Sea-level stands from the Western Mediterranean over the past 6.5 million years

Abstract

Sea-level reconstructions are important for understanding past ice sheet variability and its response to past and future warming. Here we present Neogene and Quaternary sea-level snapshots using phreatic overgrowths on speleothems (POS) from caves on Mallorca, Spain. POS are excellent sea level index points because of their clear relationship to sea level and precise U-Pb chronology. We find that local sea-level before and at the onset of the Messinian Salinity Crisis was at 33.3 ± 0.25 m (6.54 ± 0.37 Ma) and 31.8 ± 0.25 m (5.86 ± 0.60 Ma) above present levels, respectively. We further present global mean sea level (GMSL) estimates, i.e. local sea level corrected for glacial isostatic adjustment and long-term uplift, for three other POS. The results show that GMSL during the Pliocene-Pleistocene Transition was 6.4 m (- 2.0-8.8 m) at 2.63 ± 0.11 Ma and during the beginning and the end of the Mid-Pleistocene Transition was - 1.1 m (- 5.6-2.4 m) and 5 m (1.5-8.1 m), respectively. These estimates provide important constraints for the past evolution of sea level and show that local sea level prior to the MSC was similar to the highest stand during the Pliocene, with markedly lower position afterwards.

Figure 1

Sites location and samples. (a) Map of Mallorca in the western Mediterranean (gray rectangle). (b) Location of caves sampled for POS (red solid dots). (c-g) Cross-section of the investigated POS: (c) CP-04, (d) AR-02i, (e) AR-19, (f) DR-D4v, and (g) SBB25-01. Maps (a, b) are available under CC Public Domain License from https://pixabay.com/illustrations/map-europe-world-earth-continent-2672639/ and https://pixabay.com/illustrations/mallorca-map-land-country-europe-968363/, respectively, on which the bathymetry and geology were overlapped.

Figure 2

Local sea level at Mallorca. (a) Plot shows the whole temporal range. (b) Enlarged views for the three most recent data points. GMSL used in the GIA calculation is shown by the cyan line and based on the benthic oxygen isotope stack. The resulting local sea level is shown by the black line. Uncertainty in local sea level that arises from uncertainties in the Earth structure is shown as a gray band around the black line (1σ). Elevation of inferred local sea level for five POS presented here is shown in red, age uncertainties are 2σ. Gray numbers and letters in panel b denote Marine Isotope stages.

Figure 3

Pliocene and Pleistocene global mean sea level estimates. POS-derived Pliocen and Pleistocene GMSL are indicated by silver and black (this study) markers, respectively (age uncertainties are 2σ; the GMSL of the marker corresponds to the mode and the error bars to the 16th and 84th percentiles). Thermal expansion correction is not applied for any of these estimates. Brown and cyan curves show two oxygen isotope based sea level reconstructions (brown is the GMSL derived estimates from the planktonic foraminifera and the marginal basin residence time and cyan is the GMSL curve derived from the conversion of LR04 benthic foraminiferal δ¹⁸O stack by scaling with a calibration of 0.011 ppt m⁻¹ as in).