EGU Journal Logos (RGB) Open Access Open Access Open Access Advances in Annales Nonlinear Processes Geosciences Geophysicae in Geophysics Open Access Open Access Natural Hazards Natural Hazards and Earth System and Earth System Sciences Sciences Discussions Open Access Open Access Atmospheric Atmospheric Chemistry Chemistry and Physics and Physics Discussions Open Access Open Access Atmospheric Atmospheric Measurement Measurement Techniques Techniques Discussions Open Access Open Access Biogeosciences Biogeosciences Discussions Open Access Open Access Clim. Past, 9, 499–515, 2013 Climate www.clim-past.net/9/499/2013/ Climate doi:10.5194/cp-9-499-2013 of the Past of the Past © Author(s) 2013. CC Attribution 3.0 License. Discussions Open Access Open Access Earth System Earth System Dynamics Dynamics Discussions Paleohydrology reconstruction and Holocene Open Access Open Access climate variability in the South Adriatic Sea Geoscientific Geoscientific Instrumentation Instrumentation G. Siani1, M. Magny2, M. Paterne3, M. Debret4, and M. Fontugne3 Methods and Methods and 1IDES UMR 8148 CNRS, Departement´ des Sciences de la Terre, Universite´ Paris Sud, 91405Data Orsay, Systems France Data Systems 2Laboratoire de Chrono-Environnement, UMR 6249 du CNRS, UFR des Sciences et Techniques, 16 route de Gray, Discussions Open Access 25 030 Besanc¸on, France Open Access 3 Geoscientific Laboratoire des Sciences du Climat et de l’Environnement (LSCE), Laboratoire mixte CNRS-CEA,Geoscientific Domaine du CNRS, Avenue de la Terrasse, 91118 Gif sur Yvette, France Model Development 4 Model Development Laboratoire Morphodynamique Continentale et Cotiˆ ere` (M2C) (UMR CNRS 6143), Discussions Universite´ de Caen Basse-Normandie et Universite´ de Rouen, 14000 Caen/76821 Mont-Saint-Aignan, France Open Access Open Access Correspondence to: G. Siani ([email protected]) Hydrology and Hydrology and Received: 9 August 2012 – Published in Clim. Past Discuss.: 7 September 2012 Earth System Earth System Revised: 27 December 2012 – Accepted: 28 January 2013 – Published: 28 February 2013 Sciences Sciences Discussions Open Access Abstract. Holocene paleohydrology reconstruction is de- logical record with previous climatic records fromOpen Access the cen- rived combining planktonic and benthic stable oxygen and tral Mediterranean area and north of the Alps reveal possible Ocean Science carbon isotopes, sea surface temperatures (SSTs) and oxygen synchronicities (withinOcean the radiocarbon-dating Science uncertainty) 18 Discussions isotope composition of seawater (δ Ow) from a high sed- between phases of lower salinity in the SAS and periods of imentation core collected in the South Adriatic Sea (SAS). wetter climatic conditions around the north-central Adriatic Core chronology is based on 10 AMS 14C measures on Sea. Finally, wavelet analyses provide new clues about the Open Access planktonic foraminifera and tephra layers. Results reveal two potential origin of climate variability in the SAS,Open Access confirm- contrasted paleohydrological periods that reflect (i) a marked ing the evidence for a mid-Holocene transition in the central 18 Solid Earth lowering of δ Ow/salinity during the early to mid-Holocene Mediterranean climate and theSolid dominance Earth of a ∼ 1670-yr pe- (11.5 ka to 6.3 ka), including the two-step sapropel S1 depo- riodicity after 6 ka, reflecting a plausible connection with the Discussions sition, followed during the mid- to upper Holocene by (ii) North Atlantic climate system. a prevailing period of increased salinity and enhanced arid conditions in the South Adriatic Basin. Superimposed on Open Access Open Access these trends, short-term centennial-scale hydrological events The Cryosphere punctuated the Holocene period in the SAS. During the 1 Introduction The Cryosphere Discussions early to mid-Holocene, two main SST coolings together with 18 Because of its geographical positioning at the transition be- prominent δ Ow/salinity lowering delineate the sapropel S1 interruption and the post-sapropel phase between 7.3 to tween two climatic zones (subtropical high pressure and sub- 18 polar depression), the Mediterranean region is particularly 6.3 ka. After 6 ka, centennial-scale δ Ow and G. bulloides δ13C lowering, mostly centered between 3 to 0.6 ka, reflect sensitive to regional impacts of climatic changes and ex- short-term hydrological changes related to more intensive treme events (Giorgi and Lionello, 2008). Giving that, ow- runoff of the Po and/or Apennine rivers. These short-term ing to the population density in this region, a forecast of the events, even of lesser amplitude compared to the early to environmental response of the Mediterranean to future cli- mid-Holocene period, may have induced a lowering of sea mate change is a crucial point, and investigations on climate surface density and consequently reduced and/or inhibited archives covering periods of time longer than the instrumen- the formation of deep bottom waters in the SAS. Compar- tal record are required to refine a proper consideration of the ison of the emerging centennial- to millennial-scale hydro- natural climate variability. In this way, a better knowledge of the Holocene climate variability in the Mediterranean area Published by Copernicus Publications on behalf of the European Geosciences Union. 500 G. Siani et al.: Paleohydrology reconstruction and Holocene climate variability is an essential step to provide new insights for predictive 2 Studied area and modern circulation pattern in the climate models. Adriatic Sea Over the last decades, the Mediterranean region has been the focus of studies carried out on the complex interactions The Adriatic Sea is a semi-enclosed basin detached from between the North Atlantic and North Africa tropical cli- the Ionian Sea by the sill of the Otranto Strait (780 m). It matic systems (Zolitschka et al., 2000). More generally, these is characterized to the north by a wide continental shelf interactions accounted for variations (1) of the position of the sloping down to 100 m and by the shallow Pelagosa sill westerlies and intensity of the African monsoon systems, and (∼ 120 m) that separates the middle basin from the southern- subsequently (2) the quantity of precipitation brought to this most part, featured by the largest topographic depression of zone (Bar-Matthews et al., 2000). In addition, proxy recon- about 1200 m, the South Adriatic Pit (Fig. 1). structions from Holocene continental and marine archives The Adriatic Sea is situated between the subtropical high- have suggested periodicities of the climate at decadal, sec- pressure zone and the mid-latitude belt, in which winds ular and millennial timescales (Kallel et al., 1997a, b; Ched- move generally from west to east with sharp seasonal differ- dadi et al., 1997; Roberts et al., 2001; Sadori and Narcisi, ences (Orlic et al., 1992). In winter, the dominant winds are 2001; Rohling et al., 2002; Magny et al., 2003, 2006; Frigola the Bora blowing from the northeast and the Sirocco from et al., 2007; Marino et al., 2009) related to changes in Earth’s the south, whereas during summer the general atmospheric orbital parameters and solar activity (Mayewski et al., 2004; circulation is dominated by the westerlies. Magny et al., 2007). The modern oceanic circulation pattern depends on several The South Adriatic Sea (SAS) is an area characterized factors including (1) episodic atmospheric events (i.e. Bora) by very high sedimentation rates that favor the analysis of that produce wind-driven currents promoting intense mixing Holocene climatic changes at centennial temporal resolution and dense water formation, (2) freshwater discharge char- and the interactions between strong atmospheric forcing, pre- acterized by strong river runoff from the Po and numerous cipitation and river runoff (Fontugne et al., 1989; Asioli et surrounding rivers, and (3) exchange flow with the Ionian al., 2001; Oldfield et al., 2003; Sangiorgi et al., 2002, 2003; Sea through the Otranto Strait. This produces a seasonal cy- Piva et al., 2008). Moreover, this basin is one of the sources clonic circulation with a northerly inflow component, flow- of modern deep-sea water formation, playing a key role in ing along the eastern coast, represented by the Mediterranean changes in the thermohaline circulation in the Mediterranean Surface Water (MSW) from the Ionian Basin through the Sea (Pinardi and Masetti, 2000), and in the North Atlantic Otranto Strait and by a second southerly outflow compo- Ocean (Schonfeld¨ and Zahn, 2000; Rogerson et al., 2005; nent, i.e. the Western Adriatic Current (WAC) along the west- Voelker et al., 2006). ern coast (Artegiani et al., 1997; Poulain, 1999). The out- Here we present a highly detailed reconstruction of the flow is reinforced by a high amount of freshwater, nutri- Holocene paleohydrology at a decadal-scale time resolu- ents and suspended matter through the Po River with an an- tion, from a high-sedimentation deep-sea core recovered nual mean freshwater discharge rate of about 1500 m3 s−1 in the SAS. Past circulation dynamic was assessed by sea (Raicich, 1996). In winter, a further inflow of more saline surface temperature (SST) using the modern analog tech- Levantine Intermediate Water (LIW) originating from the nique (MAT) coupled with oxygen and carbon isotope mea- eastern Mediterranean Sea spread along the eastern Adri- surements performed on the planktonic foraminifera Glo- atic coast. The mixing between LIW and MSW in the South bigerina bulloides and on the benthic foraminifera