Paleoceanography of the Eastern Tropical North Pacific on millennial timescales
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Date
2010Author
Arellano-Torres, Elsa
Metadata
Abstract
The occurrence of large scale and rapid climate shifts at millennial time-scales (suborbital)
remains an enigma between records from high and low latitudes spanning the Late
Quaternary. This thesis studies such variations in the eastern tropical North Pacific (ETNP)
using marine sediment cores retrieved from Mexico and Nicaragua. The main goals are to
understand the nature of millennial timescale climate-changes in the Pacific low latitudes, to
identify the atmospheric and oceanic teleconnections involved, to document the impacts on
the biogeochemical cycles of carbon, nitrogen and silicon, and their potential to regulate
Greenhouse Gas (GHG) concentrations during the last two glacial cycles (the last 240,000
years before present).
In this thesis, we use a suite of multi-proxy records from the Core MD02-2519,
which are compared to others records from adjoining regions to study the climatic history of
the ETNP at millennial timescales. The Core MD02-2519, was retrieved from 955 mbsl off
NW Mexico. It is strategically located within the North Pacific Intermediate Water (NPIW),
underlying the coastal upwelling and denitrification zones of the ETNP. The
paleoceanography of the region is studied using proxy records of productivity,
denitrification, intermediate water circulation and radiocarbon activity, which are discussed
in 5 separated chapters. In Chapter 1, we use records of organic carbon (%OC) and diffuse
spectral reflectivity (DSRa*) to document changes in productivity, which are shown in phase
with Northern Hemisphere (NH) timing at millennial scale, suggesting a direct atmospheric
teleconnection with higher northern latitudes. In Chapter 2, reconstruction of nitrogen
isotope records (δ15N) show that abrupt changes in denitrification are in phase with NH
timing over the last glacial period; however, the advection of heavy nitrate from southern
sources is also documented, possibly from the denitrification zone off Peru-Chile. Records of
opal (%opal – Chapter 3) and carbon isotopes from benthic foraminifera (δ13C-Uvigerina –
Chapter 4) support the inference of oceanic teleconnections between the ETNP and the
South Pacific via subthermocline circulation. In Chapter 4, the δ13C records also suggest that
intermediate water circulation changed over glacial periods and terminations, being the result
of intrusion of southern component waters. In Chapter 5, the reconstruction of radiocarbon
activity (Δ14C) records from surface (planktonic foraminifera) and intermediate water
(benthic foraminifera) suggest oceanic degassing of old-carbon from the deep ocean during the last termination. In this way, the ETNP upwelling system could be an important locus of
CO2 release at millennial timescales.