Sea Level Change
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Transcript of 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 sea-level 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
• island covered by local ice caps
• Labrador covered by large Laurentide glacier
• Maximum thickness 2000 m
• Weight of ice causes glacio-isostatic depression
Glaciation
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Glaciation & deglaciation
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Deglaciation
• 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 sea-level 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?
Sequence of “raised beaches” formed as sea level gradually withdrew,
Coastal Labrador
oldest
younger
youngest
Raised Beach, Sandy Cove, Eastport Peninsula
Sea Level 12,000 years ago
What kinds of proxy data would tell us this?
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 sea-level 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 – 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
Ship Cove,
Placentia Bay
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
Outline
• Patterns and processes of sea-level rise in Atlantic Canada– Glaciation, deglaciation, and isostatic rebound
• Types of evidence used to determine rates of sea-level 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, Louisbourg, NS
Mooring ring was installed above high tide position ca. 1750;
today high tide rises above ring (approx to person’s helmet)
Eroding archaeological site,
The Beaches, Bonavista Bay
Currently rising at 2 mm/a, the wall is necessary to prevent this Beothuk site from being washed away
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 sea-level 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
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005-0.5
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Year
Water Level (m)
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– 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 sea-level 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
FerrylandBauline 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 sea-level rise– Longterm
• Geomorphological & sendimentological evidence
• C14 dating
– Medium term– Short term
• Adaptations to sea-level rise in Atlantic Canada