Proceedings of the Coastal Benthic Boundary Layer Key West Workshop

Abstract

REPORT DOCUMENTATION PAGE OBMNo 0704-0W88Public reporting burden for this collection of information is estimated to average 1 hour per response, Including the time for reviewing Instructlons, searching existing data sources, gathednganenid maintaining the data needed, and completing and revIewing the collection of irnformation. Send comments regarding this burden or any otheraspect of this collection Approved for public release; distribution unlimited. ABSTRACT (Maximum 200 words)The coastal benthic boundary layer (CBBL) research program is a 5-year Office of Naval Research study that addresses the physical characterization and modeling of benthic boundary layer processes and the impact of these processes on seafloor structure, properties, and behavior. The lower Florida Keys, specifically the Dry Tortugas and Marquesas Keys, were selected as experimentsites totestthe CBBL hypotheses and provide dataforcomprehensive modeling efforts. Aworkshop was held to provide a forum for initial research results and to define the models that relate the controlling geologic processes and observed sediment behavior. This report contains the extended abstracts from this workshop. IntroductionThe Key West Workshop, held between February 4-7, 1997, had two main objectives:(1) to provide a forum for initial research results from the Key West Campaign and (2) to define the models that relate the controlling geological processes and observed sediment behavior.The presentation of research is organized in categories from the large scale regional descriptions to the small scale microfabric and modeling efforts. The initial section "Geologic Background" includes papers by Mallinson who interprets Chirp seismic data to describe the geology of the Dry Tortugas Experiment Site, and Brunner who uses microfossils to interpret the past history of the region.A major portion of the workshop was devoted to "Sediment Classification" issues. Tooma and Richardson, 1996).Benthic fauna at the Dry Tortugas site are vertically tiered and can be divided into three functional groups: a shallow fauna, surface deposit and suspension feeders, which thoroughly mix the upper 4-5 cm in days to weeks; an intermediate fauna,carnivores/scavengers, deep deposit feeders, and head-down deposit feeders, which intensely mix sediment to depths of 15 cm over time scales of 10-20 years; and a deeper fauna, gallery creating callianassid shrimp, which only partially mix sediments.Rates and depths of sediment mixing, rates of deposition and the depth and frequency of erosion can be used to predict the preservation potential of sediment layers and structure generated by both physical and biogenic processes. g Ut @ ~~- Sediments recovered by gravity core reveal three units (Units 1, 2, and 3, in ascending stratigraphic order) within the Holocene section. Chirp sonar data reveal low amplitude, subbottom reflectors in the Holocene sediments which correlate to coarse pelecypod and gastropod shell beds of Unit 2, and to lagoonal muds of Unit 1.The three units record an evo...