Scottish Marine and Freshwater Science Volume 5 Number 1: UK Ocean Acidification Coastal Monitoring Network - Expanding the Network - Defra Contract C5801/ME5309

Conclusions

1. There is a requirement for a commitment to long-term monitoring of carbonate chemistry at sites in coastal, inshore and offshore waters to distinguish long-term anthropogenic signals from short-term spatial and temporal variability.

2. The use of automated water samplers deployed on instrumented moorings for the collection of water samples for DIC analysis was trialled by AFBI at their mooring in 2013. DIC concentrations were lower for samples collected by the automated water sampler, which may be as a consequence of the effect of longer storage. Results demonstrated that this methodology is not an advanced enough stage to permit routine use. A further, more detailed comparison should be undertaken to include a moored sampler with sample preservation, the introduction of a procedure to minimise aeration of samples during processing and filtration, a more robust analytical procedure with regular quality control and precise judgement of depth and sample timing.

3. TA and DIC have been measured at MSS's long term monitoring site at Stonehaven since 2009. A seasonal trend was observed for both TA and DIC in nearly all years. TA concentrations reach a maximum around the spring bloom while DIC concentrations were lowest during this period. However, in 2012 no seasonal cycle was observed and there is no indication it has returned for TA in 2013. The long-term monitoring at Stonehaven highlights the need for robust data set to distinguish temporal variability.

4. Discrete water samples were collected in the Minch North between January and August 2013 . Both TA and DIC concentrations dropped during May. Analysis for chlorophyll-a indicated there was an algal bloom at the end of May beginning of June. Although you would expect a decrease in DIC, TA concentrations would be expected to increase around an algal bloom and it is unclear why the concentration decreased.

5. Discrete water samples were collected at the three buoys (Celtic Deep, Liverpool Bay and AFBI mooring) in March (except Celtic Deep), May and August 2013 by AFBI. TA and DIC concentrations were higher at the offshore buoys (Celtic Deep and AFBI mooring) than at the coastal sites (Liverpool Bay and Stonehaven).

6. The initial six month sampling period financed by UK- IMON does not allow for observation of seasonal trends, but informs the design of future long-term monitoring programmes.