Hydrogen Peroxide (H2O2) is an important oxidant species in both the atmosphere and the surface ocean.The dominant source term in seawater is formation via dismutation reactions from the more reactive superoxide (O2 - ) – itself a product of photochemically induced reactions between organic matter and dissolved O2.In the surface ocean H2O2 can also be produced by biochemical processes in phytoplankton,which are also the major sink term for H2O2 via catalase and peroxidase activity.Knowledge of H2O2 concentrations in the ocean are important for understanding trace metal redox cycling and the role of photochemistry and mixing in surface waters.As part of preliminary German SOLAS work we have examined the distribution,diel cycling and decomposition kinetics of H2O2 in surface waters in the Atlantic,from the tropics to the Southern Ocean.Recent results will be presented on H2O2 dynamics from a variety of environments: (i) EIFEX a Southern Ocean Iron Enrichment Experiment and from (ii) Extensive field work in the Tropical Atlantic (iii) A recent north-south transect in the Eastern Atlantic.