Publication Date:
2017-01-27
Description:
Abundant hydroclimatic evidence from western Amazonia and the adjacent Andes documents wet
conditions during Heinrich Stadial 1 (HS1, 18–15 ka), a cold period in the high latitudes of the North
Atlantic. This precipitation anomaly was attributed to a strengthening of the South American summer
monsoon due to a change in the Atlantic interhemispheric sea surface temperature (SST) gradient.
However, the physical viability of this mechanism has never been rigorously tested. We address this
issue by combining a thorough compilation of tropical South American paleorecords and a set of
atmosphere model sensitivity experiments. Our results show that the Atlantic SST variations alone,
although leading to dry conditions in northern South America and wet conditions in northeastern Brazil,
cannot produce increased precipitation over western Amazonia and the adjacent Andes during HS1.
Instead, an eastern equatorial Pacific SST increase (i.e., 0.5–1.5 °C), in response to the slowdown of
the Atlantic Meridional Overturning Circulation during HS1, is crucial to generate the wet conditions in
these regions. The mechanism works via anomalous low sea level pressure over the eastern equatorial
Pacific, which promotes a regional easterly low-level wind anomaly and moisture recycling from central
Amazonia towards the Andes.
Repository Name:
EPIC Alfred Wegener Institut
Type:
Article
,
isiRev
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