Oceanography of Anoxic and Hypoxic Basins

Question 1

Why does hypoxia occur in Saanich Inlet

Answer 1

The sill at the mouth of the inlet blocks dense oxygenated water from entering into the Inlet, but may build up behind the sill and eventually spill over and resupply oxygen to deep basin of Saanich Inlet (natural)

Question 2

What consumes oxygen at depth?

Answer 2

Bacteria remineralizing organic matter fallen from the surface due to high organic matter production during the growing season

Question 3

Why does hypoxia occur in the Northern Gulf of Mexico?

Answer 3

Due to excess nitrogen delivered by the Mississippi River Basin in combination with stratification of Gulf waters (anthropogenic - fertilizer use in Mississippi river), organic matter remineralized at depth using oxygen

Question 4

What causes low oxygen in oregon coastal waters?

Answer 4

Recent occurrence, due to climate change effects where intensified upwelling (increased wind) is bringing up deeper water with less O2 further up the coast and more nutrients which enhance phyto blooms but also bacterial remineralization at depth

Question 5

What causes hypoxia in the St. Lawrence Estuary and Gulf of St. Lawrence?

Answer 5

Climate change and anthropogenic: change in circulation patterns where less oxygenated Labrador Coastal Water and more low-oxygen North Atlantic Coastal Waters are getting into the estuary, and fertilizers in land are ending up in river and estuary