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 breathing Alaska 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 Positive feedback Indirect evidence of 20th century warming Warming the planet increases evaporation Water Vapor is a green house gas Something preserved that represents a particular aspect of climate Retreating Not retreating in Antarctica Greenland melting more and more rapidly Climate proxies Glaciers Ice shelves Breaking up Rising sea level 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 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 Permafrost melts add to greenhouse gas making atmosphere warmer Positive feedbacks as warming releases trapping CO2 methane CH4 and gas hydrates methane from sea floor permafrost Huge distribution of permafrost Melting snow banks ice caps and glaciers Reveals some really old stuff human and human tools ensure that warming has occurred The Iceman Swiss Alps Alaskan Snow banks What do they tell us about 20th Century warming There hasn t been any time that has been warmer than the past century because really old stuff has been buried for thousands of years KEY QUESTIONS FROM UNIT VI Is the planet warming How do we know how confident are we If it is warming where has it been warming how long has