Benthic foraminiferal response to Late Quaternary variations in surface water productivity and oxygenation in the northern Arabian Sea. Geologica Ultraiectina (188)

This thesis discusses benthic foraminifera in Late Quaternary records
from within and below the northern Arabian Sea OMZ and their
interpretation in terms of past changes in surface water productivity and midwater
oxygenation (Chapters 2-5). Because the present contention is that
multiproxy studies lead to better assessment of the paleoenvironment, this
research has been conducted in a multidisciplinary way. In particular, various
geochemical tracers are employed (Chapters 2-4, 6), but a comparison is also
made with a number of lithogenic proxies (Chapter 3). The overall picture
shows that large variations occurred in the intensity of the OMZ during the
last 225 kyr, and that the base of the OMZ occasionally extended well below
its present-day position. Variability took place on orbital and sub-orbital time
scales and is presumably controlled by 1) changes in summer monsoon wind
strength, which controls summer surface water productivity via coastal and
open ocean upwelling and thus subsurface oxygen consumption, and 2) deep
convective mixing during periods of cold and intensified winter monsoons.
The close correlation of sub-orbital monsoon-driven OMZ variability in the
Arabian Sea with rapid climatic fluctuations at high northern latitudes
suggests a close coupling between high and low latitude climates (Chapter 3).