Slope Water I Tidal Mixing! 

 Gulf Stream Meanders and Rings 

 April-May 1979 



21 April 



The CZCS pigment image (36-1) reveals a complex set of plumes (light 

 tones nearly perpendicular to coastline) associated with the Carolina 

 capes. These are superimposed upon a generally enhanced pigment 

 concentration within 10 to 30 km of the coast. This concentration is the 

 result of higher primary productivity caused by the introduction of 

 nutrients by river runoff and vertical mixing due to tidal stresses in the 

 shallow waters. The winds are also conducive to upwelling along this coast 

 although this is probably of minor significance, except in summer and fall. 

 The plumes associated with the capes might be explained as a combination 

 of simple offshore advection of high pigment water and an upwelling 

 response as the flow rounds the capes. Similar plumes are observed in 

 many regions of the world in relation to equatorward flow around capes 

 (Arthur. 1965; Brink et ai. 1983). The image also shows an entrainment of 

 a filament (narrow, white-tone band) of inshore high-pigment water into 

 the Gulf Stream at Cape Hatteras. This feature is about 10 km in width 

 suggesting low cross-scale mixing along its nearly 300-km length. 

 Entrainment of shelf water into the northern edge of the stream seems to 

 be a common occurrence at Cape Hatteras. Features similar to this 

 filament are reported by Ford and Miller (1952). and Fisher ( 1972). based 

 on the presence of low salinity shelf water along the edge of the stream. 



In addition, the image also contains a cold-core, cyclonic ring which 

 seems to be advecting a streamer of low-chlorophyll fluid out of the Gulf 

 Stream. The ring is manifest as a high-pigment region in the Sargasso Sea, 

 The lowest pigment concentrations are not associated with the Sargasso 

 waters around the ring in the image, but rather with the Gulf Stream core. 

 A patch of this low-chlorophyll fluid appears to the west of the ring and 

 may indicate the advection of waters by the cyclonic ring out of the stream 

 core and into the Sargasso Sea. 



2 May 



The CZCS pigment image off the East Coast (37-1) gives a reasonable 

 coverage of the Gulf Stream between Cape Hatteras and the New England 

 Seamounts. In this image, the Gulf Stream appears as an abrupt reduction 

 in pigment concentration (A-B) as one proceeds from north to south. As 

 in the 21 April image (36-1), the stream core exhibits consistently lower 

 values of pigment concentration compared to the slope water to the north 

 and the Sargasso Sea to the south. 



To the south, in the northern Sargasso Sea (37-1), there is an 

 approximately 30-km area of high pigment. This small, nearly circular 

 feature is probably associated with the core of a cyclonic ring. High 

 chlorophyll concentrations in cold-core ring centers in fall and spring are 

 described by Wiebe et at. (1976). They found carbon-14 measured 

 productivity in a ring during spring to be nearly double that in the 

 surrounding Sargasso Sea. This is attributed to enhanced nutrient levels as 

 compared to the Sargasso Sea and higher light penetration than that 

 found in the slope waters. The scale of the feature in this image is 

 somewhat less than the radius of the velocity maximum in a typical 

 cyclonic ring, suggesting that the high-pigment zone is associated with 

 increased productivity in a small region near the ring center or on the edge 

 of the ring in response to some asymmetry forced on the ring. 



The structure of the meanders in the Gulf Stream and the warm-core 

 rings in the North American slope water is discussed below in relationship 

 to the images (37-2, 38-1, and 38-2). Structures of interest in this set of 

 images include the complicated patterns present in the slope water as 



manifest north of the Gulf Stream meander, just downstream of Cape 

 Hatteras (37-1). Further east there is a large, warm-core ring and a large 

 (nearly 200 km), elongated filament of high-pigment water that appears to 

 the south of the eddy in each of the images. 



3 May 



This East Coast CZCS pigment image (37-2) shows features similar to 

 those along the Carolina capes (36-1) and Gulf Stream extension (37-1, 

 38- 1 , and 38-2). The higher pigment values associated with the capes (37-2) 

 are apparent. Note that the large-scale meander pattern in the Gulf Stream 

 is essentially the same as in the other images in this set. The details of the 

 pattern to the east of the warm-core ring are worth further comment in 

 relation to the time of this image and those on 7 and 8 May (38-1 and 38-2). 



To the east of the warm-core ring (37-2) is a cyclonic (counterclockwise) 

 hook or streamer of low-pigment water. This feature and its time evolution 

 (38-1 and 38-2) suggest a cyclonic circulation of scale comparable to the 

 ring. Features such as these may imply a pairing of vortices which may be 

 of considerable import.''nce to the dynamics of regions, which are 

 characterized by strong non-linear eddies such as western boundary 

 current exte isions. 



continued 



i 



ORBIT 02480 21APRT9 160716 TO 160916 GMT OhKI 1-4=2 THPEiHOLD OFF 

 GRID CENTER DATA: 16081T GMT 33.96N 070. 51N SUN EL 67 AZ 160 POLL -0 



TILT ANGLE 8-0 

 1 PITCH -0.0 YAW - 



algorithms: 01 00 00 00 00 02 01 00 00 00 



809 SCAN LINES PROCESSED 161 SCAN LINES MISSING 



1.28 2-U 3.46 5.69 



CIP VER CRT NO DPS VER 

 V801005 2E40401- V820208 



9.35 11-98 25.25 32.0 



SPEC- # FRAME # 

 F732040 ZG040401 



36-1. Nimbus-7. Orbit 2480. 21 April 1979. CZCS Pigment Image. 



36 



