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

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

High-frequency fluctuations in redox conditions during the latest Permian mass extinction

This study was supported financially by NERC Fellowship NE/H016805/2 (to AZ), NERC Standard Grant NE/J023485/2 (to AZ and MC), NSFEAR-1455258 (to CJK). Samples were collected by RJT, who thanks G. Cuny and the Danish National Research Foundation for logistics and financial support.New high-resolution geochemical and sedimentological data from Fiskegrav, East Greenland, reveal fluctuations in marine redox conditions associated with the final disappearance of bioturbating organisms during the latest Permian mass extinction (LPME). Sedimentological observations imply a transgressive episode, and associated geochemical evidence for decreasing oxygen availability and the establishment of persistently ferruginous (Fe2 +-rich) conditions implies the shoreward migration of oxygen deficient waters. The long-term decline in dissolved oxygen (DO) availability could have been exacerbated by increasing water temperatures, reducing the solubility of oxygen and promoting thermal stratification. Mixing of the water column could have been further inhibited by freshwater influxes that could have generated salinity contrasts that reinforced thermal stratification. Enhanced runoff could also have increased the delivery of nutrients to the marine shelf, stimulating biological oxygen demand (BOD). During the transition to persistently ferruginous conditions we identify intervals of intermittent benthic meiofaunal recolonization, events that we attribute to small transient increases in DO availability. The mechanism controlling these fluctuations remains speculative, but given the possible centennial- to millennial-scale frequency of these changes, we hypothesise that the mid-latitude setting of Fiskegrav during the Late Permian was sensitive to changes in atmospheric circulation patterns, which may have influenced local precipitation and intermittently modulated some of the processes promoting anoxia.Publisher PDFPeer reviewe

Pozno holocenski podnebni dogodki kot poglavitni dejavniki kulturnega zatona v severnem delu centralnega Irana v bronasti dobi

During the Bronze Age, the cultural region of North Central Iran (NCI) suffered a longterm cultural decline, probably due to severe droughts. According to paleoclimate research, during the overall period c. 5.4–3.5 ka BP, four widely observable climatic events occurred at c. 5.3–5.0, 4.9–4.7, 4.2–3.9, and 3.8–3.5 ka BP, and these appear to have caused widespread environmental damage in the Near East. Archaeological evidence of the NCI-region reveals political events that can be associated with the observed climatic variability. Paleoclimate research and archaeological studies can attribute, in combination, the cultural decline of NCI during the Bronze Age to the Late Holocene climate change.V času bronaste dobe je prišlo na območju severnega dela centralnega Irana do dolgoročnega kulturnega zatona, ki so ga verjetno povzročila obdobja hude suše. Glede na paleoklimatske raziskave lahko prepoznamo štiri zelo izrazite podnebne dogodke v obdobju med ok. 5,4 in 3,5 tisoč let pred sedanjostjo (le-ti so: 5,3–5,0 tisoč let, 4,9–4,7 tisoč let, 4,2–3,9 tisoč let ter 3,8–3,5 tisoč let pred sedanjostjo), ki so povzročili razširjeno okoljsko škodo na Bližnjem Vzhodu. Arheološki zapisi v tej regiji kažejo na politične dogodke, ki jih lahko povežemo s podnebno spremenljivostjo. S pomočjo paleoklimatskih in arheoloških raziskav lahko bronastodobni kulturni zaton na območju severnega centralnega Irana vežemo na pozno holocenske podnebne spremembe

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

Orbital-scale climate variability in Arabia as a potential motor for human dispersals

The Arabian Peninsula is situated at an important crossroads for the movement of Pleistocene human populations out of, and into, Africa. Although the timings, routes and frequencies of such dispersals have not yet been confirmed by genetic, fossil or archaeological evidence, expansion into Arabia would have been facilitated by humid periods driven by incursions of monsoon rainfall, potentially from both Indian Ocean and African monsoon systems. Here we synthesise terrestrial and marine core palaeoclimatic data in order to establish the spatial and temporal variability of humid periods in Arabia between late Marine Isotope Stage (MIS) 7 and 3. Incursions of monsoon rainfall occurred during periods of insolation maxima at ca. 200–190, 170, 155, 130–120, 105–95, 85–75 and 60–55 ka, providing multiple ‘windows’ of favourable climatic conditions that could have facilitated demographic expansion through Arabia. Strong summer monsoons are generally associated with mid-high latitude interglacials, however, enhanced monsoon convection also brought rainfall into Arabia during global glacial phases, possibly due to a strengthened winter monsoon and a greater influence of southern hemispheric temperature changes. Key periods for dispersal into northern regions of Arabia correspond with the synchronous intensification of both eastern Mediterranean and monsoon rainfall systems at insolation maxima during MIS 7 and MIS 5, which may have facilitated demographic connectivity between the Levant and the Arabian interior. Environmental conditions throughout southern and southeast regions were also favourable to expansion during these times, although strong monsoons in these regions during MIS 6 and MIS 3 suggest further opportunities for demographic expansion and exchange. Terrestrial and marine evidence show that during early MIS 3 (ca. 60–50 ka), a strengthened monsoon led to the activation of interior drainage systems and increased productivity in coastal zones, indicating that favourable environmental conditions existed along both coastal and interior routes at that time

State dependence of climatic instability over the past 720,000 years from Antarctic ice cores and climate modeling

Climatic variabilities on millennial and longer time scales with a bipolar seesaw pattern have been documented in paleoclimatic records, but their frequencies, relationships with mean climatic state, and mechanisms remain unclear. Understanding the processes and sensitivities that underlie these changes will underpin better understanding of the climate system and projections of its future change. We investigate the long-term characteristics of climatic variability using a new ice-core record from Dome Fuji, East Antarctica, combined with an existing long record from the Dome C ice core. Antarctic warming events over the past 720,000 years are most frequent when the Antarctic temperature is slightly below average on orbital time scales, equivalent to an intermediate climate during glacial periods, whereas interglacial and fully glaciated climates are unfavourable for a millennial-scale bipolar seesaw. Numerical experiments using a fully coupled atmosphere-ocean general circulation model with freshwater hosing in the northern North Atlantic showed that climate becomes most unstable in intermediate glacial conditions associated with large changes in sea ice and the Atlantic Meridional Overturning Circulation. Model sensitivity experiments suggest that the prerequisite for the most frequent climate instability with bipolar seesaw pattern during the late Pleistocene era is associated with reduced atmospheric CO2 concentration via global cooling and sea ice formation in the North Atlantic, in addition to extended Northern Hemisphere ice sheets

Tracing hydrological millennial-scale cycles in the late Quaternary of the Cariaco Basin and the southern Gulf of Cádiz using coccoliths and dinoflagellate cysts

Climate fluctuations in tropical to subtropical regions are coupled to hydrological changes. The reconstruction of these hydrological changes during rapid late Quaternary climate oscillations is crucial for climate change study. The present study demonstrates that coccoliths and dinoflagellate cysts are very useful as paleoclimatological indicators for the elucidation or a better understanding of the late Quaternary regional and global palaeoclimate. This study also reveals new insights in coccolithophore and dinoflagellate palaeoecology. At the outset, two fundamental studies were undertaken to strengthen dinoflagellate cysts as a proxy for paleoecological studies. Since so-called ‘standard’ palynological processing methods are still very variable and inflict damage on organic-walled microfossils to a certain extent, the effect on the determination of dinoflagellate cyst concentrations needed to be sorted out. Furthermore, since there were indications that process length variation of Lingulodinium machaerophorum is related to salinity, there was a need to assess its use for quantitative palaeosalinity reconstruction, which is of critical importance for better understanding of global climate change. Two locations were chosen for a high-resolution micropalaeontological study of hydrological millennial-scale cycles during Late Quaternary times: the Cariaco Basin, an anoxic basin offshore Venezuela and the Southern Gulf of Cádiz, offshore Morocco. Because of the high sedimentation rates, both sites contain a relatively undisturbed Late Quaternary climate record. Both record rapid, large climatic oscillations related to major hydrological changes caused by respectively the intertropical convergence zone (ITCZ) and the North Atlantic Oscillation (NAO). Results of the micropalaeontological analysis indicate that the changes in the dominance of river influx or upwelling cause important variations in plankton productivity in both locations. These variations are reflected in both assemblage changes and absolute abundance variation. Apart from the productivity reconstruction, changes in assemblage or morphology reflect changes in temperature and salinity. The seasonal and multi-year changes between upwelling and river dominated ecosystems, related in both regions to climatological shifts of respectively the ITCZ and NAO, can be extended to millennial-scale cycles and results in specific productivities, temperatures and salinities. Since millennial-scale shifts of both phenomena occur during the same periods (e.g. Younger Dryas), future work should elucidate the precise timing of both phenomena by comparing detailed multi-proxy records from north-south transects