Analysis of Nitrite Concentrations Over Time in the Eastern Tropical North Pacific

Abstract

The Oxygen Minimum Zone in the Eastern Tropical North Pacific is the largest and most intense in the world. The lack of oxygen causes bacteria to respire anaerobically and therefore changes the nitrogen cycle. Nitrite has previously been measured in this zone 4 times from 1972 to 2012. I collected and compared data from 2016/17 to previous data and conclusions. In particular, data was collected from a profile at a time series station for direct comparison to the 2012 data. In 2012 the maximum nitrite concentration in the area was 8.51 μmol/L and the maximum at the time series station was 5.86 μmol/L whereas in 2016/17 the maximum concentration in the area was 4.13 μmol/L and the maximum at the time series station was 1.51 μmol/L. The data from 2012 showed nitrite concentration that were much higher than previous years. However, the data from 2016/17 does not show the same high concentrations implying that 2012 may have been an anomaly. The data from the time series station was then used as representative of the study area for an analysis of how the area of high nitrite changes in spatial area and intensity given the changes in maximum nitrite concentration. Using GLODAP data in ODV nitrite concentrations were raised by a constant proportion for 2012 and 2016/17 forcing the maximum nitrite concentration in the ETNP to match the concentration measured at the time series station for each year respectively. Based on this simple analysis it is shown that while more data is needed it is likely that when the maximum nitrite concentration increases, the zone of high nitrite concentration both expands and intensifies.