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

[摘要] This study examined fluxes across the ice-water interface utilizing the eddycorrelation technique. Temperature eddy correlation systems were used todetermine rates of ice melting and freezing, and O₂ eddy correlationsystems were used to examine O₂ exchange rates driven by biological andphysical processes. The study was conducted below 0.7 m thick sea-ice inmid-March 2010 in a southwest Greenland fjord and revealed low rates of icemelt at a maximum of 0.80 mm d⁻¹. The O₂ flux associated withrelease of O₂ depleted melt water was less than 13 % of the averagedaily O₂ respiration rate. Ice melt and insufficient vertical turbulentmixing due to low current velocities caused periodic stratificationimmediately below the ice. This prevented the determination of fluxes 61 %of the deployment time. These time intervals were identified by examiningthe velocity and the linearity and stability of the cumulative flux. Theexamination of unstratified conditions through vertical velocity and O₂spectra and their cospectra revealed characteristic fingerprints ofwell-developed turbulence. From the measured O₂ fluxes aphotosynthesis/irradiance curve was established by least-squares fitting.This relation showed that light limitation of net photosynthesis began at4.2 μmol photons m⁻² s⁻¹, and that algal communities werewell-adapted to low-light conditions as they were light saturated for 75 %of the day during this early spring period. However, the sea-ice associatedmicrobial and algal community was net heterotrophic with a daily grossprimary production of 0.69 mmol O₂ m⁻² d⁻¹ and a respirationrate of −2.13 mmol O₂ m⁻² d⁻¹ leading to a netecosystem metabolism of −1.45 mmol O₂ m⁻² d⁻¹. Thisapplication of the eddy correlation technique produced high temporalresolution O₂ fluxes and ice melt rates that were measured withoutdisturbing the in situ environmental conditions while integrating over anarea of approximately 50 m² which incorporated the highly variableactivity and spatial distributions of sea-ice communities.

[学科分类] 地球化学与岩石