Benthic organic carbon flux and oxygen penetration depth in the Southern Ocean

For the investigation of organic carbon fluxes reaching the seafloor, oxygen microprofiles were measured at 145 sites in different sub-regions of the Southern Ocean. At eleven sites, an in situ oxygen microprofiler was deployed for the measurement of oxygen profiles and the calculation of organic carbon fluxes. At four sites, both in situ and ex situ data were determined for high latitudes. Based on this dataset as well as on previous published data, a relationship was established for the estimation of fluxes derived by ex situ measured O2 profiles. The fluxes of labile organic matter range from 0.5 to 37.1 mgC m**2/day. The high values determined by in situ measurements were observed in the Polar Front region (water depth of more than 4290 m) and are comparable to organic matter fluxes observed for high-productivity, upwelling areas like off West Africa. The oxygen penetration depth, which reflects the long-term organic matter flux to the sediment, was correlated with assemblages of key diatom species. In the Scotia Sea (~3000 m water depth), oxygen penetration depths of less than 15 cm were observed, indicating high benthic organic carbon fluxes. In contrast, the oxic zone extends down to several decimeters in abyssal sediments of the Weddell Sea and the southeastern South Atlantic. The regional pattern of organic carbon fluxes derived from micro-sensor data suggest that episodic and seasonal sedimentation pulses are important for the carbon supply to the seafloor of the deep Southern Ocean.

为探究抵达海底的有机碳通量，研究团队在南大洋不同子区域的145个测点开展了氧微剖面（oxygen microprofile）测量。其中11个测点部署了原位（in situ）氧微剖面仪（oxygen microprofiler），用于获取氧剖面数据并计算有机碳通量。另有4个高纬度测点同时获取了原位（in situ）与异位（ex situ）观测数据。基于本数据集及已发表的既往研究数据，研究人员建立了通过异位（ex situ）实测氧剖面估算有机碳通量的关联模型。活性有机质（labile organic matter）的通量范围为0.5至37.1 mgC m⁻²·d⁻¹。原位测量得到的高通量值出现在极锋区域（Polar Front region，水深超过4290米），其数值可与西非外海等高生产力上升流区域的有机质通量相媲美。反映沉积物长期接收有机质通量的氧穿透深度（oxygen penetration depth），与关键硅藻（diatom）物种的群落组成具有相关性。在水深约3000米的斯科舍海（Scotia Sea），观测到氧穿透深度不足15厘米，表明该区域的底栖有机碳通量较高。与之相反，威德尔海（Weddell Sea）与南大西洋东南部的深海沉积物（abyssal sediments）中，氧化带（oxic zone）可延伸至数分米深度。基于微传感器数据得到的有机碳通量区域分布模式表明，突发性与季节性沉积脉冲对深海南大洋的海底碳补给具有重要意义。