A warm winter and a calm spring: Sea of Marmara warming, winds and the 2021 mucilage outbreak
Ilık bir kış ve durgun bir bahar: Marmara Denizi'nde ısınma, rüzgârlar ve 2021 müsilaj salgını
Abstract
The Sea of Marmara links the Black Sea and the Aegean through the Istanbul and Çanakkale Straits and suffered a severe mucilage outbreak in 2021. We examined surface temperature, wind and biogeochemical indicators for this system using NASA MERRA-2 reanalysis, NOAA OISST v2.1, a Copernicus Marine rim-current index and BGC-Argo floats, all retrieved live from the open GOMD platform by a notebook that stops when a series is unavailable. Over 1996–2025, annual mean skin temperature rose by 0.610 °C per decade over the Sea of Marmara, 0.641 over the Istanbul Strait, 0.418 over the Çanakkale Strait and 0.434 over the Aegean (p ≤ 0.0002). In the reanalysis, the winter preceding the 2021 outbreak (December 2020–March 2021) was 1.30 °C warmer than the 1997–2020 mean, the fifth warmest of 29 winters, whereas April–June 2021 was 0.12 °C below the 1996–2020 mean (18th of 30). The same spring had 37 calm days with maximum wind below 5 m/s, the sixth-highest number in 30 years. Between the two ends of the Straits, the annual SST difference between the Aegean and Black Sea boxes had a Sen slope of −0.149 °C per decade over 1982–2025 (p = 0.0039), because the Black Sea is warming faster than the Aegean. Black Sea surface oxygen and chlorophyll-a from BGC-Argo co-varied positively over 76 common months (r = 0.43). The results support the view that warm antecedent conditions and calm weather accompanied the 2021 event, while showing that coarse reanalysis does not capture the local spring anomalies reported from station data; they do not measure mucilage or establish causation.
Keywords
Sea of Marmara; Turkish Straits; Black Sea; Mucilage; MERRA-2; Sea surface temperature; BGC-Argo; Reproducibility
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