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Suppression of El Ni??o during the Mid-Holocene by changes in the Earth's orbit
Abstract
A number of recent reports have interpreted paleoproxy data to describe
the state of the tropical Pacific, especially changes in the behavior of
the El Niño-Southern Oscillation (ENSO), over the Holocene. These
interpretations are often contradictory, especially for the eastern
tropical Pacific and adjacent areas of South America. Here we suggest a
picture of the mid-Holocene tropical Pacific region which reconciles the
data. ENSO variability was present throughout the Holocene but underwent
a steady increase from the mid-Holocene to the present. In the
mid-Holocene, extreme warm El Niño events were smaller in
amplitude and occurred less frequently about a mean climate state with a
cold eastern equatorial Pacific and largely arid coastal regions as in
the present climate. This picture emerges from an experiment in which a
simple numerical model of the coupled ocean-atmosphere system in the
tropical Pacific was driven by orbital forcing. We suggest that the
observed behavior of the tropical Pacific climate over the mid- to late
Holocene is largely the response to orbitally driven changes in the
seasonal cycle of solar radiation in the tropics, which dominates
extratropical influences.
... Given the simultaneous shifts in climate patterns over East Asia and the El Niño-like conditions in the tropical Pacific, we suggest that the emergence of an El Niño-like state may primarily drive the climate transition around 3600 cal yr B.P. Our findings establish that the interaction between paleo-ENSO and East Asian precipitation is evident not only on tectonic (Lu et al., 2021), orbital , suborbital (Chen et al., 2015b;Zhang et al., 2021d), and inter-decadal (Huang et al., 2012) scales but also at centennial scales. The Late Holocene's El Niño-like state in the tropical Pacific could be influenced by orbital forcings (e.g., Clement et al., 1999Clement et al., , 2000Liu et al., 2014b). The decline in boreal summer insolation during the Late Holocene might generate zonally consistent sea surface temperature (SST) anomalies. ...
... The decline in boreal summer insolation during the Late Holocene might generate zonally consistent sea surface temperature (SST) anomalies. However, the atmospheric response to these SST anomalies is more pronounced in the western Pacific compared to the eastern Pacific (Clement et al., 1999(Clement et al., , 2000, resulting in more significant cooling of the atmosphere over the western Pacific and fostering El Niño-like conditions (Clement et al., 1999(Clement et al., , 2000Zhang et al., 2021c). The intensification of paleo-ENSO during the Late Holocene might also correlate with amplified positive ocean-atmosphere feedbacks driven by precession forcings (Liu et al., 2014b). ...
... The decline in boreal summer insolation during the Late Holocene might generate zonally consistent sea surface temperature (SST) anomalies. However, the atmospheric response to these SST anomalies is more pronounced in the western Pacific compared to the eastern Pacific (Clement et al., 1999(Clement et al., , 2000, resulting in more significant cooling of the atmosphere over the western Pacific and fostering El Niño-like conditions (Clement et al., 1999(Clement et al., , 2000Zhang et al., 2021c). The intensification of paleo-ENSO during the Late Holocene might also correlate with amplified positive ocean-atmosphere feedbacks driven by precession forcings (Liu et al., 2014b). ...
... The results show that the Holocene paleomegafloods matched well with the periods during which the ENSO frequency was higher (with the only exception being FL2). This consistency also agrees with the model simulations of a gradual intensification of ENSO during the mid-to late Holocene (Clement et al., 2000;Donders et al., 2008), which may be caused by increasing positive ocean-atmosphere feedbacks (Liu et al., 2014;Zhang et al., 2018). A great number of studies have shown close links between ENSO and heavy precipitation in China (Duan et al., 2017;Kundzewicz et al., 2020). ...
... (g) ENSO amplitude (standard deviation of Niño3.4 interannual (1.5-7 years) SST variability) in 100-year windows (Liu et al., 2014). (h) Number of ENSO events that occurred when the mean December-February NINO3 SST anomaly exceeded 3 K (Clement et al., 2000). ...
Reconstructing the Holocene megaflood history is a key component of understanding the mechanism of past climate change and assessing the potential impact of future catastrophic events. The Pearl River is the longest watercourse in southern China, and its lower reach has been identified as one of the world's most vulnerable regions for flood exposure. However, there is a complete lack of millennial-scale geological records of paleomegafloods for the future prediction of once-in-a-hundred (even once-in-a-thousand) year floods in southern China. Here, we identified a series of paleomegaflood deposits interbedded with wood-rich peat layers in the lower West Pearl River area. All paleoflood layers have been well dated using AMS 14C dating method. According to the regional correlation of the flood sequence, sediment characteristics and provenance analysis, there have been at least 7 megafloods corresponding to once-in-a-thousand-year events in the lower reaches of the West Pearl River during the past 6000 years, with an average return period of approximately 855 years. The identified paleomegafloods were coeval with periods of strong El Niño-Southern Oscillation (ENSO), indicating that weakening of the Asian summer monsoon, associated with enhanced ENSO variability, may have triggered abnormally high precipitation leading to flooding of exceptional magnitude in southern China. In addition, the most prominent paleomegafloods identified in the lower Pearl River coincided with intervals of lower precipitation and fewer storms in central-eastern China, indicating the intensification of the meridional "tripole" pattern of precipitation across eastern China during the latter half of the Holocene. Increased land use and deforestation over the last 2000 years have resulted in soil loss and rapid degradation of local primeval forest ecosystems, leading to more catastrophic flooding. Large amounts of rice pollen in the uppermost flood layer during the Song Dynasty indicate that this megaflood may have inundated a large area of cultivated land. The periodic occurrence of Holocene megafloods not only caused damage to human existence, but also affected the evolution of local civilization. This study reveals for the first time a series of Holocene millennial-scale megafloods and sheds new light on the importance of atmosphere-ocean interactions in the tropical Pacific and monsoon subtropical climate dynamics for precipitation anomalies in East Asia. Our data yield valuable information for future research into climate extremes and hazard prevention.
... The productivity recorded in Hole 807A was highest during the late part of most glacial (Fig. 3), when the eastern equatorial Pacific was probably dominated by El Niño-like conditions with weakening equatorial currents carrying nutrients westward (Koutavas et al., 2002), and the intensity of the eastern equatorial upwelling decreased in circulation models (Bopp et al., 2003). According to previous reports, ENSO-like patterns of changes in oceanic productivity associated with thermocline gradient variation also exist for long time-scaled records, in addition to interannual and decadal periods in the tropical Indian and Pacific Ocean region (Clement et al., 2000;Beaufort et al., 2001Beaufort et al., , 2003Perks et al., 2002). Variations in equatorial productivity are primarily caused by glacial-interglacial variability and precession-controlled changes in the east-west thermocline slope of the Indo-Pacific. ...
... In Fig. 3, it can be seen that the 30 ka cycle recorded in paleoproductivity and δ 66 Zn variations in core ODP 807A and atmospheric CO 2 levels recorded in the EPICA Dome C ice core support the hypothesis that equatorial Indo-Pacific productivity, controlled by ENSO-like variations of the west to east thermocline gradient, acts as a significant carbon sink in the global carbon cycle, and that the low-latitude biological pump effect might play an important role in controlling atmospheric CO 2 concentrations (Beaufort et al., 2001). Furthermore, seaatmospheric modeling of ENSO behavior based on glacial-interglacial cycles implied that frequency and intensity were forced by precessioncontrolled low-latitude insolation variations (Clement et al., 2000) thus affecting the productivity changes in the tropical Pacific Ocean by changing the west-to-east thermocline gradient. (Beaufort et al., 2001). ...
... For example, in the middle Holocene perihelion was in the southern hemisphere winter, and consequently there was lower ENSO variability, partly as a result of the generation of cooling winds that inhibited the growth of El Niño events. (Clement et al. 2000 discuss the complexities of these relationships). ...
... Temporal change in ENSO is often expressed as inferred rainfall levels and/or frequency of El Niño 'events'. An example is shown in Fig. 3C and 3B, which presents the predicted curve and amplitude of ENSO events (see Clement et al. 2000). The trend is from infrequent and low amplitude events in the Early Holocene to consistently far higher frequency and amplitude ones in the Late Holocene. ...
... These include records from the eastern Pacific, such as lake sediments from Ecuador and the Galapagos (Rodbell et al., 1999;Conroy et al., 2008), foraminifera (Koutavas & Joanides, 2012) and western Pacific records, for example pollen from Australasia (Shulmeister & Lees, 1995) and corals from Papua New Guinea (Tudhope et al., 2001). According to a numerical model (Clement et al., 2000), this reduction in ENSO strength during the mid-Holocene was a response to orbitally driven seasonality changes. However, other authors whose records indicated reduced mid-Holocene ENSO variance suggested that the driver was a change in the equatorial Pacific mean state (Cobb et al., 2013;Chen et al., 2016;White et al., 2018). ...
El Niño-Southern Oscillation dynamics affect global weather patterns, with regionally diverse hydrological responses posing critical societal challenges. The lack of seasonally resolved hydrological proxy reconstructions beyond the observational era limits our understanding of boundary conditions that drive and/or adjust El Niño-Southern Oscillation variability. Detailed reconstructions of past El Niño-Southern Oscillation dynamics can help modelling efforts, highlight impacts on disparate ecosystems and link to extreme events that affect populations from the tropics to high latitudes. Here, mid-Holocene El Niño-Southern Oscillation and hydrological changes are reconstructed in the southwest Pacific using a stalagmite from Niue Island, which represents the period 6.4-5.4 ka BP. Stable oxygen and carbon isotope ratios, trace elements and greyscale data from a U/Th-dated and layer counted stalagmite profile are combined to infer changes in local hydrology at sub-annual to multi-decadal timescales. Principal component analysis reveals seasonal-scale hydrological changes expressed as variations in stalagmite growth patterns and geochemical characteristics. Higher levels of host rock-derived elements (Sr/Ca and U/Ca) and higher δ18O and δ13C values are observed in dark, dense calcite laminae deposited during the dry season, whereas
... The third experiment (NoENSO) shows an enhancement in rainfall over the Maritime Continent during boreal summer-to-autumn which is likely due to the relaxation of the El Nino-induced dry climate (Fig. 3. d, h;Clement et al. 2000;Hendon 2003;Jiang et al., 2018). However, the NoENSO experiment simulates significantly less rainfall over Borneo than the mid-Holocene scenario (Fig. 4). ...
Both paleoclimate proxy records and Community Climate System Model version 4 (CCSM4) simulations show that rainfall over large islands in the Maritime Continent (e.g., Borneo) increased substantially during the mid-Holocene relative to the pre-industrial time. The rainfall increase is hypothesized to be caused by enhanced local autumn insolation, but is also attributed to increased sea surface temperature in the Indo-Pacific warm pool (IPWP) and/or weakened El Nino Southern Oscillation (ENSO). Here, we performed numerical experiments based on the output of the CCSM4 simulations and examined the underlining mechanisms of the enhanced rainfall and how they may have impacted the surrounding regions. Our numerical experiments, performed with the Community Atmospheric Model version 4 (CAM4), show that a wetter climate in the mid-Holocene, mainly during July, August, September, and October (JASO), is a direct response to stronger insolation rather than being chiefly impacted by a weaker magnitude of ENSO. The results reveal that stronger insolation can enhance rainfall over large islands through the convection-moisture positive feedback. However, the same mechanism acting over the warmer South China Sea (SCS) would instead reduce the convection over the large islands. On the other hand, the island convection suppresses oceanic convection by weakening the low-level southerly wind over the SCS. The suppressed convection over the SCS during the mid-Holocene weakens the local Hadley circulation, but without dramatically shifting the latitudinal position of the Intertropical Convergence Zone (ITCZ).
... These include eastern Pacific records such as lake sediments from Ecuador and the Galapagos [403,406] and foraminifera from deep-sea sediments [407], as well as western Pacific records such as pollen from Australasia [408] and corals from Papua New Guinea [402]. According to a numerical model [409], this reduction in ENSO strength during the mid-Holocene (3-5 ka) was a response to orbitally driven seasonality changes. Other authors whose records showed a reduction in ENSO variance during the mid-Holocene suggested that the driver was a change in the equatorial Pacific mean state [405,401,410]. ...
Our ability to predict the state of a system relies on its tendency to recur to states it has visited before. Recurrence also pervades common intuitions about the systems we are most familiar with: daily routines, social rituals and the return of the seasons are just a few relatable examples. To this end, recurrence plots (RP) provide a systematic framework to quantify the recurrence of states. Despite their conceptual simplicity, they are a versatile tool in the study
of observational data. The global climate is a complex system for which an understanding based on observational data is not only of academical relevance, but vital for the predurance
of human societies within the planetary boundaries. Contextualizing current global climate change, however, requires observational data far beyond the instrumental period. The palaeoclimate record offers a valuable archive of proxy data but demands methodological approaches that adequately address its complexities. In this regard, the following dissertation aims at
devising novel and further developing existing methods in the framework of recurrence analysis (RA). The proposed research questions focus on using RA to capture scale-dependent
properties in nonlinear time series and tailoring recurrence quantification analysis (RQA) to characterize seasonal variability in palaeoclimate records (‘Palaeoseasonality’).
In the first part of this thesis, we focus on the methodological development of novel
approaches in RA. The predictability of nonlinear (palaeo)climate time series is limited by abrupt transitions between regimes that exhibit entirely different dynamical complexity (e.g. crossing of ‘tipping points’). These possibly depend on characteristic time scales. RPs are well-established for detecting transitions and capture scale-dependencies, yet few approaches have combined both aspects. We apply existing concepts from the study of self-similar textures to RPs to detect abrupt transitions, considering the most relevant time scales. This combination of methods further results in the definition of a novel recurrence based nonlinear
dependence measure. Quantifying lagged interactions between multiple variables is a common problem, especially in the characterization of high-dimensional complex systems. The
proposed ‘recurrence flow’ measure of nonlinear dependence offers an elegant way to characterize such couplings. For spatially extended complex systems, the coupled dynamics of
local variables result in the emergence of spatial patterns. These patterns tend to recur in time. Based on this observation, we propose a novel method that entails dynamically distinct
regimes of atmospheric circulation based on their recurrent spatial patterns. Bridging the two parts of this dissertation, we next turn to methodological advances of RA for the study of Palaeoseasonality. Observational series of palaeoclimate ‘proxy’ records involve inherent limitations, such as irregular temporal sampling. We reveal biases in the RQA of time series with a non-stationary sampling rate and propose a correction scheme.
In the second part of this thesis, we proceed with applications in Palaeoseasonality. A review of common and promising time series analysis methods shows that numerous valuable
tools exist, but their sound application requires adaptions to archive-specific limitations and consolidating transdisciplinary knowledge. Next, we study stalagmite proxy records from the
Central Pacific as sensitive recorders of mid-Holocene El Niño-Southern Oscillation (ENSO) dynamics. The records’ remarkably high temporal resolution allows to draw links between
ENSO and seasonal dynamics, quantified by RA. The final study presented here examines how seasonal predictability could play a role for the stability of agricultural societies. The Classic
Maya underwent a period of sociopolitical disintegration that has been linked to drought events. Based on seasonally resolved stable isotope records from Yok Balum cave in Belize, we
propose a measure of seasonal predictability. It unveils the potential role declining seasonal predictability could have played in destabilizing agricultural and sociopolitical systems of
Classic Maya populations.
The methodological approaches and applications presented in this work reveal multiple exciting future research avenues, both for RA and the study of Palaeoseasonality.
重建全新世大洪水的历史是探讨过去极端气候变化以及预测未来潜在自然灾害风险的关键内容. 珠江水系是中国南方最大的河流系统, 珠江三角洲曾被认为是世界上受洪水和风暴潮灾害影响最为脆弱的地区之一. 然而, 迄今为止在中国南方地区缺少千年尺度的洪水地质记录研究, 从而难以从认识过去的角度来检验对未来百年甚至千年一遇大洪水灾害预测的可信度. 本研究在珠江干流(西江)下游发现了一系列发育在厚层黑色泥炭腐木堆积中的灰白色黏土夹层, 根据沉积序列对比、 沉积物特征和物源分析结果, 确定为洪水沉积. 对每个洪水沉积层采用AMS 14C方法进行了精确定年, 揭示出西江下游在距今6000年以来至少发生了7次千年一遇规模的超级大洪水, 平均再现期约为855年. 西江流域特大洪水事件的发生均对应于较强的ENSO活动期, 表明东亚夏季风减弱和ENSO增强是引发中国南方异常高降水和特大洪水灾害的重要原因. 此外, 珠江下游特大洪水事件的发生与中国中东部降水减少在时间上大致耦合, 反映了全新世后半期中国东部经向分布的降水“三极”模式显著增强. 在过去2100年, 人类土地利用增强和森林破坏导致当地的原始植被生态系统迅速退化, 水土流失导致大洪水的破坏力和灾难性增大, 特别是宋代以后的洪水沉积层中含有丰富的水稻型禾本科花粉, 反映洪水曾经淹没了大面积农用土地. 此外, 全新世古洪水事件不仅对流域内的人类生存造成危害, 同时还影响着区域文明的演化. 本研究揭露了全新世一系列千年一遇的特大洪水历史, 证明了热带太平洋的海-气相互作用与亚热带季风气候变化对东亚降水异
常的重要性, 研究结果为预测未来的极端气候变化和洪水灾害提供了有价值的重要证据.
SEA surface temperatures in the tropical Pacific Ocean increased on average by serveral tenths of a degree during the 1980s and early 1990s1-4, contributing to the observed global warming during this period5. Here we investigate the possible causes of this Pacific warming, using a global coupled ocean-atmosphere general circulation model incorporating increasing concentrations of atmospheric carbon dioxide. In the model, cloud cover and cloud albedo feedbacks contribute to tropical Pacific sea surface temperature increases that are greater east of 180° longitude, with attendant shifts in large-scale precipitation patterns and mid-latitude circulation anomalies in the north Pacific. These anomalies resemble some aspects of El Niño events, as well as features associated with recent observed Pacific-region climate anomalies. The resemblance to El Niño complicates the problem of detection and attribution of climate change, and suggests that depletion of freshwater resources6 may be an additional hazard of greenhouse warming for populations in the western Pacific region.
Nonlinear interactions between the seasonal cycle and interannual variations in the coupled ocean-atmosphere system have recently been proposed as the cause of irregularity of El Niño-Southern Oscillation (ENSO). We investigated such a hypothesis using a coupled ocean-atmosphere model which allows coupling between total sea surface temperature (SST) and total surface winds. Numerical simulations indicate that the model is capable of capturing the essential SST variability on seasonal-to-interannual time scale. Furthermore, it is shown that, as the seasonal forcing amplitude is gradually increased from zero, the coupled model undergoes several transitions between periodic (frequency-locking) and chaotic states before it finally ‘gives up’ its intrinsic ENSO mode of oscillation entirely and acquires the frequency of the seasonal forcing. Chaotic response is found as the forcing amplitude approaches the observed value and the route to ENSO chaos is identified to be the period-doubling cascade. The study suggests that the response of a coupled system, coupled General Circulation Models of the ocean and atmosphere for example, can be very sensitive not only to changes in the internal model parameters but also to changes in the external forcing conditions.
An attempt is made to provide the background for a coupled model of ENSO (El Nino-Southern Oscillation) with emphasis placed on the oceanography (i.e. on El Nino). Observations of the normal annual cycle in the Pacific and of the evolution of a typical El Nino event are reviewed, and a theory for the oceanography of El Nino is proposed. The influence of SST anomalies on the tropical atmosphere is assessed, and results from a numerical model for the coupled system able to generate El Nino events are presented. Implications for the real ENSO cycle are discussed. In both the model and nature, ENSO has the character of a relaxation oscillation of the coupled system, and its cycle is aperiodic. Results on the predictability of dynamical systems show the impossibility of predicting ahead several events.
A sequence of numerical simulations was performed in order to assess the role of early- to mid-Holocene orbital forcing on the coupled atmosphere-ocean system. Results from both an atmosphere-only general circulation model (GCM) forced by specified sea surface temperatures and a coupled atmosphere-ocean GCM consistently suggest a stronger south Asian monsoon and a strengthened Pacific Walker circulation. The latter feature interacts dynamically with the equatorial ocean in the coupled model to produce enhanced Pacific upwelling, a more pronounced cold tongue, and an even stronger monsoon. Results suggest that the climate of the equatorial Pacific was more similar to the La Niña phase of the modern Southern Oscillation rather than the El Niño phase.