Ice features of the northern caspian under sea level fluctuations and ice coverage variations

Abstract

The Caspian Sea seasonal ice cover develops each winter despite of it being in mid-latitudes. Increasing development of oil and gas fields challenges researchers to ensure operational safety. The Caspian Sea has seen significant water level fluctuations in its recent history. And in the same time, it is vulnerable to effects of climate change. Extensive studies on ice conditions conducted in the region don’t provide insights on influence of these factors in combination to describe ice cover behavior and ice features distribution. We classify winter seasons of the Northern Caspian by their severity calculating the cumulative freezing-degree days (CFDD). Ice charts based on aerial reconnaissance with support of the OSI-450 reanalysis provided data on the ice coverage, the timing of ice formation and destruction, the duration of the ice seasons from 1979 to 2015. We analyzed the stamukhi distribution on the Northern Caspian from aerial reconnaissance for 1973–1980 and satellite imagery deciphering for 2013–2019 periods along with sea level dynamics. We found out that the amount of severe and moderate winters reduces while mild winters number increases. This leads to a decrease in the mean ice area and ice duration at the Northern Caspian. Comparison of two periods with different sea levels and ice coverage showed that both factors affect the distribution of stamukhi by depth and distance to coast in the Northern Caspian. Comparison of stamukhi locations in moderate winter seasons showed that their distribution is determined by the area of ice cover. In case of similar ice conditions, the stamukhi distribution is determined by sea level. The zone of their highest concentration shifts along with the coastline offset.