Science : Ancient trash mounds and Byzantine collapse

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The FINANCIAL — Archaeological evidence for the role of climate in the decline of the Byzantine Empire during the sixth and seventh centuries CE is sparse. Guy Bar-Oz et al. used ancient trash mounds to document urban decline in the Byzantine settlement of Elusa in the Negev Desert of the southern Levant.

The presence of organized large-scale trash disposal serves as a proxy for high-level urban functioning. Excavation and sediment analysis of four mounds surrounding the ancient settlement revealed that the mounds consisted largely of refuse from domestic fire installations and construction debris.

The authors recovered an abundance of ceramic sherds from the Early and Middle Byzantine Periods, around 350–550 CE, and significantly fewer sherds from earlier or later periods.

Carbon dating of seeds and charcoal yielded no dates later than the mid-sixth century CE. The results suggest that organized trash disposal at Elusa ended and the decline of the settlement began around the mid-sixth century, approximately one century before the Islamic conquest ended Byzantine control over the region.

The end of organized trash removal coincides with other evidence for Byzantine urban upheaval, the beginning of the Late Antique Little Ice Age climate event, and the outbreak of the Plague of Justinian, suggesting a link between climate change and Byzantine decline, according to the authors.

Biodiversity changes in the Early Paleozoic Era

Marine biodiversity underwent large and abrupt changes during the Early Paleozoic Era. However, the temporal resolution of current Paleozoic biodiversity estimates is insufficient to attribute these changes to potential environmental causes. Christian Rasmussen et al. constructed a high-resolution reconstruction of genus-level biodiversity during the first 120 million years of the Paleozoic Era based on fossil occurrences from a paleobiology database.

The reconstruction exhibited two distinct bursts of biodiversity accumulation corresponding to the Cambrian Explosion and the Great Ordovician Biodiversification Event (GOBE), separated by 50 million years of slow accumulation. The rapid onset of the latter coincided with equatorial sea-surface temperatures falling to present-day levels, suggesting that 470 million years ago, marine biodiversity required a narrow temperature window. Fifteen million years after the start the GOBE, diversity declined sharply in three successive phases corresponding to the end Ordovician mass extinctions, after which biodiversity did not rebound for tens of millions of years. The mass extinctions were associated with the formation of large igneous provinces and abrupt increases in 13C enrichment, consistent with increased volcanic activity. The results suggest that the end Ordovician extinctions may have begun several million years earlier than previously thought, were triggered by increased volcanism, and had a longer lasting impact on global diversity than recognized, according to the authors.

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Migratory routes of prehistoric baleen whales

Baleen whales tend to feed in cool, high-latitude waters during summer before returning to warm waters to breed in winter, and researchers have hypothesized that migration is integral to the evolution of baleen whales. Although fossil records of baleen whales’ migration history are limited, whale barnacles can provide a record of the whales’ migration cycles by preserving the oxygen isotopic (δ18O) signature of the whales’ movements. Larry Taylor et al. compared the oxygen isotope composition of modern whale barnacle shells from Alaska and California to fossilized Pleistocene-age barnacle shells from California and Panama. Both the prehistoric and modern specimens exhibited δ18O profiles with a wide range of values, indicating time spent in varied waters, as well as a continuous progression between the 18O-enriched and 18O-depleted values, suggesting that barnacles grow throughout the whales’ migration. The δ18O profiles of the fossil barnacles exhibited signatures of a summer feeding season and winter breeding season, mirroring the migration patterns of the modern specimens. The findings suggest that baleen whale migration patterns have been similar for hundreds of millennia, and that the Pacific coast of Panama has served as a meeting point for several whale subpopulations for at least 270,000 years, according to the authors.

Whitefly manipulation of plant odor signals

Whiteflies are major invasive crop pests. Upon infestation by whiteflies, plants mobilize salicylic acid-dependent defenses, which target pathogens, while suppressing jasmonic acid-dependent defenses, rendering the plants susceptible to insects. Peng-Jun Zhang et al. demonstrate that such host–plant manipulation extends to neighboring plants through airborne signals.

Using interconnected glass chambers, the authors exposed healthy tomato plants to volatiles released by other plants that were either uninfested or infested by whiteflies. Compared with plants that had been exposed to volatiles from uninfested plants, plants that had been exposed to volatiles from infested plants were more susceptible to whiteflies.

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Exposure to airborne signals from infested plants helped accelerate the development of whitefly nymphs and suppressed the production of jasmonic acid, while increasing salicylic acid levels in response to whitefly infestation. Together, the findings suggest that whitefly-infested plants release volatiles that prime a defense against pathogens in neighboring plants, at the cost of defenses against insect herbivores, making the neighboring plants more suitable for whitefly development. According to the authors, the ability of whiteflies to manipulate plant defense responses through induced volatile emissions might explain the rapid spread of whiteflies, and the findings could help develop effective control strategies.

Sustainability Science; Environmental Sciences
Canopies, impervious surfaces, and urban heat

The urban heat island effect causes increased temperatures in urban environments compared with surrounding areas, with potential human health consequences.

As the climate warms, cities explore strategies to mitigate heat. Carly Ziter et al. examined the relationship between canopy cover, which reduces heat, and impervious surface cover, which increases heat, on urban air temperature in Madison, Wisconsin.

In the summer of 2016, the authors used a bicycle-mounted sensor to repeatedly sample the air temperature approximately every 5 m along 10 urban transects during the day, as well as four transects at night, spanning gradients of both impervious and canopy cover. Daytime temperature decreased nonlinearly with increasing canopy cover, with the greatest cooling occurring when canopy cover was more than 40% and at the scale of a typical city block (60–90 m).

However, canopy cover exhibited limited cooling at night, whereas air temperatures increased with the amount of impervious surfaces both during the day and at night. The results suggest that effective urban heat mitigation requires efforts to both increase urban canopy cover and decrease impervious surface cover, according to the authors.

Source: National Academy of Sciences of the United States of America


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