EARSeL eProceedings Vol. 3, No. 2, 227-238, 2004

Abstract
Measuring the chromophoric fraction of dissolved organic matter (CDOM) in natural waters using its fluorescence signal is extremely useful in a variety of marine and freshwater applications. The aim of this research was to study the changes in CDOM optical properties at low temperatures and during ice formation from seawater. In a laboratory study it was found that CDOM fluorescence intensity reversibly decreases with increasing water temperature. The study of the temperature effect is important for future calibration of lidar data measured in regions with horizontal temperature gradients, and for correction of in situ measured CDOM fluorescence depth profiles.

Changes in CDOM fluorescence due to variations in concentration and possibly composition under controlled conditions of ice cover developing were studied during experiments using artificial ice sheets produced in large-scale tank experiments. Fluorescence emission, fluorescence excitation and absorption spectra of filtered samples from ice, ice brine and melted ice were measured in the laboratory at fixed room temperature. Sea ice brines showed high fluorescence signals due to the accumulation of CDOM in channels filled with brine during ice growth. CDOM fluorescence slightly increased in seawater underlying the ice sheet due to exclusion of DOM from ice. Ice samples separated from brine had low fluorescence signals. Humic-type fluorescence intensity (270, 308 or 355 nm excitation) was directly proportional to salinity as well as to dissolved organic carbon (DOC) concentrations in many samples of ice to highly concentrated brine.

ISSN 1729-3782