ISSN 0001-4370, Oceanology, 2017, Vol. 57, No. 1, pp. 19–30. © Pleiades Publishing, Inc., 2017. Original Russian Text © A.A. Polukhin, P.N. Makkaveev, 2017, published in Okeanologiya, 2017, Vol. 57, No. 1, pp. 25–37. MARINE CHEMISTRY Features of the Continental Runoff Distribution over the Kara Sea A. A. Polukhin* and P. N. Makkaveev Shirshov Institute of Oceanology, Russian Academy of Sciences, Moscow, Russia *e-mail: [email protected] Received March 23, 2016; in final form, June 8, 2016 Abstract—This paper considers different types of the continental runoff distribution over the Kara Sea depending on hydrological and meteorological processes based on 1993–2014 expedition data of the Shirshov Institute of Oceanology. The results of calculating the relative contribution of fresh water from several sources (the Ob and Yenisei rivers and melted ice) using hydrochemical parameters are also given. DOI: 10.1134/S0001437017010143 INTRODUCTION can be combined with the western type. Naturally, The Kara Sea is the receiving basin for the runoff of such river runoff propagation is mainly determined by Siberia’s two largest rivers: the Ob and Yenisei [4]. In wind [7]. The second important factor is the volume of addition, the sea also receives waters from the Pur, fresh waters supplied from the Ob, Yenisei, and other Taz, Pyasina, and other rivers. The total runoff of riv- rivers (this work took into account only waters of the ers emptying in the Kara Sea is 1350 km3/yr, 82% is Ob two former rivers, which make up over 80% of the total and Yenisei waters [15]; i.e., the waters of these rivers freshwater runoff in the Kara Sea). make up the majority of freshwater runoff. The study Only the total input of fresh waters (including con- of river water propagation over the sea basin and esti- tinental runoff, atmospheric precipitates, and melted mation of the contribution of each of these rivers in the ice) can be estimated from physical parameters alone surface layer structure is of great significance. (salinity and temperature). Chemical parameters The problem of river water propagation over the sea should be applied to determine the contribution of basin has been discussed at least since 1930s [26], and individual sources of fresh waters. Stunzhas was the the alkali–chlorine ratio is one of the major indicators first to attempt separation of Ob and Yenisei waters in of river runoff. In addition to the hydrochemical the surface layer of the Kara Sea [28]. Using salinity– parameters, the distribution of continental runoff is alkalinity and salinity–silicon regression equations, also estimated from hydrophysical data, results of sat- Stunzhas showed that the desalinated lens found in ellite analysis, and modeling [6, 8, 37]. The boundar- autumn 1993 near the northern coast of Novaya Zem- ies of the continental runoff distribution can also be lya [2] consists of Yenisei waters. Work on distinguish- determined using the hydrochemical characteristics of ing the waters of different sources in the Kara Sea was mixing waters, in particular, the dissolved silicon con- continued using the equation of mixing of quasi-con- tent [21, 26]. According to the literature data, this servative substances [13]. boundary is determined by the 10 μm-silicon isoline It was demonstrated in previous works that the val- [23, 24]. Another reliable criterion for the presence of ues of the total alkalinity (Alk), content of dissolved continental runoff waters is the alkalinity/salinity inorganic carbon (Ctot), and dissolved silicon are more (Alk/S) ratio. The change in salinity can be also caused suitable for determining the origin of high-latitude by melting ice (marine, river, and continental), atmo- surface waters, because they are the most sensitive spheric precipitates, and permafrost degradation. indicators of continental runoff and better match the However, changes in the Alk/S (or Alk/Cl) ratios are quasi-conservative conditions than other hydrochem- mainly controlled by river runoff. Alk/S > 0.06–0.08 ical parameters [3, 13, 28]. confidently indicates the significant contribution of In addition to the areal distribution of continental river waters [15, 22]. runoff over the sea basin, it is also important to take Several schemes of continental runoff propagation into account the vertical influence of fresh waters on in the Kara Sea basin are known from the literature the hydrological and hydrochemical structure of the data (Fig. 1). In particular, three schemes—eastern, Kara Sea. Analysis of results of 271 CTD soundings central, and western—are proposed in [7, 16]. An during the expeditions of the Shirshov Institute of additional southwestern type, distinguished in [25], Oceanology from 1993 to 2014 showed that the desali- 19 20 POLUKHIN, MAKKAVEEV 82° N FJL Severnaya Zemlya Archipelago 80° 78° . 3 ° Arch 76 lya 2 em Z a y Taimyr a v 1 74° o Peninsula N 72° Yamal Pen. 70° 68° 60° 65° 70° 75° 80° 85° 90° 95° 100° E Fig. 1. Types of distribution of river runoff in Kara Sea: 1, western type (combined with southwestern type); 2, central type; 3, eastern type. nation of the seawater surface layer occurs within a Several methods can be applied to study the contri- range from 3–5 m to 15–20 m. bution of separate sources to the formation of surface waters. The first is regression analysis. Regression equations for alkalinity and silicon content versus MATERIALS AND METHODS salinity were obtained from natural observations for different sea regions: All data used for calculations were obtained during a comprehensive oceanographic expedition of the C = A0 + SA1,(1) Shirshov Institute of Oceanology, Russian Academy of where A and A are empirical coefficients, S is the Sciences, in 1993 [9], 2007 [30], 2011, 2013, and 2014. 0 1 salinity, and C is the content of some chemical param- In all these expeditions, works on hydrological stations eter. were supplemented by sampling during as the vessel moved. The obtained distribution of the fields of hydro- The value of the free term A0 can be interpreted as chemical parameters and vertical hydrochemical struc- the value of the parameter at zero salinity and in the ture of waters are presented in detail in [10–12]. Mate- given case implies the content of salinity or silicon in rials of 2013 and 2014 expeditions have not been pub- river waters. lished yet. In these expeditions, samples were analyzed using standard techniques recommended for marine Another approach is based on the assumption that hydrochemical studies [19, 20, 27], while hydrological the value of the conservative (or quasi-conservative) data (temperature and water salinity) were obtained parameter С0 during mixing will be described by the from СTD sounding. The NCEP/NCAR reanalysis following equation: (http://www.cdc.noaa.gov) was used to obtain data on С V = C V + C V + C V + … ,(2) the dynamic influence of wind on the surface sea layer 0 0 1 1 2 2 3 3 [35]. This work was also based on river discharge data where V , is the volume of the ith water mass, while available free of charge at http://www.arcticgreatriv- i Сi is the value of the corresponding parameter; taking ers.org/. This is the Arctic Great Rivers Observatory into account that V = ∑V , the relative contribution of Project, which has collected data on runoff from the 0 i each separate water mass can be expressed as Ki = Ob, Yenisei, Lena, Kolyma, Yukon, and Mackenzie V /V . Then the equation is transformed as follows: rivers since 1999 to the present. Hydrographs of the Ob i 0 and Yenisei rivers are shown in Fig. 2. С0 = ∑(CiVi/∑Vi) = ∑(KiCi). (3) OCEANOLOGY Vol. 57 No. 1 2017 FEATURES OF THE CONTINENTAL RUNOFF DISTRIBUTION OVER THE KARA SEA 21 (а) (b) 80000 80000 1993 2007 Yenisei Yenisei 60000 Ob 60000 Ob /s /s 3 3 40000 40000 Discharge, m Discharge, m 20000 20000 0 0 1 23456789101112 1 23456789101112 Month Month (c) (d) 100000 50000 2011 2013 Yenisei Yenisei 80000 40000 Ob Ob /s /s 3 60000 3 30000 40000 20000 Discharge, m Discharge, m 20000 10000 0 0 1 23456789101112 1 23456789101112 Month Month (e) 80000 2014 Yenisei 60000 Ob /s 3 40000 Discharge, m 20000 0 1 23456789101112 Month Fig. 2. Monthly discharge of Ob and Yenisei rivers in (a) 1993, (b) 2007, (c) 2011, (d) 2013, and (e) 2014. Data from Arctic Great Rivers Observatory Project http://www.arcticgreatrivers.org/. OCEANOLOGY Vol. 57 No. 1 2017 22 POLUKHIN, MAKKAVEEV Values of mineralization, alkalinity, and content of dissolved silicon and inorganic carbon in water of near-estuary areas of Yenisei and Ob bays obtained during expedition works and calculated from regression equations Measured parameters Using regression equation Year River (using salinity minimum) B/A (y = aS + b) Sal Alk Si Ctot Alk Si Ctot 0.681 36.89 8.75 1993 Ob 0.745* 0.712 36.83 9.20 0.049 –0.449 0.567 1.094 74.24 13.64 1993 Yenisei 0.047 1.226 81.00 15.34 0.034 –1.834 0.402 0.584 65.21 8.16 2007 Ob 0.049 0.656 65.21 8.16 0.052 –0.887 0.597 0.965 86.79 11.96 2011 Yenisei 0.068 1.017 107.44 12.62 0.041 –2.536 0.471 1.028 49.92 12.70 2013 Ob 0.227 0.980 29.94 12.34 0.040 –0.581 0.473 0.669 64.16 8.56 2014 Ob 0.036 0.398 9.39 5.51 0.054 –1.428 0.620 0.583 53.88 7.47 2014 Yenisei 1.094 0.727 55.24 9.21 0.054 –0.874 0.639 * Calculated using regression equation Assuming the total of the relative contribution of waters, which, in turn, are enriched in silicon and car- each water mass is ∑Ki = 1 and knowing the values of bonate carbon as compared to the Ob [11].