Carbon monoxide apparent quantum yields and photoproduction in the Tyne estuary

Abstract

Abstract. Carbon monoxide (CO) apparent quantum yields (AQYs) are reported for a suite of riverine, estuarine and sea water samples, spanning a range of coloured dissolved organic matter (CDOM) sources, diagenetic histories, and concentrations (absorption coefficients). CO AQYs were highest for high CDOM riverine samples and almost an order of magnitude lower for low CDOM coastal seawater samples. CO AQYs were between 47 and 80% lower at the mouth of the estuary than at its head. Whereas, a conservative mixing model predicted only 8 to 14% decreases in CO AQYs between the head and mouth of the estuary, indicating that a highly photoreactive pool of terrestrial CDOM is lost during estuarine transit. The CDOM absorption coefficient (a) at 412 nm was identified as a good proxy for CO AQYs (linear regression r 2 > 0.8; n = 12) at all CO AQY wavelengths studied (285, 295, 305, 325, 345, 365, and 423 nm) and across environments (high CDOM river, low CDOM river, estuary and coastal sea). These regressions are presented as empirical proxies suitable for the remote sensing of CO AQYs in natural waters, including open ocean water, and were used to estimate CO AQY spectra and CO photoproduction in the Tyne estuary based upon annually averaged estuarine CDOM absorption data. A minimum estimate of annual CO production was determined assuming that only light absorbed by CDOM leads to the formation of CO and a maximum limit was estimated assuming that all light entering the water column is absorbed by CO producing photoreactants (i.e. that particles are also photoreactive). In this way, annual CO photoproduction in the Tyne was estimated to be between 0.99 and 3.57 metric tons of carbon per year, orCorrespondence to: A. Stubbins (aron.stubbins@skio.usg.edu) 0.004 to 0.014% of riverine dissolved organic carbon (DOC) inputs to the estuary. Extrapolation of CO photoproduction rates to estimate total DOC photomineralisation indicate that less than 1% of DOC inputs are removed via photochemical processes during transit through the Tyne estuary.

Marine Photochemistry of Organic Matter

“…For example, in a salinity transect in the Delaware Estuary (from salinity 3 to 21), AQYs at 350 nm were remarkably constant, at about 1 × 10 −4 mol DIC (mol quanta) −1 (±~10% RSD), while corresponding CO AQYs decreased by a factor of about 1.6 with increasing salinity (from ~1.6 × 10 −5 mol CO (mol quanta) −1 to ~1.0 × 10 −5 mol CO (mol quanta) −1 ), suggesting that DIC and CO are formed by different photochemical mechanisms (White et al, 2010). A similar decrease in CO AQYs down a temperate estuary was observed by Stubbins et al (2011).…”

Variability of carbon monoxide and carbon dioxide apparent quantum yield spectra in three coastal estuaries of the South Atlantic Bight

“…5). This is in contrast to other studies in the St. Lawrence River estuary (Zhang et al, 2006), the Beaufort Sea (Xie and Zafiriou, 2009) and the Tyne River estuary (Stubbins et al, 2011). These studies did not address CO 2 photochemistry, but all three found an increase in CO AQY values with increasing CDOM absorption coefficients using transect data from high absorption (upper estuary) to low absorption (coastal) waters.…”

“…Each have shown a decrease in the photochemical efficiency of CO production with decreasing salinity. Stubbins et al (2011) also found an inverse trend between CO AQYs and salinity in the Tyne River estuary. This was not explained by simple conservative mixing and suggests that this relationship is more strongly tied to CDOM.…”

Utilizing colored dissolved organic matter to derive dissolved black carbon export by arctic rivers

“…Ultrapure water (Milli-Q) provided a blank. Blank corrected absorbance spectra were corrected for offsets due to scattering and instrument drift by subtraction of the average absorbance between 700 and 800 nm (Stubbins et al, 2011). Data output from the spectrophotometer were in the form of dimensionless absorbance (i.e., optical density, OD) and were subsequently converted to the Napierian absorption coefficient, a (m −1 ) (Hu et al, 2002).…”