(Paleo)oceanography of semi-enclosed seas with a focus on the Mediterranean region; Insights from basic theory

Abstract

To provide context for the interpretation of their sedimentary and paleoceanographic record, semi-enclosed seas are here investigated through the application of basic theory. The principles of conservation of water, salt and heat, in combination with a representation of flow through the seaway to the ocean, are used to chart how basin geometry, connectivity and atmospheric forcing together control basin-averaged salinity and temperature and the exchange flux. Data on present-day semi-enclosed seas of the wider Mediterranean region are used for illustration. First, ignoring the heat balance and with forcing constant in time, a dimensionless form of the governing equations is derived which clarifies the role of the various controlling parameters. This is applied to aspects of the Messinian Salinity Crisis. In the second part of the analysis the forcing is made a generalised periodic function of time. This informs us how basin salinity, its amplitude of variation and lag relative to the forcing, depend on basin and strait properties and varies with the period of forcing. Insights are applied to the precessional variation observed in the record of the Mediterranean Sea. In the third and fourth part of the analysis we include the balance of heat and basin-averaged temperature. Examination of the budget equations allows us to derive a relationship between the average air-sea heat flux and basin restriction. Finally, re-introducing strait flow, we study the interplay of basin temperature and salinity and establish under which conditions heat flux and temperature play a role, in addition to net evaporation and salinity.