Deep-sea sedimentary processes in the Argentine Basin revealed by 3.5 kHz echograms
by Adam Klaus, "A thesis presented to the faculty of Moss Landing Marine Laboratories.", Thesis (M.S.) -- San Jose State University, 1986., The regional distribution of eleven 3.5 kHz seismic echo types reveals the areal extent of deep-sea sedimentary processes in the Argentine Basin. A correlation between echo character and the relative abundance of sand and silt layers in piston cores allows the pattern of coarse terrigenous sediment dispersal to be identified. This relationship indicates that the majority of coarse sediment bypasses the continental slope and rise. This coarse sediment is deposited on the proximal abyssal plain with progressively lower amounts basinward, and lower abundances on the shallow margin. Scarps, irregular and blocky hyperbolic zones, and transparent layers along the Argentine continental margin have echo characteristics similar to those of documented gravity-controlled mass flow deposits. A large area of mass flow deposits, covering at least 5x10^4 km^2, is located on the continental rise and adjacent abyssal plain east of the Rio de la Plata. A field of migrating mud waves, approximately 1.0x10^6 km^2 in extent, occurs on the sediment drifts of the central basin. Mud waves range in amplitude up to 137m and average 26m, and have wavelengths of about 3 to 7 km. The presence of migrating mud waves suggests widespread current-controlled sedimentation. It is inferred, however, that these mud waves form in areas of relatively weak flow in the interior basin because the benthic circulation is characterized by strong Antarctic Bottom Water (AABW) flow along the western and southern margins and by weak flow in the central basin. A variety of hyperbolic echoes on the abyssal plain adjacent to the Argentine continental margin, south of the Rio Grande Rise, and in the Georgia Basin, are interpreted as current-produced erosional / depositional bedforms, although downslope sedimentary processes may also produce similar hyperbolic echoes. The distribution of bedforms inferred from seismic echo character suggests that sediment is supplied to the basin principally by gravity-controlled mass flows. Sediment entrained in AABW is a secondary source. Gravity-controlled mass flows are predominantly limited to the Argentine continental margin. Sediment from both sources is winnowed by strong AABW flow along the Argentine continental rise. The fine-grained chaff is transported to the central basin where it is deposited as migrating mud waves in regions of relatively weaker bottom current.
Distribution, abundance, habitat use, and respiration patterns of harbor porpoise (Phocoena phocoena) off the northern San Juan Islands, Washington
Boat and shore-based surveys were conducted from June to August 1991 and June to October 1992 to determine harbor porpoise distribution, density, abundance, and habitat use off the northern San Juan Islands, Washington. An estimated 299 harbor porpoise (1.26 harbor porpoise/km2) occurred patchily within 237 km2. Harbor porpoise occurred in water of 10.1° to 16.3°, were generally observed in expected depths>125 m and over shallow slopes (<10%), and less than expected in depths <75 m. Abundance of harbor porpoise in relation to deep waters, flood tides, and tide rips off Point Doughty, Orcas Island, may indicate the importance of these waters as foraging areas. Mean duration of dives for individuals and groups (n = 95) was 6.6 sec (SE = 0.11, n = 1,551) for dives <30 sec and 125 sec (SE = 5.32, n = 156) for dives >30 sec duration.