Biogenic Carbon Fluxes Research Articles

A first account of pteropod taxa from off Saurashtra, western offshore of India: Implications for palaeohydrological studies

Pteropod aragonitic shells contribute to 12% of biogenic inorganic carbon flux to the world ocean but are also prone to dissolution. Though their state of preservation and generic ratios, namely Creseis/Limacina have been used as a proxy for palaeoclimatic reconstruction, their taxonomic attributes have remained unexplored. The present study reports 20 pteropod species from a single location in the northeastern Arabian Sea offshore of Saurashtra, all of which show the same degree of preservation throughout the core. The occurrence of mesopelagic fauna in the study area located on the shelf region however points to palaeoenvironmental changes and underscores the importance of employing pteropod assemblages for palaeoclimatic reconstructions in the study area.

Assessing Impacts of Environmental Perturbations on Urban Biogenic Carbon Exchange in the Chicago Region

AbstractCarbon dioxide (CO2) quantification is critical for assessing city‐level carbon emissions and sustainable urban development. While urban vegetation has the potential to provide environmental benefits, such as heat and carbon mitigation, the CO2 exchange from biogenic sectors and its impact from the environmental perturbations are often overlooked. It is also challenging to simulate the plant functions in the complex urban terrain. This study presents a processed‐based modeling approach to assess the biogenic carbon fluxes from the vegetated areas over the Chicago Metropolitan Area (CMA) using the Weather Research and Forecast—Urban Biogenic Carbon exchange model. We investigate the change of CO2 sink power in CMA under heatwaves and irrigation. The results indicate that the vegetation plays a significant role in the city's carbon portfolio and the landscaping management has the potential to reduce carbon emissions significantly. Furthermore, based on the competing mechanisms in the biogenic carbon balance identified in this study, we develop a novel Environmental Benefit Score metrics framework to identify the vulnerability and mitigation measures associated with nature‐based solutions (NbS) within CMA. By using the generalized portable framework and our science‐policy confluence analysis presented in this study, global cities can maximize the effectiveness of NbS and accelerate carbon neutrality.

Small-scale oxygen distribution patterns in a coral reef

One mechanism giving fleshy algae a competitive advantage over corals during reef degradation is algal-induced and microbially-mediated hypoxia (typically less than 69.5 µmol oxygen L−1). During hypoxic conditions oxygen availability becomes insufficient to sustain aerobic respiration in most metazoans. Algae are more tolerant of low oxygen conditions and may outcompete corals weakened by hypoxia. A key question on the ecological importance of this mechanism remains unanswered: How extensive are local hypoxic zones in highly turbulent aquatic environments, continuously flushed by currents and wave surge? To better understand the concert of biological, chemical, and physical factors that determine the abundance and distribution of oxygen in this environment, we combined 3D imagery, flow measurements, macro- and micro-organismal abundance estimates, and experimentally determined biogenic oxygen and carbon fluxes as input values for a 3D bio-physical model. The model was first developed and verified for controlled flume experiments containing coral and algal colonies in direct interaction. We then developed a three-dimensional numerical model of an existing coral reef plot off the coast of Curaçao where oxygen concentrations for comparison were collected in a small-scale grid using fiberoptic oxygen optodes. Oxygen distribution patterns given by the model were a good predictor for in situ concentrations and indicate widespread localized differences exceeding 50 µmol L-1 over distances less than a decimeter. This suggests that small-scale hypoxic zones can persist for an extended period of time in the turbulent environment of a wave- and surge- exposed coral reef. This work highlights how the combination of three-dimensional imagery, biogenic fluxes, and fluid dynamic modeling can provide a powerful tool to illustrate and predict the distribution of analytes (e.g., oxygen or other bioactive substances) in a highly complex system.

High resolution modeling of vegetation reveals large summertime biogenic CO2 fluxes in New York City

Abstract Cities are beginning to monitor atmospheric carbon dioxide (CO2) to assess the efficacy of their climate policies. However, changes in anthropogenic CO2 emissions must be separated from biospheric CO2 fluxes which have a large seasonal cycle. Urban vegetation (e.g. lawns, trees along street and in parks, etc) in developed land covers is often omitted in regional biogenic CO2 flux models. We set up a biosphere model to estimate the regional biogenic CO2 fluxes in New York City (NYC) and assess the importance of vegetation within developed land covers. The model incorporates a high-resolution (30 m) land cover map which identifies the mixture of impervious surfaces and vegetation that is ubiquitous across developed land covers. We designed three model scenarios to evaluate the role of developed land covers in regional biogenic CO2 fluxes by assuming (a) there is no vegetation versus scenarios where all remotely sensed vegetation in developed land covers is either (b) grassland or (c) deciduous forest. Despite relatively low tree canopy cover in NYC, the regional biogenic CO2 fluxes are surprisingly large when vegetation within the developed land covers is included. Furthermore, the types of vegetation within the developed land covers are crucially important for estimating regional biogenic CO2 fluxes, demonstrated by a doubling in estimates of total biogenic CO2 flux when this vegetation is assumed to be grassland compared to forest. Using a Lagrangian atmospheric transport model, we find that the regional biogenic CO2 uptake offsets up to 40% of atmospheric CO2 enhancements attributed to anthropogenic emissions in summer afternoons and completely balances on-road traffic in one of the most congested cities in the United States. Accurate characterization of the vegetation and biogenic carbon fluxes in cities are essential to the development of effective atmospheric monitoring tools. Future measurements should focus on constraining CO2 fluxes in urban grasslands (i.e. lawns).

Influence of Riverine Discharge and Timing of Ice Retreat on Particle Sedimentation Patterns on the Laptev Sea Shelf

AbstractWe studied the influence of river discharge and timing of ice retreat on sinking fluxes of total particulate matter and its components in the Laptev Sea in August–September 2017 and 2018. Vertical fluxes were measured with short‐term sediment traps located on the shelf adjusted to the Lena and Khatanga Rivers inflows (four shallow stations in 2017) and in Vilkitski Strait/Trough area (two deeper stations) in 2018. One station outside the Khatanga plume was repeated in both years. The effect of river discharge manifested by high total particle flux (1–1.6 g m−2 d−1), high Si (0.3 g m−2 d−1) and Al (0.1 g m−2 d−1) fluxes, a high proportion of terrigenous organic carbon (10.7%–27.5% total organic carbon) was clearly recognizable only in the shelf area closest to the Lena inflow. Large contribution of the lithogenic matter to the flux on the Laptev shelf is suggested to result also from sediment resuspension (caused by the tidal mixing and upwelling events), lateral offshore transport of sediment just above the seabed, and coastal abrasion. The magnitude of vertical fluxes of total particulate matter and organic carbon was two to three times higher in 2017 (late ice retreat) than in 2018 (early ice retreat). Centric diatoms dominated protist flux in 2017 while in 2018, dinoflagellates and tintinnids dominated. The contribution of protists to the biogenic organic carbon flux reached 62% in 2018 versus <1% in 2017. Zooplankton fecal pellet flux was not influenced by river discharge but was higher soon after ice melt.

A model for urban biogenic CO<sub>2</sub> fluxes: Solar-Induced Fluorescence for Modeling Urban biogenic Fluxes (SMUrF v1)

Abstract. When estimating fossil fuel carbon dioxide (FFCO2) emissions from observed CO2 concentrations, the accuracy can be hampered by biogenic carbon exchanges during the growing season, even for urban areas where strong fossil fuel emissions are found. While biogenic carbon fluxes have been studied extensively across natural vegetation types, biogenic carbon fluxes within an urban area have been challenging to quantify due to limited observations and differences between urban and rural regions. Here we developed a simple model representation, i.e., Solar-Induced Fluorescence (SIF) for Modeling Urban biogenic Fluxes (“SMUrF”), that estimates the gross primary production (GPP) and ecosystem respiration (Reco) over cities around the globe. Specifically, we leveraged space-based SIF, machine learning, eddy-covariance (EC) flux data, and ancillary remote-sensing-based products, and we developed algorithms to gap-fill fluxes for urban areas. Grid-level hourly mean net ecosystem exchange (NEE) fluxes are extracted from SMUrF and evaluated against (1) non-gap-filled measurements at 67 EC sites from FLUXNET during 2010–2014 (r>0.7 for most data-rich biomes), (2) independent observations at two urban vegetation and two crop EC sites over Indianapolis from August 2017 to December 2018 (r=0.75), and (3) an urban biospheric model based on fine-grained land cover classification in Los Angeles (r=0.83). Moreover, we compared SMUrF-based NEE with inventory-based FFCO2 emissions over 40 cities and addressed the urban–rural contrast in both the magnitude and timing of CO2 fluxes. To illustrate the application of SMUrF, we used it to interpret a few summertime satellite tracks over four cities and compared the urban–rural gradient in column CO2 (XCO2) anomalies due to NEE against XCO2 enhancements due to FFCO2 emissions. With rapid advances in space-based measurements and increased sampling of SIF and CO2 measurements over urban areas, SMUrF can be useful to inform the biogenic CO2 fluxes over highly vegetated regions during the growing season.

Biogenic carbonate fluxes and preservation in the northwestern Labrador Sea since the Last Glacial Maximum

The important changes that took place in the glacial cycle at the termination, from the Last Glacial Maximum to the present interglacial, deserve an examination of ocean sedimentary records that document past productivity, carbon fluxes, and carbonate preservation. In this study, we analyzed coccoliths, alkenones, and foraminifers in core HU2008–029-004 PC (61.46°N and 58.04°W, water depth = 2,674 m) from the northwestern Labrador Sea to document linkages between hydrographic conditions, biogenic carbonate fluxes to the seafloor, and their preservation/dissolution during the last 25,000 years. Large changes in coccolith and foraminifer concentrations are recorded, with sediments from the last glacial interval containing significantly less carbonate microfossils (9.5 ± 3.9 × 105 coccoliths g−1 and 2,860 ± 580 planktonic foraminifers g−1) than sediments from the deglacial and postglacial intervals (up to 3.1 × 108 coccoliths g−1 and 2.9 × 104 foraminifers g−1). Three foraminifer-based calcite dissolution indices were used to evaluate biogenic carbonate preservation: the planktonic foraminifer fragmentation index, the ratio of benthic-to-planktonic foraminifers (B/P), and the ratio of organic linings to benthic foraminifers (OL/B). Fragmentation remained low throughout the postglacial (mean of 4%) but reached up to 8% in the deglacial and peaked at 16% in samples from the Bølling-Allerød of the late glacial interval. Samples from the Bølling-Allerød and the deglacial interval also display a slightly elevated B/P index (>0.15), which suggests that some dissolution may have occurred. In contrast, with the exception of the Bølling-Allerød and the deglacial interval, near zero OL/B values characterize most of the sequence, suggesting good biogenic carbonate preservation, which implies that the low biogenic carbonate and coccolith content in sediments of the glacial stage mirror low productivity of calcifying organisms. The elevated fragmentation of foraminifers during the Bølling-Allerød and the deglacial interval, a time of elevated productivity and low percentages of ice-rafted debris, may indicate the development of calcite undersaturated porewaters and consequent dissolution resulting from oxic remineralization of sedimentary organic matter. We also identify a significant decoupling of coccolith and alkenone concentrations throughout the core. Colder-than-expected UK37-SST estimates from the alkenones of the glacial interval rule out possible allochthonous inputs from lower-latitude locations. Instead, our records imply that at least during the glacial interval, alkenones were produced by non-calcifying haptophytes that may not follow the canonical UK37-based temperature calibrations.

Annual cycle of biogenic carbon export in the Gulf of St. Lawrence

A multi-institutional initiative was created in a context of potential oil exploration at the Old Harry site to monitor the marine ecosystem and manage resources of the Gulf of St. Lawrence (GSL). As part of this initiative, two sediment traps were deployed at depths of 34 m and 100 m at a site northwest of Cabot Strait in the Laurentian Channel to measure downward carbon fluxes from October 2014 to October 2015. Fluxes of particulate organic carbon (POC), biogenic silica (BSi), chloropigments, protists and zooplankton fecal pellets were used to evaluate vertical and temporal changes in the magnitude and composition of biogenic carbon fluxes and to provide baseline information prior to any exploration activities in the region. Peaks in POC, BSi, chloropigment and diatom fluxes at both depths at the end of April 2015 indicated the rapid export of a locally-produced bloom mainly composed of pennate diatoms. A coincident peak in fecal pellet carbon fluxes at 100 m indicated a match between the spring ascent of copepods and the diatom bloom. The distinct composition of protist fluxes at 34 and 100 m following the formation of the winter mixed layer highlighted the influence of the pycnocline as a physical barrier for the export of particles in the region. Among identifiable components, dinoflagellates and fecal pellets, followed by diatoms and foraminifera, contributed most to the annual POC flux at 100 m, indicating a balance between lateral advection of slow-sinking protists and rapid export of fast-sinking diatoms and fecal pellets in the supply of POC toward the seafloor in the GSL. These measurements of biogenic carbon export provide insight into the fate of large and small particles in the Cabot Strait region to consider in the potential development of oil and gas activities.

Vertical niche definition of test‐bearing protists (Rhizaria) into the twilight zone revealed by in situ imaging

AbstractThe Rhizaria is a super‐group of amoeboid protists with ubiquitous distributions, from the euphotic zone to the twilight zone and beyond. While rhizarians have been recently described as important contributors to both biogenic silica and carbon fluxes, we lack the most basic information about their ecological habitats and preferences. Here, using in situ imaging (Underwater Vision Profiler 5), we characterize the vertical ecological niches of different test‐bearing pelagic rhizarian taxa in the southernCalifornia Current Ecosystem. We define three vertical layers between 0 and 500 m occupied, respectively, by (1) surface dwelling and mostly symbiont‐bearing rhizarians (Acantharia and Collodaria), (2) flux‐feeding phaeodarians in the lower epipelagic (100–200 m), and (3) Foraminifera and Phaeodaria populations adjacent to the oxygen minimum zone. We then use Generalized Additive Models to analyze the response of each rhizarian category to a suite of environmental variables. The models explain between 9% and 93% of the total variance observed for the different groups. While temperature and the depth of the deep chlorophyll maximum appear as the main abiotic factors influencing populations in the upper 200 m, dissolved silicon concentration is related to the abundance of mesopelagic phaeodarians, though it explains only a portion of the variance. The importance of biotic interactions (e.g., prey availability, predation, parasitism, symbiosis) is still to be considered, in order to fully incorporate the dynamics of test‐bearing pelagic rhizarians in ecological and biogeochemical models.

Including albedo in time‐dependent LCA of bioenergy

AbstractAlbedo change during feedstock production can substantially alter the life cycle climate impact of bioenergy. Life cycle assessment (LCA) studies have compared the effects of albedo and greenhouse gases (GHGs) based on global warming potential (GWP). However, using GWP leads to unequal weighting of climate forcers that act on different timescales. In this study, albedo was included in the time‐dependent LCA, which accounts for the timing of emissions and their impacts. We employed field‐measured albedo and life cycle emissions data along with time‐dependent models of radiative transfer, biogenic carbon fluxes and nitrous oxide emissions from soil. Climate impacts were expressed as global mean surface temperature change over time (∆T) and as GWP. The bioenergy system analysed was heat and power production from short‐rotation willow grown on former fallow land in Sweden. We found a net cooling effect in terms of ∆T per hectare (−3.8 × 10–11 K in year 100) and GWP100 per MJ fuel (−12.2 g CO2e), as a result of soil carbon sequestration via high inputs of carbon from willow roots and litter. Albedo was higher under willow than fallow, contributing to the cooling effect and accounting for 34% of GWP100, 36% of ∆T in year 50 and 6% of ∆T in year 100. Albedo dominated the short‐term temperature response (10–20 years) but became, in relative terms, less important over time, owing to accumulation of soil carbon under sustained production and the longer perturbation lifetime of GHGs. The timing of impacts was explicit with ∆T, which improves the relevance of LCA results to climate targets. Our method can be used to quantify the first‐order radiative effect of albedo change on the global climate and relate it to the climate impact of GHG emissions in LCA of bioenergy, alternative energy sources or land uses.

A Multiyear Gridded Data Ensemble of Surface Biogenic Carbon Fluxes for North America: Evaluation and Analysis of Results

AbstractAccurate and fine‐scale estimates of biogenic carbon fluxes are critical for measuring and monitoring the biosphere's responses and feedback to the climate system. Currently available data products from flux towers and model‐intercomparison projects struggle to adequately represent spatiotemporal dynamics of surface biogenic carbon fluxes, and to quantify their uncertainties, which also are crucial to atmospheric inversion systems. To address these gaps, we introduce a new perturbed‐parameter model ensemble with the CASA model to estimate surface biogenic carbon fluxes at monthly and 3‐hourly scales for North America at ~500‐m and 5‐km resolutions. We first use the Extended Fourier Amplitude Sensitivity Testing to choose the three most sensitive parameters to be perturbed, maximum light use efficiency (Emax), optimal temperature of photosynthesis (Topt), and temperature response of respiration (Q10). The initial range for each parameter is broadly sampled for the L1 ensemble, but then we pruned Emax with site‐level primary productivity to derive an L2 ensemble with narrower uncertainty ranges. Ensembles are strongly correlated with site‐level results at both monthly and 3‐hourly scales, and the spread across L1/L2 ensemble members encompasses the range of AmeriFlux observations. Monthly variability in the L2 ensemble mean is 85% of the observed variability. The L2 ensemble outperforms diverse data products with the highest Taylor skill scores at diurnal to annual scales. The ensemble's seasonality agrees well with other models for most biome types and in high and middle latitudes, but inconsistencies are found in subtropical and tropical ecoregions and for annual totals over North America.

Seasonal Characteristics of Model Uncertainties From Biogenic Fluxes, Transport, and Large‐Scale Boundary Inflow in Atmospheric CO2 Simulations Over North America

AbstractRegional estimates of biogenic carbon fluxes over North America from both atmospheric inversions (“top‐down” approach) and terrestrial biosphere models (“bottom‐up”) remain highly uncertain. We merge these approaches with an ensemble‐based, regional modeling system able to diagnose and quantify the causes of uncertainties in top‐down atmospheric estimates of the terrestrial sink over North America. Our ensemble approach quantifies and partitions the uncertainty stemming from atmospheric transport, the biosphere, and large‐scale CO2 boundary inflow (boundary conditions). We use meteorological data, CO2 fluxes, and CO2 mole fraction measurements to assure the reliability of the ensemble system. Our results show that all uncertainty components have clear seasonal variations. The biogenic flux component dominates modeled boundary layer CO2 uncertainty, ranging from 2.5 ppm in summer and winter to 1.5 ppm in fall and spring. Spatially, it remains highly uncertain in the U.S. Corn Belt regions. Transport uncertainty reaches a maximum of 2.5 ppm in the summer months and stays at 1.2 ppm for the rest of the year and is highly correlated with the biogenic CO2 fluxes. Boundary conditions play the smallest role in atmospheric boundary layer CO2 uncertainty with a magnitude smaller than 1 ppm. However, boundary conditions are the most important uncertainty component in column‐averaged CO2 (XCO2). The spatiotemporal variations of the uncertainties in modeled XCO2 are similar to those in atmospheric boundary layer CO2.

Coccolithophore export in three deep-sea sites of the Aegean and Ionian Seas (Eastern Mediterranean): Biogeographical patterns and biogenic carbonate fluxes

Coccolithophore export fluxes were investigated via the analysis of sinking matter, obtained from Eastern Mediterranean time-series sediment traps moored in three open sites of the north-eastern Mediterranean Sea located in the Athos Basin of North Aegean (M2 site), Cretan Sea of South Aegean (M3 site) and at Ionian Sea (Nestor site). The aim of our study was to determine the spatial, temporal and seasonal variability in coccolithophore fluxes, as well as to estimate coccolith biogenic carbonate contribution to the sedimentation process. Data from an additional time-series sediment trap located in the southwestern Black Sea were also considered for the comparison of the oligotrophic Eastern Mediterranean setting with the eutrophic Black Sea. Coccolithophore fluxes revealed a highly seasonal pattern during February–March in the North Aegean (peak in late February 2015: 85.6 x 105 coccospheres m−2 day−1; 27.9 x 108 coccoliths m−2 day−1), during March–May in the Cretan Sea (peak in late March 2015: 33.7 x 105 coccospheres m−2 day−1; 19.5 x 108 coccoliths m−2 day−1) and during February–March and May–June in the Ionian Sea (peak in late May 2012: 14.3 x 105 coccospheres m−2 day−1; 1.53 x 108 coccoliths m−2 day−1). The recorded maxima coincide with low sea surface temperatures, increased precipitation and high PIC fluxes. Coccosphere fluxes were dominated by Emiliania huxleyi comprising ~70% of the total abundance, in the North Aegean and ~50% in the Cretan and Ionian Seas. Syracosphaera pulchra was also prominent in the study sites, where its abundance reached 14% in the North Aegean and ~10% in the Cretan and Ionian Seas respectively. Florisphaera profunda represented one of the major taxa in the coccolith fluxes of all three Eastern Mediterranean sites (~25% in North Aegean, ~20% in Cretan and Ionian Seas), while Algirosphaera robusta and Umbilicosphaera sibogae were the most abundant among the minor taxa. The North Aegean Sea exhibited a considerably higher coccolith flux when compared to other sediment traps due to the prominent seasonal peak of E. huxleyi during winter (February–March) (>95% of the total abundance). In contrast to the Eastern Mediterranean sediment traps, the time-series data from the Black Sea showed presence of monospecific E. huxleyi assemblage increasing its abundance during late September–November (max 320 x 105 coccospheres m−2 day−1; at least 7.79 x 108 coccoliths m−2 day−1, coccolith flux derived only from coccospheres converted to coccoliths). In the Eastern Mediterranean, biogenic carbonate fluxes followed the general pattern of the total mass flux in all investigated areas, with the Black Sea coccolithophore CaCO3 flux being the lowest due to low the E. huxleyi coccolith mass. Overall, in the North Aegean Sea, coccolithophore fluxes are strongly dependent on surface waters nutrients enrichment due to winter vertical water column mixing, riverine inputs and Black Sea water inflows, while the fertilization and/or formation of fast-sinking aggregates due to episodic dust input event are affecting the coccolithophore fluxes in the Cretan and Ionian Seas. The intercomparison of the coccolith export fluxes in the studied NE-SW mooring transects implies a north-south and east-west decreasing pattern, depending on the variable oceanographic regimes and the associated environmental factors controlling the investigated areas.

Quantifying the climate change effects of bioenergy systems: Comparison of 15 impact assessment methods

AbstractOngoing concern over climate change has led to interest in replacing fossil energy with bioenergy. There are different approaches to quantitatively estimate the climate change effects of bioenergy systems. In the present work, we have focused on a range of published impact assessment methods that vary due to conceptual differences in the treatment of biogenic carbon fluxes, the type of climate change impacts they address and differences in time horizon and time preference. Specifically, this paper reviews fifteen different methods and applies these to three hypothetical bioenergy case studies: (a) woody biomass grown on previously forested land; (b) woody biomass grown on previous pasture land; and (b) annual energy crop grown on previously cropped land. Our analysis shows that the choice of method can have an important influence on the quantification of climate change effects of bioenergy, particularly when a mature forest is converted to bioenergy use as it involves a substantial reduction in biomass carbon stocks. Results are more uniform in other case studies. In general, results are more sensitive to specific impact assessment methods when they involve both emissions and removals at different points in time, such as for forest bioenergy, but have a much smaller influence on agricultural bioenergy systems grown on land previously used for pasture or annual cropping. The development of effective policies for climate change mitigation through renewable energy use requires consistent and accurate approaches to identification of bioenergy systems that can result in climate change mitigation. The use of different methods for the same purpose: estimating the climate change effects of bioenergy systems, can lead to confusing and contradictory conclusions. A full interpretation of the results generated with different methods must be based on an understanding that the different methods focus on different aspects of climate change and represent different time preferences.

Climate impact and energy efficiency of woody bioenergy systems from a landscape perspective

The climate impact of bioenergy is debated, especially due to potential land use change effects and biogenic carbon fluxes. This study assessed the climate impact and energy efficiency of conventional long-rotation forest residues (branches, tops and stumps) and short-rotation forestry (willow) from a landscape perspective. A time-dependent life cycle assessment method, which considers the timing of biogenic carbon fluxes and the impact on global temperature over time, was combined with GIS mapping to assess the impact for a specific Swedish region (Uppsala County), i.e. a ‘real’ landscape. The results showed that harvesting forest residues decreased the forest carbon stocks over the landscape, while growing willow on previous fallow land increased the total carbon stocks. On average, energy ratios of 49 MJ MJ−1 for branches and tops, and 30 MJ MJ−1 for stumps and willow was found. Harvesting forest residues from the studied landscape resulted in climate impacts of around 0.8∙10−15 K MJ−1 heat for branches and tops, and 1.3∙10−15 K MJ−1 heat for stumps. Willow energy gave the lowest climate impact of about −0.6∙10−15 K MJ−1 heat. The landscape analysis showed that spatial variations in the region had an effect on energy efficiency and climate impact, but that this effect was relatively small. A more important factor was the time frame chosen for the analysis, especially for long-rotation forest systems. Methodological choices such as spatial scale (stand or landscape perspective), allocation method and functional unit also influenced the results.

Small copepods could channel missing carbon through metazoan predation.

Global ecosystem models are essential tools for predicting climate change impacts on marine systems. Modeled biogenic carbon fluxes in the ocean often match measured data poorly and part of this could be because small copepods (<2 mm) are modeled as unicellular feeders grazing on phytoplankton and microzooplankton. The most abundant copepods from a seasonal upwelling region of the Eastern North Atlantic were sorted, and a molecular method was applied to copepod gut contents to evaluate the extent of metazoan predation under two oceanographic conditions, a trophic pathway not accounted for in global models. Scaling up the results obtained herein, based on published field and laboratory estimates, suggests that small copepods could ingest 1.79–27.20 gigatons C/year globally. This ignored metazoan‐copepod link could increase current estimates of biogeochemical fluxes (remineralization, respiration, and the biological pump) and export to higher trophic levels by 15.6%–24.4%. It could also account for global discrepancies between measured daily ingestion and copepod metabolic demand/growth. The inclusion of metazoan predation into global models could provide a more realistic role of the copepods in the ocean and if these preliminary data hold true at larger sample sizes and scales, the implications would be substantial at the global scale.

Atmospheric CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; inversions on the mesoscale using data-driven prior uncertainties: quantification of the European terrestrial CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes

Abstract. Optimized biogenic carbon fluxes for Europe were estimated from high-resolution regional-scale inversions, utilizing atmospheric CO2 measurements at 16 stations for the year 2007. Additional sensitivity tests with different data-driven error structures were performed. As the atmospheric network is rather sparse and consequently contains large spatial gaps, we use a priori biospheric fluxes to further constrain the inversions. The biospheric fluxes were simulated by the Vegetation Photosynthesis and Respiration Model (VPRM) at a resolution of 0.1° and optimized against eddy covariance data. Overall we estimate an a priori uncertainty of 0.54 GtC yr−1 related to the poor spatial representation between the biospheric model and the ecosystem sites. The sink estimated from the atmospheric inversions for the area of Europe (as represented in the model domain) ranges between 0.23 and 0.38 GtC yr−1 (0.39 and 0.71 GtC yr−1 up-scaled to geographical Europe). This is within the range of posterior flux uncertainty estimates of previous studies using ground-based observations.

Greenhouse gas emissions of local wood pellet heat from northeastern US forests

We explored greenhouse gas (GHG) implications of locally-sourced and produced wood pellets to heat homes in the US Northern Forest region. Using data from regional pellet industries, forest inventories and harvests, we analyzed pellet GHG emissions across a range of harvest and forest product market scenarios over 50 years. We expanded an existing life cycle assessment (LCA) tool, the Forest Sector Greenhouse Gas Assessment Tool for Maine (ForGATE) to calculate GHG balances associated with the harvest, processing, and use of wood pellets for residential heating vs. alternative heating fuels. Market assumptions and feedstock mix can create diverging GHG emission profiles for pellet heat. Outcomes are predominantly influenced by biogenic carbon fluxes in the forest carbon pool. An industry-average pellet feedstock mix (50% sawmill residues, 50% pulpwood) appeared to generate heat that was at least at parity with fossil-fuel heating alternatives when harvest levels remain unchanged due to pellet production. If harvest levels increase due to pellet production, using pellet heat increased GHG emissions. If baseline harvest levels drop (e.g., following the loss of low-grade markets), GHG emissions from pellet heat would at least remain stable relative to fossil alternatives.

High dark carbon fixation in the tropical South China Sea

Dark carbon fixation (DCF) has been usually assumed to be insignificant in the study of microbial production and carbon cycling. In order to evaluate DCF distribution and its contribution to biogenic carbon flux, surface and vertical distribution of DCF, primary production (PP) and bacterial production (BP) were investigated in both offshore and coastal waters in the South China Sea (SCS). Surface DCF was ~ 0.058μgCL−1h−1 (~ 10% of PP), within the same order of magnitude as BP of ~ 0.047μgCL−1h−1 in the offshore waters. Integrated over the 1500m water column, DCF was ~ 196mgCm−2h−1, corresponding to ~ 384% of PP, and represented a newly produced source of organic matter. This suggested that DCF was an important microbial metabolic pathway in the SCS, which might support ~ 83% carbon demand of heterotrophic prokaryotes. Interestingly, the DCF was higher in the deep water (~ 0.140μgCL−1h−1) than the surface water (~ 0.089μgCL−1h−1). In addition to the different microbial community, this different vertical distribution of DCF was likely due to the nutrient status, as our nutrient enrichment experiment showed that the addition of glucose, ammonium and phosphate stimulated the DCF rates, especially the addition of glucose plus ammonium.

Accounting for urban biogenic fluxes in regional carbon budgets

Many ecosystem models incorrectly treat urban areas as devoid of vegetation and biogenic carbon (C) fluxes. We sought to improve estimates of urban biomass and biogenic C fluxes using existing, nationally available data products. We characterized biogenic influence on urban C cycling throughout Massachusetts, USA using an ecosystem model that integrates improved representation of urban vegetation, growing conditions associated with urban heat island (UHI), and altered urban phenology. Boston's biomass density is 1/4 that of rural forests, however 87% of Massachusetts' urban landscape is vegetated. Model results suggest that, kilogram-for-kilogram, urban vegetation cycles C twice as fast as rural forests. Urban vegetation releases (RE) and absorbs (GEE) the equivalent of 11 and 14%, respectively, of anthropogenic emissions in the most urban portions of the state. While urban vegetation in Massachusetts fully sequesters anthropogenic emissions from smaller cities in the region, Boston's UHI reduces annual C storage by >20% such that vegetation offsets only 2% of anthropogenic emissions. Asynchrony between temporal patterns of biogenic and anthropogenic C fluxes further constrains the emissions mitigation potential of urban vegetation. However, neglecting to account for biogenic C fluxes in cities can impair efforts to accurately monitor, report, verify, and reduce anthropogenic emissions.