Particulate organic carbon export fluxes and size-fractionated POC/

E.A. Speicher, S.B. Moran, A.B. Burd, R. Delfanti, H. Kaberi, R.P. Kelly, C. Papucci, J.N. Smith, S. Stavrakakis, L. Torricelli, V. Zervakis

Research output: Contribution to journalArticle

31 Citations (Scopus)


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.
Original languageEnglish
Pages (from-to)1810 - 1830
Number of pages21
JournalDeep-Sea Research Part I: Oceanographic Research Papers
Issue number11
Publication statusPublished - Nov 2006
Externally publishedYes


All Science Journal Classification (ASJC) codes

  • Oceanography
  • Aquatic Science

Cite this

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.