Annual cycle of hypoxia off the Changjiang (Yangtze River) Estuary.

The annual cycle of hypoxia off the Changjiang Estuary, China, was assessed from data acquired during nine cruises in 2006-2007. Hypoxia began to develop in late spring and early summer, reached its maximum in August, weakened in the autumn and finally disappeared in the winter. Hypoxia first developed south-east of the Changjiang Estuary in June, appeared in the east and north-east in July, and spread both south and north of the Changjiang Estuary in August. By September, it had started to recede in the north-east, and had dissipated in the southern part of the studied area by winter. The geographical displacement of the hypoxic zone was controlled by both seasonal changes in regional water column stratification and variations of the northward extension of the Taiwan Warm Current toward the Changjiang Estuary.