Lecture13_2011r

Lecture13_2011r -...

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Unformatted text preview: http://scrippseducation.ucsd.edu/faculty/driscoll/water/ Oceans Depths/hypsometry Stratification Wind driven currents Ekman Langmuir cells Geostrophic currents Tides No Reason to Worry Water a Regional Problem: Lake Mead August 1985 August 2010 Colorado River already has a water crisis!! Most water use in CA and AZ for agriculture Photo Credit: NASA THE PROBLEM IN BRIEF Fresh Water for Feed in USA •~80% of agriculture is for animal feed •>50% of irrigation water in USA for animal feed •~70% of irrigation water in Imperial Valley for alfalfa and hay http://scrippsnews.ucsd.edu/Releases/?releaseID=876 Atlantic Ocean Puerto Trench 8,648 m Pacific Ocean Mariana Trench 10, 924 m Indian Ocean Java Trench 7, 258 m The World continental shelf - the submerged top of the continent's edge between the shoreline and the continental slope. The shelf is made more shallow by deposition of material eroded from the land. The shelf has a gentle slope (<1°) and is the shallowest portion of the ocean. Usually the shelf edge is less than 200 meters deep (650 feet); in Antarctica the continental shelf averages 500 meters (1,640 feet)! continental slope - the narrow, steep (3° to 6° gradient) transition zone between the shallow shelf and the deep ocean floor. Sedimentary material on the continental slope is very unstable because of the steep gradient. continental rise - at the base of the continental slope with slopes ~1˚. It is a depositional feature, comprised of sediment that has moved down off the shelf and slope. The rise overlies the transition between the continent and the ocean basin, and it commonly receives material slumped off the steeply inclined slope. Transition zones exists between surface layer and deep layer sharp vertical changes in temperature, salinity, and therefore density thermocline – layer of sharp vertical temperature change halocline – sharp salinity gradient layer pycnocline – zone of marked density change with depth underlying deep layer includes about 80% of the total global ocean volume Thermal Structure of the Ocean • Well over half of the solar radiation reaching the Earth’s surface is absorbed by the oceans, so that it figures prominently in the regulation of the global climate. •T he mean temperature of the global ocean is only ~3.6˚C, it represents a huge heat sink in the global climate system. • Primary heat source for the oceans is solar radiation entering through the ocean surface. Almost all this insolation is absorbed in the top 100 meters. Turbulent mixing in the surface layer is promoted by the interaction of wind and waves. • In the mixed layer of the ocean, convection and turbulence are so effective that the temperature and salinity are almost uniform (constant) with depth. The global average thickness of the mixed layer is 70-100 metres. • Below the thermocline layer, the ocean is thermally stratified and tends to a uniform temperature (around 4˚C). The deep ocean comprises about 80% of the total volume of the oceans. • Below the thermocline layer, in the deep ocean, there exist slow circulations driven primarily by density gradients. These currents are quite weak, and it is estimated that the time required for complete overturning is on the order of 1000 years. • The mixed layer responds quickly to changes in the surface climate, whereas the deep ocean layer does not. The thermal capacity of the mixed layer implies response times to surface changes on the order of years. • The thermal properties of the deep ocean constitute a time lag in the climate system on the scale of 1000 years. Distribution of Temperature: warmest water develops at low latitudes coldest surface waters occur near the poles • downward mixing of heat occurs under summer surfaceheating conditions • upward mixing of heat develops during winter surface cooling reduces the actual change in ocean surface temperatures over the annual cycle tropical ocean surface is warm year-round, varying seasonally about 1º to 2ºC mid-latitude ocean temperatures vary ~ 8ºC over the course of the annual cycle surface temperature is uniformly low (typically less than 3.5ºC) in polar latitudes Distribution of Salinity: - departures from mean sea surface salinity result from several processes: • evaporation and ice formation remove water molecules and increase salinity • rainfall, runoff, and melting of ice add water molecules and decrease salinity • rates of evaporation depend strongly on temperature and vary directly with latitude evaporation is lowest in polar regions and highest in tropics and subtropics rainfall maxima occur in tropical and temperature latitudes subtropics and high latitudes characterized by rainfall minima Wind Driven Currents and Upwelling Ocean Surface Currents: wind energy is transferred to surface waters by frictional processes flow of wind 'pulls' surface waters along into specific currents surface current patterns therefore closely resemble surface wind patterns trade winds generate currents that flow to the west in tropical latitudes westerlies produce belt of currents that flow to the east in the mid-latitudes current flow is complicated by deflection associated with continental land masses eastward mid-latitude and westward equatorial currents result in 'gyre' formation wind-driven circulation also controlled by Coriolis deflection and gravitational force Review Sessions Wednesday - Warren Hall 2111 9:00 - 9:50 AM Thursday - Petersen Hall 102 9:30 - 10:50 AM Radiolarians are singlecelled protistan marine organisms. During their life cycle, radiolarians absorb silica compounds from their aquatic environment and secrete tests. Radiolarians reproduce asexually, usually by division of the cell (including the exoskeleton), with the remaining daughter cells each regenerating a complete organism. Dead radiolarians accumulate in the ocean floor sediment. Diatoms are actually microscopic single-celled algae that can be found in every body of water on Earth. Foraminifera (forams for short) are singlecelled protists with shells. Their shells are also referred to as tests because in some forms the protoplasm covers the exterior of the shell. The shells are commonly divided into chambers which are added during growth. http://www.thedailyshow.com/video/index.jhtml? videoId=126522&title=other-news-fissure-price Water Masses: climatic zonation imparts significant influence on ocean temperature and salinity changes in water temperature and salinity alter water mass densities produces oceanic regions with specific density characteristics surface water masses become more dense due to cooling or increased salinity as density changes, water masses will sink to reach depth of comparable density temperature, salinity variation at depth ultimately determined by surface condition movement an attempt to balance temperature and salinity-driven density changes water mass circulation collectively referred to as thermohaline circulation Past research has highlighted many of the major processes involved in the biological pump. However, many key questions remain: 1.What is the strength of the biological pump and how does it differ between biogeographical provinces? How do we most accurately measure its strength? 2.How does the structure and composition of the biological pump change in space and time? How might community structure affect it, and what is the importance of selected functional groups (e.g., nitrifiers, calcifiers, large grazers)? What are the relative roles of the microbial and zooplankton communities? 3.What is the sensitivity of the biological pump to perturbations in forcing (upwelling, dust and Fe deposition, North Atlantic Oscillation, El Niño)? How do we quantify this variability (e.g., time series) Stable Carbon Isotopes Ocean Conveyor Belt of Circulation Pacific Ocean estuarine circulation Atlantic Ocean anti-estuarine circulation CO 2 ...
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