Stocks and Distribution of Carbohydrates and the Bioreactivity of DOC Along Meridional Transects in the North Atlantic Basin

Oceanic dissolved organic carbon (DOC) demonstrates a broad range of bioreactivity with turnover rates ranging from seconds to millennia. While the majority of dissolved organic matter remains uncharacterized through current chemical analyses, the ratio of total hydrolyzable carbohydrate (TCHO) contribution to bulk DOC does provide insight into the bioreactivity of DOC (Cowie and Hedges, 1994). Here we present a high spatial resolution data set of TCHO, dissolved combined neutral sugars (DCNS) and the ratio of TCHO and DCNS to the bulk DOC pool over the surface 1000 m. The samples were collected during two meridional transects of the U.S. Repeat Hydrography Program conducted in the North Atlantic during the autumn of 2003. Vertically, the TCHO concentrations were highest in the surface 50 m and decreased over 1000 m. Meridionally, TCHO were most concentrated in subtropical and tropical latitude surface waters (15-19 μ M C) yet the ratio of TCHO:DOC in these waters decreased from 26% in the subtropical latitudes to < 21% in more permanently stratified regions. Such a trend indicates an overall decrease in the degree of bioreactivity of bulk DOC from 35° N to the south concomitant with increased stratification. Interestingly, the highest levels of bacterial productivity did not coincide with the regions of high TCHO:DOC. Because TCHO pool consists of hydrolyzed material that is both labile and recalcitrant in nature, use of the TCHO:DOC as an index bioreactivity reveals that the TCHO portion of the DOC pool is reactive on longer time scales than those used to support rapid and instantaneous heterotrophic bacterial production.