TY - JOUR T1 - Climate control on terrestrial biospheric carbon turnover JF - Proceedings of the National Academy of Sciences Y1 - 2021 A1 - Eglinton, Timothy I. A1 - Galy, Valier V. A1 - Hemingway, Jordon D. A1 - Feng, Xiaojuan A1 - Bao, Hongyan A1 - Blattmann, Thomas M. A1 - Dickens, Angela F. A1 - Gies, Hannah A1 - Giosan, Liviu A1 - Haghipour, Negar A1 - Hou, Pengfei A1 - Lupker, Maarten A1 - McIntyre, Cameron P. A1 - Montluçon, Daniel B. A1 - Peucker-Ehrenbrink, Bernhard A1 - Ponton, Camilo A1 - Schefuß, Enno A1 - Schwab, Melissa S. A1 - Voss, Britta M. A1 - Wacker, Lukas A1 - Wu, Ying A1 - Zhao, Meixun KW - Carbon cycle KW - carbon turnover times KW - fluvial carbon KW - plant biomarkers KW - radiocarbon AB - Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon (C-14) ages on two groups of molecular tracers of plant-derived carbon-leaf-wax lipids and lignin phenols-from a globally distributed suite of rivers. We find significant negative relationships between the C-14 age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil C-14 ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change-induced perturbations of soil OC turnover and stocks. VL - 118 UR - https://www.researchgate.net/publication/349357864_Climate_control_on_terrestrial_biospheric_carbon_turnover IS - 8 ER - TY - JOUR T1 - Holocene paleodepositional changes reflected in the sedimentary microbiome of the Black Sea JF - Geobiology Y1 - 2019 A1 - More, Kuldeep D. A1 - Giosan, Liviu A1 - Grice, Kliti A1 - Coolen, Marco J. L. KW - geomicrobiology KW - palaeo-environment KW - paleoecology KW - sedimentary metagenomes KW - subsurface microbiome KW - sulfur cycle. AB - Subsurface microbial communities are generally thought to be structured through in situ environmental conditions such as the availability of electron acceptors and donors and porosity, but recent studies suggest that the vertical distribution of a subset of subseafloor microbial taxa, which were present at the time of deposition, were selected by the paleodepositional environment. However, additional highly resolved temporal records of subsurface microbiomes and paired paleoenvironmental reconstructions are needed to justify this claim. Here, we performed a highly resolved shotgun metagenomics survey to study the taxonomic and functional diversity of the subsurface microbiome in Holocene sediments underlying the permanently stratified and anoxic Black Sea. Obligate aerobic bacteria made the largest contribution to the observed shifts in microbial communities associated with known Holocene climate stages and transitions. This suggests that the aerobic fraction of the subseafloor microbiome was seeded from the water column and did not undergo post-depositional selection. In contrast, obligate and facultative anaerobic bacteria showed the most significant response to the establishment of modern-day environmental conditions 5.2 ka ago that led to a major shift in planktonic communities and in the type of sequestered organic matter available for microbial degradation. No significant shift in the subseafloor microbiome was observed as a result of environmental changes that occurred shortly after the marine reconnection, 9 ka ago. This supports the general view that the marine reconnection was a gradual process. We conclude that a high-resolution analysis of downcore changes in the subseafloor microbiome can provide detailed insights into paleoenvironmental conditions and biogeochemical processes that occurred at the time of deposition. VL - 17 UR - https://pubmed.ncbi.nlm.nih.gov/30843322/ IS - 4 ER - TY - JOUR T1 - The Mighty Susquehanna—Extreme Floods in Eastern North America During the Past Two Millennia JF - Geophysical Research Letters Y1 - 2019 A1 - Toomey, Michael A1 - Cantwell, Meagan A1 - Colman, Steven A1 - Cronin, Thomas A1 - Donnelly, Jeffrey A1 - Giosan, Liviu A1 - Heil, Clifford A1 - Korty, Robert A1 - Marot, Marci A1 - Willard, Debra AB - The hazards posed by infrequent major floods to communities along the Susquehanna River and the ecological health of Chesapeake Bay remain largely unconstrained due to the short length of streamgage records. Here we develop a history of high‐flow events on the Susquehanna River during the late Holocene from flood deposits contained in MD99‐2209, a sediment core recovered in 26 m of water from Chesapeake Bay near Annapolis, Maryland, United States. We identify coarse‐grained deposits left by Hurricane Agnes (1972) and the Great Flood of 1936, as well as during three intervals that predate instrumental flood records (~1800–1500, 1300–1100, and 400–0 CE). Comparison to sedimentary proxy data (pollen and ostracode Mg/Ca ratios) from the same core site indicates that prehistoric flooding on the Susquehanna often accompanied cooler‐than‐usual winter/spring temperatures near Chesapeake Bay—typical of negative phases of the North Atlantic Oscillation and conditions thought to foster hurricane landfalls along the East Coast. VL - 46 UR - https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GL080890 IS - 6 ER - TY - JOUR T1 - Temporal deconvolution of vascular plant-derived fatty acids exported from terrestrial watersheds JF - Geochimica et Cosmochimica Acta Y1 - 2019 A1 - Vonk, Jorien E. A1 - Drenzek, Nicholas J. A1 - Hughen, Konrad A. A1 - Stanley, Rachel H.R. A1 - McIntyre, Cameron A1 - çon, Daniel B. A1 - Giosan, Liviu A1 - Southon, John R. A1 - Santos, Guaciara M. A1 - Druffel, Ellen R.M. A1 - Andersson, August A. A1 - öld, Martin A1 - Eglinton, Timothy I. KW - british-columbia KW - CARIACO BASIN KW - compound-specific radiocarbon KW - MACKENZIE DELTA KW - marine-sediments KW - odp leg 169s KW - saanich inlet KW - SANTA-MONICA BASIN KW - SOIL ORGANIC-MATTER KW - TROPICAL VEGETATION AB - Relatively little is known about the amount of time that lapses between the photosynthetic fixation of carbon by vascular land plants and its incorporation into the marine sedimentary record, yet the dynamics of terrestrial carbon sequestration have important implications for the carbon cycle. Vascular plant carbon may encounter multiple potential intermediate storage pools and transport trajectories, and the age of vascular plant carbon accumulating in marine sediments will reflect these different pre-depositional histories. Here, we examine down-core C-14 profiles of higher plant leaf wax-derived fatty acids isolated from high fidelity sedimentary sequences spanning the so-called "bomb-spike", and encompassing a ca. 60-degree latitudinal gradient from tropical (Cariaco Basin), temperate (Saanich Inlet), and polar (Mackenzie Delta) watersheds to constrain integrated vascular plant carbon storage/transport times ("residence times"). Using a modeling framework, we find that, in addition to a "young" (conditionally defined as < 50 y) carbon pool, an old pool of compounds comprises 49 to 78 % of the fractional contribution of organic carbon (OC) and exhibits variable ages reflective of the environmental setting. For the Mackenzie Delta sediments, we find a mean age of the old pool of 28 ky (+/- 9.4, standard deviation), indicating extensive pre-aging in permafrost soils, whereas the old pools in Saanich Inlet and Cariaco Basin sediments are younger, 7.9 (+/- 5.0) and 2.4 (+/- 0.50) to 3.2 (+/- 0.54) ky, respectively, indicating less protracted storage in terrestrial reservoirs. The "young" pool showed clear annual contributions for Saanich Inlet and Mackenzie Delta sediments (comprising 24% and 16% of this pool, respectively), likely reflecting episodic transport of OC from steep hillside slopes surrounding Saanich Inlet and annual spring flood deposition in the Mackenzie Delta, respectively. Contributions of 5-10 year old OC to the Cariaco Basin show a short delay of OC inflow, potentially related to transport time to the offshore basin. Modeling results also indicate that the Mackenzie Delta has an influx of young but decadal material (20-30 years of age), pointing to the presence of an intermediate reservoir. Overall, these results show that a significant fraction of vascular plant C undergoes pre-aging in terrestrial reservoirs prior to accumulation in deltaic and marine sediments. The age distribution, reflecting both storage and transport times, likely depends on landscape-specific factors such as local topography, hydrographic characteristics, and mean annual temperature of the catchment, all of which affect the degree of soil buildup and preservation. We show that catchment-specific carbon residence times across landscapes can vary by an order of magnitude, with important implications both for carbon cycle studies and for the interpretation of molecular terrestrial paleoclimate records preserved in sedimentary sequences. VL - 244 UR - https://linkinghub.elsevier.com/retrieve/pii/S0016703718305702https://api.elsevier.com/content/article/PII:S0016703718305702?httpAccept=text/xmlhttps://api.elsevier.com/content/article/PII:S0016703718305702?httpAccept=text/plain ER - TY - JOUR T1 - Using Stable Carbon Isotopes to Quantify Radiocarbon Reservoir Age Offsets in the Coastal Black SeaAbstract JF - Radiocarbon Y1 - 2019 A1 - Soulet, Guillaume A1 - Giosan, Liviu A1 - Flaux, Clément A1 - Galy, Valier KW - Black Sea KW - Carbon cycle KW - freshwater reservoir effect KW - Geochronology KW - Reservoir age AB - Constraining radiocarbon (C-14) reservoir age offsets is critical to deriving accurate calendar-age chronologies from C-14 dating of materials which did not draw carbon directly from the atmosphere. The application of C-14 dating to such materials is severely limited in hydrologically sensitive environments like the Black Sea because of the difficulty to quantify reservoir age offsets, which can vary quickly and significantly through time, due to the dynamics of the biogeochemical cycling of carbon. Here we reconstruct C-14 reservoir age offsets (Rshell-atm) of Holocene bivalve shells from the coastal Black Sea relatively to their contemporaneous atmosphere. We show that the C-14 reservoir age offset and the stable carbon isotope composition of bivalve shells are linearly correlated in this region. From a biogeochemical standpoint, this suggests that inorganic stable carbon isotope and C-14 compositions of Black Sea coastal waters are controlled by the balance between autochthonous primary productivity and heterotrophic respiration of allochthonous pre-aged terrestrial organic matter supplied by rivers. This provided an important implication for Black Sea geochronology as the reservoir age offset of C-14-dated bivalve shell can be inferred from its stable carbon isotope composition. Our results provide a fundamental and inexpensive geochemical tool which will considerably improve the accuracy of Holocene calendar age chronologies in the Black Sea. VL - 61 UR - https://www.cambridge.org/core/product/identifier/S0033822218000619/type/journal_articlehttps://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0033822218000619 IS - 1 ER - TY - JOUR T1 - Climatic control of Mississippi River flood hazard amplified by river engineering JF - Nature Y1 - 2018 A1 - Munoz, Samuel E. A1 - Giosan, Liviu A1 - Therrell, Matthew D. A1 - Remo, Jonathan W. F. A1 - Shen, Zhixiong A1 - Sullivan, Richard M. A1 - Wiman, Charlotte A1 - O’Donnell, Michelle A1 - Donnelly, Jeffrey P. AB - Over the past century, many of the world’s major rivers have been modified for the purposes of flood mitigation, power generation and commercial navigation1. Engineering modifications to the Mississippi River system have altered the river’s sediment levels and channel morphology2, but the influence of these modifications on flood hazard is debated3,4,5. Detecting and attributing changes in river discharge is challenging because instrumental streamflow records are often too short to evaluate the range of natural hydrological variability before the establishment of flood mitigation infrastructure. Here we show that multi-decadal trends of flood hazard on the lower Mississippi River are strongly modulated by dynamical modes of climate variability, particularly the El Niño–Southern Oscillation and the Atlantic Multidecadal Oscillation, but that the artificial channelization (confinement to a straightened channel) has greatly amplified flood magnitudes over the past century. Our results, based on a multi-proxy reconstruction of flood frequency and magnitude spanning the past 500 years, reveal that the magnitude of the 100-year flood (a flood with a 1 per cent chance of being exceeded in any year) has increased by 20 per cent over those five centuries, with about 75 per cent of this increase attributed to river engineering. We conclude that the interaction of human alterations to the Mississippi River system with dynamical modes of climate variability has elevated the current flood hazard to levels that are unprecedented within the past five centuries. VL - 556 UR - https://www.nature.com/articles/nature26145 IS - 7699 ER - TY - JOUR T1 - On the Holocene evolution of the Ayeyawady megadelta JF - Earth Surface Dynamics Y1 - 2018 A1 - Giosan, Liviu A1 - Naing, Thet A1 - Min Tun, Myo A1 - Clift, Peter D. A1 - Filip, Florin A1 - Constantinescu, Stefan A1 - Khonde, Nitesh A1 - Blusztajn, Jerzy A1 - Buylaert, Jan-Pieter A1 - Stevens, Thomas A1 - Thwin, Swe AB - The Ayeyawady delta is the last Asian megadelta whose evolution has remained essentially unexplored so far. Unlike most other deltas across the world, the Ayeyawady has not yet been affected by dam construction, providing a unique view on largely natural deltaic processes benefiting from abundant sediment loads affected by tectonics and monsoon hydroclimate. To alleviate the information gap and provide a baseline for future work, here we provide a first model for the Holocene development of this megadelta based on drill core sediments collected in 2016 and 2017, dated with radiocarbon and optically stimulated luminescence, together with a reevaluation of published maps, charts and scientific literature. Altogether, these data indicate that Ayeyawady is a mud-dominated delta with tidal and wave influences. The sediment-rich Ayeyawady River built meander belt alluvial ridges with avulsive characters. A more advanced coast in the western half of the delta (i.e., the Pathein lobe) was probably favored by the more western location of the early course of the river. Radiogenic isotopic fingerprinting of the sediment suggests that the Pathein lobe coast does not receive significant sediment from neighboring rivers. However, the eastern region of the delta (i.e., Yangon lobe) is offset inland and extends east into the mudflats of the Sittaung estuary. Wave-built beach ridge construction during the late Holocene, similar to several other deltas across the Indian monsoon domain, suggests a common climatic control on monsoonal delta morphodynamics through variability in discharge, changes in wave climate or both. Correlation of the delta morphological and stratigraphic architecture information on land with the shelf bathymetry, as well as its tectonic, sedimentary and hydrodynamic characteristics, provides insight on the peculiar growth style of the Ayeyawady delta. The offset between the western Pathein lobe and the eastern deltaic coast appears to be driven by tectonic–hydrodynamic feedbacks as the extensionally lowered shelf block of the Gulf of Mottama amplifies tidal currents relative to the western part of the shelf. This situation probably activates a perennial shear front between the two regions that acts as a leaky energy fence. Just as importantly, the strong currents in the Gulf of Mottama act as an offshore-directed tidal pump that helps build the deep mid-shelf Mottama clinoform with mixed sediments from the Ayeyawady, Sittaung and Thanlwin rivers. The highly energetic tidal, wind and wave regime of the northern Andaman Sea thus exports most sediment offshore despite the large load of the Ayeyawady River. VL - 6 UR - https://esurf.copernicus.org/articles/6/451/2018 IS - 2 ER - TY - JOUR T1 - Arctic Deltaic Lake Sediments As Recorders of Fluvial Organic Matter Deposition Y1 - 2016 A1 - Vonk, Jorien E. A1 - Dickens, Angela F. A1 - Giosan, Liviu A1 - Hussain, Zainab A. A1 - Kim, Bokyung A1 - Zipper, Samuel C. A1 - Holmes, Robert M. A1 - Montluçon, Daniel B. A1 - Galy, Valier A1 - Eglinton, Timothy I. AB - Arctic deltas are dynamic and vulnerable regions that play a key role in land-ocean interactions and the global carbon cycle. Delta lakes may provide valuable historical records of the quality and quantity of fluvial fluxes, parameters that are challenging to investigate in these remote regions. Here we study lakes from across the Mackenzie Delta, Arctic Canada, that receive fluvial sediments from the Mackenzie River when spring flood water levels rise above natural levees. We compare downcore lake sediments with suspended sediments collected during the spring flood, using bulk (% organic carbon, % total nitrogen, 13C, 14C) and molecular organic geochemistry (lignin, leaf waxes). High-resolution age models (137Cs, 210Pb) of downcore lake sediment records (n=11) along with lamina counting on high-resolution radiographs show sediment deposition frequencies ranging between annually to every 15 years. Down-core geochemical variability in a representative delta lake sediment core is consistent with historical variability in spring flood hydrology (variability in peak discharge, ice jamming, peak water levels). Comparison with earlier published Mackenzie River depth profiles shows that (i) lake sediments reflect the riverine surface suspended load, and (ii) hydrodynamic sorting patterns related to spring flood characteristics are reflected in the lake sediments. Bulk and molecular geochemistry of suspended particulate matter from the spring flood peak and lake sediments are relatively similar showing a mixture of modern higher-plant derived material, older terrestrial permafrost material, and old rock-derived material. This suggests that deltaic lake sedimentary records hold great promise as recorders of past (century-scale) riverine fluxes and may prove instrumental in shedding light on past behaviour of arctic rivers, as well as how they respond to a changing climate. VL - 4 SN - 2296-6463 UR - http://journal.frontiersin.org/article/10.3389/feart.2016.00077 ER - TY - JOUR T1 - South Asian monsoon history over the past 60 kyr recorded by radiogenic isotopes and clay mineral assemblages in the Andaman Sea JF - Geochemistry, Geophysics, Geosystems Y1 - 2015 A1 - Ali, Sajid A1 - Hathorne, Ed C. A1 - Frank, Martin A1 - Gebregiorgis, Daniel A1 - Stattegger, Karl A1 - Stumpf, Roland A1 - Kutterolf, Steffen A1 - Johnson, Joel E. A1 - Giosan, Liviu AB - The Late Quaternary variability of the South Asian (or Indian) monsoon has been linked with glacial-interglacial and millennial scale climatic changes but past rainfall intensity in the river catchments draining into the Andaman Sea remains poorly constrained. Here we use radiogenic Sr, Nd, and Pb isotope compositions of the detrital clay-size fraction and clay mineral assemblages obtained from sediment core NGHP Site 17 in the Andaman Sea to reconstruct the variability of the South Asian monsoon during the past 60 kyr. Over this time interval εNd values changed little, generally oscillating between −7.3 and −5.3 and the Pb isotope signatures are essentially invariable, which is in contrast to a record located further northeast in the Andaman Sea. This indicates that the source of the detrital clays did not change significantly during the last glacial and deglaciation suggesting the monsoon was spatially stable. The most likely source region is the Irrawaddy river catchment including the Indo-Burman Ranges with a possible minor contribution from the Andaman Islands. High smectite/(illite + chlorite) ratios (up to 14), as well as low 87Sr/86Sr ratios (0.711) for the Holocene period indicate enhanced chemical weathering and a stronger South Asian monsoon compared to marine oxygen isotope stages 2 and 3. Short, smectite-poor intervals exhibit markedly radiogenic Sr isotope compositions and document weakening of the South Asian monsoon, which may have been linked to short-term northern Atlantic climate variability on millennial time scales. VL - 16 UR - http://doi.wiley.com/10.1002/2014GC005586 IS - 2 ER - TY - JOUR T1 - Monsoon-influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore Mahanadi Basin, northern Bay of Bengal JF - Marine and Petroleum Geology Y1 - 2014 A1 - Phillips, Stephen C. A1 - Johnson, Joel E. A1 - Giosan, Liviu A1 - Rose, Kelly AB - The Indian monsoon drives seasonal changes in precipitation and weathering across India as well as circulation and productivity in the northern Indian Ocean. Variation in paleo-monsoon intensity and its effect on productivity and lithogenic fluxes is poorly constrained in the Bay of Bengal. In this paper, we present analysis of a sediment record from the offshore Mahanadi Basin recovered during the Indian National Gas Hydrate Program Expedition 01 (Site NGHP-01-19B). We reconstruct variation in biogenic and lithogenic components during the last 110 kyr using measurements of total organic carbon (TOC), total nitrogen (TN), TOC/TN, CaCO3, biogenic silica (BSi), δ13TOC, δ15TN, bulk mineralogy from X-ray diffraction, bulk and lithogenic grain size distribution, magnetic susceptibility, bulk density, and Ca, Br, and Zr/Rb from x-ray fluorescence (XRF). The mass-accumulation rate (MAR) of CaCO3, a function of marine productivity, drastically increased between 70 and 10 ka and is correlated to previously-documented elevated Asian dust fluxes and increased Bay of Bengal salinity during a weakened southwest monsoon. Decreased freshwater input over this period likely diminished stratification, allowing for increased mixing and nutrient availability, thus enhancing productivity despite weaker southwest monsoon winds. The MAR of lithogenic material is highest during the Holocene suggesting that sediment supply driven by monsoon intensity is a stronger control on margin sedimentation than sea level at the Mahanadi Basin. Over the entire record, magnetic susceptibility and XRF Zr/Rb are strongly correlated with CaCO3, suggesting higher primary mineral input under a weakened southwest monsoon. TOC/TN and δ13TOC also increase under glacial conditions, suggesting higher relative input of terrestrial C4 organic matter. These results highlight the Mahanadi Basin as a supply-dominated margin where terrigenous sedimentation is strongly influenced by monsoon intensity, and that productivity is limited by variation in monsoon-driven stratification on glacial-interglacial timescales rather than a direct response to monsoon winds. VL - 58 N1 - AAy4wyTimes Cited:4Cited References Count:253 JO - Monsoon-influenced variation in productivity and lithogenic sediment flux since 110 ka in the offshore Mahanadi Basin, northern Bay of Bengal ER - TY - JOUR T1 - First high-resolution marinopalynological stratigraphy of Late Quaternary sediments from the central part of the Bulgarian Black Sea area JF - Advancing Pleistocene and Holocene climate change research in the Carpathian-Balkan region Y1 - 2013 A1 - Filipova-Marinova, Mariana A1 - Pavlov, Danail A1 - Coolen, Marco A1 - Giosan, Liviu AB - Spores, pollen and dinoflagellate cysts of Late Pleistocene and Holocene sediments were analyzed from Giant Gravity Core 18 from the Black Sea continental slope, recovered from a water depth of 971 m. The investigated length of the core is 203.5 cm. It includes 3 lithological units: light grey clay, sapropels and coccolith-bearing ooze. The core was sampled at 5–10 cm intervals. Sampling of the interval 141.5–126 cm was carried out at every cm. AMS radiocarbon dating of bulk organic carbon was performed on 18 selected sediment layers. This chronological data allowed the first high-resolution pollen stratigraphy of Late Quaternary sediments from the western Black Sea area to be presented. The percentage spore–pollen diagram is divided into 6 local pollen assemblage zones. The trends in the vegetation dynamics and climate changes and the early history of migration of the majority of the arboreal taxa that nowadays occur in the Eastern Balkan Range were traced out. The palynological record suggests that open oak forests were spread in the Eastern Balkan Range at the beginning of the Holocene and shows early migration of the major temperate arboreal species such as Quercus, Ulmus, Tilia and Carpinus betulus. This vegetation palaeosuccession continues with the spreading of mixed oak forests from 8950 until 2620 cal. BP (8650 ± 40 until 3120 ± 35 14C BP) followed by destructive changes due to human impact and climate deterioration. A cooling of Holocene climate that is well known in the North Atlantic region as the “8200 yrs cold event” is identified for the first time in marine records from the Bulgarian Black Sea area. The assemblages of dinoflagellate cysts and acritarchs were investigated to provide a reconstruction of surface seawater salinity and surface seawater temperature changes. Two main dinoflagellate cyst assemblages, one dominated by fresh- to brackish water species such as Spiniferites cruciformis and Pyxidinopsis psilata and a subsequent one, that is characterized by euryhaline marine Mediterranean species such as Lingulodinium machaerophorum, Spiniferites belerius, Spiniferites bentorii, Operculodinium centrocarpum and acritarchs Cymatiosphaera globulosa testified a change in SSS from low salinity ( VL - 293 UR - http://www.sciencedirect.com/science/article/pii/S1040618212003229 N1 - id: 2330 JO - First high-resolution marinopalynological stratigraphy of Late Quaternary sediments from the central part of the Bulgarian Black Sea area ER - TY - JOUR T1 - Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta JF - Anthropocene Y1 - 2013 A1 - Giosan, Liviu A1 - Constantinescu, Stefan A1 - Filip, Florin A1 - Deng, Bing AB - Over the last half century, while the total sediment load of the Danube dramatically decreased due to dam construction on tributaries and its main stem, a grand experiment was inadvertently run in the Danube delta: the construction of a dense network of canals, which almost tripled the water discharge toward the interior of the delta plain. We use core-based and chart-based sedimentation rates and patterns to explore the delta transition from the natural to an anthropogenic regime, to understand the effects of far-field damming and near-field channelization, and to construct a conceptual model for delta development as a function sediment partition between the delta plain and the delta coastal fringe. We show that sediment fluxes increased to the delta plain due to channelization counteracting sea level rise. In turn, the delta coastal fringe was most impacted by the Danube's sediment load collapse. Furthermore, we suggest that morphodynamic feedbacks at the river mouth are crucial in trapping sediment near the coast and constructing wave-dominated deltas or lobes. Finally, we suggest that increased channelization that mimics and enhances natural processes may provide a simple solution for keeping other delta plains above sea level and that abandonment of wave-dominated lobes may be the most long term efficient solution for protecting the internal fluvial regions of deltas and provide new coastal growth downcoast. VL - 1 UR - http://www.sciencedirect.com/science/article/pii/S221330541300012X JO - Maintenance of large deltas through channelization: Nature vs. humans in the Danube delta ER - TY - JOUR T1 - Clay mineral variations in Holocene terrestrial sediments from the Indus Basin JF - Quaternary Research Y1 - 2012 A1 - Alizai, Anwar A1 - Hillier, Stephen A1 - Clift, Peter D. A1 - Giosan, Liviu A1 - Hurst, Andrew A1 - VanLaningham, Sam A1 - Macklin, Mark AB - We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6– VL - 77 UR - http://www.sciencedirect.com/science/article/pii/S0033589412000099 IS - 3 N1 - id: 2333 JO - Clay mineral variations in Holocene terrestrial sediments from the Indus Basin ER - TY - JOUR T1 - Pb isotopic variability in the modern-Pleistocene Indus River system measured by ion microprobe in detrital K-feldspar grains JF - Geochimica et Cosmochimica Acta Y1 - 2011 A1 - Alizai, Anwar A1 - Clift, Peter D. A1 - Giosan, Liviu A1 - VanLaningham, Sam A1 - Hinton, Richard A1 - Tabrez, Ali R. A1 - Danish, Muhammad AB - The western Himalaya, Karakoram and Tibet are known to be heterogeneous with regard to Pb isotope compositions in K-feldspars, which allows this system to be used as a sediment provenance tool. We used secondary ion mass spectrometry to measure the isotopic character of silt and sand-sized grains from the modern Sutlej and Chenab Rivers, together with Thar Desert sands, in order to constrain their origin. The rivers show a clear Himalayan provenance, contrasting with grains from the Indus Suture Zone, but with overlap to known Karakoram compositions. The desert dunes commonly show 207Pb/204Pb and 206Pb/204Pb values that are much higher than those seen in the rivers, most consistent with erosion from Nanga Parbat. This implies at least some origin from the trunk Indus, probably reworked by summer monsoon winds from the SW, a hypothesis supported by bulk Nd and U–Pb zircon dating. Further data collected from Holocene and Pleistocene sands shows that filled and abandoned channels on the western edge of the Thar Desert were sourced from Himalayan rivers before and at 6–8 ka, but that after that time the proportion of high isotopic ratio grains rose, indicating increased contribution from the Thar Desert dunes prior to ∼4.5 ka when flow ceased entirely. This may be linked to climatic drying, northward expansion of the Thar Desert, or changes in drainage style including regional capture, channel abandonment, or active local Thar tributaries. Our data further show a Himalayan river channel east of the present Indus, close to the delta, in the Nara River valley during the middle Holocene. While this cannot be distinguished from the Indus it is not heavily contaminated by reworking from the desert. The Pb system shows some use as a provenance tool, but is not effective at demonstrating whether these Nara sediments represent a Ghaggar-Hakra stream independent from the Indus. Our study highlights an important role for eolian reworking of floodplain sediments in arid rivers such as the Indus. VL - 75 UR - http://www.sciencedirect.com/science/article/pii/S0016703711003164 IS - 17 N1 - id: 2171 JO - Pb isotopic variability in the modern-Pleistocene Indus River system measured by ion microprobe in detrital K-feldspar grains ER - TY - JOUR T1 - A new look at old carbon in active margin sediments RID F-1809-2010 JF - Geology Y1 - 2009 A1 - Drenzek, Nicholas J. A1 - Hughen, Konrad A. A1 - Montluçon, Daniel B. A1 - Southon, John R. A1 - dos Santos, Guaciara M. A1 - Druffel, Ellen R. M. A1 - Giosan, Liviu A1 - Eglinton, Timothy I. AB - Recent studies suggest that as much as half of the organic carbon (OC) undergoing burial in the sediments of tectonically active continental margins may be the product of fossil shale weathering. These estimates rely on the assumption that vascular plant detritus spends little time sequestered in intermediate reservoirs such as soils, freshwater sediments, and river deltas, and thus only minimally contributes to the extraneously old (14)C ages of total organic matter often observed on adjacent shelves. Here we test this paradigm by measuring the (14)C and delta(13)C values of individual higher plant wax fatty acids as well as the d13C values of extractable alkanes isolated from the Eel River margin (California). The isotopic signatures of the long chain fatty acids indicate that vascular plant material has been sequestered for several thousand years before deposition. A coupled molecular isotope mass balance used to reassess the sedimentary carbon budget indicates that the fossil component is less abundant than previously estimated, with pre-aged terrestrial material instead composing a considerable proportion of all organic matter. If these findings are characteristic of other continental margins proximal to small mountainous rivers, then the importance of petrogenic OC burial in marine sediments may need to be reevaluated. VL - 37 IS - 3 N1 - id: 1987; PT: J; UT: WOS:000263842200012 JO - A new look at old carbon in active margin sediments RID F-1809-2010 ER -