By Kate Holland
PhD candidate Kate Holland teams up with a small crew of scientists from the Lamont-Doherty Earth Observatory to make small gains in our current understanding of how planktic foraminifers record information in their calcium carbonate shells.
Aside from the obvious selling points of Puerto Rico, the homeland of Ricky Martin and of Enrique Iglesias’s father (and more), its tropical location means we can catch and grow tropical species of foraminifers.
I’ve been fortunate enough to have participated in foraminifer culturing on Catalina Island (see: https://oncirculation.com/2013/08/15/how-to-catch-a-foram-on-catalina-island/). The prevalent species found there, O. universa is not used for paleoreconstructions. O. universa make a wonderful spherical shell when they are an adult, however, this makes them very different to most other foraminifers. This means work on O. universa is often criticised as being not relatable to other foraminifer species.
The tropical foraminifers we catch in the tropical Puerto Rican waters are G. ruber and G. sacculifer. These species are both used to reconstruct past ocean conditions, so the things we find out, stand to make more of an impact to the work of paleoceanograhers!
A typical day of culturing foraminifers involves travelling 8 nautical miles from the lab, off the continental shelf, to reach the open ocean habitat of planktic foraminifers. We then dive and capture foraminifers individually in glass jars to bring them back to the laboratory! The jar is ideal, when foraminifers are caught in a net their spines break and fall off. Catching foraminifers by scuba ensures the foraminifers are as healthy as possible.
Once back at the laboratory, we spend hours identifying which species each foraminifer is, and measuring them. The measurement is very important; this is so that we know their size when they started the experiment, so that we can tell what they grew during the experiment, in our controlled conditions. The foraminifers live out their days in experiment seawater where we might have changed the salinity, the pH, or the dissolved inorganic carbon (DIC) content. This is to see how foraminifers tell us about how the seawater conditions influence the way they make their shell, and how this might influence the trace elements that they incorporate into their calcite.
We observe every single foraminifer in culture every day, to see that they are alive and happy, or on the bottom of their jar looking very unhappy. We feed the happy foraminifers their favourite fatty snack, 1-day old brine shrimps (aka. baby sea monkeys), give second or third chances to unhappy foraminifers to get their acts together, and archive the shells of foraminifers which have finished their life cycles. Repeat this for seven weeks and you have my time in Puerto Rico, interspersed with some lap swimming in a 26° C ocean on non-dive days and the occasional mojito.