Fractured Systems

Maui, Hawaii

Recent work in the Galapagos Islands suggests that noble gas temperatures (NGTs) in fractured groundwater systems reflect the temperature of the ground surface at the precise time of infiltration rather than the mean annual air temperature (MAAT) value as commonly assumed in sedimentary systems where NGTs are typically used as indicators of past climate. This suggests that noble gases in fractured areas may record seasonality, and thus, provide information about timing of recharge in addition to location. Calculation of NGTs assumes that rain-derived recharge at the water table is in equilibrium with ground air. Lack of noble gas equilibration with respect to surface conditions, however, was observed in high-altitude springs in the Galapagos Islands (Warrier et al., 2012) and in a rainwater pilot study in Michigan (Warrier et al., 2013), supporting the NGT seasonality hypothesis. Developing this new NGT application will lead to a better understanding of fractured and karstic groundwater flow systems and will contribute to improved water resource management plans.

The main goal of this project is to test these hypotheses and to assess whether or not NGTs in fractured and karstic systems can be routinely used to determine location and timing of recharge. The latter point is directly dependent on the premise that NGTs do record seasonality rather than MAAT. Testing these hypotheses requires knowledge of three critical end-members for which the noble gas composition is currently either entirely unknown or poorly constrained: fog, rain and snow. It also requires the presence of springs at high and low altitude as well as access to the regional (basal) aquifer system. Thus, this work is being carried out to a great extent on the windward side of East Maui, Hawaii, where the presence of fog is prominent, where both orographic and synoptic precipitation occur, and where there is an abundance of high and low altitude springs and wells. Snow and ice collected in Michigan are currently being analyzed. We are also collecting local (Maui, Hawaii) weather data that will facilitate the development of models capable of explaining observed, previously unknown noble gas patterns in groundwater, in addition to the analysis of the stable isotopes of hydrogen and oxygen as well as groundwater tritium measurements.

Field trip Maui, Hawaii, June 2014.

This project is being conducted in collaboration with Drs. Steve Gingerich (USGS Honolulu) and Martha Scholl (USGS Reston). 

It is being funded by the NSF EAR Hydrologic Sciences Program (EAR #1344357) and it was first presented at the AGU 2014 Fall Meeting in San Francisco. A presentation at the 2015 Goldschmidt in Prague will be also given. A manuscript is in preparation.

Publications:

Castro, M.C., , Niu Y., Hall C.M., Gingerich S.B., Scholl M.A., Warrier R.  Noble Gas Signatures in Groundwater and Rainwater on the Island of Maui, Hawaii – Understanding the behavior of Noble Gases in Fractured Systems, in preparation, Geophys. Res. Lett.

Castro, M.C., , Niu Y., Warrier R.B., Hall C.M., Gingerich S.B., Scholl M.A., Bouvier L. (2014). Noble Gas Signatures in Groundwater and Rainwater on the Island of Maui, Hawaii – Understanding the behavior of Noble Gases in Fractured, Volcanic Systems. AGU Fall Meeting. San Francisco, Calif., 9-13 Dec
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M. Clara Castro,
May 5, 2017, 6:19 PM
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M. Clara Castro,
May 27, 2015, 9:28 AM
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M. Clara Castro,
May 27, 2015, 12:23 PM