Precise positioning for near-bottom equipment using a relay transponder

The Marine Physical Laboratory of the Scripps Institution of Oceanography has developed an acoustic relay transponder for precise relative positioning of near-bottom instruments and geologic sampling devices. Although specifically designed to position equipment lowered on standard wire ropes without a need to maintain direct electrical contact with the surface ship, the relay transponder may be used to track free vehicles, such as deep submersibles, from the surface. The relay transponder is positioned relative to an array of bottom-anchored acoustic transponders. It is interrogated acoustically from the surface ship; it then sequentially interrogates the bottom transponders which, in turn, reply to the ship. From the measurement of the total travel time (ship to relay transponder to bottom transponder to ship) and assuming, or knowing, the sound velocity of the water, we obtain a relayed range measurement. These relayed ranges, used in conjunction with ship to bottom-transponder ranges, allow us to calculate the position of the relay transponder. A recent application of this technique is described in which several gravity core samples from the crest of the Horizon Guyot were positioned with respect to the detailed bathymetry and the geology within the area. The estimated error in positioning the samples is less than 20 m inside a navigational net extending over 100 km².Contribution of the Scripps Institution of Oceanography, new series.     

Sources and distribution of terrigenous organic matter delivered by the Atchafalaya River to sediments in the northern Gulf of Mexico

Suspended sediments (SS) from the Atchafalaya River (AR) and the Mississippi River and surficial sediment samples from seven shallow cross-shelf transects west of the AR in the northern Gulf of Mexico were examined using elemental (%OC, C/N), isotopic (δ¹³C, Δ¹⁴C), and terrigenous biomarker analyses. The organic matter (OM) delivered by the AR is isotopically enriched (∼−24.5‰) and relatively degraded, suggesting that soil-derived OM with a C4 signature is the predominant OM source for these SS. The shelf sediments display OC values that generally decrease seaward within each transect and westward, parallel to the coastline. A strong terrigenous C/N (29) signal is observed in sediments deposited close to the mouth of the river, but values along the remainder of the shelf fall within a narrow range (8-13), with no apparent offshore trends. Depleted stable carbon isotope (δ¹³C) values typical of C3 plant debris (−27‰) are found near the river mouth and become more enriched (−22 to −21‰) offshore. The spatial distribution of lignin in shelf sediments mirrors that of OC, with high lignin yields found inshore relative to that found offshore (water depth > 10 m).The isotopic and biomarker data indicate that at least two types of terrigenous OM are deposited within the study area. Relatively undegraded, C3 plant debris is deposited close to the mouth of the AR, whereas more degraded, isotopically enriched, soil-derived OM appears to be deposited along the remainder of the shelf. An important input from marine carbon is found at the stations offshore from the 10-m isobath. Quantification of the terrigenous component of sedimentary OM is complicated by the heterogeneous composition of the terrigenous end-member. A three-end-member mixing model is therefore required to more accurately evaluate the sources of OM deposited in the study area. The results of the mixing calculation indicate that terrigenous OM (soil-derived OM and vascular plant debris) accounts for ∼79% of the OM deposited as inshore sediments and 66% of OM deposited as offshore sediments. Importantly, the abundance of terrigenous OM is 40% higher in inshore sediments and nearly 85% higher in offshore sediments than indicated by a two-end-member mixing model. Such a result highlights the need to reevaluate the inputs and cycling of soil-derived OM in the coastal ocean.     

Properties of unstable waves in the lower St Lawrence Estuary

Abstract

The lower St Lawrence Estuary is an interesting case amongst estuaries in that it is wide enough to accommodate the development of mesoscale unstable waves and eddies. These features are generated by the runoff‐driven jet along this body's south shore. We present data yielding estimates of the length, time and velocity scales of these unstable disturbances. To relate these quantities to the dynamics we employ a 2‐layer quasigeos‐trophic instability model featuring realistic lateral shear. All model runs show short time and length scales, e‐folding periods of less than 10 days and wavelengths less than 50 km.     

EMPLOYMENT DATA AND THE CLASSIFICATION OF URBAN SETTLEMENTS

Classifications of urban settlements have traditionally used total employment data in place of basic (export-oriented) employment data. While urban analysis agree upon the superiority of basic employment data for these classifications, usually only total employment data are available. This paper uses the Arizona Community Data Set, a unique survey-generated body of information that describes the major economic characteristics of numerous Southwestern communities and includes both basic and total employment data, to explore the extent to which misclassification results when using total employment data.     

A Queer Country? A case study of the politics of gay/lesbian belonging in an Australian country town

The present paper examines the complex politics of gay/lesbian belonging through a case study of Daylesford, Victoria, an Australian country town. It contributes to two research bodies: gay/lesbian rural geographies and the politics of belonging. Daylesford hosts ChillOut, Australia's largest rural gay/lesbian festival, which provides a telling context for investigating gay/lesbian belonging in rural Australia. We use qualitative data from the 2006 ChillOut Festival, including interviews with local residents, newspaper commentaries, and visitors’ surveys, to explore how Daylesford has been constructed, imagined, and experienced as a ‘unique’ site of gay/lesbian belonging in rural Australia. We find that ChillOut crucially contributes to its wider reputation as a gay-friendly country town, but also, we argue, to the contested nature of gay/lesbian belonging. This was most powerfully demonstrated by the local council's refusal to fly the gay-identified rainbow flag on the Town Hall during the 2006 Festival and its subsequent banning of the display of all festival flags from that key public building. Because ChillOut was the catalyst for this protocol, the resolution was viewed as homophobic. Indeed, the homophobic and heterosexist rhetoric that ensued in the Letters to the Editor section of the local newspaper revealed some residents’ underlying antagonism towards ChillOut and the local gay/lesbian community. Moreover, appealing to a shared ‘Australian identity’ and associated normative ‘family values’, these letter writers deployed a multi-scalar politics of belonging, where a sense of gay/lesbian belonging to Daylesford at the local scale was contested by the assertion of a ‘more meaningful’ national scale of allegiance fashioned by heteronormativity.     

Abrupt changes as indicators of decadal climate variability

 A statistical test has revealed that abrupt regional climate changes are produced in a coupled atmosphere-ocean general circulation model. Abrupt changes are detected over much of the globe although the occurrence frequency is small over the continents. Over the tropical Pacific Ocean and northern Pacific Ocean, surface air temperature (SAT) and sea level pressure (SLP) shift rapidly on decadal time scales. The regional climate changes presented here have been classified into three types. The first type consists of statistically significant shifts in SLP and statistically significant shifts in SAT which are of opposite sign, and which are reinforced through a positive feedback between the atmosphere and the ocean. The second type is for those occurrences where changes are of the same sign. The third type includes those with a significant shift in only one meteorological element. The second and third types are generally generated by changes in air pressure and wind fields induced by changes of the first type. For example, when SLP increases and sea surface temperature (SST) decreases abruptly in the tropical Pacific Ocean, it triggers abrupt regional changes in middle and high latitudes. The abrupt changes in the model climate have characteristics which are very similar to those of observed rapid shifts. Thus, it is concluded that abrupt changes are a predominant part of regional climate change on decadal time scales. Received: 11 February 1999 / Accepted: 18 May 2000     

Structuring subjectivities? Using Q methodology in human geography

This paper presents a critical and reflexive account of using Q methodology in human geography. Q methodology has a long pedigree in psychological, political and sociological research, but is only recently beginning to be used by human geographers. We discuss, in particular, the parts of the process(es) of Q methodology that are often glossed over in the literature, through reflecting on our learning in using Q within a project examining the use and production of environmental science by NGOs. We conclude that Q may be a useful supplement to existing methods in human geography, as long as it is used creatively and reflexively and with full awareness of its interpretative dimensions.     

Boreal temperature variability inferred from maximum latewood density and tree-ring width data, Wrangell Mountain region, Alaska

Variations in both width and density of annual rings from a network of tree chronologies were used to develop high-resolution proxies to extend the climate record in the Wrangell Mountain region of Alaska. We developed a warm-season (July–September) temperature reconstruction that spans A.D. 1593–1992 based on the first eigenvector from principal component analysis of six maximum latewood density (MXD) chronologies. The climate/tree-growth model accounts for 51% of the temperature variance from 1958 to 1992 and shows cold in the late 1600s–early 1700s followed by a warmer period, cooling in the late 1700s–early 1800s, and warming in the 20th century. The 20th century is the warmest of the past four centuries. Several severely cold warm-seasons coincide with major volcanic eruptions. The first eigenvector from a ring-width (RW) network, based on nine chronologies from the Wrangell Mountain region (A.D. 1550–1970), is correlated positively with both reconstructed and recorded Northern Hemisphere temperatures. RW shows a temporal history similar to that of MXD by increased growth (warmer) and decreased growth (cooler) intervals and trends. After around 1970 the RW series show a decrease in growth, while station data show continued warming, which may be related to increasing moisture stress or other factors. Both the temperature history based on MXD and the growth trends from the RW series are consistent with well-dated glacier fluctuations in the Wrangell Mountains and some of the temperature variations also correspond to variations in solar activity.     

A comprehensive model current system for high-latitude magnetic activity -II. The substorm component

Summary. In paper I of this series (Hughes & Rostoker) we have presented a composite model three-dimensional current system whose magnetic perturbation pattern is in good agreement with that observed at high latitudes during periods of moderate magnetospheric activity. In this paper we extend the model current system to demonstrate its ability to reproduce the magnetic perturbation pattern associated with the magnetospheric substorms. In agreement with previous workers, we find it necessary to include a region of intense equatorward current flow at the western edge of the westward travelling surge. For the particular substorm event presented in this paper, we find that the main eastward and westward electrojets intensified slightly before the appearance of the surge form, and we are able to evaluate quantitatively the amount of change involved.     

The Gaojiacun Mafic-Ultramafic Complex （Sichuan, SW China）：Neoproterozoic Magmatic Activity at the Western Margin of the Yangtze Craton

1 Introduction The Gaojiacun intrusive complex is one of the numerous ultramafic-mafic intrusions in Sichuan Province of China. It was mapped during the 1970s and studied mainly by Chinese scientists (e.g. Geological Team 106, 1975; Shen et al., 1986, 1989; CGGJC, 1986; Yang et al., 1993; Li et al., 1995; Shen et al., 2003; Zhu et al., 2004a). Since the year 2000, China has become one of the largest PGE consumers. While the country can produce only less than 1 ton PGE/year, the Chin…