A-68 was part of Larsen C, a section of the Larsen Ice Shelf. Scientists found the crack beginning to form in November 2016. Scientists assess that A-68 "didn't just break through in one clean shot, [but] it formed a lace-network of cracks first."[5] The resulting iceberg was around 175 km long and 50 km wide, 5,800 km² in area, 200 m thick and weighed an estimated one trillion tonnes.[8][5]
I’m not sure if Wikipedia is right here however because the linked sources have changed to remove mentions of mass.
That said we should be able to do a pretty dumb calculation. 1 km3 of water weighs ~1 gt.
5800 km2 x 0.2 km = 1160 km3
1160 km3 of ice x 0.9 (density of ice compared to water) x 1 gt / 1 km3 leaves us with a mass of about 1044 gt or around 1 trillion tons.
Edit: also, I am not able to find an original source for the mass of B-15 being in the few billions range
More importantly, the article mentions removing annual effects on Polar Motion. They are averaging - somehow - to look at permanent changes. The annual effects may be an order of magnitude greater, it is not relevant.
- Based on a cursory search, a large iceberg may weigh in at ~1 trillion tons. The calving process moves mass hundreds of kilometers away from Antarctica. This should be an effect of similar magnitude!
- The water cycle moves ~500 trillion tons of water each year. This water is moved hundreds of kilometers and isn’t evenly distributed over the course of a year. We should expect the impact of seasonal fluctuations in water distribution to thus have a comparatively much larger impact on the earth’s rotation.
I don’t think these numbers add up. I think we’re reading this story because it feeds into a certain kind of “we are hurting Mother Earth” mindset.