Abstract
Climate change is rapidly altering the habitat of Antarctic krill (Euphausia superba), a key species of the Southern Ocean food web. Krill are a critical element of Southern Ocean ecosystems as well as biogeochemical cycles, while also supporting an international commercial fishery. In addition to trends forced by global-scale, human-driven warming, the Southern Ocean is highly dynamic, displaying large fluctuations in surface climate on interannual to decadal timescales. The dual roles of forced climate change and natural variability affecting Antarctic krill habitat, and therefore productivity, complicate interplay of observed trends and contribute to uncertainty in future projections. We use the Community Earth System Model Large Ensemble (CESM-LE) coupled with an empirically derived model of krill growth to detect and attribute trends associated with “forced,” human-driven climate change, distinguishing these from variability arising naturally. The forced trend in krill growth is characterized by a poleward contraction of optimal conditions and an overall reduction in Southern Ocean krill habitat. However, the amplitude of natural climate variability is relatively large, such that the forced trend cannot be formally distinguished from natural variability at local scales over much of the Southern Ocean by 2100. Our results illustrate how natural variability is an important driver of regional krill growth trends and can mask the forced trend until late in the 21st century. Given the ecological and commercial global importance of krill, this research helps inform current and future Southern Ocean krill management in the context of climate variability and change.
Highlights
The Southern Ocean, which surrounds Antarctica, is a critical component of the Earth system and supports a marine ecosystem of immense economic and intrinsic value
Temperature exerted a strong control on growth potential (GP), with elevated GP values typically found within the optimal temperature range (−1 to 2◦C) and located in coastal regions with high chlorophyll concentrations
The distribution of growth habitat was strongly constrained on its northern boundary by the edge of the 5◦C isotherm that coincides with the Polar Front of the Antarctic Circumpolar Current (ACC) (Figure 1)
Summary
The Southern Ocean, which surrounds Antarctica, is a critical component of the Earth system and supports a marine ecosystem of immense economic and intrinsic value. It is among the most sensitive areas to climate change (Hagen et al, 2007) and has already experienced physical changes in ocean temperature, sea-ice dynamics, stratification, and currents (Flores et al, 2012). In addition to trends forced by global-scale, human-driven warming, the Southern Ocean is subject to highly-dynamic natural climate variability, which can exert important influence on the system on interannual to multi-decadal timescales (Mayewski et al, 2009). In the context of climate change and the highly dynamic Southern Ocean, the framework we present provides insights that are important for decision makers to consider regarding climate change adaptation strategies
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