Elsevier

Quaternary Science Reviews

Volume 185, 1 April 2018, Pages 122-134
Quaternary Science Reviews

MIS 5e relative sea-level changes in the Mediterranean Sea: Contribution of isostatic disequilibrium

https://doi.org/10.1016/j.quascirev.2018.01.004Get rights and content

Abstract

Sea-level indicators dated to the Last Interglacial, or Marine Isotope Stage (MIS) 5e, have a twofold value. First, they can be used to constrain the melting of Greenland and Antarctic Ice Sheets in response to global warming scenarios. Second, they can be used to calculate the vertical crustal rates at active margins. For both applications, the contribution of glacio- and hydro-isostatic adjustment (GIA) to vertical displacement of sea-level indicators must be calculated. In this paper, we re-assess MIS 5e sea-level indicators at 11 Mediterranean sites that have been generally considered tectonically stable or affected by mild tectonics. These are found within a range of elevations of 2–10 m above modern mean sea level. Four sites are characterized by two separate sea-level stands, which suggest a two-step sea-level highstand during MIS 5e. Comparing field data with numerical modeling we show that (i) GIA is an important contributor to the spatial and temporal variability of the sea-level highstand during MIS 5e, (ii) the isostatic imbalance from the melting of the MIS 6 ice sheet can produce a >2.0 m sea-level highstand, and (iii) a two-step melting phase for the Greenland and Antarctic Ice Sheets reduces the differences between observations and predictions. Our results show that assumptions of tectonic stability on the basis of the MIS 5e records carry intrinsically large uncertainties, stemming either from uncertainties in field data and GIA models. The latter are propagated to either Holocene or Pleistocene sea-level reconstructions if tectonic rates are considered linear through time.

Introduction

Sea-level changes are primarily a reflection of water mass transfer between continents, where water is stored as ice during cold periods, and oceans, where meltwater is introduced during warmer periods. This process is known as glacial eustasy (Suess, 1906) and occurs in response to changes in atmosphere and ocean temperatures related to variations in atmospheric CO2 concentrations and Milankovitch-driven insolation (Stocker et al., 2013). A fundamental aspect for the study of past climate change over glacial-interglacial time scales is the collection, analysis and interpretation of Relative Sea Level (RSL) indicators, that are fossil landforms, deposits or biological assemblages with a known relationship with a paleo sea level (Hibbert et al., 2016, Rovere et al., 2016a). Once vertical movements associated with Glacial Isostatic Adjustment (GIA) (Lambeck and Purcell, 2005), tectonics (Simms et al., 2016) or other post-depositional processes (Rovere et al., 2016b) are taken into account, paleo RSL indicators can be used to constrain ice-mass variations in response to changes in atmospheric and ocean temperatures during past interglacials (Dutton et al., 2015). In turn, estimates of paleo global mean sea level can be used to constrain processes regulating ice melting in paleo ice-sheet models, which eventually may be used to gauge the sensitivity of present-day polar ice sheets to future scenarios of global warming (e.g. Deconto and Pollard, 2016).

The most studied past interglacial is the Marine Isotopic Stage 5e (MIS 5e, 117–127 ka), which is the last period of the Earth's history when climate was warmer than today. Generally, MIS 5e sea-level studies are oriented towards two main goals. The first is to understand how to account for processes causing departures from eustasy (e.g., GIA, tectonics) in order to produce reliable estimates of past global mean sea levels. The second consists on the calculation of tectonic movements starting from the elevation of RSL indicators and assumptions on eustatic sea-level changes. This aspect is particularly relevant for the understanding of the long-term vertical movement of coastal areas, which is in turn important for the planning of coastal infrastructures in active geodynamic settings and need to be accounted for to correct future climate-related rates of RSL change (Antonioli et al., 2017).

Despite the common consideration in isolation, the two aims outlined above are mutually dependent and they are both tied to GIA predictions. In fact, to achieve the second goal, one must calculate the climate-related and GIA-modulated RSL elevations, which are the result of the first goal. The latter, however, stems from a priori information on long-term tectonic motions, which is the result of this second goal. Studies on MIS 5e RSL change in the Mediterranean Sea have often either adopted standard ESL values to calculate vertical tectonic rates at active sites or neglected the GIA overprint in the calculation of the ESL signal (Ferranti et al., 2006).

In this paper we focus on MIS 5e sea-level variations in the Mediterranean Sea. We investigate the GIA contributions to the spatiotemporal variability of RSL change during MIS 5e within the basin using GIA numerical simulations that incorporate the solid Earth and gravitational response to three glacial-interglacial cycles prior to MIS 5e and that evolve towards present. We also evaluate the GIA-modulated contribution of four scenarios for GrIS and AIS melting during MIS 5e. We compare our RSL predictions to observations from 11 sites that have been previously hypothesized as tectonically stable based on the low elevation of the MIS 5e shoreline.

We use field data and numerical GIA predictions at these sites to address the following questions:

  • 1.

    How much of the observed MIS 5e RSL variability in the Mediterranean can be explained by GIA?

  • 2.

    How significant are the uncertainties in GIA, as well as GrIS and AIS melting scenarios when using MIS 5e shorelines to calculate tectonic vertical motions?

Section snippets

Paleo relative sea-level indicators

The Mediterranean Sea has been a central focus for studies on sea level changes for over two centuries (Benjamin et al., 2017). The basin is characterized by different tectonic regimes (Fig. 1, see Supplementary Text for a brief outline) and its relatively low tidal amplitudes and low wave energy helped to preserve RSL indicators almost ubiquitously (see Fig. 1 in Ferranti et al., 2006 for an overview and detailed reports in Anzidei et al., 2014, Ferranti et al., 2006, Galili et al., 2007, Mauz

RSL data

The difference between the measured elevation of the RSL indicators and the actual paleo sea level can be significant once the indicative meaning is properly accounted for (Fig. 2g, see Supplementary Materials for details on the calculation of the indicative meaning at each site and the Supplementary Text for a working example). The set of 11 revised RSL sites from supposedly stable areas in the Mediterranean shows a MIS 5e RSL highstand in the range of 2–10 m above present-day sea level (Fig. 2

Discussion

Our numerical simulations show that the Earth is not in isostatic equilibrium during the MIS 5e. The GIA processes that accompany and follow the melting of GrIS and AIS during the MIS 5e (scenarios 1–4) add up to the background GIA to increase the regional RSL variability. Each location, within the Mediterranean Sea and during MIS 5e, is characterized by a local RSL curve that can be significantly different from the eustatic.

The GIA-induced spatial variability of the RSL change is small if

Conclusions

  • 1.

    The observed range of MIS 5e RSL highstand from 11 tectonically stable sites in the Mediterranean is comprised between 2 and 10 m above present msl. The observed highstands are not necessarily coeval. Evidences of two MIS 5e RSL stands are found in Mallorca, northern Tyrrhenian coast of Italy, southeastern Sardinia and Tunisia.

  • 2.

    The GIA-induced RSL changes across the Mediterranean are characterized by a significant regional variability throughout the MIS 5e. The Earth is in isostatic imbalance

Acknowledgments

AR and TL's research is financially supported by the Institutional Strategy of the University of Bremen, funded by the German Excellence Initiative [ABPZuK-03/2014] the ZMT, the Leibniz Centre for Tropical Marine Research. BdB is funded by NWO Earth and Life Sciences (ALW), project 863.15.019. The authors acknowledge USSP Urbino Summer School in Paleoclimatology (Urbino, Italy), MOPP-MEDFLOOD - Modeling Paleo Processes (INQUA CMP projects 1203P and 1603P), PALSEA (PAGES/INQUA working group) and

References (64)

  • E. Galili et al.

    Beach deposits of MIS 5e high sea stand as indicators for tectonic stability of the Carmel coastal plain, Israel

    Quat. Sci. Rev.

    (2007)
  • P.J. Hearty et al.

    Global sea-level fluctuations during the Last Interglaciation (MIS 5e)

    Quat. Sci. Rev.

    (2007)
  • F.D. Hibbert et al.

    Coral indicators of past sea-level change: a global repository of U-series dated benchmarks

    Quat. Sci. Rev.

    (2016)
  • K. Lambeck et al.

    Sea-level change in the Mediterranean Sea since the LGM: model predictions for tectonically stable areas

    Quat. Sci. Rev.

    (2005)
  • K. Lambeck et al.

    Sea level in Roman time in the Central Mediterranean and implications for recent change

    Earth Planet Sci. Lett.

    (2004)
  • T. Lorscheid et al.

    Paleo sea-level changes and relative sea-level indicators: precise measurements, indicative meaning and glacial isostatic adjustment perspectives from Mallorca (Western Mediterranean)

    Palaeogeogr. Palaeoclimatol. Palaeoecol.

    (2017)
  • J.X. Mitrovica et al.

    On the origin of late Holocene sea-level highstands within equatorial ocean basins

    Quat. Sci. Rev.

    (2002)
  • D.R. Muhs et al.

    Uranium-series ages of fossil corals from Mallorca, Spain: the “Neotyrrhenian” high stand of the Mediterranean Sea revisited

    Palaeogeogr. Palaeoclimatol. Palaeoecol.

    (2015)
  • K. Pedoja et al.

    Coastal staircase sequences reflecting sea-level oscillations and tectonic uplift during the Quaternary and Neogene

    Earth Sci. Rev.

    (2014)
  • E.J. Rohling et al.

    Differences between the last two glacial maxima and implications for ice-sheet, δ18O, and sea-level reconstructions

    Quat. Sci. Rev.

    (2017)
  • A. Rovere et al.

    The analysis of Last Interglacial (MIS 5e) relative sea-level indicators: reconstructing sea-level in a warmer world

    Earth Sci. Rev.

    (2016)
  • I. Shennan

    Interpretation of flandrian Sea-level data from the Fenland

    England. Proc. Geol. Assoc.

    (1982)
  • D. Sivan et al.

    Eastern Mediterranean sea levels through the last interglacial from a coastal-marine sequence in northern Israel

    Quat. Sci. Rev.

    (2016)
  • G. Spada et al.

    SELEN: a Fortran 90 program for solving the “sea-level equation.”

    Comput. Geosci.

    (2007)
  • P. Stocchi et al.

    Influence of glacial isostatic adjustment upon current sea level variations in the Mediterranean

    Tectonophysics

    (2009)
  • M. Vacchi et al.

    Multiproxy assessment of Holocene relative sea-level changes in the western Mediterranean: variability in the sea-level histories and redefinition of the isostatic signal

    Earth Sci. Rev.

    (2016)
  • C. Zazo et al.

    Pleistocene raised marine terraces of the Spanish Mediterranean and Atlantic coasts: records of coastal uplift, sea-level highstands and climate changes

    Mar. Geol.

    (2003)
  • C. Zazo et al.

    Retracing the Quaternary history of sea-level changes in the Spanish Mediterranean–Atlantic coasts: geomorphological and sedimentological approach

    Geomorphology

    (2013)
  • J. Angelier et al.

    Les déformations du Quaternaire marin, indicateurs néotectoniques. Quelques exemples méditerranéens

    Rev. Geogr. Phys. Geol. Dyn.

    (1976)
  • F. Antonioli et al.

    I sedimenti quaternari nella fascia costiera della Piana di Fondi (Lazio meridionale)

    Boll. Soc. Geol. Ital.

    (1988)
  • F. Antonioli et al.

    Geomorfologia costiera e subacquea e considerazioni paleoclimatiche sul settore compreso tra S. Maria Navarrese e Punta Goloritzé (Golfo di Orosei, Sardegna)

    G. Geol. (Bologna)

    (1992)
  • M. Anzidei et al.

    Coastal structure, sea-level changes and vertical motion of the land in the Mediterranean

    Geol. Soc. London

    (2014)
  • Cited by (0)

    View full text