SWEET Team Blog 5, March 2019

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Philip – Studying sediment chemistry to find out about past climate

Who am I, and how did I come to work on this project?

My name is Philip Staudigel and I am a geochemist on the SWEET team. I recently completed my PhD studies at the University of Miami, the focus of my PhD was studying the processes by which rocks and minerals can be transformed either by heat or by chemical reactions. In particular, I was looking at the stability of certain paleothermometers over these processes. A paleothermometer is exactly what it sounds like, a thermometer in the past. By measuring certain chemical or isotopic signatures in fossils or minerals, scientists can learn the temperature at which they formed. My PhD focused on studying how these records can be changed over time. My work on the SWEET project is an extension of this work, and I am working to simulate the effects of the slow, but very important, chemical reactions that happen beneath the seafloor and how they affect our estimates of ancient climate.

Over the eons, creatures called foraminifera pull dissolved salts out the water and make a shell, called a test, around themselves. When the foraminifera die, their shells will fall to the bottom of the ocean and is buried over time. The chemistry that forms these tests is understood well enough that chemists can learn all sorts things about the lives these creatures lived. One of the most useful techniques is called paleothermometry, where scientists try to learn how warm or cool the water was when the foram was alive. To do this, scientists use a machine called a mass spectrometer, which is a tool which will separate different weights of atoms and molecules. They use this to count the number of heavy oxygen atoms (Oxygen-18) and the number of light oxygen atoms (Oxygen-16) in a foram. This technique works because when it is cold, forams prefer to make their shell using the heavier atoms; when it is warm, they prefer lighter oxygen. By using this technique on organisms that lived at different times, scientists can learn about changes in global climate, which is the goal of the SWEET Project.

What will I be doing?

My job in this project is to study the chemistry that happens after these shells are buried. If sediments are like a tape recorder, then these chemical reactions can disturb that record, changing or blurring the signals we want to read. After sediment is emplaced, the minerals it’s made of can dissolve and reprecipitate, which allows for the chemical makeup of the material to be changed. This can happen very quickly, or over millions of years. Depending on where this happens, the chemical composition can be more or less resilient to this alteration. If we can study exactly how this happens, we can correct for some of these effects, or use different techniques which are less susceptible to alteration. I use a computer to simulate these chemical reactions over thousands to millions of years in order to see how the chemistry of sediments has been changed. The goal of this is to see if we can still tease an original signal out of potentially valuable records which were altered over time.

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