Life in a sinkhole

The karst landscapes of China have been an essential part of their figurative art and painting since time immemorial, capturing the imagination and providing a sense of wonder at nature. The sinkholes here form when underground rivers carve out underground channels by chemical erosion whose roofs later collapse when they weaken. These windows allow sunlight to pour within, and extensive and unique ecosystems to develop underground.

Loz

Image credit: Song Wen/Barcroft Media
http://on.wsj.com/1SdIVxD

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Iceberg B-15

In March 2000 a slab of ice larger than Jamaica broke away from the Ross Ice Shelf in Antarctica - Iceberg B-15. The iceberg was 270km long and 40km wide and took over a decade to melt away, slowly breaking up into smaller and smaller pieces. By late 2011, the iceberg was literally in thousands of pieces, and sections of it were still floating around in 2013.

B-15 began to fragment almost as soon as it broke off, and the majority of the fragments began drifting north. Iceberg B-15a (the largest fragment of the iceberg) and iceberg C-16 (an iceberg that was knocked off by B-15) did not drift north, which created a barrier that restricted the northward flow of pack ice. These two large icebergs remained in the area for several years which resulted in very high sea ice concentrations throughout the summer months around Ross Island, higher levels of sea ice to the south east of the icebergs (less open water), and a 40% decrease in primary productivity due to the decrease in open water.

The iceberg did create a few problems for the ecosystems in the region, for example organisms that depend on primary production had to travel much further to find food. The penguins in the region had a particularly difficult period because of these icebergs. They had to travel further away from their nests just to get to open water and then travel further in the open water to find food, ultimately meaning they were away from their nests for longer periods of time. This voyage meant that their nests were exposed to predators (mainly Skuas) that feed on the eggs and chicks for much longer. Breeding success was observed to be significantly lower in the years that the icebergs were there, and many penguins shifted their nesting locations further north, closer to the open water. Some penguin breeding grounds were found to be completely abandoned!

The calving event produced the largest recorded iceberg and was a rare event, but not unusual. It is estimated that icebergs of this size generally break off every 150-200 years. At the current rate of change the future may see many more icebergs like this, with many Antarctic ice shelves set for rapid disintegration. B-15 is an interesting example of how breakup of ice on the Antarctic continent can lead to temporary increases in ice on the seas around the continent. 

-MJA

Image credit: Landcare Research (satellite image, retrieved from http://bit.ly/1LQbAEs) and Josh Landis, NSF (Iceberg photo, retrieved from: http://bit.ly/1AF7kWQ).

Further reading:
http://stanford.io/1FeSFxO

cedar-glade:

Calcareous impact breccia, Im extremely jealous of ecosystems in temperate regions where extraterrestrial impacts occur on sedimentary rock and are old enough for extreme evolution to occur. Our impact In Ohio, although the cause of some strange disjunct populations and globally rare habitat, has no endemics associated with it. What is impact breccia? It’s a specific kind of ultra metamorphic rock caused by extreme jarring, heat, and pressure of large impacts. There are other types of breccia out there, but this one is caused by an impact and is always irregular and nebulous in form. The mixing of strata can lead to fracturing in the shape of the sharp jagged shards of impact breccia, these sharp shards shatter in different shapes/sizes and may be found in a distort density enough to weather the rock irregularly and a poorly deposited spatial imbrication of the mixed strata. Whats funny was that originally this impact was diagnosed as polymict to monomict mixing and was dismissed until much later. The strata that were involved with our impact were that of the Middle-Late Silurian, much before the impact, and are associated from Peebles Dolomite to Brassfield members. Other breccia is formed as secondary breccia but that’s not what you are looking at. Uplift breccia(involving Ordovician), fault breccia, and transitional breccia( Lower Silurian= Rochester (Estill) Shale to the Upper Devonian Ohio Shale) can be seen on the site as well. These large scale uplift/depression sites cause some strange localized anomalies as far as microclimates, soil chemistry, hydrology, and tallusing is concerned. So it makes sense why we have disjunction but it would also make sense to have some endemic evolution. I suppose that’s just wishful thinking.

One man’s trash is another man’s treasure

Spoil heaps may be considered uneconomic waste by many companies, but to geologists they are a treasure trove of sparkling minerals and criss crossing veins. My sixth form geology teacher would regularly raid a white gold spoil heap in Wales, giving specimens to her students as good luck charms for their exams. We still don’t know if her activities were entirely legal, but they did help spark a love of minerals within her students that lasts to this day.

However, these rocks aren’t just pretty to look at; they can also provide an insight into the type, age and order of mineralisation that occurred. So much information can be gathered from such sites that universities will take students to spoil heaps as a field based exercise in mineral exploration.

Of course they are also the perfect place to add to any rock hounds collection, after all one man’s trash is another man’s treasure!

- Watson

Image Credit: Wikipedia

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