Land System Model Research Articles

A multiresolution method for climate system modeling: application of spherical centroidal Voronoi tessellations

During the next decade and beyond, climate system models will be challenged to resolve scales and processes that are far beyond their current scope. Each climate system component has its prototypical example of an unresolved process that may strongly influence the global climate system, ranging from eddy activity within ocean models, to ice streams within ice sheet models, to surface hydrological processes within land system models, to cloud processes within atmosphere models. These new demands will almost certainly result in the develop of multiresolution schemes that are able, at least regionally, to faithfully simulate these fine-scale processes. Spherical centroidal Voronoi tessellations (SCVTs) offer one potential path toward the development of a robust, multiresolution climate system model components. SCVTs allow for the generation of high-quality Voronoi diagrams and Delaunay triangulations through the use of an intuitive, user-defined density function. In each of the examples provided, this method results in high-quality meshes where the quality measures are guaranteed to improve as the number of nodes is increased. Real-world examples are developed for the Greenland ice sheet and the North Atlantic ocean. Idealized examples are developed for ocean–ice shelf interaction and for regional atmospheric modeling. In addition to defining, developing, and exhibiting SCVTs, we pair this mesh generation technique with a previously developed finite-volume method. Our numerical example is based on the nonlinear, shallow-water equations spanning the entire surface of the sphere. This example is used to elucidate both the po tential benefits of this multiresolution method and the challenges ahead.

Submarine landforms characteristic of glacier surges in two Spitsbergen fjords

Well-preserved submarine landforms, all less than 100 years old, are imaged on high-resolution swath bathymetry obtained from Van Keulenfjorden and Rindersbukta (inner Van Mijenfjorden), Spitsbergen, Svalbard. Several tidewater glaciers in these fjords have surged in the last few hundred years. Streamlined landforms, found within the limits of known surges, are interpreted as mega-scale glacial lineations (MSGL) formed subglacially beneath actively surging ice. Large transverse ridges are terminal moraines formed by thrusting at the maximum position of glacier surges. Sediment lobes at the distal margins of terminal moraines are interpreted as glacigenic debris flows, formed either by failure of the frontal slopes of thrust moraines or from deforming sediment extruded from beneath the glacier. Sinuous ridges are eskers, formed after surge termination by the sedimentary infilling of subglacial conduits. Concordant ridges, parallel to former ice margins, are interpreted as minor push moraines, probably formed annually during winter glacier readvance. Discordant ridges, oblique to former ice margins, are interpreted as crevasse-squeeze ridges, forming when soft subglacial sediments are injected into basal crevasses. These submarine landforms have been deposited in the following sequence based on cross-cutting relationships between them, linked to stages of the surge cycle: (1) MSGL; (2a) terminal moraines and (2b) lobe-shaped debris flows; (3) isolated areas of crevasse-fill ridges; (4) eskers and (5) annual retreat ridges. A descriptive landsystem model for tidewater surge-type glaciers has been developed, whose wider applicability is emphasised by comparison with two areas in Isfjorden, Spitsbergen. The model also has a number of features in common with landsystem models for terrestrial surge-type glaciers, but is likely to be more complete since submarine landforms are particularly well preserved. The landforms discussed here may be produced and preserved in different proportions in the varied environmental settings where surging glaciers are found.

A fast version of LASG/IAP climate system model and its 1000-year control integration

A fast version of the State Key Laboratory of Numerical Modeling for Atmospheric Sciences and Geophysical Fluid Dynamics (LASG)/Institute of Atmospheric Physics (IAP) climate system model is briefly documented. The fast coupled model employs a low resolution version of the atmospheric component Grid Atmospheric Model of IAP/LASG (GAMIL), with the other parts of the model, namely an oceanic component LASG/IAP Climate Ocean Model (LICOM), land component Common Land Model (CLM), and sea ice component from National Center for Atmospheric Research Community Climate System Model (NCAR CCSM2), as the same as in the standard version of LASG/IAP Flexible Global Ocean Atmosphere Land System model (FGOALS g). The parameterizations of physical and dynamical processes of the atmospheric component in the fast version are identical to the standard version, although some parameter values are different. However, by virtue of reduced horizontal resolution and increased time-step of the most time-consuming atmospheric component, it runs faster by a factor of 3 and can serve as a useful tool for longterm and large-ensemble integrations. A 1000-year control simulation of the present-day climate has been completed without flux adjustments. The final 600 years of this simulation has virtually no trends in global mean sea surface temperatures and is recommended for internal variability studies. Several aspects of the control simulation’s mean climate and variability are evaluated against the observational or reanalysis data. The strengths and weaknesses of the control simulation are evaluated. The mean atmospheric circulation is well simulated, except in high latitudes. The Asian-Australian monsoonal meridional cell shows realistic features, however, an artificial rainfall center is located to the eastern periphery of the Tibetan Plateau persists throughout the year. The mean bias of SST resembles that of the standard version, appearing as a “double ITCZ” (Inter-Tropical Convergence Zone) associated with a westward extension of the equatorial eastern Pacific cold tongue. The sea ice extent is acceptable but has a higher concentration. The strength of Atlantic meridional overturning is 27.5 Sv. Evidence from the 600-year simulation suggests a modulation of internal variability on ENSO frequency, since both regular and irregular oscillations of ENSO are found during the different time periods of the long-term simulation.

Geomorphology of upland peat: erosion, form and landscape change

Series Editors' Preface. Acknowledgements. 1. Introduction. 1.1 The aims of this volume. 1.1.1 Thematic coverage. 1.1.2 Geographical context. 1.2 Terminology, definitions and peatland geomorphology. 1.2.1 Definitions of Peat. 1.2.2 The Physical and geotechnical properties of peat. 1.2.3 Peatland classification. 1.3 The geography of blanket mire complexes. 1.4 Patterns of peat erosion in space and time. 1.4.1 The onset of peat erosion. 1.4.2 Direct observation of the onset of erosion. 1.5 Causes of peat erosion. 1.6 A brief history of the evolution of peatland geomorphology. 1.6.1 Accounts of erosion in the natural science tradition. 1.6.2 Descriptive accounts of widespread peat erosion. 1.6.3 Quantitative observations of blanket peatlands. 1.7 Structure of this volume and the peat land system model. 2. The Hydrology of Upland Peatlands. 2.1 Introduction. 2.2. Controls on water movement in peatland systems. 2.2.1 Hydraulic conductivity of upland peat soils. 2.2.2 The diplotelmic mire hypothesis. 2.2.3 Groundwater flow in upland peatlands. 2.2.4 Evaporation. 2.2.5 Runoff generation. 2.2.6 The Water balance of ombrotrophic mires. 2.3 Geomorphology and the hydrology of upland peatlands. 3. Sediment Production. 3.1 Introduction. 3.1.1 Monitoring sediment production using erosion pins. 3.1.2 Sediment trap data. 3.2 Sediment production as a control on catchment sediment flux. 3.3 Evidence from field observation. 3.3.1 Climate correlations with trap data. 3.3.2 Direct observations of surface change. 3.4 Evidence from controlled experiments. 3.5 Timescales of sediment supply. 3.6 Conclusion. 4. Fluvial Processes and Peat Erosion. 4.1 Introduction. 4.2 Gully erosion of blanket peat. 4.2.1 Gully morphology and topology. 4.2.2 Processes of Gully erosion. 4.3 Erosion and transport of peat in perennial stream channels. 4.3.1 Production of peat blocks by fluvial erosion. 4.3.2 Transport of peat blocks in stream channels. 4.3.3 The fate of fine peat sediment in channel. 4.4 Sediment yield. 4.4.1 A conceptual model of sediment dynamics in eroding blanket peatlands. 4.4.2 Sediment yield, sediment supply and assessing catchment erosion status. 4.5 Conclusions. 5. Slope Processes and Mass Movements. 5.1 Introduction. 5.2 Peat covered hillslopes. 5.2.1 Limits to the stability of peat on slopes. 5.2.2 Creep on peat hillslopes. 5.3 Morphology of rapid peat mass movements. 5.3.1 Source zone. 5.3.2 Rafted peat debris. 5.3.3 Runout track. 5.3.4 Secondary tension and compression features. 5.3.5 Bog burst and peat slides - are they different?. 5.4 Mechanism of peat failure. 5.4.1 Speed of failure and movement. 5.5 Significance of surface hydrology in peat failures. 5.5.1 Water content and pore pressures. 5.5.2 Rainfall. 5.5.3 Slope drainage. 5.6 Stability analysis and modelling of peat mass movements. 5.7 The changing frequency of peat mass movements over time. 5.8 Summary and overall framework. 6. Wind Erosion Processes. 6.1 Introduction. 6.2 Wind erosion in the uplands and the significance in peatland environments. 6.3 Mechanisms of wind erosion. 6.4 The significance of wet or dry wind erosion processes. 6.5 Direct measurements of wind erosion of peat. 6.6 Aeolian landforms. 6.7 The significance of wind erosion for landscape development in upland peatlands. 6.8 Conclusions. 6.8.1 Further research - an agenda for pluvio-aeolian studies of upland peat. 7. Peat Erosion Forms - from Landscape to Micro-relief. 7.1 Rationale and introduction. 7.2 Macroscale - Region / Catchment Scale. 7.3 Mesoscale - Slope-Catena Scale. 7.4 Microscale - material structure scale. 7.5 Linking the geomorphological and the ecohydrological. 7.6 Conclusions. 8. Sediment Dynamics, Vegetation, and Landscape Change. 8.1 Introduction. 8.2 The effect of peatland dynamics on long term sediment budgets. 8.3 Mass balance evidence of patterns of long term erosion. 8.4 Re-vegetation of eroding peatlands. 8.4.1 Artificial re-vegetation of bare peat surfaces. 8.4.2 Natural revegetation of eroded landscapes. 8.5 Controls and mechanisms of natural re-vegetation. 8.5.1 Extrinsic controls on re-vegetation. 8.5.2 Intrinsic controls on re-vegetation. 8.5.3 Eriophorum spp. as Keystone Species for Re-vegetation of Eroded Peatlands. 8.5.4 Geomorphology, ecology, and 'erosion-regeneration complexes'. 8.5.5 Re-vegetation dynamics and long term patterns of erosion. 8.6 Stratigraphic evidence of erosion and re-vegetation. 8.7 The future of blanket peat sediment systems. 8.8 Changes in pollution climate. 8.9 Climate change impacts. 8.9.1 Increased summer drought. 8.9.2 Increased summer and winter storminess. 8.9.3 Changes in the growing season and vegetation. 8.9.4 Overall response of the peat land system. 8.10 Relative importance of peat erosion in wider upland sediment budgets. 8.11 Conclusions. 9. Implications and Conclusions. 9.1 Implications of widespread peat erosion. 9.2 Upland peatland erosion and carbon budgets. 9.2.1 Case Study Example: the Rough Sike sediment-carbon budget. 9.3 Release of stored contaminants from eroding peatlands. 9.4 Restoration of eroded upland peatlands. 9.4.1 Frameworks for restoration. 9.4.2 Approaches to restoration. 9.4.3 Implications of the landsystems model and sediment budget work for restoration. 9.5 Conclusions. 9.5.1 The nature of upland peatlands. 9.5.2 Geomorphological processes in upland peatlands. 9.5.3 The future of upland peatlands. 9.5.4 Representativeness of the peat land system model. Index.

Mise en évidence d’une dynamique de fleuves de glace durant la glaciation ordovicienne par l’enregistrement géomorphologique

On Contemporary Ice streams the most important factor controlling polar ice-sheet sheet stability and ice flowing occurs in ice streams. On Pleistocene Ice Sheet, Ice stream can be located using several geomorphologic criteria predict from known characteristic of contemporary ice streams, these criteria defining the conceptual Ice Stream land system model. But nowadays, during fossil glaciations, ice streams characterization is still poorly documented and only few studies illustrate fast ice velocity. In this work, we characterize geomorphological markers of ice stream activity in order to define the Ordovician ice stream glacial landsystem. The study area is located in Sahara from Niger to Algeria. In this area, Ordovician glacial landforms have been investigated using satellite images and field investigations. According to these observations, Ordovician paleo ice stream are characterize by their size (20 to 200 km), by the increase of the length or ratio L/l of sub-glacial lineations changing from ice flute to mega scale glacial lineation at the margin of the ice sheet, by the evolution of sub glacial valley morphology ranging from areal scouring to glacial linear incision, and by sub glacial deformation. Finally, marine outlet of ice stream show ice contact deltas deposit. Individually, these criteria may not necessarily be exclusive to ice stream activity, but collectively they are thought to discriminate the characteristic Ordovician ice stream landsystem.

An ice cap landsystem for palaeoglaciological reconstructions: characterizing the Younger Dryas in western Scotland

This paper reviews the contrasting behaviours of ice caps and icefields, defines a generic landsystem model that can effectively discriminate between them, and applies the model to landform-sediment assemblages in an area of western Scotland. Such a model is necessary, since many palaeoenvironmental inferences from formerly glaciated terrains are based on the geometry, extent and dynamics of reconstructed ice masses. The validity of these glacier reconstructions is dependent on the accurate initial interpretation of relict landforms and sediments, and their inter-relationships. A new landsystems model is presented here, in which individual geological and geomorphological elements are checked against a set of eight theoretical diagnostic criteria that characterize the style of former glaciation. When applied to a 1200 km 2 area of the western Scottish Highlands, the landsystem tool predicts (1) an extensive Younger Dryas ice cap with a maximum surface elevation of 900 m above sea level, implying colder or wetter conditions than previously thought, and (2) the survival of an independent mountain icefield in part of the area during deglaciation. Glaciological theory, proxy palaeoenvironmental data and established glacier-climate-topography relationships support these predictions, thereby giving credibility to the landsystem methodology as a generic tool for palaeoglaciological reconstructions.

Younger Dryas glacial landsystems in North West Scotland: an assessment of modern analogues and palaeoclimatic implications

By explicitly linking process to form, landsystem models developed in modern environments provide powerful tools for the reconstruction of past environments from the sedimentological and geomorphological record. Some landform characteristics, however, may originate by more than one process (equifinality), so although a particular depositional model may “fit” the data, it is not necessarily the correct one. Here, we critically examine the use of modern analogues to interpret glacial landforms, focusing on “hummocky moraine”, a distinctive landform association consisting of numerous sharp-crested moraine mounds and ridge fragments, which occurs on many valley floors in upland Britain. Detailed studies of examples of Younger Dryas age in the North West Highlands of Scotland show that they represent ice-contact fans which have been affected to varying degrees by ice push and subglacial deformation, and that they formed at active, oscillating ice margins. The sedimentological data are inconsistent with an origin by englacial thrusting, as has been proposed for similar moraines elsewhere in upland Britain on the basis of morphological criteria. Comparison with modern glacial landsystems shows that, although aspects of “hummocky moraines” in the study area have close modern counterparts, none provides an exact analogue in all respects. This may reflect the distinctive climate of western Scotland during the Younger Dryas. Estimates of mean July temperatures in the Younger Dryas in Scotland, based on chironomid assemblages, are c. 8 °C at sea-level. When combined with reconstructed equilibrium line altitudes for contemporaneous glaciers, these estimates indicate mean annual precipitation totals in the range of 2358±337 mm yr −1 at sea-level in NW Scotland, c. 26% higher than present-day values. The implied heavy snowfall suggests that glaciers in western Scotland during the Younger Dryas were of high activity type, unlike modern glaciers in Svalbard, for example. High glacier velocities and high winter precipitation would suppress permafrost development, despite low mean annual temperatures. The climatic environment also favoured rapid oscillations of glacier margins, during both glacier build-up and retreat phases. Climatic factors, combined with the availability of large quantities of subglacial debris, led to the development of distinctive glacial landsystems, which may have no direct modern analogue.

Assemblages of submarine landforms produced by tidewater glaciers in Svalbard

High‐resolution swath bathymetry from the marine margins of several Svalbard tidewater glaciers shows an assemblage of submarine landforms that is probably linked to glacier surging. These landforms are essentially unmodified since their initial deposition over the past hundred years or so because they have not been subjected to subaerial erosion or periglacial activity. Swath images comprise an assemblage of superimposed landforms, allowing reconstruction of relative age of deposition: (1) large transverse ridges, interpreted as recessional moraines overridden by a subsequent ice advance; (2) a series of curvilinear streamlined bedforms orientated parallel to former ice flow, interpreted as lineations formed subglacially during rapid advance; (3) large terminal ridges, marking the farthest extent of ice at the last advance, with flow lobes immediately beyond interpreted as submarine debris flows; (4) a series of interconnected rhombohedral ridges, interpreted as a product of soft sediment squeezing into crevasses formed at the glacier bed, probably formed during immediate post‐surge stagnation; and (5) a series of fairly evenly spaced small transverse ridges, interpreted as push moraines produced annually at tidewater glacier termini during retreat. A simple descriptive landsystem model for tidewater glaciers of probable surge type is derived from these observations. We also show that megascale glacial lineations can form not only beneath large ice streams, but are also produced beneath surging tidewater glaciers lying on deforming sedimentary beds.

The active temperate glacial landsystem: a model based on Breiðamerkurjökull and Fjallsjökull, Iceland

Accurate interpretations of ancient glaciated terrains rely heavily on our knowledge of process–form relationships in contemporary glacierized basins. A landsystems model for temperate, actively receding glaciers is presented based upon Breiðamerkurjökull and Fjallsjökull, Iceland. Historical documentation, maps and/or aerial photography documenting recession since 1903 provide a unique series of “snapshots” of the evolving glacial geomorphology at these snouts. This documentation is employed in association with sedimentological investigations to assess the evolution of sediment–landform assemblages at active temperate glacier margins, using the wealth of geomorphological and sedimentological information produced during the recent recession of Breiðamerkurjökull and Fjallsjökull. Three depositional domains are recognized: (1) areas of extensive, low amplitude marginal dump, push and squeeze moraines derived largely from material on the glacier foreland and often recording annual recession of active ice; (2) incised and terraced glacifluvial forms, such as recessional ice-contact fans and hochsandur fans, and simple and complex, anabranched eskers and small areas of pitted outwash; (3) subglacial landform assemblages of flutes, drumlins and overridden push moraines located between ice-marginal glacifluvial depo-centres. The lack of supraglacial sediment in active temperate glaciers like Breiðamerkurjökull and Fjallsjökull generally precludes the widespread development of chaotic hummocky moraine. The hummocky terrain previously termed “kame and kettle topography” has mostly evolved by melt-out into a complex network of anabranched eskers over the period 1945–1998 or actually comprises pitted or kettled outwash (sandar). The tills across the foreland were emplaced by subglacial deformation and lodgement, and comprise materials derived from pre-existing stratified sediments in addition to localized abrasion of rock surfaces and patches of lake sediments. Till sequences thicker than 2 m have been constructed by the sequential plastering of till layers onto stratified sediments and bedrock. Because this stacking is a sub-marginal process, it is suggested that complex till sequences similar to those observed at Breiðamerkurjökull/Fjallsjökull may be employed in the reconstruction of ancient glacier margins. Additionally, the geomorphology of the active, temperate landsystem at east Breiðamerkurjökull may contain subtle surge signatures, verifying the historical record of small surges by this part of the glacier. This illustrates the danger of employing landform–sediment associations from restricted study areas (e.g. parts of landsystems) as representative process–form models for glaciated terrains.

Simulation of climate change induced by CO2 increasing for East Asia with IAP/LASG GOALS model

Two simulations, one for the control run and another for the perturbation run, with a global coupled ocean—atmosphere—land system model (IAP/ LASG GOALS version 4) have been carried out to study the global warming, with much detailed emphasis on East Asia. Results indicate that there is no climate drift in the control run and at the time of CO2 doubling the global temperature increases about 1.65°C. The GOALS model is able to simulate the observed spatial distribution and annual cycles of temperature and precipitation for East Asia quite well. But, in general, the model underestimates temperature and overestimates rainfall amount for regional annual average. For the climate change in East Asia, the temperature and precipitation in East Asia increase 2.1°C and 5% respectively, and the maximum warming occurs at middle—latitude continent and the maximum precipitation increase occurs around 25°N with reduced precipitation in the tropical western Pacific.

The North Atlantic oscillation simulated by versions 2 and 4 of IAP/ LASG GOALS Model

The capabilities of two versions of the Global–Ocean–Atmosphere–Land–System model (i.e. GOALS–2 and GOALS–4) developed at State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG), are validated in terms of the simulations of the winter North Atlantic Oscillation (NAO), which is currently the subject of considerable scientific interest. The results show that both GOALS–2 and GOALS–4 exhibit a realistic NAO signal associated with relatively reasonable spatial patterns of sea level pressure, surface air temperature, and precipitation. Generally speaking, the associated patterns of precipitation in GOALSs match better with the observation in comparison with the case of surface temperature. For the imprint of NAO on the ocean, or perhaps a coupling between the two fluids, the associated tripole patterns of the North Atlantic SST anomaly are presented distinctly in GOALS–2, for GOALS-4 however, this is not the case. Spatially, the models’ main deficiencies appear to be that the simulated Icelandic lows shift northward apparently, which in turn result in the blemish of GOALSs in reproducing the accompanied surface wind anomalies. For the interannual and even longer time scale variations of DJF sea level pressure (SLP) over the North Atlantic region, GOALSs reproduce the center with the strongest variability rationally, but the intensities are far weaker than the observation.

Response of IAP/ LASG GOALS model to the coupling of air-Sea fresh water exchange

The process of air—sea fresh water exchange is included successfully in the Global— Ocean—Atmosphere Land—System model developed at the State Key Laboratory of Atmospheric Sciences and Geophysical Fluid Dynamics (LASG). The results of the coupled integration show that the climate drift has been controlled successfully. Analyses on the responses of ocean circulation to the changes of surface fresh water or salinity forcing show that the ocean spin-up stage under flux condition for salinity is the key to the implementation of air-sea fresh water flux coupling. This study also demonstrates that the Modified—Monthly—Flux—Anomaly coupling scheme (MMFA) brought forward by Yu and Zhang (1998) is suitable not only for daily air—sea heat flux coupling but also for daily fresh water flux coupling.

Geomorphology and sedimentology of surging glaciers: a land-systems approach

AbstractThe identification of surging glaciers and ice streams in glaciated landscapes is of major importance to the understanding of ice-sheet dynamics and for reconstructing ice sheets and climate. No single landform or diagnostic criterion has yet been found with which to identify surging glaciers. A surging-glacier land-system model is constructed using observations and measurements from contemporary surging-glacier snouts in Iceland, Svalbard, U.S.A. and Canada for differentiating ancient surging margins from other non-surging palaeoglaciers. This integrates the suite of landforms, sediments and stratigraphy produced at surging-glacier margins. Landforms produced during surging include thrust moraines, concertina eskers and subglacial crevasse-squeeze ridges. Sedimentary sequences are usually characterized by multiple stacked diamictons and stratified interbeds, which display severe glaciotectonic contortion and faulting. Hummocky moraine, comprising interbedded stratified sediments and mass-flow diamictons, has also been associated with surge margins where large quantities of supraglacial and englacial debris entrained during the surge event have melted out in situ. An example of the application of the land-system model is presented for east-central Alberta, Canada. A surging palaeo-ice stream is identified within this part of the southwestern Laurentide ice sheet, where thrust-block moraines, crevasse-squeeze ridges, flutings, hummocky moraine and glaciotectonized sediments are juxtaposed.

Geomorphological criteria for identifying Pleistocene ice streams

AbstractIce streams are critical regulatory mechanisms in contemporary ice sheets. It has been inferred that they also had a significant effect on the dynamics of former ice sheets. Subsequently, many people have invoked their widespread occurrence from a variety of formerly glaciated areas. Hypothesised locations, however, have often outweighed meaningful evidence. This paper addresses the problem, using the characteristics of contemporary ice streams as a basis for their identification from former ice-sheet beds. A convergence of knowledge gained from contemporary ice-stream research, coupled with theories of glacial geomorphology, allows several geomorphological criteria to be identified as suggestive signatures of ice-stream activity. It is envisaged that the geomorphological criteria developed here will introduce a more objective approach to the study of former ice streams. The criteria are used to construct conceptual land-system models of the beds of former ice streams, and it is hoped such models can provide an observational template upon which hypotheses of former ice streams can be better based.