Climate change during the Triassic and Jurassic

The transition from the Triassic to Jurassic is associated with dramatic changes in Earth's climate. Pangaea was breaking up as North America rifted away from Africa, the Central Atlantic Magmatic Province erupted, and the concentration of atmospheric carbon dioxide increased dramatically. This article summarises the changes in Earth's climate associated with this transition, including a discussion of the various impacts of the increased carbon dioxide on the Earth system, the question of whether the wet episode in the Carnian was a global or regional event, the formation of bauxite deposits, and how dinosaur distributions changed over time. Palaeoclimate model simulations reveal the spatial changes in climate between the Triassic and Jurassic, illustrating the subtropics becoming slightly cooler and wetter despite the warming trend for the Earth's average temperature.     

Induction of DNA strand breaks in the mussel (Mytilus trossulus) and clam (Protothaca staminea) following chronic field exposure to polycyclic aromatic hydrocarbons from the Exxon Valdez spill

In 2002, 13 years after the Exxon Valdez spill, mussels and clams were examined for lingering oil exposure and damage. Known oil patches were sampled at four locations, and compared to nearby reference areas (same bay), and were also compared to "hot reference" sites to verify the methods used (Cordova harbor and fresh diesel spill at Port Chalmers). Passive samplers deployed for a month at the sites, along with tissue samples, confirmed that the oiled sites were oiled (fingerprinting back to Exxon Valdez oil) and that reference sites were clean. The highest PAH loads were detected in sub-surface interstitial waters at oiled sites. Exposure at the surface was generally low level, and probably intermittent. DNA damage was assessed in blood cells using sensitive comet analyses. DNA strand breakage was detected in both mussels and clams, with the highest level of damage detected at "hot reference" sites of Cordova harbor and Port Chalmers. Bioavailability and DNA damage at the oiled sties was low, indicating there has been substantial progress in recovery from the spill 13 years before, yet low level bioavailability and damage were still detectable.     

On the shapes and spins of “rubble pile” asteroids

We examine the shape of a “rubble pile” asteroid as it slowly gains angular momentum by YORP torque, to the point where “landsliding” occurs. We find that it evolves to a “top” shape with constant angle of repose from the equator up to mid-latitude, closely resembling the shapes of several nearly critically spinning asteroids imaged by radar, most notably (66391) 1999 KW4 [Ostro, S.J., Margot, J.-L., Benner, L.A.M., Giorgini, J.D., Scheeres, D.J., Fahnestock, E.G., Broschart, S.B., Bellerose, J., Nolan, M.C., Magri, C., Pravec, P., Scheirich, P., Rose, R., Jurgens, R.F., De Jong, E.M., Suzuki, S., 2006. Science 314, 1276-1280]. Similar calculations for non-spinning extremely prolate or oblate “rubble piles” show that even loose rubble can sustain shapes far from fluid equilibrium, thus inferences based on fluid equilibrium are generally useless for inferring bulk properties such as density of small bodies. We also investigate the tidal effects of a binary system with a “top shape” primary spinning at near the critical limit for stability. We find that very close to the stability limit, the tide from the secondary can actually levitate loose debris from the surface and re-deposit it, in a process we call “tidal saltation.” In the process, angular momentum is transferred from the primary spin to the satellite orbit, thus maintaining the equilibrium of near-critical spin as YORP continues to add angular momentum to the system. We note that this process is in fact dynamically related to the process of “shepherding” of narrow rings by neighboring satellites.     

New insights on the binary Asteroid 121 Hermione

We report on the results of a 6-month photometric study of the main-belt binary C-type Asteroid 121 Hermione, performed during its 2007 opposition. We took advantage of the rare observational opportunity afforded by one of the annual equinoxes of Hermione occurring close to its opposition in June 2007. The equinox provides an edge-on aspect for an Earth-based observer, which is well suited to a thorough study of Hermione’s physical characteristics. The catalog of observations carried out with small telescopes is presented in this work, together with new adaptive optics (AO) imaging obtained between 2005 and 2008 with the Yepun 8-m VLT telescope and the 10-m Keck telescope. The most striking result is confirmation that Hermione is a bifurcated and elongated body, as suggested by Marchis, et al. [Marchis, F., Hestroffer, D., Descamps, P., Berthier, J., Laver, C., de Pater, I., 2005. Icarus 178, 450-464]. A new effective diameter of 187 ± 6 km was calculated from the combination of AO, photometric and thermal observations. The new diameter is some 10% smaller than the hitherto accepted radiometric diameter based on IRAS data. The reason for the discrepancy is that IRAS viewed the system almost pole-on. New thermal observations with the Spitzer Space Telescope agree with the diameter derived from AO and lightcurve observations. On the basis of the new AO astrometric observations of the small 32-km diameter satellite we have refined the orbit solution and derived a new value of the bulk density of Hermione of 1.4 + 0.5/−0.2 g cm⁻³. We infer a macroscopic porosity of ∼33 + 5/−20%.     

The Effects of Reduced Tidal Flushing on Mangrove Structure and Function Across a Disturbance Gradient

The effects of reduced tidal flushing on post-hurricane mangrove recovery were measured across a gradient of hurricane disturbance (in order of decreasing wind intensity: Captiva, North Sanibel, Central Sanibel, and East Sanibel). Each region consisted of replicate study plots with either reduced tidal exchange (tidally restricted location) or an open tidal connection (tidally unrestricted location). Locations with reduced tidal exchange displayed significantly lower (two-way ANOVA, p ≤ 0.0001) tidal amplitude, decreased seedling densities, and decreased productivity (recruitment, growth, and litter fall) when compared to the tidally unrestricted locations. Results also indicated significant regional variations in measures of mangrove stand structure (seedlings and canopy) and productivity (recruitment, growth, and litter fall) up to 4-years post-hurricane disturbance. These findings suggest that the legacy effects from hurricane disturbance vary with degree of wind intensity, acting both independently and synergistically with the effects of tidal restriction to influence post-hurricane mangrove structure and function.     

The Green Bay ecosystem and assessment of climate change impacts

Climate change will have major impacts in the Great Lakes region of North America. Particularly vulnerable are shallow freshwater estuaries, such as Lake Michigan’s Green Bay, located in the north-eastern part of the State of Wisconsin. Green Bay and the Lower Fox River, its major tributary, were considered to be severely polluted as early as 1925. As a result of large expenditures of money and a major research effort that has been conducted over the past 40 years or more, some progress has been made toward the restoration of ecosystem integrity. However, work remains, and within this context, potential climate change impacts pose additional challenges. We discuss in this paper a methodology that can be used to assess climate change impacts on ecosystems, and describe an application to the Green Bay ecosystem. The methodology employs numerical methods to evaluate the inputs from scientific, policy, and management experts who are knowledgeable about the ecosystem under study. The Green Bay ecosystem application reveals that runoff from agriculture and urban sources, already a major ecosystem stressor, will be exacerbated in the future as a result of climate change impacts.