Eocene-Oligocene mass accumulation rates of ODP Site 124-707

Brown clay accumulated below the calcite compensation depth (CCD) at the deeper Site 767 throughout this time interval. At the shallower Site 770, nannofossil clay accumulated just above the CCD during middle to late Eocene and early Oligocene time, interrupted by a brief episode of noncalcareous clay deposition in earliest Oligocene time.

Depth backtracking of these sites and the alternation of calcareous and noncalcareous sediments at Site 770 indicate that an abrupt lowering of the CCD by as much as 500 m occurred in the Celebes Sea region in earliest Oligocene time. This event was synchronous with an equally abrupt but larger-magnitude drop in the CCD in the Pacific and Atlantic Oceans, which has been attributed to changes in ocean circulation, increasing biological productivity, and the accelerated influx of cold Antarctic Bottom Water into the deep ocean basins.