JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

A (Atmospheric and Hydrospheric Sciences ) » A-CG Complex & General

[A-CG44] Extratropical oceans and atmosphere

convener:Youichi Kamae(Faculty of Life and Environmental Sciences, University of Tsukuba), Toyama Katsuya(Meteorological Research Institute), Hyodae Seo(Woods Hole Oceanographic Institution), Yoshi N(Hokkaido University)

[ACG44-01] Western boundary currents and their extension regions as conduits for the ejection of bomb-radiocarbon from the thermocline

★Invited Papers

*Keith Bradley Rodgers1,2, Ping Zhai3, Richard D Slater3, Brendan R Carter4,5, Daniele Iudicone6, Olivier Aumont7, Jesse Farmer8,9, Ivy Frenger10, Yves Plancherel11, Laure Replandy12, Andrea Fassbdner13, Katsuya Toyama14 (1.IBS Center for Climate Physics, Busan, Republic of Korea, 2.Pusan National University, Busan, Republic of Korea, 3.Atmospheric and Oceanic Sciences Program, Princeton University, NJ, 4.Joint Institute for the Study of the Atmosphere and Ocean, University of Washington, Seattle, WA, 5.NOAA Pacific Marine Environmental Laboratory, Seattle, WA, 6.Department of Integrated Marine Ecology, Stazione Zoologica, Anton Dohrn, Naples, Italy, 7.Sorbonne Universités, UPMC, Univ. Paris 06-CNRS-IRD-MHNH, LOCEAN/IPSL, Paris, France, 8.Princeton University, Department of Geosciences, Princeton, NJ, 9.Climate Geochemistry, Max-Planck INstitute for Chemistry, Mainz, Germany, 10.GEOMAR Helmholz Centre for Ocean Research, Kiel, Germany, 11.Grantham Institute, Imperial College, London, UK, 12.Princeton Environmental Institute, Princeton, NJ, 13.Monterey Bay Aquarium Research Institute, Moss Landing, CA, 14.Oceanography and Geochemsitry Research Department, Meteorological Research Insistute, Japan Meteorological Agency, Tsukuba, Japan)

Keywords:Western Boundary Currents, Air-Sea Interaction, Radiocarbon, Thermocline

The western boundary currents and their extension regions have long been expected to play an important role in the ocean’s carbon cycle. However, it is still uncertain how western boundary currents impact the ocean uptake pathways of anthropogenic carbon (Cant), and if they sustain a new transfer of Cantfrom thermocline to subpolar water masses. Here we consider water mass transformation diagnostics applied to a forward ocean circulation model in conjunction with an analysis of bomb-DI14C (bomb-radiocarbon) as a proxy for a “pulsed” atmospheric source function of Cantover the period 1955-1963. Our main result is that the extension regions of the western boundary currents play an important role in sustaining rapid (32±3 years) renewal timescales for the full ocean volume above the density horizon of the base of the thermocline. This rapid renewal timescale sustains a vigorous exchange of the waters with maximum bomb-DI14C content. In 1995 in the model (mid-WOCE) 66% of the global cumulative air-sea flux of bomb-14CO2enters the ocean directly into thermocline densities, but with only 42% of the inventory in the thermocline. Approximately 70% of the net transfer of bomb-DI14C from subtropical to subpolar waters in 1995 is shown to occur south of 30°S, sustained largely through the densification of near-surface waters through the release of heat to the atmosphere within the western boundary currents and their extension regions. The results may help to understand pathways of Cantwithin the ocean under a future transition to zero or negative emissions.