BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-10-1379-2013 Technical Note: A simple method for air–sea gas exchange measurements in mesocosms and its application in carbon budgeting Czerny J. 1 Schulz K. G. 1 Ludwig A. 1 Riebesell U. 1 GEOMAR – Helmholtz Centre for Ocean Research Kiel, 24105 Kiel, Germany 01 03 2013 10 3 1379 1390 Copyright: © 2013 J. Czerny et al. 2013 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/10/1379/2013/bg-10-1379-2013.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/10/1379/2013/bg-10-1379-2013.pdf

Mesocosms as large experimental units provide the opportunity to perform elemental mass balance calculations, e.g. to derive net biological turnover rates. However, the system is in most cases not closed at the water surface and gases exchange with the atmosphere. Previous attempts to budget carbon pools in mesocosms relied on educated guesses concerning the exchange of CO<sub>2</sub> with the atmosphere. Here, we present a simple method for precise determination of air–sea gas exchange in mesocosms using N<sub>2</sub>O as a deliberate tracer. Beside the application for carbon budgeting, transfer velocities can be used to calculate exchange rates of any gas of known concentration, e.g. to calculate aquatic production rates of climate relevant trace gases. Using an arctic KOSMOS (<b>K</b>iel <b>O</b>ff <b>S</b>hore <b>M</b>esocosms for future <b>O</b>cean <b>S</b>imulation) experiment as an exemplary dataset, it is shown that the presented method improves accuracy of carbon budget estimates substantially. Methodology of manipulation, measurement, data processing and conversion to CO<sub>2</sub> fluxes are explained. A theoretical discussion of prerequisites for precise gas exchange measurements provides a guideline for the applicability of the method under various experimental conditions.

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