Several lines of evidence confirm that tephra T3 in Livingston Island lake sediments was produced by the Deception Island caldera-forming episode. On Deception Island, the Outer Coast Tuff Formation (OCTF; Fig. 2b) is accepted to be the stratigraphic unit that corresponds to the caldera-forming eruption. This formation, the most compositionally distinctive unit on Deception Island, is a sequence of pyroclastic density current deposits of mafic to intermediate composition9,10,12 (Fig. S2). The syn-caldera rocks contain evidence of mingling and co-eruption of two discrete magmas with geochemically distinct compositions, a feature found on Deception Island only in the OCTF. A first group of glass and bulk rock analyses of the OCTF fall within the main geochemical trend for Deception Island defined by the composition of pre- and post-caldera samples (Fig. 4 and Supplementary Fig. S2). By contrast, a second cluster groups at lower TiO 2 and FeOt values, and for the same SiO 2 have slightly higher concentrations of MgO, Al 2 O 3 and CaO than the pre- and post-caldera rocks in major elements vs. SiO 2 Harker diagrams (Fig. 4b and Supplementary Fig. S2). The presence of these two magmas suggests that the explosive eruption leading to caldera formation was triggered by the arrival of hotter and more primitive magmas into an existing reservoir12.

Figure 4 Glass and bulk rock magma composition of Deception Island’s pre-, post- and syn-caldera (OCTF) juvenile fragments. (A) Total Alkali vs. Silica diagram (TAS)53. Major elements are normalized to 100% (anhydrous) with Fe distributed between FeO and Fe 2 O 3 following ref.54. The grey dashed line discriminates between the alkaline-subalkaline fields55. (B) Major element vs. SiO 2 content Harker Diagrams. Major element compositions have been normalized to 100% in anhydrous base with Fe as FeOt. See Supplementary Information File 2 for details on composition and exact latitude-longitude coordinates of the rock samples. This figure was generated with RStudio Version 1.0.143 (https://www.rstudio.com/) using ggplot2 Version 2.1.9000. Final layout of this figure was achieved using Adobe Illustrator CC 2015.3.1 (Copyright © 1987–2016 Adobe Systems Incorporated and its licensors). Full size image

Like the OCTF, the T3 tephra layer’s glass geochemistry also suggests the presence of two magma series (Fig. 5); when T3’s volcanic glasses are compared to those of the OCTF, there is a clear match of all major element relationships as well as locations on the Total Alkali Silica (TAS) diagram (Fig. 5 and Supplementary Fig. S3). Based on these correlations, we conclude that tephra T3 is analogous to the syn-caldera OCTF formation and therefore corresponds to distal fallout from the event shortly before or during the caldera collapse.

Figure 5 T3 glass compositions plotted over glass and bulk rock magma composition of Deception Island’s pre-, post- and syn-caldera (OCTF) juvenile fragments. (A) Total Alkali vs. Silica diagram (TAS)53. Major elements are normalized to 100% (anhydrous) with Fe distributed between FeO and Fe 2 O 3 following ref.54. The grey dashed line discriminates between the alkaline-subalkaline fields55. (B) Major element vs. SiO 2 content Harker Diagrams. Major element compositions have been normalized to 100% in anhydrous base with Fe as FeOt. See Supplementary Information File 2 for details on composition and exact latitude-longitude coordinates of the rock samples. This figure was generated with RStudio Version 1.0.143 (https://www.rstudio.com/) using ggplot2 Version 2.1.9000. Final layout of this figure was achieved using Adobe Illustrator CC 2015.3.1 (Copyright © 1987–2016 Adobe Systems Incorporated and its licensors). Full size image

Magmatic temperatures and pressures calculated by applying silica-activity geothermobarometry to volcanic glasses (T1: 1094 ± 40 °C, 3.1 ± 0.2 kbar; T2: 1098 ± 40 °C, 3.2 ± 0.2 kbar; T3: 1110 ± 40 °C, 3.2 ± 0.2 kbar) closely reflect the basaltic-andesite source at ca. 10 km depth. Given that tephra T3 contains abundant microlite-poor juvenile sideromelane, while other tephra layers are characterised by more microlite-rich crystalline textures (juvenile tachylite15), we conclude that the magma ascent of T3 was rapid and without prolonged shallow storage and associated late-stage crystallisation prior to eruption. T3 is also the only tephra in Byers Peninsula lakes that contains juvenile clasts coarser than 2 mm in diameter, whose deposition here requires an eruption column tall enough to transport the coarse particles over 40 km against the prevailing wind direction. Their presence is thus indicative of a major eruptive event; the finer grain-size distributions (all particles <250 µm)15 characteristic of all other lacustrine tephra layers are consistent with much smaller eruptions.

Hydrogen (δD) and oxygen (δ18O) isotopes in ejecta record the modification of the original magmatic signal by interaction with meteoric fluids and seawater. The measured isotopic values from Byers Peninsula provide evidence for the pre-collapse characteristics of the T3 magma as well as the evolution of Deception Island magmas during subsequent eruptions (tephras T2 and T1; 2370 ± 100 and 1890 ± 140 cal y BP, respectively; Fig. 3). T3 δD (−51.2‰; Supplementary Fig. S4) reflects its equilibrium with primary magmatic fluids and indicates that the T3 eruption occurred prior to seawater infiltration into the magma chamber and therefore prior to caldera collapse. By contrast, the post-collapse tephra layers T2 and T1 are characterised by progressive δD shifts towards oceanic values (−26.3‰ and −4.4‰, respectively; Supplementary Fig. S4) that document the admixture of seawater into the evacuated magmatic system during subsequent volcanic episodes24. The minimal variation in δ18O between the three tephra layers (range: 5.6–6.1‰) is consistent with limited fractionation typical of such high-T magmas and the relatively small δ18O differences between magmatic and non-magmatic waters.

Whereas geochemical analyses record information about the eruptive process, the stratigraphic setting of lacustrine tephra provides insights into associated palaeoseismicity. Deposits up to 112 cm thick are immediately superposed upon T3 in each of the four studied Byers Peninsula lakes (Fig. 3). The genesis of these beds was determined by characterizing the temporal evolution of several depositional proxies, which included lithology, geochemistry, diatom assemblages and radiocarbon ages. These proxies showed that these were event beds that resulted from rapid mass-wasting of allochthonous sediments. Above and below the deposits, sediments consist of a centimetre-scale alternation of dark brown moss-rich layers and light brown massive lacustrine clays and silty clays. Strikingly different characteristics within the mass-wasting beds include massive lithology, an absence of mosses, and sediment geochemical properties. Radiocarbon ages immediately above and below the beds confirm their rapid deposition. Within the beds, however, anomalous radiocarbon dates that deviate several thousand years from the chronosequence reflect the 14C-depleted carbon associated with the redeposition of catchment material (Fig. 3). Marked differences in organic matter geochemistry provide further evidence for the terrestrial origin of the rapid post-seismic deposition sediments (Fig. 6). The differences in TOC, TN, and δ15N between Lake Escondido sediments within event beds and those of pre- and post-event sediments are significant (p < 0.05) and indicate shifts between long-term organic lacustrine deposition and values that more closely reflect the soils of nearby terrestrial environments25, providing parallel evidence of the catchment origin of the sediments in seismic event beds. Above the event deposits, geochemical characteristics returned to ‘typical’ lacustrine values.

Figure 6 Sediment organic geochemical variables in Lake Escondido, Byers Peninsula. The shaded gray area represents the portion of the record with rapid terrestrial sedimentation. TOC, TN and δ15N all differ significantly (p < 0.05) between event sediments and those deposited during the pre- and post-event periods. Full size image

Diatom analysis of the Lake Limnopolar sedimentary record clearly showed that the species present in the mass-wasted sediments were derived from terrestrial and aerophilic assemblages, while those before and after the event were lacustrine taxa. There were three distinct periods in Lake Limnopolar sediments: prior to (Pre-Event), during (Event) and following (Post-Event) the rapid sedimentation event. Diatom assemblages in Pre- and Post-Event sediments were dominated by taxa that are typical of lakes on the Byers Peninsula plateau, as expected with normal lacustrine deposition26. Interestingly, Post-Event assemblages (Supplementary Fig. S5) differed from Event diatoms but also from Pre-Event assemblages, which may indicate an ecological reorganisation due to the perturbation of algal communities by the eruption and its associated post-seismic event. In contrast to abundant deposition in pre- and post-Event sediments, diatoms were scarce in sediments laid down during the rapid deposition event; the minimum threshold for inclusion statistical analyses was not reached in all samples. In all cases, however, event samples were characterised by strikingly different assemblages than those in lacustrine sediments (Supplementary Fig. S5) and were dominated by species observed in soils, mosses and seepage samples in the Antarctic and sub-Antarctic regions (refs26,27, Table S2 and Supplementary Information).

Biological, geochemical and radiochronological data thus showed significant differences between the mass-wasted beds and adjacent sediments, indicating that event beds contained rapidly deposited terrestrial material. We propose that this deposition was triggered by an extreme seismic episode associated with the Deception Island caldera collapse. Distinctive mass-wasting deposits have been generated in lake sediments due to the extreme seismic activity that has accompanied other caldera collapse eruptions; analogous, meter-thick event beds are found in lakes hundreds of kilometres from the 1960 magnitude 9.5 Chilean earthquake, the largest ever recorded23,28. Numerous earthquakes up to Magnitude 7 were recorded in association with the Mt. Katmai caldera collapse in 1912 (caldera diameter 4 km)23 and, given its much greater size, it is reasonable to infer that seismic events of similar or superior magnitude were associated with the collapse of the Deception Island caldera. Seismic seiches, which have been observed in lakes located hundreds to thousands of kilometres from the epicentres of high magnitude earthquakes, are known to cause rapid post-seismic remobilisation of large volumes of terrestrial material from catchments to lake sediments, and are the likely mechanism for the deposition of the Byers Peninsula mass-wasting beds28,29.

To establish a rigorous chronology, we constrained the tephrostratigraphy with a total of 54 AMS 14C dates based on aquatic moss samples and three thermoluminescence ages (refs30,31, Fig. 3 and Supplementary Table 1). Bayesian age-depth models indicate that the caldera collapse eruption occurred 3980 cal y BP. We specifically avoided dating bulk sediment samples, given their well-demonstrated problems in providing reliable dates in Antarctic lake and ocean samples14,32, with the exception of samples taken within the rapid deposition event where no mosses were present. Twenty-nine radiocarbon dates encompassing five cores and three lakes (Escondido, Chester and Cerro Negro) were used to determine the age of the caldera collapse event based on calibrated ages immediately above the rapid sedimentation event and immediately below T3 (Fig. 3). Lake Escondido served as the basis for our chronology given the abundance of moss remains, the availability of suitable dating material immediately above and below collapse event sediments, and its robust age-depth model. In this lake, moss from 0.5 cm below T3 returned an age of 4060 ± 50 cal y BP, while moss 1.3 cm above the rapid deposition event was aged 3890 ± 50 cal y BP. Bayesian age-depth modelling further constrained this age, placing the caldera collapse at 3980 cal y BP, with a 95% confidence age range of 3860–4110 cal y BP30. Chester Lake sediments confirmed the timing of the caldera collapse, with moss radiocarbon ages in sediments above the termination of the rapid deposition event indicating that it occurred just prior to 3930 ± 25 cal y BP (Core CH12-0501G, 0.6 cm above event sediments), 3940 ± 30 cal y BP (Core CH12-0401; 9.4 cm above) and 3960 ± 50 cal y BP (Core CH12-0801; 0.5 cm above) (Fig. 3). Due to a lack of datable material, no older bounding age was available from Chester Lake; heavily folded sediments below the termination of the rapid deposition event and limited overlap between cores prevented the construction of a robust composite age model30.

In Lake Cerro Negro, the radiocarbon age nearest to event sediments was aged 3130 ± 50 cal y BP, however this age was 8.6 cm above the event’s termination. No material suitable for radiocarbon dating was found below this horizon, either above or below T3. Bayesian age-depth modelling indicated a minimum age for the caldera collapse event of 3635 ± 440 cal y BP, however the Lake Cerro Negro model was based on five moss ages (vs. 17 in the Escondido model) and before 3130 cal y BP was based entirely on a single thermoluminescence age30. Although the modelled collapse event age in Lake Cerro Negro is broadly consistent with those determined in the other cores, we gave primacy to the ages from lakes Escondido and Chester due to the stronger age model and the position of radiocarbon samples in stratigraphic proximity to event beds and tephra. Lake Limnopolar ages were not used to constrain the collapse event as our data suggest that they were subject to large and variable reservoir effect due to ancient carbon contamination most likely stored in catchment soils (see Supplementary Information for details).

Now firmly established as a Holocene event, the erupted volume of 30–60 km3 and volcanic explosivity index (VEI) of 69,10,12 make the Deception Island caldera-forming eruption the largest eruption documented in Antarctica during the Holocene, exceeding the Hudson Mountains Subglacial Volcano (VEI 3-4; ref.33) by several orders of magnitude. Although an event of this magnitude would be expected to have widespread environmental consequences, until now, the lack of firm chronological constraint for the Deception Island caldera collapse had precluded an evaluation of the scope of its impacts. We therefore examined Antarctic ice cores, and lacustrine and marine sediments throughout the SSI and the Antarctic Peninsula, in search of contemporaneous volcanogenic layers and comparable event beds, revealing at least 18 such sites around Antarctica that preserve a record of the caldera collapse eruption (Fig. 1 and Supplementary Table 3). The distribution suggests that volcanic ejecta were transported by a predominantly westerly airstream and deposited across a wide region of the sub-Antarctic, with deflection onto the Antarctic continent mediated by the polar vortex, as indicated by modelling of recent Deception Island eruptions34. Glaciochemical signatures record a major volcanic event in Antarctic ice cores reaching >4600 km from Deception Island, with modelled ice ages that closely matched the Deception Island caldera-forming event. These included Talos Dome (3998 ± 130 y BP); Dome C (4004 ± 200 y BP); Dronning Maud Land (3995 ± 200 y BP); and Vostok (3942 ± 600 y BP)35,36,37,38,39,40, as well as Plateau Remote (3969 ± 100 y BP)41, whilst a tephra tentatively aged 3910 ± 200 y BP was deposited in a James Ross Island ice core18, although the correlations remain tenuous until they can be confirmed by geochemical composition data for these tephra. Tephra layers that we correlated to the Deception Island caldera collapse by a combination of chronology and/or geochemistry were also found in sediment cores and terrestrial sites situated across the SSI, James Ross Island and the Antarctic Peninsula, as well as in palaeoceanographic records from Bransfield Strait and the Scotia Sea (Fig. 1 and Supplementary Information). Several lakes from the Barton, Fildes and Potter peninsulas of King George Island, ~120–130 km downwind of Deception Island, contain eruptive-seismic depositional sequences with tephra, gravity flows and rapid-deposition events that in some instances reach 1.5 m thickness (Fig. 1 and Supplementary Table S3; refs42,43). The sedimentary record of another two King George Island lakes record tephra and periods of accelerated sedimentation, combined with the deposition of terrestrial diatoms and reductions in organic matter content due to inputs of allochthonous material, that are consistent with our event chronology44. These singular, largely unexplained stratigraphic features mirror those on Livingston Island and underline the magnitude of both the Deception Island eruption and the seismic episode.

Taken together, our study reveals conclusive, multidisciplinary evidence for a major volcanic episode with far-reaching effects at 3980 cal y BP. Ejecta from the caldera-forming eruption were deposited widely across the Antarctic, whilst a major coeval earthquake affected the Antarctic Peninsula region. In addition to resolving the long-lasting controversy regarding the timing of this major volcanic episode, these findings provide a valuable tie point for the calibration of ice and sediment core chronologies and will therefore contribute to an improved understanding of past Antarctic environmental change. Much remains to be elucidated about the effects of large eruptions on climate, and the data available at present are insufficient to provide a detailed characterisation of the climatic and ecological response to this and other profound but short-lived Antarctic events1,7. However, our study establishes a precise chronology for the Deception Island caldera collapse, a volcano-climatic event with a likely hemispheric impact. Future, high-resolution re-examination of ice and sediment records should help to clarify the influence of such volcanic forcing on Antarctic climate.