South West Arm Research Articles

Polymetallic mineralisation associated with Carboniferous I-type granitoids in central Stewart Island, New Zealand

ABSTRACTCarboniferous granitoids in central Stewart Island host two metalliferous hydrothermal systems that formed during emplacement of the c. 306 ± 2 Ma old Euchre Pluton and 303 ± 2 Ma Hill 267 leucogranitoid, respectively. The Ogles Creek–Silvertown Hydrothermal System (OST) on the eastern side of South West Arm, Paterson Inlet is centred on the scheelite-bearing, ilmenite-syenogranite core of the Euchre Pluton. Here pyritic-potassic alteration and related veins contain Mo, Bi, Ag, Co, Cu, W, Pb, Zn, U–Th and rare Earth element (REE) sulphide, telluride, oxide and phosphate minerals. Peripheral quartz-rich veins contain various Ag, Au, Pb and Zn-bearing sulphide, telluride and oxide minerals. The Hill 267 Hydrothermal System (HHS) is centred on the ridge between the Scott Burn and Forked Creek where strongly altered leucogranitoid riddled with miarolitic cavities contains pyrite, W- and Nb-bearing rutile, molybdenite, tourmaline and 2–10 times background Bi, Ag, Te, Cu and Se. More prospective parts of both systems have probably been removed by erosion, but less deeply eroded correlative hydrothermal systems may be present elsewhere in New Zealand near the outboard margin of the Takaka Terrane.

Relict proglacial deltas in Bradshaw and George sounds, Fiordland, New Zealand

New Zealand fjords (Fig. 1e) contain submerged, relict, proglacial lacustrine and marine deltas that formed after glaciers retreated from the west coast by 17 ka (Pickrill et al. 1992). Many of these deltas, for example those in Bradshaw and George sounds, are exceptionally well preserved because postglacial sedimentation rates have been low. Fig. 1. Relict proglacial deltas in Bradshaw and George sounds, Fiordland, New Zealand. ( a ) Swath-bathymetric image of the head of George Sound superimposed on a hill-shaded DEM. Acquisition system Kongsberg EM300. Frequency 30 kHz. Grid-cell size 5 m. EB, Elder Basin; WB, Whitewater Basin; SWB, South-West Basin; AD, Anchorage Delta; WD, Whitewater Delta; SWAD, South-West Arm Delta; ALD, Alice Delta; AF, Alice Falls. ( b ) Head of Bradshaw Sound. BB, Bradshaw Basin; GAD, Gaer Arm Delta; PD, Precipice Delta. ( c ) Long-axis profile from EB to Lake Alice (LA), across the relict proglacial ALD and WB. VE×11. ( d ) Long-axis profile across the modern and relict proglacial components of GAD. VE ×10. ( e ) Location of study area (red box; map from GEBCO_08). ( f ) Enlargement showing bathymetric details of the AD foreset slope off Anchorage Cove. ( g ) Head …

SPIRAL DENSITY WAVES IN M81. II. HYDRODYNAMIC SIMULATIONS OF THE GAS RESPONSE TO STELLAR SPIRAL DENSITY WAVES

Gas response to the underlying stellar spirals is explored for M81 using unmagnetized hydrodynamic simulations. Constrained within the uncertainty of observations, 18 simulations are carried out to study the effects of selfgravity and to cover the parameter space comprising three different sound speeds and three different arm strengths. The results are confronted with those data observed at wavelengths of 8 $\mu$m and 21 cm. In the outer disk, the ring-like structure observed in 8 $\mu$m image is consistent with the response of cold neutral medium with an effective sound speed 7 km s$^{-1}$, while for the inner disk, the presence of spiral shocks can be understood as a result of 4:1 resonances associated with the warm neutral medium with an effective sound speed 19 km s$^{-1}$. Simulations with single effective sound speed alone cannot simultaneously explain the structures in the outer and inner disks. This justifies the coexistence of cold and warm neutral media in M81. The anomalously high streaming motions observed in the northeast arm and the outward shifted turning points in the iso-velocity contours seen along the southwest arm are interpreted as signatures of interactions with companion galaxies. The level of simulated streaming motions narrows down the uncertainty of observed arm strength toward larger amplitudes.

Potential submerged Aboriginal archaeological sites in South West Arm, Port Hacking, New South Wales, Australia

Abstract Sealed, submerged palaeoenvironmental deposits date the time range for lithic technologies and enable inferences about cultural change – potentially more accurately than radiometric methods. Sea-level rises triggered by global warming reduce available land, and change the availability of flora, fauna, geological resources, rivers and wetlands. Australian archaeological studies on human adaptation to climate change focus mainly on terrestrial sites, coastal intensification and the few archaeological sites that were not inundated. The South West Arm project at Port Hacking, south of Sydney, looks at the potential for rock shelters to survive inundation and expand the sites available for studying human adaption to climate change. Site prediction was based on recorded terrestrial rock-shelter landforms at South West Arm. Underwater surveys were conducted by divers who located, photographed and mapped similar formations. No excavation was conducted. The pre-disturbance survey examined approximately 1800 m of seabed, between water depths of 0 and 9 m, primarily along the eastern shoreline of South West Arm where the seabed emulates the steep slope, with sandstone rock outcrops that form terraces and rock overhangs above water. Twelve submerged rock overhangs were recorded and confirmed the potential for rock-shelter sites to survive the process of inundation.

Modern distribution of ostracodes and other limnological indicators in southern Lake Malawi: implications for paleocological studies

This modern distribution study from the southwest arm of Lake Malawi quantitatively relates variables of the lake environment to surficial assemblages of ostracodes and other paleoenvironmental indicators (molluscs, Botryococcus, fish, and charcoal) from 102 sites, across a gradient of littoral to shallow profundal conditions. The goal of this research is to use the resultant relationships to help quantify paleoecological interpretations of the fossil record from sediment cores. Site locations varied by depth (1–60 m) and adjacent shoreline environment. Thirty-three ostracode species are identified from 54 sites including four new, undescribed species of Cypridopsinae (2) and Limnocythere (2). Ostracodes are extremely abundant between 1 and 25 m water depth, but are rare to absent between 30 and 60 m. This disappearance is probably taphonomically controlled, with carbonate dissolution in the death assemblage since abundant live ostracodes have been found in the lake at greater than 30 m depth, where bottom sediments lack calcium carbonate. Constrained correspondence analysis (CCA) of ostracode species abundance suggests depth and dissolved oxygen (DO) content to be the primary environmental variables affecting their distribution. Additional CCA models using all biological indicators suggest limnologic variables correlated with depth (e.g., bottom water temperature and DO) and adjacent shoreline environment were most significant.

Discovery of a Bright Transient Ultraluminous X-Ray Source, Suzaku J1305–4931 in NGC4945

Abstract An X-ray source, Suzaku J1305$-$4931, was discovered in the south-west arm of a nearby Seyfert II galaxy, NGC4945, at 0.5-10keV flux of $2.2 \times 10^{-12}$ergcm$^{-2}$s$^{-1}$ during a Suzaku observation conducted on 2006 January 15-17. It was undetectable in a shorter observation on 2005 August 22-23, with an upper limit of $1.7 \times 10^{-14}$ergcm$^{-2}$s$^{-1}$. At a distance of 3.7Mpc, the bolometric luminosity of the source became $L_{\rm bol} = 4.4 \times 10^{39} \alpha$ergs$^{-1}$, where $\alpha = ({\rm\cos} 60^\circ \!/ \cos i)$ and $i$ is the disk inclination. The time-averaged X-ray spectrum of the source is described by a multi-color disk model, with an innermost disk temperature of $T_{\rm in} = 1.69_{-0.05}^{+0.06}$keV. It varied by a factor of $2$ in intensity, following a clear correlation of $L_{\rm bol} \propto T_{\rm in}^4$. The innermost disk radius is inferred to stay constant at $R_{\rm in} = 79_{-3.9}^{+4.0} \alpha^{1/2}$ km, suggesting the presence of a standard accretion disk. Relating $R_{\rm in}$ with the last stable orbit around a non-rotating black hole yields a rather low black-hole mass, $\sim 9 \alpha^{1/2}$ solar masses, which would imply that the source is shining at a considerable super-Eddington luminosity. These results can be better interpreted by invoking sub-Eddington emission from a rapidly spinning black hole with 20-130 solar masses.

Origin Of Calcareous Sediments in the Holocene Pigeon Creek Tidal Lagoon and Tidal Delta, San Salvador Island, Bahamas

A sedimentological survey of the southwest arm of the Holocene Pigeon Creek tidal lagoon on San Salvador Island, Bahamas was conducted to determine the origin and distribution of calcareous sediments. Transect surveys, surface samples, and sediment cores were collected and examined to determine the abundance and distribution of sediments and sediment producers in the lagoon and associated tidal delta. The study area has three regions: an extensive tidal to shallow, subtidal flat; a tidal channel near the entrance to the lagoon; and a lobate, ebb-dominated tidal delta. Tidal flat sediments were extensively bioturbated and heavily rooted by Thalassia testudinum. Tidal flat sediments ranged from coarse, calcareous sand to calcareous muds, and were rich in gastropod shells, foraminifera, calcareous algae, and pelletal calcareous mud. The tidal flat sediments are assigned to a pellet-lime wackestone to muddy lime packstone lithofacies. Calcareous green algae are the primary producers of calcareous sediments in the lagoon with species of Halimeda and Penicillus being the dominant genera. Surface samples taken from the coarse channel lag of the tidal channel consisted primarily of whole and fragmented bivalves and gastropods. Most of the bivalves were oriented convex upward. Surface samples taken from ripples, mega-ripples, and sand waves of the tidal delta are dominated by well-sorted, well-rounded, and polished sand-size grains (1-2 mm in diameter). This sediment was dominated by bioclasts (bivalves, gastropods, calcareous algae, foraminifera) and minor ooids. Sediments of the tidal channel and tidal delta are assigned to a lime packstone to grainstone lithofacies. The coarsest fraction (> 2 mm) accumulated on the lee slopes and troughs of large, tidal and wave produced ripples. Ripples for both ebb- and flood tides are strongly asymmetrical, but symmetrical ripples are common, indicating that significant migration of the tidal delta does not occur during normal tidal events. A low energy, shallowing upward cycle is well illustrated in the lagoon, and the presence of a depaurperate biofacies and heavily bioturbated and rooted lithofacies typify a carbonate lagoon depositional environment.

An assessment of a light-attraction fishery in southern Lake Malawi

This study provides the first quantitative assessment of the light-attraction component of a small-scale purse seine, locally known as a chilimira net, fishery in two areas of southern Lake Malawi. For monitoring purposes the shoreline of Lake Malawi is divided into a number of statistical strata. Two strata ('2.1' in the southeast arm and '3.1' in the southwest arm of the lake) were selected for this study. Catch per unit effort in stratum 2.1 was generally lower than that recorded in stratum 3.1 but nets in stratum 2.1 fished more frequently, leading to similar annual catches in the two strata. Annual catch was estimated as 19.4 (CI = 15.9–23.5) tons net–1 year–1 in stratum 2.1 and 23.5 (CI = 19.5–28.1) tons net–1 year–1 in stratum 3.1 respectively. A total of 62 species from 28 cichlid genera, and 13 species from nine non-cichlid genera, were identified from the samples. Of the 37 genera identified, only five; Copadichromis, Dimidiochromis, Engraulicypris, Oreochromis and Rhamphochromis, contributed more than 5% to the total annual catch in either stratum. Their combined contribution to the annual catch was in excess of 85% in both strata. Comparisons showed that catch-composition was dependent on area. Length-frequency distributions of major target species in the catch showed that the fishery targeted juveniles in stratum 2.1, while in stratum 3.1 most individuals were harvested after reaching their length-at-maturity. The dependence of catch-composition and size-selection on area indicates that management interventions for this fishery need to be area-specific. Since the fishery targets a diverse species assemblage, effort limitation or area closure may be the only viable management options, until such time as additional biological and fisheries data are available for the application of stock assessment models.

Seasonal and Spatial Patterns of Experimental Trawl Catches in the Southwest Arm of Lake Malawi

Experimental demersal trawl samples were collected in the same manner at the same sites on a monthly basis over an annual cycle in the southwest arm (SWA) of Lake Malawi. Catch composition in terms of species representation and mass was compared over time and depth (10, 30, 50, 75, 100 and 125 m). The average catch per unit effort was calculated per species and depth. Haplochromine cichlids dominated the catches at every depth, making up 75 to 92% of the biomass. The remainder was made almost exclusively of catfishes. Despite catching more than 140 species in the trawls, 60 to 80% of the catches consisted of ten or fewer species, including three catfishes. About twenty species accounted for 90 to 95% of the catches at any depth, suggesting that many species are uncommon or rare. Previous authors reported dramatic changes in species composition at 50 m in the southwest arm. Data presented here suggest that this might be due to a change in the nature of the substratum at 50 m. The greatest diversity of species is in shallow waters, but the highest catches in terms of biomass were recorded between 50 and 125 m and peaked at 75 and 100 m. As catches in the deep waters were dominated by fishes with favorable life history characteristics and which are large relative to species in the shallow waters (though the largest species of cichlid occur in the shallow water, the catches are dominated by small species), it is recommended that the possibility for increased exploitation of the SWA deep demersal stocks should be explored by encouraging controlled development of a demersal commercial fishery in the SWA.

The 1.1-Ga Midcontinent Rift System, central North America: sedimentology of two deep boreholes, Lake Superior region

Abstract The Midcontinent Rift System (MRS) of central North America is a 1.1-Ga, 2500-km long structural feature that has been interpreted as a triple-junction rift developed over a mantle plume. As much as 20 km of subaerial lava flows, mainly flood basalts, are overlain by as much as 10 km of sedimentary rocks that are mostly continental fluvial red beds. This rock sequence, known as the Keweenawan Supergroup, has been penetrated by a few deep boreholes in the search for petroleum. In this paper, two deep boreholes in the Upper Peninsula of Michigan are described in detail for the first time. Both the Amoco Production #1-29R test, herein referred to as the St. Amour well, and the nearby Hickey Creek well drilled by Cleveland Cliffs Mining Services, were 100% cored. The former is 7238 ft (2410 m) deep and the latter is 5345 ft (1780 m) deep. The entirety of the stratigraphic succession of the Hickey Creek core correlates very well with the upper portion of the St. Amour core, as determined by core description and point-counting of 43 thin sections selected out of 100 studied thin sections. Two Lower Paleozoic units and two Keweenawan red bed units—the Jacobsville Sandstone and the underlying Freda Sandstone—are described. The Jacobsville is largely a feldspatholithic sandstone and the Freda is largely a lithofeldspathic sandstone. Below the Freda, the remaining footage of the St. Amour core consists of a thick quartzose sandstone unit that overlies a heterogenous unit of intercalated red bed units of conglomerate, sandstone, siltstone, and shale; black shale; individual basalt flows; and a basal ignimbritic rhyolite. This lower portion of the St. Amour core presents an enigma, as it correlates very poorly with other key boreholes located to the west and southwest. While a black shale sequence is similar to the petroleum-bearing Nonesuch Formation farther west, there is no conglomerate unit to correlate with the Copper Harbor Conglomerate. Other key boreholes are distributed over a 1300-km distance along the better known southwest arm of the triple-junction MRS, and can be correlated rather well with the units that are exposed in the Lake Superior region. However, a definitive explanation of the anomalous, deeper St. Amour stratigraphy is elusive and any explanation is tenuous. A possible explanation for this anomalous stratigraphy may be the geographic proximity of the St. Amour borehole to the Keweenawan Hot Spot (mantle plume), the suggested thermal force behind the development of the MRS. Similarly, a drastic change in structural architecture may be explained by this geographic relationship. Thus, within the locale of this rifting center, complexities of expansion tectonics may well be responsible for igneous and sedimentary sequences that differ considerably from those found farther west along the rift arm.

A New High‐Resolution CO Map of the Inner 2.́5 of M51. I. Streaming Motions and Spiral Structure

The Owens Valley millimeter array has been used to map the CO 1-0 emission in the inner 25 of the grand-design spiral galaxy M51 at 2''-3'' resolution. These new images reveal the molecular spiral arms with unprecedented clarity; the emission in the two major arms (northeast and southwest) originates from supermassive cloud complexes, giant molecular associations (GMAs), which are for the first time resolved both along and perpendicular to the arms. The overall morphology of the CO emission is symmetric in reflection about the nucleus, with major complexes occurring opposite each other in the two major arms. On the other hand, the CO line flux in the area of the southwest arm closest to the nucleus is approximately twice as bright as that from the analogous location in the northeast arm. Streaming motions can be studied in detail and appear with great clarity along the major and minor axes of M51. The streaming velocities are very large, 60-150 km s-1. Our maps offer, for the first time, sufficient resolution to resolve the structure in the molecular streaming motions. Both the radial and tangential velocity components show steep gradients, in qualitative accordance with predictions of the density-wave models of Roberts & Stewart. Our data thus support the presence of galactic shocks in the arms of M51. In general, velocity gradients across arms are higher by a factor of 2-10 than previously found. They vary in steepness along the spiral arms, becoming particularly steep in between GMAs. The steep gradients cause conditions of strong reverse shear in several regions in the arms, and thus the notion that shear is generally reduced by streaming motions in spiral arms will have to be modified. Of the three GMAs studied on the southwest arm, only one shows reduced shear. We find an unusual structure, an expansion in the northeast molecular arm at 25'' radius (1.2 kpc) southeast of the center. This broadening occurs right after the end of the northeast arm at the inner Lindblad resonance (ILR). Multiple-peak spectra, velocity twists, and structures with apparently high velocity dispersion are associated with this feature. Bifurcations in the molecular spiral arm structure, at a radius of ≈3.3 kpc (73''), may be evidence of a secondary compression of the gas caused by, and occurring near, the 4/1 ultraharmonic resonance. Several molecular spurs protrude from the main spiral arms, in particular on the western side of the map. Inside the radius of the ILR, we detect narrow (≈5'') molecular spiral arms, possibly related to the K-band arms found in the same region. We find evidence of noncircular motions in the inner 20'' of M51. The magnitude of these deviations is 20-30 km s-1, and they are consistent with gas on elliptical orbits in a bar.

Metasedimentary, granitoid, and gabbroic rocks from central Stewart Island, New Zealand

A NNE—NE trending strip, 3–8 km wide, extending from the Freshwater valley across Mt Rakeahua, Table Hill, and Mt Allen to the northern end of the Tin Range was mapped at a scale of 1:12 500 to locate and investigate the boundary between the Median Tectonic Zone (MTZ) and Western Province on Stewart Island. A NNE‐trending fault, herein termed the Escarpment Fault, separates predominantly ductily deformed rocks on its south side from essentially undeformed rocks to the north. North of the Escarpment Fault, a small (2–3 km2) pluton of alkali‐feldspar granite (Freds Camp) intrudes gabbroic rocks tentatively considered to be associated with gabbro/ anorthosite/diorite of the Rakeahua pluton, centred on Mt Rakeahua. Both units were subsequently intruded by I‐type biotite granite of the South West Arm pluton. South of the Escarpment Fault the oldest intrusions are biotite tonalite‐granite orthogneisses (Ridge and Table Hill plutons) intercalated with the sillimanite‐cordierite‐bearing Pegasus Group metasedimentary rocks, considered to represent the Western Province. They contain titanite, allanite, and magmatic epidote‐bearing assemblages, implying affinities with I‐type granitoids. These older granitoids have been affected by at least three phases of ductile deformation. Immediately south of the Escarpment Fault, the Escarpment pluton (hornblende, biotite quartz monzonite‐quartz monzodiorite) only exhibits effects of the third phase of deformation. Minor gabbroic intrusives concordant with with the S3 fabric intrude the Pegasus Group and intercalated orthogneisses. Plutons of two‐mica, garnet ± cordierite granite (Blaikies and Knob) and younger biotite‐titanite‐magmatic epidote granite (Campsite) cut fabrics associated with the third phase of ductile deformation. Preliminary U‐Pb dating indicates Devonian‐Carboniferous, Carboniferous, Jurassic, and Early Cretaceous emplacement ages for Ridge Orthogneiss, Freds Camp pluton, South West Arm pluton, and Blaikies pluton, respectively. South West Arm and Rakeahua plutons are provisionally correlated with the MTZ, which extends the (south) western boundary of the MTZ at least 12 km further southwest from the Freshwater faults. Correlation of gabbroic rocks south of the Escarpment Fault with the MTZ would imply an autochthonous rather than allochthonous relationship of the latter to the Western Province.

CO(J = 2 - 1) study of molecular clouds in the southwest arm of M31

view Abstract Citations (11) References (42) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS CO(J = 21) Study of Molecular Clouds in the Southwest Arm of M31 Kutner, Marc L. ; Verter, Frances ; Rickard, Lee J. Abstract We present the first map of M31 in the CO(J = 2-> 1) transition, for a 3' x 3' section of the southwest arm-interarm region. We have detected 25 positions out of 31 observed in a field centered at major and minor axis coordinates (-42.5', +7.5'). The map is sampled at intervals of one beamwidth, with an angular resolution of 30", or 100 x 460 pc along the M31 major and minor axes, respectively. In this section of our field covering the arm, as defined by H II regions, the CO spectra are characterized by strong, narrow features. We interpret these to be giant molecular clouds with masses of about a few x 10^5^ M_sun_. In the section of our field that is off the arm, the CO spectra are weaker and broader. We interpret the interarm emission to be an ensemble of small clouds, with masses of about a few x 10^4^ M_sun_, that fill most of the allowed velocity space. We estimate that on the arm ~ 70% of the emission comes from large clouds, and off the arm essentially all of the emission comes from small clouds. The mass surface density on this section of the M31 arm is approximately the same as a comparable section of the Scutum arm in the Milky Way. We also find that the velocities of the giant clouds in the arm are shifted, with respect to the rest of the molecular and atomic gas, by ~ 15 km s^-1^. If this is due to a change in orbital speed, then it is a boost in rotation velocity which we interpret as a result of the cloud response to passage through the spiral arm potential. Publication: The Astrophysical Journal Pub Date: December 1990 DOI: 10.1086/169470 Bibcode: 1990ApJ...365..195K Keywords: Andromeda Galaxy; Carbon Monoxide; H Ii Regions; Interstellar Matter; Molecular Clouds; Astronomical Spectroscopy; Galactic Rotation; Galactic Structure; Spiral Galaxies; Astrophysics; GALAXIES: INDIVIDUAL MESSIER NUMBER: M31; GALAXIES: INTERNAL MOTIONS; GALAXIES: INTERSTELLAR MATTER; INTERSTELLAR: MOLECULES full text sources ADS | data products SIMBAD (1) NED (1)

Chemical properties of a low-oxygen water column in port hacking (Australia): Arsenic, iodine and nutrients

In a study of a water column in a basin of the South West Arm of Port Hacking, changes in dissolved oxygen, temperature and salinity were determined for several weeks. When there was < 1 ml 1 −1 oxygen in the bottom water, the water column was sampled to study the vertical distribution of dissolved nutrients (ammonia, nitrate, nitrite, orthophosphate and reactive silicate) and the oxidized and reduced forms of arsenic and iodine. Results showed that changes in the water column were dominated by inputs of these elements from the anoxic sediment. Near-bottom waters were enriched in all nutrients, arsenate and iodide. The mechanisms that influence the speciation of the redox elements arsenic and iodine are discussed. Low dissolved iodate concentration is proposed as a recorder of the occurrence of oxygen-depleted conditions in isolated marine water bodies.

VLA observations of solar flares, interpreted with optical, X-ray, and other microwave data

view Abstract Citations (25) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS VLA observations of solar flares, interpreted with optical, X-ray, and other microwave data. Marsh, K. A. ; Hurford, G. J. ; Zirin, H. Abstract Three small solar flares were observed from the active region McMath 14979 during 1655- 1725 UT on 1977 October 12, using the southwest arm of the Very Large Array (VLA) at 4.9 0Hz. These observations showed the presence of two distinct flare components: (1) A dominant broad component of size 10", with gradual rise-and-fall behavior and circular polarization, and (2) small impulsive components of size 2"-4", 53 987o circularly polarized. Simultaneous interferometric observations of the 1703 UT flare with the Owens Valley solar interferometer at 10.7 0Hz, together with the VLA data, fixed the location of the broad component in two dimensions. Comparison with Ha photographs and magnetograms showed that this component was located in the magnetic arch at whose footpoints the Ha flare occurred. The electron temperature and emission measure implied by OSO8 soft X-ray observations yielded a corresponding free-free microwave flux which entirely accounted for the observed emission at 10.7 0Hz. The microwave spectrum at lower frequencies (2.7 0Hz and 4.9 0Hz) was then consistent with thermal gyroresonance radiation in a magnetic field of 300 gauss. The radio, optical, and X-ray observations thereby suggest that the broad microwave component was a thermal cloud trapped in a magnetic arch. The impulsive events probably occurred at the positive-polarity footpoints of this arch. Subject headings: Sun: flares - Sun: radio radiation - Sun: X-rays Publication: The Astrophysical Journal Pub Date: March 1979 DOI: 10.1086/156885 Bibcode: 1979ApJ...228..610M Keywords: Microwave Spectra; Solar Flares; Solar Radio Emission; Solar X-Rays; Spaceborne Astronomy; Electron Energy; H Alpha Line; Oso-8; Plasma Resonance; Satellite Observation; Stellar Models; Thermal Plasmas; Solar Physics; Radio Radiation:Solar Flares; Solar Flares:X Rays full text sources ADS |

Description and use of an improved method for determining estuarine zooplankton grazing rates on phytoplankton

A method of rapidly determining zooplankton grazing rates on natural mixed phytoplankton populations using 14C is described. The method simplifies the design of grazing experiments as the grazing time can be kept short enough to prevent recycling of the isotope, and growth of the phytoplankton substrate. Very high specific activity, 14C-labelled phytoplankton concentrated either by centrifugation or sieving, may be used either as the sole grazing substrate, or as a tracer in natural mixed phytoplankton. Zooplankton, confined in glass jars at either ambient, or higher than ambient concentrations, are permitted to feed on the phytoplankton for periods of 30 min and 2 h, and are then separated by sieving. The zooplankton community grazing rate, or, if the samples are sorted into species, the individual species grazing rates, can be determined after scintillation counting of the zooplankton. The rate of appearance of 14C-labelled phytoplankton in the zooplankton is an estimate of the grazing rate, and the slope of the line joining the grazing rates at various phytoplankton concentrations gives an estimate of the grazing rate constant for the zooplankton population. The method provides a quick way of obtaining both zooplankton population, and individual species grazing rates on natural mixed phytoplankton. In two experiments, labelled phytoplankton was used as the sole grazing substrate in concentrations ranging between 0.4 and 5 times ambient levels. Grazing rate constants, for net-caught zooplankton concentrated to 46 times (Experiment 1) and 28 times (Experiment, 2) ambient estuarine levels were-0.14and-0.12 of the phytoplankton standing stock per day, respectively. There was a linear increase in the amount of phytoplankton grazed with an increase in phytoplankton concentration up to four times ambient phytoplankton levels. When tracer amounts of labelled phytoplankton were added to samples containing both phytoplankton and zooplankton at ambient concentrations the grazing rate constants were-0.28 and-0.42 of the phytoplankton standing stock per day. We conclude that zooplankton grazing was the major control factor of phytoplankton population size during October–November 1975 in South West Arm, Port Hacking, near Sydney, Australia.

Reconnaissance palaeomagnetic results from sulawesi, indonesia, and their bearing on palaeogeographic reconstructions

Magnetic remanence of Jurassic radiolarian chert from the southwest arm of Sulawesi (Celebes) yields a palaeomagnetic pole at 55°N,32°E, indicating rotation of about 35° anticlockwise since the late Mesozoic. This pole is close to those obtained from Cretaceous rocks of the Malay Peninsula and West Kalimantan and suggests that the three areas may have formed part of the same plate since the late Mesozoic, or at least that Sulawesi has not moved much relative to the other two areas. Measurements from Jurassic cherts from the southeast arm of Sulawesi show a magnetic inclination of 61° ; although too few samples were obtained for firm conclusions to be drawn, this does suggest that the cherts in the southeast arm were formed at higher latitudes and is compatible with the hypothesis that eastern Sulawesi was part of an Australian plate and was welded onto west Sulawesi in the Cainozoic. Measurements on tuffs, sills and lavas of late Cainozoic age on the flanks of the Lompobatang volcano mostly show directions near the existing field, four sites in a reversed sense, and one normal.

Direct measurement of dissolved organic carbon release by phytoplankton and incorporation by microheterotrophs

It is now possible to divide particulate primary production into algal and heterotrophic components without physical separation. This depends on two innovations, the introduction of isotope in the form of labelled dissolved product(s) of primary production and the employment of a data analysis specifically designed for tracer kinetic incorporation experiments. The 14C technique described by Steemann Nielsen (1952) is inapplicable in the analyses of certain classes of systems and kinetic tracer incorporation experiments must be employed instead. We show that measurement of PDOC production rate requires such kinetic tracer analyses. Measurements made in the laboratory on water taken from 2 m depth in South West Arm of the Port Hacking estuary showed that: (1) the steady-state rate of PDOC production was 0.10 to 0.13 mg C.m-3.h-1; (2) the rate of PDOC incorporation into microheterotroph particulate organic carbon was 0.10 to 0.12 mg C.m-3.h-1; (3) the rate at which PDOC was respired to CO2 was 0.001 to 0.003 mg C.m-3.h-1. (4) the PDOC makes up only about 0.1% of the total dissolved organic carbon. The size class of particles associated with PDOC production differed from the size class responsible for uptake of PDOC. More than 50% of the PDOC production was associated with particles having a nominal diameter range of 20 to 63 μm, while this fraction was responsible for <10% of the incorporation.

Report of a Journey across the Island of Newfoundland, Undertaken at the Instance of His Excellency Sir J. H. Glover, from the South-West Arm of Green Bay, Via Gold Cove in White Bay, to the East Arm of Bonne Bay

Report of a Journey across the Island of Newfoundland, Undertaken at the Instance of His Excellency Sir J. H. Glover, from the South-West Arm of Green Bay, Via Gold Cove in White Bay, to the East Arm of Bonne Bay