1,523 research outputs found
Seawater carbonate chemistry distributions across the Eastern South Pacific Ocean sampled as part of the GEOTRACES project and changes in marine carbonate chemistry over the past 20 years
No full textThe US GEOTRACES Eastern Pacific Zonal Transect in 2013 that sampled in the South Pacific Ocean has provided an opportunity to investigate the biogeochemical cycling of trace elements and isotopes (TEIs) and seawater carbon dioxide (CO2)-carbonate chemistry. Across the Peru to Tahiti section, the entire water column was sampled for total alkalinity (TA) and dissolved inorganic carbon (DIC), in addition to core hydrographic and chemical measurements conducted as part of the GEOTRACES cruise. From the nutrient-rich, low-oxygen coastal upwelling region adjacent to Peru to the oligotrophic central Pacific, very large horizontal gradients in marine carbonate chemistry were observed. Near the coast of Peru, upwelling of CO2-rich waters from the oxygen-deficient zone (ODZ) impinged at the surface with very high partial pressures of CO2 (pCO2; >800-1,200 μatm), and low pH (7.55-7.8). These waters were also undersaturated with respect to aragonite, a common calcium carbonate (CaCO3) mineral. These chemical conditions are not conducive to pelagic and shelf calcification, with shelf calcareous sediments vulnerable to CaCO3 dissolution, and to the future impacts of ocean acidification. A comparison to earlier data collected from 1991 to 1994 suggests that surface seawater DIC and pCO2 have increased by as much as 3 and 20%, respectively, while pH and saturation state for aragonite (Ωaragonite) have decreased by as much as 0.063 and 0.54, respectively. In intermediate waters (~200-500 m), dissolved oxygen has decreased (loss of up to -43 μmoles kg-1) and nitrate increased (gain of up to 5 μmoles kg-1) over the past 20 years and this likely reflects the westward expansion of the ODZ across the central Eastern South Pacific Ocean. Over the same period, DIC and pCO2 increased by as much as +45 μmoles kg-1 and +145 μatm, respectively, while pH and Ωaragonite decreased by -0.091 and -0.45, respectively. Such rapid change in pH and CO2-carbonate chemistry over the past 20 years reflects substantial changes in the ODZ and water-column remineralization of organic matter with no direct influence from uptake of anthropogenic CO2. Estimates of anthropogenic carbon (i.e., CANT) determined using the TrOCA method showed no significant changes between 1993 and 2014 in these water masses. These findings have implications for changing the thermodynamics and solubility of intermediate water TEIs, but also for the marine ecosystem of the upper waters, especially for the vertically migrating community present in the eastern South Pacific Ocean.</p
Acceleration of ocean warming, salinification, deoxygenation and acidification in the surface subtropical North Atlantic Ocean
No full textOcean chemical and physical conditions are changing. Here we show decadal variability and recent acceleration of surface warming, salinification, deoxygenation, carbon dioxide (CO2) and acidification in the subtropical North Atlantic Ocean (Bermuda Atlantic Time-series Study site; 1980s to present). Surface temperatures and salinity exhibited interdecadal variability, increased by ~0.85 °C (with recent warming of 1.2 °C) and 0.12, respectively, while dissolved oxygen levels decreased by ~8% (~2% per decade). Concurrently, seawater DIC, fCO2 (fugacity of CO2) and anthropogenic CO2 increased by ~8%, 22%, and 72% respectively. The winter versus summer fCO2 difference increased by 4 to 8 µatm decade−1 due to seasonally divergent thermal and alkalinity changes. Ocean pH declined by 0.07 (~17% increase in acidity) and other acidification indicators by ~10%. Over the past nearly forty years, the highest increase in ocean CO2 and ocean acidification occurred during decades of weakest atmospheric CO2 growth and vice versa
Eddy transport of organic carbon and nutrients from the Chukchi Shelf : impact on the upper halocline of the western Arctic Ocean
No full textAuthor Posting. © American Geophysical Union, 2007. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 112 (2007): C05011, doi:10.1029/2006JC003899.In September 2004 a detailed physical and chemical survey was conducted on an anticyclonic, cold-core eddy located seaward of the Chukchi Shelf in the western Arctic Ocean. The eddy had a diameter of ∼16 km and was centered at a depth of ∼160 m between the 1000 and 1500 m isobaths over the continental slope. The water in the core of the eddy (total volume of 25 km3) was of Pacific origin, and contained elevated concentrations of nutrients, organic carbon, and suspended particles. The feature, which likely formed from the boundary current along the edge of the Chukchi Shelf, provides a mechanism for transport of carbon, oxygen, and nutrients directly into the upper halocline of the Canada Basin. Nutrient concentrations in the eddy core were elevated compared to waters of similar density in the deep Canada Basin: silicate (+20 μmol L−1), nitrate (+5 μmol L−1), and phosphate (+0.4 μmol L−1). Organic carbon in the eddy core was also elevated: POC (+3.8 μmol L−1) and DOC (+11 μmol L−1). From these observations, the eddy contained 1.25 × 109 moles Si, 4.5 × 108 moles NO3 −, 5.5 × 107 moles PO3 −, 1.2 × 108 moles POC, and 1.9 × 109 moles DOC, all available for transport to the interior of the Canada Basin. This suggests that such eddies likely play a significant role in maintaining the nutrient maxima observed in the upper halocline. Assuming that shelf-to-basin eddy transport is the dominant renewal mechanism for waters of the upper halocline, remineralization of the excess organic carbon transported into the interior would consume 6.70 × 1010 moles of O2, or one half the total oxygen consumption anticipated arising from all export processes impacting the upper halocline.This work was
supported by the National Science Foundation, and office of Naval
Research; DH OPP-0124900, NB OPP-0124868, DK OPP 0124872, RP
N00014-02-1-0317
Dissolved organic nitrogen dynamics in the Arctic Ocean
No full textLittle is known about the distribution and dynamics of dissolved organic nitrogen (DON) within Arctic Ocean surface waters, though seasonal inputs from both rivers and marine phytoplankton production are likely important. Here we combine multiple datasets to provide the first quasi-synoptic view of DON concentrations in the summertime Arctic Ocean Polar Surface Layer (PSL) and western Arctic shelves, and infer controlling processes. Distributions indicate inputs of DON by Arctic rivers followed by net consumption of up to 70% of this terrigenous material across the resulting salinity gradients over time scales of years. Coupling of DON losses to PSL residence times indicates first order decay constants (?) of 0.15 ± 0.07 yr? 1 and 0.08 ± 0.01 yr? 1 for terrigenous DON in the eastern and western Arctic systems, respectively. Riverine delivery of both inorganic and organic nitrogen have only a minor (< 15%) impact on Arctic shelf export production. In the Pacific Ocean-influenced Chukchi Sea, net biological production of ~ 2 ?M DON, representing ~ 8% of net community production, is observed in surface waters following seasonal sea-ice retreat. These findings highlight the contrasting roles and locations of terrigenous versus marine derived DON in the cycling of nitrogen in the surface Arctic Ocean
Preserving Linked Data Integrity on the Semantic Web by application of techniques from Hypermedia
No full textThis report presents a Literature Review of past work in Hypertext link integrity and current work in the emerging area of Semantic Web link integrity. A design and prototype for a system which applies some ideas from Hypertext link integrity to the Semantic Web is presented alongside plans for future enhancements of this system. In addition other possible avenues of research regarding ideas from traditional Hypertext link integrity are briefly discussed
Conservative and non-conservative variations of total alkalinity on the southeastern Bering Sea shelf
No full textRecent observations of calcium carbonate (CaCO3) mineral undersaturations on the Bering Sea shelf have prompted new interest in the physical and biological factors that control the inorganic carbon system in the region. Understanding of the dynamics that influence the spatio-temporal variability of total alkalinity (TA) – one major component of the seawater carbonate system – has been constrained by limited historical data collected across the shelf, and the consensus has been that TA is largely conservative. However, the recently documented undersaturated conditions have the potential to cause substantial non-conservative variability in TA in this region through the dissolution of carbonate minerals. In order to quantify the contribution of carbonate mineral precipitation and dissolution to variability in TA on the southeastern Bering Sea shelf, we examined seasonal observations of TA that were made between 2008 and 2010 as part of the BEST-BSIERP Bering Sea Project. Conservative influences accounted for most of the variability in TA concentrations, with well-constrained mixing dominating in spring and summer of 2008. Bering Shelf Water (BSW) contained a constant ratio of TA to salinity, while river discharge (RW) added TA relative to salinity at a predictable rate. Although substantial organic carbon production and denitrification can cause some non-conservative variation in TA concentrations (a maximum of ~ 15 ?mol kg SW? 1 combined), carbonate mineral dissolution and precipitation were shown to be the most important processes responsible for non-conservative TA–salinity relationships. CaCO3 uptake by the dominant pelagic phytoplankton calcifier (i.e., coccolithophores) was shown to alter TA concentrations by as much as 59 ?mol kg SW? 1. Evidence for shallow-water CaCO3 mineral dissolution was also observed, which caused TA concentrations to increase by as much as 36 ?mol kg SW? 1. Therefore, contrary to our previous understanding, the non-conservative physico-biogeochemical factors observed in this study play an important role in controlling the ocean carbon cycle of the Bering Sea shelf
Formation and transport of corrosive water in the Pacific Arctic region
No full textOcean acidification (OA), driven by rising anthropogenic carbon dioxide (CO2), is rapidly advancing in the Pacific Arctic Region (PAR), producing conditions newly corrosive to biologically important carbonate minerals like aragonite. Naturally short linkages across the PAR food web mean that species-specific acidification stress can be rapidly transmitted across multiple trophic levels, resulting in widespread impacts. Therefore, it is critical to understand the formation, transport, and persistence of acidified conditions in the PAR in order to better understand and project potential impacts to this delicately balanced ecosystem. Here, we synthesize data from process studies across the PAR to show the formation of corrosive conditions in colder, denser winter-modified Pacific waters over shallow shelves, resulting from the combination of seasonal terrestrial and marine organic matter respiration with anthropogenic CO2. When these waters are subsequently transported off the shelf, they acidify the Pacific halocline. We estimate that Barrow Canyon outflow delivers ~2.24 Tg C yr-1 to the Arctic Ocean through corrosive winter water transport. This synthesis also allows the combination of spatial data with temporal data to show the persistence of these conditions in halocline waters. For example, one study in this synthesis indicated that 0.5–1.7 Tg C yr-1 may be returned to the atmosphere via air-sea gas exchange of CO2 during upwelling events along the Beaufort Sea shelf that bring Pacific halocline waters to the ocean surface. The loss of CO2 during these events is more than sufficient to eliminate corrosive conditions in the upwelled Pacific halocline waters. However, corresponding moored and discrete data records indicate that potentially corrosive Pacific waters are present in the Beaufort shelfbreak jet during 80% of the year, indicating that the persistence of acidified waters in the Pacific halocline far outweighs any seasonal mitigation from upwelling. Across the datasets in this large-scale synthesis, we estimate that the persistent corrosivity of the Pacific halocline is a recent phenomenon that appeared between 1975 and 1985. Over that short time, these potentially corrosive waters originating over the continental shelves have been observed as far as the entrances to Amundsen Gulf and M'Clure Strait in the Canadian Arctic Archipelago. The formation and transport of corrosive waters on the Pacific Arctic shelves may have widespread impact on the Arctic biogeochemical system and food web reaching all the way to the North Atlantic.</p
Robert D. Richardson, Jr., 25th Annual ODU Literary Festival
No full textRobert D. Richardson, Jr. is the author of Henry Thoreau: A Life of the Mind, and Emerson: The Mind on Fire, for which he won the Bancroft Award in History. His work is widely acclaimed, and he has been recipient of the Francis Parkman Prize for literary distinction in the writing of history and biography, The Society of American Historians Melcher Book Award, the Unitarian Universalist Association Certificate of Merit, and the Gale Research Company St. Nicholas Society Literary Award. He has taught at Harvard University, University of Colorado and Wesleyan University. He is a co-editor of the recently published Three Centuries of American Poetry
Competition Policy in Network Industries: An Introduction
No full textThe author discusses issues of the application of antitrust law and regulatory rules to network industries. In assessing the application of antitrust in network industries, we analyze a number of relevant features of network industries and the way in which antitrust law and regulatory rules can affect them. These relevant features include (among others) network effects, market structure, market share and profits inequality, choice of technical standards, relationship between the number of active firms and social benefits, existence of market power, leveraging of market power in complementary markets, and innovation races. The author finds that there are often significant differences on the effects of application of antitrust law in network and non-network industries.
Students read from their original, award wining works at the 2006 Michigan State University Student Writers Awards Night
No full textAt the 2006 Michigan State University Student Writers Awards Night, students read from their original, award wining works. Readers include: double winner Nicholas Miller, Lauren Linsalata, Patrick Walchak, and Chris Goetz. The event is convened and hosted by MSU Professor of English and co-director of Film Studies Jeff Wray. A special appearance to present awards is made by noted author Paul Beatty. Part of the MSU Libraries' Michigan Writers Series. Held in the MSU Main Library
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