Potential forcings of summer temperature variability of the southeastern Tibetan Plateau in the past 12 ka

Investigating potential forcing mechanisms of terrestrial summer temperature changes from the Asian summer monsoon influenced area is of importance to better understand the climate variability in these densely populated regions. The results of spectral and wavelet analyses of the published chironomid reconstructed mean July temperature data from Tiancai Lake on the SE Tibetan Plateau are presented. The evidence of solar forcing of the summer temperature variability from the site on centennial timescales where key solar periodicities (at 855±40, 465±40, 315±40 and 165±40 yr) are revealed. By using a band-pass filter, coherent fluctuations were found in the strength of Asian summer monsoon, Northern Hemisphere high latitude climate and high elevation mid-latitude (26 °N) terrestrial temperatures with solar sunspot cycles since about 7.6 ka. The two abrupt cooling events detected from the Tiancai Lake record, centered at ∼9.7 and 3.5 ka were examined respectively. Coupled with the paleoclimate modelling results, the early Holocene event (9.7 ka) is possibly linked to an ocean-atmospheric feedback mechanism whereas the latter event (3.5 ka) may be more directly related to external forcing

Holocene variability in sea surface temperature off the southwest coast of Korea and its implications for East Asia climate changes

본 연구에서는 한반도 서남해 연안에 위치한 흑산머드벨트에서 채취된 2개의 심부시추코어 (HMB-102, HMB-103) 퇴적물과 같은 곳에서 별도로 채취된 81개 표층퇴적물의 알케논 분석을 통해 홀로세동안 표층수온변화를 복원하였다. 먼저 81개 표층퇴적물의 알케논수온과 관측수온을 비교하여 연구지역에서 해양퇴적물로부터 복원한 알케논수온은 4-10월 평균 표층수온을 대표함을 확인하였다. 특히 표층퇴적물 알케논 수온분포는 북쪽은 낮고, 남쪽은 높은 관측수온 분포와 유사하다. 이는 퇴적물의 재부유나 수평이동이 과거 표층수온 복원에 주는 영향은 작다는 것을 의미한다. 심부시추코어 퇴적물 알케논 분석을 통해 지난 홀로세동안 표층수온변화를 복원하였다. 초기 홀로세부터 현재까지 알케논수온은 전반적으로 1℃정도 감소한다. 그리고 특징적으로 3-5 kyr B.P.와 6.6-8.4 kyr B.P. 사이에 2℃정도의 강하고 지속적인 한랭기간이 존재함을 발견하였다. 이 기간은 동아시아 다른 지역 (티벳고원, 중국 북동부, 양쯔강 유역, 오키나와트러프)에서도 발견되며 동아시아 중위도 지역의 지역적인 특징임을 확인하였다. 동아시아 중위도 지역에서 전반적으로 관찰되는 홀로세동안 두 번의 장기간 한랭기는 당시 Westerly Jet 경로가 상대적으로 남쪽으로 이동한 것과 연관된 것으로 생각된다. 반면 홀로세 해수면 변동과 그와 관련된 조석변화를 고려하면 이들은 흑산머드벨트 표층수온 변화에 큰 영향을 주지는 못한 것 같다. HMB-103 시추코어퇴적물의 추가적인 알케논 분석을 통해 지난 6.5 kyr B.P. 동안 표층수온 변화를 고해상도로 (10-20년 변화) 복원하였다. 이때 연구지역에서 수백 년 규모의 수온변동이 존재함을 확인하였다. 알케논 수온자료의 spectral과 wavelet 분석결과 90%이상의 신뢰구간에서 415, 227, 145, 102, 83, 73년의 주기가 뚜렷하다. 알케논 수온변화에서 발견된 주기들은 홀로세동안 태양활동변화 주기인 ~400, 210 (Suess/de Vries cycles), 150, and 120-60 years (Gleissberg cycles)와 유사하다. 이는 지난 6.5 kyr B.P.동안 태양활동변화와 HMB-103 알케논 수온의 수백 년 주기변동 사이에 관련이 있음을 의미한다. |To reconstruct the variations in sea surface temperature (SST) during the Holocene, the alkenone unsaturation index of marine sediments from two deep-drilled cores and 81 different core-top surface sediments recovered from the Heuksan Mud Belt, located off the southwestern coast of the Korean Peninsula, was measured. First, comparison of the alkenone temperature estimates of 81 core-top sediments with in situ temperatures indicates that the alkenone temperatures correspond to the average SST in April to October. The spatial distribution pattern of the core-top alkenone SST shows a north-south temperature gradient, which represents the in situ temperatures well. This indicates that the effects of the resuspension and lateral transport of sediments on the past temperature estimation might be insignificant. Based on the two deep-drilled cores, variations in the alkenone SST during the Holocene were reconstructed. In general, the alkenone SST decreased by less than 1℃ from the early to late Holocene. An interesting feature is the presence of two long and pronounced cold (approximately 2℃) periods, which occurred at 3-5 kyr and 6.6-8.4 kyr B.P. These cold periods were also observed in other mid-latitude regions in East Asia, indicating that the cooling pattern was regional. The cold periods appear to be associated with the southward migration of the westerly jet at that time. Investigations into the effects of local sea level changes and resultant changes in tidal regime on changes in the SST during the Holocene period suggest that they were insignificant in the study area. Herein, we elucidate continuous variations of alkenone SST over the last 6.5 kyr B.P. at a high-resolution (10-20 year) by using records from marine sediments of deep-drilled core HMB-103, which are recovered from the Heuksan mud belt. The high-resolution SST record allows the detection of centennial-scale fluctuations with various cycles. The spectral and wavelet analysis of alkenone SST revealed significant periodicities of 415, 227, 145, 102, 83, and 73 years at >90% confidence level. These periods exhibit extreme proximity to the solar activity cyclicities of ~400, 210 (Suess/de Vries cycles), 150, and 120-60 years (Gleissberg cycles). This indicates a linkage between the variations of HMB-103 alkenone SST and solar activity at the centennial scale over the last 6.5 kyr B.P.List of Tables ⅲ List of Figures ⅳ Abstract ⅷ Chapter 1. Introduction 1 Chapter 2. Two long and pronounced cold periods 3,000-5,000 and 6,600-8,400 years B.P. in East Asia and the southward migration of the westerly jet 2.1 Introduction 3 2.2 Geological and oceanographic settings 6 2.3 Materials and methods 9 2.4 Results 12 2.4.1 Core-top sediments 12 2.4.2 Deep-drilled core sediments 16 2.5 Discussion 18 2.5.1 Regional surface temperature changes 18 2.5.2 Potential factors affecting the SST changes 22 2.6 Conclusions 29 Chapter 3. Holocene centennial-scale variability in sea surface temperature in the southeast Yellow Sea 3.1 Introduction 31 3.2 Materials and methods 32 3.3 Results 33 3.4 Discussion 37 3.4.1 Centennial variations in SST and solar activity 37 3.4.2 Validation of the centennial-scale SST variations 40 3.5 Conclusions 45 Chapter 4. Conclusions 46 Acknowledgements 47 References 48 Appendix A. Supplementary data 60Docto

홀로세 환경변화와 인간의 영향: 동해안 포매호를 사례로

학위논문 (석사)-- 서울대학교 대학원 : 지리학과, 2016. 2. 박정재.Climate change continues to be at the forefront of scientific research and global political debate. The ability to understand and predict future climate patterns is an important concern. Reconstruction of the paleoclimate is a vital step in modeling future climate change. The Holocene epoch(11700cal yr BP-present) contains periods that were warmer and cooler than present conditions. Careful examination of past climate events can provide researchers with greater predictive accuracy for modelling future climate change. Until now, there have not been many paleolimnological studies carried out in Korea due a lack of natural lakes and undisturbed sediments. However, lakes on the east coast of Korea have remained relatively undisturbed and are providing a wealth of climate data for Korean researchers. The purpose of this study is to reconstruct mid- and late Holocene climate and environmental changes around Lake Pomeho on the east coast of Korea. Pollen analysis, grain-size analysis, organic content analysis, magnetic susceptibility analysis and radiocarbon dating were performed on an approximately seven meter long section of a core taken from the northern edge of Lake Pomeho. The sediment core was radiocarbon dated to approximately 6700 cal yr BP. Based on statistical analysis(CONISS) of the pollen data, five zones were created. The climate in Zone PM 1(??-6700 cal yr BP) had a high percentage of Quercus and other mesic hardwoods, likely representing the Holocene Climate Optimum(HCO) in Korea. In zone PM 2(6700-4000 cal yr BP), the percentage of Quercus pollen decreased while Pinus increased at around 5800-5500 cal yr BP. This likely represents the end of HCO in Korea. Magnetic susceptibility data and grain-size analysis indicate that erosion levels remained heavy until around 5600 cal yr BP, when both decrease, suggesting the stabilization of sea level rise. At around 4300-4000 cal yr BP, there was a sudden decrease in arboreal species and an increase in cold tolerant plants, indicating climate conditions deteriorated, corresponding to the 4.2 kiloyear cold event found in other parts of the northern hemisphere. This study presents the first evidence for it in Korea. Zone PM 3 (4000-2500 cal yr BP) is characterized by either a deterioration of the climate after 4000 cal yr BP due to decreased EASM activity or a localized amelioration of the climate possibly due to the Tsushima Warm Current(TWC). In the first scenario, Pinus, thought to be of the relatively warm weather species Pinus thunbergii, decreases while Quercus increases, indicating cooler conditions. The percentages of Artemisia and Poaceae both decrease, possibly due to shifting soil conditions. In the second scenario, a warm phase could be indicated by the return of several hardwood species after the 4.2 kiloyear event. Quercus showed a significant increase from the previous zone, possibly indicating warmer and wetter conditions. Zone PM 4 (2500-850 cal yr BP) represents the beginning of agriculture in the area around Lake Pomeho. Disturbance indicator species Artemisia, Poaceae and Amaranthaceae increase in this zone, as does Oryza type pollen. Pollen concentrations in PM 4 are very low, while mean grain size is relatively high. This data suggests agriculture began in the region around 2500-2100 cal yr BP. Zone PM 5 (850-350 cal yr BP) is characterized by the intensification of agricultural activity around Lake Pomeho. Wild and domesticated Poaceae both continue to increase, as does Artemisia. Quercus continued to decline while Pinus and Betula, both sunlight loving trees, increased. High mean grain size indicates increased erosion, probably due to land clearance resulting from intensified agriculture. This study attempts to reconstruct the mid- to late-Holocene environment around Lake Pomeho on the east coast of Korea. Because there are few areas in Korea with undisturbed sediments, this study can be a meaningful contribution to paleoclimate research in Korea and East Asia. The end of the HCO, stabilization of sea level rise and the intensification of agricultural activities around Lake Pomeho correspond with data from other nearby study sites, indicating continuity in the area. Furthermore, this study is the first in Korea to find evidence of the 4.2 ky event, making it a meaningful contribution to the study of paleoclimate reconstruction. Keyword: multi-proxy analysis, east coast of Korea, coastal lagoon, paleoenvironmental reconstruction, paleoclimate, mid- and late-HoloceneChapter 1. Introduction 1 1.1. Background 1 1.2. Regional Setting 3 1.3. Climate 6 1.4. Vegetation 7 1.5. Research Purpose 8 Chapter 2. Literature Review. 10 2.1. Pre-rice Cultivation Period Environmental and Climate Change in East Asia 11 2.2 Environmental Change after the Beginning of Rice Cultivation in Korea 17 Chapter 3. Methodology 27 3.1. Sedimentation Characteristics 27 3.2. Radiocarbon Dating 30 3.3. Organic Content Analysis 30 3.4. Grain Size Analysis 31 3.5. Magnetic Susceptibility 32 3.6. Pollen Analysis 33 Chapter 4. Results 37 4.1 Zonation 37 Zone PM 1. (1197-1180 cm)(-6700 cal yr BP) 37 Zone PM 2. (1180-998 cm)(6700-4000 cal yr BP) 38 Zone PM 3. (998-890 cm)(4000-2500 cal yr BP) 39 Zone PM 4. (890-639 cm)(2500-850 cal yr BP) 39 Zone PM 5. (639-516 cm)(850-350 cal yr BP) 40 4.2 Radiocarbon Dating and Sedimentation Rate 50 Chapter 5. Discussion 52 Zone PM 1. (-6700 cal yr BP) Holocene Climate Optimum(HCO) 52 Zone PM 2. (1180-998 cm)(6700-4000 cal yr BP) Post-HCO, Sea Level Stabilization, 4.2 kiloyear Event 53 Zone PM 3. (998-890 cm)(4000-2500 cal yr BP) Climate Deterioration 55 Zone PM 4. (890-639 cm)(2500-850 cal yr BP) Human Disturbance and Agriculture 57 Zone PM 5: ∽850-350 cal yr BP (Intensification of Agriculture) 58 Chapter 6. Conclusion 61 Bibliography 64 Abstract in Korean 71Maste

Ciclos Históricos Universales

¿Se repite la historia? ¿Qué se repite exactamente y cada cuanto tiempo lo hace? ¿Qué causa las repeticiones o qué factores influyen en ellas? Esta tesis analiza y compara las teorías sobre ciclos históricos propuestas por unos 50 autores, y realiza un estudio de caso específico sobre la historia del arte occidental. En la introducción, se analiza el concepto de “historia cíclica” y se especifican los objetivos: 1) estudiar las principales teorías existentes hasta el momento, compararlas y sintetizarlas, 2) conocer qué causas podrían estar originando o influyendo en la formación de estos ciclos según los diversos investigadores, y 3) realizar un estudio de caso específico sobre la historia del arte occidental. Nuestra hipótesis es que las oscilaciones estilísticas en la historia del arte pudieran estar influidas por ciclos de distinta naturaleza: económicos, climáticos, generacionales, etc. Para tratar este tema complejo, nos propusimos utilizar las metodologías mixtas de la prospectiva en el marco de la macrohistoria, y también las específicas de la historia comparada. Los materiales serían las teorías cíclicas de los diferentes autores, y artículos científicos sobre ciclos naturales (como posibles causas). Y para el estudio de caso, los datos relativos a los periodos del arte occidental. El estado del arte está dividido en dos secciones: ciclos naturales (en los astros, las mareas, el clima, etc.), y ciclos humanos. Este segundo bloque, el más amplio, se divide en tres partes: ciclos en el mito, la religión y la filosofía; ciclos en las artes del tiempo y del espacio; y ciclos en las ciencias sociales y la historia. Las secciones relativas a las creencias y las artes, muestran cómo en Occidente se pasó de una concepción cíclica del tiempo a una básicamente lineal, pero que sigue admitiendo de modo relativo el concepto de ciclo temporal. En el apartado de las ciencias sociales y la historia, las teorías se organizan en distintas categorías para facilitar su análisis: 1) ciclos antiguos y medievales, 2) de las culturas y civilizaciones, 3) bélicos, políticos y sociales, 4) económicos y derivados, 5) hegemónicos, y 6) generacionales. En el apartado dedicado a la metodología, comenzamos explicando las ventajas para nuestro estudio de escoger procedimientos de carácter mixto, y situamos nuestra investigación en el marco de la macrohistoria. Sobre las metodologías mixtas empleadas en la prospectiva, destacamos en primer lugar corrientes como la llamada de “ciclos de larga duración”, que encaja exactamente con el tema de nuestra tesis. Dentro de las metodologías cuantitativas, resaltamos la estructura cíclica que a menudo presentan los resultados de los análisis exploratorios de series temporales, y en las metodologías cualitativas nos centramos en la analogía histórica. A esta última, le prestamos una atención especial en el apartado dedicado a la historia comparada. Por último, establecimos nuestros materiales y fases de trabajo, en las que siempre aparecerían una recogida de datos inicial, un estudio comparado de los resultados, y una síntesis y clasificación finales. Respecto a los resultados, establecimos dos grandes bloques: ciclos humanos, y ciclos naturales. En el primer apartado realizamos un estudio comparado de las numerosas teorías cíclicas, entre las que incluimos nuestro estudio de caso sobre los ciclos artísticos. En la síntesis, destacamos que de modo general, estas suelen presentar sistemas de ciclos combinables entre sí, semejantes hasta cierto punto, y a veces con carácter sistémico, dado que por ejemplo, un mismo ciclo puede aparecer en temas tan dispares como la economía, el arte o la guerra. Finalmente establecimos una clasificación general en ciclos cortos o generacionales, medios o seculares, y largos o milenarios. Respecto a los ciclos naturales como causantes o condicionantes de los ciclos humanos, concluimos que podíamos hablar de causas endógenas (el punto de vista subjetivo del investigador, la influencia de unos ciclos en otros, y el factor generacional), y exógenas (ciclos climáticos principalmente, en los que a su vez influyen una serie de ciclos naturales diversos). En el estudio de caso, comprobamos que efectivamente la sincronía entre ciclos naturales y entre estos y los humanos en ocasiones se dan, pero que la simple coincidencia no implica una relación de tipo causal. Y por último, en el apartado de las conclusiones realizamos una síntesis por capítulos, y tratamos de dar respuesta a las preguntas iniciales. Básicamente, resumimos los conceptos fundamentales sobre el tiempo que incluyen en mayor o menor grado la idea de ciclo, y clasificamos las teorías estudiadas por su naturaleza (ciclos culturales, sociales, económicos, etc.) y cuantitativamente (cortos, medios y largos). Concluimos que las sinergias entre ellos pueden observarse, y también que existen numerosos ciclos naturales que ocurren al mismo tiempo que los humanos. De todos ellos, los ciclos generacionales y los climáticos son los más citados en las diversas teorías, sin que la mera coincidencia entre ellos pueda tomarse como un argumento definitivo o concluyente. Respecto al estudio de caso, comprobamos que pueden establecerse ciclos en la Historia del Arte, y que como en los demás campos de estudio, sus ciclos tienen claras afinidades con otros naturales y humanos. En los apartados finales, dedicamos unas líneas a reparar en las utilidades que los ciclos podrían tener en la perspectiva, retrospectiva y prospectiva históricas, y concluimos con una reflexión final sobre las conclusiones extraídas, así como sobre los nuevos campos de investigación y las posibilidades que estas abren ante nosotros. Por último, en la bibliografía recogimos unas 400 obras citadas en el texto, y en los dos anexos los respectivos artículos que hemos publicado hasta ahora sobre la investigación desarrollada en esta tesis. Este estudio se ilustró con unas 100 tablas y figuras.Does History repeat itself? What is repeated and on what frequency? What causes repetition or what factors affect it? This thesis analyses and compares the theories on historical cycles proposed by about fifty authors, and carries out a specific case study on the history of Western art. In the introduction, the concept of "cyclical history" is analyzed and the objectives are specified: 1) to study the existing theories to date, compare and synthesize them, 2) to know what causes the various researchers point to as the originators or influencial in these cycles, and 3) to carry out a specific case study on the history of Western art. Our hypothesis is that the stylistic oscillations in the history of art could be influenced by cycles of a different nature: economic, climatic, generational, etc. To deal with this complex issue, we proposed to use the mixed methodologies of foresight in the context of macrohistory, as well as those specific to comparative history. The materials would be the cyclical theories of various authors, and scientific papers on natural cycles as possible causes. And for the case study, the data related to the periods of Western art. The state of the art is divided into two sections: natural cycles (in the stars, tides, climate, etc.), and human cycles. This second block, the largest, is divided into three parts: cycles in myth, religion and philosophy; cycles in the arts of time and space; and cycles in the social sciences and history. The sections related to beliefs and the arts show how the West went from a cyclical conception of time to a basically linear one, but which still admits the concept of temporal cycle in a relative way. The section on social sciences and history divides theories into different categories to facilitate their analysis: 1) ancient and medieval cycles, 2) cultures and civilizations, 3) war, political and social, 4) economic and derived, 5) hegemonic, and 6) generational. In the methodology section, we begin by explaining the advantages for our study of choosing mixed procedures, and we place our research within the framework of macrohistory. Regarding the mixed methodologies used in foresight, we first highlight currents such as the so-called "long-term cycles", which fit exactly with the theme of our thesis. Within the quantitative methodologies we highlight the cyclical structure that the results of the exploratory analyzes of time series often present, and in the qualitative methodologies we focus on the historical analogy. We pay special attention to the latter in the section devoted to comparative history. Finally, we established our materials and work phases, in which an initial data collection, a comparative study of the results, and a final synthesis and classification would always appear. Regarding the results, we established two large blocks: human cycles and natural cycles. In the first section we carry out a comparative study of the numerous cyclical theories, among which we include our case study on artistic cycles. In the synthesis we highlight that, in general, these tend to present systems of cycles that can be combined with each other, similar to a certain extent, and sometimes with a systemic character, given that, for example, sometimes the same cycle appears in disparate topics such as the economy, the art or war. Finally, we established a general classification into short or generational cycles, medium or secular, and long or millennial cycles. Regarding natural cycles as causes or conditioning factors of human cycles, we concluded that we could speak of endogenous causes (the subjective point of view of the researcher, the influence of some cycles on others, and the generational factor), and exogenous (mainly climatic cycles, which in turn are influenced by a series of diverse natural cycles). In the case study, we verified that indeed the synchrony between natural cycles and between these and humans sometimes occurs, but that the simple coincidence does not imply a causal relationship. And finally, in the conclusions we make a synthesis by chapters and try to answer the initial questions. Basically, we summarize the fundamental concepts about time that include the idea of a cycle to a greater or lesser degree, and we classify the theories studied by their nature (cultural, social, economic cycles, etc.) and quantitatively (short, medium and long). We conclude that the synergies between them can be established, and also that there are numerous natural cycles that occur at the same time as the human ones. Of all of them, the generational and climatic cycles are the most cited in the various theories, without the mere coincidence between them being taken as a definitive or conclusive argument. Regarding the case study, we verified that cycles can be established in the History of Art, and that as in other fields of study, its cycles have clear affinities with other human and natural ones. In the final sections, we dedicate a few lines to repair the utilities that the cycles could have in the historical perspective, retrospective, and prospective (foresight), and we conclude with a final reflection on the conclusions drawn and on the new fields of research and the possibilities that these open before us. Finally, in the bibliography we collected some 400 works cited in the text, and in the two annexes the respective articles that we have published so far on the research developed in this thesis. This study was illustrated with about 100 tables and figures