The smell of the sea – a key to understanding climate change?

How does the smell of the sea impact the world’s climate? This question lies at the heart of the Cyano-VOC research project. Within this endeavour, aerosol chemists collaborate with microbiologists to investigate the volatile organic compounds emitted by cyanobacteria and other plankton residing along the coastlines of the Baltic Sea.


In a warmer climate, cyanobacterial blooms in the Baltic Sea are anticipated to increase. However, these blooms could also impact the Earth’s climate by releasing gases into the atmosphere.

"The familiar 'smell of the sea' is actually a mixture of volatile organic compounds, known as VOCs”, explains, Sneha Aggarwal, a PhD student in the Department of Environmental Science at Stockholm University. “We are investigating the specific components responsible for this scent."

Matt Salter och Snega Aggarwal during a three-day sampling expedition aboard R/V Electra analysing volatile organic compounds (VOCs) released by cyanobacteria blooms. Photo: Lisa Bergqvist

Critically, some VOCs are detrimental and can affect air quality at ground level. In addition, certain VOCs can form aerosols, which, in turn, contribute to cloud formation. Depending on the characteristics of these clouds and their altitude, they can either cool the climate (by blocking solar radiation) or contribute to warming (by trapping heat in the atmosphere). 

Matt Salter, an aerosol physicist and researcher specializing in ocean-atmosphere interactions at the Department of Environmental Science at Stockholm University, points out that the most significant uncertainty in climate models relates to the impact of aerosols and clouds. 

“While we have a solid understanding of the consequences of releasing greenhouse gases into the atmosphere, the effects of aerosols and VOCs that form them remain relatively uncertain”, he says. “Expanding our knowledge in this area is crucial for predicting future climate.”.

Sneha Aggarwal and Matt Salter on R/V Electra. Photo: Lisa Bergqvist

Research missing from coastal environments

In recent decades, there has been significant research focused on VOCs emitted from terrestrial environments”, explains Matt Salter. However, emissions from the sea, particularly in coastal regions, have remained relatively unexplored. Bridging these knowledge gaps is the central goal of the Cyano-VOC project, jointly led by Matt Salter, Sneha Aggarwal, and microbiologist Elias Broman from the Department of Ecology, Environment, and Plant Sciences at Stockholm University.

Sneha Aggarwal, Depatment of Environmental Science,  Stockholm University. Photo: Lisa Bergqvist

"Our primary interest lies in understanding emissions originating from cyanobacterial blooms in the Baltic Sea.”, Sneha Aggarwal says. “To achieve this, we are conducting measurements both within the bloom, in areas outside the bloom, and during our journey to the bloom. We are also comparing various stations with varying levels of bloom intensity to examine differences in emissions and their potential impact on atmospheric chemistry."

R/V Electra. Foto: Lisa Bergqvist

Measurements onboard a ship

To measure the VOCs, Matt Salter and Sneha Aggarwal have equipped the research vessel Electra with an advanced mass spectrometer. The process involves pumping seawater onto the ship and passing it through a closed tank, where the emitted gases are collected and then directed to the mass spectrometer. Here, the compounds are separated and detected.

While the tank's activity can be monitored in real-time on a display, identifying the specific compounds corresponding to each peak in the signal requires thorough data analysis. This is a time-intensive process conducted in multiple stages, and it is expected to take several months.

As Matt Salter explains, "We are among the pioneers in bringing this machine onto a ship for such measurements. Consequently, we cannot simply cross-reference the data with existing databases, as no such databases currently exist. However, with each subsequent deployment, we will gain a better understanding of what to expect, potentially enabling us to make more immediate identifications of the compounds."

The seawater is pumped through a tank and the gases emitted are sent to the mass spectrometer. Photo: Lisa Bergqvist

Combination of techniques required

The researchers are not only interested in obtaining general information about emissions from the sea but also in understanding how these emissions vary based on the level of eutrophication and the specific species of plankton and cyanobacteria present in the water. To achieve this, they conduct VOC measurements across extensive areas, complemented by the collection of physical water properties data, such as chlorophyll levels. Additionally, seawater filter samples will be subjected to genetic analysis using DNA and RNA analysis techniques known as "omic" techniques.

"Integrating all this information should provide us with insights into how VOC concentrations correlate with the presence of cyanobacteria and other microorganisms in the water”, says Matt Salter. “Furthermore, it can help us identify which VOCs are attributable to specific species. Collectively, this knowledge can contribute to reducing some of the remaining uncertainties in climate models and add another piece to the puzzle of how eutrophication of the sea impacts the climate."  

Text and Photo: Lisa Bergqvist

Mr Salter and Ms Sneha Aggarwal are planning today's sampling together with Mr Thomas Strömsnäs, Master of the R/V Electra. Photo: Lisa Bergqvist

Facts: Cyano-VOC

The Cyano-VOC project, led by Matt Salter and Sneha Aggarwal from the Department of Environmental Science at Stockholm University, and Elias Broman from the Department of Ecology, Environment, and Plant Sciences, will run from 2023-2025. 

The aim of the project is to enhance our understanding of the release of VOCs by cyanobacteria and their impact on atmospheric chemistry and climate. To achieve this, advanced mass spectrometry techniques in combination with RNA and DNA techniques (omics) are being utilised. These methods help identify and quantify the cyanobacteria species present and determine the genes responsible for VOC production in cyanobacteria.

The project is a part of the joint research initiative, ‘CoastClim’, between Stockholm University and the University of Helsinki.

The water samples will be compared with information from the mass spectrometer to determine which marine species are associated with which VOCs. Photo: Lisa Bergqvist