Predictability of South China Sea Summer Monsoon Onset

Predicting monsoon onset is crucial for agriculture and socioeconomic planning in countries where millions rely on the timely arrival of monsoon rains for their livelihoods. In this study we demonstrate useful skill in predicting year-to-year variations in South China Sea summer monsoon onset at up to a three-month lead time using the GloSea5 seasonal forecasting system. The main source of predictability comes from skillful prediction of Pacific sea surface temperatures associated with El NiÑo and La NiÑa. The South China Sea summer monsoon onset is a known indicator of the broadscale seasonal transition that represents the first stage of the onset of the Asian summer monsoon as a whole. Subsequent development of rainfall across East Asia is influenced by subseasonal variability and synoptic events that reduce predictability, but interannual variability in the broadscale monsoon onset for East Asian summer monsoon still provides potentially useful information for users about possible delays or early occurrence of the onset of rainfall over East Asia.     

GLACIATION OF MT ALLEN, STEWART ISLAND (RAKIURA): THE SOUTHERN MARGIN OF LGM GLACIATION IN NEW ZEALAND

The origin of two ridges on the eastern slopes of Mt Allen, southern Stewart Island, has remained equivocal, with differences of opinion over the exact process-mechanisms of formation. A variety of approaches was used to test a number of possible hypotheses about the origin of the ridges. These include topographic and spatial positioning, geomorphology, sedimentology and palaeoclimatological extrapolations to reconstruct two small former cirque glaciers with equilibrium line altitudes (ELAs) of c. 600 m. It would appear the two ridges reflect a glacial origin, the glaciers interpreted as forming during the Last Glacial Maximum (LGM) in New Zealand. Whilst glaciation during this time (18–19 ka) was extensive in the Southern Alps, the restricted nature of glaciation on Mt Allen suggests the low altitude restricted glaciation to niche sites on the lee side of upland areas.     

STRUCTURAL GLACIOLOGY OF A TEMPERATE MARITIME GLACIER: LOWER FOX GLACIER,NEW ZEALAND

This paper describes the structural glaciology of the lower Fox Glacier, a 12.7 km‐long valley glacier draining the western side of the Southern Alps, New Zealand. Field data are combined with analysis of aerial photographs to present a structural interpretation of a 5 km‐long segment covering the lower trunk of the glacier, from the upper icefall down‐glacier to the terminus. The glacier typifies the structural patterns observed in many other alpine glaciers, including: primary stratification visible within crevasse walls in the lower icefall; foliation visible in crevasses below the lower icefall; a complex set of intersecting crevasse traces; splaying and chevron crevasses at the glacier margins; transverse crevasses forming due to longitudinal extension; longitudinal crevasses due to lateral extension near the snout; and, arcuate up‐glacier dipping structures between the foot of the lower icefall and the terminus. The latter are interpreted as crevasse traces that have been reactivated as thrust faults, accommodating longitudinal compression at the glacier snout. Weak band‐ogives are visible below the upper icefall, and these could be formed by multiple shearing zones uplifting basal ice to the glacier surface to produce the darker bands, rather than by discrete fault planes. Many structures such as crevasses traces do not show a clear relationship with measured surface strain‐rates, in which case they may be ‘close to crevassing’, or are undergoing passive transport down‐glacier.     

桑沟湾和胶州湾沉积物耗氧率研究

为评价浅海海域底层在碳元素生物地化循环中的作用,采用现场取样培养法测定了黄海桑沟湾和胶州湾的沉积物耗氧率。桑沟湾5月和8月的沉积物耗氧率分别为15和24 mmol.m-2.d-1;胶州湾8月的沉积物耗氧率为18 mmol.m-2.d-1。回归分析表明,2个湾的沉积物耗氧率分别与沉积物表层的有机碳和总氮含量正相关。取呼吸商为0.8,得到桑沟湾底层对有机碳的矿化率占水层初级生产力的102%(5月)和67%(8月),胶州湾底层对有机碳的矿化率占水层初级生产力的28%(8月)。取桑沟湾颗粒有机碳的生物沉积速率为236 mg.m-2.d-1,得到底层对有机碳的埋置效率为40%(5月)和3%(8月),埋置的有机碳占水层初级生产力的69%(5月)和2%(8月);胶州湾颗粒有机碳的自然沉积速率为251 mg.m-2.d-1,底层对有机碳的埋置效率为32%(8月),埋置的有机碳占水层初级生产力的13%(8月)。     

Lunar Pyroxene-Phyric Basalts: Crystallization Under Supercooled Conditions

Pyroxene-phyric basalts constitute a distinct petrologic groupin samples from lunar maria at both Apollo 12 and Apollo 15sites. Textures of pyroxene-phyric basalts from both sites aresimilar, but bulk compositions and mineralogy are somewhat different.Pyroxene-phyric basalts are characterized by large pyroxenephenocrysts with cores of magnesian pigeonite and mantles ofaugite grading to ferroaugite, usually set in a distinctly finergroundmass of iron-rich pyroxene, plagioclase, ilmenite, andother minor minerals. Olivine is scarce or absent modally andnormatively. Controversy has arisen over whether the porphyritictexture is a result of (1) a two-stage cooling history, e.g.phenocrysts formed at depth, and groundmass formed on extrusion;or (2) single stage, rapid cooling under supercooled conditions(cooling history here refers to cooling conditions imposed byexternal factors, and is not to be equated with ‘crystallizationhistory’). A study of six rocks belonging to this groupfrom Apollo 15 rake samples is reported here. A considerablerange of textures is present in these rocks, and they may beranked in order of decreasing late-stage cooling rate (15125,15666, 15682, 15118, 15684, 15116) on the basis of groundmasscrystal size. The same ranking is obtained from delta-beta (measuredin X-ray precession photos) of pigeonite and augite exsolvedfrom once homogeneous crystals, or of epitaxially overgrownaugite and pigeonite. The size of the phenocrysts in these rocks tends to be positivelycorrelated with the coarseness of the groundmass. Furthermorethe same correlation is evidently present in almost all otherApollo 12 and Apollo 15 pyroxene-phyric rocks. This constitutesa strong argument in favor of a single-stage cooling historyfor all pyroxene-phyric rocks, because the correlation wouldbe fortuitous for a two-stage cooling history. On the basisof this and many other arguments advanced previously and inthis paper, it is concluded that all the pyroxene-phyric rocksoriginated in a single-stage cooling process. A crystallization model for pyroxene-phyric rocks accounts forthe bimodal distribution of crystal size by two episodes ofsupercooling and nucleation during the continuous cooling process,the first of pyroxene, which nucleates homogeneously, the secondof plagioclase, which nucleates heterogeneously on the pyroxenephenocrysts. The more rapidly cooled rocks attained greaterdegrees of supercooling in both stages, hence greater nucleationrates and smaller crystals.     

Emplacement of the Cleveland Dyke: Evidence from Geochemistry, Mineralogy, and Physical Modelling

The igneous rocks of the British Tertiary Volcanic Province(BTVP) comprise intrusive central complexes and associated lavafields in northwest Scotland and northern Ireland. These centresare associated with linear dyke swarms which are radial aroundthe major central complexes. The most extensive dyke swarm isrelated to the Mull intrusive complex and includes the Clevelanddyke, which appears to extend some 430 km from Mull throughthe Scottish Midland Valley (SMV) to the coast of northeastEngland. The dyke may have been emplaced by lateral magma migrationfrom Mull, by vertical magma migration, or by a combinationof these processes associated with the emplacement of the Mullcentre and the presence of a regional stress field in northernBritain. Petrographic, mineralogical, and geochemical data for samplescollected across and along the Cleveland dyke have been usedto evaluate its petrogenesis and emplacement mechanism. Thesegment of the dyke north of, and along, the Southern UplandsFault, the southern boundary of the SMV, is not comagmatic withthat to the south, which is now defined as the Cleveland dykesensu stricto. The Cleveland dyke is an olivine-free, plagioclase-and pyroxene-phyric basaltic andesite. Plagioclase mineralogyand bulk composition indicate that it experienced a complexmagmatic history involving polybaric fractional crystallizationand minor crustal contamination. Despite this complex evolution,the dyke magma is relatively homogeneous and shows chemicalcharacteristics closely similar to tholeiitic rocks from Mull.The data substantiate lateral emplacement from this BVTP centre,rather than by vertical emplacement through heterogeneous lithosphere. Numerical modelling of dyke dynamics is consistent with emplacementof the Cleveland dyke as a single pulse of magma from the Mullcentre, flowing in a manner transitional between laminar andturbulent conditions. According to this model, the dyke (volumec. 85 km³ was initiated in a large magma chamber below Mullsubject to a small excess magmatic pressure. Lateral migrationat relatively high velocity (1–5 ms^–1) caused emplacementof the dyke in 1–5 days. Following emplacement, minorvertical ascent of magma may have contributed to the local enechelon distribution of dyke segments.     

A regionalized IO-model to value seasonal recreational ecosystem services in a mountain National Park in Spain

Recreational Ecosystem Services (RES) are among the most frequently evaluated ecosystem services.RES are seen as a major opportunity for sustainable development...     

Traçage chimique et isotopique (Cl−, 18O) d'une crue d'automne sur un petit bassin versant Méditerranéen incendié

Résumé

A la suite des incendies qui ont ravagé le massif des Maures au cours de l'été 1990, le petit bassin du Rimbaud (bassin versant du Réal Collobrier) a vu son comportement hydrologique fortement modifié. Parallèlement au suivi hydrologique et hydrochimique habituel, les isotopes stables ont été mesurés sur les précipitations et l'écoulement. La disparition de la végétation et donc de son influence sur les pluviolessivats nous a incité à comparer l'évolution respective des teneurs en oxygène 18 et en chlorure. Au cours de la crue du 9 décembre 1990, ces deux éléments présentent un comportement très similaire et, fait original, les décompositions d'hydrogramme qu'ils permettent d'établir sont comparables. En considérant les facteurs habituels d'évolution des chlorures et de l'oxygène 18, il apparaît qu'une proportion de l'ordre de 45% d'eau “ancienne” participe aux écoulements de crue et que la zone non saturée ne joue dans ce cas précis aucun rôle significatif. En outre, en s'appuyant sur l'évolution des températures de l'eau qui révèle l'arrêt du ruissellement, la quantité d'eau qui rejoint le réservoir souterrain peut être estimée à au moins 30%.