Structure and Inter-Annual Variability of the Freshened Surface Layer in the Laptev and East-Siberian Seas During Ice-Free Periods

Abstract

This work is focused on the structure and inter-annual variability of the freshened surface layer (FSL) in the Laptev and East-Siberian seas during ice-free periods. This layer is formed mainly by deltaic rivers among which the Lena River contributes about two thirds of the inflowing freshwater volume. Based on in situ measurements, we show that the area of this FSL during certain years is much greater than the area of FSL in the neighboring Kara Sea, while the total annual freshwater discharge to the Laptev and East-Siberian seas is 1.5 times less than to the Kara Sea (mainly from the estuaries of the Ob and Yenisei rivers). This feature is caused by differences in morphology of the estuaries and deltas. Shallow and narrow channels of the Lena Delta are limitedly affected by sea water. As a result, undiluted Lena discharge inflows to sea from multiple channels and forms relatively shallow plume, as compared to the Ob-Yenisei plume, which mixes with subjacent saline sea water in deep and wide estuaries. Due to small vertical extents of FSL in the Laptev and East-Siberian seas, wind conditions strongly affect its spreading and determine its significant inter-annual variability, as compared to relatively stable FSL in the Kara Sea. During years with prevailing western and northern winds, FSL is localized in the southern parts of the Laptev and East-Siberian seas due to southward Ekman transport, meridional extent (<250 km) and area (∼250,000 km2) of FSL are relatively small. During years with strong eastern winds FSL spreads northward over large area (up to 500,000 km2), its meridional extent increases up to 500–700 km. At the same time, area and position of FSL do not show any dependence on significant variability of the annual river discharge volume and ice coverage during warm season.

Structure and variability of the Pechora plume in the southeastern part of the Barents Sea

“…To the extent of our knowledge, this paper provides the first thorough description of structure and variability of the Pechora plume. This work continues our previous studies of large river plumes in the Eurasian Arctic including the Ob-Yenisei plume in the Kara Sea (Osadchiev et al, 2017;Osadchiev et al, 2019;Osadchiev et al, 2021a;Osadchiev et al, 2021c), the Khatanga, Lena, Indigirka and Kolyma plumes in the Laptev and East-Siberian seas (Osadchiev et al, 2020b;Osadchiev et al, 2020c;Spivak et al, 2021;Osadchiev et al, 2021b), the large-scale freshwater transport in the Eastern Arctic (Osadchiev et al, 2020a;Osadchiev, 2021). Note that in this paper, we describe the response of a medium-size river plume (with area ~10 000 km 2 ) to external forcing, while our previous studies of the Arctic River plumes were focused on large river plumes (with area ~100 000 km 2 ).…”

“…The vertical structure of the Pechora River plume was investigated using in situ data obtained during the surveys of RV Kartesh and Dalnie Zelentsy in July-August 1993-1995, 2017-2021. The isohaline of 25 is regarded as the outer boundary of the Pechora plume, similarly to other large river plumes in the Arctic Ocean (e.g., Ob-Yenisei, Lena, Khatanga) (Osadchiev et al, 2020a;Osadchiev et al, 2021a;Osadchiev et al, 2021b). In case of the Pechora plume, in situ measurements demonstrate that both horizontal and vertical salinity gradients are observed at the isohalines of 23-27 (Figures 5, 6).…”

Large River Plumes Detection by Satellite Altimetry: Case Study of the Ob–Yenisei Plume

“…However, these river plumes affect a number of key physical, biological and geochemical processes (water balance, stratification, nutrient cycle, carbon cycle, acidification, etc.) across large marine areas including the Bay of Bengal [28,56,57], the South China Sea [58], the central Atlantic [59,60], and the Arctic Ocean [8,9,[35][36][37][61][62][63]. Moreover, spreading and mixing of Ob-Yenisei and Lena plumes in the Arctic Ocean determine the sea stratification in the area of seasonal sea ice formation, thereby affecting ice formation in the Arctic Ocean, seasonal variability in the Earth's albedo and planetary climate [64,65].…”

“…Previous research revealed significant seasonal variability of both characteristics of the Ob-Yenisei plume during ice-free season [8,35]. In June-July, during the peak river discharge, the Ob-Yenisei plume is low-saline (5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15) and relatively shallow (10 m). Then, in August-October salinity of the plume steadily increases to 15-25, its depth also increases to 10-15 m. Total freshwater volume contained in the Ob-Yenisei plume accumulates during the ice-free season from ~600 km 3 in June-July to ~900 km 3 in October.…”

“…Generally, river plumes have large area but small depth. Area of a river plume exceeds its thickness by 3-5 orders of magnitude, therefore, even small rivers (with a water flow rate of several cubic meters per second) form river plumes with spatial extents of tens and hundreds of meters [1-5], while the spatial extents of river plumes formed by the largest rivers in the World are hundreds of kilometers [6][7][8][9]. Thus, despite the relatively small volume of global continental runoff into the World Ocean (38,000 km 3 annually) compared to the volume of shelf seawater (66,600,000 km 3 ), river plumes, depending on the season, occupy from 7% to 21% of the total shelf area of the World Ocean, i.e., several millions of square kilometers [10].…”