Nicholas J. Cox

Daily mean sea level pressure reconstructions for the European-North Atlantic region for the period 1850-2003

Abstract The development of a daily historical European–North Atlantic mean sea level pressure dataset (EMSLP) for 1850–2003 on a 5° latitude by longitude grid is described. This product was produced using 86 continental and island stations distributed over the region 25°–70°N, 70°W–50°E blended with marine data from the International Comprehensive Ocean–Atmosphere Data Set (ICOADS). The EMSLP fields for 1850–80 are based purely on the land station data and ship observations. From 1881, the blended land and marine fields are combined with already available daily Northern Hemisphere fields. Complete coverage is obtained by employing reduced space optimal interpolation. Squared correlations (r 2) indicate that EMSLP generally captures 80%–90% of daily variability represented in an existing historical mean sea level pressure product and over 90% in modern 40-yr European Centre for Medium-Range Weather Forecasts Re-Analyses (ERA-40) over most of the region. A lack of sufficient observations over Greenland and...

A climatic index for soil erosion potential (CSEP) including seasonal and vegetation factors

Abstract The concept of Cumulative Erosion Potential (CEP) proposed by De Ploey, Kirkby and Ahnert in 1991 (Earth Surf. Process. Landforms, 16: 399–409) provides a simple climatic index of erosion potential based on annual rainfalls and their distribution, which is assumed to be exponential (or gamma with shape parameter 1). A modified CEP (CSEP) is presented here, extending the original in three ways. First, the index is disaggregated by month to include the effects of seasonality. Second, a mixed gamma(1) distribution is used to provide a better fit to the whole of the daily rainfall distribution. Third, the index is calculated both for a bare soil and for a natural vegetation cover, giving an additional index to the potential for managing erosion through landuse change. For the natural vegetation, the index is based on an estimate of equilibrium soil organic matter which is associated with differences in soil moisture storage capacities and derived from monthly rainfall and temperature values. The index thus remains a measure of climatic potential only, based on widely available monthly data on temperature, rainfall and number of rain days. It may be compared with the patterns shown by the European Soil Erosion Map and by the CORINE classification, which are dominated by a combination of climate and lithology.

Applying flow resistance equations to overland flows

Resistance to flow determines routing velocities and must be adequately represented both within stream channels and over hillslopes when making predictions of streamflow and soil erosion. The limiting assumptions inherent in flow resistance equations can be relaxed if the spatial and temporal scale over which they are applied is restricted. This requires a substantial methodological advance in the study of overland flows over natural surfaces. It is suggested that terrestrial laser scanning will allow a greater understanding of overland flow hydraulics and present opportunities to investigate resistance to flow over complex morphologies. The Darcy-Weisbach, Chézy and Manning equations are the most widely used empirical equations for the calculation of flow velocity in runoff and erosion models. These equations rest on analyses originally developed for one-dimensional pipe flows and assume conditions which are not met by overland flows. The following assumptions are brought into question: flow can be described as uniform; flow is parallel to the surface; flow is of a constant width and the boundary to the flow is longitudinally uniform; grain roughness is homogeneous over the wetted perimeter and can be considered as random; form roughness and other sources of flow resistance can be ignored; resistance is independent of flow depth; and resistance can be modelled as a function of the Reynolds number. A greater appreciation of the processes contributing to resistance to overland flows must be developed. This paper also presents a brief history of the development of flow resistance equations.

Rapid, climate-driven changes in outlet glaciers on the Pacific coast of East Antarctica

Observations of ocean-terminating outlet glaciers in Greenland and West Antarctica indicate that their contribution to sea level is accelerating as a result of increased velocity, thinning and retreat. Thinning has also been reported along the margin of the much larger East Antarctic ice sheet, but whether glaciers are advancing or retreating there is largely unknown, and there has been no attempt to place such changes in the context of localized mass loss or climatic or oceanic forcing. Here we present multidecadal trends in the terminus position of 175 ocean-terminating outlet glaciers along 5,400 kilometres of the margin of the East Antarctic ice sheet, and reveal widespread and synchronous changes. Despite large fluctuations between glaciers—linked to their size—three epochal patterns emerged: 63 per cent of glaciers retreated from 1974 to 1990, 72 per cent advanced from 1990 to 2000, and 58 per cent advanced from 2000 to 2010. These trends were most pronounced along the warmer western South Pacific coast, whereas glaciers along the cooler Ross Sea coast experienced no significant changes. We find that glacier change along the Pacific coast is consistent with a rapid and coherent response to air temperature and sea-ice trends, linked through the dominant mode of atmospheric variability (the Southern Annular Mode). We conclude that parts of the world’s largest ice sheet may be more vulnerable to external forcing than recognized previously.

Global variations of local asymmetry in glacier altitude : separation of north-south and east-west components.

North-south and east-west differences in firn-line altitude, equilibrium-line altitude or middle altitudes of glaciers can be separated by regression on the cosine and sine of glacier aspect (accumulation area azimuth). Allowing for regional trends in altitude, the north-south differences expected from radiation and shade effects can be reliably quantified from World Glacier Inventory (WGI) data. The north-south differences are greater in sunnier climates, mid-latitudes and steeper relief. Local altitude differences between north- and south-facing glaciers are commonly 70-320 m. Such asymmetry is near-universal, although weak in the Arctic and tropics. East-west contrasts are less, and found mainly in the tropics and areas most exposed to strong winds. Altitude, latitude, glacier gradient and height range, calculable from most of the WGI data, are potential controls on the degree of north-south contrast, as well as surrogates for climatic controls (temperature, precipitation, radiation and cloudiness). An asymmetric sine-cosine power model is developed to describe the variation of north-south contrast with latitude. Multiple regression over 51 regions shows altitude and latitude to be the strongest controls of this contrast. Aspect-altitude analysis for former glaciers provides new evidence of cloudiness.

Toward a dynamic representation of hydrological connectivity at the hillslope scale in semiarid areas

Smith, M. W., Bracken, L. J. (2010). Toward a dynamic representation of hydrological connectivity at the hillslope scale in semiarid areas. Water Resources Research, 46, Article Number: W12540.

A comparison of different instruments for measuring soil creep

Summary The difficulties in measuring rates of soil creep imply that a comparison of different instruments is important to allow evaluation of measurement errors. Annual linear creep rates were derived using six different instruments for twenty plots in an instrumented basin in upper Weardale, northern England. The results show that acceptable levels of error can be attained by careful choice of instrument and measurement procedure. Two new instruments, inclinometer pegs and a tube, performed best and are recommended to other workers. The rates obtained (on average 1.3 mm/yr) are in broad agreement with results from other humid temperate sites.

Climatogenic north-south asymmetry of local glaciers in Spitsbergen and other parts of the Arctic

Abstract Although World Glacier Inventory (WGI) data for 241 local glaciers (>1 km2 in area) in Svalbard show a mean aspect of 014˚ ± 24˚, their mid-altitudes are lowest for an aspect of 109˚ ± 46˚, which is inconsistent. Further data are generated here for the altitude, length and source aspect of 205 local glaciers (0.3–6.0 km long) in the main area of local glaciation in Svalbard, Nordenskiöld Land. All four mountain blocks have mean glacier source aspects of 356˚ to 018˚; the overall mean is 011˚ ± 8˚. Mid-altitudes are lowest at 042˚ ±21˚, predicted to be 53 m lower than on opposite aspects. Lowest altitudes are predicted at 009˚ to 030˚, averaging 157 m lower than on opposite aspects. These results show that local, land-terminating glaciers around 78˚ N are affected more by north-south radiation receipt contrasts than by wind effects, consistent with the trend found across most other Arctic regions. It is concluded that, although weaker than in mid-latitudes, contrasts due to slope climates are substantial even in Arctic glaciers. This is apparent only when small, steep glaciers are inventoried: WGI data are incomplete and users need to check the thresholds of coverage.

Alkenones, alkenoates, and organic matter in coastal environments of NW Scotland: Assessment of potential application for sea level reconstruction

Reconstruction of late Quaternary sea level history in areas of glacioisostatic uplift often relies on sediment archives from coastal isolation basins, natural coastal rock depressions previously isolated from or connected to the sea at different times. Proxy indicators for marine, brackish, or lacustrine conditions combined with precise dating can constrain the time when the sea crossed the sill threshold and isolated (or connected) the basin. The utility of isolation basins in investigations of sea level change is well known, but investigations have been mostly limited to microfossil proxies, the application of which can be limited by preservation and nonanalog problems. Here we investigate the potential of long-chain alkenones, alkenoates, and bulk organic parameters (TOC, Corg/N) for reconstructing past sea level changes in isolation basins in NW Scotland. We analyze organic biomarkers and bulk parameters from both modern basins (at different stages of isolation from the sea) and fossil basins (with sea level histories reconstructed from established proxies). Logit regression analysis was employed to find which of the biomarker metrics or bulk organic measurements could reliably characterize the sediment samples in terms of a marine/brackish or isolated/lacustrine origin. The results suggested a good efficiency for the alkenone index %C37:4 at predicting the depositional origin of the sediments. This study suggests that alkenones could be used as a novel proxy for sea level change in fossil isolation basins especially when microfossil preservation is poor.

Geotechnical properties of rock masses: their control on slope form and mechanisms of change along the Napier range, Western Australia

Abstract Slope form and the mechanisms of change which slope profiles exhibit are frequently subject to scrutiny by geomorphologists. However, the majority of studies do not consider fundamental material properties and rock mass geotechnical characteristics. The results presented here highlight the importance of synthesisistandard geomorphological site investigation techniques with quantifiable rock geotechnical parameters, in order to understand slope form and development. Field research has been undertaken along the Napier Range of the Kimberly region, Western Australia. The Napiers are an extensive, upraised, Devonian limestone reef, along which a number of characteristic slope profiles can be identified. Laboratory studies of yield strength, stress-strain characteristics, elastic properties and discontinuity parameters have been conducted on material sampled at sites representative of each slope profile type. The results suggest that highly concave slopes have formed in limestone which exhibits little deformation before yield, has a high modulus of elasticity and few irregular fractures. Convexo-concave slopes, on the other hand, are characteristic of material which displays a greater ability to strain below yield, a relatively low modulus of elasticity and a pronounced discontinuity pattern. It is the combination of field investigation and laboratory study which most successfully explains variations in slope form.