Presentation on theme: "When you hear climate change, what do you think? Rising temperatures Rising levels of CO 2 in atmosphere Rising levels of CO 2 in oceans"— Presentation transcript:
When you hear climate change, what do you think? Rising temperatures Rising levels of CO 2 in atmosphere Rising levels of CO 2 in oceans Rising sea level melting of land ice thermal expansion of water
Life in a hotter, higher CO 2 world What role do the oceans play in climate? Exchange and transfer of heat Oceans carry heat from the tropics (equator) to the poles, to maintain Earth's temperature Exchange and transfer of CO 2 (and O 2 ) What are the sources of increased CO2 in the atmosphere? Deforestation Fossil fuels Cement production Oceans are main reservoirs of readily available carbon dioxide (CO 2 ) The cold, deep water in the ocean is the main reservoir of dissolved CO 2
Oceans and heat Solar energy is absorbed by both oceans and continents. BUT-- because the oceans cover over 70% of Earth's surface and are darker than the continents--they absorb more of the sun's energy Oceans not only absorb lots of energy from the sun--they can also store lots of solar energy in the form of heat AND they can do this with very little change in temperature High specific heat of water 80% of heat generated by global warming is stored in the oceans
Atmosphere and Oceans in Motion Half of the incoming solar radiation is absorbed by the ocean Energy is stored in the water as it is picked up by winds which blow over the ocean surface When the wind releases the water as precipitation the heat energy of the water is released into the atmosphere causing an increase in temperature The oceans' waters are constantly on the move
Sunlight warms the surface of the ocean in the tropics Wind-driven surface currents carry the heat toward the poles In the North Atlantic, the warm currents from the tropics feed the North Atlantic Current (in red on figure on next slide) As the current flows northward toward Norway and Greenland, it loses heat to the atmosphere and cools down In winter the water near Norway and Greenland gets so cold and dense it sinks all the way to the bottom of the ocean The cold bottom water feeds bottom currents (in blue and green on figure) Eventually, mixing brings the bottom water back to the surface in other parts of the ocean, sometime as far away as the North Pacific When the water gets to the surface, sunlight warms the water, and the cycle starts over Global Conveyor Belt – thermohaline circulation
Surface processes determine density (and other properties) of water Because of the high specific heat of water, the oceans store heat Currents transport heat
Global Carbon Cycle Exchange of carbon between different reservoirs (atmosphere, ocean, fossil fuels, land) Ocean is largest active reservoir More CO 2 in atmosphere, more CO 2 in oceans
Global Carbon Cycle How much carbon is in each reservoir? Land = Most in rock/soil Ocean = Most in deep ocean What is the residence time in each reservoir? Alive = 5 yrs Dead = 30 yrs. Soil/rocks = 1000 yrs. 3 yrs. Surface = 6 yrs Mid-water = 100 yrs. Deep = 100,000 yrs.
Oceans in a High CO 2 World Oceans absorb and release CO 2 More CO 2 in the atmosphere, more CO 2 in the oceans CO 2 reacts with water to form an acid
What is an acid? A ny chemical compound that, when dissolved in water, gives a solution with a hydrogen ion (H + ) greater than in pure water Measured by pH scale pH = -log [H + ] higher [H+] = lower pH 0–6 = acid, 7 = neutral, 8–14 = alkaline Each is a power of 10 difference in acidity pH scale
Oceans in a High CO 2 World When CO 2 dissolves, it reacts with water to form a balance of chemical species: dissolved free carbon dioxide (CO 2 (aq)), carbonic acid (H 2 CO 3 ), bicarbonate (HCO 3 ) and carbonate (CO 2 3 ) The ratio of these species depends on temperature and pH Dissolving CO 2 increases [H + ] Lower pH
What are the factors that determine how much CO 2 dissolves in seawater? Solubility determined by temperature Colder water holds more CO 2 than warmer water Ocean circulation Areas of convergence = downwelling = sink for CO 2 Old, dense water Areas of divergence = upwelling = source of CO 2 More CO 2 than atmosphere Biology Photosynthesis/respiration Recycling of matter in surface versus burial to deep ocean
Oceans are a sink for CO 2 Circulation transports dissolved CO 2 Areas of deep water formation have high CO 2 What happens as water gets older and makes voyage around the globe? What happens when this water surfaces?
Oceans in a High CO 2 World Where do we see the most change in CO 2 ? Why?
CO 2 and Old Water CO 2 CO 2 + H2O organic carbon + O 2 euphotic zone CO 2 + H2O organic carbon + O 2 sediments photosynthesis respiration
120m Aragonite Saturation State in West Coast Waters May-June 2007 Old, CO 2 rich water Ocean Acidification in WA Waters
Effects of Ocean Acidification Impacts on organisms that build shells and plates out of calcium carbonate (CaCO 3 ) More acidic (lower pH) = less carbonate Vulnerable organisms: Bivalves (mussels, clams, oysters) Coccolithophorids (phytoplankton) Pteropods, foraminifera (zooplankton) Coral reefs Coccolithophore PteropodCorals
Status of Ocean Acidification Slowing growth of Great Barrier Reef 14% reduction in skeletal formation since 1990 Experimental corrosion of calcium shells Pteropod (48 hrs) b = acid, c = normal seawater Deformed coccoliths
Status of Ocean Acidification Impact on biodiversity Number of species Ecosystem function Impact on marine foodwebs
Ocean Acidification & Marine Foodweb What will the impact of ocean acidification be on the marine foodweb?
What will happen to the Deadliest Catch? Coccolithophore bloom in the Bering Sea Benthic organisms Salmon Marine Mammals
Status of Ocean Acidification ~1/3 of fossil-fuel CO 2 dissolves in ocean Between 1751 and 1994 surface ocean pH is estimated to have decreased from approximately 8.2 to 8.1 Logarithmic scale of pH; approximately a 25% increase in H + Estimated that it will drop by a further 0.3 to 0.5 units by 2100
Global Conveyor Belt The deep circulation shown in the picture is important for two reasons: Cold water carries carbon dioxide deep into the ocean, taking it away from the atmosphere and Surface currents that sink and feed deep currents carry much more heat toward Europe than currents that stay on the surface
Understanding Ocean Acidification Chemistry of oceans depends on chemistry of atmosphere More CO 2 in atmosphere = more CO 2 in oceans More CO 2 in oceans = more acidic oceans (lower pH) More acidic oceans = negative impact on algae and animals with shells or skeletons made of calcium carbonate