Five Large 13th Century C.E. Volcanic Eruptions Recorded in Antarctica Ice Cores

: Major explosive volcanic eruptions impact the climate by altering the radiative balance of the atmosphere and through feedback mechanisms in the climate system. The extent of the impact depends on the magnitude (aerosol mass loading) and the number or frequency of such eruptions. Multiple Antarctica ice core records of past volcanic eruptions reveal that the number (5) of major eruptions (volcanic sulfate deposition flux greater than 10 kg km − 2 ) was the highest in the 13th century over the last two millennia. Signals of four of the five eruptions are dated to the second half of the century, indicating consecutive major eruptions capable of causing sustained climate impact via known feedback processes. The fact that signals of four corresponding eruptions have been found in a Greenland ice core indicates that four of the five 13th century eruptions were probably by volcanoes in the low latitudes (between 20 ◦ N and 20 ◦ S) with substantial aerosol mass loading. These eruptions in the low latitudes likely exerted the strongest volcanic impact on climate in the last two millennia.


Introduction
Major explosive volcanic eruptions emit large amounts of particulate and gaseous substances into the atmosphere in a very short period.While in the atmosphere, the volcanic substances can impact the climate by altering important properties of the atmosphere, including the critical energy balance between incoming (shortwave solar) and outgoing (longwave thermal) radiation [1].Specifically, volcanic aerosols composed of mainly sulfatewater droplets, formed in the atmosphere from volcanic sulfur dioxide, scatter incoming solar radiation and may cause significant reductions in solar energy reception at the Earth's surface.Volcanic eruptions are one of the main causes of natural climate variations; the volcano-climate connection is an important aspect of the global climate system [2].
Records of past volcanic eruptions and of climate are necessary to understand and quantify the role of volcanism in climate change.Volcanic particles and aerosols can distribute globally through atmospheric circulation, and the fallout on polar ice sheets is preserved in snow strata through continuous snow accumulation.These physical and chemical markers of past volcanic eruptions can be detected in polar ice cores [3] and used to reconstruct valuable volcanic records, which are studied to understand how explosive eruptions impact the atmospheric environment and the global climate system [4].
Measurements of volcano-derived chemical species (i.e., sulfur, sulfate, and sulfuric acid) in polar ice cores have been used to reconstruct records of past volcanic eruptions [3,5,6].Ice core records show that the last millennium (1000-2000 C.E./A.D.) was probably the most active in terms of frequency of major volcanic eruptions in the Holocene [7].In particular, the number of very large volcanic eruptions in the 13th century (1200-1300 C.E.) was higher than in any other century in the last several thousand years.The high number makes this century highly important and most susceptible to volcanic influence on climate Atmosphere 2024, 15, 661 2 of 10 variations in the last millennium, which provides the backdrop for the current climate change, forced mainly by anthropogenic emissions of greenhouse gases.
Here, we evaluate chronological volcanic records from Antarctica and Greenland ice cores to ascertain the number and magnitude of large eruptions in the 13th century, and to explore the role these eruptions may have played in climate variations in the last two millennia.

Ice Cores and Chemical Analysis
The newest among the ice cores studied in this work is the 1751 m South Pole intermediate-depth ice core (SPC14), drilled at the South Pole (~90 • S) beginning in 2014.SPC14 drilling, handling, and processing for analysis have been described in detail by Winski et al. [8].The top 800 m (Holocene) of the core was sampled at high temporal resolution (~1 cm per sample) for measurement of the concentrations of major ions (Cl − , NO 3 − , SO 4 2− , Na + , Mg 2+ , and Ca 2+ ) with ion chromatography [8,9].Descriptions of the other Antarctica ice cores (WAIS Divide 2006 (WDC), South Pole 2004 Core 5 (SP04 C5), Plateau Remote 1984 Core B (PR84)) and two Greenland ice cores (Summit 2007 (SM07 C4), NEEM (NEEM S1)) have been provided elsewhere [7,[10][11][12][13].Relevant details about these cores are provided in Table 1.Similar to SPC14, samples from these cores were prepared in the laboratory and analyzed for major ion concentrations with ion chromatography [14].

Ice Core Dating
To construct chronological records of atmospheric aerosol chemical components preserved in polar snow and ice cores, ice core dating-determining the ages of stratigraphic snow/ice layers-is usually accomplished with one or more established methods.The dating methods used for cores in this study (Table 1), including the accurate method of annual layer counting (ALC), have been described in previously published work [7,10,11,15].
Dating accuracy and precision vary depending on core characteristics and dating method.The WAIS Divide core (WDC) was dated with multi-parameter annual layer counting; the WDC timescale (WD2014) is considered to be highly accurate and precise [15].Timescales of other polar ice cores can be synchronized to WD2014 by identifying outstanding signals (tie points) of prominent volcanic eruptions common in multiple cores and setting tie-point dates in the other cores to those in WD2014 [16].The timescales of SPC14 [8] and SP04 [11] have been synchronized with WD2014.No synchronization has been performed on the PR84 volcanic record [10].The dating of the Greenland SM07 core was accomplished with ALC and is independent of the timescales of the Antarctica cores, i.e., no synchronization with WD2014.

Volcanic Flux Calculation
In ice core analysis, the concentrations of chemical species (acidity, sulfur, and sulfate) in ice core samples are measured experimentally.Volcanic signals are usually detected when the concentrations exceed a variable but relatively stable non-volcanic background [10].The deposition flux or mass of volcanic material in snow can be obtained by integrating the concentration over the duration of deposition.
Procedures to calculate volcanic deposition flux have been described in detail in previous publications [7,10,11].Those procedures are used in this work to determine the volcanic sulfate deposition flux of large eruptions in the 13th century.

Results and Discussion
Five prominent volcanic signals from the 13th century have been found in all four Antarctica ice cores (Figure 1).The largest signal is dated to the year 1259 in the WDC chronology [7,17].A volcanic signal was detected at depth 156.5 m in the WDC core (Figure 1a), and the signal appears in 1241 in the WD2014 chronology.No corresponding signals at the same time are detected in the other cores.This signal may be either spurious or from an eruption of a local (West Antarctica) volcano with no significant climate impact, and is not considered further in this work.
In a pioneering work relating ice core chemical measurement to evidence of past explosive volcanic eruptions, Hammer, Clausen and Dansgaard [6] found an outstanding signal of an unreported ("unknown") volcanic eruption in the mid-13th century in a 400 m northern Greenland ice core (Crête, drilled in 1974).The signal in the Crête core was dated to 1259, astonishingly the same as the large signal of the volcanic eruption in WDC after advances in ice core science in the ensuing decades.Not long after the Crête finding, Langway, Clausen and Hammer [18] found signals of this eruption in two Antarctica ice cores (Byrd Station 1968 and South Pole 1978).Because of the presence of signals of this eruption in bipolar ice cores, they deduced that the erupting volcano was located in the low latitudes or near the equator (the tropics), and that its fallout could be found in all polar ice cores.The dating of these Antarctica ice cores using the method of average snow accumulation rate and firn densification calculations [19] was not as accurate as that for the Greenland cores at that time.Due to high confidence in the age of the 1259 signal in the Crête core, Langway, Clausen and Hammer [18] proposed that the signal dates of this eruption in the Byrd Station and South Pole ice cores be reassigned to 1259.The 1259 eruption signal has been used as a time stratigraphic marker and timescale synchronization tie point in both Antarctica and Greenland ice cores.
The "1259 Eruption" in ice cores was studied extensively to determine the volcano responsible for this prominent ice core signal.Tephra (fine volcanic ash) associated with the sulfate signal was found in South Pole [20] and Summit, Greenland [21] ice cores, and the chemical composition of the tephra suggests the El Chichón volcano in Mexico to be the source of the volcanic fallout.The eruption remained unknown until Lavigne et al. [22] found compelling evidence of an extraordinarily explosive eruption of the Samalas volcano (8 • S; 116 • E) on Lombok Island, Indonesia, in 1257.
The 1257 Samalas eruption signal was detected in early ice core work probably due to its large magnitude.Other eruptions with less outstanding signals were not found because the analytical techniques for the chemical measurements were less sensitive than those used in subsequent investigations [3].Later research discovered that the 1257 Samalas eruption was not the only large eruption in the 13th century.Signals of three eruptions including Samalas were detected in a 1982 South Pole core [23]; up to five eruptions were found in that century in a 1989 Byrd Station, Antarctica core as a result of a new measurement method with high sensitivity [24].Five unambiguous signals were found in an ice core from the East Antarctica Plateau by Cole-Dai et al. [10].Similar findings were reported in subsequent Greenland ice cores [24,25].
Despite their highly visible appearance in many bipolar ice core volcanic records, the signals of these 13th century eruptions have not been systematically examined.
eruptions were found in that century in a 1989 Byrd Station, Antarctica core as a result of a new measurement method with high sensitivity [24].Five unambiguous signals were found in an ice core from the East Antarctica Plateau by Cole-Dai et al. [10].Similar findings were reported in subsequent Greenland ice cores [24,25].Despite their highly visible appearance in many bipolar ice core volcanic records, the signals of these 13th century eruptions have not been systematically examined.

Dates of the Eruptions
Due to the uncertainty of dating methods, the signal of a particular eruption may appear at slightly different dates or years in different ice cores.For example, the signal of the 1257 Samalas eruption was dated at 1258-1260 in WDC [26].The highest concentrations of the 1257 Samalas signal appear in 1258 in WDC because of the slow meridional transport of volcanic aerosols [27].The signal of the same eruption was dated to 1260 in SP04 [11] before timescale synchronization (Table 2).The Samalas signal was used as a time stratigraphic marker (1260) for dating the PR84 core.The signals representing five volcanic events are numbered chronologically from A13-1 to A13-5 (Table 2).Because the WD2014 timescale is considered the most accurate and precise, we adopt the WD2014 dates (years) for the 13th century volcanic signals in all other Antarctica ice core records (Table 2).The date of an eruption may precede the signal date by one or two years, if the erupting volcano is located in the tropics.
Usually, the duration of a signal or of volcanic fallout is between several months and two years, depending on the distance between the erupting volcano and the ice core location, due to the spreading of volcanic plumes during atmospheric transport [27].For the same volcanic eruption, the duration may vary owing to variations in snow accumulation rate and sampling frequency for ice core chemical analysis.The data in Table 2 show that the durations for these five 13th century volcanic events are in the range of 2 to 4 years in Antarctica ice cores.The exception is longer durations in the PR84 core (Table 2); the longer durations were understood to result from post-deposition redistribution to layers adjacent to the original snow layers of volcanic deposit in a location (on the East Antarctica Plateau) of extremely low snow accumulation rates [10].

Magnitude of Volcanic Signals
The magnitude of the volcanic signals, measured with volcanic sulfate deposition flux, is an important quantitative measure, as it is related to the quantity of volcanic substances emitted into the atmosphere, which in turn is an indicator of the climate impact potential of the eruption [28].
The volcanic sulfate deposition flux of all the 13th century events exceeds 10 kg km −2 in all the cores (Table 3).The eruptions responsible for the signals are ranked Large (30 > flux > 10 kg km −2 ) or Very Large (>30 kg km −2 ), according to the scale proposed by Cole-Dai et al. [7].These Very Large and Large eruptions are among the approximately 38% of all volcanic signals (426) in the WDC Holocene Volcanic Record (WHV2020) [7].The number (5) of Very Large and Large eruptions in the 13th century is significantly higher than the Holocene century average (~1.5)[7].In both SPC14 and WDC, the frequency of major eruptions recorded in the 13th century is the highest over the last two millennia (Figure 2).The volcanic flux of the 1257 Samalas eruption (Event A13-2) is the largest from the last millennium in almost all Antarctica ice cores [16].It is certainly the largest of the 13th century eruptions in cores examined in this study (Table 3), except for PR84, probably due to post-deposition redistribution [10].When averaged among the cores, the volcanic flux of Samalas is still the largest (Table 3).The smallest volcanic flux belongs to Event A13-3 (Eruption Year 1267).The volcanic flux values of A13-1 and A13-4 are approximately 50% that of A13-2 (Samalas), and suggest that these eruptions are among the largest in terms of aerosol mass loading.The average volcanic sulfate flux (19.2 kg km −2 ) of A13-5 (Eruption Year 1286) in Antarctica cores is comparable to that of A13-3.However, a volcanic sulfate signal appeared at the same time in Greenland ice cores (Table 3).This indicates that A13-5 is from a large eruption of a volcano in the low latitudes with a significant climate impact (see discussion in Section 3.3).Together, these major eruptions probably exerted a significant impact on the climate during the last millennium (discussed in Section 3.3).The volcanic flux of the 1257 Samalas eruption (Event A13-2) is the largest from the last millennium in almost all Antarctica ice cores [16].It is certainly the largest of the 13th century eruptions in cores examined in this study (Table 3), except for PR84, probably due to post-deposition redistribution [10].When averaged among the cores, the volcanic flux of Samalas is still the largest (Table 3).The smallest volcanic flux belongs to Event A13-3 (Eruption Year 1267).The volcanic flux values of A13-1 and A13-4 are approximately 50% that of A13-2 (Samalas), and suggest that these eruptions are among the largest in terms of aerosol mass loading.The average volcanic sulfate flux (19.2 kg km −2 ) of A13-5 (Eruption Year 1286) in Antarctica cores is comparable to that of A13-3.However, a volcanic sulfate signal appeared at the same time in Greenland ice cores (Table 3).This indicates that A13-5 is from a large eruption of a volcano in the low latitudes with a significant climate impact (see discussion in Section 3.3).Together, these major eruptions probably exerted a significant impact on the climate during the last millennium (discussed in Section 3.3).

Volcano Locations
Large eruptions by volcanoes in the Southern Hemisphere and in the low latitudes (the tropics) of both hemispheres (between 20 • N and 20 • S) are likely to leave sulfate/sulfur/sulfuric acid deposits in Antarctic snow, and may be detected in Antarctica ice cores [3].Volcanic signals in Greenland cores are most likely from volcanoes in the Northern Hemisphere and the tropics.Therefore, when signals of an eruption are found in both Antarctica and Greenland ice cores, the so-called bipolar signals, the volcano responsible for the signals is likely located in the tropics [16].The only exception is the global distribution of volcanic aerosols from extraordinarily explosive eruptions of volcanoes in the high or mid-latitudes of Northern Hemisphere [16].Based on this criterion, all five 13th century eruptions (A13-1 to A13-5) were most likely produced by volcanoes in the Southern Hemisphere and/or the tropics.
Four volcanic signals from the 13th century have been detected in an ice core from central Greenland (Figure 3).The volcanic events are numbered from G13-1 to G13-5 (Table 3).The largest signal (G13-2) appears at 1259, according to the independent ALC dating of the Summit, Greenland core [14].This signal is that of the 1257 eruption of the Samalas volcano located in the tropics (8 • S).This is consistent with findings in other Antarctica and Greenland cores [6,18,24].
sponsible for the signals is likely located in the tropics [16].The only exception is the global distribution of volcanic aerosols from extraordinarily explosive eruptions of volcanoes in the high or mid-latitudes of Northern Hemisphere [16].Based on this criterion, all five 13th century eruptions (A13-1 to A13-5) were most likely produced by volcanoes in the Southern Hemisphere and/or the tropics.
Four volcanic signals from the 13th century have been detected in an ice core from central Greenland (Figure 3).The volcanic events are numbered from G13-1 to G13-5 (Table 3).The largest signal (G13-2) appears at 1259, according to the independent ALC dating of the Summit, Greenland core [14].This signal is that of the 1257 eruption of the Samalas volcano located in the tropics (8° S).This is consistent with findings in other Antarctica and Greenland cores [6,18,24].The almost identical timing between A13-4 and G13-4 and between A13-5 and G13-5 strongly suggests that these are from the same volcanic eruptions, respectively.For A13-1 and G13-1, the difference in the signal years (1228 and 1231, respectively) is within the dating uncertainty of these cores [14], and they may be regarded as from the same volcanic eruption.The bipolar signals of these volcanic events indicate that the erupting volcanoes were located in the low latitudes.No volcanic signal was detected in SM07 in the period of 1263-1276 (depth range 199.5-203.5 m in Figure 3).This is consistent with the lack of volcanic signals in that period in other Greenland cores, including NEEM [13] (Table 3) and GISP2 [25].This suggests that the A13-3 volcanic deposit is from an eruption in the high or mid-latitudes of the Southern Hemisphere, rather than an eruption in the tropics.

Potential Climate Impact
The direct radiative impact of an explosive eruption usually lasts no more than two or three years following the eruption due to the relatively short atmospheric residence time of volcanic aerosols [1,3].Eruptions occurring within a short span of several years may have a compounding impact on climate for up to a decade [12].
However, prolonged climate impact is possible via feedback mechanisms in the climate system, such as polar sea-ice expansion and ocean circulation [29].Such feedbacks operate on the time scale of several decades.The five eruptions occurred over a span of approximately 55 years in the 13th century.The most recent four eruptions, A13-2 The almost identical timing between A13-4 and G13-4 and between A13-5 and G13-5 strongly suggests that these are from the same volcanic eruptions, respectively.For A13-1 and G13-1, the difference in the signal years (1228 and 1231, respectively) is within the dating uncertainty of these cores [14], and they may be regarded as from the same volcanic eruption.The bipolar signals of these volcanic events indicate that the erupting volcanoes were located in the low latitudes.No volcanic signal was detected in SM07 in the period of 1263-1276 (depth range 199.5-203.5 m in Figure 3).This is consistent with the lack of volcanic signals in that period in other Greenland cores, including NEEM [13] (Table 3) and GISP2 [25].This suggests that the A13-3 volcanic deposit is from an eruption in the high or mid-latitudes of the Southern Hemisphere, rather than an eruption in the tropics.

Potential Climate Impact
The direct radiative impact of an explosive eruption usually lasts no more than two or three years following the eruption due to the relatively short atmospheric residence time of volcanic aerosols [1,3].Eruptions occurring within a short span of several years may have a compounding impact on climate for up to a decade [12].
However, prolonged climate impact is possible via feedback mechanisms in the climate system, such as polar sea-ice expansion and ocean circulation [29].Such feedbacks operate on the time scale of several decades.The five eruptions occurred over a span of approximately 55 years in the 13th century.The most recent four eruptions, A13-2 to A13-5, occurred at an approximate interval of one each decade during the second half of the 13th century (Figure 1 and Table 3).This is significant because the cumulative and positive feedback impact on climate may be more severe when eruptions occur on an interval of a decade or two.Such frequency and pacing of large volcanic eruptions are not seen in other centuries in the last millennium.For example, four major eruptions occurred in the 19th century [14]: 1809 Unknown, Tambora (1815), Cosigüina (1835), and Krakatoa (1883).In contrast to the 13th century, the latter two 19th century eruptions (Cosigüina (1835) and Krakatau (1883)) occurred a few decades from the earlier two and from each other (Figure 4).interval of a decade or two.Such frequency and pacing of large volcanic eruptions are not seen in other centuries in the last millennium.For example, four major eruptions occurred in the 19th century [14]: 1809 Unknown, Tambora (1815), Cosigüina (1835), and Krakatoa (1883).In contrast to the 13th century, the latter two 19th century eruptions (Cosigüina (1835) and Krakatau (1883)) occurred a few decades from the earlier two and from each other (Figure 4).Of these four climatically important 13th century volcanic eruptions, only A13-2 has been positively attributed to the volcano responsible (Samalas [22]).The others remain "unknown" with respect to source volcanoes.It would be valuable to identify the source volcanoes in future research, as the climatic impact of a large eruption is also influenced by the exact location and the eruption characteristics.

Figure 2 .
Figure 2. Frequency (number per century) of major eruptions (Large and Very Large; volcanic sulfate flux > 10 kg km −2 ) in WDC and SPC14 in the last two millennia (1-2000 C.E.).The highest frequency occurs in the 13th century C.E.

Figure 2 .
Figure 2. Frequency (number per century) of major eruptions (Large and Very Large; volcanic sulfate flux > 10 kg km −2 ) in WDC and SPC14 in the last two millennia (1-2000 C.E.).The highest frequency occurs in the 13th century C.E.

Figure 3 .
Figure 3. Sulfate signals of four large volcanic eruptions from the 13th century in the 2007 Summit Greenland ice core (SM07).

Figure 3 .
Figure 3. Sulfate signals of four large volcanic eruptions from the 13th century in the 2007 Summit Greenland ice core (SM07).

Figure 4 .
Figure 4. Four large volcanic eruptions in the 19th century in the 2014 South Pole ice core (SPC14).
Signals of five major (Large and Very Large) volcanic eruptions during the 13th century C.E. were detected and quantified in several well-dated Antarctica ice cores, including a recent (2014) South Pole core.Four of the five eruptions occurred in the second half of the 13th century.This centennial frequency of major climate-impacting eruptions is unmatched in the last two millennia, and suggests the strongest climate impact by explosive volcanism in that period.The near-perfect matching of the signals of four of the five eruptions with the signals in Greenland ice cores indicates that the eruptions responsible for the four matching signals took place in the low latitudes, which tend to distribute volcanic aerosols globally with probable global climate impacts.

Table 2 .
Signal years and durations of the five large volcanic events in Antarctica ice cores.