- Methane release at very low flow rates over too wide an area.
- Release at very high rates over a small area such as a well blow-out.
- Rough seas during deployment.
- The presence of obstructions such as wreckage, rock outcrops, munitions or steep slopes.
- Fast, variable-direction or unpredictable currents.
- Equipment sinking into very soft ooze on the seabed.
- Hydrogen sulphide toxicity.
- Unacceptable biological consequences due to the presence of equipment.
- The need to recover everything at some date in the future.
- The pressure ridges shown by Peter Wadhams at the Chiswick workshop.
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Frankenberg, C., I. Aben, P. Bergamaschi, E. J. Dlugokencky, R. van Hees, S. Houweling, P. van der Meer, R. Snel P. Dol (2011), Global column-averaged methane mixing ratios from 2003 to 2009 as derived from SCIAMACHY: Trends and variability, Journal of Geophysical Research-Atmospheres, 116(D04302), 1-12, 10.1029/2010JD014849.
Montzka, S. A., E. J. Dlugokencky and J. H. Butler (2011), Non-CO2 greenhouse gases and climate change, NATURE, 476, 43-50, 10.1038/nature10322.