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PhD's awarded


June 2014 – Well done to Andi Smith on the successful defence of his PhD thesis: Speleothem Climate Capture – A Holocene Reconstruction of Northern Iberian Climate and Environmental Change.

An extensive 4 year cave monitoring program has been undertaken at Asiul Cave, a previously unstudied site in Cantabria (Spain). Monitoring indicates that this cave has the potential for long term speleothem development and that stalagmites are ideal for the reconstruction of palaeoclimatic conditions, including importantly palaeorainfall amount reconstruction. Two speleothem samples were therefore removed from the cave and analysed for a suite of geochemical proxies. Coeval oxygen isotope records from Asiul Cave indicate that northern Iberia has experienced considerable deviations in rainfall during the last 12,500 years. These high resolution records are strongly coupled with changes in other regionally important climate archives, helping to add to our understanding of northern Iberian climate evolution. The Asiul speleothem records however, go beyond explaining local changes in environmental conditions by exhibiting a strong coupling between atmospheric conditions, in the form of the North Atlantic Oscillation (NAO) and North

 

Atlantic Ocean circulation. These speleothem archives indicate that the NAO controls not only the positioning of atmospheric storm tracks throughout Europe but through interactions with the surface layer of the ocean can cause major changes in oceanic circulation. These NAO controlled changes in North Atlantic Ocean circulation have been shown to cause significant cooling within the northern North Atlantic and the southerly transport of ice rafted debris, with a millennial periodicity of ~1500 years. The Asiul cave speleothem record is one of the first convincing archives of a millennial scale NAO system which has the capacity to force changes in oceanic circulation. These speleothems also act to extend existing archives of the NAO back into the Younger Dryas; in doing so the Asiul records challenge our current understanding of NAO dynamics and the exact timing of initial NAO development.

Andi Smith

Andi was supervised by Dr Peter Wynn and Prof Phil Barker at Lancaster University and Prof Melanie Leng and Dr Steve Noble at the BGS.


March 2014 – Congratulations to Annemarie Valentine on successfully defending her PhD thesis: An investigation into the seasonality of the Pliocene southern North Sea Basin: a sclerochronological approach.

The Pliocene world c. 5.3 Ma to c. 2.58 Ma exhibited a relatively stable climate with a warmer global mean surface temperature than present-day by ~2 °C to 3 °C, and palaeoclimate analysis from this interval is used to understand climate drivers in 'warmer world'. Previous oxygen isotope thermometry investigations of Pliocene southern North Sea Basin (SNSB) Aequipecten opercularis from the Coralline Crag Formation in Suffolk, UK repeatedly reveal evidence of a cold-temperate climate regime. Contrastingly, other biological proxies record a warm-temperate/sub-tropical regime. This investigation concentrated on oxygen, carbon and microgrowth increment widths (MIWS) of fossil shell material from Pliocene SNSB spanning an interval of~4.4 Ma to ~2.5 Ma. The study sites included shallow marine Pliocene formations from the western and eastern SNSB, the Ramsholt Member of the Coralline Crag Formation, Suffolk UK, and the Luchtbal Sands and Oorderen Sands Members of the Lillo Formation, Belgium, and the Oosterhout Formation in the Netherlands. Oxygen isotopic palaeotemperature results showed cooler summer temperatures

 

than presently in the SNSB, which were reflective of a cool-temperate regime. There was no evidence of warm-temperate or sub-tropical summer palaeotemperatures in the Pliocene SNSB as suggested by other planktonic proxies. This investigation discussed the possible causal factors for the cooler – than– expected winter and summer palaeotemperatures in the 'warmer' Pliocene world as recorded by this proxy. Discrepancies between the cool summer benthic palaeotemperatures from the bivalves and the warmer sub-tropical or warm-temperate summer palaeotemperature estimations from planktonic biological proxies was rectified by the application of a theoretical summer stratification factor (SSF). However, rectifying the discrepancies between cooler (cold-temperate) benthic winter palaeotemperatures and the warmer winter palaeotemperatures from other proxies was difficult because stratification does not occur during the winter. Dormancy behaviours in the warm– temperate – sub–tropical organisms was proposed as a suitable mechanism to allow their coexistence with the cool-tolerant bivalves, which were able to grow and feed underneath the thermocline during the summer months. Therefore, the investigation showed how the Pliocene SNSB exhibited a greater seasonality than occurs presently in the SNSB. The driver for the cooler winter temperatures in the Pliocene SNSB was not identified. Localised explanations including continental wind effects, interannual variations in MOC strength, and increased storm activity in the winter bringing cooler water into the SNSB were all suggested as potential drivers. Global features of climate including interglacial/glacial cycles and orbital forcing effects were factors also proposed for the overall mixed palaeotemperature signal in the Pliocene SNSB.

AnneMarie Valentine

Annemarie was supervised at University of Derby by Dr Andy Johnson and by Prof Melanie Leng at the BGS.


March 2014 – Congratulations to Hayley Manners on the successful defence of her thesis: A Multi-Proxy Study of the Palaeocene - Eocene Thermal Maximum in Northern Spain.

At the boundary between the Palaeocene and Eocene epochs (ca. 56 Ma) a significant global warming event, termed the Palaeocene-Eocene Thermal Maximum (PETM), occurred. Records of this event are characterised by a negative carbon isotope excursion (CIE) which has been associated with the release of thousands of petagrams of isotopically light carbon into the ocean-atmosphere system, initiating changes in the carbon cycle, the climate system, ocean chemistry and the marine and continental ecosystems. The amount of isotopically light carbon that was required to cause the event, its source and the rapidity of its release are, however, are still debated. This study uses δ13CTOC, δ13Cn-alkane, δ13<CCARB and palynological data to evaluate the PETM CIE in terms of the magnitude of the CIE in both continental and marine settings, rapidity of release and drawdown of carbon, and mobilisation of different organic matter (OM) pools as a response to the climate change. The sections studied span a continental to marine transect in northern Spain. This represents the first organic geochemical study of these PETM sections, one of the first comparisons of CIE magnitude between continental and marine sections within the same sediment routing system, and one of the first comparisons of the same OM proxies within different depositional

 

environments. The data suggest that different OM pools were mobilised in response to the PETM, with reworking of older material, soil residence times, and contemporaneous vegetation all contributing. CIE profile shapes predominantly suggest a rapid onset and recovery from the event. The magnitude of the CIE was also assessed. The current resolution of the data suggests that the differences between continental and marine CIE magnitudes could be minimal within a single sediment routing system, perhaps establishing a realistic CIE magnitude for the PETM, for use in future modelling scenarios.

Hayley Manners

Hayley’s main supervisor was Dr Stephen Grimes (Plymouth) and Prof Melanie Leng at BGS.


March 2014 – Congratulations to Jonathan Dean who gained his PhD entitled: Stable Isotope Analysis and U-Th Dating of Late Glacial and Holocene Lacustrine Sediments from Central Turkey.

Water is a politically sensitive resource in the Near East and water stress is increasing. It is therefore vital that there is a strong understanding of past hydrological variability, so that the drivers of change can be better understood, and so that the links between the palaeoclimate and archaeological records in this key region in the development of human civilisation can be investigated. To be of most use, this requires high resolution records and a good understanding of palaeoseasonality. A sediment sequence spanning ~14,000 years was retrieved from Nar Gölü, a lake in central Turkey. My thesis focussed in particular on oxygen isotope analysis of carbonates and comparing δ18Ocarbonate and δ18Odiatom data in order to examine palaeoseasonality. Due to the high resolution δ18Ocarbonate data, it was possible to show that the rapidity of the Younger Dryas to Holocene transition at Nar Gölü was similar to that seen in North Atlantic records and that centennial scale arid events in the Holocene seem to occur at the time of cold periods in the North Atlantic. Taken together, this suggests a strong teleconnection between the two regions. However, the longer duration of the aridity peaks ~9,300 and ~8,200 years BP at Nar Gölü, compared with the more

 

discrete cooling events at this time in the North Atlantic, suggest that there are additional controls on Near East hydroclimate. There is a multi-millennial scale trend of increasing δ18Ocarbonate values from the early to late Holocene. This ‘Mid Holocene Transition’ has previously been identified in the Near East, however here it is demonstrated that water balance and not a shift in the seasonality of precipitation was the primary cause. Finally, for the first time, the stability of Near East climate in the early Holocene is robustly demonstrated, suggesting that this could have been a key enabler of the development of agriculture at this time.

Jon was supervised at University of Nottingham by Dr Matthew Jones and Prof Sarah Metcalfe, at NIGL he was supported by Dr Stephen Noble and Prof Melanie Leng

Jon Dean


December 2013 – congratulations to Sven Könitzer who was granted a doctorate for his PhD research entitled: Primary biological controls on UK Lower Namurian shale gas prospectivity: A step towards understanding a major potential UK unconventional gas resource.

Sven’s research is the first to analyse the abundance and type of organic matter preserved in deeper-water mudstones deposited in a Late Mississippian UK basin alongside a detailed sedimentological study to determine the key depositional processes and the palaeoenvironment. This study is a key step in understanding where, and why, organic matter is concentrated in fine-grained sedimentary rocks. Mudstones of this age, deposited across central and northern England, are known oil and gas source rocks and are currently the focus of attention for onshore shale gas exploration. Shale gas is formed from organic matter present during maturation and is mostly retained in the same rock formation.

 

Sven Könitzer

Sven was supervised by Prof Sarah Davies (Leicester) and Prof Mike Stephenson, Prof Melanie Leng, and Dr Chris Vane at the BGS

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