Climate history in the south Atlantic subtropical gyre over the last 4 Ma
Abstract
The early Pliocene (3-5 Ma) is the most recent time in the Earth’s history when climate was significantly warmer than today. Even though the climatic boundary conditions (i.e. incoming solar radiation, distribution of continents, atmospheric pCO2) were similar to today, the average global temperature was about 3-4°C warmer, ice sheets were smaller, and the sea level was about 35 m higher. Previous studies show that in the early Pliocene, in both Pacific and Atlantic Oceans, sea surface temperatures (SST) of the eastern equatorial and coastal upwelling regions were warmer than today (by ~2-9°C), while western equatorial warm pools had SST similar to today. As a consequence, zonal and meridional SST gradients were reduced. According to atmospheric modeling studies, the reduced gradients played a role in sustaining Pliocene warmth and the increasing gradients, caused by the cooling of the upwelling regions, favored the northern hemisphere glaciation. However, the lack of data from non-upwelling regions forces these models to interpolate SSTs based on the gradients in the modern ocean. This research is the first to provide data from a non-upwelling region in the south Atlantic subtropical gyre. We present G.sacculifer Mg/Ca and δ18O records at the ODP site 1264 (28.53°S; 2.85°E, 2505 m water depth), located on the Walvis Ridge in the south Atlantic subtropical gyre. The Mg/Ca SST record displays no long-term trend over the past 4 Ma. The south Atlantic subtropical gyre was not affected by the forcing that caused the 8-9°C cooling of the Benguela upwelling, as recorded at ODP sites 1082 and 1084. The difference between SST trends at ODP sites 1082 and 1084 and the ODP site 1264 indicate a significant change in SST gradients between south Atlantic subtropical gyre and the Benguela upwelling region. The complementary δ18O record will provide information about local salinity changes due to ice volume changes. The combined records will give us a thorough picture of local changes of the surface water at ODP site 1264 during the Pliocene-Pleistocene climate transition.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFMPP13D1554W
- Keywords:
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- 4900 PALEOCEANOGRAPHY;
- 4924 PALEOCEANOGRAPHY / Geochemical tracers;
- 4944 PALEOCEANOGRAPHY / Micropaleontology;
- 4954 PALEOCEANOGRAPHY / Sea surface temperature