Resampling of C. fasciatus shell with improved setup

Here is a quick update on the most recent changes to our LIBS setup and a newer map of elemental ratios (Mg/Ca and Sr/Ca) from our Conomurex fasciatus shell recently published in JAAS.

The preliminary verdict here is that C. fasciatus from the Farasan Islands still remain difficult to interpret and are far from being used as a seasonality proxy. A more detailed report that compares the elemental ratios with stable oxygen isotopes is currently under review and I'll post it here when it comes out.

Our LIBS setup now uses a new focusing lens for infrared light and with 10x magnification, which decreases our sampling area to a diameter of ~40 µm. We also added a cleaning step before measuring each location, by simply using a number of shots that ablate the material at the surface and expose "fresh" carbonate.

The sampling rate has been improved somewhat, by simply taking less spectra per location. The peaks for Mg at 279.6 nm and for Ca at 315.9 nm are actually clear enough to map shells with a single spectrum instead of our usual 10 spectra per location. That way we can get almost 4,500 sample points per hour (0.81s/point). Previously this was 2,100 sample points per hour. Sadly, the Sr peak at 407.8 nm is less clear and single spectra are too variable for my taste, which is why 3 spectra per sample point seemed more appropriate, when measuring Sr/Ca. Sampling rate here is about 3,600 per hour (1s/spot).

These numbers can still be improved by using newer equipment (ours is on average 15 years old). Right now the biggest problem is our pretty old computer and the fact, that the sample stages do not move constantly, but stop at each point to take one or more spectra. Single spectra analysis of Mg/Ca could allow us to have the stages move at a constant speed and make full use of our 10 Hz laser. That way we could achieve an almost tenfold increase in speed (not counting the cleaning step). So that is something to aim for before the end of the project in 10 months(!).

I was hoping to update this project more frequently, but in the next few weeks, I'll be busy with collecting more samples in Denmark as well as with Matthew Meredith-Williams in Melbourne. But I am looking forward to sharing new data as soon as it becomes available.

Until then!