Annual cycle in coastal sea level from tide gauges and altimetry

Tide gauges provide a unique data set extending many decades back in time, but coverage is restricted to continental boundaries and a few oceanic islands and the extent to which the tide gauge records can be used to infer low-frequency, large-scale sea level behavior remains unclear. Since 1992, satellite altimetry provides near-global coverage of sea level variability, including coastal regions. We compare variability at 345 continental and island tide gauge coastal locations and adjacent shallow and deep oceans, as inferred from altimetry. Initial focus is on the dominant annual cycle. On average, annual amplitudes in tide gauges are comparable to but larger than those in the nearby shallow ocean (<200 m). Substantial differences are found in areas adjacent to strong river outflows and narrow coastal currents. The annual cycle in shallow areas is usually enhanced relative to the open ocean, apart from areas with strong western boundary currents offshore. Differences of 1-2 months in annual phases for coastal, shallow, and deep ocean are typical. Our analysis points to the presence of considerable spatial variability in the annual cycle across deep, shallow, and coastal regions, and to the importance of both tide gauge and altimeter measurements for proper resolution and interpretation of such variability.