Variations in the difference between mean sea level measured either side of Cape Hatteras and their relation to the North Atlantic Oscillation
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We consider the extent to which the difference in mean sea level (MSL) measured on the North American Atlantic coast either side of Cape Hatteras varies as a consequence of dynamical changes in the ocean caused by fluctuations in the North Atlantic Oscillation (NAO). From analysis of tide gauge data, we know that changes in MSL-difference and NAO index are correlated on decadal to century timescales enabling a scale factor of MSL-difference change per unit change in NAO index to be estimated. Changes in trend in the NAO index have been small during the past few centuries (when measured using windows of order 60–120 years). Therefore, if the same scale factor applies through this period of time, the corresponding changes in trend in MSL-difference for the past few centuries should also have been small. It is suggested thereby that the sea level records for recent centuries obtained from salt marshes (adjusted for long-term vertical land movements) should have essentially the same NAO-driven trends south and north of Cape Hatteras, only differing due to contributions from other processes such as changes in the Meridional Overturning Circulation or ‘geophysical fingerprints’. The salt marsh data evidently support this interpretation within their uncertainties for the past few centuries, and perhaps even for the past millennium. Recommendations are made on how greater insight might be obtained by acquiring more measurements and by improved modelling of the sea level response to wind along the shelf.
KeywordsTide gauge measurements Salt marsh sediments Mean sea level variability Gulf Stream North Atlantic Oscillation Meridional overturning circulation
All observational data used in this paper may be obtained from the sources mentioned above, while model data may be obtained from P.L. Woodworth (email@example.com) or M.Á. Morales Maqueda (firstname.lastname@example.org). Andrew Kemp (Tufts University) is thanked for comments on a draft of this paper, especially for advice on the regional salt marsh records, and for the data in Fig. 7. We thank our colleagues Antony Long, Tasha Barlow and Margot Saher in the UK Natural Environment Research Council (NERC) project “North Atlantic sea-level variability during the last half-millennium” (NE/G004757/1) for many discussions on North Atlantic sea level change. In addition, we are grateful to three reviewers for their useful comments. The NERC project “Climate variability in the North Atlantic Ocean: wind-induced changes in heat content, sea level and overturning” (NE/H02087X/1) also provided input to this study. Part of this work was funded by UK Natural Environment Research Council National Capability funding. Some of the figures in this paper were generated using the Generic Mapping Tools (Wessel and Smith 1998).
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