Sources and degradation of organic matter in the surface sediments of the Chukchi Sea:insights from amino acids

In the context of global warming and rapid environment change in the Arctic,the supply of organic matter(OM)has increased significantly and a large amount of OM are buried on the Arctic shelf.Studying the fate of OM in Arctic shelf sediments is crucial to understanding the global carbon sink.As a marginal sea of the Arctic Ocean,the Chukchi Sea is one of the most critical areas where OM is buried.Based on the surface sediment samples collected during the sixth Chinese National Arctic Research Expedition in the summer of 2014 and the SinoRussian joint Arctic Research Expedition in the summer of 2016,this study takes amino acids(AAs)as the primary tool to explore the source and degradation of OM in the surface sediments of the Chukchi Sea.This study shows that total hydrolyzable amino acid(THAA)concentrations(dry weight)are high,with a mean value of(32.7±15.8)μmol/g.Their spatial distribution is related to primary productivity,hydrodynamic conditions,sediment properties and other factors.The source of OM in the surface sediments of the Chukchi Sea is dominated by diatom-dominated marine productivity,with some input from terrestrial sources.Bacteria,as the main source of the D-enantiomer of AA(D-AA),not only have transforming effect on OM,but their cell walls and remnants likewise supply the OM pool.Based on a series of diagenetic indicators,we conclude that the OM in the surface sediments of the Chukchi Sea has undergone extensive degradation[DI(degradation index)=-0.59±0.44],and the degradation degree in the slope is higher than that in the shelf.This study uses AA to explore the sources and degradation of OM in the sediments of the Chukchi Sea,which facilitates our understanding of OM transport and transformation on the Arctic shelf.

Present State of Pasture Types of the Central Kyzylkum

The modern state of desert pastures of the Central Kyzylkum has been studied. The pasture territories of the Central Kyzylkum are distributed on sandy soils (14%), salt marshes (6%), gravellyloamy gray-brown soils (75%) and riparian nature-territorial complexes (5%). The main (75%) areas of pasture are occupied by the gravelly-loamy gray-brown soils which are dominated by species of sagebrushes. There are formed of 8 pasture types depending on the properties of natural complexes. The main type of pasture is sagebrushes (Mixto artemisieta), which occupy 60% of the pasture area, and then follow Peganeta harmala, Mixto calligoneta, Halocnemeta strobilacei, Tamariceta varia, Haloxyleta aphylli, Convolvuleta hamadae and Mixshrubs pasture types. The share of fodder plants is high (an average of 83%) in the flora of the study area. According to seasonal grazing, pastures of the Central Kyzylkum can be divided 5 groups: year-round, spring, spring-summer, autumn-winter and unsuitable pastures for grazing. Among them are prevail year-round grazing pastures. The numbers of annual plants and abundance venomous plants in the flora are indicators of pasture degradation in the study area. Annual plants may occupy 55% of composition of plant communities on degraded sites, besides the pasture types which formed under the influence of anthropogenic factors. In Central Kyzylkum newly formed and transformed pasture types occupy 25% of pastures.