highest and lowest points on the curve of cumulative degree-days. The longer 

 the season and the colder the temperature, the greater is the freezing 

 index. The mean air-freezing index, the highest in 10 years, and the highest 

 in 30 years at weather stations in the coastal zone, are given in table 2-7. 

 These data clearly show the moderating effect of coastal waters on winter air 

 temperatures. The stations nearest the coast register indices between 1071 

 and 1227 degree-days, while those farthest inland record indices between 1519 

 and 1874 degree-days. 



The ecological consequences of low temperatures during severe winters are 

 related primarily to the depth to which the ground freezes. This depth can 

 be estimated from the air-freezing indices and soil composition. Frost depths 

 are defined as the seasonal maximum penetration of the 32°F (0°C) isotherm. 

 Estimations of frost depths using air freezing indices involve heat transfer 

 theory and cannot account for local variability. An area's exposure to 

 sunlight and wind can have a marked modifying influence. 



Sanger (1963) used frost-penetration curves and air-freezing indices to 

 estimate frost depths. He considers seven soil-composition grades and three 

 surface conditions. The results of applying the characterization area indices 

 to his curves are summarized in tables 2-8 through 2-10. Depths associated 

 with turf are the upper bound for most of the areas involved , with the 12- 

 inch snow cover as a lower bound. Areas nearest the coast frequently are not 

 covered with 12 inches of snow, however, so the turf values only should be 

 considered in those areas. 



In an average year, with a coastal air freezing index of approximately 800 

 degree-days and an inland index of approximately 1300 degree-days, frost 

 penetration in similar soils is about equal if the "turf" category is used for 

 the coast and the "turf + 12 inches snow" category is used inland. Similarly, 

 the same result is obtained when the coldest season in 10 indices are used 

 (1300 degree-days near the coast, 1800 degree-days inland). Consequently, 

 average frost penetration in the inland regions may be less severe than might 

 be expected, since snow depths are greater and last longer there than in the 

 warmer coastal regions. 



River and harbor ice . The formation of ice on the rivers and bays of 

 Maine's coastal region is a prominent though poorly documented characteristic 

 of the winter season. Many factors contribute to ice formation. Not only 

 does the salt content of estuarine water reduce freezing temperature, but 

 mechanical agitation from winds, currents, and tides also prevents the 

 formation of ice cover at temperatures below 32°F (0° C) . As a result, the 

 more isolated, brackish, and inland waters are most susceptible to ice cover, 

 and the salt water bays and inlets are least susceptible. 



The annual reports of the U. S. Coast Guard on ice-breaking activities are the 

 most comprehensive summary of river and harbor ice occurrence in coastal Maine 

 (U. S. Coast Guard 1970 to 1978). Their activity reports on the Penobscot 

 River document significant ice formation from an inland river environment to a 

 coastal bay environment, and ice conditions in the Penobscot region are likely 

 to be indicative of ice conditions elsewhere in the coastal zone. 



A second source of data on ice occurrence on the eastern coast is the 

 personal records of Mr. Richard Rhine of North Lubec, Maine (personal 



2-31 



10-80 



