Sea-level change, monsoon variability, and eastern Mediterranean climate over the Late Pleistocene

Abstract

A new, radiometrically constrained chronology is developed for a continuous, highresolution relative sea-level (RSL) record from the Red Sea that spans the past 500,000 years (500 ka BP). The method is based on indirect correlation of the RSL record with speleothem ?18O records from Soreq cave, Israel (for the period 0-150 ka BP), and from Sanbao Cave, China (for the period 150-500 ka BP). The new RSL record allows ice-volume (sea-level) phase relationships with key climate-system variables to be examined, without bias from icecore or orbital timescales. The effects of ice-volume changes on monsoon variability are also examined. In a separate development, the Soreq-synchronised interval of the RSL record is used to produce residual oxygen isotope (?18O) records for the eastern Mediterranean; these represent regional environmental signals which are unbiased by ice-volume and sourcewater effects.

Results suggest that, over the last glacial cycle, changes in polar climate and ice-volume were tightly coupled, with centennial-scale response times, and rates of sea-level rise reached at least 1.2 m per century during periods of significant ice-volume reduction. Results also suggest that, at the last five glacial terminations, ice-volume changes generally lagged insolation and atmospheric CO2 rises by ~2-7 kyr. This supports the Milankovitch theory of ice-age cycles, and disputes suggestions that CO2-driven feedback processes initiated glacial terminations.

It is shown that ice-volume changes can partly explain East Asian monsoon (EAM) variability. In particular, rapid rates of ice-volume reduction at glacial terminations can account for rapid, millennial-scale variability in summer and winter EAM proxies. This observation is consistent with meltwater pulses into the North Atlantic at terminations leading to a delayed intensification of the summer EAM. Evidence also suggests that changes in different monsoon systems of the northern hemisphere were synchronous during periods of ice-volume minima. Regarding the East African summer monsoon (EAfSM), no systematic phasing is observed between precession minima and EAfSM maxima, and so the common use of a 3-kyr lag to date EAfSM records appears to be too generalised.

The new palaeo-environmental reconstructions for the Mediterranean presented here suggest that local precipitation did not increase substantially during the deposition of sapropels S1, S3 and S4, whereas net moisture availability may have been elevated during the interval of sapropel S5 deposition, and within colder glacial periods of the last glacial cycle. The most climatically variable period of the last glacial cycle in the Mediterranean (~30-60 ka BP) coincides with marine isotope stage (MIS) 3.

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Identifiers

ORCID for E.J. Rohling: orcid.org/0000-0001-5349-2158

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