Persistent seasonal deoxygenation alters benthic metabolic processes and accelerates hypoxia feedbacks in the Baltic Sea
Abstract
Nutrient enrichment and warming cause widespread costal deoxygenation, leading to hypoxia or even anoxia in bottom waters. The benthic-water-column-feedbacks that develop under persistent seasonal oxygen depletion and amplify hypoxia remain poorly constrained. A 15-month study of a seasonally hypoxic to anoxic costal system in the southwestern Baltic Sea combined water-column monitoring, sediment chemistry, metabolic rates and microbial analyses with historic data to reveal pronounced seasonal shifts in sediment processes. During winter oxygenation, organic matter degradation, fermentation, aerobic respiration, nitrate- and iron-reduction and microbial competition increased. Re-ventilation following anoxia did not reset sediment biogeochemistry, but initiated intensified oxygen consumption, microbial biosynthetic activity and anaerobic carbon re-cycling. Reactive ironoxyhydroxides became exhausted, the sulfidic zone shoaled and sulfate reduction and pyrite formation rates increased through fall. These processes reinforced benthic feedbacks, progressively reducing the sediment’s capacity to retain sulfide over years. This weakening of sedimentary resilience exacerbates sulfide accumulation in eutrophic costal environments with growing chances of sulfidic deep-water upwelling.
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BibTeX
@article{alampalli2026persistent,
title = {{Persistent seasonal deoxygenation alters benthic metabolic processes and accelerates hypoxia feedbacks in the Baltic Sea}},
author = {Shuba Varshini Alampalli and Stefanie Böhnke-Brandt and Nicole Adam-Beyer and Katja Laufer-Meiser and Klaus Wallmann and Hermann W. Bange and Helmke Hepach and Matthias Thiele and Florian Scholz and Emanuel Wyler and Markus Landthaler and Isabel Diercks and Janina Fuß and Mirjam Perner},
journal = {Communications Earth \& Environment},
year = {2026},
month = oct,
doi = {10.1038/s43247-026-04120-8},
url = {https://www.nature.com/articles/s43247-026-04120-8},
note = {CC BY 4.0},
}
RIS
TY - JOUR
TI - Persistent seasonal deoxygenation alters benthic metabolic processes and accelerates hypoxia feedbacks in the Baltic Sea
AU - Shuba Varshini Alampalli
AU - Stefanie Böhnke-Brandt
AU - Nicole Adam-Beyer
AU - Katja Laufer-Meiser
AU - Klaus Wallmann
AU - Hermann W. Bange
AU - Helmke Hepach
AU - Matthias Thiele
AU - Florian Scholz
AU - Emanuel Wyler
AU - Markus Landthaler
AU - Isabel Diercks
AU - Janina Fuß
AU - Mirjam Perner
PY - 2026
DA - 2026/10/23
JO - Communications Earth & Environment
DO - 10.1038/s43247-026-04120-8
UR - https://www.nature.com/articles/s43247-026-04120-8
AB - Nutrient enrichment and warming cause widespread costal deoxygenation, leading to hypoxia or even anoxia in bottom waters. The benthic-water-column-feedbacks that develop under persistent seasonal oxygen depletion and amplify hypoxia remain poorly constrained. A 15-month study of a seasonally hypoxic to anoxic costal system in the southwestern Baltic Sea combined water-column monitoring, sediment chemistry, metabolic rates and microbial analyses with historic data to reveal pronounced seasonal shifts in sediment processes. During winter oxygenation, organic matter degradation, fermentation, aerobic respiration, nitrate- and iron-reduction and microbial competition increased. Re-ventilation following anoxia did not reset sediment biogeochemistry, but initiated intensified oxygen consumption, microbial biosynthetic activity and anaerobic carbon re-cycling. Reactive ironoxyhydroxides became exhausted, the sulfidic zone shoaled and sulfate reduction and pyrite formation rates increased through fall. These processes reinforced benthic feedbacks, progressively reducing the sediment’s capacity to retain sulfide over years. This weakening of sedimentary resilience exacerbates sulfide accumulation in eutrophic costal environments with growing chances of sulfidic deep-water upwelling.
SN - 2662-4435
ER -