Observed tides on the northeastern Bering Sea shelf

Bottom pressure observations (November 1981 to August 1982) show that the diurnal tides dominate the outer reaches of the northeastern Bering Sea shelf. The diurnal tides decrease inshore from the shelf break (maximum K1 amplitude of 38 cm) and appear to be evanescent Sverdrup (Poincare) waves on the outer shelf. The K1 amplitude (2.3 cm) in the Bering Strait is 6% of that at the shelf break. The diurnal phase lags vary little (322°–359°G for the K1 tide) between the stations. North and eastward from the shelf break, the tides become smaller and more semidiurnal. The semidiurnal amplitudes vary considerably between stations; these observations show the effects of semidiurnal amphidromic systems predicted by numerical models. The M2 amplitude (7.6 cm) in the Bering Strait is about a third of that at the shelf break (M2 amplitude of 23 cm). The semidiurnal phase lags are earliest at the shelf break (87°G for M2) and appear to increase toward St. Lawrence Island (336°G for M2 in Shpanberg Strait) and the Bering Strait (202°G for M2). The tidal harmonic constants fluctuated seasonally, possibly in response to the variations in ice cover. The diurnal amplitudes generally increased during winter, while the semidiurnal amplitudes decreased. At the shelf break the K1 amplitude increased 2.5 cm or 7%, but the O1 and semidiurnal M2 amplitudes (0.4 cm or 2% for M2) showed little variation. In Bering Strait the variations in M2 amplitude (up to 3.0 cm) amounted to 37% of the mean amplitude; the decrease may be due to attenuation of the M2 tide from the Arctic Ocean in addition to damping of the M2 tide on the northeastern Bering Sea shelf. Shorter-term fluctuations were also observed in the tides. The tidal fluctuations may contribute to those observed in the deep sea. Numerical models show a set of amphidromic systems (including a semidiurnal system off Cape Navarin) and rapid phase transitions in the vicinity of some of the stations; these models are in relatively good agreement with the observations.

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