An ARGO and XBT observing system for the Atlantic Meridional Overturning
Circulation and Meridional Heat Transport (AXMOC) at 22.5ºS
Abstract
Changes in the Atlantic Meridional Overturning Circulation (AMOC) and
associated Meridional Heat Transport (MHT) can affect climate and
weather patterns, regional sea levels, and ecosystems. However, despite
its importance, direct observations of the AMOC are still limited
spatially and temporally, particularly in the South Atlantic. The main
goal of this study is to implement a cost-effective trans-basin section
to estimate for the first time the AMOC at 22.5°S, using only sustained
ocean observations. For this, an optimal mapping method that minimizes
the difference between surface in-situ dynamic height and satellite
altimetry was developed to retrieve monthly temperature and salinity
profiles from Argo and XBT data along the 22.5°S section. The mean AMOC
and MHT for 22.5°S were estimated as 15.55±2.81 Sv and 0.68±0.18 PW,
respectively, and are stronger during austral fall/winter and weaker in
spring. The high-resolution XBT data available at the western boundary
are vital for capturing the highly variable Brazil Current, and our
section shows a significant improvement when compared to Argo database.
The mean values, interannual and seasonal time series of AMOC and MHT
were compared with other products. At 22.5S the North Atlantic Deep
Water is divided into two cores that flow along both western and eastern
boundaries near 2500 m depth. Our results suggest a greater influence of
western boundary system on the AMOC variability at 22.5°S; highlight the
importance of high resolution in situ data for AMOC estimations; and
contribute for a better understanding of AMOC and MHT variability in the
South Atlantic.