The role of tropical Pacific sea surface temperature
(SST) variability in the global-scale climate
reorganization that occurred during the last
deglaciation is investigated, using multiproxy
geochemical SST reconstructions in sediment cores
from the eastern equatorial Pacific (EEP).
A detailed view of deglacial and Holocene SST history
is reconstructed from a site near the center of the EEP
cold tongue. Based on Mg/Ca paleothermometry and
dated extensively by radiocarbon, this record reveals
modest surface cooling of ~1.2°C during the Last
Glacial Maximum (LGM). When compared with LGM
temperature anomalies of ~3°C from warmer tropical
waters to the north and west it suggests a reduction of
zonal and meridional SST gradients in the glacial
tropical Pacific, indicative of an El Niño-like time-
averaged SST pattern. The record also constrains the
timing of the last deglaciation at ~20,000 years before
present, and reveals cooler mid-Holocene SSTs,
indicative of an intensified, La Niña-like upwelling
response.
Oxygen-isotope ratios measured in the planktonic
foraminifera Globigerinoides sacculifer and
Globigerinoides ruber in a number of EEP cores are
used as tracers of hydrographic variability in the cross-
equatorial frontal zone between the cold tongue and
the Intertropical Convergence Zone. The meridional
oxygen-isotope gradient, reflecting the gradients in
temperature and salinity, is found to have been weaker
by about 50% during the LGM. Since this gradient is
maintained by upwelling-favorable southeast trade
winds across the equator, it is suggested that the
equatorial trades were weaker in glacial times.
Evidence is presented in support of an intermediate
water link between the Southern Ocean and the EEP
during deglaciation. It is based on comparison of two
radiocarbon-dated climate records from the
Subantarctic and the EEP, which demonstrate low- and
high-latitude synchrony of surface warming and
carbon-isotope variability. It is proposed that the two
regions are linked through temperature variability of
southern source intermediate waters upwelling in the
EEP.
Finally, downcore SST reconstructions based on
alkenone paleothermometry are used to evaluate this
method’s potential for paleoceanographic studies in
this region. Similarities and differences with existing
records from other proxies are highlighted, and it is
concluded that additional steps are needed for reliable
climatic interpretation of alkenone data, including
radiocarbon dating of the alkenones.