Mid-to-late Holocene climate variability in coastal East Asia and its impact on ancient Korean societies

The sustainability of human societies is contingent upon our ability to accurately predict the effects of future climate change on the global environment and humanity. Wise responses to forthcoming environmental alterations require extensive knowledge from historical precedents. However, in coastal East Asia, a region with a long history of agriculture, it is challenging to obtain paleoenvironmental proxy data without anthropogenic disturbances that can be used to assess the impact of late Holocene climate change on local communities. This study introduces a high-resolution multi-proxy sedimentary record from an isolated crater in Jeju Island, Korea, to elucidate the mechanisms underlying mid-to-late Holocene climate change and its impacts on ancient societies. Our findings suggest that hydroclimate changes were predominantly governed by sea surface temperature fluctuations in the western tropical Pacific, with low-frequency variability in solar activity and a decrease in summer insolation identified as primary drivers of temperature change. Moreover, ancient societies on the Korean peninsula were significantly affected by recurring cooling events, including the 2.8 ka event, 2.3 ka event, Late Antique Little Ice Age, maunder minimum, and others.


Study area
Site description.The Dongsuak crater (33° 21′ 41ʺ N, 126° 37′40ʺ E) is located in the eastern region of Jeju Island, South Korea (Fig. 1).Jeju Island is a shield volcano that emerged from the continental shelf of the Yellow Sea; it comprises layers of basaltic lava and some pyroclastic deposits.The island contains > 450 Quaternary satellite cones, including cinder (scoria) cones, lava cones/domes, and hydromagmatic tuff rings/cones.The Figure 1.(a) Locations of the study site (yellow star) and the paleoclimate records used or mentioned in this study: site MD98-2181, Mindanao, Philippines 24 (Fig. 5), Liang Luar Cave, southeastern Indonesia 31 (Fig. 7), Dongge Cave, southern China 59 .(b) Coring site location (red square), Dongsuak crater, Jeju Island, South Korea.These location maps were created using the GMRT Map tool (www.gmrt.org/ GMRTM apTool/) 85 .(c) Coring location (red square).Line AB indicates the position of the vegetation profile shown in Fig. 2a.This image was created using Google Earth (www.google.co.kr/ intl/ ko/ earth/).
Several lower elevation regions have been repurposed for agriculture 12,14 .Historical records indicate that over the past millennium, semi-natural lowland grasslands have been used to raise horses and cattle.The grazed areas are predominantly populated by species such as Trifolium repens, Botrychium virginianum, Rosa multiflora, Miscanthus sinensis, and Imperata cylindrica 15 .
The evergreen broadleaved forest mainly consists of species such as Castanopsis sieboldii, Quercus acuta, Distylium racemosum, Camellia japonica, Eurya japonica, Ligustrum lucidum, Ilex crenata, and Daphniphyllum Paleoenvironmental proxy data.For ease of discussion, the pollen diagrams were divided into five zones and three subzones based on clustering results (Fig. 4).The same zones were also utilized to describe other proxy data (Figs. 5 and 6).

Table 1.
Radiocarbon dates for Dongsuak sediments.The data were calibrated using rbacon 3.0.0software 72 and the IntCal20 dataset 73 .

Sample depth (cm)
Material dated Laboratory no.δ 13   Pollen zone 1 (150-55 cm): 4350-1700 cal year BP.This zone was divided into three subzones.Zone 1a (150-128 cm) exhibited a high pollen percentage of herbaceous plants, including Artemisia and Poaceae, as well as aquatic plants such as Cyperaceae (Fig. 4).TOC percentages were relatively high, whereas MS values and CARs were low (Fig. 5).Notably, there was a negative correlation between TOC and MS throughout the sediment profile.
In zone 1b (128-90 cm), there were consistent decreases in Artemisia and Poaceae percentages, whereas Quercus subg.Lepidobalanus showed an increase.Cyperaceae frequencies were lower, and tree pollen index of temperature (TPIT) values were higher, compared with the previous subzone (Fig. 6).TOC percentages gradually increased, whereas MS values declined.
Zone 1c (90-55 cm) was characterized by a significant increase in Lepidobalanus percentages.Similar to zone 1b, Artemisia and Poaceae percentages steadily decreased.Cyperaceae frequencies and CARs both showed a substantial increase around 2300 cal year BP, followed by a gradual decline.(250-year moving average) (a), Dongsuak multi-proxy data from this study (b-g), and reconstructed sea surface temperatures of the western tropical Pacific 24 (e).Dry periods are highlighted by pale orange boxes, whereas wet periods are indicated by pale green boxes.Note that charcoal data were charted using a log scale on the y-axis (f), as well as a normal scale (g Pollen zone 4 (26-8 cm): 700-100 cal year BP.Zone 4 showed patterns similar to the findings in zone 2. The proportions of Artemisia and Poaceae decreased again.However, there were considerable increases in the abundances of tree taxa such as Carpinus, Lepidobalanus, Betula, Ericaceae, and Pinus.Notably, Pinus was rare in previous periods but began to show an increase in zone 4.Among the key tree taxa, only Castanopsis demonstrated a noticeable decline.Botryococcus displayed a sharp increase and reached 80%.Cyperaceae percentages and CARs, which remained low in the first half of the zone, rapidly increased beginning around 500 cal year BP.Conversely, both MS and TPIT values declined at the same time.
Pollen zone 5 (8 cm-surface): 100 cal year BP to present.In zone 5, human activities had a significant effect on vegetation.Pinus and herbaceous plants, especially Poaceae, displayed increasing importance.However, other Paleoclimate proxy records of Dongsuak sediments.The Dongsuak proxy records, particularly the charcoal data, imply that mid-to-late Holocene hydroclimate variations in the study area were primarily driven by fluctuations in sea surface temperatures (SSTs) in the western tropical Pacific (WTP).The study area likely experienced drier periods when WTP SSTs were lower and wetter periods when WTP SSTs were higher.
The results of previous pollen studies in the Korean peninsula have suggested that the climate was comparatively dry during periods when WTP SSTs cooled because of long-term El Niño-Southern Oscillation-type variations 2,[19][20][21][22] .The frequency of El Niño events may have increased, leading to reduced WTP SSTs and a smaller amount of atmospheric water vapor above the oceanic source region where the East Asian summer monsoon originates.Our CARs data support the notion that reduced precipitation, induced by lower WTP SSTs, resulted in more frequent and intense local wildfires in coastal East Asia, including the Korean peninsula and Jeju Island.
Comparisons between Dongsuak proxy records and 250-year moving averages of total solar irradiance (TSI) data 23 suggest that varying levels of dryness or wetness in the study area were influenced by centennial-scale fluctuations in solar activity.Enhanced solar activity on this timescale resulted in drier conditions, and vice versa.These long-term shifts in TSI may have controlled multi-centennial, low-frequency variations in Holocene El Niño-Southern Oscillation; increased TSI likely triggered El Niño-like conditions and lower WTP SSTs 24 .The lower WTP SSTs may have led to decreased precipitation in the study area (Fig. 5).
The impacts of solar activity and WTP SSTs on the study area's hydroclimate are clearly captured in TOC, MS, Botryococcus, Cyperaceae, and charcoal records of Dongsuak sediments.TSI values were negatively correlated with TOC % and Botryococcus % over most of the period investigated, but positively correlated with Cyperaceae %, CARs, and MS values.During dry periods, likely triggered by low WTP SSTs, there would have been a decrease in both autochthonous productivity and the influx of allochthonous organic matter (indicated by low Botryococcus % and TOC %) 25 .Reduced precipitation could have led to more frequent wildfires (high CARs values), decreased tree density on the slope, and increased erosion (high MS values), in a successive manner.Additionally, increased influx of clastic materials into the lake may have caused a reduction in lake area, providing more space for Cyperaceae colonization.
The resemblance between our TPIT data and temperature reconstructions from Greenland ice cores 26 suggests that TPIT can be used to gather local information regarding Holocene temperature change, although the data are not strictly quantitative.The TPIT records imply that temperature shifts in the study area were influenced by variation in both solar activity 27 and summer insolation, which declined consistently during the mid-to-late Holocene (Fig. 6).
Our TPIT data, Greenland temperature reconstructions, and 50-year moving averages of TSI show significant similarities in periodicity, including ~ 1000-year warming cycles and ~ 500-year cooling cycles over the past 4000 years.These findings all indicate a connection between solar activity variability and mid-to-late Holocene temperature change in the study area (Fig. 6).
Intriguingly, the comparison between our proxy records and TSI data suggests that long-term (250 years) moving averages of TSI provide insights into hydroclimate change in the study area, whereas shorter-term (50 years) moving averages are more indicative of paleotemperature change.
Hydroclimate changes since 2600 cal year BP.Our pollen data suggest that the study area became progressively wetter during the mid-to-late Holocene.A consistent increase in arboreal taxa and a decrease in non-arboreal taxa indicate forest expansion in and around the crater, supplanting grassland as rainfall increased.From ~ 2600 cal year BP to 1700 cal year BP (pollen zone 1c), trees such as deciduous oak and hornbeam became increasingly prominent in the study area, whereas the abundances of herbaceous plants decreased.
The causes of these observed changes (i.e., whether they were related to increased precipitation or higher temperatures) remain unclear.Considering the low WTP SSTs and high CARs in zone 1c, it is highly probable that the climate during this period was relatively dry with decreased precipitation (Fig. 5).Annual mean temperatures also appeared to decrease, consistent with a gradual decrease in summer insolation (Fig. 6).However, deciduous oaks exhibited a particularly competitive advantage over grasses during this period.Our findings suggest that deciduous trees benefited from a slight but steady increase in late Holocene winter insolation 19,28 since 2600 cal year BP.
Additionally, high CARs in zone 1c indicate frequent wildfires because of the prevailing dry conditions between 2600 and 1700 cal year BP.These wildfires likely influenced slope stability, resulting in a significant influx of clastic materials into the lake.The increased area created by these deposits could have provided favorable conditions for colonization by sedges at the lake margin, as indicated by the increased prevalence of Cyperaceae.
From 1700 cal year BP to 1150 cal year BP (zone 2; DACP), precipitation increased, resulting in a wetter climate (as indicated by Dongsuak proxy records).Increased frequencies of Botryococcus and Carpinus suggest greater productivity in and around the lake.Furthermore, percentages of herb taxa, MS values, Cyperaceae percentages, and CARs all decreased during this period.These changes imply that the wet climate led to increased tree density, decreased wildfires, and reduced erosion.The wet conditions were likely related to a decrease in low-frequency solar activity and an increase in WTP SSTs.
There was a relatively warm period between 1150 and 700 cal year BP (zone 3), commonly referred to as the Medieval Climate Anomaly (MCA).However, hydroclimate conditions were particularly dry, as indicated by a reduction in the abundances of Carpinus and Botryococcus, a contrasting increase in frequencies of herb and aquatic taxa, and an increase in MS values and CARs.During the subsequent period from 700 to 100 cal year BP (zone 4), corresponding to the Little Ice Age (LIA), wet conditions returned.Changes were evident in MS values, Cyperaceae percentages, and CARs.Notably, the first half of this period likely included a significant increase in precipitation, as implied by rapid declines in the values of all three proxies.However, the sudden rebound at ~ 1600 CE suggests a transition to drier conditions during the middle of the LIA, consistent with paleoenvironmental proxy records from Northeast China 29,30 and the western tropical Pacific 31,32 .
For instance, western Pacific hydroclimate reconstructions from stalagmite δ 18 O data for southeastern Indonesia clearly demonstrated sudden drying at ~ 1600 CE (Fig. 7).The similarity between Indonesian data and Dongsuak records supports our conclusion that Holocene climate change on Jeju Island was primarily controlled by variations in WTP SSTs.Furthermore, the Annals of the Joseon Dynasty (official state records) indicate a dramatic decrease in typhoon landfalls beginning at ~ 1600 CE 33 .This information suggests that decreasing WTP SSTs suppressed typhoon generation, reducing the influx of water vapor into coastal East Asia (Fig. 7).
After ~ 1850 CE (zone 5), variations in the proxy data no longer indicate natural climate change but instead reflect the effects of human activities.
The results of autospectral analysis on charcoal data showed hydroclimate cycles of 124, 106, and 81 years, which were significant at the 90% Monte Carlo false alarm level.Additionally, there was significant statistical coherence between CARs and WTP SSTs for cycles of 215, 106, and 86 years (Fig. 8).These cycles closely resemble sunspot periodicity at 230-year 34 , 212-year 35 , 130-year 36 , 106-year 35 , and 88-year 35 cycles.These findings indicate that hydroclimate variability in the study area, driven by variations in WTP SSTs, was connected with major cycles of solar activity.Past temperature variability.The Greenland temperature reconstructions 26 and our TPIT data showed similar trends and fluctuations since ~ 4000 cal year BP.These changes were characterized by gradual cooling punctuated by periods of relative warmth occurring at ~ 1000-year intervals.The overall temperature decline was likely to have been connected to a consistent decrease in Holocene summer insolation.Both records also revealed short-term cooling periods at 400-600-year intervals, suggesting periodic climate variation in the study area.Paleoclimatological studies from various regions, globally, increasingly show abrupt climate changes, including late Holocene cooling events at 4.2 ka 37,38 , 3.7 ka 39 , 3.2 ka 40 , 2.8 ka 41,42 , 2.3 ka 43 , 1.8 ka 44 , 1.2 ka 45 , and 0.6 ka 46 .The ~ 500-year cyclicity is presumably associated with low-frequency sunspot variability 47 and subsequent shifts in WTP SSTs 1,2,29 .Simultaneously, temperatures appear to have dropped at ~ 230-year intervals throughout the period investigated, potentially in relation to periodic changes in Holocene solar activity.The 210-year Suess/de Vries cycle has been detected most frequently in Holocene paleoenvironmental proxies 48 .
The autospectral analysis of our TPIT data revealed that the 230-, 130-, and 80-year periodicities were significant.These periodicities were similar to the 210-year de Vries cycle and 88-year Gleissberg cycle, both of which had substantial effects on global climate variability during the Holocene 54,55 .Additionally, key solar cycles were confirmed in the coherency spectrum between TPIT data and TSI records (Fig. 8).Coherent periodicities of 505, 350, 231, 125, and 90 years were significant at the 90% Monte Carlo false alarm level.They correspond to the solar cycles of 504, 355, 230, 130, and 88 years reported in previous studies [34][35][36]56 . Thee findings collectively suggest that changes in TSI were highly likely to be responsible for mid-to-late Holocene temperature shifts in the study area.www.nature.com/scientificreports/events at 2.8 ka and 2.3 ka are suspected to have significantly impacted ancient Korean societies.Recent Korean paleoenvironmental studies increasingly recognize these events, with time gaps of ~ 500 years between them 2,57 .Furthermore, Holocene WTP SST reconstructions 24 , TSI data 23 , and stalagmite δ 18 O records from Dongge Cave, China 58,59 , all revealed distinct changes around 2800 and 2300 cal year BP.The amount of water vapor reaching the Korean Peninsula appears to have diminished during the 2.8 ka and 2.3 ka events, likely because of decreased WTP SSTs under sustained El Niño-like conditions.Specifically, around 2300 cal year BP, the study area experienced extreme dryness, as indicated by the highest CARs throughout the investigation period (Fig. 9).

Societal response to climate change.
Around 3000 cal year BP, a new group of farmers (known as the Songguk-ri assemblage) emerged in the southern Korean peninsula.The culture of these farmers, based on early rice agriculture, reached its peak 200 years later.However, the Songguk-ri societies, which once dominated the southern part of the peninsula, began to weaken around 2800 cal year BP and finally ended 2300 cal year BP.The abrupt disappearance of Songguk-ri culture is recognized as important by Korean archaeologists.Nevertheless, the exact cause of the culture's rapid decline remains unknown.Recent paleoclimate data from the Korean Peninsula suggest that the cause was climate deterioration around 2800 and 2300 cal year BP, likely to have been related to changes in WTP SSTs 2,22,57 .
During the warm periods, occurring at ~ 1000-year intervals, local societies may have remained stable because of reduced migration inflow.However, during the intervening cold periods, massive influx of migrating northern people might have caused chaos among the prehistoric societies of the peninsula.Asian paleoenvironmental studies increasingly suggest that late Holocene climate deterioration often drove northern people southward [60][61][62][63][64] .
During the Middle Bronze Age Cold Period (MBACP, 3800-3400 cal year BP), IACP (2800-2300 cal year BP), and DACP (1750-1200 cal year BP), people from Liaoxi and Liaodong likely migrated south to the peninsula.Conversely, during the MWP (3400-2800 cal year BP), RWP (2300-1900 cal year BP), and MCA (1200-750 cal year BP), local societies likely experienced stabilization because of the milder climate.Each cold spell presumably caused northern people to migrate southward, leading to internal and external conflicts in southern peninsula societies.This is not to say that climate change was the only factor driving these migrations and social upheavals.Many other factors were probably involved.
However, the northern people also brought advanced culture, which helped drive cultural development in the area.There is evidence that they introduced rice farming during the MBACP 65 , bronze dagger culture during the IACP 66 , and horse-riding culture during the DACP 67 .These material cultures helped the tribal societies of the Korean Peninsula to form ancient state systems.
In 427 CE, King Jangsu, who led the Kingdom of Goguryeo at its peak, made the decision to move the capital to Pyongyang.According to our TPIT data, the year of that move was within the coldest part of the DACP www.nature.com/scientificreports/(Fig. 9).Therefore, it is difficult to dismiss climate change as a factor in King Jangsu's decision to move the capital over 200 km south of the original capital, away from the country's center.As the population grew, Goguryeo more heavily relied on crop farming; moving the capital to the warmer location of Pyongyang would have been a strategic decision in response to decreasing temperatures.The DACP also includes the so-called Late Antique Little Ice Age (LALIA, 536-660 CE), identified through tree-ring data 68 .This period of climate deterioration, triggered by massive volcanic eruptions and lasting for over 120 years because of a subsequent decrease in solar activity, led to a series of social upheavals in Western Eurasia.In 541 CE, the Justinian Plague spread in the Eastern Roman Empire, causing tens of millions of deaths 69 .This pandemic may have been worsened by climate change and the resulting decline in crop yield.On the Korean Peninsula, the official historical record of the Three Kingdoms, the Samguk Sagi, shows that numerous people in the Kingdom of Goguryeo experienced severe famine in 536-537 CE.This tragedy was presumably caused by the volcanic eruptions of 536, which marked the onset of the LALIA 70 .Our TPIT data clearly record this drop in temperature during the mid-sixth century (Fig. 9).
The maunder minimum (1645-1715 CE), a period of extremely low sunspot activity, brought sudden famine to the Korean peninsula in 1670-1671 CE.The cold spring weather and typhoon-induced summer floods resulted in devastatingly poor crop yields.Additionally, because people displayed famine-induced deterioration of immunity, an epidemic of plague rapidly spread throughout the country, causing substantial population decline 71 .Korean historians refer to this disaster as the Kyungshin Great Famine.The low temperatures that likely led to lean years during the late seventeenth century are clearly visible in the TPIT data (Fig. 9).
In summary, cooling and drying events at 2.8 and 2.3 ka may have played important roles in the overall southward migration of Korean agriculturalists during the third millennium BP.The relocation of King Jangsu's capital at 427 CE, the Goguryeo famine at the beginning of LALIA, and the Kyungshin famine during the maunder minimum all seem to have been associated with a decline in temperatures.

Conclusions
This study has focused on the reconstruction of mid-to-late Holocene climate changes in coastal East Asia using a high-resolution multi-proxy record from Jeju Island, Korea.Additionally, it explored the potential effects of abrupt short-term climate events on ancient societies in the Korean peninsula.This exploration was conducted by reconstructing hydroclimate and temperature variability over the past 4000 years.The primary study findings are summarized below.
First, our proxy records, particularly charcoal data, suggest that mid-to-late Holocene hydroclimate changes were primarily governed by SST variations in the WTP.A multi-centennial increase in TSI may have induced long-term El Niño-like conditions and lower WTP SSTs, which could have resulted in less precipitation in the study area.Overall, our records highlight a shift to drier conditions around 1600 CE during the middle of the LIA in the study area.
Second, temperature changes in the study area during the mid-to-late Holocene were largely driven by solar variability and a gradual decrease in summer insolation.Our TPIT data reveal a ~ 1000-year cycle of warming and a ~ 500-year cycle of cooling.
Finally, ancient societies on the Korean peninsula appear to have been significantly affected by abrupt shortterm climate change events.Examples include the 2.8 ka event, the 2.3 ka event, the LALIA, and the maunder minimum.Notably, the decision to move the capital of Goguryeo, an ancient kingdom on the Korean peninsula, southward in 427 CE may have been influenced by a drop in temperature.

Materials and methods
Core materials and multi-proxy data.In June 2021, we retrieved a 300-cm-long sediment core from the Dongsuak swamp using a Russian-type peat corer (Fig. 2c).Nine bulk sediment samples and one macroscopic plant fragment were sent to Beta Analytic for accelerator mass spectrometry radiocarbon dating (Table 1).High δ 13 C values between − 20 and − 19‰ in the deeper samples suggest that C4 plants were dominant before C3 trees colonized inside the crater.We calculated the calibrated age ranges using rbacon 3.0.0software 72 and the IntCal20 dataset 73 .For this study, we utilized only the top 150 cm of sediments.
We collected 145 samples for pollen analysis at approximately 1-cm intervals from a depth of 3 cm to 150 cm.Pollen was extracted using standard palynological procedures 74 .The samples underwent sequential treatments with HCl, KOH, HF, and acetolysis; they were sieved with a 180-µm mesh filter to remove large debris after KOH treatment.Pollen counts were conducted on a Leica microscope with a 40 × objective at a total magnification of 400 ×.Each slide had a minimum of 300 pollen grains counted.We identified 95 pollen taxa, the alga Botryococcus, and two types of spores (monolete and trilete).We did not count other algae, such as Pediastrum, since their numbers were insufficient for any meaningful discussion.The frequency of Botryococcus is sometimes a very good climate-sensitive indicator of aquatic productivity 25 .It has been particularly useful in paleoenvironmental studies of sediment cores from Jeju Island 20,21,75,76 .A pollen diagram was produced using TILIA 77 .A stratigraphically constrained cluster analysis was done using CONISS.Pollen concentrations were calculated based on the ratios of added Lycopodium spores 78 .All percentages shown in the pollen diagram are based on the total sum of non-aquatic pollen and spores.
To reconstruct past local fire events, we counted > 125-μm macrocharcoal particles using a Leica EZ4 stereoscope 79,80 .This analysis was conducted for each depth between 6 and 140 cm, yielding 135 analyzed samples.For sample preparation, each sediment sample of 1.25 mL was soaked in H 2 O 2 (6%) and incubated at room temperature overnight to bleach dark organic materials that could be mistaken for charcoal particles 80 .Then, materials < 125 μm and > 1 mm were discarded via sieving.Sieving with a grid size of 1 mm was conducted to remove only large plant fragments; it did not affect charcoal particles.The residual materials were poured into a Petri dish, and the number of particles bigger than 125 μm in axis length were counted manually for each sample without any weighting by further size fractions.Then, the counts were transferred to accumulation rates (# cm −2 year −1 ) using CharAnalysis ver.1.1 81 .
MS was measured at 1-cm intervals using an MS2 meter (Bartington Instruments).TOC and total nitrogen were measured at the National Center for Inter-University Research Facility located at Seoul National University, Republic of Korea.Samples collected at 1-cm intervals from a depth of 3 cm to 150 cm were analyzed using the Flash 2000 CHNS/O Analyzer (Thermo Fisher Scientific, Bremen, Germany) with an accuracy of 0.3%.Prior to analysis, each sample was treated with HCl (10%) to remove inorganic carbonates.
Tree pollen index of temperature.To estimate past temperature variability from the pollen record, TPIT values were derived using the following equation: (Quercus subg.Cyclobalanopsis + Castanopsis)/(Quercus subg.Cyclobalanopsis + Castanopsis + Quercus subg.Lepidobalanus + Carpinus).This index essentially calculates the ratio of evergreen broadleaf pollen to the total major tree pollen.
Previous studies, involving the collection and analysis of mosses from the slopes of Mt.Hallasan in Jeju Island 82 , revealed that Castanopsis pollen was predominant in moss samples from slopes below 450 m altitude, whereas pollen from Quercus subg.Cyclobalanopsis was prevalent in samples from 360 to 500 m altitude 82 .These broadleaved evergreens are characteristic of low elevation forests on Jeju Island.Conversely, deciduous tree taxa such as Quercus subg.Lepidobalanus and Carpinus were mainly observed in samples from higher-elevation areas between 600 and 1100 m 82 .The altitudinal distributions of these major tree species were consistent with the altitudes at which their pollen was deposited, confirming a strong correlation between the two parameters.
The arboreal pollen deposited over time on Dongsuak crater predominantly originated from four taxa: Quercus subg.Cyclobalanopsis, Quercus subg.Lepidobalanus, Castanopsis, and Carpinus.Because different types of trees flourish at specific altitudes based on their temperature preferences, the distribution of tree taxa on Mt.Hallasan follows an expected pattern.Altitude and temperature are inversely related; thus, we can qualitatively infer past temperature changes using TPIT data.
The proportion of broadleaf evergreen pollen may also be positively correlated with wetness.However, considering that Mt.Hallasan receives more precipitation at higher altitudes (Fig. 2a), we hypothesized that changes in the proportion of broadleaf evergreen pollen on the slope of Mt.Hallasan primarily reflect temperature variations.Additionally, we assumed that precipitation is negatively correlated with CARs because drought conditions tend to promote wildfires.Therefore, the analysis of Dongsuak sediments allowed us to reconstruct distinct mid-tolate Holocene shifts in temperature and precipitation.

Figure 2 .
Figure 2. (a) Vegetation profile on the eastern slope of Jeju Island and altitudinal variations in annual mean temperature and precipitation 86 .(b) Dominant plants in each vegetation zone.(c) A photograph from inside the crater.It was taken by Jieun Choi.

Figure 3 . 20 C a s t a n o p s i s 20 P i n u s s u b g . D ip lo x y l o n 4 B e t u l a 4 E r i c a c e a e 20 40 AFigure 4 .
Figure 3. (a) The Dongsuak sediment core age depth profile.The optimal age depth model (red dotted line), with a 95% confidence interval (gray dotted line), was established based on Bayesian principles using rbacon 3.0.0software.(b) Sedimentation rates, pollen concentration, and total organic carbon (TOC) in Dongsuak sediments.This diagram was generated using pro Fit 7.0.19software (www.quans oft.com).

Figure 5 .
Figure 5.Comparison of the total solar irradiance (ΔTSI) data23 (250-year moving average) (a), Dongsuak multi-proxy data from this study (b-g), and reconstructed sea surface temperatures of the western tropical Pacific 24 (e).Dry periods are highlighted by pale orange boxes, whereas wet periods are indicated by pale green boxes.Note that charcoal data were charted using a log scale on the y-axis (f), as well as a normal scale (g).LIA Little Ice Age, MCA Medieval Climate Anomaly, DACP Dark Ages Cold Period.This diagram was generated using pro Fit 7.0.19software (www.quans oft.com).

Figure 7 .
Figure 7.Comparison of the ΔTSI data 23 (250-year moving average) (a), stalagmite δ 18 O records from Liang Luar, southeastern Indonesia 31 (b), charcoal accumulation rates (CARs) from this study (c), Cyperaceae percentages from this study (d), and Joseon Dynasty records of typhoon landfalls 33 (e).Dry periods are highlighted by pale orange boxes, whereas wet periods are indicated by pale green boxes.Beige box indicates drier conditions during the latter half of the LIA.LIA Little Ice Age, MCA Medieval Climate Anomaly, DACP Dark Ages Cold Period.This diagram was generated using pro Fit 7.0.19software (www.quans oft.com).

Figure 8 .
Figure 8. Autospectral analyses of TPIT data (a) and charcoal accumulation rates (CARs) data (c).Crossspectral analyses between TPIT data and ΔTSI records 23 (b) and between CARs data and SST reconstructions from the western tropical Pacific 24 (d).Significant periodicities are labeled in years.This diagram was created using pro Fit 7.0.19software (www.quans oft.com).

Figure 9 .
Figure 9. Late Holocene climate deteriorations (cooling and/or drying) and societal responses on the Korean peninsula.LALIA Late Antique Little Ice Age.This diagram was created using pro Fit 7.0.19software (www.quans oft.com).