Chasing the offshore wind farm wind-wake-induced upwelling/downwelling dipole

The operational principle of offshore wind farms (OWF) is to extract kinetic energy from the atmosphere and convert it into electricity. Consequently, a region of reduced wind speed in the shadow zone of an OWF, the so-called wind-wake, is generated. As there is a horizontal wind speed deficit between the wind-wake and the undisturbed neighboring regions, the locally reduced surface stress results in an adjusted Ekman transport. Subsequently, the creation of a dipole pattern in sea surface elevation induces corresponding anomalies in the vertical water velocities. The dynamics of these OWF wind-wake induced upwelling/downwelling dipoles have been analyzed in earlier model studies, and strong impacts on stratified pelagic ecosystems have been predicted. Here we provide for the first time empirical evidence of the existence of such upwelling/downwelling dipoles. The data were obtained by towing a remotely operated vehicle (TRIAXUS ROTV) through leeward regions of operational OWFs in the summer stratified North Sea. The undulating TRIAXUS transects provided high-resolution CTD data which enabled the characterization of three different phases of the ephemeral life cycle of a wind-wake-induced upwelling/downwelling dipole: development, operation, and erosion. We identified two characteristic hydrographic signatures of OWF-induced dipoles: distinct changes in mixed layer depth and potential energy anomaly over a distance < 5 km and a diagonal excursion of the thermocline of ~10–14 m over a dipole dimension of ~10–12 km. Whether these anthropogenically induced abrupt changes are significantly different from the corridor of natural variability awaits further investigations

Depleted marine fish stocks and ecosystem-based management: on the road to recovery, we need to be precautionary

Depleted marine fish stocks and ecosystem-based management: on the road to recovery, we need to be precautionary. -ICES Journal of Marine Science, doi:10.1093/icesjms/fsq158. Precautionary management for fish stocks in need of recovery requires that likely stock increases can be distinguished from model artefacts and that the uncertainty of stock status can be handled. Yet, ICES stock assessments are predominantly deterministic and many EC management plans are designed for deterministic advice. Using the eastern Baltic cod (Gadus morhua) stock as an example, we show how deterministic scientific advice can lead to illusive certainty of a rapid stock recovery and management decisions taken in unawareness of large uncertainties in stock status. By (i) performing sensitivity analyses of key assessment model assumptions, (ii) quantifying the uncertainty of the estimates due to data uncertainty, and (iii) developing alternative stock and ecosystem indicators, we demonstrate that estimates of recent fishing mortality and recruitment of this stock were highly uncertain and show that these uncertainties are crucial when combined with management plans based on fixed reference points of fishing mortality. We therefore call for fisheries management that does not neglect uncertainty. To this end, we outline a four-step approach to handle uncertainty of stock status in advice and management. We argue that it is time to use these four steps towards an ecosystem-based approach to fisheries management

Predation risk triggers copepod small-scale behavior in the Baltic Sea

Predators not only have direct impact on biomass but also indirect, non-consumptive effects on the behavior their prey organisms. A characteristic response of zooplankton in aquatic ecosystems is predator avoidance by diel vertical migration (DVM), a behavior which is well studied on the population level. A wide range of behavioral diversity and plasticity has been observed both between- as well as within-species and, hence, investigating predator–prey interactions at the individual level seems therefore essential for a better understanding of zooplankton dynamics. Here we applied an underwater imaging instrument, the video plankton recorder (VPR), which allows the non-invasive investigation of individual, diel adaptive behavior of zooplankton in response to predators in the natural oceanic environment, providing a finely resolved and continuous documentation of the organisms’ vertical distribution. Combing observations of copepod individuals observed with the VPR and hydroacoustic estimates of predatory fish biomass, we here show (i) a small-scale DVM of ovigerous Pseudocalanus acuspes females in response to its main predators, (ii) in-situ observations of a direct short-term reaction of the prey to the arrival of the predator and (iii) in-situ evidence of pronounced individual variation in this adaptive behavior with potentially strong effects on individual performance and ecosystem functioning

Evidence of local conformational fluctuations and changes in bacteriorhodopsin, dependent on lipids, detergents and trimeric structure, as studied by 13C NMR

AbstractWe examined how the local conformation and dynamics of [3-13C]Ala-labeled bacteriorhodopsin (bR) are altered as viewed from 13C NMR spectra when the natural membrane lipids are partly or completely replaced with detergents. It turned out that the major conformational features of bR, the αII-helices, are generally unchanged in the delipidated or solubilized preparations. Upon partial delipidation or detergent solubilization, however, a significant conformational change occurs, ascribed to local conversion of αII→αI-helix (one Ala residue involved), evident from the upfield displacement of the transmembrane helical peak from 16.4 ppm to 14.5 ppm, conformational change (one or two Ala residues) within αII-helices from 16.4 to 16.0 ppm, and acquired flexibility in the loop region (especially at the F–G loop) as manifested from suppressed peak-intensities in cross-polarization magic angle spinning (CP-MAS) NMR spectra. On the other hand, formation of monomers as solubilized by Triton X-100, Triton N-101 and n-dodecylmaltoside is characterized by the presence of a peak at 15.5 ppm and a shifted absorption maximum (550 nm). The size of micelles under the first two conditions was small enough to yield 13C NMR signals observable by a solution NMR spectrometer, although 13C CP-MAS NMR signals were also visible from a fraction of large-sized micelles. We found that the 16.9 ppm peak (three Ala residues involved), visible by CP-MAS NMR, was displaced upfield when Schiff base was removed by solubilization with sodium dodecyl sulfate, consistent with our previous finding of bleaching to yield bacterioopsin