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冰封的湖泊中含有丰富的微生物垫，这种垫材料的出口可以使周围的极地沙漠生态系统肥沃。这些沙漠土壤是地球上最缺乏有机物的土壤之一，但却拥有一个微生物群落。当气泡在垫中形成时，微生物垫材料从湖泊的浅的气体过饱和区域输出，将它们提升到冰盖;常年冰盖保持气体过饱和。这些垫冻结并通过冰消融出口到周围的土壤。弗里克塞尔湖历史上最大的季节性减少和最薄的冰盖记录在2022-2023年南方夏季。在这个薄冰年，水柱溶解氧比以前的观测增加，气泡破裂垫的湖底表面积是1980-1981年和2006-2007年观测到的两倍多。这项工作将限制垫动员内外弗里克塞尔湖在麦克默多干旱河谷在一个前所未有的冰变薄的时期，以了解如何未来不断变化的区域气候和预测的季节性湖冰覆盖的损失将影响养分运输的麦克默多干旱河谷。特殊年份的垫出口假设有最显着的影响，养分输出到土壤群落，垫起飞的变化，从而发挥作用，在麦克默多干谷生态系统应对气候变化。南极洲麦克默多干谷湖泊的常年冰盖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。这些湖泊中生物量的输出是由常年冰盖下浅水区大气气体的过饱和驱动的。气泡在冰垫中成核，产生浮力将它们提升到冰底，在那里它们冻结并通过冰消融出口到周围的土壤。这些垫子代表了麦克默多干谷土壤的生物量和营养物质的重要来源，而干谷土壤是地球上最缺乏有机物的土壤之一。然而，这种生物量仍然不占有机碳循环模型的麦克默多干谷。来自麦克默多干旱河谷长期生态研究项目的冰盖数据显示，在过去40年中，冰层厚度经历了周期性变化，在2022-2023年的夏季，弗里克塞尔湖的冰层厚度达到了有记录以来最大的季节性减少和最薄的冰层厚度。初步工作表明，弗里克塞尔湖的垫升空表面积是1980-1981年和2006-2007年观察到的两倍多，与冰盖前所未有的变薄和水柱溶解O2的增加相吻合。这项研究将限制生物量动员内外的弗里克塞尔湖在麦克默多干旱山谷在一个前所未有的冰变薄的时期。研究人员假设，较薄的冰盖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，刺激现有气体过饱和沃茨中产生额外的气泡，以产生微生物垫升空，2）促进更深，更厚的微生物垫中的垫升空，3）这种生物质可以通过表征其化学和模拟最可能的沉积环境来追踪土壤。这项工作将使用微生物垫样本，湖泊溶解氧和光合有效辐射数据以及记录2023年1月升空垫深度分布的水下无人机镜头，以及由麦克默多干旱山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来测试假设1-3。将使用混合单粒子拉格朗日积分轨迹（HYSPLIT）模型对暴露在弗里克塞尔湖表面的升空垫的扩散进行建模。假设像现在这样的特殊起飞年份对土壤群落产生最显着的影响，因为土壤呼吸速率随着碳的增加而增加。然而，未来10 - 40年的持续变暖可能导致冰盖的季节性丧失和升空垫出口的停止。该奖项反映了NSF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.