Articles | Volume 11, issue 1
https://doi.org/10.5194/os-11-93-2015
https://doi.org/10.5194/os-11-93-2015
Research article
 | 
21 Jan 2015
Research article |  | 21 Jan 2015

Consequences of artificial deepwater ventilation in the Bornholm Basin for oxygen conditions, cod reproduction and benthic biomass – a model study

A. Stigebrandt, R. Rosenberg, L. Råman Vinnå, and M. Ödalen

Abstract. We develop and use a circulation model to estimate hydrographical and ecological changes in the isolated basin water of the Bornholm Basin. By pumping well-oxygenated so-called winter water to the greatest depth, where it is forced to mix with the resident water, the rate of deepwater density reduction increases as well as the frequency of intrusions of new oxygen-rich deepwater. We show that pumping 1000 m3 s−1 should increase the rates of water exchange and oxygen supply by 2.5 and 3 times, respectively. The CRV (cod reproduction volume), the volume of water in the isolated basin meeting the requirements for successful cod reproduction (S > 11, O2 > 2 mL L−1), should every year be greater than 54 km3, which is an immense improvement, since it has been much less in certain years. Anoxic bottoms should no longer occur in the basin, and hypoxic events will become rare. This should permit extensive colonization of fauna on the earlier periodically anoxic bottoms. Increased biomass of benthic fauna should also mean increased food supply to economically valuable demersal fish like cod and flatfish. In addition, re-oxygenation of the sediments should lead to increased phosphorus retention by the sediments.

Download
Short summary
The hydrographical and ecological changes in the deep part of the Bornholm Basin in response to pumping well-oxygenated so-called winter water down to the greatest depth are investigated. By pumping 1000 m3s-1, the rates of water exchange and oxygen supply increase by 2.5 and 3 times, respectively. Anoxic bottoms should no longer occur and hypoxic events will become rare. This should mean much improved conditions for successful cod reproduction, extensive colonization of fauna on earlier periodi