ESP SPECIAL GUEST SEMINAR - THURSDAY 14 MARCH

[Earth System Physics Section]

Earth System Physics
SPECIAL GUEST SEMINAR
Thursday, 14 March - 11:00
Central Area, 2nd Floor, ex-SISSA Bldg.

Joke Lübbecke
GEOMAR
Germany

Understanding Tropical Atlantic Warming over the Last Decades

The tropical Atlantic has warmed in recent decades, in particular in the 
equatorial and coastal upwelling regions. This warming was not directly 
forced by local heat exchange with the atmosphere, and also wind stress 
in the tropical Atlantic that drives oceanic upwelling rather increased 
than decreased. Remote forcing from outside the tropical Atlantic might 
thus have played a role.

In this presentation, the contribution of different potential drivers is 
assessed utilizing a series of hindcast and sensitivity experiments with 
a high-resolution ocean model. It is shown that both an increase in the 
inflow of warm Indian Ocean waters through Agulhas leakage and a 
slowdown of the Atlantic Meridional Overturning Circulation (AMOC) can 
lead to a general warming in the tropical Atlantic ocean.

Compared to a control simulation, an experiment in which Agulhas leakage 
was artificially increased by strengthening the Southern Hemisphere 
Westerlies shows a pronounced warming trend in the upper tropical 
Atlantic Ocean. The SST pattern that arises in response to an idealized 
slowdown of the AMOC due to enhanced freshwater input around Greenland 
is reminiscent of the observed warming trend. In this context, the role 
of the Atlantic subtropical-tropical cells (STCs) and in particular the 
strengthening of the northern cell is discussed. Mean pathways and 
transports between the subtropical and tropical Atlantic Ocean are also 
inferred from Argo observations for the last decade.