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1.
Proc Natl Acad Sci U S A ; 121(15): e2322127121, 2024 Apr 09.
Artículo en Inglés | MEDLINE | ID: mdl-38568978

RESUMEN

Soil moisture (SM) is essential for sustaining services from Earth's critical zone, a thin-living skin spanning from the canopy to groundwater. In the Anthropocene epoch, intensive afforestation has remarkably contributed to global greening and certain service improvements, often at the cost of reduced SM. However, attributing the response of SM in deep soil to such human activities is a great challenge because of the scarcity of long-term observations. Here, we present a 37 y (1985 to 2021) analysis of SM dynamics at two scales across China's monsoon loess critical zone. Site-scale data indicate that land-use conversion from arable cropland to forest/grassland caused an 18% increase in SM deficit over 0 to 18 m depth (P < 0.01). Importantly, this SM deficit intensified over time, despite limited climate change influence. Across the Loess Plateau, SM storage in 0 to 10 m layer exhibited a significant decreasing trend from 1985 to 2021, with a turning point in 1999 when starting afforestation. Compared with SM storage before 1999, the relative contributions of climate change and afforestation to SM decline after 1999 were -8% and 108%, respectively. This emphasizes the pronounced impacts of intensifying land-use conversions as the principal catalyst of SM decline. Such a decline shifts 18% of total area into an at-risk status, mainly in the semiarid region, thereby threatening SM security. To mitigate this risk, future land management policies should acknowledge the crucial role of intensifying land-use conversions and their interplay with climate change. This is imperative to ensure SM security and sustain critical zone services.

2.
Environ Int ; 186: 108654, 2024 Apr.
Artículo en Inglés | MEDLINE | ID: mdl-38621322

RESUMEN

Investigating the occurrence of antibiotic-resistance genes (ARGs) in sedimentary archives provides opportunities for reconstructing the distribution and dissemination of historical (i.e., non-anthropogenic origin) ARGs. Although ARGs in freshwater environments have attracted great attention, historical variations in the diversity and abundance of ARGs over centuries to millennia remain largely unknown. In this study, we investigated the vertical change patterns of bacterial communities, ARGs and mobile genetic elements (MGEs) found in sediments of Lake Chenghai spanning the past 600 years. Within resistome preserved in sediments, 177 ARGs subtypes were found with aminoglycosides and multidrug resistance being the most abundant. The ARG abundance in the upper sediment layers (equivalent to the post-antibiotic era since the 1940s) was lower than those during the pre-antibiotic era, whereas the ARG diversity was higher during the post-antibiotic era, possibly because human-induced lake eutrophication over the recent decades facilitated the spread and proliferation of drug-resistant bacteria. Statistical analysis suggested that MGEs abundance and the bacterial community structure were significantly correlated with the abundance and diversity of ARGs, suggesting that the occurrence and distribution of ARGs may be transferred between different bacteria by MGEs. Our results provide new perspectives on the natural history of ARGs in freshwater environments and are essential for understanding the temporal dynamics and dissemination of ARGs.


Asunto(s)
Eutrofización , Sedimentos Geológicos , Lagos , Lagos/microbiología , Sedimentos Geológicos/microbiología , Sedimentos Geológicos/química , Bacterias/genética , Bacterias/efectos de los fármacos , Farmacorresistencia Microbiana/genética , Antibacterianos/análisis , Antibacterianos/farmacología , Genes Bacterianos , China , Farmacorresistencia Bacteriana/genética
3.
Proc Natl Acad Sci U S A ; 121(14): e2321645121, 2024 Apr 02.
Artículo en Inglés | MEDLINE | ID: mdl-38527201

RESUMEN

Central Asia (CA) is one of the world's most significant arid regions, which is markedly impacted by global warming. A better understanding of the dynamical processes governing its Holocene climate variability is critical for a better understanding of possible future impacts of climate change in the region. To date, most of the existing CA paleoclimate records are from the summer precipitation-dominated eastern CA (ECA), with few records from the winter precipitation-dominated western CA (WCA). Here, we present a precisely dated (~6‰) and highly resolved (<4-y) record of hydroclimatic variations from the WCA covering the period between 7,774 and 656 y BP. Utilizing multiple proxies (δ18O, δ13C, and Sr/Ca) derived from a stalagmite from the Fergana Valley, Kyrgyzstan, we reveal a long-term drying trend in WCA, which is in contrast with the wetting trend in ECA. We propose that different responses of winter and summer westerly jets to seasonal solar insolation over the past 8,000 y may have resulted in an antiphased precipitation relationship between the WCA and ECA. Our data contain dominant quasiperiodicities of 1,400, 50 to 70, and 20 to 30 y, indicating close connections between the WCA climate and the North Atlantic. We further identified a series of droughts and pluvials on centennial-to-decadal timescales, which may have influenced regional societies and trans-Eurasian culture exchanges during historical and prehistorical times.

4.
Sci Total Environ ; 926: 172031, 2024 May 20.
Artículo en Inglés | MEDLINE | ID: mdl-38552985

RESUMEN

Long-term deposition of atmospheric radioactive iodine-129 (129I) is important for assessing the impact of human nuclear activities (HNAs), but still not well understood in East Asia. In this study, we quantitatively reconstructed the deposition history of airborne 129I using varved sediment from Sihailongwan Maar Lake (SHLW) in northeast China. Our results revealed significant increases in 129I concentrations and 129I/127I atomic ratios since the 1950s, indicating the influence of HNAs on the environment and marking the onset of the Anthropocene. The variation of 129I in the investigated site can be primarily attributed to the global fallout of ANWT as well as nuclear fuel reprocessing in Europe, Russia and the USA. Notably, neither the Chernobyl nor the Fukushima nuclear accidents have had any discernable impact on the SHLW Lake. Over the past 170 years (1846-2021), the reconstructed fluxes indicate a rapid increase in 129I deposition from the early 1950s until the 1970s followed by dramatic changes thereafter. The measured 129I fluxes range between (1.26-349) × 109 atoms m-2 yr-1 in the SHLW Lake, which are consistent with similar latitude zones across East Asia, but differ significantly from those observed in high-elevation glaciers within the Northern Hemisphere due to prevailing atmospheric circulation patterns. The total 129I inventory was calculated to be 11.9 × 1012 atoms m-2, with natural and anthropogenic 129I accounting for 2.86 % and 97.1 %, respectively, suggesting an overwhelming artificial contribution. The reconstructed fluxes and inventory of atmospheric 129I deposition quantitatively distinguish the natural and artificial contributions, and provide a novel insight into the historical environmental impact of HNAs in East Asia and the characteristics of the Anthropocene.

5.
Proc Natl Acad Sci U S A ; 121(3): e2308994121, 2024 Jan 16.
Artículo en Inglés | MEDLINE | ID: mdl-38190536

RESUMEN

The relationship between initial Homo sapiens dispersal from Africa to East Asia and the orbitally paced evolution of the Asian summer monsoon (ASM)-currently the largest monsoon system-remains underexplored due to lack of coordinated synthesis of both Asian paleoanthropological and paleoclimatic data. Here, we investigate orbital-scale ASM dynamics during the last 280 thousand years (kyr) and their likely influences on early H. sapiens dispersal to East Asia, through a unique integration of i) new centennial-resolution ASM records from the Chinese Loess Plateau, ii) model-based East Asian hydroclimatic reconstructions, iii) paleoanthropological data compilations, and iv) global H. sapiens habitat suitability simulations. Our combined proxy- and model-based reconstructions suggest that ASM precipitation responded to a combination of Northern Hemisphere ice volume, greenhouse gas, and regional summer insolation forcing, with cooccurring primary orbital cycles of ~100-kyr, 41-kyr, and ~20-kyr. Between ~125 and 70 kyr ago, summer monsoon rains and temperatures increased in vast areas across Asia. This episode coincides with the earliest H. sapiens fossil occurrence at multiple localities in East Asia. Following the transcontinental increase in simulated habitat suitability, we suggest that ASM strengthening together with Southeast African climate deterioration may have promoted the initial H. sapiens dispersal from their African homeland to remote East Asia during the last interglacial.


Asunto(s)
Pueblo Asiatico , Migración Humana , Tiempo (Meteorología) , Humanos , África , Asia , Asia Oriental
6.
Proc Natl Acad Sci U S A ; 120(17): e2211495120, 2023 Apr 25.
Artículo en Inglés | MEDLINE | ID: mdl-37068228

RESUMEN

Whether there are links between geomagnetic field and Earth's orbital parameters remains unclear. Synchronous reconstructions of parallel long-term quantitative geomagnetic field and climate change records are rare. Here, we present 10Be-derived changes of both geomagnetic field and Asian monsoon (AM) rainfall over the last 870 kyr from the Xifeng loess-paleosol sequence on the central Chinese Loess Plateau. The 10BeGM flux (a proxy for geomagnetic field-induced 10Be production rate) reveals 13 consecutive geomagnetic excursions in the Brunhes chron, which are synchronized with the global records, providing key time markers for Chinese loess-paleosol sequences. The 10Be-derived rainfall exhibits distinct ~100 kyr glacial-interglacial cycles, and superimposed precessional (~23 kyr) cycles that match with those in Chinese speleothem δ18O record. We find that changes in the geomagnetic field and AM rainfall share a common ~100 kyr cyclicity, implying a likely eccentricity modulation of both the geomagnetic field and climate.

7.
Nat Commun ; 13(1): 5867, 2022 Oct 04.
Artículo en Inglés | MEDLINE | ID: mdl-36195764

RESUMEN

Our understanding of climate dynamics during millennial-scale events is incomplete, partially due to the lack of their precise phase analyses under various boundary conditions. Here we present nine speleothem oxygen-isotope records from mid-to-low-latitude monsoon regimes with sub-centennial age precision and multi-annual resolution, spanning the Heinrich Stadial 2 (HS2) - a millennial-scale event that occurred at the Last Glacial Maximum. Our data suggests that the Greenland and Antarctic ice-core chronologies require +320- and +400-year adjustments, respectively, supported by extant volcanic evidence and radiocarbon ages. Our chronological framework shows a synchronous HS2 onset globally. Our records precisely characterize a centennial-scale abrupt "tropical atmospheric seesaw" superimposed on the conventional "bipolar seesaw" at the beginning of HS2, implying a unique response/feedback from low-latitude hydroclimate. Together with our observation of an early South American monsoon shift at the HS2 termination, we suggest a more active role of low-latitude hydroclimate dynamics underlying millennial events than previously thought.

8.
Environ Sci Technol ; 56(3): 1534-1543, 2022 02 01.
Artículo en Inglés | MEDLINE | ID: mdl-35007066

RESUMEN

Fossil fuel (FF) combustion emissions account for a large, but uncertain, amount of the soot in the atmosphere, play an important role in climate change, and adversely affect human health. However, historical estimates of FF contributions to air pollution are limited by uncertainties in fuel usage and emission factors. Here, we constrained FF soot emissions from southeastern China over the past 110 years, based on a novel radiocarbon method applied to sedimentary soot. The reconstructed soot accumulations reflect the integrated effects of increased FF use caused by economic development and reductions in emissions due to pollution controls. A sharp increase in FF soot started in 1950 as southeastern China industrialized and developed economically, but decreased FF soot fluxes in recent years suggest that pollution controls reduced soot emissions. We compare FF soot history to changes in CO2 emissions, industrial and economic activities, and pollution controls and show that FF soot fluxes are more readily controlled than atmospheric CO2. Our independent FF soot record provides insights into the effects of economic development and controls on air pollution and the environmental impacts from the changes in soot emissions.


Asunto(s)
Combustibles Fósiles , Hollín , Carbono/análisis , Dióxido de Carbono , China , Monitoreo del Ambiente/métodos , Combustibles Fósiles/análisis , Humanos , Hollín/análisis
9.
Sci Adv ; 7(51): eabk2318, 2021 Dec 17.
Artículo en Inglés | MEDLINE | ID: mdl-34910508

RESUMEN

Constraining monsoon variability and dynamics in the warm unipolar icehouse world of the Late Oligocene can provide important clues to future climate responses to global warming. Here, we present a ~4-thousand year (ka) resolution rubidium-to-strontium ratio and magnetic susceptibility records between 28.1 and 24.1 million years ago from a distal alluvial sedimentary sequence in the Lanzhou Basin (China) on the northeastern Tibetan Plateau margin. These Asian monsoon precipitation records exhibit prominent short (~110-ka) and long (405-ka) eccentricity cycles throughout the Late Oligocene, with a weak expression of obliquity (41-ka) and precession (19-ka and 23-ka) cycles. We conclude that a combination of eccentricity-modulated low-latitude summer insolation and glacial-interglacial Antarctic Ice Sheet fluctuations drove the eccentricity-paced precipitation variability on the northeastern Tibetan Plateau in the Late Oligocene high CO2 world by governing regional temperatures, water vapor loading in the western Pacific and Indian Oceans, and the Asian monsoon intensity and displacement.

10.
Nat Commun ; 12(1): 6935, 2021 11 26.
Artículo en Inglés | MEDLINE | ID: mdl-34836960

RESUMEN

Across the Miocene-Pliocene boundary (MPB; 5.3 million years ago, Ma), late Miocene cooling gave way to the early-to-middle Pliocene Warm Period. This transition, across which atmospheric CO2 concentrations increased to levels similar to present, holds potential for deciphering regional climate responses in Asia-currently home to more than half of the world's population- to global climate change. Here we find that CO2-induced MPB warming both increased summer monsoon moisture transport over East Asia, and enhanced aridification over large parts of Central Asia by increasing evaporation, based on integration of our ~1-2-thousand-year (kyr) resolution summer monsoon records from the Chinese Loess Plateau aeolian red clay with existing terrestrial records, land-sea correlations, and climate model simulations. Our results offer palaeoclimate-based support for 'wet-gets-wetter and dry-gets-drier' projections of future regional hydroclimate responses to sustained anthropogenic forcing. Moreover, our high-resolution monsoon records reveal a dynamic response to eccentricity modulation of solar insolation, with predominant 405-kyr and ~100-kyr periodicities between 8.1 and 3.4 Ma.

11.
Sci Total Environ ; 770: 145258, 2021 May 20.
Artículo en Inglés | MEDLINE | ID: mdl-33513516

RESUMEN

Several recent studies showed that leaf wax n-alkane δ2H values (δ2Hwax) within a leaf were heterogeneous in a small number of species. It still remains unclear whether the heterogeneity of intra-leaf δ2Hwax values is general for various species, how δ2Hwax values vary spatially and temporally, and whether there is a common explanation for the intra-leaf δ2Hwax heterogeneity in higher plants. Here we compared the hydrogen isotope compositions of leaf wax and corresponding leaf water (δ2Hlw) across leaf sections among a variety of monocot and dicot plant species. There is significant and consistent heterogeneity for both δ2Hwax and δ2Hlw, i.e., base-to-tip 2H-enrichment for monocots (except Hemerocallis citrina, and Dactylis glomerata) whereas base-to-tip and center-to-edge increases in δ2Hwax and δ2Hlw for dicots. The consistent occurrence of variations of δ2Hlw and δ2Hwax values within a leaf imply that δ2Hwax values probably inherit point-to-pint from in-situ δ2Hlw values, and thus the intra-leaf δ2Hwax heterogeneity mainly results from the spatial pattern of intra-leaf δ2Hlw values associated with veinal structures between dicots and monocots. The general heterogeneity of intra-leaf δ2Hwax values further intensifies that it is necessarily needed for in-depth understanding leaf wax biomarker.


Asunto(s)
Hidrógeno , Agua , Isótopos , Hojas de la Planta , Ceras
12.
Sci Bull (Beijing) ; 66(11): 1136-1145, 2021 Jun 15.
Artículo en Inglés | MEDLINE | ID: mdl-36654347

RESUMEN

Orbital-scale global climatic changes during the late Quaternary are dominated by high-latitude influenced ~100,000-year global ice-age cycles and monsoon influenced ~23,000-year low-latitude hydroclimate variations. However, the shortage of highly-resolved land temperature records remains a limiting factor for achieving a comprehensive understanding of long-term low-latitude terrestrial climatic changes. Here, we report paired mean annual air temperature (MAAT) and monsoon intensity proxy records over the past 88,000 years from Lake Tengchongqinghai in southwestern China. While summer monsoon intensity follows the ~23,000-year precession beat found also in previous studies, we identify previously unrecognized warm periods at 88,000-71,000 and 45,000-22,000 years ago, with 2-3 °C amplitudes that are close to our recorded full glacial-interglacial range. Using advanced transient climate simulations and comparing with forcing factors, we find that these warm periods in our MAAT record probably depends on local annual mean insolation, which is controlled by Earth's ~41,000-year obliquity cycles and is anti-phased to annual mean insolation at high latitudes. The coincidence of our identified warm periods and intervals of high-frequent dated archaeological evidence highlights the importance of temperature on anatomically modern humans in Asia during the last glacial stage.

13.
Sci Bull (Beijing) ; 66(6): 603-611, 2021 Mar 30.
Artículo en Inglés | MEDLINE | ID: mdl-36654430

RESUMEN

Arid Central Asia (ACA), with its diverse landscapes of high mountains, oases, and deserts, hosted the central routes of the Silk Roads that linked trade centers from East Asia to the eastern Mediterranean. Ecological pockets and ecoclines in ACA are largely determined by local precipitation. However, little research has gone into the effects of hydroclimatic changes on trans-Eurasian cultural exchange. Here, we reconstruct precipitation changes in ACA, covering the mid-late Holocene with a U-Th dated, ~3 a resolution, multi-proxy time series of replicated stalagmites from the southeastern Fergana Valley, Kyrgyzstan. Our data reveal a 640-a megadrought between 5820 and 5180 a BP, which likely impacted cultural development in ACA and impeded the expansion of cultural traits along oasis routes. Instead, it may have diverted the earliest transcontinental exchange along the Eurasian steppe during the 5th millennium BP. With gradually increasing precipitation after the megadrought, settlement of peoples in the oases and river valleys may have facilitated the opening of the oasis routes, "prehistoric Silk Roads", of trans-Eurasian exchange. By the 4th millennium BP, this process may have reshaped cultures across the two continents, laying the foundation for the organized Silk Roads.

14.
Proc Natl Acad Sci U S A ; 117(52): 33005-33010, 2020 Dec 29.
Artículo en Inglés | MEDLINE | ID: mdl-33323486

RESUMEN

Anthropogenic combustion-derived water (CDW) may accumulate in an airshed due to stagnant air, which may further enhance the formation of secondary aerosols and worsen air quality. Here we collected three-winter-season, hourly resolution, water-vapor stable H and O isotope compositions together with atmospheric physical and chemical data from the city of Xi'an, located in the Guanzhong Basin (GZB) in northwestern China, to elucidate the role of CDW in particulate pollution. Based on our experimentally determined water vapor isotope composition of the CDW for individual and weighted fuels in the basin, we found that CDW constitutes 6.2% of the atmospheric moisture on average and its fraction is positively correlated with [PM2.5] (concentration of particulate matter with an aerodynamic diameter less than 2.5 µm) as well as relative humidity during the periods of rising [PM2.5]. Our modeling results showed that CDW added additional average 4.6 µg m-3 PM2.5 during severely polluted conditions in the GZB, which corresponded to an average 5.1% of local anthropogenic [PM2.5] (average at ∼91.0 µg m-3). Our result is consistent with the proposed positive feedback between the relative humidity and a moisture sensitive air-pollution condition, alerting to the nontrivial role of CDW when considering change of energy structure such as a massive coal-to-gas switch in household heating in winter.

15.
Nat Commun ; 11(1): 5249, 2020 10 16.
Artículo en Inglés | MEDLINE | ID: mdl-33067447

RESUMEN

The first major build-up of Antarctic glaciation occurred in two consecutive stages across the Eocene-Oligocene transition (EOT): the EOT-1 cooling event at ~34.1-33.9 Ma and the Oi-1 glaciation event at ~33.8-33.6 Ma. Detailed orbital-scale terrestrial environmental responses to these events remain poorly known. Here we present magnetic and geochemical climate records from the northeastern Tibetan Plateau margin that are dated precisely from ~35.5 to 31 Ma by combined magneto- and astro-chronology. These records suggest a hydroclimate transition at ~33.7 Ma from eccentricity dominated cycles to oscillations paced by a combination of eccentricity, obliquity, and precession, and confirm that major Asian aridification and cooling occurred at Oi-1. We conclude that this terrestrial orbital response transition coincided with a similar transition in the marine benthic δ18O record for global ice volume and deep-sea temperature variations. The dramatic reorganization of the Asian climate system coincident with Oi-1 was, thus, a response to coeval atmospheric CO2 decline and continental-scale Antarctic glaciation.

16.
Sci Rep ; 10(1): 16927, 2020 10 09.
Artículo en Inglés | MEDLINE | ID: mdl-33037270

RESUMEN

Massive gully land consolidation projects, launched in China's Loess Plateau, aim to restore 2667 [Formula: see text] agricultural lands in total by consolidating 2026 highly eroded gullies. This effort represents a social engineering project where the economic development and livelihood of the farming families are closely tied to the ability of these emergent landscapes to provide agricultural services. Whether these 'time zero' landscapes have the resilience to provide a sustainable soil condition such as soil organic carbon (SOC) content remains unknown. By studying two watersheds, one of which is a control site, we show that the consolidated gully serves as an enhanced carbon sink, where the magnitude of SOC increase rate (1.0 [Formula: see text]) is about twice that of the SOC decrease rate (- 0.5 [Formula: see text]) in the surrounding natural watershed. Over a 50-year co-evolution of landscape and SOC turnover, we find that the dominant mechanisms that determine the carbon cycling are different between the consolidated gully and natural watersheds. In natural watersheds, the flux of SOC transformation is mainly driven by the flux of SOC transport; but in the consolidated gully, the transport has little impact on the transformation. Furthermore, we find that extending the surface carbon residence time has the potential to efficiently enhance carbon sequestration from the atmosphere with a rate as high as 8 [Formula: see text] compared to the current 0.4 [Formula: see text]. The success for the completion of all gully consolidation would lead to as high as 26.67 [Formula: see text] sequestrated into soils. This work, therefore, not only provides an assessment and guidance of the long-term sustainability of the 'time zero' landscapes but also a solution for sequestration [Formula: see text] into soils.

17.
Proc Natl Acad Sci U S A ; 117(40): 24729-24734, 2020 10 06.
Artículo en Inglés | MEDLINE | ID: mdl-32958667

RESUMEN

Midlatitude Asia (MLA), strongly influenced by westerlies-controlled climate, is a key source of global atmospheric dust, and plays a significant role in Earth's climate system . However, it remains unclear how the westerlies, MLA aridity, and dust flux from this region evolved over time. Here, we report a unique high-resolution eolian dust record covering the past 3.6 Ma, retrieved from the thickest loess borehole sequence (671 m) recovered to date, at the southern margin of the Taklimakan desert in the MLA interior. The results show that eolian dust accumulation, which is closely related to aridity and the westerlies, indicates existence of a dry climate, desert area, and stable land surface, promoting continuous loess deposition since at least ∼3.6 Ma. This region experienced long-term stepwise drying at ∼2.7, 1.1, and 0.5 Ma, coeval with a dominant periodicity shift from 41-ka cyclicity to 100-ka cyclicity between 1.1 Ma and 0.5 Ma. These features match well with global ice volume variability both in the time and frequency domains (including the Mid-Pleistocene Transition), highlighting global cooling-forced aridity and westerlies climate changes on these timescales. Numerical modeling demonstrates that global cooling can dry MLA and intensify the westerlies, which facilitates dust emission and transport, providing an interpretive framework. Increased dust may have promoted positive feedbacks (e.g., decreasing atmospheric CO2 concentrations and modulating radiation budgets), contributing to further cooling. Unraveling the long-term evolution of MLA aridity and westerlies climate is an indispensable component of the unfolding mystery of global climate change.

18.
Proc Natl Acad Sci U S A ; 117(38): 23408-23417, 2020 09 22.
Artículo en Inglés | MEDLINE | ID: mdl-32900942

RESUMEN

The Younger Dryas (YD), arguably the most widely studied millennial-scale extreme climate event, was characterized by diverse hydroclimate shifts globally and severe cooling at high northern latitudes that abruptly punctuated the warming trend from the last glacial to the present interglacial. To date, a precise understanding of its trigger, propagation, and termination remains elusive. Here, we present speleothem oxygen-isotope data that, in concert with other proxy records, allow us to quantify the timing of the YD onset and termination at an unprecedented subcentennial temporal precision across the North Atlantic, Asian Monsoon-Westerlies, and South American Monsoon regions. Our analysis suggests that the onsets of YD in the North Atlantic (12,870 ± 30 B.P.) and the Asian Monsoon-Westerlies region are essentially synchronous within a few decades and lead the onset in Antarctica, implying a north-to-south climate signal propagation via both atmospheric (decadal-time scale) and oceanic (centennial-time scale) processes, similar to the Dansgaard-Oeschger events during the last glacial period. In contrast, the YD termination may have started first in Antarctica at ∼11,900 B.P., or perhaps even earlier in the western tropical Pacific, followed by the North Atlantic between ∼11,700 ± 40 and 11,610 ± 40 B.P. These observations suggest that the initial YD termination might have originated in the Southern Hemisphere and/or the tropical Pacific, indicating a Southern Hemisphere/tropics to North Atlantic-Asian Monsoon-Westerlies directionality of climatic recovery.

19.
Sci Total Environ ; 748: 141359, 2020 Dec 15.
Artículo en Inglés | MEDLINE | ID: mdl-32798869

RESUMEN

The marine bivalve, Tridacna spp. is an iconic invertebrate of the Indo-Pacific coral reef communities from Eocene to present. However, field observations found that the population of Tridacna spp. has declined in recent decades and some species are now endangered in the northern South China Sea (SCS) of western Pacific, which are speculated to be connected with the human overfishing and/or climate changes. Thus distinguishing the impacts of human activities and climate changes on Tridacna spp. populations is essential for understanding the dynamic of Tridacna spp. population variability. Such effort will be important in launching conservation policies and restoring population. Here, extensive sampling was applied on sub-fossil Tridacna spp. shells at the North Reef of the northern SCS, and the long-lived (with a lifespan more than 30 years) Tridacna spp. population index (LTPI) over the past 4500 years was obtained based on the AMS14C dating method. The results show that LTPI has experienced several short-term collapses (shorter than 200 years) over the past 4500 years, which may be associated with excessive cold winter temperatures. Remarkably, LTPI usually recovered rapidly after the rewarming of temperatures, indicating a robust self-recruitment mechanisms in response to natural climate changes. However, the last catastrophic collapse of LTPI that occurred at around ~1820 CE - ~1900 CE didn't rebound despite the significant rise in temperature over the recent 100 years. The decoupling between LTPI and climate changes in recent hundred years was probably induced by the increased commercial fishing in the SCS, which has overwhelmed and exacerbated the self-recruitment mechanisms between Tridacna spp. population and climate changes.


Asunto(s)
Bivalvos , Conservación de los Recursos Naturales , Animales , China , Arrecifes de Coral , Explotaciones Pesqueras
20.
Sci Total Environ ; 742: 140498, 2020 Nov 10.
Artículo en Inglés | MEDLINE | ID: mdl-32623167

RESUMEN

The intensive introduction of shrubs to drylands can alter species composition and affect a series of biotic and abiotic processes. This topic has attracted increasing attention by researchers. To assess the response of soil properties to vegetation succession in arid regions of China, we measured the soil water content (SWC) to a depth of 5-m and determined soil properties of surface (0-5 cm) and subsurface (20-25 cm) layers in areas of natural grasses (NGs) and planted shrubs (PSs). The patch size of Caragana korshinskii shrubs resulted in different soil water storage losses (small shrub patch: 206.67 ± 35.58 mm; medium shrub patch: 416.88 ± 35.12 mm; large shrub patch: 588.63 ± 72.00 mm; degraded shrub patch: 740.54 ± 17.00 mm). Shrub cover showed an initial increase but then decreased as shrubs extracted soil water from the deep soil layers (>1 m). The species richness index in the PSs decreased with increasing shrub patch sizes. Surface soil organic carbon (SOC), extractable nitrogen (NH4+-N and NO3--N), and available phosphorous contents and saturated soil hydraulic conductivity (Ks) in the PSs were all significantly (p < 0.05) lower than those in NGs. Soil particles in the range of 0.002-0.2 mm explained 28.0% and 47.3% of the total variability of these surface indices under NGs and PSs, respectively. The differences in SOC, NH4+-N, NO3--N, Ks, and field capacity between the surface and subsurface layers declined significantly (p < 0.05). The introduction of shrubs affected the plant community by increasing the spatial heterogeneity of soil resources (e.g. water and nutrient contents). Therefore, the strong feedback between SWC and vegetation succession should be carefully considered when revegetating drylands. The evaluation of regional soil property responses to vegetation succession aids in a better understanding of soil water-vegetation feedback and provides important implications for future revegetation in arid regions.


Asunto(s)
Caragana , Suelo , Carbono/análisis , China , Clima Desértico , Ecosistema
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