In conversation with Dr Mark Belchier: the second deepest trench in the Atlantic Ocean - Vol 4 Sneak Peek

The South Sandwich Islands Trench is one of the ten deepest oceanic trenches in the world. Charlotte O’Neill speaks with expert, Dr Belchier, to learn more about this unique ecosystem and what you’ll find within it.

Article by: Charlotte O’Neill

Artwork by: Katie de Lusignan

The South Sandwich Islands trench is an isolated abyss, found where the South Atlantic and Southern Oceans meet. It hosts an array of unique and extreme environments, from deep sea volcanic ecosystems to deep sediment deposits. The trench was formed by the subduction of the South American plate beneath the much smaller South Sandwich continental plate. As the larger plate was sucked downwards, it created the Meteor Deep; exceeding 8000 metres. It is the deepest point of the South Atlantic, comparable in size to other more famous trenches, such as the Mariana or Puerto Rican Trench.

So what is it exactly that makes this particular oceanographic feature unique? We asked Dr Mark Belchier, Director of Fisheries and Environment for the UK Overseas Territories of South Georgia and the Sandwich Islands to find out more! 

So what is it that makes the Sandwich Islands Trench so unique? 

“What makes the environment interesting, apart from its overall depth, is that it is situated in one of the coldest and most stable marine environments in the world. When the trench was first discovered, ocean depths were usually measured by dropping a lead line to the seafloor. Now it’s a lot more sophisticated and multibeam echosounders can accurately record depths. In 2019, a survey of the entire trench was made by the vessel ‘Pressure Drop’. During the survey, the deepest part of the trench was found to be deeper than earlier estimates.

It is likely that there are many unique and endemic species living at depth in the trench that await discovery. It is probably a very stable habitat, because of its depth. The surface currents in that area are very strong, but little is known of the oceanography within the trench.  However,  a new British Antarctic Survey project aims to deploy oceanographic moorings in the region, to measure the flow of Weddell Sea water moving north away from the Antarctic continent, and how that interacts with the deep water trench.”

How hard is it to access the trench? 

“As with all trenches of that depth, hardly anyone has ever visited. It has been very difficult to put scientific monitoring equipment in these areas and the South Sandwich Islands are exceedingly remote. The whole region is partially ice-covered in the winter, so the seasonal sea ice is variable year on year. Although, in 2023, sea ice extent was at a record low.

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