scholarly journals Rapidly changing high-latitude seasonality: Implications for the 21st century carbon cycle in Alaska

2021 ◽  
Author(s):  
Ian A Shirley ◽  
Zelalem A. Mekonnen ◽  
Robert F Grant ◽  
Baptiste Dafflon ◽  
Susan Hubbard ◽  
...  
Keyword(s):  
21St Century ◽  
High Latitude ◽  
Process Model ◽  
N Uptake ◽  
Net Ecosystem Exchange ◽  
Plant Productivity ◽  
Environmental Drivers ◽  
Spring Temperature ◽  
C Cycle ◽  
Temperature Limitation

Abstract Seasonal variations in high-latitude terrestrial carbon (C) fluxes are predominantly driven by air temperature and radiation. At present, high-latitude net C uptake is largest during the summer. Recent observations and modeling studies have demonstrated that ongoing and projected climate change will increase plant productivity, microbial respiration, and growing season lengths at high-latitudes, but impacts on high-latitude C cycle seasonality (and potential feedbacks to the climate system) remain uncertain. Here we use ecosys, a well-tested and process-rich mechanistic ecosystem model that we evaluate further in this study, to explore how climate warming under an RCP8.5 scenario will shift C cycle seasonality in Alaska throughout the 21st century. The model successfully reproduced recently reported large high-latitude C losses during the fall and winter and yet still predicts a high-latitude C sink, pointing to a resolution of the current conflict between process-model and observation-based estimates of high-latitude C balance. We find that warming will result in surprisingly large changes in net ecosystem exchange (NEE; defined as negative for uptake) seasonality, with spring net C uptake overtaking summer net C uptake by year 2100. This shift is driven by a factor of 3 relaxation of spring temperature limitation to plant productivity that results in earlier C uptake and a corresponding increase in magnitude of spring NEE from -19 to -144 gC m-2 season-1 by the end of the century. Although a similar relaxation of temperature limitation will occur in the fall, radiation limitation during those months will limit increases in C fixation. Additionally, warmer soil temperatures and increased carbon inputs from plants lead to combined fall and winter C losses (163 gC m-2) that are larger than summer net uptake (123 gC m-2 season-1) by year 2100. However, this increase in microbial activity leads to more rapid N cycling and increased plant N uptake during the fall and winter months that supports large increases in spring NPP. Due to the large increases in spring net C uptake, the high-latitude atmospheric C sink is projected to sustain throughout this century. Our analysis disentangles the effects of key environmental drivers of high-latitude seasonal C balances as climate changes over the 21st century.

scholarly journals From sink to source: long-term (2002-2019) trends and anomalies in net ecosystem exchange of CO2 from a Scottish temperate peatland.

2020 ◽  
Author(s):  
Karen Hei-Laan Yeung ◽  
Carole Helfter ◽  
Neil Mullinger ◽  
Mhairi Coyle ◽  
Eiko Nemitz
Keyword(s):  
Water Table ◽  
Ecosystem Respiration ◽  
Net Ecosystem Exchange ◽  
Growing Season ◽  
Water Table Depth ◽  
Sink Strength ◽  
Summer Drought ◽  
C Cycle ◽  
Dry Spell

<p>Peatlands North of 45˚ represent one of the largest terrestrial carbon (C) stores. They play an important role in the global C-cycle, and their ability to sequester carbon is controlled by multiple, often competing, factors including precipitation, temperature and phenology. Land-atmosphere exchange of carbon dioxide (CO<sub>2</sub>) is dynamic, and exhibits marked seasonal and inter-annual variations which can effect the overall carbon sink strength in both the short- and long-term.</p><p>Due to increased incidences of climate anomalies in recent years, long-term datasets are essential to disambiguate natural variability in Net Ecosystem Exchange (NEE) from shorter-term fluctuations. This is particularly important at high latitudes (>45˚N) where the majority of global peatlands are found. With increasing pressure from stressors such as climate and land-use change, it has been predicted that with a ca. 3<sup>o</sup>C global temperature rise by 2100, UK peatlands could become a net source of C.</p><p>NEE of CO<sub>2</sub> has been measured using the eddy-covariance (EC) method at Auchencorth Moss (55°47’32 N, 3°14’35 W, 267 m a.s.l.), a temperate, lowland, ombrotrophic peatland in central Scotland, continuously since 2002. Alongside EC data, we present a range of meteorological parameters measured at site including soil temperature, total solar and photosynthetically active radiation (PAR), rainfall, and, since April 2007, half-hourly water table depth readings. The length of record and range of measurements make this dataset an important resource as one of the longest term records of CO<sub>2</sub> fluxes from a temperate peatland.</p><p>Although seasonal cycles of gross primary productivity (GPP) were highly variable between years, the site was a consistent CO<sub>2</sub> sink for the period 2002-2012. However, net annual losses of CO<sub>2</sub> have been recorded on several occasions since 2013. Whilst NEE tends to be positively correlated with the length of growing season, anomalies in winter weather also explain some of the variability in CO<sub>2</sub> sink strength the following summer.</p><p>Additionally, water table depth (WTD) plays a crucial role, affecting both GPP and ecosystem respiration (R<sub>eco</sub>). Relatively dry summers in recent years have contributed to shifting the balance between R<sub>eco</sub> and GPP: prolonged periods of low WTD were typically accompanied by an increase in R<sub>eco</sub>, and a decrease in GPP, hence weakening the overall CO<sub>2</sub> sink strength. Extreme events such as drought periods and cold winter temperatures can have significant and complex effects on NEE, particularly when such meteorological anomalies co-occur. For example, a positive annual NEE occurred in 2003 when Europe experienced heatwave and summer drought. More recently, an unusually long spell of snow lasting until the end of March delayed the onset of the 2018 growing season by up to 1.5 months compared to previous years. This was followed by a prolonged dry spell in summer 2018, which weakened GPP, increased R<sub>eco</sub> and led to a net annual loss of 47.4 ton CO<sub>2</sub>-C km<sup>-2</sup>. It is clear that the role of Northern peatlands within the carbon cycle is being modified, driven by changes in climate at both local and global scales.</p>

scholarly journals Diverging responses of high-latitude CO<sub>2</sub> and CH<sub>4</sub> emissions in idealized climate change scenarios

2020 ◽  
Author(s):  
Philipp de Vrese ◽  
Tobias Stacke ◽  
Thomas Kleinen ◽  
Victor Brovkin
Keyword(s):  
Climate Change ◽  
Organic Matter ◽  
Global Warming ◽  
21St Century ◽  
High Latitude ◽  
Climate Change Scenarios ◽  
Climate Scenarios ◽  
Soil Co2 ◽  
Linear Dependency ◽  
Soil Co2 Emissions

Abstract. The present study investigates the response of the high latitude's carbon cycle to in- and decreasing atmospheric greenhouse gas (GHG) concentrations in idealized climate change scenarios. For this, we use an adapted version of JSBACH – the land-surface component of the Max-Planck-Institute for Meteorology's Earth system model (MPI-ESM) – that accounts for the organic matter stored in the permafrost-affected soils of the high northern latitudes. To force the model, we use different climate scenarios that assume an increase in GHG concentrations, following the Shared Socioeconomic Pathway 5, until peaks in the years 2025, 2050, 2075 or 2100, respectively. The peaks are followed by a decrease in atmospheric GHGs that returns the concentrations to the levels at the beginning of the 21st century. We show that the soil CO2 emissions exhibit an almost linear dependency on the global mean surface temperatures that are simulated for the different climate scenarios. Here, each degree of warming increases the fluxes by, very roughly, 50 % of their initial value, while each degree of cooling decreases them correspondingly. However, the linear dependency does not mean that the processes governing the soil CO2 emissions are fully reversible on short timescales, but rather that two strongly hysteretic factors offset each other – namely the vegetation's net primary productivity and the availability of formerly frozen soil organic matter. In contrast, the soil methane emissions show almost no increase with rising temperatures and they are consistently lower after than prior to a peak in the GHG concentrations. Here, the fluxes can even become negative and we find that methane emissions will play only a minor role in the northern high latitudes' contribution to global warming, even when considering the gas's high global warming potential. Finally, we find that the high-latitude ecosystem acts as a source of atmospheric CO2 rather than a sink, with the net fluxes into the atmosphere increasing substantially with rising atmospheric GHG concentrations. This is very different to scenario simulations with the standard version of the MPI-ESM in which the region continues to take up atmospheric CO2 throughout the entire 21st century, confirming that the omission of permafrost-related processes and the organic matter stored in the frozen soils leads to a fundamental misrepresentation of the carbon dynamics in the Arctic.

scholarly journals Small-Scale Forest Structure Influences Spatial Variability of Belowground Carbon Fluxes in a Mature Mediterranean Beech Forest

Forests ◽  
2020 ◽  
Vol 11 (3) ◽  
pp. 255 ◽  
Author(s):  
Ettore D’Andrea ◽  
Gabriele Guidolotti ◽  
Andrea Scartazza ◽  
Paolo De Angelis ◽  
Giorgio Matteucci
Keyword(s):  
Spatial Variability ◽  
Forest Structure ◽  
Net Primary Production ◽  
Beech Forest ◽  
Environmental Drivers ◽  
Root Production ◽  
Small Scale ◽  
Co2 Efflux ◽  
Area Index ◽  
C Cycle

The tree belowground compartment, especially fine roots, plays a relevant role in the forest ecosystem carbon (C) cycle, contributing largely to soil CO2 efflux (SR) and to net primary production (NPP). Beyond the well-known role of environmental drivers on fine root production (FRP) and SR, other determinants such as forest structure are still poorly understood. We investigated spatial variability of FRP, SR, forest structural traits, and their reciprocal interactions in a mature beech forest in the Mediterranean mountains. In the year of study, FRP resulted in the main component of NPP and explained about 70% of spatial variability of SR. Moreover, FRP was strictly driven by leaf area index (LAI) and soil water content (SWC). These results suggest a framework of close interactions between structural and functional forest features at the local scale to optimize C source–sink relationships under climate variability in a Mediterranean mature beech forest.

scholarly journals A systematic approach for comparing modeled biospheric carbon fluxes across regional scales

2011 ◽  
Vol 8 (6) ◽  
pp. 1579-1593 ◽  
Author(s):  
D. N. Huntzinger ◽  
S. M. Gourdji ◽  
K. L. Mueller ◽  
A. M. Michalak
Keyword(s):  
Variable Selection ◽  
Spatial Variability ◽  
Carbon Flux ◽  
Systematic Approach ◽  
Ecosystem Respiration ◽  
Net Ecosystem Exchange ◽  
Environmental Drivers ◽  
Model Formulation ◽  
Variogram Analysis ◽  
Fire Emissions

Abstract. Given the large differences between biospheric model estimates of regional carbon exchange, there is a need to understand and reconcile the predicted spatial variability of fluxes across models. This paper presents a set of quantitative tools that can be applied to systematically compare flux estimates despite the inherent differences in model formulation. The presented methods include variogram analysis, variable selection, and geostatistical regression. These methods are evaluated in terms of their ability to assess and identify differences in spatial variability in flux estimates across North America among a small subset of models, as well as differences in the environmental drivers that best explain the spatial variability of predicted fluxes. The examined models are the Simple Biosphere (SiB 3.0), Carnegie Ames Stanford Approach (CASA), and CASA coupled with the Global Fire Emissions Database (CASA GFEDv2), and the analyses are performed on model-predicted net ecosystem exchange, gross primary production, and ecosystem respiration. Variogram analysis reveals consistent seasonal differences in spatial variability among modeled fluxes at a 1° × 1° spatial resolution. However, significant differences are observed in the overall magnitude of the carbon flux spatial variability across models, in both net ecosystem exchange and component fluxes. Results of the variable selection and geostatistical regression analyses suggest fundamental differences between the models in terms of the factors that explain the spatial variability of predicted flux. For example, carbon flux is more strongly correlated with percent land cover in CASA GFEDv2 than in SiB or CASA. Some of the differences in spatial patterns of estimated flux can be linked back to differences in model formulation, and would have been difficult to identify simply by comparing net fluxes between models. Overall, the systematic approach presented here provides a set of tools for comparing predicted grid-scale fluxes across models, a task that has historically been difficult unless standardized forcing data were prescribed, or a detailed sensitivity analysis performed.

Weebly, Wikis, and Digital Storytelling

2013 ◽  
pp. 1104-1114 ◽  
Author(s):  
Brian Kissel
Keyword(s):  
Web 2.0 ◽  
21St Century ◽  
Process Model ◽  
Digital Storytelling ◽  
New Technologies ◽  
Digital Technologies ◽  
Digital Portfolios ◽  
Web 2.0 Tools ◽  
Online Technologies ◽  
K 12

In this chapter, the author explores three questions: 1. How is the practice of writing in K-12 classrooms influenced by this era of new technologies? 2. How can online technologies be brought into the classroom so students can understand that they read and write everyday in digital forms? 3. In what ways can teachers create technology-rich experiences to support 21st century writers? To answer these questions the author briefly examines the theoretical foundation of the process model for writing and how online technologies have impacted this model in classrooms. Next, the author describes three Web 2.0 tools that are available to teachers to use in their classrooms during writing: digital portfolios, wikis, and digital storytelling. The author explains how he uses these tools within his own college classroom. Finally, the author provides a rationale for why teachers should consider using these within their own K-12 classrooms so that digital technologies become a natural part of students’ writing experiences.

Influence of spatial coherence of temperature anomalies on the supposed breakdown of the warmer spring – larger carbon uptake mechanism in northern high latitudes

2020 ◽  
Author(s):  
Peter Joyce ◽  
Manuel Gloor ◽  
Roel Brienen ◽  
Wolfgang Buermann
Keyword(s):  
High Latitude ◽  
Large Scale ◽  
Atmospheric Transport ◽  
Carbon Uptake ◽  
High Latitudes ◽  
Spring Temperature ◽  
Uptake Mechanism ◽  
Temperature Anomalies ◽  
Northern High Latitude ◽  
Significant Change

&lt;p&gt;Land vegetation growth in the northern high latitudes (north of 50&amp;#730;N) is strongly temperature limited, thus anomalously warm years are expected to result in an increased drawdown of Carbon Dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) and vice versa. Piao et al (2017) concluded in an analysis of climate and CO&lt;sub&gt;2&lt;/sub&gt; data from Point Barrow, Alaska that there was a weakening response of northern high latitude spring carbon uptake to temperature anomalies over the last 40 years. They proposed that this is due to a weakening control of temperature on productivity. We have analysed northern high latitude climate and remote sensing vegetation indices, as well as atmospheric CO&lt;sub&gt;2&lt;/sub&gt; data at Point Barrow, with atmospheric transport analyses of the footprint seen at Barrow. Our results show no large-scale significant change in the spring NDVI-temperature relationship inside the footprint of Barrow, and across the high northern latitudes as a whole. This casts doubt on the assertion that the changing relationship between CO&lt;sub&gt;2&lt;/sub&gt; uptake and temperature is driven by a change in vegetation response to temperature. We thus tested several alternative mechanisms that could explain the apparent weakening, including a change in interannual variability of atmospheric transport (i.e. the footprint seen by Barrow) and the spatial agreement of temperature anomalies. We find that the heterogeneity of temperature anomalies increased over time, whereas there is no significant change in interannual variation in the footprint seen by Barrow. These results offer an additional explanation for the apparent decrease in spring temperature sensitivity of northern high latitude CO&lt;sub&gt;2&lt;/sub&gt; uptake.&lt;/p&gt;

scholarly journals Predicting Soil Respiration from Plant Productivity (NDVI) in a Sub-Arctic Tundra Ecosystem

2021 ◽  
Vol 13 (13) ◽  
pp. 2571
Author(s):  
Olivia Azevedo ◽  
Thomas C. Parker ◽  
Matthias B. Siewert ◽  
Jens-Arne Subke
Keyword(s):  
Soil Respiration ◽  
Vegetation Index ◽  
Vegetation Type ◽  
Net Ecosystem Exchange ◽  
Plant Productivity ◽  
Ecosystem Monitoring ◽  
Vegetation Communities ◽  
Direct Measurements ◽  
Tundra Ecosystem ◽  
Normalised Difference Vegetation Index

Soils represent the largest store of carbon in the biosphere with soils at high latitudes containing twice as much carbon (C) than the atmosphere. High latitude tundra vegetation communities show increases in the relative abundance and cover of deciduous shrubs which may influence net ecosystem exchange of CO2 from this C-rich ecosystem. Monitoring soil respiration (Rs) as a crucial component of the ecosystem carbon balance at regional scales is difficult given the remoteness of these ecosystems and the intensiveness of measurements that is required. Here we use direct measurements of Rs from contrasting tundra plant communities combined with direct measurements of aboveground plant productivity via Normalised Difference Vegetation Index (NDVI) to predict soil respiration across four key vegetation communities in a tundra ecosystem. Soil respiration exhibited a nonlinear relationship with NDVI (y = 0.202e3.508 x, p < 0.001). Our results further suggest that NDVI and soil temperature can help predict Rs if vegetation type is taken into consideration. We observed, however, that NDVI is not a relevant explanatory variable in the estimation of SOC in a single-study analysis.

scholarly journals Humic surface waters of frozen peat bogs (permafrost zone) are highly resistant to bio- and photodegradation

2019 ◽  
Author(s):  
Liudmila S. Shirokova ◽  
Artem V. Chupakov ◽  
Svetlana A. Zabelina ◽  
Natalia V. Neverova ◽  
Dahedrey Payandi-Rolland ◽  
...  
Keyword(s):  
Organic Matter ◽  
High Temperature ◽  
Dissolved Organic Matter ◽  
Water Column ◽  
Surface Waters ◽  
High Latitude ◽  
Peat Bogs ◽  
Photo Degradation ◽  
Thermokarst Lake ◽  
C Cycle

Abstract. Bio- and photo-degradation of dissolved organic matter (DOM) is identified as dominant vector of C cycle in boreal and high-latitude surface waters. In contrast to large number of studies of humic waters from permafrost-free regions and oligotrophic waters from permafrost-bearing regions, the bio- and photo-lability of DOM from humic surface waters of permafrost-bearing regions has not been thoroughly evaluated. Following standardized methods, we measured biodegradation (low, intermediate, high temperature) and photodegradation (one intermediate temperature) of DOM in surface waters along the hydrological continuum (depression → stream → thermokarst lake → river Pechora) within a European Russian frozen peatland. In all systems, there was no measurable (≥ 10 %) bio- or photodegradation of DOM over 1 month of incubation. It is possible that the main cause of the lack of degradation is the dominance of allochthonous refractory (soil, peat) DOM in all studied waters. Yet, all surface waters were supersaturated with CO2. Thus, this study suggest that, rather than bio- and photo-degradation of DOM in the water column, other factors such as peat porewater DOM processing and respiration of sediments are the main drivers of elevated pCO2 and emission in humic boreal waters of frozen peat bogs.

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