Dynamics of a mesoscale eddy off Cape Ann, Massachusetts in May 2005

Observations and numerical modeling indicate that a mesoscale anti-cyclonic eddy formed south of Cape Ann at the northern entrance of Massachusetts Bay (MB) during May 2005, when large river discharges in the western Gulf of Maine and two strong Nor'easters passing through the regions led to an unprecedented toxic Alexandrium fundyense bloom (red tide). Both model results and field measurements suggest that the western Maine Coastal Current separated from Cape Ann around May 7–8, and the eddy formed on around May 10. The eddy was trapped at the formation location for about a week before detaching from the coastline and moving slowly southward on May 17. Both model results and theoretical analysis suggest that the separation of the coastal current from the coast and subsequent eddy formation were initiated at the subsurface by an adverse pressure gradient between Cape Ann and MB due to the higher sea level set up by onshore Ekman transport and higher density in downstream MB. After the formation, the eddy was maintained by the input of vorticity transported by the coastal current from the north, and local vorticity generation around the cape by the horizontal gradients of wind-driven currents, bottom stress, and water density induced by the Merrimack River plume. Observations and model results indicate that the anti-cyclonic eddy significantly changed the pathway of nutrient and biota transport into the coastal areas and enhanced phytoplankton including Alexandrium abundances around the perimeter of the eddy and in the western coast of MB.     

Optical spectroscopy of high proper motion stars: new M dwarfs within 10 pc and the closest pair of subdwarfs

We present spectra of 59 nearby star candidates, M dwarfs and white dwarfs, previously identified using high proper motion catalogues and the DENIS database. We review the existing spectral classification schemes and spectroscopic parallax calibrations in the near-infrared J band and derive spectral types and distances of the nearby candidates. Forty-two stars have spectroscopic distances smaller than 25 pc, three of them being white dwarfs. Two targets lie within 10 pc, one M8 star at 10.0 pc (APMPM J0103−3738), and one M4 star at 8.3 pc (L 225−57). One star, LHS 73, is found to be among the few subdwarfs lying within 20 pc. Furthermore, together with LHS 72, it probably belongs to the closest pair of subdwarfs we know.     

Modelling China’s potential maize production at regional scale under climate change

With the continuing warming due to greenhouse gases concentration, it is important to examine the potential impacts on regional crop production spatially and temporally. We assessed China’s potential maize production at 50 × 50 km grid scale under climate change scenarios using modelling approach. Two climate changes scenarios (A2 and B2) and three time slices (2011–2040, 2041–2070, 2071–2100) produced by the PRECIS Regional Climate Model were used. Rain-fed and irrigated maize yields were simulated with the CERES-Maize model, with present optimum management practices. The model was run for 30 years of baseline climate and three time slices for the two climate change scenarios, without and with simulation of direct CO₂ fertilization effects. Crop simulation results under climate change scenarios varied considerably between regions and years. Without the CO₂ fertilization effect, China’s maize production was predicted to suffer a negative effect under both A2 and B2 scenarios for all time slices, with greatest production decreases in today’s major maize planting areas. When the CO₂ fertilization effect is taken into account, production was predicted to increase for rain-fed maize but decrease for irrigated maize, under both A2 and B2 scenarios for most time periods.     

A governance perspective on the large marine ecosystem approach

The large marine ecosystem (LME) concept and approach has had a global impact on marine ecosystem-based management. The LME approach provides a framework for assessing and monitoring LMEs and is based on five modules: productivity, fish and fisheries, pollution and ecosystem health, socioeconomics, and governance. It appears that the LME approach is also being used to structure interventions to bring about change. Its appropriateness for the latter purpose is questioned. The major concerns are that the LME approach is not consistent with current thinking about enabling governance and its compartmentalized structure does not facilitate effective governance intervention. Current thinking on good governance suggests that it is more appropriate to approach governance interventions at the LME scale through multi-level governance policy cycles.     

Estimating rockfall release frequency from blocks deposited in protection barriers,growth disturbances in trees,and trajectory simulations

Landslides - The spatial and temporal quantification of rockfall frequency remains a major challenge in mountain environments, especially also in terms of rockfall management. Approaches that have...     

Taking Better Advantage of Fold Axis Data to Characterize Anisotropy of Complex Folded Structures in the Implicit Modeling Framework

Mathematical Geosciences - When too few field measurements are available for the geological modeling of complex folded structures, the results of implicit methods typically exhibit an...     

Return migration of 1.5 generation Korean New Zealanders: Short‐term and long‐term motives

Through in‐depth interviews and participant observation with 40 1.5 generation Korean New Zealander returnees, we explore life trajectories and identify both short‐ and long‐term reasons for return. Short‐term reasons for return include moving home when entering adulthood in order to begin a career, gaining new experiences and finding a future spouse. Longer term influences include the difficulties of living as minority‐status immigrants in the host society, transnational connections and a longing for a sense of ‘home’. Our consideration of longer term migration strategies sheds light upon the often forgotten difficulties and complexities that can underlie an individual's return.     

Osmium,tungsten, and chromium isotopes in sediments and in Ni‐rich spinel at the K‐T boundary: Signature of a chondritic impactor

Abstract— It is now established that a large extraterrestrial object hit the Earth at the end of the Cretaceous period, about 65 Ma ago. We have investigated Re‐Os, Hf‐W, and Mn‐Cr isotope systems in sediments from the Cretaceous and the Paleogene in order to characterize the type of impactor. Within the Cretaceous‐Tertiary (K‐T) boundary layer, extraterrestrial material is mixed with terrestrial material, causing a dilution of the extraterrestrial isotope signature that is difficult to quantify. A phase essentially composed of Ni‐rich spinel, formed in the atmosphere mainly from melted projectile material, is likely to contain the extraterrestrial isotopic signature of the impactor. We show that the analysis of spinel is indeed the best approach to determine the initial isotope composition of the impactor, and that W and Cr isotopes confirm that the projectile was a carbonaceous chondrite.