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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
PNAS (15 April 2015) 111: 5628-5633
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
Much larger than the size of Belgium (30,528 km2)
Area with hypoxia averages ca. 49,000 km2
Sweden
Norway
Denmark
Finland
Poland Germany
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?
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)
Carstensen et al. (2014)
Calculation using sparse data and AOU
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
Carstensen et al. (2014)
2oC
Lower salinity and increased mixing across halocline (ca 1990)
Carstensen et al. (2014)
Development of AOU through time
Development of hypoxic area through time
Carstensen et al. (2014)
1,500 km2 65,000 km2 25,000 km2
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%
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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