Journal Article

Seasonal Cycle in Sea Level Across the Coastal Zone

Ponte, Rui M., Schindelegger, Michael

2024

Overview

Data from tide gauges and satellite altimeters are used to provide an up‐to‐date assessment of the mean seasonal cycle in sea level (ζ$\\zeta $ ) over most of the global coastal ocean. The tide gauge records, where available, depict a ζ$\\zeta $seasonal cycle with complex spatial structure along and across continental boundaries, and an annual oscillation dominating over semiannual variability, except in a few regions (e.g., the northwestern Gulf of Mexico). Comparisons between tide gauge and altimeter data reveal substantial root‐mean‐square differences and only slight improvements in agreement when using along‐track data optimized for coastal applications. Quantification of the uncertainty in the altimeter products, inferred from comparing gridded and along‐track estimates, indicate that differences to tide gauges partly reflect short‐scale features of the seasonal cycle in proximity to the coasts. We additionally probe the ζ$\\zeta $seasonal budget using satellite gravimetry‐based manometric estimates and steric terms calculated from the World Ocean Atlas 2023. Focusing on global median values, the sum of the estimated steric and manometric harmonics can explain ∼${\\sim} $65% (respectively 40%) of the annual (semiannual) variance in the coastal ζ$\\zeta $observations. We identify several regions, for example, the Australian seaboard, where the seasonal ζ$\\zeta $budget is not closed and illustrate that such analysis is mainly limited by the coarse spatial resolution of present satellite‐derived mass change products. For most regions with a sufficiently tight budget closure, we find that although the importance of the manometric term generally increases with decreasing water depth, steric contributions are non‐negligible near coastlines, especially at the annual frequency. Key Points Altimetry and tide gauges disclose the complex spatial structure of the mean sea level seasonal cycle from the coast to adjacent deep waters Sum of steric and manometric effects, deduced from observations, explains ∼65% of the annual sea level variance in global set of tide gauges Satellite gravimetry is useful for examining near‐shore manometric seasonality but coarse spatial resolution remains a limiting factor

• Publisher: John Wiley & Sons, Inc,American Geophysical Union (AGU)
• Subject: Altimeters / Beaches / Climate change / Coastal zone / Coasts / Gauges / GRACE / Gravimetry / Oceans / Rivers / satellite altimetry / Sea level / sea level budget / seasonal cycle / tide gauge / Time series / Water depth