Showing papers on "Monterey Canyon published in 1998"

Observations of the Internal Tide in Monterey Canyon

Abstract: Data from two shipboard experiments in 1994, designed to observe the semidiurnal internal tide in Monterey Canyon, reveal semidiurnal currents of about 20 cm s21, which is an order of magnitude larger than the estimated barotropic tidal currents. The kinetic and potential energy (evidenced by isopycnal displacements of about 50 m) was greatest along paths following the characteristics calculated from linear theory. These energy ray paths are oriented nearly parallel to the canyon floor and may originate from large bathymetric features beyond the mouth of Monterey Bay. Energy propagated shoreward during the April experiment (ITEX1), whereas a standing wave, that is, an internal seiche, was observed in October (ITEX2). The difference is attributed to changes in stratification between the two experiments. Higher energy levels were present during ITEX1, which took place near the spring phase of the fortnightly (14.8 days) cycle in sea level, while ITEX2 occurred close to the neap phase. Further evidence of phase-locking between the surface and internal tides comes from monthlong current and temperature records obtained near the canyon head in 1991. The measured ratio of kinetic to potential energy during both ITEX1 and ITEX2 was only half that predicted by linear theory for freely propagating internal waves, probably a result of the constraining effects of topography. Internal tidal energy dissipation rate estimates for ITEX1 range from 1.3 3 1024 to 2.3 3 1023 Wm 23, depending on assumptions made about the effect of canyon shape on dissipation. Cross-canyon measurements made during ITEX2 reveal vertical transport of denser water from within the canyon up onto the adjacent continental shelf.

Particulate matter fluxes into the benthic boundary layer at a long time-series station in the abyssal NE Pacific: composition and fluxes

Abstract: Sediment traps were deployed to collect contiguous 10-day samples of sedimenting particulate matter at 600 and 50 meters above bottom (mab) at an abyssal station off of the central California coast (Sta. M, 4100-m depth) over a 6-yr time period. Interannual variations were manifested in fluxes at both depths with high fluxes in 1991, 1993, and 1994. Low particulate matter fluxes observed in 1992 may have resulted from a well-documented El Nino-Southern Oscillation (ENSO) event, but the mechanisms responsible for the low fluxes observed in 1995 and 1996 were not resolved. Particulate fluxes were impacted by upwelling with a lag time of ∼50 days between the Bakun upwelling index and the arrival of particulate matter to the 600-mab trap. Allowing time between the upwelling of nutrients and the flux of material from the photic zone, we estimate a sinking rate of ∼100 m day-1. There was generally a peak in particulate fluxes in the summer with a secondary peak in the fall. Decreased concentrations (mg gdwt-1 of total particulates) of organic carbon, CaCO3, and particulate nitrogen in the summer were attributed to dilution effects from siliceous plankton. Particulate fluxes were higher at 50 mab (4050 m depth) than at 600 mab (3500-m depth), suggesting an input of laterally advected material at 50 mab, possibly from the Monterey Canyon northeast of Sta. M. The variability of particulate and component fluxes during this 6-yr period illustrates the importance of long time-series studies for interpreting organic matter input and its importance to deep-sea communities.