Abstract
<p>The decline in ocean primary production is one of the most alarming consequences of anthropogenic climate change. This decline could indeed lead to a decrease in marine biomass and fish catch, as highlighted by recent policy-relevant reports. Because of computational constraints, current Earth System Models used to project ocean primary production under global warming scenarios have to parameterize flows occurring below the resolution of their computational grid (typically 1°). To overcome these computational constraints, we use an ocean biogeochemical model in an idealized configuration representing a mid-latitude double-gyre circulation, and perform global warming simulations under increasing horizontal resolution  (from 1° to 1/27°) and under a large range of parameter values for the eddy parameterization employed in the coarse resolution configuration. In line with projections from Earth System Models, all our simulations project a marked decline in net primary production in response to the global warming forcing. Whereas this decline is only weakly sensitive to the eddy parameters in the eddy-parametrized coarse resolution, the simulated decline in primary production is halved at the finest eddy-resolving resolution (-12% at 1/27° vs -26 at 1°). This difference stems from the high sensitivity of the subsurface nutrient transport to model resolution. Our results call for improved representation of the role of eddies on nutrient transport below the seasonal mixed-layer to better constrain the future evolution of marine biomass and fish catch potential for decision-making.</p>
Highlights
A decrease in global marine animal biomass and in fisheries’ catch potential is projected over the 21st century under all emission scenarios, and this decrease is mostly driven by the projected decline in phytoplankton primary production in response to anthropogenic climate change (Bindoff et al, 2019)
The net primary production (NPP) declines differ markedly between each other depending on the resolution, with the decline in NPP halved at the finest resolution compared with the decline projected at the coarse resolution
Based on a wind- and buoyancy-driven double-gyre model configuration with an idealistic scenario of global warming, we have shown that the projected decline in NPP is strongly sensitive to horizontal grid resolution, with a decline which is halved at an eddy resolution: −13 ± 1 % versus −26 ± 1 % at the coarse resolution (Fig. 7)
Summary
A decrease in global marine animal biomass and in fisheries’ catch potential is projected over the 21st century under all emission scenarios, and this decrease is mostly driven by the projected decline in phytoplankton primary production in response to anthropogenic climate change (Bindoff et al, 2019). Phytoplankton are microorganisms essential to the Earth system through their influence on the global carbon cycle and biological sequestration of atmospheric CO2 (Volk and Hoffert, 1985; Falkowski et al, 1998; Field et al, 1998). They are at the base of most oceanic food webs and as such constrain fish biomass and fish catch potential in the ocean (Pauly and Christensen, 1995; Chassot et al, 2010; Friedland et al, 2012; Stock et al, 2017). Multi-model ensemble mean projections show that under a wide range of emission scenarios, global ocean NPP will decline in the 21st century and beyond, principally due to the reduced supply of inorganic nutrients from the sub-surface where they are abundant to the sunlit ocean where phytoplankton photosynthesis occurs
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