How did glaciation change Ordovician ocean currents and upwelling?

During the Ordovician Period, most ocean circulation was characterized by sluggish movement, as deep waters were primarily generated in warm, saline tropical epicontinental seas rather than at the poles. This lack of vigorous circulation often led to anoxic conditions in deep marine environments.1

However, the onset of continental glaciation significantly altered these patterns. As surface waters were chilled by glacial activity, they became denser and descended, displacing the warmer, deep ocean water. Because cold polar water sinks more rapidly than warm, saline tropical water, this process accelerated ocean circulation.1

This intensification of circulation directly enhanced the strength of major ocean currents and increased the rate of upwelling—the movement of colder, nutrient-rich water from the depths to the surface. This increased upwelling likely fostered higher productivity among photosynthetic organisms, which in turn helped remove additional carbon dioxide from the atmosphere. Some scientists suggest that these changes created new, nutrient-rich habitats that may have accelerated the rate of speciation during the period.12