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® Meteorol. Z. (Contrib. Atm. Sci.), PrePub DOI 10.1127/metz/2020/0986 
© 2020 The authors 
DACH 2019 
Regional distributed trends of sea ice volume in the Baltic Sea 
for the 30-year period 1982 to 2019 
Sandra Schwegmann* and Jürgen Holfort 
Bundesamt für Seeschifffahrt und Hydrographie, Rostock, Germany 
(Manuscript received June 29. 2019; in revised form May 18. 2020; accepted May 19. 2020) 
Abstract 
Since more than 100 years, winters in the Baltic Sea have been classified according to their strength and 
have been compared to each other. In the beginning, the winter strength was only related to the ice coverage 
along the coasts. However, since the 1980s, also the ice thickness was observed consistently and has therefore 
been included into the classification scheme. Owing to the international cooperation between the European ice 
services, we have all the needed information about the winter strength, sea ice coverage, distribution and mass 
for the entire Baltic Sea available. Thus, we have been able to compute changes in the sea ice conditions for 
this area covering the last decades and to compare them with changes in the air and sea surface temperatures. 
For the first time, we show the distribution of the mean accumulated sea ice concentration and sea ice volume 
as well as its trends for the Baltic Sea. Consistently data reveal a decreasing amount of sea ice that is produced 
over a winter season for nearly all the sections of the Baltic Sea. The reduced sea ice production correlates 
generally well with the increase in air and sea surface temperatures over winter months. 
Keywords: sea ice, sea ice volume, Baltic Sea, climate change, sea surface tem] 
1 Introduction 
Sea ice forms every winter at least in the northern parts 
of the Baltic Sea and has been subject to several stud 
ies concerning its physical behavior, changes and inter 
actions with the atmosphere, ocean and biosphere (see, 
e.g., Stigebrandt and Gustafsson, 2003; Granskog 
etal., 2006; Feistel etal., 2008; Lehmann etal., 2011; 
Haapala etal., 2015). However, studies concerning its 
changes concentrate on maximum winter sea ice extent 
(e.g., Omstedt et al., 2004; Haapala et al., 2015), or fo 
cus only on special regions of interest (e.g., Schmelzer 
et al., 2012 for the southern Baltic Sea; Jevrejeva et al., 
2004, only for coastal areas; Jaagus, 2006, only for the 
Estonian coast). These studies discovered a general de 
crease in maximal sea ice extent by 2 % per decade over 
the past 100-200 years. Nevertheless, sea ice extent is 
highly variable to changes in the wind field and can 
not reveal how the entire ice mass that is produced in 
each winter has changed. A more significant parame 
ter for sea ice changes is the sea ice volume, as it com 
prises changes in sea ice coverage and those in sea ice 
thickness. Therefore, we calculated in this study the re 
gional distributed changes in the accumulated sea ice 
volume for the Baltic Sea from 1982 through 2019 as 
linear trend for the entire winter season as well as for 
single months. Furthermore, we discuss the response of 
sea ice volume to changes of atmospheric teleconnec 
tion patterns as well as sea surface and air temperatures, 
such as those arc the main drivers for changes in both 
* Corresponding author: Sandra Schwegmann, Bundesamt für Seeschiff 
fahrt und Hydrographie, Neptunallee 5, 18057 Rostock, Germany, e-mail: 
Sandra.Schwegmann @ gmx.net 
ture 
sea ice parameters. Sea surface temperatures (SST) in 
the Baltic Sea have been analyzed by, e.g., Bradtke 
et al. (2010), Stramska and Biaeogrodzka (2015) and 
H0yer and Karagali (2016). They used different data 
sets but consistently found that SST has mostly in 
creased in the Baltic Sea by about 0.3°C-0.7 °C per 
decade. SST changes are closely related to those in the 
air temperature (7^, Omstedt and Hansson, 2006), 
which are also known to increase in the Baltic Sea 
(Omstedt etal., 2004; Stigebrandt and Gustafsson, 
2003). With this study, we want to present for the first 
time the spatial and temporal (in terms of which winter 
months shows the largest trends) distribution of accumu 
lated sea ice volume trends over the Baltic Sea and want 
to answer the question whether these trends arc consis 
tent with those observed for SST and T Lur . Section 2 de 
scribes the data used for this study. In Section 3 we show 
how the accumulated sea ice concentration (ASIC) and 
volume (ASIV) has changed over the last decades, and 
in Section 4 we look at the changes in SST and T Lur . 
Section 5 discusses how the trends found correlate to 
each other and gave a discussion on uncertainties. In 
Section 6 we summarize the most important findings of 
this study. 
2 Data description 
2.1 Sea ice data 
Our study is based on sea ice data collected over six 
decades at the Bundesamt für Seeschifffahrt und Hydro 
graphie (BSH) combining sea ice concentration and sea 
ice thickness information. The ice data originate from 
DOI 10.1127/metz/2020/0986 
© 2020 The authors 
Gebrüder Bomtraeger Science Publishers, Stuttgart, www.borntraeger-cramer.com