【地球科学】论文精选集：利用耐旱植物节水对气候的影响，气候模型中的冰山 等

亮点：洋中脊为何表现出分段性；海冰在南大洋浅层海水翻转中扮演何种角色；气候模型是否应考虑冰山大小；圣安德列斯断层震间垂直运动是否可预测；采用耐旱植物节水对气候有何影响

精选 & 翻译 刘小鸥

审校 吴倩

地球动力学

《自然-地球物理》

Segmentation of mid-ocean ridges attributed to oblique mantle divergence

洋中脊分段是偏斜的地幔离散所致

（图片来源：http://www.nature.com/ngeo/journal/v9/n8/abs/ngeo2745.html）                            

地幔离散与板块扩张方向具有系统性偏斜；

产生的构造不连续面决定了岩浆运动中段落尺度的差异；

分段受到软流圈流动中演化模式与岩石圈张裂作用动力学的控制。

B. P. VanderBeek, D. R.Toomey, E. E. E. Hooft & W. S. D. Wilcock

http://www.nature.com/ngeo/journal/v9/n8/abs/ngeo2745.html

The origin of mid-ocean ridge segmentation—the systematic along-axis variation intectonic and magmatic processes—remains controversial. It is commonly assumed that mantle flow is a passive response to plate divergence and that between transform faults magma supply controls segmentation. Using seismic tomography, we constrain the geometry of mantle flow and the distribution of mantle melt beneath the intermediate-spreading Endeavour segment of the Juan de Fuca Ridge.Our results, in combination with prior studies, establish a systematic skew between the mantle-divergence and plate-spreading directions. In all three cases studied, mantle divergence is advanced with respect to recent changes in the plate-spreading direction and the extent to which the flow field is advanced increases with decreasing spreading rate. Furthermore, seismic images show that large-offset, non-transform discontinuities are regions of enhancedmantle melt retention. We propose that oblique mantle flow beneath mid-oceanridges is a driving force for the reorientation of spreading segments and theformation of ridge-axis discontinuities. The resulting tectonic discontinuities decrease the efficiency of upward melt transport, thus defining segment-scalevariations in magmatic processes. We predict that across spreading ratesmid-ocean ridge segmentation is controlled by evolving patterns inasthenospheric flow and the dynamics of lithospheric rifting.

洋中脊分段是指构造运动与岩浆运动中的系统性轴向差异，其来源仍然具有争议。通常假设，地幔流动是板块离散的被动反应，转换断层间的岩浆补给控制着洋中脊的分段。我们运用地震层析成像，限制了以中速扩张的胡安德富卡洋脊（Juan de Fuca Ridge）因代沃（Endeavour）段之下地幔流动的几何结构与分布。结合先前的研究，我们的结果建立了地幔离散与板块扩张方向间的系统性偏斜。在三个研究案例中，地幔离散先于近期板块扩张方向改变，而流场的提前程度随着扩张速率降低而增加。除此之外，地震图像表明，大断错距非转换不连续面是增强的地幔融化滞留的区域。我们提出，洋中脊下偏斜的地幔流动是扩张段重定向与洋脊轴部不连续面形成的驱动力。产生的构造不连续面降低了地幔向上迁移的效率，因此决定了岩浆运动中段落尺度的差异。我们预测，所有扩张速率的洋中脊分段均受到软流圈流动演化模式与岩石圈张裂作用动力学的控制。

海洋科学

《自然-地球物理》

Water-mass transformation by sea ice in the upper branch of the Southern Ocean overturning

南大洋翻转上部分支中海冰促成水体转换

（图片来源：http://www.nature.com/ngeo/journal/v9/n8/full/ngeo2766.html）

通过海洋与海冰监测的最新数据同化量化海冰通量；

海冰是南大洋海水翻转上部分支中水体转换的主要因素；

南大洋剩余翻转与风力驱动的海冰迁移紧密耦合。

R. P. Abernathey, I.Cerovecki, P. R. Holland, E. Newsom, M. Mazloff & L. D. Talley

http://www.nature.com/ngeo/journal/v9/n8/full/ngeo2749.html

Ocean overturning circulation requires a continuous thermodynamic transformation of the buoyancy of seawater. The steeply sloping isopycnals of the Southern Ocean provide a pathway for Circumpolar Deep Waterto upwell from mid depth without strong diapycnal mixing, where it istransformed directly by surface fluxes of heat and freshwater and splits intoan upper and lower branch. While brine rejection from sea ice is thought to contribute to the lower branch, the role of sea ice in the upper branch is lesswell understood, partly due to a paucity of observations of sea-ice thicknessand transport. Here we quantify the sea-ice freshwater flux using the Southern Ocean State Estimate, a state-of-the-art data assimilation that incorporates millions of ocean and ice observations. We then use the water-masstransformation framework to compare the relative roles of atmospheric, sea-ice,and glacial freshwater fluxes, heat fluxes, and upper-ocean mixing intransforming buoyancy within the upper branch. We find that sea ice is adominant term, with differential brine rejection and ice melt transformingupwelled Circumpolar Deep Water at a rate of ~22 × 10⁶m³s⁻¹.These results imply a prominent role for Antarctic sea ice in the upper branchand suggest that residual overturning and wind-driven sea-ice transport aretightly coupled.

海洋翻转环流需要持续的海水浮力热力变化。南大洋（Southern Ocean）陡斜的等密面为绕极深水层（CircumpolarDeep Water）从中深度上涌且不产生明显的跨密度面混合提供了路径，并直接通过表面热通量和淡水通量转换，且形成上部与下部分支。盐水从海冰析出被认为促成下部分支产生，但由于缺乏对海冰厚度与迁移的监测以及其他原因，我们对海冰在上部分支中的作用知之甚少。本研究中，我们使用整合大量海洋与海冰监测的最先进的数据同化的南大洋状态估测（Southern Ocean State Estimate），量化了海冰的淡水通量。随后我们使用水体转换框架，比较了上部分支中，大气、海冰和冰川的淡水通量与热通量，及上层海水混合对浮力改变等因素的相对作用。我们发现，海冰是主要因素，差异盐水析出与冰融以约22× 10⁶m³s⁻¹的速率转换上涌的绕极深水层。这些结果意味着南极海冰在上部分支中具有重要作用，同时暗示剩余翻转与风力驱动下的海冰迁移紧密耦合。

 冰雪圈

《地球物理研究杂志：海洋》

The effects of Antarctic iceberg calving-size distribution in a global climate model

全球气候模型中南极冰山崩解大小分布的影响

（图片来源：http://onlinelibrary.wiley.com/doi/10.1002/2016JC011835/full）

耦合环流模型表明冰山崩解大小与淡水输送、海冰增长相互作用；

冰山将影响气候模型准确度。

A. A.Stern, A. Adcroft & O. Sergienko

http://onlinelibrary.wiley.com/doi/10.1002/2016JC011835/full

Icebergs calved from the Antarctic continent act as moving sources of freshwater while drifting in the Southern Ocean. The lifespan of these icebergs strongly depends on their original size during calving. In order to investigate the effects (ifany) of the calving size of icebergs on the Southern Ocean, we use a coupled general circulation model with an iceberg component. Iceberg calving length isvaried from 62 m up to 2.3 km, which is the typical range used in climate models. Results show that increasing the size of calving icebergs leads to an increase in the westward iceberg freshwater transport around Antarctica. Insimulations using larger icebergs, the reduced availability of meltwater in the Amundsen and Bellingshausen Seas suppresses the sea-ice growth in the region.In contrast, the increased iceberg freshwater transport leads to in creasedsea-ice growth around much of the East Antarctic coastline. These results suggest that the absence of large tabular icebergs with horizontal extent oftens of kilometers in climate models may introduce systematic biases in sea-ice formation, ocean temperatures, and salinities around Antarctica.

从南极洲崩解的冰山在南大洋漂浮时是移动的淡水源。这些冰山的寿命极大地取决于它们崩解时的原始大小。我们运用含有冰山组件的耦合常规环流模型，研究了南大洋冰山崩解大小的影响（或其是否具有影响）。冰山崩解长度在62米至2.3千米之间，是气候模型中的典型范围。结果表明，崩解冰山大小的增加导致南极洲周围向西冰山淡水输送增加。在使用更大冰山的模拟中，阿蒙森海与别林斯高晋海（Amundsen and Bellingshausen Seas）融水可得性的降低抑制了该区域海冰增长。而提高的冰山淡水输送导致东南极海岸线许多区域周围海冰增长增加。这些结果暗示，气候模型中缺少大型平顶冰山可能造成南极洲周围海冰形成、海洋温度及盐度的系统偏差。

地震科学

《自然-地球物理》

The vertical finger print of earthquake cycle loading in southern California

南加州地震循环荷载的垂直指纹图

（图片来源：http://www.nature.com/ngeo/journal/v9/n8/abs/ngeo2741.html）

全球定位系统导出的垂直速度显示跨越断层系统的隆起与沉降；

分离出的垂直速度场与物理地震周期模型预测的垂直运动吻合；

运动显示了细微但仍可辨认的远场挠曲的构造指纹图。

S. Howell, B. Smith-Konter, N. Frazer, X. Tong& D. Sandwell

http://www.nature.com/ngeo/journal/v9/n8/abs/ngeo2741.html

The San Andreas Fault System, one of the best-studied transform plate boundaries on Earth, is well known for its complex network of locked faults that slowly deform the crust in response tolarge-scale plate motions. Horizontal interseismic motions of the fault systemare largely predictable, but vertical motions arising from tectonic sources remain enigmatic. Here we show that when carefully treated for spatialconsistency, global positioning system-derived vertical velocities expose as mall-amplitude (±2mmyr⁻¹),but spatially considerable (200km), coherent pattern of uplift and subsidence straddling the fault system in southern California. We employ the statistical method of model selection to isolate thisvertical velocity field from non-tectonic signals that induce velocity variations in both magnitude and direction across small distances (less thantens of kilometres), and find remarkable agreement with the sense of vertical motions predicted by physical earthquake cycle models spanning the past few centuries.We suggest that these motions reveal the subtle, but identifiable, tectonic fingerprint of far-field flexure due to more than 300 years of fault lockingand creeping depth variability. Understanding this critical component of interseismic deformation at a complex strike–slip plate boundary will better constrain regional mechanics and crustal rheology, improving the quantification of seismic hazards in southern California and beyond.

圣安德烈亚斯断层系统（San Andreas Fault System）是地球上研究最透彻的转换板块边界之一，因其复杂的闭锁断层网络而闻名。闭锁断层使地壳缓慢变形进而响应大尺度的板块运动。断层系统的震间水平运动很大程度上能够被预测，但构造来源导致的垂直运动仍然未知。我们在本研究中指出，当仔细处理空间一致性后，全球定位系统导出的垂直速度显示出小幅（±2mmyr⁻¹）但空间上较大（200km）的跨越南加州断层系统的隆起与沉降的连贯模式。在短距离上（小于数十千米）引起速度大小与方向变化的非构造信号中，我们使用模型选择的统计方法分离出垂直速度场，并发现它与跨越过去几世纪的物理地震周期模型所预测的垂直运动明显吻合。我们认为，这些运动显示超过300年的断层闭锁与蠕变深度变化导致细微但仍可辨认的远场挠曲的构造指纹图。了解这一复杂走滑板块边界上震间变形的关键部分，将更好地约束地区力学与地壳流变，改善南加州及其它地区地震灾害的定量研究。

气候科学

《地球物理研究通讯》

Climatic consequences of adopting drought tolerant vegetation over Los Angeles as are sponse to California drought

洛杉矶采用抗旱植物应对加州干旱的气候后果

（图片来源：http://guardianlv.com/2014/05/california-drought-greatly-affecting-wildlife/）

修正的区域气候模型显示采用耐旱植物造成日间温度上升1.9° C而夜间温度下降约3° C；

若所有城市植被被耐旱植物取代，则造成平均日间降温0.2° C；

地表粗糙度在洛杉矶地区具有的重要作用。

P.Vahmani & G. Ban-Weiss

http://onlinelibrary.wiley.com/doi/10.1002/2016GL069658/abstract

During 2012-2014, drought in California resulted in policies to reduce waterconsumption. One measure pursued was replacing lawns with landscapes that minimize water consumption, such as drought tolerant vegetation. If implemented at broad scale, this strategy would result in reductions in irrigation, and changes in land surface characteristics. In this study, we employ a modifiedregional climate model to assess the climatic consequences of adopting drought tolerant vegetation over the Los Angeles metropolitan area. Transforming lawns to drought tolerant vegetation resulted in daytime warming of up to 1.9° C, largely due to decreases inirrigation that shifted surface energy partitioning toward higher sensible andlower latent heat flux. During night time, however, adopting drought tolerant vegetation caused mean cooling of about 3° C,due to changes in soil thermodynamic properties and heat exchange dynamicsbetween the surface and ground. Our results show that nocturnal cooling effects, which are larger in magnitude and of great importance for publichealth during heat events, could counterbalance the daytime warming attributed to the studied water conservation strategy. A more aggressive implementation,assuming all urban vegetation was replaced with drought tolerant vegetation,resulted in an average day time cooling of 0.2°C, largely due to weakened sea-breeze patterns,highlighting the important role of land surface roughness in this coastal megacity.

2012至2014年间，加州干旱导致了减少耗水量政策的实行。一种方法是用耗水最少的景观（如耐旱植物）来代替草坪。如果大规模地推行，该政策将减少灌溉并改变地表特征。本研究中，我们采用修正的区域气候模型，评估在整个洛杉矶城区应用耐旱植物的气候后果。将草坪换成耐旱植物使得日间温度上升1.9摄氏度，这在很大程度上是由于灌溉减少改变了地表能量分配，使得感热通量增加而潜热通量减少。但在夜间，由于土壤热力性质及地表与地下热交换动力学的改变，应用耐旱植物造成平均降温约3摄氏度。我们的结果显示，夜间降温效应在数值上更大且在酷热事件中对公共健康具有重要意义，可能抵消节水政策所致的日间变暖。进一步假设所有城市植被被耐旱植物取代，主要由于海风模式被削弱，可造成平均日间降温0.2摄氏度，这突出了地表粗糙度在这座沿海大城市中的重要作用。

阅读更多

▽ 故事

▽ 论文推荐

▽ 中文摘要

---

内容合作请联系

[e-mail]。

---

这里是“科学美国人”中文版《环球科学》服务科研人的微信号“科研圈”。我们：

· 关注科学进展与科研生态

· 推荐重要前沿研究

· 发布科研招聘

· 推送学术讲座与会议预告。

欢迎长按二维码关注。