A regional analysis of new production on the northwest European shelf using oxygen fluxes and a ship of opportunity

Seasonal new production (g C m?2) estimates obtained from dissolved oxygen and nitrate concentrations in surface waters (5 m depth) along a track between the UK (Portsmouth) and northern Spain (Bilbao) are compared. An oxygen flux method, in combination with a ship of opportunity (SOO), was tested on the northwest European shelf for its value in distinguishing high production in frontal regions. Dissolved oxygen, nitrate and chlorophyll a samples were collected monthly from February to July 2004, alongside continuous autonomous measurements of salinity, temperature and chlorophyll fluorescence. Depth integrated new production estimates for all the individually analysed hydrographic regions of the route were produced.Results from three widely used gas-exchange parameterizations gave seasonal (February–July) new production estimates of 54–68 g C m?2 for the Ushant region of the western English Channel and 31–40 g C m?2 for the shelf slope, averaging 24–31 g C m?2 for the route. This is double the route average obtained using the nitrate assimilation method (17 g C m?2) and within the ranges of previous estimates in the same region. The oxygen flux method gave a fivefold enhancement compared to the nitrate method in the Ushant frontal region and a threefold enhancement in the English Channel and shelf break regions. Determining oxygen fluxes to estimate new production may be more reliable than nitrate assimilation in active tidal or frontal regions of shelves where nitrate may be added to the system post-winter through advection or entrainment. <br/

A study of gas exchange during the transition from deep winter mixing to spring bloom in the Bay of Biscay measured by continuous observation from a ship of opportunity

Monitoring from ships of opportunity allows a wide range of parameters to be measured, thereby extending the coverage of operational oceanographic studies. Observation of dissolved oxygen using new sensors offers an effective way of monitoring changes in biological production. The limits of the application were tested following the transition from winter storms to the spring bloom (2007). Calculation of dissolved nitrogen enables changes in gas saturation due to physical and biological processes to be separated. By combining these measurements with data from numerical models and Argo floats the critical role of subsurface processes in determining rates of change at the surface can be assessed

Assessing trends in nutrient concentrations in coastal shelf seas: a case study in the Irish Sea

Single point time-series data collected in the Irish Sea since 1954 by Allen et al. (1998) have been re-evaluated using more recent data and areal winter surveys of the Celtic and Irish Seas. Survey data illustrate the heterogeneity of nutrient distributions with N (?28 M) and P (2·0 M) enrichment of the eastern Irish Sea relative to the western Irish Sea (7–8 M N and 0·7 M P). Salinity nutrient relationships demonstrate distinct regional differences throughout the two seas. Trends in the Isle of Man time-series are unlikely to have resulted from changes in analytical procedures and personnel. Concerns over data quality cannot be resolved and there are no independent data to validate the time-series. Including more recent data shows P has declined since the late 1980s and N concentrations have remained stable since the mid 1970s. The absence of a Si trend is consistent with limited anthropogenic influence on riverine Si concentrations. Trends in N and P are consistent with changes in riverine concentrations of these two nutrients and the biogeochemical processes controlling their cycling in shelf waters. Denitrification is the most likely reason for offshore Irish Sea concentrations of N being lower than expected