The waters of the Southern Ocean exhibit extreme seasonality in primary production, with marine life living below 0 °C for much of the year. The metabolic cold adaptation (MCA) hypothesis suggests that polar species need elevated basal metabolic rates to enable activity in such cold which should result in higher metabolic rates, or at least rates similar to temperate species. This study aimed to test whether any of the five common marine invertebrates around Adelaide Island (Western Antarctic Peninsula) displayed MCA: the suspension-feeding holothurian Heterocucumis steineni, the grazing limpet Nacella concinna, and the omnivorous brittle star, cushion star and sea-urchin Ophionotus victoriae, Odontaster validus and Sterechinus neumayeri, respectively. We also tested a second hypothesis that secondary consumers will exhibit less seasonal variation of metabolic rate than primary consumers. Routine oxygen consumption was measured in both the austral summer and winter using closed circuit respirometry techniques. Metabolic rates for all the species studied were low compared with temperate species, in a fashion consistent with expected temperature effects on biological systems and, therefore, the data do not support MCA. All the species studied showed significant seasonal differences for a standard mass animal except N. concinna. In two species N. concinna and H. steineni, size affected the seasonality of metabolism. There was no difference in seasonality of metabolism between primary and secondary consumers. Thus, for secondary consumers seasonal factors, most likely food availability and quality, vary enough to impact metabolic rates, and produce seasonal metabolic signals at all trophic levels. Other factors such as reproductive status that are linked to seasonal signals may also have contributed to the metabolic variation across trophic levels.
Recent ice loss from the West Antarctic Ice Sheet has been caused by ocean melting of ice shelves in the Amundsen Sea.Eastward wind anomalies at the shelf break enhance the import of warm Circumpolar Deep Water onto the Amundsen Seacontinental shelf, which creates transient melting anomalies with an approximately decadal period. No anthropogenic influence on this process has been established. Here, we combine observations and climate model simulations to suggest that increased greenhouse gas forcing caused shelf-break winds to transition from mean easterlies in the 1920s to the near-zero mean zonal winds of the present day. Strong internal climate variability, primarily linked to the tropical Pacific, is superimposed on this forced trend. We infer that the Amundsen Sea experienced decadal ocean ariability throughout the twentieth century, with warm anomalies gradually becoming more prevalent, offering a credible explanation for the ongoing ice loss. Existing climate model projections show that strong future greenhouse gas forcing creates persistent mean westerly shelf-break winds by 2100, suggesting a further enhancement of warm ocean anomalies. These wind changes are weaker under a scenario in which greenhouse gas concentrations are stabilized.