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Phosphorus in Caves: A new methodological development being pioneered at the BCSC

Alistair Morgan is a masters by research student at Lancaster University, his research is focussed on understanding how phosphorous enters cave systems and if, when it is incorporated into stalagmites, it could be used to unravel past temperatures. Here Alistair discusses the ideas behind his work at the BCSC.

Water that enters caves has travelled from the ocean, evaporated and precipitated as rain, moved through rivers and soils before percolating into the cave environment. Along the way, this water picks up dissolved nutrients including carbon (C), phosphorus (P) and nitrogen (N) and these offer a wealth of scientific information. Under certain conditions, cave drip waters form calcite features such as stalagmites; much like those found in Poole’s Cavern. Similar to tree rings and ice cores, stalagmites incorporate this wealth of environmental information as they grow, building a “nutrient record” layer by layer over time.

Alistair (left) and his supervisor Dr Peter Wynn setting up drip water collection sites and measuring cave drip water chemistry in Pooles cavern.

As a MRes student at Lancaster University, my dissertation is looking at the P cycle within caves and especially using the oxygen isotope signature of phosphate (PO4) to understand P cycling and its use as a palaeotemperature proxy. PO4 is a key component for microbiological function, including the formation of DNA. A metabolic process exists in many bacteria (pyrophosphatase hydrolysis) that swaps out oxygen within the PO4 molecule with O from cave drip waters. This process is controlled by the temperature at which the reaction occurs. This means that we can potentially back calculate the formation temperature using the PO4 oxygen isotope signature. PO4 is naturally found in some stalagmites and because these stalagmites take many years to grow, they could hold a record of temperature locked up in their PO4 that is 10,000’s of years old. However currently this is all theory, we are still unsure exactly where the oxygen within PO4 is exchanged or how, and whilst we believe this should take place near to or within the cave this novel approach needs testing. These are the questions on which my research will focus.

Some of the water collection stations set up as part of this MRes research project.

With its abundance of temperature and CO2 probes that log continuously, the British Cave Science Centre at Poole’s Cavern offers an excellent venue for hosting this project. Water is being collected from stalagmite drip sites and dosed with PO4. It is hoped that natural bacteria in the water will metabolise this PO4, ‘locking in’ the oxygen isotope signature as a factor of temperature. The water will then be dripped onto glass plates to precipitate calcite (mimicking natural cave stalagmite formation), analysed and compared to cave temperature. By conducting the experiment at different temperatures, it is thought that an equation can be formulated that maps temperature Vs. PO4 oxygen. If successful, a trend could be tracked through each layer that makes up the stalagmite, producing a temperature record though time without direct measurement.

For myself, I hope this experience will add significantly to the field of palaeoclimate research in caves and put me in better stead for a PhD studentship within the cave science field.

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