Particulate barium fluxes and export production in the northwestern Mediterranean

Biogenic barium, mostly in the barite (BaSO₄) form, has been proposed as a tracer for export production in the ocean. Here we report on biogenic barium (Ba_xs) and particulate organic carbon (POC) fluxes from sediment traps deployed at the DYFAMED site in the Northwestern Mediterranean Sea. Ba_xs fluxes display average values of 37 ± 45 and 50 ± 58 μg/m²/d at 200 and 1000 m respectively, and are linearly correlated to POC fluxes (mean values of 7.9 ± 9.3 and 6.8 ± 6.8 mg C/m²/d at 200 and 1000 m). Export production estimates, calculated using published Ba_xs- or POC-based algorithms, all fall below or close to the lower limit of potential export values proposed in the literature. This work clearly demonstrates the usefulness of Ba_xs as a tracer of oceanic export production in the Northwestern Mediterranean Sea. However, development of a quantitative export production proxy requires a clear understanding of the underlying cause(s) for the observed spatial variations in the relationship between Ba_xs and POC fluxes. The present study confirms that the processes leading to barite formation differ between margin and open-ocean sites and probably account for much of the regional variability in the POC/Ba_xs ratio.     

From desert to Mediterranean rangelands: will increasing drought and inter-annual rainfall variability affect herbaceous annual primary productivity?

Climate change is predicted to alter the rainfall regime in the Eastern Mediterranean Basin: total annual rainfall will decrease, while seasonal and inter-annual variation in rainfall will increase. Such changes in the rainfall regime could potentially lead to large-scale changes in aboveground net primary productivity (ANPP) in the region. We conducted a data-driven evaluation of herbaceous ANPP along an entire regional rainfall gradient, from desert (90 mm MAR [Mean Annual Rainfall]) to Mesic-Mediterranean (780 mm MAR) ecosystems, using the largest database ever collated for herbaceous ANPP in Israel, with the aim of predicting consequences of climate change for rangeland productivity. This research revealed that herbaceous ANPP increases with increasing rainfall along the gradient, but strong dependence on rainfall was only apparent within dry sites. Rain Use Efficiency peaks at mid-gradient in Mediterranean sites without woody vegetation (560 and 610 mm MAR). Inter-annual coefficients of variation in rainfall and herbaceous ANPP decrease along the rainfall gradient up to ca. 500 mm MAR. Climate change is more likely to affect herbaceous ANPP of rangelands in the arid end of the rainfall gradient, requiring adaptation of rangeland management, while ANPP of rangelands in more mesic ecosystems is less responsive to variation in rainfall. We conclude that herbaceous ANPP in most Mediterranean rangelands is less vulnerable to climate change than generally predicted.     

Measurements of boundary-layer flow and boundary roughness over Campeche Bank, Yucatan

Aseries of boundary-layer measurements was made at three anchor stations on Campeche Bank, Yucatan. Measurements consisted of current speed at six levels within 1.5 m of the bed, current direction, and stereophotographs of boundary. Analysis of the drag coefficient revealed that the boundary-layer flow was hydrodynamically transitional and the magnitude of the drag coefficient varied between 2·10⁻³ and 6·10⁻² as a function of the flow conditions and bed configuration. These data appear to be representative of flows of an intermediate nature, not only in the observed variations of the drag coefficient with respect to Reynolds number but in the way that the drag coefficient correlates with other measurements made in low- and high-velocity environments, respectively.     

Isotopic signatures of organic matter in sediments of the continental shelf facing the Orinoco Delta: Possible contribution of organic carbon from savannas

The ⁸⁷Sr, ¹³C, and ¹⁵N isotopic signatures of organic matter in sediments from the continental shelf facing the Orinoco Delta were measured to determine the contribution of sediments transported from the Amazon River by the coastal Guayana current and the sediments transported by the Orinoco River. Box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the Orinoco Delta were analyzed. Carbon and nitrogen concentrations decreased with depth under water on the shelf, and were strongly correlated indicating homogeneity of organic matter composition. Phosphorus content was also associated to organic matter in most samples, but some of them revealed deposition of P-enriched sediments. The ⁸⁷Sr/⁸⁶Sr ratios showed a strong continental signature averaging 0.7117, therefore, limiting the possible carbon and nitrogen sources associated with these sediments to C3 trees, C4 grasses, or freshwater phytoplankton. The δ¹³C values were relatively high averaging −21‰, above values reported for sediments on the Amapá shelf and the Amazon River in Brazil. Average δ¹³C values did not differ significantly among transects. High δ¹³C values point to the influence of organic matter transported from the C4-plants dominated savannas in the northern fringe of the Orinoco River. δ¹⁵N values were positive and averaged 5‰, being within the range of values measured in the Marajo island (Amazon River) and the estuary of the Pará River. The δ¹⁵N values differed significantly among transects (4.9–5.2‰), lowest values corresponding to the northernmost transect near the coast of Trinidad, and the highest values corresponding to the transect located at the southernmost position.     

Clinoform mechanics in the Gulf of Papua, New Guinea

The largest islands of the Indo-Pacific Archipelago are estimated to account for 20–25% of the global sediment discharge to the ocean, and much (>50%) of this sediment is supplied to wide (>150 km) continental shelves. These conditions are conducive to creation of large-scale morphologic features known as clinoforms—sigmoidal-shaped deposits on the continental shelf. The Gulf of Papua (GOP) receives 3.84 ×10⁸ tons of sediment annually from three principal sediment suppliers, the Fly, Kikori and Purari Rivers, and its prograding clinoform is the focus of this study. During three research cruises, 80 cores and 37 CTD/optical backscatter casts were collected, and an instrumented tripod was deployed twice. Sedimentological and radiochemical results indicate that the GOP clinoform has characteristics similar to those seaward of other major rivers (e.g., Amazon, Ganges–Brahmaputra), specifically sand/mud interbedding on the topset, rapidly accumulating muds on the foreset, and siliciclastic mud mixed with carbonate sand on the bottomset.Using core data and field observations, the mechanics of clinoform progradation are examined. Discrete, large sedimentation events are identified as processes building the clinoform feature. X-radiographs from foreset cores reveal thick beds (>5 cm) between bioturbated sections. Detailed ²¹⁰Pb and grain-size data indicate that low activities and increased clay contents are associated with these beds. They are hypothesized to be formed by fluid–mud deposition in response to periods of large wave-tide bed shear stresses, more likely during the SE-tradewind season, and their regular occurrence produces high rates of mean accumulation (4 cm/y). Bed preservation is determined by the rates of sediment accumulation and bioturbation.To assess the influence of physical oceanographic factors on clinoform shape, bottom shear stresses from tides and surface waves were calculated using available wave and tripod data. This effort reveals that the depth range (25–40 m) of the clinoform rollover point (seaward edge of the topset region) is roughly consistent with the sediment-transport regime. Furthermore, calculations corroborate the core data that suggest possible seasonal sediment storage in the inner topset region (<15-m water depth, during the NW-monsoon winds) with subsequent transfer to foreset beds (more probable during SE-tradewind conditions).A 100-yr sediment budget created with accumulation rate data suggests approximately 20% of the total sediment supplied to the GOP accumulates on the clinoform (creating the clinoform morphology). Less than 5% is believed to escape to the adjacent slope, and much of the remaining 75% is likely trapped on the inner-topset region (<20 m water depth) and within the mangrove forests and flood/delta plains of the northern GOP.     

Peat extraction, conservation and the rural economy in Northern Ireland

Northern Ireland has a tradition of peat cutting; 78 per cent by area of remaining lowland bogs and 46 per cent of blanket bogs have been cut in the past. Since the early 1980s, machine peat extraction for fuel and horticulture has increased, against a background of changing economic support for agriculture, high rural unemployment and agricultural underemployment. Cutting fuel peat can reduce household fuel costs and some peat fuel is sold to gain income. Horticultural peat is cut mainly for sale. Expansion of machine extraction, with possible environmental impacts, occurred as interest in peatland conservation increased. Potential conflict arises between local economic needs and conservation. Machine cutting for fuel is widespread, but affects only 2.6 per cent of the blanket peat area; horticultural extraction is more localized and is only one-fifth of the extent of fuel extraction. Altitude, distance from roads, land ownership and rights, turbary, religious affiliation, local economic needs and the role of government departments all contribute to explaining the distribution and extent of extraction.     

The influence of shrimp farms organic waste management on chemical water quality

We evaluated the physical–chemical properties and nutrient concentrations in two shrimp ponds under conventional management, intensive (I-P) and semi-intensive (SI-P), and one under organic management (O-P), three days after loading and before stoking. The mean’s total alkalinity concentrations were 2.26 ± 0.04 mM, 2.28 ± 0.01 mM and 2.59 ± 0.01 mM, respectively for I-P, SI-P and O-P. Bicarbonate and carbonate accounted for 62% and 37% in I-P, 64% and 36% in SI-P and 83–17% in O-P, respectively. Aragonite and calcite were oversaturated around Ω = 5. Mean total phosphate (TP) concentrations were 441.37 ± 92.06 μg/L, 449 ± 48 μg/L and 473.64 ± 84.17 μg/L, under I-P SI-P and O-P management respectively. Following this sequence, NO₃⁻ concentration was 2.98 ± 0.7 μg/L, 1.16 ± 0.16 μg/L and 0.32 ± 0.12 μg/L, under I-P, SI-P and O-P management respectively. Thus, the data suggest that different management of farm organic waste leads to different chemical water quality.     

State-of-the art and perspectives of economic geography — taking stock from a German point of view

This article presents an evaluation of the current status of economic geography in general and German economic geography in particular with respect to research topics. A comparison with Anglo-American economic geography, more specifically, its actual research fields are also undertaken on the basis of a bibliometrical analysis of German and international journals dedicated to economic geography. On the basis of this analysis suggested actions are formulated, which could contribute to improved performance of research in German economic geography.