The Cryogenian Period (720-635 Ma) witnessed two Snowball Earth glaciations: the largest known perturbations to the geologic carbon cycle in Earth history. These two runaway ice-albedo catastrophes naturally test planetary climate stability and habitability. Geochronological data show that the Sturtian glaciation lasted 56 m.y., and the Marinoan was as short as 4 m.y., which is an unexplained difference previously attributed to changing volcanic outgassing rates and dust or ice albedo. Here, we propose that this difference in duration is instead due to changes in the extent of seafloor weathering, which was elevated during both glaciations by an acidic ocean under relatively high CO2. By assuming modern volcanic outgassing rates and a conservative range of ice albedos, we find that seafloor weathering rates 25-53 times higher than modern are required to suppress atmospheric CO2 and maintain glaciation for a 56 m.y. Sturtian glaciation, whereas <15 times higher than modern are required for a 4 m.y. Marinoan glaciation. Rates were plausibly enhanced further by reduced deep-sea sedimentation and low marine sulfate, which would have prevented hydrothermal anhydrite production and created more porous, weatherable oceanic crust. Geochemical data indicate low marine sulfate (<2 mM) during the Sturtian, which rebounded for the Marinoan (up to ~30 mM), and can account for the different seafloor weathering rates required by our model. Thus, our results suggest seafloor weathering and evolving ocean redox chemistry are critical for determining the duration of Snowball Earth glaciations.
Biomass burning is a major global source of atmospheric ammonia (NH3), significantly influencing air quality, aerosol formation, and nitrogen cycling. Nitrogen isotope composition (delta 15N) of NH3 has been proposed as a powerful tool for source apportionment, yet values for several emission sources remain poorly constrained. This study presents the first field-based delta 15N of total reduced inorganic nitrogen (NH x = NH3 + pNH4) measurements from fresh and aged biomass-burning plumes, collected during the Fire Influence on Regional to Global Environments and Air Quality (FIREX-AQ) campaign in the western United States during summer 2019. The NH x concentrations were strongly correlated with carbon monoxide (CO) and fine particulate matter (PM2.5), reflecting elevated emissions during smoldering conditions. The delta 15N(NH x ) ranged from -9.1 parts per thousand to 2.1 parts per thousand (x +/- sigma: -3.3 +/- 2.9 parts per thousand; n = 16). Using a Keeling plot approach, we derived a representative biomass-burning delta 15N(NH3) value of -4.7 +/- 1.3 parts per thousand, that integrates measurements across the sampled biomass burning events, while also accounting for background NH x influences. This field-based isotopic signature is clearly distinct from agricultural and vehicular sources and substantially lower than the +12 parts per thousand value commonly assumed for biomass burning in delta 15N-based source apportionment studies. Overall, this work improves our ability to track NH3 emissions using novel isotopic constraints. Field-based nitrogen isotope measurements of ammonia emissions from biomass burning reveal distinct isotopic signatures, enabling improved source apportionment and nitrogen cycling insights.
Quartz occurs ubiquitously in felsic plutons. The development of a methodology to reveal the quartz growth process in a granitic body provides essential insights into magma chamber processes. Cathodoluminescence (CL) characterization combined with Ti concentration of quartz crystals in granite is a prevalent tool for identifying the crystal growth and crystallization temperature of quartz in granitic magmas. This study focused on quartz crystal growth in the Kuki granite (KKG), northeast Japan, and Kurobegawa granite (KBG), central Japan. In the KKG quartz crystals, the difference in luminescence corresponds to Ti concentration: high luminescence corresponds to high Ti concentrations, which is consistent with our previous studies on the Toki and Okueyama granites. In the KBG quartz crystals, the Ti concentrations do not correspond to the luminescence level, whereas the Al concentrations are negatively correlated with the luminescence level. Therefore, quartz crystallizations in KKG and KBG are characterized by Ti- and Al-diffusion-controlled growth, respectively. Using the difference in the time-temperature history among the target rock bodies, this study provides insight into the nature of the relationship between quartz crystallization and magma chamber processes. Quartz crystallizations in the KKG were accompanied by gradual variations from oscillatory zonation through gradual zonation to homogeneous CL patterns with decreasing temperature in the cooling magma chambers. The quartz internal structure of the KBG was resulted from the rapid cooling of the KBG magma and the scarcity of Ti and enrichment of Al in the magma during quartz crystallization.
Magnetohydrodynamic waves redistribute energy in magnetic structures of the lower solar atmosphere, yet constraints on how wave power and dominant frequencies are organized above sunspots remain limited, because most studies use only a few well-separated diagnostics. Here, we present multiline wave signatures in a sunspot from near-ultraviolet (near-UV) spectroscopy with the S unrise-iii UV Spectropolarimeter and Imager (SUSI). We analyse a 2 hr time series of repeated raster scans of a sunspot near disc center in the 327–329 nm spectral window (>100 lines). From these, we select 44 lines that radiative-transfer calculations suggest sample effective formation heights within the umbral core, from the deep photosphere toward the low chromosphere. For each line, we extract line-core intensity and line-of-sight velocity time series using a dedicated multiline fitting routine and compute Morlet wavelet power spectra. The refined global wavelet spectra show that most lines (in both intensity and velocity) are genuinely multifrequency, with a dominant peak and substantial statistically significant power up to 12 mHz. Unsupervised clustering of the normalized spectra groups lines into families with similar spectral shapes and reveals a progression of dominant frequencies from ∼2 to ∼10 mHz across the ensemble, for both intensity and velocity (not necessarily in the same lines). This behavior is not reproduced by a simple formation-height ranking, suggesting that uncertainties in the formation-height estimates and line-dependent diagnostic response together shape the ordering. These S unrise-iii /SUSI observations open a new regime for near-UV multiline wave studies and provide the first systematic characterization of frequency-structured sunspot wave behaviour in this spectral region.
