The multiple fates of sinking particles in the North Atlantic Ocean

Abstract

The direct respiration of sinking organic matter by attached bacteria is often invoked as the dominant sink for settling particles in the mesopelagic ocean. However, other processes, such as enzymatic solubilization and mechanical disaggregation, also contribute to particle flux attenuation by transferring organic matter to the water column. Here we use observations from the North Atlantic Ocean, coupled to sensitivity analyses of a simple model, to assess the relative importance of particle-attached microbial respiration compared to the other processes that can degrade sinking particles. The observed carbon fluxes, bacterial production rates, and respiration by water column and particle-attached microbial communities each spanned more than an order of magnitude. Rates of substrate-specific respiration on sinking particle material ranged from 0.007 ± 0.003 to 0.173 ± 0.105 day À1. A comparison of these substrate-specific respiration rates with model results suggested sinking particle material was transferred to the water column by various biological and mechanical processes nearly 3.5 times as fast as it was directly respired. This finding, coupled with strong metabolic demand imposed by measurements of water column respiration (729.3 ± 266.0 mg C m À2 d À1, on average, over the 50 to 150 m depth interval), suggested a large fraction of the organic matter evolved from sinking particles ultimately met its fate through subsequent remineralization in the water column. At three sites, we also measured very low bacterial growth efficiencies and large discrepancies between depth-integrated mesopelagic respiration and carbon inputs.

Quorum Sensing Plays a Complex Role in Regulating the Enzyme Hydrolysis Activity of Microbes Associated with Sinking Particles in the Ocean

“…Such changes could be critical in affecting the rates of POC degradation, particle flux attenuation, and the depths at which carbon is remineralized and sequestered in the deep sea (Armstrong et al, 2001;Kwon et al, 2009). Furthermore, the relative balance of two of the major processes that contribute to particle flux attenuation, microbial respiration and enzyme hydrolysis (Collins et al, 2015), may also be affected. Thus, quorum sensing mechanisms certainly have the potential to affect the biological carbon pump on a global scale.…”

Prediction of the Export and Fate of Global Ocean Net Primary Production: The EXPORTS Science Plan

“…Zooplankton also contribute to export through their diurnal and seasonal migrations from the EZ to several 100 m's deeper into the twilight zone (TZ), where carbon consumed at the surface is subsequently respired as CO 2 , excreted as DOC or released as fecal pellets (e.g., Steinberg et al, 2000;Bianchi et al, 2013;Jónasdóttir et al, 2015). Further in the TZ, a host of remineralization processes driven by bacteria and zooplankton recycle sinking and suspended organic matter, further influencing the attenuation of the vertical carbon flux (e.g., Carlson et al, 2004;Steinberg et al, 2008;Burd et al, 2010;Giering, 2014;Collins et al, 2015).…”

“…For example, the transport of suspended POC and DOC from the EZ to the TZ via subduction, isopycnal exchange and seasonal convective mixing represents up to 20% of global carbon export from the EZ and provides another carbon source for TZ microbial communities (e.g., Hansell et al, 2009;Carlson et al, 2010). Further, intense upwelling and downwelling motions (several 10's m's per day) induced by the submesoscale (∼1-20 km) flow field also have the potential to transport large amounts of organic matter to depth where a portion is remineralized by microbial processes resulting in a net export of carbon from the upper ocean (e.g., Carlson et al, 2004;Lévy et al, 2013;Collins et al, 2015;Omand et al, 2015).…”

The remineralization of marine organic matter by diverse biological and abiotic processes

“…Finally, I apply the measurements of particulate organic carbon (POC) fluxes and substrate-specific respiration in a series of sensitivity analyses of a simple, yet mechanistic model of particle flux attenuation. Observational data and the results of these sensitivity analyses are combined to (1) constrain the relative contribution to particle flux attenuation by particle-attached microbial respiration compared to other processes and (2) determine how differences in the average sinking speed of marine particles Schematic showing the major processes that ultimately remove sinking particle material in the mesopelagic ocean, as conceptualized in Chapter 2 of the thesis (Collins et al, 2015). Also shown are the accompanying first-order rate constants ( ; units of day −1 ) through which we represent these attenuation processes in the model described in that chapter.…”

“…The potency and specificity that make lipids useful as biomarkers of oxidative stress also support their function as bioactive "infochemicals" (Ianora and Miralto, 2010;Pohnert, 2008;Vardi, 2008). In the ocean, for example, oxylipins have been shown to regulate different interspecific interactions among marine microbiota (Balestra et al, 2011;Casotti et al, 2005;Miralto et al, 1999;Ribalet et al, 2008) and the metabolism of sinking marine particles by heterotrophic bacteria (Edwards et al, 2015).…”