Glacial-Interglacial sea level reconstruction of the last 570 kyr: Inferences from a new benthic δ18O record of IODP Site U1386 (Gulf of Cadiz)

Abstract:

Sea level reconstructions on geological time scales are crucial for our understanding of glacial-interglacial cycles in the past, and thus offer context for current and projected changes.

Global sea-level variations since the last glacial maximum have been well established based on numerous well-dated coral reef terraces and speleothem records. Throughout the Late Pleistocene, the coral and speleothem based data sets become more incomplete and reliable dated sea-level points, though showing the general amplitude of sea-level changes, are insufficient to establish the exact pattern and timing of millennial-scale changes.

To gain further insight into glacial-interglacial sea level variations throughout the Late Pleistocene, we generated a new benthic δ¹⁸O record of IODP Site U1386 in the Gulf of Cadiz for the past ~ 570 kyr. Site U1386 is located within the Gulf of Cadiz Contourite Depositional System (CDS). These sediments are characterized by high sedimentation rate (~35 cm/kyr), providing a unique opportunity to study sea level oscillations in high resolution. To estimate ice volume and deep-water temperature changes we used an inverse forward modeling approach based on our benthic δ¹⁸O data. The coupled model includes four ice-sheet-shelf components that simulate glaciation on Eurasia, North America, Greenland and Antarctica, thereby explicitly accounting for all individual ice-volume contributions throughout the investigated time period.

Our initial findings suggest that older glacial periods were characterized by repeated and substantial δ¹⁸O enrichment events preceding their respective glacial maximum. We argue that the observed δ¹⁸O enrichment events are not an expression of local hydrographic changes of salinity and/or temperature limited to the Gulf of Cadiz but probably relate to global ice volume changes. In this regard, our results contrast estimates derived from the global mean benthic δ¹⁸O LR04 stack. On a regional scale, our results show similarities to recently published sea-level estimates from the Red Sea and Mediterranean Sea.

The in-depth correlation of our initial findings with existing open ocean and regional sea level estimates for the last ~ 570 kyr provides new insights into the sea level evolution on glacial-interglacial timescales.