sea level

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iGlass EGU session


CL5.11: Sea level in interglacials as a constraint on future changes

iGlass will be running a session at EGU2014. We would like to strongly encourage you to submit an abstract to our session (deadline for abstract submission: 16th January 2014)

Session details: Sea level appears to have been at a higher level than today in at least some of the recent interglacial periods. In this session, we aim to understand how the respective climate histories led to those higher sea levels, and assess how this information can help us constrain projections for future sea level over a range of timescales. Contributions will be welcome that:

  • derive sea level in any of the Quaternary interglacials, either at a single site or across the globe
  • describe or model the (polar) climates that led to higher sea levels
  • model interglacial ice sheet histories, or the respective sea levels
  • link past sea levels with future projections

The session will include work from the UK project iGLASS, but other contributions addressing the above questions will be equally welcome.

Convenors: Eric Wolff, Fiona Hibbert and Dan Lunt


iGlass paper: A geological perspective on potential future sea-level rise

Sea-level versus carbon dioxide concentrations

A new paper by iGlass members suggest modern sea level changes is rapid by past interglacial standards (Rohling et al., 2013 Scientific Reports).

“During ice-age cycles, continental ice volume kept pace with slow, multi-millennial scale, changes in climate forcing. Today, rapid greenhouse gas (GHG) increases have outpaced ice-volume responses, likely committing us to > 9 m of long-term sea-level rise (SLR). We portray a context of naturally precedented SLR from geological evidence, for comparison with historical observations and future projections. This context supports SLR of up to 0.9 (1.8) m by 2100 and 2.7 (5.0) m by 2200, relative to 2000, at 68% (95%) probability.”

The research led by Prof. Eelco Rohling and Dr Ivan Haigh suggests that comparison of present changes in sea level to the natural context outlined in this paper, may be used to identify if and when sea-level response becomes ‘special’ (i.e., unprecedented during geological interglacials).

Professor Rohling concludes: “For the first time, we can see that the modern sea-level rise is quite fast by natural standards. Based on our natural background pattern, only about half the observed sea-level rise would be expected. Although fast, the observed rise still is (just) within the ‘natural range’. While we are within this range, our current understanding of ice-mass loss is adequate. Continued monitoring of future sea-level rise will show if and when it goes outside the natural range. If that happens, then this means that our current understanding falls short, potentially with severe consequences.”

Australia’s 9 News interview with Prof. Eelco Rohling:

UK Wave 102 radio interview with Dr Ivan Haigh:


Big, unicellular science


A shallow water foraminifer, Ammonia sp. (it’s about 0.4 mm big)

Metres of sea-level change. Hundreds of thousands of years. The entire globe. The scale of the iGlass research project is rather large. But some of the research is based on the humblest of creatures: benthic foraminifera.
If you have a really big one it might be an entire millimetre. Benthic foraminifera are unicellular protists who live on top of, or in the top layer of, marine sediment. Every species has its own niche; for instance, some like coarse sediments, some like fresh food, some like warm water, etcetera. Some of the more adventurous species even live in salt marshes. These are, if you will, the scuba divers among foraminifera; all foraminifera need salt water to live, but these brave souls have become accustomed to do without for substantial amounts of time.

Three specimens of Aubignyna perlucida; two of these have their shells filled with pyrite nodules

The reason why foraminifera, in spite of being such modest creatures, get so much attention from the palaeoclimate community is that they build some sort of skeleton, and aretherefore often very well preserved in sediments. They can be tens of millions of years old and still look like they died last week. They take the information they contain into their graves, and in this case that’s a good thing. If you know which species prefers what environment, you can “read” sediments they are found in.

Drilling a core in sediments that are several hundreds of thousands of years old

The York and Durham teams drilled cores through interglacial sediments.

We drilled in the middle of Norfolk, but we know that area has been inundated in previous interglacials, and indeed, we found both freshwater and marine sediments in our cores. And using the foraminifera in them, we are reading them. We are looking for changes reflected in the various species encountered; will we get a gradual change from the shallowest foraminifera, which are the ones that actually live above sea level but still within reach of high tide, through the ones that live in shallow water, to those that prefer deeper waters? Or will we see several of such sequences? Or an instantaneous shift from no foraminifera to relatively deep-water species? Watch this space for results…

The foraminifera sorted by species
(each numbered rectangle is about 2.3 mm wide)

We found some 10, 000 foraminifera (and counting). They were picked out of the samples by two different scholars, so we keep them all in order to be able to check we have comparable ideas of which species is which (since you ask; no, identifying the species is not a straightforward task). Keeping them also allows us to always go back to the source material in case of questions arising. And after the questions iGlass asks have been answered, who knows what other questions such a collection can help tackle!

June 2019
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