Environmental change in the Southern Ocean: observations, trends, bioregions and species-distribution models

Earth-observation satellites and models can provide powerful information on environmental variability and change in the Southern Ocean. “Essential Climate Variables” (ECVs) are physical, chemical and/or biological properties (or a group of linked variables) that critically contribute to the characterisation of the state of a natural system. Around the Antarctic, multi-decadal observations are available of many key parameters including: (1) ocean circulation and water masses; (2) mixed-layer temperature; (3) phytoplankton biomass and primary production (by phytoplankton and algae in sea-ice); (4) sea-ice concentration; and (5) sea-state (significant wave height). We recommend defining sets of ECVs for Antarctic systems targeted to CCAMLR purposes. Analysis of ECVs can reveal complex patterns of long-term change and provide a context for understanding climate-driven changes in important organisms including krill, fish, benthos, seabirds and marine mammals. Identifying regions of the Southern Ocean where multiple environmental characteristics are changing in the same way (“bioregions of change”) will likely extend the usefulness of rend analyses for CCAMLR purposes. For example, multivariate analysis of patterns of change of ECVs could be used with species distribution models and biological/fisheries observations to: (1) provide an understanding of environmental drivers of key biological and ecological processes such as productivity; (2) investigate changes to spatial or seasonal distributions of key species; (3) interpolate across observation gaps (in space or time); and (4) (when linked to future projections from Earth System Models) to anticipate future ecological changes.