Harrow and Hillingdon Geological Society

Previous Meetings

Ocean Drilling - a Journey to the South Atlantic

If all the presentations for the New Year are as good as this one we will be extremely lucky. This talk was a power-point presentation and the speaker was able to utilise all the facets of the computer technology very well. Since the voyage of HMS Challenger in 1872 a large number of investigations had been done, throughout the 20^th centure, to examine the composition of the oceanic floor, mineral deposits, temperature or topography.

In 1968 work was recommenced and by 2003 more than 1200 cores had been examined. The purpose of this expedition, which started in Rio de Janerio was to determine if core samples collected at Walvis Ridge off the west coast of Africa, would help unravel previous patterns of global warming. The actual collection and manipulation of the cores was quite a delicate procedure, each sample of 1.5 metre length, being divide into two halves, one for current examination, the other for future reference. There were hundreds of lab samples to be examined, just in Palaeontology.

It was apparent from data shown that there had been global cooling over the last 50 million years but over the last 25 million years CO₂ concentrations were low and can't be responsible for the cooling. Possibly the most significant investigation was that of the gas hydrates which are widespread throughout the world. They are methane in nature and obviously associated with organic deposits. These gas hydrates are unstable at warm temperature and low pressure. CH₄ has 62 times more heating effect than CO₂, and dissociates to form more CO₂ and water thereby reducing the pH of the ocean. These data are highly significant because by destabilizing the gas hydrates a runaway “greenhouse” effect will occur. In passing it was also suggested that an alteration in pressure could liberate gas hydrates, which could explain the effects known as the Bermuda triangle.

The Paleocene-Eocene event is assumed to be associated with a massive dissociation of gas hydrates. These led to a short-lived global warming in the ocean and atmosphere, a mass extinction of organisms in the sea and changes in the species on land.

We were shown slides of the crew, the port area and the research vessel itself including the labs. It was apparent that everyone was kept extremely busy and that peace and quiet was at a premium. There were masses of statistics, which I found a little difficult to absorb but overall it was a really interesting talk and no one could fault the speaker for her enthusiasm.

 

	The Joides Resolution portside, with the drilling rig clearly seen.
	The first core being gently brought on board.
	Dr. Daniella Schmidt and colleague enjoying the Paleocene Eocene boundary.
	Worldwide location of known and inferred gas hydrate systems on present-day continental margins [Kvenvolden, 1998]. Natural gas hydrate deposits were first discovered in the 80's. New deposits are regularly found. The red dot is the Blake Ridge one of the best investigated gas hydrate deposits. courtesy Gerald Dickens (Rice University)
	The seafloor and methane venting on Southern Hydrate Ridge [Tréhu et al., 2002]. A. carbonate sample from the top of the Pinnacle showing the porous nature of carbonates from this environment. B. A sample of sediment from near the seafloor at southern Hydrate Ridge showing hydrate lenses parallel to bedding connected to hydrate veins perpendicular to bedding. C. Landscape at southern Hydrate Ridge showing mounds covered by bacterial mats. A clam colony is seen in the right edge of the picture taken during an Alvin dive. D. Illustration of the complex biogeochemical relationships expected near the southern summit of Hydrate Ridge. courtesy Gerald Dickens (Rice University)
	Burning gas hydrates. (Sorry, no larger picture is available) Image by Geomar

 

Back to Top