Table 1.
Sediment cores used in this study.
Fig 1.
(a) Map of northeast Canada and Greenland showing the location of Baffin Bay and core 83029−052 (small red box in panel a), and (b) locations of cores 2013029−064, 2013029−77, and 2008029−67 sampled for this study (small red boxes).
The map was created using the NCEI Bathymetric Data Viewer and is public domain. (https://www.ncei.noaa.gov/maps/bathymetry/).
Fig 2.
Bayesian radiocarbon analyses of cores.
Bayesian analyses were generated to produce age-depth models for the four cores (see SI, Figs S3-S6, and SI, Tables S2-S5, [https://zenodo.org/uploads/15330698]). We also generated calibrated ages for each core’s YDB layer, which contains abundance peaks in microspherules, MDPs, and PGE-enriched nanoparticles. The results here list the core, depth interval of the YDB in each core, and calibrated ages (cal BP) at 95.4% Confidence Intervals (CI). The Bayesian interpolated mean age is displayed as a white dot. Confidence Intervals (CI) of 68.3% CI are shown as dark gray horizontal bars, 95.4% CI as medium gray, and 99.7 CI as light gray. The previously published YDB age range of 12,835–12,735 cal BP [44] is shown as a vertical red bar. (a) Core 52, for the 625-630-cm interval, the 68.3%, 95.4%, and 99.7% CI bars overlap the YDB age range. (b) Core 64, for the 312-318-cm interval, the 68.3%, 95.4%, and 99.7% CI bars overlap the YDB age range. (c) Core 67, for the 32-35-cm interval, the 68.3%, 95.4%, and 99.7% CI bars overlap the YDB age range. (d) Core 77, for the 161-162-cm interval, the 95.4% and 99.7% CI bars overlap the YDB age range, suggesting that this sample may slightly post-date the YDB and the proxies have been redeposited upward. Alternatively, for the 171-173-cm sample, which was not analyzed for proxies, the 68.3%, 95.4%, and 99.7% CI bars overlap the YDB age range, suggesting that this may be the YDB layer. OxCal version 4.4.4 was used with the IntCal20 Marine calibration curve, and reservoir corrections were applied to all radiocarbon dates.
Fig 3.
Comparison of Baffin Bay core lithofacies, Bayesian-modeled calibrated radiocarbon ages (SI, Tables S2-S5), and microspherule peaks (SI, Table S6) for Core 83023−052; and lithofacies, pXRF Ca/Ti ratios, and microspherule peaks (SI, Table S6) for Cores 2013029−064, 2013029−067, and 2013029−077 (https://zenodo.org/uploads/15330698).
The core 52 log is adapted from the Geological Survey of Canada marine core archives. Core logs for Cores 64, 67, and 77 are adapted from Fig 4 in Jenner et al. 2018 [19]. Notes: 1Bayesian- modeled calibrated radiocarbon dates from Jenner et al.[19] and 2Bayesian-modeled calibrated radiocarbon dates (this study). Red boxes (a-d) are core sections examined for impact proxies, as shown in Fig 4. Figure generated from data in Jenner et al. [19].
Fig 4.
Closeup of areas shown in Fig 3 (red boxes) illustrating core lithology, core x-ray images, microspherule (MSp) and metallic dust particle (MDP) peaks (spherules/kg), and calibrated radiocarbon ages.
1Bayesian-modeled calibrated radiocarbon dates are from Jenner et al.[19] and 2this study (see SI, Table S1 and Bayesian-modeled ages in SI, Tables S2-S5, [https://zenodo.org/uploads/15330698]). The x-ray images in panels a) and d) are stretched laterally to improve visibility. A yellow star indicates the YDB microspherule peak. Refer to Fig 3 for lithology keys and optical and x-ray images for cores in SI, Figs S254-257 (https://zenodo.org/uploads/15330698). The figure was generated from data from Jenner et al. [19].
Fig 5.
Examples of Fe-rich and silica-rich impact microspherules from Baffin Bay cores: Core 83023−052 (a-d); Core 2013029−064 (e-h); Core 2008029−067 (i-n); and Core 2013029−077 (o-p).
Features include aerodynamically-shaped microspherules (panels a and l); a broken microspherule revealing a hollow interior (panel c); a hollow microspherule with a bleb of a low-oxygen transitional mineral phase between chromite (FeCr2O4) and (Fe2Cr2O4). (panel d); microspherules with rounded blebs consisting of a mix of iron sulfide and iron silicide (FeSi and FeS), indicating formation in a reducing environment (panels e and h); multiphase microspherules with possible secondary impacts of melted material containing iron phosphide (FeP) (panels k and m), also indicating a reducing environment; microspherules a, d, g, i, j, l, and o showing dendritic texture; and conjoined microspherules showing dendritic textures, areas of melting, and interior fragments (panels o and p). Microspherules c, e, f, and h are silica-rich (See SI, Fig S9, [https://zenodo.org/uploads/15330698]); all others are Fe-rich. Diameters for 73 microspherules ranged from 163 to 4 μm, with an average of 64 μm. See SI, Figs S10-S58 (Core 52); S117-S127 (Core 64); S168-179 (Core 67); S223-S231 (Core 77) for EDS analysis of microspherules (https://zenodo.org/uploads/15330698).
Fig 6.
Examples of meltglass from Baffin Bay cores: (a) Agglutinated cluster of aluminosilicate and Fe-rich microspherules (Core 64_312–318 cm); (b) Partially melted quartz grain (Core 52_574-579 cm); (c) Fe and Cr-rich aluminosilicate meltglass (Core 52_625–630 cm); (d) Agglutinated potassium-enriched aluminosilicate meltglass (Core 52_630–635 cm); (e) Optical image; and (f) SEM image of Ti-rich aluminosilicate meltglass particle (Core 52_574–579 cm).
See SI, Figs S87-S102 (Core 52) and S157-S167 (Core 64) for EDS data (https://zenodo.org/uploads/15330698).
Fig 7.
Examples of Baffin Bay metallic dust particles (MDPs).
The MDPs range from unmelted to partially-melted. They are typically enriched in Fe, Ni, and Cr and are oxygen-deficient (low-O2 Fe), as labeled on each panel. Core 83023−052 (a-d); Core 2013029−064 (e-l); Core 2008029−067 (m-t); and Core 2013029−077 (u-x). MDPs in this figure range from ~20 to 150µm in diameter. See SI, Figs S59-S86 (Core 52), S128-156 (Core 64), S180-S209 (Core 67), and S231-S240 (Core 77) for EDS data (https://zenodo.org/uploads/15330698).
Fig 8.
Comparison of metallic melt splatter on quartz grains from Baffin Bay versus similar melt splatter from South Carolina, USA [37].
(a) Baffin Bay quartz grain (Q) splattered with FeCr. (b) South Carolina ilmenite grain (Ilm) splattered with native Ni [37] (c) Baffin Bay quartz grain splattered with FeCr and FeCrNi. (d) Garnet (Gr) splattered with native Ni [37]. (e) Baffin Bay quartz grain splattered with FeCr. (f) South Carolina quartz grain splattered with native Ni [37]. Baffin Bay melt splatter morphologically and chemically matches many MDPs (i.e., FeCr and FeCrNi) that peak during the YD onset for all cores (see Fig 7). See SI, Figs S103-S116 (Core 52), S159-S167 (Core 64), S210-S222 (Core 67), and S241-253 (Core 77) for EDS data (https://zenodo.org/uploads/15330698).
Fig 9.
Bulk Sediment Elemental abundance peaks in nanoparticles, Core 67 determined by SP-ICP-TOF-MS. The mean mass abundances of six key elements (Pt, Ir, Ni, Co, Cr, and Cu) peak in the YDB layer; they are also typically enriched in extraterrestrial material, suggesting an ET component in the nanoparticles.
The layer with peaks in inferred impact microspherules and CDPs is darker green, and the layer with lesser abundances of apparently reworked impact material is lighter green. Similar elemental profiles for Core 64 data can be found in SI, Figs S7 and S8 (https://zenodo.org/uploads/15330698).
Fig 10.
Bulk sediment nanoparticle elemental mass ratios for Core 67 determined by SP-ICP-TOF-MS. Mean mass elemental ratios within individual nanoparticles of seven key elements (Pt, Pd, Ir, Fe, Ni, Co, and Cr) that are typically enriched in extraterrestrial material.
The layer with peaks in inferred impact microspherules and CDPs is darker green, and the layer with lesser abundances of apparently reworked impact material is lighter green. These ratios indicate a relative increase in the masses of Pt, Co, Cr, and Ni assemblages relative to other elements. Nearly all ratios begin to increase in the upper part of the YDB layer, reaching peaks a few cm above the arrows. The same elemental mass ratios for Core 64 are shown in SI, Figs S7 and S8 (https://zenodo.org/uploads/15330698). The ratio of Pt to Pd > 1.0 is expected if an exogenic ET input of Pt occurred, as noted by Moore et al.[50].
Fig 11.
Comparison of Fe/Cr and Fe/Ni ratios between Baffin Bay microspherules (MSp), cometary material, and cosmic dust.
(a) Particles retrieved from the debris trail of Comet Wild (orange; n = 33) do not overlap with Baffin Bay microspherules (blue; n = 18), suggesting that the microspherules are not dominated by ET material. (b) However, if it is inferred that the Cr and Ni were mostly derived from an ET source comprising ~1 wt% of the impactor, there is excellent correspondence, e.g., as reported by Koeberl et al.[16](c) Cosmic dust particles (n = 129) collected from the stratosphere also do not overlap. (d) If Cr and Ni are inferred to comprise ~1 wt% of the impactor, this results in excellent correspondence. The ratios show that Baffin microspherules typically contain less Cr and Ni than most cometary materials, consistent with a dominance of terrestrial materials. See SI, Tables S8a,b, and S9 for Baffin LA-ICP-MS data and sources of proxy comparisons (https://zenodo.org/uploads/15330698).
Fig 12.
Comparison of Fe/Cr and Fe/Ni ratios between Baffin Bay microspherules (MSp), micrometeorites, and cosmic dust.
(a) Antarctic ET micrometeorites (n = 80) only weakly overlap with Baffin Bay microspherules (blue; n = 18), suggesting that most Baffin microspherules are not dominated by ET material. (b) However, if it is inferred that the Cr and Ni were mostly derived from an ET source comprising ~1 wt% of the impactor, there is excellent correspondence. (c) Inferred cosmic dust from peat deposits in Russia (n = 6) [21–23] and the USA (n = 6) [37] also do not overlap. (d) If Cr and Ni are inferred to comprise ~1 wt% of the impactor, this results in excellent correspondence. The ratios show that Baffin microspherules typically contain less Cr and Ni than most cosmic materials, consistent with a dominance of terrestrial materials. See SI, Tables S8a,b and S9 for Baffin LA-ICP-MS data and sources of proxy comparisons (https://zenodo.org/uploads/15330698).
Fig 13.
Comparison of Fe/Cr and Fe/Ni ratios between Baffin Bay microspherules (MSp) and various meteoritic materials.
(a) Fe/Cr and Fe/Ni ratios of chondrites (orange; n = 111) partially overlap with Baffin Bay microspherules (blue; n = 18), as do (b) achondrites (altered chondrites; n = 26); (c) iron meteorites (n = 15); and (d) meteoritic microspherules (n = 229), from Antarctic ice and deep-sea deposits. These ratios show that Baffin microspherules typically contain less Cr and Ni than most ET material, consistent with a dominance of terrestrial materials. See SI, Tables S8a,b and S9 for Baffin LA-ICP-MS data and sources of proxy comparisons and references (https://zenodo.org/uploads/15330698).
Fig 14.
Comparison of Fe/Cr and Fe/Ni ratios between Baffin Bay microspherules (MSp) and various terrestrial materials.
(a) Impactites (orange; n = 23), typically consisting of >98 wt% terrestrial material, partially overlap with Baffin Bay microspherules (blue; n = 18), as well as (b) Ratios of mantle material (n = 26); and (c) Ratios of volcanic/magmatic materials (n = 31). (d) Ratios of crustal materials (n = 37) strongly overlap with Baffin Bay microspherules. The ratios indicate that terrestrial materials typically dominate Baffin microspherules. See SI, Tables S8 and S9 for Baffin LA-ICP-MS data and sources of proxy comparisons (https://zenodo.org/uploads/15330698).
Fig 15.
Baffin Bay metallic dust particles (MDPs) compared to cometary material.
The Fe/Cr and Fe/Ni ratios of Baffin Bay MDPs overlap those of four types of cometary material: (a) CDPs retrieved from the debris trail of Comet Wild during the Stardust mission (orange; n = 33; green; n = 15).; (b) CDPs collected from the stratosphere (n = 129). (c) CDPs found in peat deposits from Selenga, Russia (n = 7), and several sites in South Carolina, USA (n = 6) [21,22,37] (see SI, Tables S9-S12). (d) CDPs of Antarctic micrometeorites (n = 80), which are considered primarily to be cometary dust (SI, Table S9) (https://zenodo.org/uploads/15330698). For comparison, upper continental crust ratios are 426 for Fe/Cr and 834 for Fe/Ni [125].
Fig 16.
Comparison of Baffin Bay metallic dust particles (MDPs) with meteoritic material.
The Fe/Cr and Fe/Ni ratios of about half of Baffin Bay MDPs partially overlap that of various meteoritic materials as follows, although some display greater enrichments in Ni and Cr relative to Fe in meteorites: (a) chondritic meteorites (orange; n = 111; green; n = 15); (b) achondrites (altered chondrites; n = 26); (c) iron meteorites (n = 15); and (d) meteoritic microspherules (n = 229), from Antarctic ice and deep-sea deposits. For comparison, in the upper continental crust, ratios of Fe/Cr = 426 and Fe/Ni = 83498. See Baffin Bay MDP data in SI, Table S10. Data sources other than Baffin Bay can be found in SI, Tables S9, S11, and S12 (https://zenodo.org/uploads/15330698).
Fig 17.
Comparison of Baffin Bay metallic dust particles (MDPs) with terrestrial material.
The Fe/Cr and Fe/Ni ratios of Baffin Bay MDPs are compared to those of various terrestrial materials. (a) Ratios from impactites (orange; n = 23), which contain over 98 wt% terrestrial material, do not overlap with Baffin Bay dust particles (green; n = 15). (b) Ratios from mantle material (n = 26) exhibit only partial overlap with Baffin Bay dust particles. (c) Ratios of magma (n = 31) do not overlap with Baffin Bay dust particles. (d) Ratios of crustal material (n = 37) minimally overlap with Baffin Bay MDPs. For the upper continental crust, ratios of Fe/Cr = 426 and Fe/Ni = 834 [125]. See Baffin Bay MDP data in SI, Table S10 Data sources other than Baffin Bay can be found in SI, Tables S9, S11, and S12 (https://zenodo.org/uploads/15330698).
Table 2.
Comparison of metallic dust particles. This table presents compositions, numbers (#), and percentages of dust particles from three different locations: Baffin Bay (n = 140), South Carolina (SC; n = 98) [37], and Selenga, Russia (n = 360) [21–23]. Fifteen elemental combinations (highlighted) are common across at least two of the three sites: Fe-native, Fe-low O2, FeO, FeCr, FeCrNi, FeNiCu, FeCrNiCu, FeP, FeZn, NiFe, Ni-low O2, Ni-native, NiO, NiZn, and CuZn. Altogether, these combinations suggest a possible common origin of dust particles at these sites, up to 10,300 km apart. Other combinations (not highlighted) are unique to one of the three sites. Some particles appear to be alloys rather than minerals, with many displaying no detectable oxygen or lower oxygen percentages than usual. Combinations missing from a given site are indicated in red.
Fig 18.
Comparison of flake-like dust particles (MDPs) from Baffin Bay with cometary dust particles (CDPs) from South Carolina, USA [37] (N 33˚48′40ʺ, W 78˚49′00ʺ), and Russia [21–23] (N 52˚, W 88˚).
The compositions of these particles include native Fe, native Ni, NiFe, NiFeCr, and FeCr, and range from melted to unmelted. (a-b) Feather-like particles. Their delicate features suggest that these particles remained in situ where deposited and were not reworked. (c-d) Twisted and layered morphologies. These particles resemble a twisted FeCr particle reported in the YDB layer from Abu Hureyra, Syria [80]. (e-f) Thin, linear morphologies. See SI, Tables S11 and S12 for elemental data for CDPs from sites in Russia and South Carolina (https://zenodo.org/uploads/15330698).
Fig 19.
Comparison of flake-like metallic dust particles (MDPs) from Baffin Bay with cometary dust particles (CDPs) from Russia [21–23] and South Carolina, USA [37].
The compositions of these particles include native Fe, native Ni, NiFe, NiFeCr, and FeCr. (a-b) Striated, curved particles. (c-d) Thin, striated, flake-like particles with folded edges (arrows). Some edges appear melted. (e-f) Thin, flake-like particles without striations. See SI, Tables S11 and S12 for elemental data for CDPs from sites in Russia and South Carolina (https://zenodo.org/uploads/15330698).
Fig 20.
Various YDB proxies have been found at 60 sites on six continents, including Antarctica. Baffin Bay cores are in yellow, and other YDB sites are in red. The base map was provided by Tom Patterson (www.shadedrelief.com).
Appendix Fig A1.
metallic dust particles (MDPs) and potential sources of anthropogenic contaminants. Most Baffin MDPs do not overlap with anthropogenic/industrial metallic particles, which typically group at the vertices. Clusters of nearly pure nickel-plated neodymium magnet coatings overlap with some MDPs, but contamination is unlikely because the magnets were shielded from the sample. Alternatively, cometary material can contain blebs of native nickel and native iron. a) O-Cr-Ni plot. Some MDPs in the middle of the plot display similar ratios of Cr to Ni but with highly variable amounts of oxygen. Most are inconsistent with the plotted contaminants and, thus, are likely to be terrestrial or ET chromite grains. b) Cr-Fe-Ni plot. The Fe abundances were divided by 5 to increase the clarity of the plot. Note that the contaminants are grouped at the vertices on the righthand Fe-Ni axis, and none overlap the MDPs along the rest of the axis. The axis is marked to show awaruite (~77 wt% Ni), taenite (~20–65 wt% Ni), and kamacite (5–10 wt% Ni), which are very rare terrestrially but common in ET material, supporting the conclusion that these are ET particles. The ternary plot was made using ProSim Ternary Diagram software. See SI, Table S13 for data (https://zenodo.org/uploads/15330698).
Table B1.
Analysis of YDB Microspherule (MSp) Influx. This table analyzes the estimated influx of microspherules (MSp) globally using the data from Baffin Bay cores. Based on an average diameter of 64 µm and an estimated number per layer (n = 20) from Baffin cores, the flux of YDB microspherules is estimated to be ~ 4.8 million metric tonnes, assuming a 6-month atmospheric fallout time, potentially extending to several years for smaller MSp. This estimate represents ~1849 times the typical 6-month flux rate of cosmic material of all diameters to Earth, estimated at 5200 tonnes/yr [29]. These values are ~ 6 × lower than, yet comparable to, predictions ranging from 400 to 30 million tonnes of cosmic dust expected from a ~ 100-km diameter disintegrating comet in a short-period orbit [6]. The estimated mass of MSps deposited globally (~4.8 million metric tonnes) constitutes a minute percentage (0.0000009%) of the mass of a 100-km-wide comet. For this analysis, we assume that: 1) the comet was ~ 100 km in diameter; 2) the compositions of MSps are homogeneous with an average density of 50 wt% SiO2 and 50 wt% Fe for mass calculations; 3) all particles entered Earth’s atmosphere over 24 hours and depending upon their size and density, took about 6 months to be deposited into Baffin Bay; and 4) concentrations and mass values in Baffin Bay are representative of those across the entire planet. Justification for assumption #4 comes from Wittke et al.[42], who estimated that ∼10 million tonnes of melted microspherules were deposited at the YDB over 50 million square kilometers on four continents, suggesting global or hemispheric deposition of YDB impact proxies. Of the MSp, only approximately 2% by weight are inferred to be cosmic in origin, with most suggested as melted target rocks from YDB airbursts and impacts. These calculations have significant uncertainties.
Table B2.
Analysis of YDB Cosmic Dust Particle (MDP) Influx: The table analyzes the estimated influx of CDPs globally based on data from Baffin Bay cores. Based on an average diameter of 30 µm and an estimated number per layer (n = 30) from Baffin cores, the global flux of CDPs is ~ 8.8 million metric tons, assuming a 6-month atmospheric fallout time, potentially extending to several years for smaller CDPs. This estimate represents ~3390 times the typical 6-month flux rate of cosmic material to Earth, estimated at 5200 tons/yr [29]. These values are ~ 3 × lower than, but still comparable to predictions ranging from 400 to 30 million tons of cometary dust expected in the trail of a 100-km diameter disintegrating comet in a short-period orbit [6]. For this analysis, we assume that 1) all particles were homogeneous with an average density of Fe; 2) all particles were introduced to Earth’s atmosphere during 24 hours but most likely took 6 months to be deposited into Baffin Bay; 3) concentrations and mass values in Baffin Bay are representative of the entire planet and; 4) the diameter of the YDB comet was a 100 km. Justification for assumption #3 comes from Wittke et al.[42], who estimated ∼10 million tons of melted microspherules were deposited at the YDB over 50 million square kilometers on four continents, suggesting global, near-global, or hemispheric deposition of YDB impact proxies, including CDPs. These calculations are estimations with large, inherent uncertainties.
Table B3.
Analysis of YDB Nanoparticle Influx. We calculated the mass of YDB NPs that exceed background concentrations. The estimated flux of YDB nanoparticles ranges from 6800 to 3400 tonnes within 24 hours, representing >200–400 times the normal daily flux rate of all cosmic material, estimated at 5200 tonnes/yr [29]. For this analysis, we made the following simplistic assumptions: 1) the nanoparticles are homogeneous, 2) all nanoparticles were introduced to Earth’s atmosphere over a duration of 24 hours but probably took considerably longer to fall out into Baffin Bay, and 3) concentrations and mass values in Baffin Bay are representative of the entire planet. These calculations have large uncertainties but serve as a useful model to understand the potential flux of cosmic material to Earth at the YD onset.