Evolution of ice conditions of the Far-Eastern Seas of Russia in the second half XX century – at the beginning of the XXI century. Plotnikov V.V. Russian Academy of SciencesFar Eastern Branch V.I.Ilichev Pacific Oceanological Institute
Ice pack has considerable time lag that results in its being optimal indicator of large scale variability of ocean/ice cover/atmosphere system. The nature of large scale variability of ice pack in some areas of water of the Northern hemisphere similar, and is determined by evolutionary processes of climatic system.
Data • The largest data sets of sea ice conditions were collected for the Japan, Okhotsk and Bering Seas (1960-2005). • As initial information to study space-temporal variability of ice conditions the next data were used: • - air surveys; • - hydrometeorological monthly reviews which include data of the coastal stations; • - satellite images of ice conditions. • As additional information the helicopter ice drift observations, opportunity ship observations and so on were used. • On a basis of these data the 10-day averaged values of ice characteristics have been calculated, when it was necessary the regions with specified ice conditions have been contoured.
Seasonal variability • Seasonal fluctuations of the ice extent conditions in the Pacific marginal seas are mainly conditioned by astronomical forcing and possess a vividly expressed annual period. These vibrations are superimposed by fluctuations conditioned by of regional hydrometeorological factors. • To represent the seasonal character of ice processes the typical curves were computed of seasonal motion of ice extent for mild, normal and severe winters were drawn, with an estimation of the standard deviations (Sl. 5) that characterize their variability.
Seasonal distribution of the extremal small (1), normal (2) and extremal large (3) ice extent . Seasonal standard deviations of the ice extent distribution
Distribution of estimates shows a vividly expressed annual motion of the ice extent and a local minimum of variability during the periods of maximal development of ice conditions. Variability maxima are generally related to the periods of development and destruction of the ice extent except the Bering Sea, where variability maximum appears to be connected with the start of the period of the ice destruction. Differences in the analyzed characteristics are expressed first in absolute values and in terms when different phases start to take place. • Thus, the ice extent maximum in the Okhotsk Sea takes place in March, that of the Japan Sea in February; and for the Bering Sea, there are, two periods of possible maxima of the ice extent: at the end of February and early of April. • Some similarity of the ice processes in the Okhotsk Sea and the Japan Sea, as well as distinct differences in the Bering Sea (in statistical sense) are probably related to the nature of the evolution of the large-scale system of hydrometeorological parameters of the North Pacific.
Long-term distribution of statistical esimations of the Okhotsk, Japan and Bering Seasice extent. In the table Lav - mean ice extent value, t - standard deviation, , - linear trend parameters (slope angle and ts standard error, respectively).
Summary of results to date: • 1. Statistical analyses if ice data did not reveal notable (statistically essential) linear trends. It lets do the conclusion that general analyses of ice condition did not reveal changes of the climate. However, it is possible to mention some changes of the nature of seasonal processes: intensification of the processes of the development of ice, that is indicated by the maximum value of incline angle of trend constituent during the period of intensive development of ice (December through February), and its decrease during the other stages of ice formation (February through May). • 2.It is shown that the major input into the formation of ice in the above-mentioned seas is done by quazi-periodic constituent with the periods of 2-3 and 7-8 years. The input of 11-year constituent is more obvious in the Bering Sea, and it is almost not represented in the processes of Okhotsk and Japan Seas. • 3.It is stated, that in general (statistical estimations of correlation during the whole period of observations) evolution processes of ice conditions in the areas of water of the Okhotsk and Japan Seas are going on within one phase, i.e. during the intensive development of ice of one sea there should be the similar process in the other sea. Evolution processes of ice conditions in the Bering sea go mainly during antiphase.
4. Provided data confirm the possibility of cyclic constituent with the period of 14 years of the processes going on in the system of the Far Eastern seas. • 5. Combined analyses of sea ice processes revealed the existence of specific areas of high-level values in the correlation space. Localization of those areas is changing due to the shift between the values being analyzed and the season. • 6.There are high-level values in certain areas between ice conditions and termokhalin fields in the correlation space. Localization of those areas is sea dependent, and they are changing depending on the shift between the values under analyses and the season. In general, Bering sea salinity distribution is well co-ordinate with the location of the edge of ice-floes. Location of the ice-floes’ edge in the middle of March (the time of ice development maximum) both in cold and warm winters repeats the configuration of surface isohaline 32pm.
CONCLUSION • Conducted investigation confirms the essential different scale variability of the climatic characteristics of the northern hemisphere. One of its indicators is ice, because the processes of ice formation prevail in the system of “atmosphere/ice extent /ocean”. Ice extent in its turn effects those processes. • FUTURE PLANS. • To investigate historical and resent variations of ice extent and concentration in the Far-Eastern Seas system in connection with Arctic and North Pacific Oscillations, and El Nino; elaboration of set of statistical models for long-term evolution of the sea ice cover in the North Pacific Region, search for connection between the resent changes in ice condition and marine biota (ecosystem changes)/