Living coccolithophores in the western Pacific Ocean with mesoscale eddies

Living coccolithophores(LCs)are regarded as a group of calcifiers and play important roles in global carbon cycle.This study used microscopic observations of LCs in the western Pacific Ocean to investigate their community structure and biodiversity,especially to test whether local physical traits(mesoscale eddies)could explain their biogeographic distributions during autumn of 2017.The coccolithophore calcite inventory based on carbon-volume transformation was estimated in this study.A total of 28 taxa of coccospheres and 19 types of coccoliths were identified from 161 samples.Gephyrocapsa oceanica was the most predominant species in all the coccolithophore community,followed by Florisphaera profunda,Emiliania huxleyi,Umbilicosphaera sibogae,Gladiolithusflabellatus and Umbellosphaera tenuis.The abundance of coccospheres and coccoliths ranged from 0 to 26.8×10^(3)cells/L and from 0 to 138.5×10^(3)coccoliths/L,averaged at 4.2×10^(3)cells/L and 10.9×10^(3)coccoliths/L,respectively.This study indicated that coccolithophore community in the survey area can be clustered into four groups.Three ecological niches of coccolithophores were characterized by their vertical profiles and multivariate statistical analysis.Coccolithophore abundance and species composition were remarkably different among warm-eddy region,G.oceanica dominated warm-eddy region,while F.profunda dominated warm-eddy and none-eddy region.The average values of estimated particulate inorganic carbon,particulate organic carbon were0.197μg/L and 0.140μg/L,respectively.The current field study widened the dataset of coccolithophores in western Pacific Ocean.

Nitrogen fixation driven by mesoscale eddies and the Kuroshio Current in the northern South China Sea and the East China Sea

N2 fixation rates(NFR,in terms of N)in the northern South China Sea(nSCS)and the East China Sea(ECS)were measured using the acetylene reduction assay in summer and winter,2009.NFR of the surface water ranged from 1.14 nmol/(L·d)to 10.40 nmol/(L·d)(average at(4.89±3.46)nmol/(L·d),n=11)in summer and 0.74 nmol/(L·d)to 29.45 nmol/(L·d)(average at(7.81±8.50)nmol/(L·d),n=15)in winter.Significant spatio-temporal heterogeneity emerged in our study:the anticyclonic eddies(AE)(P<0.01)and the Kuroshio Current(KC)(P<0.05)performed significantly higher NFR than that in the cyclonic eddies or no-eddy area(CEONE),indicating NFR was profoundly influenced by the physical process of the Kuroshio and mesoscale eddies.The depth-integrated N2 fixation rates(INF,in terms of N)ranged from 52.4μmol/(m2·d)to 905.2μmol/(m2·d)(average at(428.9±305.5)μmol/(m2·d),n=15)in the winter.The contribution of surface NFR to primary production(PP)ranged from 1.7%to 18.5%in the summer,and the mean contribution of INF to new primary production(NPP)in the nSCS and ECS were estimated to be 11.0%and 36.7%in the winter.The contribution of INF to NPP(3.0%–93.9%)also decreased from oligotrophic sea toward the eutrophic waters affected by runoffs or the CEONE.Furthermore,we observed higher contributions compared to previous studies,revealing the vital roles of nitrogen fixation in sustaining the carbon pump of the nSCS and ECS.

Evaluation of nine major satellite soil moisture products in a typical subtropical monsoon region with complex land surface characteristics

Assessing accuracies of satellite soil moisture(SM)products in areas with strong anthropogenic activities,abundant precipitation,and dense vegetation is important but limited.In this study,performances of nine satellite SM products,including the European Space Agency Climate Change Initiative(ESA CCI),and the ascending and descending products of the Advanced Microwave Scanning Radiometer 2(AMSR2),Chinese Fengyun-3B(FY3B),Chinese Fengyun-3C(FY3C),and Soil Moisture Active Passive(SMAP),were evaluated against in-situ SM in the Yangtze River Delta(YRD)from 2015 to 2018.Results showed that the ESA CCI outperformed other products,with averaged correlation coefficient(R)of 0.522,correlation coefficient for SM anomalies(Rano)of 0.419,and unbiased root mean square error(ubRMSE)of 0.040 m^(3)m^(-3),followed by the SMAP_A and SMAP_D.Overestimation was observed in the AMSR2 products(Bias>0.081 m^(3)m^(-3)),while underestimation was found in the FY3B and FY3C products(Bias<-0.104 m^(3)m^(-3)).Moreover,R values decreased with the increase in water area percentage(WAP),land cover heterogeneity(GSI),fractional vegetation cover(FVC),and precipitation(PRE).Threshold values were observed at 3%for the WAP,0.05 for the FVC,and 900 mm yr^(-1)for the PRE,below which sharp declines of accuracy were observed.The WAP,GSI,and FVC were divided into five sub-classes with their values increasing with the sub-class level(I to V).Correlations coefficients between these perturbing factors and R(correlation between satellite and in-situ SM)increased as sub-class levels increased.Under sub-classes I,II,and III,these three factors had limited influences on accuracies of satellite SM products.However,under sub-classes IV and V,significant impacts of these three perturbing factors were observed.Moreover,when sub-classes of the PRE increased from I to V,correlations between Bias and PRE decreased first and then increased.These findings can help to determine suitable satellite SM products in the YRD and similar areas.

Expanding Asgard members in the domain of Archaea sheds new light on the origin of eukaryotes

The hypothesis that eukaryotes originated from within the domain Archaea has been strongly supported by recent phylogenomic analyses placing Heimdallarchaeota-Wukongarchaeota branch from the Asgard superphylum as the closest known archaeal sister-group to eukaryotes. However, our understanding is still limited in terms of the relationship between eukaryotes and archaea, as well as the evolution and ecological functions of the Asgard archaea. Here, we describe three previously unknown phylum-level Asgard archaeal lineages, tentatively named Sigyn-, Freyr-and Njordarchaeota. Additional members in Wukongarchaeota and Baldrarchaeota from distinct environments are also reported here, further expanding their ecological roles and metabolic capacities. Comprehensive phylogenomic analyses further supported the origin of eukaryotes within Asgard archaea and a new lineage Njordarchaeota was supposed as the known closest branch with the eukaryotic nuclear host lineage. Metabolic reconstruction suggests that Njordarchaeota may have a heterotrophic lifestyle with capability of peptides and amino acids utilization, while Sigynarchaeota and Freyrarchaeota also have the potentials to fix inorganic carbon via the Wood-Ljungdahl pathway and degrade organic matters. Additionally, the Ack/Pta pathway for homoacetogenesis and de novo anaerobic cobalamin biosynthesis pathway were found in Freyrarchaeota and Wukongrarchaeota,respectively. Some previously unidentified eukaryotic signature proteins for intracellular membrane trafficking system, and the homologue of mu/sigma subunit of adaptor protein complex, were identified in Freyrarchaeota. This study expands the Asgard superphylum, sheds new light on the evolution of eukaryotes and improves our understanding of ecological functions of the Asgard archaea.

The late Archaean to early Proterozoic origin and evolution of anaerobic methane-oxidizing archaea

Impact statement Microorganisms,called anaerobic methane-oxidizing archaea(ANME),can reduce a large amount of greenhouse gas methane and therefore have the potential to cool the Earth.We collected nearly all ANMEs genomes in public databases and performed a comprehensive comparative genomic analysis and molecular dating.Our results show that ANMEs originated in the late Archaean to early Proterozoic eon.During this period of time,our planet Earth was experiencing the Great Oxygenation Event and Huronian Glaciation,a dramatic drop in the Earth's surface temperature.This suggests that the emergence of ANMEs may contribute to the reduction of methane at that time,which is an unappreciated potential cause that led to the Huronian Glaciation.