Spectrophotometric measurement of seawater carbohydrate concentrations in neritic and oceanic waters from the U.S. Middle Atlantic Bight and the Delaware estuary

Total carbohydrate concentrations were measured in unfiltered seawater samples collected in the U.S. Middle Atlantic Bight during spring 1998, and in the Delaware Estuary during fall 1998. Surface and vertical profiles were determined in five distinct marine regimes: the Delaware Estuary; the continental shelf; the continental shelfbreak; the Gulf Stream; and the oligotrophic ocean at the Bermuda Atlantic Time Series Station (BATS). Concentrations of free monosaccharides [MCHO] were measured at sea using the spectrophotometric reagent 2,4,6-tripyridyl-s-triazine (TPTZ). Total seawater carbohydrate concentrations [TCHO] were determined after acid hydrolysis with 0.09 N HCl, and acid-hydrolyzable polysaccharide concentrations [PCHO] were calculated by difference, assuming [TCHO]=[PCHO]+[MCHO]. Total carbohydrates comprised 4–14% of the total organic carbon (TOC) in these waters. Free monosaccharides were measurable only in neritic waters; in oligotrophic surface waters, free monosaccharide concentrations were below detection limits using the TPTZ method. Total carbohydrates measured in surface waters during spring 1998 decreased 1.9-fold from the continental shelf to BATS, from 16.9 μM C in the Delaware Estuary to 8.7 μM C at BATS. The highest concentration of total carbohydrates was measured within the Delaware estuary during fall 1998. Total carbohydrate concentrations of 67.2 μM C were measured at station 03, the least saline (salinity=11.4 ppt) site examined in this study. Seven estuarine seawater samples were analyzed using the TPTZ method and compared to values obtained using the more established, 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) method. Our results show that the TPTZ method detected similar polysaccharide and total carbohydrate values as the MBTH method, but it was less precise than the MBTH method for determining monosaccharide concentrations in seawater.