Combined North Atlantic and anthropogenic forcing of changes in the marine environments in the Gulf of Taranto (Italy) during the last millennium

Abstract. This study examines the multi-decadal to centennial variability of benthic ecosystems, depositional environments and biogeochemical processes in the Gulf of Taranto (Italy) over the last millennium. Our study is based on sediment cores from two sites in the eastern Gulf of Taranto (Mediterranean Sea), and benthic foraminifera data of 43 surface sediment samples from the western Adriatic Sea reflecting modern conditions. We use the data to unravel relative contributions of natural and anthropogenic forcing to conditions at the sediment-water interface in a marine setting with a long history of human impacts in river catchments. High abundances of infaunal foraminifera in surface sediments trace the nutrient-rich Po river outflow and display an area of high organic matter deposition in the north-eastern Gulf of Taranto. Decreasing Ca / Ti ratios suggest increasing terrigenous fluxes at ~ 1300 AD driven by wetter conditions during persistent negative phases of the North Atlantic Oscillation (NAO). A strong NAO connection is also evident in high-resolution clay mineral data. The smectite / illite ratio reflects variable Po river runoff, and correlates well with NAO strength for the past 300 years. Benthic ecosystem variability as reflected by foraminifera is closely linked to the Northern Hemisphere temperature evolution during the past millennium. Spectral analysis reveals a quasi-periodic variability of ~ 50 to ~ 70 years suggesting an Atlantic Multidecadal Oscillation (AMO) forcing of Italian hydrology. Coeval with increasing anthropogenic activity, the effects of rising temperatures and nutrient discharge during the past 200 years further enhanced nutrient and organic matter fluxes. This is reflected by a substantial rise in the abundance of shallow to intermediate infaunal benthic foraminifera (SIIBF) and a concurrent decrease of Uvigerina mediterranea δ¹³C since at least 1800 AD. The SIIBF decrease in the youngest samples likely reflects environmental effects of stricter regulations on fertilizer use in Italy and the reduction of sediment transport due to the stabilization of river banks.