Hydrated salts

A few days ago while we dug soil pits in the moraine near camp, we discovered ice buried beneath the surface.  This find is exciting as the ice could be remnant glacial ice from the last glacial period.  If it's glacier ice, then we definitely know that the ice sheet extended to that point and that the local climate on Black island has remained cold enough for ice to survive for over 10,000 years. Once we have the sample back in the lab, we can analyze the oxygen isotopes of the ice to determine the origin of the ice; it could be glacial (ice sheet), marine (the ocean), or meteoric (snowfall). 

Natalie and I begin to dig a pit.

Digging can be a long process, first you have to clear the large boulders, then the gravel, and then the fine sediment that covers the ice like a blanket. It takes a lot of forearm strength. However, this time as we dug we found something strange: a 20cm thick layer of salt on top of the ice! And not just any salt but a hydrated salt. Usually a little salt is normal, as it is left behind as the ice or snow sublimates away from the moraine, but this large of an amount was unexpected. We're still not really sure what it means, but it was really cool!

Drew and Nat document their pit.

Dirty ice.

Sediment sampling.

Drew clears off the ice.

20 cm of salt!!!!

Plus, they're hydrated salts and that's always fun to see in action.  A hydrated salt, also called a hydrate, is a salt that has a distinct number of water molecules associated with ions in its crystalline structure that is stable under a narrow range of temperature, pressure, and humidity. When we first dug into the salt layer we could see large salt crystals, but as the salt was exposed to air, the water sublimates and the remaining salt turns into a fine, dry white powder. It took only about 5 minutes for the top layer to disintegrate, then you can just rub it off and watch the whole process again!  The hydrated salt crystals were most likely mirabilite (Na₂SO₄·10H₂O), that formed from sublimating marine ice.  It was fantastic to see a true hydrated salt in nature, as you hear about them in chemistry class all the time.

Clean ice surrounded by powdery salt.

Gravel-salt-soft sediment-ice.

Hunk of chipped off salt crystals.

Close up of the crystals.

Before the dig, a salty hummock.

After the dig, clean ice pit.

Drew making notes against a cloudy Royal Society Range.

Natalie and me on our way back to camp after a day of sampling. Bye Folks!

It's thrilling to find something you didn't expect. But I guess that's the beauty of science, we go out looking for answers, but more often than not, we just find more questions. I wonder how many more questions we'll ask before we have to head back stateside. But for now, we just have to be content with collecting our samples and the knowledge of an intriguing discovery!


-Emelia Chamberlain