A global paleoclimate observing system

Chloride tracer of the loess unsaturated zone under sub-humid region: A potential proxy recording high-resolution hydroclimate

A high-resolution hydroclimate archive is critical to understanding the past changes, but such hydroclimatic reconstructions are extremely limited. Our study aims to examine the potential of the chloride tracer (Cl) within unsaturated zone (USZ) to reconstruct high-resolution hydroclimate records. We investigated a representative sub-humid monsoon area of the Chinese Loess highland, where piston flow recharge dominates and a constant rate of Cl input occurs. We successfully reconstructed a 1007-yr hydroclimate record with a 2-yr sampling resolution using a 95-m USZ Cl profile. Excluding the recycling and mixing zone, and the groundwater affecting zone, six relatively humid phases and five relatively dry phases were discernible. The uncertainty in the time of wet/dry phase decreases as the accumulated time increases, and the minimal recharge uncertainty is 16% over a 10-yr time scale. The reconstructed hydroclimate record from the semi-humid region has a much higher resolution than that of the arid zones, likely because the semi-humid, fine-grained thick USZ, possesses higher velocity piston flow, relatively to diffusion and dispersion of Cl signals. The record compared well with other related records, suggesting that the Cl proxy can be used in sub-humid areas, and is sensitive to wet/dry alternations that are largely driven by the Asian monsoon intensity. To the best of our knowledge, this is the first investigation of the USZ Cl to hydroclimatic reconstruction in a non-arid region. The high-resolution hydroclimate record may deepen our understanding of the hydrological process in the deep USZ, past climate and water resources, and promote developments of the hydropedology and global change science.

Survival of Igα-Deficient Mature B Cells Requires BAFF-R Function

Expression of a functional BCR is essential for the development of mature B cells and has been invoked in the control of their maintenance. To test this maintenance function in a new experimental setting, we used the tamoxifen-inducible mb1-CreER(T2) mouse strain to delete or truncate either the mb-1 gene encoding the BCR signaling subunit Igα or the VDJ segment of the IgH (H chain [HC]). In this system, Cre-mediated deletion of the mb-1 gene is accompanied by expression of a GFP reporter. We found that, although the Igα-deficient mature B cells survive for >20 d in vivo, the HC-deficient or Igα tail-truncated B cell population is short-lived, with the HC-deficient cells displaying signs of an unfolded protein response. We also show that Igα-deficient B cells still respond to the prosurvival factor BAFF in culture and require BAFF-R signaling for their in vivo maintenance. These results suggest that, under certain conditions, the loss of the BCR can be tolerated by mature B cells for some time, whereas HC-deficient B cells, potentially generated by aberrant somatic mutations in the germinal center, are rapidly eliminated.

Role of multidecadal climate variability in a range extension of pinyon pine

Evidence from woodrat middens and tree rings at Dutch John Mountain (DJM) in northeastern Utah reveal spatiotemporal patterns of pinyon pine (Pinus edulis Engelm.) colonization and expansion in the past millennium. The DJM population, a northern outpost of pinyon, was established by long-distance dispersal (approximately 40 km). Growth of this isolate was markedly episodic and tracked multidecadal variability in precipitation. Initial colonization occurred by AD 1246, but expansion was forestalled by catastrophic drought (1250-1288), which we speculate produced extensive mortality of Utah Juniper (Juniperus osteosperma (Torr.) Little), the dominant tree at DJM for the previous approximately 8700 years. Pinyon then quickly replaced juniper across DJM during a few wet decades (1330-1339 and 1368-1377). Such alternating decadal-scale droughts and pluvial events play a key role in structuring plant communities at the landscape to regional level. These decadal-length precipitation anomalies tend to be regionally coherent and can synchronize physical and biological processes across large areas. Vegetation forecast models must incorporate these temporal and geographic aspects of climate variability to accurately predict the effects of future climate change.

Climate change in the North Pacific region over the past three centuries

The relatively short length of most instrumental climate records restricts the study of climate variability, and it is therefore essential to extend the record into the past with the help of proxy data. Only since the late 1940s have atmospheric data been available that are sufficient in quality and spatial resolution to identify the dominant patterns of climate variability, such as the Pacific North America pattern and the Pacific Decadal Oscillation. Here we present a 301-year snow accumulation record from an ice core at a height of 5,340 m above sea level-from Mount Logan, in northwestern North America. This record shows features that are closely linked with the Pacific North America pattern for the period of instrumental data availability. Our record extends back in time to cover the period from the closing stages of the Little Ice Age to the warmest decade in the past millennium. We find a positive, accelerating trend in snow accumulation after the middle of the nineteenth century. This trend is paralleled by a warming over northwestern North America which has been associated with secular changes in both the Pacific North America pattern and the Pacific Decadal Oscillation.