3 Ocean Circulation Learning objectives: Mass flow of ocean water is driven by two forces - wind (10%) and gravity (90%)Surface currents are driven by wind – Coriolis effect; Ekman transportDeep ocean, slow and density driven currents - Thermohaline circulation;Waves (transmit energy not water mass) and Tides (the longest of all ocean waves)
18 Coastal Dynamics California Filaments and Phytoplankton Hawaiian Island Wakes
19 Some important differences between ocean and atmosphere Ocean is heated from aboveFeels bothMechanical forcing by the winds&Thermal forcing from the sunBoundaries and complex geometry associated with continents and bottom topography, and bathymetryOcean is denser than atmosphereTidesSalinityAtmosphere has clouds and moisture
30 Some practical rules to remember: Applies to the Ocean same as Atmosphere!FpressureLow PressureHigh PressureFCoriolisParticle will have the Coriolis effect 90 degrees to the rightParticles will tend to move along line of constant pressureParticles will have the high pressure on their right (same as Coriolis)
34 Evidence of Global Warming in the Climate System: Glacier meltingKilimanjaro: ice caps are 80% gone since early 1900’sAll glaciers in tropics are melting rapidlyImpacts: water supply, power generation, tourism, local climate and ecology
35 To understand how climate has changed in the past, we need to use records of climate preserved in ice cores, ancient tree rings, coral bands, and other “paleoclimatic” sources:
38 Arctic - the most sensitive ecosystem? Arctic sea ice has shrunk by 1 million sq km and thinned from 3.1m to 1.8m averageMore freshwater, reduced ability to travel over iceAll summer ice gone in this centuryEcological consequences huge!
39 Arctic warming 1979 2003 Sea ice melting Warming temperature Key feedback! (animation)Reduces albedo (reflectivity) of earth, allowing more radiation to be absorbedWarming temperatureMelts permafrostIce sheet stability? Key sea level question!Rate of warming 8x faster in last 20 years than in last 10019792003
40 Arctic ecosystems impacts Reduced ice: less algal production under ice = undermines base of food chainSeal pups emerge just when ice is melting - earlier melt means they are exposed before ready to thriveCaribou need ice to island-hop; they are falling through as ice thinsPolar bears hunt on ice in winter, retreat to land in summer. Less ice forces them onto land earlier
41 Higher sea level… As water warms, it expands (“thermal expansion”). Glaciers are meltingObservation: 3mm/yr in past few decadesPrediction: ~0.5m rise by the end of this century, 2-4m in 500 yearsThis will have a major impact onDeveloped coastal regionsLow-lying island nationsIntensity of coastal flooding during storm surgesCoastal ecosystems (e.g. mangroves, estuaries)
42 More intense storms…Hurricanes get their energy and staying power from warm water in the tropical oceans.As waters get warmer, we expect that hurricanes will become more intense.Significant change not yet observed.
43 Map of predicted temperature change for a doubling of atmospheric CO2 Warmer temperatures…Prediction: Doubled CO2 will warm the planet by °C (before 2100)Some areas warm up more than others.Continents warm faster than oceans.Higher latitudes warm more than low.Map of predicted temperature change for a doubling of atmospheric CO2
44 Oceanography and Climate - millennial timescales Vertical circulation of the oceanMOVIE:The Day After Tomorrow