Impacts of Hypoxia on Zooplankton Spatial Distributions in the Northern Gulf of Mexico

The northern Gulf of Mexico (NGOMEX) was surveyed to examine the broad-scale spatial patterns and inter-relationships between hypoxia (<2?mg?L^?1 dissolved oxygen) and zooplankton biovolume. We used an undulating towed body equipped with sensors for conductivity, temperature, depth, oxygen, fluorescence, and an optical plankton counter to sample water column structure, oxygen, and zooplankton at high spatial resolution (1?m??vertical; 0.25?C1?km??horizontal). We contrast the distribution of zooplankton during summer surveys with different freshwater input, stratification, and horizontal and vertical extent of bottom-water hypoxia. Bottom-water hypoxia did not appear to influence the total amount of zooplankton biomass present in the water column or the areal integration of zooplankton standing stock in the NGOMEX region surveyed. However, where there were hypoxic bottom waters, zooplankton shifted their vertical distribution to the upper water column during the day where they normally would reside in deeper and darker waters. When bottom waters were normoxic (>2?mg?L^?1 dissolved oxygen), the daytime median depth of the water column zooplankton was on average 7?m deeper than the median depth of zooplankton in water columns with hypoxic bottom waters. A reduction in larger zooplankton when there were hypoxic bottom waters suggests that if zooplankton cannot migrate to deeper, darker water under hypoxic conditions, they may be more susceptible to size-selective predation by visual predators. Thus, habitat compression in the northern Gulf of Mexico due to hypoxic bottom water may have implications for trophic transfer by increasing the contact between predators and prey.     

Hazard assessment of the Tidal Inlet landslide and potential subsequent tsunami, Glacier Bay National Park, Alaska

An unstable rock slump, estimated at 5 to 10 × 10⁶ m³, lies perched above the northern shore of Tidal Inlet in Glacier Bay National Park, Alaska. This landslide mass has the potential to rapidly move into Tidal Inlet and generate large, long-period-impulse tsunami waves. Field and photographic examination revealed that the landslide moved between 1892 and 1919 after the retreat of the Little Ice Age glaciers from Tidal Inlet in 1890. Global positioning system measurements over a 2-year period show that the perched mass is presently moving at 3–4 cm annually indicating the landslide remains unstable. Numerical simulations of landslide-generated waves suggest that in the western arm of Glacier Bay, wave amplitudes would be greatest near the mouth of Tidal Inlet and slightly decrease with water depth according to Green’s law. As a function of time, wave amplitude would be greatest within approximately 40 min of the landslide entering water, with significant wave activity continuing for potentially several hours.     

Plastic deformation of orthoenstatite and the ortho- to high-pressure clinoenstatite transition: a metadynamics simulation study

Atomic-scale mechanisms of plastic deformation in orthoenstatite, MgSiO₃ are studied by computer simulation methods. The combined use of metadynamics and molecular dynamics allows a direct observation of the structural changes during the creation of stacking faults in the (100) plane. A sequence of slip deformations in two different (100) planes at P = 15 GPa and T = 1,000 K reveals a probable transformation mechanism for the ortho- to high-pressure clinopyroxene transition. Each of the observed slips consists of at least four partial deformations crossing high-energy intermediate structures. In agreement with experimental studies, both (100)[010] and (100)[001] slip systems are activated in the deformation process. The observation of a dominant (100)[001] single slip system in pyroxenes may be related to the fact that high-energy intermediate dislocations with (100)[010] component are not stable on geological or experimental timescales.     

Failed magmatic eruptions: late-stage cessation of magma ascent

When a volcano becomes restless, a primary question is whether the unrest will lead to an eruption. Here we recognize four possible outcomes of a magmatic intrusion: “deep intrusion”, “shallow intrusion”, “sluggish/viscous magmatic eruption”, and “rapid, often explosive magmatic eruption”. We define “failed eruptions” as instances in which magma reaches but does not pass the “shallow intrusion” stage, i.e., when magma gets close to, but does not reach, the surface. Competing factors act to promote or hinder the eventual eruption of a magma intrusion. Fresh intrusion from depth, high magma gas content, rapid ascent rates that leave little time for enroute degassing, opening of pathways, and sudden decompression near the surface all act to promote eruption, whereas decreased magma supply from depth, slow ascent, significant enroute degassing and associated increases in viscosity, and impingement on structural barriers all act to hinder eruption. All of these factors interact in complex ways with variable results, but often cause magma to stall at some depth before reaching the surface. Although certain precursory phenomena, such as rapidly escalating seismic swarms or rates of degassing or deformation, are good indicators that an eruption is likely, such phenomena have also been observed in association with intrusions that have ultimately failed to erupt. A perpetual difficulty with quantifying the probability of eruption is a lack of data, particularly on instances of failed eruptions. This difficulty is being addressed in part through the WOVOdat database. Papers in this volume will be an additional resource for scientists grappling with the issue of whether or not an episode of unrest will lead to a magmatic eruption.     

Aeolization on the Atlantic coast of Galicia (NW Spain) from the end of the last glacial period to the present day: Chronology,origin and evolution of coastal dunes linked to sea-level oscillations

The Atlantic coast of Galicia (NW Spain) is a high-energy environment where shingle beaches are currently developing. These coarser sediments alternate with sandy deposits which are also considered as beaches typical of a low-energy environment. The physical association of both types of sediment with contrasted sedimentary significance raises problems of interpretation. The study of four outcrops of fossil aeolianites on this coast has allowed us to reconstruct their evolution from the end of the Upper Pleistocene to the present day. Their chronology, estimated by optically stimulated luminescence between 35 and 14 ky at the end of the last glaciation (MIS2), coincides with a local sea level 120 m below the present one. This implies a coastline shifted several kilometres from its current location and the subaerial exposure of a wide strip of the continental shelf covered by sands. The wind blew sand to form dunes towards the continent, covering the coastal areas, which then emerged with no other limitation than the active river channels. Sea-level rise during the Holocene transgression has progressively swamped these aeolian deposits, leaving only flooded dunes, relict coastal dunes and climbing dunes on cliffs up to 180 m high. The aeolian process continued as long as there was a sandy source area to erode, although accretion finished when the sea reached its current level (Late Holocene). Since then, the wind turned from accretion to erosion of the dunes and sand beaches. This erosion exposes the older shingle beaches (probably of Eemian age) buried under the aeolian sands, as well as old, submerged forest remains and megalithic monuments. The destruction of sand beaches and dunes currently observed along the Galician coast is linked, according to most researchers, to anthropogenic global warming. However, their management should consider these evolutive issues.     

Evidence of high sea level during isotope stage 5c in Queensland,Australia

Thirty-nine species of scleractinian corals have been recovered from under a high dune on the western (mainland) side of North Stradbroke Island, eastern Australia. The corals are associated with thin intertidal sediments and their good condition implies burial in situ and preservation in a saturated zone. Most likely this occurred as the coast prograded and a large dune advanced into the littoral zone, burying intertidal sediments and coral. The species assemblage indicates a sheltered environment but one open to the ocean without wide fluctuations in salinity. Three species yielded a mean ${}^{230}\text{Th}{}^{234}\text{U}$ age of 105,000 yr B.P. which is significantly younger than the nearest Pleistocene corals at Evans Head, New South Wales. The corals provide evidence of a sea stand near present sea level during isotope Stage 5c, which is considerably higher than previously suggested for this period. Their good condition implies that the overlying parabolic dune is of comparable age and formed during that high stand of sea level. Also, the isotope age provides a maximum period for the development of giant podzols in the podzol chronosequences on coastal dunes in southern Queensland.     

Earthquake processes in a micromorphic continuum

Summary The paper introduces a new model earthquake process based on the theory of micromorphic continua. The processes in a focal region are described by deformations of microstructure in time. It is assumed that the fracturing processes as well as phase transformation of metamorphic phenomena have caused in the past certain non-reversible changes which determine the microstructure of focal region. These internal microstructural elements form the attaching points around which the couple stresses arise. The properties of focal region are determined by the constitutive equations. The micromorphic mechanics considers the existence of body couples as determined by a regional stresses and looks after a response field of stresses, stress moments and strains in the focal region. Further, it is explained how microdislocation field is connected with microdeformations and micromorphic structure. In the considered earthquake structure model a microanisotropy is assumed through the tensor of microinertia. This tensor describes a distribution of microelements. Simple solutions of wave processes in a focal region are presented. The dispersion of waves is discussed.     

Crustal analysis of the Ulleung Basin in the East Sea (Japan Sea) from enhanced gravity mapping

To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.     

Plane Strain Testing with Passive Restraint

A plane strain condition for testing rock is developed through passive restraint in the form of a thick-walled cylinder. The so-called biaxial frame generates the intermediate principal stress that imposes a triaxial state of stress on a prismatic specimen. Major and minor principal stresses and corresponding strains are accurately measured, providing data to calculate the elastic (Young’s modulus and Poisson’s ratio), inelastic (dilatancy angle), and strength (friction angle and cohesion) parameters of the rock. Results of experiments conducted on Indiana limestone in plane strain compression are compared with the results of axisymmetric compression and extension. With proper system calibration, Young’s modulus and Poisson’s ratio are consistent among the tests. The plane strain apparatus enforces in-plane deformation with the three principal stresses at failure being different, and it allows one to determine the Paul-Mohr-Coulomb failure surface, which includes an intermediate stress effect.