North Atlantic Surface and Deep-Water Hydrography during the Early Pliocene Warm Period

Wednesday, 17 December 2014: 8:45 AM
Antje H L Voelker1, Helen F Evans2, Bernhard David Naafs3, Catarina Dinis Cavaleiro1,4, Andreia Rebotim4, Cristina Ventura1, Ruediger H Stein5 and James E T Channell6, (1)Instituto Português do Mar e da Atmosfera (IPMA), Divisão de Geologia e Georecursos Marinhos, Lisbon, Portugal, (2)Integrated Ocean Drilling Program, College Station, TX, United States, (3)Cabot Institute, University of Bristol, Organic Geochemistry Unit, School of Chemistry, Bristol, United Kingdom, (4)MARUM - University of Bremen, Bremen, Germany, (5)Alfred Wegener Institute Helmholtz-Center for Polar and Marine Research Bremerhaven, Bremerhaven, Germany, (6)University of Florida, Ft Walton Beach, FL, United States
The early Pliocene, with atmospheric carbon dioxide concentrations at levels similar to today, is seen as a case study for Earth’s future climate evolution. During this period the progressive closing of the Central American Seaway led to increased poleward heat and salt transport within the Atlantic with North Atlantic Deep Water (NADW) becoming warmer and saltier and resulting in an enhanced Atlantic Meridional Overturning Circulation (AMOC). In order to understand how stable the AMOC really was we produced millennial-scale (1-2 kyr) surface and deep-water records for IODP Site U1313 (41°N, 33°W, 3412m) for the interval from 3.4 to 4.1 Ma. This site is ideally located to monitor past AMOC changes with North Atlantic Drift waters at the surface and NADW in the deep. Although interglacial/glacial cycles are visible, the higher frequency oscillations recorded in both the planktonic G. ruber (white) and benthic Cibicidoides sp. δ18O records impede tuning to the LR04 stack (Lisiecki and Raymo, 2005). We therefore exploit a different approach: using the magnetic polarity chrons (Gilbert, Cochiti) as recorded at Site U1313 as framework, we tune our benthic δ18O record to that of ODP Site 1085 (on LR04 ages). The benthic δ13C record shows millennial-scale oscillations, and the values indicate nearly continuous NADW presence and confirm a strong AMOC, also during most of the glacial periods. Varying surface water conditions, especially during the younger interglacial periods, are reflected in the G. ruber isotope data and appear to be linked to salinity changes since they are not recorded in the alkenone sea-surface temperature data. Although glacial stages Gi 2 and Gi 4 show the expected higher benthic δ18O values, Gi 6 was the glacial period with the strongest impact on the AMOC as revealed by cooler, less ventilated surface waters and a less ventilated NADW. Overall, the AMOC was strong throughout, but experienced high frequency oscillations at a level similar to the middle Pleistocene interglacial periods.

Lisiecki, L.E., Raymo, M., 2005. Paleoceanography 20, PA1003, doi: 10.1029/2004PA001071.