| Title | 234Th-based carbon export during an ice-edge bloom; sea-ice algae as a likely bias in data interpretation |
| Author | Rodriguez y Baena, A.M.; Boudjenoun, R.; Fowler, S.W.; Miquel, J.C.; Masqué, P.; Sanchez-Cabeza, J.; Warnau, M. |
| Author Affil | Rodriguez y Baena, A.M., International Atomic Energy Agency, Marine Environment Laboratories, Monaco. Other: Istitut de Ciència i Tecnologia Ambientals, Spain |
| Source | Earth and Planetary Science Letters, 269(3-4), p.595-603, . Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0012- 821X |
| Publication Date | May 30, 2008 |
| Notes | In English. 39 refs. GeoRef Acc. No: 284865. CRREL Acc. No: 62005210 |
| Index Terms | algae; carbon isotopes; ice; ice shelves; isotopes; metals; plankton; radioactive isotopes; Antarctica; Southern Ocean--Weddell Sea; actinides; algal blooms; carbon; interpretation; isotope ratios; organic carbon; phytoplankton; Plantae; sea ice; sea water; Southern Ocean; Th-234; theoretical models; thorium; U-238; U-238/U- 234; uranium; Weddell Sea |
| Abstract | Total 234Th and 238U vertical profiles in the water column were determined along a three-station transect perpendicular to the Eastern Weddell Sea ice shelf. The transect was sampled during pre-bloom (6-7 December 2003) and bloom (19-20 December 2003) conditions to follow changes occurring in the particulate organic carbon (POC) flux during an Antarctic phytoplankton ice-edge bloom. During the pre-bloom period, 234Th:238U ratios ›1 (up to 1.3) were measured just above the thermocline at all stations, and throughout the entire mixed layer at the ice- edge. These water column data appear to be the first which support the hypothesis that sea-ice algae could represent an input of 234Th-rich material in polar waters due to cellular uptake of the radionuclide and/or its adsorption onto the extracellular polymeric substances (EPS) produced by these organisms. A simple conceptual model is proposed to link observed 234Th:238U ratios to the input of 234Th-enriched sea-ice algae caused by ice-melting. The extensive, deep- water 234Th deficit observed during the second transect likely results from the combination of vertical particle export and water-seafloor exchange processes. POC steady- state (SS) fluxes out of the photic layer were negative or ~nil (-11 to 2 mmol m-2 d-1) under pre-bloom conditions, probably due to ice-algae input at the ice-edge and remineralization elsewhere, whereas POC non- steady-state (NSS) fluxes were generally higher (7 to 33 mmol m-2 d-1) when the bloom was developing. We have estimated that these flux values could change by as much as 75% if a sea-ice algae 234Th input term were included in the simple one-box model used. This suggests that failure to consider the sea-ice algae compartment, when using 234Th as a proxy to assess carbon export in seasonally ice-covered regions, could at times lead to significant biases in the interpretation of 234Th-based particle flux estimates. |
| URL | http://hdl.handle.net/10.1016/j.epsl.2008.03.020 |
| Publication Type | journal article |
| Record ID | 84215 |