On the distribution of UV-blue fluorescent organic matter in the Southern Ocean

Abstract

The purpose of the work presented in this paper was to study the components of fluorescent organic matter (FOM) resulting from multi-way decomposition of excitation-emission matrices (EEMs) and to find out how their relative distributions and amounts were affected by the changing hydrography and productivity in the Southern Ocean. Data were collected during the austral summer 97/98 along the 6°E meridian covering the area between the spring ice edge and the Subtropical Front. By multiway PARAllel FACtor (PARAFAC) analysis, fluorescence EEMs could be decomposed into components that could be used for relative quantification. It is shown that three components suffice to model the fluorescence in this specific region. Two of the components obtained were protein-like and directly related to in-situ production/degradation; they were correlated with chlorophyll a, and were found to mix down to the core of the Antarctic intermediate water (AAIW) in the Subtropical Front. One component was classified as UV/Visible humic-like and showed a distribution that was very closely related to the qsu-calibrated fluorescence, i.e. indicative of terrestrial input, and of long term processes in the ocean. We suggest that the UV/Visible humic-like component consists of refractory material that is not produced or degraded significantly. It is concluded that a small number of components from PARAFAC analysis were satisfactory representatives of the major types of UV-blue fluorescent structural units present. The qualitative and quantitative results from the PARAFAC model also correlated well with other chemical and physical parameters.