Northwest Indian Ocean Research Articles

Characterization of Sulfurimonas hydrogeniphila sp. nov., a Novel Bacterium Predominant in Deep-Sea Hydrothermal Vents and Comparative Genomic Analyses of the Genus Sulfurimonas.

Bacteria of the genus Sulfurimonas within the class Campylobacteria are predominant in global deep-sea hydrothermal environments and widespread in global oceans. However, only few bacteria of this group have been isolated, and their adaptations for these extreme environments remain poorly understood. Here, we report a novel mesophilic, hydrogen- and sulfur-oxidizing bacterium, strain NW10T, isolated from a deep-sea sulfide chimney of Northwest Indian Ocean.16S rRNA gene sequence analysis showed that strain NW10T was most closely related to the vent species Sulfurimonas paralvinellae GO25T with 95.8% similarity, but ANI and DDH values between two strains were only 19.20 and 24.70%, respectively, indicating that strain NW10 represents a novel species. Phenotypic characterization showed strain NW10T is an obligate chemolithoautotroph utilizing thiosulfate, sulfide, elemental sulfur, or molecular hydrogen as energy sources, and molecular oxygen, nitrate, or elemental sulfur as electron acceptors. Moreover, hydrogen supported a better growth than reduced sulfur compounds. During thiosulfate oxidation, the strain can produce extracellular sulfur of elemental α-S8 with an unknown mechanism. Polyphasic taxonomy results support that strain NW10T represents a novel species of the genus Sulfurimonas, and named as Sulfurimonas hydrogeniphila sp. nov. Genome analyses revealed its diverse energy metabolisms driving carbon fixation via rTCA cycling, including pathways of sulfur/hydrogen oxidation, coupled oxygen/sulfur respiration and denitrification. Comparative analysis of the 11 available genomes from Sulfurimonas species revealed that vent bacteria, compared to marine non-vent strains, possess unique genes encoding Type V Sqr, Group II, and Coo hydrogenase, and are selectively enriched in genes related to signal transduction and inorganic ion transporters. These phenotypic and genotypic features of vent Sulfurimonas may explain their thriving in hydrothermal environments and help to understand the ecological role of Sulfurimonas bacteria in hydrothermal ecosystems.

Spatial and temporal variations of nutrients and chlorophyll a in the Indus River and its deltaic creeks and coastal waters (Northwest Indian Ocean, Pakistan)

Nutrient dynamics play an important role in mangroves and adjacent coastal ecosystems. This paper discusses the spatiotemporal variation of physicochemical factors in two monsoons and intermonsoons and their influence on chlorophyll a and the dissolved inorganic nutrient concentrations in selected creeks. The present study focused on dense mangrove cover creeks (Waddi Khuddi (WK) and Dabbo (DC)), sparse mangrove cover creek (Hajamro (HC)), and no mangrove to mixed terrestrial and agricultural vegetation (Khobar (KC)) along with the Indus River and adjacent NE Arabian Sea. Silicate (SiO32–) was the most abundant nutrient, and its concentration increased from the northeast to the southwest monsoon and decreased during the fall intermonsoon. Erosion of the riverbank catchment area, weathering, and sand mining are the major sources of elevated SiO32–. The highest concentration of nitrate (NO3–) was found in the main river channel (KC) throughout the year, with maximum concentration (37.42 ± 5.05 μM) in the river (KC) during the rainy season (SW monsoon) due to the agricultural runoff that resulted in an increase in chlorophyll a. The concentration of nitrite (NO2–) was high in the creek (DC) with mangroves and agricultural runoff input. The concentration of phosphate (PO43–) was high in mangrove-dominated creeks (WK and DC), suggesting litterfall as a major source of PO43− from the creeks. The river with no mangrove cover (KC) indicated that PO43– was a limiting factor. In the case of DSi:DIN ratios, SiO32–was not limited throughout the sampling period for primary production. The chlorophyll a concentration increased from upstream to downstream in the river and was positively correlated with SiO32– and NO3–, resulting in the dominance of diatoms during the SW monsoon. The study confirms that natural sources (river/terrestrial runoff and geomorphological factors) and anthropogenic factors (application of fertilizers, manure, construction of dams, and industrialization) significantly influenced the nutrients and chlorophyll a, both spatially and temporally. On a global scale, SiO32– concentrations in the Indus River during the southwest monsoon were lower than those in the Himalayan rivers (Brahmaputra, Ganges, Huanghe, and Yangtze Rivers). The NO3– concentration is comparable with that of Narmada, Tapti, and Pangani Rivers but lower than that for rivers originating from the Himalayas. Nutrient enrichment and eutrophication in coastal waters were mainly caused by urbanization and population increase, which affect the higher trophic level productivity and fish abundance in the coastal and shelf areas. Therefore, an integrated approach for the management and monitoring of upstream river systems is required for a better future.

The temporal variability of hydrothermal activity of Wocan hydrothermal field, Carlsberg Ridge, northwest Indian Ocean

The Wocan is a basalt-hosted hydrothermal field on the slow-spreading Carlsberg Ridge (CR), northwest Indian Ocean. It consists of two hydrothermal sites: Wocan-1 which is active, and Wocan-2 which is inactive. Three push-cores collected by the manned submersible Jiaolong from these two sites were investigated on their mineralogy, geochemistry, Pb-Sr isotopes, and chronology to understand the characteristics of hydrothermal sediments and their hydrothermal history. Core JL125-S17 (26-cm long) was collected from the Wocan-1 site with its lithology characterized by metalliferous sediments, mainly composed of sulfides, sulfates, Fe-oxides, and Fe-oxyhydroxides. Cores JL123-S03 (18-cm long) and JL124-S04 (20 cm long) were retrieved from the Wocan-2 site, mainly composed of calcareous oozes. Geochemically, Wocan-1 sediments exhibit strong metal and S enrichment. Ag, As, Cd, Co, Cu, Fe, Mg, Pb, Zn, and S are mainly incorporated into sulfides, while As, Ga, Mo, P, U, and V are mainly scavenged from seawater by Fe-Mn oxyhydroxides. In contrast, Wocan-2 sediments are rich in Ca and have much lower heavy metal content. The temporal variations of hydrothermal metal fluxes, which corrected for lithogenic input with Ti show that the intensity of hydrothermal activity at the Wocan-1 site has been extremely strong over the past ~1069 years, with hydrothermal Fe (FeH) fluxes varying from 9483 to 10834 mg·cm−2·kyr−1. During this period, 699–1069 yr BP and 0–411 yr BP represent two stages of increased hydrothermal activity. The Wocan-2 site has been inactive since 4864 ± 114 years before present (yr BP) but the cores still contained weak hydrothermal signatures evidenced by a slightly elevated flux of FeH at the base of the cores, which could be explained by the mineralization of low-temperature diffuse flow and distal plume fall-out from Wocan-1.

Iron and sulfur isotopes of sulfides from the Wocan hydrothermal field on the Carlsberg Ridge, Indian Ocean

The basalt-hosted Wocan hydrothermal field (WHF) was identified in 2013 during Chinese Dayang 28th cruise, which is located on the slow-spreading Carlsberg Ridge, northwest Indian Ocean. Few investigation has been carried out on the hydrothermal activities and associated sulfide deposit in this area. Herein, we report Fe and S isotope compositions of sulfide minerals including chalcopyrite, bornite, pyrite and sphalerite collected from the WHF. The results showed that all sulfide minerals display small δ34S variations (2.44‰ to 5.37‰, with an average of 4.00‰), and a wide δ56Fe range (−2.05‰ to 0.10‰, with an average of −0.92‰). Sulfur and iron isotopes in paired pyrite and chalcopyrite minerals reveal that it did not reach the equilibrium fractionation during pyrite precipitation, and support that the FeS precipitates first during the pyrite formation. The δ56Fe values of chalcopyrite and concurrent bornite are characterized by a well-defined negative correlation, which may be related to the repeated dissolution-reprecipitation of these copper-bearing sulfides under Fe-limited conditions. Most pyrites from the WHF demonstrate a positive correlation between δ56Fe and δ34S values, in accord with those from other hydrothermal fields, which can be explained by the temperature gradient and similar degrees of isotope exchange in the stable hydrothermal system. Conversely, the δ56Fe and δ34S values of chalcopyrite exhibit a slightly negative correlation, in which the temperature gradient can explain the negative correlation, but cannot cover the wide ranges of δ56Fe and δ34S values. More work on fractionation parameters and chalcopyrite formation mechanisms is still needed. In summary, the coupling of Fe and S isotopes is a useful tool in helping to delineate processes of sulfide mineralization in hydrothermal systems

Sulfurimonas indica sp. nov., a hydrogen- and sulfur-oxidizing chemolithoautotroph isolated from a hydrothermal sulfide chimney in the Northwest Indian Ocean.

A novel mesophilic, hydrogen- and sulfur-oxidizing bacterium, designated strain NW8NT, was collected from a sulfide chimney at the deep-sea hydrothermal vent on the Carlsberg Ridge of the Northwest Indian Ocean. The cells were Gram-stain-negative, motile, short rods with a single polar flagellum. The temperature, pH and salinity ranges for growth of strain NW8NT were 4-40 °C (optimum, 33 °C), pH 4.5-7.5 (optimum, pH 5.5) and 340-680 mM NaCl (optimum, 510 mM). The isolate was an obligate chemolithoautotroph capable of growth using hydrogen, thiosulfate, sulfide or elemental sulphur as the sole energy source, carbon dioxide as the sole carbon source and molecular oxygen as the sole electron acceptor. The major cellular fatty acids of strain NW8NT were summed feature 3 (C16 : 1 ω7c and/or C16 : 1 ω6c), C16 : 0 and summed feature 8 (C18 : 1 ω7c and/or C18 : 1 ω6c). The total size of its genome was 2 093 492 bp and the genomic DNA G+C content was 36.9 mol%. Phylogenetic analysis based on 16S rRNA gene sequences and core genes showed that the novel isolate belonged to the genus Sulfurimonas and was most closely related to Sulfurimonas paralvinellae GO25T (97.4 % sequence identity). The average nucleotide identity and DNA-DNAhybridization values between strain NW8NT and S. paralvinellae GO25T was 77.8 and 21.1 %, respectively. Based on the phylogenetic, genomic and phenotypic data presented here, strain NW8NT represents a novel species of the genus Sulfurimonas, for which the name Sulfurimonas indica sp. nov. is proposed, with the type strain NW8NT (=MCCC 1A13988T=KTCC 15780T).

A new blue whale song-type described for the Arabian Sea and Western Indian Ocean

Blue whalesBalaenoptera musculusin the Indian Ocean (IO) are currently thought to represent 2 or 3 subspecies (B. m. intermedia, B. m. brevicauda,B. m. indica), and believed to be structured into 4 populations, each with a diagnostic song-type. Here we describe a previously unreported song-type that implies the probable existence of a population that has been undetected or conflated with another population. The novel song-type was recorded off Oman in the northern IO/Arabian Sea, off the western Chagos Archipelago in the equatorial central IO, and off Madagascar in the southwestern IO. As this is the only blue whale song that has been identified in the western Arabian Sea, we label it the ‘Northwest Indian Ocean’ song-type to distinguish it from other regional song-types. Spatiotemporal variation suggested a distribution west of 70°E, with potential affinity for the northern IO/Arabian Sea, and only minor presence in the southwestern IO. Timing of presence off Oman suggested that intensive illegal Soviet whaling that took 1294 blue whales in the 1960s likely targeted this population, as opposed to the more widely distributed ‘Sri Lanka’ acoustic population as previously assumed. Based upon geographic distribution and potential aseasonal reproduction found in the Soviet catch data, we suggest that if there is a northern IO subspecies (B. m. indica), it is likely this population. Moreover, the potentially restricted range, intensive historic whaling, and the fact that the song-type has been previously undetected, suggests a small population that is in critical need of status assessment and conservation action.

Plectorhinchus makranensis (Teleostei, Haemulidae), a new species of sweetlips from the Persian Gulf and the Gulf of Oman.

Plectorhinchus makranensissp. nov. is described on the basis of 16 specimens from the Persian Gulf and Gulf of Oman, in the Northwest Indian Ocean. The new species can be distinguished from congeners by a combination of dorsal fin rays XII, 18–20, pectoral-fin rays 16–17, tubed lateral-line scales 55–57, gill rakers count (10–12 on the upper limb and 16–17 on the lower limb), 17–18 scales between the lateral line and the first anal-fin spine, 30–31 circumpeduncular scale rows and color pattern. Plectorhinchus makranensissp. nov. is distinguished from P. schotaf by having the posterior margin of the opercular membrane grey (vs. red in P. schotaf), fewer circumpeduncular scale rows, and a shorter base of the soft portion of the dorsal fin, 27.6–29.4% of standard length (SL) (vs. 31–32.3% of SL in P. schotaf). The new species resembles P. sordidus but is differentiated from it by having more gill rakers, a smaller orbit diameter 27.5–32.1% of head length (HL) (vs. 35.5–37.2% of HL in P. sordidus), a longer caudal peduncle 19.2–21.3% of SL (vs. 17.1–17.9% of SL in P. sordidus), and the first to third pectoral-fin rays light gray (vs. dark gray in P. sordidus). The new species can also be distinguished from the other species, including P. schotaf and P. sordidus, based on COI and Cyt b molecular markers. The phylogenetic position of this new species indicates that it is a sister taxon of P. schotaf.

Wocania indica gen. nov., sp. nov., isolated from deep sea hydrothermal sulfide in the northwest Indian Ocean, and proposal to reclassify Flaviramulus ichthyoenteri as Wocania ichthyoenteri comb. nov.

A novel Gram-stain-negative, non-motile, strictly aerobic, rod-shaped bacterium was isolated from deep-sea hydrothermal sulfide in the northwest Indian Ocean Ridge and designated as strain IOP_32T. Strain IOP_32T could grow at 4-40 °C (optimum, 37 °C), pH 5-9 (optimum, pH 7-8) and salinity of 0-12 % NaCl (w/v; optimum, 2-3 %). The 16S rRNA gene sequence of strain IOP_32T is most similar to Bizionia fulviae EM7T, Bizionia berychis RA3-3-1T, Bizionia paragorgiae KMM 6029T and Oceanihabitans sediminis S9_10T with 95.5-95.3 % similarity. The phylogenomic analysis indicated that strain IOP_32T forms a distinct lineage with Flaviramulus ichthyoenteri Th78T within the family Flavobacteriaceae. The average nucleotide identity, average amino acid identity and percentage of conserved protein values between strain IOP_32T and the type strains of close genera were 72.3-78.5 %, 67.4-76.9 % and 56.3-61.6 %, respectively. The major cellular fatty acid was anteiso-C15 : 0. The respiratory quinone was MK-6. The polar lipids were mainly composed of phosphatidylethanolamine, an unidentified aminophospholipid and five unidentified polar lipids. Strain IOP_32T is significantly different from related genera, which is reflected by the wide adaptability to temperature and salinity levels, the composition of phospholipids and fatty acids, and the results of phylogenetic analyses. The phenotypic properties and phylogenetic data suggest that the lineage represents a novel genus and species within the family Flavobacteriaceae, for which the name Wocania indica gen. sp. nov. is proposed, with the type strain IOP_32T (=MCCC 1A14017 T=KCTC 62660 T). We also propose the reclassification of Flaviramulus ichthyoenteri as Wocania ichthyoenteri comb. nov. (Th78T=DSM 26285T=JCM 18634T=KCTC 32142T).

Evaluating the Long-Term Trend and Management of a Globally Important Loggerhead Population Nesting on Masirah Island, Sultanate of Oman

Nest count surveys provide an important means for tracking trends in marine turtle populations. In 2015 the IUCN Red List global status review changed the loggerhead turtle (Carretta caretta) from Endangered to Vulnerable status, and, with a revised regional management unit (RMU) assessment system in place, concluded that the Northwest Indian Ocean loggerhead turtle RMU was Critically Endangered (CR). We analyzed annual time series nest count survey data between 1978 and 2016 to evaluate population trend and characterize the existing spatial and temporal attributes of a globally significant rookery on Masirah Island, Oman. A two-point trend assessment using a subset of historical data (1985-1996) combined with recent data (2008-2016) on a representative, 9-km section of index beaches revealed a change from 584 tracks-1 km-1 season-1 (SD = 109.5) to 122.43 tracks-1 km-1 season-1 (SD = 37.3), representing a statistically significant 79% decline. Comparative data were tested for spatial and temporal conformity, and the influence of other parameters on the trend result were considered, such as nesting success ratios and spatial shifts in density. Our analyses confirm that the decline occurred within a single loggerhead generation. Mean multiyear nest counts from recent surveys provides an estimate of 55,202 nests year-1 (SD=16,814, CI 0.95 53,326- 57,078) across 83 km of nesting beach. Considering recent clutch frequency estimates the mean number of nesting loggerheads per year is estimated between 10,223 (CI 0.95 9,875- 10,570) and 11,500 (CI 0.95 11,109- 11,891). The Northwest Indian Ocean RMU is thought to represent 35% of the global nesting population. Recognizing a pressing need to address the decline in this population we identify potential threats on nesting beaches and at sea which point towards priority actions for conservation of this CR RMU.

Interdecadal Change of Drought Characteristics in Mahaweli River Basin of Sri Lanka and the Associated Atmospheric Circulation Difference

Understanding the spatiotemporal characteristics of drought at the river basin scale is vital for water resources management. In this study, the interdecadal variation of drought characteristics over the Mahaweli River Basin (MRB) in Sri Lanka was investigated for the 1985-2015 period, using the standardized precipitation-evapotranspiration index (SPEI). Remarkable interdecadal change of yearly drought characteristics between 1985-1999 and 2000-2015 periods in the wet region of MRB can be found for medium-term and long-term drought, with indications of that more frequent and severer drought events as well as longer duration of total drought months, occurred during 2000-2015 period. Furthermore, interdecadal enhancement of yearly drought in the wet region can be attributed to changes of seasonal drought in southwest monsoon season, and this is coherent with the interdecadal shift of the SWM rainfall amount from wet to dry situations since the year 2000. However, no significant interdecadal change of drought was found in the intermediate and dry regions of MRB, as well as the short-term drought in the wet region. The interdecadal difference of atmospheric circulation demonstrates that the South Asian monsoon was weakened after 2000, which is accompanied by the weakening of monsoon trough, reduced cross-equatorial flow from the southern hemisphere from wind circulation at 850 hPa, and positive anomalies of geopotential height at 500 hPa over south Asian region. The weakening of South Asian monsoon leads to lesser moisture transport from the northwest Indian Ocean to Sri Lanka, inducing net moisture divergence anomalies in Sri Lanka, and ultimately results in more drought events during SWM season in the region since the year 2000.

Beak morphological and growth characteristic of Sthenoteuthis oualaniensis in the northwest Indian Ocean in winter and spring

Beak is one of the most important hard tissues of cephalopods, and thus is widely used in the study of cephalopod fisheries ecology and fishery resource assessment. With 1009 Sthenoteuthis oualaniensis samples collected by Chinese light falling-net fishery during February to May in the northwest Indian Ocean, we examined the morphologic and growth characteristics of beak. Results of the principal component analysis showed that the upper hood length (UHL), the upper crest length (UCL), the upper lateral wall length (ULWL), the lower crest length (LCL), the lower wing length (LWL) and the lower lateral wall length (LLWL) could be used as the morphological cha-racteristic parameters to examine the morphological changes of the beak. Results of the analysis of covariance (ANCOVA) showed that there were significant differences in the relationships between all of the morphological characteristic parameters and mantel length (ML) for males and females except UCL. There were significant differences in the relationships between all of the morphological characteristic parameters and body weight (BW) for males and females. The relationships between LCL, UCL and ML were optimally described by the linear functions. Power functions were best for UHL, LWL and linear functions were best for ULWL, LLWL for females. The relationships between ULWL and ML were optimally described by power functions, while the logarithm functions were best for UHL, LLWL and LWL for males. The relationships between all of the morphological characteristic parameters and BW were optimally described by the power functions for females, while the logarithm functions for males except the power function for ULWL. Our results provided scientific basis for the research of the fisheries ecology and stock assessment for S. oualaniensis.

Anomalous distribution of distinctive water masses over the Carlsberg Ridge in May 2012

Abstract. In May 2012, we conducted a hydrographic survey over the Carlsberg Ridge in the northwest Indian Ocean. In this paper, we use these station data, in combination with some free-floating Argo profiles, to obtain the sectional temperature and salinity fields, and subsequently, the hydrographic characteristics are comprehensively analyzed. Through the basic T–S diagram, three salty water masses, Arabian Sea High-Salinity Water, Persian Gulf Water, and Red Sea Water, are identified. The sectional data show a clear ventilation structure associated with Arabian Sea High-Salinity Water. The 35.8 psu salty water sinks at 6.9∘ N and extends southward to 4.4∘ N at depths around the thermocline, where the thermocline depth is in the range of 100 to 150 m. This salty thermocline extends much further south than climatology indicates. Furthermore, the temperature and salinity data are used to compute the absolute geostrophic current over the specific section, and the results show mesoscale eddy vertical structure different from some widely used oceanic reanalysis data. We also find a west-propagating planetary wave at 6∘ N, and the related features are described in terms of phase speed and horizontal and vertical structures.

Development and application of a temperature gradient detector for manned underwater robot

Manned underwater robot is an important platform to carry various sensors and working tools to finish the in situ measurement and sampling in the deep sea. Due to its limited loading capacity, the device it will be carried, usually, requires to be able to dive to its working depth with a small volume and weight. According to the application requirements of deep-sea sediment temperature gradient in situ measurement observed, a detector system that can obtain data in situ is designed, which mainly includes a titanium alloy electronic cabin and a temperature probe. A comprehensive design analysis method is used to compare and analyze the ultimate static pressure, stability limit load, bending moment load, and transient temperature field on the underwater operation conditions. Optimal dimensions and filled media in the probe are decided. Finally, the pressure resistance test is finished in the lab, and scientific application is conducted on Jiaolong’s 127th dive in the Northwest Indian Ocean, which successfully sampling the temperature gradient data of deep-sea sediments in the Daxi hydrothermal area. The method introduced in this article can effectively improve the safety and reliability of deep-sea structure and greatly reduce costs throughout the design cycle.

Gimesia benthica sp. nov., a planctomycete isolated from a deep-sea water sample of the Northwest Indian Ocean.

A Gram-stain-negative, stalked, oval-shaped and budding bacterial strain, designated E7T, was isolated from a deep-sea water sample collected from the Northwest Indian Ocean. The novel strain was strictly aerobic, and catalase- and oxidase-positive. It grew at 6-40 °C (optimum 30 °C) and pH 5.5-8.0 (optimum pH 7.0-7.5). The strain required 0.5-9.0 % (w/v) NaCl (optimum 3.0-5.0 %) for growth. Aesculin, starch, pectin and Tween 20 were hydrolysed. Based on 16S rRNA gene sequence analysis, strain E7T showed the highest similarity with Gimesia maris DSM 8797T (97.5 %). The average nucleotide identity and in silico DNA-DNA hybridization values between strain E7T and G. maris DSM 8797T were 78.0 and 19.3 %, respectively. The predominant cellular fatty acids of strain E7T were C16 : 0 and summed feature 3 (comprising C16 : 1ω7c and/or C16 : 1ω6c). The major respiratory quinone was menaquinone-6 (MK-6) and the major polar lipids were phosphatidylethanolamine (PE), phosphatidylmonomethylethanolamine (PMME), phosphatidyldimethylethanolamine (PDME), phosphatidylcholine (PC) and diphosphatidylglycerol (DPG). The genomic DNA G+C content of strain E7T was 52.8 mol%. On the basis of phylogenetic inference and phenotypic characteristics, it is proposed that strain E7T represents a novel species of the genus Gimesia, for which the name Gimesia benthica sp. nov. is proposed. The type strain is E7T (=CGMCC 1.16119T=KCTC 72737T).

Halovulum marinum sp. nov., isolated from deep-sea water of the Indian Ocean, and emended description of the genus Halovulum.

A novel Gram-stain-negative, aerobic, motile by peritrichous flagella, oval to rod-shaped bacterium, designated strain 2CG4T, was isolated from a deep-sea water sample collected from the Northwest Indian Ocean. The results of phylogenetic analysis of both 16S rRNA gene and RpoC protein sequences indicated that this strain was affiliated with the genus Halovulum in the Amaricoccus clade of the family Rhodobacteraceae of the class Alphaproteobacteria, sharing 95.3 % similarity at the 16S rRNA gene sequence level with the type strain of Halovulum dunhuangense YYQ-30T, the only species in the genus Halovulum. The predominant fatty acids (>10 %) of 2CG4T were summed feature 8 (C18 : 1ω7c and/ or C18 : 1ω6c; 61.1 %) and cyclo-C19 : 0ω8c (15.6 %). The polar lipids of 2CG4T were phosphatidylethanolamine, phosphatidylmethylethanolamine, phosphatidylglycerol, diphosphatidylglycerol, phosphatidylcholine and sulfoquinovosyldiacylglycerol. The only isoprenoid quinone of 2CG4T was ubiquinone-10. The DNA G+C content of 2CG4T was determined to be 69.4 %. The central gene pufLM for the photosynthetic reaction was not detected. No growth occurred for 2CG4T in the absence of NaCl. On the basis of these data, it is concluded that the 2CG4T represents a novel species of the genus Halovulum, for which the name Halovulum marinum sp. nov. is proposed. The type strain is 2CG4T (=CGMCC 1.16468T=JCM 32611T).

Moisture sources associated with heavy rainfall over the Limpopo River Basin, southern Africa

Moisture sources and pathways over the Limpopo River Basin (LRB) in southern Africa were identified using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model applied to NCEP II (2.5° × 2.5°) reanalysis data for 1981–2016. The 10-day air parcel backward trajectories were produced for the extended wet season (October–April) as well as the early and late summer. Analysis of a 36-year climatology of air parcel trajectories indicated seven moisture source regions for the LRB; namely, local continental, tropical southeast Atlantic Ocean, midlatitude South Atlantic Ocean, tropical northwest Indian Ocean, tropical southwest Indian Ocean, subtropical southwest Indian Ocean, and the Agulhas Current. The results have shown that important differences in moisture source regions and pathways exist between early (October–December) and late (January–April) summers, with the tropical northwestern Indian Ocean and the northern Agulhas Current sources more prominent during JFMA than OND. On interannual time scales, there are notable differences in moisture source regions between anomalously wet and dry summers, with the South Indian Ocean moisture contribution and transport over the LRB smaller during dry summers than wet summers. Changes in specific humidity for trajectory linked to heavy daily rainfall events (defined from CHIRPS data) showed that subtropical South Indian Ocean source is more extensive for the heavy rainfall than for the moderate case. Generally, moisture source regions and transport pathways for LRB tend to be influenced by both the regional summer season circulation and the synoptic setting.

Imprints of ancient recycled oceanic lithosphere in heterogeneous Indian Ocean mantle: Evidence from petrogenesis of Carlsberg ridge basalts from Northwest Indian Ocean

This paper reports new petrological, geochemical and isotopic data for Carlsberg Ridge Basalts (CRB) of northwest Indian Ocean and evaluates their petrogenetic aspects in the context of the geochemical and tectonic evolution of the Indian Ocean mantle. The CRB samples exhibit tholeiitic to transitional composition of precursor melts derived by high degree, shallow level partial melting of a spinel peridotite mantle source. CRB reflects distinct E-MORB affinity with selective enrichment in incompatible trace elements. Higher values of Zr/Hf (33.8–47.3) and Zr/Sm (24.9–36.4) in conjunction with lower Nb/Ta (1.7–7.3) ratio corroborate their origin from an enriched mantle source. Negative Nb anomalies with lower Nb/Y (0.04–0.11) and Zr/Y (2.5–3.5) conform to a non-plume origin of these basalts. Higher Zr/Nb (25.5–71.5) and Th/Nb (0.6–0.42) compared to OIB substantiate contributions from recycled subduction-processed components in the source mantle. Lower Nb/U (6.2–37.9) values with higher Ba/Nb (6.1–21.9), Ba/Th (27.7–147.5), Zr/Nb (25.5–71.5) and Th/Nb (0.6–0.42) compared to OIB and N-MORB attest to role of a metasomatized oceanic lithosphere that recycled into the depleted upper mantle attributing to the source heterogeneity. Sr-Nd isotopic signatures (87Sr/86Sr: 0.702668 to 0.702841 and 143Nd/144Nd: 0.512972 to 0.513068) of CRB suggest a HIMU source component preserved in the northwest Indian Ocean Ridge mantle. The compositional diversity of the Indian Ocean mantle can be translated in terms of periodic refertilization of depleted N-MORB type mantle through delamination and recycling of oceanic (HIMU component) and continental lithosphere (EM I component) concurrent with Neoproterozoic-Palaeozoic amalgamation and Jurassic dispersal of Gondwana Supercontinent respectively. This study complies with the derivation of CRB from a geochemically heterogeneous Indian Ocean mantle that experienced a protracted residence beneath the Gondwana Supercontinent prior to the opening of Indian Ocean and trapped recycled metasomatized oceanic lithosphere genetically linked with multiple stages of paleo-ocean closure and continental convergence during Gondwana assembly.

Large‐Scale Dynamics and Moisture Sources of the Precipitation Over the Western Tibetan Plateau in Boreal Winter

AbstractOne of the heaviest precipitations over the Asian continent in winter is located in the western Tibetan Plateau (TP). In this study, the dynamics of the precipitation over the western TP (PWTP) in boreal winter and its interannual variability are explored. The moisture origins and paths are detected using a Lagrangian Integrated Trajectory model. In climatology, the PWTP is generated as results of upward air motions on the windward side of the TP and ranges from 0.5 to 2.5 mm·day−1. Under the influence of midlatitude westerlies and the subtropical high over the Arabian Peninsula, three key moisture sources (by percentage contribution) are identified: South Asia‐North Indian Ocean (56.6%), Central Eurasia‐North Africa (37.7%), and Central‐North Atlantic (5.6%). The dominant precipitating cloud types are nimbostratus and stratus/stratocumulus derived from satellite data. On the interannual timescale, PWTP variation is closely associated with El Niño‐Southern Oscillation (ENSO) and midlatitude cyclones. ENSO warm events lead to an anomalous anticyclone over the tropical northwest Indian Ocean and intensify moisture transport northward in the lower troposphere, as well as abnormal divergence in upper troposphere. However, ENSO explains only about 38.1% of the PWTP variance. Midlatitude teleconnection also contributes to the PWTP variability, which is comparable to the effect of ENSO. The cyclones imbedded in the subtropical jet are part of the teleconnection, with an anticyclone upstream over the North Atlantic and an cyclone over the western TP. Further evidence suggests that the transient eddies in the North Atlantic help to maintain the teleconnection.

Precipitation of Calcite Veins in Serpentinized Harzburgite at Tianxiu Hydrothermal Field on Carlsberg Ridge (3.67°N), Northwest Indian Ocean: Implications for Fluid Circulation

Serpentinization and calcite precipitation of mantle peridotites exhumed along detachment faults at the slow- to ultraslow-spreading centers can provide important clues to the hydrothermal alteration processes. The Tianxiu hydrothermal field is a new-found active and ultramafichosted hydrothermal vent site along the Carlsberg Ridge, Northwest Indian Ocean. Two types of calcite veins are recognized in serpentinized harzburgite samples collected from the seafloor at the water depth of 3 500 m (3.67°N/63.83°E) and 400 m north of Tianxiu hydrothermal field. Calcite veins I occur in the fractures that cut through mesh texture in the highly serpentinized harzburgite, while calcite veins II precipitate within the mesh texture in the relatively weaker serpentinized harzburgite. Both veins show similar δ13CPDB (+0.54‰ and +0.58‰) but different δ18OPDB(−16.67‰ and +4.46‰) values, suggesting that they were derived from the same carbon source but precipitated at different temperatures. Taking the deep seawater temperature of 2 °C as the precipitation temperature of the calcite veins I, the equilibrium δ18OV-SMOW of calcite-precipitating fluid was calculated to be 1.78‰, which is close to the average δ18OV-SMOW value (1.74‰) of vent fluid samples from the ultramafic-hosted hydrothermal systems worldwide. The formation temperature of calcite veins II is inferred to be approximately 134 °C, based on the calculated δ18OV-SMOW above. The temperature differences of calcite precipitation probably resulted from the fluid cooling conductively and mixing with seawater along the presumed fractures during slow upflow. The low-temperature calcite postdates the mesh texture, while the high-temperature calcite may precipitate under relatively low water/rock ratios, alkaline and reduced conditions among the mesh texture, which is revealed by the geochemical models. Therefore, it is suggested that they both have been influenced by hydrothermal fluids and the sampling site is near the discharge zone of hydrothermal circulation.

Influence of northwest Indian Ocean sea surface temperature and El Niño–Southern Oscillation on the winter precipitation in Iran

Abstract This paper studies the impact of northwest Indian Ocean (NIO) sea surface temperature (SST) anomalies between the regions 0–29°N and 45–80°E and El Niño–Southern Oscillation (ENSO) on the winter precipitation in Iran. The data include monthly precipitation from 45 weather stations in Iran, monthly NIO SST with a 2° horizontal resolution and Southern Oscillation Index (SOI) for a 40-year period (1975–2014). This study utilizes canonical correlation analysis and partial correlation to investigate the simultaneous relationship between SST, SOI, and winter precipitation variability. A running correlation method is also used to test the stationarity of these relationships. Analyses of the results reveal that both NIO SST and ENSO index are significantly correlated with the winter precipitation in Iran but with opposite sign. Moreover, a clear variability exists in the correlations revealing a distinct non-stationarity in the relationship over time. The results of partial correlation analysis suggest that the ENSO index has a stronger effect on the winter precipitation in Iran than NIO SST.