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Title: Probing the deep critical zone beneath the Luquillo Experimental Forest, Puerto Rico

Abstract

Recent work has suggested that weathering processes occurring in the subsurface produce the majority of silicate weathering products discharged to the world s oceans, thereby exerting a primary control on global temperature via the well-known positive feedback between silicate weathering and CO2. In addition, chemical and physical weathering processes deep within the critical zone create aquifers and control groundwater chemistry, watershed geometry and regolith formation rates. Despite this, most weathering studies are restricted to the shallow critical zone (e.g., soils, outcrops). Here we investigate the chemical weathering, fracturing and geomorphology of the deep critical zone in the Bisley watershed in the Luquillo Critical Zone Observatory, Puerto Rico, from two boreholes drilled to 37.2 and 27.0 m depth, from which continuous core samples were taken. Corestones exposed aboveground were also sampled. Weathered rinds developed on exposed corestones and along fracture surfaces on subsurface rocks slough off of exposed corestones once rinds attain a thickness up to ~1 cm, preventing the corestones from rounding due to diffusion limitation. Such corestones at the land surface are assumed to be what remains after exhumation of similar, fractured bedrock pieces that were observed in the drilled cores between thick layers of regolith. Some of thesemore » subsurface corestones are massive and others are highly fractured, whereas aboveground corestones are generally massive with little to no apparent fracturing. Subsurface corestones are larger and less fractured in the borehole drilled on a road where it crosses a ridge compared to the borehole drilled where the road crosses the stream channel. Both borehole profiles indicate that the weathering zone extends to well below the stream channel in this upland catchment; hence weathering depth is not controlled by the stream level within the catchment and not all of the water in the watershed is discharged to the stream.« less

Authors:
 [1];  [2];  [3];  [2];  [4];  [3];  [3];  [5];  [6];  [7]
  1. University of Bristol, UK
  2. Pennsylvania State University, University Park, PA
  3. University of Pennsylvania
  4. U.S. Geological Survey, Boulder, CO
  5. U.S. Geological Survey, Menlo Park, CA
  6. ORNL
  7. Ohio State University
Publication Date:
Research Org.:
Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1069348
DOE Contract Number:  
DE-AC05-00OR22725
Resource Type:
Journal Article
Journal Name:
Earth Surface Processes and Landforms
Additional Journal Information:
Journal Volume: 38; Journal Issue: 10; Journal ID: ISSN 1096-9837
Country of Publication:
United States
Language:
English

Citation Formats

Buss, Heather, Brantley, S. L., Scatena, Fred, Bazilevskaya, Ekaterina, Blum, Alex, Schulz, M, Jimenez, M, White, Art, Rother, Gernot, and Cole, David. Probing the deep critical zone beneath the Luquillo Experimental Forest, Puerto Rico. United States: N. p., 2013. Web. doi:10.1002/esp.3409.
Buss, Heather, Brantley, S. L., Scatena, Fred, Bazilevskaya, Ekaterina, Blum, Alex, Schulz, M, Jimenez, M, White, Art, Rother, Gernot, & Cole, David. Probing the deep critical zone beneath the Luquillo Experimental Forest, Puerto Rico. United States. doi:10.1002/esp.3409.
Buss, Heather, Brantley, S. L., Scatena, Fred, Bazilevskaya, Ekaterina, Blum, Alex, Schulz, M, Jimenez, M, White, Art, Rother, Gernot, and Cole, David. Tue . "Probing the deep critical zone beneath the Luquillo Experimental Forest, Puerto Rico". United States. doi:10.1002/esp.3409.
@article{osti_1069348,
title = {Probing the deep critical zone beneath the Luquillo Experimental Forest, Puerto Rico},
author = {Buss, Heather and Brantley, S. L. and Scatena, Fred and Bazilevskaya, Ekaterina and Blum, Alex and Schulz, M and Jimenez, M and White, Art and Rother, Gernot and Cole, David},
abstractNote = {Recent work has suggested that weathering processes occurring in the subsurface produce the majority of silicate weathering products discharged to the world s oceans, thereby exerting a primary control on global temperature via the well-known positive feedback between silicate weathering and CO2. In addition, chemical and physical weathering processes deep within the critical zone create aquifers and control groundwater chemistry, watershed geometry and regolith formation rates. Despite this, most weathering studies are restricted to the shallow critical zone (e.g., soils, outcrops). Here we investigate the chemical weathering, fracturing and geomorphology of the deep critical zone in the Bisley watershed in the Luquillo Critical Zone Observatory, Puerto Rico, from two boreholes drilled to 37.2 and 27.0 m depth, from which continuous core samples were taken. Corestones exposed aboveground were also sampled. Weathered rinds developed on exposed corestones and along fracture surfaces on subsurface rocks slough off of exposed corestones once rinds attain a thickness up to ~1 cm, preventing the corestones from rounding due to diffusion limitation. Such corestones at the land surface are assumed to be what remains after exhumation of similar, fractured bedrock pieces that were observed in the drilled cores between thick layers of regolith. Some of these subsurface corestones are massive and others are highly fractured, whereas aboveground corestones are generally massive with little to no apparent fracturing. Subsurface corestones are larger and less fractured in the borehole drilled on a road where it crosses a ridge compared to the borehole drilled where the road crosses the stream channel. Both borehole profiles indicate that the weathering zone extends to well below the stream channel in this upland catchment; hence weathering depth is not controlled by the stream level within the catchment and not all of the water in the watershed is discharged to the stream.},
doi = {10.1002/esp.3409},
journal = {Earth Surface Processes and Landforms},
issn = {1096-9837},
number = 10,
volume = 38,
place = {United States},
year = {2013},
month = {1}
}