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Five cross‐strait hydrographic sections repeated several times during the Gibraltar Experiment in 1985–1986 are used to examine the structure of the interface layer between the inflowing Atlantic waters and outflowing Mediterranean waters in the Strait of Gibraltar. The interface is 60–100 m thick, with a strong vertical salinity gradient identified by fitting individual salinity profiles to a piecewise‐linear, three‐layer model. The interface is deeper, thicker, fresher, and colder on the west end of the strait than in the Narrows, where there is a minimum in thickness and a maximum in salinity gradient. Farther east, the interface thickens again and continues to get saltier, warmer, and shallower. Property variations in all three layers are also cast in terms of the three principal water types involved in the exchange. The traditional Knudsen model of exchange is extended to three layers, assuming that the interface is a transport‐carrying third layer with uniform vertical shear. As much as half of the inflowing or outflowing transport occurs in the interface layer. Transport converges in both the upper and lower layers, implying, over the length of the strait, vertical exchange between layers that is comparable to about half the horizontal exchange. The richness of structure and complexity of interaction between the interface and the upper and lower layers argues against the use of two‐layer models to characterize exchange through the Strait of Gibraltar.

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Located on the extensive continental shelf of the Bering Sea, the Pribilof Islands, Alaska are the site of one of the largest breeding colonies of seabirds in the northern hemisphere. During summer these islands are surrounded by a front that separates vertically homogeneous waters from well stratified waters farther seaward. We studied the front with hydrographic data and the bird distributions with concurrent counts during summer 1977 and spring, summer and fall 1978. Murres (Uris lomvia and U. aalge) sitting on the water aggregated near the front during summer 1977 and probably during summer 1978. Other species, such as northern fulmars (Fulmarus giacialis) and auklets (Aethia pusilla and A. cristatella) were unaffected by the front. We hypothesize that the aggregation of the murres was related to an enhanced availability of their food near the front.

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