Persistent warm Mediterranean surface waters during the Roman period

G Margaritelli,R Rettori,L G Bellucci,C Lubritto,I Cacho,F Lirer,M Barra,A Català

doi:10.1038/s41598-020-67281-2

Abstract

Reconstruction of last millennia Sea Surface Temperature (SST) evolution is challenging due to the difficulty retrieving good resolution marine records and to the several uncertainties in the available proxy tools. In this regard, the Roman Period (1 CE to 500 CE) was particularly relevant in the socio-cultural development of the Mediterranean region while its climatic characteristics remain uncertain. Here we present a new SST reconstruction from the Sicily Channel based in Mg/Ca ratios measured on the planktonic foraminifer Globigerinoides ruber. This new record is framed in the context of other previously published Mediterranean SST records from the Alboran Sea, Minorca Basin and Aegean Sea and also compared to a north Hemisphere temperature reconstruction. The most solid image that emerges of this trans-Mediterranean comparison is the persistent regional occurrence of a distinct warm phase during the Roman Period. This record comparison consistently shows the Roman as the warmest period of the last 2 kyr, about 2 °C warmer than average values for the late centuries for the Sicily and Western Mediterranean regions. After the Roman Period a general cooling trend developed in the region with several minor oscillations. We hypothesis the potential link between this Roman Climatic Optimum and the expansion and subsequent decline of the Roman Empire.

Highlights

Reconstruction of last millennia Sea Surface Temperature (SST) evolution is challenging due to the difficulty retrieving good resolution marine records and to the several uncertainties in the available proxy tools
We argue that this trans-Mediterranean compilation provides the basis to discuss main SST features during the last two millennia focussing the attention into the Roman period since it underscores as the warmest period with interesting implications on civilization development in the Mediterranean region
The SST estimates from the Mg/CaG.ruber ratio range from 16.4 °C ± 1.5 °C to 22.7 °C ± 1.5 °C with a mean value of 19.5 °C ± 1.5 °C (Fig. 2); to document the main trends of variability [95% Confidence Interval (CI)] in SST reconstruction we adopted a Monte Carlo approach that use a non-parametric regression (LOESS function, see Material and Methods paragraph)

Summary

Introduction

Reconstruction of last millennia Sea Surface Temperature (SST) evolution is challenging due to the difficulty retrieving good resolution marine records and to the several uncertainties in the available proxy tools. The last report of the Intergovernmental Panel on Climate Change (IPCC 2018) underlines the requirement to assess climate feedbacks during past episodes of moderately warmer (1.5–2 °C) conditions[26,27] In this framework, we present a new generated SST record reconstruction from the central part of the Mediterranean Sea based on Mg/Ca ratios measured in the planktonic foraminifera Globigerinoides ruber covering the last 5 kyr BP. This new record is compared with other previously published SST records from the Alboran Sea, Menorca Basin and Aegean Sea based on different geochemical proxies and with a reconstruction of the NAO index[28] We argue that this trans-Mediterranean compilation provides the basis to discuss main SST features during the last two millennia focussing the attention into the Roman period since it underscores as the warmest period with interesting implications on civilization development in the Mediterranean region. The northern branch, called the Atlantic Ionian Stream (AIS), forms the MAW transport into the eastern Mediterranean off the southern coast of Sicily and baths the studied location[38]

Methods

Results

Conclusion