Researchers at UCD


Vanessa Johnston

Senior Postgrad. Demonstrator

School Of Geological Sciences

Tel: +353 1 7162138


Vanessa's interest in geochemistry and speleology began during her M.Sci course in Environment Geoscience at the University of Bristol (UK). During which she undertook fieldwork sampling the freshwater lens of the Pacific island of Guam from caves and monitoring boreholes as part of her Master's project studying the geochemistry of an uplifted tropical karst aquifer. In 2005, Vanessa moved to Dublin to commence a PhD as part of the Palaeoclimate Research Group, under the supervision of Prof. Frank McDermott. In addition to using cave deposits for research purposes, Vanessa also enjoys speleology as a hobby and is an active member of both the UCD Caving and Potholing Club and the University of Bristol Spelaeological Society.



Peer Reviewed Journals

Johnston, V.E. and McDermott, F.; (2008) 'The distribution of meteoric Cl-36 in precipitation across Europe in spring 2007'. Earth and Planetary Science Letters, 275 :154-164. [DOI] [Details]
Whitaker FF, Paterson RJ, Johnston VE ; (2006) 'Meteoric diagenesis during sea-level lowstands: Evidence from modern hydrochemical studies on northern Guam'. Journal of Geochemical Exploration, 89 (1-3):420-423. [DOI] [Details]

Conference Publications

Johnston, V.E. and McDermott, F.; (2010) Cosmogenic Cl-36 in meteoric waters and cave materials Trinity College Dublin, Geology Department Lunchtime Seminar Trinity College Dublin, [Details]
Johnston, V.E.; (2009) Reconstructing past climate changes from speleothems and other cave deposits 25th Annual Speleological Union of Ireland Symposium Ballyvaughan, Co. Clare, Ireland, [Details]
Vanessa Johnston and Frank McDermott; (2009) Quantifying the sources of cosmogenic 36Cl in the karst environment: modelling the inputs as a function of altitude, latitude, and hydrogeology 52nd Annual Irish Geological Research Meeting Trinity College Dublin, , 20-FEB-09 - 22-FEB-09 [Details]
Johnston, V.E. and McDermott, F.; (2008) An investigation of cosmogenic Cl-36 as a solar irradiance proxy: preliminary production results from European rainfall 51st Annual Irish Geological Research Meeting University College Dublin, [Details]

Published Reports

Whitaker, F.F., Smart, P., and Johnston, V.; (2004) A review of rates of surface lowering and early carbonate diagenesis. Exxon Mobil, Report to Exxon Mobil Upstream Research Company. [Details]


Research Interests


Project Title: Chlorine-36 systematics in karst systems and the precise delineation of solar-forced palaeoclimate events in late-Glacial/Holocene mid-latitude speleothems

Supervisor(s): Prof. Frank McDermott

Funding Agency: Science Foundation Ireland

Project Description:

Solar forcing has been emphasised in recent reviews (e.g. Mayewski et al., 2004) as a potential driver of climate variability. However, the link remains controversial because proxies for solar output can appear contradictory, and the nature of the amplification mechanisms for small (<1%) changes in solar irradiance remains elusive.

We are adopting a new approach, namely to reconstruct time-series of meteoric 36Cl fluxes in mid-latitude European speleothems in conjunction with climate-sensitive proxy data such as δ18O. The cosmogenic 36Cl flux into growing speleothems is our preferred proxy for solar output because 36Cl is dominantly produced in the atmosphere and its extremely hydrophilic conservative nature should ensure rapid transfer of meteoric 36Cl into speleothems. This contrasts with existing cosmogenic solar proxies such as 14C, which experiences variable residence times in surface biota, and 10Be that can become adsorbed onto surficial deposits.

As a prelude to this speleothem study, variability of chloride, the 36Cl/Cl ratio, and 36Cl fallout in precipitation is being investigated to identify the optimum sampling localities. In addition, dripwater monitoring and modelling of 36Cl transport through the karst systems will be undertaken to assess the inert nature of the chosen solar proxy and the suitability of the preferred archive.