Oxygen concentration in Residence time of Explanatory remark Example (see testing Oxygen type Stratification near-bottom water water/mixing results below) Oxygenated average of lower quartile of thermo- and/or haloclines < 1 year, vertical natural condition in Bay of Mecklenburg near-bottom monthly measurements do not lead to hypoxia or circulation and lateral areas of the Baltic (areas <15 m depth) waters throughout the year anoxia in the water below, mixing occur frequently Sea where no (?Belt Sea, Kattegat in exceeds type-specific no permanent stratification "morphological barriers" general?), Quark threshold /or/ like e.g. in deep basins or concentration above the fjords naturally obstruct type-specific threshold value mixing processes throughout the year Seasonal hypoxia average of lower quartile of water column is seasonally < 1 year, vertical seasonal stratification is a Arkona Basin (deep monthly measurements stratified; thermo- and/or circulation seasonally natural phenomenon in areas), during (Dec)Jan-May is haloclines prevent mixing of obstructed by thermo- some areas of the Baltic shallow areas of Belt Sea above the type-specific bottom water with and/or halocline Sea and may (as in lakes) and Kattegat with depths threshold, but falls below a oxygenated water from formation, in enclosed temporarily lead to >15 m and in areas where threshold under the growth surface and, if morphological areas (e.g. between sills) hypoxia, e.g. after the halocline lies at such a season /or/ concentration barriers like e.g. sills are lateral transport may be of the spring depth that only a small drops below the present, from adjacent areas obstructed as well bloom. Degree of hypoxia volume of deep water is threshold during the depends on amount of left at the bottom, growth season (summer, organic matter arrived at Gulf of Riga autumn) but returns to the sea-floor, oxygen levels above the threshold concentration present in winter and spring/early before sedimentation of summer bloom, morphological characteristics of the (lateral transport/ mixing processses) and volume of water below halocline.
Oxygen type Oxygen concentration in near-bottom water Stratification Residence time of water/mixing Explanatory remark Example (see testing results below) Oxygenated near-bottom waters average of lower quartile of monthly measurements throughout the year exceeds type-specific threshold /or/ concentration above the type-specific threshold value throughout the year thermo- and/or haloclines do not lead to hypoxia or anoxia in the water below, no permanent stratification < 1 year, vertical circulation and lateral mixing occur frequently natural condition in areas of the Baltic Sea where no "morphological barriers" like e.g. in deep basins or fjords naturally obstruct mixing processes Bay of Mecklenburg (areas <15 m depth) (?Belt Sea, Kattegat in general?), Quark Seasonal hypoxia average of lower quartile of monthly measurements during (Dec)Jan-May is above the type-specific threshold, but falls below a threshold under the growth season /or/ concentration drops below the threshold during the growth season (summer, autumn) but returns to levels above the threshold in winter and spring/early summer water column is seasonally stratified; thermo- and/or haloclines prevent mixing of bottom water with oxygenated water from surface and, if morphological barriers like e.g. sills are present, from adjacent areas < 1 year, vertical circulation seasonally obstructed by thermo- and/or halocline formation, in enclosed areas (e.g. between sills) lateral transport may be obstructed as well seasonal stratification is a natural phenomenon in some areas of the Baltic Sea and may (as in lakes) temporarily lead to hypoxia, e.g. after of the spring bloom. Degree of hypoxia depends on amount of organic matter arrived at the sea-floor, oxygen concentration present before sedimentation of bloom, morphological characteristics of the (lateral transport/ mixing processses) and volume of water below halocline. Arkona Basin (deep areas), shallow areas of Belt Sea and Kattegat with depths >15 m and in areas where the halocline lies at such a depth that only a small volume of deep water is left at the bottom, Gulf of Riga