Scientific Ocean Discovery

374: Ross Sea West Antarctic Ice Sheet History

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Figure 1. Bathymetric map with Expedition 374 sites and previous Deep Sea Drilling Program Leg 28, ANDRILL sites, as well as Cape Roberts Project (CRP) sites. Ross Sea bathymetry is from the International Bathymetric Chart of the Southern Ocean (Arndt et al., 2013a, 2013b). Existing seismic network is from the Antarctic Seismic Data Library System and includes some single-channel seismic-reflection profiles (McKay et al., 2019). Figure from IODP Expedition 374 Summary.

Expedition 374 took place from 4 January to 8 March 2018, during which five sites were drilled in the eastern Ross Sea of Antarctica, ranging from the outer continental shelf to the continental  slope and rise (Fig. 1). Three sites (U1521, U1522, and U1523) were on the continental shelf, while U1524 and U1525 were from the continental rise and slope, respectively (Fig. 1).

The study of western Antarctica and the Ross Sea region  is crucial because computer models have shown this area is  highly sensitive to changes in ocean temperature and sea level. The West Antarctic Ice Sheet (WAIS) contains a vast amount of ice, and its complete melting could result in a 4.3 meter rise in global sea level (Patterson et al., 2012). Therefore, by understanding how the ice sheet in this region has changed in the past, researchers can predict how it may change in the future under different climate conditions, which can better prepare societies  for the inevitable future (McKay et al., 2019). 

The primary objective of Expedition 374 was to comprehend how the evolution of the WAIS during the Neogene (23–2.58 million years ago) and Quaternary (2.58 million years ago to Recent) geologic periods relates to changes in climate and oceanic conditions. Scientists wanted to determine the contribution of West Antarctica to overall ice volume and sea level rise, comprehend past polar temperature changes and causes of such changes in temperatures, understand the effect of changes in ocean temperature and sea level on the stability of the Antarctic Ice Sheet, determine how the Earth’s position in its orbit influences the stability of the Antarctic Ice Sheet under different climate conditions, and analyze the relationship between seafloor geometry in the eastern Ross Sea and the stability of the ice sheet and global climate.

Despite challenges such as drifting sea ice and mechanical vessel failure during drilling at Site U1524, the team managed to retrieve significant recoveries. Although about 39% of operational days at sea were lost, making it challenging to achieve all the proposed goals of Expedition 374. Regardless, the recovered samples can still be effectively compared with those from other sites, such as U1522, U1525, and sites from similar projects like the Antarctic Geological Drilling Project (ANDRILL). The goal is to create a continental shelf to rise transect of the Pliocene (5.33–2.58 million years ago) to the Pleistocene (2.58–0.017 million years ago) periods, which is an essential component of the expedition’s overall objectives.

Figure 2: (a) Lithostratigraphic column for Site U1524, with the position of the studied tephra layer highlighted in red. From left to right: Depth of the core, with ‘0’ representing the sediment-water interface, in units of meters below sea floor; core numbers; core recovery (black indicates depths where sediment was recovered, white indicates intervals where no sediments were recovered); age is how old the sediments are; Lith. unit indicates the major types of lithologies, or sediment types, that were recovered; and graphic lithology is the visual description of the different sediment types. (b) Core photographs of Section 374-U1524A-6H-2A and detail of the rhyolite tephra studied in this work. The scale is in cm (Di Roberto et al., 2021). Figure from Di Roberto et al., (2021).

During Expedition 374, 1292.70 meters of cores were recovered from five drill sites spanning the early Miocene (~15 million years ago) to late Quaternary (Recent). The sediments in the Ross Sea near Antarctica were studied by several scientists to gain insights into the history of the West Antarctic Ice Sheet (WAIS). A study by King et al., (2022) focused on how ice and ocean currents interacted during past ice ages (about 2.4 million years ago) to estimate the future extent of the ice sheets and help improve future models of the ice sheet. The study also   fostered an understanding of how the ice sheet formed and grew under different oceanographic conditions. Also, findings from Expedition 374 inspired a new WAIS drilling project that will predict how the ice sheet will respond to future global warming scenarios, including how melting of the ice could contribute to sea-level rise, based on how the ice sheet responded to warming scenarios in the geologic past (Patterson et al., 2012).

In 2022, a study by Lelieveld analyzed sediments from Expedition 374 to investigate how the Antarctic Ice Sheets impacted sea level variations and vegetation changes during the Miocene Period (23–5.33 million years ago) in the Ross Sea. The Miocene Period is a time when atmospheric carbon dioxide levels were much higher than today, and reached levels projected for the coming decades. As such, the Miocene Period is a good geologic analogue for how Earth systems behave and change under increased greenhouse gasses and increased warming. The study found that despite the climate being conducive to higher-order plants, the region’s vegetation was dominated by shrubs and tundra due to the reduced land available for plant growth caused by erosion resulting from glacial advances of the West and East Antarctic Ice Sheets. Another study presented geological evidence of large WAIS expansions from sediment samples obtained during Expedition 374 (Marschalek et al., 2021). The findings from Marschalek et al. (2021) supported the hypothesis  that during the intensely warm Miocene Period , East Antarctica experienced significant ice loss, which contradicted the view of other scientists who suggested that the ice in East Antarctica mostly remained intact during this period of time.

Expedition 374 also contributed to providing valuable information on the history of a volcano! A study by Di Roberto et al., (2021) examined a layer of volcanic ash, known as tephra, found in marine sediments in Antarctica’s Ross Sea (Figure 2). The tephra was estimated to be around 1.3 million years old and matched a deposit discovered at Chang Peak volcano, located 1,300 km away from the study site. This discovery adds a new reference point for dating and correlating early Pleistocene records in West Antarctica.

References

Di Roberto, A., Scateni, B., Di Vincenzo, G., Petrelli, M., Fisauli, G., Barker, S.J., Del Carlo, P., Colleoni, F., Kulhanek, D.K., McKay, R., De Santis, L., and the IODP Expedition 374 Scientific Party, 2021. Tephrochronology and provenance of an early Pleistocene (Calabrian) tephra from IODP Expedition 374 Site U1524, Ross Sea (Antarctica). Geochemistry, Geophysics, Geosystems, 22(8):e2021GC009739. https://doi.org/10.1029/2021GC009739

King, M.V., Gales, J.A., Laberg, J.S., McKay, R.M., De Santis, L., Kulhanek, D.K., Hosegood, P.J., and Morris, A., 2022. Pleistocene depositional environments and links to cryosphere-ocean interactions on the eastern Ross Sea continental slope, Antarctica (IODP Hole U1525A). Marine Geology, 443:106674. https://doi.org/10.1016/j.margeo.2021.106674

Lelieveld, N.J.C., 2022. Antarctic paleoenvironment and vegetation reconstructions during the early and middle Miocene using biomarkers from Ross Sea sediment drill cores [MS thesis]. Victoria University of Wellington, Wellington, NZ. https://openaccess.wgtn.ac.nz/articles/thesis/Antarctic_paleoenvironment_and_vegetation_reconstruction_during_the_early_and_middle_Miocene_using_biomarkers_from_Ross_Sea_sediment_drill_cores/21554862

Marschalek, J.W., Zurli, L., Talarico, F., van de Flierdt, T., Vermeesch, P., Carter, A., Beny, F., Bout-Roumazeilles, V., Sangiorgi, F., Hemming, S.R., Pérez, L.F., Colleoni, F., Prebble, J.G., van Peer, T.E., Perotti, M., Shevenell, A.E., Browne, I., Kulhanek, D.K., Levy, R., Harwood, D., Sullivan, N.B., Meyers, S.R., Griffith, E.M., Hillenbrand, C.D., Gasson, E., Siegert, M.J., Keisling, B., Licht, K.J., Kuhn, G., Dodd, J.P., Boshuis, C., De Santis, L., McKay, R.M., and the IODP Expedition 374 Scientists, 2021. A large West Antarctic Ice Sheet explains early Neogene sea-level amplitude. Nature, 600(7889):450-455. https://doi.org/10.1038/s41586-021-04148-0

McKay, R.M., De Santis, L., Kulhanek, D.K., Ash, J.L., Beny, F., Browne, I.M., Cortese, G., Cordeiro de Sousa, I.M., Dodd, J.P., Esper, O.M., Gales, J.A., Harwood, D.M., Ishino, S., Keisling, B.A., Kim, S., Kim, S., Laberg, J.S., Leckie, R.M., Müller, J., Patterson, M.O., Romans, B.W., Romero, O.E., Sangiorgi, F., Seki, O., Shevenell, A.E., Singh, S.M., Sugisaki, S.T., van de Flierdt, T., van Peer, T.E., Xiao, W., Xiong, Z., the Expedition 374 Scientists, 2019. Expedition 374 summary. In: Proceedings of the International Ocean Discovery Program, 374: College Station, TX (International Ocean Discovery Program). https://doi.org/10.14379/iodp.proc.374.101.2019.

Patterson, M.O., Levy, R.H., Kulhanek, D.K., van de Flierdt, T., Horgan, H., Dunbar, G.B., Naish, T.R., Ash, J., Pyne, A., Mandeno, D., Winberry, P., Harwood, D.M., Florindo, F., Jimenez-Espejo, F.J., Läufer, A., Yoo, K.-C., Seki, O., Stocchi, P., Klages, J.P., Lee, J.I., Colleoni, F., Suganuma, Y., Gasson, E., Ohneiser, C., Flores, J.-A., Try, D., Kirkman, R., Koch, D., and the SWAIS 2D Science Team, 2022. Sensitivity of the West Antarctic Ice Sheet to +2 °C (SWAIS 2C). Scientific Drilling, 30:101-112. https://doi.org/10.5194/sd-30-101-2022

113: Weddell Sea, Antarctica

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Ocean Drilling Program Leg 113: Weddell Sea, Antarctica

Location map of where sites were drilled during Leg 113. Figure from ODP Leg 113 Initial Reports, Introduction

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. 

Cross section of the Weddell Sea and Maud Rise, indicating where the sites were drilled with respect to water depth. Figure from ODP Leg 113 Initial Reports, Introduction

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. 

he Paleocene-Eocene Thermal Maximum (PETM) that occurs in Core 19 drilled from Site 690 during Leg 113. The snowy white sediments on the left (sections 1, 2) are full of microfossils. As the bottom of the ocean became more acidic with warming, the fossils were dissolved and the sediments became darker tan to brown in color (sections 3, 4, 5, CC on the right).

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).

130: Ontong Java Plateau

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Ocean Drilling Program Leg 130: Ontong Java Plateau

Location map for sites that were drilled during Leg 130 on Ontong Java Plateau. Figure from Leg 130 Initial Reports, Introduction

Ontong Java Plateau (OJP) is an oceanic plateau or region of elevated ocean crust that rises up higher than the surrounding ocean crust. The OJP was formed around 120 million years ago during the Cretaceous Period, and when it was first formed from volcanic processes, mainly the eruption of basalt (a volcanic rock) on the seafloor. Today, the OJP remains the largest oceanic plateau on Earth.  

The main objective of Ocean Drilling Program (ODP) Leg 130 was to drill a series of sediment cores from atop OJP, with the recovery of sediments aged from the late Cretaceous Period to the Recent. As OJP is a shallower-water region, shells of marine plankton, which are single-celled organisms, collect in great quantities in warm, shallow-water regions. Using properties of the sediments, the fossils themselves, and the chemical signatures from the shells of fossil plankton through time, scientists aimed to reconstruct the ancient climate in this region through time using the sediments recovered from OJP. The secondary objective of Leg 130 was to drill into the seafloor basalts on OJP to better understand the origin and development of the oceanic plateau.  

Thin section images of fossil plankton, called foraminifera, that are present in great numbers from the Leg 130 sections. These microfossils are tiny, and can only be viewed with the help of a microscope. Their tests are made of calcium carbonate, the same material as seashells you would find at the beach! Figure from ODP Leg 130 Initial Reports, Site 806

Leg 130 drilled a total of 5889 meters (3.65 miles!) of sediment and basalt, which amounted to a total of 639 cores. The recovered sediments were full of microfossils – tiny fossils that can only be viewed with the help of a microscope. Using these fossil-laden sediments, scientists were able to conduct studies related to evolution of marine plankton, and use the chemistry of fossil tests (shells), along with other properties of the sediments, to reconstruct ancient climate conditions. 

Some studies focused on how evolution of marine plankton occurs at sea (Hull & Norris, 2009) and when certain species evolved and went extinct from 23 million years ago to the Recent (Chaisson & Leckie, 1993). Scientists were also able to reconstruct atmospheric carbon dioxide (CO2; a greenhouse gas) levels for the past 20 million years of Earth’s history (Tripati et al., 2009, 2011). The early Pliocene (4.5–3.0 million years ago) was a time in Earth’s history when CO2 was at or near present-day conditions, and as such this time period is useful to investigate Earth systems processes and how they behave under elevated greenhouse gas concentrations. Across this time interval, scientists used chemical methods from Leg 130 cores to reconstruct of western equatorial Pacific sea surface temperatures (Wara et al., 2005). The sea surface temperature data from Leg 130 sites was compared with sea surface temperatures from eastern equatorial Pacific sites. Scientists found that during the early Pliocene, the equatorial Pacific Ocean had a reduced east to west temperature gradient, which resembles El Niño states today.  Reconstruction of atmospheric circulation patterns from Leg 130 sediments indicated atmospheric circulation and wind patterns began to resemble modern-day patterns around 900,000 years ago (McClymont & Rosell-Melé, 2005). 

An image of a core section that was drilled during Leg 130. This section shows darker colored lines that cross the core. These are trace fossils, or ancient tracks, trails, and burrows, from organisms that were moving through the sediments and feeding on organic matter. These traces are called Zoophycos. Figure from ODP Leg 139, Initial Reports Site 806

References

Chaisson, W.P., and Leckie, R.M., 1993. High-resolution Neogene planktonic foraminifer biostratigraphy of Site 806, Ontong Java Plateau (western equatorial Pacific). In Berger, W.H., Kroenke, L.W., Mayer, L.A., et al., Proc. ODP, Sci. Results, 130: College Station, TX (Ocean Drilling Program), 137–178. doi:10.2973/odp.proc.sr.130.010.1993

Hull, P.M., and Norris, R.D., 2009. Evidence for abrupt speciation in a classic case of gradual evolution. Proc. Natl. Acad. Sci. U. S. A., 106(50):21224–21229. doi:10.1073/pnas.0902887106

McClymont, E.L., and Rosell-Melé, A., 2005. Links between the onset of modern Walker circulation and the mid-Pleistocene climate transition. Geology, 33(5):389–392. doi:10.1130/G21292.1

Tripati, A.K., Roberts, C.D., and Eagle, R.A., 2009. Coupling of CO2 and ice sheet stability over major climate transitions of the last 20 million years. Science, 326(5958):1394–1397. doi:10.1126/science.1178296

Tripati, A.K., Roberts, C.D., Eagle, R.A., and Li, G., 2011. A 20 million year record of planktic foraminiferal B/Ca ratios: systematics and uncertainties in pCO2 reconstructions. Geochim. Cosmochim. Acta, 75(10):2582–2610. doi:10.1016/j.gca.2011.01.018

Wara, M. W., Ravelo, A. C., & Delaney, M. L. (2005). Permanent El Niño-like conditions during the Pliocene warm period. Science, 309(5735), 758-761.