outline for monday = sea level 1. review of ocean records...
TRANSCRIPT
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Outline for Monday = sea level 1. Review of ocean records of glaciation through time 2. Sea level change why do we care? 3. Absolute sea level changes 4. Relative sea level change 5. Global warming and sea level
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When does terminus RETREAT
Change in ice volume = snow – melt If snow < melt, ice volume decreases WARMER temperature or LESS PRECIPITATION
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Shelton photo Field trip up a valley Another moraine
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Large portion of N. America covered by continental glaciers
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Basic Idea: 1. Glaciers advanced: when temperature lower or more
precipitation 2. Glaciers retreated: when temperature higher or less
precipitation
When did this happen? How many times did this happen? Why did it happen? could it happen again?
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Isotopes of H2O
H2O16 most common
Marine organisms make skeletons out of CaCO3
A diatom: SiO2 skeleton
H2O18 accounts for 1 in 1000 water molecules
Ratio of O16/O18 of sea water
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When there is lots of ice on land,
A) Ratio of O16:O18 in ocean water is relatively high
B) Ratio of O16:O18 is ocean water is relatively low
C) I am guessing
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ICE SHEET
Water stored in ice sheets has relatively few H2O18 molecules
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When there is lots of ice on land,
A) Ratio of O16:O18 is relatively high B) Ratio of O16:O18 is relatively low
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Record of ice volume from ocean sediments Lots of ice: H2O18 relatively high in oceans Little ice: H2O18 relatively low in oceans
WOW 1. Many, many ice ages !!!!!!! 2. Interval varies; timescales of 10,000 to 100,000 years 3. ORBITAL FORCING via effects on solar radiation
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Why do we have glaciers advance and retreated over and over again?
Hypothesis: linked to variations in Earth’s orbit and variations in solar input 1. eccentricity 2. precession 3. tilt
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When do we have winter?
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Comparison of orbital variations with isotope records
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Ice sheet reconstructions
21 ka 14 ka 12 ka
10 ka 8 ka 0 ka
Peltier (1994)
As ice sheets melt, what happens to sea level???
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Rel
ativ
e se
a le
vel (
m)
1000’s of years ago
Sea level rise from melting glaciers during last major glaciation = 120 m Last glacial maximum
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2. Sea level changes: why do we care?
HISTORY: people live near ocean
10 m rise in sea level floods 25% of US population
11 of world’s 15 largest cities
along coast/estuary
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The Netherlands
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Sea level changes: past, present, future
Questions: 1) How has sea level changed in the past? 2) Is sea level changing right now? 3) How could it change in future
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3. ABSOLUTE sea level change:
Sea level goes up or down relative to a datum
Datum provides a fixed point, against which you can measure changes center of the Earth GOOD some point on coast BAD
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Why would absolute sea level change? 3 reasons
1. Change in geometry of continents and ocean basins PLATE TECTONICS, happens over millions of years
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Why would absolute sea level change? 1. Change in geometry of continents and ocean basins 2. Change in volume of water in different reservoirs
Land 16,000
Oceans 1,400,000
Atmosphere 13.5
Cryosphere (ice and snow) 43,000
water moves from cryosphere to oceans, sea level ------?
Dams, groundwater, etc.
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Why would absolute sea level change? 1. Change in geometry of continents and ocean basins 2. Change in volume of water in different reservoirs
3. Change in temperature of water in ocean warmer water is less dense
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Why would absolute sea level change? 1. Change in geometry of continents and ocean basins 2. Change in volume of water in different reservoirs
3. Change in temperature of water in ocean warmer water is less dense
So, if temperature increases, from 4 to 8 degrees,
volume of sea water ------? a. Increases b. decreases
1 deg C would increase sea level by ~20 cm
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-3.8 km
840 m 0
4
8
-4
-8
0 100% 5 0%
sea
leve
l ele
vatio
n, k
m
8 %
≈130 m Everest
M ariannas Trench
30 %
~10% of continents within 150 m of sea level
Hypsometric Curve for the Earth (% area above specified elevation)
Hypsometry: controls how change in volume
change in sea level
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4. Relative sea level change:
Sea level goes up or down relative to some point that may be moving itself
Measuring changes in moving reference frame
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3. Relative sea level change: Any location on LAND may be moving up or down
relative to datum
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WHY does land move up and down?
1. Subsidence, from groundwater pumping 2. TECTONICS: big changes during earthquakes
1964 Alaska earthquake
3. ISOSTATIC REBOUND from glacial loading Earth’s surface flexes slowly to heavy loads like ice
sheets or deposition of sediments in deltas
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100 km
1 m
4 m
Nile Delta - No new sediments
70% of industrial Egypt < +1 m
Cairo>800/km2>1200/km2
15% of arable Egypt
f Milli l 198
projected submergence >1 m by 2100 projected population 100 million
population
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5. PEOPLE, global warming, and sea level
Since industrial revolution: Concentration of greenhouse gases have increased in atmosphere believed to increase temperature of atmosphere and oceans
1980 2000 Year
Mauna Loa CO2 record
1960
CO
2 (pp
m)
320
34 0 36 0
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Global average air temperature appears to be increasing
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Predicted changes in air temperature for 21st century ~3 deg C
Global temperature and sea level:
1. Decrease density of sea water -- > sea level up 2. Alpine glaciers have retreated over past century
3. WHAT about continental glaciers Grow or shrink?
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Current rate of absolute sea level rise = 2-3 mm/year or 25 cm per 100 years
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Pt. Lookout
CB
1862 shoreline1997 shoreline
Shoreline retreat Chesapeake Bay
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5 m of sea level rise equal to melting of west antarctic ice sheet
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