Organic and inorganic carbon production in the Gulf of Maine

Gulf of Maine carbon budgets have not included estimates of calcification r ates and the flux of calcite to the sediments, processes which are thought to rival organic production in terms of carbon ultimately buried in the sed iments. Measurements of inorganic (calcification) and organic (photosynthet ic) carbon production were made in March, June, and November of 1996 throug hout 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 t otal carbon production, or 26 mg C m(-2) d(-1). Calcite (inorganic C) produ ction in June was > 10% of total C production over deeper areas such as Wil kinson Basin, the Northeast Channel, and the shelf break. This ratio was lo west (1.3%) in tidally mixed, high-nutrient regions near Cape Sable and the Bay of Fundy, where diatoms were abundant and euphotic zone nitrate concen trations exceeded 2.2 mu M. The turnover time of calcite particles in the w ater 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 es timated at 182 g m(-2) organic C and 3.7 g m(-2) inorganic C, in the absenc e 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 appro ximately equal amount of each deposited in Gulf sediments. Inorganic carbon production by coccolithophores may therefore be an important contributor t o Gulf and slope sediments, even during the non-bloom conditions studied he re. (C) 2000 Published by Elsevier Science Ltd. All rights reserved.