Sediment trap and in-situ pump size-fractionated POC/ super(2) super(3) super(4)Th ratios in the Mediterranean Sea and Northwest Atlantic: Implications for POC export

• Published in: Deep-sea research. Part I, Oceanographic research papers Vol. 56; no. 4; pp. 599 - 613
• Main Authors: Lepore, K, Moran, S B, Burd, AB, Jackson, G A, Smith, J N, Kelly, R P, Kaberi, H, Stavrakakis, S, Assimakopoulou, G
• Format: Journal Article
• Language: English
• Published: 01.04.2009
• Subjects: Marine; MED, Aegean Sea; MED, Eastern Mediterranean; MED, Western Mediterranean
• ISSN: 0967-0637
• DOI: 10.1016/j.dsr.2008.11.004

Measurements of particle size-fractionated POC/ super(2) super(3) super(4)Th ratios and super(2) super(3) super(4)Th and POC fluxes were conducted using surface-tethered, free-floating, sediment traps and large-volume in-situ pumps during four cruises in 2004 and 2005 to the oligotrophic eastern Mediterranean Sea and the seasonally productive western Mediterranean and northwest Atlantic. Analysis of POC/ super(2) super(3) super(4)Th ratios in sediment trap material and 10, 20, 53, 70, and 100km size-fractionated particles indicate, for most stations, decreasing ratios with depth, a weak dependence on particle size, and ratios that converge to 61-5kmoldpm super(-) super(1) below the euphotic zone (6100-150m) throughout the contrasting biogeochemical regimes. In the oligotrophic waters of the Aegean Sea, super(2) super(3) super(4)Th and POC fluxes estimated using sediment traps were consistently higher than respective fluxes estimated from water-column super(2) super(3) super(4)Th- super(2) super(3) super(8)U disequilibrium, observations that are attributed to terrigenous particle scavenging of super(2) super(3) super(4)Th. In the more productive western Mediterranean and northwest Atlantic, super(2) super(3) super(4)Th and POC fluxes measured by sediment trap and super(2) super(3) super(4)Th- super(2) super(3) super(8)U disequilibrium agreed within a factor of 2-4 throughout the water column. An implication of these results is that estimates of POC export by sediment traps and super(2) super(3) super(4)Th- super(2) super(3) super(8)U disequilibrium can be biased differently because of differential settling speeds of POC and super(2) super(3) super(4)Th-carrying particles.