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21.
Analysis of Carbon Dioxide Variations in the Atmosphere of Srednja Bijambarska Cave,Bosnia and Herzegovina 总被引：4，自引：0，他引：4
The results of one year’s monitoring in Srednja Bijambarska Cave (Bosnia and Herzegovina) are presented and discussed. Temporal
variations of the carbon dioxide (CO2) concentration are controlled by the switching between two ventilation regimes driven by outside temperature changes. A regression
model with a simple perfectly mixed volume applied to a cave sector (“Music hall”) resulted in an estimate of ventilation
rates between 0.02 h−1 and 0.54 h−1. Carbon dioxide input per plan surface unit is estimated by the model at around 50 × 10−6 mh−1 during the winter season and up to more than 1000 × 10−6 mh−1 during the first temperature falls at the end of summer (0.62 μmoles m−2 s−1 and 12.40 μmoles m−2 s−1 for normal conditions respectively). These values have been found to be related to the cave ventilation rate and dependent
on the availability of CO2 in the surrounding environment. For airflow close to zero the values of CO2 input per plan surface have a range in the order of magnitude of a few units × 10−6 mh−1. Based on two experiments, the anthropogenic contribution from cave visitors has been calculated, at between 0.35 lCO2 min−1 person−1 and 0.45 lCO2min−1person−1. 相似文献
22.
Inception of the Northern European ice sheet due to contrasting ocean and insolation forcing 总被引：1，自引：0，他引：1
Bjørg Risebrobakken Trond Dokken Eystein Jansen Yongqi Gao Helge Drange 《Quaternary Research》2007,67(1):128-135
About 115,000 yr ago the last interglacial reached its terminus and nucleation of new ice-sheet growth was initiated. Evidence from the northernmost Nordic Seas indicate that the inception of the last glacial was related to an intensification of the Atlantic Meridional Overturning Circulation (AMOC) in its northern limb. The enhanced AMOC, combined with minimum Northern hemisphere insolation, introduced a strong sea-land thermal gradient that, together with a strong wintertime latitudinal insolation gradient, increased the storminess and moisture transport to the high Northern European latitudes at a time when the Northern hemisphere summer insolation approached its minimum. 相似文献
23.
S. Lorenz B. Grieger Ph. Helbig K. Herterich 《International Journal of Earth Sciences》1996,85(3):513-524
We present atmospheric simulations of three different time slices of the late Quaternary using the ECHAM 3 general circulation
model in T42 resolution. In this work we describe the results of model runs for the time slices 6000 years BP (last climate
optimum), 21 000 BP (last glacial maximum) and 115 000 years BP (glacial inception). Although the solar insolation is known
for all time slices, a complete data set of the other boundary conditions which are necessary for running the atmospheric
model exists only for the last glacial maximum in the form of the CLIMAP reconstruction. For the other two time slices, which
are interglacial states like the modern climate, sea surface temperatures, land albedo and ice sheet topography are kept at
modern values and only the solar insolation is changed appropriately. The response of the model to solar insolation changes
is quite reasonable. The modelled anomalies are small and roughly opposite in sign for 6000 BP and 115 000 BP, respectively.
In the case of last glacial maximum, the glacial ice sheet topography and ice albedo produce a much larger climate anomaly
in the model. However, to enable a real test of model performance under glacial boundary conditions, the CLIMAP sea surface
temperatures, which are now known to be partly inaccurate, should be replaced by an updated “state-of-the-art” reconstruction. 相似文献
24.
Comparing the concentration of molybdenum (Mo) (ppm) and total organic carbon (TOC) (wt%) within sediments allows interpretation of the relative degrees of bottom water restriction within the geologic record. The Woodford Shale is interpreted as transgressive systems tract (TST) grading into highstand systems tract (HST). The lowermost Woodford preserves a Mo-TOC signal that is consistent with a restricted basin that periodically received influxes of water consistent with rising sea levels flowing into restricted sub-basins that became isolated by localized conditions. The middle Woodford preserves a signal that indicates an increased ventilation at the sediment-water interface persisting until the maximum flooding surface. The presence of phosphate nodules in the uppermost Woodford suggests sufficient oxygen to retain the Mo in solution and indicates active upwelling and circulation with the Paleotethys.It is also possible to document changing ventilation patterns, non-destructively, within a basin by utilizing changing trends in redox-sensitive trace metals (Mo, Ni, and Cu) and an approximation of the degree of pyritization (aDOP) based on an idealized formula for pyrite (FeS2). This chemofacies approach produces a qualitatively similar interpretation to the changing Mo-TOC signal and can evaluate lateral trends in bottom water ventilation where destructive sampling is not permitted. Distal regions preserve the greatest degree of bottom water ventilation. Proximal regions preserve highly variable conditions with more restricted conditions being common in the lowermost Woodford Shale and ventilation improving upsection.Interpreting changing levels of bottom water anoxia enable greater degrees of precision in targeting potential hydrocarbon resources. Furthermore, this information improves our understanding of the changing environmental conditions of the Woodford Shale. The Framvaren Fjord is a reasonable modern analog for bottom water restriction in the lowermost portion of the Woodford Shale. The Cariaco Basin is a good modern analog for bottom water restriction in the middle and uppermost Woodford Shale. 相似文献
25.
Flow of winter-transformed Pacific water into the Western Arctic 总被引：1，自引：0，他引：1
Robert S. Pickart Thomas J. Weingartner Lawrence J. Pratt Sarah Zimmermann Daniel J. Torres 《Deep Sea Research Part II: Topical Studies in Oceanography》2005,52(24-26):3175
The dynamics of the flow of dense water through Barrow Canyon is investigated using data from a hydrographic survey in summer 2002. The focus is on the winter-transformed Bering water—the highest volumetric mode of winter water in the Chukchi Sea—which drains northward through the canyon in spring and summer. The transport of this water mass during the time of the survey was 0.2–0.3 Sv. As the layer flowed from the head of the canyon to the mouth, it sank, decelerated, and stretched. Strong cyclonic relative vorticity was generated on the seaward side of the jet, which compensated for the stretching. This adjustment was incomplete, however, in that it did not extend across the entire current, possibly because of internal mixing due to shear instabilities. The resulting vorticity structure of the flow at the canyon mouth was conducive for baroclinic instability and eddy formation. Multiple eddies of winter-transformed Bering water were observed along the Chukchi–Beaufort shelfbreak. Those to the west of Barrow Canyon were in the process of being spawned by the eastward-flowing shelfbreak current emanating from Herald Canyon, while the single eddy observed to the east originated from the Barrow Canyon outflow. It is argued that such an eddy formation is a major source of the ubiquitous cold-core anti-cyclones observed historically throughout the Canada Basin. Implications for the ventilation of the upper halocline of the Western Arctic are discussed. 相似文献
26.
《地学前缘(英文版)》2022,13(6):101285
The infectious emission rate is a fundamental input parameter for airborne transmission risk assessment, but data are limited due to reliance on estimates from chance superspreading events. This study assesses the strength of a predictive estimation approach developed by the authors for SARS-CoV-2 and uses novel estimates to compare the contagiousness of respiratory pathogens. We applied the approach to SARS-CoV-1, SARS-CoV-2, MERS, measles virus, adenovirus, rhinovirus, coxsackievirus, seasonal influenza virus and Mycobacterium tuberculosis (TB) and compared quanta emission rate (ERq) estimates to literature values. We calculated infection risk in a prototypical classroom and barracks to assess the relative ability of ventilation to mitigate airborne transmission. Our median standing and speaking ERq estimate for SARS-CoV-2 (2.7 quanta h?1) is similar to active, untreated TB (3.1 quanta h?1), higher than seasonal influenza (0.17 quanta h?1), and lower than measles virus (15 quanta h?1). We calculated event reproduction numbers above 1 for SARS-CoV-2, measles virus, and untreated TB in both the classroom and barracks for an activity level of standing and speaking at low, medium and high ventilation rates of 2.3, 6.6 and 14 L per second per person (L s–1 p–1), respectively. Our predictive ERq estimates are consistent with the range of values reported over decades of research. In congregate settings, current ventilation standards are unlikely to control the spread of viruses with upper quartile ERq values above 10 quanta h?1, such as SARS-CoV-2, indicating the need for additional control measures. 相似文献
27.
The annual subduction rate of the North Pacific was calculated based on isopycnally averaged hydrographic climatology (HydroBase), high-resolution winter mixed-layer climatology (NWMLC), and various wind stress climatologies from ship reports, numerical weather prediction products, and satellite products. The calculation was performed using Lagrangian coordinates in the same manner as in previous works, except a less smoothed oceanic climatology (HydroBase and NWMLC) was used instead of a World Ocean Atlas. Differences in the wind stress climatologies have very little effect on subduction rate estimates. The subduction rate census for density classes showed peaks corresponding to subtropical mode water (STMW), central mode water (CMW), and eastern subtropical mode water (ESTMW). The deeper mixed layer and the associated sharper mixed-layer fronts in the present climatology resulted in a larger lateral induction, which boosted the subduction rate, especially for the potential density anomaly (σθ) range of the lighter STMW (25.0 < σθ < 25.2 kg m−3) and lighter CMW (26.0 < σθ < 26.2 kg m−3), compared to previous estimates. The renewal time of permanent pycnocline water was estimated as the volume of water divided by the subduction rate for each σθ class: 2–4 years for ESTMW (24.5 < σθ < 25.2 kg m−3), 2 years for the lighter STMW (25.0 < σθ < 25.3 kg m−3), 5–9 years for the denser STMW (25.3 < σθ < 25.6 kg m−3), 10–20 years for the lighter CMW (26.0 < σθ < 26.2 kg m−3), 20–30 years for the middle CMW (26.2 < σθ < 26.3 kg m−3), and 60 years or longer for the denser CMW (26.3 < σθ < 26.6 kg m−3). A comparison of the water volume and subduction rate in potential temperature–salinity (θ–S) space indicated that the upper permanent pycnocline water (25.0 < σθ < 26.2 kg m−3) was directly maintained by nondiffusive subduction of winter surface water, including STMW and lighter CMW. The lower permanent pycnocline water (26.2 < σθ < 26.6 kg m−3) may be maintained through the subduction of fresher and colder water from the subarctic–subtropical transition region and subsequent mixing with saltier and warmer water. Diagnosis of the potential vorticity (PV) of the subducted water demonstrated that the low PV of STMW was mainly due to the large subduction rate, whereas that of both ESTMW and CMW was due mainly to the small density advection rate (cross-isopycnal flow). Additionally, a relatively large subduction rate probably contributes to the low PV of part of the lighter CMW (ESTMW) formed in the region around 38°N and 170°W (28°N and 145°W), which is characterized by a relatively thick winter mixed layer and an associated mixed-layer front, causing a large lateral induction rate. 相似文献
28.
On Shear-Driven Ventilation of Snow 总被引：1，自引：1，他引：0
Andrew Clifton Costantino Manes Jean-Daniel Rüedi Michele Guala Michael Lehning 《Boundary-Layer Meteorology》2008,126(2):249-261
A series of experiments have been made in a wind tunnel to investigate the ventilation of snow by shear. We argue that the
zero-plane displacement can be used as a convenient indicator of ventilation, and that this can be obtained from measurements
of mean velocity profiles in conditions of zero pressure gradient. Measurements made over a natural snow surface show a zero-plane
displacement depth of less than 5 mm, but practical considerations preclude extensive use of snow for these measurements.
Instead, the influence of permeability is investigated using reticulated foams in place of snow. We demonstrate that the foam
and snow have similar structure and flow-relevant properties. Although the surface of the foam is flat, the roughness lengths
increase by two orders of magnitude as the permeability increases from 6 × 10−9 to 160 × 10−9 m2. The zero-plane displacement for the least permeable foams is effectively zero, but more than 15 mm for the most permeable
foams. Our data compare well to the few studies available in the literature. By analogy to conditions over snow surfaces,
we suggest that shear-driven ventilation of snow is therefore limited to the upper few millimetres of snow surfaces. 相似文献
29.
Alice M. Milner Ulrich C. Müller Katherine H. Roucoux Richard E. L. Collier Jörg Pross Stavros Kalaitzidis Kimon Christanis Polychronis C. Tzedakis 《第四纪科学杂志》2013,28(2):113-117
A new high‐resolution Last Interglacial pollen record from the Tenaghi Philippon peatland, northeast Greece, documents variability in forest composition and cover, which we attribute to changes in temperature and moisture availability. The declining stage of the interglacial was marked by a stepwise decrease in temperate tree populations and culminated in the complete collapse of forest at the onset of the ensuing stadial. The coincidence of the onset of the stepwise declining trend with the increased prominence of North Atlantic ice‐rafting events suggests that ecological thresholds in southern Europe were only crossed once ice rafting events intensified, and implies that changes in North Atlantic ocean circulation were an important contributing factor to the declining temperate forest cover in southern Europe. Our results provide evidence for intra‐interglacial variability in the low mid latitudes and suggest a coupling between the high northern latitudes and the northeast Mediterranean during this interval. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
30.
Hendrik M. van Aken M. Femke de JongIgor Yashayaev 《Deep Sea Research Part I: Oceanographic Research Papers》2011,58(5):505-523
Time series of profiles of potential temperature, salinity, dissolved oxygen, and planetary potential vorticity at intermediate depths in the Labrador Sea, the Irminger Sea, and the Iceland Basin have been constructed by combining the hydrographic sections crossing the sub-arctic gyre of the North Atlantic Ocean from the coast of Labrador to Europe, occupied nearly annually since 1990, and historic hydrographic data from the preceding years since 1950. The temperature data of the last 60 years mainly reflect a multi-decadal variability, with a characteristic time scale of about 50 years. With the use of a highly simplified heat budget model it was shown that this long-term temperature variability in the Labrador Sea mainly reflects the long-term variation of the net heat flux to the atmosphere. However, the analysis of the data on dissolved oxygen and planetary potential vorticity show that convective ventilation events, during which successive classes of Labrador Sea Water (LSW) are formed, occurring on decadal or shorter time scales. These convective ventilation events have performed the role of vertical mixing in the heat budget model, homogenising the properties of the intermediate layers (e.g. temperature) for significant periods of time. Both the long-term and the near-decadal temperature signals at a pressure of 1500 dbar are connected with successive deep LSW classes, emphasising the leading role of Labrador Sea convection in running the variability of the intermediate depth layers of the North Atlantic. These signals are advected to the neighbouring Irminger Sea and Iceland Basin. Advection time scales, estimated from the 60 year time series, are slightly shorter or of the same order as most earlier estimates, which were mainly based on the feature tracking of the spreading of the LSW94 class formed in the period 1989-1994 in the Labrador Sea. 相似文献