Linda Dämmer, Geologist and Paleoclimate Proxy Developer

The great thing about science is that there is always something new to discover, always something new to try, always a new question to answer, always a new challenge. If you’re curious enough, there will always be ways to improve our understanding of how the world works. And as a scientist you’re free to explore all these avenues. Even though every single scientist is only looking at a tiny fraction of everything there is to discover, we still all contribute to the same, big, never ending puzzle. And I find that strangely appealing.

Inspecting a shallow marine site near an active submarine volcanic vent field on the Aeolian island of Panarea, Italy in May of 2017 (Mount Stromboli erupting in the background). Photo by Caitlyn Witkowski (NIOZ/Utrecht University).

By developing and improving methods for paleoclimatologists and paleoceanographers my research helps other scientists understand how the complex system that is our planet’s climate developed and changed over time and reacted to changing parameters in the past. Only if we understand this well enough we will be able to predict reliably how the climate system will be behave in the future.

The main problem we, as geoscientists, have with learning about the climate of the past is that we can’t go back in time to directly measure the temperature or the composition of the atmosphere and oceans (unfortunately our colleagues who are working on time travel are way behind their schedule, but they say it doesn’t matter 😉 ). And unless you’re only interested in the last few centuries, nobody has left us their notes in a neat lab book with all the information we are looking for listed up in a table. Therefore, we have to look at the next best thing: ‘nature’s lab book’, natural records of past environmental conditions. For example we can use ice cores, tree rings, sediment cores, corals and other fossils to learn about the past. But what exactly do we look for in these natural archives? Which particles, organisms, compounds, molecules or minerals have stored valuable information about, for example, temperature, sea water salinity, or composition of the atmosphere? And how do we unlock these data? That is what I’m working on. I’m trying to connect the environmental conditions with the resulting signals in the natural records that we find all over the world.

A benthic foraminifera (Amphistegina lessonii) up close. The scale bar here is 200 microns (1 micron = one millionth of a meter). The bright green, fluorescent part of the shell grew during an experiment that included a fluorescent dye. This way we can tell which areas of the shell are relevant for our measurements.

I do most of my work on living foraminifera (unicellular organisms with a carbonate shell) and the ratio of different elements in their shells. I use benthic (bottom dwelling) foraminifera and keep them under a range of different controlled conditions in the lab to improve our understanding of how environmental signals can be found in their shells.

In addition to this I also do field studies, where I sample foraminifera and collect environmental data from different locations and compare them to the relationships that were previously found in the laboratory settings. This means I get to travel a lot and use a wide range of sampling methods. I get some of my samples from the bottom of the Mediterranean Sea, more than 3 km (≈1.9 miles) below the surface, by taking sediment cores with a research vessel. I crawl through the mud of the intertidal zones along the Dutch Wadden Sea coast to collect living benthic foraminifera from the mud surface by scraping off the top layers of the sediment. I snorkel through the acidified ocean around the volcanoes of the Aeolian Islands in southern Italy to find species that survive these harsh conditions. I scuba dive in the Caribbean Sea to collect living planktic foraminifera one by one using a glass jar. I take hundreds of cubic meters of sea water during scientific cruises to filter out all the plankton in there and then spend hours and hours staring through a microscope to identify all the tiny species.

I’m currently trying to develop a new proxy that will help us learn more about the ocean pH and the atmosphere’s CO2 concentration of the past. To do so, a graduate student and I are using tropical benthic foraminifera. We keep the foraminifera under several different CO2 levels, which represent today’s as well as pre-industrial conditions and concentrations that are expected for the next century.

In addition to that, I’m now calibrating an already existing proxy (the ratio of magnesium (Mg) to calcium (Ca) in carbonates, which correlates well with temperature) to a species of oysters. This method has not been applied to these oysters yet. Doing this will improve the paleoceanographers’ ‘toolbox’ for climate reconstruction in intertidal (the area at a beach between low and high tides) settings, where the most commonly used proxies can’t be applied, since they are based on planktic foraminifera and most of them live in the open ocean, far away from the coast.

Linda is a PhD student at the NIOZ Royal Netherlands Institute for Sea Research in the Department of Ocean Systems; Utrecht University, Faculty of Geosciences, Department of Stratigraphy & Paleontology. To learn more about Linda and her work, visit the Royal Netherlands Institute for Sea Research New Generation of Foraminiferal Proxies website.

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