Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation
- 1Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia, USA
- 2Greenland Climate Research Centre, Greenland Institute of Natural Resources, Nuuk, Greenland
- 3Centre for Earth Observation Science, CHR Faculty of Environment Earth and Resources, University of Manitoba, Winnipeg, Canada
- 4Scottish Association of Marine Sciences, Oban, Scotland, UK
- 5Southern Danish University and NordCee, Odense M, Denmark
Abstract. This study examined fluxes across the ice-water interface utilizing the eddy correlation technique. Temperature eddy correlation systems were used to determine rates of ice melting and freezing, and O2 eddy correlation systems were used to examine O2 exchange rates driven by biological and physical processes. The study was conducted below 0.7 m thick sea-ice in mid-March 2010 in a southwest Greenland fjord and revealed low rates of ice melt at a maximum of 0.80 mm d−1. The O2 flux associated with release of O2 depleted melt water was less than 13 % of the average daily O2 respiration rate. Ice melt and insufficient vertical turbulent mixing due to low current velocities caused periodic stratification immediately below the ice. This prevented the determination of fluxes 61 % of the deployment time. These time intervals were identified by examining the velocity and the linearity and stability of the cumulative flux. The examination of unstratified conditions through vertical velocity and O2 spectra and their cospectra revealed characteristic fingerprints of well-developed turbulence. From the measured O2 fluxes a photosynthesis/irradiance curve was established by least-squares fitting. This relation showed that light limitation of net photosynthesis began at 4.2 μmol photons m−2 s−1, and that algal communities were well-adapted to low-light conditions as they were light saturated for 75 % of the day during this early spring period. However, the sea-ice associated microbial and algal community was net heterotrophic with a daily gross primary production of 0.69 mmol O2 m−2 d−1 and a respiration rate of −2.13 mmol O2 m−2 d−1 leading to a net ecosystem metabolism of −1.45 mmol O2 m−2 d−1. This application of the eddy correlation technique produced high temporal resolution O2 fluxes and ice melt rates that were measured without disturbing the in situ environmental conditions while integrating over an area of approximately 50 m2 which incorporated the highly variable activity and spatial distributions of sea-ice communities.