Oxygen budget methods to determine the vertical flux of particulate organic matter with application to the coastal waters off western Scandinavia

Abstract

Oxygen budget methods to determine the vertical flux of particulate organic matter in the sea are presented and discussed. Most attention is devoted to oxygen budgets for aphotic stagnant waters, e.g. in fjordic sill basins, but oxygen budgets for the photic layer are also covered. Overall results on the vertical flux of organic matter obtained from the two oxygen budget methods are presented. It is found that the vertical flux of organic matter generally decreases with depth. This should be an effect of pelagic remineralization. Starting in the Baltic Sea, the contemporary vertical flux of organic matter along the Scandinavian west coast shows a minimum in Öresund from where it increases to a maximum in the coastal zone of eastern and northern Skagerrak. Along the Norwegian west coast the vertical flux appears to be approximately constant and about the same as in the open Skagerrak. The vertical flux of organic matter has increased in the Baltic since the 1950s and there is strong evidence that there has been an increase along the eastern and northern coasts of Skagerrak and in Kattegat during the last 15 years, approximately. The open Skagerrak, less influenced by outflowing Baltic Sea water, showed a decrease in the vertical flux of organic matter in the period 1957–1982. Highly elevated rates of oxygen consumption are found in some fjordic sill basins. For fjords discharging directly into the open sea, it is thought that this may be due to transient transport of large quantities of macroalgae into the fjords which had previously been dislodged in the coastal zone during events of extremely strong winds and waves.