Amatzia Genin | USGS Science

USGS1989

Tidal currents and anticyclonic motions on two North Pacific seamounts

Near-bottom currents were measured for several days at three sites on the summits of Fieberling Guyot (32°26′N, 127°46′W) and Horizon Guyot (19°15′N, 160°00′W). Three moorings comprised of two current meters were deployed on each summit; two moorings were deployed on opposite sides of the rim of the summit and one mooring was deployed near the center of the summit. The observed currents were strong, with maximum speeds of 48 and 24 cm s −1 on Fieberling and Horizon, respectively. The currents at specific frequencies were enhanced relative to those in the surrounding ocean. Diurnal currents were the dominant component of the current field on Fieberling Guyot. They accounted for 39–68% of the energy and had amplitudes around 12 cm s −1 . We suspect that these diurnal currents were waves trapped over the seamount. Semidiurnal internal tidal currents were the strongest currents over Horizon Guyot, with amplitudes around 4 cm s −1 . The flow patterns determined in this study seemed to affect the biological and geological characteristics of the seamounts.

Deep Sea Research Part A, Oceanographic Research P↗

USGS1988

Maps showing the Seabeam bathymetry and sedimentologic and biologic sample locations on Horizon Guyot, Mid-Pacific Mountains and a summary of existing data

Horizon Guyot (Fig. 1) is a 300-km-long, 75-km-wide volcanic ridge with a relatively flat summit that is diagnostic of guyots (Hess, 1946). The U. S. Geological Survey (USGS) began a study of Horizon Guyot in 1983 as part of a program on the origin, distribution, and composition of ferromanganese-oxide precipitates that encrust the hard substrate of sea floor edifices, such as seamounts and volcanic ridges (Hein and others, 1985a). Mass movement and bedload transport of sediment appears to influence the thickness of these crusts on seamount flanks (Hein and others, 1985b). Because Horizon Guyot has been studied more extensively than any other volcanic edifice in the Mid-Pacific Mountains (Heezen, Fischer, and others, 1971; Lonsdale and others, 1972; Winterer, Ewing, and others, 1973), it was chosen as the principal site for a USGS study of sediment transport processes and the geotechnical behavior of sediment on seamounts (Cacchione and others, 1988; Schwab and others, 1988). In March, 1987, Horizon Guyot was again investigated using the R/V ATLANTIS II and the D.S.R.V. ALVIN (cruise 118-12); sponsored by the National Science Foundation. Although primarily a biologic investigation, observations from 10 submersible dives, bottom samples collected at depth using ALVIN and from the surface using the ATLANTIS II, and Seabeam swath-bathymetry (sponsored by the USGS and the Office of Naval Research) add to the overall Horizon Guyot data set. In this report, we summarize the existing data base, present a Seabeam bathymetric map of the study area, ALVIN dive tracklines, the sample locations, and a brief description of the samples collected or other station activities on the ATLANTIS II cruise 118-12. The detailed bathymetric map of the study area (Plate 1) was constructed by merging data obtained by a Deep-Tow study (Lonsdale and others, 1972) (Fig. 1) with data obtained from the swath-bathymetry mapping system onboard the ATLANTIS II. Detailed information on the Seabeam bathymetric system is given by Renard and Allenou (1979).

Open-File Report↗