Recurring polynyas in the coastal lagoons of the Northern hemisphere

Highlights

• Recurring polynyas in coastal lagoons were quite common, at least 115 out of 246 lagoons demonstrate this (47% of lagoons).

• Typology: the inlet polynya with three subtypes – the inward, outward, «window» polynyas and the flowing polynya.

• Zoning by the presence of the recurring polynyas were made for coasts of the Atlantic, Pacific and Arctic Oceans.

• Recurring polynyas are the manifestations of thermal or mechanical mechanisms guided the polynya origin and support.

• Statistical distributions of the normalized areas and relative sizes of the polynyas are expressed by lognormal function.

Abstract

After visual analysis of more than 3000 satellite images for 2013–2020, it was found that the presence of recurring (stationary or stable) polynyas in coastal lagoons in the Northern Hemisphere of the boreal and polar climate zones of the Atlantic, Pacific and Arctic Oceans was quite common. At least 115 out of 246 lagoon-type coastal objects demonstrated this (47%). Polynyas were primitively classified into two types: the flowing polynya (due to a river inflow in a lagoon), and the inlet polynya (with three subtypes: the inward, outward and «window» ones) attached to the lagoon inlet. The geographical distribution of the lagoons with polynyas was discussed. Some comments on different mechanisms (thermal and mechanical) that guided the polynyas’ appearance in the lagoons were presented. It was noted that statistical distributions of the number of the polynyas by polynya areas or relative size of polynya areas (ration of polynya areas to lagoon areas) could be expressed by lognormal distribution function.

Introduction

The (World Meteorological Organization, 1970) defines a polynya as “any non-linear shaped opening enclosed in (sea) ice …“. Sometimes the polynya is limited on one side by the coast and is called ashore (or coastal) polynya (e.g., St. Lawrence Island Polynya) or by landfast ice and is called a flaw polynya (e.g., Laptev Sea Polynya) (Morales Maqueda et al., 2004). Polynya sizes range from 100 or 1000 m to 100 km (Smith et al., 1990) or, in terms of their areas, from 10 to 10⁵ km² (Barber et al., 2001a).

According to the mechanism of formation and maintenance, polynyas are traditionally divided into two classes: “sensible heat” polynyas and “latent heat” polynyas, but a problem with the classification of polynyas into these two types is that many polynyas are formed by a combination of the two mechanisms (although one of them is ordinarily predominant) (Morales Maqueda et al., 2004).

Another classification was proposed basing on the polynya's location: “deep water” versus “shelf water” polynyas. Deepwater polynyas are polynyas that form at or beyond the continental shelf break, while polynyas that occur over the shelves are shelf water polynyas (Morales Maqueda et al., 2004).

Polynyas tend to appear recurrently at fixed geographical locations and periods of the year. If a polynya recurs in the same position every year, it is called a recurring polynya (Morales Maqueda et al., 2004).

The majority of articles is dedicated to polynyas of Arctic Ocean Basin in the Northern Hemisphere, ex. North water polynya (Dumont et al., 2009), St. Lawrence Island polynya, Storfjorden polynya, and South Ocean Basin in the Southern Hemisphere, ex. Cosmonaut Sea polynya (Comiso, Gordon, 1996), Weddell Sea polynya (Smith, Barbere, 2007).

The presence of stationary or stable polynyas is also typical for coastal reservoirs. In particular in the lagoons, which are relatively shallow objects wholly or partially separated from the open sea area by accumulative sand or pebble barrier (spit, a chain of islands) that rises above the level of the highest tide (surge) and formed as a result of wave action (Bird, 2008). According to the geomorphological classification (Day et al., 1989; Davis, 1964), there are two types of coastal reservoirs of the lagoon type: the actual lagoon and estuarine lagoon (significantly affected by river flow). According to their shape, which depends on the barrier that prevents water from entering and leaving the lagoon, lagoons are divided into choked, restricted and leaky (Kjerfve, 1994). The size of lagoons varies from 0.01 km² to more than 10,000 km², and the depth of lagoons rarely exceeds a few meters (Kjerfve, 1994).

There are about three hundred lagoons (Domnina, Chubarenko, 2012) in the Northern hemisphere, potentially possible for ice formation. They are located in a temperate climate zone with cold winters and warm summers – between 40°N and 65°N (boreal thermal zone with average annual temperatures of −4...+4 °C) and in subarctic and Arctic climate zones located above 65°N (polar thermal zone with average annual temperatures of −23...-15 °C).

The number of published works on the analysis of iced lagoon's hydrology and hydraulics is relatively small (Chubarenko et al., 2018). Interest in freezing lagoons was first noted in Japan (SARES project 1992-93, Saroma-Resolute research). Work on the analysis of subglacial conditions of the Saroma-ko Lagoon, Hokkaido, began with studying the development of microalgae (Kawamura, 2004; Shirasawa et al., 2002). There were no publications about the polynyas in the frozen lagoons.

The phenomenon of recurring polynya has interdisciplinary dimensions, as ensure the navigation possibility for local communities during winter isolation (Zhelezova et al., 2018) and the apparent effect for biota (Deming et al., 2002; Ringuette et al., 2002). According to (Romanenko et al., 2012) the size of a stationary polynya in the Bolshaya Salma Strait of the Kandalaksha Bay of the White Sea serves as an “indicator of the winter severity”. The quadcopter-based measurements (along with horizontal transects over the polynya) have shown the polynya-induced effects on air temperature and humidity and formation of convective boundary layers over the polynya (Varentsov et al., 2019).

A typical example of a stationary polynya in a coastal lagoon is the polynya located near the Baltiysk Strait of the Vistula Lagoon in the South-Eastern part of the Baltic Sea (Zhelezova et al., 2018). This annually appearing polynya (in the case of the ice cover is present in the lagoon) is a manifestation of the interaction zone of the non-freezing sea and the freezing coastal lagoon (Chubarenko, Zhelezova, 2020). Similar polynyas can also occur in other lagoons of the Baltic Sea (Zhelezova, 2020).

This work aims to prove that a stationary polynya is a characteristic feature of the lagoons of the boreal, subarctic and arctic climate zones of the Northern hemisphere, introduce the primitive classification based on polynya location and comment on possible forcing factors of polynya's appearance.