C-Change in GEES Changing Coastal Environments Session 2: Reconstruction Techniques

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Photo: AlishaV (flickr.com) Session Outline 1) Salt Marsh Coring 2) Core Analysis Techniques Sedimentology Geochemistry Microfossils 3) Dating Diatoms Photo: AlishaV (flickr.com)

Understanding past sea-level change Monitoring present day sea-level change Predicting future sea-level rise (modelling) Sea-level research falls into four broad categories....... Coastal management, hazard mitigation 5

Salt Marsh Coring The composition and structure of salt marsh communities are sensitive to sea-level change Stratigraphic record provides an archive of changing sea levels Preserved in microfossils and soil properties – microfossils tell us about changing salinity conditions Accumulation of sediment over thousands of years –salt marsh core records date back ~12000 years K. Szkornik

Core Analysis Core Analysis Methods Sedimentology (e.g. grain size, organic content, soil moisture) Microfossils (Diatoms, foraminifera) Dating (radiocarbon dating, lead-210 dating) K. Szkornik

Sedimentology Sediments record changing sea levels through time Shifts between marine sediments and terrestrial and fluvial sediments Marine transgression and regression Peats = freshwater Clays = marine Evidence of changing environmental conditions in the salt marsh K. Szkornik

Chronological Control Radiocarbon Dating: Carbon is fixed into organic material through process of photosynthesis When a plant dies, the unstable carbon-14 isotope decays exponentially Unstable/stable carbon isotope ratio is an indicator of age of organic material Able to date back ~60,000 years Lead-210 Dating (commonly used to date the more recent material from salt march cores): Uses ratio of radioactive lead-210 to stable isotope lead-206 Lead-210 has a half life of ~22 years so techniques is appropriate for around 150 year old sediments Caesium 137 – highest recording sample used as a dating horizon – corresponds to fallout from nuclear weapons testing between 1962 and 1965

Microfossils: Diatoms Microscopic unicellular algae Composed of silica Identified to species level Well preserved in sediments Indicators of environmental change Distribution of species is affected by water salinity, nutrient content, pH, temperature Photos: PROYECTO AGUA** (flickr.com)

Microfossils: Foraminifera Marine, single-celled organisms Found in the inter-tidal zone Usually well preserved Applications in sea-level studies Limited use in areas above tidal limit Photos: MuseumWales (flickr.com)

Other Microfossils Testate amoebae Pollen Images from wikimedia commons A developing technique used in mangrove environments Used in freshwater marsh – intolerant of salinity 12

Reconstructing Holocene Sea Levels What do we need to know? - Age - Present day altitude - Indicative meaning (& range) - tendency of sea-level (?) Indicative meaning = Elevation relative to a reference tide level at which the sea-level indicator is found in the present environment (See Shennan, 1982, 1986; van de Plassche, 1986) Relative sea level (RSL) = H – I Where H is the present day altitude of the sample and I is the indicative meaning. Sea-level index point (SLIP)

Transfer Functions Transfer functions – quantitative approach to inferring the indicative meaning. Investigate relationship between microfossils (diatoms, forams) and environmental variables in the modern environment. Apply these relationships to interpret known microfossil assemblages in the cores and infer the past environmental conditions and therefore indicative meaning. Representation of transfer function – X, Y and X0 information is used to infer Y0 See Szkornik et al (2006)

Sea-level change in western Denmark Sea-Level Index Point (SLIP) Ho Bugt Embayment Chronology: Optically stimulated luminescence (OSL), or Radio-carbon dating (14C) + Diatom-based transfer function: surface elevation at which the sample was formed relative to sea level = Sea-Level Index Point (SLIP) Figure from: Szkornik, K.; Gehrels, W.R.; and Murray, A.S. (2008) ‘Aeolian sand movement and relative sealevel rise in Ho Bugt, western Denmark, during the ‘Little Ice Age’’ The Holocene 18(6): 951-965 Reproduced with permission of Sage Publications Limited

Session Summary Introduction to technique for reconstructing past sea-level change Microfossils, geochemistry and sediment structures all indicate changing environmental conditions The application of radiocarbon dating and optically stimulated luminescence helps to understand the chronology of changing coastal environments Chronological control is very important for understanding the timescales of changes

References Szkornik, K., Gehrels, W.R. and Kirby, J. (2006) ‘Salt-marsh diatom distributions in Ho Bugt (western Denmark) and the development of a diatom-based transfer function for reconstructing relative sea-level change’. Marine Geology 235, 137–50 Szkornik, K., Gehrels, W.R., and Murray, A.S. (2008) ‘Aeolian sand movement and relative sea-level rise in Ho Bugt, western Denmark, during the ‘Little Ice Age’ The Holocene 18(6): 951-965

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Dr Katie Szkornik, Keele University, k.szkornik@esci.keele.ac.uk Item Metadata Author Dr Katie Szkornik Stephen Whitfield Institute – Owner Keele University, School of Physical and Geographical Sciences Title Reconstruction Techniques Powerpoint Presentation Date Created December 2009 Description Reconstruction Techniques - Powerpoint Presentation – Part Two of Changing Coastal Environments Educational Level 3 Keywords (Primary keywords – UKOER & GEESOER) UKOER, GEESOER, Microfossil, Transfer Function, Holocene Creative Commons License Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales Dr Katie Szkornik, Keele University, k.szkornik@esci.keele.ac.uk C-Change in GEES Themes 2 and 3: Changing Coastal Environments – Reconstruction Techniques