ICESat-2 Observations of Blowing Snow Over Arctic Sea Ice During the 2019–2020 MOSAiC Expedition

Blowing snow plays a key role in the surface mass and energy budgets of polar regions and can be a significant source of water vapor to the atmosphere. In this study, we optimize the algorithm for detecting blowing snow from NASA's Ice, Cloud, and land Elevation Satellite 2 (ICESat-2) satellite for use over Arctic sea ice. We analyze six months (November 2019 through April 2020) of observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) campaign together with 612 nearly coincident (within 100 km) ICESat-2 overpasses to evaluate the ICESat-2 detection algorithm and inferred blowing snow properties. Both ICESat-2 and MOSAiC suggest a blowing snow occurrence frequency of 17% during the period of study. Blowing snow particle number and inferred from ICESat-2 show broad agreement with in situ observations made at 10 m above the surface during MOSAiC but are often well below observations made at 8 cm. Within a 100 km radius around the MOSAiC observatory, we find a cumulative blowing snow sublimation of 2.38 cm snow-water-equivalent (SWE), comparable to MOSAiC (2.56 cm SWE) and SnowModel-LG (2.35 cm SWE) estimates. This suggests that blowing snow sublimation removed 22%–33% of snowfall during MOSAiC. Across the central Arctic, ICESat-2 and SnowModel-LG indicate blowing snow occurrence frequencies as high as 18%–25%, with cumulative blowing snow sublimation fluxes (1.74–1.79 cm SWE) removing 16%–17% of snowfall. These findings highlight the importance of blowing snow sublimation for the Arctic snow on sea ice budget

Stable isotopes constrain the genesis of Thar Desert gypsum playas and reveal Holocene paleoenvironmental variability in Northwest India

Numerous evaporative saline playa lakes exist within the Thar Desert in Northwest India. Some are active seasonally, whereas others are dry and preserve up to several meters of sedimentary deposits. These deposits feature a variety of evaporite minerals, including the hydrated mineral gypsum (CaSO4⋅2H2O). The isotopic composition of gypsum hydration water preserves the δ18O and δD of paleolake water at the time of gypsum formation. This provides a way to understand the hydrologic balance in a part of the world where it is typically very difficult to obtain any paleoclimate records. We present paleohydrological records from two dry playas (Karsandi, Khajuwala) and one active playa (Lunkaransar) in the Thar Desert using the oxygen and hydrogen isotopic composition of gypsum hydration water. We present a theoretical model to explain differences in how the gypsum records water isotopic composition from perennial playas (consistent paleoclimate recorders) as opposed to seasonally fed or ephemeral playas (that reflect evaporated meteoric water inconsistently). Results suggest that enhanced direct precipitation, with associated higher groundwater and possibly fluvial sources, maintained active playa lake basins in the central Thar Desert for the Early through Middle Holocene. We also examine δ34SSO4, δ18OSO4, and 87Sr/86Sr of the gypsum sulfate to explore the source and evolution of solutes in the Thar Desert playas. Results indicate that seasalt aerosols likely accumulated in aeolian sands during glacial dry periods and concentrated in playa deposits once a threshold level of moisture was reached in the Early Holocene. By the Late Holocene, after c. 4.4 ka BP, these water sources diminished and some playas were again covered by aeolian deposits. The Thar Desert gypsum deposits provide valuable insight into local moisture balance during a time period that featured important cultural transformation in the surrounding region, including the South Asian Neolithic agricultural societies around 8 ka BP, the full span of the Indus Civilization (5.3–3.3 ka BP), and periods of human occupation after 3 ka BP

Modelling the impact of large-scale hydroclimate change on prehistoric Polynesian island life

The South Pacific was one of the last regions on earth to be colonised by humans and offers a unique opportunity to study early climate-human interactions in environments previously untouched by people. Palaeoclimate evidence suggests the South Pacific has experienced shifts between dry and wet periods throughout the past three thousand years, the broad period of colonisation, with extremes in both modes being prevalent. Drought has significant repercussions for small Pacific islands, affecting water and food resources, with potential consequences on the viability of life on these islands leading to internal stress, conflict, collapse or migration. Previously, socio-ecological models have been developed to test mechanisms of change within prehistoric societies worldwide that can lead to migration or societal change, but thus far the connections between past climatic change and prehistoric island life within the tropical South Pacific have not been fully explored. This study utilises palaeoclimatic data alongside a new system dynamics socio-ecological model to explore the relationship between climate, agricultural carrying capacity and population dynamics on the Polynesian island of Mangaia (Cook Islands) in the tropical South Pacific. Model results suggest that as the population density of the island increases, the impact of drought events on population dynamics increases. We also show that the severity of the drought rather than the return frequency drove the largest changes in carrying capacity and population dynamics. Changes in long-term rainfall leading to persistent dry conditions impacted the timing and rate of population growth due to its role as a limiting factor for agricultural productivity. We compare our modelled results with the known history of population stress and societal change from Mangaia and found these corresponded with drought periods and low food availability. We demonstrate the potential for droughts to have impacted on the early colonisation and societal change on Eastern Polynesian islands

Changes in atmospheric oxidants teleconnect biomass burning and ammonium nitrate formation

Open biomass burning has major impacts on the Earth system, including on air quality via the emission of primary fine particulate matter (PM 2.5 ). Its effect on secondary inorganic PM 2.5 formation is comparatively little investigated. Simulations with the EMEP MSC-W WRF atmospheric chemistry transport model reveal that global biomass burning emissions lead to elevated annual mean ammonium nitrate (NH 4 NO 3 ) concentrations in densely populated regions where biomass burning mostly does not occur. These regions include eastern USA, northwestern Europe, the Indo-Gangetic Plain and eastern China, where NH 4 NO 3 conditional on biomass burning emissions constitutes between 29% and 51% of the annual mean PM 2.5 conditional on biomass burning emissions. Biomass burning emissions of CO, NO x (NO and NO 2 ) and volatile organic compounds perturb the HO x (OH and HO 2 ) cycle globally, such that there is increased oxidation of anthropogenic NO x to HNO 3 . This results in additional contributions to local-scale secondary NH 4 NO 3 in areas with high emissions of anthropogenic NO x and NH 3 . These teleconnections increase, by up to a factor of two, the contribution of biomass burning emissions to long-term PM 2.5 concentrations, which measurements alone cannot identify as an impact of biomass burning activity. This may become relatively more important as anthropogenic sources of PM 2.5 are reduced and as the wildfire component of biomass burning increases under climate change

​​Polar Ocean Mixing by Internal Tsunamis ​(POLOMINTS)​

Mixing of the ocean around Antarctica is a key process that exerts influences over large scales and in multiple ways. By redistributing heat in the ocean, it exerts strong influences on the Antarctic Ice Sheet, with implications for sea level rise globally. Similarly, the redistribution of ocean heat affects the production of sea ice in winter and its melt in summer, with consequences for climate. Mixing also affects the distribution of nutrients in the ocean, with direct impacts on the marine ecosystem and biodiversity and with consequences for fisheries. It was long thought that mixing of the seas close to Antarctica was predominantly caused by winds, tides and the loss of heat from the ocean especially in winter. However, we recently discovered that when glaciers calve in Antarctica, they can trigger underwater tsunamis. These are large (multi-metre) waves that move rapidly away from the coastline and when they break, they cause sudden bursts of very intense mixing. Simple calculations indicated that the net impact of these underwater tsunamis could be as strong as winds, and much more important than tides, in driving mixing. It was also argued that they are likely to be relevant everywhere that glaciers calve into the sea, including Greenland and across the Arctic. As our ocean and atmosphere continue to heat up, it is very possible that glacier calving will become more frequent and intensify, increasing further the impact of underwater tsunamis on large-scale climate, the cryosphere and ecosystems. This is an exciting new avenue of scientific investigation and many key questions remain unanswered. We need to know how widespread and frequent the generation of underwater tsunamis is, how far they travel from the coastline before breaking, and how variable this is. We need to measure what impacts the extra mixing has on ocean temperature and nutrient concentrations, and to determine what this means for the cryosphere and ocean productivity. There is a pressing need to include the effects of underwater tsunamis in the computer models that are used for projecting future ocean climate and ecosystem conditions and to determine the feedbacks between climate change and the generation of more underwater tsunamis. To answer these questions, our project will deploy innovative techniques for measuring the ocean and ice in close proximity to a calving glacier, including robotic underwater vehicles and remotely-piloted aircraft, and cutting-edge deep-learning techniques applied to satellite data. We will use advanced computer simulations to fully understand the causal mechanisms responsible for the creation and spread of the underwater tsunamis and their impacts on ocean climate and marine productivity. We will make our developments in computer simulation available to the whole community of users, for widespread uptake and future use. This project will have significant benefits for academics seeking to predict the future of Antarctica and its impacts on the rest of the world, for Governments and intergovernmental agencies seeking to understand how best to respond to climate change, and for the curious general public wanting to learn more about the extremes of the planet and why they matter. The fieldwork will be especially photo- and video-genic and will lead to outstanding outreach and impact opportunities, and we will work with media agencies seeking to tell compelling stories about the extremes of the Earth

Ring current local time dependence during geomagnetic storms using equatorial Dst-proxies

Abstract In this paper, we calculate Local Disturbance indices (LDi) using data from two equatorial observatories (Ascension ASC and Fúquene FUQ) to use them as Disturbance Storm-time (Dst) index proxies. We find that the LDi response to geomagnetic storms is different depending on the observatory’s local time at the storm onset. In order to explore this local time influence on the measurements on the ground at low latitudes, we build new proxies using two observatories located at approximately the same longitude, in order to balance measurements in the north and south averaging meridional and measuring only zonal variations. The average of the longitude pairs and Dst-index proxies from single observatories exhibit strong correlation to the Dst index ( ≥ 0.88) during active periods and a moderate correlation ( ≤ 0.5) during quiet periods. We find that the storm intensity is associated with local time. We confirm that the fastest variation in the geomagnetic field during the storm is recorded between dusk and midnight, while the region between dawn and noon records more moderate variations, sometimes missing the storm effects altogether. Our results show an azimuthal asymmetry of the magnetospheric ring current, becoming most intense on the night side of the dusk terminator during active periods. We propose a new configuration for local time Dst proxies including the use of equatorial observatories. This will get insights of the evolution of storms in an area where there are limited geomagnetic observatories. Graphical abstrac

Simulation-based inference advances water quality mapping in shallow coral reef environments

Human activities are altering coral reef ecosystems worldwide. Optical remote sensing via satellites and drones can offer novel insights into where and how coral reefs are changing. However, interpretation of the observed optical signal (remote-sensing reflectance) is an ill-posed inverse problem, as there may be multiple different combinations of water constituents, depth and benthic reflectance that result in a similar optical signal. Here, we apply a new approach, simulation-based inference, for addressing the inverse problem in marine remote sensing. The simulation-based inference algorithm combines physics-based analytical modelling with approximate Bayesian inference and machine learning. The input to the algorithm is remote-sensing reflectance, and the output is the likely range (posterior probability density) of phytoplankton and suspended minerals concentrations, coloured dissolved organic matter absorption, wind speed and depth. We compare inference models trained with simulated hyperspectral or multispectral reflectance spectra characterized by different signal-to-noise ratios. We apply the inference model to in situ radiometric data ( n = 4) and multispectral drone imagery collected on the Tetiaroa atoll (South Pacific). We show that water constituent concentrations can be estimated from hyperspectral and multispectral remote-sensing reflectance in optically shallow environments, assuming a single benthic cover. Future developments should consider spectral mixing of multiple benthic cover types

Economic methods for the selection of renewable energy sources: a case study

Governments need to evaluate technologies generating electricity from different sources; levelised cost of energy (LCOE) is a widely used metric. However, LCOE is weak at comparing disparate technologies, especially where they have different operational lifespans. The discrepancy is demonstrated using UK government data to examine a range of technologies, namely combined cycle generation (natural gas and hydrogen), sustainable renewable technologies along with independent data describing nuclear power and tidal range schemes. Three methods of analysis were used: LCOE, the internal rate of return (IRR), and a novel analysis. A new metric, the sustained cost of energy (SCOE), negates some of the LCOE shortcomings such as the application of discounting. SCOE examines a fixed period of continuous generation, using the lowest common length of operating life of the technologies analysed. It appears to be a useful metric, especially when interpreted with IRR. The analyses produce broadly similar ordering of technologies, but the longer-lasting systems with high initial costings perform better in SCOE. Subsidies, carbon tax, or credit schemes are essential government incentives if net zero emissions targets are to be met without overly burdening consumers with rapidly growing electricity rates

Radiosonde Measurements and Polar WRF Simulations of Low-Level Wind Jets in the Amundsen Sea Embayment, West Antarctica

We show that low-level jets (LLJs) occurred in 11 out of 22 radiosonde profiles in late austral summer over the coastal region of the Amundsen Sea Embayment, with ten of the LLJs directed offshore. The LLJs had core speeds from 9 to 32 m s −1 , jet core heights from 80 to 800 m, and were associated with strong, low-level temperature inversions. Seven of the observed offshore LLJs were reasonably simulated by the polar-optimized Weather Research and Forecasting (Polar WRF) model, with output from the model subsequently used to elucidate their generation mechanisms. This study shows that one of the offshore LLJs simulated by the Polar WRF was caused by katabatic winds, while the remaining six were caused by the enhancement of katabatic winds by synoptic forcing in response to a low-pressure system over the Bellingshausen Sea, i.e., the offshore wind component associated with this system plays a crucial role in the enhancement of the katabatic LLJ. Examination of the Polar WRF output further shows that the LLJs extended over large areas of the Amundsen Sea Embayment, resulting in substantially enhanced near-surface wind speeds over both the Thwaites and Pine Island ice shelves, as well as the open ocean over the continental shelf. The wind-driven forcing associated with the LLJs could perhaps have important impacts on the redistribution of snow over the ice shelves significantly, as well as to affecting sea-ice and ocean circulation variability, including the transport of relatively warm water over the continental shelf to the ice shelf cavities and extension basal melting