1. C-Change in GEES Changing Coastal Environments
Session 1: Postglacial
Sea-Level Change

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These slides were last updated in December 2009

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4. Session Outline Key definitions Postglacial sea-level change
Meltwater pulses
Sea-level fingerprinting
Holocene sea level change
Reconstructing Holocene sea-level change
Photo: wonderlane (flickr.com)
What you need to know about:
The history of sea-level change
The causes of sea-level change
The effects of sea-level change

5. Why is Sea-Level Change Important?
It is an important driving mechanism for (rapid?) coastal change, especially over glacial/interglacial cycles
Photo: skagman (flickr.com)
Sea-level change has always been a contributing driver of geomorphic change within coastal environments

6. Understanding past sea-level change
Need to fully understand this before we can predict the future!
Monitoring present day sea-level change
Predicting future sea-level rise
Coastal management, hazard mitigation

7. Eustasy + Isostasy = Relative 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

8. Source: NASA Image Exchange
The Geoid
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
Source: NASA Image Exchange
(nix.nasa.gov)

9. ISOSTASY Key Definitions
Eustasy + Isostasy = Relative Sea-level Change
ISOSTASY
The 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, Kele University,
C-Change in GEES Themes 2 and 3: Changing Coastal Environments - Post-Glacial Sea Level Change

10. Glacial Forebulge Image adapted from: Peltier and Andrews (1976)
Where this occurs in coastal locations it has important implications for relative sea level history

11. Images adapted from Gehrels & Long (2008)
Ocean Siphoning
Continental Levering
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
Many of these processes are not fully considered by the IPCC & other agencies involved in predicting future sea-level rise…….
Images adapted from Gehrels & Long (2008)

12. 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’

13. Postglacial sea-level changes
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
Eustatic changes: global and rapid
Isostatic changes: regional and slow(er)

14. 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
Existence and magnitude has implications for understanding rapid climate and coastal change
*Meltwater
pulses*

15. 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)

16. Where is the source location for these events?
Source area is highly debated
Current area of intense research (& funding!)
SUGGESTION ONE
Peltier (2005):
N. Hemisphere (Laurentide?)
SUGGESTION TWO
Bassett et al. (2005) & Clark et al. (2002):
Antarctic
Photos: cloudzilla (above); 23am.com (below) (flickr.com)

17. 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)

18. Source of Meltwater Pulse Events
IMAGE
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.
Normalised sea-level change associated with melting from the southern Laurentide Ice Sheet
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.
Normalised sea-level change associated with melting from the West Antarctic Ice Sheet

19. Holocene Sea Level Changes
Changes in land above sea level during the sea level rise of the Holocene
The Holocene Transgression (period of ice melt/ice sheet collapse in the early Holocene)
Younger Dryas ice had melted by about 6000 years BP

20. Holocene sea-level curves
Clark, J.A. et al. (1978) ‘Global Changes in Post Glacial Sea Level: A Numerical Calculation’
Quaternary Research v.9

21. Reconstructing Holocene sea levels
Dee Estuary salt marshes
Case study examples and key researchers:
Isolation basins (microfossils, stratigraphy)
Shennan, Lloyd
Salt marshes (microsfossils, stratigraphy)
Gehrels, Horton, Edwards, Haslett, Charman
Raised beach, Isle of Skye

22. 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 meaning
The 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.

23. 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

24. 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 :
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,
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):
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

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26. Item Metadata 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