Garrett W. Brass

Stability of brines on Mars

Abstract The detection of high chlorine and sulfate abundances and duricrusts on Mars strongly suggests the occasional presence of brines on the Martian surface. Ternary phase diagrams for the likely chloride and sulfate brines indicate that the minimum temperature at which a brine can be stable is near 210°K with a water concentration of approximately 70 wt% and a high concentration of calcium chloride. The dominance of sulfate over chlorine in the Martian regolith suggests precipitation of salts at temperatures higher than the minimum.

The solubility of ferric ion in marine mineral aerosol solutions at ambient relative humidities

Abstract The solubility of ferric ion from Fe 2 O 3 , FeO(OH) and Fe(OH) 3 in hygroscopic marine aerosol solutions was estimated from free energies at the pHs and ionic strengths that are characteristic of ambient trade wind aerosol particles collected at Barbados, West Indies, under conditions when significant concentrations of Saharan dust were present. The chemical composition of these mineral-containing particles was based on measurements made with cascade impactor samples with the assumptions that the particles in a given size fraction were internally mixed and that the NO 3 − and nonsea-salt (nss) SO 4 2− in the particles were initially in the form of HNO 3 and H 2 SO 4 . At typical local relative humidities (RH) above 80%, the pH of the aerosol solution could be lower than 1.0 and the ionic strength could be higher than 3.0 even when part of the acid has been neutralized by NH 3 and CaCO 3 . The concentration of ferric ion increases by three orders of magnitude for each unit decrease in pH. By considering changes in speciation and ionic strength, the ferric ion solubilities at pHs of 2, 5 and 8 are estimated to be, respectively, 6.67 × 10 −5 mol kg −1 , 5.53 × 10 −14 mol kg −1 , 3.17 × 10 −15 mol kg −1 from Fe 2 O 3 , 1.10 × 10 −4 mol kg −4 , 8.68 × 10 −14 mol kg −1 , 5.04 × 10 −15 mol kg −1 from FeO(OH) and 1.55 × 10 1 mol kg −1 , 1.12 × 10 −8 mol kg −1 , 6.61 × 10 −10 mol kg −1 from Fe(OH) 3 . The ferric ion solubilities in aerosol solutions are far higher than those normally expected for seawater, fresh water and even rain water in which the pHs are usually higher. Thus aerosol solution processes may be a major factor affecting the fraction of iron that will readily dissolve when the atmospheric mineral particles enter the ocean. These same aerosol solution processes may explain the unusually large solubilities that have been observed for other aerosol metals in aqueous solutions.

On the possibility of plate tectonics on Venus

Abstract Several arguments have been put forward suggesting that Venus has no place tectonics. We examine some of these arguments and suggest that because conditions on the surface of Venus are very different from those on Earth, the arguments should be reconsidered. We show that in the absence of an ocean, the differential hypsographic curve of Earth would probably have only one mode, like that for Venus. We show that the atmosphere of Venus is quite capable of erosion, provided that near-surface velocities are about 1 m · sec−1 or more, and that therefore the “oceanic” areas on Venus, should they exist, are probably covered with some thickness of sediment. If sedimentation on Venus is at all rapid, it is likely that subduction zones could be filled up and made unrecognizable topographically. Because Venus does not have an ocean, and because its surface temperature is much greater than that on Earth, ridge crests on Venus have a much smaller topographic expression than those on Earth. If significant sedimentation occurs they would be completely unrecognizable topographically.

Magnesium in continental runoff

Abstract A mass balance for Mg in continental runoff has been constructed. The sources of runoff Mg in this model are cyclic salts, carbonate rock and silicate rock weathering. The calculations indicate that the Mg concentration reported for average continental runoff is anomalously high. The anomaly may be due to recent disturbances in the weathering regimes of calcite, dolomite and silicates, or to unreliable Mg concentrations reported in older analyses.