Improved coastal boundary condition for surface water waves

Abstract Surface water waves in coastal waters are commonly modeled using the mild slope equation. One of the parameters in the coastal boundary condition for this equation is the direction at which waves approach a coast. Three published methods of estimating this direction are examined, and it is demonstrated that the wave fields obtained using these estimates deviate significantly from the corresponding analytic solution. A new method of estimating the direction of approaching waves is presented and it is shown that this method correctly reproduces the analytic solution. The ability of these methods to simulate waves in a rectangular harbor is examined

The Art of Reviewing: Holding up quality in the scientific quality control system

International audienc

Effect of oxygen manipulations on benthic foraminifera: A preliminary experiment

235-239Three sediment cores were collected at 50 m water depth on the west coast of India, off Ratnagiri, and were subjected to oxygen manipulations maintaining natural temperature and salinity. The objective was to understand foraminiferal response to changed oxygen conditions. After a fortnight, the experimental cores were sub-sectioned and analyzed for their live foraminiferal content. This data was compared with background field data obtained from the non-experimental core. The data indicate that any change in natural oxygen conditions causes lowering of foraminiferal numbers. It is clearly evident that Fursenkoina and Nonions are more adaptive to changed oxygen conditions in contrast to Bolivinids and Rotalids, which quickly die out. This study clearly demonstrates the change in foraminiferal distribution in response to oxygen changes. This experimental study further can help develop foraminifera as a proxy to decipher the past fluctuations in the OMZ in the past, including assessment of their anthropogenic origin

The dispersal dynamics of juvenile plantigrade mussels (Mytilus edulis L.) from eelgrass (Zostera marina) meadows in Maine,USA

Field and modelling studies of the distribution of mussel larvae and juvenile plantigrade mussels in and around eelgrass meadows at Mt. Desert Narrows, Lamoine, Maine have demonstrated the following sequence of events which results in the establishment of mussel beds in shallow subtidal and intertidal waters. Mussel larvae increase on the flood tide in early July and are concentrated in the low current regions above the eelgrass blades. Larger mussel pediveligers decrease in concentration in water masses as they pass over the eelgrass meadow on the flood tide, where they settle on the eelgrass blades, especially the taller reproductive shoots. Mussel plantigrades grow from setting size to about 1 mm shell length by mid-August, when they detach from the eelgrass blades and drift inshore on the flood tide using a byssal sail. A wave of secondary settlement in late summer results in a significant drop in mussel concentration on the eelgrass blades, just prior to the release of eelgrass shoots during their fall die-off. A combined flow and particle tracking model of Mt. Desert Narrows, Maine successfully predicted the patterns of both primary and secondary settlement of mussels in the eelgrass meadows at Old Point, and their eventual dispersal inshore of the meadows in late summer. By using size frequency distributions of mussels collected from plankton tows, eelgrass blades, floating collectors and bottom cultch, we observed the absence of drifting juvenile mussels in the 0.4–0.8 mm size range, and most drifting juveniles in the 1–2 mm size groups. Eelgrass blades provide a predator refuge for mussels during metamorphosis, and allow growth of the stem glands in the foot to form a byssal sail. Successful recruitment to bottom cultch results from the combination of available substrate (eelgrass) for primary settlement, and hydrodynamics

Oxygen minimum seafloor ecological (mal) functioning

Although organic matter (OM) settling on the seafloor is generally rapidly recycled, a key ecological process, large scale burial events manifest itself in the marine sedimentary record as organic carbon (Corg)-rich layers. Presently, this prevails under certain oceanic settings such as the oxygen minimum zones (OMZ) where OM accumulates in underlying sediments. A basic question that remains is as to what extent this Corg accumulation reflects ecological “malfunctioning” or a shunting of ecological processes? Experimenting with eastern Arabian Sea OMZ sediment we found no evidence that Corg accumulation here is not due to trophic satiation or to low tolerance of biota to severe oxygen depletion. However, we found direct evidence that suggests that the OMZ sediment Corg has very low bioavailability that probably impairs biological transformation. In the first set of experiments, the impact of oxygenation on the benthic ecological functioning was examined by following the fate of fresh, highly degradable OM (13C-labelled diatoms) in intact sediment cores incubated for 7 days under normoxic versus suboxic bottom water conditions. Tracer organic matter assimilation (by bacteria and fauna) and respiration was evident and similar under both treatments and demonstrates that the benthic response was not hindered by severe oxygen depletion. Furthermore, relatively low biomass standing stock of fauna and bacteria, in spite of sediment high Corg content, together with this clear uptake of fresh tracer OM suggest that the benthic community was not food saturated. In a second set of experiments, the bioavailability of in situ OMZ organic matter was determined directly through CO2 production rate measurements in bottle sediment–water slurry incubations. In sharp contrast to fresh tracer algal carbon which had a half-life 0.07 years, the OMZ surficial sediment OM half-life was ~ 67 years already in very early diagenesis. Clearly, a distinct difference in functioning and indicates that a large fraction of OMZ sediment organic matter is evidently excluded from immediate first-hand biotic transformation but on its own represents a link between the “fast (biological)” and the “slow (geological)” carbon cycle along the continuum of OM recycling. Furthermore, while this rapid shift out of the “fast” biological cycle may be common or characteristic of large scale OM accumulation events, a comparison with an ancient Corg-deposit suggest that the trigger mechanisms may not be uniform.