ScienceDirect - Earth and Planetary Science Letters : 234Th-based carbon export during an ice-edge bloom: Sea-ice algae as a likely bias in data interpretation

Earth and Planetary Science Letters
Volume 269, Issues 3-4, 30 May 2008, Pages 596-604

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doi:10.1016/j.epsl.2008.03.020

²³⁴Th-based carbon export during an ice-edge bloom: Sea-ice algae as a likely bias in data interpretation

Alessia M. Rodriguez y Baena^a^,^b^,^,^,, Redouane Boudjenoun^a^,^c^,, Scott W. Fowler^a^,¹^,, Juan Carlos Miquel^a^,, Pere Masqué^d^,, Joan-Albert Sanchez-Cabeza^a^, and Michel Warnau^a^,²^,

^aInternational Atomic Energy Agency, Marine Environment Laboratories, 4 Quai Antoine 1^er, MC-98000, Monaco ^bDipartimento per lo Studio del Territorio e delle sue Risorse, Università di Genova, Corso Europa 26, I-16132 Genova, Italy ^cCentre de Recherche Nucléaire d'Alger, Commissariat à l'Energie Atomique, 02 Bd. F. Fanon, BP 399 Alger-Gare, 16000 Alger, Algeria ^dInstitut de Ciència i Tecnologia Ambientals, Department de Física, Universitat Autònoma de Barcelona, 08193 Barcelona, Spain

Received 3 October 2007;

revised 28 February 2008;

accepted 3 March 2008.

Editor: H. Elderfield.

Available online 18 March 2008.

References and further reading may be available for this article. To view references and further reading you must purchase this article.

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 not, vert, similar 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.