Early history of the Arctic Ocean

摘要

The Lomonosov Ridge divides the Arctic Ocean into two basins with different histories. The older Amerasian Basin consists of a ridge‐basin complex reflecting multiple tectonic cycles that are poorly understood. The younger Eurasian Basin includes the present Arctic Mid‐Ocean Ridge. Its origin is linked to Cenozoic spreading. The entire older sediment record of the Arctic Ocean is known from only four short piston cores, all recovered from the Alpha Ridge of the Amerasian Basin. The oldest sediment recovered is a single core of black mud consisting of abundant terrestrial plant material deposited in a marine environment. Dinoflagellates are late Campanian. The black mud resulted from rapid accumulation of organic matter rather than from any of the well‐known Cretaceous anoxic events. Two cores taken 100 to 200 km from the black mud consist of late Maastrichtian siliceous ooze of diatoms and silicoflagellates. This sediment has been interpreted to represent oceanic upwelling and high productivity in the Late Cretaceous Arctic Ocean. A Paleogene core consisting of similar biogenic silica has been recovered approximately 100 km from the Cretaceous cores. Silicoflagellates of this core are either Paleocene or middle to late Eocene. The sediment, like that of the Maastrichtian cores, has been interpreted to represent oceanic upwelling and high productivity. The older Arctic cores were recovered as a result of fortuitous sampling in areas of thin late Cenozoic sediment. All other Arctic cores consist of late Cenozoic sediment. The older sediment record is strong evidence of a Late Cretaceous to early Paleogene Arctic Ocean with no perennial ice and with high productivity of dinoflagellates or siliceous organisms in water that circulated with lower‐latitude oceans. Recent modeling predicts some of the same climatic and oceanographic events recognized in the oldest sediment of the Arctic Ocean. The sequence of events from a warm Arctic Ocean to an ice‐covered condition involved circulation changes, seasonality, and uneven spreading rates that increased North Atlantic‐Arctic