Estimating the carbon transfer between the ocean, atmosphere and the terrestrial biosphere since the last glacial maximum

Carbon dioxide records from polar ice cores and marine ocean sediments indicate that the last glacial maximum (LGM) atmosphere CO₂ content was 80–90 ppm lower than the mid-Holocene. This represents a transfer of over 160 GtC into the atmosphere since the LGM. Palaeovegetation studies suggest that up to 1350 GtC was transferred from the oceans to the terrestrial biosphere at the end of the last glacial. Evidence from carbon isotopes in deep sea sediments, however, indicates a smaller shift of between 400 and 700 GtC. To understand the functioning of the carbon cycle this apparent discrepancy needs to be resolved. Thus, older data have been reassessed, new data provided and the potential errors of both methods estimated. New estimates of the expansion of terrestrial biomass between the LGM and mid-Holocene are 700 GtC ± > 300 GtC, using the ocean carbon isotope-based method, compared with of 1100 GtC ± > 500 GtC using the palaeovegetation estimate. If these estimates of the carbon shift to the terrestrial biosphere are equilibrated with the dissolved carbon in the oceans, and the CaCO₃ compensation of the ocean is taken into account, then the glacial atmospheric CO₂ would have been between 50 (± 30) ppm and 95 (± 50) ppm higher. The glacial atmosphere therefore should have had a CO₂ partial pressure of between 330 and 375 μatm. Hence, a rise of between 130 and 175 μatm in atmospheric CO₂, rather than 80 μatm, at the end of the last glacial must be accounted for.     

Simulating the transient evolution and abrupt change of Northern Africa atmosphere–ocean–terrestrial ecosystem in the Holocene

We present the first synchronously coupled transient simulation of the evolution of the northern Africa climate-ecosystem for the last 6500 years in a global general circulation ocean–atmosphere–terrestrial ecosystem model. The model simulated the major abrupt vegetation collapse in the southern Sahara at about 5 ka, consistent with the proxy records. Local precipitation, however, shows a much more gradual decline with time, implying a lack of strong positive vegetation feedback on annual rainfall during the collapse. The vegetation change in northern Africa is driven by local precipitation decline and strong precipitation variability. In contrast, the change of precipitation is dominated by internal climate variability and a gradual monsoonal climate response to orbital forcing. In addition, some minor vegetation changes are also simulated in different regions across northern AfricaThe model also simulated a gradual annual mean surface cooling in the subtropical North Atlantic towards the latest Holocene, as well as a reduced seasonal cycle of SST. The SST response is caused largely by the insolation forcing, while the annual mean cooling is also reinforced by the increased coastal upwelling near the east boundary. The increased upwelling results from a southward retreat of the North Africa monsoon system, and, in turn, an increased northeasterly trade wind. The simulated changes of SST and upwelling are also largely consistent with marine proxy records, albeit with a weaker magnitude in the model.The mismatch between the collapse of vegetation and gradual transition of rainfall suggests that the vegetation collapse is not caused by a strong positive vegetation feedback. Instead, it is suggested that the Mid-Holocene collapse of North African vegetation is caused mainly by a nonlinear response of the vegetation to a precipitation threshold in the presence of strong climate variability. The implication to the modeling and observations is also discussed.     

Provenance of the terrestrial planets

Earlier work on the simultaneous accumulation of the asteroid belt and the terrestrial planets is extended to investigate the relative contribution to the final planets made by material from different heliocentric distances. As before, stochastic variations intrinsic to the accumulation processes lead to a variety of final planetary configurations, but include systems having a number of features similar to our solar system. Fifty-nine new simulations are presented, from which thirteen are selected as more similar to our solar system than the others. It is found that the concept of "local feeding zones" for each final terrestrial planet has no validity for this model. Instead, the final terrestrial planets receive major contributions from bodies ranging from 0.5 to at least 2.5 AU, and often to greater distances. Nevertheless, there is a correlation between the final heliocentric distance of a planet and its average provenance. Together with the effect of stochastic fluctuations, this permits variation in the composition of the terrestrial planets, such as the difference in the decompressed density of Earth and Mars. Biologically important light elements, derived from the asteroidal region, are likely to have been significant constituents of the Earth during its formation.     

History of the terrestrial planets

A time table showing the history of the terrestrial planets is submitted in this paper. The planetary evolution is presented within the framework of global tectonics, whereby a distinction is made between exogenous and endogenous processes. Beginning with the age of 4.5 × 10⁹ years and extending to the age of 3.0 × 10⁹ years all terrestrial planets are characterized by a primordial-meteoric-vulcanic period. The development of the Moon and Mercury had been terminated with the end of this primordial period. Even until most recent times endogenous mantle processes and exogenous erosion processes shape the lithospheres on Mars, Venus, and the Earth. The Earth represents here the extreme case with highly dynamic plate tectonics. The degree of evolution of a planet is proportional to its mass. This leads to the following evolutionary scheme:

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Zusammenfassung Eine Zeittafel zur Entwicklungsgeschichte der terrestrischen Planeten wird vorgelegt. Die Planetengeschichte wird in den Rahmen einer globalen Tektonik gestellt, wobei exogene und endogene Prozesse unterschieden werden. Von ca. 4.5 bis 3.0 × 10⁹ Jahre werden alle terrestrischen Planeten von einer ur-meteorischen-vulkanischen Periode geprägt. Damit ist für den Mond und den Merkur die Entwicklung im wesentlichen abgeschlossen. Bei dem Mars, der Venus und der Erde formen bis in die jüngste Zeit endogene Mantelprozesse und exogene Erosionsprozesse die Lithosphäre, wobei die Erde den Extremfall mit einer hochdynamischen Plattentektonik repräsentiert. Der Entwicklungsgrad eines Planeten ist proportional seiner Masse. Das führt zu folgendem Entwicklungsschema:

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Résumé Une table chronologique décrivant l'évolution des planètes terrestres est proposée dans cette publication. L'évolution des planètes est présentée dans le cadre de la tectonique globale, où distinction est faite entre processus exogènes et endogènes. Entre environ 4.5 et 3.0 × 10⁹ années toutes les planètes terrestres sont caractérisées par une période primordiale-météorique-volcanique. Le développement de la Lune et de Mercure s'est terminé vers la fin de cette période primordiale. Dans Mars, Vénus et la Terre, les processus endogènes du manteau et une érosion exogène ont formé la lithosphère jusque dans les périodes les plus récentes; la Terre représente le cas extrème avec une tectonique de plaques à caractère dynamique très prononcé. Le degré d'évolution d'une planète est proportionnel à sa masse. Ceci conduit au schéma d'évolution suivant:

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Latitudinal distribution of terrestrial lipid biomarkers and n-alkane compound-specific stable carbon isotope ratios in the atmosphere over the western Pacific and Southern Ocean

We investigated the latitudinal changes in atmospheric transport of organic matter to the western Pacific and Southern Ocean (27.58°N-64.70°S). Molecular distributions of lipid compound classes (homologous series of C₁₅ to C₃₅n-alkanes, C₈ to C₃₄n-alkanoic acids, C₁₂ to C₃₀n-alkanols) and compound-specific stable isotopes (δ¹³C of C₂₉ and C₃₁n-alkanes) were measured in marine aerosol filter samples collected during a cruise by the R/V Hakuho Maru. The geographical source areas for each sample were estimated from air-mass back-trajectory computations. Concentrations of TC and lipid compound classes were several orders of magnitude lower than observations from urban sites in Asia. A stronger signature of terrestrial higher plant inputs was apparent in three samples collected under conditions of strong terrestrial winds. Unresolved complex mixtures (UCM) showed increasing values in the North Pacific, highlighting the influence of the plume of polluted air exported from East Asia. n-Alkane average chain length (ACL) distribution had two clusters, with samples showing a relation to latitude between 28°N and 47°S (highest ACL values in the tropics), whilst a subset of southern samples had anomalously high ACL values. Compound-specific carbon isotopic analysis of the C₂₉ (−25.6‰ to −34.5‰) and C₃₁n-alkanes (−28.3‰ to −37‰) revealed heavier δ¹³C values in the northern latitudes with a transition to lighter values in the Southern Ocean. By comparing the isotopic measurements with back-trajectory analysis it was generally possible to discriminate between different source areas. The terrestrial vegetation source for a subset of the southernmost Southern Ocean is enigmatic; the back-trajectories indicate eastern Antarctica as the only intercepted terrestrial source area. These samples may represent a southern hemisphere background of well mixed and very long range transported higher plant organic material.     

Paleogeographic forcing of the strontium isotopic cycle in the Neoproterozoic

The period spanning from 825 to 540 Ma is characterized by major changes in the surficial Earth system. This extraordinary interval starts with the breakup of the Rodinia supercontinent and eruption of a series of large igneous provinces and ends with the assembly of Gondwana, giving rise to the Pan-African orogenies. This paleogeographic reorganization is accompanied by a global climatic cooling, including the paroxysmal Cryogenian “snowball” glacial events. The ⁸⁷Sr/⁸⁶Sr of seawater displays a major long-term rise over this interval that is punctuated by episodic, smaller declines and inflections. We use a coupled deep time climate-carbon numerical model to explore the complex role of tectonics and climate on this distinct evolution in seawater ⁸⁷Sr/⁸⁶Sr. We show that the modulation of the weathering of the erupted large igneous provinces by continental drift explains the changes in seawater ⁸⁷Sr/⁸⁶Sr from 800 to 635 Ma. The subsequent sharp rise in seawater ⁸⁷Sr/⁸⁶Sr from 635 to 580 Ma is the result of erosion of radiogenic crust exposed in the Pan-African orogens. Coeval evolution of atmospheric CO₂ displays a decrease from about 80 times the pre-industrial level around 800 Ma to 5 times just before the beginning of the Phanerozoic.     

Investigating the preservation of orbital forcing in peritidal carbonates

Metre‐scale cycles in ancient peritidal carbonate facies have long been thought to represent the product of shallow water carbonate accumulation under orbitally controlled sea‐level oscillations. The theory remains somewhat controversial, however, and a contrasting view is that these cycles are the product of intrinsic, and perhaps random, processes. Owing to this debate, it is important to understand the conditions that do, or do not, favour the preservation of orbital forcing, and the precise stratigraphic expression of that forcing. In this work, a one‐dimensional forward model of carbonate accumulation is used to test the ability of orbitally paced sea‐level changes to reconstruct cyclicities and cycle stacking patterns observed in greenhouse peritidal carbonate successions. Importantly, the modelling specifically tests insolation‐based sea‐level curves that probably best reflect the pattern and amplitude of sea‐level change in the absence of large‐scale glacioeustasy. This study found that such sea‐level histories can generate precession and eccentricity water depth/facies cycles in models, as well as eccentricity‐modulated cycles in precession cycle thicknesses (bundles). Nevertheless, preservation of orbital forcing is highly sensitive to carbonate production rates and amplitudes of sea‐level change, and the conditions best suited to preserving orbital cycles in facies/water depth are different to those best suited to preserving eccentricity‐scale bundling. In addition, it can be demonstrated that the preservation of orbital forcing is commonly associated with both stratigraphic incompleteness (missing cycles) and complex cycle thickness distributions (for example, exponential), with corresponding implications for the use of peritidal carbonate successions to build accurate astronomical timescales.     

Weekly cycle in the atmosphere

Doklady Earth Sciences -     

Precessional forcing of tropical vegetation carbon storage

Since the Mid Pleistocene Revolution, which occurred about one million years ago, global temperatures have fluctuated with a quasi‐periodicity of ca. 100 ka. The pattern of past change in the extent of woodlands, and therefore by inference vegetation carbon storage, has been demonstrated to have a strong positive link with this global temperature change at high and mid latitudes. However, understanding of climate systems and ecosystem function indicates that the pattern of woodland change at low latitudes may follow a fundamentally different pattern. We present output from the intermediate complexity model GENIE‐1, comprising a single transient simulation over the last 800 ka and a 174‐member ensemble of 130 ka transient simulations over the last glacial cycle. These simulations suggest that while vegetation carbon storage in mid–high northern latitudes robustly follows the characteristic ca. 100 ka cycle, this signal is not a robust feature of tropical vegetation, which is subject to stronger direct forcing by the precessional (21 ka) orbital cycle (albeit with a highly uncertain response). We conclude that the correlation of palaeoenvironmental records from low latitudes with global temperature change must be done with caution. Copyright © 2011 John Wiley & Sons, Ltd.     

Rossby-Haurwitz wave perturbations under tropical forcing

This study explores the zonal flow in the form of Legendre polynomials. The basic flow is divided into a zonally symmetric flow and a Rossby-Haurwitz (RH) wave. Several features of this (more realistic) zonal flow make it particularly interesting, such as the midlatitude westerly jet streams and an easterly wind around the equator, which closely resembles the mean horizontal flow at 200 mb of the December-February period. The zonal flow is combined with the RH wave, in order to test the blocking formation mechanism on early stages for the northeastern Pacific. A numerical simulation has been performed using a linear barotropic model with tropical forcing and damping to check the extra-tropical response of the mechanism of eddies reinforcement of the ridge along the western coast of North America.     

Paleogeography as a climatic forcing factor

The cause of warm, equable ice free climates which dominate Phanerozoic earth history and the cause of the transition to glacial epochs are fundamental problems in paleoclimatology. Based on several criteria, paleogeography is one of the most likely mechanisms of climatic change on this time scale. Paleogeography modifies climate by inducing changes in atmospheric and oceanic circulation patterns, and by modifying the global albedo because of the contrasts in the albedo of different surfaces (e. g. ocean, land and snow) and because incoming solar radiation is a strong function of latitude. Using both simple and state-of-the-art planetary albedo models, the importance of this second hypothesis is tested as a mechanism of climatic change. It is concluded that paleogeography, by directly altering the planetary albedo, operates in the correct sense to explain the Tertiary global cooling and close to the correct order of magnitude to explain the contrast between warm, equable Mesozoic climates and the present glacial climates.

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Zusammenfassung Die Ursache des warmen, ausgewogen eisfreien Klimas, das in phanerozoischer Erdgeschichte dominiert, und die Ursache des Übergangs zu glazialen Epochen sind fundamentale Probleme in der Paläoklimatologie. Aufgrund mehrerer Kriterien wird Paläogeographie als einer der wahrscheinlichsten Mechanismen für Klimaänderungen auf dieser Zeitskala angesehen. Paläogeographie verändert das Klima durch Änderungen atmosphärischer und ozeanischer Zirkulationssysteme, durch Modifizierung der weltweiten Albedoverteilung auf Grund unterschiedlicher Albedo über verschiedenen Oberflächen (Ozean, Land, Schnee) sowie durch die starke Abhängigkeit der einfallenden Sonneneinstrahlung von der geographischen Breite.Die Benutzung einfacher und — beim heutigen Stand der Theorie — fortgeschrittener Modelle erlaubt eine Überprüfung der Bedeutung dieser zweiten Hypothese für klimatische Änderungen. Es wird gefolgert, daß Paläogeographie, durch die direkte Modifizierung planetarischer Albedo, den globalen Kühlungstrend im Tertiär vorzeichenrichtig andeutet und größenordnungsmäßig den Unterschied zwischen dem warmen, ausgewogenen mesozoischen Klima und dem derzeitigen glazialen Klima erklärt.

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Résumé La cause de l'existence de climates chauds, dépourvus de fluctuations extrêmes et de glaciations, qui ont dominé l'histoire de la Terre durant le Phanérozoique et la cause de la transition à des périodes glaciaires posent des problèmes fondamentaux à la paléoclimatologie. Basée sur plusieurs évidences, la paléogéographie est un des méchanismes les plus probables qui soit à l'origine des changements climatiques considérés sur cette échelle de temps. La paléogéographie introduit des changements de climat en induisant des perturbations dans les modèles de circulation atmosphérique et océanique et en modifiant l'albedo global à cause des contrastes dans l'albedo des différentes surfaces (ex: océan, continent et neige), et parce que la radiation solaire reçue est en étroite relation avec la latitude. A partir de deux modèles, l'un simple et le second le plus éllaboré à l'heure actuelle, l'importance de la seconde hypothèse est testée comme un méchanisme de changement climatique. On arrive à la conclusion que la paléogéographie, en modifiant d'emblée l'albedo à l'échelle du globe, joue dans le bon sens pour expliquer le refroidissement général durant le Tertiaire, et est très voisin de l'ordre de grandeur correct pour expliquer l'opposition entre les climats chauds, dépourvus d'extrêmes fluctuations durant le Mésozoique, et les climats glaciaires d'aujourd'hui.

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Stratigraphical evidence for the terrestrial age of australites

Australites in an excellent state of preservation are common (up to 1 specimen per 300 m²) in lag gravels flooring corridors between seif dunes in the Motpena and Myrtle Springs areas of the Lake Torrens plain, South Australia. A study of the Quaternary stratigraphy of the region indicates that late Wisconsinan relict dunes (Lake Torrens Formation) are the most likely source of the australites. Radiocarbon dating indicates that the Lake Torrens Formation was deposited between about 24,000 and 16,000 years B.P. As the excellent preservation of most of the australites indicates that they have undergone negligible transport since their infall, it is concluded that the australites fell into the dune field sometime between about 24,000 and 16,000 years B.P.     

Pitfalls in the AMS radiocarbon-dating of terrestrial macrofossils

The AMS ¹⁴C technique has the advantage that small samples of Late Quaternary age can be dated with high accuracy, and that errors due to reservoir effects can be avoided if specifically determined terrestrial micro- and macrofossils are measured. However, to obtain such high-accuracy measurements, it is important how small samples are handled prior to treatment in the radiocarbon laboratories. Here we present a set of 51 AMS ¹⁴C measurements, of which 31 dates gave expected ages and 20 dates resulted in anomalously young ages, despite the fact that all samples consisted of clearly identified Late Weichselian terrestrial plant macrofossils. To evaluate possible sources of error, we compared these samples in respect to preparation methods, sample storage and sample weight. Our results show that the long-term storage of wet macrofossil samples appears to have a significant effect on the radiocarbon age obtained, even when the samples are kept cool. Fungi or micro-organisms may easily be incorporated into a sample during preparation and identification, and can easily contribute to the contamination of a sample, if stored cool and wet for several months. © 1998 John Wiley & Sons, Ltd.     

Impacts in the primordial history of terrestrial planets

Collisions played a very important role in the formation of terrestrial planets. These planets are believed to have formed from a system of planetary embryos, with masses comparable to that of the Moon or of Mars. Giant collisions between proto-planets and embryos were, therefore, the rule. The collision which gave origin to the Earth’s moon was just one of these collisions. We review the state of the art concerning numerical modeling of the terrestrial planets accretion process and we compare the results with the available observational or geochemical constraints. After the completion of the formation process, the history of the bombardment of the terrestrial planets was peculiar. After a period most likely characterized by a weak bombardment rate, about 3.9 Gyr ago, the planets experienced the ‘Late Heavy Bombardment’, a cataclysmic episode characterized by a bombardment rate of about 20,000 times the current one, during a time-span of 50–150 Myr. We review a recent model that has been proposed to explain the origin of this cataclysm.