The composition and distribution of semi-labile dissolved organic matter across the southwest Pacific

Type Article
Date 2019-01
Language English
Author(s) Panagiotopoulos Christos1, Pujo Pay Mireille2, Benavides Mar1, Van Wambeke France1, Sempéré Richard1
Affiliation(s) 1 : Aix -Marseille Université, Université de Toulon, CNRS, IRD, Mediterranean Institute of Oceanography (MIO), UM 110, 13288, Marseille, France
2 : Laboratoire d’Océanographie Microbienne (LOMIC), Observatoire Océanologique, Sorbonne Université s, UPMC Univ . Paris 06, CNRS, 66650 Banyuls/Mer, France
Source Biogeosciences (1726-4170) (Copernicus GmbH), 2019-01 , Vol. 16 , N. 1 , P. 105-116
DOI 10.5194/bg-16-105-2019
WOS© Times Cited 4
Note Special issue Interactions between planktonic organisms and biogeochemical cycles across trophic and N2 fixation gradients in the western tropical South Pacific Ocean: a multidisciplinary approach (OUTPACE experiment) Editor(s): T. Moutin, S. Bonnet, K. Richards, D. G. Capone, E. Marañón, and L. Mémery
Abstract

The distribution and dynamics of dissolved organic carbon (DOC) and dissolved combined neutral sugars (DCNS) were studied across an increasing oligotrophic gradient (−18 to −22°N latitude) spanning from the Melanesian Archipelago (MA) area to the western part of the south Pacific gyre (WGY), in austral summer, as a part of the OUTPACE project. Our results showed DOC and DCNS concentrations exhibited little differences among the MA and WGY areas (0–200m: 55–78µMC for DOC and 1.5–2µMC for DCNS), however, a deeper penetration of DOC was noticeable at 150m depth at the WGY area. This finding was also reflected to the DOC and semi-labile DOC (DOCSL) stocks values (integration 0–200m) for which we found higher values in the WGY than the MA area. The high excess DOCSL measured in WGY was characterized by a high residence time (130±31 days (n=3)) about three times higher than the MA region (Tr=40±7 days (n=8)) suggesting an accumulation of the semi-labile DOM in the surface waters of WGY. DCNS yields (DCNS-C x DOC−1%) also followed this pattern with higher values recorded in the WGY (3.2±1.3%) than MA (2.8±0.8%) highlighting the presence of semi-labile dissolved organic material (DOM) in the form of polysaccharides. These polysaccharides also exhibited a higher residence time in WGY (Tr=8±4 days, n=3) than in MA (Tr=3±1days, n=8) suggesting that this DCNS pool persists longer in the surface waters of the WGY. The accumulation of DOCSL in the surface waters of WGY is probably due to the very slow bacterial degradation due to nutrient limitation indicating that biologically produced DOC can be stored in the euphotic layer for a very long period.

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