Abstract
AbstractMarine phytoplankton contribute about one half of global primary production and play a key role in global biogeochemical cycles. High cell densities in extensive phytoplankton blooms are expected to be modified by global changes in ocean circulation and stratification, acidification and carbonation, solar radiation, temperature, and eutrophication. Although photochemical gas production from chromophoric dissolved organic matter (CDOM) has been widely studied, ultraviolet (UV) effects on emissions from phytoplankton cells themselves have not been fully explored. We therefore investigated UV‐driven emissions of carbon monoxide (CO), carbon dioxide (CO2), methane (CH4), ethene (C2H4), ethane (C2H6), and nitrous oxide (N2O) from cell suspensions of 16 phytoplankton species and their filtrates under controlled experimental conditions. These gases make direct or indirect contributions to radiative forcing of the atmosphere or contribute to atmospheric chemistry including stratospheric ozone (O3) depletion. We observed production of CH4, CO, CO2, C2H4, and N2O from cell suspensions and CO, CO2, and N2O after 0.45 μm‐filtration to remove phytoplankton cells. CH4 production was only observed with cells present, whereas N2O was still produced after filtration. Production of CO from filtrates was 30%–90% of that from cell suspensions in all but two species with a CO2:CO mole ratio from filtrates always below one. Our results clearly demonstrate a need to quantify the production potentials of these climate‐relevant gases in situ under natural sunlight using key phytoplankton species, especially those forming blooms which are predicted to change in prevalence and distribution with future global change scenarios.
Highlights
Photochemical emissions to the atmosphere from the marine and freshwater environment have recently received attention for their role and contribution to biogeochemical cycles of carbon (Cory et al, 2014; Günthel et al, 2019; Koehler et al, 2014; Li et al, 2020; Neale et al, 2021; Royer et al, 2018)
There was no detectable production of C2H6 from any species
Our constant irradiance of 4.3 and 4.0 W m−2 UVA and UVB provided 8-h integrated doses of 124.1 and 114.9 kJ m−2 UVA and UVB, respectively. These compare with global values for monthly mean daily doses calculated using the Tropospheric Ultraviolet-Visible (TUV) model using the mean O3 column and cloud cover over 11 years (Lee-Taylor & Madronich, 2007) of up to 2,000 kJ m−2 day−1 UV-A and 60 kJ m−2 day−1 UV-B
Summary
Photochemical emissions to the atmosphere from the marine and freshwater environment have recently received attention for their role and contribution to biogeochemical cycles of carbon (Cory et al, 2014; Günthel et al, 2019; Koehler et al, 2014; Li et al, 2020; Neale et al, 2021; Royer et al, 2018). Oxidation of dissolved organic carbon (DOC) by ultraviolet (UV) and visible radiation was reported to contribute 70%–95% of DOC breakdown and 40% of CO2 emissions in arctic lakes and rivers (Cory et al, 2014). UV-driven production of methane (CH4), ethene (C2H4), and ethane (C2H6) were recently reported from plastic particles in seawater (Royer et al, 2018).
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