Deep-ocean dissolved organic matter reactivity along the Mediterranean Sea: does size matter?

Martínez-Pérez, Alba María; Álvarez‐Salgado, Xosé Antón; Arı́stegui, Javier

doi:10.1038/s41598-017-05941-6

Cited by 18 publications

(7 citation statements)

References 48 publications

(55 reference statements)

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“…The degradation of this high molecular weight DOM, which here probably included polysaccharides and molecules containing amino acids, would result in the generation of CDOM (and FDOM) of higher molecular weight than what was initially present in the mesocosms, hence yielding the observed changes in spectral slopes. Similar results have been reported for the open ocean, as apparent oxygen utilization has been linked to the decreases in S 275-295 and increases in humic-like fluorescence (Catalá et al, 2015b, 2018; Martínez-Pérez et al, 2017).…”

Section: Discussionsupporting

confidence: 86%

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Gómez‐Letona

Sebastián

Baños

et al. 2022

Preprint

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In the face of climate change there is a need to reduce atmospheric CO2 concentrations. Artificial upwelling of nutrient-rich deep waters has been proposed as a method to enhance the biological carbon pump in oligotrophic oceanic regions in order to increase carbon sequestration. However, the fate of the newly produced organic matter, and specifically of its resulting dissolved fraction, is not clearly understood. Here we examine the effect of different upwelling intensities and modes (single pulse versus recurring pulses) on the dissolved organic matter pool (DOM). We introduced nutrient-rich deep water to large scale mesocosms (∼44 m3) in the oligotrophic subtropical North Atlantic and found that artificial upwelling strongly increased DOM concentrations and changed its characteristics. The magnitude of the observed changes was related to the upwelling intensity: more intense treatments led to higher accumulation of dissolved organic carbon (>70 μM of excess DOC over ambient waters for the most intense) and to comparatively stronger changes in DOM characteristics (increased proportions of chromophoric DOM (CDOM) and humic-like fluorescent DOM), suggesting a transformation of the DOM pool at the molecular level. Moreover, the single upwelling pulse resulted in higher CDOM quantities with higher molecular weight than the recurring upwelling mode. Together, our results indicate that under artificial upwelling, large DOM pools may accumulate in the surface ocean without being remineralised in the short-term. Possible reasons for this persistence could be a combination of the molecular diversification of DOM due to microbial reworking, nutrient limitation and reduced metabolic capabilities of the prokaryotic communities inside the mesocosms. Our study demonstrates the importance of the DOC pool when assessing the carbon sequestration potential of artificial upwelling.

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Section: Discussionsupporting

confidence: 86%

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Gómez‐Letona

Sebastián

Baños

et al. 2022

Preprint

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“…TEPs) acting as "biological glue" for the formation of larger sized aggregates (Bar-Zeev et al, 2011;Parinos et al, 2017;Ortega-Retuerta et al, 2019). In support of this, Martínez-Pérez et al (2017), recorded a substantial increase of high molecular weight dissolved organic matter (TEP precursors) in a transect spanning from the Atlantic and Gibraltar to the Levantine Sea (from 40-55% to 68-76%, respectively) thus providing independent evidence of more important aggregation potential in the eastern sub-basin.…”

Section: Particle Dynamics In the Mediterranean Sea As Inferred From Optical Properties And Biochemical Indicesmentioning

confidence: 77%

Optical Properties and Biochemical Indices of Marine Particles in the Open Mediterranean Sea: The R/V Maria S. Merian Cruise, March 2018

et al. 2021

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A rich data set on particulate matter optical properties and parameters (beam attenuation coefficient, volume concentration, particle size and PSD slope), accompanied by measurements of biochemical indices (particulate organic carbon, particulate nitrogen and their stable isotopic composition) was obtained from the surface to deep waters across the Mediterranean Sea, in March-April 2018. A decrease of beam attenuation coefficients, total particle volume concentrations, particulate organic carbon and nitrogen concentrations was noted towards the eastern Mediterranean Sea (EMed) in comparison to the western Mediterranean Sea (WMed). LISST-derived optical properties were significantly correlated with water mass characteristics. Overall, the most turbid water mass identified in the Mediterranean Sea was the Surface Atlantic water (AW), and the most transparent was the Transitional Mediterranean Water (TMW) in the Cretan Sea, whereas a general decrease in particulate matter concentration is observed from the WMed towards the EMed. Relatively depleted δ13C-POC values in the particle pool of the open Mediterranean Sea can be attributed to contribution from terrestrial inputs, mainly via atmospheric deposition. Throughout the entire water column, a significant positive correlation between particle beam attenuation coefficient and particulate organic carbon concentration is observed in the open Mediterranean Sea. Such relationship suggests the predominance of organic particles with biogenic origin. POC concentration and particle median diameter D50 are significantly and negatively correlated both in the WMed and the EMed Sea, confirming that small particles are POC-rich. At depth, a prominent decrease of most measured parameters was observed, with the exception of particle median diameter that increased substantially in the EMed towards the deep sea, suggesting potentially enhanced aggregation processes. The low particle size distribution slope ξ observed in the EMed, corresponding to larger particle populations, supports the above notion. Basin-wide Rayleigh-type isotopic fractionation in vertical profiles of δ15N-PN across the Mediterranean Sea, underlines the differences in the trophic characters of the two sub-basins and highlights the role of circulation changes on biogeochemical parameters and the redistribution of particulate matter as a source of nutrients in the water column.

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“…The decrease of DOM molecular weight in the L-DOM treatment (observed by a higher increase of the s275-295 values; Helms et al, 2008), in parallel with a coupling to peak M and a254 (Figure 4), may indicate the ability of the assemblages growing on L-DOM to degrade older/more reworked DOM (Martínez-Pérez et al, 2017). Nevertheless, this coupling could also be related to the generation of refractory compounds (humic-like compounds, peak M) as subproducts of the remineralization processes (Jiao et al, 2010;Martínez-Pérez et al, 2017). Conversely, the H + L-DOM treatment was linked to peak T (protein-like compounds), pointing to a more important bond with the assimilation of labile material by the microbial communities growing on this niche.…”

Section: Changes In Bacterial Bulk Properties and Links With Dom Optimentioning

confidence: 99%

“…Subsequently, 50 L of the filtrate were filtered again using a tangential flow ultrafiltration system with a 1 kDa ultrafiltration membrane (GE Series, GE Power and Water), splitting (size-fractionating) the sample into high (>1 kDa, final volume 1.75 L) and low (<1 kDa, final volume 48.25 L) molecular weight fractions. The concentration factor (CF = sample volume/retentate volume) was quite low (∼28) to ensure a pure low-molecular-weight fraction (Martínez-Pérez et al, 2017). Three different base treatments were performed: (i) a CONTROL treatment using 0.1 µm filtered seawater (which is representative of all-size DOM without further manipulation); (ii) a L-DOM treatment using the 1 kDa filtered seawater (which is representative of low-molecular-weight DOM; <1 kDa) and (iii) a H + L-DOM treatment that was prepared by recombining the 1 kDa filtered seawater (<1 kDa; low-molecular-weight DOM) and the retentate seawater (<0.1 µm and >1 kDa, high-molecular-weight DOM) in the same proportion as the tangential flow separation (which is also representative of all-sizes DOM).…”

Section: Sampling and Experimental Set-upmentioning

confidence: 99%

Changes in Activity and Community Composition Shape Bacterial Responses to Size-Fractionated Marine DOM

et al. 2020

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To study the response of bacteria to different size-fractions of naturally occurring dissolved organic matter (DOM), a natural prokaryotic community from North Atlantic mesopelagic waters (1000 m depth) was isolated and grown in (i) 0.1-μm filtered seawater (CONTROL), (ii) the low-molecular-weight (<1 kDa) DOM fraction (L-DOM), and (iii) the recombination of high- (>1 kDa) and low-molecular-weight DOM fractions (H + L-DOM), to test the potential effect of ultrafiltration on breaking the DOM size continuum. Prokaryotic abundance and leucine incorporation were consistently higher in the H + L-DOM niche than in the L-DOM and CONTROL treatments, suggesting a different interaction with each DOM fraction and the disruption of the structural DOM continuum by ultrafiltration, respectively. Rhodobacterales (Alphaproteobacteria) and Flavobacteriales (Bacteroidetes) were particularly enriched in L-DOM and closely related to the colored DOM (CDOM) fraction, indicating the tight link between these groups and changes in DOM aromaticity. Conversely, some other taxa that were rare or undetectable in the original bacterial community were enriched in the H + L-DOM treatment (e.g., Alteromonadales belonging to Gammaproteobacteria), highlighting the role of the rare biosphere as a seed bank of diversity against ecosystem disturbance. The relationship between the fluorescence of protein-like CDOM and community composition of populations in the H + L-DOM treatment suggested their preference for labile DOM. Conversely, the communities growing on the L-DOM niche were coupled to humic-like CDOM, which may indicate their ability to degrade more reworked DOM and/or the generation of refractory substrates (as by-products of the respiration processes). Most importantly, L- and/or H + L-DOM treatments stimulated the growth of unique bacterial amplicon sequence variants (ASVs), suggesting the potential of environmental selection (i.e., changes in DOM composition and availability), particularly in the light of climate change scenarios. Taken together, our results suggest that different size-fractions of DOM induced niche-specialization and differentiation of mesopelagic bacterial communities.

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Deep-ocean dissolved organic matter reactivity along the Mediterranean Sea: does size matter?

Cited by 18 publications

References 48 publications

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Artificial upwelling leads to a large increase in surface dissolved organic matter concentrations

Optical Properties and Biochemical Indices of Marine Particles in the Open Mediterranean Sea: The R/V Maria S. Merian Cruise, March 2018

Changes in Activity and Community Composition Shape Bacterial Responses to Size-Fractionated Marine DOM

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