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.
Highlights
The shallow Laptev and East-Siberian seas are located in the Eastern Arctic and comprise approximately a quarter of the Arctic shelf (Figure 1)
Strong eastern winds prevailed in August 2011 (7–9 m/s) followed by moderate winds with complex pattern in September 2011 (4–5 m/s) and strong eastern wind in October 2011 (9–10 m/s)
Strong eastern winds prevailed in August– September 2019 (6–9 m/s), which switched to western winds in October 2019
Summary
The shallow Laptev and East-Siberian seas are located in the Eastern Arctic and comprise approximately a quarter of the Arctic shelf (Figure 1) These seas receive large river discharge that forms sea-wide freshened surface layer (FSL). Various regional features, such as coastline configuration, river mouth morphology, bathymetry, interaction between neighboring river plumes, sea ice, among others, strongly affect river plumes, which results in significant variety of spreading and mixing patterns of river plumes in the World Ocean (Horner-Devine et al, 2015). This fact supports necessity of regional field studies of river plumes in different climatic and oceanographic conditions
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