Deep Ocean Gas Exchange Experiment

Project Description
The rates at which gases exchange between the oceans and the atmosphere are extremely important to global biogeochemical cycles and to predicting and modelling future climate change, but quantifying them accurately currently remains elusive. Some important issues requiring accurate such estimates include the rate at which anthropogenic carbon dioxide can be taken up by the oceans, quantifying the marine sources of other important atmospheric greenhouse gases such as methane and nitrous oxide, and investigating the roles of other marine derived atmospheric gases in a range of climate and atmospheric chemistry related issues. Although advances have been made in our understanding of the gas exchange process in recent years, these advances are still not sufficient to enable us to understand and predict the effects of the major controlling processes. A major problem in the past has been that individual controlling processes have tended to be addressed in isolation, although it is clear that they are all interconnected. What is now required in order to build on past advances is a fully integrated study of the problem using a variety of state-of-the-art techniques. We will achieve this aim by bringing together for the first time, a team of UK experts with diverse interests and expertise within the field of air-sea gas exchange, but with the common goal of understanding these processes more fully. The UK SOLAS directed programme is an ideal framework within which to do this. We plan to participate in two research cruises in the North Atlantic Ocean, during which we will make a variety of key measurements and observations (measure seastate, whitecapping and wave breaking, evaluate the role of bubbles and surfactants in gas transfer, and employ a combination of direct gas flux measurement techniques for CO2, DMS, halocarbons and other gases), supported by a suite of ancillary water column and meteorological data. Our overarching strategy is to constrain these various measurements within an experiment in which we will release gaseous tracers to the water column. By measuring the rates at which these tracers escape to air we will derive important information on gas exchange rates that will provide a framework for interpreting our other measurements. Our cruises will be timed to coincide with times of maximum air-sea exchange fluxes of climatically relevant trace gases. During one of these we will release a natural surfactant along with the gaseous tracers, in order tto investigate the role of surface organic slicks, which are known to suppress air-sea gas exchange. We also anticipate the participation of a number of US-based groups with aims and measurement capabilities complimentary to our own, which will bring "added value" to the programme. However these are conditional upon external funding from NSF and other US government funding agencies.

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