The first determined search for New South Greenland came during the Second German Antarctic Expedition, 1911–13, under Wilhelm Filchner. The expedition's ship, "Deutschland", had become trapped in heavy sea ice while attempting to establish a shore base at Vahsel Bay. Her subsequent north-westerly drift had, by mid-, brought her to a position east of Morrell's recorded sighting. Filchner left the ship on and, with two companions and sufficient provisions for three weeks, sledged westward across the sea ice in search of Morrell's land. Daylight was limited to two or three hours a day, and temperatures fell to −31 °F (−35 °C), making travel difficult. In these conditions the group covered , taking frequent sightings. They found no signs of land; a lead weight dropped through the ice reached a depth of before the line snapped, a depth which confirmed there was no land in the vicinity. Filchner concluded that what Morrell had seen had been a mirage.
On 17 August 1915 Sir Ernest Shackleton's ship "Endurance", trapped in the ice like "Deutschland" three years earlier, drifted to a point 10 miles west of Morrell's charted position. Here, a depth sounding recorded 1,676 fathoms (10,060 feet, 3,065 m), leading Shackleton to write: "I decided that Morrell Land must be added to the long list of Antarctic islands and continental coasts that have resolved themselves into icebergs". On a further sounding of 1,900 fathoms (11,400 feet, 3,500 m) gave Shackleton additional evidence of the non-existence of New South Greenland.
Although Filchner's and Shackleton's investigations and observations were accepted as conclusive proof that New South Greenland was a myth, there remained the question of Sir James Ross's reported appearance of land in a position around 65°S, 47°W. Ross's reputation was sufficient for this possibility to be taken seriously, and for his alleged sighting to be recorded on maps and Admiralty charts. In 1922 Frank Wild, leading the Shackleton-Rowett Expedition aboard "Quest" after Shackleton's death early in the expedition, investigated the location of Ross's sighting. Nothing was seen; prevented by ice conditions from reaching the exact spot, Wild took a sounding at 64°11'S, 46°4'W, which revealed of water. This showed that no land was near.
According to W.J. Mills, Morrell had the reputation among his contemporaries as "the biggest liar in the Southern Ocean". Mills calls the westward journey from Morrell's claimed farthest east position "impossible ... unbelievably fast, quite apart from lying south of the coastline for much of the way". In search of an explanation Mills suggests that since Morrell's account was written nine years after the voyage he may not have had access to the ship's log, and hence may "have felt constrained to invent details that appeared plausible" in order to sustain his narrative. This would explain the profusion of positional and date errors.
Hugh Robert Mill, writing in 1905 before the non-existence of New South Greenland had been proved conclusively, refers to the sheer absurdity of some of the incidents described in Morrell's account, and concludes that because of Morrell's blunders, and his habit of incorporating the experiences of others into his story, all his claims must be treated as not proven. Nevertheless he concedes that "a man may be ignorant, boastful and obscure, and yet have done a solid piece of work". Canadian geographer Paul Simpson-Housley adopts a more sympathetic approach. Although dubious about much of Morrell's account, Simpson-Housley suggests that the speeds claimed for the western journey, though fast, are not impossible. He believes that the claimed farthest south in the Weddell Sea, queried by Mill, is entirely plausible, given that James Weddell had sailed four degrees further south just a month earlier.
Another inclined to defend Morrell's integrity is the writer Rupert Gould, who included a lengthy essay on New South Greenland in his collection "Enigmas", published in 1929. The assumption that the New South Greenland sighting was simply invented by Morrell is dismissed, primarily on the grounds of the very little weight given to the discovery in Morrell's 500-page account. Gould writes: "If Morrell wished to gain an undeserved reputation as an Antarctic explorer, one would think he could have gone a better way about it than to bury his "pièces justificatives", after he had forged them, in an undistinguished corner of so bulky a book." In the relatively few pages devoted to the Antarctic, Morrell's account of his discovery is brief and entirely matter-of-fact, crediting it to Captain Johnson two years earlier rather than to himself.
Gould also discusses the possibility that what Morrell sighted was indeed the eastern coast of Graham Land, the so-called "Foyn Coast", despite its being 14° further west from position of the New South Greenland sighting. In support, Gould asserts that the peninsula's eastern coast corresponds very closely with the stretch of coastline described by Morrell. This theory supposes that Morrell miscalculated the ship's position, perhaps because he lacked the chronometer necessary for proper navigational observation. In his account Morrell writes that he was "destitute of the various nautical and mathematical instruments", but other parts of his narrative make it clear that the occasional dead reckoning calculation was the exception to the norm. In any circumstances a longitudinal error of 14° is very large, and the additional distance of about to the Foyn coast seems too great to have been covered within the ten-day voyage from the South Sandwich Islands, where the ship's position is recorded accurately. Even so, Gould maintains that a "balance of evidence" shows that what Morrell saw was the Foyn coast.
Filchner's view that the supposed sighting of New South Greenland could be explained by a mirage is echoed by Simpson-Housley. He suggests that Morrell and his crew saw a superior mirage. One form of superior mirage, sometimes described as a Fata Morgana, distorts distant flat coastlines or ice edges both vertically and horizontally, so they can appear to have tall cliffs and other features such as high mountain peaks and valleys. In his expedition account "South", Shackleton gives a description of a Fata Morgana observed on 1915, coincidentally as his ship "Endurance" drifted close to the recorded position of New South Greenland: "The distant pack is thrown up into towering barrier-like cliffs, which are reflected in blue lakes and lanes of water at their base. Great white and golden cities of Oriental appearance at close intervals along these cliff-tops indicate distant bergs ... The lines rise and fall, tremble, dissipate, and reappear in an endless transformation scene".
Morrell's four voyages finally ended on 1831, with his return to New York. He then wrote his "Narrative of Four Voyages", which was published the following year. He attempted to resume his seafaring career, seeking employment with the London-based shipping firm of Enderby Brothers, but his reputation had preceded him and he was rejected. Charles Enderby stated publicly that "he had heard so much of him that he did not think fit to enter into any engagement with him." Morrell also sought to join Dumont D'Urville's expedition to the Weddell Sea in 1837, but his services were again declined. He reportedly died in 1839, and is commemorated by Morrell Island, 59°27'S, 27°19'W, an alternative name for Thule Island in the Southern Thule sub-group of the South Sandwich Islands. Robert Johnson, who coined the name New South Greenland, disappeared with his ship in 1826, while investigating the Antarctic waters in the vicinity of what would later be known as the Ross Sea.
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