Early Pliocene deep water circulation in the western equatorial Atlantic: Implications for high-latitude climate change

Abstract

High-resolution (∼3-4 kyr) stable isotope stratigraphies from sites drilled along a depth transect on Ceara Rise (Ocean Drilling Program Leg 154, Sites 925 and 929) are used to reconstruct the deep water circulation response to the long- and short-term climate changes of the early Pliocene (3.2-4.7 Ma). Over the long term, benthic foraminiferal carbon isotope records show that the vertical δ13C gradient in this region was similar to that of the late Holocene, implying a steady flux of Northern Component Deep Water (NCDW) into the deep Atlantic during most of the early Pliocene. The vertical benthic foraminiferal oxygen isotope gradient is reversed with respect to that of the late Holocene. On the basis of density constraints imposed by seawater stability along this depth transect we attribute the reversed gradient to warmer and more saline NCDW (5°C and 35.1). On orbital timescales we find that the phase relationship between δ18O and δ13C values at the deeper Site 929 differs from the late Pliocene/Pleistocene, while that at the shallower Site 925 was essentially the same.