Selvaraj Kandasamy

Bio: Selvaraj Kandasamy is an academic researcher from Xiamen University. The author has contributed to research in topics: Sediment & Provenance. The author has an hindex of 13, co-authored 35 publications receiving 559 citations. Previous affiliations of Selvaraj Kandasamy include National Sun Yat-sen University.

A global multiproxy database for temperature reconstructions of the Common Era

Abstract: Reproducible climate reconstructions of the Common Era (1 CE to present) are key to placing industrial-era warming into the context of natural climatic variability. Here we present a community-sourced database of temperature-sensitive proxy records from the PAGES2k initiative. The database gathers 692 records from 648 locations, including all continental regions and major ocean basins. The records are from trees, ice, sediment, corals, speleothems, documentary evidence, and other archives. They range in length from 50 to 2000 years, with a median of 547 years, while temporal resolution ranges from biweekly to centennial. Nearly half of the proxy time series are significantly correlated with HadCRUT4.2 surface temperature over the period 1850–2014. Global temperature composites show a remarkable degree of coherence between high- and low-resolution archives, with broadly similar patterns across archive types, terrestrial versus marine locations, and screening criteria. The database is suited to investigations of global and regional temperature variability over the Common Era, and is shared in the Linked Paleo Data (LiPD) format, including serializations in Matlab, R and Python.

Evaluation of elemental enrichments in surface sediments off southwestern Taiwan

Abstract: Surface slices of 20 sediment cores, off south- western Taiwan, and bed sediment of River Kaoping were measured for major and trace elements (Al, As, Ca, Cd, Cl, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, S, Si, Ti, V, and Zn) to evaluate the geochemical processes responsible for their distribution, including elemental contamination. Major element/Al ratio and mean grain size indicate quartz- dominated, coarse grained sediments that likely derived from sedimentary rocks of Taiwan and upper crust of Yangtze Craton. Bi-plot of SiO2 versus Fe2O3 suggests the possible iron enrichment in sediments of slag dumping sites. Highest concentrations of Cr, Mn, P, S, and Zn found in sediments of dumping sites support this. Correlation analysis shows dual associations, detrital and organic car- bon, for Cr, P, S, and V with the latter association typical for sediments in dumping sites. Normalization of trace elements to Al indicates high enrichment factors (>2) for As, Cd, Pb, and Zn, revealing contamination. Factor analysis extracted four geochemical associations with the principal factor accounted for 25.1% of the total variance and identifies the combined effects of dumped iron and steel slag-induced C-S-Fe relationship owing to authigenic precipitation of Fe-Mn oxyhydroxides and/or metal sul- fides, and organic matter complexation of Fe, Mn, Ca, Cr, P, and V. Factors 2, 3, and 4 reveal detrital association (Ti, Al, Ni, Pb, Cu, and V), effect of sea salt (Cl, Mg, Na, and K) and anthropogenic component (As and Zn)-carbonate link, respectively, in the investigated sediments.

Perspectives on the terrestrial organic matter transport and burial along the land-deep sea continuum: Caveats in our understanding of biogeochemical processes and future needs

Abstract: The natural carbon cycle is immensely intricate to fully understand its sources, fluxes and the processes that are responsible for their cycling in different reservoirs and their balances on a global scale. Anthropogenic perturbations add another dimension to such a complex cycle. Therefore, it is necessary to update the global carbon cycle by combining both natural and anthropogenic sources, fluxes and sinks along the land-sea continuum to assess whether these terms are currently in balance or not. Here, we review the export and it burial rates of terrestrial organic carbon in the oceans to understand the issue of “missing terrigenous carbon” by comparing data- and model-based estimates of terrestrial carbon fluxes. Our review reveals large disparities between field-based data and model output in terms of dissolved and particulate organic carbon/matter (OC/OM) fluxes and their ratios, especially for Oceania and Arctic rivers, suggesting the need of additional investigations in these regions to refine terrestrial OC export budget. Based on our budgeting of global sources and sinks of OC with updated estimates of marine productivity and terrestrial OM burial rate, we find that the marginal sediments are key burial sites of terrestrial OM, which is consistent with earlier views of Berner (1982) and Hedges and Keil (1995). While about 60‒80% of TOM is remineralized in the margins, the estimated budget further reveals the ocean derived OM is efficiently remineralized than that of terrestrial OM, emphasizing the need of further improvements of carbon burial estimation in the marine realm. When we look back in the past, higher terrestrial OC burial (by ~50%) in the deep ocean during the glacials than during the interglacials suggests the subdued role of continental margins and an efficient transfer of OM from the shelf to deep sea in glacials. Based on the review of terrestrial and marine OM burial, we suggest some critical regions/ways that need to be investigated/addressed further, identification of new biogeochemical proxies and their grouping to better constrain the global carbon cycle along the land-deep sea continuum in future.

East China Sea increasingly gains limiting nutrient P from South China Sea

Abstract: The Taiwan Strait (TS) directly connects two of the richest fishing grounds in the world - the East China Sea (ECS) and the South China Sea (SCS). Carbon and nutrient supplies are essential for primary production and the Yangtze River is an important source for the ECS. However the ECS is severely P-limited. The TS transports an order of magnitude more carbon and a factor of two more phosphate (P) to the ECS than the Yangtze River does. To evaluate the temporal variability of these supplies, the total alkalinity (TA), dissolved inorganic carbon (DIC), nitrate plus nitrite (N), P, and silicate (Si) fluxes through the TS were estimated using empirical equations for these parameters and the current velocity, which was estimated using the Hybrid Coordinate Ocean Model (HYCOM). These empirical equations were derived from in situ salinity and temperature and measured chemical concentrations that were collected during 57 cruises (1995–2014) with a total of 2096 bottle samples. The 24-month moving averages of water, carbon, and nutrient fluxes significantly increase with time, so does the satellite chlorophyll a concentration. More importantly, the increased supply of the badly needed P from the TS is more than that from the Yangtze River.

Gas hydrates in sustainable chemistry

Abstract: Gas hydrates have received considerable attention due to their important role in flow assurance for the oil and gas industry, their extensive natural occurrence on Earth and extraterrestrial planets, and their significant applications in sustainable technologies including but not limited to gas and energy storage, gas separation, and water desalination Given not only their inherent structural flexibility depending on the type of guest gas molecules and formation conditions, but also the synthetic effects of a wide range of chemical additives on their properties, these variabilities could be exploited to optimise the role of gas hydrates This includes increasing their industrial applications, understanding and utilising their role in Nature, identifying potential methods for safely extracting natural gases stored in naturally occurring hydrates within the Earth, and for developing green technologies This review summarizes the different properties of gas hydrates as well as their formation and dissociation kinetics and then reviews the fast-growing literature reporting their role and applications in the aforementioned fields, mainly concentrating on advances during the last decade Challenges, limitations, and future perspectives of each field are briefly discussed The overall objective of this review is to provide readers with an extensive overview of gas hydrates that we hope will stimulate further work on this riveting field

Nitrogen in the sea : forms, abundances, and rate processes

Abstract: INTRODUCTION. A HISTORICAL OVERVIEW OF NITROGEN STUDY IN THE SEA. Determination of Nitrogenous Compounds in the Sea. Biological Transformation of Nitrogen. Stoichiometric Model of Organic-Matter Mineralization. Natural 15N Abundance. THE NITROGEN CYCLE. PHYSICO-CHEMICAL PROPERTIES OF NITROGEN. PROPERTIES OF THE NITROGEN ATOM AND BONDING. THERMODYNAMIC FUNCTIONS OF NITROGEN. BIOGEOCHEMICAL SKETCH OF NITROGEN. NITROGEN ISOTOPES. GENESIS OF ISOTOPES OF LIGHT ELEMENTS. ISOTOPE ABUNDANCE AND FRACTIONATION. ISOTOPIC EXCHANGE REACTIONS. KINETIC ISOTOPE EFFECTS. OVERALL ISOTOPIC FRACTIONATION. One-Step Reaction. Unidirectional Two-Step Reaction at Steady State. Two-Step Reaction with a Reversible First Step at a Steady State. Three-Step Reactions. Multistep Reactions. ISOTOPIC EXCHANGE EQUILIBRIA OF NITROGEN. NITROGEN KINETIC ISOTOPE EFFECTS DURING NITRATE REDUCTION. Chemical Systems. Biological Systems. ISOTOPE FRACTIONATION IN BRANCHED REACTIONS AND ITS ECOLOGICAL SIGNIFICANCE. ISOTOPE MASS BALANCE IN MARINE ECOSYSTEMS. Two-Source Model. Three-Source Model. COMPONENTS, SYSTEMS, AND PROCESSES. NITROGENOUS COMPOUNDS IN THE SEA: ABUNDANCE, SOURCES, AND SINK. PHYSICAL FACTORS. Water Movement and Mixing of Water. Solar Radiation. Effects of Temperature and Pressure on Chemical and Biochemical Reactions. Nitrogen Supply by River Runoff and Precipitation. CHEMICAL FACTORS. Chemical Behavior of Nitrogenous Compounds in the Sea. Hydrogen Ion Concentration. Oxidation-Reduction Potential. BIOCHEMICAL PROCESSES. Nitrogen Uptake and Assimilation. Mineralization. Nitrification. Nitrate Respiration and Denitrification. N2 Fixation. ABUNDANCE AND DISTRIBUTION OF NITROGEN IN THE SEA AND THEIR PHYSICAL, CHEMICAL, AND BIOCHEMICAL REGULATION. ROLES OF THE OCEAN IN THE GLOBAL NITROGEN CYCLE. The Buildup of the Biogeochemical Cycle. Nitrogen Inventories. Nitrogen Budgets. DISSOLVED NITROGEN GAS. Atmospheric Pressure. Occlusion of Air Bubbles. Effect of Mixing of Different Water Masses. Biological Effects. AMMONIUM, NITRITE, AND NITRATE. Distribution of Ammonium. Distribution of Nitrite. Distribution of Nitrate. NITROUS OXIDE. UREA. OTHER NITROGENOUS COMPOUNDS IN A WATER COLUMN. NITROGEN UPTAKE BY PHYTOPLANKTON. MECHANISM OF FORMATION OF THE PRIMARY NITRITE MAXIMUM. Nitrification in the Sea. Nitrite Production from Nitrate by Microalgae. Nitrite Assimilation. Formation of Primary Nitrite Maximum. NITROGEN DYNAMICS IN VARIOUS OCEANIC SYSTEMS. HIGH LATITUDINAL AREAS RICH IN NITRATE. OLIGOTROPHIC AREAS. Kuroshio Area. Anticyclonic Gyre Off Shikoku. SUBTROPICAL AND TROPICAL AREAS WITH SUPPLY OF NITRATE. Upwelling Region. Regional Upwelling. SEA AREAS WHERE NITROGEN FIXATION OCCURS. Trichodesmium Ecosystems. Local Ecosystems Characterized by N2 Fixation. SUBSURFACE ECOSYSTEMS. Decomposition of Organic Matter in the Subsurface Water. Nitrogen Diagenesis in Sediments. SEA AREAS WHERE DENITRIFICATION OCCURS. Denitrification in the Subsurface Water. Marine Sediments. NEAR SHORE AND ESTUARINE SYSTEMS. Flooded Soil Ecosystems. Tokyo Bay. VARIATION OF 15N/14N IN NITROGEN CYCLING AND ITS SIGNIFICANCE IN MARINE ENVIRONMENTS. ISOTOPE FRACTIONATION IN THE NITROGEN CYCLE. Isotope Exchange Reactions. Fractionation in Biological Metabolic Processes. DISTRIBUTION OF 15N IN NATURE. General Patterns of 15N Distribution. 15N in Antarctica. 15N Abundance and the Biogeochemical Cycle. INTEGRATED NITROGEN ISOTOPE FRACTIONATION IN ECOSYSTEMS. Enrichment of 15N in a Feeding Process. d15N-d13C Relationship. MARINE ECOSYSTEMS. Phytoplankton and Particulate Organic Matter. The Area Characterized by N2 Fixation. Isotope Biogeochemistry of the Antarctic Ecosystem. Dentrification in the Marine Aquatic System as Investigated Based on 15N Abundance Data. 15N and 13C Abundance in River, Estuarine, and Coastal Areas. Seabird Rookeries. The Deep-Sea World. Animal Behavior. FUTURE STUDIES ON NITROGEN DYNAMICS. HUMAN IMPINGEMENT ON THE NITROGEN CYCLE IN MARINE SYSTEMS. Long-Term Effects. Short-Term Effects. A NEW PARADIGM. Isotope Biogeochemistry. From Components to Systems. REFERENCES. INDEX.

No evidence for globally coherent warm and cold periods over the preindustrial Common Era

Abstract: Earth’s climate history is often understood by breaking it down into constituent climatic epochs1. Over the Common Era (the past 2,000 years) these epochs, such as the Little Ice Age2–4, have been characterized as having occurred at the same time across extensive spatial scales5. Although the rapid global warming seen in observations over the past 150 years does show nearly global coherence6, the spatiotemporal coherence of climate epochs earlier in the Common Era has yet to be robustly tested. Here we use global palaeoclimate reconstructions for the past 2,000 years, and find no evidence for preindustrial globally coherent cold and warm epochs. In particular, we find that the coldest epoch of the last millennium—the putative Little Ice Age—is most likely to have experienced the coldest temperatures during the fifteenth century in the central and eastern Pacific Ocean, during the seventeenth century in northwestern Europe and southeastern North America, and during the mid-nineteenth century over most of the remaining regions. Furthermore, the spatial coherence that does exist over the preindustrial Common Era is consistent with the spatial coherence of stochastic climatic variability. This lack of spatiotemporal coherence indicates that preindustrial forcing was not sufficient to produce globally synchronous extreme temperatures at multidecadal and centennial timescales. By contrast, we find that the warmest period of the past two millennia occurred during the twentieth century for more than 98 per cent of the globe. This provides strong evidence that anthropogenic global warming is not only unparalleled in terms of absolute temperatures5, but also unprecedented in spatial consistency within the context of the past 2,000 years.

An intercomparison and evaluation of aircraft-derived and simulated CO from seven chemical transport models during the TRACE-P experiment : NASA global tropospheric experiment transport and chemical evolution over the pacific (TRACE-P): Measurements and analysis (TRACEP1)

Abstract: [1] Four global scale and three regional scale chemical transport models are intercompared and evaluated during NASA's Transport and Chemical Evolution over the Pacific (TRACE-P) experiment. Model simulated and measured CO are statistically analyzed along aircraft flight tracks. Results for the combination of 11 flights show an overall negative bias in simulated CO. Biases are most pronounced during large CO events. Statistical agreements vary greatly among the individual flights. Those flights with the greatest range of CO values tend to be the worst simulated. However, for each given flight, the models generally provide similar relative results. The models exhibit difficulties simulating intense CO plumes. CO error is found to be greatest in the lower troposphere. Convective mass flux is shown to be very important, particularly near emissions source regions. Occasionally meteorological lift associated with excessive model-calculated mass fluxes leads to an overestimation of middle and upper tropospheric mixing ratios. Planetary Boundary Layer (PBL) depth is found to play an important role in simulating intense CO plumes. PBL depth is shown to cap plumes, confining heavy pollution to the very lowest levels.