nasa-gesdisc/es-publications-researchareas huggingface dataset:
Priority coral conservation areas under global warming in the Amami Islands, Southern Japan (2022)

Coral reef ecosystems are highly sensitive to climate change. The Amami Islands in Southern Japan were selected as the study area. It is important to select areas that should be given priority for conservation and subsequently direct resources there. The objective of this study was to identify locations with low bleaching potential against future increases in water temperature, as well as high larval recruitment from other areas and high larval supply capacity to other areas based on connectivity. We simulated the coral bleaching rate and larval connectivity under historical (2000s) and future (RCP2.6 and RCP8.5 in the 2090s) climate conditions using a high-resolution (1/30  1/50) future ocean regional projection dataset. From the model simulation, coral bleaching did not occur in most areas in the 2000s. However, the bleaching frequency would increase significantly under RCP8.5 in the 2090s, and it is projected that mass coral bleaching events will occur in more than half of the years of that decade. Larval dispersion simulation shows that some particles released from the Amami Islands remain in the same area. However, fluctuations in both the sink strength and the source strength among the islands were larger than those within each island, and differences in connectivity between scenarios were not apparent. Grid cells that have a low bleaching rate and high potential for a larval sink and source under each scenario were selected. Since our results can identify priority conservation areas, it is important to conduct conservation and/or adaptation strategies according to the specific characteristics of each island.

Research areas: Ecosystems
Seasonal controlling factors of CO2 exchange in a semiarid shrubland in the Chihuahuan Desert, Mexico (2023)

The still significant uncertainties associated with the future capacity of terrestrial systems to mitigate climate change are linked to the lack of knowledge of the biotic and abiotic processes that regulate CO2 net ecosystem exchange (NEE) in space/time. Mainly, rates and controls of CO2 exchange from arid ecosystems, despite dominating the global trends in interannual variability of the terrestrial CO2 sink capacity, are probably the most poorly understood of all. We present a study on rates and controls of CO2 exchange measured with the eddy covariance (EC) technique in the Chihuahuan Desert in the Northeast of Mexico, to understand how the environmental controls of the NEE switch throughout the year using a multilevel approach. Since this is a water-limited ecosystem, the hydroecological year, based on the last precipitation and the decay of air temperature, was used to compare the wet (from May 16 to October 30, 2019) and dry (November 1, 2019 to May 15, 2020) seasons' controlling mechanisms, both at diurnal and nocturnal times. Annual NEE was 303.5 g C m2, with a cumulative Reco of 537.7 g C m2 and GPP of 841.3 g C m2. NEE showed radiation, temperature, and soil moisture sensitivity along the day, however, shifts in these controls along the year and between seasons were identified. The winter precipitations during the dry season led to fast C release followed by lagged C uptake. Despite this flux pulse, the ecosystem was a net sink throughout most of the year because the local vegetation is well adapted to grow and uptake C under these arid conditions, even during the dry season. Understanding the controls of the sink-source shifts is relevant since the predictions for future climate include changes in the precipitation patterns.

Research areas: Greenhouse Gases
Uncertainties in eddy covariance CO2 fluxes in a semiarid sagebrush ecosystem caused by gap-filling approaches (2021)

Abstract. Gap-filling eddy covariance CO2 fluxes is challenging at dryland sites due to small CO2 fluxes. Here, four machine learning (ML) algorithms including artificial neural network (ANN), k-nearest neighbors (KNNs), random forest (RF), and support vector machine (SVM) are employed and evaluated for gap-filling CO2 fluxes over a semiarid sagebrush ecosystem with different lengths of artificial gaps. The ANN and RF algorithms outperform the KNN and SVM in filling gaps ranging from hours to days, with the RF being more time efficient than the ANN. Performances of the ANN and RF are largely degraded for extremely long gaps of 2 months. In addition, our results suggest that there is no need to fill the daytime and nighttime net ecosystem exchange (NEE) gaps separately when using the ANN and RF. With the ANN and RF, the gap-filling-induced uncertainties in the annual NEE at this site are estimated to be within 16 g C m2, whereas the uncertainties by the KNN and SVM can be as large as 27 g C m2. To better fill extremely long gaps of a few months, we test a two-layer gap-filling framework based on the RF. With this framework, the model performance is improved significantly, especially for the nighttime data. Therefore, this approach provides an alternative in filling extremely long gaps to characterize annual carbon budgets and interannual variability in dryland ecosystems.

Research areas: Greenhouse Gases
Comparison of species-specific qPCR and metabarcoding methods to detect small pelagic fish distribution from open ocean environmental DNA (2022)

Environmental DNA (eDNA) is increasingly used to noninvasively monitor aquatic animals in freshwater and coastal areas. However, the use of eDNA in the open ocean (hereafter referred to OceanDNA) is still limited because of the sparse distribution of eDNA in the open ocean. Small pelagic fish have a large biomass and are widely distributed in the open ocean. We tested the performance of two OceanDNA analysis methodsspecies-specific qPCR (quantitative polymerase chain reaction) and MiFish metabarcoding using universal primersto determine the distribution of small pelagic fish in the open ocean. We focused on six small pelagic fish species (Sardinops melanostictus, Engraulis japonicus, Scomber japonicus, Scomber australasicus, Trachurus japonicus, and Cololabis saira) and selected the Kuroshio Extension area as a testbed, because distribution of the selected species is known to be influenced by the strong frontal structure. The results from OceanDNA methods were compared to those of net sampling to test for consistency. Then, we compared the detection performance in each target fish between the using of qPCR and MiFish methods. A positive correlation was evident between the qPCR and MiFish detection results. In the ranking of the species detection rates and spatial distribution estimations, comparable similarity was observed between results derived from the qPCR and MiFish methods. In contrast, the detection rate using the qPCR method was always higher than that of the MiFish method. Amplification bias on non-target DNA and low sample DNA quantity seemed to partially result in a lower detection rate for the MiFish method; the reason is still unclear. Considering the ability of MiFish to detect large numbers of species and the quantitative nature of qPCR, the combined usage of the two methods to monitor quantitative distribution of small pelagic fish species with information of fish community structures was recommended.

Research areas: Ecosystems
High spatial resolution solar-induced chlorophyll fluorescence and its relation to rainfall precipitation across Brazilian ecosystems (2023)

The detection of Solar-Induced chlorophyll Fluorescence (SIF) by remote sensing has opened new perspectives on ecosystem studies and other related aspects such as photosynthesis. In general, fluorescence high-resolution studies were limited to proximal sensors, but new approaches were developed to improve SIF resolution by combining OCO-2 with MODIS orbital observations, improving its resolution from 0.5 to 0.05 on a global scale. Using a high-resolution dataset and rainfall data some SIF characteristics of the satellite were studied based across 06 contrasting ecosystems in Brazil: Amazonia, Caatinga, Cerrado, Atlantic Forest, Pampa, and Pantanal, from years 20152018. SIF spatial variability in each biome presented significant spatial variability structures with high R2 values (>0.6, Gaussian models) in all studied years. The rainfall maps were positively and similar related to SIF spatial distribution and were able to explain more than 40% of SIF's spatial variability. The Amazon biome presented the higher SIF values (>0.4 W m2 sr1 m1) and also the higher annual rainfall precipitation (around 2000 mm), while Caatinga had the lowest SIF values and precipitations (<0.1 W m2 sr1 m1, precipitation around 500 mm). The linear relationship of SIF to rainfall across biomes was mostly significant (except in Pantanal) and presented contrasting sensitivities as in Caatinga SIF was mostly affected while in the Amazon, SIF was lesser affected by precipitation events. We believe that the features presented here indicate that SIF could be highly affected by rainfall precipitation changes in some Brazilian biomes. Combining rainfall with SIF allowed us to detect the differences and similarities across Brazil's biomes improving our understanding on how these ecosystems could be affected by climate change and severe weather conditions.

Research areas: Ecosystems
Ecoregions and stream types help us understand ecological variability in Neotropical reference streams (2019)

Stream site classification is a fundamental step in defining reference conditions for freshwater bioassessments globally. Landscape regionalisation and stream typology approaches have both been used to determine classes that reduce inherent environmental variation and to show classes with ecological meaning. We evaluated the applicability of ecoregion and stream typology approaches in a river basin located between the Neotropical Savanna and the Atlantic Forest biomes in south-eastern Brazil. We delimited two ecoregions and assessed whether stream types within each ecoregion would further reduce environmental and macroinvertebrate assemblage variability. In addition, we determined indicator taxa for each of the reference condition classes. Our results confirm the importance of defining ecoregions a priori and for using a nested a posteriori stream typology approach for further explaining macroinvertebrate assemblage variation. Geology and natural vegetation physiognomy were the key ecoregion factors likely to influence macroinvertebrate assemblages, and stream dimension attributes best delimited meaningful stream types. Although stream classification is a very important step in any monitoring, management or restoration program, it has been widely neglected in many tropical regions. In this study we demonstrated how it can be conducted to determine macroinvertebrate assemblage potentials even with a relatively limited number of sites.

Research areas: Ecosystems
Evaluation of Environmental Controls on Terrestrial Net Ecosystem Exchange of CO
            2
            : A Global Perspective From the FLUXNET Sites (2022)

Net ecosystem exchange (NEE) of CO<SUB>2</SUB> is a key process modulating carbon exchanges between terrestrial ecosystems and the atmosphere; however, it remains a grand challenge to elucidate how the interactions of NEE with environmental variables vary among ecosystems and climate regimes across timescales. The FLUXNET and AmeriFlux data sets were used to diagnose the environmental controls on NEE. Based on the sites with long-term observations (≥7 years), the results showed that the couplings between NEE and surrounding environments were stronger at daily and monthly scales than at annual scales, highlighting the temporal dependence of environmental variables influencing NEE. Moreover, the boosted regression tree method was applied to quantify the relative impacts of environmental controls on daily NEE variations. It revealed that leaf area index (LAI) and shortwave radiation (R<SUB>s</SUB>) were the major divers of daily NEE variations at most sites with the average contribution of 35.5% and 27.8%, respectively. Particularly, LAI was the principal control in deciduous broadleaf forested, non-forested, and arid sites, while R<SUB>s</SUB> was the leading factor in evergreen forested sites. Meanwhile, air temperature (T<SUB>a</SUB>), soil water content (SWC), and vapor pressure deficit (VPD) exerted smaller influences with the average contribution of 14.6%, 13.2%, and 8.9%, respectively. The relative impacts of LAI, R<SUB>s</SUB>, SWC, and VPD also varied with aridity index, and mean annual precipitation and T<SUB>a</SUB>. Furthermore, NEE was more sensitive to vegetation dynamics in drier climate regions. This study provides additional understanding of how environmental factors regulate NEE dynamics across diverse land surface and climatic conditions.

Research areas: Ecosystems
Variability in fin whale (Balaenoptera physalus) occurrence in the Bering Strait and southern Chukchi Sea in relation to environmental factors (2020)

Fin whales (Balaenoptera physalus) are common summer visitors to the Pacific Arctic, migrating through the Bering Strait and into the southern Chukchi Sea to feed on seasonally-abundant prey. The abundance and distribution of fin whales in the Chukchi Sea varies from year-to-year, possibly reflecting fluctuating environmental conditions. We hypothesized that fin whale calls were most likely to be detected in years and at sites where productive water masses were present, indicated by low temperatures and high salinities, and where strong northward water and wind velocities, resulting in increased prey advection, were prevalent. Using acoustic recordings from three moored hydrophones in the Bering Strait region from 20092015, we identified fin whale calls during the open-water season (JulyNovember) and investigated potential environmental drivers of interannual variability in fin whale presence. We examined near-surface and near-bottom temperatures (T) and salinities (S), wind and water velocities through the strait, water mass presence as estimated using published T/S boundaries, and satellite-derived sea surface temperatures and sea-ice concentrations. Our results show significant interannual variability in the acoustic presence of fin whales with the greatest detections of calls in years with contrasting environmental conditions (2012 and 2015). Colder temperatures, lower salinities, slower water velocities, and weak southward winds prevailed in 2012 while warmer temperatures, higher salinities, faster water velocities, and moderate southward winds prevailed in 2015. Most detections (96%) were recorded at the mooring site nearest the confluence of the nutrient-rich Anadyr and Bering Shelf water masses, ~35 km north of Bering Strait, indicating that productive water masses may influence the occurrence of fin whales. The disparity in environmental conditions between 2012 and 2015 suggests there may be multiple combinations of environmental factors or other unexamined variables that draw fin whales into the Pacific Arctic.

Research areas: Ecosystems
Parasitoids indicate major climate‐induced shifts in arctic communities (2020)

AbstractClimatic impacts are especially pronounced in the Arctic, which as a region is warming twice as fast as the rest of the globe. Here, we investigate how mean climatic conditions and rates of climatic change impact parasitoid insect communities in 16 localities across the Arctic. We focus on parasitoids in a widespread habitat, Dryas heathlands, and describe parasitoid community composition in terms of larval host use (i.e., parasitoid use of herbivorous Lepidoptera vs. pollinating Diptera) and functional groups differing in their closeness of host associations (koinobionts vs. idiobionts). Of the latter, we expect idiobiontsas being less finetuned to host developmentto be generally less tolerant to cold temperatures, since they are confined to attacking hosts pupating and overwintering in relatively exposed locations. To further test our findings, we assess whether similar climatic variables are associated with host abundances in a 22 year time series from Northeast Greenland. We find sites which have experienced a temperature rise in summer while retaining cold winters to be dominated by parasitoids of Lepidoptera, with the reverse being true for the parasitoids of Diptera. The rate of summer temperature rise is further associated with higher levels of herbivory, suggesting higher availability of lepidopteran hosts and changes in ecosystem functioning. We also detect a matching signal over time, as higher summer temperatures, coupled with cold early winter soils, are related to high herbivory by lepidopteran larvae, and to declines in the abundance of dipteran pollinators. Collectively, our results suggest that in parts of the warming Arctic, Dryas is being simultaneously exposed to increased herbivory and reduced pollination. Our findings point to potential drastic and rapid consequences of climate change on multitrophiclevel community structure and on ecosystem functioning and highlight the value of collaborative, systematic sampling effort.

Research areas: Ecosystems
Benefits of satellite XCO2 and newly proposed atmospheric CO2 observation network over India in constraining regional CO2 fluxes (2022)

Top-down modeling estimates are among the most reliable information available on the CO2 fluxes of the earth system. The inadequate coverage of CO2 observing stations over the tropical regions adds a limitation to this estimate, especially when the satellite XCO2 is strictly screened for cloud contamination, aerosol, dust, etc. In this study, we investigated the potential benefit of a global ground-based observing station network, 17 newly proposed stations over India, and global satellite XCO2 in reducing the uncertainty of terrestrial biospheric fluxes of Tropical Asia-Eurasia in TransCom cyclo-stationary inversion. The data from selected 80 global ground-based CO2 observation stations, together with two additional stations from India (i.e., Cape Rama and Sinhagad) and satellite XCO2, helps to reduce the temperate Eurasian terrestrial flux uncertainty by 23.8%, 26.4%, and 36.2%, respectively. This further improved to 54.7% by adding the newly proposed stations over India into the inversion. By separating the Indian sub-continent from temperate Eurasia (as inspired by the heterogeneity in the terrestrial ecosystems, prevailing meteorological conditions, and the orography of this vast region), the inversion evinces the capacity of existing CO2 observations to reduce the Indian terrestrial flux uncertainty by 20.5%. The largest benefit (70% reduction of annual mean uncertainty) for estimating Indian terrestrial fluxes could be achieved by combining these global observations with data from the newly proposed stations over India. The existing two stations from India suggest Temperate Eurasia as a mild source of CO2 (0.33  0.57 Pg C yr1), albeit with prominent anthropogenic influences visible in these two stations during the dry seasons. This implies that the proposed new stations should be cautiously placed to avoid such effects. The study also finds that the newly proposed stations over India also have an impact in constraining nearby oceanic CO2 fluxes.

Research areas: Greenhouse Gases
The changing CO2 sink in the western Arctic Ocean from 1994 to 2019 (2022)

The Arctic Ocean has turned from a perennial ice-covered ocean into a seasonally ice-free ocean in recent decades. Such a shift in the air-ice-sea interface has resulted in substantial changes in the Arctic carbon cycle and related biogeochemical processes. To quantitatively evaluate how the oceanic CO<SUB>2</SUB> sink responds to rapid sea ice loss and to provide a mechanistic explanation, here we examined the air-sea CO<SUB>2</SUB> flux and the regional CO<SUB>2</SUB> sink in the western Arctic Ocean from 1994 to 2019 by two complementary approaches: observation-based estimation and a data-driven box model evaluation. The pCO<SUB>2</SUB> observations and model results showed that summer CO<SUB>2</SUB> uptake significantly increased by about 1.4 ± 0.6 Tg C decade<SUP>-1</SUP> in the Chukchi Sea, primarily due to a longer ice-free period, a larger open area, and an increased primary production. However, no statistically significant increase in CO<SUB>2</SUB> sink was found in the Canada Basin and the Beaufort Sea based on both observations and modeled results. The reduced sea ice coverage in summer in the Canada Basin and the enhanced wind speed in the Beaufort Sea potentially promoted CO<SUB>2</SUB> uptake, which was, however, counteracted by a rapidly decreased air-sea pCO<SUB>2</SUB> gradient therein. Therefore, the current and future Arctic Ocean CO<SUB>2</SUB> uptake trends cannot be sufficiently reflected by the air-sea pCO<SUB>2</SUB> gradient alone because of the sea ice variations and other environmental factors.

Research areas: Atmospheric/Ocean Indicators
Upper Ocean Stratification in the Eastern Pacific during the SPURS‐2 Field Campaign (2021)

The region between a shallow mixed layer and a deep isothermal layer resulting from salinity stratification is called a barrier layer (BL). Since BLs hinder the surface heat and momentum exchange with the ocean subsurface, they play an important role in air sea interaction. Synoptic features and formation of BLs and associated temperature inversions (TIs) in the Eastern Pacific Fresh Pool (EPFP) were investigated using shipboard observations. BLs and TIs were found in the high precipitation EPFP, a frontal transition zone (FTZ) and in the sea surface salinity (SSS) front during a 2016 boreal summer cruise. During a 2017 boreal autumn cruise, BLs and TIs were found from the southern part of the EPFP to the SSS front. The BLs in the SSS front and the FTZ were meridionally displaced from the precipitation maximum during both the 2016 and 2017 cruises. Freshening and cooling by tilting of both the isohalines and isotherms of the SSS front occurred via Ekman and geostrophic flow during both cruises, and also within the EPFP during 2016. The SSS front was a dominant contributor to the density gradient in the horizontal plane. A high dissolved oxygen content observed within BLs confirmed that the surface flow plays an important role in the BL and TI formation through the tilting process. Patchy distribution of freshening and cooling by tilting implies an intermittent BL and TI formation with short time scales.

Research areas: Atmospheric/Ocean Indicators