Organic and inorganic carbon production in the Gulf of Maine

Abstract

Gulf of Maine carbon budgets have not included estimates of calcification rates and the flux of calcite to the sediments, processes which are thought to rival organic production in terms of carbon ultimately buried in the sediments. Measurements of inorganic (calcification) and organic (photosynthetic) carbon production were made in March, June, and November of 1996 throughout the Gulf of Maine and Georges Bank. Photosynthetic rates ranged from 1.3–182 mg C m −3 d −1, and calcification rates from 0–9.3 mg C m −3 d −1, for all depths and locations sampled. June calcite production integrated over the euphotic zone (based on 17 profiles of 6 depths) averaged 5% of total carbon production, or 26 mg C m −2 d −1. Calcite (inorganic C) production in June was >10% of total C production over deeper areas such as Wilkinson Basin, the Northeast Channel, and the shelf break. This ratio was lowest (1.3%) in tidally mixed, high-nutrient regions near Cape Sable and the Bay of Fundy, where diatoms were abundant and euphotic zone nitrate concentrations exceeded 2.2 μM. The turnover time of calcite particles in the water column, estimated from calcite production rates and suspended calcite concentrations, averaged 11.8 days in June and nearly 200 days in November, when calcite standing-stocks were high and calcification rates relatively low. Advective loss of calcite from the Gulf before settling is likely with long turnover times. Yearly carbon production for the Gulf of Maine was estimated at 182 g m −2 organic C and 3.7 g m −2 inorganic C, in the absence of an E. huxleyi bloom. If 1% of the organic carbon produced were buried in sediments, and 50% of the inorganic carbon, the result would be an approximately equal amount of each deposited in Gulf sediments. Inorganic carbon production by coccolithophores may therefore be an important contributor to Gulf and slope sediments, even during the non-bloom conditions studied here.