Measurements of234Th/238U disequilibria and particle size-fractionated (1, 10, 20, 53, 70, 100 μm) organic C and234Th were made to constrain estimates of the export flux of particulate organic C (POC) from the surface waters of the Ligurian, Tyrrhenian and Aegean Seas in March-June 2004. POC exported from the surface waters (75-100 m depth) averaged 9.2 mmol m-2d-1in the Ligurian and Tyrrhenian Seas (2.3±0.5-14.9±3.0 mmol m-2d-1) and 0.9 mmol m-2d-1in the Aegean Sea. These results are comparable to previous measurements of234Th-derived and sediment-trap POC fluxes from the upper 200 m in the Mediterranean Sea. Depth variations in the POC/234Th ratio suggest two possible controls. First, decreasing POC/234Th ratios with depth were attributed to preferential remineralization of organic C. Second, the occurrence of maxima or minima in the POC/234Th ratio near the DCM suggests influence by phytoplankton dynamics. To assess the accuracy of these data, the empirical234Th-method was evaluated by quantifying the extent to which the234Th-based estimate of POC flux, PPOC, deviates from the true flux, FPOC, defined as the p-ratio (p-ratio=PPOC/FPOC=STh/SPOC, where S=particle sinking rate). Estimates of the p-ratio made using Stokes' Law and the particle size distributions of organic C and234Th yield values ranging from 0.93-1.45. The proximity of the p-ratio to unity implies that differences in the sinking rates of POC- and234Th-carrying particles did not bias234Th-normalized POC fluxes by more than a factor of two. © 2006 Elsevier Ltd. All rights reserved.
|Pages (from-to)||1810 - 1830|
|Number of pages||21|
|Journal||Deep-Sea Research Part I: Oceanographic Research Papers|
|Publication status||Published - Nov 2006|
All Science Journal Classification (ASJC) codes
- Aquatic Science
Speicher, E. A., Moran, S. B., Burd, A. B., Delfanti, R., Kaberi, H., Kelly, R. P., ... Zervakis, V. (2006). Particulate organic carbon export fluxes and size-fractionated POC/. Deep-Sea Research Part I: Oceanographic Research Papers, 53(11), 1810 - 1830. https://doi.org/10.1016/j.dsr.2006.08.005