Warming and ocean acidification may decrease estuarine dissolved organic carbon export to the ocean

Simone, Michelle N.; Schulz, Kai G.; Oakes, Joanne M.; Eyre, Bradley D.

Relative to their surface area, estuaries make a disproportionately large contribution of dissolved organic carbon (DOC) to the global carbon cycle, but it is unknown how this will change under a future climate. As such, the response of DOC fluxes from microbially dominated unvegetated sediments to individual and combined future climate stressors of temperature change (from inline-formulaΔ−3 to inline-formulaΔ+5 inline-formulaC compared to ambient mean temperatures) and ocean acidification (OA, inline-formula∼ 2inline-formula× current COinline-formula2 partial pressure, inline-formulapCOinline-formula2) was investigated ex situ. Warming alone increased sediment heterotrophy, resulting in a proportional increase in sediment DOC uptake; sediments became net sinks of DOC (3.5 to 8.8 mmol C minline-formula−2 dinline-formula−1) at warmer temperatures (inline-formulaΔ+3 and inline-formulaΔ+5 inline-formulaC, respectively). This temperature response changed under OA conditions, with sediments becoming more autotrophic and a greater sink of DOC (up to 4inline-formula× greater than under current inline-formulapCOinline-formula2 conditions). This response was attributed to the stimulation of heterotrophic bacteria with the autochthonous production of labile organic matter by microphytobenthos. Extrapolating these results to the global area of unvegetated subtidal estuarine sediments, we find that the future climate of warming (inline-formulaΔ+3 inline-formulaC) and OA may decrease estuarine export of DOC by inline-formula∼ 80 % (inline-formula∼ 150 Tg C yrinline-formula−1) and have a disproportionately large impact on the global DOC budget.



Simone, Michelle N. / Schulz, Kai G. / Oakes, Joanne M. / et al: Warming and ocean acidification may decrease estuarine dissolved organic carbon export to the ocean. 2021. Copernicus Publications.


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