A stochastic, Lagrangian model of sinking biogenic aggregates in the ocean (SLAMS 1.0): model formulation, validation and sensitivity

We present a new mechanistic model, stochastic, Lagrangian aggregate model of sinking particles (SLAMS) for the biological pump in the ocean, which tracks the evolution of individual particles as they aggregate, disaggregate, sink, and are altered by chemical and biological processes. SLAMS considers the impacts of ballasting by mineral phases, binding of aggregates by transparent exopolymer particles (TEP), zooplankton grazing and the fractal geometry (porosity) of the aggregates. Parameterizations for age-dependent organic carbon (orgC) degradation kinetics, and disaggregation driven by zooplankton grazing and TEP degradation, are motivated by observed particle fluxes and size spectra throughout the water column. The model is able to explain observed variations in orgC export efficiency and rain ratio from the euphotic zone and to the sea floor as driven by sea surface temperature and the primary production rate and seasonality of primary production. The model provides a new mechanistic framework with which to predict future changes on the flux attenuation of orgC in response to climate change forcing

Global niche of marine anaerobic metabolisms expanded by particle microenvironments

In ocean waters, anaerobic microbial respiration should be confined to the anoxic waters found in coastal regions and tropical oxygen minimum zones, where it is energetically favourable. However, recent molecular and geochemical evidence has pointed to a much broader distribution of denitrifying and sulfate-reducing microbes. Anaerobic metabolisms are thought to thrive in microenvironments that develop inside sinking organic aggregates, but the global distribution and geochemical significance of these microenvironments is poorly understood. Here, we develop a new size-resolved particle model to predict anaerobic respiration from aggregate properties and seawater chemistry. Constrained by observations of the size spectrum of sinking particles, the model predicts that denitrification and sulfate reduction can be sustained throughout vast, hypoxic expanses of the ocean, and could explain the trace metal enrichment observed in particles due to sulfide precipitation. Globally, the expansion of the anaerobic niche due to particle microenvironments doubles the rate of water column denitrification compared with estimates based on anoxic zones alone, and changes the sensitivity of the marine nitrogen cycle to deoxygenation in a warming climate

Marine Oil Snow Sedimentation and Flocculent Accumulation (MOSSFA) Events: Learning from the Past to Predict the Future

Despite interest as early as in the 1880s, it was not until 1953 that Tokimi Tsujita (Seikai Fisheries Research Laboratory, Japan) was able to carefully collect and describe the matrix of microorganisms embedded in suspended organic matter (Tsujita, J Oceanogr Soc Jpn 8:1–14, 1953) that today we call marine snow. Subsequent studies reported that marine snow consisted of phytoplankton, small zooplankton, fecal material, and other particles (Nishizawa et al., Bull Fac Fish, Hokkaido Univ. 5:36–40, 1954). Across the ocean, Riley (Limnol Oceanogr 8:372–381, 1963) called this material “organic aggregates” which in addition to the organic material included nonliving material that was a “substrate for bacterial growth.” More than a decade later, Silver et al. (Science 201:371–373, 1978) quantified the abundance of marine snow, and its contribution to the total community in situ, and showed that marine snow particles were “metabolic hotspots,” with concentrations of microorganisms 3–4 orders of magnitude greater than those in the surrounding seawater. Alldredge and Cohen (Science 235:689–691, 1987) emphasized the importance of marine snow as unique chemical and physical microhabitats. The importance of transparent exopolymer particles (TEP), which form the matrix that embeds the individual component particles of marine snow, were described and quantified in the early 1990s (Alldredge et al., Deep-Sea Res I 40: 1131–1140, 1993; Passow and Alldredge, Mar Ecol Prog Ser 113:185–198, 1994; Passow et al., Deep-Sea Res Oceanogr Abstr 41:335–357, 1994). The long-held belief that marine snow was both a specialized habitat and potential food source for those living in the deep ocean was also demonstrated at that time (Silver and Gowing, Prog Oceanogr 26:75–113, 1991). More recently it was confirmed that marine snow does indeed contribute significantly to the metabolism of the deep sea and provides hotspots of microbial diversity and activity at depth (e.g., Burd et al., Deep-Sea Res II 57:1557–1571, 2010; Bochdansky et al., Sci Rep 6:22633, 2016). Moreover, marine snow is now considered a transport vehicle for its biota and associated particulate matter (Volk and Hoffert, The carbon cycle and atmospheric CO: natural variations archean to present. American Geophysical Union, Washington, D.C., pp. 99–110, 1985; Alldredge and Gotschalk, Limnol Oceanogr 33:339–351, 1988). Rapidly sinking marine snow is important in the marine carbon cycle as it is responsible for vertical (re)distribution and remineralization of carbon. The transport of carbon from the surface to the deep sea is known as the “biological carbon pump” (De La Rocha and Passow, Deep Sea Res II 54:639–658, 2007; De La Rocha and Passow, Treatise on Geochemistry. Vol. 8, Elsevier, Oxford, 2014). This pump, which leads to the uptake and sequestration of atmospheric CO2 (e.g., Volk and Hoffert, The carbon cycle and atmospheric CO: natural variations archean to present. American Geophysical Union, Washington, D.C., pp. 99–110, 1985; Finkel et al., J Plankton Res 32:119–137, 2010; Zetsche and Ploug, Mar Chem 175:1–4, 2015), also plays an important role in the biogeochemical cycling of elements (e.g., Quigg et al., Nature 425:291–294, 2003; Quigg et al., Proc R Soc: Biol Sci 278:526–534, 2011). How climate change will change these processes is the subject of intense interest but beyond the scope of this chapter