Geology topics

Greg H. Rau

Publications and source records attributed to Greg H. Rau.

4 recordsLinked to original sources

USGS2007

Reducing energy-related CO 2 emissions using accelerated weathering of limestone

The use and impacts of accelerated weathering of limestone (AWL; reaction: CO 2 +H 2 O+CaCO 3 →Ca 2+ +2(HCO 3 - ) is explored as a CO 2 capture and sequestration method. It is shown that significant limestone resources are relatively close to a majority of CO 2 -emitting power plants along the coastal US, a favored siting location for AWL. Waste fines, representing more than 20% of current US crushed limestone production (>10 9 tonnes/yr), could provide an inexpensive or free source of AWL carbonate. With limestone transportation then as the dominant cost variable, CO 2 mitigation costs of $3-$4/tonne appear to be possible in certain locations. Perhaps 10–20% of US point–source CO 2 emissions could be mitigated in this fashion. It is experimentally shown that CO 2 sequestration rates of 10 -6 to 10 -5 moles/sec per m 2 of limestone surface area are achievable, with reaction densities on the order of 10 -2 tonnes CO 2 m -3 day -1 , highly dependent on limestone particle size, solution turbulence and flow, and CO 2 concentration. Modeling shows that AWL would allow carbon storage in the ocean with significantly reduced impacts to seawater pH relative to direct CO 2 disposal into the atmosphere or sea. The addition of AWL-derived alkalinity to the ocean may itself be beneficial for marine biota.

Energy↗

USGS2004

CO 2 mitigation via accelerated limestone weathering

We evaluate accelerated weathering of limestone (AWL: CO 2 + CaCO 3 + H 2 O=> Ca 2+ + 2HCO 3 - ) as a low-tech, inexpensive, high-capacity, environmentally-friendly CO 2 capture and sequestration technology. With access to seawater and limestone being essential to this approach, significant limestone resources are close to most CO 2 -emitting power plants along the coastal US. Waste fines, representing more than 20% of current US crushed limestone production (>10 9 tonnes/yr), could be used as an inexpensive source of AWL carbonate. Under such circumstances CO 2 mitigation cost could be as low as $3-$4/tonne. More broadly, 10-20% of US point-source CO 2 emissions could be treated at $20-$30/tonne CO 2 . AWL end-solution disposal in the ocean would significantly reduce effects on ocean pH and carbonate chemistry relative to those caused by direct atmospheric or ocean CO 2 disposal. Indeed, the increase in ocean Ca 2+ and bicarbonate offered by AWL should enhance growth of corals and other calcifying marine organisms.

Conference Paper↗

USGS2003

Molecular and isotopic tracers used to examine sources of organic matter and its incorporation into the food webs of San Francisco Bay

Multiple indicators (Chl a , C : N ratios, [ δ 13 C]POC, and two classes of lipid biomarker compounds- sterols and phospholipid ester-linked fatty acids) were used to evaluate spatial and temporal variations in the origin of particulate organic matter (POM) in the San Francisco Bay (SFB) estuary. Comparisons were made between the northern and southern subestuaries of SFB, as well as along the salinity gradient of northern SFB. Two sample types were collected-seston, which was used to characterize the bulk POM, and tissues of the suspension-feeding bivalve Potamocorbula amurensis -in order to evaluate the assimilable portion of the POM. Samples were collected around biological and physical events (phytoplankton blooms and freshwater inflow) thought to be the primary mechanisms controlling temporal variability in organic matter sources. Seston samples indicate that phytoplankton sources of POM are important throughout the entire SFB system, with additional inputs of organic matter from bacterial and terrestrial vascular plant sources delivered to the northern region. Analysis of biomarker compounds in P. amurensis tissues indicates that phytoplankton supply a large fraction of the assimilable carbon to clams throughout SFB, although isotopic analysis of clam tissues suggests that the origin of this reactive carbon varies spatially and that freshwater algae are an important source of reactive organic matter to clams living in northern SFB.

California↗

USGS1987

15N/14N variations in Cretaceous Atlantic sedimentary sequences: Implication for past changes in marine nitrogen biogeochemistry

At two locations in the Atlantic Ocean (DSDP Sites 367 and 530) early to middle Cretaceous organic-carbon-rich beds (“black shales”) were found to have significantly lower δ 15 N values (lower 15 N/ 14 N ratios) than adjacent organic-carbon-poor beds (white limestones or green claystones). While these lithologies are of marine origin, the black strata in particular have ° 15 N values that are significantly lower than those previously found in the marine sediment record and most contemporary marine nitrogen pools. In contrast, black, organic-carbon-rich beds at a third site (DSDP Site 603) contain predominantly terrestrial organic matter and have C- and N-isotopic compositions similar to organic matter of modern terrestrial origin. The recurring 15 N depletion in the marine-derived Cretaceous sequences prove that the nitrogen they contain is the end result of an episodic and atypical biogeochemistry. Existing isotopic and other data indicate that the low 15 N relative abundance is the consequence of pelagic rather than post-depositional processes. Reduced ocean circulation, increased denitrification, and, hence, reduced euphotic zone nitrate availability may have led to Cretaceous phytoplankton assemblages that were periodically dominated by N 2 -fixing blue-green algae, a possible source of this sediment 15 N-depletion. Lack of parallel isotopic shifts in Cretaceous terrestrially-derived nitrogen (Site 603) argues that the above change in nitrogen cycling during this period did not extend beyond the marine environment.

Earth and Planetary Science Letters↗