Fluorescence of Dissolved Organic Matter As a Marker for Distribution of Desalinated Waters in the Kara Sea and Bays of Novaya Zemlya Archipelago A

ISSN 0001-4370, Oceanology, 2017, Vol. 57, No. 1, pp. 41–47. © Pleiades Publishing, Inc., 2017. Original Russian Text © A.N. Drozdova, S.V. Patsaeva, D.A. Khundzhua, 2017, published in Okeanologiya, 2017, Vol. 57, No. 1, pp. 49–56. MARINE CHEMISTRY Fluorescence of Dissolved Organic Matter as a Marker for Distribution of Desalinated Waters in the Kara Sea and Bays of Novaya Zemlya Archipelago A. N. Drozdovaa, *, S. V. Patsaevab, and D. A. Khundzhuab aShirshov Institute of Oceanology, Moscow, Russia bMoscow State University, Department of Physics, Moscow, Russia *e-mail: [email protected] Received September 2, 2016; in final form, September 22, 2016 Abstract—The optical properties and distribution of dissolved organic matter in the surface waters of the Kara Sea and bays of Novaya Zemlya archipelago were studied during the 63th cruise of the R/V Akademik Mstislav Keldysh. The fluorescence of dissolved organic matter has been studied over wide excitation (230–550 nm) and emission (240–650 nm) wavelength ranges. Based on the results of fluorescence measurements, we propose a simple technique for estimating the relative content of humic compounds entering the Kara Sea shelf region with Ob and Yenisei river runoff. We have found that the blue shift parameters of the DOM fluorescence are Δ270–310 = 28 ± 2 nm and Δ355–310 = 29 ± 2 nm. The highest contents of humic compounds in surface waters were measured on the transect across the desalinated layer of the Kara Sea, near the continental slope on the transect along the St. Anna Trough, and in the area of Sedova, Oga and Tsivol’ki bays. Traces of labile terrigenous organic matter were found in the region of the Voronin Trough, in the bays of the Severny Island of Novaya Zemlya, as well as in some freshwater reservoirs and ice samples of the archipelago. We established a conserva- tive distribution of dissolved organic matter, whose content in water varied from 1.25 to 8.55 mg/L. DOI: 10.1134/S0001437017010039 1. INTRODUCTION 6] and investigating the degradation processes of DOM [17]. A high HS content is typical of Siberian rivers, Dissolved organic matter (DOM) of natural origin including the Ob and Yenisei [2, 15]. This makes it pos- is one of the most important components of marine sible to use the peculiar features of riverine DOM fluo- ecosystems and the carbon cycle [8]. In the Arctic 15 rescence described in [2, 14] to reveal the occurrence of Basin, the DOM pool was estimated as 9 × 10 g [20]. terrigenous DOM in the Arctic Basin. For example, The annual supply of Corg from large Siberian rivers to traces of terrigenous DOM have been discovered in the the Arctic shelf is roughly 3 × 1013 g [7, 21]. The Kara Kara Sea north of 76° N [2]. Sea receives the largest river runoff over the entire Arc- The goal of the present study is to examine the dis- tic Basin, which is about 45% of the total runoff of the tribution and fluorescence of DOM in the upper water Arctic region [11, 22]. layer of the Kara Sea and the bays of Novaya Zemlya. Currently, optical methods are widely used in study- We investigated the spreading of desalinated waters in ing the origin and dynamics of DOM [12, 18, 19, 22, the Kara Sea as well as in the Voronin and St. Anna 25]. They and based on the ability of the colored frac- troughs and revealed the areas of predominance of tion of DOM, in particular, fluorescent DOM, to labile autochthonous DOM in the surface waters. absorb the ultraviolet (UV) light and to emit UV and visible light. A typical spectrum of UV-excited fluorescence of DOM in natural water involves two superim- 2. MATERIALS AND METHODS posed bands. The first one represents a peak at 300– The water samples were collected during cruise 63 350 nm and is due to emission of proteins, aromatic of the R/V Akademik Mstislav Keldysh in August– amino acids, and phenolic compounds, while the sec- October 2015 at 28 stations in the Kara Sea and bays of ond band is due to fluorescence of humic substances Novaya Zemlya. Oga, Tsivol’ki, and Sedov bays are (HS) in the blue spectral range [16, 23]. The composi- located on the eastern shore of Severny Island of the tion and ratios of DOM components are liable to differ archipelago, while Stepovoy and Abrosimov bays are from one aquatic area to another. That is why optical situated on Yuzhny Island (Fig. 1). Ten samples of markers are successful in identifying natural waters [3, river, lake, and ice water were collected to study the 41 42 DROZDOVA et al. Ν VoroninV Trough o r o 80 n 52415241 h i n g T u r o 52405240 o r 79 u T g a h 52395239 n n 52385238 78 A . t St.S Anna Trough 52375237 52365236 77 52115211 5214,5214, 5214-25214-2 76 52325232 75 OgaOga BayBay SSedovaedova BBayay 5205,5205, 5205-25205-2 a Tzivol'kiTzivol'ki BBayay y l 74 m 52035203 e Z a y 52005200 73 a YeniseiY Bay v e o StepovoyStepovoy BayBay y n i 51995199 a s NovayaN Zemlya e B i B 72 AmbrosimovAmbrosimov BBayay b a ObO Bay y 71 52655265 52665266 70 50 55 60 65 70 75 80 85 90 Ε Fig. 1. Stations of water sampling for content and optical properties of DOM (August 30–October 6, 2015). optical properties of fresh waters entering the Kara Sea natural DOM [9, 18]. The wavelength accuracy of from Novaya Zemlya. excitation and emission monochromators is ±1 nm, Water samples were filtered through precombusted and their spectral resolution is 15 nm. at 430°С Whatman GF/F filters with an average pore A Unico spectrophotometer was used to record the size 0.6–0.7 μm. The filtrate for recording the absorp- absorption spectra. It was performed with respect to tion spectra was placed into glass vials 22 mL in vol- distilled water in the 1-cm cell over the spectral range ume and stored at 2–3°С for subsequent analysis 200–900 nm with an increment of 1 nm. The spectral under stationary conditions. For the dissolved organic resolution was 2 nm. carbon (DOC) measurements, the filtrate was addi- The quantum yield of fluorescence (QYF) was deter- tionally acidified with hydrochloric acid up to pH 2. mined for each excitation wavelength by referencing to Fluorescence of water was measured on board imme- the fluorescence of quinine sulfate fluorophore [5, 23], diately after filtration without additional conservation the QYF of which is 0.55 [23]. of samples. The DOC content was determined by high-temperature combustion with a Shimadzu analyzer 3. RESULTS AND DISCUSSION TOC-VCPH/CPN. Its instrumental error is 1%. The Station 5205, located on a transect across a lens of reproducibility of the results was ±5%. desalinated waters along the eastern coast of Novaya The fluorescenсe spectra were recorded at indoor Zemlya, was chosen as the reference site, distinguished temperature using a cell 1 cm in length and a Lumex by minimal salinity (16.4 psu). Figure 2a shows the flu- Fluorat-02-PANORAMA spectrofluorometer. Con- orescence spectra of water from this station at different sidering that the spectral response of natural DOM excitation wavelengths, (Fig. 2b) the 2D fluorescence depends on the excitation wavelength [3, 23], the spectrum, and (Fig. 2c) the wavelength dependence of spectra were recorded from 240 to 650 nm with a 1-nm QYF. There was no fluorescence of proteins or aromatic increment, and the excitation wavelengths from 230 to amino acids in the short-wavelength spectral range 650 nm with a 5-nm increment. The 2D fluorescence from 310 to 380 nm, but fluorescence of HS within the spectra, known also as excitation emission matrices range 400–550 nm was quite intense (Figs. 2a and 2b). (EEMs), are widely used to identify fluorophores of This example shows that the maximum of HS fluores- OCEANOLOGY Vol. 57 No. 1 2017 FLUORESCENCE OF DISSOLVED ORGANIC MATTER AS A MARKER FOR DISTRIBUTION 43 cence depends on the excitation wavelength: the fluorescence band maximum shifts towards shorter wavelengths when the excitation wavelength increases from 270 to 310 nm. A further increase in the excitation wavelength results in a shift of the fluorescence maximum towards longer wavelengths. This peculiarity of fluorescence differentiates the colored fraction of natural DOM from other organic luminophores. The numerical characteristic of this effect, namely, the (c) parameters of the blue shift of fluorescence, is a distinc- tive feature of natural DOMs of different origin [3, 6]. Table 1 gives the parameters of the blue shift and fluorescence band maxima of the HS transported with Excitation wavelength, nm wavelength, Excitation river runoff to the Kara Sea shelf. Similar to the DOM 300 450 500 550 600 spectra of Ob and Yenisei fresh waters given in [13], the 2D spectrum of water from station 5205 (Fig. 2b) 250 350 400 reveals the presence of fluorophores A and C accord- 1.8 1.6 1.4 1.2 1.0 2.4 2.2 2.0 0.8 0.6 0.4 ing to Cobble’s classification [16]. The latter provides % ﬂuorescence, of additional evidence of abundance of riverine HS in the yield Quantum water samples. The QYF depends on the excitation wavelength and varies from 0.5 to 2.3%. It is shown in [4] that melting of the Novaya Zem- lya ice cover may contribute to desalination of surface waters of the coastal zone of Novaya Zemlya in addi- tion to westward propagation of Ob and Yenisei waters in the Kara Sea Basin.

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