Investigating mid-Pliocene warming: insights from onshore Iceland

(L-R) Max, Jonathan, Matthew and Steve at the Tjörnes Peninsula

Dr Steve Jones, his DR student Jonathan Hall and MSci students Matthew Allison and Max Papadopoulos are completing the first phase of a project to unlock new records of past climate in the North Atlantic.

The project began when they travelled to Iceland in September 2018 to undertake fieldwork on the Tjörnes Peninsula, northern Iceland.  Located at the centre of the Greenland-Scotland Ridge and above the Icelandic mantle plume, the thick sedimentary sequence at Tjörnes is a potentially valuable but hitherto little-known archive of North Atlantic palaeoenvironmental change during the early to mid-Pliocene.  

This important time interval is considered an analogue for late 21st Century climate change, when global surface temperatures were naturally 2−3°C higher than present and atmospheric CO2 concentrations peaked around 400 ppmv.  Discrepancies between sea surface temperature estimates derived from the geological record and predictions by Global Circulation Models currently occur in the North Atlantic during the mid-Pliocene.  The project aims to explain these discrepancies by generating new palaeo-temperature estimates throughout the region, including the first evidence of terrestrial surface temperatures inferred using organic biomarker temperature proxies (branched-GDGTs) extracted from lignite (brown coal) seams.

photo of group taking rock samplesAfter flying to Reykjavík, the group drove north east for 7 hours to our base for fieldwork, the fishing town of Húsavík, also known as the Whale Watching Capital of Iceland. Fieldwork began by mapping the geology and logging the c. 500 m of exposed sediments along the coastal cliffs and incised valleys to understand the sedimentology and structural relationships, and to develop a revised stratigraphic framework to incorporate the new palaeo-temperature results.

In a landscape dominated by volcanism, the Tjörnes sequence has the longest time span and thickest accessible rock column of any sedimentary succession onshore Iceland. It comprises a range of terrestrial sediments (lignites, conglomerates and sandstones) and marine sediments (sandstones, mudstones), which display well-preserved sedimentary structures and fossils, including molluscs and petrified wood.

After mapping the many lignites seams accurately for the first time since the original survey in the 1920s, we sampled them in preparation for biomarker analysis. The Tjörnes succession is bounded by basaltic lavas which were also sampled for radiometric dating, using a sledgehammer and a lot of brute strength, to clarify the age of the sequence.

Upon returning with significantly heavier bags, the lignite samples were crushed to extract organic biomarkers in the Birmingham Molecular Climatology laboratory, headed by James Bendle.  After winning a NERC Life Science Mass Spectroscopy Facility grant for analytical support (£31k), the extracted compounds were sent to the Organic Geochemistry Unit at the University of Bristol for analysis.  

Jonathan presenting the UOB PER funded Tjörnes geology leaflets to Martin Varga at Tungulending.Preliminary results confirm the presence of branched-GDGTs in the majority of the sampled lignite seams.  Further work is underway to establish associated palaeotemperature estimates and assess the compatibility and implications on regional palaeoenvironmental trends.  The group then secured a NERC Isotope Geosciences Facility grant (£38k) to determine the age of the succession using 40Ar/39Ar radiometric dating of the basalts, in collaboration with the Scottish Universities Environmental Research Centre. These ages will provide insight into the onset, rate and duration of biomarker-based temperature estimates, and enable their integration with climate trends inferred from complementary marine sedimentary records.

Whilst in Iceland, the group discussed their research project with community members and tourist facilities in Húsavík including Martin Varga, a local entrepreneur who owns the Tungulending guest lodge and café that looks out onto some of the most impressive Tjörnes sequence outcrops. Martin described how over 5000 international visitors explore Tjörnes each year to experience the geology and to investigate the unique fossil layers exposed in the low-lying cliffs. He described his frustration at the lack of information resources for these visitors, and highlighted the need for accessible educational literature to explain the geology.  Upon returning to Birmingham, Jonathan secured a UOB Public Engagement with Research grant (£2k) to produce and deliver leaflets to local community stakeholders.

Lignite seams exposed above the coastal Skeifá waterfall on the Tjörnes peninsula.Jonathan co-designed the leaflets, which include information on the location, rock types, fossils, past environments and geological history, in collaboration with Elena Schneider, an Icelandic graphic designer based in Húsavík, who formatted the typography, layout and colours to give the leaflet (Available here) a distinctive and appealing Nordic theme.  Jonathan and Matthew recently returned to Tjörnes to deliver the printed leaflets to Tungulending and other community, educational and tourism outlets. They presented our work to a community committee that included representatives from local businesses, government and the University of Iceland’s Research Centre in Húsavík.

This project has proved a great opportunity to develop international public engagement alongside scientific research at a world-class geological site. Results of the various geochemical analyses will filter through over the next year to complete Jonathan's PhD thesis and associated papers, with involvement of the MSci students. At the same time, we are discussing further public engagement funding with the Icelandic Ministry of Education, Science and Culture to further highlight the significance of Tjörnes as an archive of past climate.