The accumulation and cycling of biogenic silica in the Southern Ocean: revisiting the marine silica budget

In many of the recent marine silica budgets (e.g., Science 268 (1995) 375), a majority of the worldʹs biogenic silica accumulation is attributed to the siliceous-ooze deposits in the Antarctic deep sea. Based on 230Th-normalized sediment accumulation rates as well as comparative studies of silica preservation (seabed accumulation compared to surface biogenic production), the rate of biogenic silica accumulation in Antarctic siliceous-ooze deposits has been over-estimated by as much as 35%. The current estimate for silica accumulation in these high-latitude deposits is 3.1×1012 mol yr−1 (as compared to previous values of 4.1–4.8×1012 mol yr−1). To maintain balance between silicate supply and biogenic silica removal in the oceans, an additional repository is needed. Evidence from continental shelf and upper slope sediments suggests that biogenic silica accumulation in continental margin deposits may account for a much larger fraction of the marine silica burial than previously thought, compensating for the diminished accumulation in the Antarctic deep sea. If biogenic silica accumulation in continental margin sediments replaces nearly a third of the silica accumulation in the Antarctic deep sea, the marine cycles of organic matter and biogenic silica are coupled to a greater extent than reported in previous budgets.