Contribution of hurricanes to local and global estimates of air–sea exchange of CO2

The effect of hurricanes on the thermal and physical structure of the upper ocean has been described1 but their influence on the ocean carbon cycle and the exchange of carbon between ocean and atmosphere is not well understood. Here we present observations from the Sargasso Sea, before and after hurricane Felix in summer 1995, that show a short-lived (2–3 weeks) surface seawater cooling of about 4 °C, and a decrease in seawater partial pressure of CO2 by about 60 microatm. Despite the localized decrease in seawater partial pressure of CO2, strong winds during the passage of hurricane Felix increased the efflux of CO2 from ocean to atmosphere. We estimate that hurricane Felix and two other hurricanes increased the summertime efflux of CO2 into the atmosphere over this part of the Sargasso Sea by nearly 55%. We estimate that hurricanes contribute to the global ocean-to-atmosphere flux of CO2 by between +0.04 to +0.51 Pg C (1015 g C) per year. Such hurricane-forced effluxes are quantitatively significant compared to regional (14° to 50° N zone)2 and global effluxes2,3. Hurricanes therefore exert an important influence on ocean–atmosphere CO2 exchange and the inferred4 year-to-year variability of CO2 fluxes over the subtropical oceans

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill

© 2017 The Author(s). A dominant Antarctic ecological paradigm suggests that winter sea ice is generally the main feeding ground for krill larvae. Observations from our winter cruise to the southwest Atlantic sector of the Southern Ocean contradict this view and present the first evidence that the pack-ice zone is a food-poor habitat for larval development. In contrast, the more open marginal ice zone provides a more favourable food environment for high larval krill growth rates. We found that complex under-ice habitats are, however, vital for larval krill when water column productivity is limited by light, by providing structures that offer protection from predators and to collect organic material released from the ice. The larvae feed on this sparse ice-associated food during the day. After sunset, they migrate into the water below the ice (upper 20 m) and drift away from the ice areas where they have previously fed. Model analyses indicate that this behaviour increases both food uptake in a patchy food environment and the likelihood of overwinter transport to areas where feeding conditions are more favourable in spring