Lecture12_2011r - Icebergs and sea ice Sea level Sierra...

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Unformatted text preview: Icebergs and sea ice Sea level Sierra Snowpack What does δO18 tell us about climate? 1. Reservoir 2. Temperature What causes the different sea level fluctuations - why is it not equivalent around the world (eustatically)? MidTerm Exam Average 84 range Sea level impacts on biohabitat and beach erosion in and around San Diego Bay Bathymetry and sub-bottom profiles of the bay. Data has many uses. this presentation = habitat maps. How Geology relates to and interacts with biology. Rose Canyon Fault Zone Rose Canyon Fault Zone Geology Mount Soledad Spanish Bight Fault Coronado Fault Silver Strand Fault SD Bay Descanso Fault (modified from Kennedy and Tan, 2005) Bend in Rose Canyon fault zone creates extensional basin “Pull-apart basin” notice artificial fill Airborne LiDAR image of San Diego Bay 0.5 m sea level rise 1.0 m sea level rise s River Cholla d ater an Sweetw Valley Otay R y le iver Val Otay River Valley 45 Methods Bathymetry - RESON 7125 SeaBat •130 swath •400 kHz •Horizontal resolution ~0.5 m •Vertical resolution ~2cm Hi Res Identify bedforms, fault scarps, outcrops BIOhabitat mapping w/ Backscatter Information Color depth profile in meters Bathymetry - RESON 7125 SeaBat 48 49 Sub-bottom - CHIRP profiles Silver Strand Fault Coronado Fault •Match Filtering •~10cm Resolution •700 Hz-3kHz Resolution = 10cm Impedence = velocity x density reflection coefficient = p1v1 - p2v2/(p1v1+p2v2) 700Hz-3kHz swept frequency - resolution =v/(f2-f1) Single freq res = 1/4L where C=Lf, C=1500m/s 50millisecond pulse Sierra Snow Pack SACRAMENTO -- Global warming means epochal changes in the Sierra Nevada snow pack that supplies two-thirds of California’s water and most of the water for northern Nevada. The snow pack will shrink and melt earlier in the year, reducing runoff in the dry spring and summer, predicts the Sierra Nevada Alliance. The snow line will climb 500 feet within decades as temperatures rise. Coupled with global warming, the environmental coalition’s report projects population increases in some Sierra counties from double to as much as five times their current level. That means increased pollution when government agencies or scientific bodies already have labeled as polluted or damaged all the 24 major Sierra watersheds except the Cosumnes River south of Sacramento. "Climate change and growth in the Sierra spell real trouble for California’s water supply," warned alliance executive director Joan Clayburgh. Spring and summer runoff in the Southern Sierra has dropped 10 percent over the last century, the report says. "Our storage reservoirs will be in the wrong place" if the trend continues, said Senate Agriculture and Water Resources Committee Chairman Mike Machado, D-Linden. California population is ~37 billion and is predicted to increase to ~45 billion by 2020. Sierra water supplies two-thirds of the state’s population, irrigates 3 million acres of California farmland and produces enough hydroelectricity to make up about a quarter of California’s power. With the Central Valley Project, the State Water Project and numerous other conduits piping water to California and Nevada urban areas, water is the Sierra’s leading export, surpassing logging, agriculture, grazing and tourism, says the study, which puts the value conservatively at $1.3 billion annually. Half of all the state’s wildlife and plants live in the Sierra, including 40 species of fish. But half the Sierra fish and amphibian populations are in trouble. Evidence for Prolonged Medieval Drought in the Lake Tahoe Basin Anyone that’s been involved with field work knows that breakthroughs often happen by serendipity. Here I’m going to report on one such example. Upright, Rooted, • • • ~40 m below the shoreline Up to 30 m tall, 4.5 m around Date to 1000 - 1300 Why are the trees down there ? Tree # 1 2 3 4 5 6 7 8 9 10 11 12 13 Table 1. Tree age and depth data Altitude of Height of Lab age (year B.P.) Cal age (year B.P.) base (m) tree (m) Samples Depth below surface 1-1, 1-2A 2-A, 2-C x 4-B, 4-C 9/18/06 7/10/03, 8/1/04 7/31/04 repeat sample 8/8/04 7/13/04 7/4/03 7/10/03 8/28/04 25.3 36 35.8 35.4 36 34.1 33.2 1918.2 907.8 1907.7 1908.1 1907 1908.1 1910.3 20.8 26.7 5.5 30.7 10.5 6.1 9.6 30.5 36.9 N/A N/A 14.3 1913 1906.7 N/A N/A 1929 5 N/A N/A 15 12.3 some older trees as well, including one from 355 Death year (range) 790 ± 50, 825 ± 40 674-738, 691-765 1185-1276 AD 810 ± 35, 830 ± 40 686-739, 694-769 1181-1264 AD x x 800 ± 35, 810 ± 35 686-733, 686-739 1211-1264 AD x x 1805 ± 40, 1815 ± 45 1703-1813, 1706-1818 132-247 AD 1930 ± 35 1826-1901 28-124 AD 3230 ± 35 960 ± 40 2175 ± 40 200 ± 40 780 ± 40 3399-3474 798-927 2121-2305 147-296 680-727 1524-1449 BC 1023-1152 AD 355-232 BC 1654-1803 AD 1223-1270 AD Age of tree at death 220 200 200 202 Graham Sidescan Sonar Survey • • • • Over 80 trees identified, ~20 are upright Submerged paleoshoreline morphology Deepest shoreline is ~60 m below present surface Almost all trees are What caused the shoreline to drop? We wanted to test if additional trees could be found using accoustics. Trees show up as shadows b/c they are smooth and don’t produce backscatter at the resolution of our instrument. Water Balance Modified from Trask (2007) Fallen Shoreline drops when precipitation drops below “Dust Bowl” conditions for ~250 years There’s lots of details that went into this, but it’s beyond the scope of this talk. I’m going to quickly touch on the results so we can continue with tectonics projects. Comunication between FLL and LT though terminal moraines, which allows us to build a more accurate hydrographic model for the region. We find that for FLL to drop, precip has to drop below 60% of normal. Summary • • FLL is very climate sensitive • Timing and severity correlates with “Medieval Warm Period” documented best in Europe, but also in the western US and South America • Assuming conditions observed at FLL are modulated by regional climate patterns, such a scenario today would devastate California’s water resources • Alpine lakes might be the key to Ancient stumps in the Walker River (e.g., Stine, 1994) Prolonged Medieval drought (>60 % of normal precip) for over 220 years is suggested by submerged trees These kinds of studies allow us to account for the potential range in magnitude and variability of precipitation in the past. *don’t talk about stumps** Although California's water supply is still adequate for a "normal" water year, it takes only a couple of drought years, such as we experienced in the extreme years of 1977 and 1978 and the lesser drought of 1987-1992, to stretch our resources to the limit and bring water rationing for both agriculture and drinking water. A drought such as the one that occurred in California and the west only 1,000 years ago would be catastrophic to both the economy and ecology of California. A Growing Population, a Finite Water Supply California's present population of 34.5 million is expected to climb to 47.5 million by 2020. Today, every suitable site for a major dam has been developed in the Sierra Nevada river canyons. Rivers have been transformed into reservoirs, with much of their water now traveling through irrigation ditches and city pipes, rather than along wetland corridors to coastal estuaries and out to the sea. ...
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This note was uploaded on 03/23/2012 for the course SIO 35 taught by Professor Driscoll,n during the Winter '08 term at UCSD.

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