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

• Published in: Biogeosciences
• Main Authors: Long, M. H., Koopmans, D., Berg, Peter, Rysgaard, Søren, Glud, Ronnie N., Søgaard, Dorte H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2012
• Subjects: Greenland; Sea ice
• Online Access: https://portal.findresearcher.sdu.dk/da/publications/7ee789bf-6677-4998-88a9-07bfd236764b; https://doi.org/10.5194/bg-9-1957-2012

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 O-2 eddy correlation systems were used to examine O-2 exchange rates driven by biological and physical processes. The study was conducted below 0.7m thick sea-ice in mid-March (2)010 in a southwest Greenland fjord and revealed low rates of ice melt at a maximum of 0.80mmd(-1). The O-2 flux associated with release of O-2 depleted melt water was less than 13% of the average daily O-2 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 O-2 spectra and their cospectra revealed characteristic fingerprints of well-developed turbulence. From the measured O-2 fluxes a photosynthesis/ irradiance curve was established by least-squares fitting. This relation showed that light limitation of net photosynthesis began at 4.2 mu mol 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 O-2 m(-2) d(-1) and a respiration rate of -2.13 mmol O-2 m(-2) d(-1) leading to a net ecosystem metabolism of -1.45 mmol O-2 m(-2) d(-1). This application of the eddy correlation technique produced high temporal resolution O-2 fluxes and ice melt rates that were measured without disturbing the in situ environmental conditions while integrating over an area of approximately 50m(2) which incorporated the highly variable activity and spatial ...