The Atlantic Meridional Overturning Circulation (AMOC), a system of currents in the Atlantic Ocean that transports warm surface waters northward and cooler, deeper waters southward, is a crucial component of Earth’s climate system. Because the AMOC is part of a conveyor belt of oceanic circulation that redistributes heat around the globe, variability in its strength can have significant climate consequences.
Previous modeling studies have concluded that the AMOC’s strength is negatively correlated to sea level along the New England coastline, such that a weakening of the North Atlantic Current or the Gulf Stream leads to a rise in sea level at the coast. This relationship, however, has been difficult to detect in observational records.
Now Piecuch et al. are challenging the conventional wisdom that a direct causal connection exists between the AMOC and coastal sea level in this region. After obtaining monthly RAPID monitoring program observations of the overturning circulation at 26°N and monthly sea level recordscollected between 2004 and 2017 at eight New England tide gauges, the team examined the physical relationships between the two records.
The authors concluded that widespread atmospheric teleconnections can simultaneously trigger changes in both the AMOC at 26°N and coastal New England sea level. Although these phenomena are temporally correlated with each other, the team concludes that they are not causally linked. The researchers argue that the local atmospheric forcing mechanisms driving coastal New England sea level change are instead related to the North Atlantic Oscillation and other surface atmospheric variations.
Although this study represents a valuable contribution to improving our understanding of how coastal sea level is related to oceanic circulation, the authors caution that their results apply to only the time period studied and that the negative correlation between coastal sea level and overturning at 26°N should not be considered representative of the AMOC at other latitudes. The researchers suggest that future studies could shed new light on the processes occurring at higher latitudes, where new AMOC monitoring arrays have recently been established. (Geophysical Research Letters, https://doi.org/10.1029/2019GL083073, 2019)
—Terri Cook, Freelance Writer