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Project Progress

Oceanic processes on Snowball Earth: Laboratory experiments.

During a Neoproterozoic “Snowball Earth” event, the ocean surface conditions would determine both the surface climate and the locations for survival of surface life. A process that may be important in the tropical zones (where evaporation exceeds precipitation), as sea ice sublimates, is accumulation of a crust of sea-salt on the ice surface. This can happen only on ice below the eutectic temperature of NaCl brine, -22.9 °C, but such temperatures are expected on Snowball Earth, even at the equator. No modern surrogate is known to exist in nature now, but we can investigate these processes in our cold-room laboratories. The salt that would accumulate is not NaCl but rather NaCl.₂H₂O, “hydrohalite,” which has not received much investigation. Dr. Bonnie Light is collaborating with Warren on this project.

In Year 4, Dr. Light invented a procedure to grow large single crystals (5 mm) of hydrohalite in isolation (i.e., not embedded in ice), so as to be able to study their inherent properties. She refined the procedure to make it reliably repeatable. She also began experiments on sublimation of sea ice to develop salt crusts. Often the solutions do not precipitate when they reach saturation; this supersaturation phenomenon is probably significant in nature.

Radiation modeling of ice on the Snowball Ocean

Richard Brandt worked with Warren to develop parameterizations for computing absorption and transmission of solar radiation by ice, for use in climate models of Snowball Earth.

The albedo and transmission of bubbly ice floating on water was calculated using a Discrete-Ordinates model for ice thicknesses ranging from 1 mm to 1 km containing uniform air bubbles of 0.1 mm radius and densities ranging from 0.01 to 100 per cubic mm. Spectrally averaged albedo and transmission were calculated for the entire solar spectrum, and also for two wavelength bands commonly used in climate models: visible (<700 nm) and near-infrared (near-IR, >700 nm).

Parameterizations for albedo in the three spectral bands, over the modeled ranges of bubble concentration and ice thickness, were developed. For each spectral band, an eleven-term parameterization fits the modeled albedo for ice thicker than 50 cm with maximum errors of 0.01 in the allwave and near-IR bands and 0.03 for the visible band. For ice thicknesses 0.1-50 cm, maximum albedo errors for near-IR, allwave and visible bands are 0.02, 0.04 and 0.06 respectively.

Currently we are developing the parameterizations for transmission.

A paper is in preparation: “Ocean surfaces on Snowball Earth: implications for survival of surface life”. This paper identifies 13 different surface types that would occur at different times and latitudes during a snowball event, and recommends their albedos for use in climate modeling.

Radiative processes in Martian climate

Gary Hansen, a former Ph.D. student of Warren, has completed the analysis of his laboratory measurements of the absorption spectrum of carbon-dioxide ice for visible and ultraviolet radiation. This information is needed for computing radiation fluxes in Martian clouds and polar caps, to study the climate of Mars. He has written a paper, based on these measurements he did as a graduate student: “The ultraviolet to near-infrared absorption spectrum of carbon dioxide ice from 0.174 to 1.8 micrometers”, submitted to J. Geophys. Res. (Planets), July 2005.