Graduate Thesis Or Dissertation
 

Precise north-south oceanographic transect in the Pacific Ocean

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  • 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 (AOU). 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.
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