USGS Scientific Investigations Map 3122 (4 sheets)

Trusel, L.; Cochrane, G.; Etherington, L.; Powell, R.; Mayer, L.

Seafloor geology and potential benthic habitats were mapped in Muir Inlet, Glacier Bay National Park and Preserve, Alaska, using multibeam sonar, ground-truth information, and geological interpretations. Muir Inlet is a recently deglaciated fjord that is under the influence of glacial and paraglacial marine processes. High glacially derived sediment and meltwater fluxes, slope instabilities, and variable bathymetry result in a highly dynamic estuarine environment and benthic ecosystem. We characterize the fjord seafloor and potential benthic habitats using the Coastal and Marine Ecological Classification Standard (CMECS) recently developed by the National Oceanic and Atmospheric Administration (NOAA) and NatureServe. Substrates within Muir Inlet are dominated by mud, derived from the high glacial debris flux. Water-column characteristics are derived from a combination of conductivity temperature depth (CTD) measurements and circulation-model results. We also present modern glaciomarine sediment accumulation data from quantitative differential bathymetry. These data show Muir Inlet is divided into two contrasting environments: a dynamic upper fjord and a relatively static lower fjord. The accompanying maps represent the first publicly available high-resolution bathymetric surveys of Muir Inlet. The results of these analyses serve as a test of the CMECS and as a baseline for continued mapping and correlations among seafloor substrate, benthic habitats, and glaciomarine processes.This study is a bottom-up approach to mapping benthic habitats (Greene et al., 2007) in Muir Inlet (fig. 1). Seafloor substrate and morphology are characterized so that they may be correlated to and associated with a specific set of benthic conditions favorable for local biota. These biota include both commercially and recreationally important species such as king crabs (Paralithodes camtschaticus), Tanner crabs (Chionoecetes bairdi), and Pacific halibut (Hippoglossus stenolepis) (Mondragon et al., 2007a,b). Seafloor substrates and, therefore, potential benthic habitats were mapped at depths ranging from just below the surface to greater than 300 m in the deepest fjord basins. The substrate was characterized by using a combination of high-resolution multibeam bathymetry and backscatter imagery, numerous ground-truth sources, and knowledge of the local fjord environment. In early June 2004, nearly 75 km2 of multibeam-sonar mapping was completed in Muir Inlet aboard the R/V Maurice Ewing during a project funded by the National Science Foundation to investigate marine paleoclimate and paleoceanographic records in southern Alaska. Multibeam records were supplemented with seismic reflection profiles and several sediment cores. Analyses from this cruise, thus far, have focused on tidewater-glacier dynamics and history inferred through glacial-sequence stratigraphy (Cowan et al., 2008) and reconstruction of glacial discharge dynamics from rhythmic sedimentary deposits (Jackolski and others, 2006). Ongoing research includes analyses of deglaciation processes inferred from submarine glacial landforms (Trusel and others, 2009) and measurements of glacial-sediment volumes and inferred sediment yields and erosion rates (Trusel et al., 2008). The multibeam bathymetric (sheet 1) and acoustic backscatter data are combined with additional information in an Environmental Systems Research Institute (ESRI™) Geographic Information Systems (ArcGIS™) database to create several geospatial products. NOAA and NatureServe’s CMECS (Madden et al., 2008) was used to classify seafloor substrate (sheets 2 and 3), potential benthic habitats, water column properties, and seafloor geomorphology (sheet 4). An estimate of modern sediment flux measurements using quantitative differential bathymetry is also presented. These geospatial products are the first high-resolution bathymetric surveys for Muir Inlet, serve as baselines for further research, and provide data for park management.

USGS Scientific Investigations Map 3122 (4 sheets)

Series