Climate Change and the legacy of the Challenger expedition

SEM images of selected planktonic foraminifera specimens; (i) T. trilobus (Tara), (j) G. ruber (Tara), (k) G. ruber (Challenger), (l) G. bulloides (Challenger), (m,n) G. ruber test cracked to reveal wall texture (Tara), (o,p) G. ruber test cracked to reveal wall texture (Challenger). From Fox et al., 2020.

It all began in 1868, with British naturalist William B. Carpenter and Sir Charles Wyville Thomson, Professor of Natural History at Edinburgh University. They persuaded the Royal Society of London to sponsor a prolonged voyage of exploration across the oceans of the globe. But it was not until 1872 that Royal Society of London obtained the use of the HSM Challenger from the Royal Navy. The ship was modified for scientific work with separate laboratories for natural history and chemistry. The cost of expedition was £200,000 – about £10 million in today’s money. The expedition was led by Captain George Nares and the scientific work was conducted by Wyville Thomson assisted by Sir John Murray, John Young Buchanan, Henry Nottidge Moseley, and the German naturalist Rudolf von Willemoes-Suhm. From 1872 to 1876, Murray developed a pioneering device which could register the temperature of the ocean at great depths, and assisted in the collection of marine samples. After the dead of Thomson in 1882, John Murray became director and edited the Challenger Expedition Reports. 

The science and ship crew of the HMS Challenger in 1874.

 
The planktonic foraminifera collected during the HMS Challenger expedition are part of the historical collection of the Natural History Museum, London. Their importance as tool for paleoclimate reconstruction was recognized early in the history of oceanography. The samples collected almost 150 years ago provide an extraordinary opportunity to understand the effects of one of the most urgent questions of our time with regards to anthropogenic environmental change: ocean acidification. 
 
Planktonic foraminifera are a group of marine zooplankton with a shell composed of secrete calcite or aragonite, with no internal structures and different patterns of chamber disposition (trochospiral, involute trochospiral and planispiral growth); with perforations and a variety of surface ornamentations like cones, short ridges or spines. Their shells take up chemical signals from the sea water, in particular isotopes of oxygen and carbon. Over millions of years, these skeletons accumulate in the deep ocean to become a major component of biogenic deep-sea sediments. By comparing the sediment samples from the HMS Challenger Expedition (1872–1876) with the recent Tara Oceans expedition material (2009–2016), the researchers found that the composition of the planktonic foraminifera has changed significantly since the pre-industrial period, and revealed that all modern specimens had up to 76% thinner shells than their historic counterparts.
 
 
 

Nano-CT representative reconstructions and measurements for Neogloboquadrina dutertrei from Tara (a–c), and Challenger (d–f). From Fox et al., 2020.

Ocean acidification affects the biogeochemical dynamics of calcium carbonate, organic carbon, nitrogen, and phosphorus and interferes with a range of processes including growth, calcification, development, reproduction and behaviour in a wide range of marine organisms like planktonic coccolithophores, foraminifera, echinoderms, corals, and coralline algae. Additionaly, ocean acidification can intensify the effects of global warming, in a dangerous feedback loop. Since the Industrial Revolution the pH within the ocean surface has decreased ~0.1 pH and is predicted to decrease an additional 0.2 – 0.3 units by the end of the century. 

After the World War II, the impact of human activity on the global environment dramatically increased. This period associated with very rapid growth in human population, resource consumption, energy use and pollution, has been called the Great Acceleration. In the coming decades, the ocean’s biogeochemical cycles and ecosystems will become increasingly stressed by ocean warming, acidification and deoxygenation. This scenario underlines the urgency for immediate action on global carbon emission reductions.

 

References:

Fox, L., Stukins, S., Hill, T. et al. Quantifying the Effect of Anthropogenic Climate Change on Calcifying Plankton. Sci Rep 10, 1620 (2020). https://doi.org/10.1038/s41598-020-58501-w

Jonkers, L., Hillebrand, H., & Kucera, M. (2019). Global change drives modern plankton communities away from the pre-industrial state. Nature. doi:10.1038/s41586-019-1230-3

Wyville Thompson, C. The Voyage of the “Challenger”. The Atlantic. 2 volumes (1878).

Dohrn, Anton. (1895). The Voyage of HMS “Challenger” A Summary of the Scientific Results. http://doi.org/10.1038/052121a0

 

 

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