1 Analytical Center for Climate and Environmental Change, Northern Illinois University

Coastal and Marine Geology, Pacific Science Center, U.S. Geological Survey

Cordell Bank National Marine Sanctuary

Center for Coastal and Ocean Mapping, University of New Hampshire

2

3

4

CMECS Substrate Map of Upper Muir Inlet, Glacier Bay National Park and Preserve, Alaska

By

Luke D. Trusel1

, Guy R. Cochrane2, Lisa L. Etherington3, Ross D. Powell1, and Larry A. Mayer4

2010

Any use of trade, rm, or product names in this publication is for descriptive

purposes only and does not imply endorsement by the U.S. Government.

When this map is printed on an electronic plotter directly from digital les. Dimensional

calibration may vary between electronic plotters and between X and Y

directions on the same plotter, and paper may change size due to atmospheric

conditions; therefore, scale and proportions may not be true on plots of this map.

For sale by U.S. Geological Survey, Information Services, Box 25286,

Federal Center, Denver, CO 80225, 1-888-ASK-USGS

Digital les available at http://pubs.usgs.gov/sim/3122

59°0'0"N

59°0'0"N

58°30'0"N

58°30'0"N

137°0' 136°30' 136°0' 135°30'

59°0'

58°30'

Pacific

Ocean

Glacier

Bay

59°00'

59°05'

136°20'W 136°15' 136°10' 136°05'

136°20' 136°15' 136°10'

59°00'

59°05'

136°05'

200

80

200

200

80

200

200

80

200

Area A

Inlarged area A shows a detailed view of the three benthic depth zones: circalittoral (30–80 m), circalittoral (offshore) 

(80–200 m), and mesobenthic (200–1,000 m). Four of the five classified substrates are depicted: mud (dark green), 

mixed sediments (light green), boulder/rubble (orange), and bedrock (red). Isobath in meters.

Area A

200

80

Shoreline

mud

 circalittoral

 (offshore) 

boulder/rubble

 circalittoral (offshore) 

mixed

sediments

 mesobenthic

 circalittoral

boulder/rubble mesobenthic

mixed sediments

 circalittoral (offshore) 

bedrock

 mesobenthic

mud

 mesobenthic

mud

 circalittoral

200

bedrock

(offshore) 

Location map showing upper Muir Inlet and Area A of map.

This seafloor character map was produced using (1) a supervised classification of multibeam

backscatter (intensity) that is divided into two classes of induration (hard and soft bottom) and (2) 

manual polygon selection using geological reasoning, seafloor property measurements from the 

multibeam bathymetry, and knowledge of substrate types from video observations, seismic reflection 

profile interpretations, and sediment sampling. The seafloor properties examined during manual 

classification were rugosity (a derivative for seafloor roughness) and seafloor slope. These were 

used to help identify steeply sloping and rugose areas that are most likely bedrock or consolidated 

glacial material. 

The Coastal and Marine Ecological Classification Standard (CMECS) (v. III June 2008 draft) by the 

National Oceanic and Atmospheric Administration (NOAA) and NatureServe was used to classify 

various substrate types (Madden and others, 2008). Units displayed on this map represent the 

Benthic Cover Component subclass level of the CMECS classification draped over the shaded 

bathymetry shown on sheet 1. Substrate distributions are summarized for the entire fjord in the 

tables below. Table 1 shows the percent and area of the substrate distribution by CMECS class. The 

unconsolidated bottom [UB] CMECS class is divided into mud [UB.3], mixed sediments [UB.6], and 

cobble/gravel [UB.1] subclasses. The rock bottom [RB] CMECS class is divided into bedrock [RB.1] 

and boulder/rubble [RB.3]. Bathymetric contours represent the division between benthic depth zones 

defined by the CMECS classes. Table 2 shows the percent and area of each benthic depth zone. 

The zones depicted in this map are deep infralittoral (5─30 m), circalittoral (30─80 m), circalittoral 

(offshore) (80─200 m), and mesobenthic (200─1,000 m). 

Mud is the dominant substrate for the measured area within Muir Inlet, comprising 89 percent or 

66.79 km2 with the greatest abundance in the mesobenthic depth zone (the fjord floor basins). 

Abundant glacimarine mud in Muir Inlet is primarilr currently derived from Muir and Riggs Glaciers. 

See the accompanying pamphlet for more information regarding sources and rates. Bedrock is the 

second most abundant substrate at 6.1 percent or 4.57 km2, the greatest percentage is located in the 

circalittoral (offshore) depth zone (the fjord walls). Mixed sediments, where the exact composition of 

the sediment was unknown but there was a higher backscatter than that of mud, comprised 3.2 

percent or 2.4 km2 as was also primarily located in the circalittoral (offshore) depth zone. These 

mixed sediment areas commonly represent areas along the fjord walls where side-entry fluvial 

systems deposit coarser sediment. The boulder/rubble substrate class comprises 1.3 or 0.99 km2 of 

the measured area in Muir Inlet. Cobble/gravel could only be confidently placed in 0.4 percent or 

0.29 km2, but likely makes up part of the mixed sediments class as well.

[RB.1] Bedrock

[RB.3] Boulder/rubble

[UB.3] Mud

[UB.6] Mixed sediments

[UB.1] Cobble/gravel

CMECS SUBCLASS LEVEL SUBSTRATES

Table 1. Substrate distribution for Muir Inlet. 

CMECS class CMECS subclass Percentage of 

total area Area (km2) 

mud 88.7 64.6 

mixed sediments 3.3 2.4 

Unconsolidated 

bottom 

cobble/gravel 0.4 0.3 

Rock bottom boulder/rubble 1.4 1.0 

bedrock 6.2 4.5 

Table 2. Substrate distribution by depth zone for Muir Inlet. 

Deep infralittoral: 

5 –30 m water depth 

Circalittoral: 

30–80 m water depth 

Circalittoral (offshore): 

80–200 m water depth 

Mesobenthic: 

200–1,000 m water depth 

CMECS subclass Percent Area (km2) Percent Area (km2) Percent Area (km2) Percent Area (km2) 

Mud 0.05 0.04 3.53 2.57 28.79 20.95 56.35 41.00 

Mixed sediments 0 0 0.11 0.08 1.94 1.41 1.26 0.91 

Cobble/gravel 0 0 0.03 0.02 0.34 0.25 0.03 0.02 

Boulder/rubble 0 0 0.01 0.01 0.56 0.41 0.79 0.57 

Bedrock 0.01 0.01 0.43 0.31 3.95 2.88 1.83 1.33 

Upper

Muir

Inlet

MAP LOCATION

ALASKA

1000 0 1000 2000 3000 4000 5000 6000 7000 FEET

1 .5 0 1 KILOMETER

1 1/2 0 1 MILE

SCALE 1:24000

LAND CONTOUR INTERVAL 100 METERS

BATHYMETRY 80 AND 200 METERS

SEA LEVEL, CYAN

Manuscript approved for publication March 31, 2010

GIS database and digital cartography by Luke D.

Trusel. Based on cartography by Karen L. Wheeler 

Seaoor Geology mapped by Luke D. Trusel, 2008.

Based on multibeam sonar data collected in June

2004 under National Science Foundation award 

OCE03-41096

Base from U.S. Geological Survey, National Elevation Dataset

NASA Landsat 7 Imagery, 1999

Universal Transverse Mercator Zone 8N Projection, WGS84

APPROXIMATE MEAN

DECLINATION, 2010

21 / ° 1 2

MAGNETIC NORTH

TRUE NORTH

U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Map 3122

Sheet 3 of 4

Pamphlet accompanies map