The California Current Vpwelling System 

 May, July, and September 1979 



Three CZCS pigment images (30-1, 31-1. and 31-2) are shown for the 

 California Current System between Cape Mendocino and San Diego. All 

 three images show that highest pigment concentrations are confined to 

 within 200 km ofshore (about the distance from Pt. Reyes to Pt. Sur). This 

 agrees with the observation that the main a.xis of the California Current 

 lies about 300 km offshore along central California (Hickey. 1979). 

 Although many of the eddies and meanders shown in these images are 

 transient features of the California Current, a persistent cyclonic 

 geostrophic eddy (E, 31-1) has been observed south of San Francisco 

 (Broenkow and Smethie, 1978: Hickey, 1979). Apparent shoreward flow 

 of lower pigment waters (L, streaks of darker tones) from the "San 

 Francisco Eddy" is shown in the 13 July (31-1) and 6 September (31-2) 

 images, and some indication of lower pigment waters (L. faint dark tones) 

 intruding into Monterey Bay are shown in the 13 May image (30-1). The 

 location of this eddy is apparently due to local change m the wind stress 

 curl (Hickey, 1979) and perhaps to the abrupt bathymetric break at 

 Monterey Bay (Broenkow and Smethie, 1978). 



Coastal jets extending normal to the coastline are frequently observed in 

 the California Current. A prominent jet (CJl) in the 13 May image (30-1) 

 may have resulted from counterrotating eddies as suggested by Mooers 

 and Robinson (1984). A similar, but larger such feature (CJl) is shown in 

 the 6 September image (31-2) at about the same latitude, but further 

 offshore. High pigment levels along the coast south of Pt. Conception in 

 the 13 May image (30-1) seem to spawn several small (50 km) filaments 

 (arrows) between Santa Cruz Island and San Diego. In addition, the large 

 arcuate feature 150 km west of Pt. Conception in the image showed high 

 radiances in the 443, 520. and 550 nm bands relative to surrounding 

 waters. Viewed in false-color CZCS imagery (not shown) this feature 

 appeared white, suggesting it was not caused entirely by phytoplankton 

 absorption. Since the feature was not sampled from ships, its origin 

 remains something of a mystery, but it is suspected to be due to 

 Coccolithophorids, which are algae with calcium carbonate shells. 



Several upwelling loci are found along the central California coast: the 

 area from Cape Mendocino to Pt. Reyes, from Pescadero Pt. to Monterey 

 Bay, and from the Big Sur coast south of Monterey Bay to Pt. Conception. 

 The 13 May image (30-1) shows high pigment levels in coastal waters just 

 north of Pt. Conception, an apparent lack of high-pigment waters along 

 the Big Sur coast, and higher levels in and north of Monterey Bay. A ship 

 station in the center of Monterey Bay on this date showed a chlorophyll 

 concentration of 8.7 mg m"'; a 2.5 mg m -' chlorophyll concentration was 

 measured in the pigment-poor tongue e,xtending into the Bay. The S^S 

 pixel averages of CZCS data at these locations showed 2. 1 and 1 . 1 mg m-\ 

 respectively. The 13 July image (31-1) is partially obscured by clouds 

 trailing southwest from Cape Mendocino where thermal infrared imagery 

 (not shown) indicated coolest surface waters and intense upwelling. It is 

 interesting that the CZCS data indicate that highest pigment 

 concentrations were located 50 to 1 00 km offshore except along the Pt. Sur 

 upwelling area. Incipient upwelling may occur with a rapid offshore 

 transport of plankton-rich coastal waters which are replaced by cool, low- 

 chlorophyll waters. As phytoplankton production proceeds, the waters 

 warm and become colored. 



Ship data at two stations in Monterey Bay just before satellite overpass 

 on 13 July (31-1) indicated chlorophyll concentrations of 6,9 and 

 11.7 mgm"\ respectively, both of which are indicative of highly productive 

 water. CZCS data at these locations gave values of 2.4 and 4.5 mg m -', 

 respectively. Wrigley and Klooster (1983) compared surface truth data 



obtained by Moss Landing Marine Laboratories with the CZCS data and 

 found that the CZCS values consistently underestimate pigment 

 concentrations in the areas where pigment levels are greater than 3 mg m '. 

 They attribute the discrepancy to excessive atmospheric correction caused 

 by phytoplankton reflectance in the 670-nm band. The small black areas 

 between San Francisco and Monterey Bays (31-1) and south of Big Sur 

 (31-2) are image processing artifacts where the water-leaving radiances at 

 443, 520, and 550 nm were reduced to zero by the atmospheric correction 

 algorithm. The condition, caused by pigment levels beyond the limits of 

 the normal CZCS correction scheme, often occurs in images along the 

 central California coast in the 443-nm band, but is rarely found in all three 

 bands. 



References 



Broenkow. W, W,. and W, M. Smelhie. Jr.. 1978: Surface circulalion and replacement of 



water in Monterey Bay. Eiluanne and Coaxial Marine Saence.b. 58.1 603. 

 Hickey. B. M.. 1979; California Current System; Hypotheses and Facts. Progress in 



Oteanugraphy. S. lil 219. 

 Mooers. C. N. K,. and A. R. Robinson. 1984; Turbulent jets and eddies in the California 



Current and inferred cross-shore transport. Science. 223. 51-53. 

 Wrigley. R. C. and S. A, Klooster. 1983; Coastal Zone Color Scanner data of rich 



coastal waters. In; Digest. International Geoscience and Remote Sensing Symposium, 



31 August-2 September 1983, San Francisco. CA 



ORBIT 02T86 13MAYT9 192845 TO 193045 GMT GAIN 1-4=1 THRESHOLD OFF TILT ANGLE 20-0 

 GRID CENTER DATA: 192946 GMT 35-llN 121. 12W SUN EL 72 AZ 156 ROLL -0-1 PITCH -0.0 YAW 



•19 -27 



algorithms; 01 00 00 00 00 02 01 00 



970 scan lines processed scan lines missing 



30-1. Nimbus-7. Orbit 2786. 13 May 1979. CZCS Pigment Image. 



30 



