Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
C-Change in GEES
Changing Coastal Environments
Session 1Session 1: Postglacial
Sea-Level Change
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
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These slides were last updated in December 2009
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
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Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
• Key definitions
• Postglacial sea-level change
• Meltwater pulses
• Sea-level fingerprinting
• Holocene sea level change
• Reconstructing Holocene sea-level change
What you need to know about:
The history of sea-level change The causes of sea-level change The effects of sea-level change
Session Outline
Photo: wonderlane (flickr.com)
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
It is an important driving mechanism for (rapid?) coastal change, especially over glacial/interglacial cycles
Why is Sea-Level Change
Important?
Photo: skagman (flickr.com)
Sea-level change has always been a contributing driver of geomorphic change
within coastal environments
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Understanding past sea-level change
Monitoring present day sea-level change
Predicting future sea-level rise
Coastal management, hazard mitigation
Need to fully understand
this before we can predict the future!
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Key Definitions
Eustasy + Isostasy = Relative Sea-level Change
EUSTASY• Glacio-eustasy (hydro-eustasy)
The exchange of water between the World’s oceans and ice sheets and glaciers
• Tectono-eustasy. Change in ocean volumes due to tectonic activity
(orogeny, sea-floor subsidence, mid-ocean ridge growth), driven by geological processes
• Geoidal-eustacy. Ocean surface responds to changes in the Earth’s gravitational
field – increasing understanding of the importance in recent years
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
The Geoid
Source: NASA Image Exchange(nix.nasa.gov)
• The ocean surface responds to changes in the gravitational field of the Earth.
• Measured relative to a reference ellipsoid on the basis of gravitational measurements
• The ocean geoid is also known as geodetic sea level.
• There is a 180 m difference between the rise at New Guinea and the depression centred on the Maldives
Map showing spatial variation in gravitational field at the Earth’s surface
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Dr Katie Szkornik, Kele University, [email protected]
C-Change in GEES Themes 2 and 3: Changing Coastal Environments - Post-Glacial Sea Level Change
Key Definitions
Eustasy + Isostasy = Relative Sea-level Change
ISOSTASYThe process by which the Earth’s crust seeks to reach equilibrium following loading or unloading by ice (glacio-isostasy) or water (hydro-isostasy)
Also need to consider:
•Sediment loading and unloading
•Volcanic loading/unloading
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Glacial Forebulge
Image adapted from: Peltier and Andrews (1976)
Where this occurs in coastal locations it has important implications for relative sea level history
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Water flows from the equator towards the collapsing forebulges
of the mid and high latitudes
Water loading of the continental shelf causes rebound at the coast
and a lowering sea bed
Images adapted from Gehrels & Long (2008)
Many of these processes are not fully considered by the IPCC & other agencies involved in predicting future sea-level rise…….
Ocean Siphoning Continental Levering
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
What else can affect sea level?
Influence of local and regional processes:
Storms, storm surges Tsunamis Earthquakes Plate tectonics Thermal expansion (steric
effects) Ocean currents Tides
Think about amplitudes and time scales over which these processes operate
Photo: ((brian)) (flickr.com)
There is no single location in the world where you can obtain a ‘global
sea-level curve’
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Abundant, accessible(?) evidence of changes
Changes resulted in the coastlines that we see in existence today – rapid coastal change
Eustatic changes – 50 million cubic km of ice melted from the land-based ice sheets & glaciers
Dominance of glacio-isostasy in regions once covered by ice sheets lead to dramatic falls in RSL of hundreds of metres
Postglacial sea-level changes
Eustatic changes: global and rapidIsostatic changes: regional and slow(er)
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Complexity of Postglacial Sea-Level Change
Differential melting of ice sheets produced a highly complex
pattern of sea-level & associated coastal change
• Ice sheets did not all melt at the same time• Antarctica and Greenland remain to this day• Phases of ‘rapid’ ice melt
*Meltwater pulses*
Existence and magnitude has implications for understanding rapid climate and coastal
change
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Rates of glacio-eustatic sea-level change
• A high degree of geographic variability
• Evidence of meltwater pulses across locations
• Shennan (1999) constrains the magnitude and timing of two meltwater pulse events (ca.14,000 yr and 11,300 yr BP)
• Observable in the records of ‘far field’ sites and identified in NW Scotland from reconstructed records of RSL (diatoms)
Dataset evidence of meltwater pulses
Barbados Bard et al. (1990); Fairbanks (1989)
Tahiti Bard et al. (1996)
Huon Chappell and Polach (1991); Cutler et al. (2003)
Bonaparte Gulf Lambeck et al. (2002);
Yokoyama et al. (2000)
Sunda Shelf Hanebuth et al. (2000)
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Where is the source location for these events?
SUGGESTION ONE Peltier (2005):
N. Hemisphere (Laurentide?)
• Source area is highly debated
• Current area of intense research (& funding!)
SUGGESTION TWO Bassett et al. (2005) & Clark et al.
(2002):Antarctic
Photos: cloudzilla (above); 23am.com (below) (flickr.com)
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Sea-level fingerprinting – the
solution?
Influence of an ice mass on the vertical displacement of the ocean surface
Adapted from:Tamisiea et al. (2003)Diagram shows the sea level fingerprint of
a melting event – sea -evel fall in the near field of the ice and a gradual rise in sea level away from it (Tamisiea et al., 2003)
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Global meltwater pulse 1A
Evidence thus far suggests that the Laurentide Ice Sheet was not the sole source of this meltwater pulse event and that the West Antarctic Ice Sheet was partially responsible
Key areas for additional research: S America (especially Argentine Shelf) and
Antarctica.
Source of Meltwater Pulse Events
Normalised sea-level change associated with melting from the southern Laurentide Ice Sheet
Normalised sea-level change associated with melting from the West Antarctic Ice Sheet
IMAGE
IMAGE
From: Clark, P.U., Mitrovica, J.X., Milne, G.A., Tamisiea, M.E. (2002) ‘Sea-level fingerprinting as a direct test for the source of global meltwater Pulse IA’ Science 295: 2438–2441. Reprinted with permission from AAAS. This figure may be used for non-commercial, classroom purposes only. Any other uses require prior written permission from AAAS.
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Holocene Sea Level Changes
• The Holocene Transgression (period of ice melt/ice sheet collapse in the early Holocene)
• Younger Dryas ice had melted by about 6000 years BP
Changes in land above sea level during the sea level rise of the Holocene
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Holocene sea-level curves
Clark, J.A. et al. (1978) ‘Global Changes in Post Glacial Sea Level: A Numerical Calculation’Quaternary
Research v.9
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Reconstructing Holocene sea levels
Case study examples and key researchers:
•Isolation basins (microfossils, stratigraphy)
Shennan, Lloyd
•Salt marshes (microsfossils, stratigraphy)
Gehrels, Horton, Edwards, Haslett, Charman
Dee Estuary salt marshes
Raised beach, Isle of Skye
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Reconstructing Holocene sea levels
What do we need to know?
- Age
- Present day altitude
- Indicative meaning (& range)
- tendency of sea-level (?)
Sea-level index point (SLIP)
Indicative meaningThe elevation relative to a reference tide level at which the sea-level indicators are found in the present environment. Commonly used RTLs: MSL, MHW, OD etc.).
Relative sea level (RSL) = H – I Where H is the present day altitude of the sample and I is the
indicative meaning.
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Session Summary
Sea-level change is an important driving mechanism for coastal change, especially over G-IG cycles
Complex interplay between glacio-eustasy, tectono-eustasy, geoidal-eustasy, glacio-isostasy, hydro-isostasy results in highly complex patterns of RSL change
The concept of a ‘global’ sea-level curve does not exist, BUT regional trends can be identified
Postglacial (Holocene) trends are the most extensively studied – due to the abundant evidence
RSL change can be reconstructed from a number of different archives, BUT potential inaccuracies in the resulting RSL curves need to be acknowledged
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
References
Bassett, S.E., Milne, G.A., Mitrovica, J.X., Clark, P.U. (2005) ‘Ice sheet and solid earth influences on far-field sea-level histories’ Science 309: 925–928
Clark, J.A., Farrell , W.E. and Peltier, W.R. (1978) ‘Global Changes in Post Glacial Sea Level: A Numerical Calculation’ Quaternary Research v.9 : 265-287
Clark, P.U., Mitrovica, J.X., Milne, G.A., Tamisiea, M.E. (2002) ‘Sea-level fingerprinting as a direct test for the source of global meltwater Pulse IA’ Science 295: 2438–2441
Gehrels, W.R. and Long, A.J., (2008) Sea level is not level. The case for a new approach to predicting UK sea-level rise. Geography 93, 11-16.
Masselink, G. and Hughes, M. (2003) Introduction to Coastal Processes and Geomorphology Edward Arnold Publishers
Peltier, W.R. and Andrews, J.T.(1976) 'Glacial isostatic adjustment I: the forward problem’ Geophys. J. Roy. Astron. Soc. 46, 669–706
Peltier (2005) ‘On the hemispheric origins of meltwater pulse’ Quaternary Science Reviews 24: 1655–1671
Shennan, I. (1999) ‘Global meltwater discharge and the deglacial sea-level record from northwest Scotland’. Journal of Quaternary Science 14(7): 715-719
Tamisiea, M.E., Mitrovica, J.X., Davis, J.L. and Milne, G.A. (2003) ‘Long wavelength sea level and solid surface perturbations driven by polar ice mass variations: fingerprinting Greenland and Antarctic Ice Sheet flux’. Space Science Reviews 108(1): 81-93
Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
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1. Slide 18: Figures from From: Clark, P.U., Mitrovica, J.X., Milne, G.A., Tamisiea, M.E. (2002) ‘Sea-level fingerprinting as a direct test for the source of global meltwater Pulse IA’ Science 295: 2438–2441. Reprinted with permission from AAAS. This figure may be used for non-commercial, classroom purposes only. Any other uses require prior written permission from AAAS.
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Dr Katie Szkornik, Keele University, [email protected]
C-Change in GEES: Changing Coastal Environments - Post-Glacial Sea Level Change
Author Dr Katie Szkornik
Stephen Whitfield
Institute – Owner Keele University, School of Physical and Geographical Sciences
Title Postglacial Sea-Level Change Powerpoint Presentation
Date Created December 2009
Description Postglacial Sea-Level Change - Powerpoint Presentation – Part One of Changing Coastal Environments
Educational Level 3
Keywords (Primary keywords – UKOER & GEESOER)
UKOER, GEESOER, Eustasy, Isostasy, Meltwater pulses
Creative Commons License Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales
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