Land and ocean nutrient and carbon cycle interactions

The biosphere’s uptake and storage of carbon have the potential to either slow or amplify global warming providing a carbon-climate feedback to global warming. The interactions between carbon (C) and the nutrient cycles, especially nitrogen (N) and phosphorus (P), are important to the biosphere’s storage of carbon. The century-scale carbon-climate feedback of the land is projected to be an order of magnitude greater than the ocean; however, the land’s importance may have been overestimated as they are based on models that neglect nutrient limitation. The omission of N limitation reduces the negative carbon-climate feedback by up to 30%, and further, we postulate as N-deposition and N-fixation increase, P limitation will become important in limiting the future land carbon-climate feedback. Process-based C, N and P land models are needed to realistically project this century carbon-climate feedback. In the ocean, the carbon and nutrient cycles are tightly coupled as a result of low living biomass relative to its annual turnover. With rapid recycling of carbon and nutrients, the ocean carbon-climate feedback is weak at the century time-scale. The land and ocean C, N and P cycle models (earth system models) are needed for both improvement of projections of climate change and more realistic investigation of the impact of climate change on land and ocean ecosystems. An earth system modelling approach can also help to assess the impact of different processes on carbon and nutrient cycling, and identify where improved process-understanding is needed.