Observation: I am not sure if this is unusual or not, but could the LEO Network help identify what causes the "oily" looking sheen right below the surface of the water at the points where freshwater flows into the saltwater? I saw this in multiple areas in Hidden Bay, on the east-side of Culross Island in Prince William Sound.
Ecosystem Science Consult: Thomas (Tom) Okey, Director writes, "If this is simply the halocline that Korie is seeing, it is a completely natural phenomenon, which is commonly observed by snorkeling or diving in places like the "fringe" (e.g. fjordal) areas of Prince William Sound where freshwater runoff floats on top of clear salt water. It is true that there is still residual EVOS¹ oil in some of the sediment in some locations, lasting much longer than people thought it would, but what Korie is seeing is most likely just the interface between the buoyant freshwater and the denser salt water, and the turbulence as currents push this interface across reefs, etc."
Tom continues, "So it's not unusual in general, but environmental changes such as changes in precipitation, snowpack, etc, can certainly change the distributions of the halocline, and that could potentially mobilize residual oil, but that is speculation, and without a baseline for this observation it seems that one cannot argue that this is unusual." West Coast Vancouver Island Aquatic Management Board, The PEW Charitable Trusts, Programs in Marine Conservation - Marine Fellows
School of Marine and Environmental Affairs Consult: Terrie Klinger, Director and Professor writes, 'Yes, I agree…from the photos, this seems most likely a freshwater effect. Oiled water tends to have a rainbow-like sheen." University of Washington
LEO says: According to Wikipedia, "ripples in the halocline between the fresh and salt water sometimes makes for a blurry view. The halocline is usually well developed in coastal regions where there is much freshwater input from rivers producing surface waters of low salinity, a zone where salinity increases rapidly with depth (the halocline), and a deeper zone of more saline, denser waters. Halocline is a sub-type of chemocline, because salinity (in concert with temperature) affects the density of seawater, it can play a role in its vertical stratification. Haloclines are common in water-filled caves near the ocean. Less dense fresh water from the land forms a layer over salt water from the ocean. For underwater cave explorers, this can cause the optical illusion of air space in caverns. Passing through the halocline tends to stir up the layers." Source: Wikipedia & YouTube — BBC Planet Earth Episode 4 Caves- The Halocline (M. Tcheripanoff)
[1] Exxon Valdez Oil Spill (EVOS)
