Purpose:

1
Purpose To provide the big picture with respect
to sea-level change What do we know? How do we
know it? What do we see in NC?

• Background on the Quaternary and sea-level change
• Pleistocene paleoshorelines in NC
• Brief presentation of some interesting findings
  regarding the Holocene barrier islands

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Quaternary Period

• 1.8 million years of ice ages (glacials), warm
  interglacials, and large-scale sea-level change
• Large continental ice-sheets waxed and waned in
  the Northern Hemisphere
• At peaks of ice ages, 30 of land area was
  covered with ice
• Consists of the Pleistocene (1.8 million to
  10,000 yrs ago) and Holocene (lt10,000 yrs ago)
  Epochs

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NORTH AMERICA 18,00020,000 YEARS
AGO
THE ICE AGE WORLD THE LAST GLACIAL MAXIMUM
ANDERSEN BORNS, 1994
TARBUCK AND LUTGENS, 1999
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Ice sheets melt Sea-level rises INTERGLACIALS
400 feet
Ice sheets grow Sea-level falls GLACIALS
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Ice Sheets Melt Sea Level Rises
Nags Head
Today
5 ky
10 ky
15 ky
20 ky
Cape Hatteras
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• So, sea-level change is critical in determining
  where the shoreline is.
• Multiple factors determine relative sea level
  (RSL)
• Melting ice sheets and glaciers (not sea ice)
• Temperature of the water (thermal expansion)
• Rise or fall of the land surface
• Isostasy (crustal movements)
• compaction and subsidence (sediments getting
  compressed)
• tectonics
• Wind patterns and ocean circulation
• Volume of ocean basin

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Forebulge collapse due to GIA (ICE5G VM2 Model of
Peltier, 2004)
Forebulge collapse 1-2 mm/yr on ACP
Our study area Ca. 5 mm/y (Horton, Kemp et al.)
Land rises, RSL falls
Land subsides RSL rises rapidly
North
South
We will continue to see sea-level rise in our
area, regardless of what happens to the ice
sheets.
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Young sediments Low gradient coastline Narrow
shelf Few inlets
Old sediments high gradient coastline wide
shelf many inlets
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How do we understand the record of sea-level
change?

• Ice cores
• Fossils
• Geochemistry
• Sediments
• Reefs
• Marsh peats
• Ancient shorelines (paleoshorelines)

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Law Dome, Antarctica
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b
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Sea Level
interglacials
glacials
ODP R/V JOIDES Resolution
d 18O Can measure it on ice from glaciers or on
CaCO3 in marine organisms Represents a proxy
for sea level, ice volume, and temperature
14
Coral reef terraces indicate where the sea
surface once was.
Huon Peninsula, Papua New Guinea
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Marsh peats provide sea-level index points
Insert photo of marsh work
16
Coastal plain geomorphic features include
ancient, stranded shorelines indicating higher
sea levels than today
LiDAR data from ncfloodmaps.com
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Geoprobing in the Dismal Swamp
Vibracoring on the Outer Banks
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• 100 MHz ground penetrating radar data
• Eolian facies
• Overwash facies
• Peat facies

19
Abundant evidence of changes in climate and sea
level in eastern NC

• Fossils
• Rocks
• Sediments
• Paleoshorelines

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Cumulative effect of climate and sea-level change
has provided the resources and geomorphology of
the coastal plain

• Mineral deposits phosphate, sand and gravel,
  heavy minerals
• Ground-water aquifers and surface-water resources
• Soils, agriculture
• Estuaries, seafood
• Beaches, Barrier Islands, Coastal Tourism

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• So lets take a closer look at the features
  corresponding to sea-level change in NC.

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LiDAR data from ncfloodmaps.com
Currituck Shorelines
Quaternary Shorelines
Suffolk Shoreline
Surry Shoreline
Walterboro Shoreline
Multiple Shorelines
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Suffolk Shoreline - ca. 125,000 to 80,000
yBP Represents 20 foot sea-level rise
Cape Fear
Cape Lookout
Cape Hatteras
Color-coded to illustrate land (light blue and
bright colors) and sea (dark blue)
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Suffolk Shoreline - ca. 125,000 to 80,000 yBP
Chowan R.
Washington
New Bern
Edenton
Tar/Pamlico
Roanoke R.
Morehead City
Neuse R.
Inner Continental Shelf
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Suffolk Shoreline - ca. 125,000 to 80,000 yBP
Washington
Plymouth
This is where the beaches were. This is where
they will likely be again.
OSL and U-series dates (Mallinson et al., in
press. Quat. Res.)
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Parham (unpublished) 125,000 80,000 years ago
Shallow continental shelf No Outer Banks
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Why was the shoreline this far west?
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Wild Card! The 3 million cubic km gorilla in
the room
Net loss of 53 km3/yr and accelerating
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Barrier islands move landward in response to
sea-level rise and storm processes
GEOMBEST model
Erosion on seaward side
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Each advance and retreat of the ocean
leaves paleoshorelines
Wilmington
Multiple paleoshoreline ridges
Cape Fear
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Neuse River
Mainland shoreline was oceanfront
Beaufort
Bogue Sound
Beaufort Inlet
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Most outboard ridges Extend northward into
VA Occupied ca. 50 to 60 kyBP
LiDAR data From ncfloodmap.com
Atlantic Ocean
Suffolk Shoreline
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The Holocene (lt10,000 yBP)

• Rapidly melting glaciers
• Rapid sea-level rise

Kitty Hawk Beach ridges
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OSL ages of 3000 to 2000 yBP Shoreline was west
of present shoreline, prograded east, before
becoming transgressive
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Short Time Scales (103 - 100 yr)
GPR surveys to identify relict inlets
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Kinnakeet Inlet
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Smith, 2006
Increased inlet activity during LIA. Greater
noreaster activity?
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Observations

• What we see today is a snap-shot in time.
• We see the same environments that have been here
  before repeated over millions of years of
  climate and sea-level change.
• Present sea level will continue to rise as it did
  in the past, and may reoccupy the Suffolk
  Shoreline in the north, and the mainland
  shoreline in the south.
• Barriers respond significantly to short term
  changes in wave and wind climate (increased inlet
  activity during LGM), as well as sea-level
  change.