Evolution of ocean circulation in the North Atlantic Ocean during the
Miocene: impact of the Greenland ice sheet and the eastern Tethys seaway
Abstract
Modern Ocean is characterized by the formation of deep-water in the
North Atlantic (i.e. NADW). This feature has been attributed to the
modern geography, in which the Atlantic Ocean is a large basin extending
from northern polar latitudes to the Austral Ocean, the latter enabling
the connection of the otherwise isolated Atlantic with the Pacific and
Indian Oceans. Sedimentary data date the establishment of the NADW
between the beginning of the Eocene (∼49 Ma) and the beginning of the
Miocene (∼23 Ma). The objective of this study is to quantify the impact
of Miocene geography on NADW through new simulations performed with the
earth system model IPSL-CM5A2. We specifically focus on the closure of
the eastern Tethys seaway (dated between 22 and 14 Ma), which allowed
the connection between the Atlantic and Indian Oceans, and on the
Greenland ice sheet, whose earliest onset remains open to discussion but
for which evidence suggest a possible existence as early as the Eocene.
Our results show that the closure of the eastern Tethys seaway does not
appear to impact the establishment of NADW, because waters from the
Indian Ocean do not reach the NADW formation zone when the seaway is
open. Conversely, the existence of an ice sheet over Greenland
strengthens the formation of NADW owing to topography induced changes in
wind patterns over the North Atlantic, which in turn, results in a
larger exchange of water fluxes between the Arctic and the North
Atlantic, and in a re-localization of deep-water formation areas.