain the co2 rise including those which rely on sea level change conveyor related nutrient redistribution or north atlantic cooling southern ocean scenarios become the front runners but the most popular mechanism iron fertilization has two problems in explaining the co2 rise before termination ii first much of the dust demise occurs prior to the change in co2 so if iron is the villain a threshold value of its supply must be called upon above which productivity does not continue to increase second the co2 rise continues for some 4 5 kyr after the dust flux has fallen to close to zero these problems may be solved if the increased iron supply in dust caused higher rates of nitrogen fixation during the glacial periods in this case the residence time of oceanic nitrate of a few thousand years would enable decreasing productivity to be a global rather than a local phenomenon and would explain the slow rampup of atmospheric co2

the response of benthic foraminifera to productivity cycles in the eastern equatorial pacific faunal and geochemical constraints on glacial bottom water oxygen levels the stage 2 glacial maximum in eastern equatorial pacific ocean sediments is characterized by a pronounced increase in the organic carbon content which has been attributed either to increased upwelling and higher production along the equatorial divergence during the last glacial period or to enhanced preservation as a consequence of a lower concentration of dissolved o2 in glacial bottom water several lines of evidence are presented based on data from two gravity cores collected from the central panama basin which support the former interpretation first both the abundance and the size of benthic foraminifera of the genus uvigerina increase in stage 2 coincident with the increase in organic carbon concentration most probably because of the greater availability of organic detritus during the glacial period the increase in foraminiferal size and associated greater requirement of oxygen for respiration argues against the probability that oxygen was substantially depleted in the upper centimeter where uvigerina spp are thought to live second the number of meiofaunal faecal pellets increases markedly during the stage 2 maximum indicating a more populous and active infauna which again argues against oxygen depletion third there is no significant decrease in the iodine organic carbon i corg ratio in the stage 2 sediments because iodine is depleted relative to carbon in anoxic basins but enriched in association with organic matter in oxic environments the absence of a depletion in the i corg ratio in stage 2 is evidence that bottom water remained oxygen replete during the last glacial fourth molybdenum is not enriched in sediments deposited in stage 2 the presence of anoxic or dysaerobic bottom water or shallow pore waters during that time would have been recorded by the addition of mo to the sediments via coprecipitation with authigenic iron sulphides the combined faunal and geochemical data are consistent with the notion that panama basin deep waters remained oxygen replete during the last glacial maximum it is concluded that the late stage 2 carbon enrichment in the eastern equatorial pacific more probably reflects higher productivity rather than enhanced preservation

phanerozoic large igneous provinces lips heatt haline euxinic acidic thermal transgression episodes and mass extinctions abstract the phanerozoic consists of three mutually exclusive climate states icehouse greenhouse and hothouse the greenhouse is the default state representing 70 of the phanerozoic it is characterized by a weak thermal mode pole driven deep water formation with little or no continental sea ice and weakly oxic cool water sinking near the poles nitrogen limitation characterizes greenhouse oceans in which ammonium may be the dominant bioavailable form of nitrogen the steady state greenhouse default must be forced to produce either of the other two states continent continent collision produces the intense chemical weathering that draws down atmospheric co2 and results in the icehouse state that comprises 20 25 of the phanerozoic icehouses have ice caps in contact with the ocean that produce icebergs and foster sea ice formation sea ice formation fills the ocean with highly oxic phosphorus limited icewater except for a thin layer of warm surface water in the tropics of the 23 most conspicuous mass extinctions of the phanerozoic including the late ediacaran 4 are associated with ice volume related regressions and 3 are problematic we suggest that the other 16 mass extinctions occurred when greenhouse climate was forced to hothouse climate large igneous provinces lips can trigger the heatt haline euxinic acidic thermal transgression mechanism which can force greenhouse climate to a hothouse climate state the rapid voluminous co2 emissions of lips cause a series of events that result in very slow but pronounced haline mode circulation mid latitude driven deep water formation that produces warm saline bottom water at very dry hot subtropical and middle latitudes this water upwells at the poles causing warm and moist equable climate hothouse development promotes deep sea anoxia that is generated in concert with co2 buildup and warming the spread of anoxia favors reduced nitrogen over nitrate and limited iron dust curtails nitrogen fixation this leads to dominance of primary productivity by primitive green algae and or cyanobacteria progression to euxinia that reaches the photic zone severely curtails primary productivity via poisoning even as availability of usable nitrogen plummets the result is eukaryotic mass extinction we suggest that the 16 phanerozoic mass extinctions referred to above resulted at least in part from the heatt process evidence for this relationship at 11 of the most severe extinctions is convincing data sets for the other 5 are strongly suggestive of heatt related mass extinction but do not yet have enough documentation to reliably characterize them as heatt episodes

iron in ice cores from law dome a record of atmospheric iron deposition for maritime east antarctica during the holocene and last glacial maximum total dissolvable iron tdfe was measured in sections of ice cores recovered from law dome on the coast of wilkes land east antarctica these samples include ice dating from the last glacial maximum lgm the last deglaciation and the early and mid holocene as well as samples from the anthropocene that have been dated with seasonal to annual resolution combining our tdfe concentration data with estimates of the ice accumulation rate we estimate the atmospheric iron deposition for law dome and the adjacent southern ocean during these periods our results indicate that the atmospheric iron deposition flux to this region during the lgm 8 mol fe m 2 yr 1 was an order of magnitude higher than the average holocene deposition flux 0 8 mol fe m 2 yr 1 this holocene flux estimate is significantly higher than recent estimates of atmospheric iron deposition based on the analysis of iron in samples of the dome c epica ice core implying that there are significant meridional gradients in eolian iron flux to the antarctic region our data also suggest that there have been significant variations in atmospheric iron deposition to law dome and adjacent ocean waters over seasonal to decadal timescales during the past century analysis of ice samples dating from calendar years 1927 to 1928 indicates an anomalously high flux of tdfe to the law dome region amounting to around half the maximum lgm flux possibly as a result of severe drought conditions on the australian continent given that chronic iron deficiency is thought to limit phytoplankton production in much of the ocean around antarctica such large secular variations in atmospheric iron supply are likely to have had profound impacts on year to year primary production and ecosystem structure in antarctic waters

vertical budgets for organic carbon and biogenic silica in the pacific sector of the southern ocean 1996 1998 abstract during the 1996 1998 antarctic environment and southern ocean process study aesops a component of us jgofs we obtained seasonal or longer term data sets on the rates of production vertical transport remineralization and burial of particulate organic carbon poc and biogenic silica bsio2 in the southern ocean at 170 w between 55 s and 68 s the aesops data records enable us to construct vertical c and si budgets for the water column and upper sediments with all estimates derived from direct measurement of the relevant fluxes we constructed annual c and si budgets for each of four ecologically distinct zonal bands within the system for both poc and bsio2 the greatest annual delivery to the sea floor 200 and 1400 mmol m 2 yr 1 respectively and burial 6 and 160 mmol m 2 yr 1 respectively were observed in the southern antarctic circumpolar current acc between 61 5 s and 65 5 s that pattern is consistent with our observation that a diatom bloom propagated southward through the southern acc during the spring and summer of 1997 1998 following the receding ice edge and that this bloom was the main source of both poc and bsio2 in the system on an annual basis in the other zones the annual fluxes of poc and bsio2 to the sea floor ranged from 19 to 67 of those in the zone traversed by the summer diatom bloom the higher benthic fluxes of both poc and bsio2 in the southern acc imply that blooms similar to the one we observed in 1997 1998 occur commonly in the southern acc and that their high productivity signature is transmitted to the sea floor the data show preferential preservation of bsio2 over poc throughout the water column and upper seabed in the four zonal bands we consider bsio2 and poc are produced in mole ratios of 0 1 0 4 exported from the upper 100 m in ratios of 0 2 0 6 arrive at 1000 m in ratios of 1 5 4 5 reach the sea floor in ratios of 2 2 7 6 and are buried in ratios of 11 6 28 despite the preferential preservation of bsio2 accumulation of opal rich sediments beneath the acc does not result from unusually efficient preservation of siliceous material the estimated bsio2 preservation efficiency burial production ranges from 1 2 to 5 5 indistinguishable from the global average of 3 instead opal rich sediment accumulation in this region reflects very high annual rates of bsio2 production in surface waters along with very low accumulation rates of other sedimentary components e g caco3 and detrital material the observed high ratios of bsio2 production to poc production in surface waters are consistent with the known tendency for the si c ratio of diatoms to increase when fe is low if greater fe availability during the last glacial maximum permitted diatoms in the southern ocean to grow with lower more normal si c ratios export of diatom produced poc could have occurred at 2 3 times its present rate a corresponding increase in opal export or opal sediment accumulation is unlikely because silicic acid is almost totally depleted north of 65 s under present conditions thus even large increases in poc production and export during glacial periods would not be reflected in the opal accumulation record

variations of terrestrial input and marine productivity in the southern ocean 48 s during the last two deglaciations various biomarkers n alkanes n alcohols and sterols have been studied in a piston core tsp 2pc taken from the southern ocean to reconstruct the paleoenvironmental changes in the subantarctic region for the last two deglaciations mass accumulation rates of terrestrial higher molecular weight n alkanes and n alcohols and marine dinosterol and brassicasterol biomarkers increased significantly at the last two glacials and stayed low during interglacial peaks early holocene and the eemian these records indicate that the enhanced atmospheric transport of continental materials and the increased marine biological productivity were synchronously linked in the southern ocean at the last two glacials this suggests that increased glacial dust inputs have relieved iron limitation in the subantarctic southern ocean these two processes however were not linked at the cooling phase from the eemian to marine isotope stage mis 5d during this period paleoproductivity may have been influenced by the latitudinal migration of the high production zone associated with the antarctic polar front

sedimentary iron records from the cape basin abstract the iron hypothesis suggests that dust derived fe delivered to the southern ocean during glacial intervals fueled primary productivity and led to co 2 drawdown clear support for a dustier glacial atmosphere comes from ice core records of dust concentrations furthermore there is unequivocal proof from open ocean fe fertilization experiments that primary productivity in the modern day southern ocean is limited by fe however substantial hemipelagic detrital sources dilute and obscure the eolian signal here we present records of fe concentrations total and reducible and fe fluxes to highlight the importance of hemipelagic fe sources to the cape basin we illustrate that on average only 7 of the fe flux to site 1089 can be accounted for by particle settling indicating that redistribution by bottom currents accounts for an order of magnitude more fe than particulate scavenging processes distribution by surface currents or eolian deposition we also find that on average only 7 of the fe content is easily reducible furthermore we speculate that a significant source of dissolved fe to the bottom waters may come from re suspended bottom sediments

sea ice diatom contributions to holocene nutrient utilization in east antarctica combined high resolution holocene 30sidiat and 13cdiat paleorecords are presented from theseasonal ice zone east antarctica both data sets re ect periods of increased nutrient utilization by diatomsduring the hypsithermal period circa 7800 to 3500 calendar years cal years b p coincident with a higherabundance of open water diatom species fragilariopsis kerguelensis increased biogenic silica productivity bsi and higher regional summer temperatures the neoglacial period after circa 3500 cal years b p isre ected by an increase in sea ice indicative species fragilariopsis curta and fragilariopsis cylindrus upto50 along with a decrease in bsi and 13cdiat 18 to 23 however over this period 30sidiatdata show an increasing trend to some of the highest values in the holocene record average of 0 43 competing hypotheses are discussed to account for the decoupling trend in utilization proxies including ironfertilization species dependent fractionation effects and diatom habitats based on mass balance calculations we highlight that diatom species derived from the semi enclosed sea ice environment may have a confoundingeffect upon 30sidowncorecompositions of the seasonal sea ice zone a diatom composition with approximately28 of biogenic silica derived from the sea ice environment diat si can account for the increased averagecompo sition of 30sidiatduring the neoglacial these data highlight the signi cant role sea ice diatoms can playwith relation to their export in sediment records which has implications on productivity reconstructions fromthe seasonal ice zone

plio pleistocene increase of erosion rates in mountain belts in response to climate change here we review an ensemble of observations that point towards a global increase of erosion rates in regions of elevated mountain belts or otherwise high relief since the onset of northern hemisphere glaciation about 2 3 ma during that period of earth s history atmospheric co2 concentrations may have dropped and global climate cooled and evolved towards high amplitude oscillating conditions that are associated with the waxing and waning of continental ice sheets in the northern hemisphere we argue for a correlation between climate change and increased erosion rates and relief production which we attribute to some combination of the observed cooling onset of glaciation and climatic oscillation at orbital timescales in our view glacial erosion played a major role and is driven by the global cooling furthermore analyses of the sedimentary fluxes of many mountain belts show peaks of erosion during the transitions between glacial and inter glacial periods suggesting that the variable climatic conditions have also played a role

imaging and sampling beneath free drifting icebergs with a remotely operated vehicle abstract a commercially available small less than 100 kg remotely operated vehicle rov was modified to image and sample the marine ecosystem surrounding free drifting icebergs east of the antarctic peninsula during three field expeditions in 2005 2008 and 2009 modifications included fitting the vehicle with an accessory tool sled additional thrusters flotation and significant changes to internal wiring to support a wide array of sensors and samplers the rov was re configured aboard the r v nathaniel b palmer to perform either general exploration and biological sampling bio dives or water sampling chemistry dives in situ sensors and a suction sampler were used for bio dives while a suction pump and hose were fastened along the full length of the rov tether to enable continuous water sampling adjacent to each iceberg during chemistry dives details of the rov system are presented along with a discussion of the 18 dives that explored the sides and bottoms of six different icebergs during the 2009 field expedition

atmospheric deposition of glacial iron in the gulf of alaska impacted by the position of the aleutian low our understanding of glacial flour dust storm delivery of iron to the gulf of alaska goa is limited here we interpret concurrent time series satellite meteorological and aerosol geochemical data from the goa to examine how interannual variability in regional weather patterns impacts offshore aerosol glacial fe deposition in 2011 when a northerly aleutian low al was persistent during fall dust emission was suppressed and highly intermittent due to prevalent wet conditions low winds and a deep early season snowpack conversely in 2012 frequent and prolonged fall dust storms and high offshore glacial fe transport were driven by dry conditions and strong offshore winds generated by persistent strong high pressure over the alaskan interior and bering sea and a southerly al twenty five fold interannual variability in regional offshore glacial aerosol fe deposition indicates that glacial dust s impact on goa nutrient budgets is highly dynamic and particularly sensitive to regional climate forcing

glacial interglacial dust and export production records from the southern indian ocean abstract we present 230th normalized dust and export production fluxes for two contrasted marine sediment cores spanning the antarctic polar front close to the kerguelen plateau in the southern indian ocean covering the last glacial cycle we report glacial lithogenic fluxes comparable to the south atlantic and higher than in the south pacific sectors of the southern ocean structural and temporal discrepancies with dust reconstructions from antarctic ice cores and the atlantic and pacific sectors of the subantarctic zone saz point towards southern africa and or the kerguelen plateau as an additional source of lithogenic material to the southern indian ocean during the last ice age in the saz export production proxies respond to iron fe fertilization with total organic carbon toc fluxes as high as those previously reported from the atlantic sector of the southern ocean however the correlation between export production and dust proxies is weaker than in the other sectors and shows a muted response of export production during peak glacials we hypothesize that this muted response may be related to macronutrient co limitation imposed on phytoplankton growth possibly induced by a northward displacement of wind driven upwelling and or the polar frontal system during peak glacials the antarctic zone az record depicts the typical pattern of enhanced export production during interglacials and comparatively low productivity during glacials suggesting a decrease in the supply of macronutrients to the az surface during ice ages compared to warm periods as previously proposed however a muted response of opal fluxes during marine isotope stage mis 5e argues for a southward migration of the frontal system during warmer mis 5e possibly causing silicic acid co limitation at this site these results illustrate the important role of fe fertilization and changes in wind driven upwelling intensities in modulating the strength and efficiency of the biological carbon pump in the southern ocean but also highlight the potential role of frontal movements in explaining export production variability at sites located close to the antarctic circumpolar current acc fronts overall our new datasets provide new insights on the regional differences in dust and export production patterns that need to be considered in order to evaluate the efficiency of carbon sequestration in the different sectors of the southern ocean during ice ages

origin of magnetic mineral concentration variation in the southern ocean 1 in the southern ocean magnetic mineral concentration increases in glacial periods the variation pattern closely resembles eolian dust flux records from antarctic ice cores but the cause of the linkage remains unclear as the dust flux is too small for the source of terrigenous materials in the southern ocean we have conducted an environmental magnetic study of late pleistocene sediments from the south indian ocean to investigate the origin of the magnetic concentration changes biogenic magnetites can be detected using the characteristics of almost no magnetostatic interactions and narrow coercivity distribution reflecting occurrence of single domain magnetites in a chain we interpret that a non interacting component on first order reversal curve diagrams and low coercivity components with small dispersion from isothermal remanent magnetization irm component analyses represent biogenic magnetites and that the interacting and middle coercivity components represent terrigenous maghemites the ratio of anhysteretic remanent magnetization susceptibility to saturation irm reflects relative abundance of the biogenic and terrigenous components it was revealed that biogenic magnetites are a dominant constituent of the magnetic minerals in glacials the abundance of both biogenic and terrigenous components increased with increased proportions of the latter increased ocean productivity in glacials is suggested from increased proportions of biogenic magnetites with elongated morphologies indicative of less oxic conditions and increased sedimentation rates these observations suggest that the increased magnetic concentration in glacials in the southern ocean may be explained by iron fertilization the production of biogenic magnetites was enhanced associated with increased ocean productivity which was fueled by increased eolian dust flux

atmospheric iron fluxes over the last deglaciation climatic implications a decrease in the micronutrient iron supply to the southern ocean is widely believed to be involved in the atmospheric co2 increase during the last deglaciation here we report the first record of atmospheric iron fluxes as determined in 166 samples of the dome c ice core and covering the last glacial interglacial transition 22 9 kyr b p it reveals a decrease in fallout flux from 24 10 2 mg fe m 2 yr 1 during the last glacial maximum to 0 7 10 2 mg fe m 2 yr 1 at the onset of the holocene the acid leachable fraction of iron determined in our samples was the 60 of the total iron mass in glacial samples about twice the value found for holocene samples this emerging difference in iron solubility over different climatic stages provides a new insight for evaluating the iron hypothesis over glacial interglacial periods

iron isotope fractionation in a buoyant hydrothermal plume 5 s mid atlantic ridge fe isotopes are a potential tool for tracing the biogeochemical redox cycle of fe in the ocean specifically it is hypothesized that fe isotopes could enable estimation of the contributions from multiple fe sources to the dissolved fe budget an issue that has received much attention in recent years the first priority however is to understand any fe isotope fractionation processes that may occur as fe enters the ocean resulting in modification of original source compositions in this study we have investigated the fe inputs from a basalt hosted deep sea hydrothermal system and the fractionation processes that occur as the hot chemically reduced and acidic vent fluids mix with cold oxygen rich seawater the samples collected were both end member vent fluids taken from hydrothermal chimneys and rising buoyant plume samples collected directly above the same vents at 5 s mid atlantic ridge our analyzes of these samples reveal that for the particulate fe species within the buoyant plume 25 of the fe is precipitated as fe sulfides the isotope fractionation caused by the formation of these fe sulfides is fe ii fes 0 60 0 12 the source isotope composition for the buoyant plume samples collected above the red lion vents is calculated to be 0 29 0 05 this is identical to the value measured in end member vent fluids collected from the underlying tannenbaum chimney the resulting isotope compositions of the fe sulfide and fe oxyhydroxide species in this buoyant plume are 0 89 0 11 and 0 19 0 09 respectively from mass balance calculations we have been able to calculate the isotope composition of the dissolved fe fraction and hypothesize that the isotope composition of any stabilised dissolved fe species exported to the surrounding ocean may be heavier than the original vent fluid such species would be expected to travel some distance from areas of hydrothermal venting and hence contribute to not only the dissolved fe budget of the deep ocean but also it s dissolved fe isotope signature

the deglacial transition on the southeastern alaska margin meltwater input sea level rise marine productivity and sedimentary anoxia 1 oxygen isotope data from planktonic and benthic foraminifera on a high resolution age model 44 14c dates spanning 17 400 years document deglacial environmental change on the southeast alaska margin 59 33 32 n 144 9 21 w 682 m water depth surface freshening i e 18o reduction of 0 8 began at 16 650 170 cal years b p during an interval of ice proximal sedimentation likely due to freshwater input from melting glaciers a sharp transition to laminated hemipelagic sediments constrains retreat of regional outlet glaciers onto land circa 14 790 380 cal years b p abrupt warming and or freshening of the surface ocean i e additional 18o reduction of 0 9 coincides with the bolling interstade of northern europe and greenland cooling and or higher salinities returned during the allerod interval coincident with the antarctic cold reversal and continue until 11 740 200 cal years b p when onset of warming coincides with the end of the younger dryas an abrupt 1 reduction in benthic 18o at 14 250 290 cal years b p likely reflects a decrease in bottom water salinity driven by deep mixing of glacial meltwater a regional megaflood event or brine formation associated with sea ice two laminated opal rich intervals record discrete episodes of high productivity during the last deglaciation these events precisely dated here at 14 790 380 to 12 990 190 cal years b p and 11 160 130 to 10 750 220 cal years b p likely correlate to similar features observed elsewhere on the margins of the north pacific and are coeval with episodes of rapid sea level rise remobilization of iron from newly inundated continental shelves may have helped to fuel these episodes of elevated primary productivity and sedimentary anoxia

vostok ice core provides 160 000 year record of atmospheric co2 direct evidence of past atmospheric co2 changes has been extended to the past 160 000 years from the vostok ice core these changes are most notably an inherent phenomenon of change between glacial and interglacial periods besides this major 100 000 year cycle the co2 record seems to exhibit a cyclic change with a period of some 21 000 years

links between iron input and opal deposition in the pleistocene equatorial pacific ocean iron is often a limiting nutrient in ocean regions that have a constant supply of other macro nutrients and changes in iron supply over time have been linked to fluctuations in primary productivity marine sediments from the equatorial pacific ocean show that over the past million years iron input was linked to the export and burial of biogenic silica

climatic effect of southern ocean fe fertilization is the jury still out 1 one of the great puzzles in oceanography has been the reason for the existence of certain areas of the world ocean like the southern ocean and equatorial and north pacific where there is an abundance of unused macronutrients essential for phytoplankton growth such as nitrate and silicic acid de baar and boyd 2000 although physical solar insolation and ocean surface mixing and grazing regimes must play a part in controlling phytoplankton standing stocks in these so called high nitrate low chlorophyll hnlc regions martin suggested that growth limitation through insufficient availability of the micronutrient iron fe might also exert an important control martin and fitzwater 1988 furthermore he proposed that stimulation of biological productivity through increased aeolian fe delivery to the southern ocean at the height of the last ice age the last glacial maximum lgm might have led to the concurrently low levels of atmospheric co2 observed martin 1990 the ironex ii open ocean fe fertilization experiment demonstrated unequivocally the role that iron played in limiting phytoplankton growth particularly of larger diatoms in the equatorial pacific coale et al 1996 more recently a similar experiment southern ocean iron release experiment soiree was carried out in the southern ocean a region suspected to play a key role in controlling variability in the concentration of atmospheric co2 over glacial interglacial timescales knox and mcelroy 1984 here too an unambiguous response of the phytoplankton standing stock to the addition of fe was observed boyd et al 2000 however for these changes to produce a significant response in the concentration of atmospheric co2 there must also be an increase in the export of carbon to the deep ocean it is here that our understanding of biogeochemical cycling in the southern ocean and in particular of the potential relationships between iron supply and climate now appears to falter

last glacial loess in the conterminous usa the conterminous united states contains an extensive and generally well studied record of last glacial loess the loess occurs in diverse physiographic provinces and under a wide range of climatic and ecological conditions both glacial and non glacial loess sources are present and many properties of the loess vary systematically with distance from loess sources united states midcontinent last glacial loess is probably the thickest in the world and our calculated mass accumulation rates mars are as high as 17 500 g m 2 yr at the bignell hill locality in nebraska and many near source localities have mars greater than 1500 g m 2 yr these mars are high relative to rates calculated in other loess provinces around the world recent models of last glacial dust sources fail to predict the extent and magnitude of dust flux from the mid continent of the united states a better understanding of linkages between climate ice sheet behaviour routing of glacial meltwater land surface processes beyond the ice margin and vegetation is needed to improve the predictive capabilities of models simulating dust flux from this region r 2003 elsevier ltd all rights reserved

quasi static eocene oligocene climate in patagonia promotes slow faunal evolution and mid cenozoic global cooling abstract new local regional climatic data were compared with floral and faunal records from central patagonia to investigate how faunas evolve in the context of local and global climates oxygen isotope compositions of mammal fossils between c 43 and 21 ma suggest a nearly constant mean annual temperature of 16 3 c consistent with leaf physiognomic and sea surface studies that imply temperatures of 16 18 c carbon isotopes in tooth enamel track atmospheric 13 c but with a positive deviation at 27 2 ma and a strong negative deviation at 21 ma combined with paleosol characteristics and reconstructed leaf area indices rlais these trends suggest aridification from 45 ma c 1200 mm yr to 43 ma c 450 mm yr quasi constant map until at least 31 ma and an increase to 800 mm yr by 21 ma comparable map through most of the sequence is consistent with relatively constant floral compositions rlai and leaf physiognomy abundance of palms reflects relatively dry adapted lineages and greater drought tolerance under higher p co2 pedogenic carbonate isotopes imply low p co2 430 300 ppmv at the initiation of the eocene oligocene climatic transition arid conditions in patagonia during the late eocene through oligocene provided dust to the southern ocean enhancing productivity of silicifiers drawdown of atmospheric co 2 and protracted global cooling as the antarctic circumpolar current formed and earth cooled wind speeds increased across patagonia providing more dust in a positive climate feedback high tooth crowns hypsodonty and ever growing teeth hypselodonty in notoungulates evolved slowly and progressively over 20 ma after initiation of relatively dry environments through natural selection in response to dust ingestion a ratchet evolutionary model may explain protracted evolution of hypsodonty in which small variations in climate or dust delivery in an otherwise static environment drive small morphological shifts that accumulate slowly over geologic time

reconstruction of paleo particulate organic carbon fluxes for the campbell plateau region of southern new zealand using the zinc content of sponge spicules 1 the zinc concentration of siliceous sponge spicules was determined from spicules recovered from four sediment cores spanning the last 160 kyr from the campbell plateau region southeast of new zealand zinc si results showed little difference between holocene and glacial aged spicules an increase in zn si was observed for core y14 where zn si peaked at about 0 6 mol mol during marine isotope stages 5a 5b to better understand the role carbon export has on sponge zn si we explored the strong relationship observed between surficial sediment particulate organic carbon poc and the zn si of sponge silica and related this to sediment trap poc flux estimates conversion of the zn si records to benthic poc fluxes suggests that there has been little change in the amount of poc reaching campbell plateau sediments over the past 30 kyr these results suggest that surface productivity over the campbell plateau has remained relatively low over the past 160 kyr and suggests that glacial productivity was not significantly higher than the present day finally this work reveals that living marine sponges appear to act as the biological equivalents of moored sediment traps recording the flux of poc to the seafloor by archiving zinc associated with sinking poc in the growing silica skeleton

iron sources and dissolved particulate interactions in the seawater of the western equatorial pacific iron isotope perspectives this work presents iron isotope data in the western equatorial pacific marine aerosols and top core margin sediments display a slightly heavy fe isotopic composition 56 fe of 0 33 0 11 2sd and 0 14 0 07 respectively samples reflecting the influence of papua new guinea runoff sepik river and rabaul volcano water are characterized by crustal values in seawater fe is mainly supplied in the particulate form and is found with a 56 fe between a0 49 and 0 34 0 07 the particulate fe seems to be brought mainly by runoff and transported across continental shelves and slopes aerosols are suspected to enrich the surface vitiaz strait waters while hydrothermal activity likely enriched new ireland waters dissolved fe isotopic ratios are found between a0 03 and 0 53 0 07 they are almost systematically heavier than the corresponding particulate fe and the difference between the signature of both phases is similar for most samples with 56 fe dfe pfe 0 27 0 25 2sd this is interpreted as an equilibrium isotopic fractionation revealing exchange fluxes between both phases the dissolved phase being heavier than the particles suggests that the exchanges result in a net nonreductive release of dissolved fe this process seems to be locally significantly more intense than fe reductive dissolution documented along reducing margins it may therefore constitute a very significant iron source to the ocean thereby influencing the actual estimation of the iron residence time and sinks the underlying processes could also apply to other elements

dissolved iron in the vicinity of the crozet islands southern ocean the annual phytoplankton bloom occurring north of the crozet plateau provides a rare opportunity to examine the hypothesis that natural iron fertilization can alleviate high nutrient low chlorophyll hnlc conditions normally associated with the southern ocean therefore during crozet natural iron bloom and export experiment crozex a large multidisciplinary study performed between november 2004 and january 2005 measurements of total dissolved iron dfe0 2 m were made on seawater from around the islands and atmospheric iron deposition estimated from rain and aerosol samples dfe concentrations were determined by flow injection analysis with n n dimethyl p phenylenediamine dihydrochloride dpd catalytic spectrophotometric detection dfe concentrations varied between 0 086 and 2 48 nm with low values in surface waters enrichment of dissolved iron 1 nm at close proximity to the islands suggests that the plateau and the associated sediments are a source of iron waters farther north also appear to be affected by this input of coastal and shelf origin although dissolved iron concentrations decrease as a function of distance to the north of the plateau with a gradient of 0 07 nm km 1 at the time of sampling using lateral and vertical diffusion coefficients derived from ra isotope profiles and also estimates of atmospheric inputs it was then possible to estimate a dfe concentration of 0 55 nm to the north of the islands prior to the bloom event which is sufficient to initiate the bloom the lateral island source being the largest component a similar situation is observed for other sub antarctic islands such as kerguelen south georgia that supply dissolved iron to their surrounding waters thus enhancing chlorophyll concentrations

contemporary glacigenic inputs to the dust cycle the importance of glacigenic dust in the earth s system during glacial periods is widely acknowledged under contemporary conditions the world s largest dust sources are in low lying hot arid regions and this is where most aeolian research is focused however the processes of dust production and emissions are still operating in cold climate regions particularly in proglacial areas this paper assesses current understanding of the relationship between glacierised landscapes and dust emissions and inputs to the global dust cycle it focuses on how elements in the glacial and aeolian geomorphic sub systems interact to determine the magnitude frequency and timing of aeolian dust emissions and on feedback mechanisms between the systems where they have been measured dust emission intensity and deposition rates in glacierised catchments are very high in some cases far exceeding those in lower latitudes however few studies span long time scales the impact of future glacier retreat on the balance between sediment supply availability and aeolian transport capacity and implications for glacigenic dust emissions is also considered this balance depends on relative spatial and temporal changes in meltwater suspended sediment concentration and wind strengths which promote dust emissions and patterns and rates of soil development and vegetation succession on recently deglaciated terrain which protect sediments from deflation retreat of the antarctic ice sheet could mean that in future glacigenic contributions to the dust cycle exceed those of non glacigenic sources in the southern hemisphere copyright 2012 john wiley sons ltd

changes in the distribution of δ13c of deep water σco2 between the last glaciation and the holocene carbon isotopic measurements on the benthic foraminiferal genus cibicidoides document that mean deep ocean 13c values were 0 46 lower during the last glacial maximum than during the late holocene the geographic distribution of 13c was altered by changes in the production rate of nutrient depleted deep water in the north atlantic during the late holocene north atlantic deep water with high 13c values and low nutrient values can be found throughout the atlantic ocean and its effects can be traced into the southern ocean where it mixes with recirculated pacific deep water during the glaciation decreased production of north atlantic deep water allowed southern ocean deep water to penetrate farther into the north atlantic and across low latitude fracture zones into the eastern atlantic mean southern ocean 13c values during the glaciation are lower than both north atlantic and pacific 13c values suggesting that production of nutrient depleted water occurred in both oceans during the glaciation enriched 13c values in shallow cores within the atlantic ocean indicate the existence of a nutrient depleted water mass above 2000 m in this ocean

dynamics of primary productivity in the northern south china sea over the past 24 000 years in this study paleoproductivity on millennial scales was precisely reconstructed from core md12 3428cq in the northern south china sea scs over the past 24 kyr based on a transfer function derived from the strong exponential negative correlation between relative abundance of florisphaera profunda fp in core top sediments and basin wide satellite based primary productivity pp in the scs to detect the potential driving mechanisms of pp correlation analyses were carried out among our pp records and other paleoenvironment parameters pp peaked during 18 15 ka in parallel with the strong east asian winter monsoon eawm from 15 ka to the early holocene a decrease in pp coincided with sea level progradation and weakening of eawm which ultimately reduced fluvial nutrient levels and wind driven upper water column mixing since the middle holocene gradually more frequent el nino southern oscillation enso events have taken place further decreasing pp by injecting oligotrophic kuroshio water masses into the northern scs associated findings conclusively indicated that the main controlling factors of pp in the northern scs have shifted from eawm glacial to enso interglacial over the past 24 kyr this article is protected by copyright all rights reserved

nutrient leakage from the north pacific to the bering sea iodp site u1341 following the onset of northern hemispheric glaciation 1 intergrated ocean drilling program expedition 323 recovered a sediment record covering the last 4 3 ma from the bering sea integrated ocean drilling program site u1341 bowers ridge 2177 m water depth to resolve pliocene pleistocene paleoenvironmental changes in this marginal basin 190 sediment samples were analyzed for their bulk element composition aluminium contents in bowers ridge sediments are variable but overall higher toward younger sediments probably related to the intensification of the northern hemispheric glaciation and increasing sea ice transport in the bering sea the gradual increase of terrigenous input is mirrored by decreasing sio2 and excess si sixs contents but the overall si enrichment of the deposits reflects continuous opal deposition since the pliocene at bowers ridge unlike in the north pacific the sixs record at site u1341 does not support a dramatic decrease in opal export following the onset of the northern hemispheric glaciation around 2 7 ma but sio2xs have higher accumulation rates up to 8 g cm2 ka between 2 6 and 1 8 ma bp during this period the major oceanic opal deposition centers shifted globally from open marine high latitude regions to upwelling areas we here discuss how the onset of north pacific stratification at 2 7 ma bp may have caused leakage of nutrient rich deep intermediate north pacific water into the bering sea via the deep kamtchatka strait leading to increased opal deposition and likely reactive organic matter export at bowers ridge as a result magnetic and geochemical records were overprinted by intensified diagenesis significantly affecting their applications as paleoceanographic proxies

size dependence of iron solubility of asian mineral dust particles 1 asian mineral dust was sampled at hokkaido northern japan in spring 2004 and 2006 iron solubility of the bulk aerosol the size segregated aerosol 0 45 4 7 m we suggest that an iron solubility of around 0 4 is typical for asian mineral dust of large particles transported to hokkaido in the high nutrient low chlorophyll region of the western subarctic north pacific near the asian continent where the mineral dust deposition is dominated by large particles the iron solubility of the mineral dust entering the ocean is around 0 4

antarctica s dry valleys a potential source of soluble iron to the southern ocean the soluble iron content and dust emission potential of sediment samples collected from the taylor valley in the mcmurdo dry valleys mdvs and sea ice in the mcmurdo sound were evaluated to determine whether inputs to the southern ocean may be sufficient to affect ocean productivity our results show that the dust generating potential from the mdvs soils are comparable to those of sediments from other major dust sources in the southern hemisphere sediments from the mdvs and sea ice are one order of magnitude richer in soluble iron than those in other dust sources in the southern hemisphere forward trajectory analyses show that the dust from the mdvs is likely to be deposited in the southern ocean these results provide evidence of the possible supply of soluble iron to the southern ocean associated with dust transport from the mdvs should climate change expand the exposed areas of the continent

atmospheric co2 forcing on glacial thermohaline circulation and climate 1 a coupled climate model study indicates the paleoclimate record of glacial thermohaline circulation thc and reversed deep sea temperature salinity t s distribution in the atlantic can be explained largely by lower glacial atmospheric co2 alone the reduced co2 leads to increased southern ocean wintertime sea ice cover and salinity increased production of dense antarctic bottom water aabw enhanced cold and saline aabw penetration into the deep north atlantic increased oceanic vertical stability and reduced north atlantic deep water nadw circulation the dominant role of co2 forcing during the glacial implies a positive feedback between the southern ocean regulated thc and the glacial global carbon cycle

dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle dust deposition and climate in the carpathian basin over an independently dated last glacial interglacial cycle

sediment delivery ratios a misaligned approach to determining sediment delivery from hillslopes correspondence to p i a kinnell school of resource environmental and heritage sciences university of canberra canberra act 2601 australia e mail peter kinnell canberra edu au considerable interest exists in the impact of land management on water quality throughout the world a large number of non point source nps pollution or water quality models exist in many cases these models use the universal soil loss equation usle wischmeier and smith 1978 or the revised version of the usle rusle renard et al 1997 to model erosion on hillslopes in conjunction with sediment delivery ratios sdrs to determine the sediment delivered from the hillslope to water bodies the sdr can be defined as the ratio of the erosion upslope of a point in the landscape to the sediment delivered from that point erosion involves detachment transport and deposition processes that operate all the time the net loss or gain of soil material depends on the balance between the rates of particle uplift and deposition in the context of modelling sediment delivery on hillslopes with respect to water quality erosion refers to the situation where there is a net loss of soil material from the soil surface and deposition to the situation where there is a net gain the use of sdrs owes its origin to the observation that using erosion predicted by the usle overestimates the amount of sediment delivered from hillslopes because sediment deposition often occurs on hillslopes and the usle does not account for deposition the usle was developed on planar surfaces and was not designed to apply to situations where there is a net gain of soil material on the area being considered however sdrs are essentially performance factors that simply relate observed or modelled amounts at the plot scale to observed amounts at a larger scale using them to predict sediment delivery from hillslopes can produce erroneous results one of the features of the usle rusle sdr approach is that the predicted amount of sediment delivered from the hillslopes varies directly with the predicted erosion for any given hillslope profile halving the erosion results in a halving of the amount of sediment delivered from the hillslope however the deposition effect results from sediment in or entering the flow exceeding the transport capacity of that flow at a point on the hillslope as a result sediment delivery is directly related to erosion if the transport capacity of the flow is not exceeded i e sdr 1 0 but it is limited by the transport capacity if erosion exceeds the capacity of the flow to transport the eroded material i e sdr 1 0 this concept is encapsulated in figure 1 and in so called process based erosion models like wepp

a 150 000 year climatic record from antarctic ice during much of the quaternary the earth s climate has undergone drastic changes most notably successive glacial and interglacial episodes the past 150 kyr includes such a climatic cycle the last interglacial the last glacial and the present holocene interglacial a new climatic time series for this period has been obtained using 18 o data from an antarctic ice core

ice core sample measurements give atmospheric co 2 content during the past 40 000 yr recent measurements1 2 on ice samples from camp century greenland 77 10 n 61 08 w byrd station antarctica 80 01 s 110 31 w and dome c 74 40 s 125 10 e suggest that during the late part of the last glaciation the atmospheric co2 concentration was significantly lower than during the holocene further investigation of this natural increase of the atmospheric co2 concentration in the past should aid our understanding of the climatic implications of the man made co2 increase since the beginning of industrialization3 here we report new and precise measurements of the co2 concentration of the air occluded in bubbles of ice samples from camp century and byrd station using a new dry extraction technique the extracted gases were analysed with an ir laser spectrometer irls samples from 22 different depths were analysed from each core the samples are distributed over a depth interval corresponding approximately to the past 40 000 yr in addition results for ice samples from selected depth horizons from a colder region north central greenland 74 37 n 39 36 w and from a warmer region dye 3 greenland 65 11 n 43 50 w are given based on these results we estimate the trend of the atmospheric co2 concentration during the past 40 000 yr

contributions from glacially derived sediment to the global iron oxyhydr oxide cycle implications for iron delivery to the oceans estimates of glacial sediment delivery to the oceans have been derived from fluxes of meltwater runoff and iceberg calving and their sediment loads the combined total 2900 tg yr 1 of the suspended sediment load in meltwaters 1400 tg yr 1 and the sediment delivered by icebergs 1500 tg yr 1 are within the range of earlier estimates high resolution microscopic observations show that suspended sediments from glacial meltwaters supraglacial and proglacial sediments and sediments in basal ice from arctic alpine and antarctic locations all contain iron oxyhydr oxide nanoparticles which are poorly crystalline typically 5 nm in diameter and which occur as single grains or aggregates that may be isolated or attached to sediment grains nanoparticles with these characteristics are potentially bioavailable a global model comparing the sources and sinks of iron present as oxyhydr oxides indicates that sediment delivered by icebergs is a significant source of iron to the open oceans beyond the continental shelf iceberg delivery of sediment containing iron as oxyhydr oxides during the last glacial maximum may have been sufficient to fertilise the increase in oceanic productivity required to drawdown atmospheric co2 to the levels observed in ice cores

ice core evidence for the extent of past atmospheric co2 change due to iron fertilisation 1 an extended high resolution ice core record of dust deposition over the past 60 ka from dome c antarctica is presented the data are in conflict with the idea that changes in aeolian iron input into the southern ocean were the major cause for the 80 ppm glacial interglacial co2 increase during the deglaciation the co2 increase shows a linear relationship with the fall of the logarithm of the nss ca2 flux a proxy for dust deposition however the very large variations in the nss ca2 flux related to the glacial antarctic warm events a1 to a4 were accompanied by small co2 variations only our data based analysis suggests that decreased southern ocean dust deposition caused at most a 20 ppm increase in co2 at the last glacial interglacial transition rapid decreases in dust deposition to the northern pacific could have been responsible for a maximum of 8 ppm in addition

quantitative estimates of asian dust input to the western philippine sea in the mid late quaternary and its potential significance for paleoenvironment we present a new high resolution multiproxy data set of sr nd isotopes rare earth element soluble iron and total organic carbon data from international marine global change study core md06 3047 located in the western philippine sea we integrate our new data with published clay mineralogy rare earth element chemistry thermocline depth and delta c 13 differences between benthic and planktonic foraminifera in order to quantitatively constrain asian dust input to the basin we explore the relationship between philippine sea and high latitude pacific eolian fluxes as well as its significance for marine productivity and atmospheric co2 during the mid late quaternary three different indices indicate that asian dust contributes between similar to 15 and similar to 50 to the detrital fraction of the sediments eolian dust flux in core md06 3047 is similar to that in the polar southern pacific sediment coherent changes for most dust flux maximum minimum indicate that dust generation in interhemispheric source areas might have a common response to climatic variation over the mid late quaternary furthermore we note relatively good coherence between asian dust input soluble iron concentration local marine productivity and even global atmospheric co2 concentration over the entire study interval this suggests that dust borne iron fertilization of marine phytoplankton might have been a periodic process operating at glacial interglacial time scales over the past 700 ka we suggest that strengthening of the biological pump in the philippine sea and elsewhere in the tropical western pacific during the mid late quaternary glacial periods may contribute to the lowering of atmospheric co2 concentrations during ice ages

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