Tidal energy in the Bering Sea

Tidal harmonics computed from TOPEX/POSEIDON altimetry are assimilated into a barotropic, finite element model of the Bering Sea whose accuracy is evaluated though comparisons with independent bottom pressure gauges. The model is used to estimate energy fluxes through each of the Aleutian Passes and Bering Strait and to construct an energy budget for the major tidal constituents. The finite element model does not conserve mass locally and this is shown to give rise to an additional term in the energy budget whose contribution is significant for the prior model, but which is reduced substantially with the assimilation technique. Though the M2 constituent is estimated to have the largest net energy flux into the Bering Sea at 31.2 GW, the K1 constituent is not far behind at 24.9 GW and the sum for the three largest diurnal constituents is found to be greater than the sum for the largest three semi-diurnals. Samalga and Amutka Passes are found to be the primary conduits for influx of semi-diurnal energy while Amchitka Pass is the primary conduit for diurnal energy. A significant portion of the diurnal energy is seen to exist in the form of continental shelf waves trapped along Bering Sea slopes.The effect of the 18.6-year nodal modulation is estimated and found to cause basin-wide variations of approximately 19% in the net incoming tidal energy flux. Larger variations in the dissipation occur in subregions that are strongly dominated by the diurnal constituents, such as Seguam Pass and south of Cape Navarin. These variations should correlate with tidal mixing and may have important consequences for biological productivity, similar to those previously found for Pacific halibut recruitment (Parker et al., 1995) and shrimp, capelin, herring, cod, and haddock biomass in the Barents Sea (Yndestad, 2004)

Bering Strait transports from satellite altimetry

TOPEX/POSEIDON altimetry data are used to compute sea level slopes across the Bering Strait and associated geostrophic transport anomalies through the strait during ice-free periods from 1992 to 2002. The satellite turning latitude near 66N is just north of the strait, allowing us to use data from seven nearly zonal altimeter tracks close to the strait and to provide estimates of mean slopes, geostrophic currents and water transports approximately every 1.5 days. The altimeter-derived transport anomalies far exceed the mean value and are in good agreement with those derived from in situ observations. Comparison to wind data from a nearby meteorological station in Uelen, Russia, shows that computed transport anomalies correlate well with strong along-strait winds and less so with winds from other directions, thus making the transport predictions from winds alone more successful in seasons with strong and persistent meridional winds

Robust Inference of Monocot Deep Phylogeny Using an Expanded Multigene Plastid Data Set

We use multiple photosynthetic, chlororespiratory, and plastid translation apparatus loci and their associated noncoding regions (ca. 16 kb per taxon, prior to alignment) to make strongly supported inferences of the deep internal branches of monocot phylogeny. Most monocot relationships are robust (an average of ca. 91 % bootstrap support per branch examined), including those poorly supported or unresolved in other studies. Our data strongly support a sister-group relationship between Asparagales and the commelinid monocots, the inclusion of the orchids in Asparagales, and the status of Petrosaviaceae as the sister group of all monocots except Acorus and Alismatales. The latter finding supports recognition of the order Petrosaviales. Also strongly supported is a placement of Petermannia disjunct from Colchicaceae (Liliales) and a sister-group relationship between Commelinales and Zingiberales. We highlight the remaining weak areas of monocot phylogeny, including the positions of Dioscoreales, Liliales, and Pandanales. Despite substantial variation in the overall rate of molecular evolution among lineages, inferred amounts of change among codon-position data partitions are correlated with each other across the monocot tree, consistent with low incongruence between these partitions. Ceratophyllum and Chloranthaceae appear to have a destabilizing effect on the position of the monocots among other angiosperms; the issue of monocot placement in broader angiosperm phylogeny remains problematic

The October 2012 magnitude (Mw) 7.8 earthquake offshore Haida Gwaii, Canada

Alison L. Bird et al. report on the Mw 7.8 earthquake offshore Haida Gwaii, Canada, from 2012 for the Summary of the Bulletin of the International Seismological Centre

Global M 2 internal tide and its seasonal variability from high resolution ocean circulation and tide modeling

The present study describes a model simulation, where ocean tide dynamics are simulated simultaneously with the ocean circulation. The model is forced by a lunisolar tidal forcing described by ephemerides and by daily climatological wind stress, heat, and fresh water fluxes. The horizontal resolution is about 0.1° and thus, the model implicitly resolves meso-scale eddies and internal waves. In this model simulation the global M2 barotropic to baroclinic tidal energy conversion amounts to 1.2 TW. We show global maps of the surface signature of the M2 baroclinic tide and compare it with an estimate obtained from 19 years of satellite altimeter data. Further, the simulated seasonality in the low mode internal tide field is presented and, as an example, the physical mechanisms causing the non-stationarity of the internal tide generated in Luzon Strait are discussed. In general, this study reveals the impact of inter-annual changes of the solar radiative forcing and wind forced ocean circulation on the generation and propagation of the low mode internal tides. The model is able to simulate non-stationary signals in the internal tide field on global scales which have important implications for future satellite altimeter missions

Seasonal variation of the M2 tide

The seasonal cycle of the main lunar tidal constituent M2 is studied globally by an analysis of a high-resolution ocean circulation and tide model (STORMTIDE) simulation, of 19 years of satellite altimeter data, and of multiyear tide-gauge records. The barotropic seasonal tidal variability is dominant in coastal and polar regions with relative changes of the tidal amplitude of 5–10 %. A comparison with the observations shows that the ocean circulation and tide model captures the seasonal pattern of the M2 tide reasonably well. There are two main processes leading to the seasonal variability in the barotropic tide: First, seasonal changes in stratification on the continental shelf affect the vertical profile of eddy viscosity and, in turn, the vertical current profile. Second, the frictional effect between sea-ice and the surface ocean layer leads to seasonally varying tidal transport. We estimate from the model simulation that the M2 tidal energy dissipation at the sea surface varies seasonally in the Arctic (ocean regions north of 60°N) between 2 and 34 GW, whereas in the Southern Ocean, it varies between 0.5 and 2 GW. The M2 internal tide is mainly affected by stratification, and the induced modified phase speed of the internal waves leads to amplitude differences in the surface tide signal of 0.005–0.0150 m. The seasonal signals of the M2 surface tide are large compared to the accuracy demands of satellite altimetry and gravity observations and emphasize the importance to consider seasonal tidal variability in the correction processes of satellite data