The influence of short-term variability in surface water on modelled air–sea exchange

Abstract

Coastal seas and estuarine systems are highly variable in both time and space and with their heterogeneity difficult to capture with measurements. Models are useful tools in obtaining a better spatiotemporal coverage or, at least, a better understanding of the impacts such heterogeneity has in driving variability in coastal oceans and estuaries. A model-based sensitivity study is constructed in this study in order to examine the effects of short-term variability in surface water p on the annual air–sea exchange in coastal regions. An atmospheric transport model formed the basis of the modelling framework for the study of the Baltic Sea and the Danish inner waters. Several maps of surface water p were employed in the modelling framework. While a monthly Baltic Sea climatology (BSC) had already been developed, the current study further extended this with the addition of an improved near-coastal climatology for the Danish inner waters. Furthermore, daily surface fields of p were obtained from a mixed layer scheme constrained by surface measurements of p (JENA). Short-term variability in surface water p was assessed by calculating monthly mean diurnal cycles from continuous measurements of surface water p, observed at stationary sites within the Baltic Sea. No apparent diurnal cycle was evident in winter, but diurnal cycles (with amplitudes up to 27 atm) were found from April to October. The present study showed that the temporal resolution of surface water p played an influential role on the annual air–sea exchange for the coastal study region. Hence, annual estimates of exchanges are sensitive to variation on much shorter time scales, and this variability should be included for any model study investigating the exchange of across the air–sea interface. Furthermore, the choice of surface p maps also had a crucial influence on the simulated air–sea exchange.

Keywords:

• Air–sea exchange
• carbon dioxide
• coastal zone
• Baltic Sea
• temporal resolution

Acknowledgements

Our utmost gratitude to Joachim Kuss, of the Leibniz Institute for Baltic Sea Research, for sharing the surface water p continuous measurements from the Arkona Sea platform. Christian Rödenbeck is appreciatively acknowledged for providing daily global maps of surface water p, for which we also extend our acknowledgement to the SOCAT data base. NOAA ERSL CarbonTracker, version CT2013B, has greatly contributed to this work, as have GLOBALVIEW-CO2, 2013, and EDGAR, IER and Aarhus University for the emissions inventories for fossil fuel emissions. Peter Stæhr and Cordula Göke at Department of Bioscience, Aarhus University, are gratefully thanked for their assistance in creating the near-coastal Danish climatology of surface water p. We are thankful for the very constructive comments from two anonymous reviewers that helped to improve and clarify the manuscript.

Notes

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was carried out as part of a PhD study within the Danish ECOCLIM project. This work was supported by the Danish Strategic Research Council [grant number 10-093901].