Martian Lakes Forming Climates Were Caused by Methane Outbursts and Short Term

Duration and rapid shutdown of Mars lake-forming climates explained by methane bursts

Authors:

Kite et al

Abstract:

Build-up of relatively young (<∼3.6 Ga) deltas and alluvial fans on Mars required lakes to persist for >3 Kyr (assuming dilute flow), but the watersheds' little-weathered soils indicate a climate history that was >99% dry. The lake-forming climates' trigger mechanism remains unknown. Here we show that these intermittency constraints, while inconsistent with many previously-proposed triggers for lake-forming climates, are consistent with a novel CH4-burst mechanism. Chaotic transitions in mean obliquity drive latitudinal shifts in temperature and ice loading that destabilize CH4 clathrate. For past clathrate hydrate stability zone occupancy fractions >∼0.2, we show that CH4(±C2H6) builds up to levels whose radiative forcing (>15 W/m2, plus feedbacks) is sufficient to modulate lake-forming climates. Such occupancy fractions are consistent with CH4+C2H6 production by >3 Ga water-rock reactions. Sub-lake CH4 destabilization provides positive feedback. UV-limited CH4 photolysis curtails individual lake-forming climates to

Methane Humidity Near TItan's Surface

The near-surface methane humidity on Titan

Authors:

Lora et al

Abstract:

We retrieve vertical and meridional variations of methane mole fraction in Titan's lower troposphere by re-analyzing near-infrared ground-based observations from 17 July 2014 UT (Adamkovics et al., 2016). We generate synthetic spectra using atmospheric methane profiles that do not contain supersaturation or discontinuities to fit the observations, and thereby retrieve minimum saturation altitudes and corresponding specific humidities in the boundary layer. We relate these in turn to surface-level relative humidities using independent surface temperature measurements. We also compare our results with general circulation model simulations to interpret and constrain the relationship between humidities and surface liquids. The results show that Titan's lower troposphere is undersaturated at latitudes south of 60N, consistent with a dry surface there, but increases in humidity toward the north pole indicate appreciable surface liquid coverage. While our observations are consistent with considerably more liquid methane existing at the north pole than is present in observed lakes, a degeneracy between low-level methane and haze leads to substantial uncertainty in determining the extent of the source region.

Carbonate deposits from the ancient aqueduct of Béziers, France as Evidence of Local Environment During Roman Empire

Carbonate deposits from the ancient aqueduct of Béziers, France — A high-resolution palaeoenvironmental archive for the Roman Empire

Authors:

Passchier et al

Abstract:

Carbonate deposits from a Roman aqueduct in Béziers, southern France, record environmental conditions during the late first century C.E. These deposits formed in a steep section of the aqueduct with a high flow velocity, which caused rapid deposition of up to 11 mm of calcite per year over a period of 22–24 years. The microstructure, trace element and stable isotope composition show that regular deposition was interrupted by high-discharge events, probably in response to heavy rainfall during autumn and winter, transporting colloidally- and particle-bound elements and depositing calcite with elevated δ18O values. Individual autumn high-discharge events coincide with abrupt decreases in δ13C from − 8 to − 12‰ giving rise to a saw-tooth profile. In some years, several high flow events persisted throughout the winter, suppressing this profile. Event horizons of micrite capping sparite growth surfaces, enriched in Mg, may represent anomalously low water levels or periods when the channel fell dry. In comparison to carbonate deposits from Roman aqueducts in the Eastern Mediterranean, visible layering is less regular and pronounced in Béziers, reflecting a more complex precipitation pattern.

Extensive Noachian fluvial systems in Arabia Terra on Mars

Extensive Noachian fluvial systems in Arabia Terra: Implications for early Martian climate

Authors:

Davis et al

Abstract:

Valley networks are some of the strongest lines of evidence for extensive fluvial activity on early (Noachian; >3.7 Ga) Mars. However, their purported absence on certain ancient terrains, such as Arabia Terra, is at variance with patterns of precipitation as predicted by "warm and wet" climate models. This disagreement has contributed to the development of an alternative "icy highlands" scenario, whereby valley networks were formed by the melting of highland ice sheets. Here, we show through regional mapping that Arabia Terra shows evidence for extensive networks of sinuous ridges. We interpret these ridge features as inverted fluvial channels that formed in the Noachian, before being subject to burial and exhumation. The inverted channels developed on extensive aggrading flood plains. As the inverted channels are both sourced in, and traverse across, Arabia Terra, their formation is inconsistent with discrete, localized sources of water, such as meltwater from highland ice sheets. Our results are instead more consistent with an early Mars that supported widespread precipitation and runoff.

Evidence of a Declining Martian Hydrological Cycle Starting 3.7 Billion Years Ago at the Noachian/Hesperian Boundary

Insights into surface runoff on early Mars from paleolake basin morphology and stratigraphy

Authors:

Goudge et al

Abstract:

We present observations on the morphology and stratigraphy of more than 400 paleolake basins on Mars. We show that there are two distinct classes of Martian paleolake basins: (1) paleolakes fed by regionally integrated valley networks (N = 251), and (2) paleolakes fed by isolated inlet valleys not integrated into broader regional drainage systems (N = 174). We conclude that valley network–fed paleolakes primarily formed prior to approximately the Noachian-Hesperian boundary, ca. 3.7 Ga, while isolated inlet valley paleolakes primarily formed later in Martian history. All 174 isolated inlet valley paleolakes are closed-basin lakes; however, there are surprisingly few (31) valley network–fed closed-basin lakes compared to a large number (220) of valley network–fed open-basin lakes. This observation is consistent with declining levels of fluvial activity over time on the Martian surface. Our results imply that during the era of valley network formation, ∼90% of topographic basins breached by an inlet valley had sufficiently high ratios of water influx to losses to fill, overtop, and form an outlet valley. This conclusion provides an important constraint on the balance between surface runoff production and water losses on early Mars that must be satisfied by any model of the early Martian climate and hydrologic cycle.

Frozen Nitrogen Lake, Channels Spotted on Pluto

NASA's New Horizons spacecraft spied several features on Pluto that offer evidence of a time millions or billions of years ago when – thanks to much higher pressure in Pluto's atmosphere and warmer conditions on the surface – liquids might have flowed across and pooled on the surface of the distant world.

"In addition to this possible former lake, we also see evidence of channels that may also have carried liquids in Pluto's past," said Alan Stern, Southwest Research Institute, Boulder, Colorado—principal investigator of New Horizons and lead author of the scientific paper.

This feature appears to be a frozen, former lake of liquid nitrogen, located in a mountain range just north of Pluto's informally named Sputnik Planum. Captured by the New Horizons' Long Range Reconnaissance Imager (LORRI) as the spacecraft flew past Pluto on July 14, 2015, the image shows details as small as about 430 feet (130 meters). At its widest point the possible lake appears to be about 20 miles (30 kilometers) across.

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The fate of ethane in Titan’s hydrocarbon lakes and seas

The fate of ethane in Titan’s hydrocarbon lakes and seas

Authors:

Mousis et al

Abstract:

Ethane is expected to be the dominant photochemical product on Titan’s surface and, in the absence of a process that sequesters it from exposed surface reservoirs, a major constituent of its lakes and seas. Absorption of Cassini’s 2.2 cm radar by Ligeia Mare however suggests that this north polar sea is dominated by methane. In order to explain this apparent ethane deficiency, we explore the possibility that Ligeia Mare is the visible part of an alkanofer that interacted with an underlying clathrate layer and investigate the influence of this interaction on an assumed initial ethane–methane mixture in the liquid phase. We find that progressive liquid entrapment in clathrate allows the surface liquid reservoir to become methane-dominated for any initial ethane mole fraction below 0.75. If interactions between alkanofers and clathrates are common on Titan, this should lead to the emergence of many methane-dominated seas or lakes.

The physical properties of Titan’s empty lake basins

Constraining the physical properties of Titan’s empty lake basins using nadir and off-nadir Cassini RADAR backscatter

Authors:

Michaelides et al

Abstract:

We use repeat synthetic aperture radar (SAR) observations and complementary altimetry passes acquired by the Cassini spacecraft to study the scattering properties of Titan’s empty lake basins. The best-fit coefficients from fitting SAR data to a quasi-specular plus diffuse backscatter model suggest that the bright basin floors have a higher dielectric constant, but similar facet-scale rms surface facet slopes, to surrounding terrain. Waveform analysis of altimetry returns reveals that nadir backscatter returns from basin floors are greater than nadir backscatter returns from basin surroundings and have narrower pulse widths. This suggests that floor deposits are structurally distinct from their surroundings, consistent with the interpretation that some of these basins may be filled with evaporitic and/or sedimentary deposits. Basin floor deposits also express a larger diffuse component to their backscatter, which is likely due to variations in subsurface structure or an increase in roughness at the wavelength scale (Hayes, A.G. et al. [2008]. Geophys. Res. Lett. 35, 9). We generate a high-resolution altimetry radargram of the T30 altimetry pass over an empty lake basin, with which we place geometric constraints on the basin’s slopes, rim heights, and depth. Finally, the importance of these backscatter observations and geometric measurements for basin formation mechanisms is briefly discussed.

The tectonics of Titan: Global structural mapping from Cassini RADAR

The tectonics of Titan: Global structural mapping from Cassini RADAR

Authors:

Yung-Chun Liu et al

Abstract:

The Cassini RADAR mapper has imaged elevated mountain ridge belts on Titan with a linear-to-arcuate morphology indicative of a tectonic origin. Systematic geomorphologic mapping of the ridges in Synthetic Aperture RADAR (SAR) images reveals that the orientation of ridges is globally E–W and the ridges are more common near the equator than the poles. Comparison with a global topographic map reveals the equatorial ridges are found to lie preferentially at higher-than-average elevations. We conclude the most reasonable formation scenario for Titan’s ridges is that contractional tectonism built the ridges and thickened the icy lithosphere near the equator, causing regional uplift. The combination of global and regional tectonic events, likely contractional in nature, followed by erosion, aeolian activity, and enhanced sedimentation at mid-to-high latitudes, would have led to regional infilling and perhaps covering of some mountain features, thus shaping Titan’s tectonic landforms and surface morphology into what we see today.

Eight-color maps of Titan’s surface from spectroscopy with Huygens’ DISR

Eight-color maps of Titan’s surface from spectroscopy with Huygens’ DISR

Authors:

Karkoschka et al

Abstract:

During the descent of the Huygens probe in Titan’s atmosphere, the Descent Imager/Spectral Radiometer (DISR) acquired spectra of 3660 locations within 250 km of the landing site. Each spectrum consisted of 200 resolution elements between 480 and 960 nm wavelength. With the help of radiative transfer models, contributions from the atmosphere and surface were separated. In eight methane windows, the data were combined into a map of Titan’s surface reflectivity with 250 km diameter near the landing site. Principal component analysis revealed three significant components, a brightness component that is consistent with a mosaic based on DISR imaging of much higher spatial resolution, a spectral slope component, and a spectral curvature component. The brightness component has stronger contrasts at longer wavelengths, or brighter areas have a larger spectral slope, consistent with previous results (Keller et al. [2008]. Planet. Space Sci. 56, 728–752). The second component corresponds to small differences in spectral slopes that are not correlated with features seen before except for an area with unusual high spectral slope found by the same authors and confirmed here. Our map of the second component gives another important parameter in characterizing and understanding Titan’s surface. The third principal component is somewhat noisy and describes variation in the spectral curvature that have never seen before at similar wavelengths. These variations require processes to differentiate surface spectra. To extend this work to longer wavelengths, 62 spectra from 850 to 1600 nm wavelength were investigated too, although the much lower number of spatial resolution points revealed only two significant components in the principal component analysis. They correlate with the first two components found in the shorter wavelength data. We also compare our results with an observation by Cassini’s Visible Imager/Mapping Spectrometer (VIMS) that imaged part of our investigated area with 4096 spatial resolution elements. Both data sets are complementary. DISR data extend to about 1500 nm wavelength while most surface features are seen in the VIMS data beyond 1500 nm.

Alluvial Fan Morphology, distribution and formation on Titan

Alluvial Fan Morphology, distribution and formation on Titan

Authors:

Birch et al

Abstract:

Titan is a hydrologically active world, with dozens of alluvial fans that are evidence of sediment transport from high to low elevations. However, the distribution and requirements for the formation of fans on Titan are not well understood. We performed the first global survey of alluvial fans on Titan using Cassini Synthetic Aperture Radar (SAR) data, which cover 61% of Titan’s surface. We identified 82 fans with areas ranging from 28 km2 to 27,000 km2. A significant fraction (∼60%) of the fans are restricted to latitudes of ±50–80°, suggesting that fluvial sediment transport may have been concentrated in the near-polar terrains in the geologically recent past. The density of fans is also found to be correlated with the latitudes predicted to have the highest precipitation rates by Titan Global Circulation Models. In equatorial regions, observable fans are not generally found in proximity to dune fields. Such observations suggest that sediment transport in these areas is dominated by aeolian transport mechanisms, though with some degree of recent equatorial fluvial activity. The fan area-drainage area relationship on Titan is more similar to that on Earth than on Mars, suggesting that the fans on Titan are smaller than what may be expected, and that the transport of bedload sediment is limited. We hypothesize that this has led to the development of a coarse gravel-lag deposit over much of Titan’s surface. Such a model explains both the morphology of the fans and their latitudinal concentration, yielding insight into the sediment transport regimes that operate across Titan today.

Structure of Titan’s evaporites

Structure of Titan’s evaporites

Authors:

Cordier et al

Abstract:

Numerous geological features that could be evaporitic in origin have been identified on the surface of Titan. Although they seem to be water–ice poor, their main properties – chemical composition, thickness, stratification – are essentially unknown. In this paper, which follows on a previous one focusing on the surface composition (Cordier, D., Barnes, J.W., Ferreira, A.G. [2013b]. Icarus 226(2),1431–1437), we provide some answers to these questions derived from a new model. This model, based on the up-to-date thermodynamic theory known as “PC-SAFT”, has been validated with available laboratory measurements and specifically developed for our purpose. 1-D models confirm the possibility of an acetylene and/or butane enriched central layer of evaporitic deposit. The estimated thickness of this acetylene–butane layer could explain the strong RADAR brightness of the evaporites. The 2-D computations indicate an accumulation of poorly soluble species at the deposit’s margin. Among these species, HCN or aerosols similar to tholins could play a dominant role. Our model predicts the existence of chemically trimodal “bathtub rings” which is consistent with what it is observed at the south polar lake Ontario Lacus. This work also provides plausible explanations to the lack of evaporites in the south polar region and to the high radar reflectivity of dry lakebeds.

Temporal variations of Titan’s surface with Cassini/VIMS

Temporal variations of Titan’s surface with Cassini/VIMS

Authors:

Solomonidou et al

Abstract:

We analyze Cassini VIMS data of several areas on Titan’s surface looking for variations with time. Three of these locations are near the equator (10–30°S), namely Hotei Regio, Tui Regio and Sotra Patera; in some cases changes in brightness and/or in appearance were reported therein. We also investigate a portion of the undifferentiated plains, areas relatively homogeneous and dark in radar observations, located near 20–25°N. This is a follow-up on a previous paper in which we had inferred surface albedos for some distinct regions of interest (RoIs) identified within the Hotei, Tui and Sotra areas through a Principal Component Analysis (PCA) and radiative transfer (RT) modeling (Solomonidou [2014]. J. Geophys. Res. 119, 1729–1747). We apply the same methods here to a larger dataset looking for variations of the surface albedo with time and using the Huygens landing site as the ‘ground truth’ for calibration purposes. As expected, the undifferentiated plains remain unchanged from January 2010 to June 2012. Our analysis of Hotei Regio data from March 2005 to March 2009 also does not show any significant surface albedo variations within uncertainties. We note however that our RT retrievals are not optimal in this case because of the use of a plane-parallel code and the unfavorable geometry of the associated datasets. Conversely, Tui Regio and Sotra Patera show surface albedo fluctuations with time with pronounced trends for darkening and for brightening respectively. The Tui Regio spectrum exhibits a surface albedo decrease from March 2005 to February 2009, at 0.94, 1.08, 2.03, and 5 μm wavelengths, while the spectrum shape remains the same over that time. On the contrary, the Sotra Patera area became at least two times brighter within a year (April 2005–February 2006), at 1.58 μm, 2.03 μm, and 5 μm. We also retrieved surface albedo spectra for three reference regions surrounding Hotei, Tui and Sotra and for three additional regions we use as ‘test cases’ that correspond to dune fields. During the time periods explored here we find that, as expected and contrary to Tui Regio and Sotra Patera, the test cases did not show any significant changes in surface albedo. We therefore suggest that temporal variations of surface albedo exist for some areas on Titan, but that their origin may differ from one region to the other. They could be due to diverse, past and/or ongoing formation processes (endogenic and/or exogenic, possibly cryovolcanic), as discussed here.

Lopingian Permian Niger had a Wildly Seasonal Arid Climate With Water Inundations Like the African Namib Desert and Australian Lake Eyre Basin

Biological and physical evidence for extreme seasonality in central Permian Pangea

Authors:

Looy et al

Abstract:

Climate models indicate increased desertification in the continental interior of Pangea during the Permian, which would have affected the composition of the flora and fauna. We present a multi-proxy paleoenvironmental reconstruction of a terrestrial ecosystem in central Pangea of Lopingian age. The reconstruction is based on biological and physical data from the Moradi Formation, located in the Tim Mersoi Basin, northern Niger. Paleosols and sedimentological evidence indicate that the prevailing climate was semi-arid to very arid with marked intervals of high water availability. Carbon stable isotope data from organic matter and paleosols suggest that both the soil productivity and actual evapotranspiration were very low, corresponding to arid conditions. Histological analysis of pareiasaur bones shows evidence of active metabolism and reveals distinct growth marks. These interruptions of bone formation are indicative of growth rhythms, and are considered as markers for contrasting seasonality or episodic climate events. The macrofossil floras have low diversity and represent gymnosperm-dominated woodlands. Most notable are ovuliferous dwarf shoots of voltzian conifers, and a 25-m long tree trunk with irregularly positioned branch scars. The combined biological and physical evidence suggests that the Moradi Formation was deposited under a generally arid climate with recurring periods of water abundance, allowing for a well-established ground water-dependent ecosystem. With respect to its environment, this system is comparable with modern ecosystems such as the southern African Namib Desert and the Lake Eyre Basin in Australia, which are discussed as modern analogues.

 

What Caused the Pliocene Neogene to get Wetter?

Pliocene reversal of late Neogene aridification

Authors:

Kale Sniderman et al

Abstract:

The Pliocene epoch (5.3–2.6 Ma) represents the most recent geological interval in which global temperatures were several degrees warmer than today and is therefore considered our best analog for a future anthropogenic greenhouse world. However, our understanding of Pliocene climates is limited by poor age control on existing terrestrial climate archives, especially in the Southern Hemisphere, and by persistent disagreement between paleo-data and models concerning the magnitude of regional warming and/or wetting that occurred in response to increased greenhouse forcing. To address these problems, here we document the evolution of Southern Hemisphere hydroclimate from the latest Miocene to the middle Pliocene using radiometrically-dated fossil pollen records preserved in speleothems from semiarid southern Australia. These data reveal an abrupt onset of warm and wet climates early within the Pliocene, driving complete biome turnover. Pliocene warmth thus clearly represents a discrete interval which reversed a long-term trend of late Neogene cooling and aridification, rather than being simply the most recent period of greater-than-modern warmth within a continuously cooling trajectory. These findings demonstrate the importance of high-resolution chronologies to accompany paleoclimate data and also highlight the question of what initiated the sustained interval of Pliocene warmth.

American Southwest may Mimic Drought Conditions That Destroyed Anasazi/Ancestral Puebloans due to Global Warming

The weather patterns that typically bring moisture to the Southwest are becoming more rare, an indication that the region is sliding into the drier climate state predicted by global models, according to a new study.

"A normal year in the Southwest is now drier than it once was," said Andreas Prein, a researcher at the National Center for Atmospheric Research (NCAR) in Boulder, Colorado, who led the study. "If you have a drought nowadays, it will be more severe because our base state is drier."

Climate models generally agree that human-caused climate change will push the southwestern United States to become drier. And in recent years, the region has been stricken by drought. But linking model predictions to changes on the ground is challenging.

For the study, the researchers analyzed 35 years' worth of data to identify common weather patterns -- arrangements of high and low pressure systems that determine where it's likely to be sunny and clear or cloudy and wet.

They identified a dozen patterns that are usual for the weather activity in the contiguous U.S., then looked to see whether those patterns were becoming more or less frequent.

"The weather types that are becoming more rare are the ones that bring a lot of rain to the southwestern United States," Prein said. "Because only a few weather patterns bring precipitation to the Southwest, those changes have a dramatic impact."

The Southwest is especially vulnerable to any additional drying. The region, already the most arid in the country, is home to a quickly growing population that is putting tremendous stress on its limited water resources.

"Prolonged drought has many adverse effects, so understanding regional precipitation trends is vital for the well-being of society," says Anjuli Bamzai, program director in the National Science Foundation (NSF) Division of Atmospheric and Geospace Sciences, which funded the research. "These researchers demonstrate that subtle shifts in large-scale weather patterns over the past three decades or so have been the dominant factor in precipitation trends in the southwestern United States."

The study also found an opposite, though smaller, effect in the Northeast, where some of the weather patterns that typically bring moisture to the region are increasing.

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Climate Variability during the Carnian Pluvial Phase (Carnian Triassic Wet Phase)

Climate variability during the Carnian Pluvial Phase — A quantitative palynological study of the Carnian sedimentary succession at Lunz am See, Northern Calcareous Alps, Austria

Authors:

Mueller et al

Abstract:

The Middle and Upper Triassic prevailing dry climate was interrupted by a global phase of increased humidity during the Early Carnian, the Carnian Pluvial Phase (CPP). It started at the Julian 1–2 boundary and lasted approximately until the latest Julian or early Tuvalian. In the Tethys this is reflected by a change from limestone deposits to, first, organic rich mudstones and then to siliciclastics. The CPP occurred along the northern rim of the Tethys and is reported from many locations within and surrounding Europe. In this study samples from Lunz am See in Austria were analyzed for palynology and for bulk carbon isotope values covering a 450 m thick succession. A known − 3‰ bulk organic carbon isotope excursion, possibly as a result of the eruption of large amounts of volcanogenic material, in the Göstling Member and the basal Reingraben Formation has been confirmed. A total of five distinctive palynology assemblages were recognized and correlated regionally. While the under- and overlying formations yield terrestrial and subordinate also marine palynomorphs, the palynoflora of the Lunz Formation is near wholly terrestrial in origin. Climate trends were inferred from multivariate statistical analysis (PCA) of the palynofloral record. Palynomorphs show a general trend from a dry climate during the Julian 1 to wetter conditions during the Julian 2. The wetter conditions were periodically interrupted by shorter periods of dryer climate. In terms of temperature trends the climate was warmer during the early Julian 2 which corresponds with the deposition of the Reingraben Formation, temperature decreased again and remained fairly stable during most of later part of the Julian 2, which corresponds to the deposition of the Lunz Formation. This study correlates with similar observations from other locations from the western Tethys region that support the theory of a wide-ranging to global Carnian Pluvial Phase.

California to Experience More Extreme Droughts, Inundations due to Climate Change

In the future, the Pacific Ocean's temperature cycles could disrupt more than just December fishing. A study published in Nature Communications suggests that the weather patterns known as El Nino and La Nina could lead to at least a doubling of extreme droughts and floods in California later this century.

The study shows more frequent extreme events are likely to occur. Other research shows the Golden State's average precipitation increasing gradually, but not enough to account for the occurrence of extreme events. A better understanding of what gives rise to El Nino and La Nina cycles -- together known as El Nino-Southern Oscillation -- might help California predict and prepare for more frequent droughts and floods in the coming century.

"Wet and dry years in California are linked to El Nino and La Nina. That relationship is getting stronger," said atmospheric scientist Jin-Ho Yoon of the Department of Energy's Pacific Northwest National Laboratory. "Our study shows that ENSO will be exhibiting increasing control over California weather."

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The Asian Monsoon Shifted to the NW From Last Glacial Maximum to Present, may Shift More due to Global Warming

Warming-induced northwestward migration of the East Asian monsoon rain belt from the Last Glacial Maximum to the mid-Holocene

Authors:

Yang et al

Abstract:

Glacial–interglacial changes in the distribution of C3/C4 vegetation on the Chinese Loess Plateau have been related to East Asian summer monsoon intensity and position, and could provide insights into future changes caused by global warming. Here, we present δ13C records of bulk organic matter since the Last Glacial Maximum (LGM) from 21 loess sections across the Loess Plateau. The δ13C values (range: –25‰ to –16‰) increased gradually both from the LGM to the mid-Holocene in each section and from northwest to southeast in each time interval. During the LGM, C4 biomass increased from less than 5% in the northwest to 10–20% in the southeast, while during the mid-Holocene C4 vegetation increased throughout the Plateau, with estimated biomass increasing from 10% to 20% in the northwest to greater than 40% in the southeast. The spatial pattern of C4 biomass in both the LGM and the mid-Holocene closely resembles that of modern warm-season precipitation, and thus can serve as a robust analog for the contemporary East Asian summer monsoon rain belt. Using the 10–20% isolines for C4 biomass in the cold LGM as a reference, we derived a minimum 300-km northwestward migration of the monsoon rain belt for the warm Holocene. Our results strongly support the prediction that Earth's thermal equator will move northward in a warmer world. The southward displacement of the monsoon rain belt and the drying trend observed during the last few decades in northern China will soon reverse as global warming continues.

The Climate of Moscovian Carboniferous Czech Republic

Middle Moscovian climate of eastern equatorial Pangea recorded in paleosols and fluvial architecture

Authors:

Opluštil et al

Abstract:

Fluvial architecture in conjunction with the morphology, petrographical, mineralogical and geochemical composition of intercalated paleosols of the Middle Moscovian upper Radnice Member of the continental Kladno-Rakovník Basin, Czech Republic, were studied in order to decipher climatic signals in the eastern Pangea region during the Late Paleozoic Ice Age. Analysis of architectural elements reveals vertical changes from strongly amalgamated channel fills of bedload-dominated braided streams, to isolated ribbon-like meandering channel fills in mud-dominated floodplain strata. The resulting large scale fining upward cycles separated by laterally widespread bounding surfaces are interpreted as having been formed in response to allocyclic processes driven by variable intensities of precipitation which affected the density of vegetation cover across the landscape and, in turn, the amount and character of sediment supply. Bedload-dominated parts of the cycles were deposited during periods of low water tables and sparse vegetation, whereas periods of maximum precipitation resulted in higher water tables and a greater density of vegetation cover, which, in turn stabilized the floodplains and fixed streams to narrow meandering/anastomosing channels in mud-dominated floodplain strata. Associated paleosols resemble modern Vertisols, which form under seasonal precipitation in modern settings. However, coeval formation of inertinite-rich peat represented by histosols and gleyed low chroma Vertisols in the stratigraphically lowest paleosol succession occurred under overlapping marginal conditions for the climatically different types of soils (i.e., under a seasonal climate where precipitation exceeds evapotranspiration for 6 to 8 months out of the year). Mean annual precipitation calculated from the geochemistry of B horizons of Vertisols (CALMAG proxy) varies between 1815 and 1730 mm/yr.