High benthic community respiration and ecosystem response to phytodetrital input in a sub-polar fjord on the West Antarctic Peninsula

Glaciomarine fjords dominate the coastal margin of the West Antarctic Peninsula. Studies in similar habitats in the Arctic have shown that benthic biodiversity and ecosystem functioning in inner and middle fjord basins are reduced by turbidity and sedimentation disturbance caused by climate-warming-enhanced glacial melting. In contrast, the inner and middle fjord basins along the West Antarctic Peninsula are characterised as productivity and biodiversity hotspots, but benthic ecosystem functions remain unevaluated. In 2015-2016, we conducted sediment-respiration and 13C pulse-chase experiments to assess benthic ecosystem functions along a five-station transect at ~500-600 m depths from the inner Andvord Bay fjord, through to Gerlache Strait, and onto the open continental shelf. Incubation samples from the inner and middle basins of Andvord Bay showed peaks in background seafloor respiration, benthic biomass, and uptake of labeled algal biomass compared to more outlying stations; the continental shelf exhibited the lowest levels of these variables, as well as dissolved inorganic carbon production. Macrofaunal community uptake was responsible for most of the C processing in the inner and middle parts of the fjord (>45%) while dissolved inorganic carbon was the dominant repository of processed C near the fjord mouth and on the continental shelf (>80%). The inner parts of Andvord Bay are hotspots of benthic C-cycling and metabolism, in addition to biodiversity. Ongoing climate warming is likely to negatively impact these inner-fjord hotspots by increasing meltwater input and sedimentation disturbance, yielding a reduction in the input and recycling of labile detritus at the seafloor in the inner-middle fjord.

南极半岛西部沿海岸带以冰川海洋峡湾（Glaciomarine Fjords）为主。针对北极同类生境的研究表明，气候变暖加剧的冰川消融所引发的浊度与沉积扰动，会降低峡湾内、中盆地的底栖生物多样性与生态系统功能。与之形成对比的是，南极半岛西部沿岸的峡湾内、中盆地被认定为生产力与生物多样性热点区域，但目前其底栖生态系统功能仍未得到评估。2015至2016年，我们在安沃尔湾（Andvord Bay）内区至杰拉许海峡（Gerlache Strait）再至开阔大陆架的500~600米水深范围内，沿一条包含5个站位的断面开展了沉积物呼吸实验与碳13（13C）脉冲追踪实验，以此评估底栖生态系统功能。对安沃尔湾内、中盆地的培养样品分析结果显示，相较于外围站位，其背景海底呼吸速率、底栖生物量以及标记藻类生物量摄取量均达到峰值；大陆架区域的上述指标与溶解无机碳产生量均为最低水平。峡湾内、中段的碳处理过程主要由大型底栖动物群落摄取主导（占比超45%），而在峡湾口与大陆架区域，溶解无机碳是经处理碳的主要储存形式（占比超80%）。除生物多样性外，安沃尔湾内区还是底栖碳循环与代谢过程的热点区域。持续的气候变暖可能通过增加融水输入与沉积扰动，对这些峡湾内热点区域产生负面影响，进而降低峡湾内、中段海底易降解碎屑的输入与循环效率。