HR: 11:15h
AN: PP22A-04 INVITED     [Abstracts]
TI: Millennial-Scale Antarctic Intermediate Water Variability over the past 340,000 Years as Recorded by Benthic Foraminiferal δ¹³C in the Mid-Depth Southwest Pacific
AU: * Pahnke, K
EM: kpahnke@mit.edu
AF: Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 United States
AU: Zahn, R
EM: rainer.zahn@icrea.es
AF: Institució Catalana de Recerca i Estudis Avancats (ICREA) i Universitat Autònoma de Barcelona, Institut de Ciencia i Tecnologia Ambientales, ICTA, Edifici Cn - Campus UAB, Bellaterra, E-08193 Spain
AB: Benthic foraminiferal δ ¹³C along a mid-depth core from the Southwest Pacific (MD97-2120, 1210m water depth) exhibits high-amplitude oscillations on orbital to millennial time scales. The variability is consistent with rapid changes in Southern Hemisphere intermediate water ventilation over the past 340,000 years. Close correlation of the benthic δ ¹³C oscillations with Southern Hemisphere temperature changes suggests direct control of ocean-climate processes at high southern latitudes on the formation and characteristics of Antarctic Intermediate Water (AAIW). Low δ ¹³C values during glacial intervals indicate increased upward mixing of deep waters in response to intensified westerlies. Increased northward Ekman freshwater transport stabilized the upper water column and led to reduced rates of intermediate water production, further contributing to decreased δ¹³C. These intervals are punctuated by abrupt positive δ ¹³C excursions that occur in pace with millennial-scale warm anomalies in the Southern Hemisphere and the relaxation of southern westerly winds. The transient ventilation events directly correlate with episodes of enhanced meltwater discharge into the northern North Atlantic and concomitant reduction in North Atlantic Deep Water (NADW) formation. Conversely, abrupt reductions in AAIW production during mid-Termination cold reversals in the Southern Hemisphere, as documented by parallel negative δ ¹³C and SST excursions in the core, correlate with the deglacial resumption of deep overturning in the North Atlantic. The indicated anti-phasing between AAIW and NADW ventilation suggests a tight coupling of Southern Hemisphere meridional overturning to the thermal bipolar seesaw. This adds a THC component to the seesaw and suggests that Southern Hemisphere water mass conversion is actively involved in interhemispheric climate variability.
DE: 1635 Oceans (4203)
DE: 4267 Paleoceanography
DE: 4294 Instruments and techniques
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2005 Joint Assembly