Mark Yu, Paleoceanographer, Isotope Geochemist, and Marine Geologist

Mark in front of the R/V JOIDES Resolution in Punta Arenas, Chile. The JOIDES Resolution brings together Earth scientists from around the globe to investigate processes underneath the marine sediments. This cruise, JR100 Chilean Margin, was focused on Patagonia climate and ocean circulation in the last ~150 Ka.

What is your favorite part about being a scientist?

The field I am specializing in, paleoceanography/paleoclimatology and biogeochemistry, represents the complex interplay between the lithosphere (Earth), hydrosphere (oceans), biosphere (life), and atmosphere. These immense variables pose great challenges in interpreting our geologic record and requires us to form interdisciplinary collaborations throughout departments. As I progressed in my studies from undergraduate work at the University of Rochester to graduate research at the Rutgers University, my mind is slowly teasing out the meaning of these variables as I attempt to decipher changes to ocean chemistry for my dissertation. In short, my love affair for science is grounded on the ability to form intellectual bridges across all fields and geographic locations while unraveling Earth history.

What do you do?

As a paleoceanographer, my goal is to decipher changes in ocean chemistry/circulation through isotopic and elemental ratios of calcareous organisms known as foraminifera that inhabit various depths of the water column. My dissertation is focused on the tropical thermocline, the upper part of the water column that is defined by a massive decrease in temperature from the mixed layer and where much of the productivity in the ocean occurs.

A scanning electron microscope image of planktonic foraminifera, Gs. ruber, used by Mark in his research. This sand sized calcareous protist inhabited the surface layer of the water column thousands of years ago

What are your data and how do you obtain them?

The geochemical data I analyze are trapped within the calcareous shells of foraminifera that are preserved in the sediment record at the bottom of ocean basins. Marine geologists undertake global expeditions on the drill boat, namely the R/V JOIDES Resolution, and other vessels to survey and core deep into the sediments. Once I have identified and picked the desired foraminiferal species, I analyze them on mass spectrometers where isotopic and elemental ratios are measured. In turn, each isotopic and elemental ratio provide us with variables in the ocean such as temperature, ice volume, productivity, ventilation, etc.

How does your research contribute to understanding climate change?

As the Earth changes with anthropogenic warming, the oceans serve as the largest buffer in dampening its effects. However, understanding how ocean circulation, ventilation, and productivity responds to temperature and carbon dioxide fluctuations is vital for our model predictions. My dissertation extends to Marine Isotope Stage 5e (MIS 5e) in the Indian Ocean. This was the last warm period (or interglacial period, as scientists call warm times within a time that is generally cool) similar to today around ~125 Ka and elucidating oceanographic properties in the sediment record will allow us to parametrize monsoon dynamics for societal and ecological implications.

Mark onboard the R/V Thomas G. Thompson in the Argentina Margin with a multicore drilling apparatus. This cruise was focused on seismic surveying and shallow coring operations to decipher water mass geometry and erosional processes in the underwater canyons.

What advice do you have for aspiring scientists?

Be curious, observant and ask questions. No question is a dumb question. Likewise, remain skeptical and challenge assumptions. Not every answer is set in stone. The dogma written in textbooks are continuously being challenged and reworked by scientists. Find a few great mentors – people who you aspire to be and will provide you with the time and expertise to show you the ropes. Lastly, find your passion in life and run off with it.

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