Hydrographic, chemical and biological sampling has been conducted along transect C monthly since 1985 (intermittently until 1990, then continuous), along transect F bimonthly beginning in 2000 and on transect B intermittently in 1985-1986. The months for transect F are altered annually so that all months are sampled over the long-term.
Transect C
The more frequent sampling along transect C on the southeastern Louisiana coast indicates that critically depressed dissolved oxygen concentrations occur below the pycnocline from as early as late February through early October and nearly continuously from mid-May through late September. Hypoxia tends to be patchy and ephemeral in March, April and May. Hypoxia is most widespread, persistent, and severe in June, July and August, when changes in its configuration occur in response to winds, currents, and tidal advection. The persistence of extensive and severe hypoxia into September and October depends on the timing of the breakdown of vertical stratification by winds from either tropical storms or passage of cold fronts. Hypoxia is rare in the late fall and winter.
These figures show seasonal evolution of bottom disolved oxygen and other water column parameters along transect C from station C1 inshore to C9 offshore. Y axis on black&white figure is distance from the shore (from Rabalais et al., 2002).
