FOCUS ON: Water Quality in the Black Sea using satellite observations

Image above: Sunset over the Black Sea, taken by PML’s Dr Liz Atwood during her time in Romania for the MARBLUE 2024 Conference

The Black Sea is a unique and ecologically important body of water, bordered by six countries – Romania, Bulgaria, Ukraine, Russia, Georgia, and Turkey. Despite its strategic location and economic significance, it has faced significant environmental challenges in recent decades, including the introduction of invasive species, overfishing, pollution, and eutrophication (excessive nutrient inputs leading to harmful algal blooms).

In a recent presentation at the MARBLUE 2024 conference, a team of international researchers including PML’s Dr Liz Atwood explored the use of satellite observations to track the dominant timescales of optical variability in the surface waters of the Black Sea.

Their findings provide valuable insights into the complex physical, chemical, and biological processes shaping this important marine ecosystem.

“By using Optical Water Types (OWTs) derived from satellite data, we were able to identify distinct water masses and their associated biogeochemical characteristics across the Black Sea,” explained Dr. Atwood.

“Importantly, we found that the dominant timescales of variability in these OWT classes differed significantly between coastal and open-ocean regions, as well as across the western and eastern basins.”

The researchers used a technique called Fuzzy c-means clustering to classify the satellite data into distinct OWT classes, which they then analysed using the MOSS (Moving Standard deviation Saturation) method to determine the dominant timescales of variability.

They found that coastal waters were largely regulated by seasonal changes in freshwater inputs and climate, with timescales of 2-5 months.

However, the team also observed interesting regional differences, with the western part of the Black Sea showing shorter timescales of variability compared to the eastern basin. Additionally, at the edges of the major current system (the Rim Current), the OWT classes varied on much longer timescales, over one year.

“These patterns of variability appear to be linked to the influence of mesoscale oceanographic features, such as the Batumi eddy, a swirling current that forms in the spring and persists through the summer and autumn,” said Dr. Atwood. “We also noticed that the timescales of variability in satellite-derived chlorophyll measurements, which indicate algal abundance, were often longer than one year, suggesting important ecological processes operating on those longer time frames.”

The researchers plan to further investigate the connections between the OWT variability, mesoscale eddies, and longer-term changes in the Black Sea ecosystem. This information can help improve monitoring, modelling, and management of this complex and vital marine environment.

“Understanding the dominant timescales of optical variability in the Black Sea is a crucial step towards better managing the challenges facing this unique ecosystem,” concludes Dr. Atwood. “By leveraging the power of satellite observations, we can gain valuable insights that support the development of more effective conservation and restoration strategies.”

During her stay in Romania, Dr Atwood took some fascinating photos that she shared with us, including the below view of freshwater ponds from between Lacul Razelm and the wild beach of Vadu, south of the Danube Delta, showing a very high amount of coloured dissolved organic matter.

She also shared the below photo from the shoreline, of Barrel jellyfish (likely Rhizostoma pulmo) washed ashore following a strong bioluminescence bloom. She commented, “The bioluminescence bloom was an amazing event to witness, it happened during the conference and continued a little into the following week.”

She continues: “To see what the spectacle looked like from space, here is the true colour enhanced Sentinel-3 image from the day that I gave my talk 23-10-2024. The conference was held in Constanta, the Danube Delta is in the upper half.”

Above: speakers, participants, organizing team and partners at the Marblue 2024 Conference in Constanta, Romania. Photo credit: The National Institute for Research and Development on Marine Geology and Geo-ecology – GeoEcoMar