A Seasonal study of two Ammonia morphotypes in a north west Scotland fjord and their Palaeoclimatic significance

Angela Roberts, William Austin, Kathryn Darling, Magali Schweizer, Martin Sayer

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Abstract / Description of output

A seasonal study of the benthic foraminifera from the “cryptic” genus Ammonia (Linné) has been produced from a sea loch near Dunstaffnage, NW Scotland. The pronounced seasonal heating of this mid-latitude shelf sea produces a large temporal change in seawater temperature ranging from 7oC to 14oC, which has the potential to be recorded in the shell chemistry of benthic foraminifera. The genus Ammonia is important as it has been readily used in paleoceanographic reconstructions in nearby Loch Sunart (30km North) (Cage and Austin 2010). This study utilises a broad taxonomic concept under the name of Ammonia beccarri. However, recent work by Hayward et al (2004) demonstrated that the widespread practice of recognising only up to three species of Ammonia should be abandoned, because of large genetic and morphological diversity. This clearly has significant implications for the Loch Sunart reconstruction.

A quantitative morphometric analysis based on the external test characteristic measurements was utilised in order to distinguish if more than one morphospecies can be found within the site. Distinct morphological features can be used in a practical scheme to separate Ammonia into two distinct morphotypes. Morphotype A can be characterised by a lack of an umbonal boss, shorter sutures and limited ornamentation. Morphotype B can be characterised by: distinct sutures, a highly ornamented test, a large test diameter and a large umbonal boss. These morphological distinctions between the two morphotypes have been verified using SSU rRNA phylogenetic analysis, which demonstrates that the two morphotypes are two distinct genotypes (unpublished Darling et al).

A replicated time series analysis of SCUBA collected surface sediments was performed over a 12 month period (September 2008-2009), to determine if there are any seasonal differences between the living (Rose Bengal stained) Ammonia genotypes present. Preliminary results demonstrate that Morphotype A has a seasonal peak in early autumn and spring, whereas Morphotype B numbers are constant throughout the year. An understanding of how Ammonia responds to seasonal changes in temperature, and a hidden diversity of species has crucial implications upon the 1000 year Loch Sunart record produced by Cage and Austin (2010), who assumed the species-specific proxy of Ammonia provided an accurate summer temperature estimate.
Original languageEnglish
Title of host publicationTMS Foraminifera and Nannofossil Groups Joint Meeting Edinburgh 2012
Subtitle of host publicationInterdisciplinary advances in foraminiferal and nannofossil research
Pages36
Number of pages1
Publication statusPublished - Jun 2012

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