Seasonal Forecasting for Climate Hazards: Prospects and Responses

One of the most promising developments for early warning of climate hazards is seasonal climate forecasting. Already forecasts are operational in many parts of the tropics and sub-tropics, particularly for droughts and floods associated with ENSO events. Prospects for further development of seasonal forecasting for a range of climatichazards are reviewed, illustrated with case studies in Africa, Australia, the U.S.A. and Europe. A critical evaluation of the utility of seasonal forecasts centres on vulnerability, communicationchannels, and effective responses. In contrast to short-term prediction, seasonal forecasts raise new issues of preparedness and the use of information.     

Nematode distribution in cultivated and undisturbed soils of Guinea Savannah and Semi-deciduous Forest zones of Ghana

Climate change affects air temperature, sea levels as well as the soil and its ecosystem. The Guinea Savannah and Semi-deciduous Forest zones of Ghana are characterized by different climatic conditions and vegetative cover. Annual average temperature has been steadily increasing whilst annual total rainfall has been decreasing in both zones, and this has been causing a southward shift of the Savannah into the Forest zone. Soil organisms provide crucial ecosystem services which are required for sustainable agriculture and food production yet crop cultivation disturbs the soil ecosystem. The harsh conditions associated with the Savannah further expose the soil ecosystem to disturbance and loss of biodiversity which threatens food production and security. Soil nematodes are the most abundant animals in the soil and play a central and critical role in the soil food web complex. Studying the nematode community structure gives a reflection of the status of the entire soil ecosystem. Soil samples were taken from cultivated and natural landscapes in the Guinea Savannah and Semi-deciduous Forest agroecological zones to analyse the nematode community. Results from the study showed the Guinea Savannah zone recording warmer soil temperatures, lower organic matter percentage and lower nematode diversity(Genus Richness) as compared to the Semi-deciduous Forest zone. If the Savannah continues to shift southward, the Forest zone soil ecosystem risks disturbance and loss of biodiversity due to the harsh Savannah conditions. Our findings indicate that prevailing crop cultivation practices also disturb soil ecosystem in the two ecological zones which span across West Africa. A disturbed soil ecosystem endangers the future of food production and food security.     

Sedimentary facies during early stages of flooding in an extensional basin: the Brèche Rouge de Carboneras (Late Miocene, Almería/SE Spain)

The intramontane basins of the Betic Cordilleras (SE Spain) formed subsequent to the main phase of orogenic deformation during the middle Miocene in a close genetic relation to the Trans-Alboran Shear zone. Left lateral movements along a local branch (Carboneras fault zone, CF; strike NE–SW) of this zone played a major role in controlling the formation and dynamics of the Nijar-Carboneras Basin. To the south of the fault, a major phase of strike-slip faulting is recorded during the late Tortonian. The expression of this event is the Brèche Rouge de Carboneras (BRC), which seals a deep denudational surface on top of dislocated fault blocks formed by volcanics of the Cabo de Gata complex and early Tortonian shallow marine calcarenite. The sedimentary facies of this widely distributed unit in the Carboneras-Subbasin mirror the submarine topography and the distribution of the fault zones. Along strike-slip fault zones, autoclastic breccias and neptunian dikes preferentially oriented NW–SE and NE–SW occur, which are interpreted to represent the near-surface expression of the faults. Red limestone forms the groundmass of the autoclastic breccia and infills of neptunian dikes, which exhibit multiple phases of opening of fissures, gravitational sedimentary infill, lithification, and renewed creation of cracks. Steep relief, probably along fault scarps, was mantled by epiclastic volcanic conglomerate with a red carbonate matrix. Well-lithified coarse skeletal limestone rich in planktonic foraminifera formed pavements along sediment starved rocky surfaces in deep water. Laterally, within topographic depressions, the pavement limestone grades into thick accumulations of skeletal rudstone composed of fragmented azooxanthellate corals and stylasterid hydrozoans, which were concentrated by powerful bottom currents and gravitiy flows. Within the shallow water zone of dip slope ramps, cross-bedded calcarenite and calcirudite formed. Based on textures, fabrics and biota, rocks of the BRC were grouped into nine genetic lithofacies which document cryptic, deep-aphotic and shallow-photic environments typical of a sediment starved extensional basin.     

Evaluation of coseismic landslide hazard on the proposed Haast-Hollyford Highway,South Island,New Zealand

Coseismic landsliding presents a major hazard to infrastructure in mountains during large earthquakes. This is particularly true for road networks, as historically coseismic landsliding has resulted in road losses larger than those due to ground shaking. Assessing the exposure of current and planned highway links to coseismic landsliding for future earthquake scenarios is therefore vital for disaster risk reduction. This study presents a method to evaluate the exposure of critical infrastructure to landsliding from scenario earthquakes from an underlying quantitative landslide hazard assessment. The method is applied to a proposed new highway link in South Island, New Zealand, for a scenario Alpine Fault earthquake and compared to the current network. Exposure (the likelihood of a network being affected by one or more landslides) is evaluated from a regional-scale coseismic landslide hazard model and assessed on a relative basis from 0 to 1. The results show that the proposed Haast-Hollyford Highway (HHH) would be highly exposed to coseismic landsliding with at least 30–40?km likely to be badly affected (the Simonin Pass route being the worse affected of the two routes). In the current South Island State Highway network, the HHH would be the link most exposed to landsliding and would increase the total network exposure by 50–70% despite increasing the total road length by just 3%. The present work is intended to provide an effective method to assess coseismic landslide hazard of infrastructure in mountains with seismic hazard, and potentially identify mitigation options and critical network segments.     

Marine Chemistry in the Coastal Environment: Principles,Perspective and Prospectus

Marine chemistry of the coastal environment starts with principles of rock weathering that use carbonic acid to mobilize elements, only some of which comprise the majority of sea salt. The principle reason is reverse weathering, extensively represented in coastal waters, and returns most elements to newly formed colloids or minerals while recycling carbon dioxide to the atmosphere. This includes the deeper ocean expanse of sediment diagenesis, plus hydrothermal plumes and attendant low-temperature basalt alteration. Within the estuarine and extended shelf regimes, both conservative and non-conservative processes can be distinguished and modeled to determine proportions of weathered elements transmitted to the sea or consumed by reverse weathering. Conceptually, the steady-state processes that lead to the composition of seawater can be viewed as heterogeneous equilibria between dissolved constituents and solid mineral products taking hundreds of millennia. However, initial processes in the estuarine and coastal environment are characterized by shorter term scavenging associated with inorganic and organic colloids. These recycle both carbon and trace elements on timescales commensurate with estuarine flushing and coastal exchange with the ocean. The natural uranium and thorium decay series provide powerful tools for quantifying the rates of estuarine processes, including those within groundwater and the subterranean estuary. In the future, new mass spectrometric and nuclear magnetic resonance techniques will help to define the molecular nature of newly formed estuarine colloids as has been done for dissolved organic matter. As the coastal environment undergoes the forces of climate change in the form of warming and sea level rise, future research should address how these will impact chemistry of the coastal environment as a net source or sink of carbon dioxide and associated organic material.     

Géomorphologie de Tromelin,océan Indien

Tromelin is a small coral reef island (1 km²) located in the Indian Ocean, approximately 440 km east of Madagascar and 580 km north of La Réunion. Despite the presence of a permanent Météo France weather station on Tromelin since the 1950 s, a detailed geomorhological study of the island has never been undertaken. In this paper, we describe results from the 2008 field season, which enabled us to map and describe seven geomorphological zones on the atoll. (1) Tromelin's bathymetry is characterised by a pronounced submarine slope, which attains depths of 1000 m at only 2.5 km from the island's coastline. This geomorphology is typical of volcanic hotspots. (2) A coral platform borders the emerged crown of the island. This platform is exposed at low tide and has been fashioned in an ancient Pleistocene substratum. The substratum has been eroded by abrasive marine action to its present shape since the stabilisation of relative sea level around 6000 years ago. Erosion of the reef yields most of the biogenic sediment supply to the island. (3) The upper foreshore is characterised by outcrops of beachrock. These formations show a stratfication in slabs and dip gently towards the sea in the same manner as the contemporary clastic sediments. (4) Tromelin's beaches are divided into three sub-units, which reflect the different energy dynamics around the island, in addition to the transfer of sediment from the windward to the leeward side: (i) the southern storm beaches are characterised by coral blocks reworked during episodic high-energy events; they form boulder ramparts. Four perched rampart ridges have been recorded at ∼1 m, ∼3 m, ∼4.5 m and ∼7 m above mean sea level; (ii) transitional beaches are observed between the south and the north, constituting storm blocks and coarse sands and gravels; and (iii) sandy beaches are noted on the northern leeward side, comprising rounded gravels and coarse sands. The northern tip of the island is characterised by a sand spit (∼125 × ∼225 m), whose geometry varies based on the seasonal and meteo-marine contexts. (5) On Tromelin, a number of dune formations are observed. These are best developed in the north of the island due to the south-north translation of clastic sediments by aeolian wind action, and the trapping of sands by the well-developed vegetation. The height of the dunes varies between 10 cm (the southern micro-dunes) to 250 cm in the Northeast of Tromelin. (6) Exceptional waves have deposited storm tracts up to 250 m from the foreshore zone, comprising coarse gravels and coral blocks. The storm tract deposits are most prevalent on the windward side of the island, due not only to the high-energy dynamics, but also to the absence of vegetation cover in this area. (7) The southern depression covers an area of ∼40,000 m². At its lowest point it is only 1.2 m above sea level.     

Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano,Panama

The easternmost stratovolcano along the Central American arc is El Valle volcano, Panama. Several andesitic and dacitic lava flows, which range in age 5–10 Ma, are termed the old group. After a long period of quiescence (approximately 3.4 Ma), volcanic activity resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows 0.9–0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline andesites and dacites. The mineralogy of the two groups is distinct; two pyroxenes occur in the old-group rocks but are commonly absent in the young group. In contrast, amphibole has been found only in the young-group samples. Several disequilibrium features have been observed in the minerals (e.g., oscillatory zoning within clinopyroxenes). These disequilibrium textures appear to be more prevalent among the old- as compared with the young-group samples and are most likely the result of magma-mixing, assimilation, and/or polybaric crystallization. Mass-balance fractionation models for major and trace elements were successful in relating samples from the old group but failed to show a relationship among the young-group rocks or between the old- and young-group volcanics. We believe that the old-group volcanics were derived through differentiation processes from basaltic magmas generated within the mantlewedge. The young group, however, does not appear to be related to more primitive magmas by differentiation. The young-group samples cannot be related by fractionation including realistic amounts of amphibole. Distinctive geochemical features of the young group, including La/Yb ratios〉15, Yb〈1, Sr/Y〉150, and Y〈6, suggest that these rocks were derived from the partial melting of the subducted lithosphere. These characteristics can be explained by the partial melting of a source with residual garnet and amphibole. Dacitic material with the geochemical characteristics of subducted-lithosphere melting is generated apparently only where relatively hot crust is subducted, based on recent work. The young dacite-genesis at El Valle volcano is related to the subduction of relatively hot lithosphere.     

Postglacial vegetation history of Mitkof Island, Alexander Archipelago, southeastern Alaska

An AMS radiocarbon-dated pollen record from a peat deposit on Mitkof Island, southeastern Alaska provides a vegetation history spanning ∼12,900 cal yr BP to the present. Late Wisconsin glaciers covered the entire island; deglaciation occurred > 15,400 cal yr BP. The earliest known vegetation to develop on the island (∼12,900 cal yr BP) was pine woodland (Pinus contorta) with alder (Alnus), sedges (Cyperaceae) and ferns (Polypodiaceae type). By ∼12,240 cal yr BP, Sitka spruce (Picea sitchensis) began to colonize the island while pine woodland declined. By ∼11,200 cal yr BP, mountain hemlock (Tsuga mertensiana) began to spread across the island. Sitka spruce-mountain hemlock forests dominated the lowland landscapes of the island until ∼10,180 cal yr BP, when western hemlock (Tsuga heterophylla) began to colonize, and soon became the dominant tree species. Rising percentages of pine, sedge, and sphagnum after ∼7100 cal yr BP may reflect an expansion of peat bog habitats as regional climate began to shift to cooler, wetter conditions. A decline in alders at that time suggests that coastal forests had spread into the island's uplands, replacing large areas of alder thickets. Cedars (Chamaecyparis nootkatensis, Thuja plicata) appeared on Mitkof Island during the late Holocene.     

Nitrogen Uptake by Native and Invasive Temperate Coastal Macrophytes: Importance of Dissolved Organic Nitrogen

We investigated if the success of the invasive common reed Phragmites australis could be attributed to a competitive ability to use dissolved organic nitrogen (DON) when compared to the dominant macrophyte Spartina alterniflora in tidal wetlands. Short-term nutrient uptake experiments were performed in the laboratory on two genetic lineages of Phragmites (native and introduced to North America) and S. alterniflora. Our results provide the first evidence for direct assimilation of DON by temperate marsh plants and indicate that amino acids are assimilated intact by all plant types at similar rates. Both Phragmites lineages had significantly greater urea–N assimilation rates than S. alterniflora, and the affinity for dissolved inorganic nitrogen (DIN) species was the greatest in native Phragmites > introduced Phragmites > S. alterniflora. Field studies demonstrated uptake of both DON and DIN in similar proportion as those determined in the laboratory experiments. Based on these uptake rates, we estimate that DON has the potential to account for up to 47% of N demand for Phragmites plants, and up to 24% for S. alterniflora plants. Additionally, we suggest that differences in N uptake between native and introduced Phragmites lineages explain one mechanism for the success of the introduced type under increasingly eutrophic conditions.     

A new particulate Mn-Fe-P-shuttle at the redoxcline of anoxic basins

Pelagic redoxclines of anoxic basins and deeps form the suboxic transition between oxygenated surface and anoxic or even sulfidic bottom waters. Intense element cycling, favoured by elevated microbial activity, causes steep gradients of physico-chemical parameters, nutrients and redox-sensitive trace metals. This study presents a conceptual model for authigenic particle formation at pelagic redoxclines, which is based on the tight coupling of Mn, Fe, and P cycles. Besides the well-known occurrence of Mn-oxides, textural (SEM-EDX) and geochemical (ICP-OES, ICP-MS) analyses of particles from the redoxclines of the Black Sea and the Baltic Sea (Gotland Basin, Landsort Deep) evidence the existence of earlier postulated Fe-oxyhydroxo-phosphates and emphasize mixed phases consisting of Mn-oxides and Fe-oxyhydroxo-phosphates as a new solid species. Most of the analyzed particles are star-shaped, of about 5 μm in size, and occur as single particles or aggregates without any morphological differences between Mn-oxides, Fe-oxyhydroxo-phosphates, and mixed phases. Throughout the redoxcline, these minerals show a general succession with maximum abundance of Mn-oxides above the redoxcline followed by mixed phases and almost pure Fe-phosphates within and below the redoxcline, respectively. Molar Fe/P ratios of single particles argue against the formation of known pure Fe-phosphates like vivianite or strengite at the lower end of the redox transition zone, but are consistent with recent experimental findings for colloidal P-bearing hydrous ferric oxides. Moreover, morphological similarities suggest the formation of irregular Fe-oxyhydroxo coatings due to oxidation of upward diffusing Fe²⁺ by oxygen and stepwise replacement of Mn(IV) by Fe(III) on sinking MnO_x particles followed by immediate adsorption or even co-precipitation of phosphate. Batch-type experiments using biogenic MnO_x particles demonstrate the efficient potential of Fe²⁺ oxidation by sinking MnO_x particles. When entering sulfidic waters MnO_x particles are progressively reduced leading to an increasing relative abundance of Fe- and P-rich particles. In deeper parts of the water column these particles are also reductively dissolved, thereby releasing Fe²⁺ and phosphate to the water column. This Mn-Fe-P-shuttle likely affects phosphate transport throughout the water column and thus impacts primary production at least over longer time scales. Furthermore, the particulate Mn-Fe-P-shuttle must have played an important role for the cycling of P and certain trace metals in ancient ocean basins, e.g., during certain periods of Cretaceous black shale formation and should be considered in future mass balances and modeling approaches dealing with oxic/anoxic interfaces of aquatic ecosystems.