Enhancement of Phytoplankton Growth by Tidal Mixing 

 June 1979 



Regions of high pigment concentration are strongly correlated with 

 water temperature; that is, pigment concentrations are highest in regions 

 where water temperatures are coolest. On 14 June, such regions of intense 

 tidal mixing on the CZCS pigment image (58-2) and the corresponding 

 false-color CZCS pigment image (59-1) are outlined by sharp ocean color 

 fronts. Inside these frontal boundaries the pigment concentration is 

 greater than 2.0 mg m'^. Outside these fronts, on the warm side, pigment 

 values are less than 0.5 mg m 3. Note that the areas of intense mixing 

 outline the major shoal regions such as Nantucket Shoals and Georges 

 Bank. 



The augmentation of phytoplankton growth by tidal stirring is 

 explained as follows: Surface waters, heated by sunlight, become more 

 buoyant than the waters they overlie. This layer of warm water over cold 

 tends to stabilize the water column, thereby isolating the deeper cold water 

 from the warm surface layers. The cold layers contain large concentrations 

 of nutrient fertilizers while the warm surface layers do not. Therefore, 

 isolation of the two layers tends to retard phytoplankton growth. Intense 

 phytoplankton growth occurs when these two layers are actively stirred, 

 such as occurs over the Georges Bank. 



The Georges Bank is a shoal region off the New England coast. The 

 energy for stirring the shallow water column over the Georges Bank comes 

 from tidal flow. As these currents move across the bottom, the friction 

 creates turbulent stirring (58-1). Generally speaking, the intensity of the 

 stirring is proportional to the speed of the current and the water depth. 



58-1. Schematic 

 of Mi.King Process 

 in Shoal Regions. 



OPEIT 03£:'6 HIUNT9 153752 TO 153952 GMT GAIN 1-4=1 THRESHOLD OFF TILT hNGLE 20-0 

 GRID CENTER DhTh: 153852 GMT 39 -TW 064 .62N SUN EL 71 AZ 150 ROLL 0-2 PITCH -0.0 YhN 0. 



58 



algorithms: 01 00 



970 SCAN LINES PROCESSED 



58-2. Nimbus-7. Orbit 3226. 14 June 1979. CZCS Pigment Image. 



