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Abstract. We document the isotopic evolution of near-surface snow at the East Greenland Ice Core Project (EastGRIP) ice core site in northeast Greenland using a time-resolved array of 1 m deep isotope (δ18O, δD) profiles. The snow profiles were taken from May–August during the 2017–2019 summer seasons. An age–depth model was developed and applied to each profile, mitigating the impacts of stratigraphic noise on isotope signals. Significant changes in deuterium excess (d) are observed in surface snow and near-surface snow as the snow ages. Decreases in d of up to 5 ‰ occur during summer seasons after deposition during two of the three summer seasons observed. The d always experiences a 3 ‰–5 ‰ increase after aging 1 year in the snow due to a broadening of the autumn d maximum. Models of idealized scenarios coupled with prior work indicate that the summertime post-depositional changes in d (Δd) can be explained by a combination of surface sublimation, forced ventilation of the near-surface snow down to 20–30 cm, and isotope-gradient-driven diffusion throughout the column. The interannual Δd is also partly explained with isotope-gradient-driven diffusion, but other mechanisms are at work that leave a bias in the d record. Thus, d does not just carry information about source-region conditions and transport history as is commonly assumed, but also integrates local conditions into summer snow layers as the snow ages through metamorphic processes. Finally, we observe a dramatic increase in the seasonal isotope-to-temperature sensitivity, which can be explained solely by isotope-gradient-driven diffusion. Our results are dependent on the site characteristics (e.g., wind, temperature, accumulation rate, snow properties) but indicate that more process-based research is necessary to understand water isotopes as climate proxies. Recommendations for monitoring and physical modeling are given, with special attention to the d parameter. 

Abstract. During the Last Glacial Period (LGP), Greenland experienced approximately 30 abrupt warming phases, known as Dansgaard–Oeschger (D–O) events, followed by cooling back to baseline glacial conditions. Studies of mean climate change across warming transitions reveal indistinguishable phase offsets between shifts in temperature, dust, sea salt, accumulation, and moisture source, thus preventing a comprehensive understanding of the “anatomy” of D–O cycles (Capron et al., 2021). One aspect of abrupt change that has not been systematically assessed is how high-frequency interannual-scale climatic variability surrounding centennial-scale mean temperature changes across D–O transitions. Here, we utilize the East Greenland Ice-core Project (EGRIP) high-resolution water isotope record, a proxy for temperature and atmospheric circulation, to quantify the amplitude of 7–15-year isotopic variability for D–O events 2–13, the Younger Dryas, and the Bølling–Allerød. On average, cold stadial periods consistently exhibit greater variability than warm interstadial periods. Most notably, we often find that reductions in the amplitude of the 7–15-year band led abrupt D–O warmings by hundreds of years. Such a large phase offset between two climate parameters in a Greenland ice core has never been documented for D–O cycles. However, similar centennial lead times have been found in proxies for Norwegian Sea ice cover relative to abrupt Greenland warming (Sadatzki et al., 2020). Using HadCM3, a fully coupled general circulation model, we assess the effects of sea ice on 7–15-year temperature variability at the EGRIP. For a range of stadial and interstadial conditions, we find a strong relationship in line with our observations between colder simulated mean temperature and enhanced temperature variability at the EGRIP location. We also find a robust correlation between year-to-year North Atlantic sea ice fluctuations and the strength of interannual-scale temperature variability at EGRIP. Together, paleoclimate proxy evidence and model simulations suggest that sea ice plays a substantial role in high-frequency climate variability prior to D–O warming. This provides a clue about the anatomy of D–O events and should be the target of future sea ice model studies. 

Abstract. Above polar ice sheets, atmospheric water vapor exchangeoccurs across the planetary boundary layer (PBL) and is an importantmechanism in a number of processes that affect the surface mass balance ofthe ice sheets. Yet, this exchange is not well understood and hassubstantial implications for modeling and remote sensing of the polarhydrologic cycle. Efforts to characterize the exchange face substantiallogistical challenges including the remoteness of ice sheet field camps,extreme weather conditions, low humidity and temperature that limit theeffectiveness of instruments, and dangers associated with flying mannedaircraft at low altitudes. Here, we present an unmanned aerial vehicle (UAV)sampling platform for operation in extreme polar environments that iscapable of sampling atmospheric water vapor for subsequent measurement ofwater isotopes. This system was deployed to the East Greenland Ice-coreProject (EastGRIP) camp in northeast Greenland during summer 2019. Foursampling flight missions were completed. With a suite of atmosphericmeasurements aboard the UAV (temperature, humidity, pressure, GPS) wedetermine the height of the PBL using online algorithms, allowing forstrategic decision-making by the pilot to sample water isotopes above andbelow the PBL. Water isotope data were measured by a Picarro L2130-iinstrument using flasks of atmospheric air collected within the nose cone ofthe UAV. The internal repeatability for δD and δ18O was2.8 ‰ and 0.45 ‰, respectively,which we also compared to independent EastGRIP tower-isotope data. Based onthese results, we demonstrate the efficacy of this new UAV-isotope platformand present improvements to be utilized in future polar field campaigns. Thesystem is also designed to be readily adaptable to other fields of study,such as measurement of carbon cycle gases or remote sensing of groundconditions. 

Abstract. Ice core water isotope records from Greenland and Antarctica are a valuableproxy for paleoclimate reconstruction, yet the processes influencing theclimate signal stored in the isotopic composition of the snow are beingchallenged and revisited. Apart from precipitation input, post-depositionalprocesses such as wind-driven redistribution and vapor–snow exchange processes at and below the surface are hypothesized to contribute to the isotope climate signal subsequently stored in the ice. Recent field studies have shown that surface snow isotopes vary between precipitation events and co-vary with vapor isotopes, which demonstrates that vapor–snow exchange is an important driving mechanism. Here we investigate how vapor–snow exchange processes influence the isotopic composition of the snowpack. Controlled laboratory experiments under forced sublimation show an increase in snow isotopic composition of up to 8 ‰ δ18O in the uppermost layer due to sublimation, with an attenuated signal down to 3 cm snow depth over the course of 4–6 d. This enrichment is accompanied by a decrease in the second-order parameter d-excess, indicating kinetic fractionation processes. Our observations confirm that sublimation alone can lead to a strong enrichment of stable water isotopes in surface snow and subsequent enrichment in the layers below. To compare laboratory experiments with realistic polar conditions, we completed four 2–3 d field experiments at the East Greenland Ice Core Project site (northeast Greenland) in summer 2019. High-resolution temporal sampling of both natural and isolated snow was conducted under clear-sky conditions and demonstrated that the snow isotopic composition changes on hourly timescales. A change of snow isotope content associated with sublimation is currently not implemented in isotope-enabled climate models and is not taken into account when interpreting ice core isotopic records. However, our results demonstrate that post-depositional processes such as sublimation contribute to the climate signal recorded in the water isotopes in surface snow, in both laboratory and field settings. This suggests that the ice core water isotope signal may effectively integrate across multiple parameters, and the ice core climate record should be interpreted as such, particularly in regions of low accumulation. 

Permutation entropy techniques can be useful for identifying anomalies in paleoclimate data records, including noise, outliers, and post-processing issues. We demonstrate this using weighted and unweighted permutation entropy with water-isotope records containing data from a deep polar ice core. In one region of these isotope records, our previous calculations (See Garland et al. 2018)revealed an abrupt change in the complexity of the traces: specifically, in the amount of new information that appeared at every time step. We conjectured that this effect was due to noise introduced by an older laboratory instrument. In this paper, we validate that conjecture by reanalyzing a section of the ice core using a more advanced version of the laboratory instrument. The anomalous noise levels are absent from the permutation entropy traces of the new data. In other sections of the core, we show that permutation entropy techniques can be used to identify anomalies in the data that are not associated with climatic or glaciological processes, but rather effects occurring during field work, laboratory analysis, or data post-processing. These examples make it clear that permutation entropy is a useful forensic tool for identifying sections of data that require targeted reanalysis—and can even be useful for guiding that analysis. 

This data set is part of a joint international effort for the East GReenland Ice-core Project (EGRIP), which has retrieved an ice core by drilling through the Northeast Greenland Ice Stream (NEGIS, 75.63°N (North), 35.98°W (West)). Ice streams are responsible for draining a significant fraction of the ice from the Greenland Ice Sheet (GIS), and the project was developed to gain new and fundamental information on ice stream dynamics, thereby improving the understanding of how ice streams will contribute to future sea-level change. The drilled core also provides a new record of past climatic conditions from the northeastern part of the GIS. The project has many international partners and is managed by the Centre for Ice and Climate, Denmark with air support carried out by US ski-equipped Hercules aircraft managed through the US (United States) Office of Polar Programs, National Science Foundation. As of May 2022, approximately 2099.2 m (meters) of ice core have been recovered from the combined efforts of drilling operations in 2017, 2018, and 2019. Here we present records of stable isotopes of oxygen and hydrogen from 21.5 meters to 2120.7 m depth. Bedrock is estimated to be at a depth of approximately 2550 m; the remaining ice is expected to be recovered in the 2022 and 2023 field seasons. The data product presented here is supported by the National Science Foundation project: Collaborative Research: The fingerprint of abrupt temperature events throughout Greenland during the last glacial period. Award # 1804098. 

This data set is part of a joint international effort for the East GReenland Ice-core Project (EGRIP), which has retrieved an ice core by drilling through the Northeast Greenland Ice Stream (NEGIS, 75.63°N (North), 35.98°W (West)). Ice streams are responsible for draining a significant fraction of the ice from the Greenland Ice Sheet (GIS), and the project was developed to gain new and fundamental information on ice stream dynamics, thereby improving the understanding of how ice streams will contribute to future sea-level change. The drilled core also provides a new record of past climatic conditions from the northeastern part of the GIS. The project has many international partners and is managed by the Centre for Ice and Climate, Denmark with air support carried out by US ski-equipped Hercules aircraft managed through the US (United States) Office of Polar Programs, National Science Foundation. As of May 2022, approximately 2099.2 m (meters) of ice core have been recovered from the combined efforts of drilling operations in 2017, 2018, and 2019. Here we present records of stable isotopes of oxygen and hydrogen from 21.5 meters to 2120.7 m depth. Bedrock is estimated to be at a depth of approximately 2550 m; the remaining ice is expected to be recovered in the 2022 and 2023 field seasons. The data product presented here is supported by the National Science Foundation project: Collaborative Research: The fingerprint of abrupt temperature events throughout Greenland during the last glacial period. Award # 1804098. 

The Internet of Things (IoT) is an emerging technology that aims to connect our environment to the internet in the same way that personal computers connected people. As this technology progresses, the IoT paradigm becomes more prevalent in our everyday lives. The nature of IoT applications necessitates devices that are low-cost, power-sensitive, integrated, unobtrusive, and interoperable with existing cloud platforms and services, for example, Amazon AWS IoT, IBM Watson IoT. As a result, these devices are often small in size, with just enough computing power needed for their specific tasks. These resource-constrained devices are often unable to implement traditional network security measures and represent a vulnerability to network attackers as a result. Few frameworks are positioned to handle the influx of this new technology and the security concerns associated with it. Current solutions fail to provide a comprehensive and multi-layer solution to these inherent IoT security vulnerabilities. This paper presents a layered approach to IoT testbed that aims to bridge multiple connection standards and cloud platforms. To solve challenges surrounding this multi-layer IoT testbed, we propose a mesh inside a mesh IoT network architecture. Our designed "edge router" incorporates two mesh networks together and performs seamlessly transmission of multi-standard packets. The proposed IoT testbed interoperates with existing multi-standards (Wi-Fi, 6LoWPAN) and segments of networks, and provides both Internet and resilient sensor coverage to the cloud platform. To ensure confidentiality and authentication of IoT devices when interoperating with multiple service platforms, we propose optimized cryptographic techniques and software frameworks for IoT devices. We propose to extend and modify the existing open-source IDS platforms such as Snort to support IoT platforms and environments. We validate the efficacy of the proposed system by evaluating its performance and effect on key system resources. The work within this testbed design and implementation provides a solid foundation for further IoT system development. 

Pleistocene Ice Ages display abrupt Dansgaard–Oeschger (DO) climate oscillations that provide prime examples of Earth System tipping points—abrupt transition that may result in irreversible change. Greenland ice cores provide key records of DO climate variability, but gas-calibrated estimates of the temperature change magnitudes have been limited to central and northwest Greenland. Here, we present ice-core δ¹⁵N-N₂records from south (Dye 3) and coastal east Greenland (Renland) to calibrate the local water isotope thermometer and provide a Greenland-wide spatial characterization of DO event magnitude. We combine these data with existing records of δ¹⁸O, deuterium excess, and accumulation rates to create a multiproxy “fingerprint” of the DO impact on Greenland. Isotope-enabled climate models have skill in simulating the observational multiproxy DO event impact, and we use a series of idealized simulations with such models to identify regions of the North Atlantic that are critical in explaining DO variability. Our experiments imply that wintertime sea ice variation in the subpolar gyre, rather than the commonly invoked Nordic Seas, is both a sufficient and a necessary condition to explain the observed DO impacts in Greenland, whatever the distal cause. Moisture-tagging experiments support the idea that Greenland DO isotope signals may be explained almost entirely via changes in the vapor source distribution and that site temperature is not a main control on δ¹⁸O during DO transitions, contrary to the traditional interpretation. Our results provide a comprehensive, multiproxy, data-model synthesis of abrupt DO climate variability in Greenland. 

Abstract. The South Pole Ice Core (SPICEcore) was drilled in 2014–2016 to provide adetailed multi-proxy archive of paleoclimate conditions in East Antarcticaduring the Holocene and late Pleistocene. Interpretation of these recordsrequires an accurate depth–age relationship. Here, we present the SPICEcore (SP19) timescale for the age of the ice of SPICEcore. SP19 is synchronized to theWD2014 chronology from the West Antarctic Ice Sheet Divide (WAIS Divide) icecore using stratigraphic matching of 251 volcanic events. These eventsindicate an age of 54 302±519 BP (years before 1950) at thebottom of SPICEcore. Annual layers identified in sodium and magnesium ionsto 11 341 BP were used to interpolate between stratigraphic volcanic tiepoints, yielding an annually resolved chronology through the Holocene.Estimated timescale uncertainty during the Holocene is less than 18 yearsrelative to WD2014, with the exception of the interval between 1800 to 3100BP when uncertainty estimates reach ±25 years due to widely spacedvolcanic tie points. Prior to the Holocene, uncertainties remain within 124 years relative to WD2014. Results show an average Holocene accumulation rateof 7.4 cm yr−1 (water equivalent). The time variability of accumulation rateis consistent with expectations for steady-state ice flow through the modernspatial pattern of accumulation rate. Time variations in nitrateconcentration, nitrate seasonal amplitude and δ15N of N2 in turn are as expected for the accumulation rate variations. The highlyvariable yet well-constrained Holocene accumulation history at the site canhelp improve scientific understanding of deposition-sensitive climateproxies such as δ15N of N2 and photolyzed chemicalcompounds.