Abstract
Abstract. To test the hypothesis whether high molecular weight dissolved organic matter (HMW-DOM) in a high latitude marginal sea is dominated by terrestrial derived matter, 10 stations were sampled along the salinity gradient of the central and northern Baltic Sea and were analyzed for concentrations of dissolved organic carbon as well as δ13C values of HMW-DOM. Different end-member-mixing models were applied to quantify the influence of terrestrial DOM and to test for conservative versus non-conservative behavior of the terrestrial DOM in the different Baltic Sea basins. The share of terrestrial DOM to the total HMW-DOM was calculated for each station, ranging from 43 to 83%. This shows the high influence of terrestrial DOM inputs for the Baltic Sea ecosystem. The data also suggest that terrestrial DOM reaching the open Baltic Sea is not subject to substantial removal anymore. However compared to riverine DOM concentrations, our results indicate that substantial amounts of HMW-DOM (> 50%) seem to be removed near the coastline during estuarine mixing. A budget approach yielded residence times for terrestrial DOM of 2.8, 3.0, and 4.5 yr for the Bothnian Bay, the Bothnian Sea and the Baltic Proper.
Highlights
Soil organic matter, which forms the major part of terrestrial DOM, is one of the world’s largest reservoirs of organic carbon
To test the hypothesis whether high molecular weight dissolved organic matter (HMW-DOM) in a high latitude marginal sea is dominated by terrestrial derived matter, 10 stations were sampled along the salinity gradient of the central and northern Baltic Sea and were analyzed for concentrations of dissolved organic carbon as well as δ13C values of HMW-DOM
It is assumed that large amounts of this released organic carbon are transported via the rivers to the coastal oceans, and one important question is how much of this DOC is either retained and degraded in the coastal systems or exported to the open ocean
Summary
Soil organic matter, which forms the major part of terrestrial DOM, is one of the world’s largest reservoirs of organic carbon. DOM plays an important role in the aquatic cycles of C, N, and P, where it serves as an energy source and as a nutrient, and in the oceans it contributes to eutrophication and hypoxia (Wiegner and Seitzinger, 2004; Stepanauskas et al, 1999; Seitzinger and Sanders, 1997) It consists of a complex mixture of organic compounds, such as lipids, amino acids, sugars, and humic or fulvic acids (Benner, 2002), and every year around 0.25 Gt C (0.25 × 1015 g) are transported as DOM via the rivers to the coastal oceans (Cauwet et al, 2002). It is assumed that large amounts of this released organic carbon are transported via the rivers to the coastal oceans, and one important question is how much of this DOC is either retained and degraded in the coastal systems or exported to the open ocean
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