Abstract
Superoxide (O2−) is a key intermediate in the cycling of organic matter and trace metals in natural waters but production rates are difficult to determine due to low steady-state concentrations, rapid decay rates, and unstable standards. On the other hand, superoxide’s dismutation product, hydrogen peroxide (H2O2), is relatively stable in filtered water. Thus, if the stoichiometry between O2− and H2O2 is known, one can derive superoxide data from H2O2 measurements. The relationship between O2− and H2O2 remains uncertain in seawater but work by Petasne and Zika (1987) presented a method for examining the relationship between O2− and H2O2 during irradiations of coastal seawater using superoxide dismutase (SOD), which forces a 2:1 stoichiometry between O2− and H2O2. Here we report the first O2− apparent quantum yield (AQY) spectra following their approach; performing irradiations of various fresh and seawater samples and measuring H2O2 accumulation with and without added SOD. For all but a single riverine sample, H2O2 AQY spectra fell in a narrow range, but O2− AQY spectra varied such that O2−:H2O2 ratios were always greater than 2 and were highest for the clear waters of the Gulf Stream (~3.4 O2− per H2O2 generated). Because this approach eliminates the need to measure O2− production rates directly, it represents a simple way to refine the stoichiometric relationships that would potentially allow global estimates of O2− photoproduction rates, O2− steady-state concentrations ([O2−]ss), and related surface ocean redox reactions based on more manageable H2O2 photochemical studies.
Highlights
It is well-known that hydrogen peroxide (H2O2) in natural waters largely results from thermal reactions involving superoxide (O−2 ) (Kieber et al, 2003)
We presented one such method to assess the photochemical production of both superoxide and hydrogen peroxide in early 2014 (Powers and Miller, 2014) by blending UV optics derived from remotely sensed ocean color data, modeled solar irradiances and H2O2 apparent quantum yield (AQY) spectra to generate monthly climatologies for both
H2O2 AQY values fell in a narrow range for South Atlantic Bight (SAB) seawater samples despite a much larger range in colored dissolved organic matter (CDOM) absorption coefficients (0.24 to 6.5 m−1 at 325 nm)
Summary
It is well-known that hydrogen peroxide (H2O2) in natural waters largely results from thermal reactions involving superoxide (O−2 ) (Kieber et al, 2003). It is clear that in order to fully understand the role of O−2 in marine biogeochemical cycling its production and decay must be modeled on global scales We presented one such method to assess the photochemical production of both superoxide and hydrogen peroxide in early 2014 (Powers and Miller, 2014) by blending UV optics derived from remotely sensed ocean color data, modeled solar irradiances and H2O2 apparent quantum yield (AQY) spectra to generate monthly climatologies for both. As the 30th anniversary of the Petasne and Zika (1987) study aHp2pOro2aacnhdesd, weteerhmavineerde-tehvealfiurasttedOt−2heApQoYrtisopneicntgrabefotwlloeewninOg−2thaneidr approach: irradiation of seawater samples and measurements of H2O2 production with and without added SOD Because this method eliminates the need to measure O−2 production rates directly, it may be a simple way to refine estimates of (O[O−2 −2p]hsso)tionprthoeduoccteiaonn. Because this method eliminates the need to measure O−2 production rates directly, it may be a simple way to refine estimates of (O[O−2 −2p]hsso)tionprthoeduoccteiaonn. rates and O−2 steady-state concentrations
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
