Much of the organic matter associated with this high productivity sinks onto the relatively wide continental shelf, where decay results in the reduction of dissolved oxygen in bottom waters [5]. (journals.plos.org)
Also, it increases the amount of dissolved oxygen in the blood. (selfcarer.com)
Of course this wasn't possible in winter, so gaps in data for dissolved oxygen, pH, and other properties would pop up depending on the weather. (fondriest.com)