Lecture 7 09 17 2014 Weathering and erosion Physical change make sediment Chemical change release sediments Chemical weathering salt in seawater weathering of rocks chemistry of all life volcanic eruptions Chemical weathering on land rock granite o granite made of 3 minerals quartz elements O Si mica elements O Si Al Fe Mg feldspar elements O Si Al Ca Na K contains elements O Si Al Na K Ca Fe Mg Quartz o Does not change no chemical weathering o Only physical weather into smaller and smaller pieces o Most sand on earth is tiny pieces of quartz Mica o Chemically weathers into clay Releases Fe Mg Feldspar o Chemically weathers into clay Releases Ca Na K Quartz sand Mica Feldspar Mud Headwaters Sediment boulders and gravel Minerals quartz mica feldspar Seawater contains Fe Mg Ca Na K These elements make seawater salty 09 17 2014 Seawater Chemistry tied very tightly to chemistry of life Ocean chemistry Salt What is salt Why is the ocean salty Volcanoes release the following into the atmosphere seawater Water Hydrogen Carbon dioxide Chlorine Sulfate Anything in the atmosphere will be found in the ocean as well Which elements are at high levels in sea water Which elements have a long residence in sea water These are the same Residence time The age of a particle at the time of its final departure from the reservoir Input rivers Reservoir Ocean Removal The mean residence time amount in reservoir rate of removal 09 17 2014 Salinity how much salt is present in the ocean all living things need some salt to survive most of the salt we get is extracted from the ocean When you add up all of the elements make up salinity of ocean they total about 3 5 by weight of seawater 96 5 of ocean is seawater other 3 5 is salt How salty is seawater Salinity average 3 5 We can measure the salinity of the ocean by satellite when you shine microwaves from satellite on the ocean surface and measure the way they bounce off the radar return the amount at which they return and the polarization of that depends on the salinity of the ocean In general in most places at higher latitudes salty water gets saltier as you go down in the water column adding salt to the water makes it heavier 09 17 2014 Concentration vs Depth General 3 profiles Basically all of the elements on the periodic table can be found in some form in the ocean Classification of Profiles Accumulated left alone o Long residence time o Can build up overtime become very well mixed as ocean circulates o Higher concentrations o Not affected by other processes Recycled biology o Medium residence time o All involved with life o Have low concentrations o Increase as you move down in the water column o Low at surface b c most living things live at surface of ocean and are removing these from ocean to incorporate them in their bodies o Living things in the ocean die or get eaten and sink down to the bottom either as dead bodies or poop and are remineralized their nutrients rot and elements return to ocean water Scavenged absorbed o Short residence time o High concentrations at surface o Low concentrations at depth o Primarily metals o Blown in from dust from deserts o Absorb onto any particular matter in the ocean removes strips them from the water as particles sink to depth o Always stuff floating in the ocean so anything dropped onto the ocean will soon find a particle to stick to and will no longer be evolved Accumulated Rough time scale of residence time Rt o it will take 100 00 years before anything removes it from the ocean Scavenged Rt less than 1 000 years either sedimented at the bottom or absorbed by something else Recycled Rt 1 000 100 000 years 09 17 2014 Biologically active elements Silicon used to make diatoms o Pull what little silicon remains out of water Takes a long time for quartz to turn to silicon Any silicon that happens to make it into ocean is usually used up very quickly by diatoms One of the main things that pull carbon out of the water are coccoliths Form hard parts out of calcium Also pull calcium out of the water Form calcite There are a ton of coccoliths in the ocean They are phytoplants so they are usually by light at surface Natural Carbon Cycle As we burn fossil fuels we are adding CO2 to atmosphere