RESEARCH

Digitalized hand-drawing of Earth and buring hydrate by Bumsoo Kim

The Instability of Marine Methane Hydrates in the Past and in the Future 
Massive amounts of methane (CH4), a potent greenhouse gas, are stored as methane hydrates beneath the seafloor. Small changes in temperature and pressure could perturb the stability of methane hydrate and release large amounts of methane into the ocean and atmosphere. However, our understanding of the hydrate stability and the impact of the potential methane release to regional and global climates, environments, and ecosystems is limited by the short time span of observational records available. Therefore, documenting hydrate destabilization and methane release events associated with ocean warming, continental slope instability or sea-level fluctuations in Earth’s history could provide a unique opportunity to research the hydrate stability under drastically different climate and environmental conditions.
A schematic of marine methane cycling (Kim, 2022, PhD dissertation)

Marine Methane Cycling 
In the ocean, methane cycling – the production and consumption of methane – are largely mediated by microorganisms. Methanogenic archaea produce a substantial portion of naturally produced methane by slowly converting organic matter buried in the deep anoxic sediment or within the anoxic water column to methane (methanogenesis). This biogenic methane together with methane from other sources (i.e., thermogenic, abiotic), however, is readily consumed by methane-consuming (methanotrophic) organisms. At present, up to 90% of methane produced in marine sediment is recycled through anaerobic oxidation of methane (AOM), largely mediated by consortia of anaerobic methanotrophic archaea (ANME groups) and sulfate-reducing bacteria (SRB). If methane reaches the oxygen-laden porewater or water column, bacterial methantrophy oxidizes methane aerobically.
Chemical structures of diagnostic lipid biomarkers related to anaerobic/aerobic methane oxidation (Kim, 2022, PhD dissertation)

Lipid Biomarkers as a Tracer for Past Methane Release 
Diagnostic lipid compounds (“biomarkers”) synthesized by methanotrophic microorganisms are powerful tools to trace methane release events in the geological past. Studies on biomarkers of microorganisms tightly coupled to methane cycling have identified a suite of organic compounds that are related to different microbial-mediated processes of methane oxidation. For example, ANME groups produce archaeal lipids such as crocetane, PMI (2,6,10,15,19-pentamethyleicosane), archaeol, hydroxyarchaeol, as well as diagnostic combination of isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) measured by ‘Methane Index (MI)’. Bacterial hopanoids such as diploptene and diplopterol, are commonly associated with aerobic methanotrophs. Combined with 13C-depleted isotopic signature, these 'molecular fossils' can be used to trace past methane release with high confidence. 
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Schematic of Arctic sea ice environment and sea ice proxies (Kim, 2023, seed grant propsoal)
The Variability of Arctic Sea Ice in Earth's History  
In the Arctic where warming is occurring at an unprecedented speed, the loss of sea ice extent is expected to accelerate in the future, strongly impacting regional and global climate, environment, and ecosystem. State-of-the-art climate models coupled with sea ice dynamics provide us insights to Arctic sea ice change in a warming world. However, large discrepancies between models and fundamental uncertainties due to Earth’s complex interactions/feedbacks continue to cloud our view of the fate of Arctic sea ice. To address this challenge, I focus on using integrated approaches of sea ice proxies (organic biomarkers, microfossils, sedimentological evidence) to systematically reconstruct the past Arctic sea ice – its occurrence, extent, and concentration –  during key global warming periods (specifically, Marine Isotope Stages 5 and 11). I will also use this integrated proxy reconstruction as a baseline data and reference to benchmark skills and performances of current generation of climate models in sea ice simulations
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Asteroid "Bennu" (google image)
Illuminating the Origin of Life 
One of the key goals of NASA’s OSIRIS-REx mission is to analyze low molecular weight volatile organic compounds (VOCs) collected from samples of Asteroid Bennu. These VOCs, including hydrocarbons, acids, ketones, aldehydes, amines, esters, and alcohols, are essential building blocks for complex organic compounds like amino acids. By studying these compounds, scientists hope to gain insights into the origin and evolution of prebiotic organic compounds and their potential interstellar heritage. At Brown, I am working with Drs. Yongsong Huang and Ewerton Santos to employ streamlined analytical methodologies to minimize sample consumption and contamination while maximizing the extraction of information. This involves the use of three analytical platforms to extract and analyze the volatiles, with the potential of further exploring higher molecular weight or less volatile organics in the residual samples. Our ultimate goal is to generate critical new data on Bennu’s organic chemistry using a relatively small sample mass.
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