The Importance of Spatial and Temporal Scales in Understanding Chlorophyll Variability in the Southern Ocean

Polar regions are undergoing dramatic, rapid, and possibly irreversible changes. Substantial shifts in patterns of sea ice extent and thickness have cascading effects on polar ecosystems (including phytoplankton), with implications for carbon cycling and global climate. Phytoplankton growth is closely tied to environmental variables such as light and nutrient availability, which are sensitive to climate‐induced changes in upper ocean circulation, stratification, and sea ice cover. Recently, Prend et al. (2022, https://doi.org/10.1029/2022GB007329) investigated temporal and spatial scales of chlorophyll (a proxy for phytoplankton biomass) variability in the Southern Ocean. They demonstrated that the dominant temporal scale of variability is sub‐seasonal (∼0.5–3 months). The implications of this are two‐fold: first, climate oscillations (such as the Southern Annular Mode) are not major drivers of year‐to‐year variation in chlorophyll; second, intermittent bursts of chlorophyll, generated by small‐scale processes such as storms and eddies, dictate the annual mean chlorophyll concentration. Additionally, spatial autocorrelation for chlorophyll concentration varied by time scale: seasonal chlorophyll variability was correlated over much larger areas than were variations in year‐to‐year chlorophyll concentration. Based on Prend et al. (2022, https://doi.org/10.1029/2022GB007329), future work should be cognizant of (a) the spatio‐temporal scales over which chlorophyll is averaged and (b) the need to focus on small‐scale, sub‐seasonal events (rather than large‐scale climate oscillations) to mechanistically explain chlorophyll variability. Plain Language Summary The distribution of carbon between the atmosphere and ocean, in part, regulates global climate. The amount of carbon transferred between the atmosphere and ocean is affected by both marine biological growth (through photosynthesis) and physical processes (such as storms and mixing). The Southern Ocean, around Antarctica, is one of the most important oceanic systems in determining how much natural carbon is transferred from the atmosphere to the ocean, but it is experiencing adverse impacts of climate change that affect both biological growth and physical processes. To predict future distributions of carbon, and thus future climate, we must first understand how and why these processes change. Prend et al. (2022, https://doi.org/10.1029/2022GB007329) tackle part of this challenge by investigating variability