. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering Circulation and hydrography of Norton Sound 89 Application of the graphical method described by Proudman (1953) to the geometry of the tongue leads then to estimates of a westward advection rate of less than 1 cm/sec along its axis. During July- August 1977 the observed lower-layer current speed at NC-21 off Cape Darby was cm/sec, a compar- able value. During summer 1978 a near-bottom mooring at the same location (LD-5) showed a net flow of less than 1 cm/se
. The Eastern Bering Sea Shelf : oceanography and resources / edited by Donald W. Hood and John A. Calder. Oceanography Bering Circulation and hydrography of Norton Sound 89 Application of the graphical method described by Proudman (1953) to the geometry of the tongue leads then to estimates of a westward advection rate of less than 1 cm/sec along its axis. During July- August 1977 the observed lower-layer current speed at NC-21 off Cape Darby was cm/sec, a compar- able value. During summer 1978 a near-bottom mooring at the same location (LD-5) showed a net flow of less than 1 cm/sec to the northwest—again in agreement. The cause of this sluggish circulation in the eastern lower layer is uncertain, but it is probably the extreme layering which could decouple the lower layer from upper layer motions. It does not appear that basin configuration plays a major role, although the promontory extending from the southern shore formed by Stuart Island may be sufficient to deflect to the north whatever easterly flow exists along that shore, preventing it from entering the eastern sound. There exists, however, no sill between these prom- ontories which might prevent interchange of deeper waters, and there are no observations to support this hypothesis. The case for decoupling of motions at the horizontal interface between upper and lower layers will be examined in more detail below. While upper- and lower-layer circulation appeared decoupled in the eastern sound, time-series observa- tions obtained from the vessel during September and October 1976 did not reveal such decoupling in the western sound. Rather, there was a monotonic decrease in current speed, along with a slight rotation of flow direction, with increasing depth (Fig. 6-9). The four stations with long enough records to allow at least a crude attempt at averaging out the tidal signal (stations 22, 24, 25, and 26) all indicated northwesterly surface flow which became westerly near the bottom. This was in
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