Kara Sea freshwater transport through Vilkitsky Strait: Variability, forcing, and further pathways toward the western Arctic Ocean from a model and observations

Abstract

Siberian river water is a first-order contribution to the Arctic freshwater budget, with the Ob, Yenisey, and Lena supplying nearly half of the total surface freshwater flux. However, few details are known regarding where, when, and how the freshwater transverses the vast Siberian shelf seas. This paper investigates the mechanism, variability, and pathways of the fresh Kara Sea outflow through Vilkitsky Strait toward the Laptev Sea. We utilize a high-resolution ocean model and recent shipboard observations to characterize the freshwater-laden Vilkitsky Strait Current (VSC), and shed new light on the little-studied region between the Kara and Laptev Seas, characterized by harsh ice conditions, contrasting water masses, straits, and a large submarine canyon. The VSC is 10-20 km wide, surface intensified, and varies seasonally (maximum from August to March) and interannually. Average freshwater (volume) transport is 500 6 120 km 3 a 21 (0.53 6 0.08 Sv), with a baroclinic flow contribution of 50-90%. Interannual transport variability is explained by a storagerelease mechanism, where blocking-favorable summer winds hamper the outflow and cause accumulation of freshwater in the Kara Sea. The year following a blocking event is characterized by enhanced transports driven by a baroclinic flow along the coast that is set up by increased freshwater volumes. Eventually, the VSC merges with a slope current and provides a major pathway for Eurasian river water toward the western Arctic along the Eurasian continental slope. Kara (and Laptev) Sea freshwater transport is not correlated with the Arctic Oscillation, but rather driven by regional summer pressure patterns.

Sea-Ice Wintertime Lead Frequencies and Regional Characteristics in the Arctic, 2003–2015

“…As stated above, the region where a surface-intensified current enters the Laptev Sea through Vilkitsky Strait (E in Figure 5), is clearly characterized by an increased lead frequency compared to its surrounding. This finding feeds the assumption that changing water masses and strong surface gradients in this region [39] could represent favorable conditions for the formation of leads. In addition, at least the region of slightly enhanced lead activity in a band between the Beaufort Sea and the New Siberian Islands (C in Figure 5) and an elongated region of strong lead frequencies northwest of Franz-Josef Land (G in Figure 5) reveal a potential influence of the Arctic circumpolar boundary current [44] on the spatial distribution of leads within the Arctic basin.…”

“…In addition, at least the region of slightly enhanced lead activity in a band between the Beaufort Sea and the New Siberian Islands (C in Figure 5) and an elongated region of strong lead frequencies northwest of Franz-Josef Land (G in Figure 5) reveal a potential influence of the Arctic circumpolar boundary current [44] on the spatial distribution of leads within the Arctic basin. From the obtained spatial distribution of predominant lead patterns, precisely speaking their alignment with isobaths, we also want to put forward the idea of tides, that potentially favor divergent motion over the shelf break and thereby influence ice break-up [39,45].…”

Hydrographic responses to regional covariates across the Kara Sea

“…During negative phase of monthly mean AO the easterly winds prevail, which creates a weaker circulation pattern: saline currents from the Barents Sea and from the Arctic Ocean entering the northern Kara Sea are depressed and the saline current along the eastern coast of NZ is reduced. Also, the freshwater current out from the Kara Sea along the northeastern coast declines [ Janout et al ., ; Panteleev et al ., ]. These are called blocking conditions because of the reduced levels of saline water inflow and freshwater export.…”

“…The region in front of the river estuaries (Region 3) is affected by annual pulses of freshwater [ Harms and Karcher , ]. The northeastern coast (Region 4) is an outflow path for freshwater export to the Laptev Sea [ Janout et al ., ]. The northern Kara Sea (Region 5) is influenced by Atlantic currents and flow from the southern Kara Sea [ Pavlov and Pfirman , ].…”

“…The Kara Sea is one of the shelf seas surrounding the Arctic Basin (Figure ). Its hydrography is characterized by freshwater inflow from the continental rivers and saline water inflow from the Barents Sea [ Pavlov and Pfirman , ], which together with seasonal ice conditions cause strong spatiotemporal hydrographic variation [ Janout et al ., ]. During the past few decades in the Kara Sea, ice concentration has declined and SST increased, which have resulted from strengthened heat flux through Atlantic currents and enhanced warm airflow from the midlatitudes [ Gerdes , ; Polyakov et al ., ].…”