Thursday, 14 February 2013

8 - Mud - a love story

Feb 14th 2013

Isis measuring the temperature of sediment around one of the areas of diffuse flow on the seafloor. The sediment at 2300 metres depth is riddled with small depressions, some of which shimmer with warm water. We sample the sediment and characterise this diffuse flow.
If mud could talk, it would tell a tale of devotion to the ocean.

The heart can think of no devotion, 
Greater than being shore to ocean; 
Holding the curve of one position, 
Counting an endless repetition.

Robert Frost's iconic love poem identifies with the seashore, a parallel that extends literally deeper than Frost intended; Sediment and seawater sit side by side, far beyond the shoreline, where sinking material expelled from the waters above rests enduringly on the seabed. Since it is St. Valentine’s Day, I'm going to tell you why this material and its relationship to the waters above it fascinate me.

Natural organic and mineral waste collecting on the seafloor is chemically altered over time; Microbes living near the surface of the seafloor feed off the rain of organic matter and exhaust their available oxygen, such that life underground has to switch to alterative metabolites, like nitrate and metals, to survive. In doing so, they accelerate the making and breaking of chemical bonds in the sediments, dissolving some minerals and precipitating others - a process with potential to return dissolved constituents back to the ocean, and nourish its water for life thriving in the sunlight far above.

The sediment corer (centre) on the Isis  rack ready for deployment
During our "Geo" dives with Isis, we're collecting a series of sediment cores (intact sections of the ocean floor) from which we are sucking the fluids dispersed between the sediment grains, and analyzing their chemical composition down through the seafloor. Using this approach, we will be able to measure gradients between the dissolved constituents of seawater and the sediments to understand the direction and magnitude of chemical exchanges between them. We will compare samples from different locations around the Von Damm and Beebe Vent Fields to learn how these deep hydrothermal vents impact the give and take of chemical constituents between sediments and the oceans.

By Will Homoky

Sample processing in the ship's controlled-temperature laboratory. We filter the sediment fluids in a cold and oxygen-depleted environment, much like they are accustomed to beneath the sediment surface.

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