Seasonal bottom water respiration in the North Sea–Baltic Sea transition zone: rates, temperature sensitivity and sources of organic material

• Published in: Marine ecology. Progress series (Halstenbek) 2014-03, Vol.499, p.19-34
• Main Authors: Hansen, Jørgen L. S., Bendtsen, Jørgen
• Format: Article
• Language: English
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps10633

Seasonal respiratory oxygen consumption was measured by bottle incubation of bottom water from 5 stations in transects across the Baltic Sea–North Sea transition zone. Respiration was measured at 3 temperatures (in situ temperature and in a 5°C colder and 5°C warmer incubation), to determine temperature sensitivity. The seasonal range in oxygen consumption was 9 to 90 mg O₂ m−3 d−1 corresponding to mineralization rates between 2.8 and 28 mg organic C m−3 d−1. The total below-halocline mineralization was estimated to be 53 g organic C m−2 yr−1 in the area; and 38 g C m−2 yr−1 when the estimate was adjusted to the mean annual temperature. Temperature sensitivity, expressed in terms of a Q 10 value, was 3.0 ± 1.1 averaged over 23 experiments. The specific decay rate of organic C ranged between 0.0027 and 0.094 d−1. To determine the seasonal lability of organic matter, the specific decay rates were normalized to a reference temperature of 10°C using the observed Q 10 values, and these estimates showed a range of decay rates between 0.0040 d−1 (January) and 0.049 d−1 (August). The C/N ratio of particulate organic matter (POM) ranged between 7 and 22. The highest decay rates were associated with low (