An estimate of plankton distribution in the ocean based on acoustic sounding

Doklady Earth Sciences -     

Acoustic studies of zooplankton in the Sea of Japan and Eastern Arctic

We present the results of sound scattering studies to estimate the distribution and dynamics of zooplankton in the upper sea layer under various conditions. The measurements of the sound scattering coefficients were carried out over different pathways during the ship motion and at individual stations at frequencies of 100–250 kHz. The studies were carried out in 2004–2014 in the Sea of Japan and in 2013 in the Eastern Arctic seas. The studies of sound scattering were performed simultaneously with net catches of plankton in situ. These data allowed us to study the details of correlation between the sound scattering coefficient and zooplankton concentration. The studies revealed significantly stronger sound scattering in the Eastern Arctic, which is related to the greater concentration of zooplankton, the migration of which differs strongly from the migration of plankton in the warm seas.     

The first discovery of cryptotephra of the catastrophic eruptions of the Baitoushan volcano in the tenth century A.D. in the shelf deposits of the Sea of Japan

The interlayers of the cryptotephra of different episodes of the catastrophic eruption of the Baitoushan volcano (Paektu-san, Changbaishan-Tianchi) in the 10th century were discovered in the sedimentary cover of Amur Bay in the Sea of Japan by the geochemical and paleomagnetic characteristics. The petrochemistry of the volcanic glass indicates the possible occurrence of pyroclastic material in the B–Tm layer and more recent episodes that have not been identified before in the sediments of the Sea of Japan. The impact of the eruption on the bay environment is noted. It is shown that the medieval state of Balhae occupying vast areas and adjacent to the volcano no longer existed after the more earlier episodes of eruption.     

Acoustic tomography for monitoring the Sea of Japan: a pilot experiment

A pilot experiment was conducted in the Sea of Japan (also called the East Sea) in September-October 1999, to assess the possibility of using acoustic tomographic techniques for monitoring water mass structure and dynamics. Acoustic m-sequence signals at various frequencies between 250 and 634 Hz were transmitted from bottom-mounted acoustic sources in shallow water off the coast of Vladivostok to vertical-array receiving systems deployed off the north coast of Ulleung-Do island (S. Korea), 558 km to the south. The data are analyzed for temporal correlation, time spread, and transmission loss and are interpreted in terms of a tomographic system for monitoring the East Sea.     

Chukchi Sea Ice Conditions for the Last Few Centuries: Reconstruction from Sedimentation Records

For the first time, the reconstruction of variations in the duration over several hundred years was conducted on the basis of models developed by comparing hydrometeorological observations and detailed scanning of the chemical composition of bottom sediments accumulated during the corresponding period. The gauge models for the reconstruction of air temperature and ice cover of the water area for three sites in the northern part of the Chukchi Sea have been developed. During the reconstruction, an insignificant increase in the duration of the ice-free period during the Little Ice Age was established, which does not coincide with the changes in the temperature regime that took place. It is concluded that the dynamics of the inflow of warm Pacific waters through the Bering Strait had the predominant influence on the ice regime of the Chukchi Sea.