Award: PLR-1043559

Our work has led to a deeper understanding of seasonal cycle of biological productivity and trace gas production in coastal Antarctic marine waters. Through the deployment of novel automated measurement devices, we were able to follow the production and consumption of oxygen (O2), carbon dioxide (CO2) and dimethylsulfide (DMS) and related compounds (DMSP and DMSO) in surface marine waters adjacent to the Antarctic continent. Oxygen and CO2 are produced and consumed in photosynthesis and respiration, such that measurements of their concentrations in surface waters provides information on the relative rates of these two processes. Photosynthesis consumes CO2, produces organic biomass that supports the entire food-web, and release O2 into the atmosphere. Respiration æburnsÆ the organic carbon, consuming O2 and releasing CO2. The amount of æexcessÆ photosynthesis (with respect to respiration) in the water column determines the overall productivity of the ecosystem and its ability to extract CO2 from the atmosphere. This in turn dictates how the system influences the global carbon cycle. Through the production of other gases, including DMS, marine ecosystems can also influence climate. DMS reacts in the atmosphere to form sulfur aerosols that reflect incoming solar radiation and act to cool the planet. The net production rate of DMS can thus also influence regional climate. Traditional measurements of biological productivity and DMS production have been limited by the need to use time-consuming and laborious methods. In this project, we deployed, for the first time, a suite of automated methods to measure CO2, O2 and DMS, and we used these data to infer rates of biological productivity rates and DMS production, and their response to various environmental changes over a seasonal cycle between late spring and early fall. Our results document, with unprecedented resolution, the rise and rapid decline of a massive algal æbloomÆ, which sustain a high productivity of fish, sea-birds and marine mammals. Using only our automated gas measurements, combined with simple model calculations, we derived productivity estimates that were in good agreement with ætraditionalÆ more laborious methods with much lower temporal resolution. Our results demonstrated strong cycles in productivity over daily, weekly and monthly cycles, corresponding to changes in environmental conditions (primarily light availability). Our gas data, combined with additional experiments, also provided new insight into the processes responsible for producing and consuming DMS in surface waters, and its release to the overlying atmosphere. Going forward our approach has the potential to revolutionize monitoring studies aimed at examining long-term impacts of climate change on the Antarctic marine ecosystem. Last Modified: 10/19/2015 Submitted by: John W H Dacey