LDEO Earth Science Colloquium presents
The potential Pacific origin of global millennial-scale climate oscillations: Testing a new hypothesis
with Dr. Maureen Walczak, Assistant Professor, University of Washington.
Meltwater from Cordilleran ice into the North Pacific Ocean precedes weakening of Atlantic Meridional Overturning Circulation during millennial-scale climate oscillations of the latest Pleistocene. Efforts to model the impact of North Pacific meltwater input on AMOC and the North Atlantic cryosphere are qualitatively consistent with these observations, however questions remain on whether the Cordilleran Ice Sheet (CIS) could supply the volume of water required to produce these impacts – as well as the possible origins of millennial-scale variability in the Pacific cryosphere. New radiocarbon-dated foraminiferal oxygen isotope records derived from marine sediment cores adjacent to the major southernmost drainages of the Cordilleran Ice Sheet – the Columbia River (CR) and Strait of Juan de Fuca (JdF) – show discharge is most active when the adjacent NE Pacific is at its coldest, likely associated with an ice sheet that is advancing towards or has achieved its greatest southward extent. The majority of the marine margin of the CIS routes meltwater directly into the Alaska Current – the northward flowing limb of the North Pacific Subpolar (or Alaskan) Gyre - contributing to stratification and inhibition of North Pacific overturning. However, available ice sheet models suggest that southward expansion of the CIS effectively increases the drainage basin of the CR and JdF outlets to the north and east. When the ice sheet is at its maximum extent, these same models suggest that >40% of the total discharge of the ice sheet may be routed through the CR and JdF into the Subtropical Gyre via the California Current. This exports buoyant, less-saline seawater southward and favors overturning and northward heat flux in the Pacific. Thus, expansion of the CIS to its maximum position may have established the conditions leading first to its own collapse, then to the retreat of the ice sheets of the North Atlantic. If correct, this hypothesis would suggest that Pacific/Atlantic phased millennial-scale climate oscillations may be triggered by unstable growth and collapse of the CIS. Testing will ultimately require recovery of new high-quality sediment archives that extend past LGM off the southern margin of the CIS, such as may be enabled by the NSF Seafloor Sampling Facility and/or US Scientific Ocean Drilling Program.
Host: Dr. Brendan Reilly, Lamont Associate Research Professor, Biology and Paleo Environment, Director, Lamont Core Repository.
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.
