LARGE-SCALE ANOMALOUS SEA SURFACE CONDITIONS IN THE NORTH PACIFIC 



John D. Isaacs 

 Scripps Institution of Oceanography 

 La Jolla, California 



Aperiodic departures from the normal sea surface tempera- 

 tures commonly occur throughout the world's oceans. Such anomalous 

 fluctuations often exceed the mean seasonal or annual fluctuations of 

 temperature in many regions, and thus constitute major features of the 

 oceans. These changes are associated with changes in weather, 

 currents, the distribution of marine organisms, the success of fish- 

 eries, and, undoubtedly, with the propagation of underwater sound, the 

 background noise, and the frequency and distribution of natural tar- 

 gets. It is thus important to inquire into the interactions, under- 

 lying nature and causes of these changes. 



It has long been recognized that ocean conditions are 

 changeable on a time scale much more abbreviated than the broad cli- 

 matic changes, such as the ice ages. Perhaps the most striking 

 example of these abbreviated changes in the last few centuries were 

 experienced in the North Atlantic in the years 1812 and 1813, when 

 conditions were so frigid that some of the now existing deep Atlantic 

 water may have been generated, and snow lay on the fields of Northern 

 Europe all summer. We are gaining some insight into the year-to-year 

 range of ocean conditions within the last thousand years or so from 

 the study of certain highly stratified basin sediments. 



The historical meteorological records also lend insight into 

 the nature of these changes. The air temperatures at marine stations 

 have been shown to follow the sea surface temperatures very closely. 

 These records, hence allow us to extend the marine temperature record 

 back in time for a few hundred years. In Figure 1, for example, is 

 shown the air temperatures at three Pacific Coast stations, extending 

 to 1925. This demonstrates a number of features, anomalously high 

 and low seasonal temperatures following one another in a complex 

 pattern. One feature of these records, besides their variations, is 

 the peculiar lack of fluctuation in the decade 1946 to 1956. 



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