Kate
Maher
Assistant Professor
Dept. of Geological & Environmental Science
Stanford University
General Research Interests
I. Weathering Processes, Biogeochemistry and Climate Change
Isotopic approaches for chemical and physical weathering processes: The decay of naturally occurring radiogenic isotopes provides a natural chronometer for tracking the rates of chemical and physical weathering and fluid flow (Maher et al., 2002, 2004, 2006ab). These chronometers can be paired with traditional (C, O, N, S) and non-traditional stable isotopes (Mg, Ca, Fe) to uniquely track the processes. My research uses the isotopic composition of soils, soil waters and sediment to understand the fundamental controls on the rates of water-rock interactions, and the timescales over which sediment is produced and transported.
Effect of climate, time, water and weathering on soil carbon: We are using a multi-disciplinary approach to understand the linkages between the soil hydrology, nutrient cycling and carbon cycling in soils in order to develop a metric for assessing the vulnerability and resilience of soils to climate change and disturbance. Specifically we are coupling U and Sr isotopes with Carbon-14 and microbiologic indicators to develop a metric for assessing the vulnerability and resilience of soil carbon pools across 15 sites in western N. America.
Reactive transport modeling: Reactive transport modeling is a particularly exciting frontier in geochemistry and hydrlogy (e.g. Steefel et al., 2005; EPSL). Weathering rates in natural systems are affected by many processes including microbial reactions and secondary mineral precipitation. In order to consider the links between these bio- and geochemical processes and the role of aqueous transport, it is necessary to use an accounting tool that is more complex than a spreadsheet. Reactive transport models can be used to uniquely track complicated reaction networks, the movement of aqueous species and the redistribution of isotopes. We are using reactive transport approaches to understand soil profile evolution (Maher et al., 2008) and to interpret complex isotopic variations and biogeochemical reactions (Maher et al., 2006).
II. Terrestrial Paleoclimate
U-series isotopes as a paleoclimate proxy: Uranium isotopic variations are recorded in many paleoclimate records including corals, speleothems, soils and vein calcite. In order to understand what causes these variations we are using the Stanford/USGS ion microprobe (SHRIMP-RG) to study long-term U isotope records in soils. If we can better understand the mechanisms that contribute to the variations, then we can use U isotopes as a paleoclimate proxy in terrestrial environments.
Mojave Cave Project: I am studying several active solution caves in the Mojave National Preserve. The primary goal is to obtain a high-resolution climate record for Southern California.
III. Landscape Evolution and Low Temperature Geochronology:
U-series and U-Pb dating of pedogenic opal: Opal is commonly found in soils
in Mediterranean to arid climates. It contains abundant Uranium and as
a result is an excellent dating tool for determining the ages of soils
and geomorphic surfaces. When analyzed at high-spatial resolution long-term
records can be generated. Current opal dating approaches include 230Th-U
(0 to 200 ka) and U-Pb (200 ka to 4 Ga).
U-series depletion
dating: Using
the depletion in the U daughter products we can determine the age of
fine-grained sediments produced in the Quaternary.
Other: Other low-temperature dating techniques are currently under development using the SHRIMP-RG. If you are interested in learning more about our dating capabilities please contact us.
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Above: Art White and Carl Steefel ponder weathering at the Santa Cruz Marine Terrracce chronosequence Left: Sampling in Fish Lake Valley, NV and also pondering weathering.
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