The offshore wind industry is expanding from shallow water to deep water. As a cost-effective and efficient anchoring solution, drag embedment anchors have been widely used for mooring floating offshore structures. However, there is currently no well-established method for predicting the installation trajectory and holding capacity of drag anchors in sand. This paper reports an integrated anchor–chain–soil large-deformation finite-element model for simulating the complete installation of drag anchors in sand. The proposed approach restores the effects of anchor chains and detailed structures of the anchor, which is essential for detailed anchor design. Sensitivity analysis is conducted to investigate the convergence of model parameters. The performance of the numerical model is benchmarked against a centrifuge test conducted at the University of Western Australia (UWA), which demonstrates satisfactory accuracy and reliability. Installation simulations are then performed using a popular commercial anchor design in sands of different friction angles. Three characteristic stages during the drag embedment process are identified. The results highlight the significant influence of the soil resistance to the shank on the anchor penetration performance. The large-deformation analysis approach proposed provides a powerful tool for further investigation on drag anchor installation behavior in sand.
John M. MacDonald, George Taylor, Euan R. Lewis
et al.
Billions of tonnes of anthropogenic geomaterials, such as slags, ashes and cementitious materials, are deposited on the Earth's surface globally every year. These materials have the potential to become rock but little is known about how they may become lithified. In this study, we document lithification of a legacy deposit of cementitious material at a former cement works in Scotland, and uncover the mechanisms and drivers for its conversion from a loose granular sediment to an anthropogenic rock. Optical and electron microscopy and chemical mapping, coupled with X-ray diffraction, indicate the presence of particles of waste cementitious material interpreted to be calcium–silicate–hydrate (C-S-H) formed through hydration of cement clinker; these particles are rimmed by a secondary calcite mineral cement which binds the C-S-H particles together. Partial dissolution of C-S-H followed by diffusion of Ca and OH− into porewaters promoted ingassing and hydroxylation of atmospheric CO2 (fingerprinted by carbon isotope analysis). The CO2 reacted with the dissolved Ca to precipitate the calcite cement rimming the C-S-H grains. This calcite mineral cement has therefore bonded the grains to create an anthropogenic rock. This process can potentially create benefits in terms of ground stabilization and atmospheric CO2 sequestration.
Kaistrenko, Victor M., Willis, Pascal, Razjigaeva, Nadezhda G.
et al.
On October 4(5), 1994, one of the strongest tsunamigenic earthquakes in the history of the Southern
Kuril Islands occurred, which was accompanied by large-scale tectonic manifestations. Intense shaking led to the
collapse of the entire infrastructure on Shikotan and Kunashir Islands; 11 people died. The tsunami that followed
the earthquake reached a height of about 10 m on the ocean side of Shikotan Island and was recorded along the
entire coast of the Pacific Ocean. Generally, the study of the manifestations of this event had been carried out
since October 1994 and ended in 1997 with the publication of extensive reviews. For the first time, the data on
the specific effects on the ocean surface (seaquake) that accompanied this earthquake have been collected and
systematized. In the following years, the interest in this extraordinary event initiated further research. At the same
time, the study of the deposits of the tsunami of October 4(5), 1994, in the general context of study of ancient
tsunami (paleotsunami) deposits in this region came to the fore. These studies allowed us to obtain estimates of
the "preservation"/ "erasure" of the traces of this tsunami and more ancient events on the coast of the Southern
Kuril Islands. Some important data presented in this review are being published for the first time.
K. G. Miller, W. J. Schmelz, J. V. Browning
et al.
We estimate ice-volume driven (barystatic; BSL) sea-level changes for the Cenozoic using new Mg/Ca data from 58 to 48 Ma and a revised analysis of Mg/Ca trends over the past 66 Myr. We combine records of BSL, temperature-driven sea level, and long-term ocean basin volume variations to derive a new global mean geocentric sea level (GMGSL; “eustatic”) estimate. Bayesian analysis with Gaussian process priors shows that our BSL estimate shares a component that covaries on the Myr scale with “backstripped” relative sea-level (RSL) estimates (accounting for compaction, loading, and thermal subsidence) from the US Mid-Atlantic Coastal Plain, validating our method and estimates with errors of ±10 m. Peak warmth, elevated GMGSL and BSL, high CO2, and ice-free conditions occurred at times in the Paleocene to Eocene (ca. 64, 57.5, 35 Ma) and in much of the Early Eocene (55–48 Ma). However, our new results show that the Early Eocene was punctuated at specific times by several Myr-scale sea level lowerings (∼20–40 m) that require growth and decay of significant continental ice sheets even in the supposedly “ice-free” world. Continental-scale ice sheets waxed and waned beginning ca. 34 Ma (>50 m BSL changes), with near complete collapse during the Miocene Climate Optimum (17–14.8 Ma). Both the BSL and RSL estimates have markedly higher Oligocene to Early Miocene Myr-scale amplitudes (20–60 m) than recently published δ18O-based estimates (<20 m) and much lower estimates than those of Exxon Production Research (>100 m), leading us to reject those estimates. The US Mid-Atlantic margin RSL was dominated by GMGSL but was overprinted by changes in mantle dynamic topography on the several Myr scale, showing approximately 50 m higher Eocene estimates and regionally propagating Miocene RSL changes.
<p>Chemical weathering of sedimentary rocks can release carbon dioxide (<span class="inline-formula">CO<sub>2</sub></span>) and consume oxygen (<span class="inline-formula">O<sub>2</sub></span>) via the oxidation of petrogenic organic carbon and sulfide minerals. These pathways govern Earth's surface system and climate over geological timescales, but the present-day weathering fluxes and their environmental controls are only partly constrained due to a lack of in situ measurements. Here, we investigate the gaseous exchange of <span class="inline-formula">CO<sub>2</sub></span> and <span class="inline-formula">O<sub>2</sub></span> during the oxidative weathering of black shales and marls exposed in the French southern Alps. On six field trips over 1 year, we use drilled headspace chambers to measure the <span class="inline-formula">CO<sub>2</sub></span> concentrations in the shallow critical zone and quantify <span class="inline-formula">CO<sub>2</sub></span> fluxes in real time. Importantly, we develop a new approach to estimate the volume of rock that contributes <span class="inline-formula">CO<sub>2</sub></span> to a chamber, and assess effective diffusive gas exchange, by first quantifying the mass of <span class="inline-formula">CO<sub>2</sub></span> that is stored in a chamber and connected rock pores. Both rock types are characterized by similar contributing rock volumes and diffusive movement of <span class="inline-formula">CO<sub>2</sub></span>. However, <span class="inline-formula">CO<sub>2</sub></span> emissions differed between the rock types, with yields over rock outcrop surfaces (inferred from the contributing rock volume and the local weathering depths) ranging on average between 73 and 1108 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">t</mi><mspace width="0.125em" linebreak="nobreak"/><mi mathvariant="normal">C</mi><mspace width="0.125em" linebreak="nobreak"/><msup><mi mathvariant="normal">km</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="864643c20a98a4114c442a17c1538a95"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esurf-12-271-2024-ie00001.svg" width="61pt" height="15pt" src="esurf-12-271-2024-ie00001.png"/></svg:svg></span></span> for black shales and between 43 and 873 <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M16" display="inline" overflow="scroll" dspmath="mathml"><mrow class="unit"><mi mathvariant="normal">t</mi><mspace linebreak="nobreak" width="0.125em"/><mi mathvariant="normal">C</mi><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">km</mi><mrow><mo>-</mo><mn mathvariant="normal">2</mn></mrow></msup><mspace linebreak="nobreak" width="0.125em"/><msup><mi mathvariant="normal">yr</mi><mrow><mo>-</mo><mn mathvariant="normal">1</mn></mrow></msup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="61pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8634a84972cdf024154194bce9242012"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esurf-12-271-2024-ie00002.svg" width="61pt" height="15pt" src="esurf-12-271-2024-ie00002.png"/></svg:svg></span></span> for marls over the study period. Having quantified diffusive processes, chamber-based <span class="inline-formula">O<sub>2</sub></span> concentration measurements are used to calculate <span class="inline-formula">O<sub>2</sub></span> fluxes. The rate of <span class="inline-formula">O<sub>2</sub></span> consumption increased with production of <span class="inline-formula">CO<sub>2</sub></span>, and with increased temperature, with an average <span class="inline-formula">O<sub>2</sub></span><span class="inline-formula">:</span><span class="inline-formula">CO<sub>2</sub></span> molar ratio of 10<span class="inline-formula">:</span>1. If <span class="inline-formula">O<sub>2</sub></span> consumption occurs by both rock organic carbon oxidation and carbonate dissolution coupled to sulfide oxidation, either an additional <span class="inline-formula">O<sub>2</sub></span> sink needs to be identified or significant export of dissolved inorganic carbon occurs from the weathering zone. Together, our findings refine the tools we have to probe <span class="inline-formula">CO<sub>2</sub></span> and <span class="inline-formula">O<sub>2</sub></span> exchange in rocks at Earth's surface and shed new light on <span class="inline-formula">CO<sub>2</sub></span> and <span class="inline-formula">O<sub>2</sub></span> fluxes, their drivers, and the fate of rock-derived carbon.</p>
A. Ringenbach, A. Ringenbach, A. Ringenbach
et al.
<p>Mountain forests have a substantial protective function in preventing natural hazards, in part due to the presence of dead wood on the forest floor. Rates of deadwood accumulation have increased within the Alps and are predicted to rise further, due to natural disturbances. In particular, higher windthrow event frequencies are expected, primarily due to large-scale even-aged forest stands in many alpine regions combined with climate change. We quantified the rockfall protection effect of mountain forests with and without deadwood, in unprecedented detail, in experiments using two rock shapes with important hazard potential and masses of 200–3200 kg. Based on a multi-camera setup, pre- and post-experimentally retrieved high-resolution lidar data, and rock data measured in situ, we precisely reconstructed 63 trajectories. The principal parameters of interest describing the rockfall kinematics were retrieved for each trajectory. A total of 164 tree impacts and 55 deadwood impacts were observed, and the currently applied energy absorption curves – partially only derived theoretically – could consequently be corroborated or even expanded to a greater absorption performance of certain species than hitherto assumed. Standing trees, in general, and deadwood, in particular, were found to strongly impede the notorious lateral spreading of platy rocks. Platy rocks featured a shorter mean runout distance than their compact counterparts of similar weight, even in the absence of deadwood. These results indicate that the higher hazard potential of platy rocks compared with more compact rocks, previously postulated for open-field terrain, applies less to forested areas. Last, reproducing the experimental setting showcases how complex forest states can be treated within rockfall simulations. Overall, the results of this study highlight the importance of incorporating horizontal forest structures accurately in simulations in order to obtain realistic deposition patterns.</p>
<p>Cold and snowy spells are compound extreme events with the potential to cause high socioeconomic impacts. Gaining insight into their dynamics in climate change scenarios could help anticipating the need for adaptation efforts. We focus on winter cold and snowy spells over Italy, reconstructing 32 major events in the past 60 years from documentary sources. Despite warmer winter temperatures, very recent cold spells have been associated with abundant and sometimes exceptional snowfall.
Our goal is to analyse the dynamical weather patterns associated with these events and understand whether those patterns would be more or less recurrent in different emission scenarios using an intermediate-complexity model (the Planet Simulator, PlaSim). Our results, obtained by considering RCP2.6, RCP4.5 and RCP8.5 end-of-century equivalent <span class="inline-formula">CO<sub>2</sub></span> concentrations, suggest that the likelihood of synoptic configurations analogous to those leading to extreme cold spells would grow substantially under increased emissions.</p>
<p>A brief summary will be given of the historical development of
Geophysical Service of Austria, which comprises the national geomagnetic,
gravimetric and seismological services as well as the “Applied Geophysics
Section” located at the Zentralanstalt für Meteorologie und Geodynamik
(ZAMG) in Vienna in Austria. The paper presents the achievements, changes
and challenges of the Department from its modest beginning in 1851 until
2020. Finally, a special emphasis is placed on the Conrad Observatory – one
of the most comprehensive geophysical research observatories in the world.</p>
<p>We examine the influence of incision thresholds on topographic and scaling properties of landscapes that follow a landscape evolution model (LEM)
with terms for stream-power incision, linear diffusion, and uniform uplift. Our analysis uses three main tools. First, we examine the graphical behavior of theoretical relationships between curvature and the steepness index (which depends on drainage area and slope). These relationships plot
as straight lines for the case of steady-state landscapes that follow the LEM. These lines have slopes and intercepts that provide estimates of
landscape characteristic scales. Such lines can be viewed as counterparts of slope–area relationships, which follow power laws in detachment-limited landscapes but not in landscapes with diffusion. We illustrate the response of these curvature–steepness index lines to changes in the values of parameters. Second, we define a Péclet number that quantifies the competition between incision and diffusion, while taking the incision threshold into account. We examine how this Péclet number captures the influence of the incision threshold on the degree of landscape dissection. Third, we characterize the influence of the incision threshold using a ratio between it and the steepness index. This ratio is a dimensionless number in the case of the LEM that we use and reflects the fraction by which the incision rate is reduced due to the incision threshold; in this way, it quantifies the relative influence of the incision threshold across a landscape. These three tools can be used together to graphically illustrate how topography and process competition respond to incision thresholds.</p>
<p>This study presents a multi-scale analysis of cross-correlations based on
Haar fluctuations of globally averaged anomalies of precipitation (<span class="inline-formula"><i>P</i></span>),
precipitable water vapor (PWV), surface temperature (<span class="inline-formula"><i>T</i></span>), and atmospheric
radiative fluxes. The results revealed an emergent transition between weak
correlations at sub-yearly timescales (down to <span class="inline-formula">∼5</span> days) to
strong correlations at timescales larger than about <span class="inline-formula">∼1</span>–2 years (up to
<span class="inline-formula">∼1</span> decade). At multiyear timescales, (i) Clausius–Clapeyron becomes the dominant control of PWV
(<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M6" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi mathvariant="italic">ρ</mi><mrow><mi mathvariant="normal">PWV</mi><mo>,</mo><mi>T</mi></mrow></msub><mo>≈</mo><mn mathvariant="normal">0.9</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="63pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="24291660959f156841c7f7a6f0a2209d"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-10-219-2019-ie00001.svg" width="63pt" height="13pt" src="esd-10-219-2019-ie00001.png"/></svg:svg></span></span>), (ii) surface temperature averaged over
global land and over global ocean (sea surface temperature, SST) become strongly correlated (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi mathvariant="italic">ρ</mi><mrow><mi mathvariant="normal">Tland</mi><mo>,</mo><mi mathvariant="normal">SST</mi></mrow></msub><mo>∼</mo><mn mathvariant="normal">0.6</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="75pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="d35b7260d9a732acc2b584a4b2ec5455"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-10-219-2019-ie00002.svg" width="75pt" height="13pt" src="esd-10-219-2019-ie00002.png"/></svg:svg></span></span>); (iii) globally averaged precipitation
variability is dominated by energetic constraints, specifically the surface
downwelling longwave radiative flux (DLR) (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M8" display="inline" overflow="scroll" dspmath="mathml"><mrow><msub><mi mathvariant="italic">ρ</mi><mrow><mi mathvariant="normal">P</mi><mo>,</mo><mi mathvariant="normal">DLR</mi></mrow></msub><mo>≈</mo><mo>-</mo><mn mathvariant="normal">0.8</mn></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="67pt" height="13pt" class="svg-formula" dspmath="mathimg" md5hash="cae7d65134fe9eed3a7e2a3bbd287df4"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="esd-10-219-2019-ie00003.svg" width="67pt" height="13pt" src="esd-10-219-2019-ie00003.png"/></svg:svg></span></span>)
displayed stronger correlations than the direct response to <span class="inline-formula"><i>T</i></span> fluctuations,
and
(iv) cloud effects are negligible for the energetic constraints in (iii),
which are dominated by clear-sky DLR. At sub-yearly timescales, all
correlations underlying these four results decrease abruptly towards
negligible values. Such a transition has important implications for
understanding and quantifying the climate sensitivity of the global hydrological
cycle. The validity of the derived correlation structure is demonstrated by
reconstructing global precipitation time series at 2-year resolution,
relying on the emergent strong correlations (<span class="inline-formula"><i>P</i></span> vs. clear-sky DLR). Such a
simple linear sensitivity model was able to reproduce observed <span class="inline-formula"><i>P</i></span> anomaly
time series with similar accuracy to an (uncoupled) atmospheric model
(ERA-20CM) and two climate reanalysis (ERA-20C and 20CR). The linear
sensitivity breaks down at sub-yearly timescales, whereby the underlying
correlations become negligible. Finally, the relevance of the multi-scale
framework and its potential for stochastic downscaling applications are
demonstrated by deriving accurate monthly <span class="inline-formula"><i>P</i></span> probability density functions (PDFs)
from the reconstructed 2-year <span class="inline-formula"><i>P</i></span> time series based on scale-invariant
arguments alone. The derived monthly PDFs outperform the statistics
simulated by ERA-20C, 20CR, and ERA-20CM in reproducing observations.</p>
<p>The Gravity Recovery and Climate Experiment (GRACE) delivered the most
accurate quantification of global mass variations with monthly temporal
resolution on large spatial scales. Future gravity missions will take
advantage of improved measurement technologies, such as enhanced orbit
configurations and tracking systems, as well as reduced temporal aliasing
errors. In order to achieve the latter, sub-monthly to daily innovative
models are computed. In addition, non-conventional methods based on radial
basis functions (RBFs) and mascons will give the ability to compute models in
regional and global representations as well. We show that the RBF modeling
technique can be used for processing GRACE data yielding global gravity field
models which fit independent reference values at the same level as commonly
accepted global geopotential models based on spherical harmonics.</p>
<p>The present study compares for the first time a complete global series of
solutions in order to quantify recent ice mass changes. We further compare
the ice-induced crustal deformations due to the dynamic loading of the
crustal layer with the Global Positioning System (GPS) uplift measurements
along Greenland's coastline. Available mass change estimates based on
Ice, Cloud, and land Elevation Satellite (ICESat) laser altimetry measurements both
in Greenland and Antarctica are used to assess the GRACE results.</p>
<p>A comparison of GRACE time series with hydrological modeling for various
basin extensions reveals overall high correlation to surface and groundwater
storage compartments. The forward computation of satellite orbits for
altimetry satellites such as Envisat, Jason-1 and Jason-2 compares the
performance of GRACE time-variable gravity fields with models including time
variability, such as EIGEN-6S4.</p>
Arezoo Moradi, Nahid Shabanian Boroujeni , Ali Reza Davoudian Dehkordy
Introduction
Studied mylonitic granite-gneiss body is located in the Northwest of the Azna region in the Lorestan province close to the June dimension stone mine. It is a part of the metamorphic- magmatic complex including granite-gneiss, amphibolite, marble and schist. The crystalline basement is attributed to late-Neoproterozoic and it indicates a Panafrican basement, which yields a laser-ablation ICP–MS U–Pb zircon ages of 608 ± 18 Ma and 588 ± 41 Ma (Shakerardakani et al., 2015). There are two granite-gneiss plutons in the complex that are Galeh– Dezh (Shabanian et al., 2009), and June plutons. The Galeh-Doz pluton are previously proposed as syn-deformation pluton with a major S-shaped bend which has been imparted during dextral shearing with a Late Cretaceous (Mohajjel and Fergusson, 2000). However, new age dating on the pluton using U–Pb in the magmatic zircon produced the late-Neoproterozoic dates (Nutman et al., 2014; Shakerardakani et al., 2015). The granite-gneiss plutons show mylonitic fabrics and microstructures (Shabanian et al., 2010). The geochemical characteristics of mylonitic granite-gneiss body near June mine in NW Azna, is in the focus of our research.
Materials and methods
Petrographic investigations of 30 thin sections were made. Then eight samples were selected and analyzed for whole rock major, trace and REE compositions by ICP-emission spectrometry and ICP-mass spectrometry using natural rock standards as reference samples for calibration at the ACME Analytical Laboratories in Vancouver, British Columbia, Canada.
Results
The studied gneiss- granitic body has lepido-granoblastic texture as its major texture. It variably shows evidence of dynamic deformation from ultramylonite to protomylonite. The gneiss- granite consists of quartz, alkali feldspar (mostly as perthite), plagioclase, biotite, white mica (muscovite and phengitic muscovite). Accessory phases in the granitoid include, tourmaline, zircon, magmatic epidote, allanite, apatite, and magnetite. The mylonitic gneiss-granite has a mantled porphyroclast texture that may be characterized by large asymmetrical porphyroclasts of K-feldspar and plagioclase with a mantle which includes white-mica, biotite, quartz and feldspar aggregates. Some of the petrographic evidence show dynamic deformation during the crystallization such as grain boundary migration (GBM) or sub-grain rotation (SGR), patchy perthite. Evidence of strain, such as deformation twins, bent or curved twins, undulatory extinction occur characteristically in plagioclase and display dynamic deformation in solid state. The rocks exhibit identical compositional ranges with 71.24–78.35 wt.% SiO2; high levels of alkalies (Na2O ranges from 3.07 to 4.02 %, K2O varies from 4.18 to 5.53 %); low levels of Fe2O3tot (0.80 to 2.60 %). Also, the trace element compositions display significant variations, such as Zr (157.7-330.5 ppm), Eu (0.07-0.28 ppm), Nb (40.9-77.3 ppm), Ga (19.7-25.97 ppm). The studied rocks are strongly enriched in LREE and HFSE and show a strong depletion in Ba, Sr, Eu and Ti and enrichment in Rb and Zr. The element contents are also similar to typical A-type granite (Whalen et al., 1987). The rocks are alkali to alkali-calcic, metaluminous to mildly peraluminous granite and ferroan in new geochemical classification scheme for granitoids (proposed by Frost et al., 2001).
Discussion
The chondrite-normalized rare-earth element patterns of the mylonitic gneiss- granitic rocks indicate the LREE over HREE fractionation with significant negative Eu anomalies. Primitive-mantle-normalized spidergrams (Sun and McDonough, 1989) normalized trace element patterns with negative Ba and Nb anomalies, and positive Rb, Th and Ce anomalies, simulate the collisional and post-collisional granitoids of Pearce et al (Pearce et al., 1984). All of the samples fall in the A2 group in Eby classification (Eby, 1992). On the tectonic discrimination plots, the granites show a within-plate granite (WPG) character (Pearce et al., 1984).
Acknowledgements
The study was completed at the Shahrekord University and it was supported by the office of graduate studies. The authors are grateful to the office for their support.
References
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Mohajjel, M. and Fergusson, C.L., 2000. Dextral transpression in Late Cretaceous continental collision, Sanandaj–Sirjan Zone, western Iran. Journal of Structural Geology, 22(8): 1125-1139.
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Z. Yin, S. C. Dekker, B. J. J. M. van den Hurk
et al.
Multiple states of woody cover under similar climate conditions are found in
both conceptual models and observations. Due to the limitation of the
observed woody cover data set, it is unclear whether the observed bimodality
is caused by the presence of multiple stable states or is due to dynamic
growth processes of vegetation. In this study, we combine a woody cover data
set with an aboveground biomass data set to investigate the simultaneous
occurrences of savanna and forest states under the same precipitation
forcing. To interpret the results we use a recently developed vegetation
dynamics model (the Balanced Optimality Structure Vegetation Model), in which
the effect of fires is included. Our results show that bimodality also exists
in aboveground biomass and retrieved vegetation structure. In addition, the
observed savanna distribution can be understood as derived from a stable
state and a slightly drifting (transient) state, the latter having the
potential to shift to the forest state. Finally, the results indicate that
vegetation structure (horizontal vs. vertical leaf extent) is a crucial
component for the existence of bimodality.