1 research outputs found
North Atlantic Midlatitude Surface-Circulation Changes Through the Plio-Pleistocene Intensification of Northern Hemisphere Glaciation
The North Atlantic Current (NAC) transports warm salty water to high northern latitudes, with important repercussions for ocean circulation and global climate. A southward displacement of the NAC and Subarctic Front, which separate subpolar and subtropical water masses, is widely suggested for the Last Glacial Maximum (LGM) and may have acted as a positive feedback in glacial expansion at this time. However, the role of the NAC during the intensification of Northern Hemisphere glaciation (iNHG) at ~3.5 to 2.5 Ma is less clear. Here we present new records from Integrated Ocean Drilling Program Site U1313 (41°N) spanning ~2.8â2.4 Ma to trace the influence of Subarctic Front waters above this midâlatitude site. We reconstruct surface and permanent pycnocline temperatures and seawater δ18O using paired Mg/Caâδ18O measurements on the planktic foraminifers Globigerinoides ruber and Globorotalia crassaformis and determine abundances of the subpolar foraminifer Neogloboquadrina atlantica. We find that the first significant glacial incursions of Subarctic Front surface waters above Site U1313 did not occur until ~2.6 Ma. At no time during our study interval was (sub)surface reorganization in the midlatitude North Atlantic analogous to the LGM. Our findings suggest that LGMâlike processes sensu stricto cannot be invoked to explain interglacialâglacial cycle amplification during iNHG. They also imply that increased glacial productivity at Site U1313 during iNHG was not only driven by southward deflections of the Subarctic Front. We suggest that nutrient injection from coldâcore eddies and enhanced glacial dust delivery may have played additional roles in increasing export productivity in the midlatitude North Atlantic from 2.7 Ma.t. Funding for
this research was provided by IODP
France (C. T. B.) and the German
Research Foundation (DFG) (grant OF
2544/2 to O. F.). I. B. is grateful to the UK
IODP for financial support for shipboard
and post-cruise participation in IODP
Exp. 306. C. T. B., K. T., T. D. G., L. V., C. S.,
and M. E. acknowledge OSU PythĂŠas.
M. M. R. acknowledges support by the
USGS Land Change Science Program