MICROFOSSIL EVIDENCE FOR EARLY PLEISTOCENE DEFLECTION OF THE GULF STREAM AT CAPE HATTERAS

The Slope Water recirculation gyre consists of cyclonic transport of 30 to 40 Sv of cool and low salinity Coastal Labrador Sea Water between the subtropical gyre (Gulf Stream) and the North American margin as far south as Cape Hatteras. The biogeographic importance of the deflection of the Gulf Stream from the margin is evident in the distinct benthic foraminiferal provinces identified in modern sediments north and south of Cape Hatteras. The Slope Water mass differs from the subtropical gyre in having substantially higher terrigenous influx and productivity, and lower salinities and temperatures. The existence of this mass above the New Jersey margin is recorded by benthic and planktonic foraminiferal data from DSDP Site 604 as well as palynological data from this site and from ODP Sites 1072 and 1073. Micropaleontological proxies in sediments deposited at these sites prior to ~1.36 m.y. ago, however, record more "oceanic" conditions (i.e. more saline, warmer, and with lower terrigenous flux) than presently exist off New Jersey. We suggest that around 1.36 m.y. ago the Gulf Stream had cooled and intensified sufficiently to cause the subtropical gyre to contract, allowing Coastal Labrador Sea Water across the Grand Banks and along the continental margin to Cape Hatteras. The establishment of a "warm" ice margin benthic foramineral fauna (Elphidium excavatum, Cassidulina reniforme and Epistominella takayanagii) by ~1.19 m.y. ago reflects the southeastward expansion of North American ice sheets once the moderating effect of the Gulf Stream was deflected at Cape Hatteras rather than the Grand Banks. This would eventually allow ice sheets to reach the coast, depositing the terminal moraine which is Long Island.