lecture climate change lesson 8 · lecture climate change lesson 8 the oceans: thermohaline...
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Course webpagehttps://www.bgc-jena.mpg.de/bgi/index.php/Lectures/HydroBioClimClimateChange
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Lesson 8
The oceans: Thermohaline circulation
1) Thermohaline circulation
2) Ocean acidification
“Global conveyor belt”
Driven by water density differences (temperature, salinity), and rotation of the Earth (Coriolis force)
Thermohaline circulationwikipedia.org
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Spatial differences in ocean salinity driven bydifferences in evaporation minus precipitation
Spatial differences in ocean temperature driven by differences in (the incidence angle of) radiation -
highest at equator, lowest at poles
Thermohaline circulation
IPCC (2013)
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Gulf stream
Gulf stream is part of the global thermohaline
circulation
Gulf stream visible in sea surface
temperature pattern
Stream called florida stream initially,
Benjamin Franklin introduced the name
gulf stream, corresponding to the
Gulf of Mexico
wikipedia.org
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European vs. American temperatures
wikipedia.org
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Europe clearly warmer than America across similar latitudes
Caused by transport of heat towards Europe through(1) Gulf stream, and more importantly (2) south-westerly winds
European vs. American temperatures5
Summary
● Gulf stream is north Atlantic branch of global thermohaline circulation driven by water density differences due to salinity and temperature anomalies
No detectable trend in Gulf Stream activity
Thermohaline circulation in recent years6
IPCC SROCC (2019)
No detectable trend in activity of North-Atlantic thermohaline circulation
Ocean’s salinity and temperature changes impact strength of thermohaline circulation
Future of thermohaline circulation
IPCC (2013)
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Weakening of North-Atlantic thermohaline circulation projected by climate models, but collapse very unlikely
Future of thermohaline circulation8
IPCC SROCC (2019)
Collapse of North-Atlantic thermohaline circulation could occur after massive global warming, after gradual weakening
Future of thermohaline circulationIPCC SROCC (2019)
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Diverse impacts in Europe, and elsewhereHighlighting relevance of North-Atlantic thermohaline circulation
Impacts of thermohaline circulation weakening10
IPCC SROCC (2019)
Distribution of total-column anthropogenic CO2 in the ocean
Most CO2 taken up in deep water formation areas
Imprints of thermohaline circulation
IPCC (2013)
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Additional heat from greenhouse gas-induced radiative forcing mostly taken up by shallow
ocean
Transport into deep ocean in deep water formation areas
Imprints of thermohaline
circulation
IPCC (2013)
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Warming of very deep ocean restricted to southern ocean
Imprints of thermohaline circulation
IPCC SROCC (2019)
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Oceans have taken up by far most of the additional heat
Imprints of thermohaline
circulation
IPCC (2013)
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Clear differences between scenarios
Ocean warming affects marine organisms15
IPCC SROCC (2019)
Surface warming stronger stratification less upwelling → → →
less nutrients less plankton less fish→ →
Ocean warming affects marine organisms16
IPCC SROCC (2019)
Decreasing fish catch potential depends linearly on global warming
Ocean warming affects marine organisms17
IPCC SROCC (2019)
Strongest impacts in the tropics where fish is very popular
Ocean warming affects marine organisms18
IPCC SROCC (2019)
Summary
● Gulf stream is north Atlantic branch of global thermohaline circulation driven by water density differences due to salinity and temperature anomalies
● Gulf stream and thermohaline circulation projected to weaken, collapse unlikely
● Thermohaline circulation controls oceanic uptake of CO2 and related additional heat, most uptake in deep water formation areas
● Considerable loss of fish and biodiversity due to surface ocean warming
Lesson 8
The oceans: Thermohaline circulation
1) Thermohaline circulation
2) Ocean acidification
Atmospheric CO2 propagates into ocean water, forms carbonic acid which in turn increases H+ concentration (pH value)
Ocean acidification
IPCC (2013)
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Decreasing pH in concert with increasing atmospheric and oceanic CO2
Ocean acidificationIPCC (2013)
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Strong differences across scenarios
Ocean acidification21
IPCC SROCC (2019)
Formation of shells is more difficult with ocean acidification
Loosing corals and their reefs22
oneillseaodyssey.org
Corals are important for fish and biodiversity
Loosing corals and their reefs23
change.org
AFTERAFTER
Summary
● Gulf stream is north Atlantic branch of global thermohaline circulation driven by water density differences due to salinity and temperature anomalies
● Gulf stream and thermohaline circulation projected to weaken, collapse unlikely
● Thermohaline circulation controls oceanic uptake of CO2 and related additional heat, most uptake in deep water formation areas
● Considerable loss of fish and biodiversity due to surface ocean warming
● Increased atmospheric CO2 enters ocean, forms carbonic acid and hence acidifies the ocean; nevertheless overall alkaline conditions (pH > 7) likely to persist into the future
● Loss of coral reefs and corresponding biodiversity