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SALT LAKE CITY — Growing up as a "small town kid" who loved science, Dustin Harper had aspirations to become a physician when he went to college.
So, how did he end up at sea on a research vessel recovering drilling cores taken from an undersea plateau in the Pacific Ocean?
"When I got to college, (I) took a geology course and fell in love. So, that's kind of how it all ended for me, the physician aspect," Harper said.
When that dream ended another was born, and Harper is now a postdoctoral researcher in the University of Utah's Department of Geology and Geophysics with a specific interest in marine geology.
Now, he's the lead author on a study published Wednesday, that looks at sea surface temperatures with levels of atmospheric carbon dioxide over a 6 million-year period that covered two hyperthermals:
- Paleocene-Eocene Thermal Maximum, or PETM, 56 million years ago.
- Eocene Thermal Maximum 2, ETM-2, 54 million years ago.
The research
The findings show that as atmospheric levels of CO2 rose, so did global temperatures.
"The main goal was to reconstruct atmospheric CO2 concentrations and subtropical sea surface temperatures through this interval of time in which climate is very dynamic," Harper said.
He and other researchers wanted to examine these global carbon release events because they can "provide analogs for future change."
What they found showed that the emissions during the two ancient "thermal maxima" are similar enough to today's anthropogenic — caused by people — climate change to help scientists forecast its consequences.
"We were interested in getting a better understanding of how the environment responds to these climate change events in the geologic record," Harper said. "By assessing how much CO2 changes, and how much temperature changes, we can get a sense of the sensitivity of the climate system to CO2 release."
He said that these ancient climate events can be used as the closest analogs to modern, anthropogenic climate change.
Today, human activities associated with fossil fuels are releasing carbon four to 10 times more rapidly than occurred during these ancient hyperthermal events. However, the total amount of carbon released during the ancient events is similar to the range projected for human emissions, potentially giving researchers a glimpse of what could be in store for us and future generations.
"These events might represent a mid-to worst-case scenario kind of case study," Harper said. "We can investigate them to answer what's the environmental change that happens due to this carbon release?"
Microscopic fossilized shells
To determine oceanic CO2 levels, researchers analyzed microscopic fossils taken from drilling cores extracted from the Shatsky Rise in the subtropical North Pacific Ocean east of Japan, which scientists say is an ideal location for recovering ocean-bottom sediments that reflect conditions in the ancient past. The fossilized remains were that of foraminifera, a shelled, single-cell organism akin to plankton.
"They die and sink to the sea floor, and they're deposited in about two kilometers of water depth," Harper said. "We're able to retrieve the complete sequence of the dead fossils. At these places in the middle of the ocean — you really don't have a lot of sediment supply from continents, so it is predominantly these fossils and that's all. It makes for a really good archive for what we want to do."
These shells accumulate small amounts of boron, isotopes of which are a proxy reflecting CO2 concentrations in the ocean at the time the shells formed, according to Harper.
"We measured the boron chemistry of the shells, and we're able to translate those values using modern observations to past seawater conditions. We can get at seawater CO2 and translate that into atmospheric CO2," Harper said. "The goal of the target study interval was to establish some new CO2 and temperature records for the PETM and ETM-2, which represent two of the best analogs in terms of modern change, and also provide a longer-term background assessment of the climate system to better contextualize those events."
Study applications and lessons learned
Harper said that when looking at a longer time scale as this study did, researchers can better understand the Earth's sensitivity to various amounts of CO2 release.
"We can actually compare these IPCC (Intergovernmental Panel on Climate Change) scenarios to, maybe, more directly to these events," Harper said. "What's continuing on ... is looking at how we can reconstruct environmental change for some of the smaller, subsequent events following the Paleocene using Thermal Maximum and combine all of these pieces of information ... to better understand the nature of environmental change to carbon release."
The study was published in the Proceedings of the National Academy of Sciences and can be read in its entirety here.
