Abstract
Observation‐based estimates of the Atlantic Meridional Overturning Circulation (AMOC) and meridional heat transport (MHT) are necessary to better understand their evolution in the coming years. The RAPID‐MOCHA‐WBTS array at 26°N is the only trans‐Atlantic observing system to provide 20+ years of continuous measurements of the AMOC and MHT. While the design of the array has continuously evolved as our understanding of the AMOC has advanced, and as new technologies have become available, a new goal is to design a lower‐cost and more sustainable observing system to continue AMOC estimations with high accuracy. Using the RAPID array data and ocean reanalyzes, we evaluate the error in the AMOC estimate due to the choice of data included in its calculation. We find that the trend and variability of the volume transport in the upper 3,000‐m of the water column are not captured with sufficient accuracy by synoptic hydrographic data or ocean reanalyzes. However, moorings in the deep ocean interior along the eastern boundary and the Mid‐Atlantic ridge can be replaced by hydrographic data from repeat trans‐Atlantic hydrographic sections to reliably estimate the AMOC trend and variability. Experiments simulating the observing system in a high‐resolution ocean model further show that the additional error in the long‐term AMOC estimate induced by the substitution of mooring measurements below 3,000‐m depth at these locations is small (0.30 Sv) as compared to the AMOC uncertainty.
An observing system at 26°N across the North Atlantic, called the RAPID‐MOCHA‐WBTS array, has been designed to observe and understand changes in the Atlantic Meridional Overturning Circulation (AMOC) over time. After more than 20 years of observations, a goal is now to redesign the array into a less expensive and more sustainable observing system to keep monitoring the AMOC in the future. We show that moorings localized below 3,000‐m depth on each side of the Mid‐Atlantic ridge and at the eastern boundary of the array could be replaced by data from repeat trans‐Atlantic hydrographic sections without losing accuracy in the AMOC estimate and without modifying the AMOC trend or its uncertainty. However, the risk of using ocean reanalysis or hydrographic data instead of moorings at the western boundary or in the upper 3,000‐m depth at the eastern boundary is unacceptably high, meaning that the moorings at these locations and depths are an essential part of the 26°N observing system.
Moorings at the western boundary and in the upper 3,000‐m depth of the array are an essential part of the 26°N observing system Hydrographic sections can replace the deepest moorings along the eastern boundary and the Mid‐Atlantic Ridge to reliably estimate the Atlantic Meridional Overturning Circulation (AMOC) A reduced RAPID array would lead to an additional error that does not compromise the accuracy of the AMOC trend and variability