198
12.1 Defining of Marine Snow: An Operational Approach
Given the heterogeneous nature of marine snow, “operationally” definitions based
upon their characteristics, size(s), and methods of quantification are used by the
community (see Quigg et al. 2016). Particulate organic matter (POM) exists along a
size continuum, from nano- and microgels (Chin et al. 1998; Verdugo et al. 2004),
to TEP and other forms of extracellular polymeric substances (EPS), to large aggregates (>500 μm) called marine snow (Engel 2000; Passow 2002; Alldredge and
Silver 1988; Grossart and Simon 1993). TEP are a class of free-floating extracellular polymeric particles ubiquitous in aquatic environments (e.g., Discart et al. 2015;
Bar-Zeev et al. 2015). These acidic polysaccharide-rich particles are observable
after staining with the dye Alcian Blue. TEP have gel-like properties and are known
for their high stickiness (Engel 2000; Xavier et al. 2017), which make them a main
driver for aggregation and sedimentation (Logan et al. 1995). Since their first
description (Alldredge et al. 1993), their ubiquity and importance for carbon flux
and the sedimentation of suspended mineral particles has been extensively documented (Kranck 1973; Bar-Zeev et al. 2015; Silver 2015). In particular, their role as
the matrix within marine snow aggregates, such as those associated with declining
diatom blooms, has been investigated in detail (e.g., Passow et al. 1994; Passow and
Alldredge 1995; Passow 2002; De La Rocha and Passow 2007), but many questions
remain regarding their composition, formation, and functional role. An extensive
review of EPS was recently published by Quigg et al. (2016). Marine snow particles
are typically >500 μm (Alldredge and Silver 1988) and either produced de novo by
mucus-producing marine zooplankton, e.g., the feeding structures cast off by appendicularians (larvaceans) or pteropods (Alldredge 2005), or as the result of biologically enhanced physical aggregation of different components (e.g., phytoplankton,
feces, detritus, mineral grains) glued together by EPS, a sticky form of POM produced by bacteria and phytoplankton (Alldredge and Silver 1988; Verdugo et al.
2004; Quigg et al. 2016).
12.2 Oil-Particle Interactions
Crude oil, as well as the oil residues remaining or forming due to biodegradation,
evaporation, photooxidation, and other weathering processes, interacts with marine
particles and dissolved substances forming different types of particles (Figs. 12.1
and 12.2). Interest on the ecological significance of oil-particle interactions following oil spills can be largely attributed to the studies following the Exxon Valdez oil
spill which described “clay-oil flocculation” as a natural process responsible for the
removal of oil stranded on low-energy shoreline environments (Bragg and Yang
1995; Bragg and Owens 1995). As this process was found to occur with a range of
fine mineral particles besides those classified as clay, the term oil-mineral aggregate
(OMA) was subsequently used to describe microaggregates formed between finegrained sediment and oil (Lee et al. 1998; Stoffyn-Egli and Lee 2003). Since then
A. Quigg et al.
12.1 Defining of Marine Snow: An Operational Approach
Given the heterogeneous nature of marine snow, “operationally” definitions based
upon their characteristics, size(s), and methods of quantification are used by the
community (see Quigg et al. 2016). Particulate organic matter (POM) exists along a
size continuum, from nano- and microgels (Chin et al. 1998; Verdugo et al. 2004),
to TEP and other forms of extracellular polymeric substances (EPS), to large aggregates (>500 μm) called marine snow (Engel 2000; Passow 2002; Alldredge and
Silver 1988; Grossart and Simon 1993). TEP are a class of free-floating extracellular polymeric particles ubiquitous in aquatic environments (e.g., Discart et al. 2015;
Bar-Zeev et al. 2015). These acidic polysaccharide-rich particles are observable
after staining with the dye Alcian Blue. TEP have gel-like properties and are known
for their high stickiness (Engel 2000; Xavier et al. 2017), which make them a main
driver for aggregation and sedimentation (Logan et al. 1995). Since their first
description (Alldredge et al. 1993), their ubiquity and importance for carbon flux
and the sedimentation of suspended mineral particles has been extensively documented (Kranck 1973; Bar-Zeev et al. 2015; Silver 2015). In particular, their role as
the matrix within marine snow aggregates, such as those associated with declining
diatom blooms, has been investigated in detail (e.g., Passow et al. 1994; Passow and
Alldredge 1995; Passow 2002; De La Rocha and Passow 2007), but many questions
remain regarding their composition, formation, and functional role. An extensive
review of EPS was recently published by Quigg et al. (2016). Marine snow particles
are typically >500 μm (Alldredge and Silver 1988) and either produced de novo by
mucus-producing marine zooplankton, e.g., the feeding structures cast off by appendicularians (larvaceans) or pteropods (Alldredge 2005), or as the result of biologically enhanced physical aggregation of different components (e.g., phytoplankton,
feces, detritus, mineral grains) glued together by EPS, a sticky form of POM produced by bacteria and phytoplankton (Alldredge and Silver 1988; Verdugo et al.
2004; Quigg et al. 2016).
12.2 Oil-Particle Interactions
Crude oil, as well as the oil residues remaining or forming due to biodegradation,
evaporation, photooxidation, and other weathering processes, interacts with marine
particles and dissolved substances forming different types of particles (Figs. 12.1
and 12.2). Interest on the ecological significance of oil-particle interactions following oil spills can be largely attributed to the studies following the Exxon Valdez oil
spill which described “clay-oil flocculation” as a natural process responsible for the
removal of oil stranded on low-energy shoreline environments (Bragg and Yang
1995; Bragg and Owens 1995). As this process was found to occur with a range of
fine mineral particles besides those classified as clay, the term oil-mineral aggregate
(OMA) was subsequently used to describe microaggregates formed between finegrained sediment and oil (Lee et al. 1998; Stoffyn-Egli and Lee 2003). Since then
A. Quigg et al.