Arctic Sea Ice & Antarctic Sea Ice Are Different Types

Fig. 1

I. Likenesses

There are some obvious likenesses in the two polar located sea ice masses, however, what is usually not expressed is the differences between the two entities.

The graphs at Fig. 1 and Fig. 2 illustrate the outward appearance of the Greenland and Antarctica sea ice in terms of size in km² (square kilometers), and it terms of increase and/or decrease in the area of ocean they cover at a given time.

The extent or area of sea ice is not the same as its volume or mass, which is expressed in km³ (cubic kilometers).

Fig. 2 Trend in Arctic sea ice

I explained the difference in a previous Dredd Blog series (How Fifth Graders Calculate Ice Volume, 2, 3, 4, 5).

In terms of volume or mass, both areas are in general decrease, which is expressed in terms of cubic miles (mi³) or cubic kilometers (km³).

This is a fundamental distinction that applies equally to the two, but it is also one of the reasons why some deniers do not understand the difference between the two entities (more on that later in this post).

II. Differences

A major difference between them is that the Antarctica sea ice is an ice shelf, while the Arctic sea ice is more properly called a polar ice cap.

Fig. 3 Sceptical Science

The reason for that is the Antarctic Ice Sheet over land extends out over the sea as an ice shelf, whereas the Arctic sea ice is not an extension of an ice sheet, thus it cannot properly be called an ice shelf.

In other words the Antarctic Ice Sheet over land extends over the ocean to become the Antarctic Ice Shelf around the land mass, however, the Arctic sea ice is not an ice shelf because it is not an extension of, an ice sheet on land extending out over the ocean.

This is one reason the extent / area of the Arctic sea ice is shrinking in size in terms of square miles (or square kilometers), while the Antarctic exhibits times of increase, in terms of square miles (or square kilometers).

Notice Fig. 3 for a comparison of the two areas at maximum ice extent and minimum ice extent on a general annual basis.

The graph at Fig. 4 shows that Arctic sea ice is on an annual record pace.

A peer-reviewed paper on the issue points out why the maximum extent is increasing:

In contrast to Arctic sea ice, sea ice surrounding Antarctica has expanded,

Fig. 4 Arctic sea ice extent

with record extent in 2010. This ice expansion has previously been attributed to dynamical atmospheric changes that induce atmospheric cooling. Here we show that accelerated basal melting of Antarctic ice shelves is likely to have contributed significantly to sea-ice expansion. Specifically, we present observations indicating that melt water from Antarctica’s ice shelves accumulates in a cool and fresh surface layer that shields the surface ocean from the warmer deeper waters that are melting the ice shelves.

(Nature Geoscience, 2013). A more recent paper is in accord with that summary:

Meltwater tends to stabilize the ocean column, inducing amplifying feedbacks that increase subsurface ocean warming and ice shelf melting. Cold meltwater and induced dynamical effects cause ocean surface cooling in the Southern Ocean and North Atlantic, thus increasing Earth's energy imbalance and heat flux into most of the global ocean's surface. Southern Ocean surface cooling, while lower latitudes are warming, increases precipitation on the Southern Ocean, increasing ocean stratification, slowing deepwater formation, and increasing ice sheet mass loss. These feedbacks make ice sheets in contact with the ocean vulnerable to accelerating disintegration.

(Hansen et al., 2016). The ice shelf is melting from below and that increasing volume of cold melt water re-freezes further out from where it originated during the melting of the bottom of the ice shelf.

It melts again during the summer (Fig. 3) to result in a minimum extent that is about ten times smaller than the maximum extent (Fig. 1).

The Arctic sea ice on the other hand is in a constant shrinking trend (Fig. 2).

III. Antarctica Mass Volume Loss Confirmation

A study of the gravitational loss indicates a volume / mass loss:

"Princeton University researchers "weighed" Antarctica's ice sheet using gravitational satellite data and found that during the past decade, Antarctica's massive ice sheet lost twice the amount of ice in its western portion compared to what it accumulated in the east. The researchers used monthly data from GRACE, or the Gravity Recovery and Climate Experiment, a dual-satellite mission that measures gravity changes; as Antarctic land ice melts, the reduction in ice mass is picked up by GRACE. In the past 11 years, the Antarctic ice sheet lost 92 billion tons of ice per year, which, if stacked on the island of Manhattan, would be more than a mile high — more than five times the height of the Empire State Building. As shown in the figure above, from Jan. 2003 to June 2014, the vast majority of ice loss was from West Antarctica's Amundsen Sea region (box a) and the Antarctic Peninsula (box b) that winds up toward South America. The ice sheet on East Antarctica (box c) primarily thickened during that same time. The color scale indicates mass — equivalent to centimeters of water — of the land ice, with red denoting the largest loss and blue standing for the largest gain. (Image by Christopher Harig, Department of Geosciences)"

(Antarctic ice sheet is melting faster, emphasis added). Recent events in East Antarctica show that ice mass loss there is happening now and will increase in the same manner as West Antarctica is (The Ghost-Water Constant - 7).

Serious sea level rise potential from Antarctica is the metaphorical equivalent of a "10 month pregnancy in a woman" ... overdue  ("This Century" and "Global Dimming")

IV. Conclusion

The counter-intuitive reality is that as the Antarctica ice sheet and ice shelf melt from below the surface, the cold melt water goes to the ocean surface to re-freeze in winter, increasing the extent of the ice shelf.

It is a sign that the ice volume / mass is decreasing not increasing.

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