title: Anticyclonic eddies are more productive than cyclonic eddies in subtropical gyres because of winter mixing.
abstract: Mesoscale eddies are ubiquitous features of ocean circulation that modulate the supply of nutrients to the upper sunlit ocean, influencing the rates of carbon fixation and export. The popular eddy-pumping paradigm implies that nutrient fluxes are enhanced in cyclonic eddies because of upwelling inside the eddy, leading to higher phytoplankton production. We show that this view does not hold for a substantial portion of eddies within oceanic subtropical gyres, the largest ecosystems in the ocean. Using space-based measurements and a global biogeochemical model, we demonstrate that during winter when subtropical eddies are most productive, there is increased chlorophyll in anticyclones compared with cyclones in all subtropical gyres (by 3.6 to 16.7% for the five basins). The model suggests that this is a consequence of the modulation of winter mixing by eddies. These results establish a new paradigm for anticyclonic eddies in subtropical gyres and could have important implications for the biological carbon pump and the global carbon cycle.
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Private Bag 5, Wembley, Western Australia 6913, Australia.
authors.forename: François
authors.initials: F
authors.lastname: Dufois
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Private Bag 5, Wembley, Western Australia 6913, Australia.
authors.forename: Nick J
authors.identifier: 0000-0001-9402-2953
authors.initials: NJ
authors.lastname: Hardman-Mountford
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Private Bag 5, Wembley, Western Australia 6913, Australia.
authors.forename: Jim
authors.initials: J
authors.lastname: Greenwood
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Ecosciences Precinct, Brisbane, Queensland 4102, Australia.; Centre for Applications in Natural Resource Mathematics, School of Mathematics and Physics, University of Queensland, St Lucia, Queensland 4072, Australia.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Richardson
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, Private Bag 5, Wembley, Western Australia 6913, Australia.
authors.forename: Ming
authors.initials: M
authors.lastname: Feng
authors.affiliation: Commonwealth Scientific and Industrial Research Organisation, Oceans and Atmosphere, GPO Box 1538, Hobart, Tasmania 7001, Australia.
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Matear
mesh_terms: D057486:Carbon Cycle; D055867:Cyclonic Storms; D008962:Models, Theoretical; D012621:Seasons; D014329:Tropical Climate
keywords: anticyclonic eddies; chlorophyll; convective mixing; eddies; primary production; subtropical gyres