A benthic front in the South Pacific
A benthic front in the South Pacific
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DOI：
10.1016/0012-821x(72)90236-1
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发表时间：
1972-09
影响因子：
5.3
通讯作者：
H. Craig;Y. Chung;M. Fiadeiro
中科院分区：
文献类型：
--
作者：
H. Craig;Y. Chung;M. Fiadeiro
East of New Zealand and the Chatham Rise a deep western boundary current separates from the eastward Circumpolar Current and swings north into the South Pacific. These two great currents form the dynamic boundaries of a 107km2triangular discontinuity surface — the benthic front — which separates the South Pacific Deep and Bottom Water. The frontal surface begins at a depth of 2 km at the Chatham Rise, strikes NW and dips 0.023° to the NE with a mean slope of 4× 10−4. The NE edge is 3.5 km deep and is pinned to the northwest-trending 5 km bathymetric contour by topographic control of bottom water flow. We have made continuous STD soundings to 4500 m in several sections across the Tonga trench, in order to verify the indications from hydrographic casts that density, temperature, and salinity discontinuities occur across the front. The STD records show abrupt and irregular decreases in potential temperature and increases in salinity at the discontinuity surface, with temperature inversions and small-scale layering. Closed-spaced hydrographic casts show that the front is also marked by sharp maxima in silicate and radium profiles, and by abrupt changes in profiles of O2and nutrients. South of the equatorial region, Si is conservative in deep water; the Si-maximum is an “induced” extremum caused by the vertical juxtaposition of low-Si Circumpolar Water and high-Si Equatorial WaterAlong the frontal surface,T,S, and Si are linearly correlated with uniqueT-SandSi-Srelationships which do not occur in vertical section above or below the front. These results indicate that conservative properties along the front are maintained by strong horizontal diffusion with a minimum “scale-length” of ∼ 104km. Below the frontal surface there is a 500 m transitional layer of maximum stability; immediately below this layer the deep salinity maximum, and an “induced” Si minimum, mark the top of the Bottom Water. Isohalines in the salinity maximum run parallel to the strike of the benthic front; salinity and potential temperature in the maximum decrease uniformly from the SW origin to the NE edge, and the maximum vanishes at all points along the NE edge, from the northern apex at 6°N to the SE apex at 43°S. Along the discontinuity surface, diffusive mixing with the underlying water is greatly reduced because of the stability maximum. Above the surface, however, the profiles are consistent with vertical diffusion - vertical advection processes, with lower boundary values fixed by the horizontal mixing along the front, and upper boundaries fixed by the characteristics of the overlying Intermediate Water at each point.
