Pacific Coastal & Marine Science Center
Monterey Bay Studies
Seafloor Morphology between Año Nuevo and Santa Cruz, California
by Roberto J. Anima, Andrew J. Stevenson, Stephen L. Eittreim, Yvonne W. Rodriguez, and Gary B. Griggs
This preliminary seafloor map displays submarine rock exposures found along the northern part of Monterey Bay National Marine Sanctuary. The extent of rock exposures on the sea floor is based on interpretations of side-scan sonar records, seismic-reflection records (not displayed here), and underwater video. The mapping defines the nearshore morphology of the central California coast between Point Año Nuevo and Point Santa Cruz. The extensive occurrence of nearshore rock outcrops poses questions concerning longshore sediment transport pathways, sediment storage sites in the nearshore zone, and identifies previously unmapped fish and wildlife habitats.
Previous studies of longshore sediment transport along the northern part of the Monterey Bay National Marine Sanctuary indicate that sediment is being transported along shore from the Golden Gate to the south and deposited into Monterey Bay (Best and Griggs, 1991). Tait and others (1994) proposed a conceptual model of a rocky coast line that detours longshore transport of littoral sediments. This survey supports the conceptual model of Tait and extends seaward the onland mapping of Clark (1981). This preliminary map of the areal distribution of seafloor rock outcrop and sediment in the nearshore extends from approximately 4 meters out to 60 meters of water depth. The map shows a shallow nearshore that has extensive rock outcrops consisting of upper Miocene to Pliocene Purisima Formation, middle to upper Miocene Santa Cruz Mudstone, and lower to middle Miocene Monterey Formation. High resolution seismic-reflection data collected coincidentally with the side-scan data show that these rock units are incised by paleo-stream valleys that extend offshore to water depths of 30 to 40 meters and may serve as sediment storage sites within the littoral zone. Verification of seafloor interpretations were attained using underwater video and grab sampling after the initial mapping was completed. This project will allow us to study the relationship of exposed bedrock highs and current patterns by mapping of bedforms on the seafloor. The results of this study can be applied to understanding the dynamics of longshore sediment transport in the nearshore environment of a rocky coast.