Conley Supporting Information
Supporting Information
Hypoxia is increasing in the coastal zone of the Baltic Sea Daniel J. Conley1, Jacob Carstensen2, Juris Aigars3, Philip Axe4, Erik Bonsdorff5, Tatjana Eremina6, Britt-Marie Haahti5, Christoph Humborg7,8, Per Jonsson8, Jonne Kotta9, Christer Lännegren10, Ulf Larsson11, Alexey Maximov12, Miguel Rodriguez Medina7, Elzbieta Lysiak-Pastuszak13, Nijolė Remeikaitė-Nikienė14, Jakob Walve11, Sunhild Wilhelms15, and Lovisa Zillén1 1
Department of Earth and Ecosystem Sciences, Lund University, SE-223 62 Lund, Sweden
2
National Environmental Research Institute, Aarhus University, DK-4000 Roskilde, Denmark
3
Latvian Institute of Aquatic Ecology, LV-1007 Riga, Latvia
4
Swedish Meteorological & Hydrological Institute, SE-426 71 Västra Frölunda, Sweden
5
Department of Biosciences, Environmental and Marine Biology, Åbo Akademi University, BioCity , FI-20520 Turku/Åbo, Finland 6
Russian State Hydrometeorological University, 195196 St. Petersburg, Russia
7
Baltic Nest Institute, Stockholm University, SE-106 91 Stockholm, Sweden
8
Department of Applied Environmental Science, Stockholm University, SE-11418 Sweden
9
Estonian Marine Institute, University of Tartu, 12618 Tallinn, Estonia
10
Stockholm Vatten, SE-106 36 Stockholm, Sweden
11
Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden
12
Zoological Institute, Russian Academy of Science, 199034 St. Petersburg, Russia
13
Institute of Meteorology and Water, Management Maritime Branch, 81-342 Gdynia, Poland
14
Environmental Protection Agency, Department of Marine Research, LT-91149 Klaipeda, Lithuania 15
Bundesamt für Seeschifffahrt und Hydrographie, D-20359 Hamburg, Germany
S1
Table S1. Data sources for the analysis of hypoxia in the coastal zone of the Baltic Sea. All known data sources for oxygen concentrations in the coastal zone of the Baltic Sea were compiled. The list of data providers are in Table S1. Most of the data assembled are archived in the Baltic Environmental Database (BED) (http://nest.su.se/models/bed.htm) of the Baltic Nest Institute, Stockholm University. However, data from Russia and from the Himmerfjärden, Ulf Larsson, Systems Ecology, Stockholm University are not archived in the BED database. Access to the data can be obtained from the original data holders identified in Table S1. The location of monitoring data used in this study were partitioned into different regions largely following the division of HELCOM – The Helsinki Commission: Baltic Marine Environmental Protection Commission (Figure S1). Country
Data Host
Provider
Access Level
Denmark
National Environmental Research
Jacob Carstensen
Public access
Institute Estonia
Estonian Marine Institute
Jonne Kotta
Restricted
Finland
Finnish Environmental Institute
Jouko Rissanen
Public access
Germany
Bundesamt fuer Seeschifffahrt und
Sunhild Wilhelms
Public access
Hydrographie (BSH) Latvia
Latvian Institute of Aquatic Ecology
Juris Aigars
Restricted
Lithuania
Environmental Protection Agency
Nijolė Remeikaitė-Nikienė
Restricted
Poland
Chief Inspectorate for Environmental
Elzbieta Lysiak-Pastuszak
Restricted
Alexey Maximov
Restricted
Protection Russia
Russian Academy of Science
Sweden
Swedish Meteorological & Hydrological Philip Axe
Public access
Institute Sweden
Stockholm University
Ulf Larsson
S2
Restricted
Sweden
Stockholm Vatten
Christer Lännergren
S3
Public access
Table S2. Identified seasonal windows for calculating trends in oxygen concentrations (Figure 4, manuscript). The seasonal windows cover the summer and autumn months when the seasonal trend in bottom oxygen becomes decoupled from the seasonal trends in the surface water. Bottom water oxygen concentrations reached their annual minimum at different times of the year and for different amounts of time partly depending upon their geographical location. Therefore, seasonal windows where hypoxia occurs were calculated using the mean monthly profiles. Region
Jan
Feb Mar Apr May Jun
Bothnian Bay The Quark Bothnian Sea Stockholm Archipelago Finnish Archipelago Gulf of Finland Gulf of Riga Western Gotland basin Eastern Gotland basin Southern Baltic Proper Belt Seas The Sound The Kattegat Limfjord
S4
Jul
Aug Sep Oct
Nov Dec
Figure S1. Location of monitoring data used in the study, partitioned into different regions, largely following the regional division from HELCOM.
S5
Frequency of hypoxic profiles
16.0%
12.0%
8.0%
4.0%
Q ua Bo rk th nia n St Se oc a kh ol m Ar ch Fi nn . ish Ar G ch ul fo . fF in la nd G ul f of W Ri G ga ot la nd E ba G sin ot la nd ba S sin Ba ltic Pr op er Be lt S ea s Th e So un Th d e Ka tte ga t Li m fjo rd
Th e
Bo th nia n
Ba y
0.0%
Figure S2. The number of hypoxic profiles relative to the total number of profiles for the different regions of the Baltic Sea over the entire period (1955-2009).
S6
2
Surface Bottom Difference
1 0
3
-1
0
-2 F
M
A
M
J
J
A
S
O
N
-1
9
3
Surface Bottom
6
2
Difference
3
1
0
D
0 J
F
M
A
M
J
Months 15
5
Surface Bottom
2
Difference
1
3
-1
3
-1 Concentration (mg l )
4
12
Difference (mg l )
-1
Concentration (mg l )
Bothnian Sea
6
0
0
-1 J
F
M
A
M
J
J
A
S
O
N
5 9
4 3
6
1 Surface Bottom Difference
0
Concentration (mg l-1)
2
6
M
A
M
-2 J
A
S
O
N
Surface Bottom
0
Difference M
J
J
A
S
-1 O
N
Concentration (mg l-1)
1
Difference (mg l-1)
Concentration (mg l-1)
2 6
A
D
5
9
3 Surface Bottom Difference
6
2
3
1
0 F
M
A
15
5
3
M
N
4
J
9
F
O
0
4
J
S
M
J
J
A
S
O
N
D
Months
12
0
A
12
D
Gulf of Riga
3
J
Gulf of Finland
Months 15
J
-1
0 J
1 0
F
15
Difference (mg l-1)
Concentration (mg l-1)
3
M
2
Surface Bottom Difference
3
6
4
A
7 6
J
7
9
M
D
0
5
F
N
Months
12
J
O
12
D
Finnish Archipelago
3
S
Stockholm Archipelago
Months 15
A
Months
15
9
J
Difference (mg l-1)
J
4
Difference (mg l-1)
6
12
12
4
9
3
6
2 Surface Bottom Difference
3
0
D
J
Months
F
M
A
M
J
J
Months
S7
5
W Gotland basin
A
S
1
0 O
N
D
Difference (mg l-1)
9
-1
3
Concentration (mg l )
4
12
5
The Quark -1 Difference (mg l )
-1 Concentration (mg l )
15
5
Bothnian Bay
Difference (mg l )
15
15
2 Surface Bottom
1
Difference
0
0
-1 J
F
M
A
M
J
J
A
S
O
N
4 -1
9
3 Surface Bottom Difference
6
2
3
1
0
D
0 J
F
M
A
M
Months
2 Surface Bottom Difference M
A
1
-1
6
Concentration (mg l )
3
-1
9
Difference (mg l )
Concentration (mg l-1)
4
F
J
J
A
S
O
N
9
3
6
2 Surface
3
1
Bottom Difference J
F
M
A
0 M
15
12
4
12
9
3
Surface Bottom Difference M
A
1 0 M
J
J
A
S
O
N
-1 Concentration (mg l )
-1
2
F
J
A
S
O
N
D
5
Limfjord Difference (mg l )
-1
Concentration (mg l )
6
J
J
Months 5
0
D
4
D
The Kattegat
3
N
12
Months 15
O
5
0
0 M
S
The Sound
12
J
A
15
5
Belt Seas
0
J
Months
15
3
J
-1 Difference (mg l )
3
12
4 3
9 Surface Bottom Difference
6
2 1
3
0
0
D
-1 J
Months
Difference (mg l-1)
6
-1 Concentration (mg l )
3 9
Difference (mg l-1)
4
12
5
S Baltic Proper
Difference (mg l )
5
E Gotland basin
-1
Concentration (mg l )
15
F
M
A
M
J
J
A
S
O
N
D
Months
Figure S3. Seasonal variation in surface and bottom water oxygen concentration as well as their difference for the 14 regions delimited in Figure S1. Bottom oxygen means were calculated only when the density difference between surface and bottom was above 0.5, i.e. indicative of a stratified water column. Seasonal patterns in water column oxygen concentrations were observed across the entire Baltic Sea coastal zone with August and September generally being the peak months for
S8
hypoxia in all regions. Further south in the Baltic Sea coastal zone hypoxia also occurred in October and in some cases into November in the Sound and the Kattegat coastal regions. The periods of time, e.g. the seasonal window when hypoxia appears, used for calculating trends in oxygen concentrations, are in Table S2.
S9
0.60%
0.60%
The Quark
0.50%
Frequency of hypoxic profiles
Frequency of hypoxic profiles
Bothnian Bay
0.40% 0.30% 0.20% 0.10%
0.50% 0.40% 0.30% 0.20% 0.10% N/A
0.00% 0-5
0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 >50
>50
50%
Stockholm Archipelago
Bothnian Sea 5.0%
Frequency of hypoxic profiles
Frequency of hypoxic profiles
N/A
Depth (m)
6.0%
4.0% 3.0% 2.0% 1.0%
40%
30%
20%
10%
0%
0.0% 0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
0-5
5-10
Depth (m)
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
15%
15%
Gulf of Finland Frequency of hypoxic profiles
Finnish Archipelago Frequency of hypoxic profiles
N/A
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
Depth (m)
10%
5%
10%
5%
0%
0% 0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
0-5
5-10
Depth (m) 2.0%
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
25%
Western Gotland basin Frequency of hypoxic profiles
Gulf of Riga Frequency of hypoxic profiles
N/A
0.00%
1.5%
1.0%
0.5%
N/A
N/A
N/A
N/A
20%
15%
10%
5%
N/A 0%
0.0% 0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
Depth (m)
S10
0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
2.0%
0.60%
Southern Baltic Proper Frequency of hypoxic profiles
Frequency of hypoxic profiles
Eastern Gotland basin 1.5%
1.0%
0.5%
N/A
N/A
N/A
0.50% 0.40% 0.30% 0.20% 0.10%
N/A
0.0%
0.00% 0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
Depth (m) 4.0%
30.0%
The Sound
25.0%
Frequency of hypoxic profiles
Frequency of hypoxic profiles
Belt Seas
20.0% 15.0% 10.0% 5.0% N/A
0.0%
N/A
N/A
3.0%
2.0%
1.0%
N/A
N/A
N/A
N/A
N/A
N/A
0.0%
0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 >50
0-5
5-10
Depth (m)
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
40%
40%
Limfjord Frequency of hypoxic profiles
The Kattegat Frequency of hypoxic profiles
>50
Depth (m)
30%
20%
10%
N/A
30%
20%
10%
N/A
N/A
N/A
N/A
N/A
N/A
0%
0% 0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
Depth (m)
0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
Figure S4. Depth-distribution of profiles with hypoxia (< 2 mg l-1) relative to the total number of profiles for the 14 regions delimited in Figure S1.
S11
15
15
5
5
The Quark
0
Difference
Months
Months 5
2
6
1
9
-1
8
-1
7 9
6 5
6
4 3
3
Surface Bottom Difference
2 1
0 -2 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Months
Months
6
4 3
6
2 Surface Bottom Difference
1
Months
6
1 0
3
-1
Surface -1
Bottom Difference
6
2
3
Surface Bottom Difference
1
7 6
12
-1
Difference (mg l )
2
Concentration (mg l )
4 3
3
Western Gotland basin
12 9
9
15
5
Gulf of Riga
4
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
15
12
-1
5 9
5
Gulf of Finland Concentration (mg l )
12
3
15
7
Finnish Archipelago
-1
15
Difference (mg l- 1)
Bottom Difference
12
5 9
4 3
6
2 3
Surface Bottom Difference
1
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
0 -2 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
S12
-1
Surface
0
Concentration (mg l )
9
Difference (mg l-1)
3
10
Stockholm Archipelago
4
12
3
15
Difference (mg l )
Concentration (mg l-1)
0
0 -1 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Bothnian Sea
Concentration (mg l- 1)
Surface Bottom Difference
0 -1 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
15
Concentration (mg l- 1)
1 3
Difference (mg l )
Surface Bottom
2 6
Difference (mg l-1)
1 3
3 9
-1
2 6
4
12
Difference (mg l )
3 9
Concentration (mg l-1)
4
12
Difference (mg l-1)
Concentration (mg l-1)
Bothnian Bay
2 1 0
Surface Bottom Difference
5 9
4 3
6
2 3
-1
Surface Bottom Difference
1
0 -2 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Months
Months 15
7
3
6 Surface Bottom Difference
2
-1
1
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
9
4 3
6
2 3
0
Surface
5
Limfjord
4 3
6
2 3
Surface Bottom Difference
1
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
Concentration (mg l- 1)
-1
5
Difference (mg l - 1)
6
9
0
15
7
The Kattegat 12
1
Bottom Difference
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
Months 15
5
Difference (mg l- 1)
-1
4
6
12
12
4
9
3
6
2
3
0
Surface Bottom Difference
Difference (mg l - 1)
9
Difference (mg l )
5
Concentration (mg l )
6
12
3
7
The Sound
Belt Seas
Concentration (mg l )
6
12
-1
3
6
Concentration (mg l )
Difference (mg l- 1)
4 9
3
7
Southern Baltic Proper
5
-1
Concentration (mg l )
12
15
Concentration (mg l- 1)
15
6
-1
7
Eastern Gotland basin
Difference (mg l )
15
1
0
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
Figure S5. Trends in surface and bottom water oxygen concentration as well as their difference for the 14 regions delimited in Figure S1 using the seasonal windows defined in Table S2. Bottom oxygen means were calculated only when the density difference between surface and bottom was above 0.5, i.e. indicative of a stratified water column. All sites, including both sites with and without hypoxia, were included.
S13
Hypoxia is increasing in the coastal zone of the Baltic Sea Daniel J. Conley1, Jacob Carstensen2, Juris Aigars3, Philip Axe4, Erik Bonsdorff5, Tatjana Eremina6, Britt-Marie Haahti5, Christoph Humborg7,8, Per Jonsson8, Jonne Kotta9, Christer Lännegren10, Ulf Larsson11, Alexey Maximov12, Miguel Rodriguez Medina7, Elzbieta Lysiak-Pastuszak13, Nijolė Remeikaitė-Nikienė14, Jakob Walve11, Sunhild Wilhelms15, and Lovisa Zillén1 1
Department of Earth and Ecosystem Sciences, Lund University, SE-223 62 Lund, Sweden
2
National Environmental Research Institute, Aarhus University, DK-4000 Roskilde, Denmark
3
Latvian Institute of Aquatic Ecology, LV-1007 Riga, Latvia
4
Swedish Meteorological & Hydrological Institute, SE-426 71 Västra Frölunda, Sweden
5
Department of Biosciences, Environmental and Marine Biology, Åbo Akademi University, BioCity , FI-20520 Turku/Åbo, Finland 6
Russian State Hydrometeorological University, 195196 St. Petersburg, Russia
7
Baltic Nest Institute, Stockholm University, SE-106 91 Stockholm, Sweden
8
Department of Applied Environmental Science, Stockholm University, SE-11418 Sweden
9
Estonian Marine Institute, University of Tartu, 12618 Tallinn, Estonia
10
Stockholm Vatten, SE-106 36 Stockholm, Sweden
11
Department of Systems Ecology, Stockholm University, SE-106 91 Stockholm, Sweden
12
Zoological Institute, Russian Academy of Science, 199034 St. Petersburg, Russia
13
Institute of Meteorology and Water, Management Maritime Branch, 81-342 Gdynia, Poland
14
Environmental Protection Agency, Department of Marine Research, LT-91149 Klaipeda, Lithuania 15
Bundesamt für Seeschifffahrt und Hydrographie, D-20359 Hamburg, Germany
S1
Table S1. Data sources for the analysis of hypoxia in the coastal zone of the Baltic Sea. All known data sources for oxygen concentrations in the coastal zone of the Baltic Sea were compiled. The list of data providers are in Table S1. Most of the data assembled are archived in the Baltic Environmental Database (BED) (http://nest.su.se/models/bed.htm) of the Baltic Nest Institute, Stockholm University. However, data from Russia and from the Himmerfjärden, Ulf Larsson, Systems Ecology, Stockholm University are not archived in the BED database. Access to the data can be obtained from the original data holders identified in Table S1. The location of monitoring data used in this study were partitioned into different regions largely following the division of HELCOM – The Helsinki Commission: Baltic Marine Environmental Protection Commission (Figure S1). Country
Data Host
Provider
Access Level
Denmark
National Environmental Research
Jacob Carstensen
Public access
Institute Estonia
Estonian Marine Institute
Jonne Kotta
Restricted
Finland
Finnish Environmental Institute
Jouko Rissanen
Public access
Germany
Bundesamt fuer Seeschifffahrt und
Sunhild Wilhelms
Public access
Hydrographie (BSH) Latvia
Latvian Institute of Aquatic Ecology
Juris Aigars
Restricted
Lithuania
Environmental Protection Agency
Nijolė Remeikaitė-Nikienė
Restricted
Poland
Chief Inspectorate for Environmental
Elzbieta Lysiak-Pastuszak
Restricted
Alexey Maximov
Restricted
Protection Russia
Russian Academy of Science
Sweden
Swedish Meteorological & Hydrological Philip Axe
Public access
Institute Sweden
Stockholm University
Ulf Larsson
S2
Restricted
Sweden
Stockholm Vatten
Christer Lännergren
S3
Public access
Table S2. Identified seasonal windows for calculating trends in oxygen concentrations (Figure 4, manuscript). The seasonal windows cover the summer and autumn months when the seasonal trend in bottom oxygen becomes decoupled from the seasonal trends in the surface water. Bottom water oxygen concentrations reached their annual minimum at different times of the year and for different amounts of time partly depending upon their geographical location. Therefore, seasonal windows where hypoxia occurs were calculated using the mean monthly profiles. Region
Jan
Feb Mar Apr May Jun
Bothnian Bay The Quark Bothnian Sea Stockholm Archipelago Finnish Archipelago Gulf of Finland Gulf of Riga Western Gotland basin Eastern Gotland basin Southern Baltic Proper Belt Seas The Sound The Kattegat Limfjord
S4
Jul
Aug Sep Oct
Nov Dec
Figure S1. Location of monitoring data used in the study, partitioned into different regions, largely following the regional division from HELCOM.
S5
Frequency of hypoxic profiles
16.0%
12.0%
8.0%
4.0%
Q ua Bo rk th nia n St Se oc a kh ol m Ar ch Fi nn . ish Ar G ch ul fo . fF in la nd G ul f of W Ri G ga ot la nd E ba G sin ot la nd ba S sin Ba ltic Pr op er Be lt S ea s Th e So un Th d e Ka tte ga t Li m fjo rd
Th e
Bo th nia n
Ba y
0.0%
Figure S2. The number of hypoxic profiles relative to the total number of profiles for the different regions of the Baltic Sea over the entire period (1955-2009).
S6
2
Surface Bottom Difference
1 0
3
-1
0
-2 F
M
A
M
J
J
A
S
O
N
-1
9
3
Surface Bottom
6
2
Difference
3
1
0
D
0 J
F
M
A
M
J
Months 15
5
Surface Bottom
2
Difference
1
3
-1
3
-1 Concentration (mg l )
4
12
Difference (mg l )
-1
Concentration (mg l )
Bothnian Sea
6
0
0
-1 J
F
M
A
M
J
J
A
S
O
N
5 9
4 3
6
1 Surface Bottom Difference
0
Concentration (mg l-1)
2
6
M
A
M
-2 J
A
S
O
N
Surface Bottom
0
Difference M
J
J
A
S
-1 O
N
Concentration (mg l-1)
1
Difference (mg l-1)
Concentration (mg l-1)
2 6
A
D
5
9
3 Surface Bottom Difference
6
2
3
1
0 F
M
A
15
5
3
M
N
4
J
9
F
O
0
4
J
S
M
J
J
A
S
O
N
D
Months
12
0
A
12
D
Gulf of Riga
3
J
Gulf of Finland
Months 15
J
-1
0 J
1 0
F
15
Difference (mg l-1)
Concentration (mg l-1)
3
M
2
Surface Bottom Difference
3
6
4
A
7 6
J
7
9
M
D
0
5
F
N
Months
12
J
O
12
D
Finnish Archipelago
3
S
Stockholm Archipelago
Months 15
A
Months
15
9
J
Difference (mg l-1)
J
4
Difference (mg l-1)
6
12
12
4
9
3
6
2 Surface Bottom Difference
3
0
D
J
Months
F
M
A
M
J
J
Months
S7
5
W Gotland basin
A
S
1
0 O
N
D
Difference (mg l-1)
9
-1
3
Concentration (mg l )
4
12
5
The Quark -1 Difference (mg l )
-1 Concentration (mg l )
15
5
Bothnian Bay
Difference (mg l )
15
15
2 Surface Bottom
1
Difference
0
0
-1 J
F
M
A
M
J
J
A
S
O
N
4 -1
9
3 Surface Bottom Difference
6
2
3
1
0
D
0 J
F
M
A
M
Months
2 Surface Bottom Difference M
A
1
-1
6
Concentration (mg l )
3
-1
9
Difference (mg l )
Concentration (mg l-1)
4
F
J
J
A
S
O
N
9
3
6
2 Surface
3
1
Bottom Difference J
F
M
A
0 M
15
12
4
12
9
3
Surface Bottom Difference M
A
1 0 M
J
J
A
S
O
N
-1 Concentration (mg l )
-1
2
F
J
A
S
O
N
D
5
Limfjord Difference (mg l )
-1
Concentration (mg l )
6
J
J
Months 5
0
D
4
D
The Kattegat
3
N
12
Months 15
O
5
0
0 M
S
The Sound
12
J
A
15
5
Belt Seas
0
J
Months
15
3
J
-1 Difference (mg l )
3
12
4 3
9 Surface Bottom Difference
6
2 1
3
0
0
D
-1 J
Months
Difference (mg l-1)
6
-1 Concentration (mg l )
3 9
Difference (mg l-1)
4
12
5
S Baltic Proper
Difference (mg l )
5
E Gotland basin
-1
Concentration (mg l )
15
F
M
A
M
J
J
A
S
O
N
D
Months
Figure S3. Seasonal variation in surface and bottom water oxygen concentration as well as their difference for the 14 regions delimited in Figure S1. Bottom oxygen means were calculated only when the density difference between surface and bottom was above 0.5, i.e. indicative of a stratified water column. Seasonal patterns in water column oxygen concentrations were observed across the entire Baltic Sea coastal zone with August and September generally being the peak months for
S8
hypoxia in all regions. Further south in the Baltic Sea coastal zone hypoxia also occurred in October and in some cases into November in the Sound and the Kattegat coastal regions. The periods of time, e.g. the seasonal window when hypoxia appears, used for calculating trends in oxygen concentrations, are in Table S2.
S9
0.60%
0.60%
The Quark
0.50%
Frequency of hypoxic profiles
Frequency of hypoxic profiles
Bothnian Bay
0.40% 0.30% 0.20% 0.10%
0.50% 0.40% 0.30% 0.20% 0.10% N/A
0.00% 0-5
0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 >50
>50
50%
Stockholm Archipelago
Bothnian Sea 5.0%
Frequency of hypoxic profiles
Frequency of hypoxic profiles
N/A
Depth (m)
6.0%
4.0% 3.0% 2.0% 1.0%
40%
30%
20%
10%
0%
0.0% 0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
0-5
5-10
Depth (m)
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
15%
15%
Gulf of Finland Frequency of hypoxic profiles
Finnish Archipelago Frequency of hypoxic profiles
N/A
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
Depth (m)
10%
5%
10%
5%
0%
0% 0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
0-5
5-10
Depth (m) 2.0%
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
25%
Western Gotland basin Frequency of hypoxic profiles
Gulf of Riga Frequency of hypoxic profiles
N/A
0.00%
1.5%
1.0%
0.5%
N/A
N/A
N/A
N/A
20%
15%
10%
5%
N/A 0%
0.0% 0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
Depth (m)
S10
0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
2.0%
0.60%
Southern Baltic Proper Frequency of hypoxic profiles
Frequency of hypoxic profiles
Eastern Gotland basin 1.5%
1.0%
0.5%
N/A
N/A
N/A
0.50% 0.40% 0.30% 0.20% 0.10%
N/A
0.0%
0.00% 0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
Depth (m) 4.0%
30.0%
The Sound
25.0%
Frequency of hypoxic profiles
Frequency of hypoxic profiles
Belt Seas
20.0% 15.0% 10.0% 5.0% N/A
0.0%
N/A
N/A
3.0%
2.0%
1.0%
N/A
N/A
N/A
N/A
N/A
N/A
0.0%
0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 >50
0-5
5-10
Depth (m)
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
40%
40%
Limfjord Frequency of hypoxic profiles
The Kattegat Frequency of hypoxic profiles
>50
Depth (m)
30%
20%
10%
N/A
30%
20%
10%
N/A
N/A
N/A
N/A
N/A
N/A
0%
0% 0-5
5-10 10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50
>50
Depth (m)
0-5
5-10
10-15 15-20 20-25 25-30 30-35 35-40 40-45 45-50 Depth (m)
>50
Figure S4. Depth-distribution of profiles with hypoxia (< 2 mg l-1) relative to the total number of profiles for the 14 regions delimited in Figure S1.
S11
15
15
5
5
The Quark
0
Difference
Months
Months 5
2
6
1
9
-1
8
-1
7 9
6 5
6
4 3
3
Surface Bottom Difference
2 1
0 -2 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Months
Months
6
4 3
6
2 Surface Bottom Difference
1
Months
6
1 0
3
-1
Surface -1
Bottom Difference
6
2
3
Surface Bottom Difference
1
7 6
12
-1
Difference (mg l )
2
Concentration (mg l )
4 3
3
Western Gotland basin
12 9
9
15
5
Gulf of Riga
4
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
15
12
-1
5 9
5
Gulf of Finland Concentration (mg l )
12
3
15
7
Finnish Archipelago
-1
15
Difference (mg l- 1)
Bottom Difference
12
5 9
4 3
6
2 3
Surface Bottom Difference
1
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
0 -2 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
S12
-1
Surface
0
Concentration (mg l )
9
Difference (mg l-1)
3
10
Stockholm Archipelago
4
12
3
15
Difference (mg l )
Concentration (mg l-1)
0
0 -1 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Bothnian Sea
Concentration (mg l- 1)
Surface Bottom Difference
0 -1 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
15
Concentration (mg l- 1)
1 3
Difference (mg l )
Surface Bottom
2 6
Difference (mg l-1)
1 3
3 9
-1
2 6
4
12
Difference (mg l )
3 9
Concentration (mg l-1)
4
12
Difference (mg l-1)
Concentration (mg l-1)
Bothnian Bay
2 1 0
Surface Bottom Difference
5 9
4 3
6
2 3
-1
Surface Bottom Difference
1
0 -2 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Months
Months 15
7
3
6 Surface Bottom Difference
2
-1
1
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
9
4 3
6
2 3
0
Surface
5
Limfjord
4 3
6
2 3
Surface Bottom Difference
1
0 0 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
Concentration (mg l- 1)
-1
5
Difference (mg l - 1)
6
9
0
15
7
The Kattegat 12
1
Bottom Difference
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
Months 15
5
Difference (mg l- 1)
-1
4
6
12
12
4
9
3
6
2
3
0
Surface Bottom Difference
Difference (mg l - 1)
9
Difference (mg l )
5
Concentration (mg l )
6
12
3
7
The Sound
Belt Seas
Concentration (mg l )
6
12
-1
3
6
Concentration (mg l )
Difference (mg l- 1)
4 9
3
7
Southern Baltic Proper
5
-1
Concentration (mg l )
12
15
Concentration (mg l- 1)
15
6
-1
7
Eastern Gotland basin
Difference (mg l )
15
1
0
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 Months
Figure S5. Trends in surface and bottom water oxygen concentration as well as their difference for the 14 regions delimited in Figure S1 using the seasonal windows defined in Table S2. Bottom oxygen means were calculated only when the density difference between surface and bottom was above 0.5, i.e. indicative of a stratified water column. All sites, including both sites with and without hypoxia, were included.
S13
