Oceanic primary production decline halved in eddy-resolving simulations of global warming

Abstract

Abstract. 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 an 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-parameterized coarse 1∘ resolution simulations, the simulated decline in primary production in the subpolar gyre is halved at the finest eddy-resolving resolution (−12 % at 1/27∘ vs. −26 % at 1∘) at the end of the 70-year-long global warming simulations. This difference stems from the high sensitivity of the sub-surface nutrient transport to model resolution. Although being only one piece of a much broader and more complicated response of the ocean to climate change, our results call for improved representation of the role of eddies in nutrient transport below the seasonal mixed layer to better constrain the future evolution of marine biomass and fish catch potential.

Persistent Uncertainties in Ocean Net Primary Production Climate Change Projections at Regional Scales Raise Challenges for Assessing Impacts on Ecosystem Services

“…The Gulf Stream plays a critical role in nutrient supply in the North Atlantic via the nutrient stream (Pelegrí et al, 1996). This means that projected changes to nutrient concentrations in the upper ocean from Earth system models result from the combination of the nutrient stream and its sensitivity to the Atlantic meridional overturning circulation (AMOC), which interact with the effect of changes to ocean stratification (Tagklis et al, 2020;Whitt and Jansen, 2020;Couespel et al, 2021). Differences in the mean state representation of the nutrient stream and the extent of AMOC slowdown across CMIP5 (Cheng et al, 2013) and CMIP6 (Weijer et al, 2020) are therefore major contributors to the magnitude and uncertainty of projected NPP declines in the region (Tagklis et al, 2020;Whitt and Jansen, 2020).…”

Eddy-enhanced primary production sustains heterotrophic microbial activities in the Eastern Tropical North Atlantic

“…However, the effects of eddies vary regionally, and studies with higher spatial resolution of eddies combined with advances in in situ observation, remote sensing, and modelling are still needed to better describe the physical and biological properties of the upper ocean (see review by McGillicuddy, 2016, and references therein). For example, Couespel et al (2021) performed global warming simulations using a representation of mid-latitude double-gyre circulation. They showed that at the finest model resolution (1/27 • ), eddies can mitigate the decline in primary production (−12 % at 1/27 • vs. −26 % at 1 • ).…”

Interactive effects of fishing effort reduction and climate change in a central Mediterranean fishing area: Insights from bio-economic indices derived from a dynamic food-web model

“…Although global climate models project that net primary productivity will very likely decline by 4-11% for RCP8.5 at the end of this century (Couespel et al, 2021;Bindoff et al, 2022) with negative consequences for fish catches (Tittensor et al, 2021), the decline has expected to show regional variations due to biological and modeling factors (Bindoff et al, 2022). For the Mediterranean Sea, the specific biogeochemical model projections under high emission scenario (Solidoro et al, 2022) suggest an increment in both plankton gross productivity and system total respiration, yielding a decrement in the concentrations of total plankton biomass, chlorophyll and particulate organic carbon, among other variables.…”