8 research outputs found
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
Biodiversity of the Deep-Sea Continental Margin Bordering the Gulf of Maine (NW Atlantic): Relationships among Sub-Regions and to Shelf Systems
Background: In contrast to the well-studied continental shelf region of the Gulf of Maine, fundamental questions regarding
the diversity, distribution, and abundance of species living in deep-sea habitats along the adjacent continental margin
remain unanswered. Lack of such knowledge precludes a greater understanding of the Gulf of Maine ecosystem and limits
development of alternatives for conservation and management.
Methodology/Principal Findings: We use data from the published literature, unpublished studies, museum records and
online sources, to: (1) assess the current state of knowledge of species diversity in the deep-sea habitats adjacent to the Gulf
of Maine (39–43uN, 63–71uW, 150–3000 m depth); (2) compare patterns of taxonomic diversity and distribution of
megafaunal and macrofaunal species among six distinct sub-regions and to the continental shelf; and (3) estimate the
amount of unknown diversity in the region. Known diversity for the deep-sea region is 1,671 species; most are narrowly
distributed and known to occur within only one sub-region. The number of species varies by sub-region and is directly
related to sampling effort occurring within each. Fishes, corals, decapod crustaceans, molluscs, and echinoderms are
relatively well known, while most other taxonomic groups are poorly known. Taxonomic diversity decreases with increasing
distance from the continental shelf and with changes in benthic topography. Low similarity in faunal composition suggests
the deep-sea region harbours faunal communities distinct from those of the continental shelf. Non-parametric estimators of
species richness suggest a minimum of 50% of the deep-sea species inventory remains to be discovered.
Conclusions/Significance: The current state of knowledge of biodiversity in this deep-sea region is rudimentary. Our ability
to answer questions is hampered by a lack of sufficient data for many taxonomic groups, which is constrained by sampling
biases, life-history characteristics of target species, and the lack of trained taxonomists
Bottom-current and wind-pattern changes as indicated by Late Glacial and Holocene sediments from western Lake Geneva (Switzerland)
The Late-Glacial and Holocene sedimentary history of the Hauts-Monts area(western Lake Geneva, Switzerland) is reconstructed combining high resolution seismic stratigraphy and well-dated sedimentary cores. Six reflections and seismic units are defined and represented by individual isopach maps, which are further combined to obtain a three-dimensional age-depth model. Slumps, blank areas and various geometries are identified using these seismic data. The sediment depositional areas have substantially changed throughout the lake during the end of the Late-Glacial and the Holocene. These changes are interpreted as the result of variations in the intensity of deep lake currents and the frequency of strong winds determining the distribution of sediment input from the Versoix River and from reworking of previously deposited sediments within the lacustrine basin. The identified changes in sediment distribution allowed us to reconstruct the lake's deep-current history and the evolution of dominant strong wind regimes from the Preboreal to present times