The role of dissolved organic matter release in the productivity of the oligotrophic North Pacific Ocean

Abstract

Based on a long‐term set of observations and measurements at a station in the subtropical North Pacific Ocean, it now appears that contemporaneous rates of primary production in low‐nutrient open ocean regions and perhaps in the ocean as a whole may be greater than had been considered in field studies conducted in previous decades. Data collected at the Hawaii Ocean Time‐Series (HOT) Station ALOHA from October 1988 to July 1997 indicate that daytime particulate organic carbon (POC) production, based on 12‐h 14C in situ incubations, averages 472 mg C m−2 d−1 (SD = 125 mg C m−2 d−1; n = 70). This carbon production rate is two‐ to three‐fold greater than most of the pre‐1980 estimates. We present evidence that particulate production rates may have been overestimated by up to 30% as a result of 14C‐labeled dissolved organic carbon (14C‐DOC) adsorption onto glass fiber filters. More importantly, when one considers the 14C‐DOC that is produced but not adsorbed onto the filters, gross primary production rates (14C‐POC plus 14C‐DOC) in the subtropical North Pacific Ocean may approach 1 g C m−2 d−1. We hypothesize that the large flux of 14C‐DOC may be a manifestation of decade‐scale habitat changes resulting from variations in climate. The balance between POC and DOC production will ultimately influence the structure of the food web, especially the interactions of phytoplankton and heterotrophic bacterial populations, and the mechanisms and rates of carbon sequestration by the biological pump.