Palaeoceanographic significance of contourite drifts

Contourites provide essential information on ocean circulation and past climate changes, which can be extracted using a wide range of geochemical, sedimentological, and geophysical research methods. This chapter provides a synthesis of the palaeoceanographic approaches and techniques that apply to the study of contourite archives. Three themes are introduced in which contourite research has brought, or has the potential to deliver, significant new insights into the ocean's role in Earth's climate system: (1) gateways, tectonics, and ocean circulation, (2) ocean circulation during warm climate extremes, and (3) rapid ocean-climate variability in the North Atlantic. These themes are not intended to represent all aspects of palaeoceanography in the realm of contourites but rather to demonstrate the range of time scales, from tectonic (millions of years) to human (tens of years), that may be extracted from sediments formed by persistent oceanic currents. The majority of palaeoceanographic studies on contourites have been performed in the Atlantic and Southern Ocean, while geophysical mapping and coring of contourite drifts in the Indian, Pacific, and Arctic Oceans are sparse. Thus, the potential for using bottom-current generated deposits as high-resolution archives on a global scale is far from being fully exploited. The role of ocean circulation, climate, and tectonic evolution during the Cenozoic is a prominent theme that is often addressed by deep-ocean drilling campaigns. The problems of extracting the control of ocean current dynamics from other factors like sea-level, climate regime and sediment properties (e.g. Faugères and Stow, 2008) demonstrate the need for multi-coring transects and more integrated seismic-sediment-proxy studies of contourite depositional systems and their bounding unconformities. High-resolution palaeoceanographic information provides "ground truthing" of the multitude of output scenarios generated by numerical modelling. Proxy records from rapidly accumulating muddy contourite deposits allow reconstruction of leads and lags between different parameters of ocean-climate change at multi-decadal time scales, thus approaching the resolution gained from ice-core archives. This information is crucial for a better understanding of global teleconnections, feedback thresholds and forcing mechanisms that determine the past and present climate system.