Abstract
Deoxygenation is the expression of atmosphere-ocean interactions that under changing climate conditions results from a wide stratification and eutrophication of the ocean. Past events of strong deoxygenation have been recorded in the Mediterranean Sea as dark, organic-rich deposits called sapropels. While sapropels in the marine environment and the effect of water stagnation have received much attention in earlier studies, the key climatic forcing that drove the Mediterranean Sea deoxygenation remains poorly understood. CLOSER tackled regional - but fundamental - aspects of the Mediterranean system by leveraging the large-scale expression of the youngest sapropel event (Sapropel S1, ~10.2-6.8 cal kyr BP) to unravel the link between the regional Adriatic climate and Mediterranean processes. CLOSER investigated the climate-ocean coupling with a multi-proxy and multi-archive approach at an unprecedented level of resolution, by combining the analysis of continental deposits, speleothems, and marine records. An integrated approach aimed at investigating one of the most remarkable climate changes of the Mediterranean has extraordinary potential to generate novel insights into the climate-ocean connections, to be integrated in the next generation of Earth System models. It can help evaluate the likelihood of sapropel-like oxygen crises due to increased stratification and weakening/shutdown of the thermohaline circulation in the coming decades.
Results achieved
The project was led by CNR-ISMAR Bologna and involved Roma-La Sapienza and Bologna universities as operational Research Units. The major focus of the Bologna University Research Unit was the three-dimensional stratigraphic analysis of Holocene, peat-rich, estuarine paleovalley systems of the Adriatic area, which are likely to represent the most promising onshore counterparts for the development of anoxic conditions during deposition of Sapropel S1. The research group also explored the marine to terrestrial influence on natural bromine distribution and the use of this geochemical element as an indicator of past depositional environments and organic matter accumulation. The research project was primarily based on a pre-existing dataset comprising sediment cores from the onshore Adriatic coastal plain and an extensive collection of seismic reflection profiles available at CNR-ISMAR for the offshore domain. In addition, two sediment cores, each 40–50 m long, were recovered beneath the modern Pescara and Biferno coastal plains, providing the basis for onshore stratigraphic correlation. Through the integration of sedimentological, paleontological, and geochemical (TOC, TN, δ¹³C, δ¹⁵N) data within a regional onshore–offshore framework, we investigated the Upper Pleistocene–Holocene infill of the Pescara and Biferno paleovalley systems (central-southern Italy) and characterized the S1-equivalent (S1eq) succession. The results document a continuous S1eq record encompassing the S1aeq, S1breakeq, and S1beq intervals. The transition from poorly drained floodplain to estuarine facies reflects rapid sea-level rise and progressive drowning of the paleovalleys. Bulk geochemical proxies exhibit a strong stratigraphic control, with δ¹³C and δ¹⁵N trends closely tracking facies changes and variations in organic matter (OM) sources. The maximum flooding surface was identified at approximately 8.1 cal kyr BP. Onshore–offshore correlations, together with stratigraphic data from other Adriatic paleovalley systems, reveal a marked decoupling in organic carbon accumulation during the S1 break, driven by the landward migration of river mouths in response to Holocene meltwater pulses. This process enhanced the storage of terrestrial OM within the paleovalleys while reducing its export to the deeper basin, with potential implications for deep-water ventilation. These findings highlight the pivotal role of onshore systems in modulating basin-scale sedimentary and geochemical dynamics. During rapid transgression, paleovalley systems acted as transient repositories of sediment and organic carbon, thereby influencing sapropel development. Their high-resolution stratigraphic record provides a critical link between continental and marine environments, offering new constraints on the mechanisms controlling S1 deposition in the Adriatic and, more broadly, the Mediterranean region. The project has demonstrated valuable dissemination outcomes. The Bologna research unit, has produced three scientific articles, one of which is currently under revision in Quaternary Science Reviews. Two manuscripts are in preparation and will be submitted to high-impact factor journals.Dettagli del progetto
Responsabile scientifico: Alessandro Amorosi
Strutture Unibo coinvolte:
Dipartimento di Scienze Biologiche, Geologiche e Ambientali
Coordinatore:
CNR - Consiglio Nazionale delle Ricerche(Italy)
Contributo totale Unibo: Euro (EUR) 37.875,00
Durata del progetto in mesi: 24
Data di inizio
30/11/2023
Data di fine:
28/02/2026
