Eleni’s “Icehouse” class at Bowdoin College

A few days ago I had the opportunity to lead a discussion on the Descent into the Icehouse in Dr. Michéle LaVigne’s upper level undergraduate course, ‘Earth climate history’ at Bowdoin College (Brunswick, ME, USA). During the class, which was arranged as a video conference, the students discussed a selection of literature related to the Descent into the Icehouse project (Pearson et al. 2009, Bijl et al. 2009, Beerlingand Royer 2011).

We had a lively discussion and several issues have been raised, some of the most interesting ones were:

1.  The timescales of global climate change are very different between early Cenozoic and future predictions; how does understanding the Cenozoic help us predict the future?
2. Ice caps seem to show a nonlinear response to climate forcing during melting due to a hysteresis effect, but will this hold true on current time scales? Could this response eventually manifest itself into hastened melting as opposed to persistence of ice caps?
3. On early Cenozoic time scales, how much does the distance of the Earth’s orbit from the sun implicate atmospheric CO2 levels and how much of that theory is guesswork?

 The most intriguing point to me was the question if the change in sea surface temperature was due to decline carbon dioxide concentrations, why/how did the tropics remain fairly stable during the Eocene? What are the possible mechanisms such as different ocean circulation, different atmospheric circulation, or something having to do with the uneven radiation from the sun based on latitude?

 Well…. the answer to this question will have to wait until we have generated more data…

Overall, it was a great experience that I would certainly do again.

Coevolution of Life and the Planet Spring School 2013

Biogeochemical Cycles and Evolution

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Oxygen Isotopes in Foraminifera: Overview and Historical Review

Prof Paul Pearson has published a paper of oxygen isotopes in foraminifera, one of the main techniques in the Descent into the Icehouse project.

The paper shows how

the oxygen isotope ratio (δ¹⁸0) of calcite depends mainly on the isotope ratio of the water it is precipitated from, the temperature of calcification, and, to a lesser extent, the pH. Foraminifera and other organisms can potentially preserve their original isotope ratio for many millions of years, although diagenetic processes can alter the ratios. Guidelines to assess the preservation of foraminifera are reviewed. A variety of empirical paleo-temperature equations have been proposed and some of the most important are discussed. Work on oxygen isotope ratios of foraminifera was instrumental in the discovery of the orbital theory of the ice ages and continues to be widely used in the study of rapid climate change. Compilations of deep sea benthic foraminifer oxygen isotopes have revealed the long history of global climate change over the past 100 million years. Planktonic foraminifer oxygen isotopes are used to investigate the history of past sea surface temperatures, revealing the extent of past ‘greenhouse’ warming and global sea surface temperatures.

Read and download the paper here

Foram art: calcite tests of selected benthic (left) and planktonic (right) foraminifera. These are from exceptionally well-preserved Paleogene sediments of Tanzania (33–45 Ma). Scale is approximate; diameters are from about 0.20–0.75 mm. Images: P. N. Pearson and I. K. McMillan. Note the literature is split between those who use the adjective ‘planktonic’ versus ‘planktic’ and between those who use ‘benthonic’ versus ‘benthic’. It so happens that planktonic and benthic are clearly in the ascendancy as of 2012, by roughly 10:1 and 30:1 respectively, as shown by a word search on abstracts. It has been argued that planktic is the correct Greek form of the adjective (Rodhe, 1974; Emiliani, 1991) but it has been pointed out that planktonic, like electronic, is perfectly good English, however ugly it may be in Greek (Hutchinson, 1974). The majority usage is followed here. Courtesy: Paul Peason Source: OXYGEN ISOTOPES IN FORAMINIFERA: OVERVIEW AND HISTORICAL REVIEW

Climate change clues from tiny marine algae – ancient and modern

Microscopic ocean algae called coccolithophores are providing clues about the impact of climate change both now and many millions of years ago. The study found that their response to environmental change varies between species, in terms of how quickly they grow.

Coccolithophores, a type of plankton, are not only widespread in the modern ocean but they are also prolific in the fossil record because their tiny calcium carbonate shells are preserved on the seafloor after death – the vast chalk cliffs of Dover, for example, are almost entirely made of fossilised coccolithophores.

Fossil and modern coccolithophore cells of species Toweius pertusus and Coccolithus pelagicus. Courtesy of Paul Bown,UCL

The fate of coccolithophores under changing environmental conditions is of interest because of their important role in the marine ecosystem and carbon cycle. Because of their calcite shells, these organisms are potentially sensitive to ocean acidification, which occurs when rising atmospheric carbon dioxide (CO2) is absorbed by the ocean, increasing its acidity.

There are many different species of coccolithophore and in an article, published in Nature Geoscience this week, the scientists report that they responded in different ways to a rapid climate warming event that occurred 56 million years ago, the Palaeocene-Eocene Thermal Maximum (PETM).

The study, involving researchers from the University of Southampton, the National Oceanography Centre and University College London, found that the species Toweius pertusus continued to reproduce relatively quickly despite rapidly changing environmental conditions. This would have provided a competitive advantage and is perhaps why closely-related modern-day species considered to be its descendants, (such as Emiliana huxleyi) still thrive today.

In contrast, the species Coccolithus pelagicus grew more slowly during the period of greatest warmth and this inability to maintain high growth rates may explain why its descendants are less abundant and less widespread in the modern ocean.

“This work provides us with a whole new way of looking at living and fossil coccolithophores,” said lead author Dr Samantha Gibbs, Senior Research Fellow at University of Southampton Ocean and Earth Science.

By comparing immaculately preserved and complete fossil cells with modern coccolithophore cells, the researchers could interpret how different species responded to the sudden increase in environmental change at the PETM, when atmospheric CO2 levels increased rapidly and the oceans became more acidic.

“We use knowledge of how coccolithophores build their calcite skeletons in the modern ocean to interpret how climate change 56 million years ago affected the growth of these microscopic plankton,” said co-author Dr Alex Poulton, a Research Fellow at the National Oceanography Centre.

“This is a significant step forward and allows us to view fossils as cells rather than dead ‘rocks’. Through this we can begin to understand the environmental controls on oceanic calcification, as well as the potential effects of climate change and ocean acidification.”

Reference: Gibbs S.J., Poulton A.J., Bown P.R., Daniels C.J., Hopkins J. Young J.R., Jones H.L., Thiemann G.J., O’Dea S.A., Newsam C. (2013) Species-specific growth response of coccolithophores to Palaeocene–Eocene environmental change. Nature Geoscience doi: 10.1038/NGEO1719

The study was primarily supported by the UK Ocean Acidification Research Programme, which is jointly funded by the Natural Environment Research Council (NERC), the Department of Environment, Food and Rural Affairs (Defra) and the Department of Energy and Climate Change (DECC).