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Q: Images of lowered sea-levels ( Answered 5 out of 5 stars,   2 Comments )
Subject: Images of lowered sea-levels
Category: Science > Earth Sciences
Asked by: rambler-ga
List Price: $15.00
Posted: 30 Jun 2005 20:13 PDT
Expires: 30 Jul 2005 20:13 PDT
Question ID: 538964
Are there any images on the Internet that illustrate what the Earth would look
like if sea-levels decreased?

A TV science program was describing the ocean "conveyor belt", and
went on to say that major ocean currents occur at 3 different depths:
the top 100 feet were the first level; the next level went down to
about 3,000 feet (I think); and I don't remember what they said about
the third level.

Anyway, I tried to imagine what these various currents look like at all these
different depths, and that's when I wondered if any images existed that showed
what the oceans would look like if sea-levels dropped significantly (or even
rose significantly).

So, what would the Earth look like if sea-levels dropped 100 feet? 3,000 feet?
Subject: Re: Images of lowered sea-levels
Answered By: crabcakes-ga on 30 Jun 2005 23:27 PDT
Rated:5 out of 5 stars
Hi Rambler,

I have found many images of different types, that show how the earth
looked when sea levels were much lower, along with illustrations of
how the earth would look if the sea levels rise further.

This PBS site has small illustrations of how parts of the Earth looked
thousands of years ago when sea levels were lower, and also how it
would look if higher. Click on each illustration for a larger view.

" As the water flows in the ocean, it carries heat from one ocean to
another, and from the equator to near the poles. Variations in the
heat transport lead to variation in weather patterns. The oceanic
component of the heat-transport system is called the Global Conveyor
Belt. The heat from the sun shining on the entire Atlantic Ocean is
carried northward by currents. The heat warms the air in the far north
Atlantic. The heat warms up Ireland, England, Norway, and the rest of
northern Europe. Northern Europe is far warmer than Labrador and
northern Canada especially in winter. Yet Norway is further north than
Labrador. As the ocean loses heat in the far north, the water gets
colder and colder. Finally it gets so cold and dense it sinks to the
bottom. It flows along the bottom and gradually comes up in different
parts of the ocean to complete the conveyor belt circulation.

Sometimes the Global Conveyor Belt slows down. When this happens,
Europe becomes cold. Sometimes the current stops, and the northern
hemispheres enter an ice age. See The Role of the Ocean in Weather for
more information."'s%20Climate%20Belt.htm

This site has a nice slide show on changes in sea level. Its a slow
loading site, but be patient.

When sea levels were lower in Europe
"In the Ice Age, land weighed down under 1500m of ice sank by over
100m. Land round the edges (like north France and southern England)
rose in compensation - like a see-saw.

When the ice melted, the fairly rigid land mass took time to return to
its original levels - so much so, that Kent and Nord-PasdeCalais are
still slowly sinking back at rate of a few cm every 100 years. This
causes long-run worries for sea-flooding. Much of the low-lying coast
on either side is protected by seawalls, which can be breached if
there's a storm at high tide. Where the land behind is former
marshland, it may be 0,5m below mean sealevel."

This site has illustrations of the Subsurface-Oceanic Conveyor Belt
Subsurface-Oceanic Conveyor Belt

This one too, Page 9

Ocean Floor Age Map

"The reason the atmosphere lost its oxygen, Ward suggests, was because
ocean levels dropped, exposing anoxic organic materials to the
atmosphere. The newly-exposed materials oxidized, pulling oxygen out
of the air, and the iron in these materials rusted, creating the red
rock layers that are so distinctive in post-Permian geology. Explosive
volcano eruptions from Siberia may have contributed to this loss of
oxygen as well, expelling huge amounts of carbon dioxide, carbon
monoxide, methane, and other gases into the atmosphere. Whatever
happened in the P-T, it happened on a geologically fast time scale,
within 50,000 years or less."

"And we're looking at the Northeastern North Carolina capes, barrier
islands, estuaries, and near shore area, trying to develop a very
detailed evolutionary history since the last glacial episode when sea
levels were down hundreds of feet below where it is today and the
shoreline was tens and tens of miles seaward of where it is today. And
the climate was tremendously different. The climate at that time in
North Carolina was very cold, very windy, semi-arid. The rivers were
braided streams that ran across the continental shelf. And the coast,
if you were a fisherman back at that time, you would have been fishing
out of villages that would have been significantly seaward of where we
are today. As the glaciers melted, in response to a warming climate,
at the end of the last glacial episode, the water from the ice began
to melt and flow back into the ocean, and sea level began to rise. And
it rose up to where it is today. But it did not rise on a regular
basis. It was quite irregular, and there's all sorts of cycles that we
see. And it reminds me more of the stock market curves than it does of
anything else. And we've had times when the sea was higher than it is
today. We've had times when it was a little bit lower than it is
today. As the climate has changed, and as the oceanagraphic conditions
of the oceans have changed through time, so has the level of the sea
changed. And as the sea level changes, so do our barrier islands and
our estuaries. And we have periods of time when the barriers are
growing and building and are healthy. We have other times when the
barrier islands coming apart. They come unwelded and they open up the
back estuaries to the ocean so that we have oceanic conditions coming
into the sound."


Voyager Map

What causes sea level to change?

Changes in sea level

Changes in sea level over millions of years

Se an animation of ice caps shrinking

" Figure 5 is a "detrended" record of the sort that corrects for a
phenomenon that places all European and North American tide gauge data
in doubt. The phenomenon is known as "Post Glacial Rebound" (PGR).
During the last Ice Age, the region in which Stockholm was located was
buried under several kilometers of ice. The Ice Age ended about 10,500
years ago with a rapid melting of the ice sheets over Europe and North
America. Their melting resulted in sea level rise. And, with the ice
gone, the plasticity of the mantle below the solid crust of the earth
began to force the crust upward because the dead weight of the ice no
longer was present. This process has gone on since the last Ice Age,
is happening now, and will continue to do so well into the future."

"From all these sites, Prof. Flood et al find that over the last 4,000
years there has been a net decline in sea level of almost 2 meters
around southern and eastern Australia. They further point out that
other researchers using similar indicators have found the same general
picture in other tectonically stable, mid-latitude, far afield sites
in Brazil, Madagascar, and New Caledonia."

Scroll down past the middle of the page to see world maps depicting
sea level changes.

"Sea level could rise 40 to 65 cm by the year 2100, due to predicted
greenhouse-gas-induced climate warming. Such a sea level rise would
threaten coastal cities, ports, and wetlands with more frequent
flooding, enhanced beach erosion, and saltwater encroachment into
coastal streams and aquifers. Therefore, it is important to study
records of how sea level has been changing.

Sea level has fluctuated dramatically in geologic times. It was 2-6 m
above the present level during the last interglacial period, 125,000
years ago, but 120 m below present during the last Ice Age, 20,000
years ago. In the last 100 years it has increased by 10-25 cm.
However, future sea level is very difficult to predict, because not
enough is known about how the ice sheets in Greenland and Antarctica
will react to global warming. Furthermore, local sea level is affected
by many regional processes, including tides, ocean currents, and
geographically-varying land movements. These Earth motions are caused
by ongoing adjustments of Earth's crust to the removal of the former
ice sheets, tectonic deformation, subsidence of river deltas under
sediment loads, and extraction of underground water, oil, or natural
gas near the coast."

Goddard Space Flight Center

Chart of Sea Levels for 140,000 years.

Pleicestecen Sea Levels in Asia

Sea Level ? 

Old Earth

You can see the sea level changes of Belize here:

Ocean Currents

"t the height of the most recent global advance: Devensian (18000
years BP), sea levels were 100-150m below current level. (the South
Coast of England experienced a rise of 150m in 20,000 years - in
recent years, the rate of rise has started to increase)

SE coasts of England are sinking at a rate of 2mm per year. Some Roman
sites in London were built 5m below current sea level.

Change of land relative to the sea is called isostatic adjustment.
Parts of Scandinavia and Canada which were heavily glaciated are
rising at rates of up to 20mm per year.

Change in sea level on a global change is referred to as
glacial-eustacy. Because all oceans are interconnected, all must be
affected by eustatic change (a difference between this and isostacy
where land areas rise"

You might find the reverse interesting!

East Coast rise of 1-100 meter sea level increase

100 meter rise, globally, in sea level

I hope this fits the bill! I got a bit carried away with this, as I
found it most interesting! If any part of this answer is unclear,
please request an Answer Clarification, before rating. This will
enable me to assist your further, if possible, on this question.

Regards, Crabcakes

Search Terms

Sea Levels dropping
Seal levels + ice age
Low sea level
Maps + sea levels

Request for Answer Clarification by rambler-ga on 01 Jul 2005 18:29 PDT
Thank you for such an amazing, in-depth response!

Global warming is a controversial and important subject. Unfortunately,
it's not really of interest to me (at the moment).

I am quite content to accept your answer as written, especially since you have
put so much work into it.  However, I'll clarify what I'm after,
just in case it's something that you can easily find.

That TV science program that I mentioned in my original question never
explained why there are 3 different levels of ocean currents, nor which
directions they travel. (The "conveyor belt" looks like it travels in more
than one level, but does it travel in all 3 levels? What exactly ARE the
3 levels?)

If one of the levels occurs at a depth of 3,000 feet, then I'd like to see
an image that shows two things:-
(1) What would the coastlines look like if the sea-level dropped 3,000 feet?
(2) In what directions does that current travel, and why?

I'd like such images for all 3 levels of ocean currents.

Thanks again for your enthusiastic effort.  If you think I should post
this clarification as a new question, I'll be happy to do so.

Clarification of Answer by crabcakes-ga on 01 Jul 2005 18:37 PDT
Thank you for the rating and the nice tip. I'll do what I can to find
you the 3 levels of ocean currents, and post when i find something!

Regards, Crabcakes

Clarification of Answer by crabcakes-ga on 01 Jul 2005 23:21 PDT
Hi again Rambler,

  I'm not sure if I have found the 3 levels of oceanic currents, but I have tried!
How about these sites?

The circulatory system of the surface waters of the Atlantic can be
depicted as two large gyres, or circular current systems, one in the
North Atlantic and one in the South Atlantic. These currents are
primarily wind driven, but are also affected by the rotation of the
earth. The currents of the North Atlantic, which include the North
Equatorial Current, the Canaries Current, and the Gulf Stream, flow in
a clockwise direction. The currents in the South Atlantic, among which
are the Brazil, Benguela, and South Equatorial currents, travel in a
counterclockwise direction. Each gyre extends from near the equator to
about latitude 45°; closer to the poles are the less completely
defined counterrotating gyres, one rotating counterclockwise in the
Arctic regions of the North Atlantic and one rotating clockwise near
Antarctica in the South Atlantic. See Ocean and Oceanography: Ocean
The Atlantic receives the waters of many of the principal rivers of
the world, among them the Saint Lawrence, Mississippi, Orinoco,
Amazon, Paraná, Congo, Niger, and Loire, and the rivers emptying into
the North, Baltic, and Mediterranean seas. Nevertheless, primarily
because of the high salinity of outflow from the Mediterranean, the
Atlantic is slightly more saline than the Pacific or Indian oceans."

"The surface currents of the ocean are characterized by large gyres,
or currents that are kept in motion by prevailing winds, but the
direction of which is altered by the rotation of the earth (see
Coriolis Force). The best known of these currents is probably the Gulf
Stream in the North Atlantic; the Kuroshio Current in the North
Pacific is a similar current, and both serve to warm the climates of
the eastern edges of the two oceans. In regions where the prevailing
winds blow offshore, such as the west coast of Mexico and the coast of
Peru and Chile, surface waters move away from the continents and they
are replaced by colder, deeper water, a process known as upwelling,
from as much as 300 m (1,000 ft) down. This deep water is rich in
nutrients, and these regions have high biological productivity and
provide excellent fishing."

"Flowing from the equator to high latitudes are the western boundary
currents. These warm water currents have specific names associated
with their location: North Atlantic - Gulf Stream; North Pacific -
Kuroshio; South Atlantic - Brazil; South Pacific - East Australia; and
Indian Ocean - Agulhas. All of these currents are generally narrow,
jet like flows that travel at speeds between 40 and 120 kilometers per
day. Western boundary currents are the deepest ocean surface flows,
usually extending 1000 meters below the ocean surface."

I've found currents described as surface, subsurface and wind
currents, updwellings, and downdwellings.

Regards, Crabcakes

Request for Answer Clarification by rambler-ga on 02 Jul 2005 06:07 PDT
Perfect!  Thank you so much for the extra effort!

Clarification of Answer by crabcakes-ga on 02 Jul 2005 10:01 PDT
Glad to help! Thank you!
Sincerely, Crabcakes
rambler-ga rated this answer:5 out of 5 stars and gave an additional tip of: $3.00
Very fast and very thorough (and very enthusiastic) answer!

Subject: Re: Images of lowered sea-levels
From: waukon-ga on 30 Jun 2005 23:41 PDT
A genuinely wonderful answer, Crabcakes. I've always been interested
in maps showing ancient sea levels. It's impressive to see how the
world looked some 20K years ago, at the height of the last ice age,
when sea level was drawn down past 400 feet. Humans *walked* to what
is now Indonesia, then Sundaland, when Sumatra, Borneo and Java were
connected to the Asian mainland.
Subject: Re: Images of lowered sea-levels
From: czh-ga on 01 Jul 2005 02:49 PDT
What a marvelous answer! The collection of maps you found is truly amazing. Thanks.

~ czh ~

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