Photo: Bogdan ONAC

Can caves record sea-level changes?

Secondary carbonate deposits in caves, known as speleothems (e.g., stalagmites and stalactites), preserve a variety of paleoclimatic and palaeoenvironmental signals.  The coastal caves of Mallorca (Spain) display an unusual type of carbonate encrustation that was precipitated on pre-existing speleothems during periods of Mediterranean sea-level high or lowstands (Figs. 1-3).  The precise timing of sea-level changes has the potential to test the Milankovitch theory of Earth’s orbital forcing on global ice-volume fluctuations.  In our Science paper we reconstructed western Mediterranean Sea level between ~82 and ~80 thousands years (kyr) based on precise U/Th TIMS ages on carbonate encrustations.  We find that the sea level on Mallorca stood ~1 m above the present during marine isotope substage (MIS) 5a.  We observe that timing of the MIS 5a sea-level highstand in Mallorca is in general agreement with data from deep-sea oxygen isotope stratigraphy. 

Although our data constrain the age of the MIS 5a sea-level maximum, its absolute altitude is unexpected because it may imply that MIS 5a was about as ice-free as MIS 5e or the late Holocene.  We find that sea-level rose after MIS 5b up to 22 m in phase relationship with insolation increase, and fell rapidly 15 m at the onset of MIS 4. With over one third of the world’s population living within 100 km of coastline, understanding the history and future impacts of global sea-level change ranks as a top priority in the Earth sciences.

The questions, now, is exactly what caused the rapid rise in sea levels and whether the research team’s findings indicate that ice formations and melting are far more volatile processes than previously believe?  Scientists have generally worked under the thought that the Earth goes through a glacial period every 100,000 years, but Onac said that doesn’t mesh with what they found in the Mallorca caves, and in fact Earth’s climate is far more complex.

Links:

SCIENCE-PERSPECTIVE
SCIENTIFIC AMERICAN
NATURE
NATURE NEWS
TIME
SPIEGEL

Prof. Univ. Dr. Bogdan Onac,

Facultatea de Biologie şi Geologie