More than half of the carbon pools in peatlands are stored in the soil layers below 30 cm,yet little is known about the carbon stabilizing factors at these depths.Although iron oxide minerals are considered to be impo...More than half of the carbon pools in peatlands are stored in the soil layers below 30 cm,yet little is known about the carbon stabilizing factors at these depths.Although iron oxide minerals are considered to be important for stabilizing organic carbon(OC),their role in the preservation of OC in peatlands,especially in the deep layers,is poorly understood.Here,we collected 1 m soil profiles from six peatlands in Central and West China to quantitatively study the vertical distribution characteristics of iron-bound OC(Fe-bound OC),and the influencing physicochemical properties of the soil.The results showed that the content of reactive iron(FeR)was enriched in the top layer and decreased gradually with depth.While Fe-bound OC was positively correlated with FeR,its concentration did not decrease with depth in the peat profile.There were no obvious trends in the distributions of FeR and Fe-bound OC with water level fluctuations in the peat profile.In addition,the proportion of Fe-bound OC to soil organic carbon in the deep peat(31 to 100 cm)was equivalent to that in the surface peat(0 to 30 cm),indicating that iron oxide mineral provides comparable protection of OC in both layers.According to upper estimates of global peatland carbon storage(612 Pg),it could be predicted that 23.81±11.75 Pg of OC is protected by association with FeR.These results indicated that iron oxide minerals are the effective"rusty sink"of OC sequestration in peatland,and a key factor for its long-term preservation.The results from this study make a valuable contribution to the carbon dynamics knowledgebase for peatlands,and provide a basis for improved predictive simulations.展开更多
Extensive organic-matter （OM） rich facies （black shales） occur in the Ordo-Silurian boundary successions in the Yangtze area, South China. To investigate the redox changes of the Yangtze Sea during the Ordo-Siluri...Extensive organic-matter （OM） rich facies （black shales） occur in the Ordo-Silurian boundary successions in the Yangtze area, South China. To investigate the redox changes of the Yangtze Sea during the Ordo-Silurian transition, two OM sections （Wangjiawan in Yichang, Hubei Province, and Sanjiaguan in Zhangjiajie, Hunan Province） straddling the Ordo-Silurian boundary are studied. The measurements finished in this study include contents of the total organic carbon （TOC）, pyrite sulphur, and different species of Fe, including dithionite-extractable Fe （FED）, pyrite Fe （FeP）, HCl-extractable Fe （FeH）, and total Fe （FeT）, in black shales, as well as other redox proxies, such as the SIC ratio, the ratio between highly reactive Fe （FeHR = FeD ＋ FeP） and FeT, and the FeP/（FeP ＋ FeH） ratio, known as the degree of pyritization （DOP）. In the Wangjiawan section, the Middle Ashgill sediments have high FeHR/FeT ratios （0.20-0.77; avg. 0.45）, high DOP values （0.21-0.72; avg. 0.54）, and a relatively constant sulfur content independent of the organic carbon content. By the contrast, the mid-early Hirnantian deposits generally have low FeHR/FeT ratios （0.10-0.35; avg. 0.21）, low DOP values （0.11- 0.40; avg. 0.28）, and SIC values are clustering on the normal marine value （SIC = 0.36）. The late Hirnantian and early Rhuddanian deposits, similar to those of the Middle Ashgill deposits, are characterized by high FeHR/FeT ratios （0.32-0.49; avg. 0.41）, high DOP values （0.46-0.68; avg. 0.53） and fairly constant sulfur contents. These data suggest the occurrences of marine anoxia on the Yangtze Sea shelf during intervals of the Mid Ashgill, Late Hirnantian and Early Rhuddanian, and ventilated and oxygenated marine conditions during the mid-early Hirnantian time. The mid-early Hirnantian ventilated event was concomitant with the global glacial period, likely resulted from the glacio-eustatic sea-level fall and subsequent circulation of cold, dense oxygenated waters upon the shelf seabed. Accordingly, the abrupt change from oxygenated to anoxic marine waters from the late Hirnantian and the early Rhuddanian were resulted from the post-glacial rise of eustatic sea level. Combined with the data from Sanjiaguan section near the subemergent highland, salinity stratification of water columns are strongly evidenced by very low S/C ratios （ 0.00-0.08, avg. 0.02）, low FeHR/FeT ratios （0.10-0.37, avg. 0.27）, low DOP values （0.01-0.27, avg. 0.10）, and TOC contents （0.72%-4.27%, avg. 2.55%）. Under this circumstance, the anoxic water columns could have formed beneath the halocline, above which desalinized waters formed. In the Wangjiawan section, TOC contents are generally high （0.94- 9.32%, avg. 4.44%）, but low （0.35%-2.12%, avg. 1.29%） in the mid-early Hirnantian that is coincident with the oceanic oxic stage, together with relation of the organic contents to the stratal thickness, suggesting that the accumulation of the organic matter was mainly controlled by the oxygen levels of the water columns; on the other hand, productivity and depositional rate may also have played a role in the organic accumulation and preservation.展开更多
基金the Second Tibetan Plateau Scientific Expedition(2019QZKK0304)the Strategic Priority Research Program of Chinese Academy of Sciences(XDA2005010404)the Youth Science and Technology Innovation Team Program of Sichuan Province of China(2021JDTD011).
文摘More than half of the carbon pools in peatlands are stored in the soil layers below 30 cm,yet little is known about the carbon stabilizing factors at these depths.Although iron oxide minerals are considered to be important for stabilizing organic carbon(OC),their role in the preservation of OC in peatlands,especially in the deep layers,is poorly understood.Here,we collected 1 m soil profiles from six peatlands in Central and West China to quantitatively study the vertical distribution characteristics of iron-bound OC(Fe-bound OC),and the influencing physicochemical properties of the soil.The results showed that the content of reactive iron(FeR)was enriched in the top layer and decreased gradually with depth.While Fe-bound OC was positively correlated with FeR,its concentration did not decrease with depth in the peat profile.There were no obvious trends in the distributions of FeR and Fe-bound OC with water level fluctuations in the peat profile.In addition,the proportion of Fe-bound OC to soil organic carbon in the deep peat(31 to 100 cm)was equivalent to that in the surface peat(0 to 30 cm),indicating that iron oxide mineral provides comparable protection of OC in both layers.According to upper estimates of global peatland carbon storage(612 Pg),it could be predicted that 23.81±11.75 Pg of OC is protected by association with FeR.These results indicated that iron oxide minerals are the effective"rusty sink"of OC sequestration in peatland,and a key factor for its long-term preservation.The results from this study make a valuable contribution to the carbon dynamics knowledgebase for peatlands,and provide a basis for improved predictive simulations.
文摘Extensive organic-matter （OM） rich facies （black shales） occur in the Ordo-Silurian boundary successions in the Yangtze area, South China. To investigate the redox changes of the Yangtze Sea during the Ordo-Silurian transition, two OM sections （Wangjiawan in Yichang, Hubei Province, and Sanjiaguan in Zhangjiajie, Hunan Province） straddling the Ordo-Silurian boundary are studied. The measurements finished in this study include contents of the total organic carbon （TOC）, pyrite sulphur, and different species of Fe, including dithionite-extractable Fe （FED）, pyrite Fe （FeP）, HCl-extractable Fe （FeH）, and total Fe （FeT）, in black shales, as well as other redox proxies, such as the SIC ratio, the ratio between highly reactive Fe （FeHR = FeD ＋ FeP） and FeT, and the FeP/（FeP ＋ FeH） ratio, known as the degree of pyritization （DOP）. In the Wangjiawan section, the Middle Ashgill sediments have high FeHR/FeT ratios （0.20-0.77; avg. 0.45）, high DOP values （0.21-0.72; avg. 0.54）, and a relatively constant sulfur content independent of the organic carbon content. By the contrast, the mid-early Hirnantian deposits generally have low FeHR/FeT ratios （0.10-0.35; avg. 0.21）, low DOP values （0.11- 0.40; avg. 0.28）, and SIC values are clustering on the normal marine value （SIC = 0.36）. The late Hirnantian and early Rhuddanian deposits, similar to those of the Middle Ashgill deposits, are characterized by high FeHR/FeT ratios （0.32-0.49; avg. 0.41）, high DOP values （0.46-0.68; avg. 0.53） and fairly constant sulfur contents. These data suggest the occurrences of marine anoxia on the Yangtze Sea shelf during intervals of the Mid Ashgill, Late Hirnantian and Early Rhuddanian, and ventilated and oxygenated marine conditions during the mid-early Hirnantian time. The mid-early Hirnantian ventilated event was concomitant with the global glacial period, likely resulted from the glacio-eustatic sea-level fall and subsequent circulation of cold, dense oxygenated waters upon the shelf seabed. Accordingly, the abrupt change from oxygenated to anoxic marine waters from the late Hirnantian and the early Rhuddanian were resulted from the post-glacial rise of eustatic sea level. Combined with the data from Sanjiaguan section near the subemergent highland, salinity stratification of water columns are strongly evidenced by very low S/C ratios （ 0.00-0.08, avg. 0.02）, low FeHR/FeT ratios （0.10-0.37, avg. 0.27）, low DOP values （0.01-0.27, avg. 0.10）, and TOC contents （0.72%-4.27%, avg. 2.55%）. Under this circumstance, the anoxic water columns could have formed beneath the halocline, above which desalinized waters formed. In the Wangjiawan section, TOC contents are generally high （0.94- 9.32%, avg. 4.44%）, but low （0.35%-2.12%, avg. 1.29%） in the mid-early Hirnantian that is coincident with the oceanic oxic stage, together with relation of the organic contents to the stratal thickness, suggesting that the accumulation of the organic matter was mainly controlled by the oxygen levels of the water columns; on the other hand, productivity and depositional rate may also have played a role in the organic accumulation and preservation.
