New paper: Hidden hypoxia at the seafloor

We are very pleased to share a paper led by Jonas Fredriksson in Limnology and Oceanography, investigating oxygen conditions in the thin layer of water immediately above the seafloor in the central Baltic Sea. The work brought together collaborators from Stockholm University, SDU and the University of Copenhagen.

The team combined continuous high-resolution oxygen profiling, reaching to within just 1 cm of the sediment surface, with aquatic eddy covariance measurements of seafloor oxygen uptake, current measurements and observations of sediment resuspension. These measurements were compared with around 30 years of conventional oxygen-monitoring data from the same area.

The results revealed frequent episodes of hypoxia within the bottom few centimetres of the water column, even though the long-term monitoring record suggested that the site remained well oxygenated. Oxygen conditions changed rapidly in response to local currents, water-column mixing and changes in seafloor oxygen consumption following resuspension events.

The study highlights an important monitoring challenge: measurements made a metre or more above the seabed may not always represent the oxygen conditions actually experienced by organisms living at the sediment surface. These transient episodes of near-seafloor hypoxia may therefore be considerably more common than existing monitoring records suggest.

Reference

Fredriksson JP, Attard K, Stranne C, Koszalka IM, Glud RN, Andersen TJ, Humborg C, Brüchert V (2024). Hidden seafloor hypoxia in coastal waters. Limnology and Oceanography 69: 2489–2502. doi: 10.1002/lno.12607. Article