Methane distribution above the Emperor Seamount chain

IF 2.3 3区 地球科学 Q2 OCEANOGRAPHY Deep-sea Research Part Ii-topical Studies in Oceanography Pub Date : 2024-10-16 DOI:10.1016/j.dsr2.2024.105431
Nikita S. Polonik, Alexey A. Legkodimov
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Abstract

Dissolved methane (CH4) concentrations were measured in the water column at 25 stations along the four sections above Koko and Jingu guyots (the southern part of Emperor Seamount chain). The measured methane concentrations were relatively low (1–6.5 nM). The patterns of CH4 vertical distributions over Koko and Jingu were different. The greatest dissolved methane concentrations (6.5 nM) were found in the near-bottom layer (357 m) above the Koko summit. For Koko guyot, the greatest CH4 content (3.9–6.5 nM) was mainly associated with the subsurface (10–300 m) layer above the summit. However, another methane plume (6 nM) was detected at 1000 m on the western slope of the guyot. We propose that methane maximum was caused by the influence of the Kuroshio Extension or deep eddies. The CH4 distribution over Jingu gyuot was similar to that in open ocean waters. The greatest methane concentrations (3.8–6 nM) were found in the subsurface layers above the summit. Methane exceeded atmospheric equilibrium concentration in the surface (5–52 % supersaturation) layer for both Koko and Jingu. The methane content and supersaturation level in the subsurface layer was at least two times higher than previously measured values for the open ocean. We believe that the high methane and supersaturation level was caused by enhanced methanogenesis in the water column above the seamounts. The estimated methane flux to the atmosphere varied from 1.4 to 16.3 μmol m−2 day−1 for Koko and from 0.5 to 6.5 μmol m−2 day−1 for Jingu, respectively. The average fluxes calculated for Koko (8.37 μmol m−2 day−1) and Jingu (2.8 μmol m−2 day−1) were significantly greater than the average flux for open and coastal oceans. Given the substantial methane atmospheric contributions, the global methane budget should be reconsidered.
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皇帝海山链上方的甲烷分布情况
在 Koko 和 Jingu guyots(帝王海山链南部)上方四个断面的 25 个站点测量了水体中的溶解甲烷(CH4)浓度。测得的甲烷浓度相对较低(1-6.5 nM)。科科和神宫上空的甲烷垂直分布模式不同。最大的溶解甲烷浓度(6.5 nM)出现在科科山顶上方的近底层(357 米)。在 Koko guyot,最大的 CH4 含量(3.9-6.5 nM)主要与山顶上方的次表层(10-300 米)有关。然而,在盖奥特西坡 1000 米处检测到了另一个甲烷羽流(6 nM)。我们认为甲烷的最大值是由黑潮延伸或深层漩涡的影响造成的。神宫巨蛋上空的 CH4 分布与开阔海域相似。最大的甲烷浓度(3.8-6 nM)出现在山顶上方的次表层。科科和神宫表层(过饱和度为 5-52 %)的甲烷浓度都超过了大气平衡浓度。次表层的甲烷含量和过饱和度至少是之前在公海测量值的两倍。我们认为,高甲烷含量和过饱和度是由海山上方水柱中甲烷生成增强造成的。据估计,甲烷进入大气的通量,科科和神宫分别为 1.4 至 16.3 μmol m-2 天-1 和 0.5 至 6.5 μmol m-2 天-1。计算得出的科科(8.37 μmol m-2 天-1)和神宫(2.8 μmol m-2 天-1)的平均通量明显高于开阔洋和沿岸洋的平均通量。鉴于甲烷在大气中的大量贡献,应重新考虑全球甲烷预算。
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来源期刊
CiteScore
6.40
自引率
16.70%
发文量
115
审稿时长
3 months
期刊介绍: Deep-Sea Research Part II: Topical Studies in Oceanography publishes topical issues from the many international and interdisciplinary projects which are undertaken in oceanography. Besides these special issues from projects, the journal publishes collections of papers presented at conferences. The special issues regularly have electronic annexes of non-text material (numerical data, images, images, video, etc.) which are published with the special issues in ScienceDirect. Deep-Sea Research Part II was split off as a separate journal devoted to topical issues in 1993. Its companion journal Deep-Sea Research Part I: Oceanographic Research Papers, publishes the regular research papers in this area.
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