a corollary to the silicic acid leakage hypothesis 1 the silicic acid leakage hypothesis salh attempts to explain part of the large and regular atmospheric co2 changes over the last glacial interglacial cycles it calls for a reduction in the carbonate pump through a growth in diatoms at the expense of coccolithophorids in low latitude surface waters driven by a leakage of high si n waters from the southern ocean recent studies that present low opal accumulation rates from the glacial eastern equatorial pacific have challenged salh in a corollary to salh we argue that the key to salh is the dominance of diatoms over coccolithophorids and this does not depend on the magnitude of diatom production per se in support of our claim we show in a numerical model that atmospheric co2 can be lowered with even a reduced absolute flux of silicic acid leakage provided that si n in the leakage is elevated and that the excess si can be used by diatoms to shift the floral composition in their favor

alteration of hyaloclastites in the hsdp 2 phase 1 drill core 1 description and paragenesis this is the publisher s version copyright 2003 by chinese geophysical society all rights reserved

large heat and fluid fluxes driven through mid plate outcrops on ocean crust geophysical data for the cocos plate sea floor suggest that basement outcrops along mid ocean ridge flanks can discharge very large quantities of heat and fluid this is indicative of high crustal permeability at the regional scale

a model for the production of sulfur floc and snowblower events at mid ocean ridges at mid ocean ridges following magmatic eruptions biogenic floc emerges from the seafloor and blankets regions of the seafloor in what have been called snowblower events the floc often consists of filaments of elemental sulfur and similar byproducts have been produced by hydrogen sulfide oxidizing bacteria in the laboratory in this paper we estimate the rate of sulfur floc production in two ways first we compare the flux of h2s from high temperature vents and adjacent diffuse flow near 9 50 n on the east pacific rise to estimate the rate at which subsurface microbes use h2s to produce elemental sulfur in the shallow crust since the 1991 eruption second we use the data from laboratory experiments to provide an upper estimate of sulfur floc production during a volcanic eruption the results suggest that that the floc observed during snowblower events is most likely a combination of a bloom event and floc that has been stored in the crust between eruption cycles the calculations also suggest that a 1 reduction in crustal porosity would result from the microbial production and storage of sulfur floc during the 1991 to 2000 time interval

a record of pleistocene diatom preservation from the amundsen sea west antarctica with possible implications on silica leakage article i nfo accumulation of fossil diatoms in marine sediments is variably affected by the production and dissolution of diatom frustules across space and time no quantitative proxy exists for estimating the amount of silica lost to dissolution in southern ocean sediment cores to address this gap cultured valves of fragilariopsis kerguelensis the dominant planktonic diatom in the pleistocene to recent southern ocean were dissolved progressively under controlled laboratory conditions expansion and eventual conjoining of the areolae of f kerguelensis advances through several phases which are presented herein as a measure of diatom dissolution in order to evaluate the validity of laboratory methods this proxy is applied to sediments from piston core ps58 254 from the amundsen sea dissolution induced degradation morphologies from laboratory experiments are seen to be identical to those preserved naturally in sediments thus suggesting the laboratory conditions accurately reflect the natural process of dissolution these resultsrepresentthe firstapplication of afullyquantitativeproxyfordiatomdissolution tosouthernocean sediments revealing that meaningful paleoceanographic data can be generated via taphonomic analysis of diatom valves intensity of diatom dissolution in core ps58 254 does not correspond to the relative abundance of any diatom species clay mineralogy or linear sedimentation rates however a correlation does exist between glacial cyclicity and diatom dissolution indicating that variation in average wall thickness and susceptibility to dissolution reflects primary conditions during formation of the silica wall transit through the water column and eventual deposition higher overall silica dissolution is observed during each glacial period and enhanced silica preservation during interglacials this result is consistent with the predictions of the silicic acid leakage hypothesis salh whereby reduced rates of si usage in the southern ocean lead to shifts in marine primary productivity in the tropics from coccolithophoriddominance duringinterglacialstodiatomdominanceduringglacials thiswouldfuela decrease in atmospheric pco2duringglacials silica acidleakage isdrivenbya decreaseinthe si nratioofdiatoms caused by increased iron input to glacial aged southern ocean waters this resulted in more lightly silicified diatom valves in the southern ocean which dissolved more quickly in the upper water column thereby maintaining the high silica content of glacial aged so waters and allowing for export of si to upwelling zones in the lower latitudes

biological mediation in ocean crust alteration how deep is the deep biosphere abstract biological mediation has been suggested as a control of the chemical exchange between the oceanic crust and seawater but very little is known about its distribution within the oceanic crust and the relative importance of biotic and abiotic processes alteration textures in glassy pillow lava margins record the proportions of biotic and abiotic alteration and the fraction of biotic alteration may be determined by point counting methods we used this method at dsdp odp sites 417d and 418a 110 ma crust south of bermuda rise and holes 504b and 896a 5 9 ma costa rica rift biotic alteration dominates glass alteration in the upper 250 m of the oceanic crust 60 85 of the total glass alteration and steadily declines in importance down to 10 20 at 500 m the consistency of data between two crustal sections of very different age and tectonic setting suggest that microbially mediated glass alteration may be largely confined to the upper oceanic crust however both sites studied are sealed by thick sedimentary layers and thus are typical for ocean crust underlying the oceanic basins rather than crust at mid ocean ridges with possibly deep and rapid hydrothermal circulation down hole temperature measurements at the costa rica rift suggest that glass altering microbes are hyperthermophilic and thrive at least up to temperatures of about 90 c microbial activity does occur at higher temperatures up to about 110 c but with reduced apparent abundance

evolution of heat flow hydrothermal circulation and permeability on the young southern flank of the costa rica rift we analyze 67 new conductive heat flow measurements on the southern flank of the costa rica rift crr heat flow measurements cover five sites ranging in oceanic crustal age between approximately 1 6 and 5 7 ma and are co located with a high resolution multi channel seismic line that extends from slightly north of the first heat flow site 1 6 ma to beyond odp hole 504b in 6 9 ma crust for the five heat flow sites the mean observed conductive heat flow is 85 mwm 2 this value is approximately 30 per cent of the mean lithospheric heat flux expected from a half space conductive cooling model indicating that hydrothermal processes account for about 70 per cent of the heat loss the advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults super critical convection in layer 2a extrusives occurs between 1 6 and 3 5 ma and flow through a thinly sedimented basement high occurs at 4 6 ma advective heat loss diminishes rapidly between 4 5 and 5 7 ma which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages 65 10 ma at 5 7 ma the crr topography is buried under sediment with an average thickness 150 m and hydrothermal circulation in the basement becomes sub critical or perhaps marginally critical the absence of significant advective heat loss at 5 7 ma at the crr is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as result of mineral precipitation and original permeability at the time of formation permeability is a non monotonic function of age along the southern flank of the crr in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge axis magma supply and tectonic extension hydrothermal circulation in the young oceanic crust at southern flank of crr is affected by the interplay and complex interconnectedness of variations in permeability sediment thickness topographical structure and tectonic and magmatic activities with age

high resolution opal records from the eastern tropical pacific provide evidence for silicic acid leakage from hnlc regions during glacial periods abstract a shift from carbonate to silica dominated primary production could significantly affect the oceanic carbon cycle via changes in the particulate carbon rain rate ratio c organic c inorganic fluxes an increase in c rain rate ratio has been invoked to explain lower glacial p co 2 however firm evidence of an ecological shift towards silica dominated productivity during the last glacial period is lacking here we present new high resolution reconstructions of biogenic silica and total production over the past 40 000 yr bp in 3 cores from the eastern tropical north pacific etnp off mexico and nicaragua these records reveal a clear regional pattern of higher siliceous productivity with higher opal accumulation during the last glacial period compared to interglacial times higher si c and si n ratios of glacial sediments in these records suggest a net increase in siliceous production over total production we attribute this to the additional supply of silicic acid to the etnp margins favouring diatoms over other non siliceous algae this suggestion for increased supply of si during glacial periods is consistent with the proposed large scale redistribution of excess silicic acid from high nitrate low chlorophyll hnlc regions like the eastern equatorial pacific eep and the southern ocean by the silicic acid leakage hypothesis salh in these hnlc regions the si isotope composition of diatom frustules 30 si has provided evidence for the generation of surplus of silicic acid during diatom growth under conditions of higher fe availability during glacial periods we suggest that silicic acid leakage from the hnlc regions to the adjoining oceans may have increased the carbon rain rate ratio and ultimately contributed to the decrease in glacial atmospheric p co 2

archaean plate tectonics revisited 1 heat flow spreading rate and the age of subducting oceanic lithosphere and their effects on the origin and evolution of continents a simple model which relates the rate of seafloor creation and the age of the oceanic lithosphere at subduction to the rate of continental accretion can successfully explain the apparent differences between archaean and phanerozoic terrains in terms of plate tectonics the model has been derived using the following parameters 1 the spreading rate at mid ocean ridges 2 the age of the oceanic lithosphere at the time of subduction 3 the area age distribution of the seafloor 4 the continental surface area as a fraction of the total surface area of the earth and 5 the erosion rate of continents as a function of continental surface area and the total number of continental masses observations in phanerozoic terranes suggest that there are profound differences in the nature and volume of subduction zone igneous activity depending upon the age of the oceanic lithosphere being subducted and the nature of the overriding plate that is either continental or oceanic the subduction of young oceanic lithosphere less than 50 m y old which is thermally buoyant appears to result in a reduced volume of igneous activity most of the igneous activity caused by subduction of young oceanic lithosphere is either siliceous plutonism or bimodal tholeiitic rhyolitic volcanism when very young lithosphere is being subducted 50 m y old appears to result in greater volumes of igneous activity including the eruption of andesitic magmas thus andesites could only begin to be abundant in the rock record when older oceanic lithosphere began to be subducted our model predicts that as the earth aged and as heat flow from the interior of the earth diminished the proportion of old oceanic lithosphere being subducted increased fundamentally changing the nature of subduction zone igneous activity and the rate of continental accretion if the subduction of old oceanic lithosphere results in an 8 10 times greater volume of subduction zone magmatism our model predicts or explains all of the following observed features of earth history 1 archaean terranes appear to record two periods of rapid continental accretion between 3 8 and 3 5 b y ago and between 3 1 and 2 6 b y ago 2 there are very few differences and many marked similarities between rocks from archaean terranes and equivalent rocks from phanerozoic terranes 3 the total continental area appears to have remained essentially constant for the past 2 b y 4 archaean andesites are comparatively rare and the relative abundances of mafic and siliceous rocks appear to change during the archaean and the proterozoic with siliceous volcanics becoming proportionately more abundant in the geologic record with time 5 plutonic tonalites and trondhjemites appear to have been relatively much more abundant during the archaean plate tectonics is thus shown to have evolved over time due to a gradually decreasing rate of creation of oceanic lithosphere meaning that archaean tectonics and phanerozoic tectonics are but two points on an evolutionary continuum

extent of the microbial biosphere in the oceanic crust we estimate the depth of the 120 c isotherm by constructing crustal thermal gradients based on theoretical and observed conductive heat flux as a function of lithospheric age we chose the 120 c isotherm because it is close to the upper limit for prokaryotic life and therefore the isotherm approximates the maximum depth at which life can persist in the ocean crust the depth of the potential microbial biosphere increases with lithospheric age from approximately 0 5 to 1 km for 1 ma lithosphere to as much as 5 km at a subduction age of 180 ma we use global models of oceanic plate creation to estimate the volume of crust occupied by the biosphere today and throughout geologic time presently the volume of the ocean crust that is capable of containing life is similar to the volume of the oceans 1018 m3 depending on the model used for the growth of continental crust the volume of rock available to house the subsurface biosphere may have remained constant or doubled since the archean although the thermal models presented here provide estimates for the potential depth and volume of rock in which microbes may live the biomass in this volume is not well constrained using a previously published model the prokaryotic biomass in the igneous ocean crust is estimated to exceed that in all aquatic and soil environments and is similar to that in the continental subsurface and in marine sediment most of the crustal biomass beneath the sediments is likely contained within the extrusive layer and this has probably been the case since microbes first colonized the oceanic crust in the archean

displaced antarctic diatoms in the amirante passage abstract displaced antarctic source diatoms are found in surface sediments below 4100 in the amirante passage area but not above this depth their distribution tends to support the conclusion that a sharp velocity gradient exists within the antarctic bottom water aabw in this region below about 4100 m flow velocities are sufficient to resuspend and transport sediment while above this level the aabw is incapable of transporting sediment in suspension

alteration of oceanic volcanic glass textural evidence of microbial activity the subsurface biosphere may constitute as much as 50 percent of earth9s biomass direct and indirect evidence suggests that an extensive biosphere exists in the rocks below the sea floor this survey of basalts of the atlantic pacific and indian oceans supports the hypothesis that bacteria have colonized much of the upper oceanic crust which has a volume estimated at 1018 cubic meters although this is the largest habitat on earth its low abundance of bacteria constitutes much less than 1 percent of earth9s biomass

influence of sedimentation local and regional hydrothermal circulation and thermal rebound on measurements of seafloor heat flux 1 we quantify the influence of environmental processes on measurements of seafloor heat flux with a new one dimensional thermal model that includes time varying sedimentation and boundary conditions represents several scales of hydrothermal and transient conductive processes within basement and allows fluid seepage through accumulating sediments variations in basement thermal conductivity the extent of hydrothermal mixing in upper basement and fluid seepage through sediments each influence seafloor heat flux by 2 8 conductive thermal rebound following the cessation of advective heat loss from the crust may lower seafloor heat flux values by 5 10 even after several to several tens of million years the new models indicate that thermal rebound takes much longer than suggested by earlier analytical calculations mainly because earlier models did not account for the heat capacitance of the conductive lithosphere application of the new model to 3 5 3 6 ma seafloor on the eastern flank of the juan de fuca ridge suggests that anomalously low heat flux in this area is best explained by incomplete conductive thermal rebound in the last 100 200 ka following the burial of numerous basement outcrops application of the new model to the eastern flank of the east pacific rise and extrapolation out to the age of some of the oldest remaining seafloor indicate that sedimentation corrections may be important even where accumulation rates are typical of global values model results also suggest that conductive thermal rebound through thick sediments may bias measurements made on moderate to old seafloor even where there is little evidence at present for ridge flank hydrothermal circulation

diatom distributions in northern north pacific surface sediments and their relationship to modern environmental variables abstract the quantitative analysis of diatom assemblages preserved in 52 samples from the bellingshausen and the amundsen seas provides the first comprehensive view on the distribution of diatoms in surface sediments of the eastern and central pacific sector of the southern ocean on a latitudinal transect along 120 w diatom valve accumulation rates ar reach maximum values 8 10 108 valves m 2 yr 1 in a zone extending over ca 900 km between the antarctic polar front and the maximum average winter sea ice extent and exceed those ars obtained from an eastern transect along 90 w by one order of magnitude lowest diatom concentrations 1 3 106 valves g 1 were encountered in sediments of the sea ice zone affected by winter and summer sea ice the accumulation rate pattern of the most abundant diatom fragilariopsis kerguelensis 50 abundance in 47 samples mirrors the pattern of the total diatom valve ar and the biogenic silica bsi ar making f kerguelensis the major contributor to the bsi preserved at the sea floor relative abundances of diatom species and species groups were statistically compared with a selection of environmental variables such as the mean summer sea surface temperature and salinity mean annual surface nutrient concentration nitrate phosphate silicon mean annual water column stratification mixed layer depth in summer and mean summer and winter sea ice concentrations polynomial canonical redundancy analysis rda revealed the biogeographic distribution of diatom species had the strongest relationship with summer sea surface temperature ssst out of the nine tested environmental variables this relationship accounted for 69 6 of the total variance of the diatom distribution with 29 7 explained by the first gradient significantly correlated to ssst with r2 0 941 and 15 6 explained by the second gradient correlated to both summer and winter sea ice and silicon concentration azpeitia tabularis hemidiscus cuneiformis and roperia tesselata were associated with warmer water conditions 4 c whereas fragilariopsis curta f separanda f rhombica and thalassiosira gracilis were correlated with cold ssst confirming these environmental relationships is crucial for the development of reference data sets used in quantitative estimations of palaeoclimatic and palaeoceanographic conditions with statistical methods this new data set represents the first modernised treatment of diatom remains from the se pacific ocean and generally supports the use of a circum polar database for the determination of summer sst sea ice and potentially biogenic silica distribution of the southern ocean back into the late quaternary

the deep history of earth s biomass the subsurface deep biosphere represents one tenth to one third of earth9s total global present day biomass the rest is dominated by land plants a relatively recent development in geological history before c 400 ma a relatively low surface biomass with high productivity and fast turnover supplied carbon to a deep biosphere with high biomass but low productivity and slow turnover here we argue that the deep biosphere outweighed the surface biosphere by about one order of magnitude for at least half of the history of life on earth this result offers a new perspective on the history of life on earth with important implications for the search for life on other worlds

a quantitative assessment of diatom dissolution and late quaternary primary productivity in the eastern equatorial pacific the eastern equatorial pacific eep is an important area for ocean atmosphere carbon exchange and yields different opal accumulation records for sites influenced by equatorial divergence and peru upwelling the divergence zone is characterized by a lower opal accumulation rate during the last glacial compared with the holocene but the reverse is true for the peru upwelling zone as a gauge of opal production versus preservation in the eep differential diatom preservation was investigated via a quantitative four stage preservation index using the vellum of the ubiquitous tropical centric diatom azpeitia nodulifer we find similar dissolution records at both sites from the last glacial maximum lgm through the holocene despite differing accumulation rates implying that production not preservation controlled the accumulation rates thus the increased silica accumulation in the peru upwelling region is related to increased production suggesting higher availability of silica in the photic zone in accord with the silica leakage hypothesis described by matsumoto et al 2002 silicic acid leakage from the southern ocean a possible explanation for glacial atmospheric co global biogeochemical cycles 5 doi 10 1029 2001gb001442 and discussed by richaud et al 2007 furthermore we suggest an ecological control on opal preservation due to silica recycling by diatoms in the water column most likely in the photic zone increased production causes rapid silica recycling and thinner walled frustules resulting in enhanced water column dissolution in this setting diatom dissolution is independent of the rate of accumulation of silica or sediment high opal productivity does not necessarily lead to high preservation as proposed for southern ocean sediments sayles f martin w chase z anderson r 2001 benthic remineralization and burial of biogenic sio2 caco3 organic carbon and detrital material in the southern ocean along a transect at 170 west deep sea research ii 48 4323 4383 our observations are compatible with a production increase in the late deglacial and early holocene as reported by loubere 2001 nutrient and oceanographic changes in the eastern equatorial pacific from the last full glacial to the present global and planetary change 29 77 98 and inferred by spero h and lea d 2002 the cause of carbon isotope maximum events on glacial terminations science 296 522 525 and rickaby r and osborne a 2006 oceanic redistribution of phosphate during the last deglaciation in preparation

structure and variability of oceanic crust on the flanks of the east pacific rise between 11 and 13 n we use over 500 seismograms collected by five ocean bottom seismometers to examine the structure and variability of 0 5 m y old crust in the rivera ocean seismic experiment rose area of the east pacific rise between 11 and 13 n there are no significant differences among the first arrival travel times for 10 independent refraction line segments along the isochron amplitude patterns recorded on the individual lines however suggest that structural boundaries within the upper crust vary by hundreds of meters in depth over lateral distances of tens of kilometers within this 200 km segment of lithosphere on the basis of the modeling of amplitude patterns at ranges of 5 10 km and of comparisons with the upper crust sampled at deep sea drilling project hole 504b and in ophiolite complexes layer 2 can be divided into three units 2a corresponds to extrusive volcanics with a steep velocity gradient 2b to extrusives with a near zero velocity gradient and 2c to a complex region of transition from extrusives to sheeted dikes the total thickness of layer 2 varies by about 0 7 km over the length of the line another amplitude peak which varies in range between 14 and 21 km may be related to the downward transition from sheeted dikes to isotropic gabbros within layer 3 the variability of these two amplitude patterns provides direct evidence that the along strike structure of oceanic crust in the rose area is definably heterogeneous and that the process of crustal accretion is likewise variable on the scale resolved by amplitude and travel time information

archean plate tectonics what can be learned from continental geology some basic questions about archean plate tectonics can be addressed by examining accretionary archean margins in particular fault zones with significant strike slip components on the canadian shield 1 were the oceanic plates typically rigid like modern plates yes significant lateral viscosity contrasts in the lithosphere between plates and plate boundaries are required for major strike slip faults to exist conversely strike slip faults are a kinematic consequence of rigid plates 2 did large oceanic plates exist in the archean probably first the length and offset of the longest preserved segments of archean faults are similar to modern examples such as in alaska less directly the duration of a period with a consistent sense of strike slip at a point on the continental side of an accretionary margin should be related to the time that a typical oceanic plate remains outboard of the margin this time varies proportionally with size of typical ocean plates and inversely with their velocity the

mathematical modeling of diffuse flow in seafloor hydrothermal systems the potential extent of the subsurface biosphere at mid ocean ridges abstract we describe a variety of one and two dimensional mathematical modeling approaches to characterizing diffuse flow circulation at mid ocean ridge hydrothermal systems the goal is to estimate the potential extent of the sub seafloor microbial biosphere based on subsurface contours of the 120 c isotherm as determined from the various models the models suggest that the sub seafloor depth for microbial life may range from less than 1 m in some places to the thickness of crustal layer 2a of 500 m in others this depth depends primarily on how diffuse flow is driven the 120 c isotherm tends to be much deeper if diffuse flow is induced as boundary layer flow near high temperature plumes than if it results from conductive cooling or mixing near the seafloor because the heat flow alone may not allow identification of the flow regime in the subsurface we highlight the use of chemical tracers as an additional constraint that sheds light into the flow and reaction patterns associated with vents we use thermodynamic modeling which connects the temperature of the diffuse fluid to its chemical composition as the temperature composition relationships differ for mixing versus conductive heating and cooling the fluid geochemistry can shed light on subsurface transport using methane as an example the geochemical models indicate subsurface microbial methane production and consumption in different regions of the vent field near epr 9 50 n

extending the upper temperature limit for life the upper temperature limit for life is a key parameter for delimiting when and where life might have evolved on a hot early earth the depth to which life exists in the earth s subsurface and the potential for life in hot extraterrestrial environments a combination of geological and

kinetics of gypsum nucleation and crystal growth from dead sea brine abstract the dead sea brine is supersaturated with respect to gypsum 1 42 laboratory experiments and evaluation of historical data show that gypsum nucleation and crystal growth kinetics from dead sea brine are both slower in comparison with solutions at a similar degree of supersaturation the slow kinetics of gypsum precipitation in the dead sea brine is mainly attributed to the low solubility of gypsum which is due to the high ca 2 so 4 2 molar ratio 115 high salinity 280 g kg and to na inhibition experiments with various clay minerals montmorillonite kaolinite indicate that these minerals do not serve as crystallization seeds in contrast calcite and aragonite which contain traces of gypsum impurities do prompt precipitation of gypsum but at a considerable slower rate than with pure gypsum this implies that transportation inflow of clay minerals calcite and local crystallization of minerals in the dead sea does not prompt significant heterogeneous precipitation of gypsum based on historical analyses of the dead sea it is shown that over the last decades as inflows to the lake decreased and its salinity increased gypsum continuously precipitated from the brine the increasing salinity and ca 2 so 4 2 ratio which results from the precipitation of gypsum lead to even slower kinetics of nucleation and crystal growth which resulted in an increasing degree of supersaturation with respect to gypsum therefore we predict that as the salinity of the dead sea brine continues to increase accompanied by dead sea water level decline although gypsum will continuously precipitate the degree of supersaturation will increase furthermore due to progressively slower kinetics

early life recorded in archean pillow lavas pillow lava rims from the mesoarchean barberton greenstone belt in south africa contain micrometer scale mineralized tubes that provide evidence of submarine microbial activity during the early history of earth the tubes formed during microbial etching of glass along fractures as seen in pillow lavas from recent oceanic crust the margins of the tubes contain organic carbon and many of the pillow rims exhibit isotopically light bulk rock carbonate 13 c values supporting their biogenic origin overlapping metamorphic and magmatic dates from the pillow lavas suggest that microbial life colonized these subaqueous volcanic rocks soon after their eruption almost 3 5 billion years ago

a switch from si oh 4 to no 3 depletion in the glacial southern ocean 1 phytoplankton in the antarctic deplete silicic acid si oh 4 to a far greater extent than they do nitrate no3 this pattern can be reversed by the addition of iron which dramatically lowers diatom si oh 4 no3 uptake ratios higher iron supply during glacial times would thus drive the antarctic towards no3 depletion with excess si oh 4 remaining in surface waters new 30si and 15n records from antarctic sediments confirm diminished si oh 4 use and enhanced no3 depletion during the last three glaciations the present low si oh 4 water is transported northward to at least the subtropics we postulate that the glacial high si oh 4 water similarly may have been transported to the subtropics and beyond this input of si oh 4 may have caused diatoms to displace coccolithophores at low latitudes weakening the carbonate pump and increasing the depth of organic matter remineralization these effects may have lowered glacial atmospheric pco2 by as much as 60 ppm

heat flow and flexure at subduction zones 1 it is often suggested that heat flow in the incoming plate at subduction zones is lower than expected for crust of that age due to increased hydrothermal circulation from flexure extending about 300 km seaward of the trench and faulting observed starting about 50 75 seaward of the trench testing this suggestion using global heat flow data shows no significant difference between heat flow near the trench and the global means for the same age crust however on average heat flow in the overriding plate is about 60 of that in the incoming plate

enhanced microbial activity in carbon rich pillow lavas ordovician great britain and ireland there is extensive evidence for the microbial colonization of seafloor basalts in the modern ocean and in the geological record the sulfur isotope composition of pyrite in the basalts commonly indicates marked isotopic fractionation due to microbial sulfate reduction sections through the nemagraptus gracilis zone ordovician in great britain and ireland are characterized by both widespread pillow lavas and organic rich seafloor sediment allowing an exceptional opportunity to assess whether the availability of organic carbon influenced the extent of microbial activity in the basalts in deep geological time whole rock data from basalts at 10 localities show that there is a relationship between sulfur isotopic composition and the carbon content of the basalt at two localities where organic carbon was entrained in the basalt isotopic compositions are heavy compared to compositions in carbon poor basalt implying that microbial activity exhausted the supply of seawater sulfate in most basalt microbial activity was limited by the supply of carbon but where the basalt incorporated carbon during emplacement on the seafloor microbial activity became sulfate limited

iron and silicic acid concentrations regulate si uptake north and south of the polar frontal zone in the pacific sector of the southern ocean abstract we investigated the relative roles of fe and silicic acid availabilities in regulating si uptake rates across the polar frontal zone in the pacific sector of the southern ocean 59 68 s 170 w during the us jgofs antarctic environment southern ocean process study aesops meridional gradients in silicic acid concentration si oh 4 of about 0 25 0 56 m km 1 were observed in this area during austral spring and summer 1997 1998 with si oh 4 ranging from 32 si oh 4 and 15 no 3 uptake rates biogenic silica concentrations and si oh 4 no3 uptake ratios fe addition had little or no effect on si uptake rates in enrichments conducted in the low si waters north of the si gradient however fe addition increased si uptake rates 3 5 times over controls in enrichments conducted in the high si waters south of the gradient in both spring and summer fe addition decreased si oh 4 no3 uptake ratios by 2 5 times largely due to stimulation of no3 uptake rates zn addition had no effect on si oh 4 and no3 uptake rates short term 24 h si additions had varying effects on si uptake rates depending on season and location in spring additions of 40 m si to water from bottle enrichments conducted north of the si gradient in situ si oh 4 15 m did not increase si uptake rates initially but did increase uptake rates after 8 days in the summer enrichment north of the si gradient in situ si oh 4 5 m 50 m si additions doubled in situ si uptake rates in the initial water collected for the enrichment and increased si uptake rates as much as 16 fold during the experiment south of the si gradient where in situ si oh 4 was 40 m in both spring and summer si addition had no effect on in situ si uptake rates in the initial enrichment water nor on any si uptake rates measured during the experiment our results indicate that both fe and si availabilities regulate si uptake rates and silica production in the southern ocean along 170 w fe limitation appears to restrict si uptake rates south of the si gradient and plays a role in preventing si depletion south of the acc where ambient si oh 4 never fell below 40 m during 1997 1998 our experiments in the seasonal ice zone at 62 suggest that si uptake in this area switched from being fe limited in the spring when in situ si oh 4 was 40 m to si limited in the summer when si oh 4 was

record of a mid pleistocene depositional anomaly in west antarctic continental margin sediments an indicator for ice sheet collapse abstract modern global warming is likely to cause future melting of earth s polar ice sheets that may result in dramatic sea level rise a possible collapse of the west antarctic ice sheet wais alone which is considered highly vulnerable as it is mainly based below sea level may raise global sea level by up to 5 6 m despite the importance of the wais for changes in global sea level its response to the glacial interglacial cycles of the quaternary is poorly constrained moreover the geological evidence for the disintegration of the wais at some time within the last ca 750 kyr possibly during marine isotope stage mis 11 424 374 ka is ambiguous here we present physical properties palaeomagnetic geochemical and clay mineralogical data from a glaciomarine sedimentary sequence that was recovered from the west antarctic continental margin in the amundsen sea and spans more than the last 1 myr within the sedimentary sequence proxies for biological productivity such as biogenic opal and the barium aluminum ratio and the supply of lithogenic detritus from the west antarctic hinterland such as ice rafted debris and clay minerals exhibit cyclic fluctuations in accordance with the glacial interglacial cycles of the quaternary a prominent depositional anomaly spans mis 15 mis 13 621 478 ka the proxies for biological productivity and lithogenic sediment supply indicate that this interval has the characteristics of a single prolonged interglacial period even though no proxy suggests environmental conditions much different from today we conclude that if the wais collapsed during the last 800 kyr then mis 15 mis 13 was the most likely time period apparently the duration rather than the strength of interglacial conditions was the crucial factor for the wais drawdown a comparison with various marine and terrestrial climate archives from around the world corroborates that unusual environmental conditions prevailed throughout mis 15 mis 13 some of these anomalies are observed in the pelagic southern ocean and the south atlantic and might originate in major ice sheet drawdown in antarctica but further research is required to test this hypothesis

3 5 billion years of glass bioalteration volcanic rocks as a basis for microbial life abstract alteration textures in volcanic glass from the seafloor fall into two classes one suggestive of abiotic diffusive hydration and chemical exchange and another likely to be caused by microbial cavity forming congruent dissolution glass bioalteration is common in submarine lavas throughout the world s ocean dominant in the upper 300 m of the oceanic crust and found in all well preserved ophiolites and greenstone belts dating back to 3 5 ga it may yield a significant fraction of the global biomass and geochemical fluxes and is relevant to the development of the earliest life on earth we present a critical review concerning these glass bioalteration textures and present new data on their microchemical environment we explore arguments for their biogenicity and further develop the prevalent model for their formation by relating corrosion morphology to the mechanism of microbial dissolution biological alteration produces conspicuous micron scale granular and tubular textures granular glass alteration is well explained by colonizing microbes that selectively dissolve the glass in their contact area forming a sponge like interconnected network of micron sized cavities along glass surfaces tubular alteration meanwhile is more likely to be caused by filamentous cell extensions in a process similar to fungal tunneling of soil feldspars and marine carbonates while we see clear functional similarities to fungal dissolution behavior we do not know whether fungal or prokaryotic organisms are involved however this functional constraint may eventually help to identify potential microbes responsible for these features potentially including eukaryotic or prokaryotic organisms yet we caution that these organisms may be difficult to identify and to study because they are likely to be sparsely distributed slow growing and difficult to cultivate

estimation of oceanic hydrothermal heat flux from heat flow and depths of midocean ridge seismicity and magma chambers the difference between the heat flow predicted by thermal models of the lithosphere and that measured at the seafloor can be used to estimate the cooling by hydrothermal circulation however this approach may yield an overestimate because measurements in thinly sedimented young crust are typically made at topographic lows where hydrothermal circulation may systematically lower heat flow to circumvent this bias we estimate the cooling using the depths of midocean ridge earthquakes and magma chambers in addition to heat flow data the results indicate deeper hydrothermal circulation at slow spreading ridges and higher near axial hydrothermal heat loss at fast spreading ridges the predicted global hydrothermal heat flux is 80 of that for models constrained only by heat flow

expanding frontiers in deep subsurface microbiology abstract the subsurface biosphere on earth appears to be far more expansive and physiologically and phylogenetically complex than previously thought here several aspects of subsurface microbiology are discussed molecular and biogeochemical data as well as characteristics from new isolates suggest that ecosystems below deep sea hydrothermal vents are inhabited primarily by thermophilic archaea and bacteria the void spaces and conduits in basalt at mid ocean ridges and even more so at sediment covered hydrothermal vent sites represent promising hunting grounds for novel chemosynthetic archaea and bacteria as examples we highlight the subsurface microbial communities within the basalt flanks of the juan de fuca ridge off british columbia and the hydrothermal sediments at the guaymas basin in the gulf of california and at middle valley on the juan de fuca ridge in the deep continental subsurface microbial studies have primarily targeted aquifers in basaltic and granitic rock with an almost exclusive emphasis on h2 driven chemolithoautotrophy for example in the subsurface water from lidy hot springs idaho usa h2 consuming methanogenic archaea represent the most populous organisms comprising 95 of all cells besides h2 other potential sources of chemical energy reducing power are considered including abiotically synthesized organic matter and reduced sulfur compounds in addition the well established sequences of redox couples in microbial metabolism are investigated at elevated temperatures using a thermodynamic approach values of peo for 11 common reduction half reactions are tabulated at 25 50 100 and 150 c although many modes of metabolism may be employed by subsurface biota sulfate reduction appears to be one of the more ubiquitous strategies recent studies of sulfate reducing archaea and bacteria in marine and continental systems are reviewed

intense summer si recycling in the surface southern ocean 1 si cycle in surface waters was investigated in summer 2003 during a transect conducted from south australia to antarctica diatoms dominated the microphytoplankton silicic acid was depleted up to 60 s a subsurface maximum of biogenic silica biosilica was observed in the permanent open ocean zone in the 100 0 01 light zone the ratio of depth integrated biosilica dissolution rate d to depth integrated biosilica production rate p ranged between 0 to 3 1 being 1 for 5 of our 6 stations the biosilica dissolution was related to the percentage of dead diatoms but not to the temperature and might be at least partially under bacteria mediation this study shows that during summer the southern ocean silicate pump can be much less efficient than usually expected existence of scenarios with intense surface si recycling in the southern ocean has major consequences both for modelers and paleoceanographers index terms 4805 oceanography biological and chemical biogeochemical cycles 1615 1615 global change biogeochemical processes 4805 4855 oceanography biological and chemical plankton 4207 oceanography general arctic and antarctic oceanography 4870 oceanography biological and chemical stable isotopes

hydrothermal recharge and discharge across 50 km guided by seamounts on a young ridge flank hydrothermal circulation within the sea floor through lithosphere older than one million years myr is responsible for 30 of the energy released from plate cooling and for 70 of the global heat flow anomaly the difference between observed thermal output and that predicted by conductive cooling models 1 2 hydrothermal fluids remove significant amounts of heat from the oceanic lithosphere for plates typically up to about 65 myr old3 4 but in view of the relatively impermeable sediments that cover most ridge flanks5 it has been difficult to explain how these fluids transport heat from the crust to the ocean here we present results of swath mapping heat flow geochemistry and seismic surveys from the young eastern flank of the juan de fuca ridge which show that isolated basement outcrops penetrating through thick sediments guide hydrothermal discharge and recharge between sites separated by more than 50 km our analyses reveal distinct thermal patterns at the sea floor adjacent to recharging and discharging outcrops we find that such a circulation through basement outcrops can be sustained in a setting of pressure differences and crustal properties as reported in independent observations and modelling studies

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

abiotic hydrogen h2 sources and sinks near the mid ocean ridge mor with implications for the subseafloor biosphere free hydrogen h2 is a basal energy source underlying chemosynthetic activity within igneous ocean crust in an attempt to systematically account for all h2 within young oceanic lithosphere

in situ enrichment of ocean crust microbes on igneous minerals and glasses using an osmotic flow through device the integrated ocean drilling program iodp hole 1301a on the eastern flank of juan de fuca ridge was used in the first long term deployment of microbial enrichment flow cells using osmotically driven pumps in a subseafloor borehole three novel osmotically driven colonization systems with unidirectional flow were deployed in the borehole and incubated for 4 years to determine the microbial colonization preferences for 12 minerals and glasses present in igneous rocks following recovery of the colonization systems we measured cell density on the minerals and glasses by fluorescent staining and direct counting and found some significant differences between mineral samples we also determined the abundance of mesophilic and thermophilic culturable organotrophs grown on marine r2a medium and identified isolates by partial 16s or 18s rdna sequencing we found that nine distinct phylotypes of culturable mesophilic oligotrophs were present on the minerals and glasses and that eight of the nine can reduce nitrate and oxidize iron fe ii rich olivine minerals had the highest density of total countable cells and culturable organotrophic mesophiles as well as the only culturable organotrophic thermophiles these results suggest that olivine a common igneous mineral in seawater recharged ocean crust is capable of supporting microbial communities that iron oxidation and nitrate reduction may be important physiological characteristics of ocean crust microbes and that heterogeneously distributed minerals in marine igneous rocks likely influence the distribution of microbial communities in the ocean crust

dissolution and preservation of antarctic diatoms and the effect on sediment thanatocoenoses abstract comparison of southern ocean diatom populations from i surface ocean production ii underlying antarctic sediments and iii laboratory dissolution experiments demonstrates that dissolution can account for the temporal and spatial variations in sedimentary diatom assemblages observed in southern ocean sediments increasing dissolution causes relative depletions in n kerguelensis k enrichments in t lentiginosa l and slight enrichments in e antarctica a this reflects the relative susceptibility to dissolution of the three species that dominate antarctic sediments we have devised a preservation index for the southern ocean based on the ratio k k l to estimate relative extents of dissolution and applied it to natural assemblages holocene southern ocean sediments display increasing opal preservation toward higher latitudes but south of the antarctic polar front preservation decreases in the order well preserved se indian s atlantic sw indian se pacific poorly preserved dissolution also accounts for the pattern of diatom assemblages in the last glacial maximum lgm sediments of the indian and pacific sectors but in the atlantic increased e antarctica abundances at lgm must have resulted from an increase in surface ocean production of this species holocene and lgm diatoms in atlantic and pacific sector sediments are equally well preserved but in the indian sectors holocene sediments are better preserved than those of lgm age paleoceanographic and paleoclimatic transfer functions derived from factor analyses of variations in the sedimentary abundances of these three diatoms have ignored the effects of differential dissolution on thanatocoenosis and thus should be interpreted with caution

high temperature seafloor hydrothermal circulation over geologic time and archean banded iron formations 1 under the assumption of simple plate tectonics with a range of continental growth scenarios we construct models of global lithospheric heat loss hydrothermal heat loss and hydrothermal iron flux to the ocean as functions of geologic time from 4 0 ga to present the models show that lithospheric heat loss scales with the square root of the plate creation rate whereas hydrothermal heat loss scales linearly with that rate thus during the archean lithospheric and hydrothermal heat losses were 3 and 10 times greater than present respectively straightforward extrapolation of hydrothermal fe flux from the present to the archean using these models indicates that hydrothermal fe may not have been sufficient to supply the large superior type banded iron formations deposited between 2 7 and 1 8 ga

quantification of the biogenic silica dissolution in southern ocean sediments abstract a transfer function has been established to quantify the dissolution of diatom silica in southern ocean sediments the relationship between the amount of silica dissolution and changes in diatom species distribution is built by controlled progressive dissolution of biogenic silica in five recent sediment samples from box core tops each representative of a modern diatom species sediment assemblage the amount of dissolved silica was measured for each experiment the resulting data set of species abundances 42 samples containing 32 diatom species and 2 silicoflagellate genera was added to the modern data base of diatom species distributed over the southern ocean 124 core tops q mode factor analysis individualizes four factors explaining 83 of the variance the first three factors are controlled by surface water properties mostly temperature the fourth factor is the only one correlated with loss of silica in the reference samples r 0 900 we quantified the dissolution factor using this correlation superficial sediments of the southeast indian ocean are characterized from low to high latitudes by a decrease in silica loss by dissolution from 50 to 10 from the subantarctic zone 40 s to around 55 s followed by an increase of silica loss to values larger than 60 between 63 and 68 s application of the dissolution factor in two cores from the southern ocean 44 and 55 s shows enhanced opal dissolution during the last glaciation particularly during emiliani s stage 3 from 40 000 to 30 000 yr b p