Showing papers on "Monterey Canyon published in 2000"

Mass wasting, ephemeral fluid flow, and barite deposition on the California continental margin

Abstract: An area of active fluid discharge characterized by authigenic barite formation and populated by vestimentiferan tubeworms has been discovered by remotely operated vehicle exploration in Monterey Canyon. Slumping and mass wasting, presumably triggered by seismic activity, have exposed barium-rich pore fluids to sulfate-rich bottom water, leading to barite precipitation on the sea floor. Age estimates based on 210Pb/226Ra dating of the barite samples and growth rates of vestimentiferan tubeworms indicate that the seep site might be as young as 100 yr. Systematic variations in sulfur and strontium isotope ratios, the lack of visible fluid flow, and the abundance of dead tubeworms indicate decreasing flow rates. This newly discovered site shows many similarities to a previously described barite deposit in the California Borderland, possibly misinterpreted as a hydrothermal vent site. The discovery of a cold seep associated with barite deposits on the seismically active, transpressional California margin raises the possibility that numerous unexplored areas along the continental margins might have similar low-temperature deposits.

Seasonal abundance and vertical distribution of mesopelagic calycophoran siphonophores in Monterey Bay, CA

Abstract: The seasonal abundance and vertical distribution patterns of a group of small calycophoran siphonophores (principally Chuniphyes multidentata and Lensia conoidea) were investigated using a remotely operated vehicle (ROV) deployed in Monterey Bay, California. Abundance was assessed along 295 horizontal transects covering a depth range of 100-1000 m over a three and a half year period. The vertical distribution of the study animals changed seasonally, coupled to the onset and cessation of upwelling in the bay. While numerical abundance peaked after upwelling, there was no significant difference between seasons. The siphonophores were more broadly distributed over the depth range sampled during the upwelling or Shallow Mixed Layer (SML) period, than during the non-upwelling or Deep Mixed Layer (DML) period. There were no significant differences in abundance or distribution patterns between years except in 1993, when there were significantly more siphonophores observed during the SML period than during the DML period. This may reflect effects resulting from the 1992-1993 El Nino event. The abundance of these siphonophores was negatively correlated with that of Nanomia bijuga, a physonect siphonophore of similar size and feeding behavior found in the bay. The siphonophores studied here appear from preliminary data to migrate vertically, possibly with two separately migrating groups.