Inert gases in groundwater from the Bunter Sandstone of England as indicators of age and palaeoclimatic trends

A paleotemperature record derived from dissolved noble gases in groundwater of the Aquia Aquifer (Maryland, USA)

“…Temperature differences of ϳ5 to 7°C were found in studies at higher latitudes in Europe (e.g., Andrews and Lee, 1979;Andrews et al, 1985;Rudolph et al, 1984;Beyerle et al, 1998). However, in some of these NGT records, the LGM could not be clearly identified, possibly because glaciation or permafrost prevented groundwater recharge during the LGM (Andrews and Lee, 1979;Beyerle et al, 1998). A substantially larger than 5°C LGM-Holocene temperature change (Ն8.6°C) was found only in the Great Hungarian Plain (Stute and Sonntag, 1992).…”

“…Three models of the formation of excess air have been proposed: total dissolution (TD) of trapped air bubbles, resulting in atmospheric composition of the excess air (e.g., Andrews and Lee, 1979;Stute and Schlosser, 1993); total dissolution followed by partial re-equilibration (PR) with the atmosphere, resulting in diffusivity-controlled fractionation of the excess air (Stute et al, 1995b); and closed-system equilibration (CE) of groundwater with only partially dissolved entrapped air, resulting in solubility-controlled fractionation (Aeschbach-Hertig et al, 2000).…”

“…He concentrations often increase with groundwater age due to accumulation of radiogenic He produced by ␣-decay of U and Th series nuclides in crustal minerals (e.g., Andrews and Lee, 1979;Torgersen and Clarke, 1985;Stute et al, 1992b;Solomon et al, 1996). There are three potential sources of radiogenic He in groundwater: i) in situ production within the 811 Noble gas paleotemperature record from the Aquia Aquifer aquifer matrix; ii) release of stored He from fresh sediments; and iii) a flux from adjacent layers or even the whole underlying crust.…”

“…The 4 He accumulation rate A He due to in situ production can be calculated as follows (Stute et al, 1992b, modified from Andrews andLee, 1979):…”

“…The release factor ⌳ He (fraction of produced 4 He which is released from minerals into the water) is usually taken to be 1 (e.g., Andrews and Lee, 1979;Torgersen and Clarke, 1985). The density of the aquifer material rock is taken as 2.6 g cm Ϫ3 for the predominant quartz sand.…”