Miocene Milieu‘Musings on the Messinian Salinity Crisis’

USSP 2010 Science Party

Outline

• Introduction: the Miocene

• Background: the Messinian Salinity Crisis– When, where & the evidence

• The hypotheses: how did it happen?– The controversies

• The implications: who cares about the MSC?– Global impact & the hydrologic budget

The Miocene

A brief introduction

The Miocene

Zachos et al.

(2001)

Antarctica

partially

glaciated

fully glaciated

Vegetation

closed forest (C3)

open land (C3)

open grassland (C4)

Period

early

middle

lateMio

cen

e Fauna

↑ dominance of

grazing species

[CO₂]

≈600 ppmv

fluctuations

≈300 ppmv

Introduction

Changing glaciation

↕ NADW

formationMessinian

Salinity

Crisis

Humid

conditions

Upwelling

cycles –

trade winds

Southern Source Water

Strong

monsoonal

Systems

Changing glaciation

Moving

continents

The Messinian Salinity Crisis

Some background

Messinian Salinity CrisisBackground

Italy

Precession Minimum

Precession Maximum

Composite

Mediterranean

stratigraphy

Pre- and post- event

deposits:

Sapropels and marls –

precession cyclicity

Messinian Salinity

Crisis deposits:

Evaporites followed by

brackish fauna

What caused the MSC?

Two, main hypotheses

DesiccationHow did it happen?

Proposed by Hsü et al. (1973)

Reflooding

Deposition of

~25 m salt

Deposition of

~25 m salt

2500 m of salt

DesiccationHow did it happen?

Hsü et al. (1973)

DesiccationHow did it happen?

Hsü et al. (1973)

Feasible scenario?

100 cycles needed & each takes 10

ka +

= 1 Ma to accumulate salt deposits

Actually deposited in 450 ka

No Desiccation

Normal marine salinity

Siphoning event

Hypersaline: GYPSUM

Betic Corridor closed

Hypersaline: HALITE

Riffian Corridor closed

Hyposaline: brackish

Straits of Gibraltar open

Normal marine salinity

How did it happen?

Age (Ma) Lithology Salinity (g l-1) Hypothesis

Two-way (anti-estuarine) flow

through Gibraltar

Gypsum and brackish water

sediments – periodic freshwater

input & Atlantic incursions

Deposition of halite – no outflow,

some inflow

Persistent Atlantic inflow during

gypsum formation – no outflow

or small-scale outflow

Two-way (anti-estuarine) flow

through both Morocco & Spain

Atlantic water siphoned through Morocco

– outflow funnelled through Spain

Spanish gateway shut – two-way flow

through Morocco – reduced outflow

• Gateway analysis

• Evidence from the basins

Will we ever know the truth?

How did it happen?

But why should we care?

...pursuing knowledge for the sake of knowledge?...

• Total desiccation = 5 m global sea level rise

• Climate: drier Med region & amplification of seasonal temps

Impact of desiccation

Implications

Surface air temperature: the effect of desiccating the Mediterranean basin

• Deep source hypothesis: Nordic Sease.g. Reid et al. (1979)

• Shallow source hypothesis: NA Sub-tropical gyree.g. McCartney & Mauritzen (2001), Bower et al. (2002)

Outflow and global THCImplications

HadCM3 5m depth HadCM3 2730m depth

• Sensitive & high-resolution process studies

Studying hydrologic budgetsImplications

?

• Aydin Cicek, Ministry of environment and forestry of Turkey.Climate change mitigation

• Harald Poigner, Alfred Wegener Institute, Germany. Antarctic near-shore biogeochemistry: trace metals in bivalves

• Iuliana Vasiliev, Utrecht University, Netherlands. Palaeomagnetism & inorganic geochemistry

• Kate ‘Tug’ Olde, Kingston University London, UK. Dinocysts as palaeo-proxies during the Cretaceous greenhouse climate

• Robin Topper, Utrecht University, Netherlands. Modelling of the Messinian Salinity Crisis using 87Sr/86Sr

• Ruža Ivanović, University of Bristol, UK. Mediterranean-Atlantic exchange: Nd geochemistry & GCM modelling

The TeamThe Miocene Team