Cheshire, H.; (2007) A high-resolution multiproxy late Neogene palaeoclimate record from Guaymas Basin, Gulf of California. Doctoral thesis , University of London.

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Abstract

The annual migration of the North Pacific Subtropical High, fuelled by tropical heat and moisture---derived partly from the Atlantic---drives seasonal coastal upwelling and, importantly, transports heat into the mid-latitudes. Interannual to orbital cyclicity affects eastern North Pacific climate by varying the relative strengths/interactions of the Subtropical High and the Aleutian Subpolar Low. In modern Guaymas Basin---situated at the wet/dry subtropical divide---dry-season diatom productivity alternates with wet-season terrestrial flux, and pre-formed low-oxygen intermediate waters ensure varve deposition. High-resolution logging of 75% laminated, 63 m, continuous piston core MD02-2515 and companion 6 m kasten core MD02-2517 has identified eight sediment fabric types, six of which are laminated with systematic variations in relative lamina thickness and presence/absence of sub-laminae. Based on observed climate and supported by climate proxies provided by continuous X-ray fluorescence, colour, magnetic susceptibility, sediment density, biogenic silica, carbon and microfossil analyses, the sediment fabric types have been interpreted as the result of climatic/oceanographic conditions produced by variations in the strength of the North Pacific Subtropical High and the extent of its migration. Varve thickness, 6180 stratigraphy and correlation with the o13C stratigraphy of nearby radiocarbon dated core JPC-56 (Keigwin, 2002) gives an age range of 0-36,000 Years. Systematic variations in the predominance of one or more sediment types reveal precessional forcing, which drives a 5000-year oscillation of millennial- and centennial-scale wet/dry cycles, the former are associated with June/December perihelion, the latter with March/September perihelion. Between 34-11,000 yr BP there are significant non-laminated intervals every 5000 years. This study indicates that the Trade Winds are confined close to the equator during the glacial. This breaks the hydrological link between the Atlantic and Pacific and reduces dysoxia in coastal waters.

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