ABSTRACT Sedimentation from radially spreading gravity currents generated at the top of ascending sediment‐laden plumes is described by a model which assumes that sediment is dispersed homogeneously by turbulence in the gravity current, resulting in an exponential decrease in the concentration of sediment with time as particles settle out of the lower boundary of the current. For radial spreading this model predicts a Gaussian distribution of sediment accumulation away from the source with an exponential constant, B , which depends on flow rate, Q , and particle settling velocity, v ( B = nv/Q ). In the experiments described, sedimentation occurs from gravity currents generated by ascent of buoyant, particle‐laden plumes of fresh water in a tank of salty water. The sediment accumulation shows close agreement with the theoretical model, and the Gaussian decay constant, B , can be determined from a maximum in the accumulated mass of sediment per unit distance and from the slope of the line In( S/S 0 ) = ‐ Br 2 , where r is the radial distance, S is the sediment mass flux per unit area and S 0 is the value of S at r =0. Data from the dispersal of volcanic ejecta from a large ( c . 24 km high) plinian eruption column in the Azores also show good agreement with the theory, confirming that it is general and independent of scale and the nature of the fluid. The experimental data also show a change in sedimentation behaviour at distances from the source corresponding to the corner of the plume where it diverts into a lateral gravity current and there is an abrupt decrease in vertical velocity. Sedimentation of coarse grain sizes, between the source and the corner, occurs from the inclined plume margins and does not behave as predicted by the theoretical model.
Research Article| November 01, 1994 Surface-water acidification and extinction at the Cretaceous-Tertiary boundary Steven D'Hondt; Steven D'Hondt 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Michael E. Q. Pilson; Michael E. Q. Pilson 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Haraldur Sigurdsson; Haraldur Sigurdsson 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Alfred K. Hanson, Jr.; Alfred K. Hanson, Jr. 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Steven Carey Steven Carey 1Graduate School of Oceanography, University of Rhode Island, Narragansett, Rhode Island 02882 Search for other works by this author on: GSW Google Scholar Geology (1994) 22 (11): 983–986. https://doi.org/10.1130/0091-7613(1994)022<0983:SWAAEA>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share MailTo Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Steven D'Hondt, Michael E. Q. Pilson, Haraldur Sigurdsson, Alfred K. Hanson, Steven Carey; Surface-water acidification and extinction at the Cretaceous-Tertiary boundary. Geology 1994;; 22 (11): 983–986. doi: https://doi.org/10.1130/0091-7613(1994)022<0983:SWAAEA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract If published estimates of SO2 volatilization and NOx generation by the Cretaceous-Tertiary (K-T) impact were atmospherically converted to sulfuric and nitric acid, globally dispersed, and rapidly rained out, the resulting acid concentrations would bracket a critical threshold in surface-ocean chemistry. Rapid and globally uniform deposition of masses corresponding to the lowest estimates would have had no major effect on sea-surface chemistry. However, similar deposition of masses corresponding to the highest estimates would have provided enough acid to destroy the carbonate-buffering capacity of the upper 100 m of the world ocean and catastrophically reduce surface-ocean pH. Despite the possible effect of the highest estimated acid yields, scenarios that rely on acid rain as the primary explanation of global K-T extinctions are not readily compatible with K-T records of terrestrial and marine survival or culturing studies of modern marine plankton. The possibility that acid rain was a primary cause of K-T extinctions can be tested further by analysis of geographic variation in extinction intensity, because such variation was a likely consequence if the impact resulted in global dispersal and rapid globally uniform deposition of more than ∼6 x 1016 mol of H2SO4 or 1.2 x 1017 mol of HNO3. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
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