Ecological Genomics of a Seasonally Anoxic Fjord; Saanich Inlet

Saanich Inlet is a seasonally anoxic fjord opening to the Strait of Georgia on the southeast coast of Vancouver Island, British Columbia. It is approximately 24 kilometers long with a maximal basin depth of 234 meters and receives limited freshwater input from the surrounding watershed. A shallow glacial entrance sill 75 meters deep restricts circulation within interior and basin waters for most of the year. During spring and summer months, restricted circulation combined with high levels of primary productivity in surface waters lead to oxygen loss with concomitant water column stratification indicated by accumulation of methane (CH4), Ammonia (NH3) and Hydrogen Sulfide (H2S). In late summer and fall, oxygenated nutrient-rich ocean waters upwelling through the Strait cascade into Saanich Inlet shoaling anoxic bottom waters upward and transforming the redox chemistry of the water column. This process is stable on decadal time scales exhibiting a relatively narrow deviation in the depth distribution of the oxycline at different times of year. The recurring seasonal development of water column anoxia followed by deep-water renewal enables spatiotemporal profiling of microbial community structure and function across a wide range of water column redox states.

萨尼奇峡湾（Saanich Inlet）是一处季节性缺氧峡湾，开口于不列颠哥伦比亚省温哥华岛东南海岸的乔治亚海峡（Strait of Georgia）。该峡湾全长约24千米，盆地最大水深达234米，周边流域汇入的淡水输入量有限。一道水深75米的浅冰蚀入口门槛，在一年中的多数时段内限制了峡湾内部与盆地水域的水体交换。春夏季期间，受限的水体环流结合表层水域的高初级生产力，导致水体溶解氧流失，同时伴随甲烷（CH₄）、氨（NH₃）与硫化氢（H₂S）的积累，形成水体柱层化现象。晚夏与秋季时节，富含溶解氧且营养充足的海水经海峡上升流涌入萨尼奇峡湾，将缺氧的底层水体向上抬升，重塑了整个水柱的氧化还原化学环境。这一过程在十年尺度上保持稳定，不同季节的氧化跃层（oxycline）深度分布偏差相对较小。这种周期性出现的季节性水体缺氧现象，随后伴随深层水体更新，使得研究者可针对涵盖广泛水柱氧化还原状态的微生物群落结构与功能开展时空剖面分析。