Quasi-conservative behaviour of Be in deep waters of the Weddell Sea and the Atlantic sector of the Antarctic Circumpolar Current

We present the first transect of dissolved ¹⁰Be depth profiles across the Antarctic Circumpolar Current (ACC) in the Atlantic sector. North of the Polar Front the ¹⁰Be concentrations increase continuously from very low values at the surface to values of up to 1600 atoms/g at depth. Deep water ¹⁰Be concentrations of particular water masses are consistent with earlier results obtained further north. South of the Polar Front and in the Weddell Sea the distribution of ¹⁰Be is also characterised by low surface concentrations but below 1000 m depth the concentrations are relatively constant and significantly higher (up to 2000 atoms/g) than further north, probably as a result of mixing and advection of water masses of Pacific origin. Overall the deep water ¹⁰Be distribution is obviously not significantly affected by scavenging processes or ice melt and comparison with the density distribution suggests that ¹⁰Be can be viewed as a quasi-conservative tracer. This provides a tool for an improved understanding of the behaviour of other more particle reactive trace metals in the Southern Ocean such as ²³⁰Th: in deep waters north of the ACC/Weddell Gyre boundary (AWB) ¹⁰Be/²³⁰Th has a relatively constant value (1.7±0.3×10⁹ atoms/dpm) over a wide density range whereas south of the AWB the ratio is significantly lower (1.1±0.2×10⁹ atoms/dpm). This normalisation to ¹⁰Be corroborates that ²³⁰Th is enriched by 50% due to accumulation south of the AWB as a consequence of minimal particulate fluxes. The quasi-conservative behaviour deduced from our results also implies that ¹⁰Be can only be used as a tracer for Southern Ocean particle fluxes in the past if ocean circulation patterns and water mass residence times did not change significantly.     

Arc-seamount collision: driver for vertical-axis rotations in Azuero,Panama

We present new paleomagnetic data of 25 sites (240 specimens) along the southwestern part of the Azuero Peninsula, Panama. The data show two paleomagnetic domains in the peninsula: a northern domain featuring uniformly large vertical-axis clockwise rotation values of 73.4 ± 12° across to Azuero Soná Fault Zone with a single mean direction with declination of 81.2° and inclination of -3.2° (95% confidence of 11.7° and precision parameter of 18.09), and a scattered paleomagnetic domain to the south. These contrasting domains could be attributed to the collision of fartravelled/ allochthonous seamounts that approached the Panama arc as subduction of the Farallon plate brought them to the margin. As consequence of this collision the fartravelled seamounts were fragmented and scattered along the margin while the Panama arc rotated into the colliding seamounts. These new paleomagnetic data suggest that the Campanian-Eocene arc segment in the Azuero Peninsula was originally oriented NE-SW, implying an original curvature for this part of the arc.     

Spatiotemporal variability of vegetation due to drought dynamics (2012–2017): a case study of the Upper Paraíba River basin,Brazil

Natural Hazards - Vegetation indices have been widely used for monitoring the spatiotemporal variables of vegetation and characterizing droughts, primarily in semiarid regions. Drought is a...     

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.     

黄龙与黄石钙华微生物沉积作用比较研究

本文通过调查黄龙风景区水体的环境地质特征与微生物群落结构及多样性,并与黄石公园对比分析,探讨了两种特殊地理环境下的微生物群落结构和多样性及其对钙华沉积的影响.结果表明:黄龙沟泉水属于地下冷泉,且景区内覆盖着大量植被,水体中有大量藻类和细菌;黄石公园猛犸象温泉区泉水属于地下热泉,植被覆盖率很低,泉水中微生物多为嗜热菌,藻...     

Acceleration waves,shock formation and stability in a gravitating atmosphere

The shock formation in a gravitating atmosphere is studied by following the general nonlinear theory of discontinuity waves. In particular, we perform a discussion on the stability of an isothermal and isoentropic atmosphere and we evaluate, when the shock appears, the critical time and the critical height. Some numerical results for the solar and terrestrial atmospheres are also given.     

Multi-model calibration and combination of tropical seasonal sea surface temperature forecasts

Different combination methods based on multiple linear regression are explored to identify the conditions that lead to an improvement of seasonal forecast quality when individual operational dynamical systems and a statistical–empirical system are combined. A calibration of the post-processed output is included. The combination methods have been used to merge the ECMWF System 4, the NCEP CFSv2, the Météo-France System 3, and a simple statistical model based on SST lagged regression. The forecast quality was assessed from a deterministic and probabilistic point of view. SSTs averaged over three different tropical regions have been considered: the Niño3.4, the Subtropical Northern Atlantic and Western Tropical Indian SST indices. The forecast quality of these combinations is compared to the forecast quality of a simple multi-model (SMM) where all single models are equally weighted. The results show a large range of behaviours depending on the start date, target month and the index considered. Outperforming the SMM predictions is a difficult task for linear combination methods with the samples currently available in an operational context. The difficulty in the robust estimation of the weights due to the small samples available is one of the reasons that limit the potential benefit of the combination methods that assign unequal weights. However, these combination methods showed the capability to improve the forecast reliability and accuracy in a large proportion of cases. For example, the Forecast Assimilation method proved to be competitive against the SMM while the other combination methods outperformed the SMM when only a small number of forecast systems have skill. Therefore, the weighting does not outperform the SMM when the SMM is very skilful, but it reduces the risk of low skill situations that are found when several single forecast systems have a low skill.     

Magnetostratigraphy and paleomagnetism of early and middle Miocene synorogenic strata: basement partitioning and minor block rotation in Argentine broken foreland

Magnetostratigraphic and paleomagnetic studies on early Andean synorogenic strata (Del Crestón Fm.), in the Famatina Belt (28.7°S, 67.5°W) clarify details of chronology that permit calculation of sedimentation rates within the broken foreland of west Argentina. The Del Crestón Fm represents the first record of broken foreland sedimentation within the southern Central Andean belt and the earliest retroarc volcanic rocks exposed several hundred kilometers from the trench. Twenty-five out of 49 sites collected along the succession presented a primary remanence, as determined through positive fold and reversal tests. Correlation of the local magnetic polarity section with the global polarity time scale indicates that the sedimentation of Del Crestón Fm started at ~16.7 Ma and continued until ~14.5 Ma. The youngest strata are represented by conglomerates bearing abundant Lower Paleozoic granite boulders indicating unroofing of the crystalline basement within the NW Sierras Pampeanas. This result supports the hypothesis of an early broken foreland stage at these latitudes of the Andes, with involvement of the basement in deformation and coeval retroarc volcanism, common attributes of flat-subduction regimes. A mean site paleomagnetic direction of Dec: 6.3°, Inc: ?43.6° (α95: 8.0°, N = 24) confirm our earlier intrepretation that the central part of the Famatina Belt within the Sierras Pampeanas did not undergo large vertical axes rotations since the Middle Miocene.     

Contributions to the kinematics of type I tails of comets

Observed irregular oscillations of the ion tail axis in comets have by some authors been brought in connection with changes in the flow conditions in the solar wind. We are defending in this paper — by arguments resting on well known observations — the conception that these oscillations are caused by slight variations in the emission conditions for the ions at their source which has always its place close to the cometary nucleus. A complete renovation of the innermost tail part up to a length of a few million km (called by Hoffmeister the primary tail) and defining the tail axis can take place within a few to several hours. Shifts of this axis are becoming visible when the new tail rays finish their closure along another direction than the earlier ones.The not so rarely observed jumps in the direction of the primary tail lead in connection with the large time scale — of about 24h — for a complete closure of a ray system from an individual ion out-break to the conclusion that we should expect occasionally the existence of two (or even more) different axis to which tail rays make their closure. Some photographs of Comet Bennett 1969i seem to show such double axis.