A recent major calving of the Ross Ice Shelf has implications for estimates of mass balance of the ice shelf, iceberg-calving rates, and our knowledge of ocean currents in the vicinity.
The calving
The mega-giant B-9 iceberg calved from the Bay of Whales, in the eastern Ross Ice Shelf to the western Byrd Land coast, in late September-early October 1987. Measuring 154 km × 35 km, it averages probably about 240 m thick and has a volume of 1100 km3. The total volume calved (1200 km3) is about eight times the average annual calving rate of the Ross Ice Shelf as estimated by Reference Jacobs, MacAyeal and ArdaiJacobs and others (1986), and is 30–100% of the annual rate of iceberg production from the whole Antarctic ice sheet.
Major calvings are episodic
It is now well known that such major calvings are episodic. The front of the ice shelf in the east was further north than it had been (Reference Jacobs, MacAyeal and ArdaiJacobs and others, 1986) this century. Clearly, the ice front does not maintain a precise equilibrium position. Major calvings may produce changes in strain-rates up-flow and in iceberg distribution.
Iceberg movement
B-9 and icebergs calved in the same event are providing information on sea currents near the Ross Ice Shelf. B-9 moved west initially then collided with the ice shelf, thereafter rotating anti-clockwise and drifting north-west to north. This north-west drift may be forced in part by an outflow from beneath the eastern Ross Ice Shelf, which might affect basal conditions there. Meanwhile, co-calved icebergs drifted parallel to the ice front at up to 11 km/d, five times as fast as B-9. The northward drift ended in late May. Between early July and mid-August 1988 B-9 moved southward in long. 172–173 °W, possibly forced by the warm core current flow mentioned in Reference Jacobs, MacAyeal and ArdaiJacobs and others (1986).
Acknowledgement
I am grateful to the U.S. Navy/NOAA Joint Ice Center in Maryland, U.S.A., for sending me B-9 position data, and to H.J. Zwally for size information.
