Physics 71 



The extinction coefficients ranged from 6.75 to 2.1 in the ponds, 

 which is equivalent to 26 to 66% of the surface light reaching a depth of 20 

 cm. For Pond B. the mean n of 3.84 equals 46% of surface light reaching 

 20 cm. In contrast, the water of Ikroavik Lake has an n which ranges from 

 0.49 to 1.22 so the water is much clearer (at 2 m, this is 37 and 8% of the 

 surface light). In arctic waters in general, the shallow bodies of water have 

 a high extinction coefficient unless they are located in a very rocky 

 watershed. Deeper lakes may be very clear; for example Taserssuaq Lake 

 in Greenland (Holmquist 1959) has an n of 0.154 for white light and 5% of 

 the light penetrates to 25 m. Some deep lakes that receive particulate 

 matter from glaciers have an n of up to 2.5. 



Most of the absorption of light in these ponds is due to the dissolved 

 organic matter; very little absorption or scattering is due to the particulate 

 material. Thus, there is a highly significant (r = 0.83, n = ll) relationship 

 (Kalff 1965) between water color, as measured in Pt-Co units, and the 

 extinction coefficients (extinction coefficient = (0.0096)(Pt-Co units) 

 -30.4). 



Sediments 



The light penetration into the sediments was measured by placing a 

 water-filled glass cylinder on top of the photocell and adding known 

 amounts of sediments. From this measure, an n of 15.22 cm ' (or 1522 

 m ') was measured, which implies that all of the light was absorbed in the 

 top 3 mm. This, of course, means that all of the photosynthesis of the 

 epipelic or benthic algae must take place in an extremely thin layer. 



CURRENTS 



A Pygmy Water Current meter (Gurley), placed just beneath the 

 water surface in Pond C, was used for eight 24-hour studies in 1973. This 

 instrument is designed for stream work so likely underestimates the pond 

 currents. Air speed data came from a hand-held anemometer, from the 



TA BLE 3-13 A verage Wind Speeds at the Barrow Weather Bureau, 

 1970-1973* 



*The anemometer is at the top of a 9-m pole; wind speeds expressed as m sec 



