Pliocene-Pleistocene shifts in tropical Atlantic Ocean-atmosphere coupling

Author(s): deMenocal, Peter B.; Raymo, M.; Lynch-Stieglitz, Jean; Philander, G.
Author Affiliation(s): Primary:
Lamont-Doherty Earth Observatory, Palisades, NY, United States
Other:
Boston University, United States
Georgia Institute of Technology, United States
Princeton University, United States
Volume Title: AGU 2006 fall meeting
Source: Eos, Transactions, American Geophysical Union, 87( Fall Meeting Suppl.); American Geophysical Union 2006 fall meeting, San Francisco, CA, Dec. 11-15, 2006. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0096-3941 CODEN: EOSTAJ
Note: In English
Summary: During boreal summer, south equatorial trades winds associated with the West African monsoon cross the equator and establish surface ocean divergence, upwelling, and cool SSTs in the eastern equatorial Atlantic. This seasonal ocean-atmosphere coupling also exists over orbital timescales. Late Pleistocene paleoceanographic records show strong, in-phase coherence between precessional (seasonal) insolation forcing, summer monsoonal intensity, and equatorial Atlantic SSTs. This has not always been so, however. Measurements of SSTs, upwelling, and vertical oxygen isotopic gradients at ODP Site 662 in the eastern equatorial Atlantic demonstrate several fundamental shifts in the response of the surface ocean to orbital forcing. During the mid-Pliocene warm period (3.2-2.9 Ma) Site 662 SSTs were warm, the thermocline was deep, and orbital-scale upwelling variability was weak at all bands, consistent with "permanent El Nino" evidence from the tropical Pacific. After 2.8 Ma, however, the tropical Atlantic became responsive to orbital forcing, but only at the 41 ka obliquity period. The phasing shows that the tropical Atlantic significantly led high-latitude ice volume and likely originated as responses to mean annual insolation changes at southern mid- to high-latitudes. The first appearance of strong precessional upwelling variability occurred only after the latest Pliocene and tropical SST variability increased markedly after this time. This may reflect the first development of a seasonally-shoaling thermocline in response to seasonal (precession) monsoonal forcing. Together, the tropical paleoceanographic data indicate increasingly greater sensitivity to orbital forcing after roughly 2.8 Ma and subsequently after 1.8 Ma.
Year of Publication: 2006
Research Program: ODP Ocean Drilling Program
Key Words: 12 Stratigraphy, Historical Geology and Paleoecology; Air-sea interface; Atlantic Ocean; Boreal environment; Cenozoic; Climate forcing; Equatorial Atlantic; Isotope ratios; Isotopes; Leg 108; Monsoons; Neogene; O-18/O-16; ODP Site 662; Ocean Drilling Program; Orbital forcing; Oxygen; Paleo-oceanography; Pleistocene; Pliocene; Quaternary; Sea-surface temperature; Stable isotopes; Terrestrial environment; Tertiary; Thermocline; Tropical environment; Upwelling; Winds
Coordinates: S012325 S012324 W0114421 W0114421
Record ID: 2009063346
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