Hydrogen peroxide concentrations in relation to optical properties in a fiord (Doubtful Sound, New Zealand)

Abstract

Hydrogen peroxide concentrations are reported for the first time in the surface low salinity layer (LSL) and underlying saline layer (SL) of a fiord. Measurements were made in Deep Cove and Hall Arm in Doubtful Sound, New Zealand under contrasting climatic conditions in early summer (October; wet, windy, and dull: November; dry, still, and sunny). Steady state peroxide concentrations in the range 100-400 nM rapidly declined with depth in the LSL and across the LSL/SL interface. Spectral measurements of absorption coefficients and downwelling irradiance indicated this is largely because of high levels of chromophoric dissolved organic matter (CDOM) in the LSL filtering out the UV component (<400 nm) of the sunlight that is mainly responsible for the photochemical formation of peroxide. The depth dependence of peroxide concentrations in the LSL was similar to that of the CDOM concentrations as measured by the corrected absorption coefficent at 340 nm. During the October sampling event there also appeared to be a contribution to the peroxide levels in the LSL at Deep Cove arising from the input of rainwater containing high levels of peroxide (1.7-7.5 μM).