PP029-0007
Investigating feedback mechanisms between ice rafted debris production and carbon export in the Pacific Sector of the Southern Ocean over the last 35,000 years
Friday, 11 December 2020
Poster
Kelly-Marie Powell, Columbia University, Chemistry, New York, NY, United States; Columbia University of New York, Chemistry, Palisades, NY, United States, Jennifer L Middleton, Lamont Doherty Earth Observatory, Palisades, NY, United States, Sidney R Hemming, Lamont-Doherty Earth Observatory, Palisades, NY, United States, Gisela Winckler, Columbia University, Department of Earth and Environmental Sciences, New York, NY, United States, Frank J Pavia, California Institute of Technology, Pasadena, CA, United States and Robert F Anderson, Lamont-Doherty Earth Obs, Palisades, NY, United States
Abstract:
Modern observations have shown that IRD releases bioavailable iron (Fe) into the surface ocean that can stimulate biologic productivity. We investigate if iceberg-fertilization generates a potential positive feedback mechanism into the climate system, in which enhanced iron delivery by calving icebergs increases the efficiency of the biologic pump and thus enhances the sequestration of atmospheric carbon dioxide. We measure the fluxes of IRD, Fe, as well as excess Barium (Ba
xs), a productivity proxy, in the NBP1702-07-01JPC sediment core retrieved from the Antarctic Zone of the Pacific Southern Ocean, to evaluate the potential effect of iceberg fertilization over the last 35 ka. We constrain these sedimentary fluxes using IRD grain counting, elemental concentrations, and the excess thorium-230 constant flux proxy.
Our results indicate that the highest flux of IRD occurs around 20 ka during the Last Glacial Maximum. The Fe flux peaks at 20 ka as well, but the flux remains consistently high at times when the IRD flux exhibit clear minima. Despite the prevalence of IRD within the 07-01JPC record, this lack of correlation suggests that there is an external source of Fe, likely dust, dominating the iron budget at this site. The highest flux of Baxs occurs around 35 ka and 10 ka but it experiences a minimum at 20 ka. This productivity pattern is consistent with previous records from the Antarctic Zone of the Southern Ocean, suggesting that productivity in this region is not iron limited over this interval. Instead, our data supports the emerging hypothesis that the Antarctic zone of the Southern Ocean is nitrate limited, not iron limited. In our dataset, Baxs is neither correlated with Fe nor IRD, so it does not appear that productivity is enhanced by iceberg fertilization. Our results do not support the hypothesized positive feedback mechanism between iceberg calving, marine productivity, and enhanced sequestration of atmospheric carbon dioxide within the study region, over the past 35 ka.
