Critical Analysis of Mediterranean Sea Level Limit Cycles During the Messinian Salinity Crisis

TL;DR

This paper critically evaluates a model explaining sea-level oscillations during the Messinian Salinity Crisis, finding that such limit cycles are unlikely under realistic conditions and questioning their role in evaporite formation.

Contribution

The study demonstrates that the proposed model's limit cycles are not robust and depend on unrealistic assumptions, challenging previous hypotheses about sea-level oscillations during the crisis.

Findings

Limit cycles occur in only 0.2% of parameter simulations.

Realistic model formulation reduces likelihood of sea-level oscillations.

Oscillations depend on an unrealistic equation formulation.

Abstract

The Messinian Salinity Crisis (5.97-5.33 Ma) may be one of the most significant periods of sea-level change in recent geologic history. During this period, evaporite deposition throughout the Mediterranean basin records a series of dramatic environmental changes as flow through the Strait of Gibraltar was restricted. In the first stage of evaporite deposition, cycles of gypsum appear in shallow basins on the margins of the Mediterranean. The complex environmental history giving rise to these cycles has been investigated for decades but remains controversial. Notably, whether the evaporites are connected to significant changes in Mediterranean sea-level is an open question. In one proposed model, competition between tectonic uplift and erosion at the Strait of Gibraltar gives rise to self-sustaining sea-level oscillations -- limit cycles -- which trigger evaporite deposition. Here I show that limit cycles are not a robust result of the proposed model and discuss how any oscillations produced by this model depend on an unrealistic formulation of a key model equation. First, I simplify the model equations and test whether limit cycles are produced in 64 million unique combinations of model parameters, finding oscillations in only 0.2 % of all simulations. Next, I examine the formulation of a critical model equation representing stream channel slope over the Strait of Gibraltar, concluding that a more realistic formulation would render sea-level limit cycles improbable, if not impossible, in the proposed model.