Sea-surface temperatures during the last interglaciation.

 

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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

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.

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Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval.

The Jurassic/Cretaceous Boundary

Map of the Jurassic/Cretaceous Boundary by C. Scotese.

The Jurassic/Cretaceous (J/K) boundary, 145 Myr ago, remains as the less understood of major Mesozoic stratigraphic boundaries. Sedimentological, palynological and geochemical studies, indicate a climatic shift from predominantly arid to semi arid conditions in the latest Jurassic to more amicable humid conditions in the earliest Cretaceous. The continued fragmentation of Pangaea across the Late Jurassic and Early Cretaceous led to large-scale tectonic processes, on both regional and global scale, accompanied by some of the largest volcanic episodes in the history of the Earth; eustatic oscillations of the sea level; potentially heightened levels of anoxia, oceanic stagnation, and sulphur toxicity; along with two purported oceanic anoxic events in the Valanginian and Hauterivian. There’s also evidence of three large bolide impacts in the latest Jurassic, one of which might have been bigger than the end-Cretaceous Chicxulub impact.

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

Painting of a late Jurassic Scene on one of the large island in the Lower Saxony basin in northern Germany (From Wikimedia Commons)

The J/K interval represents a period of elevated extinction, and involves the persistent loss of diverse lineages, and the origins of many major groups that survived until the present day (e.g. birds). The magnitude of this drop in diversity ranges from around 33% for ornithischians to 75–80% loss for theropods and pterosaurs. Mammals suffered an overall loss of  diversity of 69%. Crocodyliforms suffered a major  decline across the Jurassic/Cretaceous boundary in both the marine and terrestrial realms; while non-marine turtles declined by 33% of diversity through the J/K boundary. In contrast, lepidosauromorphs greatly increased in diversity (48%) across the J/K boundary, reflecting the diversification of major extant squamate clades, including Lacertoidea, Scincoidea and Iguania.

In the marine realm, sauropterygians and ichthyosaurs show evidence for a notable decline in diversity across the J/K boundary, which continued into the Hauterivian for both groups.

Stratigraphic ranges of major Jurassic–Cretaceous theropod (A), sauropod (B), and ornithischian (C) dinosaur clades through the Middle Jurassic to Early Cretaceous (From Tennant et al,. 2016)

Stratigraphic ranges of major Jurassic–Cretaceous theropod (A), sauropod (B), and ornithischian (C) dinosaur clades through the Middle Jurassic to Early Cretaceous (From Tennant et al,. 2016)

Eustatic sea level is the principal mechanism controlling the Jurassic–Cretaceous diversity of tetrapods. Rising sea levels leads to greater division of landmasses through creation of marine barriers, modifying the spatial distribution of near-shore habitats and affecting the species–area relationship, which can lead to elevated extinctions. This fragmentation can also be a potential driver of biological and reproductive isolation and allopatric speciation, the combination of which we would expect to see manifest in the diversity signal. Additionally, the diversity of fully marine taxa was more probably affected by the opening and closure of marine dispersal corridors, whereas that of terrestrial and coastal taxa was more probably dependent on the availability of habitable ecosystems, including the extent of continental shelf area (Tennant, et al., 2016).

References:

Tennant J,P., Mannion P. D., Upchurch P., Sea level regulated tetrapod diversity dynamics through the Jurassic/Cretaceous interval, Nature Communications, ISSN: 2041-1723 DOI: 10.1038/ncomms12737

Tennant, J. P., Mannion, P. D., Upchurch, P., Sutton, M. D. and Price, G. D. (2016), Biotic and environmental dynamics through the Late Jurassic–Early Cretaceous transition: evidence for protracted faunal and ecological turnover. Biol Rev. doi:10.1111/brv.12255 

Butler, R. J., Benson, R. B. J., Carrano, M. T., Mannion, P. D. & Upchurch, P. Sea level, dinosaur diversity and sampling biases: investigating the ‘common cause’ hypothesis in the terrestrial realm. Proc. R. Soc. B 278, 1165–1170 (2011).