Ocean Drilling Program Leg 130: Ontong Java Plateau
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.
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).
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.