Transcript Sea Level Change

Sea Level Change
Geography 1050
Trout River
Outline
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Longterm
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada
Sea Level Change
• driven by local, regional, hemispheric, & global factors
• Changes in sea level are not uniform
• Each area is affected differently
• “Global” sea level is only a theoretical concept
Atlantic Canada
• Effects of glacial activity
• melting of ice, adding more water to ocean
• glacio-isostatic rebound: recovery of land as ice
weight is removed
NL Glaciation
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island covered by local ice caps
Labrador covered by large Laurentide glacier
Maximum thickness 2000 m
Weight of ice causes glacio-isostatic depression
Glaciation
www.bio.umass.edu/biology/conn.river/iceages.html
Glaciation & deglaciation
www.homepage.montana.edu/.../GLACIER%20LAB.htm
Deglaciation
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Melting began 15,000 years ago
Complete between 9,000 and 7,000 years ago
Sea flooded into isostatically-depressed areas
135 m a.s.l. at Gull Island Rapids, Labrador
170 m at St. Anthony
58 m at Laurenceton, Bay of Exploits (photo)
35 m at Terra Nova National Park
Glacio-isostatic Rebound
• Removal of weight of ice allows land to rebound
• Sea forced to recede, relative sea level drops
• Land ‘springs’ back, then subsides
• Still happening around Lake Melville (1 mm per year)
• Currently, rising sea levels around island of Newfoundland
Outline
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Long term
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada
Marine Clay
at Springdale
indicates sea
level was 75
m higher than
today 12,000
years ago
How would you find out if this were marine clay or not? What proxy data would you use?
Dropstone indicates
iceberg rafting, in
marine clay near
Lower Churchill
project site
What makes this stone peculiar?
What proxy data could you use to
find out more?
youngest
Sequence of
“raised beaches”
formed as sea level
gradually withdrew,
Coastal Labrador
younger
oldest
Raised Beach, Sandy Cove, Eastport Peninsula
What kinds of proxy data
would tell us this?
Sea Level 12,000 years ago
Old Man
sea stack,
Trout River,
NL
Outline
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Long term
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada
Sea-Level History in Atlantic Canada
• Higher sea levels immediately following deglaciation;
• Dropping to levels lower than present between 8,000 and
5,000 a ago (varying from place to place);
• Currently rising (except for Lake Melville)
How do we know?
 for long time scales (100s or 1000s of years):
 Maps & bathymetric charts
 Archaeological sites
 14C dating
14C
dating
• Radiometric decay of 14C
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Organic deposits only
Not valid for deposits younger than 1950
Used for deposits up to 30,000 years old
Dates expressed as “BP”
Broad Cove, Avondale
Submerged black spruce stump
For a reliable date, the stump should be rooted in peat under
the beach gravel (so it is not a piece of driftwood).
This stump indicates sea level rise at
about 2.5 – 3 mm per year over the past 1800 years
Ship Cove,
Placentia Bay
Outline
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Long term
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada
Medium (intermediate) Time Scales
 Assessment over decades through human infrastructure (docks,
moorings) and/or tide gauge records
 Airphotos and satellite imagery indicate coastal erosion, beach retreat
 Personal photographs
Topsail Beach, ca. 1910
Mooring ring was installed above high tide position ca. 1750;
today high tide rises above ring (approx to person’s helmet)
Mooring Ring, Louisbourg, NS
Currently rising at 2 mm/a,
the wall is necessary to prevent this Beothuk site from being washe
Eroding archaeological site,
The Beaches, Bonavista Bay
Middle Cove
Middle Cove
Outline
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Longterm
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada
Short Term
• Humans cannot look at the sea from one year to the next
and recognize rising levels visually
– natural tidal changes in sea level
– daily variations due to storms
• Recognition of relative sea level rise based on long-term
and intermediate-term analyses.
• Tidal component must be accounted for (‘filtered out’)
before sea level rise can be recognized.
Elevations of tidal position over time (diamonds) at Cuxhaven, Germany
• although individual levels vary, the overall trend indicates rise 1788-1995
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Water Level (m)
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-0.1
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-0.4
-0.5
1960
1965
1970
1975
1980
1985
1990
1995
2000
2005
Year
Port-aux-Basques: Sea level rise approx. 3.3 mm/year
Sea Level change-net results
• Observed rates of sea level change (from all causes
combined) in Atlantic Canada vary from 1 mm per year to
more than 5 mm per year
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S. & E. Newfoundland – 3 to 5 mm per year
Fundy and SW Nova Scotia – 3 mm per year
Gulf of St. Lawrence coast – 2 to 3 mm per year
Labrador - +1 to – 1 mm per year
Outline
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Longterm
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada
If you live on the shore …
• Sea level is rising, regardless of cause
• If your property is eroding, the cause is less important than
is taking action
• Adaptation is required
Adaptation Strategies
• Reinforce (armour) the coast
• Retreat and rebuild
• Rezone the coastal area
Ferryland
Bauline East
Conception Bay South
Conception Bay
South
Summary
• Patterns and processes of sea-level rise in Atlantic
Canada
– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sealevel rise
– Longterm
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term
– Short term
• Adaptations to sea-level rise in Atlantic Canada