Climate-ice sheet-ocean interactions in the Gulf of Alaska through
the Pliocene and Pleistocene

Abstract

Global climate is characterised by a long term cooling trend since the Pliocene.
However, we lack climate records from the North Pacific to confirm this. The
proximity of the GOA to the Mount St. Elias, the highest mountain in the world
uplifted during the Plio-Pleistocene, makes the location a target to study the Pacific
climate evolution towards present climate, the influence over the growth of large
ice sheets over North America as well as the tectonic-ice sheet-climate
interactions. This is important as the mid-Pliocene and MIS 5e have been identified
as potential analogues for current climate. This thesis focuses on the Pliocene and
Pleistocene study of Site U1417 (~700km away from the coast) and U1418
(~150km away from the coast) from the Gulf of Alaska, recovered during IODP
Expedition 341. Biomarker extraction and analyses are used for sea surface
temperature (SSTs from UK37 and UK37’ indices), sea surface salinity (C37:4),
terrestrial and aquatic organic carbon inputs (long, short chain n-alkanes, TAR
index, TOC, TON, δ13C and δ15N), marine productivity (alkenone, β-sitosterol,
brassicasterol, dinosterol, TOC, TON, δ13C and δ15N concentrations)
reconstructions at both sites. We conclude that SST during the early Pleistocene in
the GOA was an average of 1°C warmer than during the late Pliocene, the last
500kyr and at modern. The Cordilleran Ice-Sheet developed since 2.8 Ma due to St.
Elias tectonic uplift. The Cordilleran Ice-Sheet growth is fed by the humidity of a
relatively warm and stratified surface ocean and orographic precipitation since the
Pliocene. During the last 500 kyr, warmer SST intervals are associated with a
decrease in ocean stratification. Nutrient availability in the GOA is the main control
for coccolithophore productivity export reduction since the early Pleistocene.
Modern ocean circulation across the North Pacific was established during the LGM
and possibly since MIS 4.