Лёд и Снег · 2021 · Т. 61 · № 2

УДК 502.6. 910.3

doi: 10.31857/S2076673421020085

Manifestation of climatic change in the ice phenology of Lake Ladoga over the past 55 years

S.G. Karetnikov

Institute of Limnology, Russian Academy of Sciences, St. Petersburg, Russia

karetser@gmail.com

Проявление климатических изменений в ледовом режиме Ладожского озера за последние 55 лет

Институт озероведения РАН, Санкт-Петербург, Россия

karetser@gmail.com

Received July 16, 2020 / Revised December 20, 2020 / Accepted March 19, 2021

Keywords: Lake Ladoga, ice coverage, spatial patterns of ice, duration of fast ice coverage, climatic change, air temperature.

Summary

The article presents results of monitoring changes in some phenological characteristics of the ice cover of Lake

Ladoga over the past 55 years. A steady tendency has been observed for a decrease in the duration of ice forma-

tion and the area of fast ice since the beginning of the 90s. A comparison is made of the average spatial patterns of

ice formation dynamics between the periods 1964-1994 and 1993-2019. Since the beginning of the 90s, there has

been a change in the ice characteristics of Lake Ladoga, directly related to a reduction in the duration of the cold

period. The duration of ice events averaged over the past 30 years has decreased by about a month compared with

the previous thirty-year period. Fast ice began to cover only 30% of the lake surface compared to 80% in previ-

ous years. The frequency of winters with incomplete freeze-up (remaining ice free areas) increased from two to six

years per decade. The warming effect is most clearly seen in the central part of the lake. Such significant changes in

the dynamics of ice phenology cannot but affect the functioning of the entire ecosystem of Lake Ladoga.

Citation: Karetnikov S.G. Manifestation of climatic change in the ice phenology of Lake Ladoga over the past 55 years. Led i Sneg. Ice and Snow. 2021.

61 (2): 241-247. doi: 10.31857/S2076673421020085.

Поступила 16 июля 2020 г. / После доработки 20 декабря 2020 г. / Принята к печати 19 марта 2021 г.

Ключевые слова: Ладожское озеро, покрытость льдом, пространственное распределение льда, продолжительность ледового

покрытия, изменение климата, температура воздуха.

Представлены изменения некоторых фенологических характеристик ледяного покрова Ладож-

ского озера за последние 55 лет. Установлена устойчивая тенденция уменьшения продолжитель-

ности ледообразования и площади припая с начала 1990-х годов, что связано с сокращением про-

должительности холодного периода. Выполненное сравнение осреднённых пространственных

закономерностей динамики ледообразования за периоды 1964-1994 и 1993-2019 гг. с перекры-

тием в один год позволило выявить уменьшение во второй период примерно на месяц по сравне-

нию с первым 30-летним периодом средней продолжительности сплошного ледостава.

Introduction

ment to varying degrees can lead to a change in limnic

characteristics. Such characteristics include the ice re

Lakes and their shores are the habitat of aquatic

gime of large lakes. Over the past 30 years, significant

organisms, fish, wildlife and humans. Each lake dif

changes in ice characteristics for lakes in the Northern

fers in terms of such characteristics as geographical

Hemisphere have been recorded [1], in particular, a

location, the influence of the catchment basin, the

decrease in the total duration of ice formation [2].

morphology of the basin, the chemical composition

The consequences of these ongoing changes due

of the water and the biota inhabiting it, hydrological

to winter warming in the phenology of ice cover can

parameters, including thermal and ice regimes. De

significantly affect the functioning of the Ladoga Lake

pending on the size of the lake, there is a limited range

ecosystem, as has already been noted for Lake Peip

of external influences which allows its ecological state

si located nearby [3]. A change in lake ice cover can

to remain stable. Noticeable changes in the environ

not but affect its thermal regime, its vertical oxygen

 241 

Sea, River and Lake Ice

exchange, the development of phytoplankton, dur

on average daily air temperature for the years from 1913

ing the period of spring heating, which begins earlier.

to 1936, when the weather station was in Finland, al

In the absence of ice, the aquatic mammals feeding

lowed [5] to reconstruct ice conditions on Lake Ladoga

cubs on ice [4] have problems. The supply of monas

in the absence of observations on the degree of ice cov

tery on the Valaam Island when stable freeze-up in the

erage of the lake. A sum of the average daily air temper

northern part of the lake was carried out along the ice

atures during the entire cold period, including seasonal

route. Recent years, shipping to the island has been

thaws, was used as an integral winter characteristic asso

carried out all year round. This paper shows how cli

ciated with the ice events. The duration of a cold period

mate warming, observed over the past 30 years, has af

was calculated between the dates of steady transition of

fected the average spatial pattern of freeze-up, break-

average daily air temperatures through 0 °C in the fall

up, and the duration of fast ice cover on Lake Ladoga.

and spring. The changes in the duration of the cold pe

riod and the sums of average daily air temperatures dur

ing this period are shown in Fig. 2. A statistically signifi

Materials and methods

cant at p-level 0.05 trend is shown by solid line.

Over the past 30 years, these changes have become

Europe’s largest freshwater dimictic Lake Ladoga is

statistically significant and indicate a decrease in the

located in northeastern Europe. Its area is 17.765 km²,

severity of winters. In 2020, the shortest winter over

its average depth is 48.3 m, the maximum depth is

the entire period of monitoring was recorded with the

233 m in the northern part of the lake, and the water

smallest sum of average daily air temperatures during

volume is 858 km³ (Fig. 1). Meteorological data from

the cold period. The reduction in the duration of the

the Sortavala weather station, located on the northern

cold period occurs mainly due to a statistically signifi

shore of the lake, were used to assess the meteorology

cant five days shift of a stable transition of the daily av

of the Lake Ladoga region. This meteorological station

erage air temperatures through 0°С in autumn to later

was chosen among others located on the coast and is

dates [6]. It should be noted that the article considers

lands of Lake Ladoga as the most filled with data. Data

only the spatial distribution of ice cover by various re

mote sensing methods, the data on ice by coastal sta

tions being of a fundamentally different nature. Regular

observations of the spatial distribution of ice on Lake

Ladoga have been made since 1943. Until 1992, aerial

reconnaissance of the ice was carried out by the Hy

drometeorological Service about two times a month,

and maps of Lake Ladoga’s ice cover indicating its co

hesion were published [7]. Starting from 1971, space

images were added to data obtained by airborne recon

naissance, which made it possible to make schemes of

the freeze-up and break-up of the lake depending on

the different direction of the prevailing winds [8]. Re

cently satellite imagery has become the main source for

studying the lake ice cover. Over the past 20 years, data

from the NOAA series of satellites with kilometer-res

olution AVHRR instruments has been supplemented

with MODIS satellites with 250-meter resolution and

from 2015 Synthesized Aperture Radar (SAR) data

from the European Sentinel-1 satellite with 100 m res

olution have become freely available.

The annual monitoring of the ice cover starts from

the moment its detected by remote sensors. Then, for

each suitable image, ice lake coverage is calculated with

Fig. 1. Lake Ladoga with its depths in meters

an accuracy of 10%, taking into account its cohesion.

Рис. 1. Ладожское озеро с указанием его глубин в метрах

The end of the ice phenomena on the lake is consid

 242 

S.G. Karetnikov

Fig. 2. The duration (a) and the sums of the average

daily air temperatures (b) of the cold period for the

years of 1913-2020.

The year number is the end of the winter; the trend is at

p-level 0.05 and its determination coefficient R²: 1 - a

statistically significant; 2 - an insignificant trend

Рис. 2. Межгодовая изменчивость продолжи

тельности (a) и максимальных алгебраических

сумм среднесуточных температур воздуха (b)

холодного периода для 1913-2020 гг.

Номер года относится к году окончания зимы;

тренд при уровне значимости 0,05 и его коэфици

ент детерминции R²: 1 - статистически значимый;

2 - незначимый

ered the date when the observed ice occupies less than

tained [5]. This dependence was used to reconstruct the

5% of the lake. The duration of ice on Lake Ladoga

seasonal change in the ice cover and to calculate the ice

remained at a stable level of about 170 days before the

cover indices for the years from 1913 to 1936, since ob

beginning of the 90s, after that the duration shows a

servations of the ice distribution over Lake Ladoga were

clear tendency to decrease (Fig. 3, a), mainly due to

not carried out during those years. Fig. 3, b shows the

a shift to a later date of the onset of ice. Lake Ladoga

change in ice cover index over the past 100 years and its

is not completely covered by ice every year. Years with

trend [5], extended now up to 2020. The last period has

remaining open water areas occur. Fig. 3, c shows the

a statistically significant decrease in the ice cover index.

number of years with incomplete ice cover per decade.

In the process of preparing data on the lake ice

Before the beginning of the 1990s, one to two winters

cover, an digital file was compiled with more than 1000

with incomplete ice cover were observed per decade. In

aerial and satellite images from 1964 to 2020. Based on

recent years this number has increased to six.

linear relationships [10], a way was proposed for cal

From constant observations of lake ice cover by re

culating the increase and decrease in the average value

mote sensing, it is possible to calculate the ice cover

of ice cover in each of 180 fixed ten-kilometer cells. To

index each winter. The ice cover index [9] is the integral

construct a smooth seasonal course of ice cover for each

of lake ice cover over the winter, normalized to the inte

cell, the data were averaged by 10 days with 5-day shifts.

gral of average lake ice cover over the period from 1945

The course of ice cover for each cell was approximated

to 1994. This period was chosen for normalization since

by two linear equations: for ice percentage increasing

it is characterized by the absence of a significant trend

and decreasing. In some cells according to the long-term

in the lake ice cover index. From 1945 to 2020 ice cover

average data, a complete ice cover can be observed for

indices were calculated from field data. At the same

a very short time, in other cells the complete ice cover

time, the linear dependence of the dates of ice cover

may last up to several months, or the area may never be

freeze-up and break-up on the sums of the average daily

completely covered with ice. To analyze the impact of

air temperatures, accumulated to these dates were ob

climate change on the ice characteristics of the lake, the

 243 

Sea, River and Lake Ice

Fig. 3. Annual variability in the ice char

acteristics of Lake Ladoga:

a - duration of ice phenomena; b - trends in

the ice cover index of Lake Ladoga; c - the

number of years with incomplete freezing per

ten year running average; see Fig. 2 for symbols

Рис. 3. Межгодовая изменчивость ледо

вых характеристик Ладожского озера:

a - продолжительность ледовых явлений;

b - тенденции изменения индекса ледови

тости; c - число лет с неполным ледоста

вом из 10 скользящих; усл. обозначения

см. на рис. 2

period from 1964 to 2019 was divided into two with one

up and break-up of the lake for subsequent analysis.

year overlap: from 1964 to 1994 and from 1993 to 2019

The formation of fixed cohesive ice in the first period

years. For each period, the areas of increasing and de

began at the end of December in shallow Petrokre

creasing of fast ice cover and the duration of the period

post Bay. The ice growth rate of each fixed cell in

with fast ice cover were calculated (Fig. 4).

creased from 0.3% to 1.5% per day as the location

of the cell off the shore and sum of negative average

daily air temperatures accumulated. The results ob

Results and discussions

tained are in a good agreement with data from neigh

boring Lake Onega [11], where the average value of

When constructing average schemes of increas

the increase in the lake ice cover per day is 1.55%.

ing and decreasing of fast ice cover of Lake Ladoga,

Over the last ten days of February, the area of the

data were obtained on the average rates of freeze-up

lake covered by fast ice increased sharply. By the be

and spring break-up of each cell. These data made it

ginning of March, the formation of fast ice stopped,

possible to assess the correctness of data processing

leaving 20% of the lake surface occupied by floating

on the smoothness of their distribution over the lake,

ice of various cohesion. In the second period, ice for

and to obtain average schemes of the rates of freeze-

mation usually started twenty days later, proceeded at

 244 

Sea, River and Lake Ice

about the same rate, but ended ten days earlier than

Conclusion

in the first period, while 70% of the lake surface re

mained occupied by floating ice of various cohesion.

Since the beginning of the 1990s, there has been a

The spring break-up of fast ice cover on Lake

change in the ice characteristics of Lake Ladoga, direct

Ladoga is faster than its freeze-up due to the significant

ly related to 12 days reduction in the duration of the cold

wind activity in this region. The wind prevents the for

period. The average winter air temperature at the same

mation of motionless ice and contributes to its destruc

time statistically insignificantly increased by 1 °C. The

tion. In the first period, spring ice break-up began in

duration of ice events averaged over the past 30 years has

the central part of the lake in early March at a rate of

decreased by about a month compared with the previ

1% and then up to 2% per day near the shore. The last

ous thirty-year period. Fast ice began to cover only 30%

formations of fast ice were observed along the north

of the lake surface compared to 80% in previous years.

eastern coast in early April. In the second period, the

The frequency of winters with incomplete freeze-up (re

process of break-up of fast ice cover usually began ten

maining ice free areas) increased from two to six years

days earlier, ended also along the northeastern coast,

per decade. The warming effect is most clearly seen in

and continued as in the first period for a whole month,

the central part of the lake. Such significant changes

despite much less initial ice. The destruction of ice in

in the dynamics of ice phenology cannot but affect the

the second period occurs slower than in the first peri

functioning of the entire ecosystem of Lake Ladoga.

od at an average rate of 1% per day. However, signifi

cant differences in the rate of rise of spring air tempera

Acknowledgments.The work was performed on the

tures between the two periods were not found. One of

topic of research work № 0154-2020-0001. The au

the possible explanations for such an unexpected result

thor expresses his gratitude and deep appreciation to

is statistically significant increase in the frequency of

meteorologist and glaciologist of Moscow State Uni

calm conditions on Ladoga in the spring that has been

versity Sidorova Tatyana for discussion and valuable

observed in recent years. Indeed, according to the data

comments during the work on this article.

at the Sortavala weather station, in March during the

first period wind speeds less than 3 m/s was observed

Благодарности. Работа выполнена по теме НИР

in 66% of the time and in the second period 76% of the

№ 0154-2020-0001. Автор выражает глубокую

time, which weakened the influence of wind as a factor

признательность метеорологу и гляциологу МГУ

accelerating the break-up of ice.

имени М.В. Ломоносова Татьяне Львовне Сидо

For more than three months, fast ice cover during

ровой за обсуждение и полезные советы при

the first period was observed in fixed cells along the

подготовке статьи.

northeast coast. The central part of the lake remained

under the fast ice for about one month. On 20% of

the lake surface near the southwestern shore floating

Расширенный реферат

ice of various concentrations was usually located. This

ice can move freely around the lake depending on the

Озёра и их берега - местообитание водных

wind. According to data averaged for the second pe

организмов, рыб, диких животных и людей.

riod, fast ice cover was recorded during a month or

Каждое озеро специфично по таким характери

less only in shallow water. In some winters the cen

стикам, как географическое положение, влия

tral part of the lake was completely ice free. Averag

ние водосборного бассейна, морфология котло

ing the second period data showed that usually 70% of

вины, химический состав воды и населяющей её

the surface of the lake was not covered by compact ice.

биоты, гидрологические параметры, в том числе

Such significant changes in the degree of ice coverage

термический и ледовый режимы. В зависимости

of the lake during the winter are manifested in an ear

от размера озера существует предельный диапа

lier beginning of the spring warming of the lake, in an

зон внешних воздействий, при котором его эко

increase in the period of vertical oxygen exchange, in

логическое состояние остаётся достаточно ста

a lengthening of the period of development of cold-

бильным. Заметные реформации окружающей

water forms of phytoplankton during spring heating,

среды в той или иной степени могут приводить к

which begins earlier. In the absence of ice, aquatic

изменению лимнических характеристик, к кото

mammals feeding cubs on ice have problems.

рым относится и ледовый режим крупных озёр.

 246 

S.G. Karetnikov

Для озёр Северного полушария за последние

привело к изменениям и характеристик ледового

30 лет были зафиксированы более интенсивные

режима озера. Самое веское изменение установ

темпы изменения ледовых явлений. Ожидается,

лено в продолжительности существования ледо

что последствия продолжающегося зимнего по

вых явлений на поверхности озера. К аналогич

тепления и изменения фенологии ледяного по

ным результатам пришли и исследователи озёр

крова будут иметь решающее значение для функ

Финляндии. Сравнение средних для двух перио-

ционирования экосистемы Ладожского озера, а

дов схем нарастания и разрушения припайного

также для расположенного рядом Чудского озера.

льда позволило определить центральный район

Задача настоящей работы - выяснить, как повли

озера как наиболее подверженный изменени

яло потепление климата на изменение средних

ям. За более короткое для второго периода хо

пространственных схем замерзания, вскрытия и

лодное время года неподвижным льдом покры

продолжительности полного ледостава Ладож

валось всего 30% поверхности озера вместо 80%

ского озера. Представлены результаты наблюде

в первый период. В свою очередь столь суще

ний за тенденцией межгодовых изменений зимних

ственные изменения степени покрытости озера

температур воздуха и некоторых фенологических

льдом за зиму проявляются в более раннем на

характеристик ледового покрытия Ладожского

чале весеннего прогрева озера в увеличении пе

озера. Сравнение схем сезонного увеличения и

риода вертикального кислородного обмена, в уд

уменьшения распределения площадей припая, по

линении периода развития холодноводных форм

строенных для двух периодов - 1964-1994 и 1993-

фитопланктона в период весеннего нагревания,

2019 гг. с перекрытием в один год, позволило оце

который начинается раньше. Испытывают проб-

нить их изменения за последние 55 лет.

лемы при отсутствии льда водные млекопитаю

По данным метеостанции Сортавала, для ре

щие, вскармливающие детёнышей на льду озера.

гиона Ладожского озера в последние 30-40 лет

Грузы в монастырь на острове Валаам при устой

статистически значимо сократились продол

чивом ледоставе в северной части озера достав

жительность холодного периода (на 12 дней) и

ляли по ледовой трассе. В последние годы судо

суммы среднесуточных температур воздуха. Это

ходство на остров ведётся круглогодично.

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 247 