Philip N. Froelich - US grants

EAR-00521201
Salters

This award, made through the Major Research Instrumentation (MRI) Program, provides partial support for the purchase of a Multicollector Inductively Coupled Plasma Mass Spectrometer (MC-ICP-MS), and associated hardware. The instrument will be housed in a new Plasma Analytical Facility (PAF) at the National High Magnetic Field Laboratory (NHMFL).
We will use the instrument for:
- mantle geochemistry to constrain the processes that result in mantle heterogeneity as the instrument allows improved analyses of Hf and Pb isotopes as well as in-situ trace element analyses;
- cosmochemistry by measurement of heavy elemental abundances in extra terrestrial materials. returned from the GENESIS and STARDUST missions. For this project the MC-ICP-MS will be coupled with a single collector instrument for the determination of the major elements.
- low temperature geochemistry where the MC-ICP-MS allows metal stable isotope analysis. Foremost will be Fe-isotope analyses to investigate the cycling of Fe in the oceans. The MC-ICP-MS will be instrumental in our development of a Biogeochemical Dynamics Program, an interdisciplinary program that will focus on the interplay between chemistry and biology in aquatic ecosystems and which will make use of the unique instrumentation at the NHMFL. We will develop the protocols to measure the isotopic composition of environmentally significant metals like Cu, Zn, Mo and Hg.
At the NHMFL the instrument will also be of use to the material science and condensed matter physics faculty.

The research team aims to study cave aerodynamics and dripwater chemistry to better understand how speleothems grow and how they incorporate paleoclimate signals into their calcite bands. This research complements an ongoing monitoring campaign established in Hollow Ridge Cave (HRC), Marianna, Florida.

As part of ongoing efforts, the researchers have been able to establish a simple model for cave air exchange with outside air and, thus, the rate of carbon dioxide ventilation in and out of this cave as it breathes. This has been achieved by continuously measuring 222Rn (radon), carbon dioxide, temperature, barometric pressure, relative humidity (in situ air density), rainfall (cave drip rates), wind speed and direction (cave air flow), and solar irradiance.

By expanding this array of in situ cave monitoring instruments to determine high resolution 3D and temporal air and water (drip) flow and chemistry through the cave (hydraulics), the researchers aim to provide a better understanding of the processes and environmental controls on using speleothems as paleoclimate proxies. In effect, the research team will calibrate the isotopic and chemical signals preserved in ?modern? calcite precipitated in a well-understood cave with the isotopic and chemical signatures in the cave air and drip.

The researchers plan several specific experiments that include: (1) deploying a dense array of micro-scale temperature and air flow sensors to map ventilation; (2) measuring existing active stalagmites for growth rates and isotopic and trace element compositions; (3) analyzing rainwater and drip water for chemistry and isotopic composition (time series); (4) running benthic flux experiments to establish rates of 222Rn emanation into the cave from limestone walls and drips; (5) establishing internal exchangeable cave air volume; (6) dye-chasers to estimate the epikarst volume and flow patterns; and (7) hydraulic groundwater gradients around the cave.

The primary broader impacts involve the potential for improved understanding of the limitations and utility of a widely used climate proxy and the support of undergraduate and graduate students.