Benthic oxygen and nitrogen fluxes measured by box core incubation and aquatic eddy covariance technique at a cold-water coral reef in the NE Atlantic@en

Cold-water coral (CWC) reefs are distributed globally and form complex three-dimensional structures on the deep seafloor, providing habitat for numerous species. Here, we measured the community O2 and dissolved inorganic nitrogen (DIN) flux of CWC reef habitats with different coral cover and bare sediment (acting as reference site) in the Logachev Mound area (NE Atlantic). Two methodologies were applied: the non-invasive in situ aquatic eddy co-variance (AEC) technique, and ex situ whole box core (BC) incubations. The AEC system was deployed twice per coral mound (69 h in total), providing an integral estimate of the O2 flux from a total reef area of up to 500 m2, with mean O2 consumption rates ranging from 11.6 ± 3.9 to 45.3 ± 11.7 mmol O2 m-2 d-1 (mean ± SE). CWC reef community O2 fluxes obtained from the BC incubations ranged from 5.7 ± 0.3 to 28.4 ± 2.4 mmol O2 m-2 d-1 (mean ± SD) while the O2 flux measured by BC incubations on the bare sediment reference site reported 1.9 ± 1.3 mmol O2 m-2 d-1 (mean ± SD). Overall, O2 fluxes measured with AEC and BC showed reasonable agreement, except for one station with high habitat heterogeneity. Our results suggest O2 fluxes of CWC reef communities in the North East Atlantic are around five times higher than of sediments from comparable depths and living CWCs are driving the increased metabolism. DIN flux measurements by the BC incubations also revealed around two times higher DIN fluxes at the CWC reef (1.17 ± 0.87 mmol DIN m-2 d-1), compared to the bare sediment reference site (0.49 ± 0.32 mmol DIN m-2 d-1), due to intensified benthic release of NH4+. Our data indicate that the amount of living corals and dead coral framework largely contributes to the observed variability in O2 fluxes on CWC reefs. A conservative estimate, based on the measured O2 and DIN fluxes, indicates that CWC reefs process 20% to 35% of the total benthic respiration on the southeasterly Rockall Bank area, which demonstrates that CWC reefs are important to carbon and nitrogen mineralization at the habitat scale.冷水珊瑚（Cold-water coral, CWC）礁广泛分布于全球海域，于深海海底构建复杂的三维立体结构，为众多物种提供栖息生境。本研究于东北大西洋洛加契夫丘（Logachev Mound）海域，针对不同珊瑚覆盖度的冷水珊瑚礁生境以及作为对照的裸露沉积物生境，测定了其群落氧（O₂）通量与溶解无机氮（Dissolved Inorganic Nitrogen, DIN）通量。研究采用两种实验方法：一是无损伤原位水体涡度协方差（Aquatic Eddy Covariance, AEC）技术，二是异位完整箱式岩心（Whole Box Core, BC）培养实验。AEC系统在每个珊瑚丘上部署两次，总时长69小时，可对总面积达500 m²的礁体区域的氧通量进行整体估算，测得的平均氧消耗速率为11.6 ± 3.9 至 45.3 ± 11.7 mmol O₂ m⁻² d⁻¹（平均值±标准误）。通过箱式岩心培养测得的冷水珊瑚礁群落氧通量范围为5.7 ± 0.3 至 28.4 ± 2.4 mmol O₂ m⁻² d⁻¹（平均值±标准差），而裸露沉积物对照样地的箱式岩心培养氧通量为1.9 ± 1.3 mmol O₂ m⁻² d⁻¹（平均值±标准差）。总体而言，除一个生境异质性较高的站位外，AEC与箱式岩心培养测得的氧通量具有较好的一致性。本研究结果表明，东北大西洋冷水珊瑚礁群落的氧通量约为同等深度沉积物的5倍，且活体冷水珊瑚是代谢水平提升的驱动因素。箱式岩心培养测得的DIN通量结果同样显示，冷水珊瑚礁生境的DIN通量约为裸露沉积物对照样地的2倍（冷水珊瑚礁生境为1.17 ± 0.87 mmol DIN m⁻² d⁻¹，对照样地为0.49 ± 0.32 mmol DIN m⁻² d⁻¹），这源于铵根离子（NH₄⁺）的底栖释放过程增强。本研究数据表明，活体珊瑚与死亡珊瑚骨架的占比是导致冷水珊瑚礁氧通量变异的主要因素。基于实测氧与DIN通量的保守估算显示，东南方向罗卡尔浅滩（Rockall Bank）海域的底栖呼吸总量中，有20%~35%由冷水珊瑚礁贡献，这证实了冷水珊瑚礁在生境尺度的碳氮矿化过程中发挥着重要作用。