FY 1984

Recent observations of tides and tidal currents from the northeastern Bering Sea shelf

Mofjeld, H.O.

NOAA Tech. Memo. ERL PMEL-57, NTIS: PB84-241785, 36 pp (1984)

Tide and tidal current observations from the Northeastern Bering Sea Shelf and a comparison of these observations with theory and numerical models are reported in this memorandum. Pressure observations (November 1981-August 1982) at seven stations show that the diurnal tides dominate the outer shelf. The diurnal amplitudes (maximum of 38 cm for K1 and 26 cm for 01 at the shelfbreak) decrease exponentially inshore from the shelfbreak at a rate consistent with subinertial Sverdrup waves. The phase lags of the diurnal tides vary little (ranging from 322°G to 359°G for the K1 tide) over the shelf. The semidiurnal amplitudes (maximum of 23 cm for M2 at the shelfbreak) change considerably between stations; on the outer shelf there is some influence of a semidiurnal amphidromic system off Cape Navarin. The phase lags of the semidiurnal tides are earliest at the shelf break (87°G for M2) and increase toward the east and north (202°G for M2 in Bering Strait and 336°G to the east of St. Lawrence Island). The tides become progressively smaller and semidiurnal toward the north and east from the shelfbreak (an M2 amplitude of 7.7 cm and a K1 amplitude of 2.7 cm in Bering Strait). Non-tidal pressure fluctuations become stronger in the same direction, dominating the pressure signal on the Northern Bering Sea Shelf. There are some seasonal variations in the observed tide and tidal current with slightly larger diurnal tidal amplitudes (increases being ~6% for the K1 tide at the shelfbreak and ~33% for the K1 current in Anadyr Strait) and smaller semidiurnal amplitudes (the strongest decreases being ~18% for the M2 tide in Bering Strait and ~10% for the M2 current in Anadyr Strait) during late winter at some stations. Numerical models reproduce the general features of the observed tides and tidal currents.