Abstract
The global oceans are considered a major sink of atmospheric carbon dioxide (CO2). Rain is known to alter the physical and chemical conditions at the sea surface, and thus influence the transfer of CO2 between the ocean and atmosphere. It can influence gas exchange through enhanced gas transfer velocity, the direct export of carbon from the atmosphere to the ocean, by altering the sea skin temperature, and through surface layer dilution. However, to date, very few studies quantifying these effects on global net sea-air fluxes exist. Here, we include terms for the enhanced gas transfer velocity and the direct export of carbon in calculations of the global net sea-air fluxes, using a 7-year time series of monthly global climate quality satellite remote sensing observations, model and in-situ data. The use of a non-linear relationship between the effects of rain and wind significantly reduces the estimated impact of rain-induced surface turbulence on the rate of sea-air gas transfer, when compared to a linear relationship. Nevertheless, globally, the rain enhanced gas transfer and rain induced direct export increase the estimated annual oceanic integrated net sink of CO2 by up to 6%. Regionally, the variations can be larger, with rain increasing the estimated annual net sink in the Pacific Ocean by up to 15% and altering monthly net flux by > ± 50%. Based on these analyses, the impacts of rain should be included in the uncertainty analysis of studies that estimate net sea-air fluxes of CO2 as the rain can have a considerable impact, dependent upon the region and timescale.
Highlights
The sea-air exchange of the greenhouse gas carbon dioxide (CO2) is a critical part of the climate system and a major factor in the biogeochemical development of the oceans
The FluxEngine has been validated with previous outputs in this research field [6] and these annual net integrated values are consistent with the original publication of Takahashi et al [13]
When the CO2 climatology was used to study subsequent years, applying sea surface temperature (SST), wind and other data from each year, the annual values are consistently negative and between -1 Pg C yr-1 and -1.6 Pg C yr-1, i.e. the global ocean is a net sink of CO2 (Figs 1 and 2 and Table 1)
Summary
The sea-air exchange of the greenhouse gas carbon dioxide (CO2) is a critical part of the climate system and a major factor in the biogeochemical development of the oceans. It is widely accepted that more accurate and higher resolution calculations of these gas exchanges (fluxes) are required if we are to fully understand and predict our future climate. Such knowledge is required for understanding and monitoring chemical water quality (e.g. in relation to ocean acidification). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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