Baltic Sea – Effect of a natural Baltic oxygenation-deoxygenation cycle

An in situ observation and modelling study of the effect of a natural Baltic oxygenation-deoxygenation cycle on benthic recycling of P, N, Si and C.

The overall purpose is to determine effects of natural oxygenation of previously anoxic bottoms of the Baltic proper, and the subsequent return to anoxia, on the capacity of sediments to recycle / sequester biogenic elements.

The specific aims are to:

  1. Define the relationship between oxygen concentration in newly oxygenated bottom waters and the benthic in situ flux of bioavailable phosphorus (P), nitrogen (N), silicon (Si) and carbon (C) in the originally long-term anoxic Baltic proper
  2. Evaluate effect of a natural oxygenation of previously anoxic bottoms on the pool size of P, N and Si nutrients in the water column of the Baltic proper via up scaling of benthic flux results and large scale Baltic modelling.
  3. Determine the influence of the subsequent declining bottom water oxygen on benthic fluxes.
  4. Evaluate the response of the capacity of Baltic proper sediments to recycle/sequester biogenic elements to a natural oxygenation-deoxygenation cycle.
  5. Characterize any benthic biogeochemical regime shift caused by the natural oxygenation-deoxygenation cycle, i.e. by the oscillation from anoxia via oxia and hypoxia, and back to anoxia on an approximately decadal time-scale.
  6. Evaluate from model results the impact of the 2014/2015s Major Baltic Inflow (MBI) of oxygenated salty water from the Kattegat on nutrient transports and eutrophication in the Baltic Sea.

Role of SMHI

SMHI participates on cruises collecting data in the Baltic proper as well as contributes to analyses of the data. SMHI is also responsible for the modelling work in this project.

Project partners and participants

Per Hall at Gothenburg University is the project leader.

Elin Almroth-Rosell, Markus Meier and Kari Eilola at SMHI

Stefan Sommer at GEOMAR


This project is funded by the Swedish Research Council.