PETRA

Description

The Arctic Ocean is exceptionally susceptible to climate change. Recent studies have shown that surface seawater is warming faster than in other oceans. In addition, atmospheric CO₂ dissolution in seawater is causing Ocean Acidification (OA). The documented retreat of sea-ice will increase light penetration, including UV. These environmental parameters (temperature, OA and UV) are highly likely to act as stressors and alter the Arctic Ocean ecosystem structure and function which in turn will feed back on climate.

One such feedback is the cycling of climatically active trace gases and their emission to the atmosphere (here: CH₄, N₂O, DMS, CO). These trace gases are rapidly produced and consumed by a number of physical and biological processes. For example, the biggest source of CO in surface seawater is via UV-induced photochemical reactions. Yet, the likely response of trace gas cycling to climate change remains largely unexplored. This hinders our ability to predict the future direction of this important climate-feedback. We propose to investigate this feedback by a) developing the basic understanding which will underpin a predictive tool, and b) developing the predictive tool itself (computer model).

We will achieve this using three complimentary tools:

• Firstly, novel, high-tech spatial observations of trace gases (with depth as well as horizontal) which will allow us to identify major controls on their cycles and estimate their present flux to the atmosphere.
• Secondly, direct experiments where the three stressors will be manipulated while trace gas cycling pathways are monitored. The novelty of our approach lies in the use of individual and combined stressor manipulation (e.g. OA alone versus high temperature and OA together). This will allow us to explore potential synergistic or antagonistic effects between stressors. We will use state-of-the-art chemical and biological observations to track changes in trace gas cycling. For example, we will monitor the abundance and activity of key genes involved in trace gas cycling. These experiments will give us explicit and refined understanding of trace gas cycling in relation to the stressors.
• Thirdly, we will employ computer modelling which will translate this understanding into a predictive tool that will be used to predict the impact of future climate change.

To rapidly translate our relevant findings to policy, we will engage with the public, policymakers, international science programmes and Intergovernmental Panel on Climate Change (IPCC) through our comprehensive impact plan.

Objectives

During this project we will investigate the impact of three stressors (temperature, ocean acidification and elevated irradiation) on the production and consumption of the climatically active gases nitrous oxide (N₂O), methane (CH₄), dimethyl sulphide (DMS) and carbon monoxide (CO) in the marine environment. Each stressor is directly or indirectly associated with the anthropogenic CO₂ burden to the atmosphere and will be investigated individually and in combination with the other two. Observational and experimental procedures will be undertaken in the Arctic Ocean, with fieldwork proposed for east of Svalbard in the Barents Sea and east of Greenland in the region of the Fram Strait. The Arctic Ocean provides an important region for the exchange of these important trace gases with the atmosphere, and factors controlling their release have been demonstrated to be sensitive to the impacts of climate change.

This study will include the disciplines of trace gas analyses, carbon and nitrogen biogeochemistry and molecular biology. An integrated modelling component will utilise ecosystem models to further our understanding of the impact of these stressors on mechanisms of consumption and production.

The overall aim of PETRA is to investigate the role of (multiple) stressors for future trace gas (i.e. N₂O, CH₄, DMS and CO) cycling in the Arctic Ocean. Specific aims to be addressed are (listed in order of priority):

• to determine how stressors (warming, acidification, light) affect future trace gas production and consumption pathways,
• to determine the surface ocean and depth distributions of the trace gases listed above,
• to determine the relevance of air/sea gas emissions for the regional (Arctic) and global atmospheric trace gas budgets,
• to provide improved models of the mechanistic understanding of stressors on trace gas fluxes, which will provide the basis for increased understanding of the regional and global importance of these gases.

To address these objectives we have designed a comprehensive research programme that includes two research cruises to the Arctic Ocean, numerical modelling and an integral pathway-to-impact component. Our research programme is thus divided into four complimentary work packages, each with specific objectives which are outlined below.

Work Package 1

a) To characterise the horizontal and vertical distribution of climatically active gases N₂O, CH₄, DMS and CO in waters of the Arctic Ocean.

b) To determine their co-variability with natural conditions of the physical environment (e.g. temperature, pCO₂, pH, irradiance), the phytoplankton community composition and trace gas-relevant microbial processes.

Work Package 2

To determine the air-sea exchange of climatically active trace gases in the Arctic Ocean by improving understanding of the control of these fluxes by sea-ice.

Work Package 3

To perform ship-based experimental manipulations over policy relevant conditions (RCP 4.5 and 8.5) in order to assess the impact of increasing temperature, ocean acidification and irradiance on the production and consumption of climatically active gases N₂O, CH₄, DMS and CO.

Work Package 4

a) To perform process based modelling of multiple stressor impacts on the production and consumption of climatically active gases.

b) To assess the relative importance of single and combined stressors on trace gas production.

In addition, to translate our scientific findings into societal impact, we will transfer state-of-the-art understanding of ocean ecosystem functions and implications to climate to key stage 3 – 5 students, key stakeholders and policy makers, by a variety of communication mechanisms.