This fjord was born as a glacial lake that was separated from the open ocean (the North Sea) when it was lifted during glacial rebound. A shallow channel (2m deep) was dug in 1850, providing a marginal connection to the North Sea. A strong pycnocline separates fresh surface water from dense, saline bottom water, and this pycnocline reduces mixing between the layers. Anoxic conditions persist below the chemocline at 20m, and the fjord has the highest levels of hydrogen sulfide in the anoxic marine world. Like the Black Sea, vertical overlap of oxygen and sulfur is limited, but the decline of HS approaching the chemocline from below is indicative of oxidation of HS, which has been attributed to manganese and iron oxides, photo-autotrophic bacteria, and entrainment of oxygen horizontally from the boundaries of the fjord. These oxidation processes are similar to those present in the Black Sea.
Two strong seawater intrusion events have occurred through the channel in recent history (1902 and 1942). Seawater intrusions to fjords force dense, salty, oxygen-rich water into the typically anoxic, sulfidic bottom waters of euxinic fjords. These events result in a temporary disturbance to the chemocline, raising the depth at which HS is detected. The breakdown of the chemocline causes HS to react with dissolved oxygen in a redox reaction. This decreases the concentration of dissolved oxygen in the biologically active photic zone which can result in basin-scale fish die-offs. The 1942 event, in particular, was strong enough to chemically reduce the vast majority of oxygen and elevate the chemocline to the air-water interface. This caused a temporary state of total anoxia in the fjord, and resulted in dramatic fish mortality.