Tag Archives: Thermohaline circulation

THE WEDDELL SEA AGAIN

2 Jan

Happy New Year!!

This January, Professor Julian Dowdeswell of the Scott Polar Research Institute will lead an international research team in the long planned expedition to the Weddell Sea. This expedition aims to investigate ice shelves around the Weddell Sea, particularly the Larsen C Ice Shelf. It also hopes to locate the wreck of Shackleton’s ship Endurance, which sank in the area in 1915.

The expedition’s progress and achievements will be followed internationally – in addition the Royal Geographical Society has created an educational programme aimed at engaging the interest of children from primary level upwards.

The Weddell Sea was discovered in 1823 by James Weddell, the British sea captain/ sealer, who sailed as far south as 74°15´S. It is a vitally important ecosystem – penguins, seals, whales, krill, corals and sponges thrive there. It is shaped as a huge bay; Coats Land (discovered by William Speirs Bruce in 1904) is at one extremity, the Antarctic Peninsula is on the other. It has been described as ‘the most treacherous and dismal region on earth’.[i]

An important aim will be to investigate the shapes of the ice shelf bases. Ice shelves stop ice from flowing outwards from the continent. Thinning of the ice shelves results in increased flow from the interior, which, in turn, causes a rising global sea level. The sea floor will be examined to assess the stability of the ice shelf.

Although the general circulation of oceans is determined by wind driven currents, the Weddell is one of few locations where deep and bottom water masses contribute to global thermohaline circulation. Bottom water is the lowest water mass with distinct characteristics in terms of physics, chemistry, and ecology and a temperature of -0.7 °C or colder. The thermohaline circulation is the motor of deep ocean currents and is driven by density gradients influenced by surface heat and freshwater fluxes. The description relates to thermo- temperature-and –haline, salt content.

The Larsen Ice Shelf, in the northwest part of the Weddell Sea, is named after Captain Carl Anton Larsen, master of a Norwegian whaling vessel who sailed along the ice front as far as 68°10′ S. in 1893. From north to south segments of the shelf are called Larsen A, B, and C (the largest), and Larsen D, E, F and G.

The 2019 expedition is focused on the Larsen C ice shelf from which a giant ice berg calved off in July 2017 (twice the area of Luxembourg), reducing the size of the iceshelf by approximately12%.

 

 

 

Dowdeswell and Shears[ii] explain in the ‘Geographical’ that measurements will be taken of salinity and temperature of the sea adjacent to the shelves, samples of marine life will be obtained and the sea ice thickness will be measured by aerial drones. Autonomous Underwater Vehicles will make echo soundings of the underwater shape of the ice shelf base, the roughness of which is a vital parameter in numerical modelling of future ice shelf stability. Ernest Shackleton’s Ship will be searched for.

Whether the team will be able to achieve these aims is uncertain — the conditions are so unpredictable that attempts to navigate south could be unsuccessful, but this expedition is of pivotal importance in attempting to obtain long-term prognostic information relating to global warming. I hope this important analysis of the Weddell Sea will be successfully accomplished.

[i] Henry, T.R.,1950,The White Continent

[ii] Dowdeswell, J. Shears, J. 2019, Geographical, p.10

 

 

 

 

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