Circumnuclear Regions and their Barred Host Galaxies

In this paper we present first results from an observational study of the connection between the global parameters of barred galaxies and the appearance of structures, such as dust lanes and star-forming rings in their circumnuclear regions. We combine near-infrared imaging of the central small-scale core structure with optical imaging of the large-scale discs of these barred galaxies. We present more detailed studies of two of our sample galaxies, NGC1530 and NGC 3504, for which we relate the presence and morphology of dust lanes (with different curvature radii) to the strength of the bar. A relation where strong bars lead to straight dust lanes and ovals or weak bars to curved dust lanes is expected theoretically and is borne out by our preliminary imaging results. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pattern speed of the stellar bar in NGC 7479

We study the pattern speed of the bar in NGC 7479 by comparing observations with numerical simulations of gas flow in a two-dimensional gravitational potential, derived from observations. The best agreement between the observations and the modelling is achieved for the fast bar pattern speed of 27 km s⁻¹ kpc⁻¹, when the corotation radius is at 50 arcsec, i.e. 1.1 times the radial length of the bar. This result is supported by the gas and dust lane morphologies, star formation distribution, projected velocity field and overall morphology. We find that star formation is most likely to be triggered close to the large-scale shocks and dust lanes in the bar. The net gas inflow rate in the simulations at 1-kpc radius is 4–6 M⊙ yr⁻¹ at intermediate times.     

Abyssal current influence on the southwest Bermuda Rise and surrounding region

Echograms (3.5 kHz) and bottom photographs reveal that the northward flowing Antarctic Bottom Water (AABW) has strongly influenced the modern depositional regime on the southwest Bermuda Rise. The spatial distribution of echo character types, the orientation and nature of current-controlled structures, and limited current meter data show that AABW flows with varying intensities along three primary pathways around and over the southwest Bermuda Rise. The main core of AABW flows clockwise around the eastern and western flanks of the southern Bermuda Rise, roughly parallel to the 5400 m isobath. This current bifurcates at 28°30′N, 69°W where a portion flows northeast over the southwest Bermuda Rise and the remainder continues north along the physiographic boundary between the southwest Bermuda Rise and the Hatteras Abyssal Plain. Secondary ribbons of AABW branch off the main core of AABW during its southerly journey along the southeastern Bermuda Rise, and flow west through fracture zones. Finally, a diffuse, northward flowing AABW sweeps the entire southwest Bermuda Rise.

A progression of current-controlled bedforms occurs beneath the main path of the AABW reflecting the spatially varying current velocities and sediment supply. The main core of AABW flows west through the narrow Vema Gap creating erosional furrows along the border between the southwest Bermuda Rise and the Vema Gap. Current velocities greater than 20 cm s⁻¹ are inferred from the bedforms in this region. Farther north along the southwestern edge of the Bermuda Rise, sediment waves become more prevalent. This transition from erosional to more depositional bedforms results from diminished current velocities (5–15 cm s⁻¹) and increased sediment supply. Although some of these bedforms on the southwest Bermuda Rise appear to be relict, their orientation is consistent with current meter data and abyssal current direction inferred from bottom photographs.     

Erosion of the Laurentide region of North America by glacial and glaciofluvial processes

Collection of seismic reflection data from continental margins and ocean basins surrounding North America makes it possible to estimate the amount of material eroded from the area formerly covered by Laurentide ice sheets since major glaciation began in North America. A minimum estimate is made of 1.62 × 10⁶ km³, or an average 120 m of rock physically eroded from the Laurentide region. This figure is an order of magnitude higher than earlier estimates based on the volume of glacial drift, Cenozoic marine sediments, and modern sediment loads of rivers. Most of the sediment produced during Laurentide glaciation has already been transported to the oceans. The importance of continental glaciation as a geomorphic agency in North America may have to be reevaluated. Evidence from sedimentation rates in ocean basins surrounding Greenland and Antarctica suggests that sediment production, sediment transport, and possibly denudation by permanent ice caps may be substantially lower than by periodic ice caps, such as the Laurentide. Low rates of sediment survival from the time of the Permo-Carboniferous and Precambrian glaciations suggest that predominance of marine deposition during some glacial epochs results in shorter lived sediment because of preferential tectonism and cycling of oceanic crust versus continental crust.     

Source Identification of Florida Bay's Methylmercury Problem: Mainland Runoff Versus Atmospheric Deposition and <Emphasis Type="Italic">In situ</Emphasis> Production

The first advisory to limit consumption of Florida Bay fish due to mercury was issued in 1995. Studies done by others in the late 1990s found elevated water column concentrations of both total Hg (THg) and methylmercury (MeHg) in creeks discharging from the Everglades, which had its own recognized mercury problem. To investigate the significance of allochthonous MeHg discharging from the upstream freshwater Everglades, we collected surface water and sediment along two transects from 2000 to 2002. Concentrations of THg and MeHg, ranging from 0.36 ng THg/L to 5.98 ng THg/L and from <0.02 ng MeHg/L to 1.79 ng MeHg/L, were elevated in the mangrove transition zone when compared both to upstream canals and the open waters of Florida Bay. Sediment concentrations ranged from 5.8 ng THg/g to 145.6 ng THg/g and from 0.05 ng MeHg/g to 5.4 ng MeHg/g, with MeHg as a percentage of THg occasionally elevated in the open bay. Methylation assays indicated that sediments from Florida Bay have the potential to methylate Hg. Assessment of mass loading suggests that canals delivering stormwater from the northern Everglades are not as large a source as direct atmospheric deposition and in situ methylation, especially within the mangrove transition zone.     

Grand-Design Spirals in the Core of NGC 5248

We report the detection of a bisymmetric nuclear spiral structure in the spiral galaxy NGC 5248.The two red spiral arms can be followed for about 3 arcsec, before they appear to end inside the radius of the circumnuclear starburst `ring' at about 5.5 arcsec or 400 pc distance from the nucleus. We combine our near-infrared Canada–France–Hawaii Telescope adaptive optics images with traditional near-infrared and optical images and show that spiral structure is present in this galaxy at spatial scales reaching from a hundred parsecs to 15 kpc. Comparison with a Hubble Space Telescope ultraviolet image shows how the starburst ring is related to the nuclear spiral structure. We also show a two-dimensional H_α velocity field that reveals no evidence for systematic streaming motions near the nuclear spiral or the starburst ring, nor for a rapidly rising rotation curve. This revised version was published online in July 2006 with corrections to the Cover Date.     

Long‐term variability in the water budget and its controls in an oak‐dominated temperate forest

Water availability is one of the key environmental factors that control ecosystem functions in temperate forests. Changing climate is likely to alter the ecohydrology and other ecosystem processes, which affect forest structures and functions. We constructed a multi‐year water budget (2004–2010) and quantified environmental controls on an evapotranspiration (ET) in a 70‐year‐old mixed‐oak woodland forest in northwest Ohio, USA. ET was measured using the eddy‐covariance technique along with precipitation (P), soil volumetric water content (VWC), and shallow groundwater table fluctuation. Three biophysical models were constructed and validated to calculate potential ET (PET) for developing predictive monthly ET models. We found that the annual variability in ET was relatively stable and ranged from 578 mm in 2009 to 670 mm in 2010. In contrast, ET/P was more variable and ranged from 0.60 in 2006 to 0.96 in 2010. Mean annual ET/PET_FAO was 0.64, whereas the mean annual PET_FAO/P was 1.15. Annual ET/PET_FAO was relatively stable and ranged from 0.60 in 2005 to 0.72 in 2004. Soil water storage and shallow groundwater recharge during the non‐growing season were essential in supplying ET during the growing season when ET exceeded P. Spring leaf area index (LAI), summer photosynthetically active radiation, and autumn and winter air temperatures (T_a) were the most significant controls of monthly ET. Moreover, LAI regulated ET during the whole growing season and higher temperatures increased ET even during dry periods. Our empirical modelling showed that the interaction of LAI and PET explained >90% of the variability in measured ET. Altogether, we found that increases in T_a and shifts in P distribution are likely to impact forest hydrology by altering shallow groundwater fluctuations, soil water storage, and ET and, consequently, alter the ecosystem functions of temperate forests. Copyright © 2013 John Wiley & Sons, Ltd.     

Proposed criteria for recognizing intrastratal deformation features in marine high resolution seismic reflection profiles

Intrastratal deformation of marine strata is ordinarily recorded in high-resolution seismic reflection profiles as acoustically transparent or chaotic intervals marked by hyperbolic echoes. Intrastratal deformation is easily confused with buried slump or slide deposits formed initially at the sea floor. Correct identification of intrastratal deformation depends on the presence of a warped continuously reflective layer overlying a chaotic/transparent layer. Decollement is the key criterion for identification in seismic reflection profiles. Other criteria include intrusive structures or faults rooted in a chaotic/transparent layer and thickening and thinning of a chaotic/transparent layer with transitions to reflective intervals.     

High resolution isotope study of the latest deglaciation based on Bermuda Rise cores

A stable isotope and ¹⁴C investigation of carbonates from three late Quaternary cores with high rates of sedimentation from the northeastern Bermuda Rise has produced the highest resolution record of the glacial maximum to Holocene stable isotope change yet obtained from an open ocean location. The record includes a three-step “termination” and the first direct evidence of an early deglacial meltwater “spike” in the open sea.