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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  studies ­
  concerning  its  physical  behavior,  changes  and  interactions ­
  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  focus ­
  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  decrease ­
  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  cannot ­
  reveal  how  the  entire  ice  mass  that  is  produced  in
each  winter  has  changed.  A  more  significant  parameter ­
  for  sea  ice  changes  is  the  sea  ice  volume,  as  it  comprises ­
  changes  in  sea  ice  coverage  and  those  in  sea  ice
thickness.  Therefore,  we  calculated  in  this  study  the  regional ­
  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  teleconnection ­
  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  Seeschifffahrt ­
  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  increased ­
  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  accumulated ­
  sea  ice  volume  trends  over  the  Baltic  Sea  and  want
to  answer  the  question  whether  these  trends  arc  consistent ­
  with  those  observed  for  SST  and  T Lur .  Section  2  describes ­
  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  Hydrographie ­
  (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