The African continental divide: Indian versus Atlantic Ocean spreading during Gondwana dispersal

ABSTRACT It is well established that plate-tectonic processes operate on a global scale and that spatially separate but temporally coincident events may be linked. However, identifying such links in the geological record and understanding the mechanisms involved remain speculative. This is particularly acute during major geodynamic events, such as the dispersal of supercontinents, where multiple axes of breakup may be present as well as coincidental collisional events. To explore this aspect of plate tectonics, we present a detailed analysis of the temporal variation in the mean half rate of seafloor spreading in the Indian and Atlantic Oceans, as well as plate-kinematic attributes extracted from global plate-tectonic models during the dispersal of Gondwana since ca. 200 Ma. Our analysis shows that during the ~20 m.y. prior to collision between India and Asia at ca. 55 Ma, there was an increase in the mean rate of seafloor spreading in the Indian Ocean. This manifests as India rapidly accelerating toward Asia. This event was then followed by a prompt deceleration in the mean rate of Indian Ocean seafloor spreading after India collided with Asia at ca. 55 Ma. Since inception, the mean rate of seafloor spreading in the Indian Ocean has been generally greater than that in the Atlantic Ocean, and the period of fastest mean half spreading rate in the Indian Ocean was coincident with a slowdown in mean half seafloor spreading rate in the competing Atlantic Ocean. We hypothesize that faster and hotter seafloor spreading in the Indian Ocean resulted in larger ridge-push forces, which were transmitted through the African plate, leading to a slowdown in Atlantic Ocean spreading. Following collision between India and Asia, and a slowdown of Indian Ocean spreading, Atlantic spreading rates consequently increased again. We conclude that the processes in the Indian and Atlantic Oceans have likely remained coupled throughout their existence, that their individual evolution has influenced each other, and that, more generally, spreading in one basin inevitably influences proximal regions. While we do not believe that ridge push is the main cause of plate motions, we consider it to have played a role in the coupling of the kinematic evolution of these oceans. The implication of this observation is that interaction and competition between nascent ocean basins and ridges during supercontinent dispersal exert a significant control on resultant continental configuration.

Large-magnitude oceanic intraplate seismicity: Implications for lithosphere evolution

ABSTRACT We analyzed 37 large oceanic intraplate earthquakes (M >6). The largest (M >7) are mainly concentrated under the Indian Ocean. Moderate events (6 < M < 7) are sparsely distributed under the Indian Ocean and other oceans where lithospheric ages are between 90 Ma and 20 Ma. Oceanic intraplate events related to mantle plumes or hotspots are rare, though low-velocity anomalies beneath hotspots are a common feature. Tomographic cross sections for Indian Ocean areas with large intraplate earthquakes indicate strong heterogeneity in the mantle. These earthquakes are explained by shallow stress variations caused by a combination of tectonic forces including slab-pull, ridge-push, drag by mantle flow, plume-push, and buoyancy forces as a consequence of low-velocity anomalies in the mantle. Oceanic intraplate seismicity in the Indian Ocean is related to the large-scale, low-velocity anomaly structure around the Ninety East Ridge.

Microwave-Assisted Desulfation of the Hemolytic Saponins Extracted from Holothuria scabra Viscera

Saponins are plant and marine animal specific metabolites that are commonly considered as molecular vectors for chemical defenses against unicellular and pluricellular organisms. Their toxicity is attributed to their membranolytic properties. Modifying the molecular structures of saponins by quantitative and selective chemical reactions is increasingly considered to tune the biological properties of these molecules (i) to prepare congeners with specific activities for biomedical applications and (ii) to afford experimental data related to their structure–activity relationship. In the present study, we focused on the sulfated saponins contained in the viscera of Holothuria scabra, a sea cucumber present in the Indian Ocean and abundantly consumed on the Asian food market. Using mass spectrometry, we first qualitatively and quantitatively assessed the saponin content within the viscera of H. scabra. We detected 26 sulfated saponins presenting 5 different elemental compositions. Microwave activation under alkaline conditions in aqueous solutions was developed and optimized to quantitatively and specifically induce the desulfation of the natural saponins, by a specific loss of H2SO4. By comparing the hemolytic activities of the natural and desulfated extracts, we clearly identified the sulfate function as highly responsible for the saponin toxicity.

Doing Action Research: The Experience of Teachers in Seychelles

Action research is regarded as a dynamic strategy to galvanise teachers to determine what works best for them and their pupils. Teachers’ experience in action research has been investigated in some developing countries without involving any of the small island states in the Indian Ocean. Hence, this study explored the experience of teachers from Seychelles regarding action research focusing on their understanding of the nature, meaning, and purpose of action research; the benefits they gained from doing action research; the difficulties and the challenges they encountered while conducting action research, including their background characteristics. Its aim was to identify their successes, concerns, and issues. Participants were 33 primary school teachers enrolled in the two-year Advanced Diploma programme at the Seychelles Institute of Education during the 2019/2020 academic year. One of their assessment tasks required them to identify a difficulty that their pupils encounter and conduct action research on it with a view to finding a solution. Data collected using a self-reporting questionnaire designed by the investigators was analysed using both descriptive and interpretive techniques. Results indicated that the participants had a mixed experience of successes, concerns, and issues.

Relationship between surface fields over Indian ocean and monsoon rainfall over homogeneous zones of India

The monthly mean atmospheric fields and surface parameters of NCEP/NCAR reanalysis for the period 1948-1998 have been studied to examine the characteristics of monsoon circulation features, sea surface temperature (SST), sea level pressure, surface wind stress and latent heat flux over the Indian Ocean and nearby seas during deficient, normal and excess rain years. The entire period of study has been classified into deficient, normal and excess rain years for all India as well as for each of the five homogeneous zones separately based on the observed seasonal mean rainfall. On the basis of the mean characteristics of the surface fields, the oceanic region covering the Indian Ocean and adjacent seas has been divided into four regional sectors. Using various statistical means the relation between the surface fields over the four regional sectors and the monsoon rainfall over five homogeneous zones of Indian landmass has been examined. Attempt have been made to identify some surface parameters which can be used as predictors for seasonal mean monsoon rainfall over the entire India and also over some homogeneous zones.

Paralomis White, 1856 (Crustacea: Decapoda: Anomura) from India, with morphological variability in Paralomis indica Alcock & Anderson, 1899

Deep-water king crabs of the genus Paralomis White, 1856 collected during three cruises of the Fishery Oceanographic Research Vessel Sagar Sampada in the western Bay of Bengal (528–777 m depths), one cruise in the eastern Bay of Bengal off Great Nicobar Island (337 m depth), and four cruises in the southeastern Arabian Sea (315–1245 m) were identified. They are referred to Paralomis ceres Macpherson, 1989, recorded for the first time from Indian waters and P. indica Alcock & Anderson, 1899, reported for the first time from the Bay of Bengal and the Andaman Sea. In addition, this study reports the morphological variability among the P. indica populations in the shape of the carapace and dorsal rostral spines, nature of the branchial and cardiac regions and abdominal marginal spines, and the relative lengths of pereopods 2–4. Mitochondrial Cytochrome oxidase I (594 base pairs) and 16S rRNA (503 bp) gene sequences of P. ceres and P. indica (602 and 497 bp, respectively) revealed that they formed distinct lineages. A key to the Indian Ocean species of Paralomis is provided.

Cloud climatology of the Indian Ocean based on ship observations

Surface cloud data based on synoptic observations made by Voluntary Observing Ships (VOS) during the period 1951-98 were used to prepare the seasonal and annual cloud climatology of the Indian Ocean. The analysis has been carried out by separating the long-term trends, decadal and inter-annual components from the monthly cloud anomaly time series at each 5° × 5° grids. Maximum zone of total and low cloud cover shifts from equator to northern parts of India during the monsoon season. During the monsoon season (June-September), maximum total cloud cover exceeding 70% and low cloud cover exceeding 50% are observed over north Bay of Bengal. Maximum standard deviation of total and low cloud cover is observed near the equator and in the southern hemisphere. Both total and low cloud cover over Arabian Sea and the equatorial Indian Ocean are observed to decrease during the ENSO events. However, cloud cover over Bay of Bengal is not modulated by the ENSO events. On inter-decadal scale, low cloud cover shifted from a "low regime" to a "high regime" after 1980 which may be associated with the corresponding inter-decadal changes of sea surface temperatures over north Indian Ocean observed during the late 1970s.

First record of the family Issidae (Hemiptera, Auchenorrhyncha: Fulgoroidea) from the Hawaiian Islands

Euroxenus vayssieresi (Bonfils, Attie & Reynaud, 2001) (Issinae, Sarimini) was described (in the genus Borbonissus Bonfils, Attie & Reynaud, 2001) from Réunion Island, in the Indian Ocean and previous to this report has not been recorded elsewhere. Euroxenus vayssieresi is here illustrated and redescribed to improved taxonomic diagnosis. Euroxenus vayssieresi is recorded for the first time from the island of Hawaii in the Hawaiian Archipelago. This is first record of the family Issidae from the Hawaiian Archipelago.

DNA Barcoding of Scavenging Amphipod Communities at Active and Inactive Hydrothermal Vents in the Indian Ocean

Hydrothermal vent areas have drawn increasing interest since they were discovered in 1977. Because of chemoautotrophic bacteria, they possess high abundances of vent endemic species as well as many non-vent species around the fields. During the survey conducted by the Bundesanstalt für Geowissenschaften und Rohstoffe (Federal Institute for Geosciences and Natural Resources, BGR) to identify inactive polymetallic sulfide deposits along Central and Southeast Indian Ridges, the INDEX project studied the scavenging amphipod community at three newly discovered hydrothermal fields. A sample consisting of 463 representatives of Amphipoda (Malacostraca: Crustacea) was collected by means of baited traps in active and inactive vents of three different sites and subsequently studied by both morphological and genetic methods. Molecular methods included the analysis of two mitochondrial (cytochrome c oxidase subunit I [COI] and 16S rRNA) and one nuclear (18S rRNA) genes. By six delimitation methods, 22 molecular operational taxonomic units (MOTUs) belonging to 12 genera and 10 families were defined. The existence of potential species complexes was noted for the representatives of the genus Paralicella. The inactive site, where 19 species were found, showed higher species richness than did the active one, where only 10 taxa were recorded. Seven genera, Ambasiopsis, Cleonardo, Eurythenes, Parandania, Pseudonesimus, Tectovalopsis, and Valettiopsis, were observed only at inactive sites, whereas Haptocallisoma, was collected exclusively at active ones. The species Abyssorchomene distinctus (Birstein and Vinogradov, 1960), Hirondellea brevicaudata Chevreux, 1910, and Hirondellea guyoti Barnard and Ingram, 1990, have been previously reported from vent sites in the Atlantic or Pacific oceans. The present study provides the first report of Eurythenes magellanicus (H. Milne Edwards, 1848) and five other already described species in the Indian Ocean. The addition of 356 sequences strongly increases the number of amphipod barcodes in reference databases and provides for the first time COI barcodes for Cleonardo neuvillei Chevreux, 1908, Haptocallisoma abyssi (Oldevig, 1959), Hirondellea guyoti, Tectovalopsis fusilus Barnard and Ingram, 1990, and the genera Haptocallisoma, Pseudonesimus, and Valettiopsis.