The Lamont Earth Science Colloquium presents:
From Pacific to Atlantic deep water formation over the last 66 million years
Dr. David Hutchinson, Researcher, University of South Wales, Sydney.
During the Cenozoic Era (66 to 0 million years ago; Ma), the ocean's meridional overturning circulation has alternated between North Pacific and North Atlantic sinking modes. Proxy evidence suggests that North Pacific sinking occurred through much of the early Cenozoic, with North Atlantic sinking being either absent or weak. Around the Eocene-Oligocene transition (34 Ma), North Atlantic sinking may have either switched on or strengthened significantly, in a long-term transition towards its modern state. North Pacific sinking appears to have gradually weakened at the same time, although some evidence exists of North Pacific sinking during later warm intervals of the Miocene and Pliocene.
Here I explore two hypotheses for why these transitions occurred. First, changes in ocean gateways between the Arctic and Atlantic Ocean may have triggered the overturning changes. This is because the Arctic surface ocean was much fresher (lower salinity), due to a more enclosed Arctic Ocean basin and net precipitation over evaporation in the high latitudes. This Arctic freshwater could have a strong influence on North Atlantic surface density, leading to Atlantic sinking switching off or on at certain intervals. Second, the long-term decline of CO2 through the Cenozoic could also drive a transition from Pacific to Atlantic sinking. This occurs since the hydrological cycle is enhanced at higher CO2, which feeds back upon the Arctic-Atlantic freshwater balance. In addition, warmer ocean temperatures more easily enable Pacific sinking than colder temperatures, due to the seawater equation of state. I will present coupled climate model simulations from several intervals that explore each of these mechanisms. These simulations show that both ocean gateways and CO2 forcing can strongly influence the prevalence of Atlantic or Pacific overturning.
Host: Dr. Bärbel Hönisch is a Professor of Earth and Environmental Sciences, Geochemistry at Lamont-Doherty Earth Observatory.
The Earth Science Colloquium Series, sponsored by Lamont-Doherty Earth Observatory and Columbia University Department of Earth and Environmental Sciences (DEES), provides a lively forum for discussing a wide variety of topics within the Earth sciences and related fields. Colloquia are attended by the full range of scientific and technical staff at LDEO. Colloquium attendance is required of all pre-orals DEES graduate students.
