Looking at the Ward Hunt Ice Shelf, the specialist literature distinguished between “basement” ice that is relatively old and firn ice that is much younger. The “basement ice” period ended with the end of the “first ablation period” which Crary 1960 dated to ~1600 BP – a date which Lyons et al 1973 noted to reset uncomfortably with dates from Greenland ice core. “Basement ice” is marked by an angular unconformity with more recent ice and by a heavy dirt layer, which is the residue of many years of ablation. Some portions of the ice shelf were confidently dated as being relatively young by virtue of the absence of the dirt layer. Some recent ice shelf calving e.g. the large 1961-1962 break at Ward Hunt ice shelf or the small 2003 break at Ward Hunt ice shelf almost certainly do not contain any “basement ice”. The Hobson’s Choice ice island (discussed in Jeffries 2002) did not have any basement ice. At present, I don’t have information on calving from Ayles ice shelf.
Today I’d like to discuss the evidence from ice island T-3, which was a prominent feature of early exploration in this area, because it was the location of an exploration camp. Jeffries 2002 (an interesting survey) reported that ice islands were discovered by reconnaissance flights following World War II and were quickly attributed as being calved from the Ellesemere Ice Shelf. Jeffries 2002:
The first ice island, named T-1, was seen in 1946, when a U.S. Army Air Force (USAAF) reconnaissance mission over the Arctic Ocean reported a heart-shaped ice mass that had dimensions of 24-29 km and an area of about 500 km surrounded by sea ice (Koenig and others, 1952). Subsequently, ice islands T-2, T-3, T-4, and T-5 were observed from the air or identified on aerial photographs between 1946 and 1950 in the Arctic Ocean, and 59 unnamed ice islands were found in aerial photographs of the Canadian Arctic Archipelago taken in 1950 (Koenig and others, 1952).
Some interesting historical information on the scientific camp can be seen if you google “t3 ice island”.
The T3 ice island proved to have a very distinctive dirt layer – similar to the dirt layer in Ward Hunt basement ice. Crary 1960 radiocarbon-dated the dirt layer obtaining dates exceeding 3000 BP and hypothesized that it was older than the Ward Hunt ice shelf as follows:
T3 may be older than the ice shelf at the Ward Hunt island area. The outcropping of a heavy dirt layer on the edges of T3 was 10 to 15 meters higher than its location at the camp site on T3; the steep dip of the ice layers south of the Ward Hunt ice rise (Marshall 1955) are best explained by a rising of the land areas. The old strand cracks found at an elevation of more than 20 meters above the present active ones on the south side of the Ward Hunt ice rise are difficult to explain except by uplift of land. Using C14 ages of the marine shell samples, which give an uplift of about 0.5 meters per centurry, a minimum age of a few thousand years could be expected for both the ice island and ice shelf.
Crary and others attributed the origin of the T3 ice island to an earlier break-up of the ice shelf at Cape Yattersley – presumably taking place at some point subsequent to the Peary expedition in the 1890s, perhaps the warm 1930s.
The interesting aspect for interpretation of this class of evidence is that T3 is an attestation of the break-up of basement ice in the 1930s. Over 90% of the Ellesmere ice shelf is said to have already taken place. I am unaware of any evidence of recent break-up of basement ice at Ward Hunt ice shelf and the maps indicate that the basement ice has remained intact. Even if the Ayles calving includes basement ice (which cannot be discerned one way or the other from the information that I’ve seen), calving (of basement ice) seems to have been much more prevalent in earlier parts of the 20th century, suggesting that recent warming is not necessarily critical in whatever is going on.
Climate Audit 