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

When does terminus RETREAT

Change in ice volume = snow – melt If snow < melt, ice volume decreases WARMER temperature or LESS PRECIPITATION

Shelton photo Field trip up a valley Another moraine

Large portion of N. America covered by continental glaciers

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?

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

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

ICE SHEET

Water stored in ice sheets has relatively few H2O18 molecules

When there is lots of ice on land,

A) Ratio of O16:O18 is relatively high B) Ratio of O16:O18 is relatively low

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

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

When do we have winter?

Comparison of orbital variations with isotope records

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???

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

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

The Netherlands

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

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

Why would absolute sea level change? 3 reasons

1. Change in geometry of continents and ocean basins PLATE TECTONICS, happens over millions of years

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.

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

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

-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

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

3. Relative sea level change: Any location on LAND may be moving up or down

relative to datum

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

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

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

Global average air temperature appears to be increasing

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?

Current rate of absolute sea level rise = 2-3 mm/year or 25 cm per 100 years

Pt. Lookout

CB

1862 shoreline1997 shoreline

Shoreline retreat Chesapeake Bay

5 m of sea level rise equal to melting of west antarctic ice sheet