How can we effectively manage the impact of climate change on Antarctic ecosystems?

Primary production by photosynthetic phytoplankton such as diatoms is the lynchpin of the Southern Ocean’s biogeochemical and ecological role. By building up the standing stock of particulate organic carbon, primary production primes the biological pump and thus regulates the contribution of Antarctic phytoplankton to the global carbon cycle. Primary production also supports the biomass and dynamics of Antarctic ecosystems, including Krill and charismatic megafauna that form the focus of conservation and commercial exploitation efforts. Forecasts of how climate change will affect primary production using our best models are hence a crucial part of any regional management efforts. The Southern Ocean is well understood to be limited by the micronutrient iron and light, but the role of manganese has also emerged in recent years. We also know that the resident phytoplankton have evolved unique adaptions to thrive in this specialized environment that makes them distinct from the rest of the global ocean. Ignoring these regional specificities, current generation models predict that climate change will confer greater productivity on the Southern Ocean, with high ‘across model’ confidence.

 

In this submission, we performed a comprehensive assessment of primary production changes in the Southern Ocean from six different remote sensing algorithms applied to the single merged ocean color dataset from 1998-2024. These trends are compared to ongoing and future trends from 14 climate models for three different climate scenarios that span low, medium and high emissions trajectories. We find that ongoing declines in regional primary production are most common in remote sensing-based data and are consistent with shorter timescale trends from BioArgo floats.  However, these trends are inconsistent with the those from ESMs that consistently project primary production increases. This highlights that there is a lack of confidence in the forecasts of increasing Southern Ocean productivity that calls for precaution in planning. We argue that this mis-match reflects the unique aspects of the Southern Ocean system that must be better understood so they can be integrated into a new generation of climate projections. This would then enable sufficiently accurate forecasting to support regional management efforts.