Phasing and amplitude of sea level and climate change during the penultimate interglacial

Andrea Dutton¹, Edouard Bard², Fabrizio Antonioli³, Tezer Esat¹, Kurt Lambeck¹ and Malcolm T. McCulloch¹

1 Research School of Earth Sciences, Australian National University, Canberra, ACT 0200, Australia
2 CEREGE, CNRS and Universite Aix-Marseille III, Europole de l'Arbois, 13545 Aix-en-Provence Cedex 4, France
3 ENEA - Special Project Global Change, Rome 00060, Italy

Figure 1. Marine serpulid overgrowths present in two stalagmites were dated by bracketing U-Th ages of speleothem calcite above and below the marine layers. A. Argentarola stalagmite N (ASN). Large scale dissolution is visible in part of the speleothem (below the areas we sampled).  B.  Argentarola stalagmite E (ASE) drawing spliced together with photographs. Sample positions denoted by black circles in ASE.

Direct markers of sea level position during the Quaternary are often limited to archives near or above present sea level, such as corals which grew near the sea surface during interglacial highstands.  Submerged speleothems provide a means to access the history of sea level oscillations across a range of depths below present sea level.  Because the dense calcite comprising speleothems is less susceptible to alteration than corals, this archive also has the potential to extend reconstructions of sea level position farther back in time.  A collection of unique speleothems from Argentarola Cave, Italy have been recovered which contain alternating layers of spelean calcite (formed during subaerial exposure) and Serpulid calcite (formed during cave submergence by seawater).  We have extended the sea level reconstruction from Argentarola farther back in time and have examined additional specimens from different depths to complement the existing dataset [1,2].  This work has resolved the timing and magnitude of multiple sea level highstands during marine isotope stage (MIS) 7.

We have generated 36 U-Th ages of the speleothem calcite to constrain the timing of cave submergence by seawater, represented in these specimens by the marine serpulid overgrowths.  Our data show that sea level highstands above -18 m were attained ~5,000-8,000 years prior to northern hemisphere (NH) insolation maxima during MIS 7.5 and 7.1.  In contrast, MIS 7.3 commences within 1,000 years of the NH insolation maximum and peaks near -18 m, despite having the strongest insolation forcing of the triplet.  This delayed phasing and dampened amplitude of the MIS 7.3 highstand is attributed to extensive glaciation during MIS 7.4 and highlights the significance of cryosphere response time to the climate system.

 [1] E. Bard, F. Antonioli and S. Silenzi, (2002) Sea-level during the penultimate interglacial period based on a submerged stalagmite from Argentarola Cave (Italy). Earth and Planetary Science Letters 196: 135-146.
[2] F. Antonioli, E. Bard, E.-K. Potter, S. Silenzi and S. Improta (2004) 215-ka History of sea-level oscillations from marine and continental layers in Argentarola cave speleothems (Italy). Global Planetary Change 43: 57-78.