Abrupt Climate Events Research Articles

Radiocarbon Dating of Small-sized Foraminifer Samples: Insights into Marine sediment Mixing

ABSTRACTRadiocarbon (14C) can be used to build absolute chronologies and reconstruct ocean ventilation over the last 40 ka. Sample size requirements have restricted14C measurements in marine cores with low foraminifer content, impeding14C-based studies focused on abrupt climate events. Recent developments have demonstrated that small-sized foraminifer samples can now be dated using a gas introduction system at the cost of a small decrease in precision. We explore the potential of gas measurements on benthic and planktonic foraminifers from core SU90-08 (43°03′1″N, 30°02′5″W, 3080 m). Gas measurements are accurate, reproducible within 2σ uncertainty and comparable to graphite measurements. Both techniques yield negative14C benthic-planktonic (B-P) age-offsets after Heinrich event 1. We argue that negative B-P ages result from bioturbation and changes in foraminifer abundances, with the chance of negative B-P especially increased when the14C age gradient between the deep and surface waters is decreased. Small-sized14C measurements seem to capture the variance of the foraminifera age distribution, revealing the active mixing in those archives. Sediment deposition and mixing effects possibly pose a greater obstacle for past14C-based dating and ocean ventilation reconstructions than the measurement precision itself, particularly in relatively low sedimentation rate settings.

Divergent mammalian body size in a stable Eocene greenhouse climate

A negative correlation between body size and the latitudinal temperature gradient is well established for extant terrestrial endotherms but less so in the fossil record. Here we analyze the middle Eocene site of Geiseltal (Germany), whose record is considered to span ca. 5 Myrs of gradual global cooling, and generate one of the most extensive mammalian Paleogene body size datasets outside North America. The δ18O and δ13C isotopic analysis of bioapatite reveals signatures indicative of a humid, subtropical forest with no apparent climatic change across Geiseltal. Yet, body mass of hippomorphs and tapiromorphs diverges rapidly from a respective median body size of 39 kg and 124 kg at the base of the succession to 26 kg and 223 kg at the top. We attribute the divergent body mass evolution to a disparity in lifestyle, in which both taxa maximize their body size-related selective advantages. Our results therefore support the view that intrinsic biotic processes are an important driver of body mass outside of abrupt climate events. Moreover, the taxonomy previously used to infer the duration of the Geiseltal biota is not reproducible, which precludes chronological correlation with Eocene marine temperature curves.

Holocene climate variability and Indian Summer Monsoon: An overview

The response of the Indian Summer Monsoon (ISM) to forcing factors and climate variables has not yet fully explored, even though the ISM plays a pivotal role in the socio-economics of the Indian subcontinent and nearby areas. The ISM progression over Indian landmass is a manifestation of the Intertropical Convergence Zone (ITCZ) migration over the northern Indian Ocean and the Indian subcontinent. The recent anomalous behaviour of ISM raises the need for a better understanding of its spatio-temporal changes during the ongoing interglacial period termed as the Holocene period. The Holocene period has been classified further based on the globally observed abrupt climatic events at 8.2 and 4.2 ka. The 8.2 ka global cooling events have been recorded from northern Indian Ocean marine archives but limited records from the continental archives of the Indian landmass has demonstrated the 8.2 ka event. At the same time, the 4.2 ka dry climate has been endorsed by both marine as well as continental records and agrees with the global studies. During the ‘Little Ice Age’ (LIA), in the India subcontinent, wet conditions prevailed in the northern, central and western regions while a dry climate existed over the greater part of peninsular India. The present review offers an account of ISM signatures and possible mechanisms associated with the monsoon variability in the Indian subcontinent and the northern Indian Ocean during the Holocene period.

Holocene environmental evolution recorded by multi-proxies from lacustrine sediments of the Hangbu River Valley, Lake Chaohu Basin, East China

在巢湖杭埠河流域中的古湖盆中心——三河圩区获取28.6 m长的湖相岩芯（SZK1507孔），利用AMS¹⁴C测年技术建立可靠的地层年代序列，通过对SZK1507孔738 cm以上段湖相沉积物平均粒径、磁化率、总氮（TN）、总有机碳（TOC）及C/N的综合分析，高分辨率重建了巢湖杭埠河流域全新世以来的古环境演变过程.结果表明，本区域的环境变化过程可以分为4个阶段，阶段Ⅰ（约10050—9700 cal.a B.P.）与阶段Ⅲ（约9250—5300 cal.a B.P.）气候较为湿润，巢湖水位较高，平均粒径、磁化率值较低，TN、TOC、C/N也偏低；阶段Ⅱ（约9700—9250 cal.a B.P.）与阶段Ⅳ（约5300 cal.a B.P.以来）气候干燥，巢湖水量减少，水位降低，平均粒径、磁化率值、TN、TOC、C/N均较高.一些全球范围内显著发生的气候突变事件在SZK1507孔沉积记录中也有体现，如9.3、8.2和4.2 ka B.P.事件等.将巢湖杭埠河流域10000 cal.a B.P.以来的平均粒径、磁化率、TN、TOC、C/N沉积记录与全新世以来的北纬30°夏季太阳辐射量、太阳黑子数、火山喷发对大气中硫酸盐含量贡献率等进行对比，发现巢湖杭埠河流域全新世气候突变事件主要受控于北半球夏季太阳辐射量变化、太阳活动以及火山活动等因素，并与它们之间复杂的响应机制有关.;Time sequence of the SZK1507 core derived from AMS¹⁴C dating, and the content of the total nitrogen (TN), total organic carbon (TOC) and the C/N values as well as the mean grain size, magnetisability are utilized to reconstruct the environmental changes in the Hangbu River Valley of the Lake Chaohu Basin, East China during the Holocene. The comprehensive analyses of multiple alternative proxies indicated that the evolutionary process of Lake Chaohu Basin in the Holocene could be divided into four periods. The climate was moist in Period Ⅰ ( from 10050 cal. a B.P. to 9700 cal. a B.P.) and Period Ⅲ (from 9250 cal. a B.P. to 5300 cal. a B.P.), and lake level of Lake Chaohu was high inferred from the low values of TN, TOC, C/N, mean grain size and magnetisability. Period Ⅱ (from 9700 cal. a B.P. to 9250 cal. a B.P.) and Period Ⅳ (from 5300 cal. a B.P. to the present) were dry, and the Lake Chaohu had low lake level, suggested by the high values of mean grain size and magnetisability, TN, TOC, C/N. Some global-scale abrupt climatic change events (e.g., 9.3 ka B.P., 8.2 ka B.P., and 4.2 ka B.P. events) were also recorded in this sediment core. Comparing the lacustrine records of SZK1507 core to other observations of climate variability, such as the northern hemisphere summer solar insolation, the sunspot numbers etc during the Holocene, we discovered that the abrupt climatic change events occurring in the Lake Chaohu Basin were affected by the variation of summer solar insolation in the northern hemisphere, the solar activities, the volcanic activities, and the complex feedback mechanism among them principally.

The response of a dune succession from Lençóis Maranhenses, NE Brazil, to climate changes between MIS 3 and MIS 2

In tropical Southern Hemisphere South America, late Quaternary marine core and speleothem records provide different proxies and accurate chronologies correlating millennial-scale intervals of increased precipitation with southward shifts of the Intertropical Convergence Zone (ITCZ). However, the climatic effect of these intervals on coastal landforms is poorly understood. Here we investigated the response of abrupt and long-lasting climate events during the Marine Isotope Stages 3 and 2 in a 13.8-m thick sand succession located in a large-scale coastal eolian system, the Lençóis Maranhenses Dunefield, NE Brazil, where winds and precipitation are anti-phased and controlled by the single action of the ITCZ. A chronology of the sediment overburden determined by optically stimulated luminescence (OSL) dating of 14 sediment samples obtained at 1-m intervals showed ages between 132.2 ± 7.0 and 12.9 ± 0.6 thousand years ago in stratigraphic order. A multi-proxy approach based on grain size, surface grain texture, heavy minerals, thermoluminescence (TL) sensitivity, inorganic geochemistry, reflectance, and magnetic parameters from 268 sediment samples collected at 5-cm intervals indicated periods of dune building and stabilization. Significant stabilization periods are synchronous with Heinrich Stadials 6, 4, 3, 2, and 1, and Greenland Stadial 4, within age model uncertainties. Heavy mineral analysis indicated a steady sand source to the dune succession, while TL sensitivity analysis of quartz grains showed the input allochthonous sediments during stadials. The preservation of peak dune activity during the Last Glacial Maximum is attributed to the enduring precipitation brought by the subsequent Heinrich Stadial 1 event.

Chronology of coastal aeolian deposition and its paleoenvironmental implications on the Liuao Peninsula of South China

Coastal dunes are a common geomorphic type in sandy coastal zones. They are a record of the coupled evolutionary processes of the wind and ocean waves. Many coastal dune fields have developed on the east coast of Fujian China and now occur as widespread typical coastal aeolian sand landforms on the Liuao Peninsula, Gulei Peninsula and Dongshan Island, but it is difficult to evaluate the dynamic geomorphologic process of sandy coast due to the lack of systematic and accurate chronological data. In this study, we selected the Hutoushan (HTS) aeolian dune on the Liuao Peninsula as the research object. Optical dating and grain-size analysis were applied to sand samples from the aeolian sequence of a profile of the HTS dune. The results show that the ages of seven samples of this profile were in the range of 37.8–0.19 ka from 4.0 to 0.2 m deep. These correspond to the Marine Isotope Stage 3 (MIS3), abrupt climatic change events of 4.2 and 1.1 ka and the Little Ice Age (LIA), respectively. These samples displayed evidence of a longer-term climate trend in this area. The period of formation of this coastal aeolian dune corresponds to a cold and arid climate associated with the East Asia Winter Monsoon (EAWM). Periods of dune fixation and rubification are evidence of a hot and humid climate. Mobilization and stabilization of the aeolian dune is an important characteristic of the coastal evolution in South China since the late Pleistocene.

Modelling the vegetation response to the 8.2 ka bp cooling event in Europe and Northern Africa

ABSTRACTThe 8.2 ka bp cooling event is assumed to be the most clearly marked abrupt climate event in the Holocene at northern mid‐ to high latitudes. In this study, we simulate the vegetation responses to the 8.2 ka bp climate change event over Europe and Northern Africa. Our results show that all dominant plant functional types (PFTs) over Europe and North Africa respond to these climate changes, but the magnitude, timing and impact factor of their responses are different. Compared with pollen‐based vegetation reconstructions, our simulation generally captures the main features of vegetation responses to the 8.2 ka bp event. Interestingly, in Western Europe, the simulated vegetation after perturbation is different from its initial state, which is consistent with two high‐resolution pollen records. This different vegetation composition indicates the long‐lasting impact of abrupt climate change on vegetation through eco‐physiological and ecosystem demographic processes, such as plant competition. Moreover, our simulations suggest a latitudinal gradient in the magnitude of the event, with more pronounced vegetation responses to the severe cooling in the north and weaker responses to less severe cooling in the south. This effect is not seen in pollen records. © 2019 The Authors. Journal of Quaternary Science Published by John Wiley & Sons, Ltd.

Unravelling the Holocene environmental history of south-western Iberia through a palynological study of Lake Medina sediments

Lake Medina is a small, shallow and endorheic salt lake sensitive to climate variation in south-western Spain, close to Cádiz in western Andalusia. It is located in an evaporitic and karstic environment, and a saline lake affected by highly seasonal precipitation and evaporation. Geochemical and mineralogical data of core CO1313 combined with a robust age model show variation that contributes to the understanding of palaeoenvironmental and palaeoclimatic change. This study shows a pollen record that has been conducted on core CO1313, together with charcoal and non-pollen palynomorph analyses. The environmental and climatological history reconstruction of Lake Medina starts in early Holocene times (at 9.5 cal. ka BP) and shows intensified pasture and land use during middle-Holocene times as well as the 8.2 and 4.2 cal. ka BP abrupt climate events. Oxidation of plant remnants and resulting non-preservation at certain times reinforces the hypothesis of intense climate effects on vegetation during the 4.2 cal. ka BP climate event. Yet, oxidation of plant residues during other episodes shows other periods that were also affected by reduced precipitation. From around 2 cal. ka BP onwards, a recent trend towards aridification and enforced seasonality was detected.

Evidence of abrupt climate change at 9.3 ka and 8.2 ka in the central Canadian Arctic: Connection to the North Atlantic and Atlantic Meridional Overturning Circulation

This study presents the results of a multi-proxy analysis of a Holocene lacustrine sediment sequence recovered from a small tundra lake in the central Canadian Arctic and links climatic variations there to the North Atlantic. Chironomid and pollen-based reconstructions of mean July air temperature (MJAT) document notable deviations at 9.3 ka and 8.2 ka. Chironomid-inferred July air temperature is depressed by 1.4 °C at 9.3 ka and 1.7 °C at 8.2 ka relative to the long-term chironomid-inferred Holocene average of 9.4 °C. These cooling events also correspond to an increase in Gramineae (Poaceae) and a decrease in Betula pollen, reflecting a decrease in the density of dwarf birch cover. Concurrent, abrupt increases in several diatom taxa, including aerophilic epiphytes, and Sphagnum indicate an expansion of moss habitats as a result of wetter conditions. The expression and timing of the cooling evidenced at TK2 during the early Holocene is consistent with abrupt climate events identified in the North Atlantic and coincides with intervals of North Atlantic cooling and weakened Atlantic Meridional Overturning Circulation (AMOC). This research, which improves our understanding of the spatial extent and magnitude of the 9.3 ka and 8.2 ka events in the central Canadian Arctic, serves as a benchmark for coupled-ocean atmosphere climate models simulating the response of the climate system to abrupt climate events and provides insight in marine-atmosphere teleconnections in the circum-North Atlantic region.

Marine N2O emissions during a Younger Dryas-like event: the role of meridional overturning, tropical thermocline ventilation, and biological productivity

Past variations in atmospheric nitrous oxide (N2O) allow important insight into abrupt climate events. Here, we investigate marine N2O emissions by forcing the Bern3D Earth System Model of Intermediate Complexity with freshwater into the North Atlantic. The model simulates a decrease in marine N2O emissions of about 0.8 TgN yr−1 followed by a recovery, in reasonable agreement regarding timing and magnitude with isotope-based reconstructions of marine emissions for the Younger Dryas Northern Hemisphere cold event. In the model the freshwater forcing causes a transient near-collapse of the Atlantic Meridional Overturning Circulation (AMOC) leading to a fast adjustment in thermocline ventilation and an increase in O2 in tropical eastern boundary systems and in the tropical Indian Ocean. In turn, net production by nitrification and denitrification and N2O emissions decrease in these regions. The decrease in organic matter export, mainly in the North Atlantic where ventilation and nutrient supply is suppressed, explains the remaining emission reduction. Modeled global marine N2O production and emission changes are delayed, initially by up to 300 years, relative to the AMOC decrease, but by less than 50 years at peak decline. The N2O perturbation is recovering only slowly and the lag between the recovery in AMOC and the recovery in N2O emissions and atmospheric concentrations exceeds 400 years. Thus, our results suggest a century-scale lag between ocean circulation and marine N2O emissions, and a tight coupling between changes in AMOC and tropical thermocline ventilation.

Western Mediterranean Sea Paleothermometry Over the Last Glacial Cycle Based on the Novel RI‐OH Index

AbstractRI‐OH (ring index of hydroxylated tetraethers) has recently been proposed to reconstruct paleotemperatures in middle‐ to low‐latitude marginal seas. However, RI‐OH has barely been tested in marginal seas under substantial terrigenous inputs. Here we analyze tetraether lipids in two adjacent marine cores from the Gulf of Lions. We then test for the first time the RI‐OH paleothermometer from 160 to 9 ka BP in the western Mediterranean Sea. While terrigenous inputs prevent TEX86 (TetraEther indeX of tetraethers consisting of 86 carbon atoms) from behaving as a paleothermometer, RI‐OH is generally consistent with other paleothermometric proxies. RI‐OH also responds systematically and coherently to glacial‐interglacial transitions as well as to abrupt climatic events. The average difference between RI‐OH temperatures and November–May UK′37 (C37 ketone unsaturation ratio) temperatures is −2.0 °C with a standard error of 0.4 °C based on 249 RI‐OH‐UK′37 comparisons. This systematic difference suggests that hydroxylated tetraethers and alkenones record different temperatures, for instance, winter and/or subsurface temperatures for RI‐OH. Another source of bias could be linked to the available RI‐OH‐temperature calibration, which clearly needs more work at the global and regional scales, notably for semienclosed basins such as the Mediterranean Sea. Nevertheless, our RI‐OH‐based interglacial‐glacial anomalies are of 10 °C, a value within the high end of anomalies from previously published temperature records in the western Mediterranean Sea (from 3 to 13 °C). The RI‐OH‐based temperature anomalies also confirm the regional differences and seasonal contrasts in interglacial‐glacial anomalies produced by models.

Climatic controls on peat swamp formation and evolution since 1300 year BP as recorded by phytoliths in the Xishan Mountains, Jiangxi Province, China

Over the past millennium, there have been several precipitation–temperature cycles characterized by instabilities in the eastern monsoon region in China, but the processes, factors, and anthropogenic activities potentially responsible remain poorly understood. In this study, we present an analysis of phytoliths from borehole core drilled through an ombrotrophic peat mire in Jiangxi Province, China. Our results record three climatic episodes over the past 1300 year: a warmer interval, c. 800–1305 CE, similar to the Medieval Warm Period (MWP); a cooler interval, c. 1305–1860 CE, similar to the Little Ice Age (LIA); and another warmer interval, as the climate entered the Present Warm Period (PWP) after c. 1860 CE. Quantitative analysis of phytolith assemblages demonstrates that the MWP comprised two intervals: the early MWP, c. 800–1140 CE, was progressively wetter in a warm–dry setting and late MWP, c. 1140–1305 CE, was warm and humid. The LIA also comprised two intervals: the early LIA, c. 1305–1610 CE, was cool and dry, and the late LIA, c. 1610–1860 CE was cool and humid. Some abrupt climate events occurred at: (1) c. 1050, 1110–1130, and 1780–1845 CE (wet events); (2) c. 1980–1990 CE (dry events); (3) c. 920 and 1770 CE (warm events); (4) c. 980 and 1050 CE (cold events). The transition from the MWP to the LIA, as indicated by phytoliths, was a gradual process that took c. 100 years, and exhibited frequent temperature fluctuations. Correlations between the phytolith assemblages and the solar activity, East Asia Summer Monsoon, El Niño, and La Niña are evident. Solar maxima and La Niña-like conditions are related to warmer and humid conditions that led to clay–sand accumulation during the MWP. Solar minima and El Niño-like conditions were associated with a cold and wet climate that led to peat accumulation during the LIA. These observations provide important insights into paleoclimatic change in the eastern monsoonal region of China, and provide a basis on which to understand the response of the Xishan Mountains in SE China to the MWP and LIA, and explore centennial-scale climate fluctuations and their driving mechanisms.

Indian Summer Monsoon variations and competing influences between hemispheres since ~35 ka recorded in Tengchongqinghai Lake, southwestern China

The southwestern Yunnan Province of China, which is located at the southeastern margin of the Tibetan Plateau and close to Bay of Bengal, is significantly influenced by the Indian Summer Monsoon (ISM). In this study, we reconstruct proxies for the ISM from 35 to 1 ka through detailed analysis of grain-size distribution, geochemical composition and environmental magnetism from a 7.96 m sediment core from Tengchongqinghai Lake, Yunnan Province, China. Globally recognized, abrupt climatic events, including Heinrich Events 0–3 (H0−H3) and the Bølling-Allerød (B/A) warm period are identified in most of our proxies, and the long-term trend is consistent with other published records such as stalagmite oxygen isotopes (δ18O) from Sangxing Cave. Northern Hemisphere (NH) temperature, which is influenced by NH solar insolation, is commonly suggested to play a dominant role in controlling the ISM. A comparison of our record with the δ18O variations of ice cores from Greenland and Antarctica, a sea surface temperature (SST) record from the Bay of Bengal, and summer solar insolation at 25°N latitude demonstrates that the general pattern of ISM change does follow variations in summer insolation; however, the ISM lags summer insolation by thousands of years. While the ISM fluctuations are highly correlated with NH temperature on shorter timescales (centennial-millennial), the gradually weakened ISM from 22.5 ka until the Last Glacial Maximum (LGM) indicates a close relationship with the rise of Southern Hemisphere (SH) temperature and the relatively cold background of the SH. Our record expands on the findings of ISM records from Heqing paleolake basin in southwestern China and the Arabian Sea sediments, suggesting that the NH and SH have a competitive influence on ISM by controlling the cross-equatorial pressure gradient. This relationship means that when NH temperatures are relatively high, it has a stronger influence on the ISM than SH influences. In contrast, when the SH temperature is relatively low, it has a dominant influence on ISM. In addition, we speculate that the change of SH temperature not only influences the cross-equatorial pressure gradient directly, but also likely modulates the circulation system of ocean energy by influencing the Atlantic Meridional Overturning Circulation (AMOC).

Holocene abrupt climatic events and the environmental effects

Holocene abrupt climatic events and the environmental effects

The role of abrupt climate change in the formation of an open vegetation enclave in northern Amazonia during the late Quaternary

Abstract The effects of climate changes on biotic expansion or divergence is a widely debated topic. This discussion is particularly relevant for northern Amazonia where patches of open vegetation environments that harbor high endemic and specialized species are present in a matrix of tall closed canopy forest. This paper presents the depositional chronology and evolution of an 8.7-m thick stabilized fluvial and eolian sediment profile in a sandy plain substrate that underpins the largest open vegetation enclave in northern Amazonia. Three depositional units were identified using optically stimulated luminescence and radiocarbon ages coupled with grain size, magnetic susceptibility, and reflectance analyses. A lower unit of coarse fluvial silt deposited between 53 and 28 ka is overlain unconformably by a 5-m thick middle unit of fine eolian sand deposited at high accumulation rates between the Last Glacial Maximum (23–19 ka) and Heinrich Stadial 1 (HS1; 18.1–14.7 ka) when persistent and long-lasting shifts of the Intertropical Convergence Zone (ITCZ) to the Southern Hemisphere promoted dry and windy conditions in northern South America. An upper ~2-m thick unit was deposited when the climate became wetter after HS1, promoting the formation of soils that support open vegetation habitats. This study indicates that abrupt millennial-scale climate events can induce significant changes in the Amazonian landscape, which in turn play an essential role in the distribution and diversification of specialized biota.

Holocene climatic and environmental evolution on the southwestern Iberian Peninsula: A high-resolution multi-proxy study from Lake Medina (Cádiz, SW Spain)

The climatic and environmental history of the SW Iberian Peninsula is explored to fill in the gap of continental palaeoclimate data by a high-resolution study of Lake Medina sediments from core Co1313. A multi-proxy approach comprising sedimentary facies analysis, elemental geochemistry, mineralogy, palynology and micropaleontology was employed to reconstruct the complex limnological response to climate change and catchment dynamics since the early Holocene. The further definition of abrupt climate change events was supported by a robust age model and rapid sediment accumulation rate at the study site. Proxies indicate arid and warm climate conditions during the Early Holocene, from around 9.5 to 7.8 cal ka BP, with a desiccation event at 8.8 cal ka BP as well as tentative evidence for the regional expression of a cold and abrupt arid climate event centering on ca. 8.2 cal ka BP. The Holocene Climate Optimum, from around 7.8 to 5.5 cal ka BP, is characterized by a humid climate and maximum lake level. Anoxic bottom water conditions are indicated by the preservation of sediment laminae and the occurrences of Sulfur mottles, which were observed for the first time within Holocene sediments of saline lakes. Mid-to Late Holocene times are governed by the 4.2 cal ka BP dry event as well as progressive aridification accompanied by the development of typical Mediterranean low-land vegetation. During recent times, further progressive loss in precipitation as well as fluctuating but overall increasing anthropogenic influence on Lake Medina sediments is observed.

Early dynamics in plant community trait responses to a novel, more extreme hydrological gradient

For temperate regions such as Northern Europe, predicted climate change patterns include an increase in winter precipitation causing increased risk of flooding, whereas periods of droughts will become more frequent in summer. The aim of this study is to explore variations in plant functional trait distributions along a hydrological gradient spanning from recurrent drought events to recurrent flooding—mimicking future precipitation patterns. The experiment was conducted in a controlled grassland experiment over a period of 3 years. A novel and more extreme hydrological regime was achieved by manipulating the flow of a nearby stream thereby creating a continuous hydrological gradient from flooding during winter to drought during summer. Plant community responses were recorded along this hydrological gradient. Community-weighted trait distribution changes along the gradient were described using null models. Six functional traits were considered: seed mass, leaf dry matter content (LDMC), leaf area, leaf thickness, specific leaf area (SLA) and height. Over time, responses in plant functional traits changed at the community level. Over the study period consistent changes occurred in the mean trait value of several traits. Communities in relatively dry plots became dominated by species with water-conserving life strategies, represented by high seed mass and thick leaves. In contrast, disturbance-resistant species (high leaf dry matter content) became dominant in flooded plots, indicating that persistence to flooding was the most important factor controlling the functional structure in those communities. Furthermore, a high abundance of small-seeded species in flooded plots likely indicates higher frequency of species with higher dispersal ability through hydrochory. In conclusion, plant traits are useful for predicting responses to climate change, but abrupt and extreme climate event may cause unexpected responses because they have no analog to previously more stable conditions. We suggest that traits related to dispersal and resistance to disturbance are useful in describing responses to flooding and that these traits should be included in future investigations of plant community responses to extreme hydrological events.

Abrupt high-latitude climate events and decoupled seasonal trends during the Eemian

The Eemian (the Last Interglacial; ca. 129–116 thousand years ago) presents a testbed for assessing environmental responses and climate feedbacks under warmer-than-present boundary conditions. However, climate syntheses for the Eemian remain hampered by lack of data from the high-latitude land areas, masking the climate response and feedbacks in the Arctic. Here we present a high-resolution (sub-centennial) record of Eemian palaeoclimate from northern Finland, with multi-model reconstructions for July and January air temperature. In contrast with the mid-latitudes of Europe, our data show decoupled seasonal trends with falling July and rising January temperatures over the Eemian, due to orbital and oceanic forcings. This leads to an oceanic Late-Eemian climate, consistent with an earlier hypothesis of glacial inception in Europe. The interglacial is further intersected by two strong cooling and drying events. These abrupt events parallel shifts in marine proxy data, linked to disturbances in the North Atlantic oceanic circulation regime.

The response of transitional pedogenic characteristics of loess in the Yunxian Basin to abrupt climatic events in the northern subtropics since the Last Glacial Maximum

The transitional pedogenic characteristics of loess deposits in the Yunxian Basin have provided solid evidence for understanding the mechanisms of dust transportation, deposition, and detailed documentation of climate instability since the Last Glacial Maximum (LGM) in the northern subtropics of China. The Heinrich Stadial 1b (HS 1b, 16.9–14.7 ka B.P.) event, Bϕlling/Allerϕd (B/A, 13.9–13 ka B.P.) period, Younger Dryas (YD, 12.9–11.7 ka B.P.) event, and an environmental event (5–4 ka B.P.) during the Holocene Optimum were imprinted by the high-resolution multi-proxy of loess-paleosol in the Yunxian Basin, China. Based on granularity and chemical analyses, the loess in the Yunxian Basin can be classified as a fine, clayey loess zone that experienced a moderate degree of chemical weathering. The mechanism forming the transitional pedogenic characteristics was explained by the dust storm frequency data (1957–2007), particle-size data, and multi-proxy records of chemical weathering extent, which was mainly caused by the moderate transport distance from the common provenance and the transitional climatic characteristics of the northern subtropical zone.

Nonlagged Response of Vegetation to Climate Change During the Younger Dryas: Evidence from High‐Resolution Multiproxy Records from an Alpine Lake in Northern China

AbstractThe use of pollen analysis to reconstruct regional vegetation changes, and subsequently climate, is a common approach in paleoclimatic reconstruction. However, it is unclear whether or not vegetation exhibits a lagged response to climate change during shifts from rapid cooling to rapid warming. The Younger Dryas (YD) cold event, spanning the last glacial/Holocene transition, was a prominent abrupt climatic event. To investigate the vegetation response to climate change during the YD, we compared profiles of independent climatic indicators from the sediments of alpine Lake Gonghai, on the margin of the modern Asian summer monsoon, with a pollen record from the same site. Our aim was to assess the phase lag of vegetation change relative to independent climate proxies that would have responded near instantaneously to climate change. The results show that the vegetation changed synchronously with the climate proxies, and consequently, we conclude that vegetation succession around Lake Gonghai exhibited a nonlagged response to climate change during the YD. This result confirms that a previous pollen‐based quantitative regional precipitation record from Lake Gonghai reliably depicts variations in the East Asian summer monsoon (EASM), especially its decreasing trend during the YD. This conclusion differs from that of related research on the Baxie loess section and Hani peat deposits. Also, we suggest that our findings provide an improved understanding of the likely response of the EASM during cooling intervals and that the YD is a useful analog for studying the response of vegetation to possible abrupt cooling events under future global warming scenarios.