2010 calving

In February 2010 about half of the Mertz Glacier Tongue, a piece of ice about 78 kilometres (48 mi) long and 33–39 kilometres (21–24 mi) wide and protruding 100 kilometres (62 mi) out into the Southern Ocean, broke away from the main body of the Tongue.^[3] The separation occurred around the 12 or 13 February along two existing rift lines on opposite sides of the Tongue.^[4] The event was helped in part when the large Iceberg B-9B collided with it. Iceberg B-9B is a 97 kilometres (60 mi) long by 30 kilometres (19 mi) wide remnant of Iceberg B-9 which broke off the Ross Ice Shelf in 1987^[5] and has recently ungrounded itself from Ninnis Bank to the east of the Tongue where it had been lodged for 18 years.

The newly formed iceberg has been named Iceberg C-28,^[6] because it is the 28th substantial iceberg to have broken off the Antarctic ice shelf, in the quadrant that faces Australia, since 1976. The iceberg is 400 metres (1,300 ft) high, has a surface area of 2,545 square kilometres (983 sq mi)^[7] and weights in at about 860 billion tonnes. According to Australian glaciologist Neal Young, such an event occurs once in 50 to 100 years.^[8] As the Tongue advances at 1 km per year this new iceberg represents about 70 years of glacier advance. Within 2 weeks the Mertz Iceberg rotated about the point of impact with B9-B and lay parallel with the coastline.^[9] The iceberg drifted westwards after the collision and in April 2010 hit a submerged peak which caused it to break into two pieces.^[10][11]

The flow of icebergs from the calved glacier tongue has reduced the effectiveness of the polynya west of Mertz Glacier that acted as one of Antarctica's major areas for the formation of dense Antarctic Bottom Water. The calving could affect future thermohaline circulation around Antarctica.^[12][13]