PP43E-08
Did the North Atlantic Ocean sequester more CO2 during the last glacial?
Thursday, 17 December 2015: 15:25
2012 (Moscone West)
Jimin Yu, Australian National University, Canberra, ACT, Australia, David J Thornalley, University College London, London, United Kingdom, Zhangdong Jin, IEE Institute of Earth Environment, Chinese Academy of Sciences, Xi'an, China, Eelco Johan Rohling, University of Southampton, Southampton, SO14, United Kingdom, Laurie Menviel, University of New South Wales, Climate Change Research Centre, Sydney, NSW, Australia and I.N. Nicholas McCave, University of Cambridge, Cambridge, United Kingdom
Abstract:
To explain the ~90 ppm lower atmospheric CO2 content during the Last Glacial Maximum, much effort has been focused on the mechanisms that helped to limit the outgassing of CO2 from the deep ocean to the atmosphere via the Southern Ocean. Field measurements and modeling studies suggest that the North Atlantic Ocean has been an important sink of CO2 during preindustrial and modern times. However, the role of the North Atlantic in sequestering atmospheric CO2 in the past largely remains unconstrained. Here, we use a suite of geochemical proxies to reconstruct nutrient and carbonate ion concentrations of both surface and deep waters in the North Atlantic during the last ~25 kyr. When normalized to the same nutrient levels, we find that the gradient in carbonate ion content between surface and mid-depth waters increased during the last glacial. Although a combination of factors including changes in Redfield ratio and rain ratio and increased CO2 absorption at the air-sea boundary might have caused the observed change, the greater gradient most likely suggests an enhanced sequestration of CO2 in the North Atlantic Ocean during the Last Glacial Maximum. Therefore, we infer that, in addition to changes in the Southern Ocean, processes in the North Atlantic Ocean enhanced the uptake of CO2 and synergistically contributed to the low atmospheric CO2 during ice ages.
