136 research outputs found
The Glacier Complexes of the Mountain Massifs of the North-West of Inner Asia and their Dynamics
The subject of this paper is
the glaciation of the mountain massifs
Mongun-Taiga, Tavan-Boghd-Ola, Turgeni-
Nuru, and Harhira-Nuru. The glaciation is
represented mostly by small forms that
sometimes form a single complex of domeshaped
peaks. According to the authors,
the modern glaciated area of the mountain
massifs is 21.2 km2 (Tavan-Boghd-Ola),
20.3 km2 (Mongun-Taiga), 42 km2 (Turgeni-
Nuru), and 33.1 km2 (Harhira-Nuru).
The area of the glaciers has been shrinking
since the mid 1960’s. In 1995–2008, the rate
of reduction of the glaciers’ area has grown
considerably: valley glaciers were rapidly
degrading and splitting; accumulation
of morainic material in the lower parts
of the glaciers accelerated. Small glaciers
transformed into snowfields and rock
glaciers. There has been also a degradation
of the highest parts of the glaciers and the
collapse of the glacial complexes with a
single zone of accumulation into isolated
from each other glaciers. Reduced snow
cover area has led to a rise in the firn
line and the disintegration of a common
accumulation area of the glacial complex.
In the of the Mongun-Taiga massif, in 1995–
2008, the firn line rose by 200–300 m. The
reduction of the glaciers significantly lagged
behind the change in the position of the
accumulation area boundary. In the past two
years, there has been a significant recovery
of the glaciers that could eventually lead to
their slower degradation or stabilization of
the glaciers in the study area
Holocene reef growth and recent carbonate production in the Red Sea
Holocene reef growth, present date bioerosion .and recorded
carbonate production were studied in the fringing
reef at Aqaba, Red Sea. Water depth, wave impact as well
as nutrient availability were considered.
The carbonate production was measured for several coral
samples. Samples of Porites-colonies were collected from
several depths and sites near the Marine Science Station at
Aqaba. Growth rate depends on water depth, size and age
of colonies. Within the coral optimum of water depth growth
rates vary between 5 and 16 mm/yr. Coral carbonate production
was calculated on the base of annual growth increments
and skeletal density using transects from shallow
subtidal down to 40 m water depth. High resolution stable
isotope data were measured to prove the origin of growth
increments. Long-term trends of sea surface temperature
and carbon isotope shift (1800-today) fit to the known global
deviations.
Bioerosion rates were determined using standard dead
coral substrates exposed in different water depths and environmental
settings. Rates vary between 0.6 and
1.4 kg/m2yr. Sediment export evaluated by means of simple
sediment traps ranges between 0.3 and 0.7 kg/m2yr.
Gross carbonate production, mainly built up by scleractinian
corals, amounts to ca. 1.57 kg/m2yr. Bioerosion alters
approx. 1.3 kg/m2yr of hard substrates into sediment. Sediment
export is estimated to be ca. 0.4-0.6 kg/m2yr. Thus a
net production of ca. 0.7 to 0.9 kg/m2yr should remain in the
present reef, which is proved by the recorded carbonate
production (reef drillings). Net production preserved in the
reef can be given with ca. 800 kg/m2kyr (=0.8 kg/m2yr)
Environmental forcing of the Campeche cold-water coral province, southern Gulf of Mexico
With an extension of >40 km2 the recently discovered Campeche cold-water coral province located at the northeastern rim of the Campeche Bank in the southern Gulf of Mexico belongs to the largest coherent cold-water coral areas discovered so far. The Campeche province consists of numerous 20 to 40 m high coral ridges that are developed in intermediate water depths of 500 to 600 m. The ridges are colonized by a vivid cold-water coral ecosystem that covers the upper flanks and summits. The rich coral community is dominated by the framework-building scleractinia Enallopsammia profunda and Lophelia pertusa while the associated benthic megafauna shows a rather scarce occurrence. The recent environmental setting is characterized by a high surface water production caused by a local upwelling center and a dynamic bottom water regime comprising vigorous bottom currents, internal waves and strong density contrasts, which all together provide optimal conditions for the growth of cold-water corals. The strong hydrodynamics – potentially supported by the diel vertical migration of zooplankton in the Campeche area – drive the delivering of food particles to the corals. The Campeche cold-water coral province is, thus, an excellent example highlighting the importance of the hydrographic setting in securing the food supply for the development of large and vivid cold-water coral ecosystems
Cold-water corals in the Bay of Biscay - occurrences and distribution in space and time (TransBiscay) - Cruise No. M84/5, May 31 - June 21, 2011, Vigo (Spain) - Brest (France)
The scientific objectives of METEOR cruise M84/5 focused on the measurement
and analysis of the environmental controls of modern and fossil cold-water coral growth
along a transect in the Bay of Biscay. In four working areas we successfully deployed lander
systems and CTD/Ro’s to document the physical and hydrochemical characteristics of bottom
water masses and the water column in general. These are used to shed light on potential
linkages to modern cold-water coral growth and distribution. These investigations were
flanked by plankton tows in surface waters. The base for all investigations was a thorough
hydroacoustic survey to characterize potential cold-water coral bearing areas with living
colonies. Based on these maps we deployed all video-guided gear such as the OFOS-video
sled, the TV grab, and the lander systems. Benthic assemblages and sedimentary structures
have been documented and sampled with the OFOS and a box corer. Simultaneously, genetic
samples of the living coral material were taken for additional studies. Furthermore, we have
taken gravity cores to investigate the paleoceanographic conditions as well as the timing of
cold-water coral colonization in the Bay of Biscay. Along with the coring efforts, a detailed
sampling and study of porewater properties was performed. An additional aim of this cruise
was to investigate the influence of boundary exchange processes on the Neodymium isotopy
in bottom waters along the pathway of the Mediterranean Outflow water (MOW) by taking
multiple samples with the CTD/Ro.
The new data and samples of this METEOR cruise will provide the framework to
investigate the timing of cold-water coral colonization in the Bay of Biscay, as well as its
interplay with the ambient hydrography and geochemistry. This successful cruise has
provided the basis to investigate the scientific aims of this expedition in great detail
The curious activity in the nucleus of NGC 4151: jet interaction causing variability?
A key characteristic of many active galactic nuclei (AGNs) is their variability, but its origin is poorly understood, especially in the radio domain. Williams et al. (2017) reported a ∼50 per cent increase in peak flux density of the AGN in the Seyfert galaxy NGC 4151 at 1.5 GHz with the e-MERLIN array. We present new high-resolution e-MERLIN observations at 5 GHz and compare these to archival MERLIN observations to investigate the reported variability. Our new observations allow us to probe the nuclear region at a factor three times higher resolution than the previous e-MERLIN study. We separate the core component, C4, into three separate components: C4W, C4E, and X. The AGN is thought to reside in component C4W, but this component has remained constant between epochs within uncertainties. However, we find that the Eastern-most component, C4E, has increased in peak flux density from 19.35 ± 1.10 to 37.09 ± 1.86 mJy beam−1, representing an 8.2σ increase on the MERLIN observations. We attribute this peak flux density increase to continue interaction between the jet and the emission line region (ELR), observed for the first time in a low-luminosity AGNs such as NGC 4151. We identify discrete resolved components at 5 GHz along the jet axis, which we interpret as areas of jet–ELR interaction
Western Indian Ocean marine and terrestrial records of climate variability: a review and new concepts on land-ocean interactions since AD 1660
We examine the relationship between three tropical and two subtropical western Indian Ocean coral oxygen isotope time series to surface air temperatures (SAT) and rainfall over India, tropical East Africa and southeast Africa. We review established relationships, provide new concepts with regard to distinct rainfall seasons, and mean annual temperatures. Tropical corals are coherent with SAT over western India and East Africa at interannual and multidecadal periodicities. The subtropical corals correlate with Southeast African SAT at periodicities of 16–30 years. The relationship between the coral records and land rainfall is more complex. Running correlations suggest varying strength of interannual teleconnections between the tropical coral oxygen isotope records and rainfall over equatorial East Africa. The relationship with rainfall over India changed in the 1970s. The subtropical oxygen isotope records are coherent with South African rainfall at interdecadal periodicities. Paleoclimatological reconstructions of land rainfall and SAT reveal that the inferred relationships generally hold during the last 350 years. Thus, the Indian Ocean corals prove invaluable for investigating land–ocean interactions during past centuries
A review of elliptical and disc galaxy structure, and modern scaling laws
A century ago, in 1911 and 1913, Plummer and then Reynolds introduced their
models to describe the radial distribution of stars in `nebulae'. This article
reviews the progress since then, providing both an historical perspective and a
contemporary review of the stellar structure of bulges, discs and elliptical
galaxies. The quantification of galaxy nuclei, such as central mass deficits
and excess nuclear light, plus the structure of dark matter halos and cD galaxy
envelopes, are discussed. Issues pertaining to spiral galaxies including dust,
bulge-to-disc ratios, bulgeless galaxies, bars and the identification of
pseudobulges are also reviewed. An array of modern scaling relations involving
sizes, luminosities, surface brightnesses and stellar concentrations are
presented, many of which are shown to be curved. These 'redshift zero'
relations not only quantify the behavior and nature of galaxies in the Universe
today, but are the modern benchmark for evolutionary studies of galaxies,
whether based on observations, N-body-simulations or semi-analytical modelling.
For example, it is shown that some of the recently discovered compact
elliptical galaxies at 1.5 < z < 2.5 may be the bulges of modern disc galaxies.Comment: Condensed version (due to Contract) of an invited review article to
appear in "Planets, Stars and Stellar
Systems"(www.springer.com/astronomy/book/978-90-481-8818-5). 500+ references
incl. many somewhat forgotten, pioneer papers. Original submission to
Springer: 07-June-201
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