Reconstruction of Pliocene-Middle Pleistocene evolution of Siberian permafrost using U-Pb dating of speleothems

Twenty three million square kilometres of northern-hemisphere land - one quarter of the total land area - is permafrost. This permanently frozen ground stores twice as much carbon as the atmosphere contains, with a significant fraction of this carbon as methane. Formation and thawing of permafrost is therefore a significant positive feedback in the climate system, removing greenhouse gas as Earth cools, and releasing it, in periods such as today, when the planet is warming. Permafrost also exerts a strong control on ecosystems and biodiversity, and it underpins human infrastructure (buildings and transport links) in many high-latitude settings.

A significant body of research exists (and continues) into active permafrost processes in the modern environment, but assessing the long-term behaviour of permafrost has proved more difficult. We do not yet have a clear idea of how the temperature of high-latitude continental regions responds to changing of global climates through time, nor of the extent of permafrost in different climate states. Such information is important for future planning in today's permafrost regions, and for our general understanding of high-latitude carbon and climate systems. How do the major permafrost regions of the northern hemisphere respond to global climate change such as orbital variation or the progressive cooling of the planet during the Plio-Pleistocene? And what role might permafrost have in these amplifying these changes through its carbon feedbacks on climate?

Here we propose to use carbonates formed in caves (speleothems) to assess the extent of permafrost in the world's largest area of permafrost - Siberia. Speleothems require water to form so, when the ground is frozen year-round, do not grow. The presence or absence of speleothems therefore constrains the extent of permafrost through time. We have been working on a sequence of three caves which stretch from the modern edge of the permafrost-free zone near Irkutsk at 52oN, northwards through patchy permafrost and to the edge of continuous permafrost at 60oN. This work has yielded a detailed reconstruction of the permafrost history during the last 450 ka, showing thawing of the permafrost in each warm interglacial period in the south. In the north (60oN) the permafrost remained stable except during the interglacial period 390-430 ka ago when global conditions were warmer than present.

We propose to continue the reconstruction of the permafrost history beyond the ~500 ka limit of the U-Th dating method in these caves, and to add a fourth cave in the centre of the continuous permafrost region at 64oN. Using a newly proven U-Pb dating ability, we will date periods of speleothem growth during the Plio-Pleistocne to assess the time, as the planet cooled after the warmth of the Pliocene, that permafrost conditions initiated in Siberia. And we will constrain the changing extent of permafrost during the variable climates of the Pleistocene. By comparing these records with information about climate elsewhere, we will learn how the high latitude northern continents respond to global climate change, particularly during periods warmer than today.

To understand how the cave temperatures in each location related to annual mean temperatures above the caves will require a campaign of monitoring in our study caves. We will conduct this work in close collaboration with Russian colleagues from the Russian Academy of Sciences and the well-established Siberian caving community. We will also use our connections in Russia to ensure that new information we learn is provided to stakeholders in regions that will be impacted by changing permafrost in the future.

About a quarter of the land area of the northern hemisphere is permafrost. This permanently frozen ground stores twice as much carbon as the atmosphere contains, with a significant fraction as methane. The formation or thawing of permafrost is therefore a significant positive feedback in the climate system. Permafrost also exerts a strong control on ecosystems and biodiversity, and it (literally) underpins human infrastructure and activity (oil, gas, mining, buildings and transport links) in many high latitude settings.

Assessing the long-term behaviour of permafrost has proved difficult. We do not yet have a clear idea of how the extent of permafrost responded to changing global climates before 500 ka BP. We expect to gain insights into this question from our research programme and analyses. Such information will be important for future planning in today's permafrost regions, and for our general understanding of high-latitude climate systems.

Capacity building for Russian science capabilities will also deliver substantial impact from our research. The extent and nature of permafrost in karst areas of Siberia over the Pliocene-Pleistocene period is best elucidated using U series dating - yet these skills are absent from Irkutsk's Institute of the Earth's Crust, despite having the technological infrastructure. To build capacity in this regard we propose to host a Russian researcher in Oxford for a two month period to learn U-Th dating both to assist to the analysis of our new field samples, but ultimately to return to set up techniques for future Russian focused, and locally led, research.

'On the ground' in Siberia, the existing fieldwork programme of P-I A. Vaks (through a NERC Fellowship NE/G013829/1, joint Royal Society grant JP080831 and Russian Foundation of Basic Research grant 09-05-92605 KO_a) has allowed us to develop strong links with regional (Siberian) scientific community which were important partners in the research, conferences and scientific publications being in preparation now. It also has provided some employment to local students and cavers to gather samples and monitor cave temperature year-round. In the final months of the project, we propose to consolidate these links by convening a meeting at the Irkutsk offices of the Siberian Branch of Russian Academy of Sciences (RAS) to disseminate results and initiate further interaction with a wider community. We expect to organise the meeting through our Irkutsk colleagues from the RAS, but will aim to bring in broader groups of stakeholders including politicians and industry. Industry, for example, will have particular focus on energy companies reliant on permafrost for infrastructure.

Oxford has a highly effective press office, with one officer dedicated to the work of the division that includes the Earth Sciences department. The Oxford science press officer also runs the Oxford Science Blog that has a wide reach (including a Facebook presence) and aims to communicate to the public, via the Internet, current research outputs by Oxford researchers. Oxford is now also part of i-Tunes U, with considerable potential for the dissemination of material to the global public in the form of downloads and podcasts. We will also populate the NERC Science Impacts Database and draft a pop science article for publication in NERC's Planet Earth magazine. Routine dissemination of research outputs from the project will include the publication of peer reviewed scientific papers and the presentation of research results at international conferences and smaller, more specialised workshops/meetings.