Sea-level fluctuations show ocean circulation impact on Atlantic multidecadal variability

We present observational evidence that ocean circulation controls the decadal evolution of heat content and consequently sea-surface temperatures (SST) in the North Atlantic. Positive (negative) phases of the Atlantic multidecadal oscillation (AMO) are associated with warmer (cooler) SSTs in the North Atlantic. Phases of the AMO have been linked with decadal climate fluctuations. It is widely believed that Atlantic circulation determines the phases of the AMO by controlling the decadal changes in heat content in the North Atlantic. However, due to the lack of ocean circulation observations, this link has not been previously proven.

The sea-level gradient along to the east coast of the United States is used to derive a measure of ocean circulation spanning nine decades. This index is closely related to the Gulf Stream and the position of the Gulf Stream North Wall, marking the inter-gyre boundary. We relate this index to heat-content changes, and use the longevity of the tide gauge record to show that circulation changes, as represented by sea-level gradient changes, have driven the major transitions in the AMO since the 1920’s

We show that the North Atlantic Oscillation is closely related to this sea-level gradient, indicating that the atmosphere drives the temporal pattern of the circulation changes. The circulation changes are essentially integrated by the ocean in the form of ocean heat content and returned to the atmosphere via the AMO.

An additional consequence of our interpretation is that recently reported accelerations in sea-level rise along the US east coast are consistent with a decline in the AMO that has been predicted by a number of authors.