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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. • A new speleothem δ18O record show significant EASM strengthening during mid-YD. • Mid-YD oscillation in EASM linked with NH sea ice variability. • Abrupt EASM intensification at YD termination synchronous with the rapid decline of sea ice. • Drier interval following the YD termination in central China. [ABSTRACT FROM AUTHOR]

Identification of Holocene climate events, their temporal and spatial characteristics, and their causal mechanisms are important for understanding past climate systems with implications for interpreting ancient cultural transformations. In this paper, we analyse globally-distributed, high-resolution climate proxy records from 58 sites to develop a comprehensive understanding of climate change around 7.2 ka BP. Analysis of the data compilation, which comprises records from lake sediments, one loess section, speleothems, marine sediments, and ice cores, show that the climate event is manifested as a weakening of the Asian summer monsoon and a strengthening of the South American summer monsoon. Climate change also involves dramatic cooling and wetter conditions in north-central Europe, widespread aridity across the Africa and west-south North America, contrasting patterns of precipitation variability throughout the Mediterranean, and notable cooling over the polar regions, suggesting that this is a global climate event. A close correspondence between the 7.2 ka event and the timing of solar irradiance minima, strong volcanic eruptions, meltwater flux into the North Atlantic Ocean, and an orbitally-induced decrease in summer solar insolation suggests a possible causal link with these phenomena. We suggest that climate anomalies around 7.2 ka BP may be specifically explained as a response to southward migration of the Intertropical Convergence Zone, onset of an increasingly El Niño-like state, reinforcement of the westerlies, and slowing of the Atlantic Meridional Overturning Circulation (AMOC). • The 7.2 ka event is well represented in 58 paleoclimatic records from the global. • Varying climatic responses are evidenced in different regions during 7.6–7.0 ka BP. • The 7.2 ka event arise of the atmosphere–ocean–land feedback in response to four forcing factors. [ABSTRACT FROM AUTHOR]

Abstract: The global oceanographic impact of large volumes of freshwater entering the Arctic Ocean from North America during Laurentide Ice Sheet deglaciation is the subject of much discussion. The model of lateglacial runoff-forced changes in ocean thermohaline circulation (THC) is constrained in part due to a lack of detailed study of the relevant terrestrial glacial sedimentary and geomorphic record. This paper reports and interprets sedimentary facies that accumulated in the former glacial Lake Mackenzie, which formed a long (~600 km) and deep (max: 200 m) lateglacial basin ponded along the lower Mackenzie Valley in Canada''s Northwest Territories. This is a key study area because the lake was dammed between approximately 10,500 14C yr bp and 9100 14C yr bp when most of the runoff from glacial Lake Agassiz was routed northward through the Mackenzie Valley to the Arctic Ocean. Detailed outcrop descriptions and geomorphic mapping in the glacial Lake Mackenzie basin fails to identify a clear record of abrupt shortlived flood outbursts but a regionally extensive deposit of massive and laminated mud at least 55 m thick, records trapping of large volumes of suspended fine sediment. Recent work shows the importance of suspended sediment content in freshwater runoff in influencing THC; too much sediment and freshwater enters the ocean hyperpycnally with little effect on surface waters. The role of Lake Mackenzie may have been to trap suspended sediment that otherwise would have been released to the Arctic Ocean, thereby acting to increase the effect of freshwater runoff on thermohaline circulation. [Copyright &y& Elsevier]

Palaeo-oceanographical archives in the Mediterranean Sea indicate the occurrence of Sapropel depositions, which are characteristic of anoxic bottom conditions and of a stratified sea. The impact of such drastic changes in the thermohaline circulation of the Mediterranean Sea on the large-scale circulations in the North Atlantic basin is not fully understood. Here we evaluate the impact of a direct perturbation of the Mediterranean Sea circulation through different idealized simulations with freshwater release rates of 20, 50, 100, and 200 mSv (1 mSv = 103 m3/s), using a the IPSL-CM5A-LR global coupled atmosphere-ocean model, with simulations up to 1000 years long. The simulations are compared to available data for the Mediterranean Sea and the North Atlantic. The Neodymium isotopic composition (ε Nd) anomalies in the North Atlantic are clearly dependent on the rate of fresh water release in the Mediterranean Sea, and subsequent modification of Atlantic meridional overturning circulation (AMOC) intensity and subpolar gyre (SPG) extension. Based on comparison with seawater ε Nd records from Rockall Trough, we suggest that a limited release of freshwater around 50 mSv may be more representative of hydrological conditions of the Mediterranean Sea during the Sapropel S1 deposition. Our results indicate that a decrease in Mediterranean overflow was clearly a factor in the intensification of upper AMOC following the Early Holocene period, when a large eastward expansion of the subpolar gyre is simulated. Also, eastward expansion of the subpolar gyre due to freshwater release in the Mediterranean (e.g. Sapropel-like events) and its impact on the ε Nd signature highlight the fact that the modification of ocean circulation in the North Atlantic basin might be more complex than a straightforward change in the AMOC, since there may also be a large impact on barotropic circulation. The simulations also produce a significant decrease in the ε Nd values of the Iceland-Scotland Overflow Water (between −3.5 and − 1.3 ε Nd unit), which is consistent with changes observed during the S1 event in the reconstructions. Thus the 3-dimensional changes in baroclinic and barotropic circulations of the ocean, as reconstructed in some ε Nd records, are broadly consistent with the sensitivity simulations performed, and might thus be partly related to changes in Mediterranean overflow, which would have contributed to modification of the Atlantic Ocean circulation following a complex 3-dimensional pattern that is detailed in the paper. • A new multi-centennial simulation of εNd distribution from the IPSL-CM5 models. • Impact of a freshening of the Mediterranean on the εNd distribution in the North Atlantic basin. • Potential impact of a Sapropel-like event on the εNd distribution in the North Atlantic basin. • Evidence of a link between millennial variations of AMOC and the MOW during Holocene. • The eastward extension of the SPG may lead to an important decrease in εNd of ISOW. [ABSTRACT FROM AUTHOR]