Thermohaline Circulation and the

Effects of Global WarmingGlobal warming is causing significant changes in

ocean currents which will in turn alter global climate, biodiversity, and human civilizations.

http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/MOVIES/Topex_Dynamic_Ocean_Topography.mpg

Lauren Eaton, Sarah Cook, and Alice Rice

Section 2, Group 2

Outline• What are ocean currents?• How global warming is a factor• How global warming and currents

are interacting • Why we care• How this is affecting Biodiversity• Phytoplankton Graph• Case Study: The ACC• Take Home Message • Bibliography

Ocean Currents

• What– Keep oceans in constant motion– Contribute to heat transport

• How– Driven by wind, tides, gravity, Coriolis Force– Create gyres – Surface current driven by wind – Deep ocean currents driven by density and

temperature• Where

– Entire world!– Major currents: North and South Equatorial

Currents, Gulf Stream, Kuroshio Current, Antarctic Circumpolar Current, East Australia Current

Global Warming • Combination of temperature and

salinity determine density

– Warming of the planet will cause an influx of freshwater from melting glaciers.

– Fresh water is less saline than salt water, won’t be as dense and sink, the density gradient that determines currents will be lower.

– Currents slow down – Northern latitudes become less salty– As the currents slow down the water

will be less mixed, fewer nutrients cycling, release of CO2 sinks

– Not currently shown because the top few meters of the ocean hold as much heat energy as the entire atmosphere

Adkins, Jess F., McIntyre, Katherine, and Daniel p. Schrang.

Our Changing Ocean

Currents• Possible slowing of Conveyor Belt

– Temperature and rising waters• As Oceans and world warms the world will also

start to cool – no heat exchange– could produce winters 2x as harsh as the worst

winter on record• Melting Glaciers

– Salinity and density fluxes, will only intensify problem Yin, J., Schlesinger, M., Adronova, N., Malyshev, S., & Li, B

Why we care….• Climate

– Temperature• As currents slow the exchange of water will

slow and climate change will intensify– Weather

• When glacial melting increases as a result of global warming there will be more ocean surface area, resulting in more precipitation in some areas and drought in others.

• Slowing currents result from more rain falling in polar regions, further melting glaciers

• Ecosystems – Biodiversity

• Plankton • As a result of changing temperature habitats

change, both aquatic and terrestrial • Social

– Population vs. Space• as oceans get warmer and rise there will be a

fight for available land– Adaptation

• Humans and other animals will be living in a warmer world Department of Earth Sciences, University of Southern California Faculty. 2006.

Changing Biodiversity• Changes in phytoplankton

concentrations over the last 20 years. Deep blues show the greatest loss of phytoplankton. Yellow represents almost no change. Browns, reds, and oranges show phytoplankton increases. Black indicates that no data is available.

• Without Ocean currents 1/50 of nutrients would be lost automatically each year as a result of sinking nutrients that aren’t redistributed.

• Ocean currents mix up layers and spread nutrients throughout the ocean, with the slowing of currents there will be less mixing, phytoplankton will receive fewer nutrients

• Also nutrients are not spread as much by the ACC •Roach, John. 2005.

How temperature and phytoplankton are correlated

(2001)

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7.5 9.5 11.5 12.5 14

Degrees C

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•NOAA. “World ocean database 2001

Antarctic Circumpolar Current

• The Antarctic is an indicator– Where oceans converge

• Largest current• Further warming melts

more glaciers• Controls circulation

throughout world– Density

Baer, Andrea. “Antarctic Current circles the World”. 2002.

What Will Our World Look Like?

• Complete failure of the conveyor belt possible– Could be restarted with a

drastic change– Mini ice age possible

• Younger dryas – Increased CO2

• Sink lost• Earth processes

– Drought– Precipitation– Cloud cover– Increased ocean surface

area •Pearce, Fred. 2005

Take Home Message

• Ocean Currents are changing and will cause significant changes on the Earth but worry not, there is still hope.

Bibliography• Adkins, Jess F., McIntyre, Katherine, and Daniel p. Schrang. “The salinity, temperature and ∂18 of the glacial deep ocean”. 2006.

<http://www.sciencemag.org/cgi/reprint/298/5599/1769.pdf> (20 November 2006)

• Baer, Andrea. “Antarctic Current circles the World”. 2002. <http://antarcticsun.usap.gov/oldissues2002-2003/Sun121502/current.html#>• (22 October 2006) The last revision was 15 December 2002. I visited the site on 22 October 2006.

• CSIRO Marine Research. “Southern Ocean and Antarctic Circumpolar Current”. 2005. <http://www.marine.csiro.au/LeafletsFolder/10ocean/10.html> (24 October 2006)

• Department of Earth Sciences, University of Southern California Faculty. “Ocean Currents and Climate”. 2006. <http://earth.usc.edu/~stott/Catalina/Oceans.html> (30 November 2006)

• Gagosian, Robert B. “Abrupt climate change: should we be worried?”. Jan 27 2003. • <http://www.whoi.edu/institutes/occi/viewArticle.do?id=9986> (1 December 2006)

• Gille, S. T. “Warming of the Southern Ocean since the 1950s.” 2002 <http://www.sciencemag.org/cgi/content/full/295/5558/1275> (1 December 2006)

• NOAA. “World ocean database 2001 - plankton abundance” 2001 <http://www.nodc.noaa.gov/OC5/WOA01/abundance.htmI> (1 December 2006)

• Pearce, Fred. “Failing ocean current raises fear of mini ice age”. 30 November 2005. <http://www.newscientist.com/article.ns?id=dn8398> (20 November 2006)

• Roach, John. “Global warming may alter atlantic currents, study says”. June 27 2005. • http://news.nationalgeographic.com/news/2005/06/0627_050627_oceancurrent.html (1 December 2006)

• Russel, J.L., Strouffer, R, and Keith Dixon. “Intercomparison of the Southern Ocean Circulations in IPCC Coupled Model Control Simulations”. 2006. <http://www.gfdl.noaa.gov/reference/bibliography/2006/jlr0601.pdf> (20 November 2006)

• Salleh, Anna. “Faster Westerlies Threaten Antarctica”. (2006).• < http://www.abc.net.au/science/news/stories/s1686723.htm> (20 October 2006)• The last revision was 14 July 2006. I visited the site on 20 October 2006.

• Stouffer, R. J., Manabe, S., and Bryan, K. “Interhemispheric Asymmetry in Climate Response to a Graudal Increase of Atmospheric CO2” 1989. <http://www.springerlink.com/content/k2272x7370171086/> (1 December 2006)

• Yin, J., Schlesinger, M., Adronova, N., Malyshev, S., & Li, B. “Is a shutdown of the thermohaline circulation irreversible?” 2006 <http://www.agu.org/pubs/crossref/2006/2005JD006562.shtml> (14 November 2006)