Environmental Program, Guangdong Technion - Israel Institute of Technology, Shantou 515063, China.
Petroleum and Marine Research Division, Korea Institute of Geoscience and Mineral Resources, 124 Gwahak-ro, Yuseong-gu, Daejeon 34132, South Korea.
Sci Total Environ. 2021 Jul 10;777:146100. doi: 10.1016/j.scitotenv.2021.146100. Epub 2021 Feb 28.
Arctic subsea permafrost contains more organic carbon than the terrestrial counterpart (~1400 Pg C vs. ~1000 Pg C) and is undergoing fast degradation (at rates of ~10 to 30 cm yr over the past 3 decades) in response to climate warming. Yet the flux of organic carbon sequestered in the sediments of subsea permafrost to overlying water column, which can trigger enormous positive carbon-climate feedbacks, remain unclear. In this study, we examined the dissolved organic matter (DOM) diffusion to bottom seawaters from East Siberian Sea (ESS) sediments, which was estimated at about 943-2240 g C m yr and 10-55 g C m yr at the continuous-discontinuous transition zone of subsea permafrost and the remainder shelf and slope sites, respectively. The released DOM is characterized by prevailing dominance (≥ 98%) of low molecular weight (M < 350 Da) fractions. A red-shifted (emission wavelength >500 nm) fluorescence fingerprint, a typical feature of sediment/soil DOM, accounts for 4-6% and 7-8% in the fluorescence distributions of seawaters and pore waters, respectively, on ESS shelf. Statistical analysis revealed that seawaters and pore waters possessed similar DOM composition. The estimated total benthic efflux of dissolved organic carbon (DOC) was ~0.7-1.0 Pg C yr when the estimate was scaled up to the entire Arctic shelf underlain with subsea permafrost assuming the width of continuous-discontinuous transition zone is 1 to 10 m. This estimation is consistent with the established ~10-30 cm yr degradation rates of subsea permafrost by estimating its thaw-out time. Compiled observation data suggested that subsea permafrost might be a major DOM source to the Arctic Ocean, which could release tremendous carbon upon remineralization via its degradation to CO and CH in the water column.
北极海底永冻层所含的有机碳多于陆地永冻层（1400 Pg C 对1000 Pg C），并且在过去 30 年里，由于气候变暖，永冻层正迅速退化（过去 30 年里，退化速率约为10 到 30 cm 年）。然而，埋藏于海底永冻层沉积物中的有机碳向覆盖水层的通量，这可能引发巨大的正碳气候反馈，仍然不清楚。在这项研究中，我们研究了从东西伯利亚海（ESS）沉积物中扩散到底部海水中的溶解有机物质（DOM），其通量分别约为 943-2240 g C m yr 和 10-55 g C m yr，在海底永冻层的连续不连续过渡带以及剩余的大陆架和斜坡地区。释放的 DOM 的特点是占主导地位的低分子量（M < 350 Da）部分（≥98%）。一个红移（发射波长> 500nm）荧光指纹，一个沉积物/土壤 DOM 的典型特征，在 ESS 大陆架上，海水和孔隙水中的荧光分布分别占 4-6%和 7-8%。统计分析表明，海水和孔隙水具有相似的 DOM 组成。当将估计值扩展到整个北极大陆架（假设连续不连续过渡带的宽度为 1 到 10 m）时，根据海底永冻层的估计降解速率（10-30 cm 年），计算出的海底永冻层总底栖溶解有机碳（DOC）的总排放量约为 0.7-1.0 Pg C yr。这个估计值与通过估计其解冻时间确定的海底永冻层的~10-30 cm 年的降解速率一致。汇编的观测数据表明，海底永冻层可能是北极海洋中主要的 DOM 来源，通过在水柱中降解为 CO 和 CH，它可能会释放大量的碳。
