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Observations of pockmark flow structure in Belfast Bay, Maine, Part 3: implications for sediment transport

Geo-Marine Letters

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, , , and
https://doi.org/10.1007/s00367-016-0474-2

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Abstract

Current observations and sediment characteristics acquired within and along the rim of two pockmarks in Belfast Bay, Maine, were used to characterize periods of sediment transport and to investigate conditions favorable to the settling of suspended sediment. Hourly averaged Shields parameters determined from horizontal current velocity profiles within the center of each pockmark never exceed the critical value (approximated with the theoretical model of Dade et al. 1992). However, Shields parameters estimated at the pockmark rims periodically exceed the critical value, consistent with conditions that support the onset of sediment transport and suspension. Below the rim in the near-center of each pockmark, depth-averaged vertical velocities were less than zero (downward) 60% and 55% of the time in the northern and southern pockmarks, and were often comparable to depth-averaged horizontal velocities. Along the rim, depth-averaged vertical velocities over the lower 8 m of the water column were primarily downward but much less than depth-averaged horizontal velocities indicating that suspended sediment may be moved to distant locations. Maximum grain sizes capable of remaining in suspension under terminal settling flow conditions (ranging 10–170 μm) were typically much greater than the observed median grain diameter (about 7 μm) at the bed. During upwelling flow within the pockmarks, and in the absence of flocculation, suspended sediment would not settle. The greater frequency of predicted periods of sediment transport along the rim of the southern pockmark is consistent with pockmark morphology in Belfast Bay, which transitions from more spherical to more elongated toward the south, suggesting near-bed sediment transport may contribute to post-formation pockmark evolution during typical conditions in Belfast Bay.

Additional publication details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Observations of pockmark flow structure in Belfast Bay, Maine, Part 3: implications for sediment transport
Series title:
Geo-Marine Letters
DOI:
10.1007/s00367-016-0474-2
Volume:
37
Issue:
1
Year Published:
2017
Language:
English
Publisher:
Springer
Contributing office(s):
Woods Hole Coastal and Marine Science Center
Description:
12 p.
First page:
23
Last page:
34
Country:
United States
State:
Maine
Other Geospatial:
Belfast Bay