Seasonal temperature variability during the past 1600 years recorded in historical documents and varved lake sediment profiles from northeastern China

Abstract

Seasonal temperature variability over longer timescales could offer new insights into understanding different forcing factors and response processes in the climate system. Here we report an alkenone-based temperature reconstruction for growing season over the past 1600 years from the varved sediment in Lake Sihailongwan, northeastern China. The most notable cold spells occurred during the periods ad 480–860, ad 1260–1300, ad 1510–1570 and ad 1800–1900 with a temperature decrease of about 1°C compared with the 20th century. Based on the historical evidence such as ‘snow or frost in the summertime’ and ‘no ice during the wintertime’, we compile extreme cold summer events and warm winter events over the past 1600 years. The ‘Little Ice Age’ time period experienced more extreme cold summer/warm winter events, while the ‘Medieval Warm Period’ had milder winters. Comparatively, the natural proxy data show a general similar pattern with historical documents at decadal time scales, except for between ad 1620 and 1720. Our results show multidecadal to centennial variations in seasonal temperature, possibly caused by interactions of external natural forcing and atmosphere–ocean circulations.

Keywords

alkenone unsaturation index atmosphere–ocean circulations historical documents seasonal temperature extreme varved sediments

Introduction

Reconstructing temperature variations during the last millennium are important to better understand natural climatic variability, evaluate the relative contributions of anthropogenic forcing, and predict future climate (Jones et al., 2009; Mann et al., 2009). Temperature reconstructions, however, have been hampered and complicated by the uncertainties in timescale and proxy indicators, strong seasonality and climatic extremity (Bradley and Jones, 1993; Briffa and Jones, 1993; Smol and Cumming, 2000). Seasonal and regional temperature reconstructions illuminate key climatic features, such as regionally very hot or cool summers/winters, that may be masked in a hemispheric or global reconstruction (Chuine et al., 2004; Jones et al., 1998; Luterbacher et al., 2004; Patterson et al., 2010; Rimbu et al., 2006).

Many temperature proxies controlled by seasonal processes respond mainly to different seasons, and give biased results in the reconstructed series in the extra tropical regions (Morgan and van Ommen, 1997; Ojala et al., 2008; Rimbu et al., 2006). For example, long chain alkenone (LCK) unsaturation index is well known for its use in marine paleotemperature reconstructions (Prahl and Wakeham, 1987). In limnic systems, recent progress shows it could be used as a temperature proxy (Chu et al., 2005a; Liu et al., 2006, 2011; Sun et al., 2007). Nonetheless, questions remain as to whether this proxy is more representative of a mean-annual temperature signal or to a certain season both in limnic and marine system (Chu et al., 2005a; Pearson et al., 2008; Prahl et al., 2010). Numerous climate-related physical properties in lakes, such as winter temperature, ice thickness and the duration of lake overturn (Rühland et al., 2008) may have an effect on the temperature in the growing season. The data from monthly sediment trap in Lake Sihailongwan indicated that there is little alga during the ice-cover period because of heavy snow limiting light into the water (Chu et al., 2005b). The alkenone-based temperature should represent the water temperature in the growing season (ice-free season).

On the other hand, long-term changes in the seasonality and climatic extreme events are of great importance to the society and ecosystems (Cook et al., 2010; Luterbacher et al., 2004). The arguments for the global appearance of classical periods, such as the ‘Dark Age’ (DA), the ‘Medieval Warm Period’ (MWP) and the ‘Little Ice Age’ (LIA) (Lamb, 1982) may partly be due to our poor knowledge about seasonality and limited year-round information from proxy data.

Here, we report an alkenone-based temperature reconstruction for growing season from varved sediments in Lake Sihailongwan and compile seasonal temperature anomaly from historical documents over the past 1600 years. With this research, we hope to gain an overall view of the regional temperature variations from independent data.

Study region and site

Lake Sihailongwan, a closed maar lake, is located in northeastern China (Figure 1). The tephra ring is 10–119 m above the lake surface and consists of pyroclastic. It makes this site a natural weather station and an ideal candidate for paleoclimatic archives. The lake is a dimictic lake with a surface area of 0.4 km², a maximum depth of 50 m, and a catchment area of 0.7 km. Historically, this remote area has suffered little human disturbance, because it was claimed as the birthplace of the Manchu people and a sacred land by the Qing dynasty (ad 1644–1911). Annually laminated sediments have been reported in earlier studies and provide a reliable timescale for paleoclimatic research in this data-sparse area (Chu et al., 2005b, 2009; Jiang et al., 2008; Mingram et al., 2004; Schettler et al., 2006a, 2006b).

Figure 1.

Location of Lake Sihailongwan. Inset bathymetric map showing the coring sites (the interval of the isobathic curve is 10 m). Changchun is the weather station for instrumental data.

The climate of the study region is strongly influenced by the East Asian monsoon. It is characterized by a warm and rainy weather in summer, and a cold and dry in winter. The mean annual air temperature of the area is 3.2°C (1955–2005). The rainy season lasts from May to August and accounts for 71% of the mean annual precipitation of 774 mm (1955–2005). The lake is ice-covered from the end of November until early April.

Material and methods

Varve sediment chronology

A series of cores (freeze-cores, gravity cores and piston cores) were retrieved from Lake Sihailongwan since 1999. In this study, core S2007-A (diameter=68 mm) and S2008-A (diameter=90 mm) were selected for investigation.

The cores were split in half longitudinally, and one half of the core was used for making thin sections, whilst the other half was used for Long chain alkenone analyses. To make thin sections, overlapped sediment slabs (6 cm × 2 cm ×1.5 cm) were sampled using aluminium trays, shock-freezed using liquid nitrogen, and then vacuum-dried. The freeze-dried slabs were vacuum-penetrated with synthetic resin and manufactured into thin sections. Thin-sections were examined at different magnifications under a Leitz polarizing microscope for counting varves. Varves appear as rhythmic units of a diatom-rich layer (autumn), followed by a light-colored siliciclastic layer (spring), and a subsequent mixed layer (summer) (Chu et al., 2005b). Previous independent radiometric dating data (¹³⁷Cs, ²¹⁰Pb and AMS¹⁴C) confirm the seasonality of Lake Sihailongwan sediments (Chu et al., 2005b; Mingram et al., 2004; Schettler et al., 2006a, 2006b). Varves were counted for each centimeter. Sample ages were calculated in the middle of each sample (Supplementary Information, Table-S1, available online).

Long chain alkenone analyses

The cores were sampled at 0.5 cm interval in the upper part, and at 1 cm intervals in the lower part. Totally, 108 samples were analyzed for the past 1600 years (Supplementary Information, Table-S2, available online). The freeze-dried samples were soxhlet extracted with CH₂Cl₂ for 48 h after addition of an internal standard (C₃₆ n-alkane). The extracts were evaporated to dryness under a nitrogen stream, following the procedure described by previous researchers (Sun et al., 2007; Villanueva et al., 1997). The evaporated extracts were saponified overnight with 6% KOH in CH₃OH to eliminate hydrolysable material, especially wax esters. The neutral fraction containing alkanes, alkenones, and alcohols was recovered by extraction with n-hexane. The n-hexane extracts were separated into sub-fractions by silica gel column chromatography (2 g silica, 30 cm × 0.4 cm i.d. column) with a mixture of CH₂Cl₂ and n-hexane (1:1). The first elution containing alkanes and alkenones was evaporated under a nitrogen stream and redissolved in toluene.

Prior to instrumental analysis, the extracts were derivatized overnight with bis-trimethylsilyl-trifluoroacetamide (BSTFA) at room temperature. These extracts were analyzed using a SHIMADZU GC-2010 gas chromatograph equipped with a with a 30 m fused silica column (DB1, J&W, 0.25 mm i.d.; 0.25 μm film thickness) and a flame ionization detector. Nitrogen was used as a carrier gas. The oven temperature was programmed from 40 to 180°C at 4°C/min (isothermal 20 min) and from 180 to 300°C at 2°C/min (isothermal 50 min). Replicated analysis of a sample showed that the analytical error was less than 5% for alkenones. Temperature was calculated using the culture equation (Sun et al., 2007). The uncertainty of the reconstructions is on the order of ±0.5–1°C.

Historical documents and analysis method

The literature sources we used in this study were restricted to official historical documents written in Chinese (three Kingdoms, Koryeo dynasty and the Annals of the Choson dynasty) in Korea peninsula, near the studied lake (Figure 1). The Annals of the Choson Dynasty (ad 1392–1910), with more than 1800 volumes, was an especially invaluable documentary source that provided daily climatic information.

Here, an extreme cold summer event was defined from direct descriptions of ‘snow or frost in the summertime’ (Supplementary Information, Table-S3, available online). The summer time was defined as March, April, May, June, July and August in the lunar calendar (generally, lunar month is delayed by one month versus the solar calendar). Extreme warm winter event was defined from direct descriptions of ‘no ice in the wintertime’, ‘warm like spring in wintertime’ (Supplementary Information, Table-S4, available online). The wintertime was defined as October, November, December and February in the lunar calendar.

On the basis of the description in different months and the severity coefficient, we developed an index of extreme cold summer (IEC) for summer season:

IEC = (S_{1} \times C_{1} + S_{2} \times C_{2} + 1) / (total events / per decade + 2)

(1)

Where S₁ and S₂ are the severe score of cold summer events. When snow or frost in May, June and July, S₁=2. When snow or frost in April and August, S₂=1. C₁ and C₂ are the number of years with extreme cold summer events, totaled as per decade. Total events include all extreme events both in summer and winter per decade.

Similarly, an index of extreme warm winter (IEW) is as follows

IEW = (W_{1} \times A_{1} + W_{2} \times A_{2} + 1) / (total events / per decade + 2)

(2)

Where W₁ and W₂ are the severe score of warm winter events, totaled as per decade. When the description ‘no ice in wintertime’ was in the historical document, W₁=2. When the description ‘winter warm as spring’ was in the historical document, W ₂=2. A₁ and A₂ are the number of years with extreme events per decade. Total events include all extreme events, both in summer and winter, per decade.

Extreme cold summer events and warm winter events are listed in the supplementary information (Tables-S3 and -S4, available online).

Results and discussion

Alkenone-derived temperature during growing season

Figure 2 shows the time series for alkenone-derived ( $U_{37}^{k^{'}}$ ) temperature during the growing season over the past 1600 years in Lake Sihailongwan (Figure 2a) (Supplementary Information, Tables-S1, -S2, available online). We also selected two windows to further compare the LCK record with yearly historical documents (ad 1400 to 1800) (Figure 2d) and instrumental data (1909–2007) (Figure 2e). The reconstructed temperature shows clear decadal to centennial warm/cold variations. Four notable cold periods occurred during the ad 480–860, 1260–1300, 1510–1570 and 1800–1900. The temperature in the interval ad 480 to 860 decreased more than 1°C compared with the temperature during the 20th century (1900 to 1990). This period may be coeval with the DA, a period of cultural and economic deterioration in Europe following the decline of the Roman Empire (Lamb, 1982). Chinese historical documents indicated several notable cold spells ad 480–500 with a decrease of 1.2°C compared with the present (ad 1951–1980) (Zheng et al., 2005), ad 500–600 (Chu, 1973), and ad 794–844 (Fei et al., 2004). Evidences for the DA cold period have been widely recorded in the North Atlantic region (McDermott et al., 2001; Patterson et al., 2010). For example, chironomid-based temperature reconstructions show a July air temperature decrease of 0.7°C for the DA compared with the temperature prevailing during the MWP (Millet et al., 2009). Comparatively, the DA recorded in the LCK record was more pronounced than other records.

Figure 2.

Comparison alkenone-derived temperatures with historical documents and instrumental data. (a) Alkenone-derived temperatures during the growing season. Alkenone-derived temperatures were calculated by using UK′37 = 0.0011×T² – 0.0157×T + 0.1057 (Sun et al., 2007, supplementary information Table-S2, available online). (b) The number of years with extreme cold summer events per decade (bar chart); green line: index of extreme cold summer (IEC) (three-point running average). (c) The number of years with extreme warm winter events per decade (bar chart); red line: index of extreme warm summer (IEW) (three-point running average). (d) Green line: the number of days (per year) that experienced extreme cold summer events; blue line: alkenone-derived temperatures. (e) Grey line: annual mean temperature during the warm season (warm season: the average monthly air temperature is more than 0°C) from Changchun Station (shown in Figure 1). Red line is three-year running average. Blue line: Alkenone-derived temperatures during the growing season. The time intervals for the DA, MWP and LIA are shown in Figure 2a.

In the MWP and LIA, three significant cold spells are at ad 1260–1300, ad 1510–1570 and ad 1800–1900, with a temperature decrease of 1°C compared with the temperature during the 20th century. A sharp cooling episode at around the late of 13th century revealed in the LCK record could be linked with the largest ad 1259 eruption (Rosanne et al., 2001; Stothers, 2000). However, caution should be taken in the episode since it is based on only one data source. In the historical documents from China and Korea, cold summer events were after ad 1259. For example, ‘Frost recorded in summertime at ad 1260, 1272, 1273 and 1275 in Korea peninsula’. In May of 1276, people had to take a fur coat as it was too cold in Korea peninsula. In China, summer frost events were documented in May 1261, May 1262, August 1262, April 1263, and August 1265 in the Annals of the Yuan Dynasty (ad 1260–1367). The cold spell around 1259 has also been identified from proxy data in Mongolia (D’Arrigo et al., 2001) and northern Siberia (Hantemirov and Shiyatov, 2002; Naurzbaev et al., 2002).

Other cold spells at ad 1510–1570 and 1800–1900 are in agreement with three major glacier advances in southern Tibet (ad 1580–1590, around ad 1800 and ad 1860–1880) (Bräuning, 2006). Although the LCK temperature series has relatively low resolution and age uncertainty, spatially it is comparable with the summer temperature reconstructions from tree-ring record in the Taymir region of northern Siberia (Naurzbaev et al., 2002) and in the Sol Dav region of Mongolia (D’Arrigo et al., 2001), and hemisphere-scale temperature reconstructions (Mann et al., 2009) (Figure 3).

Figure 3.

Spatial pattern of temperature reconstructions during the past 1600 years in (a) Alkenone-derived temperatures for the growing season in Lake Sihailongwan. (b) Summer temperature anomalies from tree-ring records in the Sol Dav region of Mongolia (Naurzbaev et al., 2002). (c) Summer temperature anomalies from tree-ring records in the Taymir region of northern Siberia (D’Arrigo et al., 2001). (d) The Northern Hemisphere temperature anomaly (Mann et al., 2009).

Extreme cold summer and warm winter events from historical documents

Historical documents provide directly evidence of climatic changes without uncertainty on the time scales (Chu, 1973; Kim and Choi, 1987; Lamb, 1982; Pfister, 1995). However, documentary information is less systematic and qualitative interpretation.

Figure 2b compiles extreme cold summer events during the past 1600 years from historical documents. Skimming through the data, the number of historical documents increased over time (Figure 2b, c). The index of IEC and IEW may be more reasonable to express extreme cold/warm events in the historical documents, both for reducing the effect of the abundance of historical documents over time, and considering cold/warm extremities. The IEC and IEW show significant decadal to centennial time scale oscillations. The LIA (ad 1400–1900) experienced more extreme cold summer/warm winter events, the MWP (ad 900–1300) with milder winters. It is not a local phenomenon. The historical document of 500-years freezing dates from Lake Suwa indicated that warm winters were common in the LIA (Arakawa, 1954; Magnuson et al., 2000). For example, there were nine years without freezing during ad 1500–1519 (Arakawa, 1954).The extreme cold/warm events can not represent mean temperature, but unusual weather could be more noteworthy than normal weather conditions in historical documents and provide insight into regional-scale climatic variations (Jones et al., 2002; Metcalfe et al., 2002).

Comparatively, the periods with more extreme cold summer events and less warm winter events corresponded with the cold spells in the LCK record (Figure 2a). A difference is between ad 1620 and 1720, when the LCK record shows a mild period, but decadal historical document indicates that it was a spell with more extreme cold summer events and warm winter events (Figure 2a, b). Abundant historical documents in the Choson Dynasty allowed us to obtain quantitative information at an annual timescale. Figure 2d shows an agreement between the LCK record and yearly historical documents (Figure 2d). The difference between decadal and yearly historical documents suggests some uncertainties in the reconstructed series since the number of historical documents was variable in different periods or dynasties. Although our method may reduce the effect of the abundance of historical documents over time, some questions (different observers, less systematic and qualitative ) still remain for obtaining quantitative series of past climate variability from historical documents.

In addition, the historical documents might not support the opinion that global warming could cause more extreme climatic events. In the MWP (ad 900–1300), 12% of the years experienced extreme warm winter/cold summer events, whereas half of the years (53%) experienced extreme warm winter/cold summer events during the LIA (ad 1400–1900). Considering the number of historical documents increased over time, we compared the cold/warm spells in the LIA (cold spells in China are ad 1470–1520, 1620–1720 and 1840–1900 defined by Chu (1973)). 60% of the years experienced extreme warm winter/cold summer events in the cold spells of the LIA, and 40% years experienced extreme warm winter/cold summer events in the warm spells of LIA.

Possible causes for regional climate variations

On timescales of the past two millennia, it is well recognized that climatic oscillations are mainly regulated by external natural forcing factors (solar irradiance and explosive volcanism), anthropogenic forcing and intrinsic variability (atmosphere–ocean circulation) in the climatic system (Rimbu et al., 2006; Solanki et al., 2004; Tan et al., 2003; Thompson and Wallace, 1998; Yang et al., 2002). In order to examine the variability of alkenone-based temperature reconstruction, spectral analysis (Schulz and Mudelsee, 2002) was performed on the time series. The spectral analysis shows two periodicities (68–70, 247–257) greater than 95% confidence level, and one periodicity (139–148) greater than 90% confidence level, similar of solar periodicities. For example, the cosmogenic isotope (Δ¹⁴C) record from tree rings shows several solar oscillations at 440, 360, 260, 230, 180, 168, 155, 147,123,106 and 88 years (Stuiver and Braziunas, 1993). Similar periodicities have been observed in various proxy data, e.g. Mg/Ca ratios from a closed-basin lake in the northern Great Plains (Yu and Ito, 1999) and the percentage of G. bulloides in sediment core off Oman Margin (Gupta et al., 2005). It suggests that the low-frequency regional temperature variations may be modulated by solar activity.

Explosive volcanic eruptions are known to be an important external natural forcing factor for temperature variations at annual to interdecadal timescales (Briffa et al., 1998; Rosanne et al., 2001). A sharp cooling episode at around the late 13th century revealed by the alkenone-based temperature reconstruction could be linked with the largest 1259 eruption discussed above. Another cold period is the DA, and some evidence has linked it to volcanic eruptions (Gil et al., 2006; Keigwin, 1996; Larsen et al., 2008).

Although there is a general agreement between external natural forcing (solar, volcanism) and the reconstructed temperature, some differences can not be explained in terms of solar irradiance, volcanism and anthropogenic forcing (Figure 4a). Atmosphere–ocean circulation could play a key role to redistribute and balance the energy on the Earth, and cause regional differences. In the recent multi-model analyses, almost all of the models (IPCC AR4 23 models) capture the Arctic Oscillation (AO) as the leading mode of the interannual variability for the extratropical atmosphere in the Northern Hemisphere (Zhu and Wang, 2010). Regionally, instrumental winter temperature in northern China is closely linked to the AO (Feng et al., 2009). We examine the correlation between the winter climate (IEW) and the reconstructed AO index (Chu et al., 2008) (Figure 4b). A weak positive correlation (Pearson coefficient r=0.22, 10-year resolution, 1300 to 1850 ce) is between the IEW and the AO index. Independently, the winter half-year temperature anomaly in eastern China from phonological records (Ge et al., 2003) also shows a positive correlation with the AO index (Pearson coefficient r=0.20, 30-year resolution, 350 to 1900 ce).

Figure 4.

Comparison of season-dependent temperatures, the combined effect of forcing (solar, volcanism) and atmosphere–ocean circulation. (a) Dark line: the combined effect of volcanism and solar variability (with 11-point smoothing) (Crowley, 2000); Blue line: alkenone-derived temperatures during the growing season. (b) Green line: standardized index of the AO (the data for ad 340–1900 are derived from the data set (Chu et al., 2008) (www.ncdc.noaa.gov/paleo/recons.html); the data for ad 1900–2005 are from monthly date set (Colorado State University, 1899–2002, http://jisao.washington.edu). The data are standardized; purple line: standardized Index of extreme warm winter in this study and instrumental winter temperature anomalies (ad 1900–2005, three-year running average) in China (Li et al., 2010); (c) Blue line: alkenone-derived temperatures during the growing season; grey line: PDO index reconstruction by MacDonald and Case (2006) (detrended data); red line: PDO reconstructed from Asian tree-ring records (D’Arrigo and Wilson, 2006) (11-year running average data).

The physical link between the AO and winter temperature may be link to changes in the frequency and tracks of cold surge. In the negative phase of the AO, the higher pressure over the pole and weaker westerlies (southward) may induce an increasing of baroclinic waves along westerly zone and southward descent of the polar jet stream, which favors the cold wave and snow occurrence in China (Chu et al., 2008; Hong et al., 2008; Jeong and Ho, 2005; Park et al., 2011). The positive phase has the reverse pattern.

Besides the AO, other circulations such as the Pacific Decadal Oscillation (PDO) and El Niño–Southern Oscillation should also play crucial role in the regional climate change (D’Arrigo and Wilson, 2006; MacDonald and Case, 2005). Instrumental data indicated a significant positive correlation (r=0.66, 9-year running mean data, 1951–2005) between PDO index and air temperature in northern China, and a notable shift in the mid-1970s (Ma, 2007). In the alkenone-based temperature reconstruction, a significant shift is also in the mid-1970s (Figure 1e, Figure 4c). It could link to the Great Pacific Climate (PDO) Shift revealed in previous literatures (Graham, 1994; Mantua et al., 1997; Marcus et al., 2011). This shift was shown to be part of a cyclical regime change showing decadal like ENSO variability (Mantua et al., 1997). In addition, the periodicities (68–70 years) resolved in the alkenone-based temperature reconstruction are typical periodicities (50–70) in the reconstructed PDO (MacDonald and Case, 2005; Minobe, 1999).

Modern observation data in northern China suggested that the positive phase of PDO matches warming and less precipitation, and the negative PDO phase corresponds to cooling and more precipitation in north China (Ma, 2007). If we consider age uncertainty in the LCK data, a generally similar pattern of variation can be observed in the reconstructed annual PDO (MacDonald and Case, 2005) and Asia PDO (D’Arrigo and Wilson, 2006) (Figure 4c). Although the dynamic process and regional response are unclear, Pacific Ocean may play an important role in regulating the temperature for growing season in the studied area.

Conclusions

Seasonal dependent temperature variations in northeastern China from natural proxy data and historical documents show clear multidecadal- to century-scale variations. Alkenone-based temperature reconstruction for growing season indicated that the four notable cold spells occurred in the periods ad 480–860, ad 1260–1300, ad 1510–1570 and ad 1800–1900 over the past 1600 years in Lake Sihailongwan. Historical documents also show clear decadal oscillations in extreme cold summer events and warm winter events over the past 1600 years. The LIA suffered more extreme cold summer/warm winter events, while the MWP had milder winters.

In addition to external natural forcing (solar, volcanism), atmosphere–ocean circulations may play a key role to regulate the seasonal temperature variation in the northeastern China. Winter temperature could be linked with the AO, whereas summer temperature may mainly be regulated by the PDO.

Footnotes

Acknowledgements

We are grateful to Professor John P. Smol for constructive comments and correcting our English. We would like to thank the editors and anonymous reviewers for helpful comments that improved the quality of this manuscript.

This study was supported by the CAS Strategic Priority Research Program (Grant No. XDA05080400), Research Program of China (973 Program, 2010CB950201) and the National Natural Science Foundation of China (Grant no. 40972121).

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