The global cryosphere, Earth's frozen water, is in precipitous decline. The ongoing and predicted impacts of cryosphere loss are diverse, ranging from disappearance of entire biomes to crises of water availability. Covering approximately one-fifth of the planet, mass loss from the terrestrial cryosphere is driven primarily by a warming atmosphere but reductions in albedo (the proportion of reflected light) also contribute by increasing absorption of solar radiation. In addition to dust and other abiotic impurities, biological communities substantially reduce albedo worldwide. In this review, we provide a global synthesis of biological albedo reduction (BAR) in terrestrial snow and ice ecosystems. We first focus on known drivers—algal blooms and cryoconite (granular sediment on the ice that includes both mineral and biological material)—as they account for much of the biological albedo variability in snow and ice habitats. We then consider an array of potential drivers of BAR whose impacts may be overlooked, such as arthropod deposition, resident organisms (e.g., dark-bodied glacier ice worms), and larger vertebrates, including humans, that transiently visit the cryosphere. We consider both primary (e.g., BAR due to the presence of pigmented algal cells) and indirect (e.g., nutrient addition from arthropod deposition) effects, as well as interactions among biological groups (e.g., birds feeding on ice worms). Collectively, we highlight that in many cases, overlooked drivers and interactions among factors have considerable potential to alter BAR, perhaps rivaling the direct effects of algal blooms and cryoconite. We conclude by highlighting knowledge gaps for the field with an emphasis on the underrepresentation of genomic tools, understudied areas (particularly high-elevation glaciers at tropical latitudes), and a dearth of temporal sampling in current efforts. We detail a global framework for long-term BAR monitoring that, if implemented, would yield a tremendous amount of insight for BAR and would be particularly valuable in light of the rapid ecological and physical changes occurring in the contemporary cryosphere.

全球冰冻圈，地球的冰冻水，正在急剧下降。冰冻圈损失的持续和预测影响是多种多样的，从整个生物群落的消失到水资源供应的危机。覆盖地球约五分之一的陆地冰冻圈的质量损失主要是由变暖的大气造成的，但反照率（反射光的比例）的减少也有助于增加对太阳辐射的吸收。除了灰尘和其他非生物杂质外，生物群落在全球范围内大幅降低了反照率。在这篇综述中，我们提供了陆地冰雪生态系统中生物反照率减少 (BAR) 的全球综合。我们首先关注已知的驱动因素——藻华和冰尘（冰上的颗粒沉积物，包括矿物和生物材料）——因为它们解释了冰雪栖息地的大部分生物反照率变化。然后，我们考虑了一系列可能会被忽视的 BAR 潜在驱动因素，例如节肢动物沉积、常驻生物（例如，黑体冰川冰蠕虫）和较大的脊椎动物，包括人类，它们会暂时访问冰冻圈。我们考虑了主要（例如，由于存在色素藻细胞而导致的 BAR）和间接（例如节肢动物沉积导致的营养添加）影响，以及生物群落之间的相互作用（例如，鸟类以冰虫为食）。总的来说，我们强调在许多情况下，被忽视的驱动因素和因素之间的相互作用有相当大的潜力改变 BAR，可能与藻华和冰尘的直接影响相媲美。最后，我们强调了该领域的知识差距，重点是基因组工具的代表性不足、研究不足的地区（特别是热带纬度的高海拔冰川）以及当前努力中缺乏时间采样。我们详细介绍了长期 BAR 监测的全球框架，如果实施该框架，将为 BAR 提供大量见解，并且鉴于当代冰冻圈中发生的快速生态和物理变化，将特别有价值。最后，我们强调了该领域的知识差距，重点是基因组工具的代表性不足、研究不足的地区（特别是热带纬度的高海拔冰川）以及当前努力中缺乏时间采样。我们详细介绍了长期 BAR 监测的全球框架，如果实施该框架，将为 BAR 提供大量见解，并且鉴于当代冰冻圈中发生的快速生态和物理变化，将特别有价值。最后，我们强调了该领域的知识差距，重点是基因组工具的代表性不足、研究不足的地区（特别是热带纬度的高海拔冰川）以及当前努力中缺乏时间采样。我们详细介绍了长期 BAR 监测的全球框架，如果实施该框架，将为 BAR 提供大量见解，并且鉴于当代冰冻圈中发生的快速生态和物理变化，将特别有价值。