Mt Arthur to MT Luxmore [caving in New Zealand’s South Island]

How’s it.

Welcome to the 2nd post on this fledgling site.

So I just wanted to write quickly about an epic field trip I was involved in last month to a bunch of caves in the South Island. We flew down via Nelson (located at the top of the South Island) and had just 10 days to collect samples of waters, soils and cave flowstone deposits from three cave systems (Nettlebed and Hodge creek (in the Mt Arthur region near Motueka), and Luxmore caves in the Fiordland National Park). I was working with John Hellstrom (University of Melbourne) and Travis Cross (NZ caving legend) and got a pretty rude awakening when we starting our caving adventure at Nettlebed “the biggest, baddest cave in the Southern Hemisphere”, so said John H. John will have some footage for us soon, but suffice to say I was left with a new-found  respect for cavers and for Nettlebed! (so named due to a particularly thick patch of the native NZ nettle near the entrance- warning not to be trifled with! Plus, for the UK readers we don’t have Dock in NZ!) http://en.wikipedia.org/wiki/Nettlebed_Cave

Syd Deaker departs from the Pearce Resurgence base camp.
Syd Deaker departs from the Pearce Resurgence base camp.

After an Air NZ flight to Nelson followed by a helicopter flight courtesy of Syd Deaker (Action Helicopters) in his Hughes 500, we arrived at the Pearce Resurgence, made camp and then hiked to the cave entrance (30 mins along a dry, boulder-strewn river bed and then a steep traverse through bush). The first day we were underground for 6 hours, the second 12 hours. It was bloody hard work physically, but an amazing experience! Nettlebed dissects the Ordovician marble of Mt Arthur (http://en.wikipedia.org/wiki/Mount_Arthur_%28New_Zealand%29), which has been so thoroughly “tectonized” (had the sh*t kicked out of it) that the cave is nearly always wet (this equates to many fractures through which water can flow). Luckily, we arrived at the end of a very long and dry summer, and the cave was comparatively dry. A normal experience for cavers in Nettlebed involves getting soaked in order to pass through a series of sumps which fill with water during periods of prolonged rainfall (not that uncommon in NZ!). So all told, this really helped a lot with the logistics of hauling sampling gear and not to mention ourselves through the cave. Anyone interested in finding out more about the Nettlebed should check out this link:https://www.youtube.com/watch?v=UyCnxytq-Dc.

JH contemplating the sampling of a flowstone deposit in Hodge Creek Cave.
JH contemplating the sampling of a flowstone deposit in Hodge Creek Cave.

Hodge Creek and Luxmore were a cakewalk by comparison but absolutely beautiful and fascinating in their own right. Unlike Mt Arthur these caves are developed in much younger (Oligocene) limestone and so have quite different, much more classically “Karst” topography. For the uninitiated, Karst is derived from German or Slovenian and denotes a landscape of sinkholes, dolines, and caves, characteristic of soluble rocks like limestone. Limestone dissolves due to acidity present in rainwater (contributed by carbon dioxide- think about ocean acidification- same deal). So anyway, both HC and Luxmore were very interesting and we got some really interesting material to work on. Luxmore is particularly interesting for the fact that ca. 95% of the speleothems (secondary carbonates) in the caves here are dissolving. It’s quite uncanny. What could be the cause? Mixing corrosion possibly. Whatever is driving it this seems to be a natural process for this mountain and has probably occurred many times before. There are some really beautifully laminated flowstones in the Luxmore caves. It was really quite sad to see them being destroyed- albeit by a natural process..

View across the karst field, Mt Luxmore. Caves are generally above the treeline  here. Still hard to find amongst the tussock.
View across the karst field, Mt Luxmore. Caves are generally above the treeline here. Still hard to find amongst the tussock.

What are flowstones you may ask? Flowstones are layered calcium carbonate deposits which build up very slowly in caves. These deposits can be cored and used to develop proxy records of environmental and climatic changes. By “proxy” scientists usually mean a property that can be measured which can be related to some other variable of broad relevance. An example of this is the thickness of the banding in the deposit which can tell us about how warm and/or wet the climate was at a given time in the past. Knowing what time in the past all comes down to the science of dating based on the decay of uranium to its daughter isotope thorium- but I will probably talk about another time. The purpose of this research is to better understand how carbon is stored in soils through time. We need to know what happens to the carbon in soils under changing climatic conditions since this carbon can be mineralised (turned back to an inorganic form) back to carbon dioxide and adding to the problem of anthropogenic global warming.

We’ll be starting to work on the flowstone cores soon. Andrew Pearson from Liverpool (UK) will be joining us in May to start his PhD research. Exciting times in the Waikato!

Thanks to JH and TC for all their help.

Adam

This work is funded through a Marsden Fund Fast-Start Award to AH  “The terrestrial carbon cycle in transition: tracking changes using novel tracers on multiple timescales”. Summary: In recent decades, the flux of dissolved organic carbon (DOC) into Northern Hemisphere inland water bodies has increased markedly (from ~0.4 to ~0.8 Pg C/yr, [IPCC, 2007]). This has shifted the balance of the terrestrial carbon cycle, potentially offsetting, or even exceeding the terrestrial carbon sink for anthropogenic emissions (currently ~-1.4 Pg C/yr). Many contemporary explanations imply a role for acidification due to increases in atmospheric sulfur emissions. An alternative hypothesis is the destabilisation of soil carbon by atmospheric warming. However, the coalescence of atmospheric warming and acidification in the Northern Hemisphere prevents the
separation of these drivers based on time series analysis in either river records or environmental archives. This project seeks to resolve the DOC debate by targeting novel geochemical proxies within high-resolution speleothem (cave carbonate) and lake sediment archives from New Zealand, which has seen pronounced positive temperature anomalies since ~1900 AD but remains unaffected by acidification. We will determine the effect of atmospheric warming on DOC release from soil ecosystems in order to refine our understanding of the mechanisms underlying historical DOC increases. In so doing, we will deliver new information on how the terrestrial carbon cycle is likely to respond to future climate transitions.

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