Rory’s ‘Eureka’ moment!

July 11, 2012

July is with us dear readers however, the weather would contest the existence of this month most assuredly as rain and floods engulf us with the UK Met Office continuing to issue flood warnings right across Britain and Northern Ireland. Although things could be worse, as you can see from the photograph, a brush with the law is no small affair in India! It would have been a shame to see: “Two thousand pounds of education, Drops to a ten-rupee jezail”, as Kipling might have portrayed that encounter. At least there was some good news on the sediments front this week, the same week that the Higgs-Boson may have been discovered (it’s within five decimal place of certainty) I had something of a little discovery of my own, a ‘Eureka’ moment which has made my year!

Right at the start of this project one of the burning questions has been: “What is the rate of sedimentation?” One might wonder why the sedimentation rate is of such importance. Firstly, there is a generally accepted view that at about five or six thousand years the Ganges River as a result of sediment deposition began to tilt from west to east and eventually joined up with the Brahmaputra at about 2,000 years ago. This has meant that the western extent of the delta plain, comprising of the Indian Sundarbans is more-or-less cut-off from a freshwater source and thus from a source of sediment. This argument has been developed through ¹⁴C radiocarbon dated material from the western delta complex, with the rate of sedimentation appearing to decrease over the course of the early to late Holocene. Sediment accumulation appears to have a westward trend in which the accumulation rates across the lower delta appear to be accelerated along the eastern side of the lower delta plain. Thus, it is necessary to know what are the rates of sedimentation as these can therefore inform whether there is a dominant geological process taking place, such as tectonic subsidence of the delta or whether it is a sea-level readjustment in which sea-level rise is the dominant or driver or in a lot of cases it is something of a mixture between tectonics and sea-level.

So setting off to work, I pursued the route of ¹⁴C radiocarbon dating for which QUB and the School of Geography, Archaeology and Palaeoecology is famous with the Accelerator Mass Spectrometer (AMS). Dating was first carried out on the bulk sediment (i.e. dried sediment with inorganic matter removed); this was somewhat successful with radiocarbon results obtained for basal sediment (bottom of the cores) for two of the cores from the uninhabited sites. However, dating more bulk sediment only led to age reversals through the core (i.e. older ages were recorded midway through one of the cores than was obtained for the base of the core). Thus, extracting pollen from a select number of samples was seen as advantageous as pollen from plants (and we are dealing with a mangrove) would be reflective of the time in which they were deposited. Pollen was extracted but true to nature in all its might, the dates this time were even older than the bulk sediments, with ages ranging from 8,000 – 10,000 ¹⁴C years, slightly older than the 4,000 – 4,500 ¹⁴C years already found! Taking a lesson from Churchill however: “Success is not final, failure is not fatal: it is the courage to continue that counts”, a final method, a last chance saloon was tried: humic acid extraction. I was feeling slightly dejected while processing the samples, consoling myself to the fact that the method will not work. However, it didn’t just work well, it worked beautifully! No age reversals and rates of sedimentation consistent for the sites. The spectre of uncertainty looms over my dates and further samples I wish to date: ‘Did it only work by fluke? What if it doesn’t work again?” I’ll savour this success and wait and see what happens to the other samples. At times such as this I am reminded by that now famous bar scene in “Ice Cold in Alex”, where John Mills’ character Capt. Anson upon finishing a cold glass of Carlsberg exclaims: “Worth waiting for”. Well folks, it certainly has in this case, it certainly has!

Till next time folks!

Rory Flood, PhD Student, Queen’s University Belfast, School of Geography, Archaeology and Palaeoecology (GAP), http://www.qub.ac.uk/schools/gap/