Large-scale, multi-temporal remote sensing of palaeo-river networks: A case study from Northwest India and its implications for the indus civilisation

© 2018 by the authors. Remote sensing has considerable potential to contribute to the identification and reconstruction of lost hydrological systems and networks. Remote sensing-based reconstructions of palaeo-river networks have commonly employed single or limited time-span imagery, which limits their capacity to identify features in complex and varied landscape contexts. This paper presents a seasonal multi-temporal approach to the detection of palaeo-rivers over large areas based on long-term vegetation dynamics and spectral decomposition techniques. Twenty-eight years of Landsat 5 data, a total of 1711 multi-spectral images, have been bulk processed using Google Earth Engine. © Code Editor and cloud computing infrastructure. The use of multi-temporal data has allowed us to overcome seasonal cultivation patterns and long-term visibility issues related to recent crop selection, extensive irrigation and land-use patterns. The application of this approach on the Sutlej-Yamuna interfluve (northwest India), a core area for the Bronze Age Indus Civilisation, has enabled the reconstruction of an unsuspectedly complex palaeo-river network comprising more than 8000 km of palaeo-channels. It has also enabled the definition of the morphology of these relict courses, which provides insights into the environmental conditions in which they operated. These new data will contribute to a better understanding of the settlement distribution and environmental settings in which this, often considered riverine, civilisation operated.ER

Volume 1

"Europe’s Lost Frontiers was the largest directed archaeological research project undertaken in Europe to investigate the inundated landscapes of the Early Holocene North Sea – the area frequently referred to as ‘Doggerland’. Funded through a European Research Council Advanced Grant (project number 670518), the project ran from 2015 to 2021, and involved more than 30 academics, representing institutions spread geographically from Ireland to China. A vast area of the seabed was mapped, and multiple ship expeditions were launched to retrieve sediment cores from the valleys of the lost prehistoric landscapes of the North Sea. This data has now been analysed to provide evidence of how the land was transformed in the face of climate change and rising sea levels. This volume is the first in a series of monographs dedicated to the analysis and interpretation of data generated by the project. As a precursor to the publication of the detailed results, it provides the context of the study and method statements. Later volumes will present the mapping, palaeoenvironment, geomorphology and modelling programmes of Europe’s Lost Frontiers. The results of the project confirm that these landscapes, long held to be inaccessible to archaeology, can be studied directly and provide an archaeological narrative. This data will become increasingly important at a time when contemporary climate change and geo-political crises are pushing development within the North Sea at an unprecedented rate, and when the opportunities to explore this unique, heritage landscape may be significantly limited in the future.

Sedimentary evidence of the Late Holocene tsunami in the Shetland Islands (UK) at Loch Flugarth, northern Mainland

Tsunami deposits around the North Sea basin are needed to assess the long-term hazard of tsunamis. Here, we present sedimentary evidence of the youngest tsunami on the Shetland Islands from Loch Flugarth, a coastal lake on northern Mainland. Three gravity cores show organic-rich background sedimentation with many sub-centimetre-scale sand layers, reflecting recurring storm overwash and a sediment source limited to the active beach and uppermost subtidal zone. A basal 13-cm-thick sand layer, dated to 426–787 cal. a CE based on 14C, 137Cs and Bayesian age–depth modelling, was found in all cores. High-resolution grain-size analysis identified four normally graded or massive sublayers with inversely graded traction carpets at the base of two sublayers. A thin organic-rich ‘mud’ drape and a ‘mud’ cap cover the two uppermost sublayers, which also contain small rip-up clasts. Grain-size distributions show a difference between the basal sand layer and the coarser and better sorted storm layers above. Multivariate statistical analysis of X-ray fluorescence core scanning data also distinguishes both sand units: Zr, Fe and Ti dominate the thick basal sand, while the thin storm layers are high in K and Si. Enriched Zr and Ti in the basal sand layer, in combination with increased magnetic susceptibility, may be related to higher heavy mineral content reflecting an additional marine sediment source below the storm-wave base that is activated by a tsunami. Based on reinterpretation of chronological data from two different published sites and the chronostratigraphy of the present study, the tsunami seems to date to c. 1400 cal. a BP. Although the source of the tsunami remains unclear, the lack of evidence for this event outside of the Shetland Islands suggests that it had a local source and was smaller than the older Storegga tsunami (8.15 cal. ka BP), which affected most of the North Sea basin.</p

Volume 1

"Europe’s Lost Frontiers was the largest directed archaeological research project undertaken in Europe to investigate the inundated landscapes of the Early Holocene North Sea – the area frequently referred to as ‘Doggerland’. Funded through a European Research Council Advanced Grant (project number 670518), the project ran from 2015 to 2021, and involved more than 30 academics, representing institutions spread geographically from Ireland to China. A vast area of the seabed was mapped, and multiple ship expeditions were launched to retrieve sediment cores from the valleys of the lost prehistoric landscapes of the North Sea. This data has now been analysed to provide evidence of how the land was transformed in the face of climate change and rising sea levels. This volume is the first in a series of monographs dedicated to the analysis and interpretation of data generated by the project. As a precursor to the publication of the detailed results, it provides the context of the study and method statements. Later volumes will present the mapping, palaeoenvironment, geomorphology and modelling programmes of Europe’s Lost Frontiers. The results of the project confirm that these landscapes, long held to be inaccessible to archaeology, can be studied directly and provide an archaeological narrative. This data will become increasingly important at a time when contemporary climate change and geo-political crises are pushing development within the North Sea at an unprecedented rate, and when the opportunities to explore this unique, heritage landscape may be significantly limited in the future.

Special External Effects on Fluvial System Evolution

Rivers are an excellent witness of the dynamics affecting Earth’s surface due to their sedimentary products and morphological expression, which may be considered as fluvial archives. Until now, the focus has been on evaluating the general impact of individual external factors. However, the importance of the specific environmental characteristics of these factors has become increasingly recognized, as highlighted in recent case studies. For example, the effects of regional climate, differentiated topography and vegetation, and frozen ground appear to play an essential role in the evolution of the fluvial system. Integration of such environmental conditions in the processes that were active within the complex fluvial system will open new perspectives in our progressive understanding of the evolution of landscape form, ecology, sediment fluxes, and hydrology of the system within the framework of the external drivers such as tectonics, general climate, and human activity. This is an appealing challenge that we wish to address in the present Special Issue under the aegis of the Fluvial Archives Group (FLAG)

Hydroclimate in Africa during the Medieval Climate Anomaly

The Medieval Climate Anomaly (MCA) is a recognized period of distinct pre-industrial climate change, with a core period of 1000–1200 CE. The field of palaeoclimatology has made major progress over the past 15 years during which a great number of high- and medium-resolution case studies were published, reconstructing climate change of the past millennia. In many parts of the world, regional data coverage has now reached a point which allows compiling palaeoclimate maps for well-defined time intervals. Here we present hydroclimatic trend maps for the MCA in Africa based on 99 published study locations. Key hydroclimatic proxy curves are visualized and compared in a series of 16 correlation panels. Proxy types are described and possible issues discussed. Based on the combined MCA dataset, temporal and spatial trends are interpreted and mapped out. Three areas have been identified in Africa in which rainfall seems to have increased during the MCA, namely Tunisia, western Sahel and the majority of southern Africa. At the same time, a reduction in precipitation occurred in the rest of Africa, comprising of NW and NE Africa, West Africa, Eastern Africa and the Winter Rainfall Zone of South Africa. MCA hydroclimate change in Africa appears to have been associated with characteristic phases of ocean cycles, as also supported by modern climate observations. Aridity in Morocco typically coincides with the positive phase of the North Atlantic Oscillation (NAO), whilst increased rainfall in the western Sahel is often coupled to the positive phase of the Atlantic Multidecadal Oscillation (AMO). Reduction in rainfall in the region Gulf of Aden/southern Red Sea to Eastern Africa could be linked to a negative Indian Ocean Dipole (IOD) or a derived long-term equivalent Indian Ocean cycle parameter. The Intertropical Convergence Zone (ITCZ) appears to have been shifted pole-wards during the MCA, for both the January and July positions. MCA hydroclimate mapping revealed major data gaps in the Sahara, South Sudan, Somalia, Central African Republic, Democratic Republic of Congo, Angola, northern Mozambique, Zambia and Zimbabwe. Special efforts are needed to fill these gaps, e.g. through a dedicated structured research program in which new multiproxy datasets are created, based on the learnings from previous African MCA studies

Laminated Sediments of Loch Ness, Scotland: Indicators of Holocene Environmental Change

Sediment cores, two approximately 6 metres and one about 1 metre in length, were recovered from the profundal plain of the northern basin of Loch Ness, Scotland. Examination revealed that the sediment is composed of irregular sequences of pale and dark laminations, most sub-millimeter in thickness, some ca 5 mm thick. Enumeration of laminae, and determination of lamination thickness, was carried out using X-radiography and image analysis. A hypothesis was developed that the finer laminations represent varves. This was tested by means of lamination counting, and by radiocarbon dating of material from one 'long' core. Comparison of the two chronologies thus derived suggested that the hypothesis was correct, and that a non-continuous chronology had been obtained, spanning the period ca 9000 to 1500 BP. Lamination thickness data derived from recent sediments was compared with meteorological data, especially rainfall, in order to test the hypothesis that prevailing climate, together with the alignment of the Loch with the predominantly southwesterly airflow, médiates in the production of the volume of allochthonous mineral material eroded from the catchment and its input to the water column. The result of this analysis bas proved inconclusive, and a more complex relationship may be involved. Other proxy climatic data were utilised in order further to investigate this aspect of the study and correlations between the sediment record and several of thèse were shown to be statistically significant. Spectral analysis of the lamination thickness datasets was also employed in order to determine if patterns of sedimentation may be linked to periodic forcing processes. Cyclicities observed in recent sediments include those of ca 210 and ca 90 years, which are also present in many other climatically-related records. Analysis of lamination thickness in the 'long' cores has proved inconclusive, producing evidence of many periodicities, but few of significance. It is believed that this result may be attributed to the non-stationary behaviour of forcing agents through time