Journal
CLIMATE DYNAMICS
Volume 49, Issue 1-2, Pages 163-172Publisher
SPRINGER
DOI: 10.1007/s00382-016-3333-y
Keywords
Coastal seas; Baltic Sea; Numerical modeling; Climate change; Global mean sea level rise; Marine biogeochemical cycles; Hypoxia
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Funding
- Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) within the project Impact of accelerated future global mean sea level rise on the phosphorus cycle in the Baltic Sea [214-2009-577]
- Stockholm University's Strategic Marine Environmental Research Funds Baltic Ecosystem Adaptive Management (BEAM)
- Swedish Research Council (VR) within the project Reconstruction and projecting Baltic Sea climate variability [2012-2117]
- Danish Agency for Science, Technology and Innovation [09-067259/DSF]
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Expanding hypoxia is today a major threat for many coastal seas around the world and disentangling its drivers is a large challenge for interdisciplinary research. Using a coupled physical-biogeochemical model we estimate the impact of past and accelerated future global mean sea level rise (GSLR) upon water exchange and oxygen conditions in a semi-enclosed, shallow sea. As a study site, the Baltic Sea was chosen that suffers today from eutrophication and from dead bottom zones due to (1) excessive nutrient loads from land, (2) limited water exchange with the world ocean and (3) perhaps other drivers like global warming. We show from model simulations for the period 1850-2008 that the impacts of past GSLR on the marine ecosystem were relatively small. If we assume for the end of the twenty-first century a GSLR of +0.5 m relative to today's mean sea level, the impact on the marine ecosystem may still be small. Such a GSLR corresponds approximately to the projected ensemble-mean value reported by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. However, we conclude that GSLR should be considered in future high-end projections (>+1 m) for the Baltic Sea and other coastal seas with similar hydrographical conditions as in the Baltic because GSLR may lead to reinforced saltwater inflows causing higher salinity and increased vertical stratification compared to present-day conditions. Contrary to intuition, reinforced ventilation of the deep water does not lead to overall improved oxygen conditions but causes instead expanded dead bottom areas accompanied with increased internal phosphorus loads from the sediments and increased risk for cyanobacteria blooms.
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