Saturday, December 29, 2007

Spectacular Highlight - B15D

B15D looking north

I have spent all my time in Antarctica along the Antarctic Peninsula but this time I finally saw the other side of Antarctica, the Ross Ice Shelf. Well, I saw a portion of the Ross Ice Shelf and I didn't even have to travel to the the Ross Ice Shelf, it came to me.

On November 12th we left Point Wild and headed east towards Clarence Island. Just south of Clarence Island was a grounded iceberg known as B15D, a portion of what was once the largest iceberg ever recorded (Elephant Island and the iceberg are located in the lower right portion of the photo above. Click on the image to make it larger). We approached the white island from the west and came within about 150 ft of the edge of the berg. It was massive, about 100 ft tall, 33 miles long and 9 miles wide. Although the edge of the berg look straight with the resolution in the satellite image from above, our vantage point showed large scalloping along the edge with cornices from snow blown across the flat top of the berg.

Cape Petrels along the face of B15D. Notice the striations in the ice. Layer upon layer of accumulated snow from the other side of the continent.

B15D started it's life in March 2000 as B15, the 15th iceberg tracked in the B quadrant of Antarctica (see photo below). When it formed it was 183 miles (295 km) long and 25 miles (40 km) wide, roughly the size of Jamaica. Shortly after it broke from the Ross Ice Shelf it began to break into smaller pieces (currently 15 tracked icebergs). In 2001, the largest portion of the iceberg, B15A blocked the normal Adelie Penguin migration route to their colonies on Ross Island. The presence of the iceberg and the resulting increased expanse of sea ice resulted nearly a complete breeding failure of some of the colonies on Ross Island (Sheperd et al. 2005), caused a decrease of nearly 40% in the primary production in the region (Arrigo et al. 2002), and disrupted shipping and resupply into the research bases on Ross Island, primarily McMurdo. In 2006, an ocean swell from a 2005 Alaskan storm broke B15A into many smaller icebergs.

Here are a couple of maps depicting the route that B15D took from the Ross Ice Shelf to Elephant Island. The top map depicts the route around East Antarctica and the bottom map continues to Elephant Island. Each mark is coded with the date of the location with the year followed by the Julian date of that year. Each position is approximately 3 months apart with a large gap in the data from 2002.

Snow Petrel along the face of B15D

1 comment:

Clare said...

That is so cool (pun sort of, kind of, intended).