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Ocean Darkening and CDOMs
Ocean Darkening and CDOMs
Ocean darkening has become an increasingly problematic phenomena over the years, in which the attenuation (the reduction in the intensity of light as it passes through a medium) of natural light due to elevated concentrations of phytoplankton, particulate matter, and dissolved organic matter has resulted in a reduction of light availability necessary for photobiology in the oceans. Consequently, the photic zone, defined as the top layer of the ocean in which sunlight penetrates and photosynthesis takes place, has seen a reduction in depth. The moon and sunlight are critical in facilitating biological processes vital for the survival and reproduction of marine organisms, thus these recent developments could prove disastrous for the health of marine life.
A study on the darkening of the global ocean by marine conservation professor Thomas W. Davies and marine scientist Tim Smyth found that Kd(490), the measure of how quickly light at the wavelength of 490 nm is attenuated as it travels downward in the water column, has increased across 21% and decreased across 10% of the global ocean, indicating that the ocean has become darker between 2003 and 2022. Their study also found that the depth of the photic zone has reduced by more than 100 m across 2.6% of the global ocean between the same time frame.
One cause of these developments is the growing population of phytoplankton and the organic matter they produce, specifically chromophoric dissolved organic matter, or CDOM, which is the part of dissolved organic matter that absorbs light.
Photo credits: WILEY Online Library
Ocean Acidification
Ocean Acidification
Ocean acidification refers to lowering pH of the ocean due to the absorption of excess carbon dioxide. Chemically, water reacts with the carbon dioxide to form H2CO3. That acid then breaks into hydrogen ions, H+, and carbonate ions, CO3-. This chemical change in the ocean harms calcifying organisms (organisms that create calcium carbonate to form shells or skeletons), a hydrogen ions react with carbonate ions in seawater, reducing the carbonate available for shell formation. It also affects non-calcifying organisms by changing their behaviors, such as their ability to detect predators. According to the National Oceanic and Atmospheric Administration, the ocean could potentially have a pH of approximately 7.8 by the end of the century.
Photo credits: NOAA and NOAA PMEL
The Gap in My Research
The Gap in My Research
While production DOM by phytoplankton and refinement of CDOM measurement methods have been performed, little is known about how the effects of ocean acidification, specifically the reduction of pH, impact the production of CDOM by Chaetoceros muerelli. By understanding how alterations in phytoplankton's environment influence their releasement of DOM, we develop a more advanced understanding of how changing conditions modify their biological functions now and in the future, opening more doorways to CDOM and pH studies.
In a broader sense, the importance of this research lies in the fact that it would help comprehend the connection between two global marine crises: ocean darkening and ocean acidification, and how the effects of each one my exponentially worsen the effects of the other. Considering a primary reason for ocean darkening are phytoplankton blooms and excess production of CDOM, if worsening ocean acidification were to increase that production, the health of the photic zone and all marine life that rely on it could be detrimentally dismantled. This study would be a start to learning more about the relationships between light absorption and pH reduction of the ocean, the the extent of severity their intertwined impacts have, and how they might change in the future.
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