The Biological Pump and Seasonal Variability of pCO₂ in the Southern Ocean: Exploring the Role of Diatom Adaptation to Low Iron

Abstract

Iron is known to limit primary production in the Southern Ocean (SO). To cope with the lack of this micronutrient, diatoms, a dominant phytoplankton group in this oceanic region, have been shown in cultures to have developed an original adaptation strategy to maintain efficient growth rates despite very low cellular iron quotas, even in low light conditions. Using a global ocean biogeochemical model, we explored the consequences of this physiological adaptation for the biological pump and the seasonal variability of both surface chlorophyll concentrations and surface partial pressure of carbon dioxide (pCO2) in this key region for global climate. In the model, we implemented a low intracellular Fe:C requirement in the SO for diatoms uniquely. This results in an increase of 10% in the relative contribution of diatoms to total SO primary production. The biological pump is also strengthened, which increases the biological contribution to the seasonal evolution of pCO2 relative to the thermodynamic component. Therefore, the seasonal evolution of both surface chlorophyll and surface pCO2 is significantly impacted, with a marked improvement, in our model, in the SO polar zone compared to the observations. Our model study underscores the potentially important consequences that this adaptive physiological behavior of diatoms could have on marine biogeochemistry in the SO. It is thus critical to improve our understanding of the physiology of this key phytoplankton group, in particular in the SO.

Iron Incorporation From Seawater Into Antarctic Sea Ice: A Model Study

“…In the Weddell Sea, MLD is greater than 260 m, which could constitute a significant bias in our model, although mixed layers deeper than 200 m have also been reported from observation‐based values (Pellichero et al., 2017). Note that the winter MLD simulated in the SO by the NEMO ocean model has recently been evaluated deeper than the observations (Person et al., 2018). MLD‐sea ice relationships can be detected by visually comparing the upper and lower panels on Figure 1.…”

Tracking Improvement in Simulated Marine Biogeochemistry Between CMIP5 and CMIP6

“…First, several recent studies show that the inclusion of a more comprehensive treatment of plankton physiology may improve model performance, in particular some systematic biases in the Southern Ocean (e.g. [ 108 , 165 ]). Then, this improvement is arguably a first step toward the representation of adaptation and fitness in ocean biogeochemical models [ 166 , 167 ].…”

Dynamics of an intense diatom bloom in the Northern Antarctic Peninsula, February 2016

“…Diatoms, a dominant phytoplankton group in the Southern Ocean (e.g., Arrigo et al 1999;Pondaven et al 2000;Armbrust 2009), are considered the core of the austral food web as they are responsible for more than 85% of its annual primary production (Rousseaux and Gregg 2014). Consequently, the diatoms play crucial role in the trophic structure and biogeochemical cycles of the region (Falkowski et al 1998;Tréguer et al 2017;Person et al 2018;Brown et al 2019). Although this group seems well adapted to regimes of intermittent light and nutrient exposure, it is particularly common in nutrient-rich environments encompassing polar regions, as well as upwelling and coastal areas (Smetacek et al 2012).…”