New age constraints for a short pulse in Ross orogen deformation triggered by East–West Gondwana suturing

Constraints on the timing of deformation within the Antarctic Ross orogenic belt are important for understanding early Paleozoic tectonic activity accompanying the assembly of Gondwana. One of the best areas for constraining the tectonic evolution of the Ross orogenic belt is the Holyoake Range in the central Transantarctic Mountains where previous work shows an abrupt change in the stratigraphic succession of the Cambrian Byrd Group possibly related to the inception of tectonism within the orogen at  515 Ma. To further constrain deformational timing, we conducted ⁴⁰Ar–³⁹Ar analyses on magmatic phases of the Holyoake Gabbro, which cross-cuts folded Lower Cambrian Shackleton Limestone of the Byrd Group. Our analyses yield average ages of 506.7 ± 3.6 Ma (2 sigma; MSWD = 0.9) and 504.1 ± 2.4 Ma (2 sigma; MSWD = 1.3) for hornblende from the early and late magmatic phases, respectively. Deformation of the Shackleton Limestone therefore occurred prior to 506.7 ± 3.6 Ma, which is  12 m.y. after the siliciclastic drowning of the carbonate platform inferred to record the start of Ross tectonism in the central Transantarctic Mountains. On a regional scale, the data are consistent with a short pulse of deformation, which was probably related to global plate motion changes following final suturing of East and West Gondwana.     

Models of dusty envelopes around Vega-like stars

Einfache Entwicklungsmodelle der Staubhüllen um Wega, die Sonne, β Pictoris und Ross 128 werden konstruiert. Die Infrarotspektren dieser Hüllen werden unter der Annahme berechnet, daß der Minimalradius der Teilchen durch den Poynting-Robertson-Effekt bestimmt wird, während ihr Wachstum bis zur maximalen Größe durch Koagulation erfolgt. Ein Vergleich mit den Beobachtungen der Staubhüllen durch IRAS zeigt, daß das Modell die Grundzüge der Entwicklung protoplanetarer Scheiben zufriedenstellend beschreibt.     

南极罗斯海–阿蒙森海2019—2020年夏季表层悬浮颗粒有机质组成及其控制因素

陆架边缘海悬浮颗粒有机质的组成及其来源研究是海洋物质生物地球化学循环研究的重要组成部分。南极的地理位置和气候环境特殊,其边缘海海洋环境受海–气–冰系统共同作用与影响,颗粒有机质的组成及来源具有独特的区域特征与全球意义,其控制因素研究对全面认识罗斯海、阿蒙森海等典型西南极边缘海生物地球化学循环以及生物泵传输效率具有重要的意义。利用中国第36次南极科学考察期间在西南极罗斯海–阿蒙森海区采集的59个表层海水悬浮颗粒物样品的有机碳、氮及其同位素和多种来源特异性的生物标志物分析测试数据,研究了罗斯海–阿蒙森海区域悬浮颗粒物中有机质的物质组成和分布特征,探讨了悬浮颗粒物中不同来源有机质含量与分布的控制因素,评估了不同有机地球化学指标在海–气–冰系统作用下的南极边缘海颗粒有机质组成及来源示踪的应用潜力。研究结果表明,罗斯海–阿蒙森海区海水表层颗粒物中颗粒有机碳（POC）的丰度与表层水体荧光值、海水pCO2、海洋浮游植物源和动物源生物标志物等的丰度分布趋势一致,这种水平分布趋势的一致性表明夏季罗斯海–阿蒙森海海水表层POC主要由浮游植物和动物现场产生。表层悬浮颗粒物总有机质C/N比普遍低于4,显示海区颗粒有机质受微生物降解改造作用明显;表层悬浮颗粒物δ13C值普遍低于−25.2‰,空间分布复杂,反映了南极冰架边缘海独特的贫13C的浮游植物源、富13C的动物源和贫13C的陆源颗粒有机组成的混合信号。表层悬浮颗粒物类脂生物标志物指标是区分不同来源POC组分的有效指标;菜籽甾醇、甲藻甾醇等浮游植物源生物标志物含量之和能较好地反映浮游植物源POC的贡献：近岸冰间湖区呈现高值,其浓度的空间变化受控于水体浮游植物活动;胆甾醇能较好地反映动物源POC的贡献：冰架边缘近岸区呈现高值,其浓度的空间变化受控于海区次级生产力水平和企鹅、海豹等生物量水平;长链的烷基类脂生物标志物较好地反映了南极岩性陆源POC的贡献,其浓度的空间变化受控于南极冰川作用主导的海陆相互作用的过程影响,往往在融冰过程明显的冰架边缘近岸区呈现高值。以上研究结果表明,生物标志物分子指标结合总有机质指标的多参数综合评估为准确辨识南极边缘海复杂的POC来源组成提供了有效的方法,在极区现代海洋（生物地球化学）过程及古海洋环境演化研究中具有广阔的应用空间。     

南极罗斯海区域可培养微生物分离鉴定及产低温酶能力初步筛选

为了利用南极微生物资源、探索南极罗斯海区域可培养微生物多样性,利用传统平板培养法对中国第33次南极科学考察采自南极罗斯海6个站位的海洋沉积物样品进行了细菌、真菌的分离培养。经细菌16S rRNA、真菌ITS基因序列检测及系统发育分析,共获得5个属的36株细菌和6个属的29株真菌。其中嗜冷杆菌属为优势细菌类群,枝孢属为优势真菌类群。该结果表明南极罗斯海区域具有丰富的微生物多样性。细菌API 20 NE生理生化及真菌产胞外酶活性实验显示,分离得到的细菌和真菌绝大多数都有低温酶活性。研究结果为南极罗斯海区域可培养微生物的多样性认识和低温酶产生菌资源获取与开发利用提供了支撑。     

裂后岩浆活动中岩床复合体的特征:以南海北部和南极西罗斯海地区为例

由于蕴含着潜在的油气勘探和资源储藏信息,岩床复合体在全球范围内被广泛研究。本文基于南海北部三维地震资料以及南极罗斯海地区二维多道地震资料,对岩床复合体的形态特征及分布进行分析,对两个地区岩床复合体的形成时间进行判断,阐述岩床复合体的侵位机制。研究发现,岩床复合体代表性产状除了菱形、碟形及复合型外,还存在沿着层位平行侵入的板状,推测它可能是夭折了的岩床侵入体,以及由几个小型岩床堆叠而成的透镜状岩床复合体。分布上,南海北部岩床主要发育于珠江口盆地白云凹陷三维工区西部,东部只零星可见;南极西罗斯海岩床主要发育于西北角的阿黛尔盆地内。根据岩床上覆的强制褶皱结合区域构造背景,推测南海北部岩床复合体的形成时间为早中新世(15.5 Ma),海底扩张结束之时。残余岩浆将盆地内裂谷时期形成的断层作为岩浆运移的通道,并最终在断层终点处即下中新统近海相砂泥岩地层中实现侵位。南极西罗斯海岩床复合体的形成时间则非常晚,不早于5.5 Ma。该区这期岩浆活动可能与构造作用无关,而是受到冰川消融的影响。研究发现岩床复合体内部的岩床个体互相供给,即深部的大岩床为上覆浅层的小岩床提供岩浆供给,并且互相组合,形成大的岩床复合体。然而,每个岩床复合体则可能由不同的岩浆供给发育而成。     

Coupled garnet Lu–Hf and monazite U–Pb geochronology constrain early convergent margin dynamics in the Ross orogen,Antarctica

The Ross orogen of Antarctica is an extensive (>3000 km‐long) belt of deformed and metamorphosed sedimentary rocks and granitoid batholiths, which formed during convergence and subduction of palaeo‐Pacific lithosphere beneath East Gondwana in the Neoproterozoic–early Palaeozoic. Despite its prominent role in Gondwanan convergent tectonics, and a well‐established magmatic record, relatively little is known about the metamorphic rocks in the Ross orogen. A combination of garnet Lu–Hf and monazite U–Pb (measured by laser‐ablation split‐stream ICP‐MS) geochronology reveals a protracted metamorphic history of metapelites and garnet amphibolites from a major segment of the orogen. Additionally, direct dating of a common rock‐forming mineral (garnet) and accessory mineral (monazite) allows us to test assumptions that are commonly used when linking accessory mineral geochronology to rock‐forming mineral reactions. Petrography, mineral zoning, thermobarometry and pseudosection modelling reveal a Barrovian‐style prograde path, reaching temperatures of ~610–680 °C. Despite near‐complete diffusional resetting of garnet major element zoning, the garnet retains strong rare earth element zoning and preserves Lu–Hf dates that range from c. 616–572 Ma. Conversely, monazite in the rocks was extensively recrystallized, with concordant dates that span from c. 610–500 Ma, and retain only vestigial cores. Monazite cores yield dates that overlap with the garnet Lu–Hf dates and typically have low‐Y and heavy rare earth element (HREE) concentrations, corroborating interpretations of low‐Y and low‐HREE monazite domains as records of synchronous garnet growth. However, ratios of REE concentrations in garnet and monazite do not consistently match previously reported partition coefficients for the REE between these two minerals. High‐Y monazite inclusions within pristine, crack‐free garnet yield U–Pb dates significantly younger than the Lu–Hf dates for the same samples, indicating recrystallization of monazite within garnet. The recrystallization of high‐Y and high‐HREE monazite domains over >50 Ma likely records either punctuated thermal pulses or prolonged residence at relatively high temperatures (up to ~610–680 °C) driving monazite recrystallization. One c. 616 Ma garnet Lu–Hf date and several c. 610–600 Ma monazite U–Pb dates are tentatively interpreted as records of the onset of tectonism metamorphism in the Ross orogeny, with a more robust constraint from the other Lu–Hf dates (c. 588–572 Ma) and numerous c. 590–570 Ma monazite U–Pb dates. The data are consistent with a tectonic model that involves shortening and thickening prior to widespread magmatism in the vicinity of the study area. The early tectonic history of the Ross orogen, recorded in metamorphic rocks, was broadly synchronous with Gondwana‐wide collisional Pan‐African orogenies.     

Microalgal Communities of the Sea Ice, Ice-Covered and Ice-Free Waters of Wood Bay (Ross Sea, Antarctica) During the Austral Summer 1993 – 94

Abstract. During the austral summer 1993 – 94, microalgal density and biomass were investigated in the sea ice, in the underlying water column, in the melt water and during the formation of the sea ice. Of the 96 taxa identified, 59 were diatoms and 32 were dinoflagellates. Among the remaining five species, Pseudopleurochloris antarctica  was very abundant both in the sea ice and in the ice-free waters. Cell densities and biomass of microalgae were higher in the bottom of the sea ice and during the formation of the ice than in the seawater, and diatoms were the dominant group at higher microalgal biomass. Among these, Entomoneis kufferathii , Chaetoceros dichaeta and Fragilariopsis species were the most common taxa.     

THE RELATIONSHIP BETWEEN EXTREME PRECIPITATION ANOMALY IN SOUTH OF CHINA AND ATMOSPHERIC CIRCULATION IN THE SOUTHERN HEMISPHERE

Based on the daily rainfall datasets of 743 stations in China and the NCEP/NCAR monthly reanalysis data during the period of 1960–2003, the relationship between the anomalous extreme precipitation (EP) in the south of China and atmospheric circulation in the Southern Hemisphere is analyzed. The phenomenon of opposite changes in the sea level pressure and geopotential height anomalies over the Ross Sea and New Zealand is defined as RN, and the index which describes this phenomenon is expressed as RNI. The results show that the RN has barotropic structure and the RNI in May is closely related to the June EP amount in the south of China (SCEP) and the East Asian summer monsoon (EASM). The positive correlations between the May RNI at each level and the June SCEP are significant, and the related simultaneous correlations between the RNI and the June SCEP are also positive, suggesting that the potential impact of RN on the SCEP persists from May to June. Therefore, RN in May can be taken as one of the predictive factors for the June SCEP. Furthermore, one possible physical mechanism by which the RN affects the June SCEP is a barotropic meridional teleconnection emanating from the Southern Hemisphere to the western North Pacific.     

南极罗斯海扇区晚更新世以来冰筏碎屑记录反映的冰川动力学史

中更新世气候转型以来,南极冰盖对全球气候的影响作用逐渐放大。西南极冰盖以海洋冰盖为主体,稳定性差,冰架前缘沉积模式复杂,对于冰期-间冰期气候旋回变化十分敏感。因此,文章通过对中国第31次南极考察在罗斯海扇区北维多利亚地岸外钻取长度达412 cm的ANT31-R22岩芯（173.152°E,67.215°S;水深2906 m）的浮游有孔虫Nps-δ¹⁸O、冰筏碎屑含量及其岩矿组成分析等研究,重建了罗斯海扇区22.8~534.0 ka B.P.期间的冰筏碎屑沉积物源和周边冰架的演化历史。R22岩芯的岩矿组合显示：MIS 13期晚期至MIS 7期,横贯山脉-维多利亚地的Ferrar组基性火成岩是罗斯海扇区的主要物源;MIS 7期之后横贯山脉-维多利亚地物源输入明显下降,花岗岩和变质岩的输入有所增加,推测马利伯德地花岗岩-变质岩物源区输入增加,西南极冰盖对于罗斯海扇区的影响逐渐增强。同时,综合对比多个太平洋扇区岩芯/站位的冰筏碎屑指标显示：自晚更新世以来,罗斯海扇区至阿蒙森海扇区的深海冰筏碎屑沉积集中出现在冰盛期-冰消期阶段,是气候回升过程中西南极高纬地区冰架消融的重要标志,而中高纬地区的冰筏碎屑沉积更可能是冰盛期的标志。

     

Thermohaline variability and Antarctic bottom water formation at the Ross Sea shelf break

We use hydrological and current meter data collected in the Ross Sea, Antarctica between 1995 and 2006 to describe the spatial and temporal variability of water masses involved in the production of Antarctic Bottom Water (AABW). Data were collected in two regions of known outflows of dense shelf water in this region; the Drygalski Trough (DT) and the Glomar-Challenger Trough (GCT). Dense shelf water just inshore of the shelf break is dominated by High Salinity Shelf Water (HSSW) in the DT and Ice Shelf Water (ISW) in the GCT. The HSSW in the northern DT freshened by ∼0.06 in 11 y, while the ISW in the northern GCT freshened by ∼0.04 in 8 y and warmed by ∼0.04 °C in 11 y, dominated by a rapid warming during austral summer 2001/02. The Antarctic Slope Front separating the warm Circumpolar Deep Water (CDW) from the shelf waters is more stable near GCT than near DT, with CDW and mixing products being found on the outer DT shelf but not on the outer GCT shelf. The different source waters and mixing processes at the two sites lead to production of AABW with different thermohaline characteristics in the central and western Ross Sea. Multi-year time series of hydrography and currents at long-term moorings within 100 km of the shelf break in both troughs confirm the interannual signals in the dense shelf water and reveal the seasonal cycle of water mass properties. Near the DT the HSSW salinities experienced maxima in March/April and minima in September/October. The ISW in the GCT is warmest in March/April and coolest between August and October. Mooring data also demonstrate significant high-frequency variability associated with tides and other processes. Wavelet analysis of near-bottom moored sensors sampling the dense water cascade over the continental slope west of the GCT shows intermittent energetic pulses of cold, dense water with periods from ∼32 h to ∼5 days.