Sediment organic matter, grain size, and results of prediction models from northern North Atlantic and Arctic Seas

Sediment samples and hydrographic conditions were studied at 28 stations around Iceland. At these sites, Conductivity-Temperature-Depth (CTD) casts were conducted to collect hydrographic data and multicorer casts were conductd to collect data on sediment characteristics including grain size distribution, carbon and nitrogen concentration, and chloroplastic pigment concentration. A total of 14 environmental predictors were used to model sediment characteristics around Iceland on regional geographic space. For these, two approaches were used: Multivariate Adaptation Regression Splines (MARS) and randomForest regression models. RandomForest outperformed MARS in predicting grain size distribution. MARS models had a greater tendency to over- and underpredict sediment values in areas outside the environmental envelope defined by the training dataset. We provide first GIS layers on sediment characteristics around Iceland, that can be used as predictors in future models. Although models performed well, more samples, especially from the shelf areas, will be needed to improve the models in future.

Age and isotopic and chemical compositions of volcanic rocks from the Japan and Okhotsk Seas

This paper reports results of petrographic and geochemical studies of Miocene-Pleistocene volcanic rocks that accompanied formation of deep-water basins of the Sea of Japan and Sea of Okhotsk. Geochemical types of these rocks, their geodynamic settings, and their derivation from different magmatic sources were determined. Marginal-sea basaltoids from the Sea of Japan are derivatives of fluid-enriched mantle (EMI), while volcanics from the Kuril basin were generated from mantle enriched in continental crust matter (EMU). In spite of different conditions of their genesis, they have some common geochemical features, in particular, their calc-alkaline signatures. These traces of influence of the sialic crust on magma generation confirm development of the basins of both these seas on the continental basement.

(Table 1) Activity of alkali phosphatase in suspended matter at 20°C and environmental temperatures, and recycling time of organic phosphorus in the Barents and Norwegian seas

Alkali phosphatase activity and hydrochemical structure of waters in the Barents and Norwegian seas were investigated. In a sea with the seasonal bioproduction cycle alkali phosphatase activity is also seasonal, rising with trophic level of waters. At the end of hydrological and biological winter activity is practically zero. Alkali phosphatase activity is especially important in summer, when plankton has consumed winter supply of phosphate in the euphotic layer and nutrient limitation of primary production begins. In summer production and destruction cycle, apparent time for recycling of phosphorus by phosphatase in suspended matter in the euphotic layer of the Barents Sea and Norwegian Sea averages from 7 to 30 hours.