Research: The Sediment Record of the Deep-Sea Circulation

Sampling deep sea muds in a box core, western Indian Ocean, 2001

My research aims to understand how the modern deep ocean circulation shapes the sea bed and controls the distribution of sediment types, grain-sizes and bedforms. I then apply that understanding to interpretation of the geological record of the changing deep-sea circulation in piston and gravity cores for the late Pleistocene, and Ocean Drilling Project cores for the Neogene and earlier Pleistocene. Insight developed over the last 30 years concerning mechanics of fine sediment erosion, transport, aggregation and deposition shows that sediments become more cohesive, and all form aggregates, below 10 µm grainsize, but above that size they increasingly behave non-cohesively and are sorted by prevailing currents. This 'sortable silt' (10-63 µm) has a mean size that provides a proxy for depositional current speed and allows insight into changes in deep circulation vigour.

The deeper objective is to understand the impact of climate change on the deep sea (and vice versa). Part of the meridional heat flux on earth is carried by warm surface ocean currents with a corresponding cold deep return flow. We look for good monitoring points for these deep flows and have studied the inflow to the North Atlantic south of Iceland, and the deep inflows to the Pacific east of New Zealand and Indian ocean east of Madagascar. Among our recent striking results are the discovery of a Holocene ~1500 year variability in the flow south of Iceland, matching the Mediaeval Warm Period - Little Ice Age climate changes, flow changes at the inception of the Antarctic circum-polar current, and Southern Ocean control of flow in the glacial deep N. Atlantic

Hypothetical variation of deposition rate with flow speed. The 20 cm/ka maximum is arbitrary (from McCave and Hall, G3, 2006) Contourite muds from the Indian ocean where the flow went too fast and produced a winnowed foram sand layer with a sedimentation rate at least 10x lower than the 2 cm/ka of muds above and below (from McCave, in Hillaire-Marcel and de Vernal (eds) 2007)

Older Publications by Professor Nick McCave

Publications: 2006-Present

Last updated on 22-Jun-10 10:32