Ocean Drilling Program Leg 113: Weddell Sea, Antarctica
Ocean Drilling Program (ODP) Leg 113 drilled sites in the Weddell Sea, which is surrounded on nearly three sides by Antarctica. Some of the sites were drilled from Maud Rise, which is an underwater plateau, representing an area that stands above the deeper seafloor crust which surrounds it. Maud Rise was formed as part of a large igneous province (LIP), which is a large extrusion of lava that erupted (non-violently) in the ocean or on land. Maud Rise was formed approximately 140 to 122 million years ago, in the Cretaceous Period.
ODP Leg 113 had several objectives. The first was to determine when Antarctic ice sheets first began to form, and if they had been permanent since their formation. The second objective was to monitor the development of Antarctic Bottom Water, a very cold and very dense water mass that flows along the bottom of the ocean floor, and forms near Antarctica. Using sediments recovered from Leg 113, scientists also wanted to determine how this very cold water mass responded to ancient warming and cooling events through time. The third and fourth objectives were related to marine organisms that live in the waters surrounding Antarctica, in the Weddell Sea. How did they live in such cold conditions, and did different species respond to such warming and cooling events through time? These objectives, in part, were addressed by drilling a transect of sites across the Weddell Sea, in shallower to progressively deeper waters, to obtain sediments from shallow- to deep-water masses.
Leg 113 recovered sediments that dated back to the Cretaceous, the time the dinosaurs were alive. Several sedimentary sections were recovered that contained the end-Cretaceous Mass Extinction that occurred 66 million years ago, the extinction event that led to the demise of non-avian dinosaurs. The sediments were used to determine the history of Antarctica through the entire Cenozoic, or the last 66 million years of Earth’s history. The earliest Cenozoic sediments from the Weddell Sea indicate that the region was warm and semi-arid (Barker et al., 1988). Within the Oligocene (~25 million years ago), the sediments were used to determine the approximate size of the Antarctic ice sheet that formed during this time, and was relatively stable (Escutia et al., 2019). Around the Middle Miocene (~15 million years ago), another expansion of Antarctic ice was found to occur (Barker et al., 1988).
Leg 113 was the first expedition to recover sediments from the Paleocene-Eocene Thermal Maximum (PETM), which was a short-lived but intense warming event that occurred around 55.5 million years ago. The PETM section recovered from Site 690 is one of the most expanded sections of the PETM ever to be drilled (Röhl et al., 2007), and as such, it is the site that is most intensively studied for this event. The PETM lasted only about 20,000–50,000 years, but within this short time frame, the Earth warmed by 5–8°C. The PETM is often studied as an analogue for future climate change, as warming happened rapidly during this event.
Most of the sediments drilled from the Weddell Sea contained microfossils, tiny fossils that can only be seen with the help of microscopes. Using these microfossils from Antarctic sediments, paleontologists were able to determine when different species of microorganisms evolved and went extinct (e.g., Harwood & Gersonde, 1990; Leckie, 1990; Funakawa & Nishi, 2005), and in turn use different species to help reconstruct the ancient environments around Antarctica.
References
Barker, P. F., Kennett, J. P., O’Connell, S., Berkowitz, S., Bryant, W. R., Burckle, L. H., … & Wise, S. W. (1988). Proceedings of the Ocean Drilling Program, Initial Reports, Vol. 113. Weddell Sea, Antarctica. Covering Leg 113 of the cruises of the drilling vessel JOIDES Resolution, Valparaiso, Chile, to East Cove, Falkland Islands, Sites 689-697, 25 December 1986-11 March 1987. Ocean Drilling Program.
Escutia, C., DeConto, R. M., Dunbar, R., Santis, L. D., Shevenell, A., & Naish, T. (2019). Keeping an eye on Antarctic Ice Sheet stability. Oceanography, 32(1), 32-46.
Funakawa, S., & Nishi, H. (2005). Late middle Eocene to late Oligocene radiolarian biostratigraphy in the Southern Ocean (maud rise, ODP Leg 113, site 689). Marine Micropaleontology, 54(3-4), 213-247.
Harwood, D. M., & Gersonde, R. (1990). 26. LOWER CRETACEOUS DIATOMS FROM ODP LEG 113 SITE 693 (WEDDELL SEA). PART 2: RESTING SPORES, CHRYSOPHYCEAN CYSTS, AN ENDOSKELETAL DINOFLAGELLATE, AND NOTES ON THE ORIGIN OF DIATOMS1. In Proceedings of the Ocean Drilling Program, scientific results (Vol. 113, pp. 403-425).
Leckie, M. R. (1990). Middle Cretaceous planktonic foraminifers of the Antarctic margin: hole 693A, ODP LEG 1131. In Proceedings of the Ocean Drilling Program, Scientific Results (Vol. 113, pp. 319-324).
Röhl, U., Westerhold, T., Bralower, T. J., & Zachos, J. C. (2007). On the duration of the Paleocene‐Eocene thermal maximum (PETM). Geochemistry, Geophysics, Geosystems, 8(12).