Browsing by Author "Zhuang, Yanpei"
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Item Rapid changes in the surface carbonate system under complex mixing schemes across the Bering Sea: a comparative study of a forward voyage in July and a return voyage in September 2018(Frontiers in Marine Science, 2023-05-02) Yang, Wei; Wu, Yingxu; Cai, Wei-Jun; Ouyang, Zhangxian; Zhuang, Yanpei; Chen, Liqi; Qi, DiRegulated by the rapid changes in temperature, mixing, and biological production during warm seasons, the surface carbonate system in the Bering Sea is subject to significant spatial-temporal variability. However, the seasonal evolution of the carbon cycle and its controls are less clear due to the lack of observations. Here, we present the carbonate data collected during a forward voyage in July and a return voyage in September 2018 across the Bering Sea. For both voyages, we show distinct dissolved inorganic carbon versus total alkalinity (DIC-TA) relationships and partial pressure of CO2 (pCO2) distribution patterns in the Southern Basin (54-57°N), the Northern Basin (57-59°N), the Slope (59-61°N), the Shelf (61-64°N), and the Bering Strait (>64°N). In the Southern Basin, the Northern Basin, and the Slope, surface water was a two end-member mixing of Rainwater and Bering Summer Water (BSW) during the forward voyage and a two end-member mixing of North Pacific Surface Water (NPSW) and BSW during the return voyage. As a result, the observed DIC was almost consistent with the conservative mixing line, with a slight DIC addition/removal of -8.6~5.8 µmol kg-1, suggesting low biological production/respiration during both voyages. Seasonally, the higher factions of NPSW featuring low pCO2 during the return voyage dominated the pCO2 drawdown from July to September in the Southern Basin and the Slope. On the Shelf, the surface water was a two end-member mixing of plume water from the Anadyr River and BSW during both voyages, but the decreased DIC consumption via biological production from 59.9 ± 25.8 µmol kg-1 to 34.8 ± 14.0 µmol kg-1 contributed to the pCO2 increase from July to September. In the Bering Strait, the coastal area was characterized by the influence of plume water from the Anadyr River in July and the coastal upwelling in September. The high biological production in plume water made a strong CO2 sink during the forward voyage, while the upwelling of carbon-enriched subsurface water with minor DIC consumption made the coastal ecosystem a strong CO2 source during the return voyage. In different geographical regions, the observed seawater pCO2 was much lower than the overlying atmospheric CO2, resulting in a net CO2 sink with fluxes of -2.1~-14.0 mmol m-2 d-1 and -2.5~-11.6 mmol m-2 d-1, respectively, during the forward and return voyages. Highlights 1. The mixing of NPSW featuring low pCO2 dominated the pCO2 drawdown from July to September in the Southern Basin and the Slope. 2. pCO2 in the Bering Strait was dominated by the strong biological production in July and the coastal upwelling in September. 3. High DIC consumption via biological production made the Bering Shelf a strong CO2 sink during both voyages.Item Sea-ice loss accelerates carbon cycling and enhances seasonal extremes of acidification in the Arctic Chukchi Sea(Limnology and Oceanography Letters, 2024-02-05) Zhang, Yixing; Wu, Yingxu; Cai, Wei-Jun; Yi, Xiangqi; Gao, Xiang; Bi, Haibo; Zhuang, Yanpei; Chen, Liqi; Qi, DiThe Chukchi Sea shelf (CSS) is a highly productive region in the Arctic Ocean and it is highly efficient for absorbing atmospheric carbon dioxide and exporting and retaining carbon in the deep sea. However, with global warming, the carbon retention time in CSS may decrease, leading to less efficient carbon export. Here, we investigate the seasonal variability of carbonate chemistry in CSS using three sets of late- vs. early-summer reoccupations of the same transect. Our findings demonstrate substantially increased and rapid degradation of biologically produced organic matter and therefore acidification over time in the southern CSS due to earlier sea-ice retreat, resulting in significantly shorter carbon retention time. In sharp contrast, no increased degradation has been observed in the northern CSS where photosynthesis has just commenced. In the future, climate change would further diminish the carbon export capacity and exacerbate seasonal acidification not only within CSS but also across other polar coastal oceans. Scientific Significance Statement The Arctic Chukchi Sea shelf (CSS) is a prominent site for the biological drawdown of atmospheric carbon dioxide, which can subsequently be transported to the deep sea in the Arctic Ocean. The efficiency of carbon export is influenced by seasonal sea-ice formation and retreat: longer period of sea-ice opening results in shorter carbon retention time and reduced carbon export due to rapid recycling of organic matter. However, this process is poorly understood due to lack of observations. Here, we present three sets of late- vs. early-summer reoccupations along the same transect in the CSS. We unveil distinct spatial patterns of carbonate chemistry and subsurface acidification between the southern CSS and northern CSS. In the sCSS, degradation of biologically produced organic matter has occurred rapidly and caused subsurface acidification since early summer due to earlier sea-ice retreat; however, no such phenomenon is observed in the northern region. As Arctic warming continues in the future, these conditions are expected to persist, further diminishing carbon export capacity and exacerbating seasonal acidification.