is an ensemble that mimics the ebb and flow of the polar day, that instantly encapsulates the seasonal progradation and retrogradation of the pack. The contrast—the proportions—accounts for the effectiveness of the scene. No single process or esthetic dominates completely. In the scene’s finest expressions, all are mixed and in motion. Each, by its contrast, heightens the other.
RETROGRADATION
The floes hesitate, suspended in an instantaneous equilibrium of seasons, like the globular clusters of an expanding universe caught at their maximum extent before gravity induces a slow collapse.
Then the retrogradation of the pack begins. Maximum progradation is reached sometime in October, just after the vernal equinox. Now comes the recession. It is not an implosion so much as an erosion of the ragged perimeter, a steady exposure of sea at the expense of ice. The processes that directed the progradation of the pack now guide its retrogradation. The same principles of positive feedback accelerate the trend. What has changed is the general climate under which these processes operate. The polar night favors ice production; the polar day, ice erosion. What makes the recession possible is not simply the removal of old ice but the failure to regenerate new ice. The net balance between ice growth and ice decay tilts toward loss. The areal extent of the Antarctic ice field is halved as the pack retreats inward, drawing back the veil, a disintegrating vortex of ice floes and bergs.
The individual floes ablate in several ways, but surface meltwater, so integral to the destruction of sea ice in the Arctic, has little role in the Antarctic. Winds from the interior polar desert sublimate the surface snow off floes and evaporate any standing meltwater. The katabatics of Antarctica are much drier and 60–100 percent stronger than Arctic winds. Only thin films of water develop over the surface, although melting does occur internally, concentrated around the black bodies of inclusions like microorganisms trapped within the rapidly assembled skeleton of the floe. Instead, open leads between floes take the place of surface meltponds. Winds drive apart those floes along the outer edge, but instead of refreezing, the interstitial leads remain open. The growth of open water reduces the albedo of the pack, encouraging solar heating of open water; warmer water upwells into the pools, promoting further melting of floes; waves penetrate the pack, leading to more thermal decay and mechanical disintegration; icebergs, increasingly mobile in the more fluid matrix of the collapsing pack, plow through floes, widening leads and crushing smaller ice masses. Since storms tend to hover over the circumpolar ring of maximum thermal upwelling, which generally coincides with the perimeter of the pack, the seasonal temperature change brought on by the waxing polar day can initiate the process of retrogradation. The storm belt, in turn, moves inward with the receding pack. Curiously, the pace of the recession outstrips that of the progression.
By February sea ice is at a minimum. Over half the total decay occurs from mid-November to mid-January. For the most part, the pack contracts steadily southward toward the coast. The Weddell Sea is again an exception. Here the pack persists, although it retreats along an axis from east to west. But the collapse is never complete. Some floes linger, mingling with bergs and other ice breccia. Some are trapped in the Weddell Sea gyre, adding another year to their life cycle. Some are caught as fast ice in protected areas of the shore, part of a coastal ice terrane that, unlike the pack, rings the continent with a nearly immobile, quasi-permanent shield. A hybrid of sea ice, snow, and firn, fast ice connects the ice terrane of the pack to the ice terrane of the continent. It is itself a partial metamorphosis of sea ice into land ice, floe to glacial tongue, pack ice to ice shelf.
The processes that shape sea ice and land ice are also responsible for fast ice, with the addition that both sets of processes here interact and their ices intercalate into a unique stratigraphy. The ice begins under the same conditions that generate sea ice. A protected embayment, perhaps sprinkled with grounded bergs; light winds, currents, and tides; and open water (a polynya is ideal) to generate fresh crystals—all lead to an ice matrix and the creation of a sheet of sea ice frozen to coastal ice or land. Anchor ice and frazil ice add to the expansion of the lower stratum. Crystal growth by congelation ice and the incorporation of other ice fragments expands the floe along its margins. Snow, recrystallizing meltwater, and (when the snow weights the floe so that the ice layer falls beneath sea level) percolating seawater all add ice strata to the surface. The saturation of surface snow (and sometimes firn) by seawater, which then freezes, can account for 25–90 percent of the total ice mass. Some seawater represents simple wash, trapped on the surface; but some enters the floe interior from beneath, along fissures that then freeze to form lenses and veins of infiltration ice. Grounded bergs promote fast ice by creating a breakwater that dampens sea and wind, traps snow, cools the adjacent sea-waters. Fast ice, in turn, helps shield the bergs from erosion.
But fast ice also erodes, and the resulting terrane represents a new outcome between the addition of new snows and ices and their subtraction. Open water seasonally erodes the sides and bottoms of the ice, winds and tides contribute to its mechanical disintegration, and winds ablate some surface snows. Solar heating melts other snows, particularly when they are contaminated with dark organic and abiotic debris. The uneven topography of the resulting ice surface leads to differential filling and emptying, an alternating relief of scourings and deposits. This asymmetric erosion is even more intense in the presence of dirty ice. By absorbing more radiation than pure ice does, dirty ice surfaces can erode into fantastic sculpturings, the most exotic shapes in Antarctica. Shore ice that is only seasonally fast breaks out in sudden surges.
In general more ice is formed than removed, and the special circumstances that favor the formation of fast ice also favor its preservation. Protected from ocean swells and chilled by a matrix of land ice—glaciers and bergs both—fast ice persists. It experiences some disintegration, some ablation and breakage. But new ice replaces the old; ices of different composition, origins, and structure combine into a unique amalgamation. Snow cover and frozen sea-slush are underlain by strata of congelation ice and veins of infiltration ice, which are in turn underlain by loosely consolidated frazil ice, congelation ice, anchor ice, and ice stalactites. In place of the annual ontogeny of growth and decay that characterizes individual floes in the open sea or the seasonal waxing and waning that accompany the life cycle of the pack, fast ice acquires an internal structure and a history.
This fragment of sea ice, now firmly fastened to the coast, is all that remains of the mighty pack. Part of an inner, less mobile perimeter, the spotty terrane of fast ice traces a new zone of cold mixing, one that mingles solids rather than fluids. The particle of fast ice thus has symbolic as well as geographic importance. It marks a ragged cryospheric boundary, the first one that is internal to The Ice. Elsewhere land ice is sloughed off into sea ice, to join the phylogeny of the pack. But here land ice replaces or metamorphoses sea ice, and sea ice is transformed into an approximation of land ice. Land replaces sea, land ice displaces sea ice, Ice supersedes Earth.
| 2 | No Middle WayThe Exploration of Antarctica |
Come, my friends,
Tis not too late to seek a newer world.
Push off, and sitting well in order smite
The sounding furrows; for my purpose holds
To sail beyond the sunset, and the baths
Of all the western stars, until I die.
—Alfred, Lord Tennyson, “Ulysses” (1842)
The Pole lay in the center of a limitless
plain.… One gets there, and that is about
all there is for the telling. It is the effort to
get there that counts.
—Richard E. Byrd,
