18 October 2019

The Relationship Between U.S. East Coast Sea Level and the Atlantic Meridional Overturning Circulation: A Review

Science

Here, we review this research, finding consistent support in numerical models for an antiphase relationship between AMOC strength and dynamic sea level. However, simulations exhibit substantial along‐coast and intermodel differences in the amplitude of AMOC‐associated dynamic sea-level variability. Observational analyses focusing on shorter (generally less than decadal) timescales show robust relationships between some components of the North Atlantic large‐scale circulation and coastal sea-level variability, but the causal relationships between different observational metrics, AMOC, and sea level are often unclear. We highlight the importance of existing and future research seeking to understand relationships between AMOC and its component currents, the role of geostrophic processes near the coast, and the interplay of local and remote forcing. Such research will help reconcile the results of different numerical simulations with each other and with observations, inform the physical origins of covariability, and reveal the sensitivity of scaling relationships to forcing, timescale, and model representation. This information will, in turn, provide a more complete characterization of uncertainty in relevant relationships, leading to more robust reconstructions and projections.

 

Impact

This paper reviews the nature of this relationship and whether, and when, it is evident in climate models and observations. Although the current generation of large‐scale climate and ocean models generally show an antiphase relationship between basin‐scale ocean current strength and coastal sea level, the spatial pattern of sea-level change differs from theory and between models. Supported by existing and emerging research, the authors hypothesize that these deviations result from important physical processes occurring on the continental shelf and slope, and the complexities of the 3‐dimensional ocean circulation. A quantitative assessment of the importance of these processes is critical for understanding past and future climate and sea-level changes in this heavily populated and vulnerable region.

 

Summary

An antiphase relationship between large‐scale North Atlantic meridional volume transport and U.S. East Coast DSL is broadly evident across a range of numerical simulations and observational analyses. This relationship can be interpreted using the simple geostrophic framework introduced in section 3. However, such a framework is insufficient to explain the widely differing along‐coast AMOC‐DSL scalings derived in models and observations or variation across climate models. Furthermore, such an interpretation limits causal attribution: Geostrophy cannot provide information about the forces that drive sea-level changes.

Contact
Aixue Hu
National Center for Atmospheric Research (NCAR)
Publications
Little, C, A Hu, C Hughes, G McCarthy, C Piecuch, R Ponte, and M Thomas.  2019.  "The Relationship Between U.S. East Coast Sea Level and the Atlantic Meridional Overturning Circulation: A Review."  Journal of Geophysical Research: Oceans.  https://doi.org/10.1029/2019jc015152.