On the role of the Gulf Stream in the changing Atlantic nutrient circulation during the 21st century
Abstract
The Gulf Stream transports macronutrients poleward as a part of the Atlantic meridional overturning circulation (AMOC). Scaling shows that this advective transport is greater than diapycnal transport from deep convection in the North Atlantic and is therefore crucial for sustaining the nutrient supply to the subpolar North Atlantic on inter-annual timescales. The question that motivates this study is as follows: How much will 21st century declines in (1) AMOC and (2) deep convection drive declines in nutrient supply to the euphotic zone and export via sinking organic particles in the sub polar North Atlantic during the 21st century, and can we separate these two effects?
I will address these questions using results from a large ensemble of simulations of the RCP8.5 emissions scenario with the Community Earth System Model (CESM), which reveal 25% declines in the Gulf Stream volume transport above the potential density surface σ = 27.5 kg/m3 and 35% declines in the associated nitrate transport between 2006 and 2080. The declining Gulf Stream transport largely explains contemporaneous 40% declines in zonally-integrated volume and nitrate transports in the subtropical part of AMOC. In addition, scaling suggests that the declining Gulf Stream nitrate transport (2.4 kmol/s per year) is the dominant driver of the declining export of particulate organic nitrogen across σ = 27.5 kg/m3 in the subpolar North Atlantic (0.57 kmol/s per year), because the declining nitrate entrainment from water with σ > 27.5 kg/m3 is only 0.44 kmol/s per year. A review of various small-scale ocean physical processes suggests that the projected decline in the Gulf Stream nutrient flux is qualitatively robust to uncertainties associated with ocean physics, but quantitatively uncertain.- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMOS31C..06W
- Keywords:
-
- 4805 Biogeochemical cycles;
- processes;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4806 Carbon cycling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4813 Ecological prediction;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICALDE: 4815 Ecosystems;
- structure;
- dynamics;
- and modeling;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL