Glacial-interglacial variability in upwelling on the NW Mexican margin is
assessed by reconstructing the history of organic carbon and biogenic opal
deposition and measuring the Ba/Al ratio in three piston cores that span the
upper to the lower continental slope. Rates of accumulation of organic carbon,
opal and to some degree biogenic barite are higher in interglacial intervals,
indicating that upwelling-induced productivity was higher during the warm
periods over the last 140,000 years. Despite cyclic changes in organic carbon
accumulation, matrix-corrected HI values in the mid- and lower- slope cores are
invariant and are similar to values in the laminated intervals from the oxygen-minimum
site. This suggests that changes in organic carbon content are
controlled by productivity variations and are not due to differential preservation
induced by variations in bottom water oxygen concentrations. The lowest HI
values in Mexican Margin sediments occur concurrently with large increases in
grain size. Thus, increased degradation resulting from winnowing is offered as
the leading explanation for the hydrocarbon impoverishments in the bioturbated
upper slope deposits.
Late Quaternary records of denitrification in the oxygen-deficient
subsurface water masses of the Eastern Tropical North Pacific (ETNP) are
constructed using ¹⁵N/¹⁴N ratios measured on bulk sediments. The profiles
show a synchronous decrease in denitrification during the glacial periods over the
last 140 kyrs. It is suggested that, because nitrate is a limiting nutrient in the
modern ocean, a consequent increase in the oceanic nitrate inventory could have
contributed to the observed decrease in glacial atmospheric pCO₂ by enhancing
the fertility of the ocean. The glacial decreases in denitrification in the ETNP are
attributed to large reductions in upwelling-induced fluxes of organic detritus on
the margin in response to glacial shifts in the wind field off NW Mexico
associated with the growth of Laurentide ice on northern North America, the
establishment of a resident high pressure cell over the ice sheet, and the
bifurcation of the Jet Stream. / Science, Faculty of / Graduate
| Identifer | oai:union.ndltd.org:UBC/oai:circle.library.ubc.ca:2429/6281 |
| Date | 11 1900 |
| Creators | Ganeshram, Raja S. |
| Source Sets | University of British Columbia |
| Language | English |
| Detected Language | English |
| Type | Text, Thesis/Dissertation |
| Format | 11867096 bytes, application/pdf |
| Rights | For non-commercial purposes only, such as research, private study and education. Additional conditions apply, see Terms of Use https://open.library.ubc.ca/terms_of_use. |
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