SILICATE WEATHERING AND MIDDLE DEVONIAN PALEOCLIMATE

AbstractGlobal climate is thought to be modulated by the supply of minerals to Earth’s surface. Whereas silicate weathering removes carbon dioxide (CO2) from the atmosphere, weathering of accessory carbonate and sulfide minerals is a geologically relevant source of CO2. Although these weathering pathways commonly operate side by side, we lack quantitative constraints on their co-variation across erosion rate gradients. Here we use stream-water chemistry across an erosion rate gradient of three orders of magnitude in shales and sandstones of southern Taiwan, and find that sulfide and carbonate weathering rates rise with increasing erosion, while silicate weathering rates remain steady. As a result, on timescales shorter than marine sulfide compensation (approximately 106–107 years), weathering in rapidly eroding terrain leads to net CO2 emission rates that are at least twice as fast as CO2 sequestration rates in slow-eroding terrain. We propose that these weathering reactions are linked and that sulfuric acid generated from sulfide oxidation boosts carbonate solubility, whereas silicate weathering kinetics remain unaffected, possibly due to efficient buffering of the pH. We expect that these patterns are broadly applicable to many Cenozoic mountain ranges that expose marine metasediments.

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Species of the Devonian aulacopleurid trilobite Cyphaspides from southeastern Morocco

Journal of Paleontology ◽

10.1017/jpa.2019.71 ◽

2019 ◽

Vol 94 (1) ◽

pp. 99-114

Author(s):

Brian D.E. Chatterton ◽

Stacey Gibb ◽

Ryan C. McKellar

Keyword(s):

New Species ◽

Middle Devonian ◽

Present Contribution ◽

Three New Species ◽

Emended Diagnosis

AbstractThree new species of Cyphaspides are proposed: C. ammari, C. nicoleae, and C. pankowskiorum. These species are based on specimens obtained from Middle Devonian (Eifelian) strata of the Bou Tchrafine Group, near Erfoud, in the Province of Errachidia, southeastern Morocco. The present contribution enhances our knowledge of Cyphaspides by providing details of three new species that are based on well-preserved, complete, and articulated types. The genus Cyphaspides is discussed, and an emended diagnosis is provided. The paleobiogeography, ontogeny, and relationships of the genus are discussed.UUID: http://zoobank.org/4a7aab8f-8c8e-4498-9cc2-6f8c69b85213

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Carbonate-silicate cycle predictions of Earth-like planetary climates and testing the habitable zone concept

Nature Communications ◽

10.1038/s41467-020-19896-2 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

Owen R. Lehmer ◽

David C. Catling ◽

Joshua Krissansen-Totton

Keyword(s):

Liquid Water ◽

Physicochemical Parameters ◽

Silicate Weathering ◽

Habitable Zone ◽

Two Dimensional ◽

Land Area ◽

Incident Flux ◽

Earth Like Planets ◽

Surface Liquid ◽

Log Linear

AbstractIn the conventional habitable zone (HZ) concept, a CO2-H2O greenhouse maintains surface liquid water. Through the water-mediated carbonate-silicate weathering cycle, atmospheric CO2 partial pressure (pCO2) responds to changes in surface temperature, stabilizing the climate over geologic timescales. We show that this weathering feedback ought to produce a log-linear relationship between pCO2 and incident flux on Earth-like planets in the HZ. However, this trend has scatter because geophysical and physicochemical parameters can vary, such as land area for weathering and CO2 outgassing fluxes. Using a coupled climate and carbonate-silicate weathering model, we quantify the likely scatter in pCO2 with orbital distance throughout the HZ. From this dispersion, we predict a two-dimensional relationship between incident flux and pCO2 in the HZ and show that it could be detected from at least 83 (2σ) Earth-like exoplanet observations. If fewer Earth-like exoplanets are observed, testing the HZ hypothesis from this relationship could be difficult.

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The Contribution of Groundwater to the Salinization of Reservoir-Based Irrigation Systems

Agronomy ◽

10.3390/agronomy11030512 ◽

2021 ◽

Vol 11 (3) ◽

pp. 512

Author(s):

Michiele Gebrehiwet ◽

Nata T. Tafesse ◽

Solomon Habtu ◽

Berhanu F. Alemaw ◽

Kebabonye Laletsang ◽

...

Keyword(s):

Water Quality ◽

Cation Exchange ◽

Irrigation Water ◽

Groundwater Potential ◽

Hydrochemical Facies ◽

Command Area ◽

Silicate Weathering ◽

Irrigation Water Quality ◽

Carbonate Minerals ◽

Watershed Area

This study evaluates the cause of salinization in an irrigation scheme of 100 ha supplied from a reservoir. The scheme is located in Gumselasa catchment (28 km2), Tigray region, northern Ethiopia. The catchment is underlain by limestone–shale–marl intercalations with dolerite intrusion and some recent sediments. Water balance computation, hydrochemical analyses and irrigation water quality analyses methods were used in this investigation. Surface waters (river and reservoir) and groundwater samples were collected and analyzed. The water table in the irrigated land is ranging 0.2–2 m below the ground level. The majority of groundwater in the effective watershed area and the river and dam waters are fresh and alkaline whereas in the command area the groundwater is dominantly brackish and alkaline. The main hydrochemical facies in the groundwater in the effective watershed area are Ca-Na-SO4-HCO3, Ca-Na- HCO3-SO4, and Ca-Na-Mg-SO4-HCO3. The river and dam waters are Mg-Na-HCO3-SO4 and HCO3-SO4-Cl types, respectively. In the command area the main hydrochemical facies in the groundwater are Ca-Na-HCO3-SO4 and Ca-Na-Mg-SO4-HCO3. Irrigation water quality analyses revealed that salinity and toxicity hazards increase from the effective watershed to the irrigated land following the direction of the water flow. The results also showed that the analyzed waters for irrigation purpose had no sodicity hazard. The major composition controlling mechanisms in the groundwater chemistry was identified as the dissolution of carbonate minerals, silicate weathering, and cation exchange. One of the impacts of the construction of the dam in the hydrologic environment of the catchment is on its groundwater potential. The dam is indirectly recharging the aquifers and enhances the groundwater potential of the area. This increment of availability of groundwater enhanced dissolution of carbonate minerals (calcite, dolomite, and gypsum), silicate weathering and cation exchange processes, which are the main causes of salinity in the irrigated land. The rising of the brackish groundwater combined with insufficient leaching contributed to secondary salinization development in the irrigated land. Installation of surface and subsurface drainage systems and planting salt tolerant (salt loving) plants are recommended to minimize the risk of salinization and salt accumulation in the soils of the irrigated land.

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