Mechanisms controlling warm water volume interannual variations in the equatorial Pacific: diabatic versus adiabatic processes

Variations of the volume of warm water above the thermocline in the equatorial Pacific are a good predictor of ENSO (El Ni?o/Southern Oscillation) and are thought to be critical for its preconditioning and development. In this study, the Warm Water Volume (WWV) interannual variability is analysed using forced general circulation model experiments and an original method for diagnosing processes responsible for WWV variations. The meridional recharge/discharge to higher latitudes drives 60% of the ENSO-related equatorial WWV variations, while diabatic processes in the eastern equatorial Pacific account for the remaining 40%. Interior meridional transport is partially compensated by western boundary transports, especially in the southern hemisphere. Diabatic equatorial WWV formation (depletions) during La Ni?a (El Ni?o) are explained by enhanced (reduced) diathermal transport through enhanced (reduced) vertical mixing and penetrating solar forcing at the 20°C isotherm depth. The respective contribution of diabatic and adiabatic processes during build-ups/depletions strongly varies from event-to-event. The WWV build-up during neutral ENSO phases (e.g. 1980–1982) is almost entirely controlled by meridional recharge, providing a text-book example for the recharge/discharge oscillator’s theory. On the other hand, diabatic processes are particularly active during the strongest La Ni?a events (1984, 1988, 1999), contributing to more than 70% of the WWV build-up, with heating by penetrative solar fluxes explaining as much as 30% of the total build-up due to a very shallow thermocline in the eastern Pacific. This study does not invalidate the recharge/discharge oscillator theory but rather emphasizes the importance of equatorial diabatic processes and western boundary transports in controlling WWV changes.     

Origins of non-equilibrium lithium isotopic fractionation in xenolithic peridotite minerals: Examples from Tanzania

Olivine, clinopyroxene and orthopyroxene in variably metasomatised peridotite xenoliths from three lithospheric mantle sections beneath the East African Rift in Tanzania (Lashaine, Olmani, Labait) show systematic differences in their average Li concentrations (2.4 ppm, 2.0 ppm and 1.5 ppm, respectively) and intermineral isotopic fractionations, with olivine being heaviest (δ⁷Li = + 2.3 to + 13.9‰, average + 5.0‰), followed by orthopyroxene (? 4.1 to + 6.5‰, average + 0.8‰) and clinopyroxene (? 6.7 to + 4.1‰, average ? 1.6‰). These features are ascribed to the effects of kinetic Li isotope fractionation combined with different Li diffusivities in mantle minerals.Two main mechanisms likely generate diffusion-driven kinetic Li isotope fractionation in mantle xenoliths (1) Li diffusion from grain boundary melt into minerals during recent metasomatism or entrainment in the host magma and (2) subsolidus intermineral Li-redistribution. The latter can produce both isotopically light (Li-addition) and heavy (Li-loss) minerals and may occur in response to changes in pressure and/or temperature.Modelling shows that non-mantle-like δ⁷Li in clinopyroxene (< + 2‰), combined with apparent equilibrium olivine-clinopyroxene elemental partitioning in most peridotite xenoliths from all three Tanzanian localities probably reflects incipient Li addition during interaction with the host magma. Low δ⁷Li (< ? 3‰), combined with high Li concentrations (> 3 ppm) in some clinopyroxene may require very recent (minutes) Li ingress from a Li-rich melt (100s of ppm) having mantle-like δ⁷Li. This might happen during late fragmentation of some mantle xenoliths caused by a volatile- (and Li-) rich component exsolved from the host basalt. In contrast, high Li concentrations (> 2 ppm) and δ⁷Li (> 4‰) in olivine from many Labait and Olmani samples are attributed to an older, pre-entrainment enrichment event during which isotopic equilibrium was attained and whose signature was not corrupted during xenolith entrainment. Low Li concentrations and mantle-like isotopic composition of olivine from most Lashaine xenoliths indicate limited metasomatic Li addition.Thus, Li concentrations and isotope compositions of mantle peridotites worldwide may reflect two processes, with olivine mainly preserving a signature of depletion in refractory samples (low Li contents and δ⁷Li) or of older (precursory) melt addition in metasomatised samples (high Li contents and δ⁷Li), while non mantle-like, low δ⁷Li in almost all clinopyroxene can be due to Li ingress during transport in the host magma and/or slow cooling, if the samples were erupted in lavas. In Tanzania, the peridotites experienced rift-related heating prior to entrainment and were quenched upon eruption, so Li ingress is the most likely process responsible for the isotopically light clinopyroxene here.     

Winter climate change in alpine tundra: plant responses to changes in snow depth and snowmelt timing

Snow is an important environmental factor in alpine ecosystems, which influences plant phenology, growth and species composition in various ways. With current climate warming, the snow-to-rain ratio is decreasing, and the timing of snowmelt advancing. In a 2-year field experiment above treeline in the Swiss Alps, we investigated how a substantial decrease in snow depth and an earlier snowmelt affect plant phenology, growth, and reproduction of the four most abundant dwarf-shrub species in an alpine tundra community. By advancing the timing when plants started their growing season and thus lost their winter frost hardiness, earlier snowmelt also changed the number of low-temperature events they experienced while frost sensitive. This seemed to outweigh the positive effects of a longer growing season and hence, aboveground growth was reduced after advanced snowmelt in three of the four species studied. Only Loiseleuria procumbens, a specialist of wind exposed sites with little snow, benefited from an advanced snowmelt. We conclude that changes in the snow cover can have a wide range of species-specific effects on alpine tundra plants. Thus, changes in winter climate and snow cover characteristics should be taken into account when predicting climate change effects on alpine ecosystems.     

Loading of a seismic zone to failure deforms nearby volcanoes: a new earthquake precursor

The South Iceland Seismic Zone (SISZ) was loaded to failure in June 2000, resulting in two M6.6 earthquakes. The SISZ is an E–W‐trending zone with an overall sinistral movement. Numerical models indicate that, when the SISZ is loaded to failure, there are stress concentrations at its ends: tensile in the north‐east and south‐west quadrants, and compressive in the north‐west and south‐east quadrants. These model predictions fit well with observations. Geodetic measurements indicate considerable compression, uplift and associated intense seismicity in recent years in the volcanoes of Hengill and Eyjafjallajokull, located in the quadrants of compression, whereas there have been unusually frequent eruptions in the past decades in the Hekla Volcano, located in one of the quadrants of extension. The models predict that following the large June 2000 earthquakes, stress relaxation within the SISZ should lead to stopping of the intense seismicity and deformation in the volcanoes of Hengill and Eyjafjallajokull, again in agreement with observations. However, when similar episodes of deformation and seismicity start again, particularly in the Hengill Volcano, a large earthquake would be expected within several years in the SISZ. The numerical models, and the deformation and seismic data, indicate that monitoring of ‘soft’ inclusions such as volcanoes (many with magma chambers) in the vicinity of a seismic zone may serve as precursors to large earthquakes.     

Reaching a climate agreement: compensating for energy market effects of climate policy

Because of large economic and environmental asymmetries among world regions and the incentive to free ride, an international climate regime with broad participation is hard to reach. Most of the proposed regimes are based on an allocation of emissions rights that is perceived as fair. Yet, there are also arguments to focus more on the actual welfare implications of different regimes and to focus on a ‘fair’ distribution of resulting costs. In this article, the computable general equilibrium model DART is used to analyse the driving forces of welfare implications in different scenarios in line with the 2?°C target. These include two regimes that are often presumed to be ‘fair’, namely a harmonized international carbon tax and a cap and trade system based on the convergence of per capita emissions rights, and also an ‘equal loss’ scenario where welfare losses relative to a business-as-usual scenario are equal for all major world regions. The main finding is that indirect energy market effects are a major driver of welfare effects and that the ‘equal loss’ scenario would thus require large transfer payments to energy exporters to compensate for welfare losses from lower world energy demand and prices.

Policy relevance

A successful future climate regime requires ‘fair’ burden sharing. Many proposed regimes start from ethical considerations to derive an allocation of emissions reduction requirements or emissions allowances within an international emissions trading scheme. Yet, countries also consider the expected economic costs of a regime that are also driven by other factors besides allowance allocation. Indeed, in simplified lab experiments, successful groups are characterized by sharing costs proportional to wealth. This article shows that the major drivers of welfare effects are reduced demand for fossil energy and reduced fossil fuel prices, which implies that (1) what is often presumed to be a fair allocation of emissions allowances within an international emissions trading scheme leads to a very uneven distribution of economic costs and (2) aiming for equal relative losses for all regions requires large compensation to fossil fuel exporters, as argued, for example, by the Organization of Petroleum Exporting Countries (OPEC).     

Geospatial data: a key ingredient for Swiss Re’s underwriting and service tools

As a leading global reinsurer, Swiss Re deals with many hazards and risks for which geospatial data are crucial in order to obtain reliable assessments of expected insured losses or large losses from catastrophes. Typically, such data are used in combination with insurance data either in pricing tools to calculate premiums, tail risks and more, or in mapping tools. In natural perils pricing applications—the most important group of tools—geospatial data are usually “not visible” but are instead used to create probabilistic event sets. For example, a flood event set may define spatially if and how frequently a given location is flooded. Mapping tools, such as Swiss Re’s CatNet^® (www.swissre.com/catnet), visualize the data in the form of maps which include many useful attributes per geographic location.

     

Determining hydrological regimes in an agriculturally used tropical inland valley wetland in Central Uganda using soil moisture,groundwater, and digital elevation data

Inadequate knowledge exists on the distribution of soil moisture and shallow groundwater in intensively cultivated inland valley wetlands in tropical environments, which are required for determining the hydrological regime. This study investigated the spatial and temporal variability of soil moisture along 4 hydrological positions segmented as riparian zone, valley bottom, fringe, and valley slope in an agriculturally used inland valley wetland in Central Uganda. The determined hydrological regimes of the defined hydrological positions are based on soil moisture deficit calculated from the depth to the groundwater table. For that, the accuracy and reliability of satellite‐derived surface models, SRTM‐30m and TanDEM‐X‐12m, for mapping microscale topography and hydrological regimes are evaluated against a 5‐m digital elevation model (DEM) derived from field measurements. Soil moisture and depth to groundwater table were measured using frequency domain reflectometry sensors and piezometers installed along the hydrological positions, respectively. Results showed that spatial and temporal variability in soil moisture increased significantly (p < .05) towards the riparian zone; however, no significant difference was observed between the valley bottom and riparian zone. The distribution of soil hydrological regimes, saturated, near‐saturated, and nonsaturated regimes does not correlate with the hydrological positions. This is due to high spatial and temporal variability in depth to groundwater and soil moisture content across the valley. Precipitation strongly controlled the temporal variability, whereas microscale topography, soil properties, distance from the stream, anthropogenic factors, and land use controlled the spatial variability in the inland valley. TanDEM‐X DEM reasonably mapped the microscale topography and thus soil hydrological regimes relative to the Shuttle Radar Topography Mission DEM. The findings of the study contribute to improved understanding of the distribution of hydrological regimes in an inland valley wetland, which is required for a better agricultural water management planning.     

Urban structures and daily mobility patterns in a city of long distances—the case of Muscat/Oman

Population growth, urban sprawl and a high degree of car dependency as well as slowly rising petrol prices contribute towards increasing challenges for everyday urban mobility in Muscat, Oman. Until now, only a few empirical studies have dealt with urban mobility in Oman. Therefore, this article draws mainly on our own empirical findings to answer the following questions: What do daily and weekly mobility patterns look like in Muscat? How do these practices differ depending on the social position of the household, i.e. their nationality, income and education? Which interdependent effects can be discerned between everyday mobility practices and the fragmented and segregated urban structures? Since our research questions focus on the interrelations between urban structures and individual mobility, we chose a mixed‐methods approach including methods derived both from social and spatial research. This article in particular draws on our quantitative survey covering 850 households and extensive mappings of three selected case study areas and secondary data analysis.     

Seasonal climate inferences from high-resolution modern diatom data along a climate gradient: a case study

This study represents a step towards developing seasonal climate inferences by using high-resolution modern data sets. The importance of seasonal climate changes is highlighted by the instrumental record of a meteorological station close to our study site (lac du Sommet in the Laurentian Mountains, Québec, Canada): Between 1966 and 2001, May temperatures increased significantly by 3.1°C (r = 0.41, n = 35, p < 0.01) but annual mean temperatures only by 0.6°C (r = 0.21, n = 35, p > 0.05). Comparison of this instrumental record with fossil diatom assemblages in a sediment core from lac du Sommet showed that axis one of a principal component analysis (PCA) of the fossil diatoms was best correlated with wind velocity in June (r = 0.62, n = 19, p < 0.005) and that past diatom production was significantly enhanced in periods with colder July temperatures (r =  ?0.77, n = 19, p < 0.0005) and higher wind velocity in June (r = 77, n = 19, p < 0.0005). The strong impact of the spring and summer conditions on overall diatom composition and productivity suggests that seasonal lake responses to climate are more important than annual mean temperatures. However, the seasonal dynamics of diatom communities are not well understood, and seasonality is rarely inferred effectively from lake sediment studies. Our research presents a pilot study to answer a twofold question: Is it possible to identify diatom communities which are typical for warmer or colder seasonal climate using sediment traps, and if it is, can this knowledge be used to infer seasonal climate conditions from fossil diatom assemblages? To address these questions, the seasonal dynamics of diatom communities and water chemistry were studied using sediment traps and water samples at biweekly intervals in four lakes distributed along an altitudinal gradient in the Laurentian Mountains from May through October 2002. Date of ice break-up was significantly related to the diatom assemblages taken in spring and uncorrelated to other significant environmental variables. Summer water temperature, circulation of the water column and pH explained a significant part of the biological variance in summer, and total nitrogen (TN) explained most of the biological variance in autumn. To infer these variables, weighted averaging partial least squares models were applied to the seasonal data sets. Inferred ice break-up dates were significantly correlated with number of days below 0°C in April (r = 0.52, n = 19, p < 0.025), inferred circulation of the water column was significantly related to measured wind velocity in June (r = 0.64, n = 19, p < 0.005), inferred summer water temperature and inferred pH was significantly related to measured July air temperature (r = 0.50, r =  ?53, n = 19, p < 0.025) and inferred TN autumn concentrations had an inverse relationship to August temperatures (r =  ?0.53, n = 19, p < 0.01). This comparison of the historical record with diatom-inferred seasonal climate signals, based on the comparison of fossil diatom assemblages with modern sediment trap data of high temporal resolution, provides a promising new approach for the reconstruction of seasonal climate aspects in paleolimnological studies.     

Geoid Validation on the Baltic Sea Using Ship-borne GNSS Data

Abstract

We studied geoid validation using ship-borne global navigation satellite systems (GNSS) on the Baltic Sea. We obtained geoid heights by combining GNSS–inertial measurement unit observations, tide gauge data, and a physical sea model. We used two different geoid models available for the area. The ship route was divided into lines and the lines were processed separately. The GNSS results were reduced to the sea surface using attitude and draft parameters available from the vessel during the campaign. For these lines, the residual errors between ellipsoidal height versus geoid height and absolute dynamic topography varied between 0 and 15?cm, grand mean being 2?cm. The mean standard deviations of the original time series were approximately 11?cm and reduced to below 5?cm for the time series filtered with 10?min moving average. We showed that it is possible to recover geoid heights from the GNSS observations at sea and validate existing geoid models in a well-controlled area.