Heavy sea ice conditions have thwarted a science mission from reaching the Larsen C Ice Shelf in Antarctica from which a large iceberg broke off in July 2017. A team of scientists, led by British Antarctic Survey (BAS), are travelling on board the RRS James Clark Ross. Sea ice, up to 4-5 metres thick, has made progress for the ship very slow. On Wednesday (28 February) the ship’s captain made the difficult decision not to continue. 
 
 Marine biologist and Principal Investigator, Dr Katrin Linse, from British Antarctic Survey is leading the team. She says: “We knew that getting through the sea ice to reach Larsen C would be difficult. Naturally, we are disappointed not to get there but safety must come first. The captain and crew have been fantastic and pulled out all the stops to get us to the ice shelf, but our progress became too slow, with just 8kms travelled in 24 hours and we still had over 400kms to travel. Mother Nature has not been kind to us on our mission! “But we have a ‘Plan B’, we will head north to areas which have never been sampled for benthic biodiversity. The Prince Gustav Channel Ice Shelf and neighbouring Larsen A Ice Shelf collapsed in 1995. We’ll be sampling deeper than we planned at Larsen C – down to 1000 metres – so we’re excited about what deep sea creatures we might find.” 
 
 The international team, from nine research institutes, will spend the remainder of their mission collecting seafloor animals, microbes, plankton, sediments and water samples using a range of equipment, including video cameras and a special sledge pulled along the seafloor to collect tiny animals. Their findings will provide a benchmark of the seafloor biodiversity in this area and provide a more accurate timeframe for retreat of ice sheets from the eastern side of the Antarctic Peninsula. 
 
 Researchers are already planning more missions to access the Larsen C ice shelf. Dr Katrin Linse and colleagues have teamed up with the Alfred Wegener Institute in Germany to visit in 2019 on their research vessel the RV Polarstern. 
 
 The research expedition to the Larsen C Ice Shelf is funded by the Natural Environment Research Council (NERC). The giant iceberg known as A68, which is four times the size of London, calved off from the Larsen Ice Shelf in July 2017. The scientists planned to collect samples from the newly exposed seabed, which covers an area of around 5,818 km2. 
 
 The Larsen C research expedition is led by British Antarctic Survey and involves scientists from the following research institutes: University of Aberdeen, University of Newcastle, Natural History Museum, University of Ghent, University of Southampton, Alfred Wegener Institute in Germany, Senckenberg Research Institute and Museum in Germany, University of Gothenburg in Sweden and Museums Victoria in Australia. ||||| When on 21st November 1915 the polar explorer ship Endurance finally yielded to the Antarctic pack ice, Ernest Shackleton and his crew began one of the most gruelling survival attempts in history. 
 
 Their five-month ordeal on the ice floes followed by the all-or-nothing 720-nautical-mile dash to South Georgia has since become the stuff of legend, pored over by scholars and adventurers for more than a century. 
 
 But of the ship itself, no trace has been detected since the day it went down. 
 
 On Monday, a British-led team announced it was setting out to find the wreck of Endurance, thought to be at rest nearly two miles beneath the Larsen C Ice Shelf in the Weddell Sea. 
 
 Operating from the research vessel SA Agulhas II, the expedition will use the most advanced unmanned submarines in the world to scour the sea bed. ||||| Media playback is unsupported on your device Media caption Prof Julian Dowdeswell: "Sea-ice conditions mean we cannot guarantee to get where we want to" 
 
 A scientific expedition will next year try to find the Endurance, the ill-fated ship of Antarctic explorer Sir Ernest Shackleton. 
 
 The vessel sank in 1915, crushed by sea-ice in the Weddell Sea and lost in 3,000m of water. 
 
 Shackleton and his crew were forced into lifeboats to make an extraordinary and heroic escape across the Southern Ocean. 
 
 UK researcher Prof Julian Dowdeswell will lead the international effort. 
 
 He expects to have the cruise on station in January/February. 
 
 Locating the shipwreck is not the primary goal of the expedition; the major objective is to visit and study the Larsen C Ice Shelf, which last July calved one of the biggest icebergs ever recorded in Antarctica. 
 
 But because Larsen is so close to the last known position of the Endurance, it makes sense to also have a go at finding the famous ship. 
 
 "It would be a shame not to," said Prof Dowdeswell, the director of the Scott Polar Research Institute (SPRI) in Cambridge. 
 
 "In our study of Larsen, we will be operating autonomous underwater vehicles (AUVs). But if we can get them in range of where Endurance is thought to be, we will send them under the ice to do a survey. 
 
 "They are fitted with downward-looking multi-beam echosounders, which can map out on a grid the shape of the seafloor. You look at that for any signs of the ship and then focus in with cameras if you find something interesting." 
 
 Image copyright RGS Image caption Endurance just before it sank: Crushed at the stern, it went down bow first 
 
 It is a very tough challenge. The sea-ice in the Weddell Sea is notoriously thick and uncooperative, as Shackleton found to his cost. 
 
 Even today's technology struggles in the region. An expedition led by the British Antarctic Survey tried to get close to Larsen C earlier this year and was thwarted by the marine floes. 
 
 Prof Dowdeswell is hoping for better luck and believes the range and capabilities of the AUVs, provided by the American company Ocean Infinity, give the expedition the best possible chance of success. 
 
 The venture is formally called the Weddell Sea Expedition 2019. It is funded by The Flotilla Foundation, a charitable trust in the Netherlands. 
 
 Prof Dowdeswell's team brings together a wealth of expertise from the SPRI, the Nekton Foundation, the University of Canterbury in New Zealand, as well as the University of Cape Town and the Nelson Mandela University in Port Elizabeth, South Africa. 
 
 Image copyright OCEAN INFINITY Image caption Ocean Infinity's technology is currently looking for missing airliner MH370 
 
 The 45-day expedition will operate from the SA Agulhas II, a modern polar research vessel. 
 
 Larsen C is one of the largest ice shelves in Antarctica. It is the floating extension of glaciers that have flowed off the eastern side of the Antarctic Peninsula and joined together to form one giant buoyant platform. 
 
 Its northern neighbours, Larsen A and Larsen B, suffered catastrophic break-ups in 1995 and 2002, respectively. 
 
 These failures unbound the feeding glaciers behind, allowing them to move faster and dump yet more of their ice in the ocean, raising global sea-levels. 
 
 The production of a near-6,000km² berg last year now has experts wondering whether Larsen C is also being set up for a collapse. 
 
 Media playback is unsupported on your device Media caption Dr Christine Batchelor is interested in the past positions of glacier grounding lines 
 
 The Weddell Sea Expedition will try to answer this question by getting in close and making a series of geophysical measurements. 
 
 The AUVs will be sent into the cavity under the shelf to map the seafloor and the overhanging ice canopy. 
 
 Drill cores will also be taken from just in front of the shelf. The aim is to establish the past history of ice advance and retreat, to look for old grounding lines - the locations where Larsen's feeding glaciers have previously rested on the seafloor. 
 
 Have these lines moved back and forward on a fairly regular basis, or have they only ever retreated and at what rate? 
 
 "We want to try to put the recent changes that we've seen at the peninsula into their longer-term context," said Dr Christine Batchelor, a SPRI fellow who will be an expedition team-member. 
 
 "We only have satellite observations for the last few decades. We want to see how those changes fit in when we look over much longer timescales - over hundreds and thousands of years. 
 
 "Is what we've been seeing typical behaviour, or something more unusual," she told BBC News. 
 
 Dr Batchelor was speaking here at the European Geosciences Union (EGU) General Assembly in Vienna, Austria. However, the Weddell Sea expedition will be formally announced in London at the Royal Geographical Society. 
 
 Image copyright RGS Image caption Endurance is acknowledged to be one of the great undiscovered shipwrecks 
 
 For the SPRI to be connected with the discovery of the Endurance would be fitting. 
 
 The institute is, in many ways, the keeper of records for Britain's "heroic era" of polar exploration. 
 
 In its archives are documents related to Endurance skipper, Frank Worsley. It is he, with sextant and chronometer, who calculated the vessel's sinking position on 21 November 1915 as 68°39'30.0" South and 52°26'30.0" West. 
 
 This is roughly 100-150 nautical miles east of Larsen C. 
 
 If sea-ice conditions are favourable, the SA Agulhas II is likely to have company on its voyage. The German research ship Polarstern also plans to visit the region of the newly calved iceberg. Its cruise will be led by the Alfred Wegener Institute in Bremerhaven. 
 
 Jonathan.Amos-INTERNET@bbc.co.uk and follow me on Twitter: @BBCAmos
– Sir Ernest Shackleton's doomed ship slumbers beneath nearly 10,000 feet of water—and a group of scientists now hopes to find it. The BBC reports on the planned January 2019 mission, whose true intention is to study the Antarctic's Larsen C Ice Shelf. But its position near the Endurance's final recorded location in the Weddell Sea proves too tempting to ignore. The plan, says lead researcher Julian Dowdeswell, is to take the autonomous underwater vehicles that will be used in their examination of Larsen C and send them under the ice in the area where the Endurance was thought to have gone down in 1915. The AUVs' echo sounders will map the seafloor, searching for anything anomalous—assuming things don't go south. The BBC notes that a February 2018 mission to the Larsen C failed. The British Antarctic Survey behind it explains the sea ice its ship encountered was up to 16 feet thick, and in 24 hours they made it just 5 miles, with more than 250 to go. The Times of London reports Dowdeswell and his team will sail on the SA Agulhas II, a Polar Class 5 ship that can break ice roughly 3 feet thick. That's not good enough, says American shipwreck hunter David Mearns, who also covets the Endurance and thinks a Polar Class 3 ship is needed. "Whatever ship you have, it's possible it won't get there," Dowdeswell allows. "It could be a better or worse sea ice year." Shackleton's survival story is legendary: After abandoning ship, he and his crew survived on ice floes for five months; five days at sea in lifeboats brought them to Elephant Island, and Shackleton and a few others then set off on a 720-nautical-mile voyage to South Georgia, per the Telegraph. (This Antarctic explorer turned back—too late.)