Abstract
Abstract. We investigate the ways in which marine biologically mediated heating increases the surface atmospheric temperature. While the effects of phytoplankton light absorption on the ocean have gained attention over the past years, the impact of this biogeophysical mechanism on the atmosphere is still unclear. Phytoplankton light absorption warms the surface of the ocean, which in turn affects the air–sea heat and CO2 exchanges. However, the contribution of air–sea heat versus CO2 fluxes in the phytoplankton-induced atmospheric warming has not been yet determined. Different so-called climate pathways are involved. We distinguish heat exchange, CO2 exchange, dissolved CO2, solubility of CO2 and sea-ice-covered area. To shed more light on this subject, we employ the EcoGEnIE Earth system model that includes a new light penetration scheme and isolate the effects of individual fluxes. Our results indicate that phytoplankton-induced changes in air–sea CO2 exchange warm the atmosphere by 0.71 ∘C due to higher greenhouse gas concentrations. The phytoplankton-induced changes in air–sea heat exchange cool the atmosphere by 0.02 ∘C due to a larger amount of outgoing longwave radiation. Overall, the enhanced air–sea CO2 exchange due to phytoplankton light absorption is the main driver in the biologically induced atmospheric heating.
Highlights
Previous studies have shown that marine biota can modify the light penetration in the ocean with consequences on the atmospheric temperature and on the climate system (Shell et al, 2003; Wetzel et al, 2006; Gnanadesikan and Anderson, 2009)
flux of CO2 across the air–sea interface (FCO2) is the air–sea CO2 flux, k corresponds to the gas transfer velocity, ρ is the ocean density, Cw is the concentration of dissolved gas in the surface ocean, α is the solubility coefficient calculated from Wanninkhof (1992) and depends on the sea surface temperature and salinity, Ca is the concentration of gas in the atmosphere, and A is the fraction of the ocean covered by sea ice
For the first time, using the EcoGEnIE model (Ward et al, 2018), we compare the role of the air–sea heat and CO2 fluxes and quantify their influence on the biologically induced atmospheric warming
Summary
Previous studies have shown that marine biota can modify the light penetration in the ocean with consequences on the atmospheric temperature and on the climate system (Shell et al, 2003; Wetzel et al, 2006; Gnanadesikan and Anderson, 2009). Manizza et al (2008) study the impact of this biogeophysical mechanism on the air–sea flux of CO2 and find that phytoplankton light absorption has a small outgassing effect on a global scale with high regional fluctuations. None of these studies have analyzed, disentangled and compared the changes in both air–sea heat and CO2 exchange due to phytoplankton light absorption. To achieve the disentangling of the specific climate pathways, we turn them on and off by prescribing values in our ESM in order to isolate their impact on the climate system
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