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Scientists Find Oldest Fresh Water In NZ


Scientists studying an aquifer in the Nelson-Motueka area have found what they believe is the oldest fresh water in New Zealand.

The Moutere aquifer contains high quality glacial-age water more than 20,000 years old, said groundwater scientist Mike Stewart of GNS (Geological and Nuclear Sciences Ltd).

The aquifer, which is 400m to 500m deep, contains a large body of water which probably extends offshore into Tasman Bay.

" We were surprised to find fresh water of this age. There are also relatively old groundwaters in deep aquifers in Manawatu, Taranaki, and Canterbury," Dr Stewart said.

The Moutere aquifer is special in that it has remained a discreet body of water for at least the past 20,000 years.

Dr Stewart said he had initially been investigating the aquifer to find out if it was being recharged by young, shallow groundwater. Isotope analysis had showed that mixing of younger water was only minor.

" Our investigation indicates the aquifer does not connect to the sea. Therefore, there is possibly a very large body of fresh water lying under Tasman Bay." During the last major glacial episode in New Zealand 20,000 years ago, Cook Strait was bridged by a large plain connecting the North and South islands.

Radiocarbon dating at GNS's Rafter Radiocarbon facility in Lower Hutt had put the water's age at 20,000-plus years.

The Moutere aquifer is an important resource for horticulture. It was discovered in the 1980s when shallow wells proved unreliable and property owners started to drill deeper.

" The water is pristine, in the sense that it is free from modern contaminants."

Scientists call such pristine old groundwater "palaeowater". The Moutere groundwater is similar in age and quality to palaeowaters found in other parts of the world. A number of these palaeowaters also originate from the last major ice age.

Dr Stewart said a better understanding of groundwater systems contributed to better management of this important resource. ENDS

Note: Fresh water is more difficult to radiocarbon date than a piece of bone or a wooden carving. There are two reasons for this. First, there is inevitably some mixing of younger water in deep aquifers. Second, old carbon in sediment at the bottom of the aquifer may mix with the water making it look older than it really is. Scientists use the term "mean residence time" when assigning an age to fresh water. This is the period during which water remains within an aquifer, lake or river. The mean residence time in the Moutere aquifer is 27,000 years.


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