Showing papers by "Xianfeng Wang published in 2023"

Boundary exchange completes the marine Pb cycle jigsaw.

Abstract: Material fluxes at the land-ocean interface impact seawater composition and global cycling of elements. However, most attention has been focused on the fluvial dissolved fluxes. For elements like lead (Pb), whose fluvial particulate flux into the ocean is two orders of magnitude higher than the dissolved counterpart, the role of particulates in elemental cycling is potentially important but currently less appreciated. Using both chemical analyses on samples collected from around equatorial Southeast Asia and model simulations, we show that particulate-dissolved exchange is an important mechanism controlling the concentration and isotopic composition of dissolved Pb in the ocean. Our model indicates that Pb contributed from particulate-dissolved exchange at ocean boundaries is larger than, or at least comparable to, other major Pb sources to the seawater before the Anthropocene, when the anthropogenic Pb was absent. Our work highlights the importance of boundary exchange in understanding marine element cycling and weathering-climate feedback.

Dissolved lead (Pb) concentrations and Pb isotope ratios along the East China Sea and Kuroshio transect ‐ evidence for isopycnal transport and particle exchange

Abstract: Lead (Pb) isotopes are widely used in tracing processes that transport Pb within the environment due to the globally spread Pb pollution. In today’s ocean, Pb is mainly sourced from anthropogenic emissions and is removed by particle scavenging. However, recent efforts involving Pb isotopes have started to indicate that sediments at ocean boundary, either suspended or benthic, are a previously underestimated source and sink of Pb to the seawater dissolved pool. To assess the contributions of Pb from seawater-sediment boundary, we measured the dissolved Pb concentrations and isotopic compositions in seawater from the outer East China Sea (ECS) and along the Kuroshio. Along the Kuroshio, depth profiles exhibit highly similar Pb concentrations across constant density planes, suggesting isopycnal transport. Pb isotope ratios in most of the samples show strong contributions of aerosol Pb, except for seawaters from the ECS and deep Okinawa Trough (>800 m), which show evidences of crustal Pb contribution. The Okinawa Trough deep water has overlapping Pb isotope ratios with ECS water, where the suspended particulate matter is abundant. Our data on Pb isotopes in the ECS and the Okinawa Trough deep water, together with data from previous studies at other continental margins suggest that the seawater-sediment boundary along the continental shelves may be an important source and sink in marine Pb cycling.

Suspension of Crustal Materials from Wildfire in Indonesia as Revealed by Pb Isotope Analysis

Abstract: Southeast Asia experiences recurring wildfire events. Aerosol particles from these wildfires include metal species, which are suggested to have critical influences on the environment and climate. However, the mechanisms for emission of these elements from the wildfires in the region remains unclear. We analyzed both the elemental composition and the isotope ratios of lead (Pb), which is an environmentally important element. Our samples were collected in Singapore as the total suspended particulate (TSP) matter during 2013, especially focusing on the wildfire haze period in June. The Pb isotope ratios for wildfire fuels as well as crustal materials in the region were also analyzed. The Pb isotopic ratios during the haze period (208Pb/207Pb = 2.448 ± 0.013 and 206Pb/207Pb = 1.169 ± 0.012) were significantly (p < 0.05) different from those of the non-haze period (208Pb/207Pb = 2.438 ± 0.006, 206Pb/207Pb = 1.159 ± 0.005). This difference demonstrates that the suspension of the crustal material is the dominant emission source of TSP. Comparison of elemental composition (Al/Pb) with previous studies in the region, which have dominantly been sampled as PM2.5, suggests that the emission mechanism of particulate matter from wildfire in the region is likely size-dependent. We suggest that the suspension of crustal soil material needs to be included in future emission inventory for wildfire emission.