Antarctic Lake Actually Two in One

Scoria writes "USA Today reports: Scientists have discovered that Lake Vostok, a liquid freshwater lake which has been isolated from the world beneath 4 km of ice for approximately 500,000 years, contains two separate basins. They believe that the basins, which are divided by a ridge that limits water exchange, may host individual ecosystems that are home to ancient microbes."

Comments

Not really

[i8a4re]

The fact that it isn't saltwater isn't very surprising at all. Almost all glacial ice is freshwater. When saltwater is frozen for a very long time, the salt actually works its way out of the ice, leaving fresh water ice. Since the lake is in the middle of one huge, relatively old piece of ice it is not surprising at all that it is not salt water.

Also, it is not too peculiar that all the ice isn't melting. If you have a few small heat sources in the middle of several kilometers of ice, you'd expect it to melt a small area of ice around it. Since the heat requirements grows exponentially to melt a larger volume of ice and there are several kilometers of ice to melt, it would take a very large heat source to melt enough ice to either melt up to the surface or to the ocean.

<Bitching>I love how I press submit and get an error. I try it again and it tells me that I have to wait xx seconds before posting again. If I couldn't post due to an error, why do I have to wait to try again?</Bitching>

To quell some of the speculation

[saforrest]

It seems, at least according to this Wikipedia entry, that there is not yet an scientific consensus on why Lake Vostok remains liquid.

Wikipedia: Lake Vostok.

Re:To quell some of the speculation

[Anonymous Coward]

I suggest that the Wikipedia entry is misleading, if not incorrect.

The lake remains liquid for two reasons:

(1) geothermal heat (flux): using a conservative estimate of the geothermal heat flux of the East Antarctic (which has never been measured directly), say 50 mW/m^2, the measured ice thickness in the area (via radio-echo sounding, or active seimic) of ~ 4000 m^2, thermal conductivity of ice ~2.3 W/m K, and mean annual surface temperautre of ~ -55C suggests that the base of the ice sheet should be at the melting point. Ah, the heat equation in 1-D!

(2) freezing point depression changes the phase transition at Vostok from 0C to ~ -3C. A small but significant correction. Other corrections involve advection in the ice column due to ice flow, the ~110 m of firn overlying the glacial ice, etc. None of these corrections change the conclusion derived from (1), above.

The ice adjacent to the lake is also at the melting point, as are many areas in both East and West Antarctica. Whether the melt water collects into a subglacial lake is determined by the local hydraulic gradient. In many places, basal melt water flows along the gradient and refreezes where the ice thickness decreses. In other place, water collects into lakes. There are ~70 subglacial lakes in the Antarctic, although none nearly as large as Lake Vostok.

A temperature change 5000 years ago will have essentially no influence on the basal ice temperature at Vostok, in contrast to what Wikipedia suggests. The thermal diffusivity is far too slow, and the accumulation rate at the surface is also too small to generate rapid enough thermal vertical advecion.

Cheers,
tom

Re:Does anyone else find it amazing...

[dragons_flight]

Your guess is basically right. The lakes under Antarctica exist because of a balance between the slow trickle of geothermal heat and the insulating qualities of kilometers of ice.

You may be aware that as one digs down into the Earth it starts to get hotter. This is because everywhere on the Earth there is a slow trickle of ambient geothermal energy being dissipated from the hot core out to the much cooler surface. This should not be mistaken for much more intense geothermal phenomena like volcanos and hot springs as they have nothing to do with most subglacial lakes.

Since everywhere on Earth a little bit of geothermal heat is being released (roughly 1% of the power/area of sunshine) this includes the bottoms of glaciers. This causes the bottoms of ice sheets to always be warmer than their tops. For most glaciers this is only a few degrees, and no cares, but as the ice sheet grows, the ice can eventually become so thick that it can't dissipate the geothermal energy effectively and the bottom will melt. This is responsible for the majority of subglacial Antarctic lakes.

Re:2 Miles of Ice?

[dragons_flight]

The average height is ~8,000 ft above sea level (far higher than any other continent). The weight of the ice depresses the ground so that most of the bedrock is technically below sea level.