Are Deltas Human Constructs?

Productive and biologically diverse, deltaic lowlands attracted humans since prehistory and may have spurred the emergence of the first urban civilizations. Deltas continued to be an important nexus for economic development across the world and are currently home for over half a billion people. But recently, under the double whammy of sea level rise and inland sediment capture behind dams, they have become the most threatened coastal landscap

Wave-angle control of delta evolution

Author Posting. © American Geophysical Union, 2011. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 38 (2011): L13405, doi:10.1029/2011GL047630.Wave-influenced deltas, with large-scale arcuate shapes and demarcated beach ridge complexes, often display an asymmetrical form about their river channel. Here, we use a numerical model to demonstrate that the angles from which waves approach a delta can have a first-order influence upon its plan-view morphologic evolution and sedimentary architecture. The directional spread of incoming waves plays a dominant role over fluvial sediment discharge in controlling the width of an active delta lobe, which in turn affects the characteristic rates of delta progradation. Oblique wave approach (and a consequent net alongshore sediment transport) can lead to the development of morphologic asymmetry about the river in a delta's plan-view form. This plan-form asymmetry can include the development of discrete breaks in shoreline orientation and the appearance of self-organized features arising from shoreline instability along the downdrift delta flank, such as spits and migrating shoreline sand waves—features observed on natural deltas. Somewhat surprisingly, waves approaching preferentially from one direction tend to increase sediment deposition updrift of the river. This ‘morphodynamic groin effect’ occurs when the delta's plan-form aspect ratio is sufficiently large such that the orientation of the shoreline on the downdrift flank is rotated past the angle of maximum alongshore sediment transport, resulting in preferential redirection of fluvial sediment updrift of the river mouth.This research was supported by NSF grants EAR‐0952146 and OCE‐0623766, the Exxon‐Mobil Upstream Research Company, and the WHOI‐USGS postdoctoral fellowship

Pliocene expansion of C-4 vegetation in the core monsoon zone on the Indian Peninsula

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Dunlea, A. G., Giosan, L., & Huang, Y. Pliocene expansion of C-4 vegetation in the core monsoon zone on the Indian Peninsula. Climate of the Past, 16(6), (2020): 2533-2546, https://doi.org/10.5194/cp-16-2533-2020.The expansion of C4 vegetation during the Neogene was one of the largest reorganizations of Earth's terrestrial biome. Once thought to be globally synchronous in the late Miocene, site-specific studies have revealed differences in the timing of the expansion and suggest that local conditions play a substantial role. Here, we examine the expansion of C4 vegetation on the Indian Peninsula since the late Miocene by constructing a ∼6-million-year paleorecord with marine sediment from the Bay of Bengal at Site U1445, drilled during International Ocean Discovery Program Expedition 353. Analyses of element concentrations indicate that the marine sediment originates from the Mahanadi River in the Core Monsoon Zone (CMZ) of the Indian Peninsula. Hydrogen isotopes of the fatty acids of leaf waxes reveal an overall decrease in the CMZ precipitation since the late Miocene. Carbon isotopes of the leaf wax fatty acids suggest C4 vegetation on the Indian Peninsula existed before the end of the Miocene but expanded to even higher abundances during the mid-Pliocene to mid-Pleistocene (∼3.5 to 1.5 million years ago). Similar to the CMZ on the Indian Peninsula, a Pliocene expansion or re-expansion has previously been observed in northwest Australia and in East Africa, suggesting that these tropical ecosystems surrounding the Indian Ocean remained highly sensitive to changes in hydroclimate after the initial spread of C4 plants in late Miocene.This research has been supported by the Ocean and Climate Change Institute Postdoctoral Scholarship at Woods Hole Oceanographic Institution to Ann Dunlea, and the U.S. National Science Foundation to Liviu Giosan (grant no. NSF OCE-0652315). USSSP post-cruise support was provided to Expedition 353 shipboard participants Liviu Giosan and Yongsong Huang

A cartographical perspective to the engineering works at the Sulina mouth

Author Posting. © The Author(s), 2010. This is the author's version of the work. It is posted here by permission of Akadémiai Kiadó for personal use, not for redistribution. The definitive version was published in Acta Geodaetica et Geophysica Hungarica 45 (2010): 71-79, doi:10.1556/AGeod.45.2010.1.11.From 1856 to 1939, the European Commission of the Danube (ECD), was responsible for technical surveys at the mouth of Sulina arm. During this period, ECD prepared general maps of Danube Delta as well as detailed charts for all the Danube mouths: Chilia, Sulina and Sf. Gheorghe (St. George) that were published in various reports or atlases. ECD used a local grid network benchmarked at Sulina, divided in 500 feet units. The reference point was the old lighthouse located on the right bank of Danube. After the Second World War, the Romanian authorities elaborated new cartographical products using the Gauss‐Kruger projection or Stereo‐70 like national grid. Our goal is to generate a cartographical background database necessary for refining the coastal evolution model of the Sulina mouth. To handle the large number of available maps, we chose GeoNetwork like a solution for catalog service, indexing and defining metadata. The service is operating at geo‐spatial.org

Comment on “Geochemistry of buried river sediments from Ghaggar Plains, NW India: Multi - proxy records of variations in provenance, paleoclimate, and paleovegetation patterns in the late quaternary” by Ajit Singh, Debajyoti Paul, Rajiv Sinha, Kristina J. Thomsen, Sanjeev Gupta

Author Posting. © The Author(s), 2016. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Palaeogeography, Palaeoclimatology, Palaeoecology 455 (2016): 65-67, doi:10.1016/j.palaeo.2016.05.001.Singh et al. (2016) published a geochemical record of sediment compositions from the flood plain of the Ghaggar River in western India and use the changing provenance, particularly as traced by Nd isotope composition, to reconstruct how erosion patterns have changed over the past 100 k.y. In doing so they propose a link between climate change and erosion, and they argue for more erosion from the Higher Himalaya during warmer interglacial periods and more from the Lesser Himalaya during glacial intervals. While we support the concept of erosion patterns being climatically modulated we here take the opportunity to compare the data presented by Singh et al. (2016) to relevant published records within the region greater Ghaggar region and to open a balanced discussion on how climate and erosion are coupled in the western Himalaya

Littoral steering of deltaic channels

© The Author(s), 2016. This is the author's version of the work and is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth and Planetary Science Letters 452 (2016): 204-214, doi:10.1016/j.epsl.2016.08.018.The typically single-threaded channels on wave-influenced deltas show striking differences in their orientations, with some channels oriented into the incoming waves (e.g., Ombrone, Krishna), and others oriented away from the waves (e.g., Godavari, Sao Francisco). Understanding the controls on channel orientation is important as the channel location greatly influences deltaic morphology and sedimentology, both subaerially and subaqueously. Here, we explore channel orientation and consequent feedbacks with local shoreline dynamics using a plan-form numerical model of delta evolution. The model treats fluvial sediment delivery to a wave-dominated coast in two ways: 1) channels are assumed to prograde in a direction perpendicular to the local shoreline orientation and 2) a controlled fraction of littoral sediment transport can bypass the river mouth. Model results suggest that channels migrate downdrift when there is a significant net littoral transport and alongshore transport bypassing of the river mouth is limited. In contrast, river channels tend to orient themselves into the waves when fluvial sediment flux is relatively large, causing the shoreline of the downdrift delta flank to attain the orientation of maximum potential sediment transport for the incoming wave climate. Using model results, we develop a framework to estimate channel orientations for wave-influenced deltas that shows good agreement with natural examples. An increase in fluvial sediment input can cause a channel to reorient itself into incoming waves, behavior observed, for example, in the Ombrone delta in Italy. Our results can inform paleoclimate studies by linking channel orientation to fluvial sediment flux and wave energy. In particular, our approach provides a means to quantify past wave directions, which are notoriously difficult to constrain.This study was supported by NSF grant EAR-0952146.2017-08-1

Middle miocene intensification of South Asian monsoonal rainfall

Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Paleoceanography and Paleoclimatology 35(12), (2020): e2020PA003853, https://doi.org/10.1029/2020PA003853.During the middle Miocene, Earth's climate changed from a global warm period (Miocene Climatic Optimum) into a colder one with the expansion of the Antarctic ice sheet. This prominent climate transition was also a period of drastic changes in global atmospheric circulation. The development of the South Asian monsoon is not well understood and mainly derived from proxy records of wind strength. Data for middle Miocene changes in rainfall are virtually non‐existent for India and the Arabian Sea prior to 11 Ma. This study presents planktic foraminiferal trace element (Mg/Ca and Ba/Ca) and stable oxygen isotope records from NGHP‐01 Site 01A off the coast of West India in the Eastern Arabian Sea (EAS) to reconstruct the regional surface hydrography and hydroclimate in the South Asian monsoon (SAM) region during the middle Miocene. The Ba/Ca and local seawater δ18O (δ18Osw) changes reveal a notable gradual increase in SAM rainfall intensity during the middle Miocene. Additionally to this long‐term increase in precipitation, the seawater δ18O is punctuated by a prominent decrease, i.e. freshening, at ~14 Ma contemporary with Antarctic glaciation. This suggests that Southern Ocean Intermediate Waters (SOIW) transmitted Antarctic salinity changes into the Arabian Sea via an “oceanic tunnel” mechanism. The middle Miocene increase in SAM rainfall is consistent with climate model simulations of an overall strengthening Asian monsoon from the Eocene to the middle/late Miocene with a further acceleration after the middle Miocene climate transition.This study has been funded by the National Natural Science Foundation of China through a grant to S. Steinke (NSFC grant No. 41776055) and Z. Jian and S. Steinke (NSFC grant No. 919582080). We express our gratitude to H. Kuhnert (MARUM, University of Bremen) and his team for stable isotope analyses. We thank P. Qiao (Tongji University Shanghai) for technical and analytical support with the ICP‐MS analyses, A. Dolman (Alfred‐Wegener‐Institute, Helmholtz Centre for Polar and Marine Research, Potsdam, Germany) for statistical analyses, and B. Wang (State Key Laboratory of Marine Environmental Science, Xiamen University) and his team for the SEM‐EDAX Energy Dispersive X‐ray Spectroscopy (EDS) analyses. L. Giosan acknowledges funding from USSP and WHOI and thanks colleagues and crew from the NGHP‐01 expedition for intellectual interactions leading to long‐standing interests in the fluvial‐continental margin systems of Peninsular India. J. Groeneveld thanks the State Key Laboratory of Marine Environmental Science (Xiamen University) for a MEL Senior Visiting Fellowship (Project No. MELRS1915).2021-05-2

Holocene palaeoenvironmental evolution of the Ebro Delta (Western Mediterranean Sea) : evidence for an early construction based on the benthic foraminiferal record

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in The Holocene 26 (2016): 1438-1456, doi:10.1177/0959683616640048.Major Mediterranean deltas began to develop during a period between 8000 and 6000 yr BP when the rate of fluvial sediment input overtook the declining rate of sea-level rise. However, different authors have argued that the Ebro Delta primarily formed during the Late Middle Ages as a consequence of increased anthropogenic pressure on its river basin and these arguments are supported by the scarcity of previous geological studies and available radiocarbon dates. To reconstruct the environmental evolution of the Ebro Delta during the Holocene, we used micropalaeontological analysis of continuous boreholes drilled in two different locations (Carlet and Sant Jaume) on the central delta plain. Different lithofacies distributions and associated environments of deposition were defined based on diagnostic foraminiferal assemblages and the application of a palaeowater-depth transfer function. The more landward Carlet sequence shows an older and more proximal progradational delta with a sedimentary record composed of inner bay, lagoonal, and beach materials deposited between 7600 yr BP and >2000 yr BP under rising sea-level and highstand conditions. This phase was followed by a series of delta-plain environments reflected in part by the Carlet deposits that formed before 2000 yr BP. The Sant Jaume borehole is located closer to the present coastline and contains a much younger sequence that accumulated in the 3 last 2.0 ka during the development of three different deltaic lobes under highstand sea40 level conditions. The results of the present study reinforce the idea that the Ebro Delta dates to the early Holocene, similar to other large Mediterranean deltas.Drilling and coring was funded by the US National Science Foundation 686 grant EAR- 0952146. Work on the cores presented in this study was partially financed by the Formation and Research Unit in Quaternary: Environmental Changes and Human Fingerprint (UPV/EHU, UFI11/09) and HAREA-Coastal Geology Research Group (Basque Government, IT767-13) projects. It was supported by an IRTA-URV Santander fellowship to Xavier Benito through “BRDI Trainee Research Personnel Programme funded by University of Rovira and Virgili R+D+I projects” and the European Community’s 7th Framework Programme through the grant to Collaborative Project RISES-AM-, Contract FP7-ENV-2013-two-stage-603396

Studying the relationship between past people and their environments

AGU Chapman Conference on Climates, Past Landscapes, and Civilizations; Santa Fe, New Mexico, 21–25 March 2011; The fortunes of human societies are intimately linked to the environments that sustain them. This has been true from the first emergence of human ancestors through to the present day. An AGU Chapman Conference was held to discuss the relationship between past people and their environments. Participants examined the state of the field, debated issues of contention, and formulated ways that such cross-disciplinary research can progress. Scientists' increasing ability to generate high-resolution climate records has proliferated studies that link the rise and fall of cultures to climate change. This meeting brought together scholars from across the divide between Earth sciences and archaeology to derive a deeper understanding of how humans have reacted to and shaped the changing environment.Anthropolog

Large-scale coastal and fluvial models constrain the late Holocene evolution of the Ebro Delta

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Earth Surface Dynamics 5 (2017): 585-603, doi:10.5194/esurf-5-585-2017.The distinctive plan-view shape of the Ebro Delta coast reveals a rich morphologic history. The degree to which the form and depositional history of the Ebro and other deltas represent autogenic (internal) dynamics or allogenic (external) forcing remains a prominent challenge for paleo-environmental reconstructions. Here we use simple coastal and fluvial morphodynamic models to quantify paleo-environmental changes affecting the Ebro Delta over the late Holocene. Our findings show that these models are able to broadly reproduce the Ebro Delta morphology, with simple fluvial and wave climate histories. Based on numerical model experiments and the preserved and modern shape of the Ebro Delta plain, we estimate that a phase of rapid shoreline progradation began approximately 2100 years BP, requiring approximately a doubling in coarse-grained fluvial sediment supply to the delta. River profile simulations suggest that an instantaneous and sustained increase in coarse-grained sediment supply to the delta requires a combined increase in both flood discharge and sediment supply from the drainage basin. The persistence of rapid delta progradation throughout the last 2100 years suggests an anthropogenic control on sediment supply and flood intensity. Using proxy records of the North Atlantic Oscillation, we do not find evidence that changes in wave climate aided this delta expansion. Our findings highlight how scenario-based investigations of deltaic systems using simple models can assist first-order quantitative paleo-environmental reconstructions, elucidating the effects of past human influence and climate change, and allowing a better understanding of the future of deltaic landforms.This study was supported by NSF grant EAR-0952146