The release of dissolved actinium to the ocean : A global comparison of different end-members
Charette, Matthew A.
Moore, Willard S.
MetadataShow full item record
KeywordActinium; Radium; Submarine groundwater discharge; Ocean mixing; Continental shelf; Global circulation models
The measurement of short-lived 223Ra often involves a second measurement for supported activities, which represents 227Ac in the sample. Here we exploit this fact, presenting a set of 284 values on the oceanic distribution of 227Ac, which was collected when analyzing water samples for short-lived radium isotopes by the radium delayed coincidence counting system. The present work compiles 227Ac data from coastal regions all over the northern hemisphere, including values from ground water, from estuaries and lagoons, and from marine endmembers. Deep-sea samples from a continental slope off Puerto Rico and from an active vent site near Hawaii complete the overview of 227Ac near its potential sources. The average 227Ac activities of nearshore marine end-members range from 0.4 dpm * m-3 at the Gulf of Mexico to 3.0 dpm *m-3 in the coastal waters of the Korean Strait. In analogy to 228Ra, we find the extension of adjacent shelf regions to play a substantial role for 227Ac activities, although less pronounced than for radium, due to its weaker shelf source. Based on previously published values, we calculate an open ocean 227Ac inventory of 1.35 * 1018 dpm 227Acex in the ocean, which corresponds to 37 moles, or 8.4 kg. This implies a flux of 127 dpm*m-2*y-1 from the deep-sea floor. For the shelf regions, we obtain a global inventory of 227Ac of 4.5 * 1015 dpm, which cannot be converted directly into a flux value, as the regional loss term of 227Ac to the open ocean would have to be included. Ac has so far been considered to behave similarly to Ra in the marine environment, with the exception of a strong Ac source in the deep-sea due to 231Paex. Here, we present evidence of geochemical differences between Ac, which is retained in a warm vent system, and Ra, which is readily released (Moore et al., submitted). Another potential mechanism of producing deviations in 227Ac/228Ra and daughter isotope ratios from the expected production value of lithogenic material is observed at reducing environments, where enrichment in uranium may occur. The presented data here may serve as a reference for including 227Ac in circulation models, and the overview provides values for some end-members that contribute to the global Ac distribution.
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 109 (2008): 409-420, doi:10.1016/j.marchem.2007.07.005.
Showing items related by title, author, creator and subject.
Cai, Wenju; Avery, Susan K.; Leinen, Margaret; Lee, Kenneth; Lin, Xiaopei; Visbeck, Martin (2014-11)A sustainable global ocean observation system requires timely implementation of a global ocean observation framework. The recent Qingdao Global Ocean Summit offers an effective mechanism for a coherent institutional response ...
Mechanisms governing interannual variability of upper-ocean temperature in a global ocean hindcast simulation Doney, Scott C.; Yeager, Stephen G.; Danabasoglu, Gokhan; Large, William G.; McWilliams, James C. (American Meteorological Society, 2007-07)The interannual variability in upper-ocean (0–400 m) temperature and governing mechanisms for the period 1968–97 are quantified from a global ocean hindcast simulation driven by atmospheric reanalysis and satellite data ...
Drilling the oceanic lower crust and mantle : a global strategy for exploring the deep oceanic crust and mantle in the 1990's Workshop on Drilling the Oceanic Lower Crust and Mantle (Woods Hole Oceanographic Institution, 1989-03)This workshop was convened to follow up on the Second Conference on Scientific Ocean Drilling (COSOD II) to devise a specific plan for deep crustal and mantle drilling over the next decade. Since COSOD II, however, there ...