Northern Hemisphere atmospheric pattern enhancing Eastern Mediterranean Transient-type events during the past 1000 years

Aleix Cortina-Guerra,Marie-Alexandrine Sicre,Juan José Gomez-Navarro,Joan O Grimalt,Juan Pedro Montávez,Belen Martrat,Alessandro Incarbona,P Graham Mortyn

doi:10.5194/cp-17-1523-2021

Abstract

Abstract. High-resolution climate model simulations for the last millennium were used to elucidate the main winter Northern Hemisphere atmospheric pattern during enhanced Eastern Mediterranean Transient (EMT-type) events, a situation in which an additional overturning cell is detected in the Mediterranean at the Aegean Sea. The differential upward heat flux between the Aegean Basin and the Gulf of Lion was taken as a proxy of EMT-type events and correlated with winter mean geopotential height at 500 mbar in the Northern Hemisphere (20–90∘ N and 100∘ W–80∘ E). Correlations revealed a pattern similar to the East Atlantic/Western Russian (EA/WR) mode as the main driver of EMT-type events, with the past 1000 years of EA/WR-like mode simulations being enhanced during insolation minima. Our model results are consistent with alkenone sea surface temperature (SST) reconstructions that documented an increase in the west–east basin gradients during EMT-type events.

Highlights

The Mediterranean Sea is a small, semi-enclosed basin connected with the Atlantic Ocean through the Strait of Gibraltar (a 284 m deep sill at a width of ∼ 30 km; Bryden and Kinder, 1991)
This pattern is reminiscent of the East Atlantic/Western Russian (EA/WR) pattern defined by the NOAA Climate Prediction Center (CPC), the latter is obtained through rotated principal component analysis (Barnston and Livezey, 1987) of the observed monthly mean 500 mbar height anomaly field in the region 20–90◦ N
The results of this analysis revealed that the EA/WR mode most likely plays a major role in the deep-water formation in the Aegean Basin (AB)

Summary

Introduction

The Mediterranean Sea is a small, semi-enclosed basin connected with the Atlantic Ocean through the Strait of Gibraltar (a 284 m deep sill at a width of ∼ 30 km; Bryden and Kinder, 1991). The Sicily channel (330 m deep sill, width of ∼ 130 km; Wüst, 1961) subdivides the Mediterranean into a western and an eastern basin. The entering colder and fresher Atlantic Waters (AW) interact with the warmer and saltier Mediterranean waters, which constitutes the main surface water mass of the Mediterranean (0–200 m) (Malanotte-Rizzoli et al, 2014, and references therein). The AW is the source of Levantine Intermediate Water (LIW; 200–600 m), and both are involved in deep-water mass formation (Malanotte-Rizzoli et al, 2014). Winds in the Adriatic Sea, where Eastern Mediterranean Deep Waters (EMDW) form, and in the Gulf of Lion, where Western Mediterranean Deep Water (WMDW) forms, are key elements for enhanced deep-water ventilation through deep convection (Millot, 1999)

Methods

Results

Conclusion