Carbon flux in the ocean's twilight zone

The twilight zone in the ocean falls between the sunlit photosynthetic layer at the surface and depths below 1,000 meters. New measurements by Ken O. Buesseler of Woods Hole Oceanographic Institute and colleagues show that the variability in the amount of carbon passing through this zone could dramatically change calculations for carbon storage in the deep ocean (Science 2007, 316, 567). What happens to carbon detritus in the little-studied twilight zone affects how much carbon is transferred from the atmosphere to the depths. The researchers developed neutrally buoyant sediment traps to collect sinking particles. Their measurements at 150 meters and 500 meters deep at two sites in the Pacific Ocean show that plankton and other resident biota have different appetites for the carbon materials. Near Hawaii, only 20% of the sinking carbon made it down to 500 meters, but in the northwestern Pacific, 50% of the carbon matter did. The researchers estimate that this variance could change previous global carbon sequestration estimates by as much as 3 petagrams (10¹⁵ g) per year.