NSF grant to investigate hydrothermal vents as a source of long-lived carbon in the deep ocean

The R/V Atlantis and HOV Alvin (left) - Photo by L. Lamar. Aromatic molecules surrounding a hydrothermal vent field (right) - Illustration by E. Pae.

Oceanic dissolved organic carbon (DOC) is one of the largest reservoirs of reduced carbon on Earth. Condensed aromatic (graphitic, soot-like) molecules are known to be the least reactive and most long-lived component of oceanic DOC. Therefore, it is important to understand where condensed aromatic DOC is formed and how it is cycled in marine environments. Sasha Wagner and researchers at the University of Delaware (Andrew Wozniak, Suni Shah Walter, and George Luther) have teamed up to answer the question: Are hydrothermal vents the source of this long-lived, soot-like carbon that persists in the deep ocean?

A few years ago, Wozniak and Luther discovered small bits of graphite in hydrothermal fluids at the East Pacific Rise 9°N vent field. Around the same time, Wagner used isotopic measurements to determine that soot-like molecules in the deep Pacific Ocean have a marine origin, and do not come from wildfires on land as previously thought. Radiocarbon dating also supports a deep sea, probably hydrothermal, source of this graphitic, soot-like carbon. With multiple studies now pointing towards hydrothermal vents as a likely source of ancient aromatic DOC, there was only one thing left to do - Go straight to the source and find out!

To answer their question, Wagner and her team will sample vent fluids directly, along with ocean water and marine sediments, and use a suite of geochemical techniques to determine whether mid-ocean ridge hydrothermal vents are a source of this long-lived, condensed aromatic DOC. The project involves a field campaign at the East Pacific Rise 9°N hydrothermal vent site located off the western coast of Central America. Project findings will reveal the role of hydrothermal vents in producing and sequestering carbon in the deep ocean.

Additional details about this project entitled “Collaborative Research: Hydrothermal vent systems mediate the formation and fate of refractory aromatic carbon in the deep ocean” are publicly available on the National Science Foundation website.

Detailed protocol to lower the barrier to entry for dissolved black carbon analysis

Various images from the detailed BPCA method protocol.

Dissolved black carbon (DBC) is the condensed aromatic portion of dissolved organic matter (DOM) that comes from wildfire, petroleum, and other thermogenic sources. The measurement of DBC allows researchers to examine the production, accumulation, and cycling of a biologically refractory (i.e. relatively inert) fraction of organic carbon in various aquatic settings. In our lab, we use the benzenepolycarboxylic acid (BPCA) method to quantify DBC along the river-to-ocean continuum, which involves the harsh oxidation of DOM extracted from water and subsequent analysis of BPCA products via high-performance liquid chromatography.

For brevity, peer-reviewed research articles and methods papers usually summarize or omit some sample preparative and analytical details. These technical omissions make it difficult for researchers who are looking to adopt or refine the BPCA method. To address this, Riley Barton led the recent publication of a step-by-step protocol and accompanying paper to lower the barrier to entry for those who want to incorporate BPCA analysis and DBC quantification into their research but do not have a high level of access to those already familiar with the method. We hope that expanding the accessibility of this method will enhance the number of DBC studies and will contribute new perspectives on DBC biogeochemistry to further the scientific understanding of this long-lived compound class in the environment.

The step-by-step protocol is freely available at protocols.io and the accompanying paper was published in the journal PLoS ONE and is entitled “Measuring dissolved black carbon in water via aqueous, inorganic, high-performance liquid chromatography of benzenepolycarboxylic acid (BPCA) molecular markers”.

Evelyn Pae wins first place at the RPI 13th Annual Undergraduate Research Symposium

Congratulations to Evelyn Pae who presented at the RPI 13th Annual Undergraduate Research Symposium last month and was awarded first place for best oral presentation in the Physical Sciences category! Her work was entitled “Effects of watershed size, hydrology, and burn extent on the composition of dissolved organic matter in fire-affected streams.”

Evelyn has spent the last year in the Wagner lab analyzing samples collected from fire-affected streams in coastal California. Before that, she published a zine entitled Molecular Tales of Marine Dissolved Organic Matter, an illustrated story that follows four molecules, who tell tales about their journey to the ocean.

We wish Evelyn the best of luck as she graduates from RPI this spring and transitions to a graduate student position at SUNY College of Environmental Science and Forestry!

Riley Barton awarded the CUAHSI Pathfinder Fellowship

Congratulations to Riley Barton who was recently awarded the CUAHSI Pathfinder Fellowship! Funds will be used to support travel to the Blue Oak Ranch Reserve (California) next winter. Barton will conduct fieldwork in headwater catchments that burned during the Santa Clara Unit Lightning Complex fires and interface with our collaborators at University of California, Santa Cruz.

The Pathfinder Fellowship program provides travel funds to graduate students in hydrology and related sciences to make an extended trip to enhance their research by adding a field site to conduct comparative research, collaborating with a research group, or working with researchers on adding an interdisciplinary dimension to a project.

Sasha Wagner named ASLO Fellow

The Association for the Sciences of Limnology and Oceanography (ASLO) recently named Sasha Wagner a 2021 Fellow. The ASLO Fellows program was initiated in 2015 to honor individuals who have given tirelessly of their time and talents to support ASLO's mission to advance the sciences of limnology and oceanography. As a named ASLO Fellow, Wagner is recognized for her exceptional contributions to the benefit of the society and its publications, meetings, and other activities.

Photochemistry as a driver of dissolved organic matter composition in glacial runoff

Mendenhall Glacier in Alaska. Photo by A. Stubbins.

The dissolved organic matter (DOM) in glacial runoff is relatively old and mostly made up of aliphatic molecules (i.e. molecules are built mainly from carbon chains rather than aromatic rings). However, the observed composition of DOM in glacial runoff is the opposite of what we would expect to observe based upon known sources of glacial DOM. We assume glacial DOM is primarily derived from organic matter in soils or deposited aerosols, like soot or other combustion products. When mixed with water, soils and aerosols release DOM that is compositionally dissimilar from DOM in glacial runoff … why is this?

In a recent study, led by Amy Holt (Florida State University) and co-authored by Sasha Wagner and others, determined that photodegradation of DOM in glacial environments may explain the difference in composition between glacial DOM sources (soils and aerosols) and DOM in glacial outflows. The researchers conducted a series of experiments, where soils and aerosols were leached in water, then exposed to sunlight in a solar simulator for several weeks. Ultrahigh resolution mass spectrometry was used to evaluate how the molecular “fingerprint” of glacial DOM sources changed during the photodegradation experiment. After extensive photo bleaching, the composition of DOM samples converged, becoming more similar to the molecular composition of DOM in glacial runoff. Taken together, the study findings suggest that photochemical degradation of aged, aromatic DOM sources could explain the observed composition of DOM in glacial outflows. This work is entitled “Assessing the role of photochemistry in driving the composition of dissolved organic matter in glacier runoff” and was published in the Journal of Geophysical Research: Biogeosciences.

Probing the source and Structure of petroleum asphaltenes

Typical images of liquid petroleum (left) and the glassy asphaltene fraction (center). Asphaltene molecules have a condensed aromatic core (right).

Petroleum is a fossil fuel and is also made up of thousands, if not millions, of different organic molecules. Some of these molecules have a condensed aromatic core structure (like a honeycomb) and are referred to as “asphaltenes” - As the name implies, these molecules are also present in road asphalt! Relative asphaltene content largely controls the viscosity and other physicochemical properties of crude oil, so we set out to gain a better understanding of this sticky petroleum component.

A new paper, led by Alex Goranov, describes how molecular markers and isotopic analysis can be used to interrogate the condensed aromatic structure and source of asphaltenes present in crude oil. The paper is entitled “Characterization of asphaltenes and petroleum using benzenepolycarboxylic acids (BPCAs) and compound-specific stable carbon isotopes” and was published in the journal Energy and Fuels as part of the 2021 Pioneers in Energy Research: Alan Marshall special issue. These investigations may also help us track organic matter inputs from oil seeps or other petrogenic carbon sources in the natural environment.

Molecular Tales of Marine Dissolved Organic Matter

The following excerpts are taken from the article “Exploring science visually“ that was originally written by Evelyn Pae and published in the RPI Every Day Matters blog on 13 October 2021.

“To study chemistry is to study the art of sequential storytelling. Each step in a chemical reaction is a new progression of events: the loss of an electron, the formation of a bond, and the introduction of a catalyst. The same actors — carbon, hydrogen, oxygen, and nitrogen — dance through scene after wondrous scene, re-enacting classic sequences in labs across the nation and in innumerable natural environments.

Look deeply into an organic chemistry reaction mechanism diagram and you can see that it is like a step-by-step cartoon — a highly precise, scientific cartoon and a visualization in symbols of the elusive processes that cannot be perceived with the naked eye. It was a fascination with this type of scientific imagery that inspired me to create Molecular Tales of Marine Dissolved Organic Matter with Rensselaer Polytechnic Institute Professor Sasha Wagner, who is supervising my undergraduate research in dissolved organic matter biogeochemistry this semester. Molecular Tales, a product of chemistry nerdery and quarantine boredom, is an illustrated booklet that follows the story of four different organic molecules, each with its own provenance and character, through their respective journeys to the sea.”

“Science communication is a field that I believe will only become more relevant in the future. It doesn’t always have to be big and flashy. Like our zine, it could be a slim booklet that fits into a pocket, refusing to take itself too seriously. Or, like dissolved organic carbon itself, it could be there in the background of your daily life: always present, critical and fundamental, yet often unnoticed until you learn a new way of looking at it. I hope Molecular Tales offers readers a new — and fun — way of looking at the world we live in.”

The zine is freely available and can be viewed as an e-booklet or downloaded as a PDF file.

TRacking molecules from an underground oil spill near Bemidji, Minnesota

Site of 1979 oil spill near Bemidji, Minnesota - Groundwater wells are seen sticking up from the ground.

Sasha Wagner received funding to investigate and track bio-refractory (i.e. resistant to microbial degradation) petroleum products in a shallow aquifer near Bemidji, Minnesota at the site of a 1979 oil spill. After clean-up efforts, ~400,000 liters of oil remains beneath the ground near the water table. The remaining oil continues to be a source of contaminants to the aquifer and has been monitored as part of the USGS National Crude Oil Spill Fate and Natural Attenuation Research Site for the last 30 years. In August, Sasha collected groundwater samples as part of the 2021 field campaign at the site. Ongoing research, led by PhD student Alex Collins, seeks to use stable carbon isotopes to track oil-derived compounds along the subterranean oil plume and to characterize natural (background) and oil-derived dissolved organic matter in groundwater.

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Top row

1. View towards unnamed lake from site tent

2. Water quality assessment at well

3. Samples collected for carbon analyses (note orange-colored iron precipitation)

4. View of oil pipeline corridor

Bottom row

1. Filtration and sample collection

2. Working at the field station

3. Remaining oil can be seen in the soil core

4. Sample extraction in the hotel room

Investigating whether wildfire ash has an effect on dissolved black carbon in coastal waters

View of the Thomas Fire smoke plume from the International Space Station. Photo by NASA.

Charcoal and soot are formed during wildfire and when these fire-derived products interact with water, some of it dissolves and enters aquatic systems. The soluble component of charcoal and soot is termed “dissolved black carbon”. The main goal of a study, recently published by Sasha Wagner and colleagues, was to investigate whether the deposition of ash from the Thomas Fire (California, USA) had a measurable effect on dissolved black carbon in coastal surface waters. Beneath the smoke plume, dissolved black carbon concentrations were higher than other areas sampled. They also found that when Thomas Fire ash was mixed with seawater, it leached a substantial amount of dissolved black carbon. The release of dissolved black carbon from ash was further enhanced when the experiment was carried out under natural sunlight. Using carbon isotopes, they tried to estimate inputs of dissolved black carbon from ash to Santa Barbara Channel surface waters during the Thomas Fire. However, ash dissolved black carbon contributions were too small for them to effectively track inputs using carbon isotopes. Given the unpredictable nature of wildfires, they are logistically challenging to study in real time. This work provides a first step toward understanding atmospheric inputs of dissolved black carbon to coastal ecosystems impacted directly by wildfire. This work is entitled “Investigating atmospheric inputs of dissolved black carbon to the Santa Barbara Channel during the Thomas Fire (California, USA)” and was published in the Journal of Geophysical Research: Biogeosciences.