Archive for oligotrophic

Tiny parasites, big impact: Species networks and carbon recycling in an oligotrophic ocean

Posted by mmaheigan 
· Tuesday, March 12th, 2024 

Parasites are everywhere in the ocean. Including the microbial realm where a diverse, widespread group of protist parasites (Syndiniales) infect and kill a range of hosts, such as dinoflagellates, radiolarians, and even larger zooplankton. A complete Syndiniales infection cycle is only 2-3 days. First, the parasite is a free-living spore. Once inside a host, the parasite consumes the host’s carbon and becomes a larger multicellular organism (a trophont) eventually causing the host to burst open and release hundreds of new spores.

Like viruses, parasite lysis is expected to reroute organic carbon to the microbial loop, potentially decreasing the amount of carbon available for export to the deep sea. Yet, the role of Syndiniales in carbon cycling has been hard to define, as depth-specific infection dynamics and links to carbon export remain poorly understood.

Parasites are everywhere in the ocean. Including the microbial realm where a diverse, widespread group of protist parasites (Syndiniales) infect and kill a range of hosts, such as dinoflagellates, radiolarians, and even larger zooplankton. A complete Syndiniales infection cycle is only 2-3 days. First, the parasite is a free-living spore. Once inside a host, the parasite consumes the host’s carbon and becomes a larger multicellular organism (a trophont) eventually causing the host to burst open and release hundreds of new spores.

Like viruses, parasite lysis is expected to reroute organic carbon to the microbial loop, potentially decreasing the amount of carbon available for export to the deep sea. Yet, the role of Syndiniales in carbon cycling has been hard to define, as depth-specific infection dynamics and links to carbon export remain poorly understood.

Figure 1. The mean relative abundance of Syndiniales (purple) in the photic zone (<140 m) is negatively correlated with particulate organic carbon (POC) flux at 150 m (p-value < 0.001). Similar correlations are not significant (p-values > 0.05) for other major 18S taxonomic groups, like Dinophyceae (red) and Arthropoda (green).

In a recent study published in ISME Communications, authors analyzed an 18S rRNA gene metabarcoding dataset from the Bermuda Atlantic Time-series Study (BATS) site that included 4 years (2016-2019) and twelve depths (1-1000 m). Syndiniales were the most dominant 18S group at BATS, present throughout the photic and aphotic zones. These parasites were prominent in species networks constructed with 18S sequence data, with significant associations with dinoflagellates and copepods in the surface, and with radiolarians in the aphotic zone. In addition, Syndiniales were the only major 18S group to be significantly (and negatively) correlated to particulate carbon flux (at 150 m), which was estimated from sediment trap data collected concurrently at BATS (Figure 1). This is in situ evidence of flux attenuation among Syndiniales, as they recycle host carbon that would otherwise transfer up to larger organisms (e.g., via grazing). Lastly, authors found 19% of the Syndiniales community is linked between photic and aphotic zones, indicating that parasites are sinking on particles and/or are recirculated via diel vertical migration. Overall, these findings elevate the role of Syndiniales in microbial food webs and further emphasize the importance in quantifying parasite-host dynamics to inform ocean carbon models.

 

Authors
Sean Anderson (University of New Hampshire / Woods Hole Oceanographic Institution)
Leocadio Blanco-Bercial (Bermuda Institute of Ocean Sciences / Arizona State University)
Craig Carlson (University of California, Santa Barbara)
Elizabeth Harvey (University of New Hampshire)

How atmospheric and oceanographic forcing impact the carbon sequestration in an ultra-oligotrophic marine system

Posted by mmaheigan 
· Wednesday, August 11th, 2021 

Sinking particles are a critical conduit for the export of material from the surface to the deep ocean. Despite their importance in oceanic carbon cycling, little is known about the composition and seasonal variability of sinking particles which reach abyssal depths. Oligotrophic waters cover ~75% of the ocean surface and contribute over 30% of the global marine carbon fixation. Understanding the processes that control carbon export to the deep oligotrophic areas is crucial to better characterize the strength and efficiency of the biological pump as well as to project the response of these systems to climate fluctuations and anthropogenic perturbations.

In a recent study published in Frontiers in Earth Science, authors synthesized data from atmospheric and oceanographic parameters, together with main mass components, and stable isotope and source-specific lipid biomarker composition of sinking particles collected in the deep Eastern Mediterranean Sea (4285m, Ierapetra Basin) for a three-year period (June 2010-June 2013). In addition, this study compared the sinking particulate flux data with previously reported deep-sea surface sediments from the study area to shed light on the benthic–pelagic coupling.

Figure Caption: a) Biplot of net primary productivity vs export efficiency (top and bottom horizontal dashed lines indicate threshold for high and low export efficiency regimes). b) Biplot of POC-normalized concentrations of terrestrial vs. phytoplankton-derived lipid biomarkers of the sinking particles collected in the deep Eastern Mediterranean Sea (Ierapetra Basin, NW Levantine Basin) from June 2010–June 2013, and surface sediments collected from January 2007 to June 2012 in the study area.

Both seasonal and episodic pulses are crucial for POC export to the deep Eastern Mediterranean Sea. POC fluxes peaked in spring April–May 2012 (12.2 mg m−2 d−1) related with extreme atmospheric forcing. Overall, summer particle export fuels more efficient carbon sequestration than the other seasons. The results of this study highlight that the combination of extreme weather events and aerosol deposition can trigger an influx of both marine labile carbon and anthropogenic compounds to the deep. Finally, the comparison of the sinking particles flux data with surface sediments revealed an isotopic discrimination, as well as a preferential degradation of labile organic matter during deposition and burial, along with higher preservation of land-derived POC in the underlying sediments. This study provides key knowledge to better understand the export, fate and preservation vs. degradation of organic carbon, and for modeling the organic carbon burial rates in the Mediterranean Sea.

 

Authors:
Rut Pedrosa-Pamies (The Ecosystems Center, Marine Biological Laboratory, US; Research Group in Marine Geosciences, University of Barcelona, Spain)
Constantine Parinos (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Anna Sanchez-Vidal (Group in Marine Geosciences, University of Barcelona, Spain)
Antoni Calafat (Group in Marine Geosciences, University of Barcelona, Spain)
Miquel Canals (Group in Marine Geosciences, University of Barcelona, Spain)
Dimitris Velaoras (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Nikolaos Mihalopoulos (Environmental Chemical Processes Laboratory, University of Crete; National Observatory of Athens, Greece)
Maria Kanakidou (Environmental Chemical Processes Laboratory, University of Crete Greece)
Nikolaos Lampadariou (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)
Alexandra Gogou (Institute of Oceanography, Hellenic Centre for Marine Research, Greece)

Tiny phytoplankton seen from space

Posted by mmaheigan 
· Thursday, November 19th, 2020 

Picophytoplankton, the smallest phytoplankton on Earth, are dominant in over half of the global surface ocean, growing in low-nutrient “ocean deserts” where diatoms and other large phytoplankton have difficult to thrive. Despite their small size, picophytoplankton collectively account for well over 50% of primary production in oligotrophic waters, thus playing a major role in sustaining marine food webs.

In a recent paper published in Optics Express, the authors use satellite-detected ocean color (namely remote-sensing reflectance, Rrs(λ)) and sea surface temperature to estimate the abundance of the three picophytoplankton groups—the cyanobacteria Prochlorococcus and Synechococcus, and autotrophic picoeukaryotes. The authors analysed Rrs(λ) spectra using principal component analysis, and principal component scores and SST were used in the predictive models. Then, they trained and independently evaluated the models with in-situ data from the Atlantic Ocean (Atlantic Meridional Transect cruises). This approach allows for the satellite detection of the succession of species across ocean oligotrophic ecosystem boundaries, where these cells are most abundant (Figure 1).

Figure 1. Cell abundances of the three major picophytoplankton groups (the cyanobacteria Prochlorococcus and Synechococcus, and a collective group of autotrophic picoeukaryotes) in surface waters of the Atlantic Ocean. Abundances are shown for the dominant group in terms of total biovolume (converted from cell abundance).

Since these organisms can be used as proxies for marine ecosystem boundaries, this method can be used in studies of climate and ecosystem change, as it allows a synoptic observation of changes in picophytoplankton distributions over time and space. For exploring spectral features in hyperspectral Rrs(λ) data, the implementation of this model using data from future hyperspectral satellite instruments such as NASA PACE’s Ocean Color Instrument (OCI) will extend our knowledge about the distribution of these ecologically relevant phytoplankton taxa. These observations are crucial for broad comprehension of the effects of climate change in the expansion or shifts in ocean ecosystems.

 

Authors:
Priscila K. Lange (NASA Goddard Space Flight Center / Universities Space Research Association / Blue Marble Space Institute of Science)
Jeremy Werdell (NASA Goddard Space Flight Center)
Zachary K. Erickson (NASA Goddard Space Flight Center)
Giorgio Dall’Olmo (Plymouth Marine Laboratory)
Robert J. W. Brewin (University of Exeter)
Mikhail V. Zubkov (Scottish Association for Marine Science)
Glen A. Tarran (Plymouth Marine Laboratory)
Heather A. Bouman (University of Oxford)
Wayne H. Slade (Sequoia Scientific, Inc)
Susanne E. Craig (NASA Goddard Space Flight Center / Universities Space Research Association)
Nicole J. Poulton (Bigelow Laboratory for Ocean Sciences)
Astrid Bracher (Alfred-Wegener-Institute Helmholtz Center for Polar and Marine Research / University of Bremen)
Michael W. Lomas (Bigelow Laboratory for Ocean Sciences)
Ivona Cetinić (NASA Goddard Space Flight Center / Universities Space Research Association)

 

A new Regional Earth System Model of the Mediterranean Sea biogeochemical dynamics

Posted by mmaheigan 
· Thursday, November 19th, 2020 

The Mediterranean Sea is a semi-enclosed mid-latitude oligotrophic basin with a lower net primary production than the global ocean. A west-east productivity trophic gradient results from the superposition of biogeochemical and physical processes, including the biological pump and associated carbon and nutrient (nitrogen, phosphorus) fluxes, the spatial asymmetric distribution of nutrient sources (rivers, atmospheric deposition, coastal upwelling, etc.), the estuarine inverse circulation associated with the inflow of Atlantic water through the Gibraltar Strait. The complex and highly variable interface between land and sea throughout this basin add a further layer of complexity in the Mediterranean oceanic and atmospheric circulation and on the associated biogeochemistry dynamics, emphasizing the need for high-resolution truly integrated Regional Earth System Models to track and understand fine-scale processes and ecosystem dynamics.

In a recent paper published in the Journal of Advances in Modeling Earth System, the authors introduced a new version of the Regional Earth System model RegCM-ES and evaluated its performance in the Mediterranean region. RegCM-ES fully integrates the regional climate model RegCM4, the land surface scheme CLM4.5 (Community Land Model), the river routing model HD (Hydrological Discharge Model), the ocean model MITgcm (MIT General Circulation model) and the Biogeochemical Flux Model BFM.

A comparison with available observations has shown that RegCM-ES was able to capture the mean climate of the region and to reproduce horizontal and vertical patterns of chlorophyll-a and PO4 (the limiting nutrient in the basin) (Figure 1). The same comparison revealed a systematic underestimation of simulated dissolved oxygen (which will be fixed by the use of a new parametrization of oxygen solubility), and an overestimation of NO3, possibly due to uncertainties in initial and boundary conditions (mostly traced to river and Dardanelles nutrient discharges) and an overly vigorous vertical mixing simulated by the ocean model in some parts of the Basin.

Figure.1 Distributions of chlorophyll-a mg/m3 (top) and PO4 mmol/m3 (bottom) in the Mediterranean Sea as simulated by RegCM-ES.

Overall, this analysis has demonstrated that RegCM-ES has the capabilities required to become a powerful tool for studying regional dynamics and impacts of climate change on the Mediterranean Sea and other ocean basins around the world.

 

Authors:
Marco Reale (Abdus Salam International Centre for theoretical physics-ICTP, National Institute of Oceanography and Experimental Geophysics-OGS)
Filippo Giorgi (Abdus Salam International Centre for theoretical physics-ICTP)
Cosimo Solidoro (National Institute of Oceanography and Experimental Geophysics-OGS)
Valeria Di Biagio (National Institute of Oceanography and Experimental Geophysics-OGS)
Fabio Di Sante (Abdus Salam International Centre for theoretical physics-ICTP)
Laura Mariotti (National Institute of Oceanography and Experimental Geophysics-OGS)
Riccardo Farneti (Abdus Salam International Centre for theoretical physics-ICTP)
Gianmaria Sannino (Italian National Agency for New Technologies, Energy and Sustainable Economic Development-ENEA)

Surface bacterial communities respond to rapid changes in the western Arctic

Posted by mmaheigan 
· Tuesday, January 7th, 2020 

During the western Arctic summer open water season, latitudinal differences in the physical and biogeochemical features of the surface water are apparent from the Bering Strait to the Chukchi Borderland. Lower latitude regions (i.e. Bering Strait to Chukchi Shelf) are primarily driven by the inflow of Pacific waters that supply nutrients and heat, leading to high primary production. Conversely, the higher latitude regions (i.e. Chukchi Borderland and Canada Basin) are relatively cold, fresh, and oligotrophic because the surface layer is influenced by freshwater inputs from melting ice and rivers via the Beaufort Gyre. Mixing of the two surface water masses in the western Arctic produces a physicochemical frontal zone (FZ) in the Chukchi Sea.

In a recent study published in Scientific Reports, authors used observations from summer 2017 to investigate latitudinal variations in bacterial community composition in surface waters between the Bering Strait and Chukchi Borderland and the underlying processes driving the changes. Results indicate three distinctive communities: 1) Southern Chukchi (SC) bacterial communities are associated with nutrient-rich conditions, including genera such as Sulfitobacter; 2) a northern Chukchi (NC) bacterial community that dominated by SAR clades, Flavobacterium, Paraglaciecola, and Polaribacter, genera associated with low nutrients and sea ice conditions. If climate-driven changes in the western Arctic continue along the same trajectory, it’s likely we will see altered bacterial communities. If the impact of warm, nutrient-rich Pacific water inflows dominates, it is likely that the productive SC region will expand ­­and the FZ will move northward, leading to nutrient enrichment in the western Arctic (Figure 1). In response, bacterial communities would be dominated by organic matter decomposers, such as Sulfitobacter, due to high primary productivity. However, if the impact of sea-ice meltwater dominates, then the oligotrophic NC region will expand and the FZ will move southward, leading to nutrient depletion in western Arctic surface waters (Figure 1). Continued monitoring in this region will enhance our understanding of how bacterial communities respond (Figure 1b) to a rapidly changing western Arctic Ocean.

Figure 1. (a) Map of the August 2017 Ice Breaker RV Araon western Arctic Ocean sampling stations used in this study. The basemap shows the Chl-a concentration contour (blue to red background colors). Pink, green, and blue circles represent stations in the South Chukchi (SC), Frontal Zone (FZ), and Northern Chukchi (NC) regions. (b) Schematic diagram of surface bacterial community distribution in response to future western Arctic Ocean changes.

Authors:
Il-Nam Kim (Department of Marine Science, Incheon National University)
Sung-Ho Kang (Korea Polar Research Institute)
Eun Jin Yang (Korea Polar Research Institute)

Elusive protists transport large quantities of silica into the ocean interior

Posted by hbenway 
· Friday, September 7th, 2018 

Phaeodaria are single-celled eukaryotes (a.k.a. protists) belonging to the supergroup Rhizaria. Like diatoms, phaeodarians build up skeletons made of opaline silica, but unlike their emblematic relatives, phaeodarians have been largely ignored in the marine silica cycle.

The contribution of phaeodarians to total biogenic silica (bSiO2) export is markedly enhanced at low total bSiO2 export (analysis did not include data from 2014 due to abnormally depleted phaeodarian population).

In a recent study published in Global Biogeochemical Cycles (also see related Research Spotlight in AGU Eos), authors used a combination of extensive sediment trap deployments and in situ imagery during four cruises of the California Current Ecosystem Long-Term Ecological Research (CCE-LTER) Program off the coast of California to quantify biogenic silica export mediated by giant phaeodarians (>600 µm). These data revealed that giant phaeodarians possess among the highest recorded cellular silica content (up to 43 µg Si cell-1). In addition, measurements of vertical fluxes suggest that these organisms can play a surprisingly large role in silica export (ranging from 10-80% of total silica export) in more oligotrophic waters. Also, because they are most abundant in waters below the euphotic zone, phaeodarians contribute to increased biogenic silica flux in the mesopelagic, in contrast with typically observed decreases in carbon flux with depth. Given their significant contribution to silica export, phaeodarians should be considered in global budgets and models of ocean silica cycles, especially in oligotrophic waters.

Authors
Tristan Biard (Scripps Institution of Oceanography)
Jeffrey W. Krause (University of Southern Alabama)
Michael R. Stukel (Florida State University)
Mark D. Ohman (Scripps Institution of Oceanography)

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