Post By: Rachael Shuttleworth
What drives glacial – interglacial CO2 level changes is what is known as the “holy grail” of palaoceanography. Though the question as to whether these changes are caused by biologically or circulation dominated process is still hotly debated. To better quantify and enhance our understanding of the processes and mechanisms which control CO2 on these timescales we must look to the past for answers. This is the focus of my PhD @thefosterlab and we are initially targeting cores taken from variety of latitudes in the southern Pacific Ocean, ranging from subtropical to polar waters. These cores are stored at NIWA in Wellington, New Zealand – someone had to do the tough job of collecting the samples...
In order to get the data we want, a lot of preparatory work on the samples has to be undertaken. Firstly we must sample to core itself, taking slices of mud at specific depths which correspond to the time periods of interest.
These cores are then put into an oven overnight to dry out.
These dried samples are then washed over a 63micrometer serve to remove the very fine mud particles. They are then put back into the oven to dry again.
The information that we want is stored in foraminifera within these sediments, and so the next step is to pick these micro fossils out one by one.
These samples are now prepped and will be sent back to @thefosterlab based at the National Oceanography Centre, Southampton where analysis on their isotopes will be undertaken. Many of these cores already have carbon, oxygen and nitrogen isotope records which can tell us about temperature, age, ice volume, and productivity. For my PhD I will focus on obtaining a boron isotope record which will tell us about the change in flux of CO2 into the oceans from the present day back to the last glacial maximum. By comparing this with dust flux and productivity records I hope to better quantify the role that relaxation of micronutrient (such as iron) limitation due to enhanced dust deposition played during the last glaciation. This will provide further insight into how much biology played a part in driving glacial-interglacial CO2 change, as well as the potential carbon storage via this mechanism of iron fertilisation.
Its still early days for my PhD, and I now have my first sample set. Next stop – the lab!