AbstractData are presented on the particulate and dissolved organic carbon at Eniwetok Atoll in the Pacific and of particulate organic carbon at South Caicos in the Caribbean. Some data from other locales are included for comparison. Proportionate increases are greater for the particulate matter released from off reefs than for the dissolved; in fact, the net flux of dissolved matter is sometimes negative.Particulate matter, in this case of the size and kinds retained on micro‐filters, is dominated by fragments and amorphous material of mixed origins. Phytoplankton is sparse in such environments.