Shedding Light on the Effects of Biology and Organic Matter in the Ocean

Living near the ocean for almost my entire life, I grew up in a coastal town called Quy Nhon in Vietnam and moved to San Diego almost 10 years ago. Despite this, I was aware that I knew very little about the sea. I did, however, understand how we all tend to take the ocean for granted: for our mini weekend vacation, for the amazing seafood, and many more reasons!

The ocean is threatened by the negative effects from our now-changing climate. The key to mitigation is being able to first understand the underlying chemistry and interactions between the ocean and the atmosphere. A great example of this was the discovery that chlorofluorocarbons (CFCs) could form ozone-destroying radicals on the surfaces of polar stratospheric cloud aerosols; knowledge that allowed us to ban such chemicals to help reverse the progression of the ozone hole in the 80’s and 90’s.

The ocean is home to a diverse ecosystem, whose activities directly and indirectly control its surroundings. It becomes very fascinating once we begin to understand the activities of the microscopic species, such as bacteria, phytoplankton, viruses, etc. These microbes are able to emit volatile organic compounds (VOCs) as resistance to environmental stresses, communications, and allelopathic and defense mechanisms. Once emitted into the air, these VOCs can act as a sink for hydroxyl radicals and form secondary marine aerosols – a focus of the SeaSCAPE study. Such aerosols are the single largest uncertainty in our quest to understand climate change (see IPCC AR5). 

For my project, bloom water collected from the wave flume is irradiated with a solar simulator for approximately 2 to 3 hours. The reaction chamber is a horizontal column capped with quartz windows on both sides and inlet/outlet at the top for N2 gas flow through the headspace, carrying the emitted VOCs into the Orbitrap Elite mass spectrometer. The VOCs are ionized using a modified gas-phase atmospheric pressure chemical ionization (APCI) method to directly measure gases using high resolution mass spectrometry. We use a timeline to collect samples for each bloom for a temporal analysis, going from when the seawater is added, to the addition of nutrients, to the peak and the death phase of the bloom. We also analyze both unfiltered and filtered (0.2 microns) bloom water to specify the biotic and abiotic VOCs. During the first bloom cycle, we observed little signal overall with the bloom water collected on June 5th, when the nutrients were just added. However, the sample on June 10th, 6 days after the nutrients are added, showed promising details with the detection of isoprene, fatty acids, aldehydes, and other compounds such as dimethyl sulfide (DMS) and terpenes that are commonly known as algal VOCs. Some signals were observed on sample collected on June 15th, just a day after the nutrient spike on the second bloom cycle; however, it was very weak. Though, similar to the first bloom cycle, an enhanced signal was observed in the sample collected on June 18th on the second bloom, 4 days after the nutrients were added! The signal intensities seem to be confidently detected with at least 4 days after the nutrients. An interesting point to make is that samples from the second bloom presented a trend in an enhancement of VOCs approximately 30 to 60 minutes from when the irradiation started. Furthermore, another enhancement typically occurred around 60 minutes after the first mysterious peak. It was hypothesized that there may be delayed (and probably multiple) metabolic processes among the marine species, that caused the pattern.

With the complexity of the biology inside the bloom water, it is difficult to pinpoint the environmental factors and species that are responsible for those mysterious peaks. The next step in this project will involve analyzing the VOC emissions of monocultures of bacteria and phytoplankton observed in the microbiome of the wave flume blooms, to create a library of VOC emissions distinctive to each bacteria strain as the reference point for future analysis.

In addition to the analysis of the volatile components of the bloom water, I work closely with David Gonzales on his project on characterizing the composition of the marine-dissolved organic matter (m-DOM), which we collected from the same water using solid-phase extraction. Together, our data presents the whole temporal compositional change of the water in the wave flume, with respect to the change of its biology. Perhaps we may be able to understand how light affects the composition of the gaseous and liquid phase at our ocean surface.

Written by: Duyen Dang, Undergraduate Student in the Grassian Research Group at UC San Diego

As I grew up, I noticed the human impacts on the environment – the increasing occurrence of hurricanes near my home, flash flooding, tornado warnings, and smog-laden air. Our daily routines affect the ecosystems around us. I started to think about how we influence our surroundings in ways in which I could study and possibly mitigate these impacts. This brought me to study chemistry at Pace University in New York City in order to gain experience that could be applied to my research and future career on the environment. 

I wanted to work at CAICE to experience the approach that atmospheric science has in studying environmental chemistry. My project in SeaSCAPE, is to characterize the broad structure and reactivity of marine dissolved organic matter (m-DOM) in the bulk water of the 30 m long wave flume. With the help of Duyen, working on VOC characterization, much of our work overlaps in terms of identifying chemical components found in seawater. To date, m-DOM is poorly understood in terms of its composition as well as its role in the ocean and atmosphere (as an aerosol). It can have anywhere from 1,000 to 10,000 or more molecular signatures. m-DOM, or specifically the chromophoric (light interacting) portion of it, has been shown to chemically enhance photo-induced reactions in the lab. This marine photochemistry is important to how m-DOM, being entrained in aerosols, can affect the composition of its surroundings.  

Throughout the summer, I have been working on different ways in which we can achieve our goal of characterizing m-DOM. We’ve tried direct injection into the Orbitrap to see if we can account for any differences with respect to biology and time. In the first bloom experiment, I’ve seen the Hydrogen:Carbon (H:C) ratio decrease with time suggesting that there are processes that are converting compounds into unsaturated molecules. An unsaturated compound of interest is benzothiazole, a natural marine product formed from the photolysis of 2-mercaptobenzothiazole. Benzothiazole was found to be the highest peak in mass spec the last day of the first wave experiment. It’s possible that this could have come from photo products as mentioned above or naturally produced from bacterium in the wave flume. We further want to characterize m-DOM by using infrared spectroscopy as another perspective on the different functional groups within the samples. We are currently in the process of thinking of different ways in which we can characterize or potentially look at its reactivity.

Written by: David Gonzales, Undergraduate Student in the Grassian Research Group at UC San Diego

There is nothing more fulfilling and exciting than to contribute through these collaborations with other researchers here at CAICE, in an attempt to answer some of the many uncertainties concerning the ocean and the atmosphere. We are extremely grateful for our mentor, Michael Alves, for his guidance throughout this summer. We would also like to give thanks to Dr. Vicki Grassian for her advisements and continued support. Finally, we want to express our gratitude to CAICE for this opportunity and other fellow researchers who have helped us along the way.  

Header photo credit: Nigella Hillgarth

Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation (NSF).

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