Meet Josimar, Alissa, Christine, and Evan: Four EAPS graduate students digging deep into Earth, Planets, Climate, and Life.
Josimar Alves da Silva
In the last 15 years, advances in recording instrumentation have led seismologists to discover a new class of earthquakes that many believe can hold the key to earthquake prediction. These new phenomena, known as episodic slow slip events (SSE), differ from conventional earthquakes because the accumulated strain energy in subduction zones is released slowly over a long period of time. GPS observations, combined with broadband seismic stations, have found that SSE occurs periodically with inter-slip intervals raging from days to months.
Three major cycles of SSE have been reported since the early 2000s in the Guerrero Gap, Mexico, on the boundary between the Cocos and North American plates. Analysis of teleseismic waveforms recorded on a dense temporary seismic network revealed low S-wave velocity and high Vp/Vs ratios at the depths corresponding to the sources of SSE, implying the possible presence of fluids and thus an active dewatering process that may result in near-lithostatic pore pressure at the plate interface.
The goal of my research is to perform a coupled flow and geomechanics analysis of the Guerrero Gap to model transient changes in the stress field in the subduction zone as a result of pore pressure fluctuations and potential fluid flow along the subduction interface. My quantitative modeling approach will provide a mechanistic understanding of the relationship between pore pressure evolution, stress transfer, and tremor migration, and help elucidate the origin of SSE in this area.
Image: 2015-16 Whiteman fellow Josimar Alves da Silva visiting the North Cascades, where slow slip earthquakes have been reported extensively.
In July of 2015 New Horizons flew through the Pluto system offering us our first up-close look at this distant, fascinating, icy world and its family of satellites.
Pluto’s orbit is highly eccentric, bringing it between roughly 30 and 50 AU over its 248 year orbit. It also has a high axial tilt, currently around 120 degrees. Pluto’s orbit varies over million year timescales and its axial tile ranges from 103 to 127 degrees over 2.8 million years. This creates a much more dramatic version of Earth’s Milanković cycles. While Pluto currently experiences equinox and perihelion around the same time—creating similar seasonal cycles for both hemispheres—in the past, Pluto underwent cycles of “super seasons” where one pole experienced a short, relatively hot summer and long winter, while the other has a short winter and much longer, but less intense summer.
My research is focused on trying to understand how these “super seasons” may affect Pluto’s surface composition and geology. Specifically, how volatile transport cycles may have differed in the past and how those differences may impact what we see on Pluto’s surface today. Pluto shows bright, volatile-rich material and dark, volatile-depleted regions, with stark dividing lines between them. Normally, we would not expect to see such high albedo contrasts existing at the same latitude but we believe Pluto’s unique orbit favors runaway albedo variations, particularly in the equatorial region, which could create the contrasts we are seeing in the images returned from New Horizons.
Image: Alissa Earle at the New Horizons mission control awaiting the first data from the flyby of Pluto in July, 2015
As a climate scientist, I study how climate change influences rainfall patterns across the globe. Climate models are powerful tools, but they don’t always agree on how rainfall patterns will change in the future, especially in places like South America. The South American summer monsoon is the primary source of water for the tropical regions of the continent, including critical ecosystems like the Amazon rainforest. We have little idea of how this rainfall system will change due to the lack of historical rainfall records in this region—not enough rain gauges! To build better models, we need better data. But how do you measure rain that has already fallen? To fill this gap, I am studying ancient high-altitude lakes in the central Andes.
The central Andes is host to one of the driest and oldest landscapes on Earth. Here, surrounding salt flats and small modern lakes, are remarkably well-preserved shorelines formed by enormous lakes that existed thousands of years ago. But here’s the cool part: Since these lake basins sit high up in the Andes and are landlocked, their water levels depend entirely on the competing forces of precipitation and evaporation. These lake basins are essentially Earth’s natural rain gauges. The ancient shorelines mark past water levels and therefore serve as a rainfall record in this region.
I have led two field seasons in northern Chile to map the extent of these shorelines and to collect carbonate samples allowing me to determine when these lakes last existed. Knowing the size and timing of these ancient lakes will help us understand the forces that drove past rainfall changes. Ultimately, we’ll use this knowledge to make better models of future rainfall changes.
I enjoy this project greatly because it combines geology, geochemistry, and computer modeling to tackle an important problem within Earth science, with broader implications for society.
Image: 2015-16 Callahan-Dee Fellow Christine Chen with samples drilled from Lake Junín, 4000 meters above sea level in the Peruvian Andes which contains a sediment record spanning several hundreds millenia over multiple glacial cycles.
Salt marshes are 50 times more efficient at storing carbon than tropical forests. This is because grasses on the marsh are very productive, but much of that production is buried as peat instead of respired by the biological community. But grass can’t grow in tidal creeks and ponds in the marsh that are tidally inundated or permanently submerged; these environments are dominated by algae. For a number of reasons (e.g. sea level rise) creeks and ponds may cover more of the marsh in the future. One goal of my research is to understand how that might change production and carbon storage of marshes.
I study the biological production and consumption of oxygen. As algae photosynthesize they consume carbon dioxide and release oxygen, and vice versa during respiration. In the process, the biological community imprints oxygen dissolved in the water with a characteristic signature of the three stable oxygen isotopes (18O, 17O, and 16O). So by measuring changes in dissolved oxygen concentrations and isotope signatures in ponds and creeks, I monitor how the ecosystem “breathes” oxygen (and by inference, carbon dioxide) over time, and can compare that to metabolism in the grassy areas.
I collaborate with scientists at the Woods Hole Oceanographic Institution and Marine Biological Laboratory who use complimentary approaches to explore this problem at the Plum Island Ecosystems Long Term Ecological Research site in Massachusetts. We’ve found that creeks and ponds can have greater respiration than photosynthesis; unlike the grassy areas, they actually consume peat and release carbon dioxide back into the atmosphere. So salt marshes might become less efficient at storing carbon in the future.
Image: Evan Howard prepares for “swampling” in a salt marsh tidal creek.
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