RAPID: Is Biomass Mobilization at Ice-covered Lake Fryxell, Antarctica reaching a Critical Threshold?

南极洲麦克默多干谷常年被冰覆盖的湖泊含有丰富的微生物垫，这些垫材料的出口可以为周围的极地沙漠生态系统施肥。这些沙漠土壤是地球上最缺乏有机物的土壤之一，但却拥有微生物群落。微生物垫层物质从湖泊的浅层、气体过饱和区域输出，当垫层中形成气泡，将它们提升到冰盖上；常年的冰盖使气体保持过饱和状态。这些草席被冻结，并通过冰消融出口到周围的土壤中。在2022-2023年的南方夏季，弗里克塞尔湖出现了历史上最大的季节性减少和最薄的冰盖。在这一薄冰年，水柱溶解氧比以往观测值有所增加，气泡破坏垫的湖底表面积比1980-1981年和2006-2007年增加了一倍以上。这项工作将在前所未有的冰变薄期间限制麦克默多干谷Fryxell湖内外的垫动员，以了解未来变化的区域气候和预测的湖泊冰盖季节性损失将如何影响麦克默多干谷的营养物质运输。假设特殊年份的草席输出对土壤群落的养分输出有最显著的影响；因此，海平面上升的变化可能在麦克默多干谷生态系统对气候变化的响应中发挥作用。南极洲麦克默多干谷的湖泊常年覆盖的冰层调节了湖泊和周围土壤之间的气体、有机和无机物质的转移。这些湖泊的生物量输出是由常年被冰覆盖的浅层大气气体的过饱和驱动的。气泡在冰垫中形成核，产生浮力，将它们提升到冰的底部，在那里它们被冻结，并通过冰的消融输出到周围的土壤中。这些草席是麦克默多干谷土壤生物量和养分的重要来源，而麦克默多干谷是地球上最缺乏有机物的土壤之一。然而，这种生物量在麦克默多干谷的有机碳循环模型中仍然没有被计算在内。麦克默多干谷长期生态研究项目的冰盖数据表明，在过去40年里，冰厚经历了周期性变化，在2022-2023年的南方夏季，弗里克塞尔湖达到了有记录以来最大的季节性减少和最薄的冰盖。初步研究表明，Fryxell湖的海平面上升面积是1980-1981年和2006-2007年观测到的两倍多，与此同时，冰盖前所未有地变薄，水柱溶解氧增加。这项研究将在前所未有的冰变薄时期限制麦克默多干谷Fryxell湖内外的生物量动员。研究人员假设，较薄的冰盖可以通过以下方式促进更多的生物质动员：1)在夏季光合作用期间，刺激现有的气体过饱和水域产生额外的气泡，从而产生微生物垫；2)促进更深、更厚的微生物垫的气泡升起；3)通过表征其化学性质和模拟最可能的沉积环境，可以追踪到这些生物量。本研究将利用微生物席样品、湖泊溶解氧和光合有效辐射数据，以及记录2023年1月上升席深度分布的水下无人机画面，以及麦克默多干谷长期生态研究项目收集的长期冰盖厚度、光合有效辐射和湖泊水位变化数据，对假设1-3进行验证。采用混合单粒子拉格朗日积分轨迹（HYSPLIT）模型对暴露在Fryxell湖表面的发射垫的扩散进行建模。假设像现在这样的特殊上升年对土壤群落有最显著的影响，因为土壤呼吸速率随着碳的增加而增加。然而，未来10 - 40年的持续变暖可能会导致冰盖的季节性损失，并停止发射垫的出口。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Perennially ice-covered lakes in the McMurdo Dry Valleys of Antarctica contain abundant microbial mats, and the export of this mat material can fertilize the surrounding polar desert ecosystems. These desert soils are one of the most organic-poor on earth yet host a community of microorganisms. Microbial mat material is exported from the shallow, gas-supersaturated regions of the lakes when gas bubbles form in the mats, lifting them to the ice cover; the perennial ice cover maintains gas supersaturation. These mats freeze in and are exported to the surrounding soils through ice ablation. The largest seasonal decrease and thinnest ice cover in the history of Lake Fryxell was recorded during the 2022-2023 Austral summer. In this thin ice year, the water column dissolved oxygen increased over prior observations, and the lake bottom surface area with bubble-disrupted mat was more than double that observed in 1980-1981 and 2006-2007. This work will constrain mat mobilization within and out of Lake Fryxell in the McMurdo Dry Valleys during a period of unprecedented ice thinning to understand how future changing regional climate and predicted seasonal loss of lake ice cover will affect nutrient transport in the McMurdo Dry Valleys. Exceptional years of mat export are hypothesized to have the most significant impact on nutrient export to soil communities; variability in mat liftoff may thus play a role in the McMurdo Dry Valleys ecosystem response to changing climate. The perennial ice cover of lakes in the McMurdo Dry Valleys of Antarctica modulates the transfer of gasses, organic and inorganic material, between the lakes and surrounding soils. The export of biomass in these lakes is driven by the supersaturation of atmospheric gasses in the shallow regions under perennial ice cover. Gas bubbles nucleate in the mats, producing buoyancy that lifts them to the bottom of the ice, where they freeze in and are exported to the surrounding soils through ice ablation. These mats represent a significant source of biomass and nutrients to the McMurdo Dry Valleys soils, which are among the most organic-poor on earth. Nevertheless, this biomass remains unaccounted for in organic carbon cycling models for the McMurdo Dry Valleys. Ice cover data from the McMurdo Dry Valleys Long Term Ecological Research Project shows that the ice thickness has undergone cyclical variation over the last 40 years, reaching the largest seasonal decrease and thinnest ice-cover in the recorded history of Lake Fryxell during the 2022-2023 austral summer. Preliminary work shows that the surface area with mat liftoff at Lake Fryxell is more than double that observed in 1980-1981 and 2006-2007, coinciding with this unprecedented thinning of the ice-cover and an increase in the water column dissolved O2. This research will constrain biomass mobilization within and out of Lake Fryxell in the McMurdo Dry Valleys during a period of unprecedented ice thinning. The researchers hypothesize that a thinner ice cover promotes more biomass mobilization by 1) stimulating additional production of gas bubbles from the existing gas-supersaturated waters during summertime photosynthesis to create microbial mat liftoff and 2) promoting mat liftoff in deeper, thicker microbial mats, and 3) that this biomass can be traced into the soils by characterizing its chemistry and modeling the most likely depositional settings. This work will use microbial mat samples, lake dissolved oxygen and photosynthetically active radiation data and underwater drone footage documenting the depth distribution of liftoff mats in January 2023, and long-term ice cover thickness, photosynthetically active radiation, and lake level change data collected by the McMurdo Dry Valleys Long Term Ecological Research Project to test hypotheses 1-3. The dispersal of the liftoff mat exposed at Lake Fryxell surface will be modeled using a Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model. Exceptional liftoff years like the present are hypothesized to have the most significant impact on the soil communities as the rates of soil respiration increase with the addition of carbon. However, continued warming in the next 10 - 40 years may result in seasonal loss of the ice cover and cessation of liftoff mat export.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.