Research project IGV| North Atlantic Deep-Water formation initiated by the closure of the Barents Sea Seaway
– a potential trigger for Antarctic glaciation
In this project we propose and test the hypothesis that the deep-water formation was triggered by the closure of the Arctic Ocean from the Atlantic, thus enabling the Atlantic surface water to become salty and dense enough to sink to great depths. The Eocene-Oligocene Transition (EOT, ca 34-33 million years ago) was a time of strong global cooling and the first occurrence of a semi-permanent Antarctic ice sheet. It was also the time that deep-water in the North Atlantic is thought to have formed for the first time.
Project description
Two major theories for the glaciation of Antarctica at the EOT are (i) the separation of South America and Australia from Antarctica and the consequent thermal isolation of Antarctica, and (ii) a large decrease in atmospheric CO2 beyond a threshold required for glaciation. Based on new proxy evidence we propose here a third hypothesis; that Antarctic glaciation was triggered by the closing of the Barents Sea Seaway between the Arctic and Atlantic, which led to the salinification of the North Atlantic and consequent initiation of North Atlantic Deep Water (NADW). The NADW is part of an Atlantic overturning circulation that transports warm surface waters northwards and cold deep waters southwards, resulting in warming of the Northern Hemisphere and cooling of the Southern Hemisphere. Antarctic cooling events are therefore routinely linked to a reduction in NADW formation.
He we test this hypothesis together with existing Antarctic glaciation hypotheses in a new state of the art climate model configuration, CM2.1, using continental distributions and climate conditions of the EOT. Experiments involve varying selected ocean gateways and the atmospheric CO2 concentration. In line with observations, we find that the Atlantic is too fresh to form deep-water during the Eocene and it is instead formed in the Pacific. When the Barents Sea Seaways is closed off and the Arctic is isolated from the Atlantic, deep water starts to form. It is not possible to start deep-water formation by opening the Southern Ocean Gateways around Antarctic or lowering CO2. Our model simulations therefore suggest that the paleogeography of the Arctic-Atlantic regions played a major role in one of the worlds largest climate transitions. They further leave open the question of whether and open connection between the Atlantic and the Arctic, as we have today, will again one day lead to a shutdown of the Atlantic deep-water formation, as the climate warms and the Arctic freshens.
The model is also adapted to simulate the peak greenhouse climate of the early Eocene and thereby able to participate in an International Paleo Model Intercomparison Project (PMIP4) for this period called DeepMIP. Several intercomparison studies have been published already, with many in the pipeline.
Project members
Project managers
Agatha de Boer
Professor of Physical paleoceanography
Members
David Hutchinson
was a postdoc at IGV during the production of the simulations
Helen Coxall
Professor of Marine micropaleontology
Matthew O'Regan
Professor of Marine geology
Johan Nilsson
Professor of Meteorology
Rodrigo Caballero
Professor of Dynamic meteorology
