John Doherty, Biogeochemist

John Doherty, PhD candidate at the University of Hong Kong.

What is your favorite aspect of being a scientist, and how did you become interested in science?

My favorite part about being a scientist is undoubtedly getting to do research for a living. While there are many stressful aspects associated with being a scientist, at the end of the day I get to spend most of my time learning about things that are deeply interesting to me. Science has also allowed me to travel the world and meet some of the most inspirational people I would have otherwise never crossed paths with.

What do you do?

When people hear the word “biogeochemistry” for the first time, the general response I get is “biogeo-what? Are you a biologist, geologist or chemist? Couldn’t you just pick one?” While this is a fair question, it is unfortunately not how the Earth system works.

I work specifically in the field of paleoceanography, the branch of science concerned with the ancient oceans and their role in climate. My research aims to understand the evolution of polar North Atlantic Ocean circulation over geological warm periods that occurred hundreds of thousands of years ago. The ocean, however, is an interconnected mess of physical, chemical and biological phenomena. To thoroughly investigate oceanographic processes, it is therefore necessary for scientists to have a broad and multidisciplinary understanding of all aspects of marine science.

As a biogeochemist, I work mainly with organic matter preserved in microfossils called foraminifera. The composition of this organic matter reflects historic upper-ocean biochemistry recorded during the foraminifer’s lifetime, which allows me to make observations about the chemical conditions of the ancient surface waters. The surface-ocean chemistry of this particular region is subsequently controlled by waters mixing together, which makes foraminifera-bound organic matter a useful proxy to reconstruct physical mixing processes in the upper-ocean water column.

Foraminifera microfossils (left) and bacteria (right) used for the isotopic analysis of organic nitrogen.

But who cares about what the surface of the polar North Atlantic used to look like? Because this is where southern-sourced Atlantic waters sink and return to tropical latitudes (the so-called “ocean conveyor belt”), this one region actually governs the strength of the entire Atlantic circulation in addition to a variety of global climatic phenomena that we are just beginning to understand. Studying how Atlantic waters used to move during past warm periods therefore allows us to get an approximate idea of how the Atlantic may continue to change in the near future, and its greater effects on Earth’s climate.

What are your data, and how do you obtain them?

My data are mostly measurements of stable nitrogen isotopes of organic matter contained within foraminifera shells, which dominate sediment core samples from the polar North Atlantic region. This isotopic signature, or the ratio of heavy to light nitrogen atoms, is a proxy for surface nutrient processes affected by upper-ocean nutrient mixing. Because foraminifera contain only miniscule amounts of organic nitrogen, extracting this organic material and turning it into a measurable form requires intensive laboratory and chemical work. I therefore spend most of my time in the laboratory rather than on a boat, which is unfortunately slightly less scenic.

One of my field sites in the Polar North Atlantic Ocean. Photo by Dr. Benoit Thibodeau.

How does your research contribute to the understanding of climate change?

There are now several lines of evidence which indicate that ocean circulation in the polar North Atlantic is slowing down, likely as a result of human-caused global warming. While today’s rate of warming is unique in the recent geological history of Earth, our planet has experienced intense warm events in the past. By investigating the behavior of the Atlantic circulation in the past, we are able to better understand the long-term climatic and oceanographic implications of our current warming. For example, we hope our research will shed light on the extent to which the modern ocean circulation will slow down, and what this slowing means for other aspects of Earth’s climate in the long term.

What advice do you have for aspiring scientists?

Stay curious and keep an open mind! I switched my major several times throughout my undergraduate career before I discovered my passion for science.

Don’t let previous failures detract from your goals. Often times, we see the finished product of science in the form of a published, peer-reviewed journal article. What we don’t see in that article is all of the failed experiments and misguided hypotheses leading to its production. Doing science means falling short many times, recognizing mistakes, learning from them and continuing to improve. The most important thing you can do is to not give up and to keep trying, because one day  this stuff will work out.

Follow John on Twitter @ocean_chemist, and read more about him and his research on his personal website


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