On the sources of the Florida Current

Abstract

In our opinion roughly 13 Sv or 45% of the transport of the Florida Current is of South Atlantic origin, as compensation for the cross-equatorial flow of North Atlantic Deep Water. Of the 8.9 Sv moving through the Straits of Florida with temperatures above 24°C in the upper 100m of the water column, 7.1 Sv is composed of comparatively fresh water coming through the southern Caribbean passages from the tropical South Atlantic. Saltier surface water, 1.8 Sv, enters from the North Atlantic through Windward Passage, as does most of the 18° Water in the Florida Current. A South Atlantic contribution for the uppermost layer is clear-cut because the surface water in the open Atlantic north of the Caribbean is comparatively cold and salty and intrudes south as Subtropical Underwater or Salinity-Maximum Water below a comparatively warm and fresh layer 50-100 m thick, which could hardly he transported from the North Atlantic. Of the 13.8 Sv transported through the Caribbean in the 12-24°C temperature range, 13.0 Sv is of North Atlantic origin, with about 0.8 Sv of comparatively fresh South Atlantic water on the western side of the Florida Straits having entered the Caribbean on the southern side of St. Vincent and St. Lucia Passages. Of the 6 Sv transported by the Florida Current in the 7-12°C temperature range, 5 Sv appears to originate in the South Atlantic. Our estimate of the 13 Sv of South Atlantic and 16 Sv of North Atlantic origin for the total transport of 29 Sv for the Florida Current, along with partitioning in the aforementioned temperature ranges, is approximately consistent with open ocean sections along 24°N and with several previous investigations.We have formed a new estimate of the transport into five key Caribbean passages, yielding 28.8 Sv for the temperature range appropriate to the Straits of Florida off Miami, in close agreement with independent transport measurements for the Florida Current. The five passages and their contributions are: Grenada (7.7 Sv), St. Vincent (7.9 Sv), St. Lucia (3.8 Sv), Dominica (2.6 Sv), and Windward (6.8 Sv). Breakdowns of these passage transport estimates into broad classes by temperature range agree to within about 2 Sv in comparison with similar quantities for the Florida Current. Anegada Passage may transport 0.5 Sv of water that exits through the upper 200 m or so of the Florida Current, and the mid-depth (5-12°C) flow in this passage and in the general vicinity of the Caribbean deserves further examination.