In:
Marine Chemistry, 3664
Description / Table of Contents:
Profiles of particulate and dissolved 234Th (t1/2=24.1 days) in seawater and particulate 234Th collected in drifting traps were analyzed in the Barents Sea at five stations during the ALV3 cruise (from June 28 to July 12, 1999) along a transect from 78°15′N–34°09′E to 73°49′N–31°43′E. 234Th/238U disequilibrium was observed at all locations. 234Th data measured in suspended and trapped particles were used to calibrate the catchment efficiency of the sediment traps. Model-derived 234Th fluxes were similar to 234Th fluxes measured in sediment traps based on a steady-state 234Th model. This suggests that the sediment traps were not subject to large trapping efficiency problems (collection efficiency ranges from 70% to 100% for four traps). The export flux of particulate organic carbon (POC) can be calculated from the model-derived export flux of 234Th and the POC/234Th ratio. POC/234Th ratios measured in suspended and trapped particles were very different (52.0±9.9 and 5.3±2.2 μmol dpm−1, respectively). The agreement between calculated and measured POC fluxes when the POC/234Th ratio of trapped particles was used confirms that the POC/234Th ratio in trap particles is representative of sinking particles. Large discrepancies were observed between calculated and measured POC fluxes when the POC/234Th ratio of suspended particles was used. In the Barents Sea, vertical POC fluxes are higher than POC fluxes estimated in the central Arctic Ocean and the Beaufort Sea and lower than those calculated in the Northeast Water Polynya and the Chukchi Sea. We suggest that the latter fluxes may have been strongly overestimated, because they were based on high POC/234Th ratios measured on suspended particles. It seems that POC fluxes cannot be reliably derived from thorium budgets without measuring the POC/234Th ratio of sediment trap material or of large filtered particles.
Type of Medium:
13
ISSN:
0304-4203
,
1872-7581
URL:
https://doi.org/10.1016/S0304-4203(02)00071-3
URL:
https://cat.telegrafenberg.de/cgi-bin/koha/opac-image.pl?thumbnail=1&imagenumber=850
Language:
English
Note:
Outline
Abstract
Keywords
1. Introduction
2. Methods
2.1. Sample collection
2.2. 234Th analyses
2.3. Particulate organic carbon analyses
3. Results
3.1. Hydrography
3.2. Nutrients
3.3. 234Th activities and POC concentrations
3.4. Trapped material
4. Discussion
4.1. Origins of 234Th/238U disequilibrium
4.2. Determining 234Th fluxes
4.3. Calibration of sediment trap with 234Th
4.4. Vertical flux of particulate organic carbon and the POC/234Thp ratio
5. Conclusion
Acknowledgements
References
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