Sea Level Change Part 2

Question 1

Eustatic Sea-level Change over Geological Time:

Answer 1

• Return to the BLAG (“spreading rate”) hypothesis
• Slowing in spreading rates during Cenozoic
• Cooler, denser seafloor -> larger ocean basins.
• Less volcanism -> decreased export of water to oceans from mantle

Question 2

Pleistocene

Answer 2

is the geological epoch that lasted from about 2,580,000 to 11,700 years ago, spanning the earth’s most recent period of repeated glaciations.

Question 3

Glacial Maximum

Answer 3

A period during which glaciers advanced to cover large parts of the earth’s surface

Question 4

Interglacial

Answer 4

relating to a period of milder climate between two glacial periods.

Question 5

Eustatic Sea-Level Change during the Pleistocene

Answer 5

• The ice sheet is not retreating. Snowing in Canada, and build up a dome of ice that starts to flow out. Does not melt as fast as it advances.
• Melting faster than you are advancing. In the summer the edge of an ice sheet is always melting but you melt less of that snow from the previous year.
• Eventually advances as far as it can get.

Question 6

Eustatic Sea Level Coming out of the Pleistocene: Post-Glacial

Answer 6

Ice sheets are at their maximum extent and holding a lot of water. Ocean levels are much lower.

Then it switches and starts to melt faster than its freezing.

Jumps in the sea level rise. As the ice sheets melt, global sea level goes up but as the ice retreats you end up creating naturally dammed lakes.

Question 7

What causes the Jumps in the sea-level curve?

Answer 7

Meltwater pulses -> bursting of glacial dams

Example: Picture this a mountain range that is to the south. You have an ice sheet that goes against the mountain range. Now it starts to melt. The water gets trapped but eventually retreats far enough back and a gap opens. The massive volume of water leaves and massive flooding events occur.

Question 8

Relative Sea Level coming out of the Pleistocene: Post Glacial

Answer 8

• Elevations are not all the same (blue line is at modern sea level).
• Very different sea-level histories in different parts of the world coming out of the last glacial maximum come into view.

Question 9

Divers of Post-Glacial Relative Sea-level Changes?

Answer 9

1. (Glacio)isostasy
2. Glacioisostatic Forebulge Dynamics

Question 10

(Glacio)isostasy & draw a diagram

Answer 10

Can make the continental crust thicker over geological time by making mountain ranges. Over short time can make the continental crust thicker by adding more solid mass on top. That solid mass is ice.

• pushes down on the asthenosphere and allows it to flow into other areas.
• Rebound causes local sea level to fall

Question 11

Glacioisostatic Forebulge Dynamics describe and draw a diagram

Answer 11

1. T0 = Canada
2. T1 = Ice is Canada and bulge is VA
   
   1. Grow an ice sheet in Canada the asthenosphere is going to flow out pushing the crust up.
3. This is called forebulge
4. As the ice sheet melts, the flowing asthenosphere back under Canada.
5. Subsidence happens in the opposite area that is rebounding.

Question 12

(Glacio)isostasy and & Glacioisostatic Forebulge Dynamics is the cause of for how much sea level rise in Va?

Answer 12

~½mm

Question 13

Holocene

Answer 13

Covering last 11,700 years of Earth’s history

Question 14

Why has the sea level been falling in the southern hemisphere in the last 6,000 years?

Answer 14

Equatorial Syphoning

Question 15

Divers of the Mid-Holocene Highstand: Equatorial Syphoning

Answer 15

Distant Imprint of Forebulge Collapse

Hydroisostatic Loading & the Creation of Acomodation

Question 16

Equatorial Syphoning: Distant Imprint of Forebulge Collapse - draw a diagram and explain.

Answer 16

By 6,000 yrs ago, most of the water is going to be ocean.

Forebulge is collapsing and so the land is subsiding.

This creates more space for water as the forebulge is collapsing.

This space will be filled by syphoning of water from other locations (equatorial syphoning).

Accounts for 60% fall in the southern hemisphere.

Question 17

equatorial syphoning

Answer 17

Taking water from the southern hemisphere and filling the new hole created by the forebulge collapsing.

Question 18

Equatorial Syphoning: Hydroisostatic Loading & the creation of accomodation - draw a diagram and explain.

Answer 18

As the forbulge subsides, water flows. That water has a mass which pushes the land further into the asthenosphere.

Creates more room for water and more syphoning from the Fairfield.

This accounts for the additional 40% of fall of sea level in the southern hemisphere.

Question 19

As we get closer to the current time frame…

Answer 19

Our data resolution becomes clearer and we notice that sea level becomes really complicated.

Question 20

Global eustatic sea level is controlled by

Answer 20

• 1. Shape of the ocean basins
• 2. How much water is in the ocean basins
• 3. The mass of water
• 4. Temperature of the water (steric effects)

Question 21

Subtle Sea-Level Change During the Late Holocene

Answer 21

Little ICe Age & Medieval Climatic Optimum

Question 22

Little Ice Age & Medieval Climatic Optimum

Answer 22

If you take out some of the regional effects and do global averaging. Can see really small subtle effects of climate (temperature) anomalies. These would be MWP and LIA.

Temperatures have gone down and back up and the thing to note is that sea level change is 10-100 cm.

This shows the effects of small temperature changes. Now this could be that some of the sea level changes is that when it gets warmer you melt more ice. When it gets colder, ice expands a little more.

Also, because the surface water expands a little.

Question 23

Why look at Eustatic Sea Level?

Answer 23

Explained in class that sea level is just a snapshot in time. Eustatic sea level is a good concept to understand over geological time. What is happening locally (relative sea level) is on a scale more important.