Research Product

We report sediment and bottom water respiration rates from 10 cruises from 2003-2007 on the Louisiana Continental Shelf (LSC) where summer hypoxia regularly occurs. Cruises were conducted during spring (5 cruises), summer (3 cruises) and fall (2 cruises). Cruise average sediment oxygen consumption (SOC) ranged from 3.9 to 31.2 mmol O2 m-2 d-1, averaging 18.3 ± 1.7 mmol O2 m-2 d-1. Bottom water plankton respiration (WR) ranged from 5.4 to 10.8 mmol O2 m-3 d-1, averaging 6.8 ± 0.6 mmol O2 m-3 d-1. Integrated below-pycnocline oxygen consumption (TR), calculated as the sum of SOC and integrated WR rates, ranged from 50.5 to 110.0 mmol O2 m-2 d-1, averaging 68.0 ± 5.5 mmol O2 m-2 d-1. While our sampling was not exhaustive, respiration rates appeared remarkably similar across the shelf, and similar among the different seasons sampled. In general, respiration rates agreed well with the literature, though we observe some stark differences with prior studies in the Gulf of Mexico. SOC appeared strongly limited by oxygen concentrations in the overlying water. In contrast to several prior studies conducted on the LCS, we found that the water column, rather than sediments, was the major sink for dissolved oxygen below the pycnocline, averaging 75% of the total below-pycnocline oxygen consumption. These findings add substantially to the data available for parameterizing and evaluating models of oxygen dynamics and hypoxia formation on the LCS