Transport Of Particles Across Continental Shelves

Transport of particulate material across continental shelves is well demonstrated by the distributions on the seabed and in the water column of geological, chemical, or biological components, whose sources are found farther landward or farther seaward. This paper addresses passive (incapable of swimming) particles and their transport across (not necessarily off) continental shelves during high stands of sea level. Among the general factors that influence across-shelf transport are shelf geometry, latitudinal constraints, and the timescale of interest. Research studies have investigated the physical mechanisms of transport and have made quantitative estimates of mass flux across continental shelves. Important mechanisms include wind-driven flows, internal waves, wave-orbital flows, infragravity phenomena, buoyant plumes, and surf zone processes. Most particulate transport occurs in the portion of the water column closet to the seabed. Therefore physical processes are effective where and when they influence the bottom boundary layer, causing shear stresses sufficient to erode and transport particulate material. Biological and geological processes at the seabed play important roles within the boundary layer. The coupling of hydrodynamic forces from currents and surface gravity waves has a particularly strong influence on across-shelf transport; during storm events, the combined effect can transport particles tens of kilometers seaward. Several important mechanisms can cause bidirectional (seaward and landward) transport, and estimates of the net flux are difficult to obtain. Also, measurements of across-shelf transport are made difficult by the dominance of along-shelf transport. Geological parameters are often the best indicators of net across-shelf transport integrated over time scales longer than a mouth. For example, fluvially discharged particles with distinct composition commonly accumulate in the midshelf region. Across-shelf transport of particulate material has important implications for basic and applied oceanographic research (e.g., dispersal of planktonic larvae and particle-reactive pollutants). Continued research is needed to understand the salient mechanisms and to monitor them over a range of timescales

Zebra finches and Dutch adults exhibit the same cue weighting bias in vowel perception

Vocal tract resonances, called formants, are the most important parameters in human speech production and perception. They encode linguistic meaning and have been shown to be perceived by a wide range of species. Songbirds are also sensitive to different formant patterns in human speech. They can categorize words differing only in their vowels based on the formant patterns independent of speaker identity in a way comparable to humans. These results indicate that speech perception mechanisms are more similar between songbirds and humans than realized before. One of the major questions regarding formant perception concerns the weighting of different formants in the speech signal (“acoustic cue weighting”) and whether this process is unique to humans. Using an operant Go/NoGo design, we trained zebra finches to discriminate syllables, whose vowels differed in their first three formants. When subsequently tested with novel vowels, similar in either their first formant or their second and third formants to the familiar vowels, similarity in the higher formants was weighted much more strongly than similarity in the lower formant. Thus, zebra finches indeed exhibit a cue weighting bias. Interestingly, we also found that Dutch speakers when tested with the same paradigm exhibit the same cue weighting bias. This, together with earlier findings, supports the hypothesis that human speech evolution might have exploited general properties of the vertebrate auditory system

More than a century of bathymetric observations and present-day shallow sediment characterization in Belfast Bay, Maine, USA: implications for pockmark field longevity

This paper is not subject to U.S. copyright. The definitive version was published in Geo-Marine Letters 31 (2011): 237-248, doi:10.1007/s00367-011-0228-0.Mechanisms and timescales responsible for pockmark formation and maintenance remain uncertain, especially in areas lacking extensive thermogenic fluid deposits (e.g., previously glaciated estuaries). This study characterizes seafloor activity in the Belfast Bay, Maine nearshore pockmark field using (1) three swath bathymetry datasets collected between 1999 and 2008, complemented by analyses of shallow box-core samples for radionuclide activity and undrained shear strength, and (2) historical bathymetric data (report and smooth sheets from 1872, 1947, 1948). In addition, because repeat swath bathymetry surveys are an emerging data source, we present a selected literature review of recent studies using such datasets for seafloor change analysis. This study is the first to apply the method to a pockmark field, and characterizes macro-scale (>5 m) evolution of tens of square kilometers of highly irregular seafloor. Presence/absence analysis yielded no change in pockmark frequency or distribution over a 9-year period (1999–2008). In that time pockmarks did not detectably enlarge, truncate, elongate, or combine. Historical data indicate that pockmark chains already existed in the 19th century. Despite the lack of macroscopic changes in the field, near-bed undrained shear-strength values of less than 7 kPa and scattered downcore 137Cs signatures indicate a highly disturbed setting. Integrating these findings with independent geophysical and geochemical observations made in the pockmark field, it can be concluded that (1) large-scale sediment resuspension and dispersion related to pockmark formation and failure do not occur frequently within this field, and (2) pockmarks can persevere in a dynamic estuarine setting that exhibits minimal modern fluid venting. Although pockmarks are conventionally thought to be long-lived features maintained by a combination of fluid venting and minimal sediment accumulation, this suggests that other mechanisms may be equally active in maintaining such irregular seafloor morphology. One such mechanism could be upwelling within pockmarks induced by near-bed currents.Graduate support for Brothers came from a Maine Economic Improvement Fund Dissertation Fellowship

The dynamics of expanding mangroves in New Zealand

In contrast to the global trend of mangrove decline, New Zealand mangroves are rapidly expanding, facilitated by elevated sediment inputs in coastal waters as a consequence of large-scale land use changes following European settlement. New Zealand mangroves are at the southern limit of the global mangrove extent, which limits the tree height of Avicennia marina var. australasica, the only mangrove species present. Mangroves in New Zealand thrive in the sheltered environments of infilling drowned river valleys with abundant supply of fine terrigenous sediments, showing various stages of mangrove succession and expansion dynamics. Bio-physical interactions and carbon dynamics in these expanding temperate mangrove systems show similarities to, but also differ from those in tropical mangrove forests, for instance due to the limited height and complexity of the mangrove communities. Likewise, ecosystem services provided by New Zealand mangroves deviate from those offered by tropical mangroves. In particular, the association of mangrove expansion with the accumulation of (the increased supply of) fine sediments and the consequent change of estuarine ecosystems, has provoked a negative perception of mangrove expansion and subsequently led to mangrove clearance. Over recent decades, a body of knowledge has been developed regarding the planning and decision making relating to mangrove removal, yet there are still effects that are unknown, for example with respect to the post-clearance recovery of the original sandflat ecosystems. In this chapter we discuss the dynamics of New Zealand’s expanding mangroves from a range of viewpoints, with the aim of elucidating the possible contributions of expanding mangroves to coastal ecosystem services, now and in the future. This chapter also reviews current policies and practice regarding mangrove removal in New Zealand and addresses the (un)known effects of mangrove clearance. These combined insights may contribute to the development of integrated coastal management strategies that recognise the full potential of expanding mangrove ecosystems