Holocene Land-Ocean-Atmosphere Interactions on the Eastern Seaboard of North America

Lead Research Organisation: University of Southampton
Department Name: School of Geography


Past terrestrial responses to climate-ocean interactions in the North Atlantic region are a critical research priority because they show how changes in key aspects of climate that will be affected by future global warming, such as ice sheet volume & ocean circulation, may be translated into phenomena of socio-economic importance, including the atmospheric water balance & soil moisture availability. Although we are beginning to understand the nature & magnitude of changes in the circulation of the North Atlantic over the last 10,000 years, terrestrial responses to these events are still poorly understood in terms of timing, magnitude & spatial pattern. It is imperative to rectify this deficiency in order to generate & test hypotheses to explain the processes of change, to understand the strength of relationships between oceanic & terrestrial climate change, & to enable future soil conditions & water resources to be predicted using computer models. Plan of work This project will investigate four sites located on a transect along the eastern seaboard of North America, from northern Newfoundland to Maine. This region was highly sensitive to past changes in ice sheet mass balance & ocean circulation. The selected sites are all raised (rain-fed) peat bogs, which provide superb climate archives. Plant & animal (testate amoebae) fossils preserved in well-dated cores extracted from these bogs will be used to reconstruct past changes in Bog Surface Wetness (an index of surface water balance) over the last 8500 years, at a time resolution of 10-100 years. The same core samples will be analysed for stable isotopes of oxygen & hydrogen. The spatial & temporal distribution of the heavy isotopes of these elements in precipitation is related to air temperature, & hence to atmospheric circulation. The isotope signal captured in the cellulose fraction of Sphagnum moss closely tracks that of the precipitation used by the plant for cellulose synthesis. Hence, fossil Sphagnum from raised peat preserves a clear signal of past changes in climate & atmospheric circulation. Modern precipitation along the eastern seaboard of North America is derived mainly from the Atlantic Ocean. A strong temperature contrast exists between the Arctic waters of the Labrador Current, which flows southwards along this coast, & the warm waters of the Gulf Stream further offshore. Past isotopic ratios in precipitation falling over coastal areas will have been strongly influenced by changes in these ocean currents & in the heat transport by the Gulf Stream. By combining the oxygen & hydrogen isotope records, we will estimate the deuterium excess, an index of the conditions prevailing at the sea surface when evaporation occurred, including the extent of sea ice. The stable isotope data will be compared with isotope measurements on ice cores from Greenland & Canadian ice caps, and more cautiously, with estimated isotope values for surface seawater & lakes that have been derived from sediment analyses. Hence, analyses of fossils & stable isotopes from the same core levels will allow us to reconstruct the timing, magnitude & spatial pattern of the terrestrial response, as well as exploring the impact of different causal factors such as meltwater discharges, changes in atmospheric & ocean circulation & solar variability on the climate of the study area. In this way, insight will be gained into the mechanisms that have driven climate change over the last 8500 years. Hypotheses to be tested: 1) Between 8500 & 6800 years ago, the climate of the study area was strongly influenced by repeated discharges of glacial meltwater from the decaying North American Ice Sheet to the north, resulting in cooling & increased bog wetness. 2) After the disappearance of the ice sheet, 6800 years ago, the climate of the study area was indirectly influenced by cyclical variations in sea ice extent, ocean currents & deepwater formation north of Iceland.


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Kaislahti Tillman P (2010) Long-term climate variability in continental subarctic Canada: A 6200-year record derived from stable isotopes in peat in Palaeogeography, Palaeoclimatology, Palaeoecology

Description PRECIP Project Research Outcomes

Geochronology - A New Tephrostratigraphy Famework

The PRECIP project has recently located ultra-distal tephras in four study sites from Newfoundland Nova Scotia and Maine. These tephras have been geochemically characterized and traced to source volcanoes in the Pacific Northwest region of the United States and to Alaska. The fine volcanic ash layers represent the first finds of ultra-distal tephra in terrestrial records from Eastern North America and their identification demonstrates that tephra isochrones can be extended right across the continent. This finding is important because it establishes a high precision chronological framework for the study of the Holocene in eastern North America. The earliest identifiable tephra is the Mazama ash, which dates to 7650 cal. BP. Details of the full tephrostratigraphy from eastern Newfoundland, Nova Scotia and Maine have been published in:

PRECIP Publication: Mackay, H, Hughes, P.D.M., Jensen, B.J.L., Langdon, P.G., Pyne-O'Donnell, S.D.F., Plunkett, G., Froese, D. G., Coulter, S. and Gardner (2016) A mid to late Holocene cryptotephra framework from eastern North America. Quaternary Science Reviews, 132, 101 - 113.

PRECIP publication: Pyne-O'Donnell, S. D. F., Hughes, P. D. M., Froese, D. G., Jensen, B. J. L., Kuehn, S. C., Mallon, G., Amesbury, M. J., Charman, D. J., Daley, T. J., Loader, N. J., Mauquoy, D., Street-Perrott, F. A., Woodman-Ralph, J. (2012) High-precision ultra-distal Holocene tephrochronology in North America. Quaternary Science Reviews 52, 6 - 11.

Peat-based reconstructions of hydrological change inferred from Holocene bog surface wetness records (BSW):

Over the last few years the PRECIP project has developed the most detailed and longest records of Holocene water table change in ombrotrophic bogs yet produced from Atlantic Canada and Maine. In the north of the study transect the records span the period 7500 cal. BP to present and the longest records from Nova Scotia cover the whole Holocene. The past water table reconstructions have been completed for all of the main study sites and they show significant down-core variability that will allow us to assess regional patterns of hydrological change in relation to the hypotheses being tested. The records will be pinned together using high quality age-depth models based on the ultra-distal tephras and AMS radiocarbon dates.

Past water table records were reconstructed using a combination of plant macrofossil and testate amoebae sub-fossil identifications. Testate amoebae surface samples from the four main study sites, and a wide range of further sites from across the study region, were used to establish a transfer function for the reconstruction of past water table variations. The transfer function has been published in:

PRECIP publication - Amesbury, M. J., Mallon, G., Charman, D. J., Hughes, P. D. M., Booth, R. K., Daley, T. J. and Garneau, M. (2012) Statistical testing of a new testate amoeba-based transfer function for water-table depth reconstruction on ombrotrophic peatlands in north-eastern Canada and Maine, United States. Journal of Quaternary Science. doi: 10.1002/jqs.2584.

This study benefitted from additional data collected as part of a collaboration with the Universite de Quebec a Montreal (UQAM).

Development of Stable Carbon and Water Isotopes as Palaeoclimate Proxies:

Results from the array of modern samples of bog and leaf waters reveal that the different bogs fall along different evaporative lines. This is a noteworthy finding because it assists in interpretation of isotopic variability down-core and importantly, between sites. The spatial patterns of different isotope parameters exhibit the expected large-scale gradients polewards and into the interior of the continent, but also suggest that the Gulf of St. Lawrence plays a significant role as a local moisture source in summer.

Both carbon and oxygen isotopes in modern cellulose show an isotopic fractionation as one moves further from the water table. This trend has not been identified previously and would indicate that the Sphagnum isotope signal can integrate several signals within it. Initial tests using the measures of distance to water table provided by the testate amoebae to "correct" the isotopes for this enrichment effect indicate that its impact on the overall trend in the isotopic data is small when viewed over centennial to millennial time scales. Further work is on going and hydrogen isotopes will shortly be added to the dataset.

Analysis of modern inter-plant variability indicates the range of uncertainty observed in isotopic data. These findings suggest that approximately 10-15 plants sampled from a single level will provide a robust mean signal and a workable oxygen-isotopic uncertainty range (95%) roughly equivalent to machine uncertainty (ca. ±0.3 per mille).

PRECIP publication - Woodley, Ewan J.; Loader, Neil J.; McCarroll, Danny; et al. (2012) High-temperature pyrolysis/gas chromatography/isotope ratio mass spectrometry: simultaneous measurement of the stable isotopes of oxygen and carbon in cellulose. Rapid Communications in Mass Spectrometry. 26, 109 - 114. DOI: 10.1002/rcm.5302 Published: JAN 30 2012.
Exploitation Route Past water table changes in peat bogs may be used in the management of peatlands. The Peatlands of Newfoundland and Nova Scotia are largely intact and they provide important examples of natural mire communities that can be used as targets for conservation of damaged peatlands.

Tephra distribution provides important information on the spread of fine volcanic clash shards after major volcanic eruptions. This work is of importance for assessing volcanic hazards and provides a means of correlating between distant palaeoclimate archives.

The identification of the eruption history of volcanoes in North America will be useful in planning for volcanic hazards. Our research gives vital information on the likely distribution of fine glass particles in the atmosphere after major volcanic eruptions. This information will be useful for modelling disruption to air traffic following major eruptions. The study of the climate gradients of eastern North America will show how terrestrial moisture balance changes in relation to movements in dominant air masses and ocean currents over long timescales. These details will be needed to produce effective regional climate models and to model likely future climate changes, for example following accelerated melting of the Greenland Ice Sheet

Peatlands act as carbon stores. The study of past bog water table levels and the effect of these changes on carbon stores will be increasingly important for the management of greenhouse gas emissions from peatlands. Recent amendments to the Kyoto Protocol now permit the accrual of carbon credits from appropriate management of peatland water table levels.

The Stable water isotope records developed in this research grant will produce isotopic records that can be compared directly with similar data from ocean cores and ice cores. The isotopic data can be directly used in some global climate models.

Volcanic ash layers are can be used as precise time markers for cross correlation between a wide variety of terrestrial and aquatic palaeo-records. Our new tephrostratigraphy framework will provide a basis for analysing climate gradients across the North American continent.
Sectors Environment,Transport

Description Data cited in IPCC AR5
Geographic Reach Multiple continents/international 
Policy Influence Type Citation in other policy documents
Title Simultaneous determination of COH stable isotopes in organic matter 
Description A technological development is developed through which the stable carbon-, oxygen- and non-exchangeable hydrogen-isotopic ratios (d13C, d18O, d2H) are determined on a single carbohydrate (cellulose) sample with precision equivalent to conventional techniques. This triple-isotope approach offers significant new research opportunities, most notably in physiology and medicine, isotope biogeochemistry, forensic science and palaeoclimatology, when isotopic analysis of a common sample is desirable or when sample material is limited 
Type Of Material Technology assay or reagent 
Year Produced 2014 
Provided To Others? Yes  
Impact The development of a triple-isotope method represents a significant improvement over existing methods. The system performs comparably with standard methods in terms of analytical precision and importantly, requires less than a third of the sample material needed for single determinations using standard techniques. Analysis time is comparable with that of a single isotope determination by continuous flow. As the samples do not require nitration prior to analysis, significant efficiencies arise in the development of multiple-isotope time series. A further benefit of running three isotopic measurements on a single common sample is the increased statistical confidence in the mean value resulting from replicate analyses in cases where sample material is limited. If the triple-isotope approach is routinely adopted, we anticipate that the added information provided by the hydrogen-isotope data from a-cellulose samples will greatly facilitate modelling of hydrogen-isotope fractionation in plants and lead to a more complete understanding of carbon-, oxygen- and hydrogen-isotopic variability in the Earth system 
Description Evaluating Isotope Enabled Earth System Models Using Stable Isotopes in Tree Rings 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Inter-disciplinary meeting resulting in proposals for closer working, collaborative working groups and potential research funding applications.

The potential value of tree ring isotope data in evaluating isotope enabled models was highlighted along with the current limitations in isotope-enabled modelling.
Year(s) Of Engagement Activity 2014
Description Poster on stable isotopes in peat 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Quaternary Research Association (QRA) Annual discussion meeting on "Drivers and Responders" in the study of climate forcing. Poster presented outlining peat research with stable isotopes.
Year(s) Of Engagement Activity 2016
Description QRA Conference on the Quaternary in Southern South America. 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Lecture presented to a QRA sponsored workshop on the Quaternary of Southern South America. Stable isotopic analysis of a late-­Holocene peat sequence from Patagonia.
Year(s) Of Engagement Activity 2015
Description Simultaneous determination of COH isotopes in organic matter 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Other academic audiences (collaborators, peers etc.)
Results and Impact Talk led to questions and discussion.

Submitted for publication.
Year(s) Of Engagement Activity 2014