Ager Thomas Gjerluff, Krause-Jensen Dorte, Olesen Birgit, Carlson Daniel F, Winding Mie Hylstofte Sichlau, Sejr Mikael K
Department of Biology, Aarhus University, 8000 Aarhus C, Denmark; Department of Ecoscience, Aarhus University, 8000 Aarhus C, Denmark.
Department of Ecoscience, Aarhus University, 8000 Aarhus C, Denmark; Arctic Research Center, Aarhus University, 8000 Aarhus C, Denmark.
Sci Total Environ. 2023 May 10;872:162224. doi: 10.1016/j.scitotenv.2023.162224. Epub 2023 Feb 15.
Despite growing attention on the contribution of macroalgae to carbon cycling and sequestration (blue carbon), more observational data is needed to constrain current estimates. In this study, we estimate the floating macroalgal carbon flux within and beyond a large sub-Arctic fjord system, Nuup Kangerlua, Greenland, which could potentially reach carbon sinks. Our study estimates 1) the fjord-scale area with macroalgal coverage and barrens caused by sea urchin grazing, 2) the floating macroalgal biomass in the fjord, and 3) the annual export flux of floating macroalgae out of the fjord system. ROV surveys documented that macroalgal habitats cover 32 % of the seafloor within the photic zone (0-30 m) with an average coverage of 39.6, 22, and 7.2 % in the depth intervals 0-10, 10-20, and 20-30 m, respectively. 15 % of the area suitable for macroalgae was denuded by sea urchin grazing. Floating macroalgae were common with an average biomass of 55 kg wet weight km. Densities and species composition varied seasonally with the highest levels after storms. The floating biomass was composed of intertidal macroalgal species (58 %) (Fucus vesiculosus, Fucus distichus, and Ascophyllum nodosum) and kelps (42 %) (Saccharina longicruris, S. latissima, and Alaria esculenta). We deployed surface GPS drifters to simulate floating macroalgal trajectories and velocity. Data indicated that 80 % of the floating biomass is retained in the fjord where its fate in relation to long-term sequestration is unknown. Export beyond the fjord was limited and indicated an annual floating macroalgal export beyond the fjord of only 6.92 t C yr, which is equal to ~0.02 % of the annual net primary production. Our findings suggest that floating macroalgae support a limited blue carbon potential beyond this fjord and that future research should focus on the fate of retained floating macroalgae and subsurface export to resolve the connectivity between macroalgal habitats and long-term carbon sinks.
尽管大型海藻对碳循环和碳固存（蓝碳）的贡献日益受到关注，但仍需要更多观测数据来限制当前的估算。在本研究中，我们估算了格陵兰努克峡湾系统（Nuup Kangerlua）内及之外的漂浮大型海藻碳通量，该峡湾可能成为碳汇。我们的研究估算了：1）大型海藻覆盖区域以及海胆啃食造成的无藻区的峡湾尺度面积；2）峡湾内漂浮大型海藻的生物量；3）漂浮大型海藻每年流出峡湾系统的通量。遥控水下机器人（ROV）调查记录显示，大型海藻栖息地覆盖了光合带（0 - 30米）内32%的海底，在0 - 10米、10 - 20米和20 - 30米深度区间的平均覆盖率分别为39.6%、22%和7.2%。适合大型海藻生长的区域有15%被海胆啃食殆尽。漂浮大型海藻很常见，平均生物量为55千克湿重/平方千米。密度和物种组成随季节变化，暴风雨后达到最高水平。漂浮生物量由潮间带大型海藻物种（58%）（囊藻、分歧囊藻和泡叶藻）和海带（42%）（长囊海带、宽叶海带和掌状海带）组成。我们部署了水面全球定位系统漂流器来模拟漂浮大型海藻的轨迹和速度。数据表明，80%的漂浮生物量滞留在峡湾内，其与长期碳固存相关的归宿尚不清楚。峡湾外的输出量有限，表明每年从峡湾输出的漂浮大型海藻仅为6.92吨碳/年，约占年净初级生产力的0.02%。我们的研究结果表明，该峡湾之外的漂浮大型海藻所具有的蓝碳潜力有限，未来的研究应聚焦于滞留的漂浮大型海藻的归宿以及次表层输出，以解决大型海藻栖息地与长期碳汇之间的连通性问题。
