deoxygenation of the baltic sea during the last...
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Deoxygenation of the Baltic
Sea during the last century
Jacob Carstensen1, Jesper H. Andersen1,
Bo G. Gustafsson2, and Daniel J. Conley3
1Aarhus University, 2Stockholm University
3Lund University, Sweden
Email: [email protected]
Twitter: @DanielJConley
Supported by: BONUS (HYPER, COCOA), FORMAS (Multistressors), Pew Marine Conservation Fellowship, Baltic Sea 2020
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PNAS (15 April 2015) 111: 5628-5633
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Gustafsson et al. 2012
Target for the
Baltic Sea Action Plan
Note: The residence time
time of the Baltic Proper
is ca. 30 years
Target for the Baltic Sea Action Plan
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Much larger than the size of Belgium (30,528 km2)
Area with hypoxia averages ca. 49,000 km2
Sweden
Norway
Denmark
Finland
Poland Germany
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Conley et al. (2002)
Baltic hypoxic area reasonably well defined from ca. 1970 to present from monitoring data
Jan - Mar
Aug - Sept
Prior to 1970?
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Savchuk (2010)
Methodology developed in 1888 by Ludwig Wilhelm Winkler at Budapest University (First measurements of dissolved oxygen in the Baltic Sea are from 1898)
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Carstensen et al. (2014)
Calculation using sparse data and AOU
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Estimated profile examples
57'04.0 N
19'50.0 E
05-11-1992
0
50
100
150
200
250
0 5 10 15 20
Oxygen deficit (mg/l)
Dep
th (
m)
Oxygen (mg/l)
Salinity
57'04.3 N
19'49.8 E
28-03-1994
0
50
100
150
200
250
0 10 20
Oxygen deficit (mg/l)
Dep
th (
m)
Oxygen (mg/l)
Salinity
58'53.0 N
20'19.2 E
02-08-2000
0
50
100
150
200
250
0 5 10 15 20
Oxygen deficit (mg/l)
Dep
th (
m)
Oxygen (mg/l)
Salinity
Before inflow 1993 After inflow 1993 More common profile
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Carstensen et al. (2014)
2oC
Lower salinity and increased mixing across halocline (ca 1990)
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Carstensen et al. (2014)
Development of AOU through time
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Development of hypoxic area through time
Carstensen et al. (2014)
1,500 km2 65,000 km2 25,000 km2
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Carstensen et al. (2014)
Implications of mass-balance of AOU
Export of TAOU exceeds import
Increases in vertical mixing, especially during staganation period
Consumption due to nutrients explain 30% of the variation
Warming of bottom waters has increased respiration by 20%
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We have developed a new method to use sparse data on oxygen concentrations over the last century to determine oxygen trends in the Baltic Sea through time The low oxygen zone has increased by a factor of 10 times over the last 115 years from about 5,000 km2 to more than 60,000 km2 in recent years Oxygen saturation has decreased about 0.5 mg L-1 over the past 115 y as a result of the temperature increase alone
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