Why Antarctica ice is fresh water

[menniandscience]

Hello everyone!

my question is why the ice of Antarctica and arctic, it is made of sweet/fresh water,even though it is water of the sea that froze as far as i know. at least in antarctica there is land underneath so just maybe it is accumulation of rain and snow and hail though it does sound unlikely, but what about arctic, there is no land just ice of frozen water, yet i always here it is fresh water. on the other hand maybe some sea water froze and it became like the land of the southern pole, i.e rain, hail and snow covered the salty ice
clear that for me please

thanks :)

 

[olivermsun]

This article on Brine rejection might explain some of what you're curious about.

But yes, freezing at high latitudes is generally what creates both (freshwater) ice and cold, salty (dense) water that tends to sink.

 

[Ophiolite]

The vast majority of Antarctic ice (and that of Greenland) is the product of snowfall. The seasonal sea ice is thin and inconsequential in volume terms.

 

[olivermsun]

Sure, but the OP asked specifically about sea ice (no land underneath) in the Arctic.

 

[Ophiolite]

Sure, but the OP asked specifically about sea ice (no land underneath) in the Arctic.

With respect, the OP asked this: "at least in antarctica there is land underneath so just maybe it is accumulation of rain and snow and hail though it does sound unlikely".

I addressed that implicit question. My response was on topic. The issue of sea ice had been accurately dealt with via your earlier response. What's the problem?

 

[olivermsun]

With respect, the OP asked this: "at least in antarctica there is land underneath so just maybe it is accumulation of rain and snow and hail though it does sound unlikely".

I addressed that implicit question. My response was on topic. The issue of sea ice had been accurately dealt with via your earlier response. What's the problem?

No problem, I just thought the OP already believed that precip was the source of Antarctic accumulation, but it was nice to have you confirm that.

 

[puncheex]

Sure, but the OP asked specifically about sea ice (no land underneath) in the Arctic.

Some proportion of "sea ice" is actually glacial ice that has spread from the land to float on the sea, called shelf ice; it is the primary source of icebergs, for example. It was originally snowfall inland.

 

[olivermsun]

Sea ice is typically defined as something like: "any form of ice found at sea which has originated from the freezing of sea water." But what you say is certainly true of "ice which is found floating at sea."

 

[Gullik]

As most people mentioned the sea ice is salty, not fresh. Fresh sea ice is more saline and since the salt gradually drains out multi year ice is much fresher.

From Desalination processes of sea ice revisited, Notz and Worster, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114.

We reexamine five processes that have been suggested to be important for the loss of
salt from sea ice. These processes are the initial fractionation of salt at the ice-ocean
interface, brine diffusion, brine expulsion, gravity drainage, and flushing with surface
meltwater. We present results from analytical and numerical studies, as well as from
laboratory and field experiments, that show that, among these processes, only gravity
drainage and flushing contribute to any measurable net loss of salt. We show that during
ice growth the salinity field is continuous across the ice-ocean interface. Hence there
is no immediate segregation of salt at the advancing front.

(Bold is mine)

So gravity drainage and flushing is the dominant ways the salt is lost by the sea ice. Sea ice is generally much less saline than sea water.

As far as I'm aware quite a few of the climate models assume fresh sea ice due to modelling simplicity, and that may have been where you have gotten the idea that sea ice is fresh. Or I think that multi year ice can be fresh enough to melt and drink.

 

[olivermsun]

As most people mentioned the sea ice is salty, not fresh. Fresh sea ice is more saline and since the salt gradually drains out multi year ice is much fresher.

From Desalination processes of sea ice revisited, Notz and Worster, JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 114.

Very interesting paper, thanks for the link!

The bulk salinity of sea ice, which is the salinity of a melted sea ice sample, is usually much lower than that of the seawater from which it has formed. Hence the formation and growth of sea ice give rise to a substantial salt flux into the underlying water, increasing both its salinity and density.
$\vdots$
The salt that remains within sea ice is not incorporated into the solid ice crystals but becomes concentrated in interstitial liquid brine. During all stages of its formation, growth and decay, sea ice remains a mixture of solid freshwater ice and liquid salty brine [e.g., Eicken, 2003, and references therein].

That's why there is an entire list of possible desalination processes (including gravity drainage and flushing)!