Department of Earth System Science

To study cycling of organic fractions in the ocean, relative abundances and radio- and stable-carbon isotope measurements of total lipid extract, acid-soluble, and acid-insoluble fractions of suspended particulate organic carbon (POC) were made. Changes in relative abundances occurred mostly in the upper 1000 m of the water column, with a decrease in total lipid extract and the acid-soluble fraction and an increase in the acid-insoluble fraction with increasing depth. We found lower Δ¹⁴C values for total lipid extract and the acid-insoluble fraction than for the acid-soluble fraction, which is consistent with the previous suggestion of incorporation of dissolved organic carbon and/or resuspended sediment to POC (Druffel and Williams, 1990; Sherrell et al., 1998). The Δ¹⁴C values of these fractions in a given organic carbon pool must be understood in terms of acquisition of ¹⁴C-depleted carbon from other carbon pools in addition to aging within the reservoir.