《自然》（20190926出版）一周论文导读

编译 | 唐一尘

Nature，26 September 2019，Volume 573 Issue7777

《自然》 2019年9月26日，第573卷7775期

海洋学Oceanography

Deep learning for multi-year ENSO forecasts

深度学习协助ENSO预测

作者：Yoo-Geun Ham、Jeong-Hwan Kim、Jing-Jia Luo

链接：

摘要：

厄尔尼诺-南方涛动（ENSO）不仅经常引起全球范围气候的显著异常变化，还深刻影响我国气候，因此在短期气候预测中被视为重要的影响因素。尽管经过几十年的努力，提前一年以上进行ENSO事件预测仍是一个很大的挑战。

本研究利用深度学习方法构建了卷积神经网络模型（CNN），该模型可以将ENSO预测时效提前到一年半，并达到80%左右的预测准确率。

研究结果显示，在预测时效超过6个月时，CNN模型对Nino3.4指数的预测能力高于目前国际上最优秀的动力预测系统，并且在预测时效为17个月时，相关系数预测技巧仍在0.5以上。

同时CNN模型还能预测海表温度异常的不同空间分布，对不同厄尔尼诺类型（东太平洋型、中太平洋型、混合型）预测也有较高的正确率，弥补了目前动力预测系统的不足。

Abstract

Variations in the El Niño/Southern Oscillation (ENSO) are associated with a wide array of regional climate extremes and ecosystem impacts. Robust, long-lead forecasts would therefore be valuable for managing policy responses. But despite decades of effort, forecasting ENSO events at lead times of more than one year remains problematic. Here we show that a statistical forecast model employing a deep-learning approach produces skilful ENSO forecasts for lead times of up to one and a half years. To circumvent the limited amount of observation data, we use transfer learning to train a convolutional neural network (CNN) first on historical simulations and subsequently on reanalysis from 1871 to 1973. During the validation period from 1984 to 2017, the all-season correlation skill of the Nino3.4 index of the CNN model is much higher than those of current state-of-the-art dynamical forecast systems. The CNN model is also better at predicting the detailed zonal distribution of sea surface temperatures, overcoming a weakness of dynamical forecast models. A heat map analysis indicates that the CNN model predicts ENSO events using physically reasonable precursors. The CNN model is thus a powerful tool for both the prediction of ENSO events and for the analysis of their associated complex mechanisms.

化学Chemistry

A 16-step synthesis of the isoryanodane diterpene (+)-perseanol

异柳烷二萜(+)-perseanol的16步合成

作者：Arthur Han、Yujia Tao、Sarah E. Reisman，et al.

链接：

摘要：

(+)-Perseanol是从热带灌木印度鳄梨中分离得到的一种异柳烷二萜，具有较强的抗饲性和杀虫性。

它在结构上与(+)-ryanodine有关，(+)-ryanodine是利阿诺定受体，该配体门控离子通道是大多数多细胞生物细胞内Ca2+信号传递的关键。

在这里，研究报告了(+)-perseanol的化学合成，利用商业上可用的(R)—长叶薄荷酮进行16步。

合成过程包括一个两步的环化过程，该过程从易接近的环戊基构建块快速组装出四环核。

这项工作演示了聚合片段如何耦合，当结合氧化策略，可以使复杂和高氧化二萜天然产物简洁合成。

Abstract

(+)-Perseanol is an isoryanodane diterpene that is isolated from the tropical shrub Persea indica and has potent antifeedant and insecticidal properties. It is structurally related to (+)-ryanodine, which is a high-affinity ligand for and modulator of ryanodine receptors—ligand-gated ion channels that are critical for intracellular Ca²⁺ signalling in most multicellular organisms. Ryanodine itself modulates ryanodine-receptor-dependent Ca²⁺ release in many organisms, including mammals; however, preliminary data indicate that ryanodane and isoryanodane congeners that lack the pyrrole-2-carboxylate ester—such as perseanol—may have selective activity in insects. Here we report a chemical synthesis of (+)-perseanol, which proceeds in 16 steps from commercially available (R)-pulegone. The synthesis involves a two-step annulation process that rapidly assembles the tetracyclic core from readily accessible cyclopentyl building blocks. This work demonstrates how convergent fragment coupling, when combined with strategic oxidation tactics, can enable the concise synthesis of complex and highly oxidized diterpene natural products.

地理与水科学

Geographical and water Sciences

Wilderness areas halve the extinction risk of terrestrial biodiversity

荒野地区将陆地生物多样性灭绝风险减半

作者：Moreno Di Marco、Simon Ferrier、Tom D. Harwood，et al.

链接：

摘要：

未开发的土地，包括公园、荒野地区和国家森林，是濒危或受威胁物种的关键避难所。但科学家并没有证据支持这一说法。

本研究发现，如果目前的全球栖息地退化趋势继续下去，栖息在野外的维管植物和无脊椎动物——从野花到蜜蜂——存活的可能性是栖息在非荒野地区的同类的两倍。

研究人员首先将地球表面划分成数百万个1平方公里的网格。除南极洲外，受保护或未受保护的荒野约占20%，其余的是受人类活动影响更严重的土地。

然后，研究人员增添了已知的40万种植物和无脊椎动物的栖息范围，并估计了每种物种的灭绝风险。

结果显示，在未来几十年里，那些生活在荒野地区的物种只有2.1%的几率灭绝，而那些生活在非荒野地区的物种有5.6%的几率灭绝。

这一发现表明，野地确实起到了防止物种灭绝的缓冲作用。

Abstract

Reducing the rate of global biodiversity loss is a major challenge facing humanity, as the consequences of biological annihilation would be irreversible for humankind. Although the ongoing degradation of ecosystems and the extinction of species that comprise them are now well-documented, little is known about the role that remaining wilderness areas have in mitigating the global biodiversity crisis. Here we model the persistence probability of biodiversity, combining habitat condition with spatial variation in species composition, to show that retaining these remaining wilderness areas is essential for the international conservation agenda. Wilderness areas act as a buffer against species loss, as the extinction risk for species within wilderness communities is—on average—less than half that of species in non-wilderness communities. Although all wilderness areas have an intrinsic conservation value, we identify the areas on every continent that make the highest relative contribution to the persistence of biodiversity. Alarmingly, these areas—in which habitat loss would have a more-marked effect on biodiversity—are poorly protected. Given globally high rates of wilderness loss, these areas urgently require targeted protection to ensure the long-term persistence of biodiversity, alongside efforts to protect and restore more-degraded environments.

Aridity is expressed in river topography globally

全球河流地形的干旱表达

作者：Shiuan-An Chen、Katerina Michaelides、Stuart W. D. Grieve、Michael Bliss Singer

链接：

摘要：

长期以来，人们认为气候通过降雨、径流和流域侵蚀之间的相互作用塑造地表地形。

河流纵剖面是反映流域演化历史的重要形态属性，其形态能判断气候区域表达及其与地表相互作用。

然而，由于缺乏全球数据以及构造、岩性、地表性质和人类活动影响等信息，相关研究面临挑战。

在这里，研究人员提供了一个333502条河流纵剖面的全球数据集，并使用它来探索整个剖面形状在气候区之间的差异。

结果表明，随着干旱程度的增加，河流剖面系统地变直。其中最重要的是不受流域面积影响的下游水流变化率。

研究结果表明，河流地形表现出干旱特征，表明气候是流域演化的一级控制因子。

Abstract

It has long been suggested that climate shapes land surface topography through interactions between rainfall, runoff and erosion in drainage basins. The longitudinal profile of a river (elevation versus distance downstream) is a key morphological attribute that reflects the history of drainage basin evolution, so its form should be diagnostic of the regional expression of climate and its interaction with the land surface. However, both detecting climatic signatures in longitudinal profiles and deciphering the climatic mechanisms of their development have been challenging, owing to the lack of relevant global data and to the variable effects of tectonics, lithology, land surface properties and human activities. Here we present a global dataset of 333,502 river longitudinal profiles, and use it to explore differences in overall profile shape (concavity) across climate zones. We show that river profiles are systematically straighter with increasing aridity. Through simple numerical modelling, we demonstrate that these global patterns in longitudinal profile shape can be explained by hydrological controls that reflect rainfall–runoff regimes in different climate zones. The most important of these is the downstream rate of change in streamflow, independent of the area of the drainage basin. Our results illustrate that river topography expresses a signature of aridity, suggesting that climate is a first-order control on the evolution of the drainage basin.

古生物学/地球科学

Palaeobiology/ Earth Sciences

A middle Cambrian arthropod with chelicerae and proto-book gills

中寒武纪节肢动物有螯状肢和原始鳃

作者：Cédric Aria、Jean-Bernard Caron

链接：

摘要：

螯肢动物是包括蝎子、蜘蛛、蜱螨和鲎等在内的庞大节肢动物类群，但科学家对于寒武纪大爆发期间该类群动物是否已经起源一直不是很清楚。

这里，研究人员在寒武纪中期布尔吉斯页岩动物群中发现了一种莫里森虫新物种，代表了目前已知最古老的螯肢类节肢动物。这项研究将包括螯肢动物的起源时间提前到了5亿年前。

莫里森虫在其口部前方发育有一对小型的钳状附肢，称为螯肢。这对典型的附肢使得节肢动物能够击杀、夹持和切碎猎物，并以此命名这类节肢动物为螯肢动物。

此外，莫里森虫身体后部的附肢上具有3片鳃一样的构造，这和螯肢类身体后部成对的特化呼吸器官“书鳃”或“书肺”相似。这进一步表明莫里森虫尽管是原始的螯肢类。

Abstract

The chelicerates are a ubiquitous and speciose group of animals that has a considerable ecological effect on modern terrestrial ecosystems—notably as predators of insects and also, for instance, as decomposers. The fossil record shows that chelicerates diversified early in the marine ecosystems of the Palaeozoic era, by at least the Ordovician period. However, the timing of chelicerate origins and the type of body plan that characterized the earliest members of this group have remained controversial. Although megacheirans have previously been interpreted as chelicerate-like, and habeliidans (including Sanctacaris) have been suggested to belong to their immediate stem lineage, evidence for the specialized feeding appendages (chelicerae) that are diagnostic of the chelicerates has been lacking. Here we use exceptionally well-preserved and abundant fossil material from the middle Cambrian Burgess Shale (Marble Canyon, British Columbia, Canada) to show that Mollisonia plenovenatrix sp. nov. possessed robust but short chelicerae that were placed very anteriorly, between the eyes. This suggests that chelicerae evolved a specialized feeding function early on, possibly as a modification of short antennules. The head also encompasses a pair of large compound eyes, followed by three pairs of long, uniramous walking legs and three pairs of stout, gnathobasic masticatory appendages; this configuration links habeliidans with euchelicerates (‘true’ chelicerates, excluding the sea spiders). The trunk ends in a four-segmented pygidium and bears eleven pairs of identical limbs, each of which is composed of three broad lamellate exopod flaps, and endopods are either reduced or absent. These overlapping exopod flaps resemble euchelicerate book gills, although they lack the diagnostic operculum. In addition, the eyes of M. plenovenatrix were innervated by three optic neuropils, which strengthens the view that a complex malacostracan-like visual system might have been plesiomorphic for all crown euarthropods. These fossils thus show that chelicerates arose alongside mandibulates as benthic micropredators, at the heart of the Cambrian explosion.

Kimberlites reveal 2.5-billion-year evolution of a deep, isolated mantle reservoir

金伯利岩揭示了一个深部孤立地幔储集层25亿年的演化过程

作者：Jon Woodhead、Janet Hergt、Andrea Giuliani，et al.

链接：

摘要：

地球地球化学演化的普遍范式认为，在过去45亿年里，地幔熔融物的连续提取形成了大陆地壳，并产生了至少一个储集层，该储集层现在被认为是大洋中脊玄武岩的上地幔源。

然而，地球化学模型和一些火山岩中高 ³He/⁴He 特征表明，相对未分化的地幔体积可能存在于更深的孤立区域。

金伯利岩是一种体积小的火山岩，是大多数钻石的来源。金伯利岩提供了对地球深层地幔组成方面的罕见洞见。

在这里，研究人员发现，全球分布的金伯利岩源自单一均质储集层的同位素组成表明一个统一的和原始地幔来源，并有25亿多年的进化史，这也是迄今为止唯一已被确认的储集层。

大约2亿年前，同一来源的大量物质受到扰动，这可能是外来物质污染的结果。

受影响金伯利岩的分布表明，这一事件可能与泛大陆超大陆边缘的俯冲有关。相关结果揭示了一个长期存在的、范围广泛的地幔储集层的历史演化。

Abstract

The widely accepted paradigm of Earth's geochemical evolution states that the successive extraction of melts from the mantle over the past 4.5 billion years formed the continental crust, and produced at least one complementary melt-depleted reservoir that is now recognized as the upper-mantle source of mid-ocean-ridge basalts. However, geochemical modelling and the occurrence of high ³He/⁴He (that is, primordial) signatures in some volcanic rocks suggest that volumes of relatively undifferentiated mantle may reside in deeper, isolated regions. Some basalts from large igneous provinces may provide temporally restricted glimpses of the most primitive parts of the mantle, but key questions regarding the longevity of such sources on planetary timescales—and whether any survive today—remain unresolved. Kimberlites, small-volume volcanic rocks that are the source of most diamonds, offer rare insights into aspects of the composition of the Earth’s deep mantle. The radiogenic isotope ratios of kimberlites of different ages enable us to map the evolution of this domain through we show that globally distributed kimberlites originate from a single homogeneous reservoir with an isotopic composition that is indicative of a uniform and pristine mantle source, which evolved in isolation over at least 2.5 billion years of Earth history—to our knowledge, the only such reservoir that has been identified to date. Around 200 million years ago, extensive volumes of the same source were perturbed, probably as a result of contamination by exogenic material. The distribution of affected kimberlites suggests that this event may be related to subduction along the margin of the Pangaea supercontinent. These results reveal a long-lived and globally extensive mantle reservoir that underwent subsequent disruption, possibly heralding a marked change to large-scale mantle-mixing regimes. These processes may explain why uncontaminated primordial mantle is so difficult to identify in recent mantle-derived melts.

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