98
Stringent measures are consequently taken to minimize biological fouling of
vehicles and sensors deployed in near-surface waters, particularly for extended
deployment.
Antifouling (AF) technologies are directed toward the mechanical and biocidal
prevention of adhesion of marine organisms to working surfaces. Application of
either biocide-containing coatings or silicone or fluorinated polymer fouling release
coatings (Salta et al. 2013; Delauney et al. 2010) follows standard practices developed in the maritime and offshore petroleum industries. Biocide coatings may be
based on toxic metal oxides or complexes such as the various copper or zinc formulations available commercially. Tributyltin was once in widespread use but its severe
environmental effects have resulted in tight restrictions on its use. The organometallic complex zinc pyrithione and the photosynthesis-inhibiting thiazine irgarol are
sometime used in conjunction with copper formulations. Self-polishing or ablative
paints are designed so that the coating slowly wears off while the structure is in
movement or subject to moving water. Hard paints, usually epoxy based, contain
high metal concentrations and do not wear off. However, the metal eventually
becomes oxidized and loses efficacy. In either case, recoating becomes necessary at
temporal ranges of months to years depending on the efficacy of the coating and the
challenge of the environment.
While many such formulations are effective in preventing macro-biofouling, less
success has been achieved in preventing micro-biofouling. Hydrophobic surfaces
such as the silicone release coatings have been found to be ineffective in preventing
bacterial adhesion. Diatoms, particularly the genus Amphora, have proven to be
quite resistant to both the biocidal and fouling release coatings but susceptible to
copper ablative formulations when in movement during dynamic tests.
For long-term deployment, metallic copper, an effective biocide, is used to sheath
instrument housings in the form of commercially available copper foil with an adhesive backing for ease of application. Other more sensitive and intricately fabricated
exposed parts may be surrounded by copper mesh (Fig. 2.14). Antifoulant cartridges
containing tributyltin (TBT), an organometallic biocide, are used in flow-through
conductivity cells to combat fouling. Optical instruments may be fitted with
mechanically operated rubber wipers to periodically remove fouling from optical
windows or copper shutters may be installed opening only for measurements. Active
means of sensor protection include chlorine gas sterilization through chloride ion
reduction at electrolytic anodes in close proximity to the subject sensor, or by periodically delivering small aliquots of acid to the sensor region (Delauney et al. 2010).
Other energy intensive methods such as periodic heating and increases of water
current flow to prevent larval settlement have been proposed and tested (Galler
1969) but are not in use for ocean observing at present.
Ocean gliders pose a unique case of vulnerability to biofouling due to their
extended missions and repeated near-surface operation. Rubber-like nonstick materials have performed well in extend glider operations. The historic Atlantic Ocean
crossing in 2009, a 4600 mile journey, performed by a Rutgers University RU
Slocum glider (Lobe et al. 2010) provided a test bed for such surfaces in ocean
observing operations. Coated surfaces suffered minimal fouling, while uncoated
4 Environmental Constraints to Instrumental Ocean Observing: Power Sources…
Stringent measures are consequently taken to minimize biological fouling of
vehicles and sensors deployed in near-surface waters, particularly for extended
deployment.
Antifouling (AF) technologies are directed toward the mechanical and biocidal
prevention of adhesion of marine organisms to working surfaces. Application of
either biocide-containing coatings or silicone or fluorinated polymer fouling release
coatings (Salta et al. 2013; Delauney et al. 2010) follows standard practices developed in the maritime and offshore petroleum industries. Biocide coatings may be
based on toxic metal oxides or complexes such as the various copper or zinc formulations available commercially. Tributyltin was once in widespread use but its severe
environmental effects have resulted in tight restrictions on its use. The organometallic complex zinc pyrithione and the photosynthesis-inhibiting thiazine irgarol are
sometime used in conjunction with copper formulations. Self-polishing or ablative
paints are designed so that the coating slowly wears off while the structure is in
movement or subject to moving water. Hard paints, usually epoxy based, contain
high metal concentrations and do not wear off. However, the metal eventually
becomes oxidized and loses efficacy. In either case, recoating becomes necessary at
temporal ranges of months to years depending on the efficacy of the coating and the
challenge of the environment.
While many such formulations are effective in preventing macro-biofouling, less
success has been achieved in preventing micro-biofouling. Hydrophobic surfaces
such as the silicone release coatings have been found to be ineffective in preventing
bacterial adhesion. Diatoms, particularly the genus Amphora, have proven to be
quite resistant to both the biocidal and fouling release coatings but susceptible to
copper ablative formulations when in movement during dynamic tests.
For long-term deployment, metallic copper, an effective biocide, is used to sheath
instrument housings in the form of commercially available copper foil with an adhesive backing for ease of application. Other more sensitive and intricately fabricated
exposed parts may be surrounded by copper mesh (Fig. 2.14). Antifoulant cartridges
containing tributyltin (TBT), an organometallic biocide, are used in flow-through
conductivity cells to combat fouling. Optical instruments may be fitted with
mechanically operated rubber wipers to periodically remove fouling from optical
windows or copper shutters may be installed opening only for measurements. Active
means of sensor protection include chlorine gas sterilization through chloride ion
reduction at electrolytic anodes in close proximity to the subject sensor, or by periodically delivering small aliquots of acid to the sensor region (Delauney et al. 2010).
Other energy intensive methods such as periodic heating and increases of water
current flow to prevent larval settlement have been proposed and tested (Galler
1969) but are not in use for ocean observing at present.
Ocean gliders pose a unique case of vulnerability to biofouling due to their
extended missions and repeated near-surface operation. Rubber-like nonstick materials have performed well in extend glider operations. The historic Atlantic Ocean
crossing in 2009, a 4600 mile journey, performed by a Rutgers University RU
Slocum glider (Lobe et al. 2010) provided a test bed for such surfaces in ocean
observing operations. Coated surfaces suffered minimal fouling, while uncoated
4 Environmental Constraints to Instrumental Ocean Observing: Power Sources…