Brendan Reilly is a historian of sorts—but not the kind who sifts through dusty reams of parchment paper. Instead, the ARCS Scholar and Ph.D. student in ocean, earth, and atmospheric sciences at Oregon State University probes deep into the Earth’s sediment, looking for magnetic minerals and other markers that provide a record of our planet’s geologic history.
Basically, we take geologic samples, mostly sediment cores from lakes and oceans, and study the magnetic minerals,” he said. “These magnetic minerals can reveal the source material and transport processes and tell us important information about environmental changes.”
Reilly’s most recent dig into the past will take him to the Indian Ocean, where he will accompany an International Ocean Discovery Program expedition as the science party’s paleomagnetist. He will be investigating how magnetic minerals deep within the ocean floor can provide important clues about monsoons. Using the orientation of magnetic minerals, his primary mission will be to develop a chronology for the drill records. These chronologies will be used as a framework for many other analyses (geochemical, sedimentologic, geophysical) and provide the context of time to their interpretations.
“We’ll be taking a really long drill core, about a kilometer or more, into the Bengal Fan in the Indian Ocean to look at the evolution of the monsoon and uplift of the Himalayans over the last few million years and how these events are recorded in the marine sediment,” Reilly said.
Just exactly how do magnetic minerals relate to monsoons? Many magnetic minerals start as igneous rocks and get weathered out. Exposure to the environment and surface processes alter the chemical composition of these minerals, and the amount of that alteration may indicate how much precipitation was present during any given time.
As you look at relative changes in the degree of chemical alterations, you start to get information on large-scale changes in monsoons,” explained Reilly.
To assist in his monsoon mission, Reilly uses the sophisticated equipment in Paleo-and-Environmental Magnetism Laboratory (P-Mag Lab) at Oregon State University. Spearheaded by Joseph Stoner, a marine geologist and paleomagnetist, as well as Reilly’s major advisor, the P-Mag Lab is an NSF-supported facility dedicated to sediment magnetism and serves as a resource for regional, national and international scientific communities.
There, Reilly uses laboratory experiments to analyze the sediment, including zapping the sample with a magnetic field to measure the response. Because each mineral has its own magnetic signature, its response (or lack of it) to a magnetic field gives scientists an idea of the sediment’s mineral composition and even its size.
But often the mineral’s signature is more nuanced and harder to define. That’s when Reilly turns to electron microscopy, a powerful tool that uses beams of electrons to create a detailed image of the sediment sample and analyze the chemical composition of micron-sized regions. This technique allows Reilly to observe the morphology, textures and composition of individual magnetic minerals, which can be used to better interpret the bulk magnetic signals.
While Reilly has yet to draw firm conclusions on the origins of monsoons, past work on magnetic minerals have proven to be reliable indicators of major climactic shifts. In one project led by Joseph Stoner, magnetic minerals derived from Greenland are shown to be distinctly different from those derived from Iceland, which are typically transported into the deep ocean. When the Greenland ice sheet retreats, the erosion of materials and the timing of these retreats can be determined in marine sediment cores. These indicate substantial reduction of the Greenland ice sheet during warmer periods within the distant past (120,000, 300,000 and 400,000 years ago).
Reilly’s up-and-coming research on the historical evolution of monsoons will help scientists anticipate the triggers of these powerful weather events—a particularly important effort as researchers seek to understand how human-induced climate change might intensify storms, floods and other natural hazards.
“Because the problem’s we’re seeking to address have impacts on economies, societies, where people live, etc., it’s important to understand climate change on a long-term scale,” he said. “Satellite data can give you images for decades, but that’s not long enough. The geologic record gives us a better understanding of how systems have changed through time so we can anticipate future thresholds.”