Oxygen exchange and ice melt measured at the ice-water interface by eddy correlation

Abstract

This study uses the eddy correlation technique to examine fluxes across the ice-water interface. Temperature eddy correlation systems were used to determine rates of ice melting and freezing, and O<sub>2</sub> eddy correlation systems were used to examine O<sub>2</sub> exchange rates as driven by biological and physical processes. The research was conducted below 0.7 m thick sea ice in mid March 2010 in a southwest Greenland fjord and revealed low average rates of ice melt amounting to a maximum of 0.80 ± 0.09 mm d<sup>−1</sup> (SE, <i>n</i>=31). The corresponding calculated O<sub>2</sub> flux associated with release of O<sub>2</sub> depleted melt water was less than 13 % of the average daily O<sub>2</sub> 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 during certain time periods, amounting to 66 % of total deployment time. The identification of these conditions was evaluated by examining the velocity and the linearity and stability of the cumulative flux. The examination of unstratified conditions through velocity and O<sub>2</sub> spectra and their cospectra revealed characteristic fingerprints of well-developed turbulence. From the observed O<sub>2</sub> 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<sup>−2</sup> s<sup>−1</sup>, and that the 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 ± 0.02 mmol O<sub>2</sub> m<sup>−2</sup> d<sup>−1</sup> (SE, <i>n</i>=4) and a respiration rate of −2.13 mmol O<sub>2</sub> m<sup>−2</sup> d<sup>−1</sup> (no SE, see text for details) leading to a net primary production of −1.45 ± 0.02 mmol O<sub>2</sub> m<sup>−2</sup> d<sup>−1</sup> (SE, <i>n</i>=4). Modeling the observed fluxes allowed for the calculation of fluxes during time periods when no O<sub>2</sub> fluxes were extracted. This application of the eddy correlation technique produced high temporal resolution O<sub>2</sub> fluxes and ice melt rates that were measured without disturbing the environmental conditions while integrating over a large area of approximately 50 m<sup>2</sup> which encompassed the highly variable activity and spatial distributions of sea ice algal communities

The relative contributions of biological and abiotic processes to carbon dynamics in subarctic sea ice

“…Using a lower growth efficiency (\0.15; e.g. Middelboe et al 2012), the seasonal net autotrophic sea ice would change to a net heterotrophic sea ice, which compares to result found by Long et al (2011) in Kapisigdlit Bight in March 2010. Thereby the biological activity would not contribute to the atmospheric CO 2 uptake at all.…”

First “in situ” determination of gas transport coefficients (, , and ) from bulk gas concentration measurements (O2, N2, Ar) in natural sea ice

“…The air temperatures during the study period ranged from −8.8°C to +2.9°C (average −3.2°C). The survey took place before the onset of the spring algal bloom: concentrations of chlorophyll‐a were 2.8 ± 0.4 μg L −1 (SE, n = 3) in the bottom 12 cm of ice, while the average concentration across the entire ice thickness was 1.0 ± 1.2 μg L −1 (SE, n = 3) [ Long et al ., ; Sogaard et al ., ].…”

In Situ Coral Reef Oxygen Metabolism: An Eddy Correlation Study

“…The EC technique has proven very useful in a variety of environments including: muddy deep-sea sediments [18], permeable sediments [19], temperate seagrass beds [14], hard-bottom substrates [20], and Arctic sea-ice production [21], and has revealed in situ rates, dynamics, and interactions which cannot be observed by other methodologies.…”