Abstract. The late Quaternary history of water-column denitrifcation of the eastern Pacific margins and the Arabian Sea is reconstructed using sedimentary •515N measurements. The •515N values in six piston cores raised from these regions show remarkably similar cyclic variations, being heavy (9-10.5%o) during the interglacials and 2-3%0 lighter during the glacials. This implies that denitrification in these regions decreased substantially during the glacial periods. The glacial decline in denitrification is attributed to reduce• upwelling and flux of organic material through the oxygen minimum zone. Since water-column denitrification in these areas accounts for about half of the fixed-nitrogen loss in the modem ocean, the inferred decrease in denitrification should have increased the oceanic nitrate inventory during glacial periods. Because nitrate is a limiting nutrient, oceanic productivity and attendant changes in CO2 may therefore have been modulated on glacial-interglacial timescales by variations in the oceanic NO3-content.

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A water balance study was used for determining recharge rate and mechanisms in the Enler Catchment, Northern Ireland. Here spatially limited data for the water balance resulted in varied calculation of the annual and monthly net infiltration rate. This paper outlines a method whereby high-resolution soil profiles (1 to 2 cm) were obtained from field cores in the upper 2 m of the unsaturated zone using delta 18O of water. These profiles show changes in isotopic composition that range from individual rainfall events to annually integrated cycles of rainfall. Recharge rates were calculated from stable isotope profiles for each of the four main soil types in the study catchment and summed over each area resulting in an average recharge in the range 55 to 70 mm/a, which is comparable with previous findings. Applied isotopic tracer tests were also conducted to evaluate the extent of preferential flow through the two main soil types in the catchment. Rates of water movement found from these experiments show good agreement with natural isotopic profiles; however, evidence suggests that preferential flow is not the dominant process controlling water movement in this catchment. This type of data provides valuable information about recharge rates and mechanisms and may facilitate better prediction of contaminant transport pathways in the vadose zone.