D/H ratio during the northern polar summer and what the Phoenix mission might measure

Abstract

The Phoenix polar mission will land close to 68°N, 233°E in May 2008 at Ls ∼ 75 and operate 90 sols until Ls ∼ 125 with possible extension to Ls ∼ 142. Phoenix Meteorology (MET), Thermal and Evolved Gas Analyzer (TEGA) and Microscopy, Electrochemistry and Conductivity Analyzer (MECA) instrument packages will measure the air's temperature, water vapor concentration, ice crystal concentration and the water's stable isotope ratio D/H, and the D/H for the uppermost ground ice. This paper summarizes what is known about the seasonal cycle of atmospheric D/H and makes a theoretical connection between the atmospheric ratio and that expected from the ground ice that Phoenix will sample. A simple mixed cloud stable isotope model is used to show that the seasonal progress of D/H in the polar region cannot be used alone. It is argued that the seasonal cycle in D/H is explained by their being an interplay between multilatitudinal sources or reservoirs that have a range of reservoir D/H values. These reservoirs have different sizes and seasonal response times so that they release their water contributions at different times of the spring and summer and together explain most of the seasonal D/H observed by Mumma et al. (2003) and Novak et al. (2005). Phoenix observations from its high‐latitude vantage point during the summer and fall will add some atmospheric D/H values, temperature, water vapor concentration, and ice cloudiness data points that will constrain the various theoretical possibilities. The D/H of the ice recovered by Phoenix from the surface of the ground ice combined with the atmospheric D/H will suggest, whether the ground ice presently is a net receiver or supplier of water to the northern ice cap.