Paleogene Climate and Deep-water Evolution in the Southwest Atlantic: Seismic Reflection and Coring Investigations in Support of IODP Proposal 862-Pre

Lead Research Organisation: NERC British Antarctic Survey
Department Name: Science Programmes

Abstract

The present-day Southwest Atlantic Ocean is a key region for: (i) the communication of deep waters between the Pacific and Atlantic ocean basins via the Antarctic Circumpolar Current (ACC); and (ii) the dispersal of deep waters produced on the Antarctic margin that fill the deepest parts of the ocean basins. The ACC is the largest oceanic current system on Earth and flows unimpeded clockwise around the Antarctic continent. Across the Drake Passage (a narrow, but deep trough between Antarctica and South America) the average volume transport of the ACC is enormous, estimated at 100 to 150 million cubic meters per second. The ACC is therefore the major conduit for surface and deep-water communication between the Pacific and Atlantic Oceans. Without this connection, global overturning circulation would not be possible, which, in the modern ocean, regulates the global transport of heat, salt, nutrients, and carbon and has a significant influence on global climate across all timescales.

Our proposed project is developed to tackle several fundamental questions concerning the Paleogene time interval (~66 to 23 million years ago) that have frustrated marine geologists and palaeoclimatologists for decades:

When was the ACC initiated?

What was the impact of its establishment on Antarctic climate, on overturning circulation, and global latitudinal heat transport?

Did the development of the ACC serve as the trigger for the initiation of Antarctic glaciation 34 million years ago or was its role completely secondary to that of declining atmospheric carbon dioxide levels?

New insight into these problems can only be gained through new geological studies in key areas, such as the Southwest Atlantic Ocean.

A major problem with previous palaeoceanographic studies in the Southwest Atlantic has been the lack of a depth-transect of sites, purposely situated to trace Paleogene changes in water mass properties. In this region, complex seafloor bathymetry restricts and controls the flow of both deep waters associated with the ACC and Antarctic-sourced bottom waters. The evolution of the deep passageways in this area, and their connection to the progressive development of the modern patterns of deep-water circulation, are unknown.

We propose a UK-IODP Site Survey Investigation (SSI) to undertake seismic reflection survey and piston coring operations on the eastern Falkland Plateau region of the sub-Antarctic southwest Atlantic Ocean. Together with a companion Alfred Wegener Institute (AWI) cruise, these survey data will allow development of a full proposal for a new International Ocean Discovery Program (IODP) expedition to drill a depth transect of sites. These sites have been chosen to serve as a geological water mass gauging station that will allow reconstruction of deep-water circulation patterns through the Paleogene. Our primary aim is to test long-standing competing hypotheses on the relative roles of declining atmospheric carbon dioxide and the initiation of the ACC in driving the onset of Cenozoic cooling and Antarctic glaciation.

The UK-IODP SSI datasets, together with data derived from the companion cruise led by AWI, will contribute new understanding of deep-water sedimentary processes, the history of drift sedimentation and bottom-current erosion in conjunction with the evolution of deep-water flow, and sediment characteristics of the Southwest Atlantic Ocean. The combined results of the UK-IODP SSI and AWI cruises will function as stand-alone, publishable datasets of interest to a large community of marine geologists and palaeoceanographers, and provide a robust foundation for a UK-led IODP drilling proposal in time for planned JOIDES Resolution operations in South Atlantic.

Planned Impact

a) Who could benefit from the research?

Identified user groups for the new knowledge that we will create include: (1) Those working in the hydrocarbon exploration industry utilising sequence stratigraphic models globally to predict shelf and deeper water plays. In this context a major specific beneficiary is Neftex, a rapidly expanding UK geoscience consultancy, the largest employer of geoscience graduates in the UK, specialising in developing products and services to support the resource exploration industries (see letter of support, Dr Andrew Davies). (2) Those working to define UK territorial sovereignty, to sustain an active and influential presence and a leadership role in South Atlantic affairs, and those with an interest in offshore science, resources, and conservation in the region. Specific beneficiaries include the HMG's Foreign & Commonwealth Office, FCO and the governments of the UK Overseas Territories of the Falkland Islands and South Georgia and the South Sandwich Islands. (3) Members of the general public interested in the physical and natural science of remote and environmentally sensitive high-latitude regions.

b) How might the potential beneficiaries benefit?

Hydrocarbon exploration:
Our immediate survey area is not itself currently (or soon likely to be) an area of active hydrocarbon exploration but it is directly adjacent to the Falkland Basin where exploration is intense (see Fig. 4 Case for Support). (1) We will help to characterize the tectonic and sedimentary history of the Falkland Plateau and the margin of the Falkland Basin with our planned geophysical and piston core work. (2) We will train two post-doctoral researchers in skills that are in demand in the oil and gas sector of the Petroleum Industry, with skills development in the acquisition, processing and interpretation of multichannel seismic reflection data and drill-core logging, dating, correlation and environmental analysis. (3) We will acquire site survey data for an IODP proposal to drill in a remote region where data is extremely sparse.

Specific examples of where exchange of information will contribute to the UK knowledge base in a key subject for petroleum exploration include: (i) New knowledge on the kinematic history of the breakup of Gondwana and opening of the South Atlantic. (ii) Knowledge of the timing and cause of build-up of ice sheets in the Southern Hemisphere, which will have important implications for high southern latitude petroleum exploration and global models of sea-level change for the past 65 million years. (iii) Provision of an improved sequence stratigraphic reference tool to help with the the stratigraphy of newly discovered reservoirs globally. (iv) Precise age dating of sedimentary units on Maurice Ewing Bank will help constrain the stratigraphy of the Falkland Basin through direct correlation of IODP drillholes to the interior of the basin via seismic stratigraphy, and development of well-calibrated regional biostratigraphies that can be applied to industry wells.

Offshore Interests:
Our work will contribute to the knowledge base in a region where data is sparse but where there is UK interest to demonstrate presence and influence and to define territorial sovereignty beyond 200 nautical miles (UK Submission no. 45 to United Nations Division for Oceans & the Law of the Sea Commission on the Limits of the Continental Shelf). The UK, under the UN rules of procedures, can add new data to its case over time. The new UKIODP and AWI seismic lines will bear on our understanding of the East Falklands Plateau and make a substantial addition to the geological and geophysical database that underpin the UK case. NERC also recognises that (i) curiosity-driven environmental science such as our project delivers benefits to society that are initially unforeseen and (ii) our international approach fosters economic growth and creates opportunities for UK leadership and competitive advantage.

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