Acoustical properties of plankton

Plankton is distributed in all oceans and seas, and therefore its acoustic properties can be essential for underwater acoustics. A sound scattering cross section of plankton can increase due to gas cavities associated with plankton cells. Such gas cavities has been found in many kinds of phyto- and zoo- plankton. The present paper gives results of investigation of plankton gas cavities with different methods. II was found in particular that sound velocity in phytoplankton suspensions varies bofh up and down compared to the sound velocity in pure water. A response of phyto- and zoo- plankton on compression and decompression is studied. It was found that species of euphausiids having long range vertical daily migration use bubbles (swimbladders) lo control their buoyancy, while species living without long vertical migration do nof have swimbladders

(Table 1) Geochemical composition of surface waters obtained aboard the R/V Rift along the Volga-Caspian canal

The Volga River discharge consists of the waters transferred by fast currents through channels and the waters which are passing through the shallow areas of the delta overgrown by cane. Using the hydrochemical data, it is possible to track distribution of the waters modified by 'biofilters' of macrophytes in the delta shallows starting from the external edge of the delta. The main distinctive features of these waters are the high content of dissolved oxygen, the abnormally high values of the pH, and the low content of dissolved inorganic carbon (both total and as CO2). These waters extend in the shape of 1 to 3-km-wide strips at a distance of 20-40 km from the outer border of the delta. The analysis of the data obtained during the expeditions run by the Institute of Oceanology of the Russian Academy of Sciences in 2003-2009, along with archived and published data, show that such 'modified' waters occur almost constantly along the outer edge of the Volga River delta

Nutrient chemistry of the Ob\u27 and Yenisey Rivers, Siberia: results from June 2000 expedition and evaluation of long-term data sets

Although containing only ∼1% of global ocean volume, the arctic Ocean receives almost 10% of global river discharge. Nutrients carried by arctic rivers influence the productivity of their estuaries and coastal seas and may serve as important indicators of changing conditions in their watersheds. The three largest arctic rivers (Yenisey, Ob\u27, and Lena) enter the arctic Ocean from Siberia and together account for nearly 35% of river-water inputs to the arctic Ocean. Although several nutrient flux estimates have been published for Eurasian arctic rivers, recent publications have highlighted uncertainties in these estimates and have cautioned against their uncritical use, particularly with respect to ammonium data. In order to help clarify the situation and evaluate the validity of existing long-term data sets, we went to Siberia during June 2000 to collect and analyze new nutrient samples from the downstream reaches of the Yenisey and Ob\u27 rivers. Samples were independently analyzed by as many as four groups/laboratories in order to maximize confidence in analytical results. Whereas long-term data sets report average ammonium concentrations of 710 and 360 μg N/l in the Ob\u27 and Yenisey rivers, respectively, we measured concentrations of only 10–15 μg N/l in both rivers in June 2000. We conclude that existing long-term data sets for these two rivers are grossly in error with respect to ammonium concentrations, and by extension that other surprisingly high values of ammonium reported for Russian arctic rivers (for example Pur, Taz, Nadym, and Pechora rivers) must be considered extremely doubtful. The situation is better for nitrate and phosphate, but our one-time sampling is insufficient to fully evaluate the reliability of existing data sets for these nutrients. Because a substantial percentage of the total freshwater input to the arctic Ocean comes from Russian rivers, the large revisions in ammonium concentrations needed for the Ob\u27, Yenisey, and probably other Eurasian arctic rivers will significantly reduce estimates of dissolved inorganic nitrogen (DIN) fluxes to the arctic Ocean as a whole