The Arctic is changing rapidly, and it is predicted that areas which are today tundra will become tree-covered as warming progresses, with, for example, forest spreading northwards to the coast of northern European Russia by 2100. In some parts of the Arctic, such as Alaska, this process, commonly referred to as "greening", has already been observed over the past few decades; woody shrubs are expanding their distribution northwards into tundra. Such vegetation changes influence nutrient cycling in soils, including carbon cycling, but the extent to which they will change the storage or release of carbon at a landscape scale is debated. Nor do we fully understand the role that lakes play in this system although it is known that many lakes in the tundra and northern forests are today releasing carbon dioxide and methane into the atmosphere in significant amounts, and a proportion of this carbon comes into the lake from the vegetation and soils of the surrounding landscape. Lakes form an important part of arctic landscapes: there are many thousands of them in our study areas in Russia and west Greenland, and they act as focal points for carbon cycling within in the wider landscape.

It is vital that we understand the interactions between plants, soils, nutrients, and lakes because there are massive carbon stores in the high northern latitudes, particularly in frozen soils, and if this carbon is transferred into the atmosphere (as carbon dioxide (CO2) or methane) it will create a positive feedback, driving further global warming. For this reason, the Arctic represents a critical component of the Earth System, and understanding how it will it respond to global environmental change is crucial. Lakes are a key link in this process.

As lakes are tightly coupled with terrestrial carbon cycling, changes in the flows of carbon to a lake are faithfully recorded in lake sediment records, as are changes in the biological processing of that carbon within the lake. We also know that similar vegetation changes to those observed or predicted today occurred in the past when climate was warmer than today, and thus past events can provide an analogue for future changes. This project will examine lake sediment records, using techniques that extract a range of chemical signals and microscopic plant and animal remains, to see how vegetation changes associated with past natural climate warming, such as migration of the tree-line northwards, affected lake functioning in terms of the overall biological productivity, the species composition, and the types of carbon processing that were dominant. Depending upon the balance between different biological processes, which in turn are linked to surrounding vegetation and soils, lakes may have contributed mostly to carbon storage or mostly to carbon emissions ?at a landscape scale.

Changes in vegetation type also influence decomposition of plant remains and soil development, and this is linked to nitrogen cycling and availability. Nitrogen is an important control over productivity and hence of carbon fixation and storage, and thus it is important to study the dynamics of nitrogen along with those of carbon.

Due to the spatial variability of climate and geology, the pace of vegetation development (and of species immigration) and the types of plants involved have not been uniform around the Arctic. By examining several lakes in each of three regions (Alaska, Greenland, Russia) we will be able to describe a broad range of different vegetation transitions and the associated responses of the lakes. Our results can be used to inform our understanding of the likely pathways of recently initiated and future changes. They can also be up-scaled to the whole Arctic and so contribute to the broader scientific goal of understanding feedbacks to global warming.

Potential Impact:
We have identified three main impact themes: i) contribution of scientific knowledge to national agencies; ii) knowledge exchange with indigenous communities; and iii) public education and awareness. Our geographical focus is on Alaska and Russia. Our partners in these themes are the US Geological Survey (USGS), the US National Park Service (NPS), and the Alaska Quaternary Center (AQC) in the USA, and the Komi Science Centre in Russia. This fundamental research is primarily of interest to governments of the countries in which we are working and their scientific organizations, such as geological surveys, who are engaged in research on arctic regions and on the functioning/management of the carbon cycle within their national boundaries. The USA is the most active in this respect, and we will work closely with the USGS and the NPS to ensure our findings benefit these organizations. Activities include working with Park scientists on the choice and sampling design of lakes to be studied and contributing data to the Park's monitoring programme and working with a USGS team linked into the USGS carbon program, sharing data and contributing to a USGS modelling effort.
Our work would take place in remote regions that are the traditional lands of indigenous people and/or managed as public conservations lands (Alaska). It is our experience in both Russia and Alaska that meetings with local communities and a sharing of knowledge about the local environment are appreciated by local people and advance the regard with which science is held in these communities. Detailed local knowledge of landscape and biota can contribute to the study design at the start of a project; findings discussed at the end of a project generate new local knowledge and provide a theme for educational activities in the local communities. We will establish contact with local communities via working in our study areas who best understand the local socio-political situation. Activities include community meetings prior to the start of fieldwork and at the end of the project, and development of materials for the NPS schools' programme in Native villages (Alaska) and meetings with local communities (Russia).
Science research concerning global warming and environmental issues is of general interest to the public at large. In Alaska, we will work with the Alaska Quaternary Center [AQC] at the University of Alaska, which specializes in public outreach for science, and the NPS. Activities include developing NPS public outreach materials, contributing information to subsistence boards, and working with the UAF-AQC on public lectures and media spots (Alaska), and informational meetings and media spots organized by our Russian partners. Both the USGS and NPS have excellent public websites, to which we will contribute.
Success in impact will be reflected in the following: development of work on catchment carbon modelling, contribution to the USGS carbon program via joint publication of reports, and establishment of a presence on the USGS website; successful input of observations and results to the monitoring programme and their evaluation in relation to other Park datasets; adaptation of our materials for the NPS schools programme and presence on their website and in other outreach materials; turnout at and feedback from local meetings and public lectures. A project PDRA will take training in public communication of science during the course of the project.