UNIT IV: CIRCULATION OF LIQUID EARTH  Convergence and Divergence  Convergence – ocean currents come together. Surface water tends to pile up at the center of gyres, where downwelling occurs. If HOT, salinity increases as surface water evaporates  Divergence – where ocean currents separate, upwelling occurs  Upwelling and Downwelling  Upwelling:  Coastal Upwelling: coastal winds can create upwelling along the coast  Scenario: If the wind is parallel to the land, which is to the right of it, the surface current moves at a right angle to the wind. Meaning surface current goes to the right, causing an upwelling in the southern hemisphere  Downwelling:  On shore winds  Scenario: If the is wind parallel to the land, which is now to the left of it, the surface current will still move at a right angle to the wind. This time it moves into the land, causing downwelling in the southern hemisphere  Shore-parallel winds: up or down welling  Coliolis Effect and resultant Ekman transport  Coriolis Effect – surface currents are deflected to right (in Northern Hemisphere) or left ( in Southern Hemisphere) of prevailing wind  Elkman Spiral – Transfer of Coriolis effect down through the water column  Responsible for the net motion of surface water  Ekman Transport – Net effect: surface water moves at right angles to the wind  Salinity, Temperature and Density  Vertical circulation is controlled by differences in density • Sea water density controlled by: Temperature and Salinity • Density = Temperature + Salinity ♦ More dense: Colder, higher salinity (saltier)  Sinks, found at bottom of the ocean ♦ Less dense: Warmer, lower salinity (less saltier)  Salinity  Sea-ice formation alters the salinity structure of surface waters • As ice forms from seawater, rejects the salt, producing cold, dense brines • Formation of salty deepwater  Mixed layer, Deepwater or Bottom Water  Deepwater  Forms in northern North Atlantic (very salty and cold) and around Antarcica (not as salty, much colder, even denser) No deepwater found in northern North Pacific • Lower pressure (more rain)  Surface Currents  Note know this question and all like it very well.  Deepwater formation and Thermohaline circulation  Thermohaline circulation: The North Atlantic, Density driven vertical circulation, formation of Bottom water and deep-ocean circulation  Primary Production, or Net Primary Productivity  Primary production: conversion of CO2 into organic matter by organisms through photosynthesis/chemosynthesis; not equally distributed  2 factors that control primary production • Sun • Nutrients ♦ At downwelling spots  Why important?  Where we can catch all those tasty fish we like to eat  Exerts strong control on global carbon cycle  Primary production removes CO2 from the atmosphere and sends it into deep ocean Upwelling areas is where most primary productivity is  Nutrients  At downwelling spots UNIT V. MONSOONS  Moonsoons: Variability of historical and longer time scales  Role of primary insolation, & how positive feedbacks from latent heat release, ocean temperature and vegetation increase monsoon vigor UNIT VI: Global Warming: The Evidence  Direct evidence  Instrumental temperature record  Draw the Temperature Record • 1.5F or .8 C • 1940 and 1970  Indentifying first and second order trends  First order trend • Regular increase in C02 trend  Second order trend • Biosphere breathingAlaska has a bigger second order trend because of a bigger seasonality South Hemisphere North Hemisphere Amplitude Low High Magnitude Lower Higher because source of CO2 in N. Hemisphere  Sources of uncertainty  “Heat Island” effect  Cities are hotter than surroundings  Ocean v land  Land warms faster than ocean because of convection and heat capacity • More energy to warm the oceans than rocks/lands  Geographic variability in temperature records  Northern Hemisphere vs. Southern Hemisphere vs. Tropics  Arctic warming v Global warming  Warming greatest in Arctic despite less land there  Mostly due to sea ice and albedo feedbacks  Precipitation and global warming?  Warming the planet increases evaporation (Water Vapor is a green house gas)  Positive feedback  Indirect evidence of 20th century warming?  Climate proxies  Something preserved that represents a particular aspect of climate  Glaciers  Retreating  Not retreating in Antarctica  Greenland melting more and more rapidly  Ice shelves  Breaking up • Causes glaciers to move faster and calve more rapidly  Floating (but disappearing), displaced as much water as they possible can • Only if land-supported ice is also lost will there be any impact on sea level  Rising sea level Tide gauges • 18 cm/century  Satellites • But only the past 20 years  Has risen and will rise * because of Glaciers melting (50) and Thermal Expansion (50) both contribute half • Glaciers (100%contribute) Sea Ice (0) Ice Shelves (0) to rising sea levels because sea ice is floating ice (ice in water example, doesn’t make it rise)  Sea Ice  2 large positive feedbacks from sea ice; one in summer and a different one in winter • Ice-albedo feedback (summer) ♦ As planet warms, sea ice cover is reduced, greatly reducing albedo. More energy is stored in the ocean. The warmer oceans delays autumn freeze up, so the peak winter extent of sea ice become smaller, and thinner ♦ Although the ice-free ocean stores much of the solar radiation, it is distributed through the surface layer, so the air temperature warms only slightly • Winter: ♦ Without sea ice, the atmosphere is no longer isolated from the ocean, which returns its stored heat to the atmosphere until freeze-up ♦ Because the polar atmosphere in winter is currently about -40°C and the ocean can’t get below -1.5°C, the winter atmosphere warms greatly without sea ice insulation  Permafrost  Permanently frozen ground (ground temperatures never rise above 0°C during the year) melting in the Arctic  Forcing v Response • Because planet is warming the permafrost is melting, releasing CO2 and methane, its is a response (positive feedback) NOT a forcing  Impacts •