Increased seasonality in the Western Mediterranean during the last glacial from limpet shell geochemistry

Abstract

Editor: P. DeMenocalKeywords: mollusc seasonality Gibraltar palaeoclimate oxygen isotopesThe seasonal cycle is a fundamental aspect of climate, with a significant influence on mean climate and on human societies. Assessing seasonality in different climate states is therefore important but, outside the tropics, very few palaeoclimate records with seasonal resolution exist and there are currently no glacial-age seasonal-resolution sea-surface-temperature (SST) records at mid to high latitudes. Here we show that both Mg/Ca and oxygen isotope (δ 18 O) ratios in modern limpet (Patella) shells record the seasonal range of SST in the western Mediterranean -a region particularly susceptible to seasonal change. Analysis of a suite of fossil limpet shells from Gibraltar shows that SST seasonality was greater during the last glacial by~2°C as a result of greater winter cooling. These extra-tropical seasonal-resolution SST records for the last glacial suggest that the presence of large ice-sheets in the northern hemisphere enhances winter cooling. This result also indicates that seasonality in the Mediterranean is not well-represented in most palaeoclimate models, which typically show little change in seasonal amplitude, and provides a new test for the accuracy of climate models.

Oxygen isotopes from Phorcus (Osilinus) turbinatus shells as a proxy for sea surface temperature in the central Mediterranean: A case study from Malta

“…On the north eastern shores of Malta, the modern interannual δ 18 O WATER variability is~0.5‰ (Table 1). This is typical of much of the eastern Mediterranean (Ferguson et al, 2011). Using Eq.…”

“…Jones et al, 1984;Walker and Surge, 2006;Wanamaker et al, 2011). Fewer studies have employed gastropod δ 18 O as a palaeothermometer (but see Andreasson et al, 1999;Fenger et al, 2007;Schöne et al, 2007;Burman and Passe, 2008;Mannino et al, 2008;Ferguson et al, 2011;Colonese et al, 2012;Surge and Barrett, 2012).…”

“…More recently, there has been a shift towards combining records of shell growth and shell chemistry to obtain detailed records of climate and environment that permit the characterization of seasonality (e.g. Andreasson et al, 1999;Ferguson et al, 2011). Oxygen isotope thermometry has been extensively applied in marine bivalves (e.g.…”

Geochemical and microstructural characterisation of two species of cool-water bivalves (<i>Fulvia tenuicostata</i> and <i>Soletellina biradiata</i>) from Western Australia

“…Freitas et al, 2006;Gillikin et al, 2005b;Lowenstam and Weiner, 1989) and environmental conditions at the time of deposition (e.g. Ferguson et al, 2011;Gazeau et al, 2010;Hahn et al, 2014;Heinemann, 2011;Henkes et al, 2013;Lowenstam and Weiner, 1989;Schöne et al, 2011). Molluscs are globally distributed and demonstrate sequential growth, thus providing high-resolution seasonal and sub-seasonal records of environmental conditions (e.g.…”

Oxygen isotopes in Molluscan shell: Applications in environmental archaeology

“…Ferguson et al (2011) also show that the seasonal range in SSTs were ∼2°C greater than present day during the last glacial, attributed to the southward extension of the polar front and winter sea-ice at lower latitudes.…”