Tropical oceans are the main global water vapor and latent heat sources, but their responses to radiative forcing remain unclear. Here, we investigate oceanic moisture dynamics of the western tropical Pacific (WTP) over the past 210,000 years through an approach of planktonic foraminiferal triple oxygen isotope (Δ′ 17 O). The Δ′ 17 O record is dominated by the precession cycles (~23,000 years), with lower values reflecting higher humidity in concert with higher Northern Hemisphere summer insolation. Our empirical and modeling results, combined with other geological archives, suggest that the enhanced moisture convergence over the WTP largely intensifies changes in the meridional and zonal hydrological cycles, affecting rainfall patterns in East Asia and northern South America. We propose that the insolation-driven WTP moisture dynamics play a pivotal role in regulating tropical hydroclimate.
Abstract The isotopic composition and abundance of sulfur in extraterrestrial materials are of interest for constraining models of both planetary and solar system evolution. A previous study that included phase‐specific extraction of sulfur from 27 shergottites found the sulfur isotopic composition of the Martian mantle to be similar to that of terrestrial mid‐ocean ridge basalts, the Moon, and nonmagmatic iron meteorites. However, the presence of positive Δ 33 S anomalies in igneous sulfides from several shergottites, indicating incorporation of atmospherically processed sulfur into the subsurface, complicated this interpretation. The current study expands upon the previous work through analyses of 20 additional shergottites, enabling tighter constraints on the isotopic composition of juvenile Martian sulfur. The updated composition (δ 34 S = −0.24 ± 0.05‰, Δ 33 S = 0.0015 ± 0.0016‰, and Δ 36 S = 0.039 ± 0.054‰, 2 s.e.m.), representing the weighted mean for all shergottites within the combined population of 47 without significant Δ 33 S anomalies, strengthens our earlier result. The presence of sulfur isotopic anomalies in igneous sulfides of some meteorites suggests that their parent magmas may have assimilated crustal material. We observed small negative Δ 33 S anomalies in sulfides from two meteorites, NWA 7635 and NWA 11300. Although negative Δ 33 S anomalies have been observed in nakhlites and ALH 84001, previous anomalies in shergottites have all shown positive values of Δ 33 S. Because NWA 7635 has formation age of 2.4 Ga and is much more ancient than shergottites analyzed previously, this finding expands our perspective on the continuity of Martian atmospheric sulfur photochemistry over geologic time.
Rare earth element (REE) contents in bulk soils and respective geochemical fractions (e.g., exchangeable, carbonate-bound, reducible, and oxidizable fractions) were determined to decipher the relationships between REE geochemistry components and climatic factors across a large-scale northern China transect. Bulk REE concentrations ranged from 55.2 μg g -1 to 241.1 μg g -1 with a main portion in the residual fraction (49-79%), followed by oxidizable fraction (2-40%), reducible fraction (3-22%), carbonate-bound fraction (0.1-16%), and negligible exchangeable fraction. The REE contents of geochemical components (carbonate-bound, reducible, and oxidizable) in topsoils positively or negatively correlated to climate factors (mean annual precipitation, mean annual temperature, potential evaporation, and aridity index (AI)). Our data in topsoils and depth-profiles collectively suggest that cycling of REE was primarily regulated by abiotic processes in area with AI < 0.2 , while the biological effect on REE circulation in soil played more effective role in area with AI > 0.3. The normalized abundances to the upper continental crust (UCC) composition show that the middle REE was generally enriched than the light REE and heavy REE in topsoils along the transect. The overall UCC-normalized bulk REE patterns in topsoils and subsoils were similar, characterized by weak negative Ce anomalies and positive Eu anomalies. The UCC-normalized REE patterns in geochemical fractions had distinguished features, however showed similar patterns in respective geochemical components (e.g., pronounced negative Ce anomalies in carbonate-bound fractions and negligible Ce anomalies in other geochemical components). Our results provide evidence for climatic influence on REE distribution patterns both in topsoils and subsoils across the continental-scale transect and give insights into future studies on vertical REE mobility and its associated biogeochemical pathways.
Atmospheric sulfate aerosols have a cooling effect on the Earth's surface and can change cloud microphysics and precipitation. China has heavy loading of sulfate, but their sources and formation processes remain uncertain. In this study we characterize possible sources and formation processes of atmospheric sulfate by analyzing sulfur isotope abundances ( 32 S, 33 S, 34 S, and 36 S) and by detailed X‐ray diffraction and scanning electron microscope (SEM) imaging of aerosol samples acquired at a rural site in northern China from March to August 2005. The comparison of SEM images from coal fly ash and the atmospheric aerosols suggests that direct emission from coal combustion is a substantial source of primary atmospheric sulfate in the form of CaSO 4 . Airborne gypsum (CaSO 4 ·2H 2 O) is usually attributed to eolian dust or atmospheric reactions with H 2 SO 4 . SEM imaging also reveals mineral particles with soot aggregates adhered to the surface where they could decrease the single scattering albedo of these aerosols. In summer months, heterogeneous oxidation of SO 2 , derived from coal combustion, appears to be the dominant source of atmospheric sulfate. Our analyses of aerosol sulfate show a seasonal variation in Δ 33 S (Δ 33 S describes either a 33 S excess or depletion relative to that predicted from consideration of classical mass‐dependent isotope effects). Similar sulfur isotope variations have been observed in other atmospheric samples and in (homogenous) gas‐phase reactions. On the basis of atmospheric sounding and satellite data as well as a possible relationship between Δ 33 S and Convective Available Potential Energy (CAPE) during the sampling period, we attribute the sulfur isotope anomalies (Δ 33 S and Δ 36 S) in Xianghe aerosol sulfates to another atmospheric source (upper troposphere or lower stratosphere).
Chalcopyrite is an important sulfide mineral in many types of ore deposits, but matrix‐matched chalcopyrite reference materials for microanalysis are lacking. A new natural chalcopyrite‐bearing specimen (HTS4‐6) was analysed in this study to investigate its potential as a reference material for microbeam sulfur isotope ratio measurement. Detailed textural examination and major element determination showed that the HTS4‐6 chalcopyrite grains have no growth rim or zoning. A total of 607 sulfur isotope ratio spot measurements with secondary ion mass spectrometry (SIMS) conducted on the cruciform sections, and over 120 randomly selected grains yielded highly consistent sulfur isotope ratio. The intermediate measurement precision for four measurement sessions of the 34 S/ 32 S measurement results was better than 0.39‰ (2 s ). Randomly selected chalcopyrite grains of HTS4‐6 were further analysed by LA‐MC‐ICP‐MS, which gave a mean δ 34 S value of +0.58 ± 0.38‰ (2 s , n = 95). The maximum variance (expressed as intermediate precision from SIMS and LA‐MC‐ICP‐MS measurements) is not worse than 0.39‰ (the SIMS value), indicating that HTS4‐6 chalcopyrite is a potential reference material for in situ microbeam sulfur isotope measurements. The mean δ 34 S value determined by gas source isotope ratio mass spectrometry (GS‐IRMS) is +0.63 ± 0.16‰ (2 s , n = 23), consistent with that derived by LA‐MC‐ICP‐MS, and can represent the recommended value for this potential reference material.
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