|Abstract or Summary
- The Geochemical Ocean Sections Study (GEOSECS) program has carried
out an intensive study of physical and chemical parameters in the
Pacific and Atlantic Ocean. As a result, an enormous collection of high
quality data has been amassed for these two oceans. To analyze the
Pacific data, fourteen stations extending from about 50°N to 69°S near
180°longitude have been selected for this study. The section chosen
provides a good continuous north-south section in the Pacific from near
the Bering Sea to the Antarctic.
To study this massive extent of the oceanic regime, three methods
were adopted. The first was to estimate, using Defant's method, the
approximate level of no motion throughout the section. Secondly, vertical
section plots were contoured for various physical and chemical
parameters to help identify and trace oceanographic features throughout
the Pacific. Finally, calculations for stability were applied to each
station in the section to evaluate the correlation between features of
stability and those seen in the section plots.
The depth of the level of no motion showed strong variability in
the Pacific Ocean, Generally, deeper levels were found in the higher
latitudes with shallowing towards the Equator. In the high southern
latitudes, no level of least motion could be identified. This is
consonant with the condition that the establishment of a level of no
motion involves noticeable stratification of the water column. In high
latitudes, the more nearly uniform distribution of density throughout
the water column inhibits the formation of layers of high stability
and stratified condition.
It is also noted that a good general agreement is found between
the depths of the layer of no motion and the observed oxygen minimum
in the GEOSECS section. This is especially apparent in midlatitudes
where the transition layer between the North and South Intermediate
Waters and the Pacific Deep Waters is the region of the oxygen minimum.
In the layer of the oxygen minimum, biochemical depletion occurs
and there is likely to be minimal replenishment by horizontal and
vertical advection and diffusion. Therefore, it is suggested that the
oxygen minimum layer is closely related to a region of minimal horizontal
movement. The calculation of the level of no motion in the
Pacific GEOSECS sections supports this hypothesis.
The large scale circulation in the Pacific Ocean is clearly
pictured by the parameter section plots obtained from the Pacific
GEOSECS expedition. The North Pacific and Antarctic Intermediate
Waters are clearly defined from their origins to disappearance by low
salinity and high nutrient levels. The extent of the Pacific Deep
Water throughout the Pacific is seen. This large mass of relatively
homogenous water can be seen from the South to the North Pacific.
As the water moves northward, a gradual increase in nutrients and
decrease in oxygen occurs. A third water type seen in the South
Pacific is Antarctic Bottom Water. It intrusion into the South
Pacific can be defined in terms of the 27.86 sigma theta surface or
by such parameters as oxygen, silicate, and apparent oxygen utilization
In an attempt to correlate the various features seen in the vertical
sections, stability profiles were prepared for each station. The
vertical stability profiles did not show any strong features other
than shallow and intermediate stability maxima. Recent discussion
concerning a "benthic front" associated with the Antarctic Bottom
Water intrusion into the South Pacific Ocean is not supported by any
stability feature. Gradients in certain physical and chemical parameters
do occur but the density gradients maximum expected in a
frontal zone is not seen.