and (2) it may have an inhibitory effect when the temperature rises above 20°C for northern 

 strains of M. pyrifera (somewhat higher than 20°C for the southern, Baja Cahfornia, plants). 

 A most important parameter, in terms of selecting an Ocean Food and Energy Farm site, is 

 the maximum temperature reached during the summer months. Figure 9 gives the mean 

 temperature of the north Pacific for September; generally, the warmest water temperatures 

 are observed during this month. The mean 20°C isothenn (68°F) runs eastward from the 

 western Pacific very close to 40°N latitude to approximately 150°W where it bends south- 

 ward meeting the west coast at about 32°N, just south of San Diego (Fig. 9). This southern 

 bending of the isotherms along the west coast is caused by significantly cooler temperatures 

 resulting from the southerly movement of the cold California Current; during some months, 

 the effect of coastal upwelling intensifies the cooling trend. Figure 10 gives the surface 

 thermal structure for maximum September temperatures. The thermal configuration is 

 basically the same (as Fig. 9) except the warmer isotherms are extended further to the 

 north. The 20°C maximum isotherm runs across the Pacific at 43°N, bends southward at 

 130°W, and meets the coast at about 39°N. 



The selection of the Ocean Farm site, again, is dependent on the surface thermal 

 structure, to the extent that (1) Macrocystis is temperature-lhnited (needs further research), 

 (2) the degree of optimization of growth rate desired, and (3) the surface water can be 

 cooled with artificial upwelling. Considering point (3) above, Fig. 1 1 shows the increment- 

 ed temperature reduction of surface waters, by artificial upwelling, required to lower the 

 mean ambient September temperature to 20°C, the estimated sustained upper temperature 

 limit for M. pyrifera. 



Figures 12 and 13 give the mean and minimum temperatures, respectively, for the 

 north Pacific for February. 



Nutrients 



Most open ocean areas under consideration for the OFEF are nutrient-limited (Refs. 

 4, 5, and 6), given the selection criteria delineated in Table 1 (3-5 Mg-at/liter nitrate mini- 

 mum, 10-15 Mg-at/liter optimum). Even in the nearshore environment where Macrocystis 

 grows, the nitrogen concentration is frequently limiting (Ref. 9). It seems apparent that 

 artificial fertilization (probably by upwelling pumps) will be necessary at most sites (Refs. 

 3 and 18). The geographic distribution of nutrients (both horizontally and vertically) is a 

 very important parameter that must be considered in the OFEF site selection process. Be- 

 cause there is strong evidence that nitrogen is the principal macro-nutrient that is limiting to 

 Macrocystis and because other nutrients generally occur in constant ratios to nitrogen, NO3 

 is the only nutrient surveyed below. 



In general, nitrate concentrations at the surface are less than 1 /xg-at/liter except for 

 certain near-coastal areas where natural upwelling occurs and two major upwelling areas, the 

 Costa Rica Dome and equatorial upwelling zone shown in Fig. 1. 



National Oceanographic Data Center data tapes were surveyed for nitrate profiles; these 

 data are presented in Appendix A. In areas 1 through 9 and 1 5 (Fig. 1 ), NODC nutrient data 

 wer6 unavailable. Because nutrient data are strongly correlated with thermal structure, a 



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