information contained within this presentation is from a currently unpublished thesis, and should...

Information contained within this presentation is from a currently unpublished thesis, and should not be used or referenced without the expressed permission of the authors

1500-yr-long sea-level reconstructions from North Carolina to Newfoundland

(Iceland)Alex Wright & Dr. Orson van de Plassche

1500-yr-long sea-level reconstructions from North Carolina to Newfoundland (Iceland)

RELATIVE SEA-LEVEL: SEA-LEVEL VARIABILITY: with trends trends removed


NH TEMPERATURES: SEA-LEVEL VARIABILITY: Mann et al. (2003 trends removed


(BRIEF) TALK OUTLINE

CONCEPT: Sea-level from salt-marshes

METHODOLOGY: 5 Steps sea-level reconstruction, with examples(RESULTS &DISCUSSION)

SUMMARY: Conclusions


CONCEPT: SALT-MARSHES

• Coastal wetlands• Upper half tidal range (MTL-HHW)


CONCEPT: SALT-MARSHES AND SEA-LEVEL

• Surface vertically accretes - maintain position with rising sea level• Sedimentary archive of palaeomarsh surfaces (PMS)


CONCEPT: VERTICAL DISTRIBUTION OF FORAMINIFERA

• Tidal inundation - strong environmental gradient - vertical distribution flora / fauna (MHW)

• Foraminifera occupy narrower vertical ranges• More precise indicators of PRESENT and PAST marsh surface height (MHW)


METHODOLOGY: 5 STEPS TO SEA-LEVEL RECONSTRUCTION

1) Height PMS’s formed (relative to PMHW)

2) Time the PMS’s formed

1) + 2) = Relative PMHW

3) Sediment compaction correction

4) Palaeotidal range correction

+ 3) + 4) = Relative PMTL

5) Detrend millennial scale relative sea level (GIA)

+ 5) = PMTL


METHODOLOGY: 1) Height PMS’s formed (relative to PMHW) • Establish contemporary vertical foraminifera distribution • Sample heights known (MHW) – TRANSFER FUNCTION foraminifera-surface

height• QUANTITATIVE PMS height reconstruction from FOSSIL foraminifera


METHODOLOGY: 1) Height PMS’s formed (relative to PMHW)

• Palaeo-record from core salt-marsh peat



• Every (other) cm - assumed PMS • Analyze for fossil foraminifera content



• TRANSFER FUNCTION - PMS heights (PMHW)• Variability from rate PMS accumulation or PMHW rise? • PMS accumulation rate - CHRONOLOGY!


METHODOLOGY: 2) Determine time at which PMS’S formed

• Resample for datable PMS indicators• Last ~200 yrs date sediment - HIGH PRECISION• Remainder data 14C of organics – LOW PRECISION



• PRECISION differences clear from age-PMS depth envelope• High resolution sampling CHECKS record completeness


RECONSTRUCTIONS:



• CHALLENGE - Define within envelope PMS accumulation rate• EXAMPLE - 2 LINEAR rates



• Illustrate importance…….


METHODOLOGY: COMBINE 1) + 2) = Relative PMHW

• PMS accumulation rate - PMS height variability due to PMHW• Correct? Cannot resolve at this scale• Combined - PMS accumulation rate defines (MULTI-)CENTENNIAL VARIABILITY


METHODOLOGY: COMBINE 1) + 2) = Relative PMHW reconstruction

• AGAIN - PMS accumulation rate defines (MULTI-)CENTENNIAL VARIABILITY• Last ~200 yrs high precision chronology - constrains PMS• Enables VALIDATION with instrumental records…..EXTENSION? (GEHRELS)


SUMMARY:


METHODOLOGY: 3) Sediment compaction correction

• COMPACTION – (post-depositional process) alters original PMS elevation• CORRECTION APPLIED - LINEAR PMHW becomes CURVED decreasing trend• (NON-)CORRECTION – impacts MULTI CENTENNIAL TRENDS


METHODOLOGY: 3) Sediment compaction correction

• CALCULATION? Comparison with basal reconstructed PMHW


METHODOLOGY: 4) Palaeotidal range correction, COMBINE 3) + 4) = Relative PMTL

• Rising relative sea level - coastline morphology - tidal range changes• Solved with modeling - relative PMHW can infer relative PMTL


METHODOLOGY: 5) Detrend (GIA), COMBINE 5) = PMTL

• Reconstructed MTL once MILLENNIAL relative rise removed• Past 1500 yr due to GIA? (assuming no SL trend)• SCENARIO 1 / 2, extent to which SL is STABLE / RISING / FALLING• Preferably long BASAL series with model prediction


SUMMARY:


RESULTS / DISCUSSION:Summary assessment of reconstructions


RESULTS / DISCUSSION:Summary assessment of reconstructions

• Falling SL trend? inc. ~1800

• High freq. variability

• Falling SL trend & oscillation? inc. ~1900• Falling SL trend? inc. ~1800 / ~1900

• inc. ~1900• High freq. variability, inc. ~1700 / ~1900

• EROSION• EROSION

• High freq. variability, inc. ~mid 1700 (PMS) / ~late 1800


SUMMARY: CONCLUSIONS

1) ARE RECONSTRUCTIONS COMPARABLE?• Once specific differences in technique/approach are

taken into account

2) MULTI-CENTENNIAL SCALE VARIABILITY?• Dependant on the reconstructed PMS accumulation

rates• Most reliable reconstructions display no coherence in

terms of a discernable influence of MWP / LIA• Due to limitations of reconstruction?


SUMMARY: CONCLUSIONS

3) FALLING SEA LEVEL TREND LAST MILLENNIA?• Still open• Trends are the result of PMS rate, (non-)correction

for compaction and detrending method• SOLVABLE?

Extrapolation of multi-millennial scale trends (basal and GIA) independent of data for recent ~1000 yrs compared to high resolution basal trends, e.g. DONNELLY, 2004, for this period

4) RECENT INCREASE LAST CENTURY?• POSTER: Dr Roland Gehrels

• High precision dating past ~200 years, helps resolve rates of sea level rise for the last century that are higher than the trend for the last 1500 years

• Precise timing is problematic• Defining such rates in past 1500 years beyond

resolution achievable with conversational AMS 14C dating techniques


ACKNOWLEDGEMENTS:Dr Orson van de PlasscheDr Roland Gehrels

THANKS TO:Prof Kurt LambeckUNESCO

POSTERS:Wright & van de Plassche: Salt-marsh accumulation rates and relative sea-level changes during the past 1500 years for three sites along the east coast of North America

Gehrels: Coupling instrumental and proxy records of recent sea-level change

information contained within this presentation is from a currently unpublished thesis, and should...

Documents

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