Thickness of the chemical weathering zone and implications for erosional and climatic drivers of weathering and for carbon-cycle feedbacks

Geology ◽  
2012 ◽  
Vol 40 (9) ◽  
pp. 811-814 ◽  
Author(s):  
A. Joshua West
Keyword(s):  
Carbon Cycle ◽  
Chemical Weathering ◽  
Climatic Drivers ◽  
Weathering Zone

Évolution géochimique superficielle naissante des anorthosites. Cas du profil de Château-Richer (Québec), Canada

1982 ◽  
Vol 19 (8) ◽  
pp. 1697-1706 ◽  
Author(s):  
J. Dejou ◽  
C. R. De Kimpe ◽  
P. Lasalle
Keyword(s):  
Chemical Weathering ◽  
Crystalline Rocks ◽  
Parent Rock ◽  
Internal Drainage ◽  
Strong Decrease ◽  
Weathering Index ◽  
Weathering Zone

The initial stages of the superficial geochemical weathering of anorthosites have been investigated in a deposit at Château-Richer, Québec. The parent rock consists almost exclusively of andesine and is weathered to a thickness of about 120 cm. A till overburden indicates that the profile was truncated by the Wisconsinian ice. The rock is not extensively disintegrated, but the chemical weathering is rather intense. The Parker diagram shows a strong decrease of the weathering index from the parent rock to the weathering zone. While this is not the case for other crystalline rocks in the area, it may be accounted for by the fragility of the plagioclase.The < 2 μm fraction, which amounts to 2% of the soil, presents an evolution that is influenced by the site, especially the drainage conditions. At the base of the profile, drainage is poor and 2:1 minerals, smectite and vermiculite, are present in addition to 40% kaolinite. The 1:1 mineral increases to 60% near the contact with the till, while the amount of 2:1 minerals decreases because of the better internal drainage conditions.

scholarly journals Deepening roots can enhance carbonate weathering

2020 ◽  
Author(s):  
Hang Wen ◽  
Pamela L. Sullivan ◽  
Gwendolyn L. Macpherson ◽  
Sharon A. Billings ◽  
Li Li
Keyword(s):  
Carbon Cycle ◽  
Reactive Transport ◽  
Numerical Experiments ◽  
Chemical Weathering ◽  
Dissolved Inorganic Carbon ◽  
Base Case ◽  
Reaction Products ◽  
Soil Co2 ◽  
Carbonate Weathering ◽  
Weathering Rates

Abstract. Carbonate weathering is essential in regulating atmospheric CO2 and carbon cycle at the century time scale. Plant roots have been known to accelerate weathering by elevating soil CO2 via respiration. It however remains poorly understood how and how much rooting characteristics (e.g., depth and density distribution) modify flow paths and weathering. We address this knowledge gap using field data from and reactive transport numerical experiments at the Konza Prairie Biological Station (Konza), Kansas (USA), a site where woody encroachment into grasslands is surmised to deepen roots. Results indicate that deepening roots potentially enhance weathering in two ways. First, deepening roots can control thermodynamic limits of carbonate dissolution by regulating how much CO2 transports downward to the deeper carbonate-rich zone. The base-case data and model from Konza reveal that concentrations of Ca and Dissolved Inorganic Carbon (DIC) are regulated by soil pCO2 driven by the seasonal fluctuation of soil respiration. This relationship can be encapsulated in equations derived in this work describing the dependence of Ca and DIC on temperature and soil CO2, which has been shown to apply in multiple carbonate-dominated catchments. Second, numerical experiments show that roots control weathering rates by regulating the amount of water fluxes that flush through the carbonate zone and export reaction products at dissolution equilibrium. Numerical experiments explored the potential effects of partitioning 40 % of infiltrated water to depth in woodlands compared to 5 % in grasslands. Soil CO2 data from wood- and grasslands suggest relatively similar soil CO2 distribution over depth, and only led to 1 % to 12 % difference in weathering rates if flow partitioning was kept the same between the two land covers. In contrast, deepening roots can enhance weathering by 17 % to 207 % as infiltration rates increased from 3.7 × 10−2 to 3.7 m/yr. Numerical experiments also indicated that weathering fronts in woodlands propagated > 2 times deeper compared to grasslands after 300 years at the infiltration rate of 0.37 m/yr. These differences in weathering fronts are ultimately caused by the contact time of CO2-charged water with carbonate rocks. We recognize that modeling results are subject to limitations in representing processes and parameters, but we propose that the data and numerical experiments allude to the hypothesis that (1) deepening roots can enhance carbonate weathering; (2) the hydrological impacts of rooting characteristics can be more influential than those of soil CO2 distribution in modulating weathering rates. We call for co-located characterizations of roots, subsurface structure, soil CO2 levels, and their linkage to water and water chemistry. These measurements will be essential to improve models and illuminate feedback mechanisms of land cover changes, chemical weathering, global carbon cycle, and climate.

Processes of the Long-Term Carbon Cycle: Chemical Weathering of Silicates

2004 ◽  
Author(s):  
Robert A. Berner
Keyword(s):  
Carbon Cycle ◽  
Time Scales ◽  
Chemical Weathering ◽  
Continental Drift ◽  
Atmospheric Co2 ◽  
Silicate Weathering ◽  
Geological Time ◽  
Orogenic Uplift ◽  
Steep Slopes ◽  
Primary Minerals

Carbon dioxide is removed from the atmosphere during the weathering of both silicates and carbonates, but, over multimillion year time scales, as pointed out in chapter 1, only Ca and Mg silicate weathering has a direct effect on CO2. Carbon is transferred from CO2 to dissolved HCO3– and then to Ca and Mg carbonate minerals that are buried in sediments (reaction 1.4). In this chapter the factors that affect the rate of silicate weathering and how they could have changed over Phanerozoic time are discussed. Following classical studies (e.g., Jenny, 1941), the factors discussed include relief, climate (rainfall and temperature), vegetation, and lithology. However, over geological time scales, additional factors come into consideration that are necessarily ignored in studying modern weathering. These include the evolution of the sun and continental drift. The aim of this book is to consider all factors, whether occurring at present or manifested only over very long times, that affect weathering as it relates to the Phanerozoic carbon cycle. Within the past decade much attention has been paid to the effect of mountain uplift on chemical weathering and its effect on the uptake of atmospheric CO2, an idea originally espoused by T.C. Chamberlin (1899). The uplift of the Himalaya Mountains and resulting increased weathering has been cited as a principal cause of late Cenozoic cooling due to a drop in CO2 (Raymo, 1991). Orogenic uplift generally results in the development of high relief. High relief results in steep slopes and enhanced erosion, and enhanced erosion results in the constant uncovering of primary minerals and their exposure to the atmosphere. In the absence of steep slopes, a thick mantle of clay weathering product can accumulate and serve to protect the underlying primary minerals against further weathering. An excellent example of this situation is the thick clay-rich soils of the Amazon lowlands where little silicate weathering occurs (Stallard and Edmond, 1983). In addition, the development of mountain chains often leads to increased orographic rainfall and, at higher elevations, increased erosion by glaciers. All these factors should lead to more rapid silicate weathering and faster uptake of atmospheric CO2.

scholarly journals Climate, cryosphere and carbon cycle controls on Southeast Atlantic orbital-scale carbonate deposition since the Oligocene (30–0 Ma)

2020 ◽  
Author(s):  
Anna Joy Drury ◽  
Diederik Liebrand ◽  
Thomas Westerhold ◽  
Helen M. Beddow ◽  
David A. Hodell ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Late Miocene ◽  
Chemical Weathering ◽  
Global Climate ◽  
Global Ocean ◽  
Equatorial Pacific Ocean ◽  
Ocean Drilling Program ◽  
Regional Variability ◽  
Caco3 Content

Abstract. The evolution of the Cenozoic Icehouse over the past 30 million years (Myr) from a unipolar to a bipolar world is broadly known; however, the exact development of orbital-scale climate variability is less well understood. Highly resolved records of carbonate (CaCO3) content provide insight into the evolution of regional and global climate, cryosphere and carbon cycle dynamics. Here, we generate the first Southeast Atlantic CaCO3 content record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca/Fe) data collected at Ocean Drilling Program Site 1264 (Angola Basin side of the Walvis Ridge, SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (~316 m; 30 Myr), which constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this site. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to major developments in climate, the cryosphere and/or the carbon cycle: 1) strong ~110 kyr eccentricity pacing prevails during Oligo-Miocene global warmth (~30–13 Ma); 2) increased eccentricity-modulated precession pacing appears after the mid Miocene Climate Transition (mMCT) (~14–8 Ma); 3) strong obliquity pacing appears in the late Miocene (~7.7–3.3 Ma) following the increasing influence of high-latitude processes. The lowest CaCO3 content (92–94 %) occur between 18.5–14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climate Optimum (~17–14.5 Ma) by 1.5 Myr. The emergence of precession-pacing of CaCO3 deposition at Site 1264 after ~14 Ma could signal a reorganisation of surface and/or deep-water circulation in this region following Antarctic reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or an influx of cooler, less corrosive deep-waters. The highest %CaCO3 and MARs indicate the late Miocene Biogenic Bloom (LMBB) occurs between ~7.8–3.3 Ma at Site 1264, which is broadly, but not exactly, contemporaneous with the LMBB in the equatorial Pacific Ocean. The global expression of the LMBB may reflect an increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes. Regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation in the late Miocene.

scholarly journals Carbon cycle extremes during the 21st century in CMIP5 models: Future evolution and attribution to climatic drivers

2014 ◽  
Vol 41 (24) ◽  
pp. 8853-8861 ◽  
Author(s):  
Jakob Zscheischler ◽  
Markus Reichstein ◽  
Jannis von Buttlar ◽  
Mingquan Mu ◽  
James T. Randerson ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
21St Century ◽  
Cmip5 Models ◽  
Future Evolution ◽  
Climatic Drivers

scholarly journals Climate, cryosphere and carbon cycle controls on Southeast Atlantic orbital-scale carbonate deposition since the Oligocene (30–0 Ma)

2021 ◽  
Vol 17 (5) ◽  
pp. 2091-2117
Author(s):  
Anna Joy Drury ◽  
Diederik Liebrand ◽  
Thomas Westerhold ◽  
Helen M. Beddow ◽  
David A. Hodell ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Ocean Circulation ◽  
Late Miocene ◽  
High Latitude ◽  
Chemical Weathering ◽  
Global Ocean ◽  
Carbonate Content ◽  
Equatorial Pacific Ocean ◽  
Regional Variability ◽  
Caco3 Content

Abstract. The evolution of the Cenozoic cryosphere from unipolar to bipolar over the past 30 million years (Myr) is broadly known. Highly resolved records of carbonate (CaCO3) content provide insight into the evolution of regional and global climate, cryosphere, and carbon cycle dynamics. Here, we generate the first Southeast Atlantic CaCO3 content record spanning the last 30 Myr, derived from X-ray fluorescence (XRF) ln(Ca / Fe) data collected at Ocean Drilling Program Site 1264 (Walvis Ridge, SE Atlantic Ocean). We present a comprehensive and continuous depth and age model for the entirety of Site 1264 (∼ 316 m; 30 Myr). This constitutes a key reference framework for future palaeoclimatic and palaeoceanographic studies at this location. We identify three phases with distinctly different orbital controls on Southeast Atlantic CaCO3 deposition, corresponding to major developments in climate, the cryosphere and the carbon cycle: (1) strong ∼ 110 kyr eccentricity pacing prevails during Oligocene–Miocene global warmth (∼ 30–13 Ma), (2) increased eccentricity-modulated precession pacing appears after the middle Miocene Climate Transition (mMCT) (∼ 14–8 Ma), and (3) pervasive obliquity pacing appears in the late Miocene (∼ 7.7–3.3 Ma) following greater importance of high-latitude processes, such as increased glacial activity and high-latitude cooling. The lowest CaCO3 content (92 %–94 %) occurs between 18.5 and 14.5 Ma, potentially reflecting dissolution caused by widespread early Miocene warmth and preceding Antarctic deglaciation across the Miocene Climatic Optimum (∼ 17–14.5 Ma) by 1.5 Myr. The emergence of precession pacing of CaCO3 deposition at Site 1264 after ∼ 14 Ma could signal a reorganisation of surface and/or deep-water circulation in this region following Antarctic reglaciation at the mMCT. The increased sensitivity to precession at Site 1264 between 14 and 13 Ma is associated with an increase in mass accumulation rates (MARs) and reflects increased regional CaCO3 productivity and/or recurrent influxes of cooler, less corrosive deep waters. The highest carbonate content (%CaCO3) and MARs indicate that the late Miocene–early Pliocene Biogenic Bloom (LMBB) occurs between ∼ 7.8 and 3.3 Ma at Site 1264; broadly contemporaneous with the LMBB in the equatorial Pacific Ocean. At Site 1264, the onset of the LMBB roughly coincides with appearance of strong obliquity pacing of %CaCO3, reflecting increased high-latitude forcing. The global expression of the LMBB may reflect increased nutrient input into the global ocean resulting from enhanced aeolian dust and/or glacial/chemical weathering fluxes, due to enhanced glacial activity and increased meridional temperature gradients. Regional variability in the timing and amplitude of the LMBB may be driven by regional differences in cooling, continental aridification and/or changes in ocean circulation in the late Miocene.

Hydrologic Regulation of Chemical Weathering and the Geologic Carbon Cycle

Science ◽  
2014 ◽  
Vol 343 (6178) ◽  
pp. 1502-1504 ◽  
Author(s):  
K. Maher ◽  
C. P. Chamberlain
Keyword(s):  
Carbon Cycle ◽  
Chemical Weathering ◽  
Hydrologic Regulation

scholarly journals Deepening roots can enhance carbonate weathering by amplifying CO<sub>2</sub>-rich recharge

2021 ◽  
Vol 18 (1) ◽  
pp. 55-75
Author(s):  
Hang Wen ◽  
Pamela L. Sullivan ◽  
Gwendolyn L. Macpherson ◽  
Sharon A. Billings ◽  
Li Li
Keyword(s):  
Carbon Cycle ◽  
Reactive Transport ◽  
Numerical Experiments ◽  
Chemical Weathering ◽  
Dissolved Inorganic Carbon ◽  
Base Case ◽  
Soil Co2 ◽  
Carbonate Weathering ◽  
Deep Subsurface ◽  
Weathering Rates

Abstract. Carbonate weathering is essential in regulating atmospheric CO2 and carbon cycle at the century timescale. Plant roots accelerate weathering by elevating soil CO2 via respiration. It however remains poorly understood how and how much rooting characteristics (e.g., depth and density distribution) modify flow paths and weathering. We address this knowledge gap using field data from and reactive transport numerical experiments at the Konza Prairie Biological Station (Konza), Kansas (USA), a site where woody encroachment into grasslands is surmised to deepen roots. Results indicate that deepening roots can enhance weathering in two ways. First, deepening roots can control thermodynamic limits of carbonate dissolution by regulating how much CO2 transports vertical downward to the deeper carbonate-rich zone. The base-case data and model from Konza reveal that concentrations of Ca and dissolved inorganic carbon (DIC) are regulated by soil pCO2 driven by the seasonal soil respiration. This relationship can be encapsulated in equations derived in this work describing the dependence of Ca and DIC on temperature and soil CO2. The relationship can explain spring water Ca and DIC concentrations from multiple carbonate-dominated catchments. Second, numerical experiments show that roots control weathering rates by regulating recharge (or vertical water fluxes) into the deeper carbonate zone and export reaction products at dissolution equilibrium. The numerical experiments explored the potential effects of partitioning 40 % of infiltrated water to depth in woodlands compared to 5 % in grasslands. Soil CO2 data suggest relatively similar soil CO2 distribution over depth, which in woodlands and grasslands leads only to 1 % to ∼ 12 % difference in weathering rates if flow partitioning was kept the same between the two land covers. In contrast, deepening roots can enhance weathering by ∼ 17 % to 200 % as infiltration rates increased from 3.7 × 10−2 to 3.7 m/a. Weathering rates in these cases however are more than an order of magnitude higher than a case without roots at all, underscoring the essential role of roots in general. Numerical experiments also indicate that weathering fronts in woodlands propagated > 2 times deeper compared to grasslands after 300 years at an infiltration rate of 0.37 m/a. These differences in weathering fronts are ultimately caused by the differences in the contact times of CO2-charged water with carbonate in the deep subsurface. Within the limitation of modeling exercises, these data and numerical experiments prompt the hypothesis that (1) deepening roots in woodlands can enhance carbonate weathering by promoting recharge and CO2–carbonate contact in the deep subsurface and (2) the hydrological impacts of rooting characteristics can be more influential than those of soil CO2 distribution in modulating weathering rates. We call for colocated characterizations of roots, subsurface structure, and soil CO2 levels, as well as their linkage to water and water chemistry. These measurements will be essential to illuminate feedback mechanisms of land cover changes, chemical weathering, global carbon cycle, and climate.

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