Distinct impacts of major El Niño events on Arctic temperatures due to differences in eastern tropical Pacific sea surface temperatures.

The El Niño Southern Oscillation (ENSO) is a climate mode in the tropical Pacific. The ENSO teleconnections are known to affect Arctic temperature; however, the robustness of this relationship remains debated. We find that Arctic surface temperatures during three major El Niño events are remarkably well simulated by a state-of-the-art model when nudged to the observed pantropical sea surface temperatures (SSTs). SST perturbation experiments show that the 1982-1983 warm pan-Arctic and the 1997-1998 cold pan-Arctic during winter can be explained by far eastern equatorial Pacific SSTs being higher during 1997-1998 than 1982-1983. Consistently, during the 2017-2018 La Niña, unusually low SSTs in the same region contributed to pan-Arctic warming. These pan-Arctic responses to the SSTs are realized through latent heating anomalies over the western and eastern tropical Pacific. These results highlight the importance of accurately representing SST amplitude and pattern for Arctic climate predictions.

Mid-Holocene Northern Hemisphere warming driven by Arctic amplification.

The Holocene thermal maximum was characterized by strong summer solar heating that substantially increased the summertime temperature relative to preindustrial climate. However, the summer warming was compensated by weaker winter insolation, and the annual mean temperature of the Holocene thermal maximum remains ambiguous. Using multimodel mid-Holocene simulations, we show that the annual mean Northern Hemisphere temperature is strongly correlated with the degree of Arctic amplification and sea ice loss. Additional model experiments show that the summer Arctic sea ice loss persists into winter and increases the mid- and high-latitude temperatures. These results are evaluated against four proxy datasets to verify that the annual mean northern high-latitude temperature during the mid-Holocene was warmer than the preindustrial climate, because of the seasonally rectified temperature increase driven by the Arctic amplification. This study offers a resolution to the "Holocene temperature conundrum", a well-known discrepancy between paleo-proxies and climate model simulations of Holocene thermal maximum.

Assessment of Zn pollution sources and apportionment in agricultural soils impacted by a Zn smelter in South Korea.

This study was conducted to assess the anthropogenic impact on the metal concentration in agricultural soils in the vicinity of a Zn smelter. We determined Pb isotope ratios to trace source of metals and calculate source apportionment. 19.7% of the agricultural soil samples had Zn concentrations exceeding the Korean worrisome level (WL). The isotopic variation in the contaminated agricultural soils reflected the input of contaminants derived from the Zn smelter. The spatial distribution of Zn concentrations and Pb isotopes suggested that the Zn smelter dust fallout was the major source of heavy metal pollution in the agricultural soils. Lead isotope compositions of soil horizon I was comparable to those of soil horizon II, indicating that smelter-origin Zn had migrated vertically. Binary mixing between Zn concentrates and background soils could explain the variations in Pb isotope ratios in the contaminated agricultural soils. Source apportionment calculations showed that for agricultural soils that were found to exceed the Korean countermeasure standard (CS), the average proportion of smelter-origin Zn was 45.8%-83.3% while for agricultural soils that exceeded the WL but were below the CS, the average proportion of smelter-origin Zn was 36.3%-68.1%. The remainder was derived from a geogenic source.

The impact of Arctic sea ice loss on mid-Holocene climate.

Mid-Holocene climate was characterized by strong summer solar heating that decreased Arctic sea ice cover. Motivated by recent studies identifying Arctic sea ice loss as a key driver of future climate change, we separate the influences of Arctic sea ice loss on mid-Holocene climate. By performing idealized climate model perturbation experiments, we show that Arctic sea ice loss causes zonally asymmetric surface temperature responses especially in winter: sea ice loss warms North America and the North Pacific, which would otherwise be much colder due to weaker winter insolation. In contrast, over East Asia, sea ice loss slightly decreases the temperature in early winter. These temperature responses are associated with the weakening of mid-high latitude westerlies and polar stratospheric warming. Sea ice loss also weakens the Atlantic meridional overturning circulation, although this weakening signal diminishes after 150-200 years of model integration. These results suggest that mid-Holocene climate changes should be interpreted in terms of both Arctic sea ice cover and insolation forcing.

Quantifying climate feedbacks in polar regions.

The concept of feedback is key in assessing whether a perturbation to a system is amplified or damped by mechanisms internal to the system. In polar regions, climate dynamics are controlled by both radiative and non-radiative interactions between the atmosphere, ocean, sea ice, ice sheets and land surfaces. Precisely quantifying polar feedbacks is required for a process-oriented evaluation of climate models, a clear understanding of the processes responsible for polar climate changes, and a reduction in uncertainty associated with model projections. This quantification can be performed using a simple and consistent approach that is valid for a wide range of feedbacks, offering the opportunity for more systematic feedback analyses and a better understanding of polar climate changes.

Microbial examination of nonheated foods served in feeding programs of elementary schools, Iksan City, Jeonbuk Province, Korea.

More than 90% of elementary school students in Korea have lunch provided by a school feeding program. This study examined nonheated foods, foods in which final ingredients were added after cooking ("heated/nonheated foods"), and desserts for microbial contamination levels and the presence of foodborne pathogens. We obtained a total of 77 food samples belonging to the above three groups from four elementary schools located in Iksan, Jeonbuk, Korea, from June to July 2010. Among the samples, 15% of nonheated foods and 9% of heated/nonheated foods contained > 6 log CFU of aerobic bacteria per g. Unacceptable coliform counts according to Korean national standards (3 log CFU/g) were also observed in 30, 4.5, and 26% of nonheated foods, heated/nonheated foods, and desserts, respectively. The foodborne pathogens Escherichia coli O157:H7, Bacillus cereus, and Cronobacter sakazakii were found in two, one, and two of the total samples, respectively. Detection of E. coli O157:H7 indicates a low level of safety in the school lunches served in Korean elementary schools. To improve food safety, hazard analysis critical control point guidelines should be applied to school food service establishments to lower the microbial risks in foods served to children.

Cronobacter sakazakii Infection Induced Fatal Clinical Sequels Including Meningitis in Neonatal ICR Mice.

Cronobacter sakazakii (C. sakazakii), formerly Enterobacter sakazakii, is an emerging pathogen associated with the ingestion of contaminated reconstituted formula that causes serious illnesses such as bacteremia, septicemia, necrotizing enterocolitis, meningitis and death in low-birth-weight preterm neonatal infants. The objective of this study was to develop an animal model for human neonatal C. sakazakii infections. We acquired timed-pregnant ICR mice and allowed them to give birth naturally. On postnatal day 3.5, each pup was administered orally a total dose of approximately 10(7) CFU C. sakazakii strain 3439. Mice were observed twice daily for morbidity and mortality. At postnatal day 10.5, the remaining pups were euthanized, and brain, liver, and cecum were excised and analyzed for the presence of C. sakazakii. C. sakazakii was isolated from cecum and other tissues in inoculated mice. In the tissues of C. sakazakii infected mice, meningitis and gliosis were detected in brain. In this study, we confirmed the neonatal ICR mice may be used a very effective animal model for human neonatal C. sakazakii infections.