scholarly journals Wildfire activity enhanced during phases of maximum orbital eccentricity and precessional forcing in the Early Jurassic

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Teuntje P. Hollaar ◽  
Sarah J. Baker ◽  
Stephen P. Hesselbo ◽  
Jean-François Deconinck ◽  
Luke Mander ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Fire Regimes ◽  
Boreal Summer ◽  
Natural Background ◽  
Orbital Eccentricity ◽  
Orbital Parameters ◽  
Elemental Analyses ◽  
Fire Activity ◽  
Climatic Drivers ◽  
Background Climate

AbstractFire regimes are changing due to both anthropogenic climatic drivers and vegetation management challenges, making it difficult to determine how climate alone might influence wildfire activity. Earth has been subject to natural-background climate variability throughout its past due to variations in Earth’s orbital parameters (Milkankovitch cycles), which provides an opportunity to assess climate-only driven variations in wildfire. Here we present a 350,000 yr long record of fossil charcoal from mid-latitude (~35°N) Jurassic sedimentary rocks. These results are coupled to estimates of variations in the hydrological cycle using clay mineral, palynofacies and elemental analyses, and lithological and biogeochemical signatures. We show that fire activity strongly increased during extreme seasonal contrast (monsoonal climate), which has been linked to maximal precessional forcing (boreal summer in perihelion) (21,000 yr cycles), and we hypothesize that long eccentricity modulation further enhances precession-forced fire activity.

Long and short orbital forcing of Jurassic wildfires.

2021 ◽  
Author(s):  
Teuntje P. Hollaar ◽  
Sarah B. Baker ◽  
Stephen P. Hesselbo ◽  
Jean-Francois Deconinck ◽  
Luke Mander ◽  
...  
Keyword(s):  
Hydrological Cycle ◽  
Seasonal Pattern ◽  
Fire Regimes ◽  
Western Tethys ◽  
Orbital Parameters ◽  
The North ◽  
Elemental Analyses ◽  
Climatic Drivers ◽  
Tethys Ocean ◽  
Strong Seasonality

<p>Fire regimes are changing due to anthropogenic climatic drivers and fuel management challenges in all regions of Earth. However, the planet is also subject to natural background variability due to Earth’s orbital parameters (Milkankovitch cycles). To date no studies have assessed a sedimentary record that is sufficiently long or has a resolution that is high enough to assess both long eccentricity and precessional forcings on fire.  Here we present a ~350,000 yr record of wildfire activity, using fossil charcoal from Jurassic sediments.<br><br>The studied interval is part of the astronomically constrained Upper Pliensbachian of the Mochras borehole, Cardigan Bay Basin. The site was located within the Laurasian Seaway, south of the Viking Corridor that linked the north-western Tethys Ocean to the Boreal Sea, at a palaeolatitude of ~35°N. Clear lithological couplets of carbonate-rich and TOC-enhanced beds are observed, which show an orbital control on deposition. High resolution macrocharcoal (>125 um) and microcharcoal (10-125 um) abundance data have been obtained at a ~2 ky resolution over the studied interval. Charcoal data are coupled to estimates of variations in the hydrological cycle using clay mineral analyses, along with palynofacies and elemental analyses, and lithological and biogeochemical signatures.</p><p>We show that fire activity was strongly increased during (1) a period of maximum eccentricity (405,000 yr cycle) and (2) inferred maximum in seasonal contrast due to precession (20,000 yr cycles). In these periods with a strong seasonality, charcoal abundance indicates enhanced wildfire activity. This is coupled to a more seasonal pattern of rainfall as indicated by the relative abundance of smectite versus kaolinite. We argue that the shift to a more seasonal climate would have led to the increase in dry-adapted conifer forests. Conifers have biochemical and morphological traits that make them particularly flammable whether dry or live.<sup></sup>This climate induced change in vegetation contributed to increased wildfire activity in the seasonal dry periods.</p><p>Increase in wildfire activity on an orbital time scale indicates that currently wildfires should be suppressed as Earth is close to an eccentricity minimum, such that man may have counteracted a relatively fire limited period.</p>

scholarly journals Age and driving mechanisms of the Eocene–Oligocene transition from astronomical tuning of a lacustrine record (Rennes Basin, France)

2021 ◽  
Vol 17 (6) ◽  
pp. 2343-2360
Author(s):  
Slah Boulila ◽  
Guillaume Dupont-Nivet ◽  
Bruno Galbrun ◽  
Hugues Bauer ◽  
Jean-Jacques Châteauneuf
Keyword(s):  
Hydrological Cycle ◽  
Sedimentary Facies ◽  
Late Eocene ◽  
Depositional Environments ◽  
Orbital Eccentricity ◽  
Pass Filter ◽  
Low Pass Filter ◽  
Climate Conditions ◽  
Driving Mechanisms ◽  
Natural Gamma

Abstract. The Eocene–Oligocene Transition (EOT) marks the onset of the Antarctic glaciation and the switch from greenhouse to icehouse climates. However, the driving mechanisms and the precise timing of the EOT remain controversial mostly due to the lack of well-dated stratigraphic records, especially in continental environments. Here we present a cyclo-magnetostratigraphic and sedimentological study of a ∼ 7.6 Myr long lacustrine record spanning the late Eocene to the earliest Oligocene, from a drill core in the Rennes Basin (France). Cyclostratigraphic analysis of natural gamma radiation (NGR) log data yields duration estimates of Chrons C12r through C16n.1n, providing additional constraints on the Eocene timescale. Correlations between the orbital eccentricity curve and the 405 kyr tuned NGR time series indicate that 33.71 and 34.10 Ma are the most likely proposed ages of the EO boundary. Additionally, the 405 kyr tuning calibrates the most pronounced NGR cyclicity to a period of ∼1 Myr, matching the g1–g5 eccentricity term, supporting its significant expression in continental depositional environments, and hypothesizing that the paleolake level may have behaved as a low-pass filter for orbital forcing. Two prominent changes in the sedimentary facies were detected across the EOT, which are temporally equivalent to the two main climatic steps, EOT-1 and Oi-1. We suggest that these two facies changes reflect the two major Antarctic cooling/glacial phases via the hydrological cycle, as significant shifts to drier and cooler climate conditions. Finally, the interval spanning the EOT precursor glacial event through EOT-1 is remarkably dominated by obliquity. This suggests preconditioning of the major Antarctic glaciation, either from obliquity directly affecting the formation/(in)stability of the incipient Antarctic Ice Sheet (AIS), or through obliquity modulation of the North Atlantic Deep Water production.

scholarly journals Can we predict the duration of an interglacial?

2012 ◽  
Vol 8 (2) ◽  
pp. 1057-1088 ◽  
Author(s):  
P. C. Tzedakis ◽  
E. W. Wolff ◽  
L. C. Skinner ◽  
V. Brovkin ◽  
D. A. Hodell ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Sea Level ◽  
Predictive Power ◽  
The Other ◽  
Systematic Evaluation ◽  
Middle Pleistocene ◽  
Boreal Summer ◽  
History Of ◽  
Background Climate ◽  
Milankovitch Forcing

Abstract. Differences in the duration of interglacials have long been apparent in palaeoclimate records of the Late and Middle Pleistocene. However, a systematic evaluation of such differences has been hampered by the lack of a metric that can be applied consistently through time and by difficulties in separating the local from the global component in various proxies. This, in turn, means that a theoretical framework with predictive power for interglacial duration has remained elusive. Here we propose that the interval between the terminal oscillation of the bipolar-seesaw and three thousand years (kyr) before its first major reactivation provides an estimate that approximates the length of the sea-level highstand, a measure of interglacial duration. We apply this concept to interglacials of the last 800 kyr by using a recently-constructed record of interhemispheric variability. The onset of interglacials occurs within 2 kyr of the peak in boreal summer insolation and is consistent with the canonical view of Milankovitch forcing dictating the broad timing of interglacials. Glacial inception always takes place when obliquity is decreasing and never after the obliquity minimum. The phasing of precession and obliquity appears to influence the persistence of interglacial conditions over one or two insolation peaks, leading to shorter (~13 kyr) and longer (~28 kyr) interglacials. Glacial inception occurs approximately 10 kyr after peak interglacial conditions in temperature and CO2, representing an interglacial "relaxation" time over which gradual cooling takes place. Second-order differences in duration may be a function of stochasticity in the climate system, or small variations in background climate state and the magnitude of feedbacks and mechanisms contributing to glacial iinception, and as such, difficult to predict. On the other hand, the broad duration of an interglacial may be determined by the phasing of astronomical parameters and the history of insolation, rather than the instantaneous forcing strength at inception.

scholarly journals The last interglacial (Eemian) climate simulated by LOVECLIM and CCSM3

2012 ◽  
Vol 8 (5) ◽  
pp. 5293-5340 ◽  
Author(s):  
I. Nikolova ◽  
Q. Yin ◽  
A. Berger ◽  
U. K. Singh ◽  
M. P. Karami
Keyword(s):  
Large Scale ◽  
Climate Models ◽  
Hydrological Cycle ◽  
The Arctic ◽  
Boreal Summer ◽  
Interglacial Period ◽  
Last Interglacial ◽  
Proxy Data ◽  
Vegetation Feedback ◽  
Depth Analysis

Abstract. This paper presents a detailed analysis of the climate of the last interglacial simulated by two climate models of different complexities, LOVECLIM and CCSM3. The simulated surface temperature, hydrological cycle, vegetation and ENSO variability during the last interglacial are analyzed through the comparison with the simulated Pre-Industrial (PI) climate. In both models, the last interglacial period is characterized by a significant warming (cooling) over almost all the continents during boreal summer (winter) leading to a largely increased (reduced) seasonal contrast in the northern (southern) hemisphere. This is mainly due to the much higher (lower) insolation received by the whole Earth in boreal summer (winter) during this interglacial. The arctic is warmer than PI through the whole year, resulting from its much higher summer insolation and its remnant effect in the following fall-winter through the interactions between atmosphere, ocean and sea ice. In the tropical Pacific, the change in the SST annual cycle is suggested to be related to a minor shift towards an El Nino, slightly stronger for MIS-5 than for PI. Intensified African monsoon and vegetation feedback are responsible for the cooling during summer in North Africa and Arabian Peninsula. Over India precipitation maximum is found further west, while in Africa the precipitation maximum migrates further north. Trees and grassland expand north in Sahel/Sahara. A mix of forest and grassland occupies continents and expand deep in the high northern latitudes. Desert areas reduce significantly in Northern Hemisphere, but increase in North Australia. The simulated large-scale climate change during the last interglacial compares reasonably well with proxy data, giving credit to both models and reconstructions. However, discrepancies exist at some regional scales between the two models, indicating the necessity of more in depth analysis of the models and comparisons with proxy data.

Earth: Imprint of Life

1999 ◽  
Author(s):  
Yuk L. Yung ◽  
William B. DeMore
Keyword(s):  
Solar System ◽  
Hydrological Cycle ◽  
Biogeochemical Cycles ◽  
Terrestrial Environment ◽  
Orbital Parameters ◽  
Planetary Scale ◽  
System P ◽  
Global Biogeochemical Cycles ◽  
The Last Glacial Maximum ◽  
Remote Past

Earth is the largest of the four terrestrial planets, three of which have substantial atmospheres. The astronomical and orbital parameters are summarized in table 9.1. Our planet has an obliquity of 23.5°, giving rise to well-known seasonal variations in solar insolation. The orbital elements are slightly perturbed by other planets in the solar system (primarily Jupiter), with time scales from 20 to 100 kyr, and these changes are believed to cause the advance and retreat of ice sheets. The last glacial maximum (LGM) occurred 18 kyr ago, at which time the planet was colder by several degrees centigrade on average. At present Earth is in an interglacial warm period. The origin of Earth may not be very different from that of the other terrestrial bodies. However, three properties may be unique to this planet. One is the formation of the Moon, probably via collision between Earth and a Mars-sized body. Second is the release of a huge amount of water from the interior (see discussion in section 8.5). Third, Earth is endowed with a large magnetic field that protects it from direct impact by the solar wind. Seventy percent of Earth's surface is covered by oceans, which have a mean depth of 3 km. There is so much water that Arthur C. Clarke proposed that "Ocean" might be a better name for our planet than "Earth." The enormous body of water became the cradle of life as early as 3.85 Gyr ago. The present terrestrial environment is the end-product of billions of years of evolution driven by the hydrological cycle and global biogeochemical cycles, in addition to the slower forces of geodynamics and geochemistry. The massive hydrological cycle and the biogeochemical cycles that operate on Earth are absent from other planets in the solar system. Mars in the remote past might have had a milder climate with liquid water on the surface, but the planet dried up a few eons ago. There is to date no observational evidence for the hypothetical oceans (composed of liquid hydrocarbons) on Titan. Life on a planetary scale equivalent to the terrestrial biosphere does not exist elsewhere in the solar system.

scholarly journals Postglacial fire history and interactions with vegetation and climate in southwestern Yunnan Province of China

2017 ◽  
Vol 13 (6) ◽  
pp. 613-627 ◽  
Author(s):  
Xiayun Xiao ◽  
Simon G. Haberle ◽  
Ji Shen ◽  
Bin Xue ◽  
Mark Burrows ◽  
...  
Keyword(s):  
Yunnan Province ◽  
Fire History ◽  
Regional Climate ◽  
Fire Regimes ◽  
Tropical Trees ◽  
Climatic Conditions ◽  
Qinghai Lake ◽  
Disturbance Factor ◽  
Fire Activity ◽  
Trees And Shrubs

Abstract. A high-resolution, continuous 18.5 kyr (1 kyr  =  1000 cal yr BP) macroscopic charcoal record from Qinghai Lake in southwestern Yunnan Province, China, reveals postglacial fire frequency and variability history. The results show that three periods with high-frequency and high-severity fires occurred during the periods 18.5–15.0, 13.0–11.5, and 4.3–0.8 ka, respectively. This record was compared with major pollen taxa and pollen diversity indices from the same core, and tentatively related to the regional climate proxy records with the aim to separate climate- from human-induced fire activity, and discuss vegetation–fire–climate interactions. The results suggest that fire was mainly controlled by climate before 4.3 ka and by the combined actions of climate and humans after 4.3 ka. Before 4.3 ka, high fire activity corresponded to cold and dry climatic conditions, while warm and humid climatic conditions brought infrequent and weak fires. Fire was an important disturbance factor and played an important role in forest dynamics around the study area. Vegetation responses to fire after 4.3 ka are not consistent with those before 4.3 ka, suggesting that human influence on vegetation and fire regimes may have become more prevalent after 4.3 ka. The comparisons between fire activity and vegetation reveal that evergreen oaks are flammable plants and fire-tolerant taxa. Alnus is a fire-adapted taxon and a nonflammable plant, but density of Alnus forest is a key factor to decide its fire resistance. The forests dominated by Lithocarpus/Castanopsis and/or tropical trees and shrubs are not easy to ignite, but Lithocarpus/Castanopsis and tropical trees and shrubs are fire-sensitive taxa. Fire appears to be unfavourable to plant diversity in the study area.

scholarly journals Where there's smoke, there's fuel: predicting Great Basin rangeland wildfire

2021 ◽  
Author(s):  
Joseph T Smith ◽  
Brady W Allred ◽  
Chad S Boyd ◽  
Kirk W Davies ◽  
Matthew O. Jones ◽  
...  
Keyword(s):  
Great Basin ◽  
Spatial Data ◽  
Ground Cover ◽  
Fire Regimes ◽  
Machine Learning Algorithms ◽  
Fire Season ◽  
Drought Indices ◽  
Area Burned ◽  
Fire Activity ◽  
Fine Fuels

Wildfires are a growing management concern in western US rangelands, where invasive annual grasses have altered fire regimes and contributed to an increased incidence of catastrophic large wildfires. Fire activity in arid, non-forested regions is thought to be largely controlled by interannual variation in fuel amount, which in turn is controlled by antecedent weather. Thus, long-range forecasting of fire activity in rangelands should be feasible given annual estimates of fuel quantity. Using a 32 yr time series of spatial data, we employ machine learning algorithms to predict the relative probability of large (>400 ha) wildfire in the Great Basin based on fine-scale annual and 16-day estimates of cover and production of vegetation functional groups, weather, and multitemporal scale drought indices. We evaluate the predictive utility of these models with a leave-one-year-out cross-validation, building spatial forecasts of fire probability for each year that we compare against actual maps of large wildfires. Herbaceous vegetation aboveground biomass production, bare ground cover, and long-term drought indices were the most important predictors of fire probability. Across 32 fire seasons, >80% of the area burned in large wildfires coincided with predicted fire probabilities ≥0.5. At the scale of the Great Basin, several metrics of fire season severity were moderately to strongly correlated with average fire probability, including total area burned in large wildfires, number of large wildfires, and average and maximum fire size. Our findings show that recent years of exceptional fire activity in the Great Basin were predictable based on antecedent weather and biomass of fine fuels, and reveal a significant increasing trend in fire probability over the last three decades driven by widespread changes in fine fuel characteristics.

scholarly journals Simulation of the isotopic composition of stratospheric water vapour – Part 2: Investigation of HDO/H<sub>2</sub>O variations

2014 ◽  
Vol 14 (21) ◽  
pp. 29459-29497 ◽  
Author(s):  
R. Eichinger ◽  
P. Jöckel ◽  
S. Lossow
Keyword(s):  
Isotopic Composition ◽  
Water Vapour ◽  
Lower Stratosphere ◽  
Hydrological Cycle ◽  
Isotope Ratios ◽  
Tape Recorder ◽  
Boreal Summer ◽  
Substantial Impact ◽  
Stratospheric Water Vapour ◽  
Water Isotope

Abstract. Studying the isotopic composition of water vapour in the lower stratosphere can reveal the driving mechanisms of changes in the stratospheric water vapour budget and therefore help to explain the trends and variations of stratospheric water vapour during the recent decades. We equipped a global chemistry climate model with a description of the water isotopologue HDO, comprising its physical and chemical fractionation effects throughout the hydrological cycle. We use this model to improve our understanding of the processes, which determine the patterns in the stratospheric water isotope composition and in the water vapour budget, itself. The link between the water vapour budget and its isotopic composition in the tropical stratosphere is presented through their correlation in a simulated 21 year time series. The two quantities depend on the same processes, however, are influenced with different strengths. A sensitivity experiment shows that fractionation effects during the oxidation of methane has a damping effect on the stratospheric tape recorder signal in the water isotope ratio. Moreover, the chemically produced high water isotope ratios overshadow the tape recorder in the upper stratosphere. Investigating the origin of the boreal summer tape recorder signal in the lower stratosphere reveals isotopically enriched water vapour crossing the tropopause over the subtropical Western Pacific. A correlation analysis confirms this link, which identifies the Asian Summer Monsoon as the major contributor for the intrusion of isotopically enriched water vapour into the stratosphere during boreal summer. Furthermore, convective ice lofting is shown to have a substantial impact on the isotope ratios of water vapour in the upper troposphere and lower stratosphere.

scholarly journals Orbital stability of S-type circumbinary planets

2021 ◽  
Vol 2145 (1) ◽  
pp. 012014
Author(s):  
N Nantanoi ◽  
N Nantanoi ◽  
S Awiphan ◽  
S Komonjinda ◽  
T Bunfong
Keyword(s):  
Orbital Stability ◽  
Physical Parameters ◽  
Orbital Eccentricity ◽  
Stable Orbit ◽  
Orbital Parameters ◽  
Inaccurate Measurement ◽  
Roche Limit ◽  
Orbital Instability ◽  
Circumbinary Planets

Abstract Nowadays, more than 4,000 exoplanets have been discovered, including a hundred of circumbinary planets. In the following work, the orbital variations of 67 S-type circumbinary planets have been studied. Their orbital evolutions for a thousand years are simulated using the REBOUND package. The published physical and orbital parameters of the systems are used to computed the systems’ orbital instability limits: Roche limit and Hill’s sphere. From 67 systems, there are two unstable circumbinary systems: Kepler-420 and GJ 86. Kepler-420 Ab orbit passes into the system’s Roche limit due to its high orbital eccentricity. For GJ 86 Ab, the planet orbits outside its Hill’s sphere. The instability of GJ 86 Ab might be caused by an inaccurate measurement of GJ 86 A physical parameters. Using the GJ 86 A mass obtained from Farihi et al., the planet orbits in the stable orbit zone.

scholarly journals Investigating future changes in Southern China precipitation characteristics based on dynamically downscaled CMIP5 climate projections

2020 ◽  
Author(s):  
Ying Lung Liu ◽  
Chi-Yung Tam ◽  
Sai Ming Lee
Keyword(s):  
Interannual Variability ◽  
General Circulation ◽  
Hydrological Cycle ◽  
Southern China ◽  
Lower Troposphere ◽  
Circulation Model ◽  
Boreal Summer ◽  
Annual Number ◽  
Climate Projections ◽  
The Mean

&lt;p&gt;In this study, general circulation model (GCM) products were dynamically downscaled using the Regional Climate Model system version 4 (RegCM4), in order to study changes in the hydrological cycle - including extreme events - due to a warmer climate by the end of the 21&lt;sup&gt;st&lt;/sup&gt; century over Southern China. The performance of 22 GCMs participating in the Coupled Model Intercomparison Project Phase 5 (CMIP5) in simulating the climate over the East Asian- western north Pacific region was first evaluated. It was found that MPI-ESM-MR, CNRM-CM5, ACCESS1-3, and GFDL- CM3 can reasonably reproduce the seasonal mean atmospheric circulation in that region, as well as its interannual variability. Outputs from these GCMs were subsequently downscaled, using the RegCM4, to a horizontal resolution of 25 km &amp;#215; 25km, for the period of 1979 to 2003, and also from 2050 to 2099, with the latter based on GCM projection according to the RCP8.5 scenario. Results show that the whole domain would undergo warming at the lower troposphere by 3 &amp;#8211; 4 &amp;#176;C over inland China and ~2 &amp;#176;C over the ocean and low-latitude locations. Compared to the 1979-2003 era, during 2050-2099 boreal summer, the mean precipitation is projected to increase by 1 &amp;#8211; 2 mm/day over coastal Southern China. There is also significantly enhanced interannual variability for the same season. In boreal spring, a similar increase in both the seasonal mean and also its year-to-year variations is also found, over more inland locations at about 25&amp;#176;N. Extreme daily precipitation is projected to become more intense, based on analyses of the 95&lt;sup&gt;th&lt;/sup&gt; percentile for these seasons. On the other hand, it will be significantly drier during autumn over a broad area in Southern China: the mean rainfall is projected to decrease by ~1 mm/day. In addition, changes in the annual number of consecutive dry days (CDD) throughout the whole calendar year was also examined. It was found that CDD over the more inland locations will increase by ~5 days. Thus, there will be a lengthening of the dry season in the region. Global warming&amp;#8217;s potential impact on sub-daily rainfall is also examined. For the rainfall diurnal cycle (DC), there is no significant change in both spatial and temporal patterns. Moisture budget analyses are also carried out, in order to ascertain the importance of change in background moisture, versus that in wind circulation, on the intensification of MAM and JJA mean rainfall as well as their interannual variability. The implication of these results on water management and climate change adaptation over the Southern China region will be discussed.&lt;/p&gt;

Sign in / Sign up

Export Citation Format

Share Document