Abstract
Abstract. To assess the regional multi-decadal to multi-centennial climate variability along the southern Iberian Peninsula during the mid- to late-Holocene record of paleo-environmental indicators from marine sediments were established for two sites in the Alboran Sea (ODP-161-976A) and the Gulf of Cádiz (GeoB5901-2). High-resolution records of organic geochemical properties and planktic foraminiferal assemblages are used to decipher precipitation and vegetation changes as well as hydrological conditions with respect to sea surface temperature (SST) and marine primary productivity (MPP). As a proxy for precipitation change, records of plant-derived n-alkane composition suggest a series of five distinct dry episodes in southern Iberia at 5.4±0.3 ka cal BP, from 5.1 to 4.9±0.1 ka cal BP, from 4.8 to 4.7±0.1 ka cal BP, from 4.4 to 4.3±0.1 ka cal BP, and at 3.7±0.1 ka cal BP. During each dry episode the vegetation suffered from reduced water availability. Interestingly, the dry phase from 4.4 to 4.3±0.1 ka cal BP is followed by a rapid shift towards wetter conditions revealing a more complex pattern in terms of its timing and duration than was described for the 4.2 ka event in other regions. The series of dry episodes as well as closely connected hydrological variability in the Alboran Sea were probably driven by NAO-like (North Atlantic Oscillation) variability. In contrast, surface waters in the Gulf of Cádiz appear to have responded more directly to North Atlantic cooling associated with Bond events. In particular, during Bond events 3 and 4, a pronounced increase in seasonality with summer warming and winter cooling is found.
Highlights
The Holocene climate is considered to be fairly stable in comparison with the large and abrupt climatic changes during the last glacial and deglacial periods (Martrat et al, 2007; Rasmussen et al, 2014)
A sharp increase towards high concentrations of up to 617 ng g−1 sediment is evident at about 4.2 ka cal BP. n-Alkane concentrations appear to remain generally above 450 ng g−1 sediment until 3.8 ka cal BP, when concentrations sharply decrease towards 209 ng g−1 sediment at 3.7 ka cal BP
Since the river discharge and the plant growing season is strongly coupled to precipitation and the rainy season at the Iberian Peninsula in winter (Fig. 1; Lionello, 2012), the n-alkane proxies are probably biased towards the winter season
Summary
The Holocene climate is considered to be fairly stable in comparison with the large and abrupt climatic changes during the last glacial and deglacial periods (Martrat et al, 2007; Rasmussen et al, 2014). For the Mediterranean realm, generally long-term trends in sea surface temperature (SST) cooling (Kim et al, 2004; Martrat et al, 2014) and continental aridification (Fletcher and Sánchez Goñi, 2008; RamosRomán et al, 2018a) are described, and are superimposed with several short cold and dry perturbations, e.g. the 8.2 ka event or the North Atlantic Bond events (Alley et al, 1997; Bond et al, 1997; Mayewski et al, 2004). Another prominent Holocene climate perturbation is the 4.2 ka event. Schirrmacher et al.: Multi-decadal atmospheric and marine climate variability
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