(U) Water Clarity

(U) Typical visibility at the reefs is between 15 - 24 m (50 – 80 ft). Seagrasses help to maintain water clarity by trapping sediments and particles with their leaves. (1, 13)

(U) The water always becomes milky following windy weather. The usual color of the water on the reefs is bluish green, and the shoal patches show dark, shading through brown to yellow as they approach the surface. The shoal sand patches show as a bright green. At depths of 3 – 4.5 m (10 – 15 ft) grass patches on the bottom look quite similar to rocks. When piloting in this area choose a time so that the Sun will be astern, conning the vessel from aloft or from an elevated position forward, for then the line of demarcation between deep water and edges of the shoal will be indicated with surprising clarity. (1)

(U) Salinity

(U) Salinity for Key West area: The average surface salinity varies only slightly with season and is nearly homogeneous in the upper 100 m (328 ft) of the water column. Surface salinity ranges from about 36.1 during summer to 36.3 during winter. Below the surface, salinity is constant to a depth of about 100 meters, where it begins to increase slightly with depth. Because of the open nature of this area, salinity probably rapidly approaches oceanic values with increasing distance from the shore. (4)

(U) Oceanic salinity generally ranges from 35.5 to 36.5 during the year, with vertical variations of less than 1. During periods of heavy run-off or during dry, sunny days salinity could vary as low as 20 to as high as 37.5. (see World's Oceans Salinity — August (Graphic) [Salinity for the Worlds Oceans in August (8)] )(4, 8)

(U) Temperature

(U) Winter water temperature is approximately 70° F)(22° C); summer temperature ranges between 28 — 33° C (80° – 90° F). (1)

(U) Thermocline

(U) During winter, the temperature is nearly isothermal throughout the water column. The intense surface heating that occurs in summer creates a layer of warm water. The interface between this water mass and the cooler water below is called the thermocline. (5)