Thermohaline Circulation and the Effects of Global Warming Global warming is causing significant changes in ocean currents which will in turn alter global climate, biodiversity, and human civilizations. 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

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

How temperature and phytoplankton are correlated (2001) 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”

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” (20 November 2006) Baer, Andrea. “Antarctic Current circles the World” (22 October 2006) The last revision was 15 December I visited the site on 22 October CSIRO Marine Research. “Southern Ocean and Antarctic Circumpolar Current” (24 October 2006) Department of Earth Sciences, University of Southern California Faculty. “Ocean Currents and Climate” (30 November 2006) Gagosian, Robert B. “Abrupt climate change: should we be worried?”. Jan (1 December 2006) Gille, S. T. “Warming of the Southern Ocean since the 1950s.” 2002 (1 December 2006) NOAA. “World ocean database plankton abundance” 2001 (1 December 2006) Pearce, Fred. “Failing ocean current raises fear of mini ice age”. 30 November (20 November 2006) Roach, John. “Global warming may alter atlantic currents, study says”. June (1 December 2006) Russel, J.L., Strouffer, R, and Keith Dixon. “Intercomparison of the Southern Ocean Circulations in IPCC Coupled Model Control Simulations” (20 November 2006) Salleh, Anna. “Faster Westerlies Threaten Antarctica”. (2006). (20 October 2006) The last revision was 14 July I visited the site on 20 October Stouffer, R. J., Manabe, S., and Bryan, K. “Interhemispheric Asymmetry in Climate Response to a Graudal Increase of Atmospheric CO2” (1 December 2006) Yin, J., Schlesinger, M., Adronova, N., Malyshev, S., & Li, B. “Is a shutdown of the thermohaline circulation irreversible?” 2006 (14 November 2006)