nasa-gesdisc/es-publications-researchareas huggingface dataset:
The impacts of biomass burning activities on convective systems over the Maritime Continent (2020)

Abstract. Convective precipitation associated with Sumatra squall lines and diurnal rainfall over Borneo is an important weather feature of the Maritime Continent in Southeast Asia. Over the past few decades, biomass burning activities have been widespread during summertime over this region, producing massive fire aerosols. These additional aerosols, when brought into the atmosphere, besides influencing the local radiation budget through directly scattering and absorbing sunlight, can also act as cloud condensation nuclei or ice nuclei to alter convective clouds and precipitation over the Maritime Continent via so-called aerosol indirect effects. Based on 4-month simulations with or without biomass burning aerosols, conducted using the Weather Research and Forecasting model coupled with a chemistry module (WRF-Chem), we have investigated the aerosolcloud interactions associated with biomass burning aerosols over the Maritime Continent. Results from selected cases of convective events have specifically shown the significant impact of fire aerosols on weak convections by their increasing of the quantities of hydrometeors and rainfall in both the Sumatra and Borneo regions. Statistical analysis over the fire season also suggests that fire aerosols have impacts on the nocturnal convections associated with the local anticyclonic circulation in western Borneo and weaken nocturnal rainfall intensity by about 9 %. Such an effect is likely to have come from the near-surface heating due to absorbing aerosols emitted from fires, which could weaken land breezes and thus the convergence of anticyclonic circulation.

Research areas: Environmental Impacts, Atmospheric/Ocean Indicators
Ocean carbonate system variability in the North Atlantic Subpolar surface water (1993–2017) (2020)

Abstract. The North Atlantic is one of the major ocean sinks for natural and anthropogenic atmospheric CO2. Given the variability of the circulation, convective processes or warmingcooling recognized in the high latitudes in this region, a better understanding of the CO2 sink temporal variability and associated acidification needs a close inspection of seasonal, interannual to multidecadal observations. In this study, we investigate the evolution of CO2 uptake and ocean acidification in the North Atlantic Subpolar Gyre (5064 N) using repeated observations collected over the last 3 decades in the framework of the long-term monitoring program SURATLANT (SURveillance de l'ATLANTique). Over the full period (19932017) pH decreases (0.0017 yr1) and fugacity of CO2 (fCO2) increases (+1.70 atm yr1). The trend of fCO2 in surface water is slightly less than the atmospheric rate (+1.96 atm yr1). This is mainly due to dissolved inorganic carbon (DIC) increase associated with the anthropogenic signal. However, over shorter periods (410 years) and depending on the season, we detect significant variability investigated in more detail in this study. Data obtained between 1993 and 1997 suggest a rapid increase in fCO2 in summer (up to +14 atm yr1) that was driven by a significant warming and an increase in DIC for a short period. Similar fCO2 trends are observed between 2001 and 2007 during both summer and winter, but, without significant warming detected, these trends are mainly explained by an increase in DIC and a decrease in alkalinity. This also leads to a pH decrease but with contrasting trends depending on the region and season (between 0.006 and 0.013 yr1). Conversely, data obtained during the last decade (20082017) in summer show a cooling of surface waters and an increase in alkalinity, leading to a strong decrease in surface fCO2 (between 4.4 and 2.3 atm yr1; i.e., the ocean CO2 sink increases). Surprisingly, during summer, pH increases up to +0.0052 yr1 in the southern subpolar gyre. Overall, our results show that, in addition to the accumulation of anthropogenic CO2, the temporal changes in the uptake of CO2 and ocean acidification in the North Atlantic Subpolar Gyre present significant multiannual variability, not clearly directly associated with the North Atlantic Oscillation (NAO). With such variability it is uncertain to predict the near-future evolution of airsea CO2 fluxes and pH in this region. Thus, it is highly recommended to maintain long-term observations to monitor these properties in the next decade.

Research areas: Atmospheric/Ocean Indicators
Hydrometeorological sensitivities of net ecosystem carbon dioxide and methane exchange of an Amazonian palm swamp peatland (2020)

Tropical peatlands are a major, but understudied, biophysical feedback factor on the atmospheric greenhouse effect. The largest expanses of tropical peatlands are located in lowland areas of Southeast Asia and the Amazon basin. The Loreto Region of Amazonian Peru contains ~63,000 km2 of peatlands. However, little is known about the biogeochemistry of these peatlands, and in particular, the cycling of carbon dioxide (CO2) and methane (CH4), and their responses to hydrometeorological forcings. To address these knowledge gaps, we established an eddy covariance (EC) flux tower in a natural palm (Mauritia flexuosa L.f.) swamp peatland near Iquitos, Peru. Here, we report ecosystem-scale CO2 and CH4 flux observations for this Amazonian palm swamp peatland over a two-year period in relation to hydrometeorological forcings. Seasonal and short-term variations in hydrometeorological forcing had a strong effect on CO2 and CH4 fluxes. High air temperature and vapor pressure deficit (VPD) exerted an important limitation on photosynthesis during the dry season, while latent heat flux appeared to be insensitive to these climate drivers. Evidence from light-response analyses and flux partitioning support that photosynthetic activity was downregulated during dry conditions, while ecosystem respiration (RE) was either inhibited or enhanced depending on water table position. The cumulative net ecosystem CO2 exchange indicated that the peatland was a significant CO2 sink ranging from 465 (279 to 651) g C m2 y1 in 2018 to 462 (277 to 647) g C m2 y1 in 2019. The forest was a CH4 source of 22 (20 to 24) g C m2 y1, similar in magnitude to other tropical peatlands and larger than boreal and arctic peatlands. Thus, the annual carbon budget of this Amazonian palm swamp peatland appears to be a major carbon sink under current hydrometeorological conditions.

Research areas: Ecosystems, Greenhouse Gases
Alternative tree-cover states of the boreal ecosystem: A conceptual model (2019)

AimPrevious analyses of remotely sensed data detected the multimodality of the tree‑cover distribution of the boreal forest, and identified areas with potentially alternative tree‑cover states. This paper aims at investigating the causes of multimodality and multistability of the boreal forest, their influence on the asymmetric tree species distribution between Eurasia and North America, and whether multistability could be associated with recent greening trends in leaf area index (LAI) and normalized difference vegetation index (NDVI).LocationEurasian and North American boreal forests.Time period2000–2010.Major taxa studiedBoreal forest plant functional types.MethodsWe employ a conceptual model based on tree species competition to simulate the sensitivity of tree cover to stochastic disturbances and to changes in environmental factors. We include different plant functional types based on survival adaptations, and force the model with remotely sensed environmental data. We analyse the model as a dynamical system. We use metrics from statistics and information theory to compare the detection of alternative tree‑cover states and greening trends in LAI and NDVI.ResultsWe find that multimodality and multistability can emerge through competition between different plant functional types. Additionally, our model is able to reproduce the asymmetry in tree species distribution between Eurasia and North America. Moreover, changes in permafrost distribution can be associated with phenomenological bifurcation points of the model. Finally, we find that the detection of multistable areas is not affected by recent vegetation trends, whereas shifts between alternative states could have affected the greening trends.Main conclusionsTree‑cover multistability in the boreal region can emerge through competition between species subject to periodic disturbances. Changes in permafrost thaw and distribution could be responsible for the asymmetry in tree species distribution between North America and Eurasia. Climate change and permafrost degradation could cause shifts in tree‑cover states and dominant species. Recent vegetation greening trends in multistable areas could have been affected by shifts between alternative states.

Research areas: Ecosystems, Land Surface/Agriculture Indicators
Eddy-Like Features Near St. Matthew Island, Eastern Bering Sea Shelf: (2020)

The eastern Bering Sea Shelf is characterized by high biological productivity, seasonal sea ice, and commercially important fisheries. Enhanced productivity is often associated with small-scale oceanographic features. Our objective was to use an autonomous underwater vehicle to examine features typically missed by ~20-km spaced shipboard sampling. A coastal glider (Oculus) sampled ~3 dives hr<SUP>-1</SUP> with horizontal spacing of ~300 m per dive in August/September 2017. In the north-south transition zone near St. Matthew Island, the glider sampled four eddy-like features associated with weaker vertical stratification. These features had diameters of 15-20 km and were associated with higher surface chlorophyll. Shipboard data collected in the same region approximately a month later showed that a similar feature was associated with high concentrations of small copepods. Incorporating higher resolution sampling available with gliders into the Bering Sea observing network will improve our understanding of ecosystem response to patchiness in the system.

Research areas: Ecosystems
Biogeophysical feedbacks enhance the Arctic terrestrial carbon sink in regional Earth system dynamics (2014)

Abstract. Continued warming of the Arctic will likely accelerate terrestrial carbon (C) cycling by increasing both uptake and release of C. Yet, there are still large uncertainties in modelling Arctic terrestrial ecosystems as a source or sink of C. Most modelling studies assessing or projecting the future fate of C exchange with the atmosphere are based on either stand-alone process-based models or coupled climateC cycle general circulation models, and often disregard biogeophysical feedbacks of land-surface changes to the atmosphere. To understand how biogeophysical feedbacks might impact on both climate and the C budget in Arctic terrestrial ecosystems, we apply the regional Earth system model RCA-GUESS over the CORDEX-Arctic domain. The model is forced with lateral boundary conditions from an EC-Earth CMIP5 climate projection under the representative concentration pathway (RCP) 8.5 scenario. We perform two simulations, with or without interactive vegetation dynamics respectively, to assess the impacts of biogeophysical feedbacks. Both simulations indicate that Arctic terrestrial ecosystems will continue to sequester C with an increased uptake rate until the 20602070s, after which the C budget will return to a weak C sink as increased soil respiration and biomass burning outpaces increased net primary productivity. The additional C sinks arising from biogeophysical feedbacks are approximately 8.5 Gt C, accounting for 22% of the total C sinks, of which 83.5% are located in areas of extant Arctic tundra. Two opposing feedback mechanisms, mediated by albedo and evapotranspiration changes respectively, contribute to this response. The albedo feedback dominates in the winter and spring seasons, amplifying the near-surface warming by up to 1.35 C in spring, while the evapotranspiration feedback dominates in the summer months, and leads to a cooling of up to 0.81 C. Such feedbacks stimulate vegetation growth due to an earlier onset of the growing season, leading to compositional changes in woody plants and vegetation redistribution.

Research areas: Ecosystems, Land Surface/Agriculture Indicators
The role of geography, environment, and genetic divergence on the distribution of pikas in the Himalaya (2020)

Pikas (Ochotona Link, 1795) are high‑altitude specialist species making them a useful bioindicator species to warming in high‑altitude ecosystem. The Himalayan Mountains are an important part of their range, supporting approximately 23%–25% of total pika species worldwide, yet we lack basic information on the distribution patterns. We combine field‑based surveys with genetics‑based identification and phylogeny to identify differences in species‑environment relationships. Further, we suggest putative evolutionary causes for the observed niche patterns.LocationHimalayan high‑altitude region.MethodsWe sampled 11 altitudinal transects (ranging from ~2,000 to 5,000 m) in the Himalaya to establish occurrence records. We collected 223 species records using genetic analyses to confirm species' identity (based on some invasive and mostly noninvasive biological samples). Niche and geographic overlap were estimated using kernel density estimates.ResultsMost pikas in the Himalaya span wide elevation ranges and exhibit extensive spatial overlap with other species. However, even in areas of high species diversity, we found species to have a distinct environmental niche. Despite apparent overlapping distributions at broad spatial scales, in our field surveys, we encountered few cases of co‑occurrence of species in the sampled transects. Deeply diverged sister‑species pair had the least environmental niche overlap despite having the highest geographic range overlap. In contrast, sister‑species pair with shallow genetic divergence had a higher environmental niche overlap but was geographically isolated. We hypothesize that the extent of environmental niche divergence in pikas is a function of divergence time within the species complex. We assessed vulnerability of species to future climate change using environmental niche and geographic breadth sizes as a proxies. Our findings suggest that O. sikimaria may be the most vulnerable species. Ochotona roylii appears to have the most unique environmental niche space, with least niche overlap with other pika species from the study area.

Research areas: Ecosystems
Landscape connectivity and genetic structure in a mainstem and a tributary stonefly (Plecoptera) species using a novel reference genome (2022)

Understanding how environmental variation influences population genetic structure can help predict how environmental change influences population connectivity, genetic diversity, and evolutionary potential. We used riverscape genomics modeling to investigate how climatic and habitat variables relate to patterns of genetic variation in 2 stonefly species, one from mainstem river habitats (Sweltsa coloradensis) and one from tributaries (Sweltsa fidelis) in 40 sites in northwest Montana, USA. We produced a draft genome assembly for S. coloradensis (N50 = 0.251 Mbp, BUSCO > 95% using insecta_ob9 reference genes). We genotyped 1930 SNPs in 372 individuals for S. coloradensis and 520 SNPs in 153 individuals for S. fidelis. We found higher genetic diversity for S. coloradensis compared to S. fidelis, but nearly identical genetic differentiation among sites within each species (both had global loci median FST = 0.000), despite differences in stream network location. For landscape genomics and testing for selection, we produced a less stringently filtered data set (3454 and 1070 SNPs for S. coloradensis and S. fidelis, respectively). Environmental variables (mean summer precipitation, slope, aspect, mean June stream temperature, land cover type) were correlated with 19 putative adaptive loci for S. coloradensis, but there was only one putative adaptive locus for S. fidelis (correlated with aspect). Interestingly, we also detected potential hybridization between multiple Sweltsa species which has never been previously detected. Studies like ours, that test for adaptive variation in multiple related species are needed to help assess landscape connectivity and the vulnerability of populations and communities to environmental change.

Research areas: Ecosystems
Synoptic meteorology explains temperate forest carbon uptake (2020)

While substantial attention has been paid to the effects of both global climate oscillations and local meteorological conditions on the interannual variability of ecosystem carbon exchange, the relationship between the interannual variability of synoptic meteorology and ecosystem carbon exchange has not been well studied. Here we use a clustering algorithm to identify a summertime cyclonic precipitation system northwest of the Great Lakes to determine (a) the association at a daily scale between the occurrence of this system and the local meteorology and net ecosystem exchange at three Great Lakes region forested eddy covariance sites and (b) the association between the seasonal prevalence of this system and the summertime net ecosystem exchange of these sites. We find that temperature, in addition to precipitation and cloud cover, is an important explanatory factor for the suppression of net ecosystem productivity that occurs during these cyclonic events in this region. In addition, the prevalence of this cyclonic system can explain a significant proportion of the interannual variability in summertime forest ecosystem exchange in this region. This explanatory power is not due to a simple accumulation of low-productivity days that cooccur with this meteorological event, but rather a broader association between the frequency of these events and several aspects of prevailing seasonal conditions. This work demonstrates the usefulness of conceptualizing meteorology in terms of synoptic systems for explaining the interannual variability of regional carbon fluxes.

Research areas: Ecosystems, Atmospheric/Ocean Indicators
Atmospheric CO<inf>2</inf> Observations Reveal Strong Correlation Between Regional Net Biospheric Carbon Uptake and Solar-Induced Chlorophyll Fluorescence (2017)

Recent studies have shown the promise of remotely sensed solar-induced chlorophyll fluorescence (SIF) in informing terrestrial carbon exchange, but analyses have been limited to either plot level ( 1 km<SUP>2</SUP>) or hemispheric/global ( 10<SUP>8</SUP> km<SUP>2</SUP>) scales due to the lack of a direct measure of carbon exchange at intermediate scales. Here we use a network of atmospheric CO<SUB>2</SUB> observations over North America to explore the value of SIF for informing net ecosystem exchange (NEE) at regional scales. We find that SIF explains space-time NEE patterns at regional ( 100 km<SUP>2</SUP>) scales better than a variety of other vegetation and climate indicators. We further show that incorporating SIF into an atmospheric inversion leads to a spatial redistribution of NEE estimates over North America, with more uptake attributed to agricultural regions and less to needleleaf forests. Our results highlight the synergy of ground-based and spaceborne carbon cycle observations.

Research areas: Ecosystems, Atmospheric/Ocean Indicators
Habitat loss and thermal tolerances influence the sensitivity of resident bird populations to winter weather at regional scales (2021)

Climate change and habitat loss pose the greatest contemporary threats to biodiversity, but their impacts on populations largely vary across species. These differential responses could be caused by complex interactions between landscape and climate change and species‑specific sensitivities. Understanding the factors that determine which species are most vulnerable to the synergistic effects of climate change and habitat loss is a high conservation priority. Here, we ask (a) whether and to what extent land cover moderates the impacts of winter weather on population dynamics of wintering birds, and (b) what role species' physiology might play in modifying their responses to changing weather conditions. To address these questions, we used thousands of observations collected by citizen scientists participating in Project FeederWatch to build dynamic occupancy models for 14 species of wintering birds. Populations of wintering birds were more dynamic, having higher rates of local extinction and colonization, in more forested landscapes during extreme cold—presumably enabling them to better track resources. However, urban areas appeared to provide refuge for some species, as demonstrated by increased local colonization during the harshest winter weather. Lastly, we found that species‑specific differences in thermal tolerances strongly influenced occupancy dynamics such that species that are less cold‑tolerant were more likely to go locally extinct at colder sites and during colder periods throughout winter. Together, our results suggest that species that are less cold‑tolerant and populations occupying less forested landscapes are most vulnerable to extreme winter weather.

Research areas: Ecosystems
Quantifying the role of seasonality in the marine carbon cycle feedback: An ESM2M case study (2022)

Observations and climate models indicate that changes in the seasonal amplitude of sea surface carbon dioxide partial pressure (A-pCO<SUB>2</SUB>) are underway and driven primarily by anthropogenic carbon (C<SUB>ant</SUB>) accumulation in the ocean. This occurs because pCO<SUB>2</SUB> is more responsive to seasonal changes in physics (including warming) and biology in an ocean that contains more C<SUB>ant</SUB>. A-pCO<SUB>2</SUB> changes have the potential to alter annual ocean carbon uptake and contribute to the overall marine carbon cycle feedback. Using the GFDL ESM2M Large Ensemble and a novel analysis framework, we quantify the influence of C<SUB>ant</SUB> accumulation on pCO<SUB>2</SUB> seasonal cycles and sea-air CO<SUB>2</SUB> fluxes. Specifically, we reconstruct alternative evolutions of the contemporary ocean state in which the sensitivity of pCO<SUB>2</SUB> to seasonal thermal and biophysical variation is fixed at preindustrial levels, however the background, mean-state pCO<SUB>2</SUB> fully responds to anthropogenic forcing. We find near-global A-pCO<SUB>2</SUB> increases of &gt;100% by 2100, under RCP8.5 forcing, with rising C<SUB>ant</SUB> accounting for ∼100% of thermal and ∼50% of nonthermal pCO<SUB>2</SUB> component amplitude changes. The other ∼50% of nonthermal pCO<SUB>2</SUB> component changes are attributed to modeled changes in ocean physics and biology caused by climate change. C<SUB>ant</SUB>-induced A-pCO<SUB>2</SUB> changes cause an 8.1 ± 0.4% (ensemble mean ± 1σ) increase in ocean carbon uptake by 2100. The is because greater wintertime wind speeds enhance the impact of wintertime pCO<SUB>2</SUB> changes, which work to increase the ocean carbon sink. Thus, the seasonal ocean carbon cycle feedback works in opposition to the larger, mean-state feedback that reduces ocean carbon uptake by ∼60%.

Research areas: Ecosystems, Atmospheric/Ocean Indicators