MAYOR— DETECTING OCEAN CURRENTS. 153 



tension is thus in balance with the atmosphere, and I find that when 

 uninfluenced by up-welHng of unusual quantities of deep water the 

 COo tension of the surface waters of the Tropical Atlantic and Pa- 

 cific is also practically in balance with the atmosphere. 



Thus on the voyage of the S. S. Niagara from Fiji to Honolulu, 

 September 6 to 12, 1918, we encountered only the prevailing westerly 

 set uninterrupted by any currents moving toward the east, and the 

 average PH was about 8.22, the average temperature 28° C, and 

 the COo tension of the water three ten-thousandths of an atmos- 

 phere and thus practically the same as that of the air. When cold 

 deep water wells upward to the surface, however, a dift'erent con- 

 dition ensues, for due to relief of pressure and increase in tempera- 

 ture this water must discharge its excess CO2 into the atmosphere. 



Thus on the voyage of the S. S. Sonoma between Honolulu and 

 Pago Pago, Samoa, June 25 to 30, 1918, we at times met with strong 

 currents set toward the east and the average PH was about 8.19 

 and the COo tension of the surface water 3.26, the average tempera- 

 ture being 28° C, as on the voyage of the Niagara. Similarly on 

 the voyage of the S. S. Ventura from Pago Pago, Samoa, to Hono- 

 lulu on April 19 to 25, 191 7, we met with several strong sets to the 

 eastward and the average PH was 8.17, the COo tension 3.35 and the 

 temperature 25.7° C. 



Henderson and Cohn, 1916, p. 621, conclude from laboratory 

 experiments that upon the whole in most places and at most seasons 

 carbon dioxide must be escaping from the sea into the air, although 

 they also state that the balance is doubtless restored by COo entering 

 the water from the air in the polar regions. These authors did not 

 consider the effect of photosynthesis by marine plants which Mc- 

 Clendon afterward showed to be such an important factor. Were it 

 not for photosynthesis it is probable that large quantities of carbon 

 dioxide would escape from the sea in the tropics, but instead of this 

 McClendon, Wells and I find that the warm waters are practically 

 in balance with the atmosphere. 



My observations along the Atlantic coast between Nova Scotia 

 and Florida in December-March show also that the coastal current 

 during these cold months has a CO2 tension somewhat below that 

 of the atmosphere, and this may be due to the great concentration 

 of plant life in these cold waters. 



