In my thesis the distribution and composition of dissolved carbohydrates as one of the largest pools of dissolved organic matter (DOM) in the Arctic Ocean was studied. From the terrestrial sources on the Eurasian continent, the riverine inflow of carbohydrates into the Arctic was investigated. In the Arctic Ocean, dissolved carbohydrates of the Siberian shelf areas, Kara and Laptev Seas, central Arctic Ocean, Fram Strait and Greenland Sea were determined. The carbohydrates were determined by two methods. The concentrations of bulk carbohydrates were determined by the colorimetric L-Tryptophan / sulphuric acid method. The composition of individual, neutral sugars of free and combined carbohydrates was determined by a high-performance anion exchange chromatography with pulsed amperometric detection (HPAEC-PAD). The high sensitivity of both methods allowed detection in freshwater and seawater samples without pre-concentration.
Main focus of this study was the composition of refractory carbohydrates, which are components of the humic substances. They were extracted by a combination of XAD-2 and-4 adsorption resins from the seawater samples and separated into four fractions according to higher and lower molecular size, and polarity, respectively.
With increasing age of DOM, the proportion of the humic substances to the total DOC increased from 45% in surface samples to 67% in the deep sea. Similar proportions were obtained for the total carbohydrates. On the other side, the extraction efficiencies of the total sugars as the sum of the individual neutral sugars were much lower, but increased also with depth from 8 to 24%. The significant differences were attributed to the chemical composition of the pool of carbohydrates. Presumably, refractory carbohydrates consist of chemically modified carbohydrates, e.g., charged uronic acids or amino sugars, which are not accessible with the chromatographic method. However, their contribution to the total carbohydrates of the seawater samples is only inferior, as the differences between the two detection methods were only marginal in these samples. More than the half of the XAD-extractable sugars of surface samples and more than 70% of deep sea samples were found in an unpolar fraction, eluted with methanol instead of aqueous solutions. Since also the molecular size of the carbohydrates decreased with increasing state of diagenesis, it was concluded that the vast majority of refractory carbohydrates and a large percentage of total carbohydrates were bound to low molecular-size unpolar compounds.

More information is available at http://elib3.suub.uni-bremen.de/publications/dissertations/E-Diss154_Engbrodt.pdf