Increase In Atmospheric CO2 Research Articles

Feast or famine: How is global change affecting forage supply for Yellowstone's ungulate herds?

The ecological integrity of US national parks and other protected areas are under threat in the Anthropocene. For Yellowstone National Park (YNP), the impacts that global change has already had on the park's capacity to sustain its large migratory herds of wild ungulates is incompletely understood. Here we examine how two understudied components of global change, the historical increase in atmospheric CO2 and the spread of nonnative, invasive plant species, may have altered the capacity of YNP to provide forage for ungulates over the last 200-plus years. We performed two experiments: (1) a growth chamber study that determined the growth rates of important invasive and native YNP grasses that are forages for ungulates under preindustrial (280ppm) versus modern (410ppm) CO2 levels and (2) a field study that compared the effect of defoliation (clipping) on the shoot growth of invasive and native mesic grassland plants under ambient CO2 conditions in 2019. The growth chamber experiment revealed that modern CO2 increased the growth rates of both invasive and native grasses, and invasive grasses grew faster regardless of CO2 conditions. The field results showed a continuum of positive to negative responses of shoot growth to defoliation, with a subgroup of invasive species responding most positively. Altogether the results indicated that the historical increase in CO2 and the spread of invasive species, some of which were planted to provide forage for ungulates in the early and mid-1900s, have likely increased the capacity of forage production in YNP. However, rising CO2 has also resulted in regional warming and increased aridity in YNP, which will likely reduce grassland productivity. The challenge for global change biologists and park managers is to determine how competing components of global change have already affected and will increasingly affect forage dynamics and the sustainability of Yellowstone's iconic ungulate herds in the Anthropocene.

Synthesized Pectin from Food Waste and Its Application in Electrolyte Gelation for CO2 Reduction

The utilization of in-situ resources such as food waste or plants grown on Mars combined with the available Martian regolith and atmosphere presents a path towards battery separators with increased sustainability, energy density, and durability. Separators that focus on CO2 reduction take advantage of both a highly relevant source of materials on Mars and a solution to an increasingly relevant problem of the increase of atmospheric CO2 on Earth.In this paper we evaluate the electrochemical and thermal properties of gel electrolytes synthesized from food waste and their performance in CO2 reduction. Our work focuses on the extraction of pectins from soybean hull and tomato pomace as sources of inedible biomass. Cross-linking and ionic activity of the pectin-based gel electrolytes are determined by the integration of monovalent and divalent cations. A biomass-based polymer electrolyte provides a novel method of using in-situ resources for chemical conversion and energy storage that is critical for long-term space travel.

Microbial biofortification: A sustainable route to grow nutrient-rich crops under changing climate

Crop improvement programs are facing serious challenges to sustain food and more importantly nutritional demand from global population, due to changing climate. Major staple cereals provide the caloric requirement for the global population, but are poor sources of micronutrients. Besides nutritional dilution due to the yield-oriented breeding, and unprecedented increase in atmospheric CO 2 , altered composition of beneficial microbes in the rhizosphere is seen as a plausible reason driving low nutrient accumulation in cereals. A complex network of signalling between plant and microbes in the rhizosphere reveals extensive links between environment, microbes and crop nutrition. Despite established roles of rhizospheric microbes on crop nutrient dynamics, limited knowledge is available on the impact of climate change on rhizosphere biology and the subsequent modulation of crop nutrition. Here, we emphasize the potential role of microbes to help sustain the global nutritional demand, achieved through the development of microbiome responsive nutrient rich staple crops. To succeed in this goal, dynamics of rhizosphere biology altered by climate change factors (CO 2 , temperature, precipitation), farming practices and soil properties needs to be untangled and a robust research pathway established to enhance crop nutrition with microbial biofortification to ensure a sustainable route to achieve global nutritional security. • Modern cultivars of major cereal crops are poor in grain nutrients. • Climate change drivers alter rhizospheric microbial diversity and activity. • Rhizospheric microbiome regulates nutrient supply to crop under variable climate. • Favourable microbial association is vital to develop nutrient rich crops.

Source‐Labeled Anthropogenic Carbon Reveals a Large Shift of Preindustrial Carbon From the Ocean to the Atmosphere

AbstractTwo centuries of anthropogenic CO2 emissions have increased the CO2 concentration of the atmosphere and the dissolved inorganic carbon (DIC) concentration of the ocean compared to preindustrial times. These anthropogenic carbon perturbations are often equated to the amount of anthropogenically emitted carbon in the atmosphere or ocean, which ignores the possibility of a shift of natural carbon between the oceanic and atmospheric carbon reservoirs. Here we use a data‐assimilated ocean circulation model and numerical tracers akin to ideal isotopes to label carbon when it is emitted by anthropogenic sources. We find that emitted carbon accounts for only about 45% of the atmospheric CO2 increase since preindustrial times, the remaining 55% being natural CO2 that outgassed from the ocean in response to anthropogenically emitted carbon invading the ocean. This outgassing is driven by the order‐10 seawater carbonate buffer factor which causes increased leakage of natural CO2 as DIC concentrations increase. By 2020, the ocean had outgassed ∼159 Pg of natural carbon, which is counteracted by the ocean absorbing ∼347 Pg of emitted carbon, about 1.8 times more than the net increase in oceanic carbon storage of ∼188 PgC. These results do not challenge existing estimates of anthropogenically driven changes in atmospheric or oceanic carbon inventories, but they shed new light on the composition of these changes and the fate of anthropogenically emitted carbon in the Earth system.

Shelf Ecosystems Along the U.S. Atlantic Coastal Plain Prior to and During the Paleocene‐Eocene Thermal Maximum: Insights Into the Stratigraphic Architecture

AbstractThe Paleocene‐Eocene Thermal Maximum (PETM) is the most pronounced global warming event of the early Paleogene related to atmospheric CO2 increases. It is characterized by negative δ18O and δ13C excursions recorded in sedimentary archives and a transient disruption of the marine biosphere. Sites from the U.S. Atlantic Coastal Plain show an additional small, but distinct δ13C excursion below the onset of the PETM, coined the “pre‐onset excursion” (POE), mimicking the PETM‐forced environmental perturbations. This study focuses on the South Dover Bridge core in Maryland, where the Paleocene‐Eocene transition is stratigraphically constrained by calcareous nannoplankton and stable isotope data, and in which the POE is well‐expressed. The site was situated in a middle neritic marine shelf setting near a major outflow of the paleo‐Potomac River system. We generated high‐resolution benthic foraminiferal assemblage, stable isotope, trace‐metal, grain‐size and clay mineralogy data. The resulting stratigraphic subdivision of this Paleocene‐Eocene transition is placed within a depth transect across the paleoshelf, highlighting that the PETM sequence is relatively expanded. The geochemical records provide detailed insights into the paleoenvironment, developing from a well‐oxygenated water column in latest Paleocene to a PETM‐ecosystem under severe biotic stress‐conditions, with shifts in food supply and temperature, and under dysoxic bottom waters in a more river‐dominated setting. Environmental changes started in the latest Paleocene and culminated atthe onset of the PETM, hinting to an intensifying trigger rather than to an instantaneous event at the Paleocene‐Eocene boundary toppling the global system.

Mature and old-growth forests contribute to large-scale conservation targets in the conterminous United States

Mature and old-growth forests (MOG) of the conterminous United States collectively support exceptional levels of biodiversity but have declined substantially from logging and development. National-scale proposals to protect 30 and 50% of all lands and waters are useful in assessing MOG conservation targets given the precarious status of these forests. We present the first coast to coast spatially explicit MOG assessment based on three structural development measures—canopy height, canopy cover, and above-ground living biomass to assess relative maturity. MOG were displayed by major forest types (n = 22), landownerships (federal, state, private, and tribal), and Gap Analysis Project (GAP) management status overlaid on the NatureServe’s Red-listed Ecosystems and species, above-ground living biomass, and drinking water source areas. MOG total ∼67.2 M ha (35.9%) of all forest structural classes and were scattered across 8 regions with most in western regions. All federal lands combined represented the greatest (35%) concentrations of MOG, ∼92% of which is on national forest lands with ∼9% on Bureau of Land Management (BLM) and ∼3% on national park lands (totals do not sum to 100% due to minor mapping errors in the datasets). MOG on national forest lands supported the highest concentration of conservation values. However, national forests and BLM lands did not meet lower bound (30%) targets with only ∼24% of MOG in GAP1,2 (5.9 M ha) protection status. The vast majority (76%, 20.8 M ha) of MOG on federal lands that store 10.64 Gt CO2 (e) are vulnerable to logging (GAP3). If federal MOG are logged over a decade, and half their carbon stock emitted, there would be an estimated 0.5 ppm increase in atmospheric CO2 by 2030, which is equivalent to ∼9% of United States total annual emissions. We recommend upper bound (100%) protection of federal MOG, including elevating the conservation status of Inventoried Roadless Areas. This would avoid substantial CO2 emissions while allowing ongoing carbon sequestration to act as natural climate solutions to aid compliance with the Paris Climate Agreement and presidential executive orders on MOG and 30% of all lands and waters in protection by 2030. On non-federal lands, which have fewer MOG, regulatory improvements and conservation incentives are needed.

How Does Long-Term Organic Matter Treatment Affect the Biological Activity of a Centre European Forest Soil?

A significant portion of the increase in atmospheric CO2 enters the environment through a decrease in the level of organic matter (SOM) in soils. One of the reasons for this is the cutting of forests and the conversion of growing areas into arable land, thus changing land use. As a result, SOM today only has approx. 70–80% of the period before the spread of intensive farming. For the long-term study of the effect of varying amounts of SOM, we set up experimental plots for litter manipulation in 2000. In the course of our investigations, we studied how changing the amount of organic matter input the soil affects the CO2 emissions of the soil and its closely related biological activity after five or ten years, in addition to the continuous maintenance of the treatments. According to our assumption, after 10 years, the biological activity of the soil will decrease as a result of the removal treatment of organic matter, and the biological activity will increase as a result of the doubling. The pH value of the soil shifted in the acidic direction over 10 years as a result of the removal of organic matter, while it did not change as a result of the increase. In the first year, we could not detect any significant differences in the enzyme activity values. From our later results, we found that a drastic reduction in the amount of leaf litter has a greater effect on soil enzyme activity and soil respiration to a greater extent than an increase in litter production above natural levels. The pH of the soil was as expected, with litter withdrawal shifting the pH towards acidic over the years.

Observation-constrained estimates of the global ocean carbon sink from Earth system models

Abstract. The ocean slows global warming by currently taking up around one-quarter of all human-made CO2 emissions. However, estimates of the ocean anthropogenic carbon uptake vary across various observation-based and model-based approaches. Here, we show that the global ocean anthropogenic carbon sink simulated by Earth system models can be constrained by two physical parameters, the present-day sea surface salinity in the subtropical–polar frontal zone in the Southern Ocean and the strength of the Atlantic Meridional Overturning Circulation, and one biogeochemical parameter, the Revelle factor of the global surface ocean. The Revelle factor quantifies the chemical capacity of seawater to take up carbon for a given increase in atmospheric CO2. By exploiting this three-dimensional emergent constraint with observations, we provide a new model- and observation-based estimate of the past, present, and future global ocean anthropogenic carbon sink and show that the ocean carbon sink is 9 %–11 % larger than previously estimated. Furthermore, the constraint reduces uncertainties of the past and present global ocean anthropogenic carbon sink by 42 %–59 % and the future sink by 32 %–62 % depending on the scenario, allowing for a better understanding of the global carbon cycle and better-targeted climate and ocean policies. Our constrained results are in good agreement with the anthropogenic carbon air–sea flux estimates over the last three decades based on observations of the CO2 partial pressure at the ocean surface in the Global Carbon Budget 2021, and they suggest that existing hindcast ocean-only model simulations underestimate the global ocean anthropogenic carbon sink. The key parameters identified here for the ocean anthropogenic carbon sink should be quantified when presenting simulated ocean anthropogenic carbon uptake as in the Global Carbon Budget and be used to adjust these simulated estimates if necessary. The larger ocean carbon sink results in enhanced ocean acidification over the 21st century, which further threatens marine ecosystems by reducing the water volume that is projected to be undersaturated towards aragonite by around 3.7×106–7.4×106 km3 more than originally projected.

Evaluating indices of soil organic carbon stability. A case study for forest restoration projects near Beijing, China

Afforestation of degraded lands close to mega-urban areas such as Beijing may help to restore some of the original soil carbon stocks and hold the potential for ameliorating the rate of increase in atmospheric CO2. However, the determinants of the stability of different soil carbon pools and the utility of indices of stability remain poorly characterized near these highly anthropogenic areas. In the current study, we compared metrics of soil organic carbon (SOC) stability taking into account different soil types and plantation forest combinations (Quartisamment soil-poplar plantation–QP, Eutrochrepts soil-Chinese pine plantation–ECP, Haplustepts soils-East-Liaoning oak plantation–HEO), in an experimental sub-humid area close to a mega-urban area (Beijing, China). We evaluated the following relative stability indices sequence: respired carbon from incubations (RI) for several incubation days to respire 5% of initial SOC (D), aggregate stability index (ASI), the ratio of SOC to total nitrogen (C: N), water-soluble carbon (WSC), particulate organic carbon (POC) and microbial biomass carbon (MBC). We examined the indices by three repeated measurements on soil samples from four soil layers (0–40 cm) in three soil-forest types in a forest area close to the peri-urban area of Beijing. Our results showed that there are inconsistencies among the six SOC stability indexes. The contribution rates of different indexes to the SOC in three plantations were different, for QP the highest contributor is WSC (54.73%), and for ECP and HEO the highest contributor is RI, contribution rates are 34.85% and 36.382%, respectively. Respired carbon from incubations registered the largest contribution rate to SOC (69.79%), and the correlation between RI and soil physical and chemical properties was the highest. We conclude that a combination of indices and knowledge of soil and vegetation types are needed for assessing SOC stability in restoration and reforestation projects close to mega-urban areas.

Spatial and temporal variability of the physical, carbonate and CO2 properties in the Southern Ocean surface waters during austral summer (2005-2019)

In situ measurements of sea surface temperature (SST), salinity (SSS), Total Alkalinity (AT) and Total Carbon (CT) were obtained during austral summer (mid-February to mid-March) from 2005 to 2019 in the Southern Ocean (SO), along a transect between Hobart, Tasmania and Dumont d’Urville French Antarctic Station. The studied transect is divided in four regions from North to South: the Subtropical Zone (STZ), the Subantarctic Region (SAR), the Antarctic Region (AAR) and the Coastal Antarctic Zone (CAZ). Latitudinal distribution of measured SST, SSS, AT, CT as well as calculated pH, CO2 parameters (seawater fugacity of CO2 (fCO2sw), difference between seawater and atmospheric fCO2 (ΔfCO2), CO2 flux (FCO2)) and satellite-derived Chlorophyll a (Chl-a) are discussed. We show that the variability of physical and carbonate parameters in the STZ and north of the SAR are related to the mesoscale activity. In the CAZ, the freshwater inputs from sea-ice melting strongly impact the variability of all parameters. The comparison between physical and carbonate parameters highlights that AT and CT are directly related to the latitudinal variability of SST and SSS. Study of the CO2 parameters shows that the transect is a sink of CO2 during February and March, with a mean FCO2 of −4.0 ± 2.8 mmol m−2 d−1. The most negative values of FCO2 are found in the STZ and SAR north of 50°S and in the AAR south of 62°S, where biological activity is high. New simple empirical relationships are developed for AT from SST and SSS and for CT using SST, SSS and atmospheric fCO2 (fCO2atm) for the austral summer in the studied area. Using high resolution SSS and SST from the SURVOSTRAL program, trends of AT and CT are determined in the SAR and the AAR from 2005 to 2019. SST, SSS and AT increase over this period in the SAR, which might be explained by the southward migration of the Subtropical Front. In the AAR, no clear trend is detected. CT increases by 1.0 ± 0.2 and 0.8 ± 0.3 μmol kg−1 yr−1 in the SAR and AAR respectively. The trend in the AAR is attributed to the increase in anthropogenic CO2 emissions in the atmosphere while, in the SAR, hydrographic changes also contribute to the increase. Using the coefficient associated with fCO2atm in the equation of CT, we estimate the impact of atmospheric CO2 increase on CT at 1.18 ± 0.14 μmol kg−1 yr−1 and 1.07 ± 0.13 μmol kg−1 yr−1 in the SAR and AAR respectively. Decreases in pH are observed in both regions (−0.0018 ± 0.0001 and −0.0026 ± 0.0003 yr−1 in the SAR and AAR respectively), indicating the sensitivity of surface waters in the area towards the development of ocean acidification processes under rising anthropogenic emissions.

Carbonate Parameter Estimation and Its Application in Revealing Temporal and Spatial Variation in the South and Mid‐Atlantic Bight, USA

AbstractTo overcome the limitations due to sporadic carbonate parameter data, this study developed and evaluated empirical multiple linear regression (MLR) models for dissolved inorganic carbon (DIC), pH in total scale (pHT), and aragonite carbonate saturation state (ΩAr) using hydrographic data (temperature, salinity, and oxygen) measured during 2007–2018 in the South Atlantic Bight (SAB) and Mid‐Atlantic Bight (MAB) along the U.S. East Coast. We first reviewed the assumptions and routines of MLR models and then generated MLR models for each cruise for all three carbonate parameters in each region and assessed model performance. Models derived from measured spectrophotometric pH have smaller uncertainties than pHT models based on pH calculated from total alkalinity (TA) and DIC. The regional differences of carbonate parameters between MAB and SAB are reflected in the coefficients of the empirical models. The MLR model temporal consistency indicates that the effect of the atmospheric CO2 increase on seawater carbonate parameters cannot be unequivocally resolved for the period of this study in the regions. Therefore, we combined different cruises to build composite models for each region. The composite models can capture the key features in the SAB and MAB. To further assess the model applicability, we applied our models to Biogeochemical‐Argo data to reconstruct carbonate parameters. The algorithm in this study helps to reconstruct seawater carbonate chemistry using proxy data of high spatial and temporal resolution, which will enhance our understanding of physical and biological processes on carbon cycle and the long‐term anthropogenic carbon inputs in coastal oceans.

Impact of terrestrial biosphere on the atmospheric CO<sub>2</sub> concentration across Termination V

Abstract. Among the 100 kyr climatic cycles of the Late Pleistocene, Termination V (TV, ∼ 433–404 kyr BP), the fifth last deglaciation, stands out for its minimum in astronomical forcing associated paradoxically with maxima in sea level, Antarctic temperature and atmospheric CO2 concentration. However, the driving mechanisms explaining TV remain only partially understood. For instance, climate models cannot fully represent the atmospheric CO2 variation observed in paleoclimate data. Aside from essential oceanic circulation processes, there is increasing evidence that terrestrial biosphere may have played a key role in the global carbon cycle. This study proposes a three-step integrated approach, combining regional and global vegetation records with modelling results, to unveil the evolution of terrestrial biosphere and its contribution to the carbon cycle during TV. First, we provide a new high-resolution (∼ 700 years) deep-sea pollen record from the Gulf of Cádiz (site U1386, 36∘49.680′ N; 7∘45.320′ W) for TV, which shows a moderate expansion of the Mediterranean forest. We then construct the first global forest pollen database for this period. Our compilation features distinct evolutions for different types of forest, highlighting a strong development of temperate and boreal forest which might have delayed the atmospheric CO2 increase during TV. Finally, the direct comparison of global simulated forests (iLOVECLIM model) to our pollen database reveals overall consistent temperate and boreal forest evolutions despite model biases, thereby supporting the hypothesis of a significant CO2 sequestration by middle and high-latitude forests of the Northern Hemisphere shortly after the onset of TV.

The effects of redistributed heat flux on ocean climate change in FAFMIP heat flux anomaly experiments

The Flux–Anomaly-Forced Model Inter-comparison Project (FAFMIP) aims to study the response of the ocean to changes in prescribed surface flux (heat, freshwater, and wind) caused by atmospheric CO2 increase. Among these surface flux perturbations, the heat flux has the greatest effect on ocean heat uptake (OHU), the Atlantic Meridional Circulation (AMOC), and sea level changes. This occurs in part because of the redistributed heat flux (Qr’), which is the component of the heat flux driven by ocean circulation changes and almost nearly doubles the initial heat flux perturbation (F) prescribed by FAFMIP in the North Atlantic (NA). In this study, we used a standalone ocean model to quantitatively investigate the impact of Qr’ on OHU and the AMOC in prescribed heat anomaly experiments (faf-heat experiment in FAFMIP). We also showed that whether the other two FAFMIP heat flux anomaly experiments (faf-heat-NA50pct and faf-heat-NA0pct) can reasonably simulate the ocean’s response to prescribed surface heat flux, especially OHU and AMOC. Our findings show that faf-heat-NA50pct is better because the redistribution-feedback (Qr’) nearly equals the initial perturbation (50%F) in the NA and thus recovers the total perturbation F in faf-heat. Although direct comparisons cannot be drawn, both faf-heat-NA50pct and faf-heat experiments with no effect of Qr’ cause AMOC weakening that is roughly comparable with the 1pctCO 2 experiments. The magnitude of simulated AMOC weakening in faf-heat-NA50pct is 3.9Sv, accounting for about 29% of the AMOC intensity in unperturbed experiment, which is closer to the faf-heat experiment (about 31%) with no effect of Qr’ relative to the faf-heat experiment. Because of negative Qr’ in all regions except the NA region especially for the Central and Eastern Equatorial Pacific and Southern Ocean, the simulated global OHU in faf-heat-NA50pct is reduced by 10% as compared to the added OHU in the faf-heat experiment. The Qr’ in the faf-heat experiment increases OHU by approximately 13% of the total OHU and further reduces AMOC intensity by 3.4 Sv, accounting for 26% of the AMOC strength in an unperturbed experiment. Faf-heat-NA0pct results in a significant reduction in OHU (approximately 26%), and the magnitude of AMOC weakening is only approximately 1.9 Sv, despite no F being added in the NA.

Quantitative reconstruction of atmospheric pCO2 sources during Eocene hyperthermal events based on data from the Fushun Basin, Northeast China

Eocene hyperthermal events are thought to be closely linked to rapid increases in atmospheric CO2. It is important to better understand the atmospheric triggers of these extreme events; however, reconstruction of pCO2 from sedimentary records remains challenging. Eocene hyperthermal events (Eocene thermal maximum, ETM; Early Eocene Climatic Optimum, EECO; Mid-Eocene Climatic Optimum, MECO) are well documented in the Fushun Basin of northeast China, but the source of organic matter (OM) used as a pCO2 archive in previous studies includes land plants, algae, mixed land and aquatic organisms in the Ypresian, Lutetian and Bartonian intervals, respectively. In this paper, we calculate pCO2 concentrations using δ13CTOC and δ13C27–31 and discuss the factors influencing discrepancies based on various calculations. Results show that both δ13CTOC and δ13C27–31 from single OM sources are reliable proxies for pCO2. During the ETM2, ETM3, EECO and MECO intervals, pCO2 was 638–2277 ppm, and palaeotemperature was approximately 2.6–8.9 °C higher than present. The background and peak values of pCO2 during hyperthermal events were compared with those related to methane hydrate, OM oxidation and volcanic sources of pCO2 carbon. The comparison revealed that pCO2 values associated with the ETM2, ETM3, EECO and MECO events were more consistent with those calculated by OM oxidation and locally overlapped with volcanic sources. These results indicate that these pCO2 estimates of hyperthermal events are predominantly derived from terrestrial OM oxidation and were influenced by volcanism.

Exploring the visible light-assisted conversion of CO2 into methane and methanol, using direct Z-scheme TiO2@g-C3N4 nanosheets: synthesis and photocatalytic performance.

The rapid growth of carbon dioxide (CO2) emissions raises concern about the possible consequences of atmospheric CO2 increase, such as global warming and greenhouse effect. Photocatalytic CO2 conversion has attracted researchers' interests to find a sustainable route for its elimination. In the present study, a direct Z-scheme TiO2/g-C3N4 composite (T-GCN) was fabricated via a facile hydrothermal route for the photocatalytic reduction of CO2 into methane (CH4) and methanol (CH3OH), under visible light irradiation without an electron mediator. The microstructure of the as-obtained TiO2/g-C3N4 nanocomposites was fully characterized for its physicochemical, structural, charge separation, electronic, and photo-excited carrier separation properties. The effect of CO2 and H2O partial pressure was studied to find the best operational conditions for obtaining maximum photocatalytic efficiency; the PCO2 and PH2O were 75.8 and 15.5kPa, respectively, whereas, by increasing the light intensity from 20 to 80 mW/cm2, a remarkable improvement in the reduction rate takes place (from 11.04 to 32.49μmol.gcat-1.h-1 methane production, respectively). Finally, under the most favorable light, PCO2 and PH2O conditions, high methanol and methane rates were obtained from the CO2 photocatalytic reduction through T-GCN (1.44μmol.gcat.-1.h-1 and 32.49μmol.gcat.-1.h-1, respectively) and an integrated proposition for the Z-scheme mechanism of photocatalytic reduction was proposed. This study offers a promising strategy to synthesize a Z-scheme T-GCN heterojunction with high photocatalytic performance for effective CO2 conversion.

Changing Sensitivity of Diverse Tropical Biomes to Precipitation Consistent with the Expected Carbon Dioxide Fertilization Effect

Abstract Global environmental changes have implications for the terrestrial ecosystem functioning, but disentangling individual effects remains elusive. The impact of vegetation responses to increasing atmospheric CO2 concentrations is particularly poorly understood. As the atmospheric CO2 concentration increases, the CO2 acts as a fertilizer for plant growth. An increase in atmospheric CO2 reduces the amount of water needed to produce an equivalent amount of biomass due to closing or a narrowing of the stomata that reduces the amount of water that is transpired by plants. To study the impacts of climate change and CO2 fertilization on plant growth, we analyzed the growing season sensitivity of plant growth to climatic forcing from alpine to semi-desert eco-climatic zones of Ethiopia for various plant functional types over the period of 1982–2011. Growing season 3rd generation Normalized Difference Vegetation Index of Global Inventory Modeling and Mapping Studies (NDVI) was used as a proxy of plant growth, while mean growing season precipitation (prec), temperature (temp), and solar radiation (sr) as the climate forcing. The sensitivities of plant growth are calculated as a partial correlation, and a derivative of NDVI with respect to prec, temp and sr for earliest and recent 15-year periods of the satellite records, and using a moving window of 15-year. Our results show increasing trends of plant growth that are not explained by any climate variables. We also find that an equivalent increase in prec leads to a larger increase in NDVI since the 1980s. This result implies a given amount of prec has sustained greater amounts of plant foliage materials over time due to decreasing transpiration with increasing CO2 concentration as expected from the CO2 fertilization effect on water use efficiency and plant growth. Increasing trends of growth in shallow-rooted vegetation tend to be associated with woody vegetation encroachment.

Persistent Ross Sea Freshening From Imbalance West Antarctic Ice Shelf Melting

AbstractA 63‐year observational record in the southwest Ross Sea shows a continuing, near‐linear salinity decrease of 0.170 and slight warming of 0.013°C through 2020. That freshening exceeded any increase in sea ice production and brine release from stronger southerly winds, while melting and freezing at the Ross Ice Shelf base contributed little to the salinity change. The parallel seawater density decline appears not to have enhanced warm deep water intrusions onto the continental shelf (CS). Confirming prior inferences, the salinity change has been mainly caused by a growing imbalance in the meltwater available from thinning ice shelves and increased iceberg calving in the upstream Amundsen and Bellingshausen Seas. Shorter‐term salinity variability has tracked winds near the Amundsen Sea CS break, in turn coherent with a broader Pacific climate variability index, and with salinity reversals on and seaward of the Ross CS. The melt driven freshening is positively correlated with global atmospheric CO2 and temperature increases, and adds to the rise in sea level from increased glacier flow into weakened ice shelves. Continued erosion of those ice shelves could end the production of high salinity shelf and bottom waters, as defined in the Ross Sea, by the 2050s.

Reconciling persistent sub-zero temperatures in the McMurdo Dry Valleys, Antarctica, with Neogene dynamic marine ice-sheet fluctuations

Abstract In the Ross Sea sector of Antarctica, periodic large-scale marine ice-sheet fluctuations since the mid-Miocene are recorded by drill core and seismic data, revealing a dynamic ice-sheet response to past increases in temperature and atmospheric CO2. In the adjacent, predominantly ice-free McMurdo Dry Valleys (MDVs), preserved terrestrial landscapes reflect persistent cold conditions and have been interpreted as indicators of a stable polar ice sheet, implying that the Antarctic Ice Sheet was largely insensitive during past warm periods. These disparate data-based perspectives highlight a long-standing debate around the past stability of the Antarctic Ice Sheet, with direct implications for the future ice-sheet response to ongoing climate warming. We reconcile marine records of dynamic ice-sheet behavior and episodic open-marine conditions with nearby ancient terrestrial landscapes recording consistent cold-polar conditions. Coupled ice-sheet and regional climate models nested at a high resolution are used to investigate surface temperatures in the MDVs during past warm periods. We find that high-elevation regions of the MDVs remain below freezing even when ice-free conditions prevail in the nearby Ross Sea. We compare observed landscapes with the spatial extent of modeled persistent cold conditions required for preservation of these ancient features, demonstrating that frozen MDVs landscapes could have coexisted with receded or collapsed ice sheets during past warm periods.

Warm northern tropical Indian Ocean strengthened the ocean circulation prior to the last glacial termination

Modern observations and model simulations suggest a strong influence of tropical processes on high-latitudinal climate. The evidence of similar tropics-high latitude climate link during glacial termination is, however, elusive. Here we show a strong influence of tropical processes in terminating the last glacial period based on multi-decadal seawater temperature, upwelling intensity and runoff records from the tropical Indian Ocean. We report a well-defined warming (1.4 °C) starting at ~20 kyr BP, coeval with abrupt increase in upwelling intensity and local CO2 outgassing, long before the beginning of increase in global atmospheric CO2 at 18.2 kyr BP. We suggest that the tropical Indian Ocean warming prior to the increase in global atmospheric CO2 was modulated by intense regional hydrographic changes caused by local summer insolation. The warming prior to Termination I (~18–11 kyr BP), at our site was synchronous with a small but evident strengthening of the Atlantic Meridional Overturning Circulation (AMOC). We conclude that the early warming in the tropical northern Indian Ocean led to stronger AMOC and the subsequent melting of the northern high latitude sea ice, which ultimately triggered the Heinrich Stadial during the last glacial termination.

Ideas and perspectives: Emerging contours of a dynamic exogenous kerogen cycle

Abstract. Growing evidence points to the dynamic role that kerogen is playing on Earth's surface in controlling atmospheric chemistry over geologic time. Although quantitative constraints on the weathering of kerogen remain loose, its changing weathering behavior modulated by the activity of glaciers suggests that this largest pool of reduced carbon on Earth may have played a key part in atmospheric CO2 variability across recent glacial–interglacial cycles and beyond. This work enunciates the possibility of kerogen oxidation as a major driver of atmospheric CO2 increase in the wake of glacial episodes. This hypothesis of centennial- and millennial-timescale relevance for this chemical weathering pathway is substantiated by several lines of independent evidence synthesized in this contribution, including the timing of atmospheric CO2 increase, atmospheric CO2 isotope composition (13C and 14C), kerogen oxidation kinetics, observations of kerogen reburial, and modeling results. The author hypothesizes that the deglaciation of kerogen-rich lithologies in western Canada contributed to the characteristic deglacial increase in atmospheric CO2, which reached an inflection point ≤ 300 years after the Laurentide Ice Sheet retreated into the kerogen-poor Canadian Shield. To reconcile the release of isotopically light carbon via kerogen oxidation with Earth surface carbon pool constraints, major oceanic degassing and biospheric regrowth must have acted in concert across glacial–interglacial transitions. Additionally, a process such as a strong shift in the ratio of C3 to C4-derived organic matter must be invoked to maintain isotope mass balance, a point key for reconciling the hypothesis with the carbon isotope record of marine dissolved inorganic carbon. In order to test this hypothesis, quantitative constraints on the contribution of kerogen oxidation to CO2 rise at glacial terminations are needed through systematic studies on (1) CO2 fluxes emanating from the weathering of different lithologies, (2) oxidation kinetics of kerogen along glacial chronosequences, and (3) high-resolution temporal changes in the aerial extent of glacially exposed lithological units and glacial flour.