Paleoclimatic Scenarios Research Articles

Modeling glaciation of the Hellas Basin, Mars, for a ‘cold and icy’ late Noachian Paleoclimatic scenario

Global climate models (GCM) predict snow accumulation/glaciation on the Hellas basin eastern rim, where Amazonian glacial landforms are observed. We explore GCM results for Late Noachian-Early Hesperian higher atmospheric pressure/higher obliquity/faint young sun conditions, assess accumulation rates, and use these as input to an ice sheet model. We assess ice sheet growth, thickness, basal temperatures, basal melting water volumes, flow/sliding-ice velocities and the fate of basin floor glacial ice/meltwater. We conclude that significant volumes of glacial ice (with shear-induced basal melting) could have flowed down the basin wall and onto the basin floor, covering the majority with glacial ice. Late Noachian water budgets of up to 1000 m global equivalent layer (GEL) and Hellas floor ice sequestration are implied. Subsequent emplacement of Hesperian volcanic plains superposed on the ice may have caused melting (contact/deferred) and deformation (loading-induced flow/diapirism), potentially accounting for several observed basin floor geologic units.

Modeling the Accumulation and Transition to the Relic State of Methane Hydrates in the Permafrost of Northwestern Siberia

This paper presents the results of numerical modeling of the permafrost thermal regime and thermobaric conditions of methane hydrates in the north of Western Siberia over the past 70 thousand years. The area of hydrate formation was determined and the rate of accumulation of hydrates was estimated in connection with the migration of fluid from the underlying gas-saturated layers under the conditions of cover glaciation. The estimates obtained for the change in hydrate saturation as a result of fluid migration during the 10 thousand-year glaciation period, depending on the permeability of the soil, are from 6 to 40% in the upper 350 m. Based on quantitative characteristics of the equilibrium and metastable states of methane hydrates, the conditions for the preservation of relict methane hydrates in permafrost under the paleoclimatic scenario were determined, taking into account periods of ice cover and transgression. It is shown that due to the effect of self-preservation at temperatures below –4°C, it is possible to preserve relict methane hydrates in the upper 200 m of soil under non-equilibrium conditions. The effect of lowering the temperature while the hydrates dissociate prevents the complete decomposition of the deposit and leads to an increase in the thickness of the frozen soil.

The fate of Holoregmia, a monospecific genus endemic to the Brazilian Caatinga, under different future climate scenarios

Background and aims – Climatic fluctuations during the Pleistocene altered the distribution of many species and even entire biomes, allowing some species to increase their range while others underwent reductions. Recent and ongoing anthropogenic climate change is altering climatic patterns very rapidly and is likely to impact species’ distributions over shorter timescales than previous natural fluctuations. Therefore, we aimed to understand how Pleistocene and Holocene climatic fluctuations might have shaped the current distribution of Holoregmia and explore its expected distribution under future climate scenarios. Material and methods – We modelled the potential distribution of Holoregmia viscida (Martyniaceae), a monospecific plant genus endemic to the semi-arid Caatinga Domain in Brazil. We used an ensemble approach to model suitable areas for Holoregmia under present conditions, Paleoclimatic scenarios, and global warming scenarios in 2050 and 2090. Key results – Holocene climates in most Caatinga were too humid for Holoregmia, which restricted its suitable areas to the southern Caatinga, similar to its current distribution. However, under global warming scenarios, the Caatinga is expected to become too dry for this lineage, resulting in a steady decline in the area suitable for Holoregmia and even its possible extinction under the most pessimistic scenario modelled. Conclusion – The predicted extinction of the ancient and highly specialized Holoregmia viscida highlights the possible consequences of climate change for some species of endemic Caatinga flora. Invaluable phylogenetic diversity may be lost in the coming decades, representing millions of years of unique evolutionary history and consequent loss of evolutionary potential to adapt to future environmental changes in semi-arid environments.

The response of the Arctic Ocean gas hydrate associated with subsea permafrost to natural and anthropogenic climate changes

We present an assessment of changes in the gas hydrates stability zone of the Arctic Ocean associated with subsea permafrost conditions. To evaluate the formation and dissociation of gas hydrates under the climatic conditions of the last glacial cycle, it is necessary to understand how the thickness of the permafrost has changed after flooding by the sea. To do this, we have combined two numerical models: a model of permafrost dynamics based on the paleoclimatic scenario of changes in temperature and ocean level, and a model of the methane hydrates stability zone (MHSZ). Calculations of changes in the thickness of the submarine permafrost and the MHSZ were carried out for the period of 120 thousand years. Our results show that, although changes in the bottom water temperature over the last-decades period affect the hydrate stability zone, the main changes with this zone occurring after flooding the Arctic shelf with the seawater. As a result of the combined simulation of the permafrost and state of MHSZ, it was found that in the shallow shelf areas (lower 50 m water depth) after flooding, the hydrate presence conditions in the upper 100-meter layer of the MHSZ are violated. This suggests that the methane coming from this reservoir is concentrated in the bottom sediments of the shelf, and then released into the water, continuing to adapt to changing sea levels, rising bottom water temperatures, and subsea permafrost melting.

Climatic refugia boosted allopatric diversification in Western Mediterranean vipers

AbstractAimThe ecological dimension of evolutionary processes has been scarcely addressed in phylogeographic studies. We reconstruct the historical biogeography of Western Mediterranean vipers to discover the role of climate in fostering diversification.LocationWestern Mediterranean Basin.TaxonVipera aspis and Vipera latastei‐monticola complex.MethodsWe used nearly range‐wide phylogeographic analyses of three mitochondrial genes followed by geographic assignment of 4,056 records to genetic units to test phylogenetic niche conservatism, under a 3D hypervolume approach, and reconstruct paleoclimatic scenarios for the diversification of main lineages during Pleistocene.ResultsBayesian inferences from mtDNA recovered three Miocene clades and nine Pliocene lineages that diversified during the Pleistocene. Diversification was mostly restricted to southern regions of Iberian and Italian peninsulas and to the north‐western African mountains until the late Pliocene. Some lineages expanded northwards during the Pleistocene. Accordingly, genetic diversity was higher in southern regions. Ecological niche tests mostly supported allopatric diversification with niche conservatism, although niche shifts occurred with two divergence events. Palaeoclimatic models identified particular requirements for the current distribution of main lineages and distinct responses to the cooling and warming events of the Pleistocene. Areas of climatic stability during the Pleistocene were identified for main lineages; however, climatic stability was weakly correlated with haplotype diversity.Main conclusionsIn the Western Mediterranean biodiversity hotspot, palaeo‐tectonic and palaeo‐climatic factors drove diversification since the Miocene. Comparisons among patterns of diversification, haplotype diversity, and climatic stability suggest that southern Iberian and Italian peninsulas, and north‐western African mountains acted as refugia since the Pliocene, while some northern areas favoured population persistence during the Pleistocene. Climate adaptation likely played a secondary role in the diversification of some lineages.

Deep-sea benthic foraminifera record of the last 1500 years in the North Aegean Trough (northeastern Mediterranean): A paleoclimatic reconstruction scenario

A 1500-year, high-resolution deep-sea benthic foraminifera record from the Athos Basin of the North Aegean Trough (northeastern Mediterranean) has been analyzed for the development of a paleoclimatic scenario. The data analysis points out that the quantity and quality of the seafloor's organic matter could be a crucial controlling factor for the faunal succession. During 550–1000 AD (within the Medieval Climate Anomaly), the relatively high benthic foraminiferal accumulation rates together with the predominance of meso-eutrophic taxa, such as Bolivina dilatata/spathulata, may be interpreted as the result of high precipitation. Consequently, increased riverine discharges into the North Aegean Sea and the associated warm climatic conditions appear to persist for a long time and are related to a negative phase of the North Atlantic Oscillation. Later on, the establishment of an oligo-mesotrophic seafloor environment is documented by the diminishing benthic foraminiferal accumulation rates associated with an increment in the abundances of Gyroidinoides altiformis. During a colder phase of the Little Ice Age (17th century), the relative abundances of the opportunistic foraminiferal species Bulimina inflata and Bulimina marginata can be related to high marine productivity, most probably due to enhanced winter mixing conditions. Finally, during the last 100 years, a faunal shift to eutrophication preferent species, and the persistent occurrence of Chilostomella mediterranensis, reflects a pronounced change in trophic conditions, characterized by high amounts of potentially low-quality organic matter in the seafloor, which are the result of a gradual temperature increase accompanied with enhanced terrigenous inputs.

Thermal anomalies and paleoclimatic diffusive and advective phenomena: example of the Anglo-Paris Basin, northern France

This study is the first quantification of the combined impact of diffusive and advective paleoclimatic phenomena to explain the weak vertical thermal flux anomaly in the upper part of the Anglo-Paris intracratonic sedimentary basin in northern France. The aim of the research is to understand the mechanisms at the origin of the thermal flux anomaly at the level of the Meso-Cenozoic sediment pile. Based on a temperature profile representative of the basin, transient thermo-hydraulic simulations were performed along a representative vertical cross-section of about 400 km within the Lower Cretaceous multi-layer aquifer. Four paleoclimatic scenarios are the combination of two paleotemperature climatic forcings and two hydrodynamic regimes, one of them taking into account the interruption of the recharge linked to permafrost development. The simulation results clearly show the transient nature of the basin’s thermal regime. Then, for the reference well, the majority of the thermal flux anomaly can be explained by advective and paleoclimatic mechanisms with a decrease in geothermal flux simulated up to a little over 30 mW/m2, depending on the scenarios. Decrease in heat flux because of basin-scale subsurface flows in the Lower Cretaceous is around 15 mW/m2. There are several ways forward from this first simple model, including simulation of development of permafrost and also the integration of vertical flows in the basin by use of a three-dimensional model to better explain the data.

Past Climate Change and Plant Evolution in Western North America: A Case Study in Rosaceae

Species in the ivesioid clade of Potentilla (Rosaceae) are endemic to western North America, an area that underwent widespread aridification during the global temperature decrease following the Mid-Miocene Climatic Optimum. Several morphological features interpreted as adaptations to drought are found in the clade, and many species occupy extremely dry habitats. Recent phylogenetic analyses have shown that the sister group of this clade is Potentilla section Rivales, a group with distinct moist habitat preferences. This has led to the hypothesis that the ivesioids (genera Ivesia, Horkelia and Horkeliella) diversified in response to the late Tertiary aridification of western North America. We used phyloclimatic modeling and a fossil-calibrated dated phylogeny of the family Rosaceae to investigate the evolution of the ivesioid clade. We have combined occurrence- and climate data from extant species, and used ancestral state reconstruction to model past climate preferences. These models have been projected into paleo-climatic scenarios in order to identify areas where the ivesioids may have occurred. Our analysis suggests a split between the ivesioids and Potentilla sect. Rivales around Late Oligocene/Early Miocene (∼23 million years ago, Ma), and that the ivesioids then diversified at a time when summer drought started to appear in the region. The clade is inferred to have originated on the western slopes of the Rocky Mountains from where a westward range expansion to the Sierra Nevada and the coast of California took place between ∼12-2 Ma. Our results support the idea that climatic changes in southwestern North America have played an important role in the evolution of the local flora, by means of in situ adaptation followed by diversification.

Paleoclimate study of mountain ecosystems by multiple group biological analysis

Methodological problems of climatic reconstruction for different periods of Holocene are discussed on the basis of a multiple group biological analysis on peat-sapropel sediments. The possibility of biological analysis is exemplified by the paleoclimatic reconstruction for Carpathian and Altai Mountain ranges. For the “Skolevsky Beskidy” national park of Carpaty the paleoclimatic scenarios have been drown up aiming at the more precise definition of climatic conditions for the period of mass mountain slope terracing. The stability of terrace systems of various designs in the current climatic conditions has been assessed. It is shown that during periods of humid climate the terraces, whose designs have been focused on drainage, were built. In periods of dry and warm climate the terrace systems capable of accumulating water were built. Both these types of terrace systems are destroyed in nowadays. Only those terrace systems are stable which were adjusted by their builders to contrast variations of precipitation.

PALAEOCLIMATE RESEARCH OF MOUNTANEOUS ECOSYSTEMS BY USING THE METHOD OF INTEGRATED GROUP BIOLOGICAL ANALYSIS

Methodological issues of climate change reconstruction in different Holocene periods are considered by the method of complex group biological analysis of peat and sapropel deposits. The possibilities of the method are demonstrated by reconstructing the climate of the Carpathian and the Altai mountain systems. For the Skolevsky Beskids of the Carpathians, paleoclimatic scenarios were prepared in order to clarify the climatic conditions during the periods of mass terracing of mountain slopes. A climatic paleoscenario was built for the Western Altai to forecast the safety of the bronze barrows with permafrost inside designs.

A 1.2 Ma record of glaciation and fluvial discharge from the West European Atlantic margin

The correlation of continental sedimentary records with the marine isotope stratigraphy is a challenge of central importance in Quaternary stratigraphy, particularly in Western Europe where long records of glaciation on land areas are particularly rare. Here we demonstrate for the first time the interrelationship of events during the last 1.2 Ma in an ocean-sediment core from the Bay of Biscay (NE Atlantic), SW of the Channel. The identification of discharge variations from tributary river systems to the ‘Fleuve Manche’ palaeoriver during glacio-eustatic sea-level lowstands demonstrates the correlation of the marine sediment stratigraphy to the expansion and recession of the European ice-sheets. The amplitude and chronology of European ice-sheet oscillations since the late Early Pleistocene is discussed and our results demonstrate that the first coalescence of the Fennoscandian and British ice-sheets in the North Sea basin ca 450 ka ago caused a profound change in lowstand European drainage alignment. This change caused a rerouting of Fennoscandian and eastern British ice-sheets-derived meltwaters from northwards into the Nordic Seas to southwards into the eastern North Atlantic thereafter. Besides allowing a thorough synchronisation of the European ice-sheet palaeogeography with the well-dated records of palaeoceanographical changes, our results improve the stratigraphy of the English Channel palaeovalleys and will provide important constraints on paleoclimatic scenarios considering the impact that such rerouting and meltwater surges might have on the stability of the oceanic conveyor belt.

Prehistoric mega-tsunami in the eastern Mediterranean and its sedimentary response

The volcanic island of Santorini that belongs to the trench-arc-backarc Aegean system of the eastern Mediterranean underwent a catastrophic eruption in the Bronze age (circa 3500 y BP), with caldera collapse and creation of a tsunami wave that was funnelled westward. The sedimentary response to this exceptional event in the deep sea was the deposition of resediments called Homogenites. The data set available after almost thirty years of active research consists of 60 sediment cores, including several giant piston cores up to 30 meters long, raised from water depths ranging from 4100 to 2500 m in discrete parts of the Ionian Sea. Two types of Homogenite are recognized. Type A Homogenite consists of pelagic turbidites typically recorded in the Calabrian Ridge and in the western Mediterranean Ridge accretionary prisms, characterized by the «cobblestone topography», only in lows or basinal settings. Their stratigraphic position consistently above the Holocene sapropel S-1 and the depositional base are interpreted as the result of liquefaction of the unconsolidated pelagic sediments draping the nearby slopes caused by the tsunami waves, followed by downslope movement and settling. Type B Homogenite is a megaturbidite of African provenance that expanded throughout the Messina and Sirte abyssal plains originating an up to 24 m thick surficial acoustically-transparent layer calibrated by coring. Type B Homogenite has a coarse and thick sandy base consisting of bioclasts deriving from the continental shelf of North Africa and is interpreted as triggered by the tsunami wave reaching the Sirte Gulf. The Dec. 26, 2004 megatsunami that hit the coastlines of SE Asia provides a real world example of how sediment dispersal can be triggered by a series of gigantic waves. Megaturbidites similar in thickness to Type B Homogenite have been recorded in all the abyssal plains of the Mediterranean, both west and east of the Ionian basin, but their age is older (late Pleistocene) and their emplacement occurred during low sea-level stands corresponding to the last glaciation. The occurrence of a Holocene megabed, postdating the Climatic Optimum, is a paradox in a paleoclimatic scenario. An exceptional event, as the megatsunami originated by the collapse of the Santorini caldera is required.

Phylogeography of the calanoid copepods Calanus helgolandicus and C. euxinus suggests Pleistocene divergences between Atlantic, Mediterranean, and Black Sea populations

Molecular systematic analyses of marine taxa are crucial for recording ocean biodiversity, so too are elucidation of the history of population divergence and the dynamics of speciation. In this paper we present the joined phylogeography of the calanoid copepod Calanus helgolandicus (Claus 1863) from the North East (NE) Atlantic and the Adriatic Sea and the closely related C. euxinus (Hulsemann 1991) from the Black Sea based on sequences of a mitochondrial Cytochrome Oxidase subunit I (COI) fragment. Coalescent-based Bayesian methods and minimum spanning networks are used to reconstruct the history of population divergence. Our results reveal that copepod populations from all three basins share a great number of haplotypes and demonstrate a close genetic affinity of C. euxinus with C. helgolandicus. The data do not support significant genetic structuring among samples within seas. Coalescent analyses suggest divergences between NE Atlantic, Mediterranean, and Black Sea populations dating back to the middle Pleistocene, with the NE Atlantic–Mediterranean divergence being the earliest and the Mediterranean–Black Sea divergence the most recent. These middle Pleistocene dates are much older than the estimated dates of colonisation of the Mediterranean and Black Seas based on paleoclimatic scenarios. Our results do not rule out that the assumed colonisations took place but they indicate that the populations colonising the Mediterranean and the Black Sea were already, and have since remained, diverged. The chaetognath Sagitta setosa, which has a comparable distribution pattern and feeds upon the copepods, provides a unique opportunity to compare phylogeographic patterns and distinguish among alternative hypotheses. The dates produced in this paper are in agreement with those estimated elsewhere for S. setosa. We propose that a great deal of the genetic make-up of marine planktonic populations comprises divergences that date back to long before the last glacial maximum. We consider questions on the taxonomic status of C. euxinus to remain open. However, its high genetic affinity to the C. helgolandicus calls for further investigation.

Origin and age of Australian Chenopodiaceae

We studied the age, origins, and possible routes of colonization of the Australian Chenopodiaceae. Using a previously published rbcL phylogeny of the Amaranthaceae–Chenopodiaceae alliance (Kadereit et al. 2003) and new ITS phylogenies of the Camphorosmeae and Salicornieae, we conclude that Australia has been reached in at least nine independent colonization events: four in the Chenopodioideae, two in the Salicornieae, and one each in the Camphorosmeae, Suaedeae, and Salsoleae. Where feasible, we used molecular clock estimates to date the ages of the respective lineages. The two oldest lineages both belong to the Chenopodioideae ( Scleroblitum and Chenopodium sect. Orthosporum/ Dysphania) and date to 42.2–26.0 and 16.1–9.9 Mya, respectively. Most lineages (Australian Camphorosmeae, the Halosarcia lineage in the Salicornieae, Sarcocornia, Chenopodium subg. Chenopodium/ Rhagodia, and Atriplex) arrived in Australia during the late Miocene to Pliocene when aridification and increasing salinity changed the landscape of many parts of the continent. The Australian Camphorosmeae and Salicornieae diversified rapidly after their arrival. The molecular-clock results clearly reject the hypothesis of an autochthonous stock of Chenopodiaceae dating back to Gondwanan times. Instead, they indicate that most lineages arrived in Australia via long-distance dispersal. Some lineages (e.g. the Halosarcia lineage) may have used the Indonesian archipelagos as stepping stones. The authors are aware that estimates of diversification times using a molecular clock can be subject to considerable levels of error. Our estimates of the age of Australian chenopod lineages based on three alternative fossils were made independently from any knowledge about shifts in climatic and geographical conditions in Australia during the times of arrival. In most cases, however, the paleoclimatic scenario indicates habitat shifts suitable for the respective chenopod colonizer, which corroborates our findings and provides a plausible scenario.

Palynological investigations in the Carnian of the Cave del Predil area (Julian Alps, NE Italy)

The palynological analysis on a continuous shallow-marine succession of the western Tethys realm allows a better characterization of the Carnian (late Triassic) paleofloristic and paleoclimatic scenario. The classic succession of the “Raibl Group”, once the “Raibler Schichten”, in the Southern Alps (northern Italy) was investigated. Ammonoids and conodonts constrain the age of the fossil-rich terrigenous-carbonate sequence to the Julian and Tuvalian, the Julian/Tuvalian boundary lying in the upper part of the Tor Formation. In order to document the pollen biostratigraphy and the paleoecologic trends of this late Triassic interval, results of qualitative and quantitative spore and pollen analysis are presented. The new combination Converrucosisporites tumulosus (Leschik) Roghi is proposed. The recognition of three palynological assemblages facilitates realistic regional palynostratigraphical correlation of Carnian successions in the Southern Alps. Quantitative analysis of the pollen/spore assemblages is used to confirm humid environmental conditions during latest Julian and earliest Tuvalian times.

Temporal variability of alpine solifluction : a modelling approach

Abstract. Holocene periods of enhanced solifluction offer new paleoclimatic information. Long-term observations of present solifluction variability and process studies on movement mechanisms, as well as model simulations of the soil heat and water regimes, show the dependence of solifluction on ground freezing. The annual variability of both processes is strongly controlled by weather and resulting snow conditions immediately before and at the beginning of the winter frost period. Simulated long-term variations during different paleoclimatic scenarios are regulated by both mean preeipitation and temperature changes. Quantitative reconstruetion of Holocene preeipitation during maximum altitudinal depression of solifluction is shown.

Paleohydrological investigation of Infernão Lake, Moji-Guaçcu River watershed, São Paulo, Brazil

A 450 cm sediment core spanning the last 3,500 years was collected from 4.6 m of water in Lake Infernao, located in the floodplain of the Moji-Guacu River in SE Brazil, to reconstruct the wetland system (river and lake) paleohydrology. A multidisciplinary approach using isotopic (13C and 15N), chemical (C/N ratio and lignin derived phenols) and physical analyses (% water content and density) were used in this study. A coarse sand unit in the lower part of the core (450–417 cm) corresponds to the paleoriver. The rest of the sediment core (dark clay) shows a gradual change from a fluvial to a lacustrine environment. 14C dates from the lower part of the core (417–200 cm), demonstrate an inversion and narrow span in age (3,000–3,500 yrs B.P.) corresponding to a period of rapid fluvial sedimentation and reworking. The lake seems to have been well established only after 3,000 yrs B.P. The change from a fluvial to a lacustrine environment is inferred from the isotopic and chemical data. Sediment of the fluvial phase is characterized by higher δ13C values, lower C and N content and a lignin content representative of woody-tissues. Sediment of the lacustrine phase show a gradual decrease in δ13C values toward the top of the core reflecting the influence of organic carbon derived by phytoplankton and aquatic macrophytes (C3 plants). The trend to higher C and N content and low C/N ratios also support this interpretation. The lower lignin content indicates increase contributions of non-vascular plants (phytoplankton). Similarly, the slight increase of non-woody tissues (higher C/V ratios) and the predominance of angiosperm plants (high S/V ratios) as organic matter source indicate an increase contribution of aquatic plants during the lacustrine phase. Our data presented here in addition to the geomorphological information and the available paleoclimatic scenario of pollen-inferred analyses for aquatic systems from the southeastern Brazil point to a climatic origin for this fluvial-lacustrine transition at about 3,000 yrs B.P. and to a climatic evolution leading to the present conditions and to a consequently gradual isolation of Lake Infernao from the influence of the Moji-Guacu River.