ALBERT

Description: Monazite and magnetite are sensitive indicators of local fluid chemistry, pressure, and temperature during metasomatism. In this study, the role of fluids, during the metamorphism of a granite to metagranite, (Jiao-Liao-Ji orogenic belt, North China Craton), is explored via monazite, magnetite, and pyrite microtextures and mineral chemistry coupled with zircon and monazite Th–U–Pb dating. CL bright zircon cores (2163 ± 17 Ma) record the crystallization age of the granite. BSE dark monazite cores (1876 ± 36 Ma) are characterized by high U and Ca and low Nd contents. The surrounding BSE bright mantle (1836 ± 14 Ma) is characterized by abundant fine-grained huttonite inclusions, a high porosity, a high Th and Si content, and a low P, La, Ce, and Y content. The monazites are surrounded by a three-layered concentric corona consisting of first fluorapatite, followed by allanite, and then epidote. TiO2 in the primary magmatic magnetite (Mag1–1) has been mobilized to form a series of compositionally and texturally distinct magnetites (Mag1–2, Mag2, Mag3, Mag4, and Mag5) associated with ilmenite, rutile, and titanite reaction textures. Combined, these results suggest that external NaCl and sulphate-bearing fluids derived from a local sulphate-bearing evaporate infiltrated the granite and induced the formation of pyrite and enriched the pre-existing monazite in S at around 1904 Ma. In situ δ34S values for pyrite range from 13.03 ‰ to 13.41 ‰, which is typical of metamorphic pyrite. Sporadic synchysite-(Y) inclusions in the pyrite indicate a local CO2-rich component in the fluid. The BSE bright mantle around monazite formed from later fluids from the same local evaporite deposit during the decompression stage of the Jiao-Liao-Ji orogenic belt at around  ~ 1840 Ma, which overlaps with zircon dark rims at 1849 ± 12 Ma. This same Na-bearing fluid induced the albitization of the feldspars, formation of apatite–allanite–epidote coronas around monazite, and formation of rutile–titanite–epidote alteration textures associated with magnetite and ilmenite exsolved from the magnetite. During subsequent much later greenschist facies metamorphism, muscovite, chlorite, and Mag5 were precipitated along mineral grain boundaries, mineral cleavage, micropores, and fractures and pyrite experienced partial alteration to goethite.

Description: Subduction-related shoshonitic and calc-alkaline plutons coexisted in the Paleoproterozoic Khondalite belt (North China Craton). They intruded at 1.97–1.96 Ga and were overprinted by 1.94–1.92 Ga high-temperature metamorphism. The mafic to intermediate (SiO2 = 51.8–55.5 wt%) Wudangzhao shoshonitic metamonzodiorite has high K2O (3.0–4.9 wt%) contents. In contrast, the mafic (SiO2 = 48.5–51.7 wt%) Yebaigou metagabbro is sodium-rich (Na2O/K2O 〉 2). In Harker diagrams, the two intrusions show different magmatic evolution trends for selected major and trace elements, suggesting that they belong to two distinct magma series. Both intrusions are enriched in light rare earth element and depleted in high field strength elements, such as Nb, Ta, and Zr, in the trace-element diagrams normalized to the primitive mantle. The low εNd 1960 Ma values (− 3.1 to + 0.6) of whole-rock samples, the low εHf(t) values (− 2.2 to + 0.9) of magmatic zircon samples, and the relatively high δ18O values (+ 5.9 to + 6.4‰) of zircon crystals indicate that the mantle source of both intrusions had been metasomatized by fluids/melts derived from subducted continental crustal material. Partial melting of the amphibole and/or phlogopite-bearing mantle yielded the calc-alkaline melt with the chemical fingerprint characteristic for the Yebaigou metagabbro. Small-volume partial melting of a similar mantle source at greater depth produced shoshonitic melts that formed the Wudangzhao metamonzodiorites. The Wudangzhao metamonzodiorites and Yebaigou metagabbros represent part of a Paleoproterozoic continental magmatic arc on an Archean basement. This study shows that shoshonitic and calc-alkaline magmatism may exist coevally above ancient subduction zones and, thus, could provide some clues for distinguishing upper and lower plates in deeply eroded ancient collisional belts.

Description: 〈h1〉Electrostatic field changes associated with K processes are known as K changes, which transfer significant charge moment during the discharge. By applying electric field change meters with the decay time constant of about 20-40ms, we report the observations of four cases of K changes by eight stations with sufficient time resolution and amplitude resolution. We find that the electric field changes of K processes appear as the typical step-like or ramp-like signatures at some places, however it can also suffer the polarity reversal thus appear as the hooked-like signature at closer places. An advancing streamer model was applied to account for signatures of electrostatic field changes at different places. It seems that K processes in this study involve a negative horizontal streamer, which serves to deposit negative charges at remote sources along the streamer channel, with a speed of the order of 10〈sup〉7〈/sup〉 m/s and the amount of charge involved of about a few tenths of coulombs.〈/h1〉

Description: Under global warming, it has been found that tropical rainfall annual cycle exhibits an evident delay. Atmospheric energetic analysis suggests that the fundamental reason responsible for the seasonal delay of tropical rainfall in a warming climate is the increase in the effective atmospheric heat capacity due to the nonlinear dependence of water vapor on temperature. The increased effective atmospheric heat capacity delays the response of atmospheric circulation to the seasonal-varying solar radiation. This seasonal delay is more evident over tropical land rather than ocean, as over ocean, the shift of rainfall in the local rainy season from land to ocean cancels out the delay caused by the increased effective atmospheric heat capacity. It is further found that in the past four decades (1979-2019), the seasonal delay of tropical rainfall has already emerged in the tropical land. Both the increase of greenhouse gas emission and decrease of anthropogenic aerosols play an important role.

Description: In response to quadrupled CO〈sub〉2〈/sub〉, the Southern Ocean primarily uptakes excess heat around 60°S, which is then redistributed by the northward ocean heat transport (OHT) and mostly stored in the ocean or released back to the atmosphere around 45°S. However, the relative roles of mean ocean circulation and ocean circulation change in the uptake and redistribution of heat in the Southern Ocean remain controversial. Here, a set of climate model experiments embedded with a novel partial coupling technique are used to separate the roles of mean ocean circulation (passive component) and ocean circulation change (active component). For the ocean heat uptake (OHU) response, the mean ocean circulation and ocean circulation change are of equal importance. The OHT response south of 50°S is mainly determined by mean ocean circulation, while the ocean circulation change generates an anomalous southward OHT north of 50°S. A heat budget analysis finds that the divergence of passive OHT acts to balance the passive surface heat gain to the south of ~50°S, while the convergence of active OHT acts to balance the active surface heat loss to the north of ~50°S. Intriguingly, all the increase in ocean heat storage (OHS) is attributable to the passive component, with the ocean circulation change playing almost no role. In the Southern Ocean, both the active and the passive ocean heat transports are overcompensated by the reverse atmospheric heat transport via the Bjerknes compensation.

Description: The tropospheric NO〈sub〉2〈/sub〉 vertical column density (VCD) values measured by the Tropospheric Monitoring Instrument (TROPOMI) were used to study the tropospheric NO〈sub〉2 〈/sub〉variability and COVID-19 impacts for the 3° by 4° areas around 261 major cities worldwide. A new method of isolation of three components: background NO〈sub〉2〈/sub〉, NO〈sub〉2〈/sub〉 from urban sources, and from industrial point sources is applied to estimate the impact of the COVID-19 lockdown on each of them. The method is based on fitting satellite data by a statistical model with empirical plume dispersion functions driven by a meteorological reanalysis. Population density and surface elevation data as well as coordinates of industrial sources were used in the analysis. Unlike other similar studies that studied plumes from emission sources, this study included the background component as a function of the elevation in the analysis. Abrupt changes in urban and industrial emissions due to COVID-19 lockdown did not immediately result in a similar decline in the background component. Different changes in background and urban components in TROPOMI NO〈sub〉2〈/sub〉 could explain the inconsistency between the surface and satellite VCD-based results: surface concentrations demonstrated a larger decline than tropospheric NO〈sub〉2〈/sub〉. While background NO〈sub〉2〈/sub〉 component remained almost unchanged during the lockdown period, the urban NO〈sub〉2〈/sub〉 component declined by -18% to -28% over most regions. India, South America, and a part of Europe (particularly, Italy, France, and Spain) demonstrated a -40% to -50% urban emissions decline.

Description: Climate Responses to Tambora-Size Volcanic Eruption and the Impact of Warming ClimateThe climatic consequences of large volcanic eruptions depend on the direct radiative perturbation and the climate variability that amplifies or dampens the initial perturbation. Potential climate responses to future eruptions, however, have been rarely studied. Here we show perturbation of Tambora-size causes significant but no inter-scenario different global average climate responses, by using Community Earth System Model simulations under preindustrial and RCP8.5 scenarios. Regionally we find severe reduction in African and Asian-Australian monsoon rainfall and emerge of El Niño-like responses, largely due to the land-ocean thermal contrast mechanism. Global warming significantly amplifies such El Niño-like responses, which feed on the enhanced climatology atmospheric moisture and cause higher sensitivity of monsoon circulation to radiative forcing in the tropics. We also find prolonged Asian-Australian monsoon suppression associated with the enhanced westerly anomalies over the Pacific, suggesting the complexity of climate responses and feedbacks to external forcing under future climate.