Reactivity of Inorganic Mn and Mn Desferrioxamine B with O2, O2–, and H2O2 in Seawater

Manganese (Mn) is a required element for oceanic phytoplankton as it plays a critical role in photosynthesis, through its unique redox chemistry, as the active site in photosystem II, and in enzymes that act as defenses against reactive oxygen species (ROS), most notably for protection against superoxide (O2?), through the action of superoxide dismutase (SOD), and against hydrogen peroxide (H2O2) via peroxidases and catalases. The distribution and redox speciation of Mn in the ocean is also apparently controlled by reactions with ROS. Here we examine the connections between ROS and dissolved Mn species in the upper ocean using field and laboratory experimental data. Our results suggest it is unlikely that significant concentrations of Mn(III) are produced in the euphotic zone, as in the absence of evidence for the existence of strong Mn(III) ligands, Mn(II) reacts with O2? to form the short-lived transient manganous superoxide, MnO2+, which may react rapidly with other redox species in a manner similar to O2?. Experiments with the strong Mn(III) chelator, desferrioxamine B (DFB), in seawater indicated that the Mn(III) species are unlikely to form, as formation of the precursor Mn(II) complex is hindered due to the stability of the Ca complex with DFB.

A molecular method for the identification of resting eggs of acartiid copepods in the Thau lagoon, France

Acartia and Paracartia species, often known to co-occur, can exhibit complex life cycles, including the production of resting eggs. Studying and understanding their population dynamics is hindered by the inability to identify eggs and early developmental stages using morphological techniques. We have developed a simple molecular technique to distinguish between the three species of the Acartiidae family (Acartia clausi, A. discaudata and Paracartia grani) that co-occur in the Thau lagoon (43�250N; 03�400E) in southern France. Direct amplification of a partial region of the mitochondrial cytochrome oxidase I gene by polymerase chain reaction and subsequent restriction fragment length polymorphism results in a unique restriction profile for each species. The technique is capable of determining the identity of individual eggs, including resting eggs retrieved from sediment samples, illustrating its application in facilitating population dynamic studies of this ubiquitous and important member of the zooplankton community.

A reconciliation of empirical and mechanistic models of the air-sea gas transfer velocity

Models of the air-sea transfer velocity of gases may be either empirical or mechanistic. Extrapolations of empirical models to an unmeasured gas or to another water temperature can be erroneous if the basis of that extrapolation is flawed. This issue is readily demonstrated for the most well-known empirical gas transfer velocity models where the influence of bubble-mediated transfer, which can vary between gases, is not explicitly accounted for. Mechanistic models are hindered by an incomplete knowledge of the mechanisms of air-sea gas transfer. We describe a hybrid model that incorporates a simple mechanistic view—strictly enforcing a distinction between direct and bubble-mediated transfer—but also uses parameterizations based on data from eddy flux measurements of dimethyl sulphide (DMS) to calibrate the model together with dual tracer results to evaluate the model. This model underpins simple algorithms that can be easily applied within schemes to calculate local, regional, or global air-sea fluxes of gases.

A reconciliation of empirical and mechanistic models of the air-sea gas transfer velocity

Models of the air-sea transfer velocity of gases may be either empirical or mechanistic. Extrapolations of empirical models to an unmeasured gas or to another water temperature can be erroneous if the basis of that extrapolation is flawed. This issue is readily demonstrated for the most well-known empirical gas transfer velocity models where the influence of bubble-mediated transfer, which can vary between gases, is not explicitly accounted for. Mechanistic models are hindered by an incomplete knowledge of the mechanisms of air-sea gas transfer. We describe a hybrid model that incorporates a simple mechanistic view—strictly enforcing a distinction between direct and bubble-mediated transfer—but also uses parameterizations based on data from eddy flux measurements of dimethyl sulphide (DMS) to calibrate the model together with dual tracer results to evaluate the model. This model underpins simple algorithms that can be easily applied within schemes to calculate local, regional, or global air-sea fluxes of gases.