PHYSICAL OOEANOGBAPHY OF THE GULF OF MAINE 823 



COLOR 



The color of the gulf was measured by percentages of yellow ^^ during the sum- 

 mers of 1912 and 1913. 



As is well known, the water is, as a whole, bluest outside the edge of the conti- 

 nent, greenest alongshore. With' only 2 per cent yellow, the water at our outermost 

 station off Nantucket on July 8, 1913 (station 10060), closely approached the pure 

 sapphire blue characteristic of the so-called "Sargasso Sea," of the Mediterranean, 

 and of certain regions in tropical Indian and Pacific Oceans. In our experience the 

 water has never shown as small a percentage of yellow as this anywhere inside the 

 edge of the continent, though with only 5 per cent of yellow off Nantucket Shoals on 

 July 9, 1913, evidently only a slight overflow of tropic water would have been required 

 to produce very blue water. This is the minimum percentage of yellow so far 

 recorded for the Gulf of Maine proper, and three stations for 1913 point to 9 per 

 cent yellow as about normal for the central basin of the gulf. 



At the other extreme, we have invariably found the percentage of yellow great- 

 «st (27 to 35 per cent) in the coastal belt along the shore of Maine, out, roughly, to 

 the 100-meter contour, with secondary smaller but very green areas (27 per cent of 

 yellow) along the outer side of Cape Cod and in the German Bank region. The 

 greenest water so far recorded has been in Casco Bay, though inclosed locations 

 probably would prove equally green all around the coast line of the gulf. In the 

 western, northern, and eastern parts of the gulf, including the Massachusetts Bay 

 region on one side and the waters off the Bay of Fundy and west of Nova Scotia 

 on the other, the percentage of yellow has usually ranged from 14 to 20. 



The Gulf of Maine, like most coastal boreal waters, thus falls among the greener 

 seas, its color agreeing fairly well with that of the English Channel and with the 

 coast water of the Bay of Biscay (Schott, 1902, pi. 36). However, as I have noted 

 in earlier publications (Bigelow, 1914, p. 81; 1915, p. 225), the distribution of color 

 does not exactly parallel either the temperature or the salinity, for while low salin- 

 ity is reflected in a high percentage of yellow, the most saline part of the basin has not 

 been the bluest. The true key to local variations in color within the gulf is to be 

 found more in variations in the density and character of the plankton and in the 

 amount and nature of the silt which the water holds suspended. 



The records for the two years combined show that the color of the gulf changes 

 but little from July to August or from year to year at that season. No measure- 

 ments of the color have been made at other times of year, but a browner hue is to 

 be expected alongshore when diatoms are flowering actively in spring. 



"The color of the sea usually is measured by the " Forel " scale, based on a combination o( blue and yellow, the former being 

 5-gram copper ammonia sulphate + 0. 5 cubic centimeter ammonia in 95 cubic centimeters water; the latter 15-gram potassium 

 chrcmate in 100 cubic centimeters of water. The combinations used are as follows; 



1 2 3 4 5 6 7 8 9 10 11 12 13 



Per cent blue.. ..100 98 95 91 86 80 73 65 56 46 35 23 10 



Per cent yellow _ 2 5 9 14 20 27 35 44 54 65 77 90 



Various comparators have been devised for use on shipboard. For descriptions of the method employed on the Qrampua 

 see Bigelow, 1914, p. 38. 



