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1 INTRODUCTION

The Northern Sea Route (North East Passage;

hereinafter referred to as the NSR) is becoming an

increasingly important shipping route. Currently, its

shipping traffic is not impressive. In last summer

navigation seasons commercial ships encountered

severe ice conditions that reminded about the

environmental uncertainties accompanying voyages

on the Northern Sea Route [4, 14]. Despite this, cargo

transport in the years after 2000 has been

systematically increasing. Currently, the increase in

transport applies to both destination shipping and

transit shipping but destination shipping was

increasing faster in the years 2017-2019 [9]. Also, more

and more ships with a flag other than Russian used

this route, treating it primarily as a transit route for

voyages between Far Eastern countries and Europe

and vice versa.

In 2021 alone, as many as four ships used the direct

transit route from China to Poland via the Northern

Sea Route [6]. Trips to the NSR took place in the

summer and autumn from August 18 to October 16.

Average speed on the NSR did not depended on the

month of voyage and was from 9.8 knots till 14.4

knots. The time necessary to pass the NSR was equal

from 9.6 days till 6.3 days respectively.

The NSR is a seasonal route. Its use by merchant

ships that are not designed to navigate in heavy ice

makes sense when its entire length - from the Barents

Sea to the Bering Strait - is ice-free and can be

navigated through without the costly assistance of an

icebreaker. Due to the bathymetry and the occurrence

of navigational obstacles, for ships with a larger draft,

for example the PANAMAX type, the most favorable

route is to pass the NSR on the route north of Novaya

Zemlya (Mys Zhelaniya), north of the Severnaya

Zemlya (Schmidt Island and Komsomolets Island)

and north from the New Siberian Islands and Wrangel

Trends of Opening and Closing date for Navigation on

the Northern Sea Route in the Light of Changes in Ice

Cover on the Seas

of the Siberian Shelf in the Years

2008

-2022

A.A

. Marsz

, T. Pastusiak

& A. Styszyńska

Association of Polish Climatologists, Poland

Gdynia Maritime University, Gdynia, Poland

ABSTRACT: The Northern Sea Route (NSR) is a seasonal route. Its use by merchant ships that are not

structurally adapted to navigation in heavy ice makes sense when it is free of ice along its entire length and can

be used without the costly assistance of icebreakers. In the paper, ice cover maps were analyzed. The number of

the Julian day of the year was determined on the first day on which the transit shipping season began, on the

last day of the year after which this season ended, and the length of the ice-free period along the whole NSR

was calculated. The analysis was carried out for the eastern and western parts of the NSR. Despite the high

inter-year variability of the opening and closing times of the transit shipping season, it is possible, 2-3 months in

advance, to obtain approximate information about the conditions of "ice-free" navigation on this route. For this

purpose, average monthly sea ice extent of the Kara Sea in May of a given year should be used.

http://www.transnav.eu

the

International Journal

on Marine Navigation

and Safety of Sea Transportation

Volume 18

Numbe

r 3

September 2024

DOI: 10.12716/1001.18.03.

488

Island (Fig. 1). This route is also the shortest.

However, its use is only possible when the ice extent

in a given navigation season moves exceptionally far

north, leaving the entire Laptev Sea and the East

Siberian Sea free of compacted ice cover.

Figure 1. Distribution of shipping routes on the Northern

Sea Route;            route northernmost of archipelagos

and islands,      intermediate route, • • • • • coastal

route; 1 - Novaya Zemlya archipelago, 2- Severnaya Zemlya

archipelago, 3 - New Siberian Islands archipelago, 4 -

Wrangel Island, 5 - Kara Gate Strait, 6 - Cape Zhelaniya, 7 -

Sannikov Strait, 8 - Smidt and Komsomolets Islands, 9 -

Dmitry Laptev Strait, 10 - Sannikov Strait, 11 - Kotelny

Island, 12 - De Long Strait, 13 - Bering Strait.

The Severnaya Zemlya Archipelago is the

northernmost point of the route. If the ice reaches the

northern edge of the Severnaya Zemlya, and the deep

water (minimum depth of 34 m) of the Vilkitsky Strait

is free from ice, it is possible to continue the voyage

through this strait. However, the consequence will be

an increase in the length of the route. Due to the small

depths in the Sannikov Strait (minimum depth 14 m)

and even smaller depths in the Dmitry Laptev Strait

(minimum depth 8 m), separating the New Siberian

Islands archipelago from the continent, if ice

conditions allow it, the route should lead north of the

New Siberian Islands archipelago [15]. If the ice cover

reaches the islands of the New Siberian Islands

archipelago and if the Sannikov Strait is also blocked

by ice, the route through the Dmitry Laptev Strait

cannot be used. Its depths are too shallow for a

PANAMAX or larger ship to use them when passing

the NSR.

Therefore, we can talk about the full "opening" of

the Northern Sea Route for navigation when, at the

same time (at the same moment), the water areas

between Mys Zhelaniya and the water areas north of

the Schmidt and Komsomolets islands or between

Mys Zhelaniya and the Vilkitsky Strait, as well as the

water areas north of the New Siberian Islands (or the

Sannikov Strait) and the area north or south of

Wrangel Island are free from ice cover (De Long

Strait; minimum depth 36 m). The "transit navigation"

season on the NSR may be considered the time that

elapses in a given year between the first day on which

ice-free conditions occur along the entire route and

the last day of the year when such conditions occur. In

recent years, there have been major changes in the

length of the transit navigation season on the NSR. It

should be emphasized that due to the variability of

the location of large areas of compacted ice that are

difficult to overcome, routes should sometimes be

plotted with a significant extension of length of the

route. This occurs when, for example, in the western

part of the NSR the route runs close to the continental

coast and in the eastern part of the NSR - closer to the

North Pole and vice versa [21, 22]. The most common

southern extremes of such a designated route may

occur in the eastern part of the Kara Sea, in the

western or eastern part of the Laptev Sea and in the

western or eastern part of the East Siberian Sea. The

most common northern extremes may occur north of

the Severnaya Zemlya archipelago, the New Siberian

Islands archipelago or Wrangel Island.

In recent years, there has been numerous

information in the media pointing to the "incredible"

improvement in ice conditions on the NSR. There is

also frequent information that as a result of the

increase in global air temperature, the ice cover on the

NSR will soon disappear and transit navigation on

this route will be possible throughout the warm half

of the year, and will even be year-round or so on [7, 8,

12, 17, 23]. More realistic are results of novel approach

for calculation beginning and end dates, and also

duration of navigation season along the NSR based on

CMIP5 data [13].

The aim of this work is to examine the trends in

changes in the beginning and end of "transit

navigation" and the length of this season on the NSR,

which occurred in the years 2008-2022. Further, when

the term "navigation season" is used, it means the

summer season for ships without ice reinforcements,

expressed in the number of days on which transit

navigation is possible along the entire length of the

NSR.

2 DATA SOURCES AND METHOD DESCRIPTION

The basic material for determining the length of the

"transit navigation" season was the analysis of daily

maps of the Mariginal Ice Zone issued by USNIC in

ESRI Shape file format [24] and after that, gridded

maps of NCEP GFS with ice concentration forecast

files in GRIB2 format, published four Times a day

[18], maps of ice cover based gridded 3125m x 3125m

data from AMSR-E (2002-2011) and AMSR (2012-2023)

swath published daily by Bremen University [2] and

later [3], and regional maps of the Arctic in raster GIF

format published by Arctic and Antarctic Research

Institute AARI „SEVER” Center every 3-4 days [19]

and later [22]. All these maps assume the boundaries

between ice-covered and ice-free areas related to the

degree of ice coverage of the water surface, regardless

of its stage of development and thickness, within 10-

18%. Waters with an ice concentration of less than 10-

18% were treated as ice-free waters.

Additionally, time series of sea ice extent within

the boundaries of individual Arctic seas and their

parts covering the NSR route provided by AARI were

used [1]. According to definitione, sice extent is a

surface of sea covered by ice of concentration from 15

till 100%.

Based on the analysis of the indicated maps, the

number of the first day of Julian calendar on which

the transit shipping season began (BNS) and the last

day of Julian calendar after which the season ended

(ENS) in the year were determined. This approach

allows for simple and clear calculations. Length of

navigation season LNS was then calculated as (ENS -

489

BNS) + 1. Standard statistical methods were used to

analyze these data.

The analysis was carried out for two parts of the

NSR - eastern and western, and for the entire potential

NSR route. The western part covers the area from the

western border of the Kara Sea to the eastern border

of the Laptev Sea within their limits as defined by the

IHO [10, 11]. Eastern part - from the southern border

of the Chukchi Sea (Bering Strait) to the western

border of the East Siberian Sea (Fig. 1). The ice cover

being on the Barents and Bering seas in the considered

period 2008-2022 does not play any role in regulating

the opening and closing times for NSR transit

navigation, because by the time the NSR opens and

closes, they are already or still ice-free.

The compiled data for individual transit

navigation seasons in 2008-2022 are presented in

Table 1. The length of the time series (15 years) does

not allow drawing more firm conclusions, but it

reveals trends in changes in the behavior of the

beginning and end of the navigation season and their

duration. It also allows to indicate a predictor that can

be used to roughly predict the ice conditions that will

occur in the current navigation season already at the

beginning of summer.

3 CHANGE TRENDS OF THE "TRANSIT

NAVIGATION SEASON” ON THE NSR

The data presented in Table 1 indicate the occurrence

of significant inter-annual variability in the beginning,

end and length of the navigation season on the NSR.

The length of the period during which "ice-free

conditions" prevail along the entire NSR ranges from

1 day (2009) to 90 days in 2020. On average, the

duration of the "transit shipping" season in 2008-2022

is 33 ± 6 days, which, with a standard deviation of 24.0

days, indicates a very high variability of this

parameter.

Table 1. The number of the day of the Julian calendar year

of the beginning (BNS) of the "transit shipping" season on

the Northern Sea Route, the last day of the "transit

shipping" season (ENS) and the number of days of the

"transit navigation" season (LNS) on the western part of the

NSR, the eastern part of the NSR and the entire NSR route

from Mys Zhelaniya to the Bering Strait

________________________________________________

Year Western part of Eastern part of The whole NSR

the NSR the NSR

BNS ENS LNS BNS ENS LNS BNS ENS LNS

________________________________________________

2008 250 265 16 250 282 33 250 265 16

2009 275 280 6 246 275 30 275 275 1

2010 256 273 18 256 285 30 256 273 18

2011 219 286 68 230 286 57 230 286 57

2012 231 294 64 250 290 41 250 290 41

2013 254 273 20 237 271 35 254 271 18

2014 244 274 31 234 290 57 244 274 31

2015 220 287 68 231 288 58 231 287 57

2016 266 287 22 228 291 64 266 287 22

2017 247 271 25 217 276 60 247 271 25

2018 231 294 64 258 291 34 258 291 34

2019 222 288 67 227 293 67 227 288 62

2020 214 303 90 214 306 90 214 303 90

2021 251 271 21 266 271 6 266 271 6

2022 230 270 41 247 285 39 247 270 24

________________________________________________

In the course of navigation time in ice-free

conditions along the entire NSR route, there is a

statistically insignificant positive trend (Fig. 2),

indicating a relatively small extension of the transit

navigation season. The trend is +1.61 ± 1.42 days per

year and is statistically insignificant (p = 0.28). A very

large error in estimating the intercept and the

regression coefficient in the equation in Fig. 2 (in the

box) makes it impossible to reject the null hypothesis,

i.e. to state that the given trend value is different from

zero.

Figure 2. The length of the shipping season in "ice-free"

conditions (LDO; number of days) along the entire length of

the Northern Sea Route from Mys Zhelaniya to the Bering

Strait in the years 2008-2020. Red solid line - fitting of a

linear function (trend), dashed lines - marking the limits of

the 95% confidence interval (p = 0.05)

Based on the trend values calculated from short

time series, no conclus

ions can be drawn about the

further pace of changes. Analyzing the course of

variability of the length of the navigation season

throughout the PDM, in a shorter series from 2008-

2020 (13 years), a statistically significant positive trend

is detected (3.96 ± 1.46, p = 0.02), indicating that the

navigation season on the NSR is extended on average

by almost 4 days each year. Observations from 2021

and 2022, when there was a significant delay in the

beginning and earlier end of the navigation season,

completely changed this picture.

An important issue from the point of view of

shipping is the cost of which processes result in the

extension of the transit navigation season. The

analysis of the moments of occurrence of the first and

last day of the transit navigation season (Fig. 3)

apparently shows that the extension of the transit

navigation time occurs as a result of the simultaneous

acceleration of the beginning of the navigation season

and delaying its end. While the acceleration of the

beginning of the transit navigation season is on

average faster (-0.95±0.99 days per year), its very large

fluctuations from year to year make the trend

statistically insignificant. This does not allow us to

draw a conclusion that, in a statistical sense, there was

an acceleration of the beginning of the navigation

season. Similarly, slightly slower (+0.66 ± 0.64 days

per year). But the timing of the end of the transit

shipping season also changes irregularly. The trend of

delaying the end of the transit navigation season is

statistically insignificant (p = 0.322).

The correlation between the beginning of the

transit navigation season (NRP) and the moment of its

490

end (NRK) is weak (r = -0.53) but statistically

significant (p = 0.043). This indicates that on the NSR

there is a general, very weak tendency to extend the

duration of the "ice-free" navigation season with its

earlier beginning. However, this relationship is only

statistical and cannot be applied to every single case.

The length of the shipping season cannot be

legitimately inferred based on its beginning date.

Figure 3. The course of the "opening" (NRP) and "closing"

(NRK; numbered consecutive days of the Julian calendar

year) moments of the transit navigation season on the NSR

in 2008-2022. Labeled linear fits to empirical points (trend

lines). Horizontal dashed lines mark the beginning of

subsequent months (1 Aug, 1 Sep, 1 Oct, 1 Nov)

The analysis of the relationship between the

average monthly ice area (extent) and the opening

and closing moments of the shipping season in the

PDM confirms the previously known regularity [15,

16] that the opening and closing moments are

determined by the ice conditions in the Laptev and

East Siberian seas, i.e. the border seas between the

western and eastern part of the NSR. In the period

under consideration, the opening of the NSR occurred

only three times simultaneously in both these seas

(2008, 2010 and 2020), while the variability of ice

conditions in each of these seas with the same

frequency (6 cases each) delayed the moment (Table 1)

of the opening of the NSR. The timing of the closure

of the transit navigation season on the NSR is much

more influenced by the variability of ice conditions in

the Laptev Sea than in the East Siberian Sea. During

the years 2008-2022, ice conditions in the Laptev Sea

resulted in the closing of the shipping season nine

times, and only four times (2009, 2012, 2013 and 2018)

in the East Siberian. In two years (2011 and 2021), ice

conditions in both seas simultaneously led to the

closure of the shipping season.

4 APPROXIMATE FORECAST OF CHANGES IN

THE LENGTH OF THE NAVIGATION SEASON

ON THE NSR

There are quite complicated, but statistically highly

significant relationships between the processes of ice

cover loss and the processes of its re-growth in

individual Arctic seas. The analysis of these

relationships shows that a kind of predictor,

providing approximate information about the number

of the day of the Julian calendar year on which the

PDM opens and closes, and the length of the PDM

navigation season, is the area of ice extent in the Kara

Sea in May (KS

E05). The Kara Sea, with an area of less

than 1 million sq. km (926,000 sq. km), is a shallow sea

(average depth ~131 m) with small heat resources in

the waters. For this reason, its ice cover responds very

strongly to changes in meteorological processes taking

place over the Arctic, as well as to changes in the

complex of hydrological processes in the Arctic Ocean

basin.

The rate of melting of ice in the Kara Sea in May of

a given year is an indicator of the acceleration of the

disappearance of the ice cover in the following

months in this sea and in the Laptev and East Siberian

seas. The behavior of the ice extent in the Kara Sea in

May (KSE05) is relatively strongly correlated with the

ice cover area in the Laptev and East Siberian Seas in

July (r = 0.69, p < 0.001; 1979-2020). In turn, the

intensity of further ice melting in July depends on the

size of the "clean water" (ice-free surface) in these seas,

which determines both the beginning and the end of

the transit navigation season. As a result, there are

relatively strong relationships between the area of ice

cover in the Kara Sea in May and the number of the

first day of the "transit navigation" season on the NSR

(BNS), the number of the last day of this season (ENS)

and the number of days of the "transit navigation"

season on the NSR (LNS) (Tab. 2, Fig. 4).

Table 2. The values of the correlation coefficient (r) and the

level of their statistical significance (p) between the average

monthly sea ice area (extent) in the entire Kara Sea in May

and the number of the day of the year, the first day of the

transit shipping season on PDM (BNS), the last day of the

transit shipping season (ENS) and the number days of the

transit shipping season (LNS). The results or correlation

period 2008-2022. r

- percentage of the explained variance

of a given variable by the average monthly ice surface

(extent) of the Kara Sea in May

________________________________________________

Parameter BNS ENS LNS

________________________________________________

r 0.70 -0.80 -0.84

p 0.004 << 0.001 << 0.001

49% 64% 70%

________________________________________________

Figure 4. The course of the average monthly ice area (extent)

in the Kara Sea in May (KS

E05; thousand sq. km) and the

length of the "transit navigation" season on the NSR (LNS

LDO; days).

On Figure 4, there is a visible sharp shortening of

the season in 2021 and 2022, related to an equally

sharp increase in the area of ice in the Kara Sea in May

in these years. Table 2 shows that the beginning of the

491

navigation season is least related to the May ice

surface (extent) in the Kara Sea, and the strongest – to

the length of this season (LNS). Significant linear

correlations presented in Table 2 allow the creation of

regression equations in which the BNS, ENS and LNS

values constitute a linear function of KS

E05, i.e. the area

of ice (extent) in the Kara Sea in May. Table 3 shows

the values of these variables calculated from the

regression equations for KS

E05 varying in the range

from 700 to 860 thousand sq. km.

Table 3. The values of the BNS, ENS and LNS (days) in a

given year as a function of the variable average monthly sea

ice area (extent) in the Kara Sea in May of a given year

(KS

E05

; thousand sq. km)

________________________________________________

KSE05 860 840 820 800 780 760 740 720 700

________________________________________________

BNS 268.1 258.1 248.1 238.1 228.1 218.1 208.1 198.1 188.1

ENS 268.5 275.9 283.3 290.7 298.1 305.5 312.9 320.3 327.7

LNS 1.5 18.9 36.3 53.7 71.1 88.5 105.9 123.3 140.7

________________________________________________

Note: Standard errors of estimation of the BNS, ENS and LNS are

equal tp ±12.2 days, ±6.7 days and ±13.5 days respectively.

The occurrence in May of a given year of the

average monthly iced area in the Kara Sea equal to or

less than 800,000 sq. km indicates that in the

upcoming "summer" ice season the length of the

transit shipping season will most likely be longer than

54 ± 13.5 days, that is, its real length should be

expected to be between 41 days (minimum) and 67

days (maximum), and the beginning of the season will

take place no later than in the second decade of

August - the first decade of September (August 25 ±

14 days).

5 CONCLUSIONS

The analysis of a short, only fifteen-year series of data

informing about the beginning, end and length of the

transit shipping season on the Northern Sea Route

indicates the occurrence of very high variability of

these parameters in this period. This variability is so

significant that it does not allow reliable conclusions

about the further development of changes in the

length of the "transit shipping" season based on

previously estimated trends.. Despite the undoubted

lengthening of the shipping season since 1979 [5], and

the acceleration of its beginning and delaying its end,

the course of this process is so unstable that it is not

possible to rely on emerging long-term trends in

possible planning of the NSR transits. To an even

greater extent, decisions about sending a ship to the

NSR crossing cannot be made based on the opinions

expressed by various "ecological" and "climate"

organizations and politicians disseminated by the

mass media.

Since so far the earliest opening of the NSR took

place in the first decade of August (2020), and on

average it occurs in the last decade of August - the

first decade of September, it is possible, 2-3 months in

advance, to obtain approximate information about the

conditions of "ice-free" navigation on this route. For

this purpose, data on the average monthly sea ice

extent of the Kara Sea in May should be used (the set

in file karamonthly.all.extent.csv, available from

AARI website [1]. Data on the ice area for May in this

set are usually completed between June 5 and 10,

which allows, using these data and the contents of the

Table 3, get an idea of the probable ice conditions on

the NSR in mid-June.

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