“Phasic” metropolitan settlers: a phase-based model for the distribution of households in US metropolitan regions

In this article, we develop a model for explaining spatial patterns in the distribution of households across metropolitan regions in the United States. First, we use housing consumption and residential mobility theories to construct a hypothetical probability distribution function for the consumption of housing services across three phases of household life span. We then hypothesize a second probability distribution function for the offering of housing services based on the distance from city center(s) at the metropolitan scale. Intersecting the two hypothetical probability functions, we develop a phase-based model for the distribution of households in US metropolitan regions. We argue that phase one households (young adults) are more likely to reside in central city locations, whereas phase two and three households are more likely to select suburban locations, due to their respective housing consumption behaviors. We provide empirical validation of our theoretical model with the data from the 2010 US Census for 35 large metropolitan regions.     

Multiple Factors driving Variability of CO2 Exchange Between the Ocean and Atmosphere in a Tropical Coral Reef Environment

In this paper, we present the results of the first automated continuous multi-year high temporal frequency study of CO₂ dynamics in a coastal coral reef ecosystem. The data cover 2.5?years of nearly continuous operation of the CRIMP-CO₂ buoy spanning particularly wet and dry seasons in southern Kaneohe Bay, a semi-enclosed tropical coral reef ecosystem in Hawaii. We interpret our observational results in the context of how rapidly changing physical and biogeochemical conditions affect the pCO₂ of surface waters and the magnitude and direction of air–sea exchange of CO₂. Local climatic forcing strongly affects the biogeochemistry, water column properties, and gas exchange between the ocean and atmosphere in Kaneohe Bay. Rainfall driven by trade winds and other localized storms generates pulses of nutrient-rich water, which exert a strong control on primary productivity and impact carbon cycling in the water column of the bay. The “La Ni?a” winter of 2005–2006 was one of the wettest winters in Hawaii in 30?years and contrasted sharply with preceding and subsequent drier winter seasons. In addition, short-term variability in physical forcing adds complexity and helps drive the response of the CO₂–carbonic acid system of the bay. Freshwater pulses to Kaneohe Bay provide nutrient subsidies to bay waters, relieving the normal nitrogen limitation of this system and driving phytoplankton productivity. Seawater pCO₂ responds to the blooms as well as to physical forcing mechanisms, leading to a relatively wide range of pCO₂ in seawater from about 250 to 650?μatm, depending on conditions. Large drawdowns in pCO₂ following storms occasionally cause bay waters to switch from being a source of CO₂ to the atmosphere to being a sink. Yet, during our study period, the southern sector of Kaneohe Bay remained a net source of CO₂ to the atmosphere on an annualized basis. The integrated net annual flux of CO₂ from the bay to the atmosphere varied between years by a factor of more than two and was lower during the wet “La Ni?a” year, than during the following year. Over the study period, the net annualized flux was 1.80?mol?C?m^?2?year^?1. Our CO₂ flux estimates are consistent with prior synoptic work in Kaneohe Bay and with estimates in other tropical coral reef ecosystems studied to date. The high degree of climatological, physical, and biogeochemical variability observed in this study suggests that automated high-frequency observations are needed to capture the short-, intermediate-, and long-term variability of CO₂ and other properties of these highly dynamic coastal coral reef ecosystems.     

Deep scattering layers resolved by narrow‐beam echo sounder along 35°s in the south pacific

The narrow‐beam echo sounder (3.5° half angle, 20 kHz) is capable of resolving the configuration of deep scattering layers to 750 m and was used to study the ecology and population density of organisms that make up the layers. Several layers to 1,000 m depth were identified in the South Pacific Ocean, and the population densities calculated. Swimming speeds of possible predators are estimated at 0.2–0.3 m.sec‐¹. Among organisms calculated to range in length from 0.01 m to 0.07 m, the larger were interpreted as grazing on smaller organisms, after comparing results from two echo sounders of 12 kHz and 20 kHz frequencies respectively.     

On the Use of Hydrological Models and Satellite Data to Study the Water Budget of River Basins Affected by Human Activities: Examples from the Garonne Basin of France

Natural and anthropogenic forcing factors and their changes significantly impact water resources in many river basins around the world. Information on such changes can be derived from fine scale in situ and satellite observations, used in combination with hydrological models. The latter need to account for hydrological changes caused by human activities to correctly estimate the actual water resource. In this study, we consider the catchment area of the Garonne river (in France) to investigate the capabilities of space-based observations and up-to-date hydrological modeling in estimating water resources of a river basin modified by human activities and a changing climate. Using the ISBA–MODCOU and SWAT hydrological models, we find that the water resources of the Garonne basin display a negative climate trend since 1960. The snow component of the two models is validated using the moderate-resolution imaging spectroradiometer snow cover extent climatology. Crop sowing dates based on remote sensing studies are also considered in the validation procedure. Use of this dataset improves the simulated evapotranspiration and river discharge amounts when compared to conventional data. Finally, we investigate the benefit of using the MAELIA multi-agent model that accounts for a realistic agricultural and management scenario. Among other results, we find that changes in crop systems have significant impacts on water uptake for agriculture. This work constitutes a basis for the construction of a future modeling framework of the sociological and hydrological system of the Garonne river region.     

Characterization of contact properties in biocemented sand using 3D X-ray micro-tomography

The mechanical efficiency of the biocementation process is directly related to the microstructural properties of the biocemented sand, such as the volume fraction of calcite, its distribution within the pore space (localized at the contact between grains, over the grain surfaces) and the contact properties: coordination number, contact surface area, contacts orientation and types of contact. In the present work, all these micromechanical properties are computed, for the first time, from 3D images obtained by X-ray tomography of intact biocemented sand samples. The evolution of all these properties with respect to the volume fraction of calcite is analyzed and compared between each other (from untreated sand to highly cemented sand). Whatever the volume fraction of calcite, it is shown that the precipitation of the calcite is localized at the contacts between grains. These results are confirmed by comparing our numerical results with analytical estimates assuming that the granular medium is made of periodic simple cubic arrangements of grains and by considering two extreme cases of precipitation: (1) The calcite is localized at the contact, and (2) the grains are covered by a uniform layer of calcite. In overall, the obtained results show that a small percentage of calcite is sufficient to get a large amount of cohesive contacts.

     

Characterization of microstructural and physical properties changes in biocemented sand using 3D X-ray microtomography

An experimental study has been performed to investigate the effect of the biocalcification process on the microstructural and the physical properties of biocemented Fontainebleau sand samples. The microstructural properties (porosity, volume fraction of calcite, total specific surface area, specific surface area of calcite, etc.) and the physical properties (permeability, effective diffusion) of the biocemented samples were computed for the first time from 3D images with a high-resolution images obtained by X-ray synchrotron microtomography. The evolution of all these properties with respect to the volume fraction of calcite is analysed and compared with success to experimental data, when it is possible. In general, our results point out that all the properties are strongly affected by the biocalcification process. Finally, all these numerical results from 3D images and experimental data were compared to numerical values or analytical estimates computed on idealized microstructures constituted of periodic overlapping and random non-overlapping arrangements of coated spheres. These comparisons show that these simple microstructures are sufficient to capture and to predict the main evolution of both microstructural and physical properties of biocemented sands for the whole range of volume fraction of calcite investigated.     

Long‐term variability of proglacial groundwater‐fed hydrological systems in an area of glacier retreat,Skeiðarársandur,Iceland

Proglacial groundwater‐fed features, such as seeps, substantially impact proglacial geomorphology, hydrology, and ecology. However, there is a paucity of research on the impacts of climate change and glacier retreat on the extent of these important features. This paper aims to investigate the impact of glacier retreat on proglacial groundwater levels and on the extent of groundwater‐fed seeps. Research has taken place in western Skeiðarársandur, the large proglacial outwash plain of Skeiðarárjökull, a retreating temperate glacier in southeast Iceland. Changes in the extent of proglacial groundwater seeps were mapped using historical aerial photographs from 1986, 1997, and 2012. Proglacial groundwater levels were monitored in shallow boreholes between 2000 and 2012. The western margin of Skeiðarárjökull has retreated approximately 1 km beyond its position in 1986. However, this retreat was punctuated by short periods of readvance. The geomorphology and groundwater systems at the site were substantially impacted by the November 1996 jökulhlaup, whose deposits altered approximately 18% of the area of groundwater seeps. The surface areas of groundwater seeps and lakes in the study area have declined by ~97% between 1986 and 2012. Most of the decline took place after 1997, when the mean annual rate of retreat increased three‐fold. Groundwater levels also declined substantially between 2000 and 2012, although this trend varies spatially. The paper provides a conceptual model of the controls on proglacial shallow groundwater systems. Direct impacts of glacier retreat are suggested as the main cause for the declines in proglacial groundwater levels and in the extent of groundwater seeps. These declines are expected to adversely impact sandur ecology. Copyright © 2014 John Wiley & Sons, Ltd.     

Polychaetes from Jan Mayen (Annelida, Polychaeta)

A thorough literature review has been undertaken to establish the first complete account of polychaetes recorded from the area around the volcanic island of Jan Mayen. The annotated checklist lists 121 species-level taxa, representing an increase from the 75 species previously recorded. The checklist is based on existing records, supplemented with material sampled in 1999, from which 42 species new to the area were reported. Some previously reported species from the area have been excluded because of inadequate documentation. The polychaete fauna of Jan Mayen is comparable with that of the mainland Norwegian coast and the Svalbard area. No taxa unique to the island were found. However, knowledge of the marine invertebrate fauna in general at Jan Mayen is sparse because few surveys have been undertaken there. It is expected that future expeditions will reveal further new taxon records for the area.     

Steric Sea-Level Change and its Impact on the Gravity Field caused by Global Climate Change

It is sometimes assumed that steric sea-level variations do not produce a gravity signal as no net mass change, thus no change of ocean bottom pressure is associated with it. Analyzing the output of two CO₂ emission scenarios over a period of 2000 years in terms of steric sea-level changes, we try to quantify the gravitational effect of steric sea-level variations. The first scenario, computed with version 2.6 of the Earth System Climate Model developed at the University of Victoria, Canada (UVic ESCM), is implemented with a linear CO₂ increase of 1% of the initial concentration of 365 ppm and shows a globally averaged steric effect of 5.2 m after 2000 years. In the second scenario, computed with UVic ESCM version 2.7, the CO₂ concentration increases quasi-exponentially to a level of 3011 ppm and is hold fixed afterwards. The corresponding globally averaged steric effect in the first 2000 years is 2.3 m. We show, due to the (vertical) redistribution of ocean water masses (expansion or contraction), the steric effect results also in a small change in the Earth’s gravity field compared to usually larger changes associated with net mass changes. Maximum effects for computation points located on the initial ocean surface can be found in scenario 1, with the effect on gravitational attraction and potential ranging from 0.0 to −0.7·10⁻⁵ m s⁻² and −3·10⁻³ to 6·10⁻³ m² s⁻², respectively. As expected, the effect is not zero but negligible for practical applications.     

An improved methodology to measure flag performance for the shipping industry

The subject of measuring the performance of registries has been a topic of policy discussions in recent years at the regional level due to the recasting of the European Union (EU) port state control (PSC) directive which introduces incentives for flags which perform better. Since the current method used in the EU region entails some shortcomings, it has therefore been the subject of substantial scrutiny. Furthermore, the International Maritime Organization (IMO) developed a set of performance indicators which however lacks the ability to measure compliance as set out in one of its strategic directions towards fostering global compliance. This article develops a methodology to measure flag state performance which can be applied on the regional or global level and to other areas of legislative interest (e.g. recognized organizations, Document of Compliance Companies). The proposed methodology overcomes some of the shortcomings of the present method and presents a more refined, less biased approach of measuring performance. To demonstrate its usefulness, it is applied to a sample of 207,821 observations for a 3-year time frame and compared to the current method.