Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23–14 Mya) is a compelling interval to study as global temperatures and atmospheric CO₂ concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3–4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO₂ concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO₂. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO₂ during the early to mid-Miocene.Knowledge regarding Antarctic ice sheet (AIS) response to warming climate is of fundamental importance due to the role ice sheets play in global sea level change. Paleoenvironmental records from Earth’s past offer a means to examine AIS variability under climatic conditions that were similar to today and those projected for the next several decades (1, 2). In this respect, the early to mid-Miocene is a compelling interval to study as proxy reconstructions of atmospheric CO₂, albeit uncertain, suggest that concentrations generally varied between preindustrial levels (PAL = 280 ppm) and values at or above 500 ppm (3–9). Additionally, global mean surface temperature during peak Miocene warmth was up to 3–4° higher than today (10), similar to best-estimate temperatures expected by 2100 under the highest projected greenhouse gas concentration pathway (Representative Concentration Pathway 8.5) (1, 2). Finally, Miocene geography was similar to today (11), and major circum-Antarctic oceanic and atmospheric circulation patterns that dominate the modern Southern Ocean were well established (12, 13).Much of our understanding regarding AIS history through the early to mid-Miocene comes from far-field records from deep ocean basins. Benthic oxygen and carbon isotope proxies for global paleoclimate suggest that early to mid-Miocene climate and glacial environments were highly variable (14–19). These records include evidence for major transient glacial episodes and sea level fall, intervals of relative ice sheet stability, and periods of climatic warmth with major ice sheet retreat and sea level rise. Furthermore, reconstructions from sedimentary sequences on the Marion Plateau, offshore northeast Australia (20), and New Jersey margin (21) suggest sea level varied by up to 100 m. Episodes of sea level maxima (+40 m) suggest loss of Antarctica’s marine-based ice sheets that, at present, occupy much of West Antarctica and large portions of East Antarctica (22), as well as substantial loss of mass from Antarctica’s terrestrial ice sheets. Episodes of maximum sea level fall (up to −60 m) suggest that the AIS occasionally grew and advanced across continental shelves.Geological records proximal to Antarctica’s coastal margin provide direct evidence of past ice sheet variability in response to changing global climate. The ANDRILL (AND)-2A drill core, a 1,138-m-long stratigraphic archive of climate and ice sheet variability from the McMurdo Sound sector of the western Ross Sea (77°45.488′S, 165°16.613′E), was recovered by drilling from an ∼8.5-m-thick floating sea ice platform in 380 m of water, located ∼30 km off the coast of Southern Victoria Land (SVL) (Fig. 1A) (23). The drill core comprises lower Miocene to Quaternary glacial-marine strata deposited in the steadily subsiding Victoria Land Basin (VLB) (24). Paleogeography was broadly similar to today, although continental shelves in the Ross and Weddell seas were likely shallower (SI Text and Fig. S1). Recovered core sediments, and the proxies they contain, allow us to assess past ice sheet dynamics along a coastal margin influenced by ice flowing from East Antarctica and across the West Antarctic continental shelf. Through analysis of an integrated proxy environmental dataset, we derive a new environmental reconstruction and combine this with a suite of global environmental data to establish a history of AIS response to global climate events and episodes during the early to mid-Miocene. This integrated dataset allows us to evaluate key drivers of high latitude climate and ice sheet variability between 21 and 13 Ma. Outcomes from research reported here and in a companion ice sheet modeling study (25) suggest the AIS advanced across continental shelves during cold orbital configurations and retreated well inland of the coast under warm orbits. This large range of AIS variability occurred under a relatively low range in atmospheric CO₂ concentration (∼280–500 ppm) and indicates the Antarctic environment was highly sensitive during the early to mid-Miocene.Open in a separate windowFig. 1.(A) Map showing Ross Sea area (Inset) and AND-2A drill site (white box indicates approximate area for schematic reconstructions shown below). (B) Stratigraphic summary of lower 925 m of AND-2A (214.13–1,138.54 mbsf) showing 61 sedimentary cycles. Glacial proximity curve tracks relative position of the grounding line through ice-contact (I), ice-marginal (IM), ice-proximal (P), ice-distal (D), and open marine (O) environments. Continuously acquired datasets include magnetic susceptibility and Niobium (Nb) XRF-CS counts. CIA (curve and bar) indicates arid (<50, blue) and less arid (>60, green) conditions. Intervals of peak palynomorph concentration shown by orange boxes. Foraminifera assemblages include cold water/ice marginal benthic species (red circles) and cool water planktonic species (blue circles). Blue bars, sea ice diatoms; M, intervals with well-preserved molluscs. Sea water temperature estimates based on TEX₈₆^L (black circles) and Δ₄₇ (blue circles, open, less well-preserved specimens). Environmental Motif curve based on the proxy environmental dataset. (C) Schematic reconstructions of region around AND-2A showing likely conditions for each environmental motif (I–IV).Open in a separate windowFig. S1.(Top Left) Ross Sea regional topography (ice sheet removed). Red square indicates area of sketch at right, which shows major geographic and topographic features in the region of the AND-2A drill hole (dashed lines indicate Late Neogene volcanic features). (Bottom Left) Miocene topography is based on a linear interpolation between an Eocene/Oligocene reconstruction (49) and an isostatically rebounded version of BEDMAP-2 (22). Sketch at right shows reconstruction of early Miocene topography in the region of the drill site.     

西藏昌都地区脂肪肝CT表现与分型的关系

目的:分析高原地区脂肪肝CT的表现.方法:38例脂肪肝均经CT扫描证实,且均在西藏昌都(海拔高度3500米)地区工作10年以上.结果:38例脂肪肝CT表现分型;弥漫型11例(重度5例、中度6例),节段型27例(中度9例、轻度18例).结论:脂肪肝CT表现分型与高海拔缺氧明显关系.高原缺氧、肥胖、饮酒促使形成脂肪肝外,更重要的是加重脂肪肝的病情程度,并与脂肪肝的CT表现分型有明显的关系.     

海洋贝类生殖腺提取物成份分析与安全毒理学研究

海洋贝类生殖腺中丰富的生理活性物质可望被开发成特殊功能的保健品或海洋药物。本文报道海洋贝类生殖腺提取物主要成份分析与安全毒理学的初步研究结果,以便为海洋贝类生殖腺的高值化开发提供科学依据。     

沙棘叶化学成分及药理作用研究进展

沙棘(Hippophae rhamnoides L.)作为一种传统的药食同源植物,其不同部位都有着悠久的用药历史。沙棘叶中含有丰富的化学成分,不同的组分还具有调节代谢、预防心血管和癌症等多种疾病的功效。对沙棘叶中的化学成分进行分离和表征,有助于更好地理解沙棘叶对疾病的作用机制。此外,阐明沙棘叶药理活性的物质基础也将对沙棘产业化的研究提供新的思路。     

东海药用微生物资源的初步调查研究

目的:对中国东海药用微生物资源进行初步调查研究.方法:从中国东海采集海水和底泥样品,选用不同的分离培养基,采用无限稀释及平板划线的方法分离出单菌落,利用纸片法和稻瘟霉模型对菌株发酵液进行活性筛选.结果:从样品中分离得到1 041株单菌落,包括506株放线菌,421株细菌和114株真菌,其中具有抗菌活性菌株303株,活性菌株分离率为29.1％.抗稻瘟霉分生孢子活性菌株219株,活性菌株分离率为21.0％.结论:分离得到的抗菌活性菌株,抗稻瘟霉分生孢子活性菌株的比例均达到20.0％以上,说明东海具有丰富的药用微生物资源.     

Concentrations of Tetrodotoxin (TTX) and Its Analogue 4,9-Anhydro TTX in Different Tissues of the Silver-Cheeked Pufferfish (Lagocephalus sceleratus,Gmelin, 1789) Caught in the South-Eastern Mediterranean Sea,Lebanon

Pufferfishes are among the best-known marine organisms that accumulate marine biotoxins such as Tetrodotoxin (TTX). In the Mediterranean Sea, the silver-cheeked toadfish Lagocephalus sceleratus is the most reported TTX-bearer, causing many fatal and non-fatal cases. In Lebanon, no previous studies have measured TTX levels although the possibility of TTX-poisoning is high since L. sceleratus is caught in different sizes and can be mistaken with other small fishes. Hence, this study reports TTX and its analogue 4,9-anhydro TTX in L. sceleratus collected from Lebanese waters in the Eastern Mediterranean Sea. The results show that TTX concentrations in fish tissues varied between 0.10 and 252.97 µg/g, while those of 4,9-anhydro TTX oscillated between 0.01 and 43.01 µg/g. Internal organs of L. sceleratus were the most toxic parts of its body, with the highest TTX levels found in gonads (mainly ovaries) and liver, followed by the muscles and skin with concentrations always exceeding the safety level. Toxicity fluctuations of L. sceleratus, its expansion, ecological and economic effects were also elucidated. Based on the present findings, it has been confirmed that L. sceleratus constitutes a health, ecological and economic risks, and therefore its trade in seafood markets should be banned to avoid any potential intoxication.     

Skin microbiome of people living at the Dead Sea area – The lowest place on earth

The Dead Sea is a salt lake with surface water at about 430 m below sea level and considered the lowest place on Earth. The Dead Sea basin is characterized by relatively high temperatures, attenuated UV radiation and the air above it has a relatively high-salt aerosol content. When we compared the skin microbiome of individuals from the hot, salty and arid Dead Sea area with that of individuals from the humid Mediterranean regions we observed a significantly lower bacterial diversity in the Dead Sea group as well as distinct differences in the composition of bacterial species. Our results suggest that these factors have a profound effect on the skin microbiome. Further study is required to understand how the local environment influences the skin microbiome, as well as the functional implications of these effects.     

海参多糖结构表征的研究进展

海参多糖是1种富含硫酸基团的杂多糖，结构复杂，具有多种生物活性，其生物活性与海参多糖本身的化学组成、相对分子质量、硫酸化模式等结构特征息息相关。为了更好地研究海参多糖的生物活性，全面总结海参多糖结构的分析方法，综述海参中性聚糖、海参岩藻糖基化硫酸软骨素和海参岩藻聚糖硫酸酯的结构特征，以期为海参多糖的生物活性及构效关系等后续研究提供理论基础。     

海上测量船人员心理健康与个性特征的相关研究

目的 研究海上测量船员心理健康与个性特征的相关性。方法 采用采用症状自评量表(SCL-90)和卡特尔16种人格因素问卷(16-PF)，时103名海上测量船人员(以下称海测人员)进行调查。结果 海测人员躯体化、焦虑、敌时、偏执、精神病性因子分和阳性项目数均明显高于军人常模(P＜0．01～0．001)；海测人员16种人格特征得分均不同程度高于全国男性常模(均P＜0．001)；紧张性进入躯体化、焦虑、敌时、偏执因子的方程；聪慧性进入躯体化、敌时因子和阳性项目数的方程；实验室进入焦虑、敌时、偏执因子的方程；自律性进入躯体化因子的方程；忧虑性进入阳性项目数方程。结论在人格特征方面，高紧张性、高忧虑性、低自律性、低聪慧性、低实验室的因素影响到海测人员的心理健康，必须健全船员人格，加强适应环境的能力。