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.

萨尼奇湾（Saanich Inlet）是一座季节性缺氧的峡湾，位于不列颠哥伦比亚省（British Columbia）温哥华岛（Vancouver Island）东南海岸，与乔治亚海峡（Strait of Georgia）相通。该峡湾全长约24公里，盆地最大水深达234米，周边流域汇入的淡水补给有限。一道深75米的冰川入口浅槛（glacial entrance sill）在一年中的多数时段限制了峡湾内部与盆地水体的环流。春夏季时段，受限环流与表层水体的高初级生产力共同导致水体缺氧，伴随甲烷（CH4）、氨（NH3）与硫化氢（H2S）的积累，形成水体分层现象。夏末与秋季，经乔治亚海峡涌升的富氧富营养海水涌入萨尼奇湾，将缺氧底层水向上抬升，改变了整个水柱的氧化还原化学特性。该过程在十年尺度上保持稳定，一年中不同时段的氧化跃层（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与随后的深水更新过程，为在涵盖多种水柱氧化还原状态的范围内开展微生物群落结构与功能的时空剖面分析提供了条件。