Twice the global average carbon burial efficiency in the Helgoland Mud Area of the North Sea: Insights into carbon sequestration in small-size depocenters on sand-dominated shelves

IF 3.6 2区地球科学 Q1 GEOCHEMISTRY & GEOPHYSICS

Chemical Geology Pub Date : 2025-02-27 DOI:10.1016/j.chemgeo.2025.122712

Bingbing Wei , Daniel Müller , Stephanie Kusch , Lu Niu , Jens Hefter , Lasse Sander , Ulrike Hanz , Gesine Mollenhauer , Guodong Jia , Sabine Kasten , Moritz Holtappels

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Abstract

Continental shelves are integral to the global carbon cycle, yet uncertainties persist about the nature and extent of carbon burial, particularly in sand-dominated areas. In the sand-dominated North Sea, the Helgoland Mud Area (HMA) emerges as a small-size mud depocenter, surrounded by sandy sediments that do not accumulate organic carbon (OC) and are separated from adjacent rivers. Such small-size depocenters, common on high-energy shelves, have underexplored OC degradation and burial efficiencies due to their limited individual size. Since sandy sediments with interspersed small-size depocenter cover ∼50 % of global shelves, these depocenters may collectively offer greater OC burial capacity than previously recognized.

This study investigated the composition, degradation, and sequestration of OC from terrestrial (OC_terr) and marine (OC_mar) sources in surface sediments of the HMA and adjacent sandy areas using bulk (mean grain size, OC content, loading and ¹³C isotope composition) and molecular (fatty acids and alkanes) analyses. Our results, derived from a two end-member mixing model based on δ¹³C values of bulk OC, revealed that OC_terr dominates (∼74 %) the sedimentary OC in both areas, with OC_mar contributing ∼26 %. The HMA exhibited OC_terr and OC_mar contents ∼5 times higher than in the sandy areas. Both OC_terr and OC_mar loadings negatively correlated with mean grain size, indicating reduced OC degradation in muddy sediments. Molecular analysis further revealed that OC_terr in the HMA is less refractory compared to adjacent sandy regions. These differences are attributed to differences in porewater transport, oxygen penetration depths and exposure times, all of which influence OC preservation, despite the important role of mineral protection. OC_terr and OC_mar accumulation fluxes in the HMA were calculated at (6.75 ± 0.61) × 10⁻³ and (2.54 ± 0.68) × 10⁻³ Tg C/yr, respectively, representing 34.3 % of OC_terr export from adjacent rivers and 2.8 % of net OC_mar production in the HMA. These values are twice the global average for shelf areas, highlighting the exceptional efficiency of the HMA as a carbon sink and hinting at the significance of small-size depocenters within sandy areas in the global carbon cycle.

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北海Helgoland泥区碳埋藏效率是全球平均水平的两倍：对砂质陆架上小型沉积中心碳封存的洞察

大陆架是全球碳循环的组成部分，但碳埋藏的性质和程度仍然存在不确定性，特别是在以沙为主的地区。在以砂为主的北海，Helgoland泥区（HMA）是一个小型的泥沉积中心，周围是不积累有机碳（OC）的砂质沉积物，与邻近的河流分离。这种小尺寸的沉积中心在高能量大陆架上很常见，由于其个体尺寸有限，对OC降解和埋藏效率的研究不足。由于分散的小型沉积中心的砂质沉积物覆盖了全球陆架的约50%，这些沉积中心可能提供比以前认识到的更大的OC埋藏能力。本研究通过体积（平均粒径、OC含量、载荷和13C同位素组成）和分子（脂肪酸和烷烃）分析，研究了HMA和邻近沙区表层沉积物中陆源（OCterr）和海源（OCmar） OC的组成、降解和封存。我们的结果来自基于大块OC的δ13C值的双端元混合模型，结果显示OCterr在两个地区的沉积OC中占主导地位（~ 74%），OCmar贡献~ 26%。HMA的OCterr和OCmar含量比沙质地区高~ 5倍。OCterr和OCmar负荷与平均粒径呈负相关，表明泥质沉积物中OC的降解减少。分子分析进一步表明，与邻近的沙质区域相比，HMA中的OCterr的难熔性较低。这些差异归因于孔隙水运输、氧气渗透深度和暴露时间的差异，尽管矿物保护起着重要作用，但所有这些都影响着OC的保存。HMA的OCterr和OCmar累积通量分别为（6.75±0.61）× 10−3和（2.54±0.68）× 10−3 Tg C/年，占HMA相邻河流OCterr输出的34.3%和净OCmar产量的2.8%。这些数值是陆架地区全球平均值的两倍，突出了HMA作为碳汇的卓越效率，并暗示了沙区内小型沉积物在全球碳循环中的重要性。

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来源期刊

Chemical Geology 地学-地球化学与地球物理

CiteScore

7.20

自引率

10.30%

发文量

374

审稿时长

3.6 months

期刊介绍： Chemical Geology is an international journal that publishes original research papers on isotopic and elemental geochemistry, geochronology and cosmochemistry. The Journal focuses on chemical processes in igneous, metamorphic, and sedimentary petrology, low- and high-temperature aqueous solutions, biogeochemistry, the environment and cosmochemistry. Papers that are field, experimentally, or computationally based are appropriate if they are of broad international interest. The Journal generally does not publish papers that are primarily of regional or local interest, or which are primarily focused on remediation and applied geochemistry. The Journal also welcomes innovative papers dealing with significant analytical advances that are of wide interest in the community and extend significantly beyond the scope of what would be included in the methods section of a standard research paper.