The Holocene hydroclimate evolution and underlying mechanisms modulating the East Asian summer monsoon (EASM) remains controversial, especially in south eastern China. Here we present a multiproxy ...peat record of monsoon evolution from southeastern China covering the last 14 ka. Our new records show a relatively weaker EASM but wetter hydroclimate during the early (10 to 8 ka) and late Holocene (after 5.4 ka), while a stronger EASM and overall drier climate during the mid-Holocene (8 to 5.4 ka). In line with nearby speleothem records, our results reveal a dominant control of the northern-latitude ice-sheet meltwater forcing on millennial-scale East Asian hydroclimate variability during the last deglaciation and early Holocene. This dominant influence, however, likely waned once the global sea level had stabilized during the mid-to-late Holocene, giving way to other drivers of the monsoon and hydroclimate, including a combination of summer insolation and teleconnection patterns associated with vegetation-dust feedbacks.
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DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
The tropics are the major source of heat and moisture for the Australasian region. Determining the tropics' response over time to changes in climate forcing mechanisms, such as summer insolation, and ...the effects of relative sea level on exposed continental shelves during the Last Glacial period, is an ongoing process of re-evaluation. We present a synthesis of climate proxy data from tropical Australasia spanning the last 30,000 years that incorporates deep sea core, coral, speleothem, pollen, charcoal and terrestrial sedimentary records.
Today, seasonal variability is governed largely by the annual migration of the inter-tropical convergence zone (ITCZ), influencing this region most strongly during the austral summer. However, the position of the ITCZ has varied through time. Towards the end of Marine Isotope Stage (MIS) 3, conditions were far wetter throughout the region, becoming drier first in the south. Universally cooler land and sea-surface temperature (SST) were characteristic of the Last Glacial Maximum, with drier conditions than previously, although episodic wet periods are noted in the fluvial records of northern Australia. The deglacial period saw warming first in the Coral Sea and then the Indonesian seas, with a pause in this trend around the time of the Antarctic Cold Reversal (c. 14.5 ka), coincident with the flooding of the Sunda Shelf. Wetter conditions occurred first in Indonesia around 17 ka and northern Australia after 14 ka. The early Holocene saw a peak in marine SST to the northwest and northeast of Australia. Modern vegetation was first established on Indonesia, then progressively south and eastward to NE Australia. Flores and the Atherton Tablelands show a dry period around 11.6 ka, steadily becoming wetter through the early Holocene. The mid-late Holocene was punctuated by millennial-scale variability, associated with the El Niño-Southern Oscillation; this is evident in the marine, coral, speleothem and pollen records of the region.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Investigating the extent and climate implications of the mid-Holocene (MH - around 6000 years ago) is essential in better understanding the uncertainties associated with the ongoing and future ...projections of global warming. South America (SA) contains the biome with the largest biodiversity in the world, its population exceeds 400 million people, and its economy is mainly agricultural. Thus, studies involving South America's climate variability have become a subject of significant importance over the years. Paleoclimate archives provide unique indirect measurements, helping us to characterize past climates. However, the derived radiometric ages from several paleoarchives in SA published before the 2000s have not yet been calibrated, which represents a large source of uncertainty. In this article, we present a climate reconstruction for eastern SA during the MH with fully calibrated age models. We compiled 173 paleoclimate records, where 50 of them were calibrated in this study using Bayesian methods. Through this multiproxy approach and the elaboration of a new homogeneous quality index for proxies, our novel climate reconstruction sheds new light on the regional climate of SA climate during MH. All high quality (higher than 1) paleoarchives agree at regional scale. Compiled paleodata confirms reduced rainfall in Amazonia and a warmer and drier Southern SA, indicating an overall weakening of the South American Summer Monsoon during the MH. North East Brazil coast show higher than present moisture during the MH, while the border between Northeast Brazil and Southern SA shows divergent behavior, pointing to a local erratic rainfall regime with inputs of higher than present moisture conditions, most likely caused by changes in precipitation over the South Atlantic Convergence Zone, and a weaker than present South Atlantic Subtropical High during MH.
•173 compiled paleorecords for South America during mid-Holocene.•Age-models were calibrated using Bayesian methods.•Precipitation, air temperature, lake levels, sea surface temperature and sea salinity were reconstructed.•New quality index calculated for different paleoarchives and proxies.•Drier than present Amazonia and Southern South America, and inhomogeneous Northeast Brazil precipitation during mid-Holocene.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Trace element and stable isotope ratios from an active stalagmite (LR06-B1) recovered from Liang Luar Cave on the island of Flores (eastern Indonesia) are used to reconstruct the position of the ...austral summer inter-tropical convergence zone and Australian-Indonesian summer monsoon variability during the Holocene. Uranium-series dating of the stalagmite shows that it commenced growth 12,640
years ago
, with hiatuses spanning 8,560 to 6,420
and 3,670 to 2,780
years ago. Stalagmite Mg/Ca and Sr/Ca ratios correlate significantly with one another, and with
δ
18O and
δ
13C, throughout the record. This suggests that the Mg/Ca and Sr/Ca ratios are dominated by prior calcite precipitation, a process whereby degassing in the vadose zone during periods of low recharge causes deposition of calcite and disproportionate loss of Ca
2+ ions (relative to Mg
2+ and Sr
2+) ‘upstream’ of the stalagmite. The degree of initial
234U/
238U disequilibrium also appears to have been controlled by recharge to the overlying aquifer. Together with the Mg/Ca, Sr/Ca, and
δ
18O values, the initial uranium isotope activity ratios (
234U/
238U
I) imply a generally drier early Holocene, coincident with a lower sea level and lower Southern Hemisphere summer insolation.
Comparison of speleothem
δ
18O time-series from Flores and Borneo shows that they vary in unison for much of the Holocene. However, there is a significant decrease in the Borneo δ
18O record ~6,000 to 4,000 years ago that does not occur in the Flores record. This anomaly may be related to a change in the Australian-Indonesian summer monsoon circulation in response to a protracted positive phase of the Indian Ocean Dipole. Under this scenario, stronger upwelling off of western Indonesia would, based on present-day effects, result in reduced summer convective activity over Flores and a subsequent northward shift of the intertropical convergence zone.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Abstract
The coastal waters of the Arabian Peninsula include a heterogeneous marine region comprising the Persian/Arabian Gulf and Sea of Oman at its northeastern boundary and the Arabian Sea, Gulf ...of Aden, and Red Sea at its southern and western boundary. The environment within this region shifts from highly variable coral cover and extreme temperatures within the Persian/Arabian Gulf to sparse coral cover, lower summer temperatures, and nutrient-rich upwelling within the Sea of Oman. Within the Gulf of Aden and Red Sea there is high coral cover and warm, stable conditions. We tested for barriers to pelagic dispersal across this peninsula for the commercially important blackspot snapper Lutjanus ehrenbergii using mitochondrial DNA sequences. We found scant evidence for population genetic differences when comparing within northern and southern sections, but instead found strong evidence of genetic differentiation between northern and southern sections, with the Persian/Arabian Gulf and Sea of Oman populations being highly differentiated from the Gulf of Aden and Red Sea populations. Low levels of haplotype sharing between the Persian/Arabian Gulf – Sea of Oman and the Gulf of Aden – Red Sea probably reflect scenarios of historical colonization into these peripheral bodies of water, or the presence of a contemporary ecological barrier preventing further genetic exchange.
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FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
Abstract
The winter and summer monsoons in Southeast Asia are important but highly variable sources of rainfall. Current understanding of the winter monsoon is limited by conflicting proxy ...observations, resulting from the decoupling of regional atmospheric circulation patterns and local rainfall dynamics. These signals are difficult to decipher in paleoclimate reconstructions. Here, we present a winter monsoon speleothem record from Southeast Asia covering the Holocene and find that winter and summer rainfall changed synchronously, forced by changes in the Pacific and Indian Oceans. In contrast, regional atmospheric circulation shows an inverse relation between winter and summer controlled by seasonal insolation over the Northern Hemisphere. We show that disentangling the local and regional signal in paleoclimate reconstructions is crucial in understanding and projecting winter and summer monsoon variability in Southeast Asia.
Childhood immunisation services have been disrupted by the COVID-19 pandemic. WHO recommends considering outbreak risk using epidemiological criteria when deciding whether to conduct preventive ...vaccination campaigns during the pandemic.
We used two to three models per infection to estimate the health impact of 50% reduced routine vaccination coverage in 2020 and delay of campaign vaccination from 2020 to 2021 for measles vaccination in Bangladesh, Chad, Ethiopia, Kenya, Nigeria, and South Sudan, for meningococcal A vaccination in Burkina Faso, Chad, Niger, and Nigeria, and for yellow fever vaccination in the Democratic Republic of Congo, Ghana, and Nigeria. Our counterfactual comparative scenario was sustaining immunisation services at coverage projections made prior to COVID-19 (i.e. without any disruption).
Reduced routine vaccination coverage in 2020 without catch-up vaccination may lead to an increase in measles and yellow fever disease burden in the modelled countries. Delaying planned campaigns in Ethiopia and Nigeria by a year may significantly increase the risk of measles outbreaks (both countries did complete their supplementary immunisation activities (SIAs) planned for 2020). For yellow fever vaccination, delay in campaigns leads to a potential disease burden rise of >1 death per 100,000 people per year until the campaigns are implemented. For meningococcal A vaccination, short-term disruptions in 2020 are unlikely to have a significant impact due to the persistence of direct and indirect benefits from past introductory campaigns of the 1- to 29-year-old population, bolstered by inclusion of the vaccine into the routine immunisation schedule accompanied by further catch-up campaigns.
The impact of COVID-19-related disruption to vaccination programs varies between infections and countries. Planning and implementation of campaigns should consider country and infection-specific epidemiological factors and local immunity gaps worsened by the COVID-19 pandemic when prioritising vaccines and strategies for catch-up vaccination.
Bill and Melinda Gates Foundation and Gavi, the Vaccine Alliance.
Abstract
The optical and UV variability of the majority of active galactic nuclei may be related to the reprocessing of rapidly changing X-ray emission from a more compact region near the central ...black hole. Such a reprocessing model would be characterized by lags between X-ray and optical/UV emission due to differences in light travel time. Observationally, however, such lag features have been difficult to detect due to gaps in the lightcurves introduced through factors such as source visibility or limited telescope time. In this work, Gaussian process regression is employed to interpolate the gaps in the Swift X-ray and UV lightcurves of the narrow-line Seyfert 1 galaxy Mrk 335. In a simulation study of five commonly employed analytic Gaussian process kernels, we conclude that the Matern
1
2
and rational quadratic kernels yield the most well-specified models for the X-ray and UVW2 bands of Mrk 335. In analyzing the structure functions of the Gaussian process lightcurves, we obtain a broken power law with a break point at 125 days in the UVW2 band. In the X-ray band, the structure function of the Gaussian process lightcurve is consistent with a power law in the case of the rational quadratic kernel while a broken power law with a break point at 66 days is obtained from the Matern
1
2
kernel. The subsequent cross-correlation analysis is consistent with previous studies and furthermore shows tentative evidence for a broad X-ray-UV lag feature of up to 30 days in the lag-frequency spectrum where the significance of the lag depends on the choice of Gaussian process kernel.
The dynamics of predator-prey pursuit appears complex, making the development of a framework explaining predator and prey strategies problematic. We develop a model for terrestrial, cursorial ...predators to examine how animal mass modulates predator and prey trajectories and affects best strategies for both parties. We incorporated the maximum speed-mass relationship with an explanation of why larger animals should have greater turn radii; the forces needed to turn scale linearly with mass whereas the maximum forces an animal can exert scale to a 2/3 power law. This clarifies why in a meta-analysis, we found a preponderance of predator/prey mass ratios that minimized the turn radii of predators compared to their prey. It also explained why acceleration data from wild cheetahs pursuing different prey showed different cornering behaviour with prey type. The outcome of predator prey pursuits thus depends critically on mass effects and the ability of animals to time turns precisely.
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