Pedogenic carbonate in the form of calcite (CaCO 3 ) accumulates within the soils of hot and cold arid continental landscapes, but much less is known about the spatial pattern and amount of carbonates in polar soils. We measured the CaCO 3 distribution in the McMurdo Dry Valleys of Antarctica, the largest ice-free expanse on the continent. Higher CaCO 3 concentrations occur in the moist coastal soils, the younger till (younger than 50,000 yr), and in lower elevation tills within Taylor Valley in the McMurdo Dry Valleys area. The average CaCO 3 in the moist coastal soils of the McMurdo Dry Valleys is 1.06%, 0.39% in intermediate-elevation soils, and only 0.02% in inland highest-elevation soils. In general, the youngest coastal tills contain the highest amounts of CaCO 3 (2.0%), and the oldest tills from Taylor IV glaciation contain the least (0.54%). There is a noticeable difference in CaCO 3 concentration near the elevation of the highest stand of ancient Glacial Lake Washburn (∼340 m), with higher concentrations found in soils previously covered by the lake. This suggests that a portion of the CaCO 3 in soils below this elevation could be lacustrine derived. The Fryxell, Hoare, and Bonney basin soils in Taylor Valley have mean inorganic C concentrations that are much lower than the average world inorganic soil C concentration of 33.2 kg C m −2 . The relatively low carbonate concentrations in Antarctic polar desert soils can be attributed to the shallow active layer, low rates of weathering, and the extreme aridity of the landscape. Los carbonatos pedogénicos, sobre todo calcita se acumulan muy frecuentemente en zonas áridas o semiáridas. Los McMurdo Dry Valleys de la Antártida son las mayores zonas sin hielo del continente y se denominan desiertos polares. Hemos medido la distribución de CaCO 3 en estos suelos con objeto de intentar comprender mejor la distribución y acumulación del carbonato en estos suelos. Las concentraciones más elevadas de CaCO 3 se dan en los suelos costeros húmedos, dentro del till más reciente (<50,000 años), y en los tills de zonas topográficas más bajas en el Valle Taylor, situado dentro de los McMurdo Dry Valleys. Usando la clasificación de Marchant y Denton (1996) de los tres mayores regímenes climáticos del McMurdo Dry Valleys, el contenido medio de CaCO 3 en los suelos húmedos costeros (Zona 1) del McMurdo Dry Valleys es 1.06%; en la zona 2 (suelos de altitudes intermedias) es de 0.39%, y en la zona 3 (altitudes mayores del interior) es sólo del 0.02%. En general, los tills costeros más recientes (5480 ± 56 14 C) contienen un 2.0% de CaCO 3 , los tills de la Glaciación Ross I (12.4–23.8 ka) presentan valores de CaCO 3 de 0.68%, en los de la Glaciación Taylor II/Bonney (74–98 ka) el contenido es 0.92%, en los de la Glaciación Taylor III (200–210 ka) estos valores son de 0.74% y en los tills más antiguos de la Glaciación Taylor IV (2100–3700 ka) el contenido medio de CaCO 3 es de 0.54%. Sin embargo, hay una notable diferencia en la concentración de CaCO 3 en el suelo a una altitud de 336 m, la situación más elevada del antiguo Glacial Lake Washburn (22,800–8500 años B.P.), por debajo de esta altitud las concentraciones son mayores. Por ello, una parte del CaCO 3 en el suelo por debajo de esta altitud puede ser de origen lacustre. El promedio mundial de carbonato inorgánico en el suelo es de 33.2 Kg C m −2 , mientras que los suelos de las cuentas Fryxell, Hoare, y Bonney en el Valle Taylor tienen valores medios de 0.38, 0.31 y 0.68 Kg C m −2, respectivamente.

The geochemistry of river water, river sediments, and suspended matter in three mountainous watersheds in New Zealand and Taiwan is used to determine chemical erosion yields in regions of rapid tectonic uplift. Suspended matter from all three rivers is depleted in soluble alkali metals and alkaline earths compared to upper continental crust material and marine clays, reflecting the bedrocks' origin as marine sediments that had undergone previous weathering cycles prior to uplift and subjection to the current chemical weathering regime. The New Zealand rivers are depleted in Mg 2+ and enriched in Ca 2+ and Na + + K + compared to global average river water, but the Taiwan river is enriched only in Mg 2+ compared to global average. The Haast compared River, draining the Southern Alps of New Zealand, is depleted in Cl + SO 4 to the global average, but has higher alkalinity and slightly higher H 4 SiO 4 . The chemical weathering yields determined here compose only a small portion (1%–5%) of the total weathering in these systems, but are still among the highest chemical yields ever reported. Our new data, in comparison to previously determined physical erosion yields in these watersheds, show that physical erosion strongly enhances chemical erosion. This work demonstrates the importance of chemical erosion as a process denuding the landscape, especially in high-standing, tectonically active mountainous landscapes.

Abstract: Kelts (1988) was the first to point out that the ionic composition of lacustrine waters could exert an important effect on the preservation of organic matter in the sediments of these systems. In lakes with high sedimentation rates, the sediments become devoid of molecular oxygen at or very near the sediment-water interface. The rates of anoxic (anaerobic) decomposition of organic matter vary with the amount and "type" of organic matter being buried as well as with the electron acceptor being reduced. The amount of energy produced per organic molecule being oxidized is more for microbial sulfate reduction than for methane production. Therefore, where sulfate is abundant, organic carbon should be more readily oxidized than where other anions such as Cl – and HCO 3 – dominate the chemistry. We have tested this hypothesis by determining in-situ sulfate reduction via radiolabel techniques in sediments from Freefight Lake, a Na + -Mg 2+ -SO 4 2– saline lake in southwestern Saskatchewan. These data are then compared to sulfate reduction rate measurements from other sedimentary environments. Of particular interest is our previous work on algal flat sediments from Na + -Mg 2+ -Cl – salt lakes and pans in Bonaire, N. A. The maximum sulfate reduction rate for the nearshore, algal flat sediments of Freefight Lake was 400 nmol/ml/d. This is 2 to 2.5 times lower than rates from similar settings in Bonaire, even though the sulfate concentrations were 10–20 times higher at Freefight Lake. In addition, the S:OC ratios of the Freefight Lake sediments were extremely low, indicating the lack of sulfate reduction in these sediments. Although the total reduced sulfur concentration increased with depth at Freefight Lake, an extremely high percentage of this total S 2– is in the form of acid-volatile sulfur. This would not have been predicted from the low sulfate reduction rates. A number of important conclusions can be drawn from this work. They include the following: (1) sulfate reduction rates in salt lake sediments are not solely dependent on SO 4 2– concentrations nor on the ionic composition of the lake waters; (2) even though the organic carbon concentrations of these sediments are high, sulfate reduction is not rapid; and (3) the low sedimentation rate (0.03 cm/yr) may lead to the utilization of the most metabolizable of the carbon present in the oxic zone by aerobic bacteria, thereby slowing sulfate reduction rates.