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doi:10.2204/iodp.sp.342.2011 IntroductionOn 15 April 1912, the RMS Titanic, en route westward from Southampton, England, to New York City, USA, hit an iceberg off the Grand Banks of Newfoundland and sank, killing more than 1500 people. The two halves of the wreck lie between the volcanic seamounts of the Southeast Newfoundland Ridge because there the southward-flowing surface waters of the cold Labrador Sea carry icebergs to their intersection with the warm tongue of the Gulf Stream. Today the Titanic is bathed by the Deep Western Boundary Current because these new abyssal waters pass at depth under the Gulf Stream on their circuit throughout the deep basins of the world oceans (Fig. F1). IODP Expedition 342 is designed to study the nature of this deep current system near its northern sources during the balmy climates of the Paleogene (65.5 to ~21.8 Ma). During the early Paleogene, global temperatures were considerably warmer than today and supported forests rather than ice sheets in the high polar latitudes (Greenwood et al., 2010). The early Paleogene greenhouse world represents a radiative forcing state that we are rapidly re-approaching. At current and projected rates of fossil fuel consumption, atmospheric greenhouse gas concentrations are set to rise to Paleogene levels in the next 80 y (National Research Council, 2011). How did the climate and ecosystems of the Paleogene world work? What should we expect in the next century? Although the Eocene is not a perfect analogue to the near future (Haywood et al., 2011), understanding Eocene climate dynamics will provide information on what to expect from a warmer planet. The primary objectives of our program are to obtain a depth transect of drill cores between ~5 and 2 km water depth. Because the ocean is layered, with different water masses formed in various parts of the planet arranged above one another, our depth transect of drill sites will permit a detailed reconstruction of the chemistry, circulation, and history of Greenhouse Earth. Furthermore, because we will target sediment drifts that accumulate faster than typical deep-sea sediments, we should also be able to reconstruct the history of a warm Earth with unusual fidelity. These two things—detailed assessment of the structure and circulation of the warm-world ocean and unusually detailed climate history—will help us test models of Earth’s climate and ecosystem evolution that have been difficult or impossible to resolve with typical deep-sea or land-based records of the Eocene. Our drilling target is J Anomaly Ridge and Southeast Newfoundland Ridge offshore Canada’s Grand Banks. The drill sites, not far from the Titanic’s resting place, are positioned to monitor the strength and chemistry of deepwater formation in the Atlantic as well as outflows from the Arctic basins through Baffin Bay and the Norwegian seaway (Fig. F2). Today, both the northward-flowing Gulf Stream and the southward-flowing Deep Western Boundary Current cross over the drilling area, leaving a record of their flow strength, chemistry, and biology in the sediment drifts beneath them (Fig. F1). The shape of the North Atlantic margin suggests that a similar current configuration occurred in the past, with any deep waters formed in the North Atlantic constrained to flow over the Newfoundland ridges. Therefore, Expedition 342 sites will be particularly useful to monitor the overturning history of the North Atlantic Ocean. The Newfoundland ridges are mantled with some of the oldest sediment drifts known in the deep sea and range in age from the Late Cretaceous to Paleogene. Pliocene–Pleistocene drifts in the northeastern Atlantic commonly have sedimentation rates of 4–20 cm/k.y. and therefore can be used to study rates of abrupt climate change (Channell et al., 2010). Previous drilling of drifts on Blake Nose (off the southeastern United States) revealed sedimentation rates in the middle Eocene of ~5–6 cm/k.y., far higher than the ~1 cm/k.y. rates typical of previous Paleogene-focused drilling targets (Norris et al., 2001b). If, as expected, the Newfoundland sediment drifts also have high accumulation rates, we will obtain records of warm-period climates and evolution with unusual fidelity, and these will be particularly useful for assessing rates of change in the Earth system during both transient episodes of extreme warming (analogous to the near future) and transitions form warm climates into the glaciated world. Expedition 342 is focused on the Paleogene record on the Newfoundland ridges. Although there is an extensive Cretaceous record of both drifts and fossil reefs in the seismic record, we do not have time to do justice to Cretaceous objectives without sacrificing our studies of the Paleogene system. Furthermore, although we will likely obtain a record from the majority of the Paleogene, our particular area of focus will be the middle Eocene to Oligocene interval where thick sediment drift deposits preserve unusually expanded records of the transition from the greenhouse world of the Eocene climatic optimum to the glaciated world of the Oligocene. Therefore, our expedition has four major objectives:
This drilling proposal completes the North Atlantic objectives laid out in a 1997 Marine Aspects of Earth System History (MESH) workshop on warm period dynamics and the Ocean Drilling Program (ODP) “Extreme Climates” program planning group (PPG) (see www.odplegacy.org/program_admin/sas/ppg.html). This proposal also addresses initiatives of the IODP Initial Science Plan in the areas of extreme climates and rapid climate change. Finally, our expedition takes up proposals of the recent National Research Council report Understanding Earth’s Deep Past: Lessons for Our Climate Future (National Research Council, 2011), which advocates focused efforts to resolve the timescale and use mechanisms of past hyperthermal events as possible analogues for future global change. |
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