Paleogroundwater in the Moutere Gravel Aquifers Near Nelson, New Zealand

Abstract

Radiocarbon, 18O, and chemical concentrations have been used to identify groundwater recharged during the last ice age near Nelson, New Zealand. Moutere Gravel underlies most of the Moutere Depression, a 30-km-wide system of valleys filled with Plio-Pleistocene gravel. The depression extends northwards into Tasman Bay, which was above sea level when the North and South Islands of New Zealand were connected during the last glaciation. The aquifers are tapped by bores up to 500 m deep. Shallow bores (50–100 m) tap “pre-industrial” Holocene water (termed the “modern” component) with 14C concentrations of 90 ± 10 percent modern carbon (pMC) and δ18O values of −6.8 ± 0.4, as expected for present-day precipitation. Deeper bores discharge water with lower 14C concentrations and more negative 18O values resulting from input of much older water from depth. The deep end-member of the mixing trend is identified as paleowater (termed the “glacial” component) with 14C concentration close to 0 pMC and more negative 18O values (-7.6). Mixing of the modern and glacial components gives rise to the variations observed in the 14C, 18O, and chemical concentrations of the waters. Identification of the deep groundwater as glacial water suggests that there may be a large body of such water onshore and offshore at deep levels. More generally, the influence of changing sea levels in the recent past (geologically speaking) on the disposition of groundwaters in coastal areas of New Zealand may have been far greater than we have previously realized.

Impact of excessive groundwater pumping on rejuvenation processes in the Bandung basin (Indonesia) as determined by hydrogeochemistry and modeling

“…The measured pMC activity exhibited an increasing tendency implying that the apparent groundwater age decreased in 2012. This phenomenon is the so-called 'rejuvenation' of groundwater age (Stewart et al 2004;Kagabu et al 2013). To discuss rejuvenation based on the observed 14 C activity, R is determined as an indicator of rejuvenation (Eq.…”

Late-glacial to late-Holocene shifts in global precipitation δ<sup>18</sup>O

“…The grey band shows the globally averaged estimate of temperature change since the last glacial maximum of −4.0 ± 0.8 • C. (b) Gridded surface air temperature anomaly from the last glacial maximum to the preindustrial era (data from Annan and Hargreaves, 2013). al., 2004;Liu et al, 2007;Pausata et al, 2011a), local seawater δ 18 O (Wood et al, 2003;Feng et al, 2014), precipitation seasonality (e.g., Fawcett et al, 1997;Werner et al, 2000;Cruz et al, 2005), moisture provenance (e.g., Sjostrom and Welker, 2009;Lewis et al, 2010), storm tracks, climate oscillation modes (e.g., North Atlantic oscillation), moisture recycling (e.g., Winnick et al, 2013Winnick et al, , 2014Liu et al, 2014a, b) and groundwater flow path architecture (Purdy et al, 1996;Stewart et al, 2004;Morrissey et al, 2010;Hagedorn, 2015). While unravelling these mechanisms and delineating the primary and secondary processes can be rather challenging, the use of climate models in combination with robust and extensive precipitation isotope data can resolve many of these complexities with meaningful interpretations and insight.…”

Groundwater age rejuvenation caused by excessive urban pumping in Jakarta area, Indonesia

“…Stewart et al () reports that the 14 C activity became older through repeated groundwater sampling deeper old water extraction by pumping activity. The reason that the result of this study is opposite to that found by Stewart et al () can be considered that the younger groundwater intruded into the groundwater sampled wells by excessive groundwater pumping.…”

“…However, the consistency of 14 C activity between the two years is apparent by comparing 14 C activity at well W18, located in the upstream area, where the groundwater flow shows no great change. Stewart et al (2004) reports that the 14 C activity became older through repeated groundwater sampling deeper old water extraction by pumping activity. The reason that the result of this study is opposite to that found by Stewart et al (2004) can be considered that the younger groundwater intruded into the groundwater sampled wells by excessive groundwater pumping.…”