Total dissolved carbohydrates were analyzed in interstitial water samples collected from 30-cm-long whole-round sediment core sections. Interstitial waters were extracted aboard ship within hours of core retrieval. The outer edge of each sediment core section was first removed and the remaining sediment was then placed in a titanium sediment squeezer for interstitial water extraction. Extracted interstitial waters were filtered through a 0.45-µm filter (polysulfone) into acid-washed syringes. Aliquots for DCHO analyses were transferred to muffled (550°C) glass vials that were sealed with polytetrafluoroethylene (PTFE)-lined septa. Samples were stored at 4°C and transported to Old Dominion University (ODU) (Norfolk VA, USA) for shore-based analysis.
Total dissolved carbohydrates were determined spectrophotometrically using a modification of the 3-methyly-2-benzothiazolinone hydrazone hydrochloride (MBTH) procedure described by Pakulski and Benner (1992). In this technique, all dissolved carbohydrates in a water sample are first hydrolyzed to individual monosaccharides and then oxidized to alditols. The terminal glycol groups of the alditols are next oxidized to formaldehyde, which is finally determined spectrophoto-metrically with MBTH. Additional details about the analytical procedures used here can be found in Burdige et al. (2000).
All carbohydrate concentrations reported here were based on standard curves constructed from glucose standards that are hydrolyzed and analyzed along with samples, yielding total carbohydrate concentrations that are "glucose equivalent" concentrations. Glucose equivalent concentrations were multiplied by 6 to express concentrations on a per mole-carbon basis, since each glucose molecule contains 6 carbon atoms (see Pakulski and Benner, 1992, for additional details).