The role of phytoplankton composition and microbial community metabolism in sea-air δpCO2 variation in the Weddell Sea

• Published in: Deep Sea Research Part I: Oceanographic Research Papers
• Main Authors: Moreau, Sébastien, di Fiori, Eugenia, Schloss, Irene R., Almandoz, Gastón O., Esteves, José L., Paparazzo, Flavio E., Ferreyra, Gustavo A.
• Other Authors: UCL - SST/ELI - Earth and Life Institute
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Pergamon 2013
• Subjects: Austral; Weddell; Weddell Sea
• Online Access: http://hdl.handle.net/2078.1/160532; https://doi.org/10.1016/j.dsr.2013.07.010

The Weddell Sea is known to be a CO 2 sink due to active biological and physical pumps. Here we study the relationships of phytoplankton biomass and composition and microbial community metabolism, estimated from simulated in situ incubations and from nutrient's difference between surface and subsurface waters, with δpCO 2 in the Weddell Sea, during four austral summers (2002-2005). The δpCO 2 was significantly negative throughout the Weddell Sea in 2002 (-17.2±28.1μatm), 2003 (-64.1±31.3μatm), 2004 (-54.9±61.8μatm) and 2005 (-63.8±60μatm), indicating that the Weddell Sea acted as an atmospheric CO 2 sink during those summers. The δpCO 2 was significantly lower in the south than in the center or north of the Weddell Sea. This was consistent with the significantly higher Chlorophyll-a concentrations (Chl-a) observed in the south (2.3±1.9μgl -1 ) than in the center (1.3±1.2μgl -1 ) or north (1.4±1.7μgl -1 ). In contrast, waters were mainly undersaturated in O 2 , due to the upwelling of oxygen poor Warm Deep Water (WDW). The negative relationship between the δpCO 2 and the %O 2 saturation suggested that planktonic metabolic activities played a role in these gases dynamics, along with the upwelling of WDW. However, these relationships could not be observed from the results of the incubation experiments, probably because of different temporal scales between gas exchanges in incubation experiments and in situ CO 2 and O 2 dynamics. The dynamics of CO 2 and O 2 were solely related to the net community production (NCP) and to the gross primary production (GPP) when only stations with Chl-a>1μgl -1 were considered. A significant relationship was, however, found between δpCO 2 and the primary production until the time of sampling for all stations when estimated from nutrients depletion between surface and subsurface waters. Finally, the distribution of CO 2 and O 2 were related to the biomass of diatoms and, contrarily to other seas, to the biomass of phytoflagellates. © 2013 Elsevier Ltd.