AGU Geophysical Research Letters: Arctic Observations Identify Phytoplankton Community Composition as Driver of Carbon Flux Attenuation

Ingrid Wiedmann (UiT) together with colleagues from Universidad de Sevilla (ES), Institute of Marine Research (NO), Alfred-Wegener Institute (DE), Bureau Waardenburg (NL), Norwegian Polar Institute (NO), and Institute of Oceanology, Polish Academy of Sciences (PL) have authored the newly accepted research letter “Arctic Observations Identify Phytoplankton Community Composition as Driver of Carbon Flux Attenuation”.

Abstract
The attenuation coefficient b is one of the most common ways to describe how strong the carbon flux is attenuated throughout the water column. Therefore, b is an essential input variable in many carbon flux and climate models. Marsay et al. (2015, https://doi.org/10.1073/pnas.1415311112) proposed that the median surface water temperature (0‐500 m) may be a predictor of b , but our observations from Arctic waters challenge this hypothesis. We found a highly variable attenuation coefficient (b = 0.43‐1.84) in cold Arctic waters (< 4.1 °C). Accordingly, we suggest that water temperature is not a globally valid predictor of the attenuation coefficient. We advocate instead that the phytoplankton composition, and especially the relative abundance of diatoms, can be used to parametrize the carbon flux attenuation in local and global carbon flux models.

Plain Language Summary
In the surface ocean, microalgae convert dissolved atmospheric CO2 into organic carbon (OC). As OC sinks in the water columns, microbes and zooplankton graze on it. It has been suggested that these organisms reduce the amount of sinking OC stronger in warm waters than in cold waters. We found, however, that the amount of sinking OC is sometimes strongly and sometimes weakly reduced in cold Arctic waters (< 4 °C). Therefore, we conclude that temperature seems not to be an important factor determining how strong the amount of sinking OC is reduced with depth. We instead advocate that the phytoplankton community composition is useful to predict how strong the amount of sinking OC is reduced with depth. When fast‐sinking algae form algal aggregates or are repackaged into copepod fecal pellets, their OC spends only a short time in the upper water column where hungry grazers are very abundant. The consumers have then much less time to prey on the OC than when the sinking particles consist of slowly sinking algae. Concluding, we argue that it is very important to include the phytoplankton community composition in computer simulations to correctly predict how much OC is stored in the oceans.

Reference: 

Wiedmann, I.; Ceballos-Romero, E.; Villa-Alfageme, M.; Renner, A.H.H.; Dybwad, C.; van der Jagt, H.; Svensen, C.; Assmy, P.; Wiktor, J.M.; Tatarek, A.; Rozanska-Pluta, M.; Iversen, M.H. (accepted): Arctic Observations Identify Phytoplankton Community Composition as Driver of Carbon Flux Attenuation. Accepted online 24 June 2020, in American Geophysical Union, Geophysical Research Letters. doi: 10.1029/2020GL087465. [intranet]