Effects of temperature on the microstructure of first‐year Arctic sea ice

Abstract

[1] While the apparent optical properties of sea ice vary with ice type and temperature throughout the annual cycle, they depend more fundamentally on how inclusions of brine, gas, precipitated salts, and other impurities are distributed within the ice. Since little is known about these distributions or about how they evolve with temperature, experiments were designed to collect detailed information on the microstructure of Arctic sea ice over a wide range of temperatures. An imaging system, capable of resolving inclusion sizes of less than 0.01 mm in diameter, was used to examine the microstructure of first-year ice in a temperature-controlled laboratory. Experiments were initially carried out at À15°C to obtain size distributions for brine inclusions and gas bubbles in cold ice. Brine inclusion dimensions were found to range from less than 0.01 mm to nearly 10 mm, with number densities averaging about 24 pockets per mm 3 . This is an order of magnitude larger than number densities previously reported. Gas bubbles in the samples were generally smaller than 0.2 mm and had number densities of approximately 1 per mm 3 , also an order of magnitude larger than previously reported. Large changes in microstructure were observed as samples were cooled to À30°C and subsequently warmed to À2°C. Observational results document the thermal evolution of the ice, as well as interactions between brine inclusions, gas bubbles, and precipitated salts. The link between the structural and optical properties of sea ice is closely tied to the total cross-sectional area of the inclusions. We show that this quantity increases dramatically when the ice cools below À23°C or warms above À5°C, but because changes in brine inclusions offset changes in precipitated salts, it remains surprisingly constant between these temperatures.INDEX TERMS: 4207 Oceanography: General: Arctic and Antarctic oceanography; 4540 Oceanography: Physical: Ice mechanics and air/sea/ice exchange processes; 4552 Oceanography: Physical: Ocean optics; KEYWORDS: sea ice, sea ice microstructure, sea ice optical properties, sea ice radiative transfer, brine inclusions, precipitated salts Citation: Light, B., G. A. Maykut, and T. C. Grenfell, Effects of temperature on the microstructure of first-year Arctic sea ice,

Role of sea ice in global biogeochemical cycles: emerging views and challenges

“…The latter effect is because brine salinity and temperature are coupled: the increase in solubility due to cooling is overcompensated by the decrease due to increasing brine salinity . Above saturation, if the sum of all dissolved gases partial pressures is higher than the local hydrostatic pressure, bubbles can nucleate and accumulate in the direct vicinity of sea ice inclusions [Tison et al, 2002;Light et al, 2003]. Internal melting also promotes gas bubble formation: melting involves a ~10% volume reduction, leaving a void where gas will flow from nearby brine until equilibrium [Perovich and Gow, 1996].…”

Drivers of inorganic carbon dynamics in first‐year sea ice: A model study

“…Particulate tracers, such as ikaite do not move with brine motion and remain where they form [as indicated by microscope observations by Light et al, 2003;Rysgaard et al, 2013]. DIC and TA are treated as passive tracers for transport and diffusion.…”

Pore space percolation in sea ice single crystals

“…These properties and processes include remote sensing signatures [Hallikainen and Winebrenner, 1992;Golden et al, 1998bGolden et al, , 1998c, optical properties [Light et al, 2003], colonization of sea ice by microorganisms [Krembs et al, 2000] and pollutant transport [Pfirman et al, 1995]. Of special note is the fluid permeability which controls fluid flow in sea ice, affecting ice albedo through melt pond development [Eicken et al, 2004], nutrient delivery to microorganisms [Krembs et al, 2000] and salinity profile evolution [Cox and Weeks, 1975;Weeks and Ackley, 1986;Wettlaufer et al, 2000;Vancoppenolle et al, 2007].…”