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Key Points: • First ever measurements with a high‐accuracy single‐particle soot photometer of black carbon (BC) concentrations in Arctic snowpack • Topography and BC emission flux strongly influenced latitudinal variations of mass concentrations and size distributions of BC • Measured BC mass concentrations 2–25 times lower than previously reported show the importance of revalidating climate models Black carbon (BC) deposited on snow lowers its albedo, potentially contributing to warming in the Arctic. Atmospheric distributions of BC and inorganic aerosols, which contribute directly and indirectly to radiative forcing, are also greatly influenced by depositions. To quantify these effects, accurate measurement of the spatial distributions of BC and ionic species representative of inorganic aerosols (ionic species hereafter) in snowpack in various regions of the Arctic is needed, but few such measurements are available. We measured mass concentrations of size-resolved BC (CMBC) and ionic species in snowpack by using a single-particle soot photometer and ion chromatography, respectively, over Finland, Alaska, Siberia, Greenland, and Spitsbergen during early spring in 2012–2016. Total BC mass deposited per unit area (DEPMBC) during snow accumulation periods was derived from CMBC and snow water equivalent (SWE). Our analyses showed that the spatial distributions of anthropogenic BC emission flux, total precipitable water, and topography strongly influenced latitudinal variations of CMBC, BC size distributions, SWE, and DEPMBC. The average size distributions of BC in Arctic snowpack shifted to smaller sizes with decreasing CMBC due to an increase in the removal efficiency of larger BC particles during transport from major sources. Our measurements of CMBC were lower by a factor of ~13 than previous measurements made with an Integrating Sphere/Integrating Sandwich spectrophotometer due mainly to interference from coexisting non-BC particles such as mineral dust. The SP2 data presented here will be useful for constraining climate models that estimate the effects of BC on the Arctic climate. Plain Language Summary Black carbon (BC) particles, commonly known as soot, are emitted from incomplete combustion of fossil fuels and biomass. They efficiently absorb solar radiation and thus heat the atmosphere. BC particles emitted at midlatitudes and in the Arctic are deposited onto snow in the Arctic, accelerating snowmelt in early spring by absorbing solar radiation. These processes contribute to warming in the Arctic. Calculations of this warming effect by using numerical models need to be validated by comparison with observed BC concentrations in snowpack. However, there are very few accurate records of concentrations of BC in snow because of technical difficulties in making these measurements. We developed a new laser-induced incandescence technique to measure BC concentrations in snowpack and applied it for the first time in six Arctic regions (Finland, Alaska, North and South Siberia, Greenland, and Spitsbergen). The BC concentrations we measured were highest in Finland and South Siberia, which are closer to large anthropogenic BC sources than the other regions, where our measured BC concentrations were much lower. On average, our BC concentrations were much lower than those previously measured by different techniques. Therefore, previous comparisons of modeled and observed BC concentrations need to be re-evaluated using the present data.

Phosphorus is a limiting nutrient for primary productivity, but little is known about past atmospheric fluxes to the open ocean. In this study, phosphate and phosphorus concentrations have been determined in the North Greenland Eemian Ice Drilling Project ice core for selected periods during the last glacial. Phosphate was determined continuously by using a molybdenum blue spectroscopic absorption method and discretely using an ion chromatograph. Total P was determined discretely using an inductively coupled plasma sector field mass spectrometer. For the last glacial period, we found concentrations of between 3 and 62 nM PO43− and 7 and 929 nM P. We find glacial atmospheric fluxes of phosphorus to Greenland were 4 to 11 times higher than in the past century, with the highest input during the cold glacial stadials (GS). Changes in P and PO43− fluxes between mild glacial interstadials (GI) and GS correlate positively with dust variability. The soluble fraction of P is larger in the mild GIs as compared to the dust-rich GSs. For the very high phosphate and phosphorus loads during the Last Glacial Maximum, the relationship between phosphate and dust is weaker than in GIs and milder GSs, suggesting either secondary phosphate sources or multiple dust sources. Based on crustal abundances, we find that dust inputs are sufficient to account for all P deposited during all periods investigated except the Last Glacial Maximum. During the glacial, sea salts contributed 10−3 nM P, while land biogenic emissions were a minor source of P.

[1] Postdepositional changes in water stable isotopes in polar firn were investigated at three sites characterized by different accumulation rates along the East Antarctic ice divide near Dome Fuji. Water stable isotopes, major ion concentrations, and tritium contents of three 2–4 m deep pits were measured at high resolution (2 cm). Temporally, the snow pits cover the past 50 years with snow accumulation rates in the range of 29–41 kg m−2 a−1 around Dome Fuji. Oxygen isotopic profiles in the three pits do not show annual fluctuations, but instead exhibit multiyear cycles. These multiyear cycles are lower in frequency at Dome Fuji as compared with the other two sites. Peaks of water stable isotopes in the multiyear cycles correspond to some ion concentration minima in the pits, although such relationships are not observed in coastal regions. We propose that the extremely low accumulation environment keeps the snow layer at the near surface, which result in postdepositional modifications of isotopic signals by processes such as ventilation and vapor condensation-sublimation. We estimate that oxygen isotopic ratios could be modified by >10‰ and that the original seasonal cycle could be completely overprinted under the accumulation conditions at Dome Fuji. Moreover, stake measurements at Dome Fuji suggest that the large variability in snow accumulation rate is the cause of the multiyear cycles.