The Last Glacial Termination Denton, G. H.; Anderson, R. F.; Toggweiler, J. R. ...
Science (American Association for the Advancement of Science),
06/2010, Letnik:
328, Številka:
5986
Journal Article
Recenzirano
A major puzzle of paleoclimatology is why, after a long interval of cooling climate, each late Quaternary ice age ended with a relatively short warming leg called a termination. We here offer a ...comprehensive hypothesis of how Earth emerged from the last global ice age. A prerequisite was the growth of very large Northern Hemisphere ice sheets, whose subsequent collapse created stadial conditions that disrupted global patterns of ocean and atmospheric circulation. The Southern Hemisphere westerlies shifted poleward during each northern stadial, producing pulses of ocean upwelling and warming that together accounted for much of the termination in the Southern Ocean and Antarctica. Rising atmospheric CO₂ during southern upwelling pulses augmented warming during the last termination in both polar hemispheres.
Glacial-Interglacial Indian Summer Monsoon Dynamics Zhisheng, An; Clemens, Steven C.; Shen, Ji ...
Science (American Association for the Advancement of Science),
08/2011, Letnik:
333, Številka:
6043
Journal Article
Recenzirano
The modern Indian summer monsoon (ISM) is characterized by exceptionally strong interhemispheric transport, indicating the importance of both Northern and Southern Hemisphere processes driving ...monsoon variability. Here, we present a high-resolution continental record from southwestern China that demonstrates the importance of interhemispheric forcing in driving ISM variability at the glacial-interglacial time scale as well. Interglacial ISM maxima are dominated by an enhanced Indian low associated with global ice volume minima. In contrast, the glacial ISM reaches a minimum, and actually begins to increase, before global ice volume reaches a maximum. We attribute this early strengthening to an increased cross-equatorial pressure gradient derived from Southern Hemisphere high-latitude cooling. This mechanism explains much of the nonorbital scale variance in the Pleistocene ISM record.
Ice Age Terminations Cheng, Hai; Edwards, R. Lawrence; Broecker, Wallace S ...
Science (American Association for the Advancement of Science),
10/2009, Letnik:
326, Številka:
5950
Journal Article
Recenzirano
²³⁰Th-dated oxygen isotope records of stalagmites from Sanbao Cave, China, characterize Asian Monsoon (AM) precipitation through the ends of the third- and fourthmost recent ice ages. As a result, AM ...records for the past four glacial terminations can now be precisely correlated with those from ice cores and marine sediments, establishing the timing and sequence of major events. In all four cases, observations are consistent with a classic Northern Hemisphere summer insolation intensity trigger for an initial retreat of northern ice sheets. Meltwater and icebergs entering the North Atlantic alter oceanic and atmospheric circulation and associated fluxes of heat and carbon, causing increases in atmospheric CO₂ and Antarctic temperatures that drive the termination in the Southern Hemisphere. Increasing CO₂ and summer insolation drive recession of northern ice sheets, with probable positive feedbacks between sea level and CO₂.
The glacial-interglacial transitions of ice ages are associated with large, rapid changes in climate, which potentially can be reconstructed from stratigraphic profiles of the chemical index of ...alteration (CIA). Here, we present a case study based on high-resolution CIA profiles of Neoproterozoic glacial deposits from South China (paleolatitude ~30° N) as a record of the climate transition at the termination of the Sturtian Glaciation (~663 Ma). Drillcore ZK2115 (Gaodi Deposit) exhibits a progressive upsection increase in mean CIA over a ~50-m interval, from 58 (range 52–65; note: all ranges are given as 16th–84th percentiles) in the synglacial upper Tiesi'ao Formation to 67 (range 64–69) in the deglacial basal Datangpo Formation cap carbonates, and to 68 (range 66–70) in the postglacial Datangpo Formation black shales. A coeval section from the Lijiawan Deposit also exhibits an increasing CIA trend upsection within shallow-water Mn-carbonate facies. These CIA patterns show no relationship to lithology and are interpreted to reflect climatic warming and intensified chemical weathering during the Sturtian deglaciation. Similar large increases in postglacial CIA values are seen in Paleoproterozoic and Late Paleozoic successions, and at least moderate increases in CIA values are recorded during warm stages of the late Quaternary (e.g., the Bølling-Allerød and Holocene) relative to the cold stages (e.g., the Last Glacial Maximum and Younger Dryas). The rapidity of CIA changes in Quaternary systems (~1 to 10 kyr) suggests that weathering intensity may have changed at similarly rapid rates in more poorly dated deep-time glacial successions, with potential implications for Snowball versus Slushball models of Cryogenian glaciations. These examples show that CIA can be a robust proxy for climate changes (i.e., enhanced chemical weathering intensity) during glacial-interglacial transitions of both ancient and recent ice ages.
•Large increases in chemical index of alteration (CIA) during major deglaciations.•Case study of CIA changes in end-Sturtian deposits of Nanhua Basin (South China).•CIA increase from 59 ± 6 in synglacial Tiesi'ao Fm. to 66 ± 3 in postglacial Datangpo Fm.•CIA increase concentrated within terminal glacial deposits of uppermost Tiesi'ao Fm.•Similar CIA increases for glacial-interglacial transitions from Paleoproterozoic to Recent.
Disinfectant quaternary ammonium compounds (Quats) have diverse uses in a variety of consumer and commercial products, particularly cleaning products. With the emergence of the COVID-19 pandemic, ...they have become a primary tool to inactivate the SARS-CoV-2 virus on surfaces. Disinfectant Quats have very low vapor pressure, and following the use phase of the products in which they are found, disposal is typically “down-the-drain” to wastewater treatment systems. Consequently, the potential for the greatest environmental effect is to the aquatic environment, from treated effluent, and potentially to soils, which might be amended with wastewater biosolids. Among the earliest used and still common disinfectant Quats are the alkyl dimethyl benzyl ammonium chloride (ADBAC) compounds and the dialkyl dimethyl ammonium chloride (DDAC) compounds. They are cationic surfactants often found in consumer and commercial surface cleaners. Because of their biocidal properties, disinfectant Quats are heavily regulated for human and environmental safety around the world. Consequently, there is a robust database of information regarding the ecological hazards and environmental fate of ADBAC and DDAC; however, some of the data presented are from unpublished studies that have been submitted to and reviewed by regulatory agencies (i.e., EPA and European Chemicals Agency) to support antimicrobial product registration. We summarize the available environmental fate data and the acute and chronic aquatic ecotoxicity data for freshwater species, including algae, invertebrates, fish, and plants using peer-reviewed literature and unpublished data submitted to and summarized by regulatory agencies. The lower limit of the range of the ecotoxicity data for disinfectant Quats tends to be lower than that for other surface active agents, such as nonionic or anionic surfactants. However, ecotoxicity is mitigated by environmental fate characteristics, the data for which we also summarize, including high biodegradability and a strong tendency to sorb to wastewater biosolids, sediment, and soil. As a result, disinfectant Quats are largely removed during wastewater treatment, and those residues discharged in treated effluent are likely to rapidly bind to suspended solids or sediments, thus mitigating their toxicity.
•Robust databases exist for environmental toxicity and fate of ADBAC and DDAC.•Ecotoxicity of ADBAC and DDAC is greater than that for other surface active agents.•ADBAC/DDAC are removed during wastewater treatment by biodegradation and sorption.•The ecotoxicity of DDAC and ADBAC is mitigated by environmental fate characteristics.
Dust can affect the radiative balance of the atmosphere by absorbing or reflecting incoming solar radiation; it can also be a source of micronutrients, such as iron, to the ocean. It has been ...suggested that production, transport and deposition of dust is influenced by climatic changes on glacial-interglacial timescales. Here we present a high-resolution record of aeolian dust from the EPICA Dome C ice core in East Antarctica, which provides an undisturbed climate sequence over the past eight climatic cycles. We find that there is a significant correlation between dust flux and temperature records during glacial periods that is absent during interglacial periods. Our data suggest that dust flux is increasingly correlated with Antarctic temperature as the climate becomes colder. We interpret this as progressive coupling of the climates of Antarctic and lower latitudes. Limited changes in glacial-interglacial atmospheric transport time suggest that the sources and lifetime of dust are the main factors controlling the high glacial dust input. We propose that the observed ∼25-fold increase in glacial dust flux over all eight glacial periods can be attributed to a strengthening of South American dust sources, together with a longer lifetime for atmospheric dust particles in the upper troposphere resulting from a reduced hydrological cycle during the ice ages.
The paper presents a comprehensive review on lake-level history of Qinghai Lake since marine isotope stage (MIS) 5, after re-examining the sedimentary and geomorphological nature of highstand ...deposits and re-evaluating the published dating results (318 luminescence ages and 17 14C ages) of shorelines, near shoreline, lacustrine, alluvial, and aeolian deposits. It is concluded that 1) Three lake shoreline sets were classified in the Qinghai Lake Basin with the corresponding elevations of 3220–3260, 3206–3215 and 3194–3205 m. 2) 14C dating on lake sediments is restricted by the upper dating limit of ∼35 thousand years (ka) BP in practice, availability of dating materials and reservoir effect, and that quartz optically stimulated luminescence (OSL) ages older than 80–60 ka may be underestimated while feldspar post-infrared infrared stimulated luminescence (pIRIR) ages could be reliable for dating these older samples. 3) Four highstands were detected by ages. The highest lake-levels at elevations of 3220–3260 m with 26–66 m above the present lake-level occurred in MIS 5, and highstands also occurred in MIS 3 (∼42–38 ka), the last deglaciation (∼16–12 ka), and the Holocene (∼6–5 ka) with similar heights at elevations of ∼3200–3209 m. During the Holocene, lake-levels were relatively low in the early Holocene (∼11–8 ka), increasing substantially after ∼8 ka and reaching the highest lake-levels (elevation of 3203.1 m) at ∼6–5 ka, then decreasing with an interruption by a highstand (elevation of 3202.4 m) at ∼1.8 ka. 4) Shoreline-based lake-level variations are consistent with major climatic proxies (e.g., δ13Corg and %thaum) of drilling cores from the lake, regional aeolian activity/pedogenesis and climate change. 5) Compared with the representative lake-levels and moisture records in the Westerlies and East Asia summer monsoon (EASM) dominances, it is suggested that lake-level variations in the southern Qilian Mountains exhibited simultaneity with changes in the intensity of EASM, while those in the northern part were synchronous with the moisture records in arid central Asia, suggesting that EASM did not extend further to the northern Qilian Mountains where the Westerlies prevailed.
•Shoreline ages of Qinghai Lake were re-evaluated using multiple dating methods.•Radiocarbon ages saturated at ∼35 ka BP, and quartz OSL at 80–60 ka.•Four lake highstands occurred in MIS 5, MIS 3, last deglaciation, and Holocene.•The Holocene highest lake-levels occurred at ∼6–5 ka, then declined continuously.•Lake-levels in the Qilian Mts were dominated by the EASM in the south, by the Westerlies in the north.
The research project ‘Response of Humans to Abrupt Environmental Transitions’ (RESET) used tephra layers to tie together and synchronise the chronologies of stratigraphic records at archaeological ...and environmental sites. With the increasing importance of tephra as chronological markers in sedimentary sequences, both in this project and more generally, comes a requirement to have good estimates for the absolute age of these volcanic horizons. This paper summarises the chronology of the key tephra in the RESET tephra lattice in the time range 10–60 ka BP, from the existing literature, from papers produced as part of the RESET project, and reanalysis conducted for this paper. The paper outlines the chronological approach taken to the dating of tephra within the RESET project, and the basis for further work, as part of the INTIMATE (INTegrating Ice core MArine and TErrestrial records) initiative. For each of the tephra layers in the lattice, the existing literature is discussed and, where relevant date estimates updated using the latest radiocarbon calibration curves (IntCal13 and Marine13) and methods. Maps show the approximate extent of tephra finds, giving a visual indication of the coverage of the lattice in different time-periods.
•The chronology of late Quaternary European tephra layers is discussed.•New age estimates are given for a number of late Quaternary European tephra layers.•Bayesian age models are used to correlate multiple cores.•The chronology of the key tephras used in the RESET project is summarised.
High-resolution speleothem records from China have provided insights into the factors that control the strength of the East Asian monsoon. Our understanding of these factors remains incomplete, ...however, owing to gaps in the record of monsoon history over the past two interglacial-glacial cycles. In particular, missing sections have hampered our ability to test ideas about orbital-scale controls on the monsoon, the causes of millennial-scale events and relationships between changes in the monsoon and climate in other regions. Here we present an absolute-dated oxygen isotope record from Sanbao cave, central China, that completes a Chinese-cave-based record of the strength of the East Asian monsoon that covers the past 224,000 years. The record is dominated by 23,000-year-long cycles that are synchronous within dating errors with summer insolation at 65° N (ref. 10), supporting the idea that tropical/subtropical monsoons respond dominantly and directly to changes in Northern Hemisphere summer insolation on orbital timescales. The cycles are punctuated by millennial-scale strong-summer-monsoon events (Chinese interstadials), and the new record allows us to identify the complete series of these events over the past two interglacial-glacial cycles. Their duration decreases and their frequency increases during glacial build-up in both the last and penultimate glacial periods, indicating that ice sheet size affects their character and pacing. The ages of the events are exceptionally well constrained and may thus serve as benchmarks for correlating and calibrating climate records.
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