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THEME 6: SEA LEVEL IN TIME AND SPACE
Sea Level in Time and Space
Ian Shennan 1 and Roland Gehrels 2
1 Department of Geography, Durham University, Durham DH1 3LE
2 Environment Department, University of York, Heslington, York YO10 5DD
In this paper we identify four revolutions that have shaped the study of sea-level changes
in recent decades.
1. The search for ‘eustasy’
In the 1960s one of the most hotly debated issues in sea-level science concerned the
search of a sea-level curve that could describe the mean global sea-level changes since
glacial times in a single graph. It is now clear that eustasy cannot be measured anywhere
on Earth due to continual deformation of the solid Earth. Nonetheless, the question is still
relevant as models of Glacial Isostatic Rebound (GIA) require input of the amount of
meltwater that has entered the world’s oceans following the demise of the large
Pleistocene ice sheets.
2. Resolution of sea-level archives
During the search for the ‘eustatic’ curve its shape was hotly debated. Was it smooth or
wiggly? This debate persists to this day, although many sea-level archives have limitations
in their resolving power. From studies of salt-marsh deposits and corals it is clear, for
example, that metre-scale sea-level fluctuations have not occurred during the middle and
late Holocene. Other archives, for example the oxygen isotope record of the Red Sea,
have been used to argue for rapidly oscillating sea levels, raising questions about the
(in)stability of ice sheets during interglacials.
3. Merging of empirical sea-level investigations and models
Sea-level research has moved towards the integration of models and data in the past two
decades. For example, GIA models provide us with hypotheses that can be tested with
empirical data. They also provide insights into the underlying processes that are
responsible for the sea-level changes that are observed. Palaeorecords provide data and
constraints for the testing and calibration of both semi-empirical and process-based
predictive models.
4. Rapid sea-level changes
Improved coring technology since the late 1980s has resulted in the identification of
meltwater pulses (e.g., Barbados, Tahiti) and sea-level oscillations during past
interglacials (Red Sea). Low frequency high magnitude events have also been
documented along seismically active shorelines, providing information on earthquake
recurrence intervals. In addition, identification of storms and tsunamis in the stratigraphic
record is a growing area of research.
A common theme between these four ‘revolutions’ is the recognition of the relevance of
sea-level research for society. Overarching research questions concern the stability of ice
sheets and the occurrences of extreme sea levels. Although fundamental sea-level
research examines the vertical component of sea-level change, ultimately it is the
horizontal component (i.e. the position of the shoreline) that justifies its funding.
Key words: Glacial Isostatic Adjustment; eustasy; meltwater pulses; Holocene; interglacial.