The Mertz Glacier Tongue, East Antarctica. Changes in the past 100 years and its cyclic nature - past, present and future

The Mertz Glacier Tongue (MGT) in East Antarctica has been studied since 1911. Early expeditions produced maps using ground or ship-based observations followed later by vertical and/or oblique aerial photography from aircraft. In the modern era, extensive digital satellite imagery is available which has also been supplemented by the resurrection and scanning of some historic U.S., now ‘declassified’, film-based satellite images. Much of the MGT became detached and drifted away following the collision by the B-9B iceberg in February 2010 and a similar sequence, or extension-detachment cycle, must have occurred some-time after Mawson's 1911–1914 observations. All the available information on the position, shape or appearance of the MGT has been re-examined in an attempt to comprehensively study its past, present and possible future motion. Feature tracking cross correlation methods have been applied for suitably detailed image pairs to accurately measure the MGT advance velocity. The derived mean rate for 1947–2010 is 1180 ± 14 m y− 1 with an accompanying ice-front loss rate of ∼ 190 m y− 1. A simple model for the MGT exhibits a ∼ 73 year quasi-periodic cycle of rebirth, growth and demise which will affect the volume of bottom water produced in the nearby polynya. Some evidence for this cyclic oceanographic change has recently been reported from regional sediment data. Somewhat speculatively, the model suggests a date of ∼ 1937 for the previous MGT break-off and around or before ∼ 2083 for the next. With the MGT being primed to break-off every ∼ 73 years, the precise date being governed by unpredictable external events such as collisions by large icebergs, such cycles have probably occurred for many thousands of years