The biological pump in a high CO&lt;sub&gt;2 world

Passow, Uta; Carlson, Craig A.

doi:10.3354/meps09985

Cited by 317 publications

(290 citation statements)

References 269 publications

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“…It is likely that both TEP and CSP contain chemical components other than those that stain with the dyes that define them (Figs 2-5). TEP plays an important role in the biogeochemistry of the biological carbon pump (Passow & Carlson, 2012) and consequently there is a need to better define its composition to determine its origin and biogeochemical significance. Much of the recent detailed work on the composition of EPS produced by diatoms has been conducted with laboratory-grown cultures of benthic epipelic diatoms (Underwood et al, 2004;Bellinger et al, 2005;Abdullahi et al, 2006).…”

Section: Chemical Characterization Of Dom Released By Phytoplanktonmentioning

confidence: 99%

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

Thornton

2014

European Journal of Phycology

356

311

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The partitioning of organic matter (OM) between dissolved and particulate phases is an important factor in determining the fate of organic carbon in the ocean. Dissolved organic matter (DOM) release by phytoplankton is a ubiquitous process, resulting in 2-50% of the carbon fixed by photosynthesis leaving the cell. This loss can be divided into two components: passive leakage by diffusion across the cell membrane and the active exudation of DOM into the surrounding environment. At present there is no method to distinguish whether DOM is released via leakage or exudation. Most explanations for exudation remain hypothetical; as while DOM release has been measured extensively, there has been relatively little work to determine why DOM is released. Further research is needed to determine the composition of the DOM released by phytoplankton and to link composition to phytoplankton physiological status and environmental conditions. For example, the causes and physiology of phytoplankton cell death are poorly understood, though cell death increases membrane permeability and presumably DOM release. Recent work has shown that phytoplankton interactions with bacteria are important in determining both the amount and composition of the DOM released. In response to increasing CO 2 in the atmosphere, climate change is creating increasingly stressful conditions for phytoplankton in the surface ocean, including relatively warm water, low pH, low nutrient supply and high light. As ocean physics and chemistry change, it is hypothesized that a greater proportion of primary production will be released directly by phytoplankton into the water as DOM. Changes in the partitioning of primary production between the dissolved and particulate phases will have bottom-up effects on ecosystem structure and function. There is a need for research to determine how these changes affect the fate of organic matter in the ocean, particularly the efficiency of the biological carbon pump.

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Section: Chemical Characterization Of Dom Released By Phytoplanktonmentioning

confidence: 99%

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

Thornton

2014

European Journal of Phycology

356

311

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“…Assessing mesopelagic C remineralization is pivotal for evaluating remineralization length scale as well as the timescale of the C storage in the deep ocean. Indeed the typical depth of the main thermocline, 1000 m (IPCC, WG1, 2007, chapter 5) is often referred to as the horizon, clearly removed from the surface ocean and atmosphere (Passow and Carlson, 2012). Overall, assessing mesopelagic C remineralization will allow one to better quantify the ocean's biological carbon pump and its efficiency in the global C cycle which holds large uncertainty and is currently under debate (e.g.…”

Section: Introductionmentioning

confidence: 99%

Early spring mesopelagic carbon remineralization and transfer efficiency in the naturally iron-fertilized Kerguelen area

et al. 2015

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Abstract. We report on the zonal variability of mesopelagic particulate organic carbon remineralization and deep carbon transfer potential during the Kerguelen Ocean and Plateau compared Study 2 expedition (KEOPS 2; OctoberNovember 2011) in an area of the polar front supporting recurrent massive blooms from natural Fe fertilization. Mesopelagic carbon remineralization (MR) was assessed using the excess, non-lithogenic particulate barium (Ba xs ) inventories in mesopelagic waters and compared with bacterial production (BP), surface primary production (PP) and export production (EP). Results for this early season study are compared with the results obtained during a previous study (2005; KEOPS 1) for the same area at a later stage of the phytoplankton bloom. Our results reveal the patchiness of the seasonal advancement and of the establishment of remineralization processes between the plateau (A3) and polar front sites during KEOPS 2. For the Kerguelen plateau (A3 site) we observe a similar functioning of the mesopelagic ecosystem during both seasons (spring and summer), with low and rather stable remineralization fluxes in the mesopelagic column (150-400 m). The shallow water column (∼ 500 m), the lateral advection, the zooplankton grazing pressure and the pulsed nature of the particulate organic carbon (POC) transfer at A3 seem to drive the extent of MR processes on the plateau. For deeper stations (> 2000 m) located on the margin, inside a polar front meander, as well as in the vicinity of the polar front, east of Kerguelen, remineralization in the upper 400 m in general represents a larger part of surface carbon export. However, when considering the upper 800 m, in some cases, the entire flux of exported carbon is remineralized. In the polar front meander, where successive stations form a time series, two successive events of particle transfer were evidenced by remineralization rates: a first mesopelagic and deep transfer from a past bloom before the cruise, and a second transfer expanding at mesopelagic layers during the cruise. Regarding the deep carbon transfer efficiency, it appeared that above the plateau (A3 site) the mesopelagic remineralization was not a major barrier to the transfer of organic matter to the seafloor (close to 500 m). There, the efficiency of carbon transfer to the bottom waters (> 400 m) as assessed by PP, EP and MR fluxes comparisons reached up to 87 % of the carbon exported from the upper 150 m. In contrast, at the deeper locations, mesopelagic remineralization clearly limited the transfer of carbon to depths of > 400 m. For sites at the margin of the plateau (station E-4W) and the polar front (station F-L), mesopelagic remineralization even exceeded Published by Copernicus Publications on behalf of the European Geosciences Union. S. H. M. Jacquet et al.: Early season mesopelagic carbon remineralizationupper 150 m export, resulting in a zero transfer efficiency to depths > 800 m. In the polar front meander (time series), the capacity of the meander to transfer carbon to depth > 800 ...

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“…Rising seawater temperatures will likely promote seawater column stratification, hindering vertical mixing and consequently impoverishing nutrient concentrations in surface waters (Passow and Carlson, 2012). In such a scenario, it is likely that nutrient-limited corals will increasingly rely on DDN to meet their nitrogen metabolic requirements.…”

Section: Does Diazotrophy Enhance Coral Resilience?mentioning

confidence: 99%

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

2017

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Coral reefs are highly productive ecosystems thriving in nutrient-poor waters. Their productivity depends largely on the availability of nitrogen, the proximate limiting nutrient for primary production. In reefs, the major nitrogen pathways include regeneration, nitrification, ammonification and dinitrogen (N 2 ) fixation. N 2 fixation is performed by prokaryotes called "diazotrophs" that abound in coral rubbles, sandy bottoms, microbial mats, or seagrass meadows. Corals, which are the main reef builders, have developed a partnership with dinoflagellates which transform dissolved inorganic nitrogen into amino acids and protein, and with diazotrophs to gain diazotrophically-derived nitrogen (DDN). Pioneering studies found active diazotrophic cyanobacteria in the corals' mucus and/or tissue, and later high throughput sequencing efforts have described diverse communities of non-cyanobacterial diazotrophs associated with scleractinian corals. Yet, the metabolic processes behind these associations and how they benefit corals are currently not well understood. While genomic studies describe the diversity of diazotrophs and isotopic tracer experiments quantify N 2 fixation rates, combined advanced methods are needed to elucidate the mechanisms behind the transfer of DDN to the coral holobiont and whether these mechanisms change according to the identity of the diazotrophs or coral species. Here we review our current knowledge on N 2 fixation in corals: the diversity and localization of diazotrophs in the coral holobiont, the environmental factors controlling N 2 fixation, the fate of DDN within the coral symbiosis as well as its potential role in coral resilience. We finally summarize the unknowns: are the diversity, abundance and localization of diazotrophs within the holobiont species-and/or site-specific? Do they have an impact on DDN production? What are the metabolic mechanisms implicated? Do they change spatially, temporally or according to environmental factors? We encourage scientists to undertake research efforts to tackle these questions in order to shed light on nitrogen cycling in reef ecosystems and to understand if coral-associated N 2 fixation can improve coral's resilience in the face of climate change.

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The biological pump in a high CO<sub>2 world

Cited by 317 publications

References 269 publications

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

Dissolved organic matter (DOM) release by phytoplankton in the contemporary and future ocean

Early spring mesopelagic carbon remineralization and transfer efficiency in the naturally iron-fertilized Kerguelen area

Diazotrophs: Overlooked Key Players within the Coral Symbiosis and Tropical Reef Ecosystems?

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