Sea-surface temperatures during the last interglaciation.

 

The relentless rise of carbon dioxide (Credit: National Oceanic and Atmospheric Administration.)

A proverb of Confucius states “Study the past if you would divine the future.” Human activity ensures that our climate will become warmer in the next century and remain warm for many millennia to come which makes particularly pertinent the study of periods in which at least sectors of the Earth system may have been “warmer” than today. The last interglaciation (LIG, 129 to 116 thousand years ago) was one of the warmest periods in the last 800,000 years with an associated sea-level rise of 6 to 9 m above present levels . A new study by Jeremy S. Hoffman and colleagues, compiled 104 published LIG sea surface temperature (SST) records from 83 marine sediment core sites. Each core site was compared to data sets from 1870-1889 and 1995-2014, respectively. The analysis revealed that 129,000 years ago, the global ocean surface temperature was similar to the 1870-1889 average. But 125,000 years ago, the global SST increased by 0.5° ± 0.3°Celcius, reaching a temperature indistinguishable from the 1995-2014 average. The result is worrisome, because it shows that changes in temperatures which occurred over thousands of years, are now occurring in the space of a single century. The study also suggests that in the long term, sea level will rise at least six meters in response to the global warming.

Data from the study by Jeremy Hoffman et al. representing sample sites, sea surface temperatures, and historic carbon dioxide level

The planet’s average surface temperature has risen about 2.0 degrees Fahrenheit (1.1 degrees Celsius) since the late 19th century. After the World War II, the atmospheric CO2 concentration grew, from 311 ppm in 1950 to 369 ppm in 2000. Glaciers  from the Greenland and Antarctic Ice Sheets are fading away, dumping 260 billion metric tons of water into the ocean every year. The ocean acidification is occurring at a rate faster than at any time in the last 300 million years, and  the patterns of rainfall and drought are changing and undermining food security which have major implications for human health, welfare and social infrastructure. In his master book L’Evolution Créatrice (1907), French philosopher Henri Bergson, wrote:  “A century has elapsed since the invention of the steam engine, and we are only just beginning to feel the depths of the shock it gave us.”

References:

J.S. Hoffman et al. Regional and global sea-surface temperatures during the last interglaciation. Science. Vol. 355, January 20, 2017, p. 276. doi: 10.1126/science.aai8464.

Past Interglacials Working Group of PAGES (2016), Interglacials of the last 800,000 years, Rev. Geophys., 54, 162–219, doi: 10.1002/2015RG000482. 

Bakker, P., et al. (2014), Temperature trends during the present and Last Interglacial periods—A multi-model-data comparison, Quat. Sci. Rev., 99, 224–243, doi: 10.1016/j.quascirev.2014.06.031.

Forgotten women of Paleontology: Emily Dix

 

Dr Emily Dix and her assistant Miss Elsie White.

In the 18th and 19th centuries women’s access to science was limited, and science was usually a ‘hobby’ for intelligent wealthy women. It was common for male scientists to have women assistants, often their own wives and daughters. But by the first half of the 20th century, a third of British palaeobotanists working on Carboniferous plants were women. The most notable were  Margaret Benson, Emily Dix, and Marie Stopes.

Emily Dix was born on 21 May 1904 in Penclawdd, in the beautiful area of the Gower Peninsula. At age 18, she gained the Central Welsh Board Higher Certificate in history, botany and geography, with distinctions in both history and botany. In 1925, she graduated with first class honours in Geology at the University College Swansea. After graduation, Emily continued at Swansea to research the geology of the western part of the South Wales Coalfield. Her work was supervised by Arthur E. Trueman, Professor of Geology at Swansea, and a pioneer in developing stratigraphical theory. Trueman realized that the only accurate way to use fossils for correlation was to divide the stratigraphical succession into biozones defined exclusively by the assemblages of species present, independently of the lithology in which they were found. Trueman’s main interest were  non-marine bivalves, so Emily’s early work was on the non-marine bivalves of the South Wales Coalfield.

Emily Dix during the 2nd International Carboniferous Congress in 1935 (From Burek and Cleal, 2005)

Emily initially studied all aspects of the Late Carboniferous biotas in South Wales, but soon, she realized that plant fossils also had considerable biostratigraphical potential. Although, Paul Bertrand developed macrofloral biozones for the French coalfields in 1914, Emily used stratigraphical range charts for the first time in paleobotany recognising the need to separate biostratigraphy from lithostratigraphy. In 1926 Emily was awarded an MSc based on her Gwendraeth Valley work: ‘The Palaeontology of the Lower Coal Series of Carmarthen and the Correlation of the Coal Measures in the Western Portion of the South Wales Coalfield’.  In 1929 she was elected a fellow of the Geological Society, and a year later she was appointed Lecturer in Palaeontology at Bedford College in London, a position that she held for the rest of her working life. The same year, she attended the International Botanical Congress in Cambridge where she met W. Gothan, P. Bertrand, W. J. Jongmans and A. Renier, leaders in Upper Carboniferous palaeobotany at the time. Five years later, she attended the Second International Carboniferous Congress in Heerlen (The Netherlands) and she delivered papers on Carboniferous biostratigraphy. In 1936, Emily was invited to become the only female on an 11-man discussion group of the British Association for the Advancement of Science on Coal Measures correlation. She was clearly at the international forefront of the field.

Emily Dix in the Auvergne 1936 (seated fourth from right, see white arrow). From Burek and Cleal, 2005.

At the start of the World War II, she was evacuated to Cambridge, along with the rest of Bedford College Geology Department. She lost a lot of valuable literature and other records in a London Blitz in May 1941. Fortunately, much of her collection of fossils survived.

At the end of the war, Emily suffered a mental breakdown. She was moved to a mental hospital run by the Quakers in the City of York. That was the end of her scientific career. She died in Swansea on 31 December 1972.

It was not until the late 1970s that her techniques were used again in Britain. Elsewhere in Europe, her approaches were adopted and can be seen in many of the papers presented at the International Carboniferous Congresses held at Heerlen during the 1950s and early 1960s.

References:

Burek, C. V. & Cleal, C. J. (2005) The life and work of Emily Dix (1904-1972). In: Bowden, A. J., Burek, C. V. & Wilding, R (ed.) History of palaeobotany: selected essays. Geological Society of London, Special Publication, 241, 181-196

Burek, C. V. (2005). Emily Dix, palaeobotanist – a promising career cut short. Geology Today, 21(4), 144-145

Climate model simulations at the end of the Cretaceous.

Artist’s reconstruction of Chicxulub crater 66 million years ago.

About thirty years ago, the discovery of anomalously high abundance of iridium and other platinum group elements in the Cretaceous/Palaeogene (K-Pg) boundary led to the hypothesis that a 10 km asteroid collided with the Earth and caused one of the most devastating events in the history of life. The impact created the 180-kilometre wide Chicxulub crater causing widespread tsunamis along the coastal zones of the surrounding oceans and released an estimated energy equivalent of 100 teratons of TNT and produced high concentrations of dust, soot, and sulfate aerosols in the atmosphere.

To model the climatic effects of the impact, a team of scientist from the Potsdam Institute for Climate Impact Research (PIK), use literature information from geophysical impact modeling indicating that for a 2.9 km thick target region consisting of 30% evaporites and 70% water-saturated carbonates and a dunite projectile with 50% porosity, a velocity of 20 km/s and a diameter between 15 and 20 km, a sulfur mass of 100 Gt is produced. This is about 10,000 times the amount of sulfur released during the 1991 Pinatubo eruption. Additionally, for a sulfur mass of 100 Gt, about 1400 Gt of carbon dioxide are injected into the atmosphere, corresponding to an increase of the atmospheric CO2 concentration by 180 ppm. There could be additional CO2 emissions from ocean outgassing and perturbations of the terrestrial biosphere, adding a total of 360 ppm and 540 ppm of CO2. The main result is a severe and persistent global cooling in the decades after the impact. Global annual mean temperatures over land dropped to -32C in the coldest year and continental temperatures in the tropics reaching a mere -22C. This model is supported by a migration of cool, boreal dinoflagellate species into the subtropic Tethyan realm directly across the K–Pg boundary interval and the ingression of boreal benthic foraminifera into the deeper parts of the Tethys Ocean, interpreted to reflect millennial timescale changes in the ocean circulation after the impact (Vellekoop, 2014).

A time-lapse animation showing severe cooling due to sulfate aerosols from the Chicxulub asteroid impact 66 million years ago (Credit: PKI)

References:

Brugger J., G. Feulner, and S. Petri (2016), Baby, it’s cold outside: Climate model simulations of the effects of the asteroid impact at the end of the Cretaceous, Geophys. Res. Lett., 43,  doi:10.1002/2016GL072241.

Alvarez, L. W., W. Alvarez, F. Asaro, and H. V. Michel (1980), Extraterrestrial Cause for the Cretaceous-Tertiary Extinction, Science, 208 (4448), 1095{1108, doi: 10.1126/science.208.4448.1095.

Galeotti, S., H. Brinkhuis, and M. Huber (2004), Records of post Cretaceous-Tertiary boundary millennial-scale cooling from the western Tethys: A smoking gun for the impact-winter hypothesis?, Geology, 32, 529, doi:10.1130/G20439.1

Johan Vellekoop, Appy Sluijs, Jan Smit, Stefan Schouten, Johan W. H. Weijers, Jaap S. Sinningh Damsté, and Henk Brinkhuis, Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary, PNAS (2014) doi: 10.1073/pnas.1319253111