Origin and fate of particulate and dissolved organic matter in a naturally iron-fertilized region of the Southern Ocean

Type Article
Date 2015
Language English
Author(s) Tremblay L.1, Caparros J.2, 3, Leblanc K.4, Obernosterer I.2, 3
Affiliation(s) 1 : Univ Moncton, Dept Chem & Biochem, Moncton, NB E1A 3E9, Canada.
2 : CNRS, Lab Oceanog Microbienne, Observ Oceanol, UMR 7621, F-66650 Banyuls Sur Mer, France.
3 : Univ Paris 06, Sorbonne Univ, Observ Oceanol, Lab Oceanog Microbienne,UMR 7621, F-66650 Banyuls Sur Mer, France.
4 : Univ Toulon & Var, Aix Marseille Univ, CNRS, IRD,MIO,UM 110, F-13288 Marseille, France.
Source Biogeosciences (1726-4170) (Copernicus Gesellschaft Mbh), 2015 , Vol. 12 , N. 2 , P. 607-621
DOI 10.5194/bg-12-607-2015
WOS© Times Cited 22
Note Special issue KEOPS2: Kerguelen Ocean and Plateau Study 2 Editor(s): S. Blain, I. Obernosterer, B. Queguiner, T. Trull, and G. Herndl
Abstract Natural iron fertilization of high-nutrient low-chlorophyll (HNLC) waters induces annually occurring spring phytoplankton blooms off the Kerguelen Islands (Southern Ocean). To examine the origin and fate of particulate and dissolved organic matter (POM and DOM), D- and L-amino acids (AA) were quantified at bloom and HNLC stations. Total hydrolyzable AA accounted for 21-25% of surface particulate organic carbon (% POCAA) at the bloom sites, but for 10% at the HNLC site. A marked decrease in % POCAA with depth was observed at the most productive stations leading to values between 3 and 5% below 300 m depth. AA contributed to only 0.9-4.4% of dissolved organic carbon (%DOCAA) at all stations. The only consistent vertical trend was observed at the most productive station (A3-2) where %DOCAA decreased from similar to 2% in the surface waters to 0.9% near 300 m. These AA yields revealed that POM and DOM were more rapidly altered or mineralized at the bloom sites compared to the HNLC site. Alteration state was also assessed by trends in C / N ratio, % D-AA and degradation index. Different molecular markers indicated that POM mostly originated from diatoms and bacteria. The estimated average proportion of POM from intact phytoplankton cells in surface waters was 45% at the bloom station A3-2, but 14% at the HNLC site. Estimates based on D-AA yields indicated that similar to 15% of POM and similar to 30% of DOM was of bacterial origin (cells and cell fragments) at all stations. Surprisingly, the DOM in HNLC waters appeared less altered than the DOM from the bloom, had slightly higher dissolved AA concentrations, and showed no sign of alteration within the water column. Unfavorable conditions for bacterial degradation in HNLC regions can explain these findings. In contrast, large inputs of labile organic molecules and iron likely stimulate the degradation of organic matter (priming effect) and the production of more recalcitrant DOM (microbial carbon pump) during iron-fertilized blooms.
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