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  • 1. Baker, Paul A.
    et al.
    Fritz, Sherilyn C.
    Dick, Christopher W.
    Eckert, Andrew J.
    Horton, Brian K.
    Manzoni, Stefano
    Stockholm University, Faculty of Science, Department of Physical Geography and Quaternary Geology.
    Ribas, Camila C.
    Garzione, Carmala N.
    Battisti, David S.
    The emerging field of geogenomics: Constraining geological problems with genetic data2014In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 135, p. 38-47Article in journal (Refereed)
    Abstract [en]

    The development of a genomics-derived discipline within geology is timely, as a result of major advances in acquiring and processing geologically relevant genetic data. This paper articulates the emerging field of geogenomics, which involves the use of large-scale genetic data to constrain geological hypotheses. The paper introduces geogenomics and discusses how hypotheses can be addressed through collaboration between geologists and evolutionary biologists. As an example, geogenomic methods are applied to evaluate competing hypotheses regarding the timing of the Andean uplift, the closure of the Isthmus of Panama, the onset of trans-Amazon drainage, and Quaternary climate variation in the Neotropics.

  • 2. Chandler, Benjamin M. P.
    et al.
    Lovell, Harold
    Boston, Clare M.
    Lukas, Sven
    Barr, Iestyn D.
    Örn Benediktsson, Ívar
    Benn, Douglas I.
    Clark, Chris D.
    Darvill, Christopher M.
    Evans, David J. A.
    Ewertowski, Marek W.
    Loibl, David
    Margold, Martin
    Otto, Jan-Christoph
    Roberts, David H.
    Stokes, Chris R.
    Storrar, Robert D.
    Stroeven, Arjen P.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Glacial geomorphological mapping: A review of approaches and frameworks for best practice2018In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 185, p. 806-846Article, review/survey (Refereed)
    Abstract [en]

    Geomorphological mapping is a well-established method for examining earth surface processes and landscape evolution in a range of environmental contexts. In glacial research, it provides crucial data for a wide range of process-oriented studies and palaeoglaciological reconstructions; in the latter case providing an essential geomorphological framework for establishing glacial chronologies. In recent decades, there have been significant developments in remote sensing and Geographical Information Systems (GIS), with a plethora of high quality remotely-sensed datasets now (often freely) available. Most recently, the emergence of unmanned aerial vehicle (UAV) technology has allowed sub-decimetre scale aerial images and Digital Elevation Models (DEMs) to be obtained. Traditional field mapping methods still have an important role in glacial geomorphology, particularly in cirque glacier, valley glacier and icefield/ice-cap outlet settings. Field mapping is also used in ice sheet settings, but often takes the form of necessarily highly-selective ground-truthing of remote mapping. Given the increasing abundance of datasets and methods available for mapping, effective approaches are necessary to enable assimilation of data and ensure robustness. This paper provides a review and assessment of the various glacial geomorphological methods and datasets currently available, with a focus on their applicability in particular glacial settings. We distinguish two overarching 'work streams' that recognise the different approaches typically used in mapping landforms produced by ice masses of different sizes: (i) mapping of ice sheet geomorphological imprints using a combined remote sensing approach, with some field checking (where feasible); and (ii) mapping of alpine and plateau-style ice mass (cirque glacier, valley glacier, icefield and ice-cap) geomorphological imprints using remote sensing and considerable field mapping. Key challenges to accurate and robust geomorphological mapping are highlighted, often necessitating compromises and pragmatic solutions. The importance of combining multiple datasets and/or mapping approaches is emphasised, akin to multi-proxy approaches used in many Earth Science disciplines. Based on our review, we provide idealised frameworks and general recommendations to ensure best practice in future studies and aid in accuracy assessment, comparison, and integration of geomorphological data. These will be of particular value where geomorphological data are incorporated in large compilations and subsequently used for palaeoglaciological reconstructions. Finally, we stress that robust interpretations of glacial landforms and landscapes invariably requires additional chronological and/or sedimentological evidence, and that such data should ideally be collected as part of a holistic assessment of the overall glacier system.

  • 3.
    Greenwood, Sarah L.
    et al.
    Stockholm University, Faculty of Science, Department of Geological Sciences.
    Clason, Caroline C.
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Helanow, Christian
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Margold, Martin
    Stockholm University, Faculty of Science, Department of Physical Geography. Durham University, UK.
    Theoretical, contemporary observational and palaeo-perspectives on ice sheet hydrology: Processes and products2016In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 155, p. 1-27Article in journal (Refereed)
    Abstract [en]

    Meltwater drainage through ice sheets has recently been a key focus of glaciological research due to its influence on the dynamics of ice sheets in a warming climate. However, the processes, topologies and products of ice sheet hydrology are some of the least understood components of both past and modem ice sheets. This is to some extent a result of a disconnect between the fields of theoretical, contemporary observational and palaeo-glaciology that each approach ice sheet hydrology from a different perspective and with different research objectives. With an increasing realisation of the potential of using the past to inform on the future of contemporary ice sheets, bridging the gaps in the understanding of ice sheet hydrology has become paramount. Here, we review the current state of knowledge about ice sheet hydrology from the perspectives of theoretical, observational and palaeo-glaciology. We then explore and discuss some of the key questions in understanding and interpretation between these research fields, including: 1) disagreement between the palaeo-record, glaciological theory and contemporary observations in the operational extent of channelised subglacial drainage and the topology of drainage systems; 2) uncertainty over the magnitude and frequency of drainage events associated with geomorphic activity; and 3) contrasts in scale between the three fields of research, both in a spatial and temporal context The main concluding points are that modem observations, modelling experiments and inferences from the palaeo-record indicate that drainage topologies may comprise a multiplicity of forms in an amalgam of drainage modes occurring in different contexts and at different scales. Drainage under high pressure appears to dominate at ice sheet scale and might in some cases be considered efficient; the sustainability of a particular drainage mode is governed primarily by the stability of discharge. To gain better understanding of meltwater drainage under thick ice, determining what drainage topologies are reached under high pressure conditions is of primary importance. Our review attests that the interconnectivity between research sub-disciplines in progressing the field is essential, both in interpreting the palaeo-record and in developing physical understanding of glacial hydrological processes and systems.

  • 4. He, Minhui
    et al.
    Yang, Bao
    Bräuning, Achim
    Rossi, Sergio
    Charpentier Ljungqvist, Fredrik
    Stockholm University, Faculty of Humanities, Department of History. University of Cambridge, United Kingdom.
    Shishov, Vladimir
    Grießinger, Jussi
    Wang, Jianglin
    Liu, Jingjing
    Qin, Chun
    Recent advances in dendroclimatology in China2019In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 194, p. 521-535Article, review/survey (Refereed)
    Abstract [en]

    Considerable progress has been made in dendroclimatological research in China during the period 2000-2017, including a significant increase in the spatial coverage of tree-ring chronologies developed for paleoclimatic research. New tree-ring sampling sites have been established across the Tibetan Plateau, as well as the north-eastern and sub-tropical eastern parts of China. Most of the studies use coniferous trees, although different plant functional types (e.g., broadleaf species and shrubs) have also been increasingly investigated. Tree-ring chronologies longer than 600 years, however, are mostly found on the Tibetan Plateau, with the longest one extending back to 2637 BCE (before Common Era). Most tree-ring records in the eastern parts of China are < 400 years long. Tree-ring width is the most commonly studied parameter, although stable isotope ratios and wood density data have also been obtained for specific sites. Stable oxygen isotope data frequently shares a common hydroclimate signal, whereas the climate or environmental signals remain inconsistent for the few available stable carbon isotope records. In general, tree-ring width-based temperature reconstructions originate from higher elevation sites (i.e., treeline) compared to hydroclimate reconstructions. Precipitation or drought reconstructions are mainly obtained from regions with an annual precipitation of < 800 mm. Most of the tree-ring reconstructions are based on individual site or local-scale chronologies, although a limited number of regional-scale and field reconstructions have been produced. The most prominent identified characteristics of the recent advances in dendroclimatological research for China have manifested in aspects such as an expanded network of sampling sites, improved climate reconstruction methodology, and improved uncertainty estimations in the latter. Furthermore, the traditional statistical-based tree growth climate relationships have been supplemented by monitoring and modeling approaches. Based on the progress from 2000 to 2017, and on the research potential of the country in this field, we expect additional widening of the dendroclimatological investigations in China during the coming years.

  • 5. Loisel, Julie
    et al.
    van Bellen, Simon
    Pelletier, Luc
    Talbot, Julie
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography. Stockholm Univ, Dept Phys Geog, Stockholm, Sweden.
    Karran, Daniel
    Yu, Zicheng
    Nichols, Jonathan
    Holmquist, James
    Insights and issues with estimating northern peatland carbon stocks and fluxes since the Last Glacial Maximum2017In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 165, p. 59-80Article, review/survey (Refereed)
    Abstract [en]

    In this review paper, we identify and address key uncertainties related to four local and global controls of Holocene northern peatland carbon stocks and fluxes. First, we provide up-to-date estimates of the current northern peatland area (3.2 M km(2)) and propose a novel approach to reconstruct changes in the northern peatland area over time (Section 2). Second, we review the key methods and models that have been used to quantify total carbon stocks and methane emissions over time at the hemispheric scale, and offer new research directions to improve these calculations (Section 3). Our main proposed improvement relates to allocating different carbon stock and emission values for each of the two dominant vegetation assemblages (sedge and brown moss-dominated vs. Sphagnum-dominated peat). Third, we discuss and quantify the importance of basin heterogeneity in estimating peat volume at the local scale (Section 4.1). We also highlight the importance of age model selection when reconstructing carbon accumulation rates from a peat core (Section 4.2). Lastly, we introduce the role of biogeomorphological agents such as beaver activity in controlling carbon dynamics (Section 5.1) and review the newest research related to permafrost thaw (Section 5.2) and peat fire (Section 5.3) under climate change. Overall, this review summarizes new information from a broad range of peat-carbon studies, provides novel analysis of hemispheric-scale paleo datasets, and proposes new insights on how to translate peat-core data into carbon fluxes. It also identifies critical data gaps and research priorities, and many ways to consider and address them.

  • 6. Marchant, Rob
    et al.
    Widgren, Mats
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Pas Schrijver, Annemiek
    Stockholm University, Faculty of Social Sciences, Department of Human Geography.
    Wright, David
    Drivers and trajectories of land cover change in East Africa: Human and environmental interactions from 6000 years ago to present2018In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 178, p. 322-378Article in journal (Refereed)
    Abstract [en]

    East African landscapes today are the result of the cumulative effects of climate and land-use change over millennial timescales. In this review, we compile archaeological and palaeoenvironmental data from East Africa to document land-cover change, and environmental, subsistence and land-use transitions, over the past 6000 years. Throughout East Africa there have been a series of relatively rapid and high-magnitude environmental shifts characterised by changing hydrological budgets during the mid- to late Holocene. For example, pronounced environmental shifts that manifested as a marked change in the rainfall amount or seasonality and subsequent hydrological budget throughout East Africa occurred around 4000, 800 and 300 radiocarbon years before present (yr BP). The past 6000 years have also seen numerous shifts in human interactions with East African ecologies. From the mid-Holocene, land use has both diversified and increased exponentially, this has been associated with the arrival of new subsistence systems, crops, migrants and technologies, all giving rise to a sequence of significant phases of land-cover change. The first large-scale human influences began to occur around 4000 yr BP, associated with the introduction of domesticated livestock and the expansion of pastoral communities. The first widespread and intensive forest clearances were associated with the arrival of iron-using early farming communities around 2500 yr BP, particularly in productive and easily-cleared mid-altitudinal areas. Extensive and pervasive land-cover change has been associated with population growth, immigration and movement of people. The expansion of trading routes between the interior and the coast, starting around 1300 years ago and intensifying in the eighteenth and nineteenth centuries CE, was one such process. These caravan routes possibly acted as conduits for spreading New World crops such as maize (Zea mays), tobacco (Nicotiana spp.) and tomatoes (Solanum lycopersicum), although the processes and timings of their introductions remains poorly documented. The introduction of southeast Asian domesticates, especially banana (Musa spp.), rice (Oryza spp.), taro (Colocasia esculenta), and chicken (Gallus gallus), via transoceanic biological transfers around and across the Indian Ocean, from at least around 1300 yr BP, and potentially significantly earlier, also had profound social and ecological consequences across parts of the region.

    Through an interdisciplinary synthesis of information and metadatasets, we explore the different drivers and directions of changes in land-cover, and the associated environmental histories and interactions with various cultures, technologies, and subsistence strategies through time and across space in East Africa. This review suggests topics for targeted future research that focus on areas and/or time periods where our understanding of the interactions between people, the environment and land-cover change are most contentious and/or poorly resolved. The review also offers a perspective on how knowledge of regional land-use change can be used to inform and provide perspectives on contemporary issues such as climate and ecosystem change models, conservation strategies, and the achievement of nature-based solutions for development purposes.

  • 7. Strauss, Jens
    et al.
    Schirrmeister, Lutz
    Grosse, Guido
    Fortier, Daniel
    Hugelius, Gustaf
    Stockholm University, Faculty of Science, Department of Physical Geography.
    Knoblauch, Christian
    Romanovsky, Vladimir
    Schädel, Christina
    Schneider von Deimling, Thomas
    Schuur, Edward A. G.
    Shmelev, Denis
    Ulrich, Mathias
    Veremeeva, Alexandra
    Deep Yedoma permafrost: A synthesis of depositional characteristics and carbon vulnerability2017In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 172, p. 75-86Article in journal (Refereed)
    Abstract [en]

    Permafrost is a distinct feature of the terrestrial Arctic and is vulnerable to climate warming. Permafrost degrades in different ways, including deepening of a seasonally unfrozen surface and localized but rapid development of deep thaw features. Pleistocene ice-rich permafrost with syngenetic ice-wedges, termed Yedoma deposits, are widespread in Siberia, Alaska, and Yukon, Canada and may be especially prone to rapid-thaw processes. Freeze-locked organic matter in such deposits can be re-mobilized on short time-scales and contribute to a carbon-cycle climate feedback. Here we synthesize the characteristics and vulnerability of Yedoma deposits by synthesizing studies on the Yedoma origin and the associated organic carbon pool. We suggest that Yedoma deposits accumulated under periglacial weathering, transport, and deposition dynamics in non-glaciated regions during the late Pleistocene until the beginning of late glacial warming. The deposits formed due to a combination of aeolian, colluvial, nival, and alluvial deposition and simultaneous ground ice accumulation. We found up to 130 gigatons organic carbon in Yedoma, parts of which are well-preserved and available for fast decomposition after thaw. Based on incubation experiments, up to 10% of the Yedoma carbon is considered especially decomposable and may be released upon thaw. The substantial amount of ground ice in Yedoma makes it highly vulnerable to disturbances such as thermokarst and thermo-erosion processes. Mobilization of permafrost carbon is expected to increase under future climate warming. Our synthesis results underline the need of accounting for Yedoma carbon stocks in next generation Earth-System-Models for a more complete representation of the permafrost-carbon feedback.

  • 8. Turnewitsch, Robert
    et al.
    Falahat, Saeed
    Stockholm University, Faculty of Science, Department of Meteorology .
    Nycander, Jonas
    Stockholm University, Faculty of Science, Department of Meteorology .
    Dale, Andrew
    Scott, Robert B.
    University of Texas Austin, USA.
    Furnival, Darran
    Deep-sea fluid and sediment dynamics-Influence of hill- to seamount-scale seafloor topography2013In: Earth-Science Reviews, ISSN 0012-8252, E-ISSN 1872-6828, Vol. 127, p. 203-241Article in journal (Refereed)
    Abstract [en]

    Deep-sea sediments play a central role in a wide range of subject areas. A number of important controls on the formation of sedimentary deposits have been studied. However, to date, the impact of submarine landscape geometry as a possible control has received comparatively little attention. This seems to be particularly true for intermediate-scale topographic features such as abyssal hills, knolls and seamounts that can be found in many regions of the global seafloor: recent estimates suggest that in the deep open oceans, away from continental margins, there might be as many as similar to 25 x 10(6) abyssal hills, knolls and seamounts. Despite this large number very little is known about how they influence environmental complexity and patchiness, biogeochemical fluxes and the formation of sedimentary records. This paper reviews the currently known types of fluid-flow interactions with abyssal hills, knolls and seamounts that could potentially influence the way sediments are formed. The main types of relevant flow components are: quasi-steady to eddying background flow; internal lee and near-inertial waves; barotropic and baroclinic tides; and seamount-trapped waves. Previous studies looking into systematic links between fluid dynamics and sediments at hills, knolls and seamounts are reviewed. Finally, a case study is presented which aims to combine our current knowledge and investigate whether a given combination of recent fluid-flow components leaves a detectable imprint in the recent sediments on and around a short seamount. The main conclusions and implications are as follows. (1) Topographically generated flow-field geometries that are composed of a number of different prevailing fluid-flow components can be reflected and detected in properties of the underlying sediments. (2) Tidal and other higher-frequency (lee-wave, near-inertial) components of deep-ocean currents can be essential for locally driving total current velocities across threshold values for non-deposition/erosion/resuspension of freshly deposited deep-sea sediments. Moreover, there is evidence suggesting that not only maximum current speeds but also intensities of higher-frequency (tidal and/or (near-)inertial) current-direction variability might control sediment dynamics and sediment formation. This relativises the view that current speed is the main, or even only, controlling factor for sediment dynamics and sediment formation. (3) When it comes to the reconstruction of paleo-flows, these findings imply that certain sedimentary records may well reveal more about variability in the higher-frequency flow components than about variability in the basin-scale net flow component that often is the focus of paleoceanographic studies. (4) Single-core paleo-records from hill-, seamount- or similarly controlled sediment deposits may be biased due to the asymmetry of flow fields around these topographic features. To arrive at unbiased paleo-records for non-fluid-dynamic parameters, the influence of the flow-field geometry would have to be removed from the record first (5) It seems the mechanistic understanding of hill- and seamount-related flow/topography interactions and their links to sediment dynamics is approaching a level that may (a) facilitate improved interpretation of topographically controlled sedimentary paleo-records, (b) help fill in the knowledge gap that exists for functional deep-sea biodiversity at intermediate space scales, and (c) improve predictive capabilities for exploration of economically relevant iron-manganese (Fe-Mn) crusts on seamounts.

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