the role of caco3 compensation in the glacial to interglacial atmospheric co2 change the only viable explanations put forth to date for the glacial to interglacial change in atmospheric co2 content suggested from measurements of the co2 content of gas extracted from ice cores involve changes in the ocean s nutrient cycles any nutrient change capable of creating the 80 atm changes in atmosphere co2 pressure suggested by the ice core results also creates significant change in the deep ocean s co3 content evidence from deep sea sediments suggests that these co3 changes are compensated on the time scale of a few thousand years by reductions or increases in amount of caco3 accumulating in deep sea sediments this compensation process has two important consequences first it significantly increases the magnitude of the co2 change per unit of nutrient forcing second it causes a delay in the response of the atmospheric co2 change while the first of these consequences is a boon to those seeking to explain the co2 change the second may prove to be a curse the ice core co2 record shows no evidence of a significant lag between the co2 response and the polar warming in any case it is important that we improve our knowledge of the magnitude and timing of the caco3 preservation events which mark the close of episodes of glaciation and of the dissolution events which mark the onset of these episodes

palaeoclimatological and chronological implications of the vostok core dust record the2 083 m vostok ice core recovered by the soviet antarctic expeditions has provided much information of climatic and environmental interest for a period covering a full glacial inter glacial cycle1 6 here we present and discuss the dust record obtained down to 2 202 m the final depth to which this core was extended in 1986 first we document the fact that major changes in aeolian deposits as recorded in the vostok core appear to be of global significance and confirm the existence of a link between high latitude aeolian deposits and the earth s orbital parameters7 8 second we propose atmospheric dust as a strati graphic marker to compare timing with other records of palaeocli mate and use the magnetic susceptibility profile measured along the rc11 120 indian ocean core9 for this purpose assuming that major dust events correspond to common aeolian inputs this approach indicates that the vostok and marine records were roughly in phase at the previous glacial interglacial transition

evidence from diatom bound nitrogen isotopes for subarctic pacific stratification during the last ice age and a link to north pacific denitrification changes higher diatom bound d 15 n 70 wt lower opal content and 1200 ppm lower biogenic barium taken together and with constraints on sediment accumulation rate these results suggest a reduced supply of nitrate to the surface due to stronger stratification of the upper water column of the bering sea during glacial times with more complete nitrate consumption resulting from continued iron supply through atmospheric deposition this finding extends the body of evidence for a pervasive link between cold climates and polar ocean stratification in addition we hypothesize that more complete nutrient consumption in the glacial age subarctic pacific contributed to the previously observed ice age reduction in suboxia and denitrification in the eastern tropical north pacific by lowering the nutrient content of the intermediate depth water formed in the subpolar north pacific in the deglacial interval of the bering sea record two apparent peaks in export productivity are associated with maxima in diatom bound and bulk sediment d 15 n the high d 15 n in these intervals may have resulted from greater surface nutrient consumption during this period however the synchroneity of the deglacial peaks in the bering sea with similar bulk sediment d 15 n changes in the eastern pacific margin and the presence of sediment lamination within the bering sea during the deposition of the productivity peaks raise the possibility that both regional and local denitrification worked to raise the d 15 n of the nitrate feeding bering sea surface waters at these times

physical and biological regulation of the soft tissue carbon pump 1 we examine the relationship between aeolian iron deposition ocean circulation and atmospheric co2 in the context of a global ocean circulation and biogeochemistry model with a coupled atmospheric reservoir of co2 in common with previous models we find only a small reduction of atmospheric pco2 in response to an enhanced aeolian iron source consistent with last glacial maximum conditions we show this to be due to a combination of limiting factors including control of deep ocean iron concentrations by complexation to an organic ligand regional compensation in changes to export production and the maintenance of high preformed nutrient concentrations in deep water formation regions we also demonstrate a significant sensitivity of atmospheric pco2 to changes in the residual mean overturning circulation of the southern ocean dominated by its regulation of the accumulation of biogenic carbon in the deep ocean although it is not enough to explain the full drawdown of pco2 to glacial levels a reduction in overturning can lead to significant reduction in atmospheric pco2 providing mechanistic basis for the control by vertical mixing inferred from box models

mechanisms controlling dissolved iron distribution in the north pacific a model study mechanisms controlling the dissolved iron distribution in the north pacific are investigated using the biogeochemical elemental cycling bec model with a resolution of approximately 1 in latitude and longitude and 60 vertical levels the model is able to reproduce the general distribution of iron as revealed in available field data surface concentrations are generally below 0 2 nm concentrations increase with depth and values in the lower pycnocline are especially high in the northwestern pacific and off the coast of california sensitivity experiments changing scavenging regimes and external iron sources indicate that lateral transport of sedimentary iron from continental margins into the open ocean causes the high concentrations in these regions this offshore penetration only appears under a scavenging regime where iron has a relatively long residence time at high concentrations namely the order of years sedimentary iron is intensively supplied around continental margins resulting in locally high concentrations the residence time with respect to scavenging determines the horizontal scale of elevated iron concentrations budget analysis for iron reveals the processes by which sedimentary iron is transported to the open ocean horizontal mixing transports sedimentary iron from the boundary into alongshore currents which then carry high iron concentrations into the open ocean in regions where the alongshore currents separate from the coast most prominently in the northwestern pacific and off of california

iron manganese and lead at hawaii ocean time series station aloha temporal variability and an intermediate water hydrothermal plume trace metal clean techniques were used to sample hawaii ocean time series hot station aloha on seven occasions between november 1998 and october 2002 on three occasions full water column profile samples were obtained on the other four occasions surface and near surface euphotic zone profiles were obtained together with three other published samplings this site may have been monitored for dissolved 0 4 or 0 2 m fe more frequently than any other open ocean site in the world low fe concentrations 2500 m the concentrations we observe 0 4 0 5 nmol kg 1 are significantly lower than some other deep north pacific stations but are similar to values that have been reported for a station 350 miles to the northeast we attribute these low deepwater values to transport of low fe antarctic bottom water into the basin and a balance between fe regeneration and scavenging in the deep water near surface waters have higher fe levels than observed in the lower euphotic zone significant temporal variability is seen in near surface fe concentrations ranging from 0 2 0 7 nmol kg 1 we attribute these surface fe fluctuations to variable dust deposition biological uptake and changes in the mixed layer depth this variability could occur only if the surface layer fe residence time is less than a few years and based on that constraint it appears that a higher percentage of the total fe must be released from north pacific aerosols compared to north atlantic aerosols surprisingly significant temporal variability and high particulate fe concentrations are observed for intermediate waters 1000 1500 m these features are seen in the depth interval where high 3he from the nearby loihi seamount hydrothermal fields has been observed the total fe 3he ratio implies that the hydrothermal vents are the source of the high and variable fe the vertical profile of mn at aloha qualitatively resembles other north pacific mn profiles with surface and intermediate water maxima but there are some significant quantitative differences from other reported profiles the 0 4 m mn concentration is highest near the surface decreases sharply in the upper 500 m then shows an intermediate water maximum at 800 m and then decreases in the deepest waters these concentrations are higher than observed at a station 350 miles to the northeast that shows similar vertical variations it appears that there is a significant mn gradient throughout the water column from hot towards the northeast compared to the first valid oceanic pb data for samples collected in 1976 pb at aloha in 1997 1999 shows decreases in surface waters and waters shallower than 200 m pb concentrations in central north pacific surface waters have decreased by a factor of 2 during the past 25 yr from 65 to 30 pmol kg 1 surface water pb concentrations in the central north atlantic and central north pacific are now comparable we attribute the surface water pb decrease to the elimination of leaded gasoline in japan and to some extent by the u s and canada we attribute most of the remaining pb in pacific surface waters to asian emissions more likely due to high temperature industrial activities such as coal burning rather than to leaded gasoline consumption a 3 year mixed layer time series from the nearby hale aloha mooring site 1997 1999 shows that there is an annual cycle in pb with concentrations 20 higher in winter months this rise may be created by downward mixing of the winter mixed layer into the steep gradient of higher pb in the upper thermocline pb concentrations double between the surface and 200 m from 200 m to the bottom pb concentrations decrease to levels of 5 9 pmol kg 1 near the bottom for most of the water column thermocline and deepwater pb concentrations do not appear to have changed significantly during the 23 yr interval

a modeling assessment of the interplay between aeolian iron fluxes and iron binding ligands in controlling carbon dioxide fluctuations during antarctic warm events 1 we add a prognostic biogeochemical model to the bern3d ocean circulation model to test the impact of increased aeolian iron fluxes in various regions of the ocean on long time scales atmospheric co2 is most sensitive when modern dust flux is increased 100 fold in the southern ocean for 1000 years resulting in a reduction of 10 ppmv seeding the indian ocean and south pacific results in increased export production and co2 drawdown in the southern ocean due to interbasinal transport of iron the non sea salt calcium record from dome c antarctica is used to scale aeolian iron deposition in the southern ocean in transient simulations over four antarctic warm events of the last glacial period our results suggest changes in dust flux to the southern ocean played a limited role in modulating co2 variations the impact of iron fluxes on co2 is dependent on parameter values chosen for the iron binding ligand

impacts of iron control on phytoplankton production in the modern and glacial southern ocean abstract paleoceanographic evidence points to the southern ocean as a strong sink for atmospheric co2 during the last glacial maximum lgm but no consensus about the responsible mechanism has yet been reached martin paleoceanography 5 1990 1 postulated that greater iron input during the lgm could have stimulated phytoplankton to consume the surface nutrients in the southern ocean increasing carbon export substantially we use a simple ecological model to elucidate the extent to which iron availability affects export production in the southwest pacific sector the model includes the effect of iron in a semi explicit way based on the physiological response of the photosynthetic apparatus the simulated phytoplankton growth rates are explicitly dependent on iron the cycling of iron in the food web is not tracked since uncertainties persist about the dynamics of iron uptake transformation and release processes within the pelagic community a simulation of the present ocean that uses the semi explicit approach to include iron is compared with a simulation that accounts for iron only implicitly by using model parameters that are typical for low iron conditions the simulations agree within the range of available observations glacial scenarios are simulated assuming an increase in iron supply and compared to the modern ocean simulation primary and export production increase in the glacial simulations in particular if we assume an adaptation of the si n cell quota of diatoms to the higher iron levels in this case the export doubles north of the polar front and in the seasonal ice zone

influence of anthropogenic combustion emissions on the deposition of soluble aerosol iron to the ocean empirical estimates for island sites in the north atlantic the results of several recent studies challenge the reigning paradigm that continental soil dust provides the only significant atmospheric source of dissolved iron to the surface ocean this evidence includes correlations between the operational solubility of aerosol iron and atmospheric loadings of black carbon and aluminum normalized vanadium and nickel each of which are associated with emissions from the combustion of fossil fuel oil these observations suggest that the relative solubility of aerosol iron hence the eolian flux of soluble iron to the surface ocean may be significantly impacted by anthropogenic oil combustion products using recent field data from the bermuda region we have developed an empirical method to estimate the solubility of aerosol iron using bulk aerosol concentrations of fe v and al we apply this method to a large body of published data from the aeroce program for north atlantic island sites on tenerife barbados bermuda and ireland where the relative proportions of anthropogenic aerosols range from minor to major respectively our aerosol iron solubility estimates suggest that anthropogenic emissions contribute approximately 70 and 85 of the annual dry deposition of soluble iron to the surface ocean near bermuda and ireland respectively implying that human activities have profoundly affected the iron budget of the north atlantic region the annual mean dry deposition of soluble iron at barbados and izana is dominated by soil dust the anthropogenic contribution at these two sites ranges from 12 to 30 and is highly dependent on the soil dust solubility of fe employed in the model the low end 12 estimate appears to be more representative of these high dust sites

enhanced stratification and seasonality in the subarctic pacific upon northern hemisphere glaciation new evidence from diatom bound nitrogen isotopes alkenones and archaeal tetraethers abstract coincident with the intensification of northern hemisphere glaciation nhg around 2 73 million years ma ago sediment cores from both the open subarctic north pacific and the antarctic indicate a rapid decline in diatom opal accumulation flux to the seabed representing one of the most abrupt and dramatic changes in the marine sediment record associated with the development of pleistocene glacial cycles in the north pacific bulk sediment nitrogen isotope data and alkenone derived sea surface temperature sst estimates suggest that the productivity decline was driven by reduced exchange between surface and deep water due to weaker wind driven upwelling and or a strengthening of the halocline i e stratification in this study of the 2 73 ma transition at ocean drilling program odp site 882 in the western subarctic north pacific diatom bound nitrogen isotopes 15 n db alkenone mass accumulation rate and alkenone and archaeal tetraether based sst reconstructions support the stratification hypothesis indicating perennially lower export production generally higher nitrate consumption and greater inter seasonal variation in sst after the 2 73 ma transition in addition the 15 n db of large and small size fractions of coscinodiscus spp suggest that these diatoms grew mostly during the spring bloom during the late pliocene switching to their current fall to winter growth period at the 2 73 ma transition this view is consistent with their decline in dominance and provides further evidence for increased stratification reduced vertical exchange in the north pacific after 2 73 ma the 15 n db data indicate that over the 100 kyr period after the 2 73 ma transition studied here nitrate consumption did not reach late pleistocene ice age levels and that nitrate consumption in post 2 73 ma warm stages was similar to that before the transition even though productivity was greatly reduced we tentatively attribute this to relatively weak dust borne iron inputs in the early post 2 73 ma period

substantial advective iron loss diminishes phytoplankton production in the antarctic zone 1 after 1 decade of research it is a well established fact that iron limits photosynthetic co2 fixation and phytoplankton growth in the southern ocean intense blooms are scarce however the input of iron to the southern ocean is considerable an important factor for diminished phytoplankton production refers to the meridional circulation of the southern ocean intense spatially relatively homogeneous upwelling of upper circumpolar deep water ucdw causes a large iron flux into the surface layer however the main entrainment of upwelled ucdw into the surface layer occurs in autumn and winter which strongly restricts the usefullness of iron supply for phytoplankton due to unfavorable light conditions moreover the meridional transport within the ekman layer is intense enough to export at least 25 of the iron input away from the antarctic zone before it can be used by phytoplankton this also depresses the potential phytoplankton primary production by at least 25 most iron that crosses the polar front unused probably leaves the surface ocean north of the polar front because the surface water participates in antarctic intermediate water mode water formation

similar rates of modern and last glacial ocean thermohaline circulation inferred from radiochemical data today the ocean thermohaline circulation transports half of the 231pa produced by radioactive decay in the atlantic ocean water column to the southern ocean this export respectively imparts low and high 231pa 230th ratios to the surface sediments of these oceans ocean sediments from the last glacial maximum bear a similar isotopic fingerprint implying that advection of north atlantic deep intermediate water into the circumpolar deep water of the southern ocean occurred at a similar or slightly higher rate during the last glacial period

iron deficiency limits phytoplankton growth in antarctic waters enrichment experiments were performed in the ross sea to test the hypothesis that iron deficiency is responsible for the phytoplankton s failure to use up the luxuriant major nutrient supplies found in these and all other offshore antarctic ocean waters nitrate uptake rates in the controls without added trace elements ranged from 0 58 to 1 22 mol kg 1 d 1 the addition of 1 to 5 nmol of unchelated fe per liter resulted in rates that were 2 to 10 times higher 2 54 to 6 00 mol no3 kg 1 d 1 rates in bottles with 2 nmol mn added were identical to those in the controls 0 57 to 1 04 mol no3 kg 1 d 1 total decreases in no3 were balanced by increases in particulate organic n these results suggest that fe deficiency is the primary reason that the present day southern ocean biological pump is shut off in contrast iron was 50 times more abundant during the last glacial maximum greater fe availability may have stimulated the biological pump and contributed to the ice age drawdown of atmospheric c02 these results also imply that large scale southern ocean fe fertilization is feasible at least in terms of the total amounts of fe required i e 100 000 to 500 000 tons yr 1

biogenic flux of al to sediment in the central equatorial pacific ocean evidence for increased productivity during glacial periods we examined the flux of al to sediment accumulating beneath the zone of elevated productivity in the central equatorial pacific ocean along a surface sediment transect at 135 w as well as downcore for a 650 kyr record at 1 3 n 133 6 w across the surface transect a pronounced broadly equatorially symmetric increase in al accumulation is observed relative to ti with al ti ratios reaching values 3 4 times that of potential detrital sources the profile parallels biogenic accumulation and the modeled flux of particulate 234th suggesting rapid and preferential adsorptive removal of al from seawater by settling biogenic particles normative calculations confirm that most al is unsupported by the terrigenous fraction the observed distributions are consistent with previous observations of the relative and absolute behavior of al and ti in seawater and we can construct a reasonable mass balance between the amount of seawater sourced al retained in the sediment and the amount of seawater al available in the overlying column the close tie between al ti and biogenic accumulation as opposed to concentration emphasizes that biogenic sedimentary al ti responds to removal transport phenomena and not bulk sediment composition thus in these sediments dominated by the biogenic component the bulk al ti ratio reflects biogenic particle flux and by extension productivity of the overlying seawater the downcore profile of al ti at 1 3 n displays marked increases during glacial episodes similar to that observed across the surface transect from a background value near al ti of average upper crust the excursions in al ti are stratigraphically coincident with maxima in both bulk and caco3 accumulation and the excess al appears to not be preferentially affiliated with opaline or organic phases consistent with the similar behavioral removal of al and 234th the latter of which responds to the total particle flux the al flux reflects carbonate accumulation only because carbonate comprises the dominant flux in these particular deposits these results collectively indicate that 1 al in biogenic sediment and settling biogenic particles is strongly affected by a component adsorbed from seawater therefore the common tenet that al is dominantly associated with terrestrial particulate matter and the subsequent use of al distributions to calculate the abundance and flux of terrestrial material in settling particles and sediment needs to be reevaluated 2 the al ti ratio in biogenic sediment can be used to trace the productivity of the overlying water providing a powerful new paleochemical tool to investigate oceanic response to climatic variation 3 the close correlation between the al ti productivity signal and carbonate maxima downcore at 1 3 n suggests that the sedimentary carbonate maxima in the central equatorial pacific ocean record increased productivity during glacial episodes

distribution of dissolved iron during the natural iron fertilization experiment keops kerguelen plateau southern ocean abstract the southern ocean is the largest high nutrient low chlorophyll hnlc region of the world ocean it is now well recognized that the low biological productivity in this region is mainly due to the limitation of phytoplankton growth by iron however in the core of the southern ocean a massive bloom occurs annually above the kerguelen plateau in the context of keops kerguelen plateau and ocean compared study we investigated the three dimensional distribution of dissolved iron dfe concentrations southeast of the island we show that in surface waters dfe was low and not significantly different above and outside the plateau 0 090 0 034 and 0 073 0 014 nm respectively by contrast below 150 m major differences in vertical profiles of dfe were observed the deep waters above the plateau were clearly enriched with dfe concentrations up to 0 6 nm near the seafloor the regeneration from sinking biogenic material and the input from the sediments are very likely the major processes delivering dfe to the deep water the deep iron rich reservoir existing above the plateau was responsible for the natural iron fertilization of the surface water by two different mechanisms i winter mixing provided 5 times more dfe to the surface waters above the plateau than outside and ii enhanced vertical gradients of dfe and elevated vertical diffusivity resulted in an 8 fold higher diapycnal diffusive flux the natural iron fertilization presented major differences from artificial iron fertilization experiments carried out in the southern ocean the amount of dfe required to stimulate the biological activity is much less and the mode of addition is clearly different the quantification of the excess of dfe supplied in the naturally fertilized area leads to the conclusion that the natural iron fertilization is 10 150 times more efficient to export carbon below 200 m than in artificial fertilization experiments the bloom above the kerguelen plateau was contingent to iron fertilization but it was also sustained by continuous input of major nutrients thus the natural fertilization described here mimics quite well glacial period scenarios where iron fertilization of the southern ocean might have occurred from below

predicting channel patterns brewer paul lewin j 2001 predicting channel patterns geomorphology 40 pp 329 339 rae2008

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

changes in micronutrient supply to the surface southern ocean atlantic sector across the glacial termination major deepwater masses upwell and reach the surface in the southern ocean forming an important conduit supplying nutrients and micronutrients to the surface and playing a key role in the regulation of global climate through ocean atmosphere gas exchange here we reconstruct changes in micronutrient distribution in this region in response to past changes in upwelling oceanic mixing and sea ice seasonality we present two downcore zn si opal records from the scotia sea and drake passage region which we interpret in the context of micronutrient distribution in the atlantic sector of the southern ocean over the last glacial termination previous work shows that micronutrient availability in the surface waters in the south atlantic appear to be controlled dominantly by upwelling and mixing of micronutrient rich deepwaters which are additionally fuelled by the terrestrial sediment sources of the scotia arc and south georgia this is supported by our reconstructions which show micronutrient availability to the west of the scotia arc and south georgia are consistently lower than to the east over the last glacial termination due to downstream transport and mixing into surface waters of continentally derived material in the antarctic circumpolar current micronutrient availability in this region was at a minimum from 20 to 25 ky bp coinciding with maximum sea ice coverage and increased due to an expansion of the seasonal sea ice zone and increased mixing of subsurface waters our findings are consistent with largely diminished upwelling of micronutrients during the maximum glacial extent and reduced mixing due to the presence of persistent sea ice during the deglacial there was an increase in micronutrient availability as well as other nutrients and inorganic carbon within the antarctic circumpolar current as a result of an increase in deep oceanic upwelling mixing and strengthened zonal transport

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

terrigenous fe input and biogenic sedimentation in the glacial and interglacial equatorial pacific ocean many ocean regions important to the global carbon budget including the equatorial pacific ocean have low chlorophyll concentrations despite high levels of conventional nutrients iron may instead be the limiting nutrient and elevated input of terrigenous fe during windy glacial episodes has been hypothesized to stimulate oceanic productivity through time and thus regulate the oceanic and atmospheric co2 balance to test whether particulate fe input is related to the accumulation of biogenic matter in one important low chlorophyll high nutrient area that is the equatorial pacific ocean we present results from a suite of sediment cores that collectively record biogenic deposition through the last six glacial interglacial cycles 600 000 years our data set includes new chemical data on total fe terrigenous and biogenic components in three cores as well as previously published mineralogic records of coljan input to the region chemical spectral and stratigraphic analysis indicates that 1 terrigenous input to the region shows no consistent pattern of either glacial or interglacial maxima 2 the accumulation of particulate fe is closely related to the accumulation of terrigenous matter linear r 2 0 81 0 98 3 there are no coherent spectral relationships between fe input and glacial periodicity i e 5180 in any of the orbital frequency bands 4 the linear and cross spectral correlations between fe or coljan input and caco3 concentration are most commonly the strongest observed relationships between fe and any biogenic component yet indicate a largely inverse pattern with higher fe being associated with low caco3 5 there is no consistent linear r 2 correlation or spectral coherence between the accumulation of fe and that of caco3 corg or opal thus in total there is no relationship between terrigenous fe input and sedimentary sequestering of carbon additionally although we cannot specifically address the potential for changes in solubility of the terrigenous fraction that may be driven by a terrigenous compositional change the fe ti ratio which monitors first order mineralogic changes records only slight variations that also are linearly and spectrally unrelated to glacial periodicity the bulk fe flux and the accumulation of any biogenic component finally we find that the paleoceanographic flux of fe is several order of magnitudes larger than modem observations of coljan fe input suggesting that the long term importance of fe input by dust storms which deliver fe on the order of the sedimentary burial may be underestimated the removal of particulate terrigenous fe from the recently discovered source within the equatorial undercurrent however remains unquanfified and may also prove significant

deglacial meltwater discharge north atlantic deep circulation and abrupt climate change high resolution paleogeochemical data from the north atlantic ocean indicate that in the interval 15 000 to 10 000 14c years before present b p north atlantic deep water nadw production was decreased or eliminated four times at about 14 500 and probably older 13 500 12 000 and 10 500 years b p each of these changes occurred at the same time as abrupt events of meltwater discharge to the surface ocean inferred from oxygen isotope studies of planktonic foraminifera and from glacial geological studies on land in addition each of these times may be associated with brief episodes of cooler climate in the north atlantic region the best example of which is the younger dryas cooling of 10 500 years ago these results support models linking meltwater discharge decreased nadw production and decreased north atlantic heat flux

southern ocean bioproductivity during the last glacial cycle new detection method and decadal scale insight from the scotia sea we present biogenic opal flux records from two deep sea sites in the scotia sea md07 3133 and md07 3134 at decadal scale resolution covering the last glacial cycle in addition to conventional and time consuming biogenic opal measuring methods we introduce new biogenic opal estimation methods derived from sediment colour b wet bulk density si ti count ratio and fourier transform infrared spectroscopy ftirs all methods capture the biogenic opal amplitude however ftirs a novel method for marine sediment yields the most reliable results 230th normalization data show strong differences in sediment focusing with intensified sediment focusing during glacial times at md07 3134 230th normalized biogenic opal fluxes vary between 0 2 and 2 5 g cm22 kyr21 our biogenic opal flux records indicate bioproductivity changes in the southern ocean strongly influenced by sea ice distribution and also summer sea surface temperature changes south of the antarctic polar front lowest bioproductivity occurred during the last glacial maximum when upwelling of mid depth water was reduced and sea ice cover intensified around 17 ka bioproductivity increased abruptly corresponding to rising atmospheric co2 and decreasing seasonal sea ice coverage

dust sources and deposition during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments mineral dust aerosols in the atmosphere have the potential to affect the global climate by influencing the radiative balance of the atmosphere and the supply of micronutrients to the ocean ice and marine sediment cores indicate that dust deposition from the atmosphere was at some locations 2 20 times greater during glacial periods raising the possibility that mineral aerosols might have contributed to climate change on glacial interglacial time scales to address this question we have used linked terrestrial biosphere dust source and atmospheric transport models to simulate the dust cycle in the atmosphere for current and last glacial maximum lgm climates we obtain a 2 5 fold higher dust loading in the entire atmosphere and a twenty fold higher loading in high latitudes in lgm relative to present comparisons to a compilation of atmospheric dust deposition flux estimates for lgm and present in marine sediment and ice cores show that the simulated flux ratios are broadly in agreement with observations differences suggest where further improvements in the simple dust model could be made the simulated increase in high latitude dustiness depends on the expansion of unvegetated areas especially in the high latitudes and in central asia caused by a combination of increased aridity and low atmospheric co2 the existence of these dust source areas at the lgm is supported by pollen data and loess distribution in the northern continents these results point to a role for vegetation feedbacks including climate effects and physiological effects of low co2 in modulating the atmospheric distribution of dust

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

southern ocean nitrogen and silicon dynamics during the last deglaciation abstract the reinvigoration of overturning in the southern ocean is hypothesized to have returned co2 from the deep ocean to the atmosphere at the end of the last ice age large peaks in opal accumulation have been put forward as evidence for an increase in wind driven upwelling between 10 and 15 ka here we use coupled nitrogen and silicon isotope records alongside opal accumulation rates to provide quasi quantitative estimates of southern ocean nutrient supply by upwelling and nutrient utilization across this interval significant changes in the consumption of n and si across the two opal accumulation peaks indicate major changes in both upwelling and nutrient demand we find n and si consumption to be relatively incomplete during peak opal accumulation at the onset of the deglaciation this indicates that nutrient supply was significantly enhanced the second deglacial peak in opal accumulation is associated with more complete si consumption and variable n consumption we suggest that this peak represents strong upwelling and more complete utilization of the available silicic acid pool differences between the si and n responses during opal peaks may stem from decreasing iron availability across the glacial termination the nutrient isotope evidence for excess nutrients during the deglaciation indicates that the high export productivity was insufficient to overcome the evasion of co2 to the atmosphere as a result of physical circulation changes previous work has demonstrated that the reinvigoration of overturning circulation during the deglaciation causes a transient peak in nutrient supply to the low latitudes this is supported by our data which indicate that relatively high macronutrient concentrations were maintained in the southern ocean surface waters that are incorporated into mode waters despite high demand

atmospheric transport of iron and its deposition in the ocean the atmospheric transport of continental weathering products is responsible for much of the mineral material and fe entering the open ocean and is probably the dominant source of nutrient fe in the photic zone in regions where other nutrients are present in high concentrations the flux of fe from the atmosphere may be a limiting factor in primary productivity due to the larger source regions for dust north of the equator 8 times more atmospheric fe is deposited in the northern hemisphere than in the southern hemisphere the mineral aerosol and fe transport and deposition are highly variable due to the episodic nature of dust generation and its transport and deposition processes between 10 and 50 of the total atmospheric fe entering the world ocean appears to dissolve i e it will pass through a 0 4 m pore size filter rapidly when the mineral matter enters the ocean much of the atmospheric fe is present as fe ii apparently produced as a result of photochemical reduction reactions taking place during atmospheric transport this readily soluble fe ii should be available immediately for use as a nutrient by phytoplankton atmospheric transport from the continents is estimated to supply 3 times as much dissolved fe to the oceans as that delivered via rivers

evidence against dust mediated control of glacial interglacial changes in atmospheric co2 the low concentration of atmospheric co2 inferred to have been present during glacial periods is thought to have been partly caused by an increased supply of iron bearing dust to the ocean surface1 this is supported by a recent model2 that attributes half of the co2 reduction during past glacial stages to iron stimulated uptake of co2 by phytoplankton in the southern ocean but atmospheric dust fluxes to the southern ocean even in glacial periods are thought to be relatively low and therefore it has been proposed that southern ocean productivity might be influenced by iron deposited elsewhere for example in the northern hemisphere3 4 which is then transported south via ocean circulation similar to the distal supply of iron to the equatorial pacific ocean5 6 7 here we examine the timing of dust fluxes to the north atlantic ocean in relation to climate records from the vostok ice core in antarctica around the time of the penultimate deglaciation about 130 kyr ago two main dust peaks occurred 155 kyr and 130 kyr ago but neither was associated with the co2 rise recorded in the vostok ice core this mismatch together with the low dust flux supplied to the southern ocean suggests that dust mediated iron fertilization of the southern ocean did not significantly influence atmospheric co2 at the termination of the penultimate glaciation

iron in east antarctic snow implications for atmospheric iron deposition and algal production in antarctic waters to evaluate the deposition and solubility of aerosol iron in the antarctic seasonal sea ice zone ssiz iron was measured in snow samples collected from three areas in the ssiz prydz bay dumont d urville sea and ross sea and one continental area princess elizabeth land of east antarctica concentrations of total dissolvable iron that soluble at ph 2 ranged from 20 2950 pg g 1 with the lowest concentrations measured in snow from the dumont d urville sea using estimates of snow accumulation rates we calculate atmospheric iron deposition fluxes of 0 017 0 11 mg m 2 yr 1 0 30 2 0 mol m 2 yr 1 which are generally lower than previously published estimates measurements of iron in filtered meltwaters of snow samples from prydz bay and princess elizabeth land suggest that 10 90 of the total atmospheric iron is readily soluble assuming our results to be broadly representative of atmospheric deposition over seasonally ice covered high nutrient antarctic waters we use our mean estimates of atmospheric iron deposition 1 1 mol m 2 yr 1 and solubility 32 to calculate that atmospheric iron potentially supports annual phytoplankton production of 1 1 1012 mole c in the antarctic ssiz which is less than 5 of the estimated total annual primary production in this ocean region

iron isotope systematics in estuaries the case of north river massachusetts usa abstract recent studies have suggested that rivers may present an isotopically light fe source to the oceans since the input of dissolved iron from river water is generally controlled by flocculation processes that occur during estuarine mixing it is important to investigate potential fractionation of fe isotopes during this process in this study we investigate the influence of the flocculation of fe rich colloids on the iron isotope composition of pristine estuarine waters and suspended particles the samples were collected along a salinity gradient from the fresh water to the ocean in the north river estuary ma usa estuarine samples were filtered at 0 22 m and the iron isotope composition of the two fractions dissolved and particles were analyzed using high resolution mc icp ms after chemical purification dissolved iron results show positive 56 fe values with an average of 0 43 0 04 relative to the irmm 14 standard and do not display any relationships with salinity or with percentage of colloid flocculation the iron isotopic composition of the particles suspended in fresh water is characterized by more negative 56 fe values than for dissolved fe and correlate with the percentage of fe flocculation particulate 56 fe values vary from 0 09 at no flocculation to 0 1 at the flocculation maximum which reflect mixing effects between river borne particles lithogenic particles derived from coastal seawaters and newly precipitated colloids since the process of flocculation produces minimal fe isotope fractionation in the dissolved fe pool we suggest that the pristine iron isotope composition of fresh water is preserved during estuarine mixing and that the value of the global riverine source into the ocean can be identified from the fresh water values however this study also suggests that 56 fe composition of rivers can also be characterized by more positive 56 fe values up to 0 3 relative to the crust than previously reported in order to improve our current understanding of the oceanic iron isotope cycling further work is now required to determine the processes controlling the fractionation of fe isotopes during continental run off

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

glacial interglacial variations in marine phosphorus cycling implications for ocean productivity 1 using a box model of organic carbon c and phosphorus p cycling in the global ocean we assess the effects of changes in the continental supply of reactive p oceanic mixing and sea level on the marine p cycle on glacial interglacial timescales our model results suggest that mixing is a dominant forcing during early glaciation causing retention of p in the deep ocean thereby lowering primary production and associated organic c and p burial sea level fall is the dominant forcing during late glaciation when reduced coastal trapping of reactive p enhances its transfer to the open ocean restoring primary production and p burial during postglacial periods changes in circulation and weathering dominate open ocean processes and oceanic primary production peaks as primary production is reduced upon glaciation changes in the marine p cycle are unlikely to drive enhanced primary production and co2 drawdown during glaciation

hydrothermal fe fluxes during the precambrian effect of low oceanic sulfate concentrations and low hydrostatic pressure on the composition of black smokers abstract modern mid ocean ridge hydrothermal systems typically release vent fluids to the ocean with dissolved h2s in excess of fe these fluids are the consequence of high temperature interactions between sulfate rich seawater and mid ocean ridge basalt at conditions near the critical point for seawater the precipitation of fes and fes2 during venting titrates most of the fe from the fluid significantly reducing the net flux of fe to the open ocean here we suggest that hydrothermal fluids emanating from precambrian seafloor systems older than 1 8 ga had fe h2s ratios 1 and with fh2 higher than today because seawater lacked its primary oxidant dissolved sulfate ion this predominance of fe over h2s would have promoted the establishment of an iron rich deep ocean and the deposition of banded iron formations bif accordingly the end of bif deposition at 1 8 ga was the result of the buildup of sulfate in seawater from oxidative weathering and its return at 750 ma the result of reductions in seawater sulfate concentrations during snowball earth episodes enhanced by elevated fe concentrations during depressurization of hydrothermal systems by large eustatic sea level falls moreover precambrian chemosynthetic vent communities may have been based on h2 synthesis rather than on h2s oxidation as they largely are today

the changing roles of iron and vertical mixing in regulating nitrogen and silicon cycling in the southern ocean over the last glacial cycle the southern ocean plays a critical role in the air sea co2 balance through biological and physical mechanisms vertical supply of deep waters returns nutrients and co2 to the surface and stimulates phytoplankton growth photosynthesis in the southern ocean is limited by iron and only a fraction of the carbon and nutrients that return to the surface are consumed for potential sequestration in the deep sea here we present the most spatially extensive data set of silicon and nitrogen isotope measurements from diatom frustules to date to examine the controls on nutrient drawdown during the last glacial period and across the glacial termination in both the antarctic and subantarctic zones the new data confirm existing views that differing silicon and nitrate consumption patterns in the antarctic zone are likely the result at least in part of iron addition during the last glacial maximum lgm however earlier in the glacial a more coordinated response in the two proxy records with both reflecting enhanced consumption during episodes of increased iron accumulation and export production implies a different system response than observed for the lgm a collapse of the expected equatorward gradient in silicon isotope values and contraction of the nitrogen isotope gradient during the deglaciation suggests that nutrient supply increased not only in the antarctic zone but also in the subantarctic perhaps due to enhanced deep mixing locally enhanced deep water ventilation across the southern ocean likely increased the nutrient content of mode waters during the deglaciation

revisiting nutrient utilization in the glacial antarctic evidence from a new method for diatom bound n isotopic analysis holocene in the indian sector is smaller than in previous measurements these data suggest no change in the degree of nitrate utilization in the atlantic sector and at most a 20 increase from 25 to 45 in the indian sector the new measurements suggest that during the last ice age in the atlantic sector of the antarctic the atmospheric source of biologically available iron was not so great as to become significant relative to the iron supply from below given the apparent spatial variability in the degree of nitrate drawdown more work is required to develop an adequate picture of the glacial antarctic nutrient field index terms 4806 oceanography biological and chemical carbon cycling 4845 oceanography biological and chemical nutrients and nutrient cycling 4894 oceanography biological and chemical instruments and techniques 9310 information related to geographic region antarctica

deep sea coral evidence for lower southern ocean surface nitrate concentrations during the last ice age the southern ocean regulates the ocean s biological sequestration of co 2 and is widely suspected to underpin much of the ice age decline in atmospheric co 2 concentration but the specific changes in the region are debated although more complete drawdown of surface nutrients by phytoplankton during the ice ages is supported by some sediment core based measurements the use of different proxies in different regions has precluded a unified view of southern ocean biogeochemical change here we report measurements of the 15 n 14 n of fossil bound organic matter in the stony deep sea coral desmophyllum dianthus a tool for reconstructing surface ocean nutrient conditions the central robust observation is of higher 15 n 14 n across the southern ocean during the last glacial maximum lgm 18 25 thousand years ago these data suggest a reduced summer surface nitrate concentration in both the antarctic and subantarctic zones during the lgm with little surface nitrate transport between them after the ice age the increase in antarctic surface nitrate occurred through the deglaciation and continued in the holocene the rise in subantarctic surface nitrate appears to have had both early deglacial and late deglacial holocene components preliminarily attributed to the end of subantarctic iron fertilization and increasing nitrate input from the surface antarctic zone respectively

addition of aeolian dusts to soils in southeastern australia red silty clay trapped in dunes bordering murrumbidgee river in the wagga wagga region in southeastern australia aeolian dust deposits are very common and have a significant influence on soil properties and soil landscapes however the characteristics of the pure dust materials and the rates of dust fall in the past are unclear because of the low overall rate of dust deposition and mixing with locally derived sediments in the wagga wagga region some dunes have functioned as dust traps thin 1 cm thick red clayey bands and thick up to 2 5 m red clayey layers within the dune sequences are likely to represent illuviated aeolian dust these dust materials are characterised by a bi modal particle size distribution one mode in the clay and another in the coarse medium silt the clay minerals are dominated by kaolinite illite and smectite both 14c and optical dating indicate the most recent period of dune formation was around 3 4 ka in an example of these young dunes there is a total of 2 cm equivalent thickness of dust materials giving a deposition rate of 0 5 0 7 cm ka 1 all three samples from an elevated dune are saturated with respect to environmental radiation dosage and give minimum optical ages in excess of 80 ka in this higher dune the total thickness of dust is 50 80 cm similar to that 50 100 cm of the yarabee parna the youngest aeolian dust deposit in the wagga wagga region this may have been deposited unevenly being more concentrated during the period 25 16 ka which has been identified as a major dust deposition period in the tasman sea if this variation occurred the dust deposition rate indicated by the 50 80 cm dust material in the dune could have been as high as 5 cm ka 1 for the period 25 16 ka

the role of the deep ocean in north atlantic climate change between 70 and 130 kyr ago the suggestion1 that changes in north atlantic deep water nadw production are linked through surface heat flux to the atmospheric temperature over greenland is supported by earlier indications2 3 that nadw production decreased during glacial times and by the subsequent finding4 6 that it declined during the younger dryas cool period at the end of the last glaciation changes in north atlantic surface temperatures have been found7 to mirror high frequency temperature changes recorded in greenland ice cores over the past 80 kyr but the connection to abyssal circulation has yet to be established except for one or two isolated oscillations8 9 here we present carbon and oxygen isotope analyses of benthic foraminifera in a high resolution north atlantic deep sea sediment core for the period 70 130 kyr ago these data allow us to reconstruct the history of nadw production which shows a close correlation with greenland climate variability for much of this time interval suggesting that the climate influence of nadw variability was widespread we see no evidence however for changes in nadw production during substage 5e the eemian interglacial period in contrast with recent ice core data10 which suggest severe climate instability in greenland during this time period our results may support suggestions based on data from a second ice core that this apparent instability is an artefact caused by ice flow11 alternatively the eemian climate instability may have had a different origin from the subsequent climate events

reactive trace metals in the stratified central north pacific abstract vertical concentration profiles of the dissolved and suspended particulate phases were determined for a suite of reactive trace metals al fe mn zn and cd during summertime at a station in the center of the north pacific gyre during summer the euphotic zone becomes stratified forming a shallow 0 25 m oligotrophic mixed layer overlying a subsurface 25 140 m strongly stratified region the physical biological and chemical structure within the euphotic zone during this period enhanced the effect of atmospheric inputs of al fe and mn on mixed layer concentrations for example the concentration of dissolved fe in the surface mixed layer was eighteen times that observed at a depth of 100 m the observed aeolian signature of these metals matched that predicted from estimates of atmospheric input during the period between the onset of stratification and sampling the distributions of suspended particulate al fe and mn all exhibited minima in the euphotic zone and increased with depth into the main thermocline particulate al and fe were then uniform with depth below 1000 m before increasing in the near bottom nepheloid layer average particulate phase concentrations in intermediate and deep waters of the central north pacific were 1 0 0 31 and 0 055 nmol kg 1 for al fe and mn respectively the distribution of particulate cd exhibited a maximum within the subsurface euphotic zone particulate zinc also exhibited a surface maximum albeit a smaller one concentrations of particulate zn and cd in intermediate and deep waters were 17 and 0 2 pmol kg 1 substantial interbasin differences in particulate trace metals occur concentrations of suspended particulate al fe and mn were three to four times lower in the central north pacific than recently reported for the central north atlantic gyre consistent with differences in atmospheric input to these two regions concentrations of suspended particulate cd and zn were enriched in the north pacific relative to the north atlantic an observation consistent with their assimilation by plankton reactive trace metals exhibit a range of biogeochemical behaviors that can be characterized by two endmembers nutrient type and scavenged type nutrient type metals best exemplified by zn and cd are primarily removed from surface waters by biogenic particles and then remineralized at depth internal biogeochemical cycles together with physical mixing and circulation patterns control the distributions of nutrient type metals scavenged type metals best exemplified by al continue to be removed onto particles in intermediate and deep waters as well as at the surface external inputs such as the deposition of aeolian dust control the concentrations and distributions of scavenged type metals other metals such as fe exhibit a mixture of the characteristic behaviors of these two endmembers

implications of the glacial co2 iron hypothesis for quaternary climate change 1 the iron hypothesis posits a role for increased supply of mineral aerosol to the ocean surface during glacial periods in driving atmospheric co2 lower that changes in co2 and climate strongly affect dust supply raises the possibility of feedback here i take a systems view in analyzing the properties and implications of such a feedback and consider three primary state variables that can be related empirically to each other dust supply atmospheric co2 and climate surface air temperature the results of this analysis suggest that the dust co2 climate feedback is primarily an intraglacial phenomenon when it can account for about a third of the temperature variability recorded in antarctic ice cores since glacial interglacial cyclicity prior to ca 800 kyr bp is characterized by the absence of a full glacial state such as the last glacial maximum it is possible that destabilization of climate by the marine iron cycle is fundamental to the differences between 41 kyr and 100 kyr climatic regimes the critical role played by the state of the land surface in this feedback also has implications for the longer term evolution of the earth system during the cenozoic

glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls 1 the valve area of fragilariopsis kerguelensis the most abundant diatom species in the southern ocean strongly changes in size in response to varying conditions in the surface ocean we examined the link both in two iron fertilization experiments and in sediment samples covering several glacial terminations between size variability in this species and environmental conditions across the antarctic polar front including sea ice extent sea surface temperature and the input of eolian dust the iron fertilization experiments show valve area to be positively correlated with iron concentrations in ambient waters which suggests the possibility of a causal relation between valve size of fragilariopsis kerguelensis and ambient surface water iron concentration larger valves are usually found during glacial times and thus seem to be related to lower sea surface temperature and wider sea ice coverage moreover our results indicate that there usually is a strong correlation between larger valve size and increased input of eolian dust to the southern ocean however this correlation obvious for the fertilization experiments and for glacial terminations i ii iii and v does not seem to be valid for termination vi where size appears to be inversely correlated to dust input citation cortese g r gersonde k maschner and p medley 2012 glacial interglacial size variability in the diatom fragilariopsis kerguelensis possible iron dust controls paleoceanography 27 pa1208 doi 10 1029 2011pa002187

sources of fe to the equatorial pacific ocean from the holocene to miocene abstract biological productivity in the modern equatorial pacific ocean a region with high nutrients and low chlorophyll is currently limited by the micronutrient fe in order to test whether fe was limiting in the past and to identify potential pathways of fe delivery that could drive fe fertilization i e dust delivery from eolian inputs vs fe supplied by the equatorial undercurrent we chemically isolated the terrigenous material from sediment along a cross equatorial transect in the central equatorial pacific at 140 w and at ocean drilling program site 850 in the eastern equatorial pacific we quantified the contribution from each potential fe bearing terrigenous source using a suite of chemical and isotopic discrimination strategies as well as multivariate statistical techniques we find that the distribution of the terrigenous sources i e asian loess south american ash papua new guinea and ocean island basalt varies through time latitude and climate regardless of which method is used to determine accumulation rate there also is no relationship between flux of any particular fe source and climate moreover there is no connection between a particular fe source or pathway eolian vs undercurrent to total productivity during the last glacial maximum pleistocene glacial episodes and the miocene biogenic bloom this would suggest an alternative process such as an interoceanic reorganization of nutrient inventories may be responsible for past changes in total export in the open ocean rather than simply fe supply from dust and or equatorial undercurrent processes additionally perhaps a change in fe source or flux is related to a change in a particular component of the total productivity e g the production of organic matter calcium carbonate or biogenic opal

modeling the geochemical cycle of iron in the oceans and its impact on atmospheric co2 concentrations iron occurs at very low concentrations in seawater and seems to be a limiting factor for primary production in the equatorial pacific and the southern ocean the global distribution of iron is still not well understood because of a lack of data and the complex chemistry of iron we develop a 10 box model to study the oceanic distribution of iron and its effect on atmospheric co2 concentration subject to our assumptions we find that a lack of interocean fractionation of deep sea iron concentrations as suggested by johnson et al 1997a is not readily explained by a balance of eolian deposition scavenging and regeneration incorporation of organic complexation in the model as suggested by johnson et al to reduce the scavenging rate of iron when concentrations fall below some ligand stabilized concentration is one solution to this difficulty alternatively the deep sea concentration may be more variable than the current rather sparse data coverage suggests in the model deep sea iron concentrations are responsive to the atmospheric source even if we adopt stabilization of concentrations by a ligand as modeled by johnson et al l997a in the southern ocean where the model suggests iron supply has an important limiting effect on the biota more than 99 of the iron supply to the surface in the present day comes from upwelling and not from the local atmospheric flux in the context of glacial interglacial changes to atmospheric co2 the model suggests that increasing atmospheric iron to the entire global ocean by a factor of 2 leads to decreases in atmospheric co2 of 10 30 ppm depending on assumptions however in our model co2 concentrations are almost unaffected by changes in southern ocean atmospheric fluxes alone unless these are unrealistically large 100 times present day the effect on atmospheric carbon dioxide is slightly stronger if accompanied by increased stratification of the southern ocean the model suggests that eolian iron fertilization of the ocean could have importantly influenced glacial atmospheric co2 concentrations but that other processes must also be at work to account for the full magnitude of the glacial interglacial change