Cross-basin differences in particulate organic carbon export and flux attenuation in the subtropical North Atlantic gyre

We compared in-situ and satellite-derived measures of the biological carbon pump efficiency at the two seemingly similar subtropical North Atlantic gyre time series sites, the Bermuda time series (BATS, Bermuda Atlantic time-series study and OFP, ocean flux program) in the western gyre and the ESTOC time series (European station for time-series in the ocean, Canary Islands) in the eastern gyre. Satellite-derived surface chlorophyll a was slightly lower at Bermuda compared to ESTOC (annual average of 0.10±0.04 vs. 0.14±0.05-mg-m^?3), as was satellite-derived primary production (annual average of 380±77 vs. 440±80-mg C-m^?2 d^?1). However, export production normalized to primary production (export ratio) was higher at Bermuda by a factor of 2–3 when estimated using mesopelagic traps moored at 500-m depth and by a factor of 3–4 when estimated using surface-tethered drifting traps. When averaged seasonally, flux at BATS was highest in spring (March, April, May) at all depths followed by summer (June, July, August) and decreasing towards fall, but this seasonality was less visible at ESTOC. Seasonal comparison showed the fastest flux attenuation at Bermuda in winter and spring, coinciding with the highest POC flux. POC/PIC ratios derived from the moored traps were significantly higher at BATS than at ESTOC in fall and winter, but this difference was not significant in spring (p>0.05). This study shows that while the western and eastern Atlantic subtropical gyres have similar rates of primary production, the biological carbon pump differs between the two provinces. Higher new nutrient input observed at Bermuda compared to ESTOC might explain part of the difference in export ratio but alone is insufficient. Greater winter mixed-layer depths and higher mesoscale eddy activity at Bermuda resulting in pulsed production events of labile organic matter might explain both the higher export flux and export ratios found at Bermuda.     

HST/STIS observations of the high-velocity interstellar cloud HVC 291.2−41.2+80: a warm, mainly ionized high-velocity cloud

We present intermediate-resolution HST /STIS spectra of a high-velocity interstellar cloud ( v _LSR=+80 km s⁻¹) towards DI 1388, a young star in the Magellanic Bridge located between the Small and Large Magellanic Clouds. The STIS data have a signal-to-noise ratio (S/N) of 20–45 and a spectral resolution of about 6.5 km s⁻¹ (FWHM). The high-velocity cloud absorption is observed in the lines of C  ii , O  i , Si  ii , Si  iii , Si  iv and S  iii . Limits can be placed on the amount of S  ii and Fe  ii absorption that is present. An analysis of the relative abundances derived from the observed species, particularly C  ii and O  i , suggests that this high-velocity gas is warm ( T _k∼10³–10⁴ K) and predominantly ionized. This hypothesis is supported by the presence of absorption produced by highly ionized species, such as Si  iv . This sightline also intercepts two other high-velocity clouds that produce weak absorption features at v _LSR=+113 and +130 km s⁻¹ in the STIS spectra.     

Synthetic Spectra of Long-Period Variables: A First Comparison with ISO Observations

Exploratory synthetic spectra were computed for carbon-rich long-period variables. We used dynamic model atmospheres of Höfner &; Dorfi (1997) and calculated partial pressures, absorption- and scattering coefficients as input for the spectral synthesis code of Jørgensen et al. (1992). First ISO SWS-observations of the carbon-Mira T Dra are compared with our synthetic spectra.     

The Qso Hosts I Zw 1 and 3C 48: Prototypes of a Merger-Driven Quasar Evolution?

I Zw 1 and 3C 48 are two neighboring template objects at a later stage of the hypothesized merger-driven evolutionary sequence from ultra-luminous infrared galaxies (ULIRGs) to quasi-stellar objects (QSOs). Since galaxy mergers are assumed to trigger the evolution, it is important to confirm the merger properties of transitionary objects. Using multi-wavelength observations and N-body simulations, the merger histories of I Zw 1 and 3C 48 have been investigated in two separate case studies. Here, the results from both studies are compared and their relevance for the evolutionary hypothesis is discussed.This research is partly based on observations with ISAAC at the Very Large Telescope (VLT) of the European Southern Observatory (ESO) under projects 67.B-0009 and 67.B-0019.     

Neptunian dykes along a drowned carbonate platform margin: an indication for recurrent extensional tectonic activity?

Three successive Mesozoic neptunian dyke generations and related unconformities suggest recurrent extensional fracturing and periods of relative sea-level rise along the NW Trento Plateau margin in the Southern Alps, Italy. The first neptunian dyke generation was induced by NNW–SSE directed extension of Early Jurassic skeletal oolitic periplatform deposits generating micritic early Middle Liassic neptunian dykes with orthogonal orientation. The second generation of neptunian dykes was possibly caused by marginal extension at the drowned platform edge penetrating Late Jurassic, red pelagic limestones with a pelagic matrix of Albian/Cenomanian age and nearly orthogonal fracture orientation. The third generation of neptunian dykes occurred after a prolonged period of submarine exposure and erosion (Aptian/Albian to Late Maastrichtian) during the rapid burial of the submarine Trento Plateau margin relief. The Late Maastrichtian neptunian dykes were caused by extension of Early to Middle Jurassic oolitic periplatform limestones along steep (inclination > 10°) submarine slopes. Generally successive neptunian dyke generations along drowned carbonate platform margins could be caused by repeated extensional brittle fracturing of lithified periplatform deposits and the filling of micritic matrix derived from overlying pelagic sediment sequences under substantial hydrostatic pressure. This would suggest that recurrent extensional fracturing is continuously recorded by neptunian dyke formation which could be used to indicate extensional tectonic activity at a foundering deep-marine carbonate platform edge.     

Mare basalt units and the compositions of their magmas

A synthesis of the majority of the available mare basalt data shows that basalts and glasses came from 28 different volcanic units. The compositions of the magmas of 12 of these units can be calculated with a high degree of confidence. Reasonable estimates can be made for the compositions of nine of the remaining units. In addition, the compositions of three general magma types can be obtained from data derived from the Luna 16, Luna 24, and Apollo 17 fines. The compositional data presented provide a firm basis for the further study of the characteristics of the mare basalt magma source region.     

I Zwicky 1: Decomposition and dynamics of the nearby QSO host

We address current theories of research on morphology, environment and evolution of active galaxies in the form of a detailed case study of the nearby QSO host I Zw 1. This study is based on sub-kpc resolution ¹²CO(1-0) observations with the BIMA mm-interferometer and on near-infrared imaging with ISAAC at the VLT. The ¹²CO(1-0) maps reveal a circumnuclear molecular gas ring with a radius of 0.9 kpc. The imaging data in the J-band are analyzed with respect to a disk-bulge decomposition. Together with a model of the gas rotation curve, the radial profile of the dynamical J-band mass-to-light ratio (M/L) is discussed. The J-band images give new evidence for an interaction between I Zw 1 and its nearby companion. First results from a sequence of N-body simulations for an extensive test of the parameter space of the interaction are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Topography and morphodynamics in the German Bight using SAR and optical remote sensing data

Morphological changes in coastal areas, especially in river estuaries, are of high interest in many parts of the world. Satellite data from both optical and radar sensors can help to monitor and investigate these changes. Data from both kinds of sensors being available for up to 30 years now, allow examinations over large timescales, while high resolution sensors developed within the last decade allow increased accuracy. So the creation of digital elevation models (DEMs) of, for example, the wadden sea from a series of satellite images is already possible. ENVISAT, successfully launched on March 1, 2002, continues the line of higher resolution synthetic aperture radar (SAR) imaging sensors with its ASAR instrument and now also allows several polarization modes for better separation of land and water areas. This article gives an overview of sensors and algorithms for waterline determination as well as several applications. Both optical and SAR images are considered. Applications include morphodynamic monitoring studies and DEM generation.

Model Atmospheres of AGB Stars: Dynamics, Molecules and Dust

The atmospheres and circumstellar envelopes of AGB stars are characterized by complex physical phenomena like shock waves caused by stellar pulsation or formation of molecules and dust which often lead to a heavy mass loss and have a strong influence on IR properties as observed by ISO. To allow a physical interpretation of various observations we have constructed improved dynamical model atmospheres of long-period variables. In this contribution we mainly investigate the dependence of the atmospheric structure and its variability on stellar pulsation, molecular opacities and time-dependent dust formation. IR spectra resulting from our models are discussed in detail by Loidl et al. (1997b) and compared to ISO-SWS spectra obtained by Hron et al. (1997). This revised version was published online in August 2006 with corrections to the Cover Date.