Neon-21 - a possible tool for dating very old groundwaters?

The importance of dating very old groundwaters requires the development of new dating methods. Such methods are available using 36Cl and 81Kr, but their range is limited to about 1 million years. Older fluids must be dated by in situ produced noble gas nuclides. The use of 21Ne is discussed for groundwaters of the north German Salzgitter District. It is likely that the use of 21Ne will not develop into a routine tool; nonetheless, 21Ne excess gives information on the level of in situ production of gases, a fact which is important for more reliable 4He dating

Origin and age of thermal waters in Cieplice Spa, Sudeten, Poland, inferred from isotope, chemical and noble gas data.

Isotope and hydrochemical data of the thermal water system in Cieplice Ṡlaskie Zdrój (Spa) indicate the existence of two subsystems that greatly differ in volume and which meet at the fault zones of a granitic horst, where they discharge at an altitude of about 340m. One of the subsystems is very small (about 4 × 103 m3) as indicated by the tritium age of the order of 10 years and a low outflow rate. Its recharge area found from the δ18O and δD values, is about 200m above the springs, most probably on the slopes of the foothills of the Karkonosze Mountains south-southwest of the spa. The large subsystem contains water which is free of tritium and whose 14C content is from 1 to 8 pmc with δ13C = -8.0 to -9.2‰. The isotopic composition of this water reflects either the climatic effect (low-altitude recharge during a cooler pre-Holocene climate) or the altitude effect (recharge in the early Holocene period at about 1000m at the heights of the Karkonosze assuming that the 14C concentration is strongly reduced by exchange with calcite in veins). For the former hypothesis, the recharge area of this water is probably either at the foot of the southeastern slopes of the Kaczawa Mountains or/and at the foot of the Rudawy Janowickie Mountains, to the east of Cieplice. The noble gas temperatures are more consistent with the pre-Holocene recharge. Similarly, the 4He excess and 40Ar 36Ar ratio support the hypothesis of a pre-Holecene age. The constant 3He 4He ratio of 26 × 10-8 for highly different helium contents indicates crustal origin of helium. For the pre-Holocene age of water its volume is calculated at >- 109m3 (stagnant water in micropores and mobile water in fractures) and the hydraulic conductivity of the host granite massif is estimated at about 7 × 10-8 ms-1. Two outflows from this subsystem have different and variable fractions of a modern water component (bomb age), most probably originating from the bank infiltration of a nearby stream

Possible evidence for ¹⁴C isotope exchange between groundwater and carbonate rocks in the eastern Donau Ried, Bavaria, Germany.

Isotope hydrological investigations of groundwaters yielded very low 14C contents, together with normal δ13C values for dissolved inorganic carbon (DIC) and correspondingly high 14CDIC model ages. However, the 2H, 18O and 4He contents suggested a Holocene age for most of the groundwaters. New data from 14C measurements on dissolved organic carbon (DOC) and 39Ar indicate significantly lower groundwater ages (<7500 years). Furthermore, the isotopic composition (34S and 18O) of the aqueous sulphates accounts for its meteoric origin. Such values also characterize recent karst groundwaters on the Swabian-Franconian Alb. The discrepancies between the different isotopic ages are possibly explained by carbon isotope exchange with terrestrial carbonates found in this area. -Author

A multi-environmental tracer study to determine groundwater residence times and recharge in a structurally complex multi-aquifer system

Despite being the main drinking water resource for over 5 million people, the water balance of the Eastern Mountain Aquifer system on the western side of the Dead Sea is poorly understood. The regional aquifer consists of fractured and karstified limestone – aquifers of Cretaceous age, and it can be separated into a Cenomanian aquifer (upper aquifer) and Albian aquifer (lower aquifer). Both aquifers are exposed along the mountain ridge around Jerusalem, which is the main recharge area. From here, the recharged groundwater flows in a highly karstified aquifer system towards the east and discharges in springs in the lower Jordan Valley and Dead Sea region. We investigated the Eastern Mountain Aquifer system for groundwater flow, groundwater age and potential mixtures, and groundwater recharge. We combined 36Cl ∕ Cl, tritium, and the anthropogenic gases SF6, CFC-12 (chlorofluorocarbon) and CFC-11, while using CFC-113 as “dating” tracers to estimate the young water components inside the Eastern Mountain Aquifer system. By application of lumped parameter models, we verified young groundwater components from the last 10 to 30 years and an admixture of a groundwater component older than about 70 years. Concentrations of nitrate, simazine (pesticide), acesulfame K (ACE-K; artificial sweetener) and naproxen (NAP; drug) in the groundwater were further indications of infiltration during the last 30 years. The combination of multiple environmental tracers and lumped parameter modelling helped to understand the groundwater age distribution and to estimate recharge despite scarce data in this very complex hydrogeological setting. Our groundwater recharge rates support groundwater management of this politically difficult area and can be used to inform and calibrate ongoing groundwater flow models.Cornelia Wilske, Axel Suckow, Ulf Mallast, Christiane Meier, Silke Merchel, Broder Merkel ... et al