Challenges in Mesozoic paleoceanography

The Cretaceous ocean was unusual in many aspects and provide opportunities to explore, quantify, and model processes that might impact our current ocean in the (near) future. A pressing issue for humankind is the understanding of the future state of the planet within the context of increasing carbon dioxide (CO2) and other greenhouse gas concentrations, climate change, and the adaptations or extinctions in the Earth\u2019s biosphere in response to Anthropocene perturbations. The ocean is the oldest and largest ecosystem on Earth, and biodiversity changes at one trophic level (primary producers) lead to a variety of responses at higher levels. To predict future effects of increasing atmCO2 and other greenhouse gases, global warming, sea level rise, ocean acidification, and eutrophication, short-term current changes require integration with long-term variations. Thus, the geologic record of past environmental perturbations is relevant for understanding current and future global changes, biotic responses, and how and at what rate pre-perturbation conditions are eventually restored. Cretaceous examples of coupled excess CO2 (and other greenhouse gases) and extreme climates are also associated with global anoxia, making the recognition of individual causes and their role extremely challenging. Major information on Cretaceous oceans was obtained from the early stages of scientific ocean drilling (DSDP), and augmented subsequently (ODP), but significant geographic and stratigraphic limitations prevent a thorough understanding of the causes and consequences of environmental changes. Cretaceous sediment in the global ocean is largely under-sampled, despite its vast geographic extent. Moreover, Cretaceous pelagic sections from the Pacific and Indian oceans, characterized by alternating hard-soft (e.g., chert-chalk) layers, have been exceedingly difficult to core dur\uacing DSDP, ODP, and IODP. It remains a major technical challenge to improve upon sparse core recovery in such section, and lack of such sections pre\uaccludes systematic studies of the geological past and applications to our future. An ad hoc Magellan Workshop will be held in April 2013 to foster new scientific (ocean and continental) drilling projects that will advance understanding of the Cretaceous world, and develop a long-term strategy of drilling targets. Some priority targets require Chikyu, a unique platform that has deep riser drilling capabilities to core (and recover) Cretaceous sedimentary sections. This white paper focuses on major challenges in Mesosozic paleoceanography\u2014Oceanic Anoxic Events, (super)greenhouse climates, marine biota and environment co-evolution\u2014in the Pacific Ocean and the in situ Tethys. In the Pacific, Chikyu riser drilling will allow good recovery of Cretaceous and Upper Jurassic sedimentary sections from the Magellan Rise, Shatsky Rise, Ontong Java Plateau, Manihiki Plateau, Hikurangi Plateau, and Hess Rise, where chert and chert-chalk alternations have hampered core recovery. The POP (Pacific Ocean Plateaus) project comprises a number of sites located in water depths currently within Chikyu\u2019s range ( 642500 m); other key sites in greater water depths (2500-4000 m) may be drilled when Chikyu gains such capabilities. Recent investigations suggest that the Ionian Abyssal Plain of the Eastern Mediterranean might be the oldest in situ ocean fragment of the world, with ocean crust of Late Triassic age. Here, the TOIS (Tethys Ocean In Situ) project proposes to sample a Cretaceous-Jurassic and Upper Triassic section uncontaminated by the Alpine orogeny and subsequent tectonics. The current water depth of the Ionian Abyssal Plain is ~4000 m, and the sedimentary section is estimated to be ~ 7000 m thick. Coring of Tethys in situ is thus an extremely ambitious target comparable to the Moho project.The deep riser-drilling vessel Chikyu is the only scientific platform capable of retrieving key data from the oceans and provides the scientific community with the opportunity to reach targets inaccessible by any other platform. Implementation of its technical capabilities in the next decade (greater water depths and deeper drilling) will be constitute milestones in scientific exploration of ocean and Earth history