The US National Ice Center refixed every tracked Antarctic iceberg on 13 August, six days after the previous fix. All 33 got a new date. Nine of them got the same coordinate they had before, to the last digit published. One of them, D33C, had gone 74.3 km due west, which is 12.4 km a day, roughly walking pace for a chunk of ice 82 square kilometres in area.
That spread, from nothing at all to twelve kilometres a day, is the interesting part. Icebergs are not a single population doing a single thing. Sort this week's 33 by how far they went and the list sorts itself by geography without being asked.
What moved
| berg | km, 7 to 13 Aug | area km² | position now |
|---|---|---|---|
| D33C | 74.3 | 81.7 | 61.5°S 53.8°W |
| C39 | 63.1 | 52.1 | 66.5°S 59.1°E |
| D33B | 57.8 | 320.7 | 60.8°S 52.8°W |
| D35 | 56.8 | 296.1 | 60.9°S 43.9°W |
| D32 | 53.7 | 106.4 | 58.9°S 37.6°W |
| A83 | 50.2 | 189.8 | 61.0°S 50.5°W |
| A81 | 38.0 | 1,341.8 | 59.2°S 51.2°W |
| A85 | 34.8 | 62.6 | 63.5°S 53.5°W |
Seven of those eight are in the same water: the Weddell Sea and the Scotia Sea, between 37 and 54 degrees west. The odd one out is C39, off Enderby Land at 59 degrees east, which ran 63 km west and is the only fast berg in the eastern hemisphere.
Now the other end of the list. The nine bergs whose coordinates did not change at all are D15B, D15D, C15, C18C, C21B, C30, C31, C36 and B22H. Every one of the nine is in the eastern hemisphere, and every one is close in to the coast. The eight fast bergs average 61.5 degrees south. The nine stationary ones average 66.7 degrees south, five degrees of latitude closer to the continent.
The obvious explanation is that the southern nine are aground and the northern eight are in open water riding the current out towards South Georgia. It is probably right and this site will not print it as a finding, because the Ice Center list does not record whether a berg is aground and we have not measured the seabed under any of them. What we have measured is the drift. The reader can do the rest.
Where the measurement stops
Positions come to two decimal places of latitude and longitude. At 61 degrees south that is about 1.1 km north to south and 0.5 km east to west, so anything under roughly a kilometre is not a movement, it is a rounding. Six bergs came in between 0.4 and 1.2 km this week and they are best read as "did not go anywhere much" rather than as slow drift. Eighteen of the 33 cleared a kilometre. The median berg moved 1.2 km in six days.
Two bergs are listed larger than they were last week. B22F went from 223.8 to 226.4 square kilometres and D35 from 290.7 to 296.1. Icebergs do not grow. Those are the analyst remeasuring an outline on a new image, and they are a useful reminder that the area column on this list is an estimate that gets redrawn, not a quantity being watched.
The list itself is a threshold list rather than a census. A berg gets a name and a weekly fix once it is large enough to matter to a ship, and it drops off when it breaks up below that. So the count changes by fracture at least as often as by melting, which is the same reason the title of largest iceberg in the world changes hands without anything having melted.
The big ones are the still ones
There is no relationship at all between how big a berg is and how far it went. The largest iceberg on the list, D15A at 3,037 square kilometres and a quarter of all 12,332 square kilometres of tracked berg area on its own, moved 0.44 km, which is under the measurement floor. D15B, at 611 square kilometres, did not move at all. Meanwhile D33C, at 82 square kilometres, covered 74 km, and A81, at 1,342 square kilometres and the second largest thing on this week's fast list, still managed 38.
The one berg most readers here will know by name is B09B, which knocked the Mertz Glacier Tongue off the coast of George V Land in February 2010 and then grounded in Commonwealth Bay that December, shutting a bay and taking an Adélie penguin colony with it. It moved 2.12 km this week and is still sitting off that coast at 66.07°S 143.15°E, 508.9 square kilometres, sixteen years later. We wrote up what it did to Cape Denison yesterday.
Why six days is not yet a track
PenguinTracker has been storing a daily snapshot of the Ice Center list since 1 August, and that store now holds three distinct positions for 14 of the 33 bergs, two for 12, and one for the remaining 7. Three points is a path with a corner in it. It is not yet a drift track worth drawing, and the honest thing to say is that another month of weekly refixes turns it into one.
What three points already give you is a total distance rather than a straight line. D33C has covered 242 km across its three fixes since 1 August, A81 186 km, D32 164 km and D33B 161 km. Add up every leg of every berg and the tracked Antarctic iceberg fleet has covered 1,343 km in a fortnight, most of it by eight objects in one sector of the Southern Ocean.
Every berg on the list has its own page here, with its area, its latest fix and its position drawn in a polar projection rather than in the web map projection that cannot render Antarctica at all. The underlying data is the free, keyless US National Ice Center tabular iceberg list, which is one file and updates about weekly.