A REEVALUATION OF THE OCEANIC URANIUM BUDGET FOR THE HOLOCENE
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dc.contributor.author | Dunk R.M. | |
dc.contributor.author | Mills R.A. | |
dc.contributor.author | Jenkins W.J. | |
dc.date.accessioned | 2021-10-16T12:26:10Z | |
dc.date.available | 2021-10-16T12:26:10Z | |
dc.date.issued | 2002 | |
dc.identifier | https://elibrary.ru/item.asp?id=32144990 | |
dc.identifier.citation | Chemical Geology, 2002, 190, 1-4, 45-67 | |
dc.identifier.issn | 0009-2541 | |
dc.identifier.uri | https://repository.geologyscience.ru/handle/123456789/30754 | |
dc.description.abstract | We present a new assessment of the pre-anthropogenic U budget for the Holocene ocean. We find that the gross input of U to the ocean lies in the range 53±17 Mmol/year, where the dominant source is river runoff (42.0±14.5 Mmol/year) and the direct discharge of groundwater could represent a significant additional input (9.3±8.7 Mmol/year). The soluble U flux associated with the aeolian input of crustal dust is minor (1.8±1.1 Mmol/year), falling well within the errors associated with the riverine flux. Removal of U to the organic rich sediments of salt marshes and mangrove swamps during river–sea mixing may significantly modify the riverine flux, such that the net U input is reduced to 42±18 Mmol/year. Evaluation of the U isotope budget demonstrates that the limits we have established on the U input flux are reasonable and suggests that direct groundwater discharge may play a significant role in maintaining the oceanic excess of 234U. The total sink of U from the ocean lies in the range 48±14 Mmol/year. We find that three major processes control the magnitude of this flux: (1) removal to oxygen-depleted sediments (26.9±12.2 Mmol/year); (2) incorporation into biogenic carbonate (13.3±5.6 Mmol/year); and (3) crustal sequestration during hydrothermal alteration and seafloor weathering (5.7±3.3 Mmol/year). The removal of U to opaline silica (0.6±0.3 Mmol/year) and hydrogenous phases (1.4±0.8 Mmol/year) is minimal, falling well within the errors associated with the other sinks. That the input and output fluxes balance within the calculated errors implies that U may be in steady state in the Holocene ocean. In this case, the input and output fluxes lie in the range 34–60 Mmol/year, giving an oceanic U residence time of 3.2–5.6×105 years. However, given the large uncertainties, a significant imbalance between the Holocene input and output fluxes cannot be ruled out. The constancy of the ancient seawater U concentration implies that the U budget is in steady state over the time period of a glacial–interglacial climate cycle (∼105 year). A Holocene flux imbalance must, therefore, be offset by an opposing flux imbalance during glacial periods or at the interglacial–glacial transition. We suggest that the storage of U in the coastal zone and shallow water carbonates during interglacial periods and the release of that U at or following the interglacial–glacial transition could be sufficient to affect the short-term stability of the U budget. Providing tighter constraints on U fluxes in the Holocene ocean is a prerequisite to understanding the U budget on the time scale of a glacial–interglacial climate cycle and using this element as a valuable palaeoceanographic proxy. | |
dc.subject | Uranium | |
dc.subject | Uranium isotopes | |
dc.subject | Mass balance | |
dc.subject | Biogeochemical cycles | |
dc.subject | Holocene | |
dc.title | A REEVALUATION OF THE OCEANIC URANIUM BUDGET FOR THE HOLOCENE | |
dc.type | Статья | |
dc.subject.age | Cenozoic::Quaternary::Holocene | |
dc.subject.age | Кайнозой::Четвертичная::Голоцен | ru |
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