Property fields in a Tortugas Eddy in the southern straits of Florida

Abstract

Sea surface temperature imagery, ship-based surveys, and moored current meters described the passage of a Tortugas Eddy as it moved east at ca. 6 km day −1 through the southern Straits of Florida (SSF). In mid-April 1999 the eddy SST signature extended across half the width of the Straits. While in the western SSF, the eddy center was ca. 30 km seaward of the outer reef. The upper pycnocline, the subsurface chlorophyll a maximum (SCM), and nutricline shoaled from ca. 80 m at the eddy edge to <60 m at the center. Maximum chlorophyll a concentrations in the SCM were highest near the eddy center, at 1 mg m −3, although the depth-integrated concentrations (mg m −2) were similar across the feature. Nutrient-density relationships show nitrate+nitrite, phosphate, and silicate decreased to detection limits at σ t < 25.0 ; the SCM was centered near this isopycnal surface. As the Eddy passed Looe Key (81.5°W) the alongshore currents reversed to the west. During this period high-nutrient, cool waters shoaled near the bottom on the outer reef. By early May, the eddy SST signature was compressed into a thin band of cool surface waters off the Middle to Upper Keys. As the feature moved towards shore in the Middle to Upper Florida Keys, the nitrate+nitrite and chlorophyll concentrations increased in bottom waters along the outer reef. Processes such as internal tidal bores and breaking internal waves are likely responsible for delivering nutrients from Tortugas Eddies to the outer reef in the Middle to Upper Keys.