On the possible changes of steric component of the World Ocean’s level

Abstract

It is shown that the steric fluctuations of World Ocean level (WOL) should be advisably considered as a sum of «fast» and «slow» components. The «fast» component is dependent on the external heat balance that determines the heat content fluctuations of ocean’s active layer. The «slow» component lies in heating (cooling) from above and redistribution of heat throughout the ocean to the lower boundary of main thermocline that lasts for not less than two decades due to the low vertical speeds. It is established that the trend formation in steric level fluctuations takes place due to the «slow» component, contribution of which amounts more than 70 % of the base process dispersion. It is described by the physicostatistical model with the input data of sea surface temperature (SST) values in 5897 nodes of two-degree grid of the World Ocean for the period from 1955 to 2002. The model’s statistical mechanism consists in using the procedure of shearing step-by-step multiple regression. The 20 prediction models have been calculated up to 2033 inclusively with different advance time with respect to SST. The absence of significant trend in prognostic estimation of steric fluctuations is established starting from 2003. This implies the considerable deceleration of WOL’s steric component in the first two decades of 21st century due to the World Ocean’s cooling as a result of its heat content decrease. The estimations of heat content carried out in recent years by different authors verify the cooling of ocean’s deep layers since 2003.