Multi-century variability in the Pacific North American circulation pattern reconstructed from tree rings

We here present a reconstruction (1725–1999) of the winter Pacific North American (PNA) pattern based on three winter climate sensitive tree ring records from the western USA. Positive PNA phases in our record are associated with warm phases of ENSO and PDO and the reorganization of the PNA pattern towards a positive mode is strongest when ENSO and PDO are in phase. Regime shifts in our PNA record correspond to climatic shifts in other proxies of Pacific climate variability, including two well-documented shifts in the instrumental period (1976 and 1923). The correspondence breaks down in the early 19th century, when our record shows a prolonged period of positive PNA, with a peak in 1800–1820. This period corresponds to a period of low solar activity (Dalton Minimum), suggesting a ‘positive PNA like’ response to decreased solar irradiance. The distinct 30-year periodicity that dominates the PNA reconstruction in the 18th century and again from 1875 onwards is disrupted during this period.     

人为强迫和自然强迫对近年来对流层顶高度变化的贡献

观测表明,自1979年以来对流层顶（平流层与对流层之间的界限）高度增加了数百米。在气候模式实验中,等量的增加也是显而易见的。气候模式实验表明,人为因素导致臭氧和均匀混合温室气体的变化,对1979-1999年对流层顶高度增加的影响占所有因素的80％。臭氧对平流层的冷却作用和均匀混合的温室气体对对流层的加热作用,使对流层顶高度增加。     

Change in the World City Network, 2000–2012

This article presents a large-scale analysis of the trajectories of individual cities and regions in the world city network between 2000 and 2012. The methodology used to examine cities' evolving network centralities is based on advanced producer services firms “interlocking” cities through their worldwide distribution of offices. We do not limit our analysis to a limited set of putative world cities, but incorporate 157 cities from all world regions into this global urban analysis. Absolute and relative measures of change are developed to reveal the major dimensions of change. The most notable finding is that significant connectivity gains have been limited to a small set of cities (Dubai, Shanghai, Beijing, and Moscow in particular) in the face of persisting core–periphery patterns at the level of the global economy, with New York and London remaining firmly at the apex. At the same time, overall levels of connectivity in the world city network have clearly risen, suggesting an increasingly integrated network. In geographical terms, a west-to-east shift is discernible, albeit uneven.     

Spatialities of data: mapping social media ‘beyond the geotag’

As emerging sources of so-called ‘big data’ are increasingly utilized in order to understand social and spatial processes, so too have these new data sources become the subject of harsh criticism from more critically-oriented geographers and social scientists. This paper argues that one of the major issues preventing a more productive dialogue between critical human geographers and those already engaging in the mapping and analysis of these new data sources is around the ways that space and spatiality are conceptualized in social media mapping. As such, this paper draws on and extends earlier critiques of the ‘spatial ontology of the geotag’, in which the geographic analysis of geotagged social media data over-privileges the single latitude/longitude coordinate pair attached to each individual data point, often leading to the kind of simplistic mappings and interpretations prevalent today. The goals of this paper are two-fold: first, to demonstrate how the spatial ontology of the geotag is implicitly operationalized within mainstream social media mapping exercises, and how this understanding of space remains incongruent with existing conceptions of space drawn from human geography. Second, using the example of tweeting in the wake of the August 2014 killing of an unarmed African–American teenager by a police officer in Ferguson, Missouri, this paper demonstrates how a more geographically-situated analysis of this kind of data, inspired by relational or multidimensional conceptualizations of space, can yield alternative understandings of the social processes embedded in such data.     

Quantitative geochemical mapping of martian elemental provinces

We present an exploratory approach to the interpretation of the elemental maps produced by the Odyssey Gamma-Ray Spectrometer (GRS). These maps benefit from a direct detection of elemental mass fractions and are used to delineate and characterize elementally homogeneous provinces in the mid-latitudinal martian surface on the basis of chemistry alone. This approach is different from assessing the elemental composition of regions previously defined by their geologic context. Multivariate statistical approaches are discussed and a combination of principal component and clustering analyses is applied on the GRS-based hydrogen, chlorine, potassium, silicon, iron, and calcium maps. At least three principal components must be considered to properly describe the compositional variability seen in the maps. The main component is likely driven by the degree of mantling through a GRS perspective, i.e. by materials enriched in mobile elements (Cl, H) and finer than 10-20 cm, at horizontal and depth scales of hundreds of kilometers and tens of centimeters, respectively. Elemental diversity is found in both mantled and less-mantled provinces, suggesting both local and regional sources for the surficial materials. The less-mantled regions appear to have compositions which include basaltic igneous rocks. Although there is an absence of obvious natural clusters in the data, a solution between five and eight elemental provinces seems optimal and is discussed (Amazonis-Tharsis and Sabaea-Arabia, Tempe and the southern highlands, Chryse and Utopia, Elysium-Tartarus, Acidalia-Arabia). Future investigation of the defined elemental provinces will involve integrating other types of data and geological information.     

Stable isotope composition of modern bryozoan skeletal carbonate from the Otago Shelf,New Zealand

The oxygen (δ¹⁸O) and carbon (δ¹³C) isotope ratios of 10 species of living Bryozoa collected from the Otago Shelf, New Zealand were analysed to assess the extent to which isotopic equilibrium (relative to inorganic equilibrium isotope fractionation) is attained during the precipitation of skeletal calcium carbonate. The data reveal that whereas eight species of Bryozoa synthesise skeletal carbonate in apparent oxygen isotope equilibrium with respect to environmental conditions, two species (Celleporina grandis and Hippomonavella flexuosa) yield δ¹⁸O_calcite values which indicate significant disequilibrium oxygen isotope fractionation during calcification. Sufficient data are available from one species (C. grandis) to demonstrate that disequilibrium is probably related to kinetic factors associated with diffusion‐controlled transport of HCO₃‐ to the site of calcite precipitation. Carbon isotope signatures indicate significant departures from inorganic isotope equilibrium in all but one bryozoan species (Hippomenella vellicata). Although greater uncertainties are associated with estimates of the isotopic composition of total dissolved inorganic carbon (δ¹³C_SDIC), the data suggest that two factors—kinetic fractionation and incorporation of respiratory CO₂—are important in controlling carbon isotope disequilibrium. Where bryozoan species exhibit evidence for disequilibrium in both oxygen and carbon isotope systems (C. grandis, H. flexuosa), it is likely that kinetic factors are primarily responsible for observed departures from carbon isotope equilibrium. In contrast, the probable explanation for those species which display evidence for carbon isotope disequilibrium only, is that skeletal carbonate is precipitated from a DIC pool modified by the incorporation of respiratory CO₂. Differences between the carbon isotope composition of skeletal elements from the same species and co‐existing species living in the same community suggests that significant variations may occur in the extent to which marine DIC and respiratory CO₂ are utilised during calcification. Additional studies of carbon pathways associated with calcification are required to assess the relative effects of kinetic, metabolic, and environmental factors on the carbon isotopic composition of bryozoan skeletal carbonate.     

Colony growth of corals transplanted for restoration depends on their site of origin and environmental factors

We determined that growth differences among coral fragments transplanted for restoration were influenced by both source population and environmental factors. In two common garden experiments, storm‐generated fragments of Acropora palmata were transplanted from two source populations in the British Virgin Islands to a restoration site (a ‘common garden’) that lacked A. palmata. In the first experiment, colonies from different sources grew at different rates in the first year after transplanting, suggesting either genetic differences among source populations or enduring acclimation to conditions at the source site. No differences in growth among source populations were detected in the second common garden experiment. To isolate environmental effects on growth, we subdivided fragments from three source populations to create genetically identical pieces that were attached separately at both source and restoration sites. Genetically identical pieces from all source populations grew slightly faster at their source than at the restoration site, implying a subtle home‐site advantage. Overall, our results suggest that matching environmental conditions at source and restoration sites may increase the success of restoration projects.     

Endemic new cyclostome bryozoans from Spirits Bay,a New Zealand marine‐biodiversity “hotspot”

Two notable species of erect cyclostome bryozoans from a nearshore benthic fauna off Spirits Bay, northernmost New Zealand, are described here for the first time. The first, Spiritopora perplexa gen. et sp. nov., is an endemic cerioporine‐grade genus which is abundant in this area. Colonies are characterised by an unusual combination of fixed‐and free‐walled skeletal morphologies: autozooids forming the extensive encrusting colony bases are normally fixed‐walled, whereas those forming the short, bifoliate erect branches are usually free‐walled. The highly distinctive morphology of S. perplexa, very different from any other fossil or Recent cyclostome, together with its success in overgrowing competitors for space, makes its restricted geographical distribution puzzling and highlights the importance of conservation in this area now closed to trawling, Danish seining, and commercial scallop dredging. The second species, Calvetia osheai sp. nov., is less common, and has small, tree‐like colonies. It is the third species assigned to this distinctive cancellate genus, previously known only from Recent of Tierra del Fuego and the Eocene of Antarctica.