Andrea Piva

Climatic cycles as expressed in sediments of the PROMESS1 borehole PRAD1‐2, central Adriatic, for the last 370 ka: 1. Integrated stratigraphy

[1] A multiproxy integrated chronological framework, based on oxygen and carbon stable isotope stratigraphy, biostratigraphy (foraminifera and nannoplankton bioevents and foraminifer assemblage-based climate cyclicity), magnetostratigraphy, sapropel stratigraphy, and (14)C AMS radiometric dates, has been achieved for borehole PRAD1-2, collected in 185.5 m water depth in the central Adriatic. This work was carried out within the European Community project Profiles across Mediterranean Sedimentary Systems (PROMESS1). The 71.2 m long borehole spans a time interval between late MIS 11 and MIS 1 (the last 370 ka), showing a chronological resolution of 500 and 250 years per cm during interglacial and glacial intervals, respectively. At present, this record is the most expanded and continuous marine record available for the Adriatic Basin. Several orbital cycles can be recognized in the PRAD1-2 record: the 100 ka glacial-interglacial fluctuations and the 23 ka precession-related cycles, which in turn control the deposition of sapropel layers. An integrated analysis of short-term oscillations within the Last Glaciation interval (MIS 4-MIS 2) allowed the identification of the Adriatic signature of Dansgaard-Oeschger events, showing the potential to achieve a more refined chronostratigraphic framework for the top part of the PRAD1-2 record. Finally, the age model obtained by this study allowed the chronological integration of the main foraminifera bioevents detected in the borehole as well as of the volcanoclastic layers present in the upper part of the record. Despite its proximal location, PRAD1-2 presents a continuous record and shows the potential to be consistently correlated both with deep-sea and continental records in the Mediterranean region and beyond.

Climatic cycles as expressed in sediments of the PROMESS1 borehole PRAD1-2, central Adriatic, for the last 370 ka: 2. Paleoenvironmental evolution

The multidisciplinary study of planktic and benthic foraminifera, alkenone SST, and O and C stable isotope records allowed reconstruction of the paleoenvironmental history of the central Adriatic basin over the last 360 ka B. P. In general, the main paleoclimatic changes documented in the central Adriatic appear in phase with climate change in the North Atlantic realm, except for intervals which correspond to the deposition of sapropel levels in the eastern Mediterranean. In particular, the interval between Marine Isotope Stage ( MIS) 7.5 and MIS 5 appears to be strongly influenced by the monsoonal regime. The comparison with other Mediterranean records also suggests that the Adriatic Basin was affected by very low sea surface temperature ( SST) ( down to 2 degrees C for MIS 2) during glacial intervals, which is uncommon for the Mediterranean Basin. In addition, the SST record indicates that this basin was unable to maintain warm interglacial/ interstadial conditions for durations similar to the western Mediterranean. This fact can be explained by the landlocked position and shallow depth of this basin, which make it particularly exposed to atmospheric forcing ( e. g., Siberian High) and to the strong influence of the nearby landmass during glacial intervals, producing a lag in the demise of glacial intervals. Moreover, the progressively higher values of the delta(18)O records of glacial intervals, alongside the SST record and the foraminifera assemblage, imply an increasing impact of the formation of cold and dense water since the penultimate glacial.

Palaeomagnetic and rock magnetic analysis of Holocene deposits from the Adriatic Sea: detecting and dating short-term fluctuations in sediment supply

We present palaeomagnetic and rock magnetic results from five cores collected in the basin of the Adriatic Sea. Four cores (PRAD2-4; KS02-246; CSS00-23 and CSS00-07) were collected along a shore-parallel transect whereas the fifth core (AMC99-01) was retrieved in the central Adriatic in 250 m water depth, on the floor of the Meso-Adriatic Depression. After alternating field demagnetization, the natural remanent magnetization (NRM) directions show a characteristic and primary magnetization of the sediments that is representative of secular variation of the geomagnetic field. By combining 14C dating and the ages of magnetic inclination features, it has been possible to establish an age—depth model for all of the cores. Precise identification of the secular variation features provides a refined chronology that allows us to quantify short-term changes in sediment flux from the Adriatic catchment as well as changes in sediment routing within the basin. Rock magnetic parameters indicate a homogeneous magnetic mineralogy dominated by fine-grained magnetite. Variations in both concentration and grain-size related magnetic parameters reflect changes in sediment supply between glacial and interglacial stages, as well as changes in environmental conditions. Selective dissolution of magnetic grains is associated with the formation of sapropel S1 during the first part of the Holocene, although the duration of the anoxic interval varies between cores. A significant modification in sediment supply characterizes the late-Holocene deposits with a marked increase in sedimentation rate occurring during the last few centuries. We interpret this as a far-reaching response to the rapid construction of the modern Po delta under increasing anthropogenic impact.

Magnetic properties of the youngest sapropel S1 in the Ionian and Adriatic Sea: inference for the timing and mechanism of sapropel formation

The youngest sapropel S1 has been investigated by a multiproxy study on a core (ET99-M11) collected in the western Ionian Sea at a water depth of 2800 m, which is considered to represent anoxic conditions in the eastern Mediterranean at the time of sapropel formation. Selected geochemical parameters (TOC, Ba/Al, MnO) as well as micropaleontological analysis (planktic foraminifera), rock magnetic data, and 14 C dating indicate that anoxic conditions prevailed between 10.4 and 5.7 ka BP. The comparison among the different proxies indicates that rock magnetic parameters can be unambiguously used to precisely identify sapropel layers, even if no iron sulphide phases have been precipitated as a bi-product of diagenetic breakdown of organic matter. By using the magnetic parameters as indicators of paleoredox conditions we compare the results with cores collected in the central and southern Adriatic Sea at different water depths. A shorter duration (9.6/9-7/6.8 ka BP) of the sapropel S1 was observed in the deepest southern part of the basin and in the Meso Adriatic Depression whereas suboxic conditions continued in cores collected at very shallow water depth of 56 m along the western margin of the basin. The formation of the Adriatic Deep Water driven by decreasing solar radiation output is considered responsible for the interruption and end of sapropel formation.