Owing to usual logistic hardships related to field-based cryospheric research, remote sensing has played a significant role in understanding the frozen components of the Earth system. Conventional spaceborne or airborne remote sensing platforms have their own merits and limitations. Unmanned aerial vehicles (UAVs) have emerged as a viable and inexpensive option for studying the cryospheric components at unprecedented spatiotemporal resolutions. UAVs are adaptable to various cryospheric research needs in terms of providing flexibility with data acquisition windows, revisits, data/sensor types (multispectral, hyperspectral, microwave, thermal/night imaging, Light Detection and Ranging (LiDAR), and photogrammetric stereos), viewing angles, flying altitudes, and overlap dimensions. Thus, UAVs have the potential to act as a bridging remote sensing platform between spatially discrete in situ observations and spatially continuous but coarser and costlier spaceborne or conventional airborne remote sensing. In recent years, a number of studies using UAVs for cryospheric research have been published. However, a holistic review discussing the methodological advancements, hardware and software improvements, results, and future prospects of such cryospheric studies is completely missing. In the present scenario of rapidly changing global and regional climate, studying cryospheric changes using UAVs is bound to gain further momentum and future studies will benefit from a balanced review on this topic. Our review covers the most recent applications of UAVs within glaciology, snow, permafrost, and polar research to support the continued development of high-resolution investigations of cryosphere. We also analyze the UAV and sensor hardware, and data acquisition and processing software in terms of popularity for cryospheric applications and revisit the existing UAV flying regulations in cold regions of the world. The recent usage of UAVs outlined in 103 case studies provide expertise that future investigators should base decisions on.

Decreased sea ice cover in the northern Bering Sea has altered annual phytoplankton phenology owing to an expansion of open water duration and its impact on ocean stratification. Limitations of satellite remote sensing such as the inability to detect bloom activity throughout the water column, under ice, and in cloudy conditions dictate the need for shipboard based measurements to provide more information on bloom dynamics. In this study, we adapted remote sensing land cover classification techniques to provide a new means to determine bloom stage from shipboard samples. Specifically, we used multiyear satellite time series of chlorophyllato determine whether in-situ blooms were actively growing or mature (i.e., past-peak) at the time of field sampling. Field observations of chlorophyllaand pheophytin (degraded and oxidized chlorophyll products) were used to calculate pheophytin proportions, i.e., (Pheophytin/(Chlorophylla+ Pheophytin)) and empirically determine whether the bloom was growing or mature based on remotely sensed bloom stages. Data collected at 13 north Bering Sea stations each July from 2013–2019 supported a pheophytin proportion of 28% as the best empirical threshold to distinguish a growing vs. mature bloom stage. One outcome was that low vs. high sea ice years resulted in significantly different pheophytin proportions in July; in years with low winter-to-spring ice, more blooms with growing status were observed, compared to later stage, more mature blooms following springs with abundant seasonal sea ice. The detection of growing blooms in July following low ice years suggests that changes in the timing of the spring bloom triggers cascading effects on mid-summer production.

This study investigates environmental drivers of fall phytoplankton blooms in the Arctic, focusing on the northern Bering and Chukchi seas. Random Forests models were used to analyze covariates of fall phytoplankton blooms from 2013 to 2018, incorporating shipboard, remote sensing, and modeled environmental properties. Four regional models and one comprehensive all‐station model considered fall as well as midsummer conditions. Midsummer properties included suspended particulate matter, chlorophyll‐ a , and the proportion of degraded pheophytin to chlorophyll‐ a used as a proxy for bloom stage. Open water duration was one of the highest ranked factors in predicting fall blooms. Open water duration also influences the stage of midsummer (July) blooms as indicated by pheophytin proportions, which in turn were the highest‐ranked factor for predicting fall bloom events in the Chirikov Basin (northern Bering Sea between St. Lawrence Island and the Bering Strait) and the Chukchi Sea. Wind direction, specifically easterly winds, was an important predictor in the northern Bering Sea. Maximum wind speed ranked highly at stations located within the nutrient‐poor Alaska Coastal Current in the Chukchi Sea. However, stormy days, average and maximum wind speeds generally ranked low in importance as a predictor of fall bloom events. Other parameters, including photosynthetic active radiation, modeled nutrient concentrations, mixed layer depth, and time since sea ice breakup date showed strong but regionally varying relationships with fall blooms. Altogether, results from these Random Forests models suggest that high wind events and storms in the absence of sea ice provide an incomplete narrative for initiating fall bloom events.

Climate change is exerting complex and transformative effects in the Arctic and Antarctic; regions that are essential to global climate, biodiversity, and sustainable futures. Given the polar regions’ roles in Earth’s system, a robust, coordinated, and innovative strategy to monitor and manage climate change effects is needed. Insufficient baseline data, inconsistent international collaboration, and short-term financing are obstacles to effectively monitor these changes. This hinders our understanding of biodiversity shifts, their implications for food security, and climate change mitigation. Confronting the impacts of climate change will require interdisciplinary collaboration and genuine participation of nations, including Indigenous communities. This sentiment includes facilitating international cooperation to address scientific objectives despite political tensions. Additional recommendations include establishing regular international requirements to track progress based on available science, optimizing the use of existing infrastructure and resources, enhancing data sharing practices, and securing long-term financing to sustain research. While the existing pan-Antarctic and pan-Arctic initiatives present useful strategies, these initiatives are not a silver bullet. They do, however, provide a starting point for further work. Ultimately, by building upon existing initiatives and harnessing their successful components, we can address limitations of short-term or fragmented studies. We outline tools and data resources for polar research, examples of existing collaborative efforts to build upon, and Indigenous knowledge systems that provide valuable resources for this undertaking.

Delayed sea ice freeze‐up and decreased sea ice extent in the Pacific Arctic region have altered light availability in marine waters, extending the ice‐free season and increasing opportunities for photosynthetic activity and energy exchanges. This study investigates phytoplankton bloom progression during the fall using chlorophyll pigments and examines the impact phytoplankton have on heat distribution within the water column. Measurements of chlorophyll‐ a concentrations and its associated degradation product pheophytin were made in conjunction with optical measurements of light transmittance within the upper water column during the Synoptic Arctic Survey cruise in the Central Arctic Ocean and northeast Chukchi Sea in September‐October 2022. Pheophytin proportions relative to chlorophyll‐ a generally increased over the course of the 2‐month cruise, indicating an overall seasonal decline in biological production. However, renewed phytoplankton growth indicated by reduced pheophytin proportions was observed within the surface ∼20 m of the water column on the Chukchi Shelf in late October. These subsurface blooms absorbed incoming solar radiation and enhanced ocean heating in the surface waters associated with the bloom while shading deeper depths from heating. Log‐linear regressions of heating rates associated each 1 μg L ⁻¹ increase of chlorophyll‐ a (at the observed chlorophyll‐ a maximum) with an approximate 15% decrease in heat input within the 10 m below the chlorophyll‐ a maximum depth. The altered vertical heat distribution caused by fall blooms trapping heat at the bloom depth can influence upper ocean stratification.