52 Techniques and Applications to Sea Floor Mapping

Friday, 26 March 2004
1:00 PM - 5:00 PM

MARINE GEOLOGY AND BENTHIC HABITAT OF GERMAN BANK, SCOTIAN SHELF, ATLANTIC CANADA

Paper number: 52-9
Program: THEME SESSIONS
Time: 3:40 PM – 4:00 PM

Authors

Abstract

Multibeam sonar sea floor mapping technologies have provided the capability to accurately, and cost effectively, image large areas of the seabed. Multibeam bathymetric and backscatter information provides base maps of sea floor topography from which targeted groundtruthing surveys can be planned to map sea floor sediments and associated benthic communities. A seven-year program of contiguous multibeam surveys carried out on German Bank on the southern Scotian Shelf of Atlantic Canada has built a map area of 5320 square kilometres. Water depths range from less than 30 m to 250 m. Predominant current flow is westward into the Bay of Fundy while the seasonal circulation is dominated by tidal rectification and baroclinic flow, with smaller contributions from wind stress. Four combined geology and biology groundtruthing surveys have collected 2133 km of high-resolution seismic reflection profiles and sidescan sonograms, complemented by 1134 sea floor photographs, 97 sea floor video transects, and 86 sediment and biological samples. Bedrock outcrop, composed of Cambrian-Ordovician metasedimentary rocks and Late Devonian-Carboniferous granitoid plutons, dominates much of the bank and has a characteristic rugged and fractured surface. The Scotian Shelf Drift (mainly glacial till) was deposited over bedrock during Wisconsinan glaciation and occurs as a blanket of variable thickness. At the seabed, the till forms remarkably well-preserved and widespread moraines and drumlins. In the deeper parts of German Bank, glacimarine Emerald Silt overlies the Scotian Shelf Drift. Wisconsinan-age iceberg furrows are preserved in Emerald Silt below a water depth of 110 metres.

The Scotian Shelf Drift surface consists of cobbles and boulders embedded in a pebble and sand lag, commonly associated with broken shell fragments. Epifauna are typically more abundant on the boulders and on bedrock outcrops, and include erect and encrusting sponges, tunicates, hydrozoa and bryozoa. Scallops and lobsters are also abundant in this habitat. In contrast, the fauna in deeper water areas floored by Emerald Silt includes polychetes and sea cucumbers. Multibeam and groundtruthing data, compiled and interpreted to produce surficial geological and benthic habitat maps, will be used to establish and manage new fisheries on German Bank.