discovery of new hydrothermal vent sites in bransfield strait antarctica we carried out a search for hydrothermal vents in the central basin of bransfield strait antarctica the zaps zero angle photon spectrometer chemical sensor and instrument package oregon state university ofos ocean floor observation system camera sled and tvg tv grab geomar were used to explore the water column and underlying seafloor these operations were supplemented with a series of dredges hydrothermal plumes over hook ridge at the eastern end of the basin are confined to the e ridge crest and se flank the plumes are complex and sometimes contain two turbidity maxima one widespread feature centered at 1150 m and a smaller more localized but broad maximum at 600 800 m we traced the source of the shallower plume to a sunken crater near the ridge crest using sensors on the zaps instrument package subsequently two tv grabs from the crater brought back hot soupy sediment 42 49 c overlain by hard siliceous crusts and underlain by a thick layer of volcanic ash we also recovered chimney fragments whose texture and mineralogy indicate venting temperatures in excess of 250 c native sulfur and fe sulfides occur in fractures and porous layers in sediment from throughout the area pore water data from the crater site are consistent with venting into a thin sediment layer and indicate phase separation of fluids beneath hook ridge the source of the deeper plumes at hook ridge has yet to be located we also explored a series of three parallel volcanic ridges west of hook ridge called three sisters we detected water column anomalies indicative of venting with the zaps package and recovered hydrothermal barites and sulfides from middle sister we spent considerable time photographing middle sister and hook ridge but did not identify classic vent fauna at either location we either missed small areas with our photography or typical mor vent fauna are absent at these sites

the relationship between silicon isotope fractionation in sponges and silicic acid concentration modern and core top studies of biogenic opal recent work has shown the silicon isotope composition denoted by 30si of deep sea sponges reflects the concentration of ambient silicic acid si oh 4 in seawater however existing calibrations are based predominantly on living sponges collected from the southern ocean these data cannot however be used to determine whether other parameters that correlate with silicic acid in the southern ocean such as temperature and salinity influence 30si of sponges furthermore the published data do not demonstrate whether disaggregated core top sedimentary spicules preserve the primary 30si signal recorded in living sponges here we address both of these issues we refine and widen the existing calibration by including a global distribution of modern sponges in addition we provide the first systematic calibration from spicules picked from core top sediments that covers sites from different ocean basins the relationship between si oh 4 and 30si in sponge spicules is the same in different ocean basins between specimens that grew in different temperature and salinity conditions our core top data agree well with the modern sponge calibration indicating there are no significant post depositional effects or early diagenetic overprints these two new datasets support the assertion that sponge 30si can be used as a proxy for silicic acid concentrations in the past

germanium silicon fractionation in the weathering environment abstract we present a detailed study of germanium behavior in the soil weathering environment as an important step toward using the ge si system as a tracer of silicate weathering processes in both modern and ancient environments intensely weathered soils developed on hawaiian basalts have bulk soil ge si ratios 2 to 10 times higher than fresh basalt e g 10 to 25 mol mol vs 2 5 mol mol soil ge concentrations increase with si and decrease with fe suggesting that ge sequestration is related to accumulation of secondary soil silicates rather than retention in soil fe oxy hydroxides sequential extractions of these soils suggest that ge si fractionation takes place by ge sequestration during the initial precipitation of secondary soil aluminosilicates principally allophane further si loss and changes in mineralogy as these soils age result in little additional ge si fractionation ge si ratios in granitic soils and saprolites are strongly influenced by relative weathering rates of primary minerals kaolinite has a ge si ratio 5 9 mol mol higher than the plagioclase from which it forms 3 1 mol mol whereas accumulation of primary quartz ge si 0 5 mol mol prevents granitic soils from attaining high ge si ratios laboratory synthesis of allophane confirms that ge is preferentially partitioned into the solid phase upon precipitation of secondary aluminosilicates from solution

circulation mixing and production of antarctic bottom water abstract the antarctic source of bottom water to the abyssal layer of the world ocean is examined as well as its large scale flow pattern and ultimate entrainment rate into the deep water above we make use of the available high quality station data in the southern ocean to construct bottom maps of neutral density and mean property maps including chlorofluorocarbon cfc for the abyssal layer underneath a selected neutral density surface the maximum density at the sill depth of drake passage is used to distinguish between the voluminous deep water mass that is a continuous component of the antarctic circumpolar current from the relatively denser bottom water originated along the antarctic continental margins based on water density antarctic bottom water aabw is defined here generically to include all volumes of non circumpolar water of antarctic origin over the shelf regime multiple localized sources of specific aabw types contribute to the abyssal layer of the adjacent antarctic basins characteristics of these dense bottom waters reflect closely those observed on the parent shelf water mass spreading paths of newly formed deep and bottom waters over the slope regime and their subsequent oceanic circulation patterns are analyzed on the basis of global property maps for the aabw layer interior mixing and interbasin exchanges of aabw are deduced from mean characteristic curves following the southern streamline of the antarctic circumpolar current outflow and mixing of aabw from the weddell sea to the argentine basin is depicted using density and cfc distributions of two zonal hydrographic lines recirculation and mixing of deep and bottom waters within the weddell gyre are also detailed using a meridional section along the greenwich meridian the strength of all localized sources of aabw combined is estimated by two independent approaches an estimate of the total production rate of aabw is calculated based on the oceanic cfc budget for the aabw layer offshore of the 2500 m isobath the sum of all downslope inputs of well ventilated bottom water types underneath the top isopycnal must account for the measured cfc content in the bottom layer the resulting total aabw production rate is about 8 sv which is a conservative figure that neglects the loss of cfc bearing waters across the top isopycnal in recent years whereas about 9 5 sv is calculated assuming a well mixed bottom layer making use of their transient nature cfc distributions at the top of the aabw layer indicate that more direct and rapid entrainment of cfc rich bottom waters below occurs over localized areas with relatively strong upwelling rates and enhanced vertical mixing a second more ad hoc but independent oceanic mass budget of the bottom layer is also constructed a typical basin wide rate of deep upwelling of 3 10 7 m s 1 requires 10 sv 1 sv 106 m3 s 1 of newly formed aabw to sink down the slope around antarctica we have also formulated a spatial distribution of deep upwelling on the isopycnal at the top of the aabw it is expressed as a combination of wind topographic and turbulent components which in turn are functions of the isopycnal depth bottom depth and bottom layer thickness this non uniform upwelling field yields about 12 sv of aabw exported across the top isopycnal fortuitously the overall average of upward speed at the top isopycnal 3 7 10 7 m s 1 compares well with previous estimates of deep upwelling in the northern basins a series of likely sites for strong vertical entrainment of aabw are clearly identified in the modeled distribution of deep upwelling consonant with the observed cfc distributions on the top isopycnal altogether regions with relatively high upwelling rates 5 10 7 m s 1 occupy only a quarter of the total areal extent of the top isopycnal but they account for as much as 45 of the total vertical transport

holocene aeolian activity in the southwestern kalahari desert southern africa significance and relationships to late pleistocene dune building events little is known about the timing of dune building episodes in the southwestern kalahari desert previously arid phases when dune activity occurred have been inferred from gaps in chronologies derived from information that attests to former humid periods to redress this optically stimulated luminescence osl dating was applied to sediment samples taken from a range of aeolian landforms in the sw kalahari four periods of dune building are identified in the late pleistocene and holocene holocene aeolian activity at 6 ka and 1 2 ka led to the construction of localised dune forms in contrast to late pleistocene times when the extensive field of linear dunes that dominates the region was emplaced late holocene aridity was however sufficient to allow rapid emplacement of the lunette dune at witpan the record of aeolian activity is evaluated in the context of humid chronologies and an ocean atmosphere model of holocene climate change with good agreement obtained it is concluded that the application of

warming phases in southern africa during the last 150 000 years an overview abstract firmly based palaeoenvironmental data for southern africa prior to 40 000 yr b p are sparse the only site which is likely to be able to provide useful information for isotope stage 6 is the pretoria saltpan warming at the end of this stage appears to have been rapid and to have been associated with increased precipitation in the interior of the sub continent in contrast dry conditions appear to have prevailed in the southwestern areas during the warmest phases of isotope stage 5 this regional difference first became apparent during the pliocene during the last glacial maximum temperatures based on isotope ratios reached their lowest values of 5 6 c below present in the southern part of the subcontinent and widespread dryness prevailed warming became quite rapid after 16 000 yr b p and was almost everywhere associated with a marked increase in wetness to around or even above present levels this warming phase continued until the beginning of the holocene the terminal pleistocene was however marked by desiccation in the arid western areas of special interest is the holocene altithermal which can be placed between 7000 and 6500 yr b p the extent of the temperature rise cannot be specified with any precision but probably did not exceed the holocene mean by more than 2 c in the southern cape and karoo more summer rain apparently occurred than during isotope stage 2 and in the early holocene and this trend towards year round rainfall appears to have become increasingly pronounced through the later holocene until about 2000 yr b p this argues in a general way for an increase in the proportion of summer rainfall with rising temperature in the present winter rainfall areas of southern africa

physical controls on biogeochemical zonation in the southern ocean the primary control on the n s zonation of the southern ocean is the wind induced transport of the antarctic circumpolar current acc the acc divides the southern ocean into three major zones the subantarctic zone saz north of the acc the acc transport zone and the zone south of the acc saccz the zone of acc transport is most often subdivided into two zones the polar frontal zone pfz and the antarctic zone aaz but it may be appropriate to define more subzones or indeed only one at some longitudes to maintain geostrophic balance isopycnals must slope upwards to the south across the acc thus raising nutrient rich deep water closer to the surface as one goes polewards in addition silicate concentrations increase polewards along isopycnals because of diapycnic mixing with silicate rich bottom water surface silicate concentrations therefore decrease northwards from high levels in the saccz to low levels in the saz within the saz and pfz and even in the northern part of the aaz silicate levels may drop to limiting levels for siliceous phytoplankton production during summer nitrate concentrations also decrease northwards but only become limiting in the subtropical zone north of the saz the second circumpolar control is the changing balance of stratification with temperature dominating near surface stratification in the saz and salinity dominating further south because of fresh water input to the surface from melting ice this results in circumpolar features such as the subsurface 2 c temperature minimum and the subduction of the salinity minimum of antarctic intermediate water which are often but not always associated with frontal jets and large transports the transport of the acc is dynamically constrained into narrow bands the number and latitudinal location of which are controlled by the bathymetry and so vary with longitude thus it is not the fronts that are circumpolar but the total acc transport and scalar properties of the salinity and temperature fields evidence of summer silicate and nitrate uptake in all zones saz pfz and aaz shows that there is productivity despite their high nutrient low chlorophyll status blooms covering large areas say 400 km across in the pfz and aaz are found in the vicinity of submarine plateaux which suggest benthic iron fertilizatio

diagenetic fractionation of ge and si in reducing sediments the missing ge sink and a possible mechanism to cause glacial interglacial variations in oceanic ge si the average ge si ratio in the ocean is determined by the budgets for each of these elements previous budget formulations have assumed that the only important sink for both elements is burial as opal based on studies of the si cycle and the close oceanic coupling observed between inorganic ge and si distributions however these budgets implied two paradoxes 1 hydrothermal flow through ocean ridges is smaller than predicted by other tracers and 2 the lower ge si ratio of opal deposited during glacial times compared to that deposited during interglacial times required enhanced weathering during cooler drier climates both paradoxes could be resolved if a significant sedimentary sink for ge other than opal burial could be identified and the objective of this study was to search for one two pore water profiles collected in equatorial pacific sediments show that ge and si behave similarly in the upper 10 cm of sediment indicating no evidence for a significant non opal sink for ge in oxic sediments by contrast profiles in several cores from the california margin demonstrate that in reducing sediments ge diagenesis is poorly coupled to si diagenesis significant ge removal is evident both downcore and sometimes in the near surface benthic flux chamber measurements at three continental slope stations all with an oxic layer less than 1 cm thick and large iron gradients in near surface pore waters showed that 55 9 of the ge released by opal dissolution is sequestered however at two locations with anoxic sediments but little pore water fe 2 in the upper 2 cm flux measurements indicated little fractionation from the oceanic ratio during diagenesis implicating the importance of iron for fractionating ge from si during diagenesis if the ge sequestration observed in the iron rich ca margin sediments is typical of all slope sediments using a depth range of 200 1000 m then the ge sink is sufficient to bring the hydrothermal budget based on ge into concurrence with that based on other tracers the temporal variation in oceanic ge si could be explained if ge and si inputs remain constant and the effective diagenetic fractionation of ge increases by a factor of 2 3 during glacial times increased fractionation would require that glacial periods are characterized by increased opal dissolution in iron rich reducing sediments this could be caused by 1 thinning of the oxygenated sediment layer in response to decreased bottom water oxygen concentrations or increased rain of organics to the sea floor 2 increased rain of iron rich detrital sediments in areas receiving high opal rain 3 increased rain of opal to sediments in margin areas if the oceanic ge si ratio reflects increased rain of diatom opal or organic carbon in margin areas during glacial periods it may indicate an increase in the efficiency of the biological pump for co2 during glacial times

germanium isotopic variations in igneous rocks and marine sediments a new technique for the precise and accurate determination of ge stable isotope compositions has been developed and applied to silicate rocks and biogenic opal the analyses were performed using a continuous flow hydride generation system coupled to a mc icpms samples have been purified through anion and cation exchange resins to separate ge from matrix elements and eliminate potential isobaric interferences variations of 74ge 70ge ratios are expressed as 74ge values relative to our internal standard and the long term external reproducibility of the data is better than 0 2 for sample size as low as 15 ng of ge data are presented for igneous and sedimentary rocks and the overall variation is 2 4 in 74ge representing 12 times the uncertainty of the measurements and demonstrating that the terrestrial isotopic composition of ge is not unique co variations of 74ge 70ge 73ge 70ge and 72ge 70ge ratios follow a mass dependent behaviour and imply natural isotopic fractionation of ge by physicochemical processes the range of 74ge in igneous rocks is only 0 25 without systematic differences among continental crust oceanic crust or mantle material on this basis a bulk silicate earth reservoir with a 74ge of 1 3 0 2 can be defined in contrast modern biogenic opal such as marine sponges and authigenic glauconite displayed higher 74ge values between 2 0 and 3 0 this suggests that biogenic opal may be significantly enriched in light isotopes with respect to seawater and places a lower bound on the 74ge of the seawater to 3 0 this suggests that seawater is isotopically heavy relative to bulk silicate earth and that biogenic opal may be significantly fractionated with respect to seawater deep sea sediments are within the range of the bulk silicate earth while mesozoic deep sea cherts opal and quartz have 74ge values ranging from 0 7 to 2 0 the variable values of the cherts cannot be explained by binary mixing between a biogenic component and a detrital component and are suggestive of enrichment in the light isotope of diagenetic quartz further work is now required to determine ge isotope fractionation by siliceous organisms and to investigate the effect of diagenetic processes during chert lithification

silicon isotope fractionation during nutrient utilization in the north pacific the distribution of silicon in the north pacific is controlled by the utilization of silicic acid by diatoms a process that fractionates silicon si isotopic compositions silicon isotope variations are presented for six water column profiles from the surface mixed layer down to the deep waters of the north pacific ocean although the observed si isotopic variations display an apparently simple inverse relationship with dissolved nutrient concentrations in fact they reflect mixing of surface waters undergoing active si isotope fractionation and deep waters with more uniform concentrations and isotope compositions samples from the surface of the subtropical gyre have the lowest dissolved si concentrations and heaviest si isotope compositions of marine waters measured thus far fractionation in the surface waters follows a typical rayleigh type distillation curve for a closed surface water reservoir resulting from stratification of the surface layer in the subarctic region in contrast an open system prevails within the subtropical gyre where there is significant recycling of silicic acid in the upper water column and lateral transport of silicon within surface currents for deep waters the si isotope composition distinguishes between the northern north pacific deep water npdw and the southerly derived bottom water the relatively light si isotope compositions measured from waters within the subarctic gyre provides evidence for isolation of the nutrient pool in the north pacific

diagenetic ge si fractionation in continental margin environments further evidence for a nonopal ge sink we present data for dissolved germanic and silicic acids from several settings sediment pore water profiles collected from the peru chile continental margin fluxes measured with in situ benthic flux chambers and shipboard whole core incubations and water column profiles from the california continental margin collectively these data show that ge and si are fractionated in these continental margin sedimentary environments during diagenesis with 50 of the ge released by opal dissolution being sequestered within the sediments the areal extent of this diagenetic fractionation covers station depths from 100 m to 1000 m sediments from these sites typically have high pore water fe2 present in the upper 2 cm at sites with low fe2 concentrations in the upper pore waters the ge si benthic regeneration ratio indicates little or no fractionation during diatom dissolution consistent with the sedimentary fractionation water column dissolved ge si ratios along the continental margin are on average lower 0 66 mol mol than the global average ratio 0 72 mol mol mortlock and froelich 1996 this lower average ratio is driven by two distinct ge si data trends having similar slopes but different intercepts data from the upper 150 m has a ge si slope of 0 74 0 04 mol mol 2 and an intercept of 0 5 0 4 whereas below 550 m the slope is 0 70 0 06 mol mol but the intercept is 5 0 8 0 assuming that the sediments sampled here are representative of all reducing marine environments an assumption requiring further testing our calculations indicate that sequestration of ge into a nonopal phase throughout the global ocean in the depth range 0 2 1 km is sufficient to balance the ge budget thus we tentatively conclude that sequestering of ge in reducing continental margin sediments is the missing ge sink

the role of quaternary environmental change in the evolution of landscapes case studies from southern africa abstract the paper begins by examining the importance of southern african quaternary environmental change the quaternary is characterised by repeated climatic changes of considerable amplitude analysis of these fluctuations reveals the ubiquity of change and the fundamental dynamism of earth systems change is normal and despite the fact that southern africa was not subject to quaternary glaciation per se the influence of variations in say amount and seasonality of rainfall has been very marked indeed the quaternary also represents the time period during which people have become a dominant environmental agent in the subcontinent southern africa has played a crucial role in the evolution of hominids and their development has been influenced strongly by accompanying environmental change the relationship between geomorphology and climate in southern africa is explored revealing the degree and extent to which its landscapes are determined by changing environmental conditions especially during the tertiary and quaternary how apparent is the legacy of the past this leads to a consideration of the types of geomorphological evidence some more reliable than others that can be utilised in order to reveal the details of quaternary environmental change arid and semiarid landscapes appear to preserve more evidence of former environmental conditions although high contemporary erosion rates and the paucity of long terrestrial sedimentary sequences hinder their complete elucidation two case studies of quaternary change in the subcontinent are presented from the southwestern cape and namibia these examples document the increasing intensity of human impact on landscapes to the extent that people now play the dominant geomorphological role especially in semiarid and coastal areas the conclusion offers pointers as to how geomorphological evidence of quaternary change can be used to assist in the better management of contemporary and future environmental conditions

germanium silicon fractionation during biogenic opal formation model results and empirical data show that germanium is fractionated from silica during biogenic opal formation in a two box model of the ocean particulate ge si can vary between the average ocean ge si and the average ocean ratio times the ge fractionation coefficient the two box model requires a ge fractionation coefficient near 0 48 to reproduce si and ge concentrations similar to the ocean analysis of paired water and opal samples yields a ge fractionation coefficient of 0 51 as a consequence of this fractionation the ge si of opal can be an upwelling indicator small shifts of opal ge si in adjacent centimeter scale lighter and darker layers in the miocene monterey formation are consistent with other sedimentologic indicators of productivity and upwelling variations opal ge si are lower in lighter layers and are consistent with interpretations that the lighter layers were formed by increased productivity in overlying waters

new chronological evidence for the nature and timing of linear dune development in the southwest kalahari desert abstract the age of the linear dunes in the southwest kalahari desert has not previously been directly established by applying the optical dating method to samples from the dunefield a number of questions relating to the timing and nature of linear dune development are addressed the last major period of simple linear dune development occurred 17 000 10 000 years ago probably from the reworking of earlier aeolian sediments dune emplacement occurred under more arid probably windier conditions than those prevailing today which are only responsible for episodic surficial dune sand movement as well as simple linear dunes the dunefield also contains more complex linear dune patterns samples from one area in the eastern dunefield demonstrate that multi phase development is more probable for complex dune patterns as opposed to single phase evolution under a complex wind regime

the geochemistry of inorganic germanium in natural waters we present the initial results from a survey of the distribution of dissolved inorganic germanium in rivers in the oceans and in hydrothermal vents and plumes in the ocean germanium cycling mimics that of silica since siliceous organisms incorporate ge as a trace constituent in biogenic opal the vertical and horizontal distributions of ge concentrations in seawater are thus identical to those of silica ge si 0 7 10 6 and reflect uptake into and dissolution from the frustules of siliceous organisms germanium enters the ocean via dissolution of continental and seafloor silicates the naturally weathered flux from continents to oceans carries a dissolved ge si atom ratio in rivers of about 0 7 10 6 which reflects the ratio in average continental granites rivers draining industrial regions with significant coal combustion are contaminated with ge leached from fly ash particles resulting in ge si ratios up to tenfold above the naturally weathered background the flux to the oceans via high temperature alteration of seafloor basalts hot springs produces a ge anomaly in hydrothermal plumes over the east pacific rise crest 20 s combining the observed ge and 3he anomalies in plumes with 3he si observations in hot springs suggests that the ge si hydrothermal flux to the oceans is about 4 10 6 near the ratio for average oceanic basalts 2 6 10 6 vent effluents from the galapagos hot springs measured directly display ge si ratios of 16 10 6 suggesting that the ratio is variable between vent fields metalliferous sediments accumulating on the epr crest 17 s are enriched in germanium suggesting that a fraction of the hydrothermal germanium source on the rise crest is scavenged into these rapidly accumulating iron and manganese hydroxyoxide phases

early diagenesis of germanium in sediments of the antarctic south atlantic in search of the missing ge sink pore water and solid phase geochemistry profiles were obtained from several cores between 41 degree s and 53 degree s in the atlantic sector of the southern ocean pore water nitrate manganese and iron profiles delineate standard redox zones in these sediments and help characterize those with classic vs burn down behaviors pore water si and ge profiles demonstrate that ge released during opal dissolution is removed pervasively throughout the uppermost interval of silicate release and also downwards into the suboxic zone by as yet unidentified precipitation mechanisms these results indicate that early diagenesis of ge is uncoupled from that of opal solid phase extractions fe mn u mo ge cu ni co v and cd in a few cores suggest that anthigenic ge removal in the suboxic zone is not associated with peaks in authigenic mn cycling mno sub 2 and related metals but rather with processes deeper in the sediments perhaps fe or u diagenesis below the interval of ge removal pre water ge increases linearly with depth by over two orders of magnitude indicating a deep below recovery source of large magnitude the fraction of opal derived ge precipitated authigenically in these sediments ranges from approximately 1 to 96 and correlates strongly with the detrital fraction asmore well as the detrital to opal ratio both of which generally decrease from north to south the ge sink observed in these sediments would need to be globally representative to account for the entire missing ge sink in today s oceanic ge balance which seems unlikely benthic fluxes of ge and si estimated from these pore water profiles and from measurements in three benthic flux chamber experiments at high carbon rain continental margin sites demonstrate that the ge si rate released from the seafloor in locations with high benthic silicate and carbon fluxes is congruent with holocene opal dissolution ge si approximately 0 7 x 10 sup minus 6 in contrast ge si flux ratios in areas with low silicate fluxes are ge depleted ge si 0 5 x 10 sup minus 6 the authors speculate that glacial interglacial changes in oceanic ge si as recorded in diatoms may be due in part to variations in this authigenic ge sink perhaps related to shifts in siliceous productivity from open ocean antarctic siliceous oozes during interglacials to areas of higher detrital input sub antarctic continental margins and possibly also to generally more reducing conditions in sediments during glacials less

differential weathering and erosion in an inselberg landscape in southern zimbabwe a morphometric study and some notes on factors influencing the long term development of inselbergs abstract a morphometric analysis of inselberg systems in southern zimbabwe indicated that there are two types of inselberg systems that differ in the mode of development inselberg systems characterized by backwearing tend to occur on granitoid rocks that are foliated highly fractured and prone to grusification the inselbergs are mostly of the koppie type and are covered to a great extent with regolith or debris the second type of inselbergs consists of sparsely fractured granitoid rocks and areas underlain by these rocks are characterized by clusters of closely spaced rock domes in the case of these inselbergs backwearing is not indicated they appear to be the result of the exposure of structurally pre designed highly resistant rock compartments the hypothesis that differences in lithology and structure may influence the rate and style of inselberg development was tested by means of a simulation model the simulations are run under the same boundary conditions with differing assumptions concerning role of divergent weathering the results show that both modes of inselberg development may occur alongside one another as long as a critical relief is maintained the modelling provided also indicates that although the inselberg systems must have integrated several sequences of environmental changes during their development these changes were not able to divert the general trend of the process response system away from its steady course lithological and structural factors which are responsible for the differences in the mobility of material on the inselberg sideslopes are thus considered to be the primary source of influence of the different modes of inselberg development it is suggested that the compositional and structural diversity in granitoid rock terrains is what enables inselbergs to pass through different development modes and sequences as rocks of differing resistance become subject to weathering during the development of the landscape

the zinc isotopic composition of siliceous marine sponges investigating nature s sediment traps article i nfo the zinc zn content and isotopic composition of marine biogenic opal have the potential to yield informa tion about the nutrient availability utilization and export of particulate organic matter from surface to deep waters here we report the first measurements of the zn isotopic composition of deep sea marine sponge skeletal elements spicules collected in the southern ocean our results highlight different zn uptake and isotopic fractionation behavior between the two major siliceous sponge clades hexactinellids and demosponges which is most likely linked to sponge feeding strategy hexactinellid spicule zn isotopic com positions are not fractionated with respect to seawater most likely due to zn transport via the open internal structure of the sponges in contrast demosponge spicules exhibit a wide range of zn isotopic compositions that are related to the opal zn concentration most likely reflecting variable zn isotope compositions in the organic matter particles on which they feed and internal fractionation processes

winter mixed layer entrainment of weddell deep water observations from the somov during the us ussr weddell polynya expedition show that the mixed layer below the sea ice just prior to the austral spring retreat in the 60 s greenwich meridian region has an oxygen content of 7 4 ml 1 this is 86 of full oxygen saturation representing an oxygen deficit relative to full saturation of 1 1 ml 1 the source of this deficit is believed to be a consequence of oxygen poor 4 5 ml 1 weddell deep water wdw entrainment by the winter mixed layer assuming effective cutoff of ocean atmosphere oxygen exchange by the nearly complete snow and sea ice cover with no net impact of oxygen content as a result of biological factors a mixing ratio of 1 3 for wdw to beginning of winter surface water is required to explain the end of winter mixed layer oxygen content accompanying the wdw transfer into the mixed layer is heat transfer of approximately 7 103 cal cm2 2 9 108 j m2 during the five winter months of sea ice coverage as well as salt transfer which requires 34 cm of fresh water to produce typical mixed layer salinity during the seven ice free months when entrainment is expected to be minor diffusive heat and salt flux continues a mean annual heat flux of 12 w m2 is suggested with an annual demand for freshwater of 46 cm yr consideration of the winter period salinity budget indicates net sea ice melting of 20 cm which can be attributed to regional convergence of sea ice the remaining freshwater is derived from excess precipitation and possibly iceberg melt oxygen undersaturation of the winter surface water suggests slightly less potential for abyssal water ventilation than might be expected from a fully saturated condition

biomarker records of palaeoenvironmental variations in subtropical southern africa since the late pleistocene evidences from a coastal peatland abstract southern africa s unique global position has given rise to a dynamic climate influenced by large sea surface temperature gradients and seasonal fluctuations in the inter tropical convergence zone due to the semi arid climate of the region terrestrial palaeorecords are rare and our understanding of the long term sensitivity of southern african terrestrial ecosystems to climatic drivers is ambiguous a 810 cm continuous peat core was extracted from the mfabeni peatland with a 14 c basal age of c 47 thousand years calibrated before present kcal yr bp positioning it as one of the oldest known sub tropical coastal peatlands in southern africa this peat core provides an opportunity to investigate palaeoenvironmental changes in subtropical southern africa since the late pleistocene biomarker n alkane n alkanoic acid and n alkanol analysis in conjunction with previously published bulk geochemical data was employed to reconstruct organic matter om sources rates of om remineralisation and peatland hydrology our results showed that the principal om source into the peatland was emergent and terrestrial plants with exception of shallow lake conditions when submerged macrophytes dominated c 44 5 42 6 29 7 26 1 23 1 16 7 7 1 and 2 2 kcal yr bp n alkane proxies suggest that local plant assemblages were predominantly influenced by peatland hydrology by incorporating temperature sensitive n alkanoic acid and n alkanol proxies it was possible to disentangle the local temperature and precipitation changes we report large variations in precipitation intensities but subdued temperature fluctuations during the late pleistocene the holocene period was characterised by overall elevated temperatures and precipitation compared to the preceding glacial period interspersed with a millennial scale cooling event a close link between the mfabeni archive and adjacent indian ocean marine core records was observed suggesting the regional ocean surface temperatures to be the dominant climate driver in this region since the late pleistocene

multiple episodes of aridity in southern africa since the last interglacial period there is generally a dearth of evidence of the nature of quaternary climate change within desert systems which has limited previous interpretations of past environmental change at low latitudes the last glacial maximum has previously been identified as the peak of late quaternary aridity when desert systems expanded to five times their present extent1 2 3 and low latitude aridity has been described for previous glaciations4 but little evidence has been derived directly for large desert basins particularly southern africa here we report new chronological optical dating evidence of arid episodes recorded in aeolian sediments from the mega kalahari sand sea episodic aeolian activity is recorded at the northeastern desert margin whereas more sustained activity is evident from the southwestern desert core several significant arid events are apparent since the last interglacial period with dune building arid phases at 95 115 41 46 20 26 and 9 16 kyr before present existing atmospheric general circulation model simulations and independent palaeoclimate data indicate that the changes in aridity are related to changes in the northeast southwest summer rainfall gradient which are in turn related to sea surface temperatures in the southeastern atlantic ocean

inorganic germanium and silica in the indian ocean biological fractionation during ge si opal formation hydrographic profiles of inorganic germanium and silica in the western indian ocean confirm the silicalike behavior of inorganic germanium in seawater combining all existing oceanic data indian atlantic pacific bering sea and antarctic these new data provide an improved oceanic ge to si relationship ge pm 0 699 0 004 si m 3 6 0 4 simple box models of the ocean demonstrate that the positive ge intercept in this relationship results from biological fractionation of the ge si ratio siliceous organisms discriminate against germanium during production of biogenic opal this result is confirmed by ge si opal analyses of diatoms and radiolaria separated from siliceous oozes of holocene core tops a rapid rise in diatom ge si opal recorded in an antarctic piston core over the interval from the last glacial 18 thousand years before present to the holocene present suggests that biosiliceous productivity was lower and preformed silica concentrations were higher in southern ocean surface waters during glacial times

tracing iron fueled microbial carbon production within the hydrothermal plume at the loihi seamount the loihi hydrothermal plume provides an opportunity to investigate iron fe oxidation and microbial processes in a system that is truly fe dominated and distinct from mid ocean ridge spreading centers the lack of hydrogen sulfide within the loihi hydrothermal fluids and the presence of an oxygen minimum zone at this submarine volcano s summit results in a prolonged presence of reduced fe within the dispersing non buoyant plume in this study we have investigated the potential for microbial carbon fixation within the loihi plume we sampled for both particulate and dissolved organic carbon in hydrothermal fluids microbial mats growing around vents and the dispersing plume and carried out stable carbon isotope analysis on the particulate fraction the 13 c values of the microbial mats ranged from 23 to 28 and are distinct from those of deep ocean particulate organic carbon poc the mats and hydrothermal fluids were also elevated in dissolved organic carbon doc compared to background seawater within the hydrothermal plume doc and poc concentrations were elevated and the isotopic composition of poc within the plume suggests mixing between background seawater poc and a 13 c depleted hydrothermal component the combination of both doc and poc increasing in the dispersing plume that cannot solely be the result of entrainment and doc adsorption provides strong evidence for in situ microbial productivity by chemolithoautotrophs including a likelihood for iron oxidizing microorganisms

germanium isotopic systematics in ge rich coal from the lincang ge deposit yunnan southwestern china abstract organic matter plays an important role in the transport and precipitation of germanium ge in coal hosted ge deposits in this paper ge isotopes of coal samples and their combustion products were analyzed in order to investigate the potential use of ge isotopes as tracers of ge sources and enrichment mechanisms in coal germanium isotopic composition of various samples mainly ge rich lignite from the lincang ge deposit yunnan southwest china was analyzed using a continuous flow hydride generation system coupled to a multi collector inductively coupled plasma mass spectrometer mc icp ms and the standard sample bracketing approach variations of 74ge 70ge ratios are expressed as 74ge values relative to nist srm 3120a ge standard solution ge rich lignite samples show large ge isotopic fractionation 74ge values range from 2 59 to 4 72 and their 74ge values negatively correlate with ge concentrations lignite samples with low ge concentrations 1000 ppm are close to zero or negative along stratigraphic sections ge is mainly concentrated in the top or the bottom of the coal seam such that high values of 74ge are usually found in the middle part of the coal seam interlayered hydrothermal chert and limestone samples in ge rich coal seams also show moderate fractionation 74ge values range from 0 14 to 2 89 and from 0 55 to 1 87 respectively the overall variations of 74ge values of ge rich lignite and organic rich chert samples can be well described by a rayleigh fractionation model indicating that preferential enrichment of light ge isotopes in coal in an open system might be the main factor controlling ge fractionation in ge rich lignite the germanium isotopic composition of hydrothermal chert and possibly limestone might also record the competitive fractionation produced by precipitation of quartz and sorption of coal elevated ge concentrations and or 74ge values of some chert limestone sandstone and claystone samples may be attributed to the mixing with ge rich organic matter furthermore similar to the fractionation of zn cd and hg isotopes observed between refinery dust or gas and slag high temperature coal combustion also fractionates ge isotopes with the ge isotopic compositions of soot being distinctly lighter up to 2 25 per mil than those of cinder the distinct enrichment of potential hazardous elements i e pb cd and as and ge in soot after coal combustion as well as the common enrichment of ge in sulfide minerals e g sphalerite highlights the possibility of using ge isotopes as useful tracers of sources of heavy metal pollution caused by high temperature industrial processes coal combustion and pb zn refining in the environment

short term variations of deep water masses in drake passage revealed by a multiparametric analysis of the ant xxiii 3 bottle data short term variations of deep water masses in drake passage revealed by a multiparametric analysis of the ant xxiii 3 bottle data j sudre v garcon c provost n sennechael o huhn and m lacombe doi 10 1016 j dsr2 2011 01 005 a multiparametric analysis is applied on the ant xxiii 3 bottle data to determine the spreading and mixing of water masses across drake passage during january february 2006 focusing our interest on the flow of the deep water masses mixing proportions are quantified along both the southward and northward journeys between the tip of south america and the antarctic peninsula the method is sensitive enough to detect a marked variability in the flow pathways of the circumpolar deep water the southeast pacific deep water spdw and the weddell sea deep water at the intersection of the shackleton fracture zone sfz and the west scotia ridge wsr between the southward and northward journeys indeed the presence of a sharp meander of the southern branch of the polar front pfs together with the displacement of the northern branch of the southern antarctic circumpolar current front saccfn above the complex bathymetric structure of the wsr induced a strong perturbation in the deep flow field during the southward journey the height of the sfz crests clearly sets the lower limit of the spdw in the ona basin an enhanced 3 he signature is confined to the north of the polar front between 55 5 s and 56 5 s in the 1500 2200 m depth range it clearly indicates the signature of the core of the southeast pacific deep slope water the entry pathway in the acc of the spdsw during ant xxiii 3 was farther to the south off the continental slope of south america than it was during the woce a21 expedition in 1990 probably due to the sharp changes in the slope orientation at the extreme tip of the south america

relationship between antarctic sea ice and southwest african climate during the late quaternary here we compare late quaternary southwest african climate records from the west coast of southern africa published winter rainfall and trade wind intensity records from a core off the coast of namibia to records of antarctic sea ice extent this comparison reveals coherent changes between antarctic sea ice extent and the southwest african winter rain region since 45 k y b p with enhanced winter rainfall and trade wind vigor during periods of increased sea ice presence we propose an oceanic and atmospheric coupling between antarctic sea ice and the winter rainfall zone of southwest africa that may lead to increased desertification in the region if global warming persists

determination of molybdenum isotope fractionation by double spike multicollector inductively coupled plasma mass spectrometry 1 molybdenum isotopic compositions are precisely determined by mc icp ms measurements using a mo double spike the double spike is added prior to chemical purification so that laboratory and instrumental mass fractionations are separated from natural mass dependent fractionation fractionation is determined on four mo mass ratios providing an internal consistency check the external standard reproducibility is at 0 06 per mil on the 98mo 95mo ratio 2 standard deviation using a normal microconcentric nebuliser with a cyclonic spray chamber the minimum quantity of mo is 1 g for high precision results a hydrothermal molybdenite shows fractionation of 0 3 per mil on the 98mo 95mo ratio relative to our standard johnson matthey 1000 g ml 0 3 icp standard solution lot 602332b fine grained sediments show fractionation of 0 1 and 0 3 per mil on the 98mo 95mo ratio the observed mo isotope fractionation is small but resolvable with the presented high resolution technique

germanium silicon as a flow path tracer application to the rio icacos watershed 1 we use dissolved silicon together with its geochemical twin germanium for the first time as a hydrologic tracer to study water delivery to the stream during storm events in the rio icacos watershed puerto rico ge and si were measured on base flow stormflow springwater and soil water samples compositions of all of these waters appear to reflect varying contributions from three components which we attribute to solutes released from bedrock weathering groundwater from short term soil water interaction quick soil water and longer term soil water interaction matrix soil water base flow stream waters have high si and moderate ge ge si ratio 0 29 mol mol consistent with a predominantly bedrock weathering source as indicated by their similarity with water sampled from springs emerging from the saprolite bedrock boundary on a hillslope landslide scar during storm events there is a shift toward more dilute compositions but higher ge si ratios similar to those measured on water samples from temporary depression storage and overland flow quick soil water geochemical mass balance shows that 80 90 of the stream chemistry can be explained by mixing groundwater with this quick soil water composition which we infer to reflect new water traveling as shallow throughflow stream water 18o values decrease to more negative values typical of precipitation supporting rapid delivery of rainwater to the stream channel during stormflow the third component with a ge rich composition characteristic of soil matrix water sampled by tension lysimeters is required to explain higher stream water ge si ratios measured during hydrograph recession we infer from this an additional slower and less dominant pathway for delivery of soil water to the stream channel

deconvolving the controls on the deep ocean s silicon stable isotope distribution abstract we trace the marine biogeochemical silicon si cycle using the stable isotope composition of si dissolved in seawater expressed as 30 si open ocean 30 si observations indicate a surprisingly strong influence of the physical circulation on the large scale marine si distribution here we present an ocean general circulation model simulation that deconvolves the physical and biogeochemical controls on the 30 si distribution in the deep oceanic interior by parsing dissolved si into its preformed and regenerated components we separate the influence of deep water formation and circulation from the effects of biogeochemical cycling related to opal dissolution at depth we show that the systematic meridional 30 si gradient observed in the deep atlantic ocean is primarily determined by the preformed component of si whose distribution in the interior is controlled solely by the circulation we also demonstrate that the 30 si value of the regenerated component of si in the global deep ocean is dominantly set by oceanic regions where opal export fluxes to the deep ocean are large i e primarily in the southern ocean s opal belt the global importance of this regionally dynamic si cycling helps explain the observed strong physical control on the oceanic 30 si distribution since most of the regenerated si present within the deep atlantic and indo pacific oceans is in fact transported into these basins by deep waters flowing northward from the southern ocean our results thus provide a mechanistic explanation for the observed 30 si distribution that emphasizes the dominant importance of the southern ocean in the marine si cycle

silica and germanium in pacific ocean hydrothermal vents and plumes dissolved silica si and inorganic germanium ge concentrations were measured in hydrothermal fluids from black smoker vents on the east pacific rise 21 n epr and the southern juan de fuca ridge 45 n sjdfr north and south cleft sites axial volcano these typically display end member concentrations ranging from 16 to 23 mm si and 150 to 280 nm ge and end member ge si ratios clustering between 8 and 14 10 6 more than 10 fold greater than the ratio entering the ocean via rivers 0 54 10 6 and being recycled in seawater 0 7 10 6 excess concentrations of dissolved si and ge above oceanic background are observed in mid water hydrothermal plumes over mid ocean ridge mor spreading centers on the southern epr sepr 10 20 s and the sjdfr the largest si and ge concentration anomalies occur over the north cleft segment of the sjdfr these are a factor of three greater than anomalies over the sepr 10 20 s excess ge correlates with excess3he in plumes at a ge 3he molar ratio of about 1 104 approximately the same ratio as in black smokers these observations combined with low abundances of ge in femn rich metalliferous sediments suggest that ge and si behave conservatively in mid ocean ridge hydrothermal plumes a simple ocean si and ge balance constrained by the global river silica flux and ge si ratios in hydrothermal vents rivers and biogenic silica suggests that the global hydrothermal silica flux is about 1 4 1011 mole yr 1 much lower than that estimated from3he either 1 70 80 of the ge flux to the ocean is removed in as yet undiscovered sinks not opal or 2 only 10 of the mantle to ocean3he and heat fluxes is associated with mor hydrothermal convection through the 350 c isotherm 90 is off ridge or 3 the oceanic ge si 3he and87sr86sr balances today are far from steady state

the marine geochemistry of germanium ekasilicon the geochemical behavior of dissolved germanium in rivers estuaries and the oceans is similar to that of silicon it is chemically weathered from continental rocks and transported by rivers to the oceans where it is taken up by siliceous organisms and deposited in biogenic opal the ratio of germanium to silicon buried in siliceous oozes must reflect the oceanic input ratios from rivers crustal weathering and sea floor vents mid ocean ridge hydrothermal weathering the opal germanium silicon ratio may thus monitor relative variations in these weathering processes and provide information about the geochemical history of seawater

shelf derived iron inputs drive biological productivity in the southern drake passage water entrainment while fe 228 ra ratios were used to calculate the fe flux in the summer of 2006 we found rapid mixing and significant lateral iron export namely a dissolved iron flux of 1 1 10 5 mol d 1 and total acid leachable iron flux of 1 1 10 6 mol d 1 all of which is transported in the mixed layer from the shelf region offshore this dissolved iron flux is significant especially considering that the bloom observed in the offshore region 0 5 2 mg chl a m 3 had an iron demand of 1 1 to 4 10 5 mol fe net vertical export fluxes of particulate fe derived from 234 th 238 u disequilibrium and fe 234 th ratios accounted for only about 25 of the dissolved iron flux on the other hand vertical upward mixing of iron rich deeper waters provided only 7 of the lateral dissolved iron flux we found that similarly to other studies in iron fertilized regions of the southern ocean lateral fluxes overwhelm vertical inputs and vertical export from the water column and support significant phytoplankton blooms in the offshore regions of the drake passage

evidence for holocene sea level change at verlorenvlei western cape south africa abstract a series of sediment cores extracted from what is today a large freshwater coastal lake verlorenvlei has been sub sampled radiocarbon dated and subjected to a range of palaeoenvironmental techniques in particular pollen analysis sedimentology and geochemistry a mid late holocene higher sea level is evident in the cores indicating the rapidity with which sea level change can occur and invoke other forms of environmental response following a hiatus in sedimentation most probably around 3800 bp the marine conditions at the site were replaced by fresh water as the dominant hydrological and ecological influence laminated organic sediments in some of the cores suggest that around 300 years ago a fresh water lake characterised verlorenvlei since then the picture revealed by high resolution palynology is one of progressive levels of human disturbance both in and around the study area sedimentological and palaeoecological analyses of additional cores from the vlei two from the distal inland and one from the proximal coastal end of the system serve further to elucidate the precise nature of sea level change in the late holocene and facilitate the construction of a refined holocene sea level curve for the region environmental changes in the late holocene are shown to be especially dynamic

dissolved silicon isotopic compositions in the east china sea water mass mixing vs biological fractionation we present the first set of dissolved silicon isotope data in seawater delta si 30 si oh 4 from the east china sea a large and productive marginal sea significantly influenced by the kuroshio current and freshwater inputs from the changjiang yangtze river in summer august 2009 the lowest surface delta si 30 si oh 4 signatures of 2 1 parts per thousand corresponding to the highest si oh 4 concentrations similar to 30 0 mu mol l 1 were observed nearshore in changjiang diluted water during advection on the east china sea inner shelf surface delta si 30 si oh 4 increased rapidly to 3 2 parts per thousand while si oh 4 became depleted indicating increasing biological utilization of the si oh 4 originating from the changjiang diluted water this is also reflected in the water column profiles characterized by a general decrease of delta si 30 si oh 4 and an increase of si oh 4 with depth on the east china sea mid shelf and slope in winter december 2009 january 2010 however the delta si 30 si oh 4 was nearly constant at 1 9 parts per thousand throughout the water column on the east china sea shelf beyond the nearshore which was a consequence of enhanced vertical mixing of the kuroshio subsurface water horizontal admixture of kuroshio surface water which is highly fractionated in si isotopes was observed only beyond the shelf break significant seasonal differences in delta si 30 si oh 4 were detected in the surface waters beyond the changjiang diluted water influenced region on the east china sea shelf where the winter values were similar to 1 0 parts per thousand lower than those in summer despite the same primary si oh 4 supply from the kuroshio subsurface water during both seasons this demonstrates significantly higher biological consumption and utilization of si oh 4 in summer than in winter

late holocene environments at verlorenvlei western cape province south africa abstract evidence on late quaternary palaeoenvironments of the western and southwestern cape of south africa has facilitated detailed reconstructions mainly for the mountains where organic sediment accumulation has been favoured by relatively humid climates on the lowlands particularly those of the west coast region the search for sites traditionally regarded as suitable for the accumulation of sediments containing preserved fossil pollen has commenced only more recently this area of the western cape province has however provided quaternary scientists with a rich archaeological record that has yet to be tested against independent lines of palaeoecological evidence a sequence of sediments which have accumulated in what is today a large freshwater coastal lake verlorenvlei has been sampled at grootdrift 15 km inland of the coast a series of seven sediment cores was extracted during 1991 and three of these have now been sub sampled radiocarbon dated and subjected to a range of palaeoenvironmental techniques in particular pollen analysis sedimentology and geochemistry three pollen diagrams are presented which reveal the vegetation history of both the immediate grootdrift environment and the wider catchment during several periods over the last 5500 years a mid holocene higher sea level is evident in two of the cores which were examined for pollen throughout their length the surrounding area appears at this time to have been somewhat more arid than today following a hiatus in sedimentation some time after 4300 bp the marine conditions at the site disappear and are replaced by fresh water as the dominant hydrological and ecological influence around the time of colonial occupation of the region some 300 years ago lacustrine conditions prevailed at grootdrift and greater moisture availability is indicated in the catchment during the last 300 years the picture revealed by high resolution palynology of the third core is one of progressive levels of human disturbance both in and around the verlorenvlei evidence from a textural and geochemical analysis of the sediments is consistent with the interpretation based on fossil pollen the implications of this information are examined against the archaeology and palaeoecology of several cave sites in the vicinity of the vlei the consistency apparent in the range of types of evidence suggests that some reliance can be placed on the mid late holocene palaeoenvironmental reconstruction at verlorenvlei the paper thus provides insight into the nature of the complex interactions between late holocene climate change sea level fluctuation vegetation change vlei hydrology and human activity in the western cape coastal region

late quaternary palaeoenvironments of the southwestern cape south africa a regional synthesis the contemporary uniqueness of the southwestern cape environemnt suggests that its response to the environmental perturbations of the late quaternary may have been correspondingly distinctive despite the wide variety of palaeoenvironmental evidence which has accumulated from within the region a coherent picture of the evolution and development of its environments has remained elusive since the publication of several regional reviews over the last decade or so a considerable body of palynological and other palaeoecological evidence has emerged which prompts a fresh synthesis as to the nature of late quaternary environmental changes in the southwestern cape s fynbos biome although there are few sediments which date to the appropriate period the last glacial maximum in contrast to the situation evident in the summer rainfall region is suggested to be a period characterised by considerably cooler and wetter conditions in certain parts of the biome the first half of the holocene appears to have been somewhat drier than much of the second half and the warmer temperatures of the holocene hypsithermal are associated with reduced moisture availability intra regional contrasts are evident in the response to late quaternary environmental changes furthermore it transpires that for much of the later quaternary and for large areas of the region precipitation may have fluctuated out of phase with changes in the interior of the subcontinent a situation which has great relevance to the prediction of future environmental changes and their impacts in the southwestern cape

deep ocean nutrients during the last glacial maximum deduced from sponge silicon isotopic compositions the relative importance of biological and physical processes within the southern ocean for the storage of carbon and atmospheric pco2 on glacial interglacial timescales remains uncertain understanding the impact of surface biological production on carbon export in the past relies on the reconstruction of the nutrient supply from upwelling deep waters in particular the upwelling of silicic acid si oh 4 is tightly coupled to carbon export in the southern ocean via diatom productivity here we address how changes in deep water si oh 4 concentrations can be reconstructed using the silicon isotopic composition of deep sea sponges we report 30si of modern deep sea sponge spicules and show that they reflect seawater si oh 4 concentration the fractionation factor of sponge 30si compared to seawater 30si shows a positive relationship with si oh 4 which may be a growth rate effect application of this proxy in two down core records from the scotia sea reveals that si oh 4 concentrations in the deep southern ocean during the last glacial maximum lgm were no different than today our result does not support a coupling of carbon and nutrient build up in an isolated deep ocean reservoir during the lgm our data combined with records of stable isotopes from diatoms are only consistent with enhanced lgm southern ocean nutrient utilization if there was also a concurrent reduction in diatom silicification or a shift from siliceous to organic walled phytoplankton

the isotope composition of inorganic germanium in seawater and deep sea sponges abstract although dissolved concentrations of germanium ge and silicon si in modern seawater are tightly correlated uncertainties still exist in the modern marine ge cycle germanium stable isotope systematics in marine systems should provide additional constraints on marine ge sources and sinks however the low concentration of ge in seawater presents an analytical challenge for isotopic measurement here we present a new method of pre concentration of inorganic ge from seawater which was applied to measure three ge isotope profiles in the southern ocean and deep seawater from the atlantic and pacific oceans germanium isotopic measurements were performed on ge amounts as low as 2 6 ng using a double spike approach and a hydride generation system coupled to a mc icp ms germanium was co precipitated with iron hydroxide and then purified through anion exchange chromatography results for the deep i e 1000 m depth pacific ocean off hawaii nearby loihi seamount and the deep atlantic off bermuda bats station showed nearly identical 74 70ge values at 3 19 0 31 2sd n 9 and 2 93 0 10 2sd n 2 respectively vertical distributions of ge concentration and isotope composition in the deep southern ocean for water depth 1300 m yielded an average 74 70ge 3 13 0 25 2sd n 14 and ge si 0 80 0 09 mol mol 2sd n 12 significant variations in 74 70ge from 2 62 to 3 71 were measured in the first 1000 m in one station of the southern ocean near sars seamount in the drake passage with the heaviest values measured in surface waters isotope fractionation by diatoms during opal biomineralization may explain the enrichment in heavy isotopes for both ge and si in surface seawater however examination of both oceanographic parameters and 74 70ge values suggest also that water mass mixing and potential contribution of shelf derived ge also could contribute to the variations combining these results with new ge isotope data for deep sea sponges sampled nearby allowed us to determine a ge isotope fractionation factor of 0 87 0 37 2sd n 12 during ge uptake by sponges although ge has long been considered as a geochemical twin of si this work underpins fundamental differences in their isotopic behaviors both during biomineralization processes and in their oceanic distributions this suggests that combined with si isotopes ge isotopes hold significant promise as a complementary proxy for delineating biological versus source effects in the evolution of the marine silicon cycle through time

the influence of water mass mixing on the dissolved si isotope composition in the eastern equatorial pacific silicon isotopes are a powerful tool to investigate the cycling of dissolved silicon si in this study the distribution of the si isotope composition of dissolved silicic acid 30si oh 4 was analyzed in the water column of the eastern equatorial pacific eep where one of the globally largest oxygen minimum zones omzs is located samples were collected at 7 stations along two meridional transects from the equator to 14 s at 85 50 w and 82 00 w off the ecuadorian and peruvian coast surface waters show a large range in isotope compositions 30si oh 4 2 2 to 4 4 with the highest values found at the southernmost station at 14 s this station also revealed the most depleted silicic acid concentrations 0 2 mol kg which is a function of the high degree of si utilization by diatoms and admixture with waters from highly productive areas samples within the upper water column and the omz at oxygen concentrations below 10 mol kg are characterized by a large range in 30si oh 4 which mainly reflects advection and mixing of different water masses even though the highly dynamic hydrographic system of the upwelling area off peru does not allow the identification of clear si isotope signals for distinct water masses therefore we cannot rule out that also dissolution processes have an influence on the 30si oh 4 signature in the subsurface water column deep water masses 2000 m in the study area show a mean 30si oh 4 of 1 2 0 2 which is in agreement with previous studies from the eastern and central pacific comparison of the new deep water data of this study and previously published data from the central pacific and southern ocean reveal substantially higher 30si oh 4 values than deep water signatures from the north pacific as there is no clear correlation between 30si oh 4 and silicic acid concentrations in the entire data set the distribution of 30si oh 4 signatures in deep waters of the pacific is considered to be mainly a consequence of the mixing of several end member water masses with distinct si isotope signatures including lower circumpolar deep water lcdw and north pacific deep water npdw

the vertical distribution of iron stable isotopes in the north atlantic near bermuda seawater dissolved iron isotope ratios 56 fe have been measured in the north atlantic near bermuda in a full depth profile seawater dissolved 56 fe is isotopically heavy compared to crustal values throughout the water column 56 fe irmm 014 0 30 to 0 71 iron isotope ratios are relatively homogenous in the upper water column between 0 30 to 0 45 above 1500 m and 56 fe increases below this to a maximum of 0 71 at 2500 m decreasing again to 0 35 at 4200 m the 56 fe profile is very different from the iron concentration profile in the upper water column fe is variable while 56 fe is relatively constant and in the deeper water column 56 fe varies while fe remains relatively constant the 56 fe profile is also not well correlated with other hydrographic tracers in the north atlantic such as temperature salinity or the concentrations of oxygen phosphate silica and cfc 11 the dissimilarity between 56 fe profiles and profiles of fe and other hydrographic tracers shows that fe isotope ratios provide a unique sort of information about ocean chemistry and they suggest that fe isotopes may therefore be a valuable new tool for tracing the global sources sinks and biogeochemical cycling of fe

geochemical behavior of inorganic germanium in an unperturbed estuary abstract eleven monthly estuarine profiles of dissolved inorganic germanium gei and silica si in a natural pristine river bay system demonstrate that ge removal and input parallel the seasonal silica cycle reflecting ge uptake by and dissolution from diatoms the ge si atom ratio of the river is 0 6 0 15 10 6 which is near the average value for continental granites and for uncontaminated remote natural rivers 0 7 0 3 10 6 the ge si ratio escaping this estuary to the ocean is 0 8 10 6 reflecting some estuarine enhancement of the fluvial ge flux probably due to release of gei from fluvial particulates nevertheless the post estuarine ge si ratio is not significantly different from the continental crustal ratio but is very different from the ratio in sea floor hot springs and mid ocean ridge hydrothermal plumes 4 2 10 6 and in oceanic basalts 2 6 10 6 thus natural estuarine processes do not obscure the contrasting ge si signatures entering the ocean from dissolution of continental and sea floor silicates

the pretoria saltpan a 200 000 year southern african lacustrine sequence abstract the pretoria saltpan is a circular crater 1130 m in diameter and is situated some 40 km n of pretoria lat 25 34 30 long 28 04 59 e a recent tube sampling and core drilling programme has revealed an infilling consisting of some 90 m of fine lacustrine sediments chiefly organic muds underlain below 30 m depth by micrites which rest upon a further 61 m of coarse clastic debris granite bedrock was encountered at 151 m broad sedimentary zones correspond with major phases in the evolution of the crater lake superimposed cyclical patterns of accumulation reflect environmental changes on millenial to seasonal timescales 14c age determinations on algal debris from the upper 20 m of the core indicate a mean rate of sedimentation of about 1 m 2000 yr suggesting that the lacustrine sequence may span almost 200 000 yr over this period major environmental changes are apparent from sedimentological chemical mineralogical and isotopic analyses of the core and studies of the pollen spectra and diatom assemblages present within it this long continental sequence is therefore providing a high resolution palaeoenvironmental record for southern mid latitudes over much the same period as is covered by the vostok ice core in antarctica

silicon isotope fractionation by marine sponges and the reconstruction of the silicon isotope composition of ancient deep water the silicon isotope composition d30si of biogenic opal provides a view of the silica cycle at times in the past reconstructions require the knowledge of silicon isotope fractionation during opal biomineralization the d30si of specimens of hexactinellid sponges and demosponges growing in the modern ocean ranged from 1 2 to 3 7 n 6 corresponding to the production of opal that has a d30si value 3 8 0 8 more negative than seawater silicic acid and a fractionation factor a of 0 9964 this is three times the fractionation observed during opal formation by marine diatoms and terrestrial plants and is the largest fractionation of silicon isotopes observed for any natural process on earth the d30si values of sponge spicules across the eocene oligocene boundary at ocean drilling program site 689 on maud rise range from 1 1 to 3 0 overlapping the range observed for sponges growing in modern seawater

coupled ge si and ge isotope ratios as geochemical tracers of seafloor hydrothermal systems case studies at loihi seamount and east pacific rise 9 50 n germanium ge and silicon si exhibit similar geochemical behavior in marine environments but are variably enriched in seafloor hydrothermal fluids relative to seawater in this study ge isotope and ge si ratio systematics were investigated in low temperature hydrothermal vents from loihi seamount pacific ocean 18 54 n 155 15 w and results were compared to high temperature vents from the east pacific rise epr at 9 50 n loihi offers the opportunity to understand contrasting ge and si behavior in low temperature seafloor hydrothermal systems characterized by abundant fe oxyhydroxide deposition at the seafloor the results show that both ge si and 74 70ge in hydrothermal fluids are fractionated relative to the basaltic host rocks the enrichment in ge vs si relative to fresh basalts together with ge isotope fractionation 74 70gefluid basalt up to 1 15 at epr 9 50 n and 1 64 at loihi are best explained by the precipitation of minerals e g quartz and fe sulfides during higher temperature seawater rock reactions in the subsurface the study of fe rich hydrothermal deposits at loihi largely composed of fe oxyhydroxides shows that ge isotopes are also fractionated upon mineral precipitation at the seafloor we obtained an average ge isotope fractionation factor between fe oxyhydroxide ferrihydrite and dissolved ge in the fluid of 2 0 0 6 2sd and a maximum value of 3 6 0 6 2sd which is consistent with recent theoretical and experimental studies the study of a hydrothermal chimney at bio 9 vent at epr 9 50 n also demonstrates that ge isotopes are fractionated by approximately 5 6 0 6 2sd during precipitation of metal sulfides under hydrothermal conditions using combined ge si and estimated ge isotope signatures of ge sinks and sources in seawater we propose a preliminary oceanic budget of ge which reveals that an important sink referred as the missing ge sink may correspond to ge sequestration into authigenic fe oxyhydroxides in marine sediments this study shows that combining ge si and 74 70ge systematics provides a useful tool to trace hydrothermal ge and si sources in marine environments and to understand formation processes of seafloor hydrothermal deposits

composition of hydrothermal fluids and mineralogy of associated chimney material on the east scotia ridge back arc spreading centre abstract the east scotia ridge is an active back arc spreading centre located to the west of the south sandwich island arc in the southern ocean initial exploration of the ridge by deep tow surveys provided the first evidence for hydrothermal activity in a back arc setting outside of the western pacific and we returned in 2010 with a remotely operated vehicle to precisely locate and sample hydrothermal sites along ridge segments e2 and e9 here we report the chemical and isotopic composition of high and low temperature vent fluids and the mineralogy of associated high temperature chimney material for two sites at e2 dog s head and sepia and four sites at e9 black white ivory tower pagoda and launch pad the chemistry of the fluids is highly variable between the ridge segments fluid temperatures were 350 c at all vent sites except black white which was significantly hotter 383 c end member chloride concentrations in e2 fluids 532 536 mm were close to background seawater 540 mm whereas cl in e9 fluids was much lower 98 220 mm indicating that these fluids are affected by phase separation concentrations of the alkali elements na li k and cs and the alkaline earth elements ca sr and ba co vary with cl due to charge balance constraints similarly concentrations of mn and zn are highest in the high cl fluids but by contrast fe cl ratios are higher in e9 fluids 3 8 8 1 10 3 than they are in e2 fluids 1 5 2 4 10 3 and fluids with lowest cl have highest cu although both ridge segments are magmatically inflated there is no compelling evidence for input of magmatic gases to the vent fluids fluid d values range from 0 2 to 1 5 ph values 3 02 3 42 are not especially low and f concentrations 34 6 54 4 m are lower than bottom seawater 62 8 m the uppermost sections of conjugate chimney material from e2 and from ivory tower and pagoda at e9 typically exhibit inner zones of massive chalcopyrite enclosed within an outer zone of disseminated sulphide principally sphalerite and pyrite in an anhydrite matrix by contrast the innermost part of the chimneys that currently vent fluids with lowest cl black white and launch pad is dominated by anhydrite by defining and assessing the controls on the chemical composition of these vent fluids and associated mineralisation this study provides new information for evaluating the significance of hydrothermal processes at back arc basins for ocean chemistry and the formation of seafloor mineral deposits

southwest african climate independent of atlantic sea surface temperatures during the younger dryas abstract to investigate land sea interactions during deglaciation we compared proxies for continental pollen percentages and accumulation rates and marine conditions dinoflagellate cyst percentages and alkenone derived sea surface temperatures the proxies were from published data from an ams radiocarbon dated sedimentary record of core geob 1023 5 encompassing the past 21 000 years the site is located at ca 2000 m water depth just north of the walvis ridge and in the vicinity of the cunene river mouth we infer that the parallelism between increasing sea surface temperatures and a southward shift of the savanna occurred only during the earliest part of the deglaciation after the antarctic cold reversal southeast atlantic sea surface temperatures no longer influenced the vegetation development in the kalahari stronger trade winds during the antarctic cold reversal and the younger dryas period probably caused increased upwelling off the coast of angola a southward shift of the atlantic anti cyclone could have resulted in both stronger trade winds and reduced impact of the westerlies on the climate of southwestern africa