Surface properties and processes of perennial Antarctic sea ice in summer

Abstract

ABSTRACT. Ice-core and snow data from the Amundsen, Bellingshausen and Weddell Seas, Antarctica, show that the formation of superimposed ice and the development of seawater-filled gap layers with high algal standing stocks is typical of the perennial sea ice in summer. The coarse-grained and dense snow had salinities mostly below 0.1ù. A layer of fresh superimposed ice had a mean thickness of 0.04^0.12 m. Gap layers 0.04^0.08 m thick extended downwards from 0.02 to 0.14 m below the water level. These gaps were populated by diatom standing stocks up to 439 mg L^1 chlorophyll a. We propose a comprehensive heuristic model of summer processes, where warming and the reversal of temperature gradients cause major transformations in snow and ice properties. The warming also causes the reopening of incompletely frozen slush layers caused by flood^freeze cycles during winter. Alternatively, superimposed ice forms at the cold interface between snow and slush in the case of flooding with negative freeboard. Combined, these explain the initial formation of gap layers by abiotic means alone. The upward growth of superimposed ice above the water level competes with a steady submergence of floes due to bottom and internal melting and accumulation of snow.

Sea ice and snow thickness and physical properties of an ice floe in the western Weddell Sea and their changes during spring warming

“…Unfortunately, we lack specific data on the occurrence of flooding throughout the study period. In contrast, the absence of flooding on SYI in late November and early December despite the widespread occurrence of negative freeboard indicates that SYI ice is largely impermeable during winter, due to cold surface temperatures and the desalination during the preceding summer (Eicken 1998;Haas et al, 2001).…”

“…During summer, the properties of sea-ice and snow change considerably as a result of increased heat fluxes both from atmosphere and ocean, causing a marked warming of the ice and snow and a reversal of vertical temperature gradients with higher temperatures at the surface than at the bottom. As a consequence, increased snow metamorphism and thinning, internal and bottom melting, and high rates of algal primary productivity are observed (e.g., Thomas et al, 1998;Haas et al, 2001;Nicolaus et al, 2006). Little is known about the atmospheric and oceanic boundary conditions of these processes in late spring and early summer.…”

The multiphase physics of sea ice: a review for model developers

“…Notably, very little difference between first-year and multiyear salinity profile shapes is observed, as pointed out by in a later study using essentially the same data set. Furthermore, Haas et al (2001) and Ackley et al (2008) note that the heavy snow layer present in the Antarctic may encourage superimposed ice formation as well as the occurrence of liquid gap layers at the snow-ice interface, providing yet more diversity in Southern Hemisphere sea ice salinity profiles.…”

Eos, Transactions, American Geophysical Union Volume 88, Number 22, 29 May 2007

“…This results from the fact that surface melting in the Antarctic differs signifi cantly from corresponding processes in the Arctic [Nicolaus et al, 2006]. The hemispheric differences are supported by extensive fi eld measurements [Massom et al, 2001;Haas et al, 2001] and fi nd expression in a reversal of the general surface radar backscatter and brightness temperature (T B ) tendencies during summer [Haas, 2001;Kern and Heygster, 2001]: In the Antarctic, sea ice backscatter increases and T B decreases when summer approaches, contrary to the Arctic. Hence, algorithms developed for Arctic sea ice are not applicable on its southern counterpart.…”