自然（20230316出版）一周论文导读

　　编译｜李言
　　Nature , 16 March 2023, Volume 615 Issue 7952
　　《自然》 ，2023年3月16日，第615卷，7952期
　　材料科学 Material science
　　Photonically active bowtie nanoassemblies with chirality continuum
　　具有手性连续体的光子活性领结形纳米组件
　　▲ 作者：Prashant Kumar, Thi Vo, Minjeong Cha et al.
　　▲ 链接：
　　https://www.nature.com/articles/s41586-023-05733-1
　　▲ 摘要：
　　在此，我们展示了具有各向异性领结形状的纳米结构微粒可展示手性连续体，并且可以调整其角度、间距、宽度、厚度和长度。领结形的自限制组装使其在不同条件下呈现的几何形状具有较高的合成再现性、尺寸单分散性和计算可预测性。
　　领结形纳米组件在吸收和散射现象下，显示出一些强圆二色性峰。与经典的手性分子不同，这些粒子表现出连续的手性测量，与圆二色性峰的光谱位置呈指数相关。
　　具有可变极化旋转的领结形粒子可打印具有光谱可调正负极化特征的光子活性超表面，用于激光探测及测距设备。
　　▲ Abstract：
　　Here we show that nanostructured microparticles with an anisotropic bowtie shape display chirality continuum and can be made with widely tuneable twist angle, pitch, width, thickness and length. The self-limited assembly of the bowties enables high synthetic reproducibility, size monodispersity and computational predictability of their geometries for different assembly conditions. The bowtie nanoassemblies show several strong circular dichroism peaks originating from absorptive and scattering phenomena. Unlike classical chiral molecules, these particles show a continuum of chirality measures that correlate exponentially with the spectral positions of the circular dichroism peaks. Bowtie particles with variable polarization rotation were used to print photonically active metasurfaces with spectrally tuneable positive or negative polarization signatures for light detection and ranging (LIDAR) devices.
　　化学 Chemistry
　　Control of stereogenic oxygen in a helically chiral oxonium ion
　　螺旋手性氧鎓离子中立体异构氧的控制
　　▲ 作者：Owen Smith, Mihai V. Popescu, Madeleine J. Hindson et al.
　　▲ 链接：
　　https://www.nature.com/articles/s41586-023-05719-z
　　▲ 摘要：
　　在此，我们描述了一个螺旋手性三芳氧鎓离子的设计、合成和表征，通过几何限制可防止氧孤对的转化，使其能够作为构型的行列式发挥作用。
　　我们使用组合合成和量子计算的方法标明其设计原则，使结构稳定和室温隔离盐能够产生。据我们所知，这构成了手性非外消旋和构型稳定的分子中氧原子是单一立体异构中心的唯一案例。
　　▲ Abstract：
　　Here we describe the design, synthesis and characterization of a helically chiral triaryloxonium ion in which inversion of the oxygen lone pair is prevented through geometric restriction to enable it to function as a determinant of configuration. A combined synthesis and quantum calculation approach delineates design principles that enable configurationally stable and room-temperature isolable salts to be generated. We show that the barrier to inversion is greater than 110?kJ?mol?1 and outline processes for resolution. This constitutes, to our knowledge, the only example of a chiral non-racemic and configurationally stable molecule in which the oxygen atom is the sole stereogenic centre.
　　地理学 Geography
　　The carbon sink of secondary and degraded humid tropical forests
　　次生和退化的潮湿热带森林碳汇
　　▲ 作者：Viola H. A. Heinrich, Christelle Vancutsem, Ricardo Dalagnol et al.
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05679-w
　　▲ 摘要：
　　在此，我们量化了三个主要热带湿润地区（亚马逊、婆罗洲和中非）中正在恢复的森林地上碳汇。在卫星数据的基础上，我们的分析涵盖了退化森林和次生林受关键环境和人为驱动因素影响的异质时空生长模式。在森林恢复期的头20年里，婆罗洲的再生率分别比中非和亚马逊高出45%和58%。
　　这是由于温度、水分亏缺和扰动等变量造成的。我们发现，在1984年至2018年期间，再生退化森林和次生林累积了107百万吨每年，抵消了潮湿热带森林在同期损失的碳排放的26%。
　　因此，保护原始森林是优先要务。此外，我们估计在主要热带地区，保护正在恢复的退化森林和次生林未来的碳汇潜力可能为53百万吨每年。
　　▲ Abstract：
　　Here we quantify the aboveground carbon (AGC) sink of recovering forests across three main continuous tropical humid regions: the Amazon, Borneo and Central Africa. On the basis of satellite data products, our analysis encompasses the heterogeneous spatial and temporal patterns of growth in degraded and secondary forests, influenced by key environmental and anthropogenic drivers. In the first 20?years of recovery, regrowth rates in Borneo were up to 45% and 58% higher than in Central Africa and the Amazon, respectively. This is due to variables such as temperature, water deficit and disturbance regimes. We find that regrowing degraded and secondary forests accumulated 107Tg C year−1(90–130 Tg C year−1) between 1984 and 2018, counterbalancing 26% (21–34%) of carbon emissions from humid tropical forest loss during the same period. Protecting old-growth forests is therefore a priority. Furthermore, we estimate that conserving recovering degraded and secondary forests can have a feasible future carbon sink potential of 53 Tg C year−1(44–62 Tg C year−1) across the main tropical regions studied.
　　Regime shift in Arctic Ocean sea ice thickness
　　北冰洋海冰厚度的变化
　　▲ 作者：Hiroshi Sumata, Laura de Steur, Dmitry V. Divine, Mats A. Granskog & Sebastian Gerland
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05686-x
　　▲ 摘要：
　　在此，我们展示了北极海冰冰盖在2007年从更厚和形态不规则到更薄和形态更一致的变化。过去三十年来，在弗拉姆海峡持续进行的海冰监测揭示了这种变化。
　　变化之后，厚冰和不规则冰的比例下降了一半，至今仍未恢复。在这一转变之前，北极盆地海冰留存时间曾有两次缩短，第一次始于2005年，第二次是2007年。
　　我们证明了一个描述动态海冰增厚随机过程的简单模型解释了由于留存时间减少而观测到的冰盖厚度变化。我们的研究强调了，在冰盖留存时间减少的情况下，气候变化对北极海冰的长期影响，以及它与相邻边缘海和大陆架中海洋-海冰耦合过程的联系。
　　▲ Abstract：
　　Here we show that the Arctic sea ice regime shifted in 2007 from thicker and deformed to thinner and more uniform ice cover. Continuous sea ice monitoring in the Fram Strait over the last three decades revealed the shift. After the shift, the fraction of thick and deformed ice dropped by half and has not recovered to date. The timing of the shift was preceded by a two-step reduction in residence time of sea ice in the Arctic Basin, initiated first in 2005 and followed by 2007. We demonstrate that a simple model describing the stochastic process of dynamic sea ice thickening explains the observed ice thickness changes as a result of the reduced residence time. Our study highlights the long-lasting impact of climate change on the Arctic sea ice through reduced residence time and its connection to the coupled ocean–sea ice processes in the adjacent marginal seas and shelves of the Arctic Ocean.
　　地质学 Geology
　　Deep, ultra-hot-melting residues as cradles of mantle diamond
　　深层超热熔残体是地幔金刚石的摇篮
　　▲ 作者：Carl Walsh, Balz S. Kamber & Emma L. Tomlinson
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05690-1
　　▲ 摘要：
　　在此，我们展示了在足够高的温度下熔化产生克拉通根的镁质橄榄石的热力学和地球化学模拟的结果。通过极深（约200公里）和极高温热熔（≥1800°C）消除了浅层熔化和堆积的需要，新的封闭系统和开放系统模型再现了观测到的克拉通地幔矿物组成。
　　就像在克拉通化石表面的绿岩带中观察到的那样，模拟中的富镁液体（科马提岩）发展成富铝和缺少钛的形式。缺钛的科马提岩意味着先进封闭系统等化学熔化（1825°C）远不如深层液体和现有难熔地幔之间的开放系统相互作用常见。
　　▲ Abstract：
　　Here we present results from thermodynamic and geochemical modelling of melting at sufficiently high temperatures to produce the very magnesian olivine of cratonic roots. The new closed-system and open-system modelling reproduces the observed cratonic mantle mineral compositions by deep (about 200?km) and very hot melting (≥1,800°C), obviating the need for shallow melting and stacking. The modelled highly magnesian liquids (komatiites) evolve to Al-enriched and Ti-depleted forms, as observed in the greenstone belts at the fossil surface of cratons. The paucity of Ti-depleted komatiite implies that advanced closed-system isochemical melting (>1,825°C) was much less common than open-system interaction between deeper liquids and melting of existing refractory mantle.
　　Weak upper-mantle base revealed by postseismic deformation of a deep earthquake
　　深源地震后形变所揭示的上地幔基底薄弱
　　▲ 作者：Sunyoung Park, Jean-Philippe Avouac, Zhongwen Zhan & Adriano Gualandi
　　▲ 链接：
　　https://www.nature.com/articles/s41586-022-05689-8
　　▲ 摘要：
　　在此，我们利用位于上地幔底部附近的深源地震（约560 km）导致的震后变形来研究地幔粘度结构。我们成功地探测和了解了2018年斐济8.2级地震引起的震后变形情况。为了寻找可以解释检测到的信号的粘度结构，我们使用一系列粘度结构进行正向粘弹性松弛建模。
　　我们发现，我们的观测需要在地幔过渡带底部有一个相对较薄（约100 km）、低粘性（1017 到1018 Pa s）的层。这样的弱带可以解释在许多俯冲带中观察到的平板扁平化和孤立现象，这些很难放到整个地幔对流体系中去研究。低粘性层可能是尖晶石后转变、弱硅酸钙矿、高含水量或脱水熔融诱导的超塑性形成的结果。
　　▲ Abstract：
　　Here, we study the mantle viscosity structure by using the postseismic deformation following a deep (approximately 560 km) earthquake located near the bottom of the upper mantle. We apply independent component analysis to geodetic time series to successfully detect and extract the postseismic deformation induced by the moment magnitude 8.2, 2018 Fiji earthquake. To search for the viscosity structure that can explain the detected signal, we perform forward viscoelastic relaxation modelling with a range of viscosity structures. We find that our observation requires a relatively thin (approximately 100 km), low-viscosity (1017to 1018Pa s) layer at the bottom of the mantle transition zone. Such a weak zone could explain the slab flattening and orphaning observed in numerous subduction zones, which are otherwise challenging to explain in the whole mantle convection regime. The low-viscosity layer may result from superplasticity induced by the postspinel transition, weak CaSiO3 perovskite, high water content or dehydration melting.