OS43A-0526 1340h
Global Distribution of Microbial Alteration of the Ocean Crust
Early evidence for a deep subsurface biosphere in ocean crust came from unusual alteration textures within petrographic thin sections. The textures are attributed to microbial activity within basalt minerals and glass. Microbial textures have now been found in DSDP and ODP holes and in sea floor surface basalt from around the globe. These samples revealed a variety of unique alteration textures, and our hypothesis is that similar textures are the result of similar conditions in ocean crust environments. One-hundred and five petrographic thin sections from DSDP and ODP drill cores from the Pacific, Atlantic, and Indian Oceans as well as the Mediterranean Sea were used to create a library of images of microbial alteration textures. Prevalent textures include straight, curving, segmented and angular twisting tunnels, mushroom shaped structures, and fungus-like groups of alteration. We are using Lossless Compression Analysis on our library of images to distinguish and classify the variety of alteration textures. Currently we are classifying textures both down-hole and across ocean basins and correlating the occurrence of similar textures with measured drill-hole properties, including age, location of the sample, water depth, basalt temperature, type and amount of sediment cover, depth within the basalt, and secondary minerals.
OS43A-0527 1340h
Microbial Community Structure of the Japan Trench Cold Seeps Sediment Determined by Phospholipid Analysis
Seafloor cold seeps support some of the most prolific and diverse ecosystems on Earth. A multitude of microbial habitats are associated with cold seeps. The seeping fluids are enriched in reduced chemical species such as sulfide and methane. These reduced species are utilized by microorganisms to gain energy from the reduction of sulfate and oxidation of methane, the so-called anaerobic oxidation of methane. The Japan Trench is characterized by abundant chemosynthesis-based communities associated with cold seeps. Chemosynthetic communities of {\it Maorithyas hadalis} and {\it Calyptogena phaseoliformis} have been discovered at depths of over 7,000 m. In this project, sediment samples were collected from communities dominated by thyasirid bivalve {\it Maorithyas hadalis} and the vesicomyid clam {\it Calyptogena phaseoliformis} and analyzed for phospholipid fatty acids (PLFA). Our objectives were to determine and compare the microbial biomass and community structure of the two sites with different megafaunal species. Result showed the average estimated microbial biomass was 2.97*109 and 4.78*109 cells (g dry wt)-1 for {\it Calyptogena} and {\it Maorithyas} sediment, respectively. Fatty acids ranging from 12 to 22 carbons were detected. The PLFA profiles suggest the presence of methanotrophic bacteria, sulfur-oxidizing bacteria as well as sulfate-reducers. The polyunsaturated fatty acids (C 18:2 and C20:5) also allow us to trace the possible source of the sediment to the piezophilic bacteria. The assemblage of fatty acids indicates the presence of complex microbial communities in the cold seeps sediments of the Japan Trench.
OS43A-0528 1340h
Biogeochemical Processes in Mid-Ocean Ridge Hydrothermal Plumes
Hydrothermal production is an important source of labile organic carbon (OC) to the deep-sea ecosystem along a ~60,000 km mid-ocean ridge corridor of enhanced productivity. Both the source flux and dispersion of OC derived from hydrothermal environments are poorly constrained. The dispersion is controlled by a complex interaction of dissolved OC to particulate OC transformations, particle scavenging and settling processes, buoyant plume dynamics and near-bottom circulation. Dissolved (DOC) and particulate (POC) organic carbon in hydrothermal plumes are derived from i) subseafloor microbial and thermochemical processes, ii) vent macrofaunal communities through exudation, sloughing, feeding, and export of reproductive products, iii) in situ production within the buoyant and neutrally buoyant plumes, iv) background deep-water entrained during plume formation, and v) descending particles delivered from surface water production. The quantitative contributions from first two sources are not presently known, whereas more measurements exist of in situ production within hydrothermal plumes and the importation of OC from the upper water column. Inspired by the early work of Jack Dymond and colleagues, the accumulating data (1980's to present) from the Endeavour Segment and other areas indicate that in situ production of POC from the oxidation of H2S, H2, CH4 and NH4, alone, may contribute $>$300% of the surface derived OC flux to plume depths along a 20 km wide corridor. It is likely that this value is conservative since `hydrothermally derived' DOC is almost totally unaccounted for Furthermore, the labile nature of this fresh `hydrothermal' OC relative to the more refractory ambient deep water OC underscores its potential significance to deep-water organisms. This production and its dispersion must strongly influence the abundance and diversity of deep water and benthic micro- and macro-fauna along the ridges and ridge flanks, creating an "oasis" of labile organic-C that focuses biological activity over and on the MORs.
OS43A-0529 1340h
Diagenetic Alteration of Hydrothermal Plume Precipitates: Transition Metal and Oxyanion Associations.
We evaluate the diagenetic alteration of hydrothermal plume precipitates and discuss implications for the magnitude of transition metal and oxyanion sinks, based on analysis of sediment mineralogy, bulk chemistry, and a four step sequential extraction procedure. All samples were collected from the EXCO (EXchange between the Crust and Ocean) study site at $\sim$14$\deg$S on the east flank of the East Pacific Rise. The sediments are lithologically simple (biogenous carbonate, plume precipitates, minor basaltic debris) and oxic (uniform Fe/Mn). This site thus provides an excellent natural laboratory to investigate the role of plume derived Fe and Mn (hydr)oxides in controlling the fate of divalent transition metals (Cu, Zn, Ni) and oxyanions (V, P, As) in the sediment column, where this study bridges the gap between laboratory experiments and studies conducted in more complex environments. The alteration of Fe (hydr)oxides in the EXCO region is dominated by transformation of ferrihydrite to goethite, where the extent of alteration (goethite-Fe / X-ray amorphous Fe) ranges from 0.3-2.1. The dominant formation of goethite over hematite is in contrast to laboratory studies. We hypothesise that the strong surface adsorption of scavenged seawater species inhibits the structural rearrangement of ferrihydrite to hematite under natural conditions. A preliminary kinetic analysis suggests that the rate of transformation to goethite displays a pseudo second order dependency on the total Fe (hydr)oxide content, in contrast to laboratory data which indicate a first order dependency. This discrepancy may reflect reaction conditions in the sediment column which are dependent on the Fe (hydr)oxide content (e.g. porosity). Cu, Zn and Ni are delivered to the sediment in association with both Fe and Mn (hydr)oxides, where $\sim$70% of Cu and Zn and $\sim$10% of Ni are associated with Fe (hydr)oxides. The Fe-associated Cu and Zn are adsorbed to the ferrihydrite surface and incorporated into the lattice structure of goethite during alteration. The Fe-associated Ni most likely represents Ni coprecipitated as Ni-Fe ferrihydrite and incorporated into goethite during alteration. The alteration of hydrothermal Fe (hydr)oxides thus represents a relatively permanent sink (where goethite dissolution is a prerequisite for metal release) for $\sim$70% of Cu and Zn and $\sim$10% of Ni. V, P and As are delivered to the sediment in association with Fe (hydr)oxides. The bulk sediment V/Fe is consistent with the plume particle signature, however only $\sim$30-40% of plume-V is incorporated into goethite during alteration, where the rejected V is most likely retained in the sediment in association with Mn-rich phases. Under oxic conditions, (no loss of hydrothermal Mn), the sediment V/Fe could therefore provide a good tracer of past seawater V content. The bulk sediment P/Fe and As/Fe are variable and lower than the plume particle signature. The loss of plume-P and As is attributed to a decrease in available surface adsorption sites with aging of the Fe (hydr)oxide precipitates, where loss continues until a steady state P/Fe or As/Fe is obtained. The difference between the plume particle P/Fe and the steady state P/Fe indicates a decrease in surface adsorption sites of $\sim$74%, in good agreement with the $\sim$60-70% reduction estimated from a comparison of the plume V/Fe to the goethite V/Fe. The remobilisation of plume-P thus impacts the global oceanic P budget, such that the net sink of plume-P is reduced by $\sim$74% to 4.4-8.0 x 10$^{10}$ gyr$^{-1}$, or only 5-9% of the riverine dissolved flux.
OS43A-0530 1340h
Trace Metal Distribution and Speciation in Pore Water of Hydrothermal Sediments From the Guaymas Basin, Gulf of California
Thirteen sediment cores were collected through out direct sampling with the MBARI/ ROV "Tiburon" in the southern trough of the Guaymas Basin in March 2003. Pore water samples from regular 2.5 cm intervals of sediment cores were extracted onboard by centrifugation. The supernatants were collected in clean polystyrene vials and stored at $4\deg$ C until analytical work on shore. Dissolved Fe, Mn, Cu, Pb, Zn and Ni concentrations in extracted fluid samples were analyzed by direct injection of atomic absorption spectrometry. Four zones in the hydrothermal field were classified according to their physical characteristics. A core located away from the influence of active vents was recovered as a background site. The second zone is characterized by low temperatures ($4.2-80\deg$ C) and sediments saturated in hydrocarbons. Sulfides formation and higher temperatures ($4-166\deg$ C) were observed in the third zone. Precipitation of carbonates on top of the sediment characterizes the fourth zone. Concentration of trace metals at the water-sediment interface appears to be the highest, probably due to metal precipitation from the hydrothermal plume, followed by diffusion into the pore water. A decrease in concentration is observed between 5-12 cm depth, suggesting that biological activity is consuming essential metals (zone of bioturbation). Metal concentrations in zones where sulfide phases are rich, exhibit smaller values in pore water (Fe=2.4-3.8 $\mu$mol/kg, Cu=0.6-0.8 $\mu$mol/kg, Pb=1.2-1.5 $\mu$mol/kg, Zn=0.4-0.5 $\mu$mol/kg and Ni= 3.4-4.4 $\mu$mol/kg) relative to samples located at hydrocarbon sites (Fe= 2.7-11.4, Cu= 0.7-1.0 $\mu$mol/kg, Pb= 1.2-2.2 $\mu$mol/kg, Zn= 0.4-0.7 $\mu$mol/kg and Ni= 3.4-5.2 $\mu$mol/kg). At sulfide zones, pH and Eh conditions help to precipitate their stable sulfides as opposed to the hydrocarbon areas, where conditions are not favorable for sulfide formation due to the absence of H$_{2}$S. In general, Fe concentrations in pore water are lower than that of Mn, very likely due to the easier precipitation and greater stability of FeS relative to MnS. As an attempt to reconstruct predominant species and their abundance in the system, aqueous chemical models were applied. The codes EQBRM and SUPCRT92 were run with total concentrations to calculate, concentrations, activity coefficients and thermodynamic properties of aqueous species. Experimental data such as total chloride, total sulfur and measured pH were used in the model. According to the prevailing conditions in the Guaymas Basin, all metals studied form chloride complexes. Iron, lead, and zinc exist mainly as hydroxy complexes, manganese as free ion and copper as CuHS. Speciation results are well supported by the Pearson's hard-soft rule which states that soft metal ion Cu$^{+}$+ bonds with soft bisulfide ligand, likewise, borderline metal ions as Fe$^{2+}$, Mn$^{2+}$, Pb$^{2+}$ and Zn$^{2+}$ bond with chloride, hydroxyl or water ligands. The results reported here provide a greater insight into the behavior of trace metals in pore waters of hydrothermal sediments.
OS43A-0531 1340h
Isotopic Constraints on Sources and Benthic Turnover at Mound 12, Western Costa Rican Margin
During several expeditions, we investigated the emission and isotopic signature of methane at several mounds of the western continental margin off Costa Rica and Nicaragua. All of the mounds investigated, either created by mud volcanism or mud diapirism, show indications of fluid venting, including authigenic carbonates, chemoautotrophic consortia, salt depleted pore waters, and methane plumes in the water column. However, the amount of methane released as well as the stable carbon isotopic ratio (del C-13) vary considerably. Here we report on results from Mound 12, a mound with a very weak morphological expression; that is only 30 m high and elongated in northeast-southwest direction with diameters of about 1 to 1.6 km. Data were gathered using standard CTD/rosette equipment, a bottom water sampler enabling to resolve the methane distribution within the lowermost meter of the water column, a benthic chamber lander (BCL), multicorer and piston corer deployments. Data show a very light biogenic methane source (del C-13 < -90 permil within the sediments), -76 permil in the lowermost water samples with concentrations up to 100 nmo/L, and a methane background of - 45 permil 20 m above the vent site. High oxygen demand immediately at a site with bacterial mats in connection to lower carbon stable isotopic ratios with increasing sediment depth is in contrast to low oxygen demand and heavier stable isotopic ratios with increasing sediment depth only one meter apart. Moreover, the relation of methane concentration vs. isotopic signature above the vent sites implies considerable oxidation and fractionation in the benthic boundary layer (BBL) above the vent site, which is supported by some biomarker investigations at the same site. Significant oxidation of methane above vent sites within the BBL has not been reported so far. An alternative explanation, which is the existence of an additional methane source with an isotopic signature similar to the background ( del C-13 =-45 permil) is unlikely, based on the investigations of numerous piston cores taken at Mound 12. However, such a heavier isotopic signature, in connection to higher amounts of higher hydrocarbons, was encountered at Mound 11, a very similar structure only a couple of hundred meters apart.
OS43A-0532 1340h
Continental Delivery of Iron to Ocean Station Papa in the Subarctic Pacific
The phytoplankton assemblage at Ocean Station Papa (OSP) in the Subarctic Pacific in February 1996 was dominated by large chain forming diatoms and abundant coccolithophores. This phytoplankton assemblage is atypical of an HNLC region and strongly suggests a recent supply of bioavailable iron. Using synchrotron X-Ray Fluorescence (XRF) and Scanning Transmission X-Ray Microscopy (STXM), we show that marine aggregates collected at this time display micron sized discrete hotspots of iron. The hotspots are observed in aggregates collected from surface to deep, and are also prevalent in the small size fraction (1-53$\micron$m). X-ray absorption spectroscopy (XAS) of several hotspots indicates that this iron is not organically bound and is predominantly oxide in nature. Aerosol monitoring stations do not show evidence of any dust delivery to the subarctic Pacific at this time, and the Ti:Fe ratios of the observed hotspots ($\sim$0.02) are well below that of Asian dust ($\sim$0.1). We conclude that the Fe hotspots at OSP originated from the continental margin. We ran an ocean general circulation model with an iron-like tracer source at the continental margin to confirm that micron-sized particulate iron can be transported to OSP on a reasonable time scale.
OS43A-0533 1340h
Finding a Paleoproxy for Upper Ocean Nitrate Concentrations: Se/S in Marine Barite?
Nitrate is a key limiting nutrient in many oceanic environments and a paleoproxy for nitrate would be invaluable for understanding mechanisms driving C export fluxes in the past. Selenate (SeO$_{4}$$^{2-}$), one of the dissolved chemical species of the trace element selenium, shows an excellent correlation with nitrate, having surface water depletion and deep water enrichment. In this respect, the biogeochemical cycle of selenium is analogous to that of nitrogen. Furthermore, selenate is almost chemically identical to sulfate and as such is incorporated into barite, a diagenetically stable mineral that is formed inorganically in the water column. In order to investigate whether the Se/S ratio in marine barite can act as a nitrate proxy, we have utilized a set of core top samples from $8\deg$N to $5\deg$S at $140\deg$W in the Equatorial Pacific Ocean, as well as sediment samples from other ocean basins. Barite was isolated from these sediments using sequential leaching and ashing, and then dissolved using a cation chelation method. Dissolved sulfate in the resulting solutions was determined by ion chromatography, while selective hydride generation-atomic absorption spectrometry was used to determine dissolved selenate. A N-S transect at $160\deg$W in the Pacific showed both dissolved selenate and nitrate to be depleted in surface waters of the northern and southern gyres, while concentrations rose to 0.6 nmol Se/L and 3.5 $\mu$mol N/L in the equatorial upwelling regime (the r for Se vs. N was 0.92). In comparison, barite Se/S in surficial sediments underlying oligotrophic waters averaged 11.5$\pm$5.8 x 10$^{-8}$, while those under the equatorial upwelling regime were 92$\pm$64 x 10$^{-8}$, values that are ca. 10-100x those in surface waters (Se enrichment in barite relative to S). These results suggest that barite may indeed be recording the upper ocean selenate, and hence nitrate, concentrations. However, more data are required and experiments to quantify the amount of Se enrichment relative to S in barite (vs. in surface waters) need to be conducted.
OS43A-0534 1340h
MEDFLUX: Organic Biomarkers in Time-Series and Sinking-Velocity Traps
During a recent field experiment at the French JGOFS DYFAMED site in the western Mediterranean, we collected sinking particles using conventional time-series traps and a trap modified to fractionate particles in-situ as a function of their sinking velocity. Our goal was to characterize the in-situ sinking nature of particles, followed by analysis of their chemical composition to evaluate relationships between organic matter, mineral ballast, sinking, and decomposition. Analyses of lipids and amino acids in these trap samples and application of multivariate analysis to compound distributions separates trap samples dominated by fresh diatom-derived organic matter from those that contain substantial amounts of OM that has been reworked by zooplankton and bacteria. The majority of particles were observed to sink at 200-500 m/d and were dominated by large diatom-derived aggregates that were delivered primarily during the spring bloom period. The more slowly sinking particles carry with them a greater zooplankton and bacterial signature.
OS43A-0535 1340h
Amino acid racemization kinetic modeling and the late Quaternary paleoclimate of the North Carolina coastal plain
Amino acids extracted from Quaternary mollusks represent a preserved residue of the original biomineralization protein. The extent of racemization of these fossilized amino acids is often used as a stratigraphic or chronologic tool. With suitable calibration, racemization data can also be used to construct a history of temperature for the samples in question. Understanding diagenetic amino acid racemization (AAR) kinetics requires a combination of laboratory kinetic experimentation and testing of kinetic models with natural field samples that have independent chronostratigraphic control. These models must also incorporate information on the temperature dependence ("apparent" or "bulk" activation energy) as derived from either elevated temperature laboratory experiments or data from field samples with known ages and diagenetic temperatures. Over the past two decades, several well-calibrated datasets and a variety of kinetic models have become available: foraminifera results provide calibration for low temperature kinetics (e.g., Muller, 1984) and paired radiocarbon-AAR results provide calibration at higher surface temperatures (e.g., Miller et al., 1997). The most recent approaches to modeling of AAR kinetics include a molecular approach (Collins and Riley, 2000) that links racemization to polypeptide breakdown reactions and a transformation approach (Manley et al., 2000) that builds upon earlier "parabolic" (Mitterer and Kriausakul, 1989) or "non-linear" models (Wehmiller et al., 1988). The parabolic model, while useful over limited time or D/L ranges, has the disadvantage that it does not predict correct equilibrium D/L values. The other three models, if calibrated to a common value, predict consistent patterns of racemization that are in good agreement, and the molecular approach has been used to extrapolate foraminifera kinetics (Muller, 1984) to estimate ages and diagenetic temperatures of Pleistocene mollusks from North Carolina, predicting a late Pleistocene cooling of ca. 7 deg. C. for the region, based on a simple square-wave model of temperature change. AAR results for seven amino acids in a suite of radiocarbon-dated Mercenaria samples from the North Carolina coastal plain expand this approach to paleotemperature estimation. Samples have been obtained from beaches, the inner shelf, and from subsurface drilling. 14C ages range from ~1 kyr to >52 kyr, with the older (radiocarbon dead) likely representing "last interglacial" (80-130 kyr) ages. Additionally, the observed AAR kinetics for the Holocene samples from different latitudes (temperatures) allow estimates of "effective activation energies" that compare well with those determined by experimental heating. These effective activation energies can then be used in combination with numerical models of racemization to predict D/L values as a function of time and optional temperature histories for the region. Full glacial temperature reductions predicted in this manner are model-dependant and range from 6 to 11 deg. C.
OS43A-0536 1340h
Paleoclimate feeback involving co-oxidation of alpha-pinene by methane oxidizers
The methane mononxygenase (MMO) enzyme of methane oxidizing bacteria is relatively non-specific and is capable of co-oxidizing a variety of methylated compounds including alpha-pinene produced by conifers. Laboratory and field experiments indicate that aquatic and soil methane oxidation is inhibited by the presence of alpha-pinene as the MMO preferentially oxidizes pinene over methane. Since methane is a potent greenhouse gas, this suggests possible climatic controls between atmospheric methane levels and coverage of coniferous pine forests which may be reflected in stable isotope records.
OS43A-0537 1340h
(More) Biogenic Barium and Organic Carbon Relationships on the Continental Margin: a Study From the Alboran Sea (Western Mediterranean)
The observed relationship between biogenic barium (bio-Ba) and organic carbon (Corg), and the relatively refractory nature of barite in non sulfate reducing sediments have led to the consideration of barite as a proxy for both modern and past biological processes. Beyond the uncertain phase partitioning between barite within total bio-Ba, recent studies have revealed that the relationship between bio-Ba and Corg fluxes in margin systems and open ocean systems differs markedly. In order to improve the knowledge of the behavior and significance of this component we present particulate bio-Ba fluxes obtained from three instrumented arrays with sediment traps moored in a continental margin area: the Alboran Sea (Western Mediterranean). The results obtained provide important insights into the influence of the oceanographic structures (upwelling off the Spanish coast, Western and Eastern Alboran Gyres), the intermittent fluvial discharge (southern Iberian Peninsula rivers) and the local bottom topography on the formation and transport of bio-Ba. Increased bio-Ba export efficiency at the end of enhanced productivity events suggest that the processes limiting bio-Ba formation in the area relate to the settling dynamics of particles. The ballasting effect of the abundant lithogenic and carbonate particles during massive aggregation processes during high productivity events may limit the decomposition of organic matter and enhance the transfer of particles rich in Corg and relatively poor in bio-Ba to the deep sea floor. We have also observed lateral transport of freshly sedimented material, including bio-Ba, from the continental slope to deeper areas. These results add to the growing caution in using bio-Ba as a productivity proxy in such highly dynamic environments.
OS43A-0538 1340h
Does Barite Form in the Oceanic Water Column?
Understanding the physical and chemical conditions that lead to the formation and preservation of barite in marine environment is important to validate the application of barium/barite abundance in ocean sediments as an index of productivity. In this work we rely on time-series sediment trap results to explore: (1) barium and strontium concentration variations; (2) the changes in the degree of saturations with respect to barite and celestite; and (3) the equilibrium relationship between barite and celestite in seawater cup solutions in order to investigate the formation of "natural" marine barite as the mixed solid phase Ba$_{x}$Sr$_{1-x}$SO$_{4}$. The data were collected along 170W between Subtropical Front and Ross Sea from November 1996 to January 1997, as part of the U.S. Joint Global Ocean Flux Study (USJGOFS-AESOPS) to study the Southern Ocean impact on biogeochemical processes of the oceans. High concentrations of barium and strontium were measured in the cup solutions of sediment traps during the high particle flux periods. The cup solutions of the sediment traps were estimated to be supersaturated with respect to pure barite between 100% and over 900%. They were undersaturated to slightly supersaturated with respect to celestite, ranging between 14 and 150%. The modeled equilibrium relationship of a mixed solid phase of barite and celestite in solution has indicated that barite with up to 23% mole fraction of SrSO$_{4(s)}$ might form in these cup solutions. The Sr/Ba ratios in the bulk solid phases collected from the same sediment trap cups were much higher (25-99%) than modeled values and are likely controlled by non-sulphate solids. These results also suggest that the precipitation of marine barite crystals is not favorable in these cup solutions due to the high solubility of high strontian barite. If the cup solutions can approximate the isolated chemical environment within particle aggregates collected by these traps, then it is unlikely that significant precipitation of marine barite occurs during their transport to the seafloor.
OS43A-0539 1340h
Excess Aluminum and the Quantification of Terrigenous Material in Pelagic Biogenic Sediment: An Update and Eye for the Future
Beginning in the mid-1990s, a series of papers documented the presence of "excess Al" in biogenic-rich sediment and particles from the equatorial Pacific Ocean (Murray et al., 1993; Murray and Leinen, 1996; Dymond et al., 1997). These papers observed a component of Al that was in excess of (or, "unsupported by") the lattice-bound terrigenous inventory. In addition to being of interest to the study of the biogeochemical cycling of Al, these works also postulated that the amount of the "excess" Al depended on either the total particle flux (Murray et al., 1993; Murray and Leinen, 1996) or the flux of only the biogenic opal component (Dymond et al., 1997). In either case, the excess Al appears to be a powerful proxy for paleoceanographic reconstructions (e.g., Murray et al., 2000 Paleocean., 15, 570-592), and it is apparent that using Al abundances to exclusively indicate the terrigenous component in settling particles or biogenic sediment may lead to inaccurate results in sedimentary regimes with less than approximately 3 to 5 % terrigenous material. We will summarize the assumptions and observations of these first papers as well as others that observe excess Al in regions other than the equatorial Pacific (e.g., Banakar et al., 1998), reinterpret some data from the 1970's and 1980's that also suggest excess Al, and highlight more recent contributions (Kryc et al., 2003, EPSL, 211, 125-141) that shed further light on the distributions of Al and other refractory elements (e.g., Ti) in pelagic sediment. The discussion of excess Al naturally trends towards larger issues regarding how to quantify the abundance of terrigenous material in biogenic sediment, which was a topic to which the late Jack Dymond contributed greatly. Dymond's thoughts on the excess Al issue, expressed both in the literature (e.g., Dymond et al., 1997), as well as through prescient private communications to us, stimulated much of our recent work. For example, building on the sequential extraction work of Kryc et al. (2003), we have recently devised a geochemical method by which the accuracy of terrigenous leaching-type extractions may be assessed. Other on-going studies of the paired (or not) behavior of Al and Ti in sediment traps and sediment will be discussed, and several other potential avenues of research will be explored.
OS43A-0540 1340h
Using Gamma ray and Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES) to Evaluate Elemental Sequences in Cap-carbonates and Cap-like Carbonates of the Death Valley Region
The Snowball Earth theory of Hoffman et al. (1998) proposes dramatic post-glacial chemical weathering as large concentrations of carbon were removed from the atmosphere. This would result in a large input of terrigenous material into the oceans; hence, we might expect that carbonates formed under these conditions would demonstrate elevated K, U, Th levels in comparison to carbonates formed under more typical conditions. In January of 2004 we collected spectral gamma data (K, U, Th) and hand samples from cap carbonates (Noonday Dolomite) and cap-like carbonates (Beck Spring Dolomite) of the Death Valley region in order to explore elemental changes in post-snowball Earth oceans. Based on our spectral gamma results, Th/U ratio trends suggested variations in the oxidation state of the Precambrian ocean. We pursued further investigations of trace elements to ascertain the reliability of these results by using ICP-OES. A suite of 25 trace elements was measured, most notably including U and Th. The ICP-OES data not only allow us to compare elemental changes between cap-carbonates and cap-like carbonates, but they also allow for a comparison of optical emission spectrometry and hand held gamma spectrometry methods. Both methods show similar trends in U and Th values for both the cap-carbonates and cap-like carbonates.
OS43A-0541 1340h
Long-term Observations of Crater Lake, Oregon: Energy, Carbon, and Nutrient Cycles in an Ultra-oligotrophic Ecosystem
Large, deep lakes offer a unique resource for the study of the interaction of the atmosphere and aquatic biogeochemical cycles. The remarkable properties of Crater Lake result in the vertical stratification of the ecosystem reminiscent of pelagic marine systems. This ultraoligotrophic lake provides a powerful natural laboratory to study the coupling of biological processes, element cycles, and the physics of the environment. Over 20 years ago, Jack Dymond established a long-term, high-resolution biogeochemical study, including sediment traps, which today provides a powerful tool to constrain processes operating over seasonal and interannual time scales. These studies enable the validation of appropriate process models, leading to a better predictive capacity in this and other large aquatic ecosystems. - We have demonstrated and modeled relationships between climate-driven vertical mixing and the upwelling of hypolimnetic nitrogen into the euphotic zone. The impacts of this nitrogen on the ecosystem are complex and are not simply reflected in export production. - The lake edges are a locus of this vertical mixing, and mass balance calculations suggest they support elevated primary production which must contribute significant particulate organic matter to the interior hypolimnion. - The extended time-series observations have allowed us to observe interannual variations in vertical mixing, deep water ventilation, and the accumulation of salt and nitrogen. - The observations have constrained models of lake physics which help evaluate the first-order impact of climate change scenarios. A nitrogen-based ecosystem model has been coupled to the physical model and validated against biological time series observations. - The functioning of large lake ecosystems are finally reflected in their sediments and may provide one of the most powerful paleorecords of climate variability on the continents.. Because Crater Lake is the centerpiece of one of the premier National Parks in the USA, it provides a unique setting to directly engage the public with compelling educational experiences demonstrating the function of complex aquatic ecosystems and the methods of interdisciplinary field research.
OS43A-0542 1340h
Teaching Scientists to Fish, as Inspired by Jack Dymond
It is almost inconceivable that as Jack Dymond's graduate student for eight years, I never mastered the skill of fly-fishing, a pursuit so near and dear to his heart. In fact, Jack did inspire me, not to tie flies and cast, but eventually to teach fellow scientists to fish. The work I'll present - connecting scientists and educators to achieve societal benefit - is profoundly influenced by Jack's dedication to applying scientific understanding and critical thinking to societal issues. With colleagues in the Centers for Ocean Sciences Education Excellence (COSEE), http://www.cosee.net/, I enable scientists to efficiently make meaningful contributions to educational outreach. A key goal of the multi-Center, national COSEE Network is helping scientists build the skills and acquire the resources needed to share their science with diverse audiences. At Scripps, we are piloting an innovative approach to helping scientists meet funding agencies' {\it broader impact} requirements. Key elements of the approach include: 1) services to identify educational outreach options that best fit scientists' research and preferences; 2) assistance establishing partnerships with educational outreach providers who have the skills and resources to develop and implement effective programs and exhibits; and 3) nuts and bolts (line and fly) assistance writing proposal text, drafting budgets, and coordinating with institutional business offices to ensure that the proposed educational outreach effort is compelling and sufficiently funded. Where does the fishing lesson come in? We facilitators of scientist-educator partnerships empower scientists to launch enduring collaborations. Once comfortable working with top-notch educational organizations, scientists can tap these resources, project after project, often with little or no additional involvement on our part. Our initial investment in brokering the relationships is richly rewarded. By helping scientists get started, it's as if we are teaching them to fish, rather than merely giving them fish.
http://www.cosee.net/