7 May 



The CZCS pigment image (38-1) shows the entire zonal extent of the 

 North American slope water and the frontal zones which border it. 

 between Cape Hatteras and Scotian Shelf. The slope water is the site of the 

 largest horizontal pigment variability in the image, in keeping with the 

 nature of transition zones. The contrast between the slope water and the 

 Sargasso Sea is clearly visible. Meanders and rings viewed in the other 

 images are also evident in this scene. The shelf front separating the slope 

 water and the water on the continental shelf can be traced here as a sharp 

 decrease in pigment as one proceeds into shallow water (depths <200 m). 



Low pigment concentrations on the outer shelf in comparison to the 

 slope waters are somewhat unexpected. The spring bloom on the mid to 

 outer shelf in the Mid Atlantic Bight typically occurs in late March to early 

 April (Walsh, 1983), while the inner shelf bloom is later, with the mean 

 euphotic-zone chlorophyll peaking in mid-May. In the time period in 

 question, the shelf should have a uniform pigment distribution from 

 Walsh's (1983) curves. This is, in fact, the case for April and May 1982 

 (Evans, 1985). By June 1979, the shelf has nearly uniform pigments (not 

 shown) as viewed from space (Gordon el at.. 1982). The slope water also 

 has lower pigment concentrations in these later images in 1979. 



The appearance of low, near-surface pigment concentrations on the 

 outer shelf (38-1) in comparison to the normal conditions (Walsh, 1983) 

 suggests that there are strong interannual variations in the phytoplankton 

 community on the North American shelf. This anomaly may just reflect a 

 deeper or better mixed distribution of pigments in the vertical in 1979. It 

 might also be a result of different offshore Ekman transports (Walsh, 

 1983) or perhaps an earlier reduction in phytoplankton by grazing. 



The Scotian Shelf also shows very low pigment concentrations in this 

 image. This may be a more common situation set up by the seasonal 

 decrease in surface salinities in this region tied to the spring melt and 

 increased fresh water output from the Gulf of St. Lawrence. Both Georges 

 Bank and Nantucket Shoals appear as high-pigment areas. This is a 

 consequence of tidal mixing in the shallow waters which leads these areas 

 to have more than double the annual primary production of the upwelling 

 zone off Oregon or at the Mid Atlantic Bight (Walsh, 1981). 



The temporal variations in the area covered are largest in the slope 

 water, which typically contains streamers of extremely low pigment fluid 

 drawn in from the Sargasso Sea and high-chlorophyll waters from the 

 shelf. In the image (38-1), the shelf is an apparent source of the low- 

 pigment waters in the slope region, with the highest chlorophyll 

 concentrations appearing in the slope water south of the Scotian Shelf. In 

 contrast, a month and a half later in the June imagery (not shown), 

 Gordon ei al. (1982), show that this region has very low pigments, 

 suggestive of a large flux of Sargasso Sea waters across the Gulf Stream 

 downstream of the New England Seamounts between May and June. 

 Much of this sort of entrainment of fluid into the slope water is tied to the 

 presence of warm-core rings in the slope and large-amplitude meanders in 

 the stream. These are discussed in relationship to the CZCS pigment image 

 of 8 May. 



8 May 



The last CZCS pigment image in this group (38-2) covers the eastern 

 portion of the slope water and gives the best coverage of the meandering of 

 the Gulf Stream. A comparison of all the images shows that the large 

 meanders in the stream evolve on a longer time scale than the two weeks 

 covered here. In addition, a careful inspection of the images reveals small 

 changes in the northern edge of the stream in connection with small- 

 amplitude features over the period, but no major changes in the large 



uPBIT 02701 07MAY79 155332 TO 155532 GMT GAIN 1-4=1 THRESHOLD OFF TILT hNGLE 20.0 

 GRID CENTER DhTA: 155432 GMT 38.96N 068. 35N SUN EL 66 HZ 158 POLL 0.2 PITCH -0-1 YAH O- 



algorithms; 01 00 00 00 00 02 01 00 00 00 

 970 scan lines processed scan lines missing 



CIP VER CRT NO 

 VB10311 ZE55101- 



DPS VER SPEC. # FRAME # 

 V820208 F732040 ZG055101 



38-1. Nimbus-7. Orbit 2701. 7 May 1979. CZCS Pigment Image. 



ORBIT 02715 08MAY79 161137 TO 161337 GMT GAIN 1-4=1 THRESHOLD OFF TILT ANGLE 20.0 

 GRID CENTER DATA: 161237 GMT 36.95N 072 .33H SUN EL 69 A2 158 ROLL 0-2 PITCH -0-0 YAN 0-2 



PIOENT IN MJLLIGR«iS/hETERS««3 „ ,„ „ 



.06 .08 .12 .19 .27 .39 .5 



ALGORITHMS; 01 00 00 00 00 02 01 00 00 00 



970 SCAN LINES PROCESSED SCAN LINES MISSING 



1.28 2.11 3.46 



CIP VER CRT NO 



V800710 ZE05301- 



5.69 



DPS VER 



V820401 



9.35 11.98 25.25 



SPEC. # FRAME # 

 F732040 ZG005301 



38-2. Nimbus-7. Orbit 2715. 8 May 1979. CZCS Pigment Image. 



38 



