Sensitivity of Red Sea circulation to sea level and insolation forcing during the last interglacial

G Trommer,S Schouten,E J Rohling,M Kucera,U Baranowski,M Siccha,K Grant,M T J Van Der Meer

doi:10.5194/cp-7-941-2011

Abstract

Abstract. This study investigates the response of Red Sea circulation to sea level and insolation changes during termination II and across the last interglacial, in comparison with termination I and the Holocene. Sediment cores from the central and northern part of the Red Sea were investigated by micropaleontological and geochemical proxies. The recovery of the planktic foraminiferal fauna following high salinities during marine isotopic stage (MIS) 6 took place at similar sea-level stand (~50 m below present day), and with a similar species succession, as during termination I. This indicates a consistent sensitivity of the basin oceanography and the plankton ecology to sea-level forcing. Based on planktic foraminifera, we find that increased water exchange with the Gulf of Aden especially occurred during the sea-level highstand of interglacial MIS 5e. From MIS 6 to the peak of MIS 5e, northern Red Sea sea surface temperature (SST) increased from 21 °C to 25 °C, with about 3 °C of this increase taking place during termination II. Changes in planktic foraminiferal assemblages indicate that the development of the Red Sea oceanography during MIS 5 was strongly determined by insolation and monsoon strength. The SW Monsoon summer circulation mode was enhanced during the termination, causing low productivity in northern central Red Sea core KL9, marked by high abundance of G. sacculifer, which – as in the Holocene – followed summer insolation. Core KL11 records the northern tip of the intruding intermediate water layer from the Gulf of Aden and its planktic foraminifera fauna shows evidence for elevated productivity during the sea-level highstand in the southern central Red Sea. By the time of MIS 5 sea-level regression, elevated organic biomarker BIT values suggest denudation of soil organic matter into the Red Sea and high abundances of G. glutinata, and high reconstructed chlorophyll-a values, indicate an intensified NE Monsoon winter circulation mode. Our results imply that the amplitude of insolation fluctuations, and the resulting monsoon strength, strongly influence the Red Sea oceanography during sea-level highstands by regulating the intensity of water exchange with the Gulf of Aden. These processes are responsible for the observation that MIS 5e/d is characterized by higher primary productivity than the Holocene.

Highlights

IntroductionThe Red Sea is an ideal natural laboratory to investigate the interplay between sea-level rise and atmospheric forcing during and after terminations, due to its sensitivity to sea-level fluctuations (Winter et al, 1983; Locke and Thunell, 1988; Thunell et al, 1988; Rohling and Zachariasse, 1996; Rohling et al, 1998, 2008a, b; Fenton et al, 2000; Siddall et al, 2003, 2004) and to monsoon-driven oceanographic changes (Almogi-Labin et al, 1991; Hemleben et al, 1996; Biton et al, 2010; Trommer et al, 2010)
Since there is no scientific concordance about the exact stratigraphic location of the marine isotopic stage (MIS) 5e boundaries (Shackleton et al, 2003) or their ages (e.g., Imbrie et al, 1984; Winograd et al, 1992; Henderson and Slowey, 2000; Thompson and Goldstein, 2005; Thomas et al, 2009), the boundaries are not used for developing the age model, but are indicated only for visual orientation in the graphics
Following Lisiecki and Raymo (2005) and Rohling et al (2008b), sea-level maximum was set at 123 ka BP and other control points were defined by visual correlation of the benthic foraminiferal δ18O record of Lisiecki and Raymo (2005) and the SPECMAP δ18O record (Imbrie et al, 1984, Table 1, Fig. 2)

Summary

Introduction

The Red Sea is an ideal natural laboratory to investigate the interplay between sea-level rise and atmospheric forcing during and after terminations, due to its sensitivity to sea-level fluctuations (Winter et al, 1983; Locke and Thunell, 1988; Thunell et al, 1988; Rohling and Zachariasse, 1996; Rohling et al, 1998, 2008a, b; Fenton et al, 2000; Siddall et al, 2003, 2004) and to monsoon-driven oceanographic changes (Almogi-Labin et al, 1991; Hemleben et al, 1996; Biton et al, 2010; Trommer et al, 2010). A wind driven surface water layer enters the basin from the south (Patzert, 1974), whereas in summer, nutrient enriched Gulf of Aden waters enter the basin in an intermediate layer (Souvermezoglou et al, 1989). Large parts of the Red Sea experience highest primary productivity during the winter (Veldhuis et al, 1997; Siccha et al, 2009), except for the very southern Red Sea, which is influenced by the inflow of the nutrient-rich intermediate water from the Gulf of Aden during the summer (Smeed, 1997)

Methods

Results

Discussion

Conclusion