Quantifying export production in the Southern Ocean: Implications for the Ba xs proxy

• Published in: Paleoceanography 2011-12, Vol.26 (4)
• Main Authors: Hernandez‐Sanchez, Maria T., Mills, Rachel A., Planquette, Hélène, Pancost, Richard D., Hepburn, Laura, Salter, Ian, FitzGeorge‐Balfour, Tania
• Format: Article
• Language: English
• ISSN: 0883-8305; 1944-9186
• DOI: 10.1029/2010PA002111

The water column and sedimentary Ba xs distribution around the Crozet Plateau is used to decipher the controls and timing of barite formation and to evaluate how export production signals are recorded in sediments underlying a region of natural Fe fertilization within the Fe limited Southern Ocean. Export production estimated from preserved, vertical sedimentary Ba xs accumulation rates are compared with published export fluxes assessed from an integrated study of the biological carbon pump to determine the validity of Ba xs as a quantitative proxy under different Fe supply conditions typical of the Southern Ocean. Detailed assessment of the geochemical partitioning of Ba in sediments and the lithogenic end‐member allows appropriate correction of the bulk Ba content and determination of the Ba xs content of sediments and suspended particles. The upper water column distribution of Ba xs is extremely heterogeneous spatially and temporally. Organic carbon/Ba xs ratios in deep traps from the Fe fertilized region are similar to other oceanic settings allowing quantification of the inferred carbon export based on established algorithms. There appears to be some decoupling of POC and Ba export in the Fe limited region south of the Plateau. The export production across the Crozet Plateau inferred from the Ba xs sedimentary proxy indicates that the Fe fertilized area to the north of the Plateau experiences enhanced export relative to equivalent Southern Ocean settings throughout the Holocene and that this influence may also have impacted the site to the south for significant periods. This interpretation is corroborated by alternative productivity proxies (opal accumulation, 231 Pa xs / 230 Th xs ). Ba xs can be used to quantify export production in complex settings such as naturally Fe‐fertilized (volcanoclastic) areas, providing appropriate lithogenic correction is undertaken, and sediment focusing is corrected for along with evaluation of barite preservation. Calibration of the Baxs proxy across a naturally iron fertilized Impact volcanic island Fe fertilization on the sedimentary record Assessment of the dynamic behavior of the ACC during the Holocene