PP43A-2254
Preformed Nitrate in the Glacial North Atlantic
Thursday, 17 December 2015
Poster Hall (Moscone South)
Kira Homola1, Arthur J Spivack2, Steven D'Hondt3, Emily R Estes4, Tania Lado Insua5, Claire Cecelia McKinley6, Richard W Murray7, Robert A Pockalny8, Rebecca S Robinson3 and Justine Sauvage9, (1)University of Rhode Island, Graduate School of Oceanography, Narragansett, RI, United States, (2)University of Rhode Island - GSO, Oceanography, Narragansett, RI, United States, (3)University of Rhode Island, Narragansett, RI, United States, (4)Woods Hole Oceanographic Institution, Woods Hole, MA, United States, (5)Test, Test, United States, (6)Texas A & M University College Station, College Station, TX, United States, (7)Boston University, Boston, MA, United States, (8)Univ Rhode Island, Narragansett, RI, United States, (9)University of Rhode Island - GSO, West Warwick, RI, United States
Abstract:
Atmospheric CO2 abundances are highly correlated with global temperature variations over the past 800,000 years. Consequently, understanding the feedbacks between climate and CO2 is important for predictions of future climate. Leading hypotheses to explain this feedback invoke changes in ocean biology, circulation, chemistry, and/or gas exchange rates to trap CO2 in the deep ocean, thereby reducing the greenhouse effect of CO2 in the atmosphere. To test these hypotheses, we use sediment pore water profiles of dissolved nitrate and oxygen to reconstruct paleo-preformed nitrate concentrations at two deep-water sites in the western North Atlantic (23°N 57°W, 5557 m water depth; 30°N 58°W, 5367 m water depth). Preformed nitrate increases down-core to 22.7 μM (25.6 m core depth) at the northern site, and to 28.5 μM (27.8 m core depth) at the southern site. The large preformed nitrate gradient between these sites reveals a paleo-boundary between a southern water source high in preformed nitrate and a northern water source with lower concentrations, similar to today’s ocean. However, the boundary between these water masses occurs north of where their modern counterparts meet, indicating that Antarctic Bottom Water (AABW) extended farther north during the Last Glacial Maximum (LGM). In addition, the southern source had a higher preformed nitrate concentration than today’s AABW (25 μM), contradicting hypotheses that nutrient utilization was more efficient in the Southern Ocean deep-water formation regions during the LGM. Comparison to our previous Pacific data reveals that the average preformed nitrate concentration of the deep ocean was slightly higher during the LGM than today. This result implies that the CO2-climate feedback was not principally due to more efficient nitrate utilization.
