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，坐落于不列颠哥伦比亚省（British Columbia）温哥华岛（Vancouver Island）东南海岸，开口连通乔治亚海峡（Strait of Georgia）。该峡湾全长约24千米，盆地区域最大水深达234米，周边流域汇入的淡水补给十分有限。75米深的冰川型入口海槛在一年中绝大多数时段都会限制峡湾内部与盆地区域的水体循环。在春夏季，受限的水体循环与表层水域高强度的初级生产力共同导致溶解氧消耗，同时伴随水层层化现象——这一过程可通过甲烷（CH4）、氨（NH3）与硫化氢（H2S）的累积得到佐证。至夏末与秋季，经乔治亚海峡上升形成的富氧富营养海水会倾泻涌入萨尼奇峡湾，将缺氧底层水向上抬升，进而改变整个水层的氧化还原化学特性。这一过程在十年尺度上保持稳定，不同季节的氧跃层（oxycline）深度分布仅存在相对较小的偏差。周期性出现的季节性水层缺氧现象与后续的深水更新过程，为在广泛的水层氧化还原状态下开展微生物群落结构与功能的时空剖面分析提供了可行条件。