Younger Dryas Termination Research Articles

Speleothem records from western Thailand indicate an early rapid shift of the Indian summer monsoon during the Younger Dryas termination

Mainland Southeast Asia experiences complex and variable hydroclimatic conditions, mainly due to its location at the intersection of Asian monsoon subsystems. Predicting future changes requires an in-depth understanding of paleoclimatic conditions that is currently hindered by a paucity of records in some regions. In this paper, we present the first speleothem stable isotope records from western Thailand detailing the Bølling-Allerød interstadial, Younger Dryas termination, and early- to mid-Holocene period. We find evidence of higher precipitation during the Bølling-Allerød (14,321–12,824 years before present (1950: BP)) compared to a Younger Dryas termination that starts 11,702–11,674 BP, has a rapid shift centered on 11,660–11,641 BP, and ends 11,603–11,589 BP. In addition, our records show Holocene monsoon intensity peaking at 8250 BP or before, a multi-millennia delay from the Northern Hemisphere summer insolation peak, followed by a trend to drier conditions until at least 750 BP. Assessment of the timing of the Younger Dryas termination in paleoclimate records across Southeast Asia reveals an earlier shift of the Indian Summer Monsoon to global climate shifts when compared to East Asian Summer Monsoon records. The causes of this are currently unknown. Some potentially important aspects include: an Indian Summer Monsoon influence on East Asian Summer Monsoon strength via the Indian Ocean Dipole climate pattern, the role of the Tibetan Plateau in monsoon dynamics, and exposure of the Sundaland shoreline. More high-resolution paleoclimate records, especially on the pathway of Indian Summer Monsoon to East Asian Summer Monsoon, are required for further discussion on the mechanisms controlling the differences between climate regimes.

Northern high-latitude sea ice variation linked with East Asian monsoon anomalies during the Younger Dryas

The abrupt weakening of the East Asian summer monsoon (EASM) during Younger Dryas (YD) has been attributed to freshwater discharge into the North Atlantic ocean and resultant Northern Hemisphere cooling. Recent studies have found that sea ice variability in the Nordic Sea during the YD exerted a great influence upon the northern high-latitude climate. However, the influence of sea ice upon EASM evolution during YD event remains unclear. In this paper, we report two precisely-dated speleothem oxygen isotope records from the EASM-dominated region of central China. Our records archive abrupt changes in EASM variability during the YD event. Initially, there was a significant strengthening of the EASM during the mid-YD following the gradually increased Atlantic meridional overturning circulation (AMOC). Later this trend reversed at ∼12.15 ka due to northern high-latitude sea ice fluctuations and a consequent reduction of AMOC. At the YD termination, abrupt intensification of the EASM was synchronous with the rapid decline of sea-ice and recovery of the AMOC indicating that sea ice variability was a significant influence on high latitude climate and EASM variation during the YD.

Early Holocene permafrost retreat in West Siberia amplified by reorganization of westerly wind systems

Rapid permafrost degradation and peatland expansion occurred in Eurasia during the Early Holocene and may be analogous to the region’s response to anthropogenic warming. Here we present a 230Th-dated, multiproxy speleothem record with subdecadal sampling resolution from Kyok-Tash Cave, at the modern permafrost margin in the northern Altai Mountains, southwestern Siberia. Stalagmite K4, covering the period 11,400 to 8,900 years before present, indicates an absence of stable permafrost within three centuries of the Younger Dryas termination. Between 11,400 and 10,400 years ago, speleothem δ18O is antiphased between the Altai and Ural ranges, suggesting a reorganization of the westerly wind systems that led to warmer and wetter winters over West Siberia and Altai, relative to the zonally adjacent regions of Northern Eurasia. At the same time, there is evidence of peak permafrost degradation and peatland expansion in West Siberia, consistent with the interpreted climate anomaly. Based on these findings, we suggest that modern permafrost in Eurasia is sensitive to feedbacks in the ocean-cryosphere system, which are projected to alter circulation regimes over the continent.

New insights into lake responses to rapid climate change: the Younger Dryas in Lake Gościąż, central Poland

The sediment profile from Lake Gościąż in central Poland comprises a continuous, seasonally resolved and exceptionally well‐preserved archive of the Younger Dryas (YD) climate variation. This provides a unique opportunity for detailed investigation of lake system responses during periods of rapid climate cooling (YD onset) and warming (YD termination). The new varve record of Lake Gościąż presented here spans 1662 years from the late Allerød (AL) to the early Preboreal (PB). Microscopic varve counting provides an independent chronology with a YD duration of 1149+14/–22 years, which confirms previous results of 1140±40 years. We link stable oxygen isotopes and chironomid‐based air temperature reconstructions with the response of various geochemical and varve microfacies proxies especially focusing on the onset and termination of the YD. Cooling at the YD onset lasted ~180 years, which is about a century longer than the terminal warming that was completed in ~70 years. During the AL/YD transition, environmental proxy data lagged the onset of cooling by ~90 years and revealed an increase of lake productivity and internal lake re‐suspension as well as slightly higher detrital sediment input. In contrast, rapid warming and environmental changes during the YD/PB transition occurred simultaneously. However, initial changes such as declining diatom deposition and detrital input occurred already a few centuries before the rapid warming at the YD/PB transition. These environmental changes likely reflect a gradual increase in summer air temperatures already during the YD. Our data indicate complex and differing environmental responses to the major climate changes related to the YD, which involve different proxy sensitivities and threshold processes.

Vegetation responses to the warming at the Younger Dryas-Holocene transition in the Hengduan Mountains, southwestern China

The Younger Dryas (YD) is one of the most abrupt climatic events in Earth's recent history. The warming at the end of the YD, in particular, is considered to be comparable to the global warming seen in the 21st century. However, the YD termination has received little attention, particularly in the Hengduan Mountains of Southwestern China, a low latitude temperate biodiversity hotspot. Here we present evidence for a rapid response in the diversity and composition of vegetation to the warming at the YD termination, based on a continuous, well-dated pollen sequence and loss-on-ignition data (12.9–9.2 cal. ka BP) from Haligu wetland in the Hengduan Mountains. Our data indicate that variations in plant diversity were correlated with relative humidity during this period, and suggest a distinct shift from Pinus-Abies-Picea forest to Pinus-dominated forest at the YD-Holocene transition, accompanied by an increase in coverage of generally temperate taxa such as Salix and Betula. This finding provides insights that may be of relevance to biodiversity conservation under future warming scenarios in similar mountain ecosystems worldwide.

Temperature variations in the southern Great Lakes during the last deglaciation: Comparison between pollen and GDGT proxies

Our understanding of deglacial climate history in the southern Great Lakes region of the United States is primarily based upon fossil pollen data, with few independent and multi-proxy climate reconstructions. Here we introduce a new, well-dated fossil pollen record from Stotzel-Leis, OH, and a new deglacial temperature record based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) at Silver Lake, OH. We compare these new data to previously published records and to a regional stack of pollen-based temperature reconstructions from Stotzel-Leis, Silver Lake, and three other well-dated sites. The new and previously published pollen records at Stotzel-Leis are similar, but our new age model brings vegetation events into closer alignment with known climatic events such as the Younger Dryas (YD). brGDGT-inferred temperatures correlate strongly with pollen-based regional temperature reconstructions, with the strongest correlation obtained for a global soil-based brGDGT calibration (r2 = 0.88), lending confidence to the deglacial reconstructions and the use of brGDGT and regional pollen stacks as paleotemperature proxies in eastern North America. However, individual pollen records show large differences in timing, rates, and amplitudes of inferred temperature change, indicating caution with paleoclimatic inferences based on single-site pollen records. From 16.0 to 10.0ka, both proxies indicate that regional temperatures rose by ∼10 °C, roughly double the ∼5 °C estimates for the Northern Hemisphere reported in prior syntheses. Change-point analysis of the pollen stack shows accelerated warming at 14.0 ± 1.2ka, cooling at 12.6 ± 0.4ka, and warming from 11.6 ± 0.5ka into the Holocene. The timing of Bølling-Allerød (B-A) warming and YD onset in our records lag by ∼300–500 years those reported in syntheses of temperature records from the northern mid-latitudes. This discrepancy is too large to be attributed to uncertainties in radiocarbon dating, and correlation between pollen and brGDGT temperature reconstructions rules out vegetation lags as a cause. However, the YD termination appears synchronous among the brGDGT record, regional pollen stack, and Northern Hemisphere stack. The cause of the larger and lagged temperature changes in the southern Great Lakes relative to Northern Hemisphere averages remains unclear, but may be due to the effects of continentality and ice sheet extent on regional climate evolution.

Heinrich 0 on the east Canadian margin: Source, distribution, and timing

The last deglaciation was marked by intervals of rapid climatic fluctuations accompanied by glacial advances and retreats along the eastern margin of the Laurentide Ice Sheet. One of these climatic events, the Younger Dryas cold reversal, was accompanied by a detrital carbonate event referred to as “Heinrich event 0” (H0) that deposited ice-rafted debris and especially detrital carbonate-rich (DC) sediment layers in the western and southern Labrador Sea. The precise age, duration, source, and geographical distribution of the H0 DC event, however, are not entirely clear. A high-sedimentation rate sequence cored off southern Newfoundland yielded an age of ~11.5–11.3 calibrated kyr B.P. for this layer, thus pointing to its deposition directly following the Younger Dryas termination, likely associated with rapid ice retreat and warming at the onset of the Holocene. At the study site, the H0 layer contains increased concentrations of detrital carbonates (calcite/dolomite ratio ~ 2.5:1) and a mature biomarker composition, similar to that found in Heinrich Layers 1, 2, 4, and 5, which together suggest an origin from Hudson Strait. Grain size analysis indicates that the H0-sediments were transported to the study site mostly through shallow plumes along the Labrador Shelf, with some hyperpycnal dispersal, deeper, along the slope and rise. Our data thus point to a large meltwater release caused by retreat of the ice margin in the Hudson Strait area. The relvatively short duration of the H0 layer, and its timing right after a major climatic transition, combined with its ubiquitous regional occurrence makes it valuable for correlating different sediment records from the western Labrador Sea.

Holocene oceanographic changes in SW Labrador Sea, off Newfoundland

Benthic foraminiferal assemblages supported by selected geochemical data from three marine sediment cores collected in Placentia Bay, SE Newfoundland, are used to construct an ~13,000-year-long record of regional oceanographic changes in the SW Labrador Sea. The area is located in the boundary zone between the cold, ice-loaded Labrador Current (LC) in the north and the warm Gulf Stream (GS) waters to the south. After the Younger Dryas termination, the influence of GS-derived water increased and was further strengthened at 10.7 cal. kyr BP through enhanced northward flow of Atlantic water via the Slopewater Current. A short-term event of increased terrestrial input and water column stratification at 8.4 cal. kyr BP was likely linked to the distal drainage of glacial Lake Agassiz. After 7.3 cal. kyr BP, a stronger LC weakened the inflow of warmer subsurface waters from the GS. This may be explained by extensive meltwater release from ice sheets in Arctic Canada and is concurrent with a general shift in oceanographic conditions in the Labrador Sea region. Around 4.0 cal. kyr BP, conditions became more stable with a slight increase in salinity, indicating a decrease in meltwater transported via the LC. The Northern Hemisphere neoglacial cooling around 2.8 cal. kyr BP was characterized off SE Newfoundland by a further stabilization of the current system, dominated by the LC with some continued influx of GS water.

A multi-proxy reconstruction of oceanographic conditions around the Younger Dryas–Holocene transition in Placentia Bay, Newfoundland

Abstract A marine sediment core from Placentia Bay off the south coast of Newfoundland was studied to reconstruct past oceanographic conditions based on a multiproxy approach, including diatoms, benthic foraminifera, grain size analysis, IP25, X-Ray fluorescence, calcium carbonate and total organic carbon content. Based on 6 radiocarbon dates, the 513.5 cm long core spans the age interval from ca. 13 to 10 cal kyrs BP and thus captures the transition from the Younger Dryas stadial into the Holocene at sub-decadal resolution. The Younger Dryas was characterized by cold Arctic water taxa of diatoms and benthic foraminifera and a stratified water column with high sea ice cover and low productivity due to strong influence of the Labrador Current. During the second half of the Younger Dryas, after ca. 12.2 cal kyrs BP, the influence of the Labrador Current gradually decreased and sea ice conditions became more variable. The transition towards the Holocene is characterized by a sequence of events starting with turnovers in the biogenic proxies followed by an abrupt retreat of sea ice and a rise in productivity. These events are believed to be related to a northward migration of the Gulf Stream–Labrador Current oceanic front. The Younger Dryas termination is directly followed by a detrital carbonate layer associated with the final phase of the Heinrich 0 event, linked to Laurentide Ice Sheet dynamics. During the early Holocene productivity remained high, with minimal sea ice cover, reduced stratification and stronger influence of warmer, Gulf Stream-derived waters.

Ocean lead at the termination of the Younger Dryas cold spell

The Younger Dryas (YD) cold interval is one of the most abrupt climate events of Earth’s recent history. The origin of this rapid, severe cooling episode is still widely debated, but it was probably triggered by a large freshwater influx to the North Atlantic resulting in disruption of the Atlantic Meridional Overturning Circulation. The YD termination, despite having been even more abrupt than the onset has, however, received significantly less attention. Here using multi-proxy data from a high-resolution marine sediment record, we present evidence for a gradual decrease of the Labrador Current influence, northward migration of the Gulf Stream oceanic front and a rapid decline of sea-ice cover at the YD termination. Our data indicate a stepwise sequence of events with changes in ocean circulation clearly preceding those in atmospheric conditions, in contrast to the hitherto commonly assumed single-event rapid climatic shift at the YD–Holocene transition.

Enrichment in <sup>13</sup>C of atmospheric CH<sub>4</sub> during the Younger Dryas termination

Abstract. The abrupt warming across the Younger Dryas termination (~11 600 yr before present) was marked by a large increase in the global atmospheric methane mixing ratio. The debate over sources responsible for the rise in methane centers on the roles of global wetlands, marine gas hydrates, and thermokarst lakes. We present a new, higher-precision methane stable carbon isotope ratio (δ13CH4) dataset from ice sampled at Påkitsoq, Greenland that shows distinct 13C-enrichment associated with this rise. We investigate the validity of this finding in face of known anomalous methane concentrations that occur at Påkitsoq. Comparison with previously published datasets to determine the robustness of our results indicates a similar trend in ice from both an Antarctic ice core and previously published Påkitsoq data measured using four different extraction and analytical techniques. The δ13CH4 trend suggests that 13C-enriched CH4 sources played an important role in the concentration increase. In a first attempt at quantifying the various contributions from our data, we apply a methane triple mass balance of stable carbon and hydrogen isotope ratios and radiocarbon. The mass balance results suggest biomass burning (42–66% of total methane flux increase) and thermokarst lakes (27–59%) as the dominant contributing sources. Given the high uncertainty and low temporal resolution of the 14CH4 dataset used in the triple mass balance, we also performed a mass balance test using just δ13C and δD. These results further support biomass burning as a dominant source, but do not allow distinguishing of thermokarst lake contributions from boreal wetlands, aerobic plant methane, or termites. Our results in both mass balance tests do not suggest as large a role for tropical wetlands or marine gas hydrates as commonly proposed.

Seasonal resolution of Eastern Mediterranean climate change since 34 ka from a Soreq Cave speleothem

The combination of ion microprobe analysis of δ18O and confocal laser fluorescent microscope imaging of annual growth bands in a Soreq Cave speleothem provides sub-annual-scale climate information between 34 and 4ka. This high-resolution methodology is ideal both for comparing seasonal climate patterns across broad windows of time and examining rapid climate events, such as the Younger Dryas termination, in detail. The sub-annual δ18O gradients we report represent a combination of seasonal variability in rainfall amount and air temperature. A distinct change in both the pattern of fluorescent banding and the gradient of δ18O measured in situ across single, annual growth bands indicates a change in seasonal climate patterns of the Eastern Mediterranean region following Heinrich event 1 and again after the Younger Dryas. Throughout the Holocene, wet winters and dry summers characterized regional climate. During the Younger Dryas, we find that regional climate may have been more arid than in the Holocene, but the fluorescent banding pattern indicates that the supply of dripwater to the cave was more consistent year-round. We suggest that a reduced gradient of seasonal precipitation, occasional snowfall, and vegetation differences may have all contributed to the isotope and fluorescent banding patterns observed during Heinrich event 1 and the last glacial stadial. Detailed investigation of the Younger Dryas termination reveals a rapid onset of regional environmental change. Fluorescent band counting indicates that the Younger Dryas termination, as recorded by rainfall in the Eastern Mediterranean, spanned a minimum of 12years.

Radiocarbon dates as data: quantitative strategies for estimating colonization front speeds and event densities

Archaeological analysis of large-scale prehistoric population history requires us to estimate rates of spatial spread during dispersals, and rates and magnitudes of temporal contraction during crashes. Using OxCal’s MCMC sampling routine, I introduce and demonstrate a simple and easily implemented method of estimating front speeds that takes due account of the uncertainty in the archaeological data (in both dates and distances), and argue that this method is more appropriate than those most often used in front speed estimation at present. I also propose a simple and easily implemented method of estimating event densities as a demographic proxy, as an alternative to summed calibrated probability distributions. I argue that this alternative is a significantly better technique, and show that its use also enables us to identify individual archaeological dates that are exerting particularly strong influence on the results, so that we can efficiently allocate our attention when assessing the possible effects of exogenous sampling uncertainty. To illustrate these methods I re-analyse two published datasets relating to the early Paleoindian colonization of North America. My results with the new technique indicate that even with a very noisy dataset, there was clear evidence in the framework of the INTCAL04 calibration curve for a drastic reduction in archaeological event densities following the Younger Dryas onset, followed by a prolonged period of reduced human activity, and a possible renewed phase of rapid growth after the Younger Dryas termination and onset of the Holocene. However, the revised estimate of the Younger Dryas marine reservoir offset in the INTCAL09 calibration curve for ∼12,550–12,900 cal BP changes the picture significantly, by flattening the peak in Clovis-age events and pushing it forward in time into the early Younger Dryas itself.

A synchronized dating of three Greenland ice cores throughout the Holocene

As part of the effort to create the new Greenland Ice Core Chronology 2005 (GICC05) a synchronized stratigraphical timescale for the Holocene parts of the DYE‐3, Greenland Ice Core Project (GRIP), and North Greenland Ice Core Project (NGRIP) ice cores is made by using volcanic reference horizons in electrical conductivity measurements to match the cores. The main annual layer counting is carried out on the most suited records only, exploiting that the three ice cores have been drilled at locations with different climatic conditions and differences in ice flow. However, supplemental counting on data from all cores has been performed between each set of reference horizons in order to verify the validity of the match. After the verification, the main dating is transferred to all records using the volcanic reference horizons as tie points. An assessment of the mean annual layer thickness in each core section confirms that the new synchronized dating is consistent for all three cores. The data used for the main annual layer counting of the past 7900 years are the DYE‐3, GRIP, and NGRIP stable isotope records. As the high accumulation rate at the DYE‐3 drill site makes the seasonal cycle in the DYE‐3 stable isotopes very resistant to firn diffusion, an effort has been made to extend the DYE‐3 Holocene record. The new synchronized dating relies heavily on this record of ∼75,000 stable isotope samples. The dating of the early Holocene consists of an already established part of GICC05 for GRIP and NGRIP which has now been transferred to the DYE‐3 core. GICC05 dates the Younger Dryas termination, as defined from deuterium excess, to 11,703 years before A. D. 2000 (b2k), 130 years earlier than the previous GRIP dating.

Paleo-environment and radiocarbon calibration as derived from Lateglacial/Early Holocene tree-ring chronologies

Abstract We present an overview of the extended Hohenheim oak chronology (HOC) and the dendrochronologically dated Preboreal pine tree-ring chronology (PPC). Both provide an absolute, annual time frame of the Holocene, extending into the Younger Dryas (YD) back to 11,919 BP. Two floating pine and larch chronologies are 14 C dated, covering large parts of the Lateglacial. Dendro-ecological parameters, such as ring width and stable isotope variation are used to infer past environmental conditions. 14 C analyses on decadal sections provide a high-precision, high-resolution data set for calibration of the radiocarbon time scale. Based on a marked change in ring-width and growth pattern, the YD termination is clearly identified in the German pine chronology. Its absolute age of 11,570 BP appears synchronous, within the errors of the respective chronologies, to related signals in the Greenland ice cores (GRIP, GISP2) and in lacustrine varve sequences. The 14 C age of the Laacher-See tephra (LST) is determined from a series of decadal tree-ring samples to 11,063±12 14 C BP; the calibrated range is 13,010–13,200 cal BP. The climatic impact of the LST is reflected in the growth pattern of our tree ring chronologies.

The Younger Dryas Termination and North Atlantic Deep Water Formation: Insights from climate model simulations and Greenland Ice Cores

Results from the GISP2 and GRIP ice cores show that the termination of the Younger Dryas (YD) climate event in Greenland was a large and extremely fast climate change. A reinitiation of North Atlantic Deep Water formation following a shutdown, and its associated winter release of heat to the atmosphere, has been suggested as the most likely cause of this climate transition. To test this idea, two general circulation model experiments using GENESIS have been completed for YD time (12,000 calendar years ago): one with low heat flux in the Nordic Seas (10 W/m², deep water shutdown) and one with high Nordic Sea heat flux (300 W/m², active deep water formation). Comparison of Greenland climate differences between these experiments with the ice core records shows that when deep water is turned on, much of the YD termination warming is achieved. The increase in precipitation is underestimated because of a model tendency to overestimate summertime precipitation, which obscures the dominantly wintertime response to the specified forcing. The winter storm track shift toward Greenland contributes much of the climate change at the YD termination.