CDOM Optical Properties and DOC Content in the Largest Mixing Zones of the Siberian Shelf Seas

Notable changes in the Arctic ecosystem driven by increased atmospheric temperature and ice cover reduction were observed in the last decades. Ongoing environmental shifts affect freshwater discharge to the Arctic Ocean, and alter Arctic land-ocean fluxes. The monitoring of DOC distribution and CDOM optical properties is of great interest both from the point of view of validation of remote sensing models, and for studying organic carbon transformation and dynamics. In this study we report the DOC concentrations and CDOM optical characteristics in the mixing zones of the Ob, Yenisei, Khatanga, Lena, Kolyma, and Indigirka rivers. Water sampling was performed in August–October 2015 and 2017. The DOC was determined by high-temperature combustion, and absorption coefficients and spectroscopic indices were calculated using the seawater absorbance obtained with spectrophotometric measurements. Kara and Laptev mixing zones were characterized by conservative DOC behavior, while the East Siberian sea waters showed nonconservative DOC distribution. Dominant DOM sources are discussed. The absorption coefficient aCDOM (350) in the East Siberian Sea was two-fold lower compared to Kara and Laptev seawaters. For the first time we report the DOC content in the Khatanga River of 802.6 µM based on the DOC in the Khatanga estuary

Geological and Geophysical Investigation of Contourite Systems from the Central and Southern Atlantic during Cruise 52 of the R/V Akademik Ioffe

The geological and geophysical expedition duringcruise 52 of the R/V Akademik Ioffe was organized bythe Shirshov Institute of Oceanology, Russian Academyof Sciences, according to the expeditionary programof FASO Russia; it was combined with transit ofthe vessel after the end of the Arctic tourist season,from September 29 to November 8, 2016 (port of exit:Gdansk, Poland; port of entry: Ushuaia, Argentina).The objectives of the expedition were formulatedby scientific supervisor I.O. Murdmaa. The scientificparty included 12 persons. The expedition was led byE.V. Ivanova and her deputy D.G. Borisov. The tasksof the expedition were carried out by the geologicalteam (head E.A. Ovsepyan) and seismic profiling andmeteorology team (head N.V. Libina).The expedition was aimed at high-resolution seismicprofiling along the ship?s track and in the centralpart of the Ioffe Drift, with collection of sedimentcores and grab samples in order to investigate theimpact of bottom circulation on sedimentation.Geological works included sediment sampling tostudy contourites (sediments formed by contour currents)and other lateral sedimentation products (turbidites,gravitites). The studies were carried out intransform valleys of the Mid-Atlantic Ridge (MAR),on the Ioffe contourite drift in the southern BrazilBasin, and on contourite terraces of the southernArgentine continental slope. The stations of sedimentsampling by gravity corers (127 mm in diameter) andan Okean 0.25 grab sampler were selected on seismicprofiles with a high-resolution SES-2000 deep subbottomecho sounder (4?7 kHz). Positioning of thevessel at the scheduled sites was assisted by GPS. Themethods of preliminary onboard analyses during theexpedition, including 5487 NM of seismic profiling,were performed along the vessel track starting from theexit to the Atlantic, except for the economic zones ofEuropean countries and Argentina, and including194 miles in a survey area in the central Ioffe Drift.Twenty-seven geological sampling stations were made(Fig. 1) with the collection of 3 sediment cores and17 grab samples or minicores.Fil: Ivanova, E. V.. Russian Academy Of Sciences; RusiaFil: Murdmaa, I. O.. Russian Academy Of Sciences; RusiaFil: Borisov, D. G.. Russian Academy Of Sciences; RusiaFil: Simagin, N. V.. Russian Academy Of Sciences; Rusia. Lomonosov Moscow State University; RusiaFil: Ovsepyan, E. A.. Russian Academy Of Sciences; RusiaFil: Libina, N. V.. Russian Academy Of Sciences; RusiaFil: Isola, José Ignacio. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Geociencias Básicas, Aplicadas y Ambientales de Buenos Aires; ArgentinaFil: Bulycheva, E. V.. Russian Academy Of Sciences; RusiaFil: Shulga, N. A.. Russian Academy Of Sciences; RusiaFil: Krek, A. V.. Russian Academy Of Sciences; RusiaFil: Lobus, N. V.. Russian Academy Of Sciences; RusiaFil: Lapidus, L. V.. Russian Academy Of Sciences; Rusi

Production of Fluorescent Dissolved Organic Matter by Microalgae Strains from the Ob and Yenisei Gulfs (Siberia)

Dissolved organic matter (DOM) is an important component of aquatic environments; it plays a key role in the biogeochemical cycles of many chemical elements. Using excitation–emission matrix fluorescence spectroscopy, we examined the fluorescent fraction of DOM (FDOM) produced at the stationary phase of growth of five strains of microalgae sampled and isolated from the Ob and Yenisei gulfs. Based on the morphological and molecular descriptions, the strains were identified as diatoms (Asterionella formosa, Fragilaria cf. crotonensis, and Stephanodiscus hantzschii), green microalgae (Desmodesmus armatus), and yellow-green microalgae (Tribonema cf. minus). Three fluorescent components were validated in parallel factor analysis (PARAFAC): one of them was characterized by protein-like fluorescence (similar to peak T), two others, by humic-like fluorescence (peaks A and C). The portion of fluorescence intensity of humic compounds (peak A) to the total fluorescence intensity was the lowest (27 ± 5%) and showed little variation between species. Protein-like fluorescence was most intense (45 ± 16%), but along with humic-like fluorescence with emission maximum at 470 nm (28 ± 14%), varied considerably for different algae strains. The direct optical investigation of FDOM produced during the cultivation of the studied algae strains confirms the possibility of autochthonous production of humic-like FDOM in the Arctic shelf regions