Platinum-group elements, shocked quartz, and nanodiamonds in a Greenland ice-margin sequence at the Younger Dryas onset

Here, we present a multidisciplinary investigation of a late-Pleistocene Greenland ice-margin sequence near Kangerlussuaq that spans the Bølling-Allerød, Younger Dryas, and early Holocene. This study investigates the cause of the Younger Dryas (YD) cooling event (~12,800 years ago) and its possible relationship to a cosmic impact. The Kangerlussuaq interval was previously identified using visible dust stratigraphy, oxygen-isotope measurements, and a peak in nanocarbon particles interpreted as nanodiamonds. We expand that record using bulk ICP-MS, single-particle ICP-time-of-flight mass spectrometry (SP-ICP-TOF-MS), microscopy, mineralogical observations, and hydrocode modeling. The Kangerlussuaq sequence preserves a dark, dust-rich YD interval bounded by clearer Holocene and Bølling-Allerød ice. Stable δ 18 O values and dust-related geochemical changes support correlation of this interval with the YD cooling episode, although the ice-margin setting introduces uncertainties related to compression, ablation, meltwater infiltration, and multi-season sample alignment. Within this framework, the Greenland record resolves three superimposed signals. First, bulk geochemistry and nanoparticle mineral-phase associations document a sustained YD-scale reorganization of atmospheric dust provenance and transport, consistent with colder, drier, and windier conditions and enhanced mineral-dust flux throughout much of the ~1,200–1,300-year YD interval. Second, a narrow proxy-rich horizon at the YDB layer (~5.5 m along the sloping ice) contains peak abundances of multiple particulate proxies, including nanocarbon particles previously interpreted as nanodiamonds, quartz grains with shocked planar microstructures, meltglass, glass-filled lithic aggregates, Fe- and Si-rich spherules, carbon-rich spherules, glasslike carbon, charcoal, and soot. Third, nanoparticle concentrations begin to rise at the YDB layer (~5.5 m), marking the onset of enrichment, but reach their maximum immediately above, at ~5.2 m. SP-ICP-TOF-MS identifies this overlying interval as the peak in nanoparticle-scale terrestrial and siderophile components, including Nb, Ta, U, As, Pb, Sb, PGEs, Ni, Co, and Re. Elemental behavior across the nanoparticle dataset can be grouped into three principal populations: climate-driven terrestrial mineral dust, high-temperature plume-derived possible ET condensates, and lower-temperature terrestrial plume derivatives. This offset between the boundary layer and the nanoparticle maximum is a key observation: concentrations are lowest within the YDB layer, increase at the boundary, and peak in the overlying sample, indicating temporally structured deposition involving initial boundary-layer input followed by delayed fallout or redistribution of fine particles. This delay is supported by independent evidence from the GISP2 ice core of a platinum anomaly coincident with the onset of Younger Dryas climate change, including a delayed peak over ~21 years, supporting non-instantaneous deposition of impact-related material and suggesting a temporal link to YD climate change. The PGE-bearing nanoparticle population provides the strongest geochemical evidence for a non-crustal contribution. At ~5.2 m, PGE sum, Ir, Pt, Os, Pd, Ni, Co, and Re are enriched relative to the YDB layer; these elements are strongly enriched in extraterrestrial (ET) materials relative to crustal abundances, suggesting a non-terrestrial source. Ratio-ratio diagrams and PGE fractionation versus Ir/Fe comparisons indicate that the YDB nanoparticle population is compositionally distinct from Greenland background dust and typical terrestrial reservoirs. The Greenland YDB value of (Os+Ir+Ru)/(Rh+Pd+Pt) is sub-chondritic, while Ir/Fe is highly elevated, consistent with a heterogeneous mixture containing a refractory PGE-rich component, possibly from ET refractory metal nuggets (RMNs), together with more volatile PGE-bearing material. This signature does not match any single impactor class (e.g., bulk chondrite, iron meteorite, or achondrite), but is consistent with a mixed, fractionated nanoparticle population superimposed on background cosmic dust influx. Hydrocode modeling demonstrates that a high-velocity impact or airburst interacting with an ice-sheet target can plausibly generate high pressures, elevated temperatures, shocked quartz, melt products, spherules, and widespread nanoparticle dispersal; however, this modeling is intended to illustrate a viable mechanism for proxy formation and does not imply that such an impact occurred at the Greenland site. Instead, these results are consistent with broader Younger Dryas Impact Hypothesis scenarios involving regionally or globally distributed impact and airburst phenomena. The combined proxy assemblage is difficult to explain by volcanism, biomass burning, authigenesis, anthropogenic contamination, or climate-driven dust deposition alone. No single proxy is uniquely diagnostic of impact; rather, the interpretation rests on the stratigraphic co-occurrence of multiple high-temperature, shocked, carbonaceous, siderophile-enriched, and PGE-bearing materials within the YD onset interval. Together, the Greenland record is consistent with a short-duration, high-energy airburst or impact-related depositional episode superimposed on and possibly a major trigger of the broader climatic transition into the Younger Dryas.