Why Antarctica ice is fresh water

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In summary, the ice in both Antarctica and the Arctic is made of fresh water even though it is formed from sea water. This is because of the process of brine rejection, where the salt is concentrated in liquid brine and eventually drained out of the ice. This results in the formation of freshwater ice, which is less dense and floats on the surface of the sea water. The presence of land underneath the Antarctic ice can also contribute to the accumulation of rain and snow, but the majority of the ice is the product of snowfall. In the Arctic, some proportion of the sea ice is actually glacial ice that has spread from land, and the dominant ways in which salt is lost from the ice are through gravity drainage and flushing. Overall
  • #1
menniandscience
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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 :)
 
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  • #2
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.
 
  • #3
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.
 
  • #4
Sure, but the OP asked specifically about sea ice (no land underneath) in the Arctic.
 
  • #5
olivermsun said:
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?
 
  • #6
Ophiolite said:
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. :smile:
 
  • #7
olivermsun said:
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.
 
  • #8
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."
 
  • #9
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.
 
  • #10
Gullik said:
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)!
 

1. Why is Antarctica's ice made of fresh water instead of salt water?

Antarctica's ice is made of fresh water because it is formed from snow that falls on the continent and accumulates over time. This snow is composed of pure water molecules that do not contain any salt or minerals.

2. How does the freezing temperature of fresh water differ from salt water?

Fresh water has a higher freezing point than salt water. This means that it will freeze at a higher temperature than salt water. In Antarctica, the average temperature is well below the freezing point of fresh water, which allows the ice to remain frozen and accumulate over time.

3. Is the ice in Antarctica completely pure fresh water?

No, the ice in Antarctica is not completely pure fresh water. It may contain small amounts of impurities such as dust, minerals, and gases. However, these impurities are present in very low concentrations and do not significantly affect the overall purity of the ice.

4. How thick is the layer of fresh water ice in Antarctica?

The thickness of the fresh water ice in Antarctica varies greatly across the continent. In some areas, the ice can be over 4 kilometers (2.5 miles) thick, while in other areas it may only be a few meters thick. The average thickness of the ice is around 1.6 kilometers (1 mile).

5. What role does the Southern Ocean play in keeping Antarctica's ice fresh water?

The Southern Ocean surrounding Antarctica plays a crucial role in keeping the continent's ice as fresh water. The ocean acts as a barrier, preventing the salt water from the surrounding seas from mixing with the fresh water ice on the continent. This allows the ice to remain pure and unaffected by the high salt content of the surrounding water.

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