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Cause?........ Evidence
Significance?
Some exceptions to the “Relatively slow”:
The Mediterranean Sea
“The Messinian Event (~6 – 5.3my) & the Zanclean Flood”
Evidence, cause and significance?
The Messinian is the last Age of the late Miocene. It spans the time
between 7.25 my - 5.3 my.
A geologic “Age” is a
subdivision of geologic
time that divides an
epoch into smaller parts.
The “Messian Event”, aka the Messinian Salinity Crisis (MSC), was a
geological event during which the Mediterranean Sea experienced partly
or nearly complete desiccation/evaporation throughout the latter part of
the Messinian age of the Miocene epoch, from ~5.96 to 5.33 my (million
years ago), as a result of tectonic collision of Africa & Spain
It took only ~2,000yrs to transform the sea into a desert!
Mediterranean basin was approximately 1.5km and 2.7km (~5,000 –
9,000ft) beneath today's sea level.
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Distribution of “Salts” recovered by the Glomar Challenger
in the 1970’s, and many others since
The MSC ended with the Zanclean Flood, when the Atlantic
reclaimed the basin.
The Zanclean Flood marked the beginning of the Zanclean Age and
the end of the Messinian, as water poured in from the Atlantic Ocean
through the Strait of Gibraltar to deluge the Mediterranean Basin.
Subsidence in the sea floor at the strait allowed water from the
Atlantic to pour slowly into the Mediterranean basin for several
thousand years, filling just 10%. However the Atlantic Ocean
floodwaters filled 90% of the Mediterranean very rapidly – likely
in less than 2 yrs.
https://www.youtube.com/watch?v=BemsLUldVAo
Catastrophic flooding 5.3my BP caused sea levels to rise in
Mediterranean by ~10 meters a day,
SL Rise may have been > 10m/day at it’s peak. Geologists call it
an “Instantaneous Flood”.
Sea Level changes; a variety of types
Relatively slow, long term changes,
with some exceptions
approx 1,000 Amazon rivers (209,000m3/sec X 1,000)
542my
Present
Sea Level changes; a variety of types
Relatively fast, short term changes
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0
Today’s sea level
0
–130
250,000
Height below present
sea level (feet)
Height above or below
present sea level (meters)
Cause, evidence and significance
–426
200,000
150,000
100,000
50,000
Years before present
0
Present
Milankovitch Cycles
100,000yrs
41,000yrs
26,000 yrs
Cities that would be severely effected by a 0.5 meter
(or 1.6ft) rise in seal level by 2070
Calcutta, India: 14 million people, $2.0 trillion in assets
Guangzhou, China: 10 million people, $3.4 trillion in assets
Mumbai, India: 11 million people, $1.6 trillion in assets
Miami, Florida: 4.8 million, $3.5 trillion in assets
Shanghai, China: 5.5 million people, $1.7 trillion in assets
Bangkok, Thailand: 5.1 million people, $1.1 trillion in assets
Tianjin, China: 3.8 million people, $1.2 trillion in assets
New York, NY: 2.9 million people and $2.1 trillion in assets
Ho Chi Minh City, Vietnam: 9.2 million people, $650 billion in assets
Dhaka, Bangladesh: 11 million people, $540 billion in assets
Ningbo, China: 3.3 million people, $1.1 trillion in assets
Tokyo, Japan: 2.5 million people, $1.2 trillion in assets
Alexandria, Egypt: 4.4 million people, $650 billion in assets
Haiphong, Vietnam:: 4.7million people, $330 billion in assets
Amsterdam, Netherlands: 1.4 million people, $843 billion in assets
Observed and predicted sea level rise. There is a strong consensus in the scientific community that the 2007
IPCC estimates of 21st century sea level rise are far too low. Obeservations in the first decade of the
century support that view. Most experts think the projections of Rahmstorf are more likely. See
http://www.nature.com/climate/2010/1004/pdf/climate.2010.29.pdf (link is external) for an update on
Rahmstorf's projections.
Evidence of Global Climate Change?
Ninety-seven percent of climate scientists agree that climate-warming
trends over the past century are very likely due to human activities. (IPCC)
http://www.businessinsider.com/cities-exposed-to-rising-sea-levels-2014-4
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The Black Sea, another exception to “Relatively fast”
An extremely rapid shoreline change
Present-day Black Sea, a salt water “inland sea”
Bathymetry: deep basin in the south, very shallow shelves in
the north. The shallow “shelves” that surround the deeper
basin are ~155,000Km2
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The Spread of Humanity
The Black Sea was a fresh water lake for much of it’s history,
over 100,000 yrs.
~8,000 yrs BP the planet’s population
was only ~ 5 million; it’s estimated 500,000 - 1 million
lived in the region adjacent to the fresh water lake.
~8000 BP evaporation caused it to be smaller
~8,000 yrs BP the planet’s population was only ~ 5 million;
(Approx 520 – 550ft lower than today).
it’s estimated 500,000 - 1 million lived in the region adjacent to the fresh water lake.
Surrounded by large fertile valleys and floodplains
Meanwhile, global sea level was rising.
About 7600 years BP (or ~5600BC), the ocean overtopped the
ridge at the Bosphorus, and ~60,000 meters3/sec of water
rushed in at 60mph, 200X Niagara Falls
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…… a major “flood” occurred; lake size increased by 30%
and rose in height by ~500 feet,
lasting <100 days!
60,000 miles2 or 155,000 kilometers2 were covered,
at a rate of ~1/2 mile/day.
People could outrun it, but they couldn’t bring all their possessions
Evidence:
Many salt water marine species of mollusks found directly over fresh water deposits, all ~7,600 yrs old. “Immigrants from the Mediterranean”.
The salt water mollusks on top of fresh water subaerial
bottom show an abrupt transition. Mud cracks; some with “fill” from sand storms with deep sea mud on top of them
Black Sea today (light blue) and in 7,600 BP (dark blue)
Light blue area is ~155,000 kilometers2
Fossil plants with deep sea mud on top of them
Source: William Ryan and Walter Pitman, 1997
Sea Level Changes
Gravel and sands from river deltas with deep sea mud on top of them
• Why Important? SL Rise: South Florida Case Study
Preservation of landforms; sand dunes with perfect morphological shape, found ancient shorelines at 90, 110 & 156 meters (~512 ft)
Robert Ballard discovered remains of an ancient structure in Sept 2000
Eventually stories of the flood reached the entire world. Found in writings of Sumerians (Epic of Gilgamesh), Romans, Greeks, Babylonians, Mexicans, Persians, Ireland. 6
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CLIMATE CHANGE: HOW DO WE KNOW?
In Summary:
Sea level changes have been happening throughout geologic time,
and will continue to do so.
There are several different types, causes and time orders
The more we know about all of them, the better off we are
Currently most places in the world are experiencing a relatively
rapid rise in sea level, and human infrastructure is in the way.
The currently rise in sea level is mostly likely related to human
activities
We need to start planning and preparing for the inevitable, there
are no signs that the current rise in sea level is going to stop.
Glaciers are retreating almost everywhere around the world — including in the Alps,
Himalayas, Andes, Rockies, Alaska and Africa. Losing ~2.2mile3/yr, 2X as much as 50
yrs ago.
Since 1950, the number of record high temperature events in the United States has been
increasing, while the number of record low temperature events has been decreasing.
Since the Industrial Revolution, the acidity of surface ocean waters has increased by
~30%. The increase is the result of humans emitting more carbon dioxide into the
atmosphere and hence more being absorbed into the oceans. The amount of carbon
dioxide absorbed by the upper layer of the oceans is increasing by ~2 billion tons per
year.
Global sea level rose about 17 centimeters (6.7 inches) in the last century. The
rate in the last decade, is nearly double that of the last century.
Global surface temperature reconstructions show that the Earth has warmed
since 1880. Most of this warming has occurred from 1970s, to present, with the
20 warmest years having occurred since 1981 and with all 10 of the warmest
years occurring in the past 12 years. Even though the 2000s witnessed a solar
output decline resulting in an unusually deep solar minimum in 2007-2009,
surface temperatures continue to increase
The oceans have absorbed much of this increased heat, with the top 700 meters
( ~2,300 feet) warming ~0.302 degrees Fahrenheit since 1969.
The Greenland and Antarctic ice sheets have decreased in mass. Between 2002
– 2006: Greenland lost 150 to 250 cubic kilometers (36 to 60 cubic miles) of
ice/year and Antarctica lost about 152 cubic kilometers (36 cubic miles) of
ice/yr.
Review Questions
List some persistent / important environmental challenges. Solutions?
How do scientists know that sea level was at times 200 – 400 meters higher than today?
What is the evidence and when did this happen?
How did scientists figure out that the Mediterranean Sea dried out and turned into a
desert in the Messinian Age?
What is the “Zanclean Flood”?
Approximately 90% of the Mediterranean Sea filled up “very rapidly” ~5.33MY BP.
How long do scientists estimate this took?
What are Milankovictch Cycles and what are the significance of them?
Satellite observations reveal that the amount of spring snow cover in the Northern
Hemisphere has decreased over the past five decades and that the snow is melting
earlier.
If global sea level rises by 0.5 meters in the next 70 years, in general who would
be effected?
http://www.cbc.ca/news/technology/july-2015-was-the-hottest-month-on-modernrecord-1.3197748
List several things that we can measure that strongly indicate we are experiencing
global climate change.
Ref: IPCC, NOAA, National Research Council (NRC) NASA, National Snow and Ice Data Center, World
Glacier Monitoring Service
Describe what happened in the Black Sea approximately 7,00 YR BP. What is the
evidence for this?
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