A seasonal carbon budget for a naturally iron-fertilized bloom over the Kerguelen Plateau in the Southern Ocean

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Jouandet, MP, Blain, S, Metzl, N, Brunet, C, Trull, T, Obernosterer, I
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon 2008
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Kerguelen; Southern Ocean
• Online Access: http://www.sciencedirect.com; https://doi.org/10.1016/j.dsr2.2007.12.037; http://ecite.utas.edu.au/54187

During the Kerguelen Ocean and Plateau compared Study (KEOPS, JanuaryFebruary 2005), a high-resolution distribution of surfacefugacity of carbon dioxide (fCO2) was obtained from underway measurements. The stations in the core of the naturally iron-fertilizedbloom were characterized by low fCO2 (31178 matm) compared to the atmosphere, thus representing a large CO2 sink. This contrastedwith stations typical of high-nutrient low-chlorophyll (HNLC) conditions where the surface water was roughly in equilibrium with theatmosphere (fCO2 37275 matm). The vertical distribution of dissolved inorganic carbon (DIC) also was obtained at stations withinand outside the bloom. Based on this data set, we constructed a carbon budget for the mixed layer that allowed us to determine theseasonal net community production (NCPseason) and the seasonal carbon export in two contrasting environments. The robustness of theapproach and the errors also were estimated. The NCPseason in the core of the bloom was 6.672.2 molm 2, typical of productive areas ofthe Southern Ocean. At the HNLC station the NCPseason was 3 times lower than in the bloom. Our estimate of the daily net communityproduction (NCPdaily) within the bloom compares well with shipboard measurements of NCP. The NCPdaily obtained above theKerguelen Plateau was of the same order as the estimates from Southern Ocean artificial iron-fertilization experiments (SOIREE andEisenEx). The seasonal carbon export was derived from NCPseason after subtraction of the seasonal accumulation of particulate anddissolved organic carbon. In the bloom, the carbon export (5.471.9 molm 2) was 3-fold higher than at the HNLC station(1.770.4 molm 2). Comparison of our results to artificial iron-fertilization experiments shows that the biological pump is enhanced bynatural iron fertilization.