dr. angela hayes, dr. teresa broggy and prof. michal kucera late quaternary investigation of...

Dr. Angela Hayes, Dr. Teresa Broggy and Prof. Michal Kucera

Late Quaternary Investigation of Planktonic Foraminiferal

Assemblages from the Western Mediterranean Sea

Mary Immaculate College Research Showcase

Research Area: The Mediterranean Sea

The Late Quaternary

Planktonic Foraminifera

(from Coloma et al., 2005)

ProtozoaNon-spinose Spinose

BiogeographicRegions

(from Kucera, 2007)

Globorotalia truncatulinoides

Dextral Sinistral

Ericson et al., 1954

Transitional

Subtropical

Tropical

Genetic Diversity

De Vargas et al. (2001) Ujiie and Lipps (2009)

Distribution of G.truncatulinoides(Type 2)

Pujol and Vergnaud-Grazzini, 1995

Core Locations

Methodology All samples were dried at 40 °C,

disaggregated in demineralised water and wet sieved through a 63 µm mesh before drying. Finally, samples were dry sieved through a 150 µm mesh. Using a random splitter, were possible, 100 specimens of G. truncatulinoides were counted to obtain a coiling record for each core.

16 radiocarbon dates

Results

It’s all about the Thermocline!

Assumptions Occurrence of G. truncatulinoides is governed by the

stability of the water column (mixed or stratified). Winter convective overturning facilitates the transference of both nutrients and juvenile populations of G. truncatulinoides into the surface waters where maximum abundances of the species develop.

Observed variation in coiling, appears to be related to the depth/presence of the thermocline. Dominant dextral populations tend to coincide with overall lower abundances of G. truncatulinoides possibly a residual population associated with increased stratification of the water column. The effects of SSTs are a potential secondary factor.

Significance of G. truncatulinoides in the Western Mediterranean Sea

Phase 1:Characterised by low numbers of G. truncatulinoides both coiling variants exist, but the sinistral variant dominates the faunal assemblage.Suggests seasonal mixing in the water column. However, the relatively low abundances and the presence of the dextral coiling variant may imply weakened vertical mixing associated with the formation of a shallow thermocline.

Phase 2:Characterised by the near absence of G. truncatulinoides from the faunal record . The absence of the species is attributed to enhanced stratification of the water column. The strong water stratification in the western Mediterranean Sea at this time could have developed due to the combined result of postglacial sea level rise (and subsequent reduction in sea surface salinities) and increased precipitation (and subsequent river runoff).

Phase 3:Significant increase in the abundances of G. truncatulinoides corresponding with the end of the African Humid Period which marks the transition from a more humid climate to the semi-arid climate that exists in the Mediterranean region today. Modern day hydrographic conditions in the western Mediterranean Sea support the development of deep vertical mixing.

Conclusions Recolonisation of G. truncatulinoides post

glaciation in the western Mediterranean Sea The presence and absence of the species during

the Holocene suggests a sequence of hydrological events associated with sea level rise.

Basin-wide temporal and spatial similarities of recolonisation

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