Local and Remote Forcing of Interannual Sea‐Level Variability at Nantucket Island

The relative contributions of local and remote wind stress and air‐sea buoyancy forcing to sea‐level variations along the East Coast of the United States are not well quantified, hindering the understanding of sea‐level predictability there. Here, we use an adjoint sensitivity analysis together with an Estimating the Circulation and Climate of the Ocean (ECCO) ocean state estimate to establish the causality of interannual variations in Nantucket dynamic sea level. Wind forcing explains 67% of the Nantucket interannual sea‐level variance, while wind and buoyancy forcing together explain 97% of the variance. Wind stress contribution is near‐local, primarily from the New England shelf northeast of Nantucket. We disprove a previous hypothesis about Labrador Sea wind stress being an important driver of Nantucket sea‐level variations. Buoyancy forcing, as important as wind stress in some years, includes local contributions as well as remote contributions from the subpolar North Atlantic that influence Nantucket sea level a few years later. Our rigorous adjoint‐based analysis corroborates previous correlation‐based studies indicating that sea‐level variations in the subpolar gyre and along the United States northeast coast can both be influenced by subpolar buoyancy forcing. Forward perturbation experiments further indicate remote buoyancy forcing affects Nantucket sea level mostly through slow advective processes, although coastally trapped waves can cause rapid Nantucket sea level response within a few weeks. Plain Language Summary The change in the rate of sea‐level rise (SLR) in the northeast coast of the United States in the past few decades was 3–4 times higher than that of the global‐mean SLR. The magnitude of interannual sea‐level variation in this region is even larger than the long‐term change over the last few decades. The causes of interannual sea‐level variation there are not well understood, limiting the knowledge of sea‐level predictability. This study identifies the causality of interannual variations of sea level near Nantucket Island with wind and buoyancy forcing. The latter is the combination of air‐sea heat and freshwater fluxes. These forcings together affect sea level. We employ a method to separate the contributions of wind and buoyancy forcings, both near and away from Nantucket, on Nantucket sea level. Wind contribution is primarily near‐local, from regions northeast of Nantucket along the New England shelf. Local and remote buoyancy for