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793 results on '"global carbon cycle"'

201. Southern Ocean ecosystem and global carbon cycle responses to iron fertilisation during the last glacial cycle

Author

Saini, Himadri

Subjects
Marine biogeochemistry, Global carbon cycle, Heinrich Events, Iron fertilisation, anzsrc-for: 3702 Climate change science
Abstract

Rising atmospheric CO2 concentration is one of the major drivers of climate change. To provide effective mitigation policies to curb these emissions, a thorough understanding of past changes in the carbon cycle is required. Decades of research on understanding carbon cycle changes during the last glacial cycle have put forward several processes impacting the concentration of atmospheric CO2. One of these processes is changes in aeolian iron flux into the Southern Ocean. Marine plankton fix dissolved inorganic carbon (DIC) during photosynthesis and transfer the fixed carbon to the deep ocean. DIC removal from the surface lowers the surface ocean partial pressure of CO2, which leads to carbon drawdown from the atmosphere. As the Southern Ocean is a high-nutrient-low-chlorophyll region, the increase in iron input can impact Southern Ocean marine ecosystems, by increasing export production, and therefore decreasing surface DIC. This thesis aims to investigate the responses of Southern Ocean marine ecosystems to changes in iron flux, and their impact on ocean biogeochemistry and atmospheric CO2 during the last glacial period. For this, I use a recently developed complex ecosystem model, which includes four different classes of phytoplankton functional types. Chapter 2 of this thesis is the first study to use this complex ecosystem model and document the competitive dynamics between different plankton species for light and nutrient availability under Last Glacial Maximum (LGM) climate boundary conditions (∼21 thousand years ago, 21 ka). Chapter 2 further assesses the impact of enhanced aeolian iron input on ecosystems. This study shows that lower sea surface temperatures and greater sea ice cover during the LGM causes a 2.4% reduction in Southern Ocean export production. However, a 78% increase in iron supply with a weaker ventilation in the Weddell Sea, increases diatoms and coccolithophores in the Southern Ocean, leading to a 4.4% higher carbon export at the LGM compared to pre-industrial (PI). Proxy records indicate a ∼32 ppm decrease in CO2 around ∼70 ka. Previous modelling studies have indicated a possible decline of 5 to 28 ppm in atmospheric CO2 driven by enhanced iron fertilization under PI and LGM boundary conditions. I constrain this contribution in chapter 3, by performing a series of sensitivity experiments under 70 ka climate boundary conditions taking into account the uncertainty associated with iron solubility in the ocean. I find that the CO2 change follows an exponential decay relationship with increasing iron flux due to saturation of biological pump at high iron values. Based on this, I suggest that enhanced iron input at 70 ka most likely led to a 9 to 11 ppm CO2 decrease with a maximum decrease of 21 ppm. Iron fertilisation could thus provide a 28 to 34% contribution to the total observed CO2 decline at 70 ka. Finally, in chapter 4, I include a unique approach to understand the processes leading to the abrupt 15 to 20 ppm increase in atmospheric CO2 during Heinrich Stadials, which are associated with a near collapse of the Atlantic Meridional Overturning Circulation (AMOC), a sudden decrease in Greenland temperature and warming in the Southern Ocean. Previous modelling studies have investigated the role of the ocean circulation in driving changes in atmospheric CO2 concentration during these abrupt events, while the role of reduced aeolian iron input during Heinrich stadials remained poorly constrained. I find that reduced iron fertilization combined with an AMOC shutdown could lead to a 7 ppm CO2 increase, 6 ppm of which is due to iron fertilisation. The research presented in this thesis improves our understanding of the impact of iron fertilization on Southern Ocean ecosystems, and on the global carbon cycle, particularly in the context of the last glacial period. This work also elucidates the importance of including changes in iron input to the ocean when investigating changes in atmospheric CO2 during abrupt climate change.

Published
2023

202. Challenges and opportunities in the global methane cycle.

Author

Peng S

Abstract

To control the atmospheric methane concentration for Paris Agreement and Global Methane Pledge, it is urgent to elucidate global methane budget, in the context of dangerous high growth rate of atmospheric methane concentration in the past three years (2020-2022). Interdisciplinary research can definitely help answer the open questions about methane budget, as some examples shown in this Special Issue on "Methane emissions, sinks, and mitigation"., (© 2023 The Author(s).)

Published
2023
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203. Using Modeling All Alternatives to explore 55% decarbonization scenarios of the European electricity sector.

Author

Pedersen TT, Andersen MS, Victoria M, and Andresen GB

Abstract

Climate change mitigation is a global challenge that, however, needs to be resolved by national-level authorities, resembling a "tragedy of the commons". This paradox is reflected at the European scale, as climate commitments are made by the EU collectively, but implementation is the responsibility of individual Member States. Here, we investigate a suite of near-optimal effort-sharing scenarios where the European electricity sector is decarbonized between 55% and 75% relative to 1990, in line with 2030 ambitions. To this end, we use a brownfield electricity system optimization model in combination with the Modeling All Alternatives methodology. Results show that only very particular effort-sharing schemes are able to reach the theoretical minimum system cost. In most cases, an additional cost of at least 5% is incurred. Results reveal large inequalities in the efforts required to decarbonize national electricity sectors., Competing Interests: The authors declare no competing interests., (© 2023 The Author(s).)

Published
2023
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204. Boreal Ecosystems in the Global Carbon Cycle

Author

Kasischke, Eric S., Caldwell, M. M., editor, Heldmaier, G., editor, Lange, O. L., editor, Mooney, H. A., editor, Schulze, E.-D., editor, Sommer, U., editor, Kasischke, Eric S., editor, and Stocks, Brian J., editor

Published
2000
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206. Decadal variations and trends of the global ocean carbon sink.

Author

Landschützer, Peter, Gruber, Nicolas, and Bakker, Dorothee C. E.

Subjects
CARBON cycle, ATMOSPHERIC carbon dioxide, OCEAN temperature, ALKALINITY, INTERPOLATION
Abstract

We investigate the variations of the ocean CO2 sink during the past three decades using global surface ocean maps of the partial pressure of CO2 reconstructed from observations contained in the Surface Ocean CO2 Atlas Version 2. To create these maps, we used the neural network-based data interpolation method of Landschützer et al. (2014) but extended the work in time from 1998 to 2011 to the period from 1982 through 2011. Our results suggest strong decadal variations in the global ocean carbon sink around a long-term increase that corresponds roughly to that expected from the rise in atmospheric CO2. The sink is estimated to have weakened during the 1990s toward a minimum uptake of only −0.8 ± 0.5 Pg C yr−1 in 2000 and thereafter to have strengthened considerably to rates of more than −2.0 ± 0.5 Pg C yr−1. These decadal variations originate mostly from the extratropical oceans, while the tropical regions contribute primarily to interannual variations. Changes in sea surface temperature affecting the solubility of CO2 explain part of these variations, particularly at subtropical latitudes. But most of the higher-latitude changes are attributed to modifications in the surface concentration of dissolved inorganic carbon and alkalinity, induced by decadal variations in atmospheric forcing, with patterns that are reminiscent of those of the Northern and Southern Annular Modes. These decadal variations lead to a substantially smaller cumulative anthropogenic CO2 uptake of the ocean over the 1982 through 2011 period (reduction of 7.5 ± 5.5 Pg C) relative to that derived by the Global Carbon Budget. [ABSTRACT FROM AUTHOR]

Published
2016
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207. Micro(nano)plastics: An un-ignorable carbon source?

Author

Hu, Duofei, Shen, Maocai, Zhang, Yaxin, and Zeng, Guangming

Abstract

Abstract Micro(nano)plastics, new emerging contaminants, are widely found in the environment due to continuous release. Massive and widespread presence of micro(nano)plastics may have a significant impact on the calculation of total organic carbon, and potentially result in misunderstanding of the overall environmental pollution level. Previous studies typically paid attention to the environmental distribution, source, analysis methods and technologies, as well as the environmental and ecological effects of micro(nano)plastics. However, little was aware of the total organic carbon consequences. There are few evidences for the contribution of micro(nano)plastics to total organic carbon. Accordingly, more efforts need to be taken to explore the contribution of micro(nano)plastics to total organic carbon. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Published
2019
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209. Global Biogeochemical Cycles

Author

Rotmans, J., den Elzen, M., Beniston, Martin, editor, Martens, Pim, editor, Rotmans, Jan, editor, Jansen, Darco, editor, and Vrieze, Koos, editor

Published
1999
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210. Looking away from the streetlight – new insights into marine calcification.

Author

Gal, Assaf

Subjects
*COCCOLITHS, *COCCOLITHOPHORES, *CYTOLOGY, *CALCIFICATION, *CELL cycle, *BIOMINERALIZATION
Abstract

The article discusses a study regarding the link between coccolith formation and cell biology. It discusses the results showing that in some coccolithophore species calcification is linked to the cell cycle, which if interrupted, will halt the the entire life cycle of the cell. Topics discussed include the impact of changing environmental conditions might have on coccolithophore physiology, biomineralization process of coccolith formation, and the need for studying coccolithophore species.

Published
2018
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211. Pyrogenic Carbon in soils: a literature-based inventory and a global estimation of its content in soil organic carbon and stocks

Author

Moritz Reisser, Ross Purves, Michael W.I. Schmidt, and Samuel Abiven

Subjects
Global carbon cycle, Soil Organic Carbon, pyrogenic carbon, Global distribution, Soil organic matter stabilisation, Fire derived organic matter, Science
Abstract

Pyrogenic carbon (PyC) is considered one of the most stable components in soil and can represent more than 30% of total soil organic carbon (SOC). However, few estimates of global PyC stock or distribution exist and thus PyC is not included in any global carbon cycle models, despite its potential major relevance for the soil pool. To obtain a global picture, we reviewed the literature for published PyC content in SOC data. We generated the first PyC database including more than 560 measurements from 55 studies. Despite limitations due to heterogeneous distribution of the studied locations and gaps in the database, we were able to produce a worldwide PyC inventory. We found that global PyC represent on average 13.7% of the SOC and can be even up to 60%, making it one of the largest groups of identifiable compounds in soil, together with polysaccharides. We observed a consistent range of PyC content in SOC, despite the diverse methods of quantification. We tested the PyC content against different environmental explanatory variables: fire and land use (fire characteristics, land use, net primary productivity), climate (temperature, precipitation, climatic zones, altitude) and pedogenic properties (clay content, pH, SOC content). Surprisingly, soil properties explain PyC content the most. Soils with clay content higher than 50% contain significantly more PyC (> 30% of the SOC) than with clay content lower than 5% (< 6% of the SOC). Alkaline soils contain at least 50% more PyC than acidic soils. Furthermore, climatic conditions, represented by climatic zone or mean temperature or precipitation, correlate significantly with the PyC content. By contrast, fire characteristics could only explain PyC content, if site-specific information was available. Datasets derived from remote sensing did not explain the PyC content.To show the potential of this database, we used it in combination with other global datasets to create a global worldwide PyC content and a stock estimation, which resulted in around 200Pg PyC for the uppermost 2 meters. These modelled estimates indicated a clear mismatch between the location of the current PyC studies and the geographical zones where we expect high PyC stocks.

Published
2016
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212. Refining national greenhouse gas inventories

Author

Mark A. Bradford, Robert B. Jackson, Jean Pierre Henry Balbaud Ometto, Benjamin Cashore, and Leehi Yona

Subjects
Greenhouse Effect, 010504 meteorology & atmospheric sciences, Ecology, Process (engineering), Climate Change, Geography, Planning and Development, Climate change, General Medicine, 010501 environmental sciences, 01 natural sciences, Global carbon cycle, Greenhouse Gases, United Nations Paris Agreement, Greenhouse gas, Perspective, Intergovernmental Panel on Climate Change, Environmental Chemistry, Business, Forest soil carbon, Environmental planning, Greenhouse gas emissions inventories, 0105 earth and related environmental sciences
Abstract

The importance of greenhouse gas inventories cannot be overstated: the process of producing inventories informs strategies that governments will use to meet emissions reduction targets. The Intergovernmental Panel on Climate Change (IPCC) leads an effort to develop and refine internationally agreed upon methodologies for calculating and reporting greenhouse gas emissions and removals. We argue that these guidelines are not equipped to handle the task of developing national greenhouse gas inventories for most countries. Inventory guidelines are vital to implementing climate action, and we highlight opportunities to improve their timeliness and accuracy. Such reforms should provide the means to better understand and advance the progress countries are making toward their Paris commitments. Now is the time to consider challenges posed by the current process to develop the guidelines, and to avail the policy community of recent major advances in quantitative and expert synthesis to overhaul the process and thereby better equip multi-national efforts to limit climate change.

Published
2020

217. Geo-LiM: a new geo-lithological map for Central Europe (Germany, France, Switzerland, Austria, Slovenia, and Northern Italy) as a tool for the estimation of atmospheric CO2 consumption

Author

Ivan Marchesini, Azzurra Zucchini, and Marco Donnini

Subjects
lcsh:Maps, Consumption (economics), Estimation, geology, global carbon cycle, 010504 meteorology & atmospheric sciences, Outcrop, Lithology, Earth science, Geography, Planning and Development, Weathering, 010502 geochemistry & geophysics, lithology, 01 natural sciences, Mineralogical composition, chemical weathering, Northern italy, Carbon cycle, lcsh:G3180-9980, Earth and Planetary Sciences (miscellaneous), computer code, europe, Geology, 0105 earth and related environmental sciences
Abstract

We present a new geo-lithological map for Central Europe (Geo-LiM). It was prepared taking into account the chemical and mineralogical composition of the outcropping rocks and paying attention in discriminating metamorphic rocks, that were classified according to the chemistry of protoliths. The map was used for estimating the atmospheric CO2 consumed by the chemical weathering of silicates and carbonates. The map is made available in vector format [Donnini et al,. 2018. A new Geo-Lithological Map (Geo-LiM) for Central Europe (Germany, France, Switzerland, Austria, Slovenia, and Northern Italy) (Version 1.2) [Data set]. Zenodo Retrieved from https://zenodo.org/record/3530257], together with the computer code used to classify the lithologies and to join original maps. As a consequence, researchers can either replicate the product, or alter the code to derive a different lithological classification of the original geological maps, following the concept of Open Science.

Published
2019

218. Genetic analysis of the tree leaf disease microfungus Rhytisma acerinum

Author

Gyulai, Gabor

Subjects
global carbon cycle, Rhytisma acerinum, microfungi
Abstract

In the work presented in silico DNA sequence and dendrogram analyses were carried out to reveal molecular diversity and genetic distances among Rhytisma entries and related species based on gene bank data mining. The study revealed that R. acerinum shows the closest genetic distance to R. polare. DNA nucleotide variation detected raised a need for consensus between the Linnean morphological and the new molecular systematics.

Published
2021

219. The future of tundra carbon storage in Greenland – Sensitivity to climate and plant trait changes

Author

Efrén López-Blanco, Peter L. Langen, Mathew Williams, Jens Hesselbjerg Christensen, Fredrik Boberg, Kirsty Langley, and Torben Røjle Christensen

Subjects
VDP::Geosciences: 450, Økosystemmodell, Environmental Engineering, Nitrogen, Climate Change, SEASONAL-VARIATION, Greenland, EARTH SYSTEM MODELS, Ecosystem modelling, CO exchange, Global carbon cycle, Arctic, DIOXIDE EXCHANGE, CO2 storage, Environmental Chemistry, Tundra, VDP::Geofag: 450, Waste Management and Disposal, Ecosystem, Future projections, Global karbon syklus, ARCTIC TUNDRA, NET ECOSYSTEM EXCHANGE, PRODUCTIVITY, Arctic Regions, CO2 exchange, Grønland, Carbon cycle, Pollution, Carbon, NITROGEN, RESPIRATION, CO2 lagring, CO2, VEGETATION, Ecosystem model
Abstract

The continuous change in observed key indicators such as increasing nitrogen deposition, temperatures and precipitation will have marked but uncertain consequences for the ecosystem carbon (C) sink-source functioning of the Arctic. Here, we use multiple in-situ data streams measured by the Greenland Ecosystem Monitoring programme in tight connection with the Soil-Plant-Atmosphere model and climate projections from the high-resolution HIRHAM5 regional model. We apply this modelling framework with focus on two climatically different tundra sites in Greenland (Zackenberg and Kobbefjord) to assess how sensitive the net C uptake will expectedly be under warmer and wetter conditions across the 21st century and pin down the relative contribution to the overall C sink strength from climate versus plant trait variability. Our results suggest that temperatures (5–7.7 °C), total precipitation (19–110 %) and vapour pressure deficit will increase (32–36 %), while shortwave radiation will decline (6–9 %) at both sites by 2100 under the RCP8.5 scenario. Such a combined effect will, on average, intensify the net C uptake by 9–10 g C m−2 year−1 at both sites towards the end of 2100, but Zackenberg is expected to have more than twice the C sink strength capacity of Kobbefjord. Our sensitivity analysis not only reveals that plant traits are the most sensitive parameters controlling the net C exchange in both sites at the beginning and end of the century, but also that the projected increase in the net C uptake will likely be similarly influenced by future changes in climate and existing local nutrient conditions. A series of experiments forcing realistic changes in plant nitrogen status at both sites corroborates this hypothesis. This work proves the unique synergy between monitoring data and numerical models to assist robust model calibration/validation and narrow uncertainty ranges and ultimately produce more reliable C cycle projections in understudied regions such as Greenland.

Published
2022

220. Understanding carbon regulation in aquatic systems - Bacteriophages as a model [version 1; referees: 2 approved]

Author

Swapnil Sanmukh, Krishna Khairnar, Waman Paunikar, and Satish Lokhande

Subjects
Research Note, Articles, Marine & Freshwater Ecology, Virology, interconversion, microbial carbon pump, carbon sequestration, refractory carbon, global carbon cycle
Abstract

The bacteria and their phages are the most abundant constituents of the aquatic environment, and so represent an ideal model for studying carbon regulation in an aquatic system. The microbe-mediated interconversion of bioavailable organic carbon (OC) into dissolved organic carbon (DOC) by the microbial carbon pump (MCP) has been suggested to have the potential to revolutionize our view of carbon sequestration. It is estimated that DOC is the largest pool of organic matter in the ocean and, though a major component of the global carbon cycle, its source is not yet well understood. A key element of the carbon cycle is the microbial conversion of DOC into inedible forms. The primary aim of this study is to understand the phage conversion from organic to inorganic carbon during phage-host interactions. Time studies of phage-host interactions under controlled conditions reveal their impact on the total carbon content of the samples and their interconversion of organic and inorganic carbon compared to control samples. A total organic carbon (TOC) analysis showed an increase in inorganic carbon content by 15-25 percent in samples with bacteria and phage compared to samples with bacteria alone. Compared to control samples, the increase in inorganic carbon content was 60-70-fold in samples with bacteria and phage, and 50-55-fold for samples with bacteria alone. This study indicates the potential impact of phages in regulating the carbon cycle of aquatic systems.

Published
2015
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221. Terrestrial Laser Scanning to Detect Liana Impact on Forest Structure

Author

Sruthi M. Krishna Moorthy, Kim Calders, Manfredo di Porcia e Brugnera, Stefan A. Schnitzer, and Hans Verbeeck

Subjects
lianas, TLS, long-term monitoring, tropical forests, aboveground competition, global carbon cycle, Science
Abstract

Tropical forests are currently experiencing large-scale structural changes, including an increase in liana abundance and biomass. Higher liana abundance results in reduced tree growth and increased tree mortality, possibly playing an important role in the global carbon cycle. Despite the large amount of data currently available on lianas, there are not many quantitative studies on the influence of lianas on the vertical structure of the forest. We study the potential of terrestrial laser scanning (TLS) in detecting and quantifying changes in forest structure after liana cutting using a small scale removal experiment in two plots (removal plot and non-manipulated control plot) in a secondary forest in Panama. We assess the structural changes by comparing the vertical plant profiles and Canopy Height Models (CHMs) between pre-cut and post-cut scans in the removal plot. We show that TLS is able to detect the local structural changes in all the vertical strata of the plot caused by liana removal. Our study demonstrates the reproducibility of the TLS derived metrics for the same location confirming the applicability of TLS for continuous monitoring of liana removal plots to study the long-term impacts of lianas on forest structure. We therefore recommend to use TLS when implementing new large scale liana removal experiments, as the impact of lianas on forest structure will determine the aboveground competition for light between trees and lianas, which has important implications for the global carbon cycle.

Published
2018
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227. Introduction

Author

Apps, Michael J., Price, David T., Apps, Michael J., editor, and Price, David T., editor

Published
1996
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233. Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Abstract

Global vegetation photosynthesis and productivity have increased substantially since the 1980s, but this trend is heterogeneous in both time and space. Here, we categorize the secular trend in global vegetation greenness into sustained greening, sustained browning and greening-to-browning. We found that by 2016, increased global vegetation greenness had begun to level off, with the area of browning increasing in the last decade, reaching 39.0 million km2 (35.9% of the world’s vegetated area). This area is larger than the area with sustained increasing growth (27.8 million km2, 26.4%); thus, 12.0% ± 3.1% (0.019 ± 0.004 NDVI a−1) of the previous earlier increase has been offset since 2010 (2010–2016, P < 0.05). Global gross primary production also leveled off, following the trend in vegetation greenness in time and space. This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought, whose impact dominated over the impacts of temperature and solar radiation. This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models. Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues, land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.

Published
2021

234. Organic Matter Degradation across Ecosystem Boundaries : The Need for a Unified Conceptualization

Abstract

The global carbon cycle connects organic matter (OM) pools in soil, freshwater, and marine ecosystems with the atmosphere, thereby regulating their size and reactivity. Due to the complexity of biogeochemical processes and historically compartmentalized subdisciplines, ecosystem-specific conceptualizations of OM degradation have emerged independently of developments in other ecosystems. Recent discussions regarding the relative importance of molecular composition and ecosystem properties on OM degradation have diverged in opposing directions across subdisciplines, leaving our understanding inconsistent. Ecosystem-dependent theories are problematic since properties unique to an ecosystem may change in response to anthropogenic stressors, including climate change. The next breakthrough in our understanding of OM degradation requires a shift in focus towards developing a unified theory of controls on OM across ecosystems.

Published
2021
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235. Recent leveling off of vegetation greenness and primary production reveals the increasing soil water limitations on the greening Earth

Abstract

Global vegetation photosynthesis and productivity have increased substantially since the 1980s, but this trend is heterogeneous in both time and space. Here, we categorize the secular trend in global vegetation greenness into sustained greening, sustained browning and greening-to-browning. We found that by 2016, increased global vegetation greenness had begun to level off, with the area of browning increasing in the last decade, reaching 39.0 million km2 (35.9% of the world’s vegetated area). This area is larger than the area with sustained increasing growth (27.8 million km2, 26.4%); thus, 12.0% ± 3.1% (0.019 ± 0.004 NDVI a−1) of the previous earlier increase has been offset since 2010 (2010–2016, P < 0.05). Global gross primary production also leveled off, following the trend in vegetation greenness in time and space. This leveling off was caused by increasing soil water limitations due to the spatial expansion of drought, whose impact dominated over the impacts of temperature and solar radiation. This response of global gross primary production to soil water limitation was not identified by land submodels within Earth system models. Our results provide empirical evidence that global vegetation greenness and primary production are offset by water stress and suggest that as global warming continues, land submodels may overestimate the world’s capacity to take up carbon with global vegetation greening.

Published
2021

236. Organic Matter Degradation across Ecosystem Boundaries : The Need for a Unified Conceptualization

Abstract

The global carbon cycle connects organic matter (OM) pools in soil, freshwater, and marine ecosystems with the atmosphere, thereby regulating their size and reactivity. Due to the complexity of biogeochemical processes and historically compartmentalized subdisciplines, ecosystem-specific conceptualizations of OM degradation have emerged independently of developments in other ecosystems. Recent discussions regarding the relative importance of molecular composition and ecosystem properties on OM degradation have diverged in opposing directions across subdisciplines, leaving our understanding inconsistent. Ecosystem-dependent theories are problematic since properties unique to an ecosystem may change in response to anthropogenic stressors, including climate change. The next breakthrough in our understanding of OM degradation requires a shift in focus towards developing a unified theory of controls on OM across ecosystems.

Published
2021
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237. Organic Matter Degradation across Ecosystem Boundaries : The Need for a Unified Conceptualization

Abstract

The global carbon cycle connects organic matter (OM) pools in soil, freshwater, and marine ecosystems with the atmosphere, thereby regulating their size and reactivity. Due to the complexity of biogeochemical processes and historically compartmentalized subdisciplines, ecosystem-specific conceptualizations of OM degradation have emerged independently of developments in other ecosystems. Recent discussions regarding the relative importance of molecular composition and ecosystem properties on OM degradation have diverged in opposing directions across subdisciplines, leaving our understanding inconsistent. Ecosystem-dependent theories are problematic since properties unique to an ecosystem may change in response to anthropogenic stressors, including climate change. The next breakthrough in our understanding of OM degradation requires a shift in focus towards developing a unified theory of controls on OM across ecosystems.

Published
2021
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238. Organic Matter Degradation across Ecosystem Boundaries : The Need for a Unified Conceptualization

Abstract

The global carbon cycle connects organic matter (OM) pools in soil, freshwater, and marine ecosystems with the atmosphere, thereby regulating their size and reactivity. Due to the complexity of biogeochemical processes and historically compartmentalized subdisciplines, ecosystem-specific conceptualizations of OM degradation have emerged independently of developments in other ecosystems. Recent discussions regarding the relative importance of molecular composition and ecosystem properties on OM degradation have diverged in opposing directions across subdisciplines, leaving our understanding inconsistent. Ecosystem-dependent theories are problematic since properties unique to an ecosystem may change in response to anthropogenic stressors, including climate change. The next breakthrough in our understanding of OM degradation requires a shift in focus towards developing a unified theory of controls on OM across ecosystems.

Published
2021
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239. Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2

Abstract

Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]‐driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre‐industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.

Published
2021
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240. Organic Matter Degradation across Ecosystem Boundaries : The Need for a Unified Conceptualization

Abstract

The global carbon cycle connects organic matter (OM) pools in soil, freshwater, and marine ecosystems with the atmosphere, thereby regulating their size and reactivity. Due to the complexity of biogeochemical processes and historically compartmentalized subdisciplines, ecosystem-specific conceptualizations of OM degradation have emerged independently of developments in other ecosystems. Recent discussions regarding the relative importance of molecular composition and ecosystem properties on OM degradation have diverged in opposing directions across subdisciplines, leaving our understanding inconsistent. Ecosystem-dependent theories are problematic since properties unique to an ecosystem may change in response to anthropogenic stressors, including climate change. The next breakthrough in our understanding of OM degradation requires a shift in focus towards developing a unified theory of controls on OM across ecosystems.

Published
2021
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241. Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2

Abstract

Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf-scale photosynthesis and intrinsic water-use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]-driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre-industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.

Published
2021

242. Historical increases in land-derived nutrient inputs may alleviate effects of a changing physical climate on the oceanic carbon cycle

Abstract

The implications of climate change and other human perturbations on the oceanic carbon cycle are still associated with large uncertainties. Global-scale modelling studies are essential to investigate anthropogenic perturbations of oceanic carbon fluxes but, until now, they have not considered the impacts of temporal changes in riverine and atmospheric inputs of P and N on the marine net biological productivity (NPP) and air–sea CO2 exchange (FCO2). To address this, we perform a series of simulations using an enhanced version of the global ocean biogeochemistry model HAMOCC to isolate effects arising from (1) increasing atmospheric CO2 levels, (2) a changing physical climate and (3) alterations in inputs of terrigenous P and N on marine carbon cycling over the 1905–2010 period. Our simulations reveal that our first-order approximation of increased terrigenous nutrient inputs causes an enhancement of 2.15 Pg C year−1 of the global marine NPP, a relative increase of +5% over the simulation period. This increase completely compensates the simulated NPP decrease as a result of increased upper ocean stratification of −3% in relative terms. The coastal ocean undergoes a global relative increase of 14% in NPP arising largely from increased riverine inputs, with regional increases exceeding 100%, for instance on the shelves of the Bay of Bengal. The imprint of enhanced terrigenous nutrient inputs is also simulated further offshore, inducing a 1.75 Pg C year−1 (+4%) enhancement of the NPP in the open ocean. This finding implies that the perturbation of carbon fluxes through coastal eutrophication may extend further offshore than that was previously assumed. While increased nutrient inputs are the largest driver of change for the CO2 uptake at the regional scale and enhance the global coastal ocean CO2 uptake by 0.02 Pg C year−1, they only marginally affect the FCO2 of the open ocean over our study's timeline., SCOPUS: ar.j, info:eu-repo/semantics/published

Published
2021

246. Molecular insights and future frontiers in cell photosensitization for solar-driven CO2 conversion

Author

Peidong Yang, Stefano Cestellos-Blanco, Rachel Rebecca Chan, Nicholas George Watanabe, and Ji Min Kim

Subjects
Multidisciplinary, global carbon cycle, Chemistry, business.industry, Science, microbiology, Nanotechnology, Solar energy, Biocompatible material, Nanomaterials, Affordable and Clean Energy, Solar light, energy engineering, business, nanomaterials
Abstract

Summary: The conversion of CO2 to value-added products powered with solar energy is an ideal solution to establishing a closed carbon cycle. Combining microorganisms with light-harvesting nanomaterials into photosynthetic biohybrid systems (PBSs) presents an approach to reaching this solution. Metabolic pathways precisely evolved for CO2 fixation selectively and reliably generate products. Nanomaterials harvest solar light and biocompatibly associate with microorganisms owing to similar lengths scales. Although this is a nascent field, a variety of approaches have been implemented encompassing different microorganisms and nanomaterials. To advance the field in an impactful manner, it is paramount to understand the molecular underpinnings of PBSs. In this perspective, we highlight studies inspecting charge uptake pathways and singularities in photosensitized cells. We discuss further analyses to more completely elucidate these constructs, and we focus on criteria to be met for designing photosensitizing nanomaterials. As a result, we advocate for the pairing of microorganisms with naturally occurring and highly biocompatible mineral-based semiconductor nanomaterials.

Published
2021

247. Dynamic global vegetation models underestimate net CO2 flux mean and interannual variability in dryland ecosystems

Author

Marcy E. Litvak, Tilden P. Meyers, Anthony P. Walker, Praveena Krishnan, Julia E. M. S. Nabel, Vivek K. Arora, Julia Pongratz, Stephen Sitch, Danica Lombardozzi, Natasha MacBean, Vladislav Bastrikov, Thomas Kolb, Sönke Zaehle, Philippe Peylin, David J. P. Moore, Joel A. Biederman, Russell L. Scott, Daniel S. Goll, Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette] (LSCE), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Modélisation des Surfaces et Interfaces Continentales (MOSAIC), Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ), Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS), and Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)-Université de Versailles Saint-Quentin-en-Yvelines (UVSQ)-Commissariat à l'énergie atomique et aux énergies alternatives (CEA)-Institut national des sciences de l'Univers (INSU - CNRS)-Université Paris-Saclay-Centre National de la Recherche Scientifique (CNRS)

Subjects
0106 biological sciences, 010504 meteorology & atmospheric sciences, global carbon cycle, [SDE.MCG]Environmental Sciences/Global Changes, Atmospheric sciences, 010603 evolutionary biology, 01 natural sciences, Carbon cycle, inter-annual variability, medicine, Ecosystem, [SDU.ENVI]Sciences of the Universe [physics]/Continental interfaces, environment, ComputingMilieux_MISCELLANEOUS, 0105 earth and related environmental sciences, General Environmental Science, [SDU.OCEAN]Sciences of the Universe [physics]/Ocean, Atmosphere, Renewable Energy, Sustainability and the Environment, Public Health, Environmental and Occupational Health, Co2 flux, Drylands, 15. Life on land, 13. Climate action, dynamic global vegetation models, Environmental science, medicine.symptom, Vegetation (pathology)
Abstract

Despite their sparse vegetation, dryland regions exert a huge influence over global biogeochemical cycles because they cover more than 40% of the world surface (Schimel 2010 Science 327 418–9). It is thought that drylands dominate the inter-annual variability (IAV) and long-term trend in the global carbon (C) cycle (Poulter et al 2014 Nature 509 600–3, Ahlstrom et al 2015 Science 348 895–9, Zhang et al 2018 Glob. Change Biol. 24 3954–68). Projections of the global land C sink therefore rely on accurate representation of dryland C cycle processes; however, the dynamic global vegetation models (DGVMs) used in future projections have rarely been evaluated against dryland C flux data. Here, we carried out an evaluation of 14 DGVMs (TRENDY v7) against net ecosystem exchange (NEE) data from 12 dryland flux sites in the southwestern US encompassing a range of ecosystem types (forests, shrub- and grasslands). We find that all the models underestimate both mean annual C uptake/release as well as the magnitude of NEE IAV, suggesting that improvements in representing dryland regions may improve global C cycle projections. Across all models, the sensitivity and timing of ecosystem C uptake to plant available moisture was at fault. Spring biases in gross primary production (GPP) dominate the underestimate of mean annual NEE, whereas models’ lack of GPP response to water availability in both spring and summer monsoon are responsible for inability to capture NEE IAV. Errors in GPP moisture sensitivity at high elevation forested sites were more prominent during the spring, while errors at the low elevation shrub and grass-dominated sites were more important during the monsoon. We propose a range of hypotheses for why model GPP does not respond sufficiently to changing water availability that can serve as a guide for future dryland DGVM developments. Our analysis suggests that improvements in modeling C cycle processes across more than a quarter of the Earth’s land surface could be achieved by addressing the moisture sensitivity of dryland C uptake.

Published
2021

248. Spatiotemporal analysis of the future carbon footprint of solar electricity in the United States by a dynamic life cycle assessment.

Author

Lu J, Tang J, Shan R, Li G, Rao P, and Zhang N

Abstract

Solar photovoltaics (PVs) installation would increase 20-fold by 2050; however, considerable greenhouse gas (GHG) emissions are generated during the cradle-to-gate production, with spatiotemporal variances depending on the grid emission. Thus, a dynamic life cycle assessment (LCA) model was developed to assess the accumulated PV panels with a heterogeneous carbon footprint if manufactured and installed in the United States. The state-level carbon footprint of solar electricity ( CFE PV-avg ) from 2022 to 2050 was estimated using several cradle-to-gate production scenarios to account for emissions stemming from electricity generated from solar PVs. The CFE PV-avg (min 0.032, max 0.051, weighted avg. 0.040 kg CO 2 -eq/kWh) in 2050 will be significantly lower than that of the comparison benchmark (min 0.047, max 0.068, weighted avg. 0.056 kg CO 2 -eq/kWh). The proposed dynamic LCA framework is promising for planning solar PV supply chains and, ultimately, the supply chain of an entire carbon-neutral energy system to maximize the environmental benefits., Competing Interests: The authors declare no competing interests., (© 2023 The Author(s).)

Published
2023
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