Last Deglaciation Research Articles

Prokaryotes in the WAIS Divide ice core reflect source and transport changes between Last Glacial Maximum and the early Holocene.

We present the first long-term, highly resolved prokaryotic cell concentration record obtained from a polar ice core. This record, obtained from the West Antarctic Ice Sheet (WAIS) Divide (WD) ice core, spanned from the Last Glacial Maximum (LGM) to the early Holocene (EH) and showed distinct fluctuations in prokaryotic cell concentration coincident with major climatic states. The time series also revealed a ~1,500-year periodicity with greater amplitude during the Last Deglaciation (LDG). Higher prokaryotic cell concentration and lower variability occurred during the LGM and EH than during the LDG. A sevenfold decrease in prokaryotic cell concentration coincided with the LGM/LDG transition and the global 19 ka meltwater pulse. Statistical models revealed significant relationships between the prokaryotic cell record and tracers of both marine (sea-salt sodium [ssNa]) and burning emissions (black carbon [BC]). Collectively, these models, together with visual observations and methanosulfidic acid (MSA) measurements, indicated that the temporal variability in concentration of airborne prokaryotic cells reflected changes in marine/sea-ice regional environments of the WAIS. Our data revealed that variations in source and transport were the most likely processes producing the significant temporal variations in WD prokaryotic cell concentrations. This record provided strong evidence that airborne prokaryotic cell deposition differed during the LGM, LDG, and EH, and that these changes in cell densities could be explained by different environmental conditions during each of these climatic periods. Our observations provide the first ice-core time series evidence for a prokaryotic response to long-term climatic and environmental processes.

Phytolith records of the climate change since the past 15000 years in the middle reach of the Yangtze River in China

Based on 14C dating and core sediments survey, phytolith records are employed to reconstruct paleovegetation and paleoclimate in the Jianghan Plain in the middle reach of the Yangtze River. Phytoliths identified are assigned into 21 well-described morphotypes and divided into four groups (Poaceae, fern, coniferous and broad-leaved). The phytolith assemblages together with warmth index (Iw) are divided into 18 ecological zones, which reflect a complete vegetation history related to climate change in the middle reach of the Yangtze River during the past 15000 years. On the basis of the correlation of phytolith records with the paleoclimatic indicators from stalagmite, peatland, North Atlantic deep-sea sediments, Loess Plateau of Central China, and Arabic Sea sediments, eight climatic phases are identified included Last Glacial Maximum (LGM) (20–14.8 cal kaBP), Last Deglaciation (LDG) (14.8–11.9 cal kaBP), low-temperature phase in the Early Holocene (11.9–8 cal kaBP), Holocene Optimum (8–4.9 cal kaBP), Holocene Katathermal (4.9–1.1 cal kaBP), Medieval Warmth Period (MWP) (1.1–0.7 cal kaBP), Little Ice Age (LIA) (0.7–0.15 cal kaBP), and Modern Warming (0.15 cal kaBP — present). Climatic events such as Bolling-Allerod warm intervals, Older Dryas, Inter-Allerod Cold Period, and Younger Dryas, and eight Holocene Bond events (B1–8) have been identified since the LDG. Our results demonstrate that the evolution of the climate in the research area has a strong link with the Indian Summer Monsoon (SW Monsoon), Asian Summer Monsoon (SE Monsoon), and Holocene events in North Atlantic simultaneously, which might indicate that solar variability affects the Earth surface climate system at the centennial and millennial scales.

TERRA BOOKS

Book reviewed in this article:GEOLOGY AND TECTONICS OF THE KARAKORUM MOUNTAINS. Mike SearleTRACKING DINOSAURS. Martin LockleyTHE MECHANICS OF EARTHQUAKES AND FAULTING. Christopher H. ScholzTHE LAST DEGLACIATION: ABSOLUTE AND RADIOCARBON CHRONOLOGIES. E. Bardand and W. S. Broecker (eds)