Ozone decline and its effect on night airglow intensity of Na 5893 Å at Dumdum (22.5°N, 88.5°E) and Halley Bay (76°S, 27°W)

The paper presents the effect of O₃ depletion on night airglow emission of Na 5893 Å line at Dumdum (22.5°N, 88.5°E), India and Halley Bay (76°S, 27°W), a British Antarctic service station. Calculations based on chemical kinetics show that the airglow intensity of Na 5893 Å line will also be affected due to the depletion of O₃ concentration. The nature of yearly variation and seasonal variation of the intensity of Na 5893 Å line for the above two stations are shown and compared. It is shown that the rate of decrease of intensity of Na 5893 Å line is comparatively more at Halley Bay due to the dramatic decrease of Antarctic O₃ concentration. A possible explanation for this dramatic decrease of Antarctic O₃ concentration is also mentioned.     

Entrainment of circumpolar water in the Indian Ocean region of the Antarctic

The net influx of the circumpolar water on the western (approximately along 10°E) and eastern (approximately 115°E) boundaries of the Indian Ocean, adopting the method of Montgomery and Stroup is computed on bivariate distribution of potential thermosteric anomaly and salinity to identify the characteristics of the flux. The zonal flux at both the boundaries indicates an alternate strong easterly and westerly flow between 36°S and 45°S, south of which the flow is mainly easterly but weak up to 56°S. At the western boundary the easterly flow is 146 Sv and westerly is 98.07 Sv, while at the eastern boundary (115°E) the corresponding fluxes are 123.46 Sv and 27.20 Sv respectively, indicating a net outflux of 48.33 Sv. This water should have been accounted by the melting of ice and influx of the Equatorial Pacific Ocean Water.     

ON THE GEOLOGY OF THE MIRNYY STATION AREA

The U. S. S. R. -IGY Antarctic station, Mirnyy [66°31'S. 93°E.], is situated on four outcrops of Precambrian charnockitic granite, crystalline schist, and gneiss. The four mounds contain numerous angular xenoliths, generally dark schist and gneiss, denoting a palingenetic origin for the bedrock. Quartz veins and sulfide mineralization indicate later hydrothermal activity. The mounds are cut by two major fissure systems perpendicular to each other and several secondary fissure systems. In general, the offshore islands (the Haswell Islets) and the mounds are similar to the ancient Antarctic shield and are, therefore, considered to be a part of it. --Editor.     

Equatorial Currents in the Indian Ocean Based on Measurements in February 2017

We analyze the results of measurements of the Tareev equatorial undercurrent in the Indian Ocean in February 2017. Sections from 3° S to 3°45′ N along 68° and 65° E crossed the current with measurements of the temperature, salinity, and current velocity at oceanographic stations. The maximum velocity of this eastward flow was recorded precisely at the equator. The velocity at a depth of 50 m was approximately 60 cm/s. The transport of the Tareev Current was estimated at 9.8 Sv (1 Sv = 10⁶ m³/s).     

Hydrography and circulation off the Antarctica in the Indian Ocean region

The hydrography and circulation pattern off Antarctica in the Indian Ocean region are studied using vertical sections of temperature, salinity and oxyty approximately along 20°E, 77°E and 90°E, and the dynamic topography of the sea surface with reference to 1000 db. Based on the oceanographic characteristics, the whole region under study can be divided into three zones, the extreme ends being characterised by the frontal structure. The dicothermal layer is conspicuous during summer south of 50°S. The surface flow around Antarctica is mainly zonal. The East Wind Drift, found as a narrow westward flow near Antarctica, is observed at a lower latitude in the eastern Indian Ocean where the land extends northword. Contrary to expectation there is evidence of a westward flowing surface current at about 35°S between 45°E and 65°E.     

Ocean model derived global surface circulation and Vertical velocity

In this article, the authors examine Sea surface temperature (SST), Sea surface circulation (SSC) and Vertical velocity (VV) fields from simulation of 25 layers coarse resolution Modular ocean model (MOM version 3.0) with prescribed wind forcing for the region 74.25°S to 65°N, 180°W-180°E. It is found that distribution of SST simulated by the model shows its consistency with the observed climatology. However, simulated SST in the areas of Arabian Sea, Bay of Bengal, Indonesian Throughflow (ITF) region and east of North America near equator exhibit slight warming with respect to observation, which may be due to model deficiency and forcing problems. Circulation features suggest that one of the strongest current viz. Antarctic circumpolar current (ACC) along with other major current systems viz. Gulf stream current, North and South Pacific current, Agulhas current, Labrador current, Canary current, etc are captured well by the model. In the Indian Ocean and other ocean basins, current patterns are well captured by the model simulation. Intense upwelling as well as downwelling areas is marked in the horizontal distribution of VV, which is as expected. VV show quasi-stagnant and convergent regions suggesting that floating materials may be accumulated during January/July in the real ocean and wind driven circulation may act as an important contribution for such transport of floating materials in these regions. An attempt has also been made to understand the fluctuations of the SST in NINO 3.4 region during the period of model simulation using SST anomalies.     

Environmental reconstructions of the upper 500 m of the southern Indian Ocean over the last 40 ka using Radiolarian (Protista) proxies

In 2007, we demonstrated that radiolarians are proxies for a wide range of oceanic physico-chemical properties from the surface to depths of up to 500 m below sea level. In this study, our results are refined and Correspondence Analysis (CA) scores derived from census counts of radiolarian subfossils from southern Indian Ocean core-tops are correlated with the physico-chemical properties of the region obtained from the 2005 World Ocean Database.Calibration and regression techniques are employed to reconstruct palaeoenvironmental conditions spanning the last 40 ka for four Indian Ocean cores MD88-769 [46°04′S 90°06′E], MD88-770 [46°01′S 96°27′E], MD94-102 [43°30′S 79°50′E], and MD94-103 [45°35′S 86°31′E], all from close to the Southeast Indian Ridge. For the first time, reconstructions of temperature, salinity, dissolved oxygen, and the silicate, nitrate, and phosphate concentrations for a range of water depths are proved possible.Changes of the oceanic environment and the movement of water masses over the last 40 ka, as suggested by these reconstructions, are discussed. During Marine Isotope Stages 2 and 3 (MIS-2 and MIS-3), the water column at some of the core sites has similar characteristics to the waters south of the Polar Front today. At the MIS-1/MIS-2 transition, the development of the Subantarctic Mode Water is apparent. Temperature reconstructions include evidence of the Antarctic Cold Reversal and the Holocene Optimum.     

Spatial Distribution and Longitudinal Variation of Clay Minerals in the Central Indian Basin

Grain size and clay mineral distribution up to 45 cm depth in the silty clay sediments from 26 box cores from 10°to 16°S along four longitudes(73.5°-76.5°E)were studied for understanding spatial variability in the Central Indian Basin(CIB).It was observed that the average sand content in the basin is 3.8%,which decreases systematically and longitudinally to 0.3%towards south.The average illite and chlorite major clay mineral abundance also decrease southwards along the four longitudes from 10°S,and show ...     

First results from imaging riometer installed at Indian Antarctic station Maitri

Cosmic noise absorption (CNA) measurred by imaging riometer, is an excellent tool to passively study the high latitude D-region ionospheric conditions and dynamics. An imaging riometer has been installed at Indian Antarctic station Maitri (geographic 70.75°S, 11.75°E; corrected geomagnetic 63.11°S, 53.59°E) in February 2010. This is the first paper using the imaging riometer data from Maitri. The present paper introduces the details of this facility, including its instrumentation, related CNA theory and its applications. Sidereal shift of around 2 hours in the diurnal pattern validates the data obtained from the newly installed instrument. Moreover, the strength of cosmic noise signal on quiet days also varies with months. This is apparently due to solar ionization of D-region ionosphere causing enhanced electron density where collision frequency is already high. The main objective of installing the imaging riometer at Maitri is to study magneotspheric–ionospheric coupling during substorm processes. In the current study, we present two typical examples of disturbed time CNA associated with storm-time and non-storm time substorm. Results reveal that CNA is more pronounced during storm-time substorm as compared to non-storm time substorm. The level of CNA strongly depends upon the strengthening of convectional electric field and the duration of southward turning of interplanetary magnetic field before the substorm onset.     

A 70 ka record of explosive eruptions from the TALDICE ice core (Talos Dome,East Antarctic plateau)

The new Antarctic TALDICE ice core (72° 49′ S, 159° 11′ E, 1620 m depth), containing abundant primary tephras, provides the opportunity to elucidate the late Quaternary volcanic history of the south polar region, as well as to broaden the East Antarctic tephrostratigraphic framework. Here grain size and glass compositional data for representative tephra layers from the last 70 ka core section are used for source identification. Results point to origin of layers from centres of the Melbourne Volcanic Province (McMurdo Volcanic Group), located ～250 km from the coring site. Occurrence of tephra layers within the ice core record suggests that explosive activity in the identified source was not constant over the considered period, with a minimum of activity between 20 and 35 ka, and increased activity back to 65 ka. In addition to palaeovolcanic implications, the TALDICE tephra layers offer prospects for firm correlations between diverse widely separated palaeoarchives and for accurate dating of the Antarctic climatic record. Copyright © 2010 John Wiley & Sons, Ltd.     

Moisture sources of a torrential rainfall event in the arid region of East Xinjiang,China, based on a Lagrangian model

Moisture sources and transport paths for precipitation are of primary importance for forecasts and early warning, but are rarely studied in the arid region of China. Our study employed the hybrid single-particle Lagrangian integrated trajectory (HYSPLIT) model to investigate and quantify the moisture sources which contributed to a torrential rainfall event on 15–18 July 2007 in the arid Xinjiang region in China. Based on the distribution of torrential rains, the target study region was selected at East Xinjiang (35°N–45°N, 80°E–95°E). The results indicate that moisture sources originating from the south, west, and north branches, and moisture sources in the Atlantic Oceans and Central Asia regions contributed to the East Xinjiang rain event by 37 and 44%, respectively. Our findings match those from diagnostic results of an Eulerian framework model, but the HYSPLIT model provided better quantitative and objective results.     

The case for near-zero production of Antarctic Bottom Water

The most generally accepted production rate of Antarctic Bottom Water is 20 × 10⁶ m³/sec required by the Stommel and Arons (1960) abyssal circulation model. According to this model, after sinking in the Weddell Sea, this water flows northward into the ocean basins and upwells through the thermocline. Antarctic Bottom Water is rich in dissolved silicon but the thermocline and surface waters are almost silicon-free. If the model is valid, it follows that a removal of silicon must take place from the upwelled waters before they return southward as required by mass conservation. In the Pacific, the amount of silicon removal necessary to satisfy the model is calculated for a transpacific (SCORPIO) section at 28°S. This calculated removal is 30 × 10¹⁴g SiO₂/yr, which is many times the rate of silicon input to the world oceans. Two mechanisms for silicon removal north of 28°S are discussed, but reasons are given for rejecting both of them. It is concluded that production of Antarctic Bottom Water is negligible at the present time.     

Discussion: Structural and stratigraphic problems of the Argylla Formation near Mary Kathleen,Queensland

Circumstantial evidence indicates that Gaussberg, an isolated, 370 m high volcanic cone on the Antarctic coast at 57°S, 89°E, is the product of subglacial eruption. The vesicular, highly potassic leucitite, of which Gaussberg is composed, has been dated by K‐Ar and fission‐track methods, the former being applied to leucite concentrates, the latter to glassy leucitite from the ropy‐textured, outer rind of a pillow‐like structure. The K‐Ar geochronology yields an average date of 56 000 ± 5000 years, jwhich is interpreted as defining the time of Gaussberg's formation. The fission‐track work yields a less precise date, which supports the K‐Ar age estimate. These new age determinations indicate that previously published K‐Ar age determinations of 20 Ma and 9 Ma for Gaussberg should be rejected.     

An analytical source function for a coupled hybrid wave model

An analytical form for the source function is formulated by comparing the fetch-limited approximation of the Ocean Wave Transport equation and the empirical equation for the fetch-dependent wave forecast nomograms. The source function thus generated has been utilised in the numerical model based on Toba’s formulation of wave transport equation and tested for the seas around the Indian subcontinent (5°S to 25°N latitude; 45°E to 100°E longitude). The grid averaged hindcast wave heights are found to be moderately matching with the GEOSAT altimeter measured significant wave heights of the 1987–1989 period, particularly for waves higher than 1 meter.     

Quaternary Antarctic Bottom-Water history: Deep-sea benthonic foraminiferal evidence from the southeast Indian Ocean

Distinct assemblages of Recent deep-sea benthonic foraminifera from the southeast Indian Ocean have been shown to be associated with Antarctic Bottom Water (AABW) and Indian Bottom Water (IBW). The AABW assemblage is divided into two groups. One is dominated by Epistominella umbonifera and is associated with AABW having temperatures between ?0.2° and 0.4°C. The second group is dominated by Globocassidulina subglobosa and is associated with AABW having temperatures between 0.6° and 0.8°C. The IBW assemblage is marked by the strong dominance of Uvigerina spp. and Epistominella exigua. The faunal-water-mass relationships have been used to infer the history of bottom-water circulation over the last 500,000 yr in this region using faunal data from four Eltanin cores. One core was taken from the Southeast Indian Ridge in association with IBW, and three were taken from the flank of the ridge associated with AABW flowing within a western boundary contour current in the South Australian Basin. Little faunal variation exists in the core beneath IBW (E48-22), indicating that IBW was present on the Southeast Indian Ridge during the last 300,000 yr. A record of the intensity of AABW circulation during the last 500,000 yr is inferred from the benthonic foraminiferal data in the three cores located within the western boundary contour current. Marked oscillations in the relative proportions of AABW and IBW faunal assemblages are found in one core, E48-03. The faunal variations are inferred to have resulted from variation in intensity of AABW circulation between 500,000 and 195,000 yr B.P. In E48-03, the AABW assemblage was present most of the time between 500,000 and 195,000 yr B.P., with low intensity of AABW circulation occurring primarily during the equivalent of stages 8 and 7 (t = 305,000 to 195,000 yr B.P.). The intensity of AABW circulation varied, with a maximum occurring during the equivalent of stage 11 (t = 420,000 yr B.P.). Two additional cores, E45-27 and E45–74, show relatively constant intensity of AABW circulation from 195,000 yr B.P. to the present. The intensity of AABW circulation at the present appears to be intermediate between a maximum during the equivalent of stage 11 (t = 420,000 yr B.P.) and the minimum during the equivalent of stage 8 (t = 275,000 yr B.P.). AABW production has occurred during both glacial and interglacial episodes. Bottom-water productivity has been suggested to play an important role in glacial/interglacial oscillations during the late Quaternary (Weyl, 1968; Newell, 1974). In this study, the relationship between bottom-water circulation and climatic fluctuations appears to be more complex than had been previously suggested, since a simple relationship between Quaternary bottom-water circulation and paleoclimatic fluctuations is not shown.     

Harmonic analysis of summer mean wind at 200 mbar level during contrasting monsoon years over India

Summer (June–August) mean zonal and meridional wind components at 200 mbar level are subjected to harmonic analysis for the years 1970, 1971, 1972 and 1979. It is found that the small scale disturbances are intense during normal monsoon years. The westerlies in the belt 10°S to 30°S are stronger during drought years. During normal monsoon years (1970, 1971) the northward transport of westerly momentum by wave number 1 at 19.6°N is large as compared to drought years (1972, 1979). The transport of westerly momentum by standing eddies is northward for all the years between 5°S and 28.7°N but large during the normal monsoon years.     

A climatological study of the relations among solar activity,galactic cosmic ray and precipitation on various regions over the globe

We apply Fourier and wavelet analyses to the precipitation and sunspot numbers in the time series (1901–2000) over Australia (27°S, 133°E), Canada (60°N, 95°W), Ethiopia (8°N, 38°E), Greenland (72°N, 40°W), United Kingdom (54°N, 2°W), India (20°N, 77°E), Iceland (65°N, 18°W), Japan (36°N, 138°E), United States (38°N, 97°W), South Africa (29°S, 24°E) and Russia (60°N, 100°E). Correlation analyses were also performed to find any relation among precipitation, sunspot numbers, temperature, and cloud-cover at the same spatial and temporal scale. Further correlations were also performed between precipitation with electron and proton fluence at the time interval, 1987–2006. All these parameters were considered in annual and seasonal scales. Though correlation study between precipitation and other parameters do not hint any linear relation, still the Fourier and wavelet analyses give an idea of common periodicities. The 9–11 year periodicity of sunspot numbers calculated by Fourier transform is also confirmed by wavelet transform in annual scale. Similarly, wavelet analysis for precipitation also supports the short periods at 2–5 years which is verified by Fourier transform in discontinuous time over different geographic regions.     

Palaeomagnetism and tectonic rotation of the Hastings Terrane,eastern Australia

The Hastings Terrane comprises two or three major fragments of the arc‐related Tamworth Belt of the southern New England Orogen, eastern Australia, and is now located in an apparently allochthonous position outboard of the subduction complex. A palaeomagnetic investigation of many rock units has been undertaken to shed light on this anomalous location and orientation of this terrane. Although many of the units have been overprinted, pre‐deformational magnetizations have been isolated in red beds of the Late Carboniferous Kullatine Formation from the northern part of the terrane. After restoring these directions to their palaeohorizontal (pre‐plunging and pre‐folding) orientations they appear to have been rotated 130° clockwise (or 230° anti‐clockwise) when compared with coeval magnetizations from regions to the west of the Hastings Terrane. Although these data are insensitive to translational displacements, a clockwise rotation is incompatible with models previously proposed on geological grounds. While an anti‐clockwise rotation is in the same sense as these models the magnitude appears to be too great by about 100°. Nevertheless, the palaeomagnetically determined rotation brings the palaeoslopes of the Tamworth Belt, facing east, and the Northern Hastings Terrane, facing west before rotation and facing southeast after rotation, into better agreement. A pole position of 14.4°N, 155.6°E (A₉₅ = 6.9°) has been determined for the Kullatine Formation (after plunge and bedding correction but not corrected for the hypothetical rotation). Reversed magnetizations interpreted to have formed during original cooling are present in the Werrikimbe Volcanics. The pole position from the Werrikimbe Volcanics is at 31.6° S, 185.3° E (A₉₅ = 26.6°). These rocks are the volcanic expression of widespread igneous activity during the Late Triassic (～ 226 Ma). While this activity is an obvious potential cause of the magnetic overprinting found in the older units, the magnetic directions from the volcanics and the overprints are not coincident. However, because only a few units could be sampled, the error in the mean direction from the volcanics makes it difficult to make a fair comparison with the directions of overprinted units. The overprint poles determined from normal polarity magnetizations of the Kullatine Formation is at 61.0°S, 155.6°E (A₉₅ = 6.9°) and a basalt from Ellenborough is at 50.7° S, 148.8° E (A₉₅ = 15.4°), and from reversed polarity magnetizations, also from the basalt at Ellenborough is at 49.4° S, 146.2° E (A₉₅ = 20.4°). These are closer to either an Early Permian or a mid‐Cretaceous position, rather than a Late Triassic position, on the Australian apparent polar wandering path. Therefore, despite their mixed polarity, and global observations that the Permian and mid‐Cretaceous geomagnetic fields were of constant polarities, the age of these overprint magnetizations appears to be either Early Permian or mid‐Cretaceous.     

Age and composition of Antarctic sub-glacial bedrock reflected by detrital zircons,erratics, and recycled microfossils in the Ellsworth Land–Antarctic Peninsula–Weddell Sea–Dronning Maud Land sector (240°E–0°–015°E)

The age and composition of the 14 × 10⁶ km² of Antarctica's surface obscured by ice is unknown except for some dated detrital minerals and erratics. In remedy, we present four new analyses (U–Pb age, T_DM^C, εHf, and rock type) of detrital zircons from Neogene turbidites as proxies of Antarctic bedrock, and review published proxies: detrital hornblendes analysed for Ar–Ar age and bulk Sm–Nd isotopes; Pb isotope compositions of detrital K-feldspars; erratics and dropstones that reflect age and composition; and recycled microfossils that reflect age and facies. This work deals with the 240°E–0°–015°E sector, and complements Veevers and Saeed's (2011) analysis of the 70°E–240°E sector. Each sample is located in its ice-drainage basin for backtracking to the potential provenance. Gaps in age between sample and upslope exposure are specifically attributable to the provenance. The major provenance of detritus west of the Antarctic Peninsula (AP) is West Antarctica, and of detritus east of the AP East Antarctica. We confirm that the Central Antarctic provenance about a core of the Gamburtsev Subglacial Mountains (GSM) and the Vostok Subglacial Highlands (VSH) contains a basement that includes igneous (mafic granitoids) and metamorphic rocks with peak U–Pb ages of 0.65–0.50, 1.20–0.9, 2.1–1.9, 2.8–2.6, and 3.35–3.30 Ga, T_DM^C of 3.6–1.3 Ga, and mainly negative εHf. The potential provenance of zircons of 650–500 Ma age with T_DM^C ages of 1.55 Ga, and of zircons of 1200–900 Ma age with positive εHf lies beneath the ice in East Antarctica south and southeast of Dronning Maud Land within the Antarctic part of the East African–Antarctic Orogen. Zircons with the additional ages of 1.7–1.4 Ga, 2.1–1.9 Ga, and 3.35–3.00 Ga have a potential provenance in the GSM.     

Palynology of seafloor samples collected by the 1911–14 Australasian Antarctic expedition: Implications for the geology of coastal East Antarctica

Fifty‐three sea‐floor samples close to Antarctica collected by Douglas Mawson during the Australasian Antarctic Expedition of 1911–1914 have beeen analysed for recycled palynomorphs. The distribution of the recycled microfossils provides a broad guide to the position of hidden sedimentary sequences on the Antarctic continental margin.

The samples were dredged off the East Antarctic coast between 91°E and 146°E. In three distinct ‐areas, concentrations of recycled palynomorphs suggest the presence nearby of eroding sedimentary sequences. Near the western edge of the Shackleton Ice Shelf the recycled suite suggests Early to Late Permian, Late Jurassic to mid‐Cretaceous, and Late Cretaceous to Early Tertiary sediments, with evidence for marine influence only in the Tertiary. Samples from the outer edge of the continental shelf and slope east of Cape Carr indicate Early Cretaceous and Late Cretaceous to Early Tertiary sequences, and the same age span is suggested by samples from the western side of the Mertz Glacier Tongue; in this area radio echosounding has suggested that inland sedimentary basins intersect the coast.

The sedimentary sequence predicted for the Shackleton Ice Shelf area probably faced the open Indian Ocean, at least since the Mesozoic. Cretaceous sequences predicted for the other localities occur at points on the Antarctic coast where they would be expected on the basis of most reconstructions. The area east of Cape Carr has as its conjugate’ coast part of the Great Australian Bight Basin; that off the Mertz Glacier, the area west of the Otway Basin. At both these areas on the southern Australian margin thick Cretaceous rift‐valley sequences occur.