scholarly journals Small phytoplankton contribute greatly to CO2-fixation after the diatom bloom in the Southern Ocean

2021 ◽  
Author(s):  
Solène Irion ◽  
Urania Christaki ◽  
Hugo Berthelot ◽  
Stéphane L’Helguen ◽  
Ludwig Jardillier
Keyword(s):  
Southern Ocean ◽  
Co2 Fixation ◽  
Carbon Fixation ◽  
Deep Ocean ◽  
Small Cells ◽  
Cell Level ◽  
Carbon Pump ◽  
Small Phytoplankton ◽  
Important Pathway

AbstractPhytoplankton is composed of a broad-sized spectrum of phylogenetically diverse microorganisms. Assessing CO2-fixation intra- and inter-group variability is crucial in understanding how the carbon pump functions, as each group of phytoplankton may be characterized by diverse efficiencies in carbon fixation and export to the deep ocean. We measured the CO2-fixation of different groups of phytoplankton at the single-cell level around the naturally iron-fertilized Kerguelen plateau (Southern Ocean), known for intense diatoms blooms suspected to enhance CO2 sequestration. After the bloom, small cells (<20 µm) composed of phylogenetically distant taxa (prymnesiophytes, prasinophytes, and small diatoms) were growing faster (0.37 ± 0.13 and 0.22 ± 0.09 division d−1 on- and off-plateau, respectively) than larger diatoms (0.11 ± 0.14 and 0.09 ± 0.11 division d−1 on- and off-plateau, respectively), which showed heterogeneous growth and a large proportion of inactive cells (19 ± 13%). As a result, small phytoplankton contributed to a large proportion of the CO2 fixation (41–70%). The analysis of pigment vertical distribution indicated that grazing may be an important pathway of small phytoplankton export. Overall, this study highlights the need to further explore the role of small cells in CO2-fixation and export in the Southern Ocean.

Mechanisms and Pathways of Small-Phytoplankton Export from the Surface Ocean

2019 ◽  
Vol 11 (1) ◽  
pp. 57-74 ◽  
Author(s):  
Tammi L. Richardson
Keyword(s):  
Carbon Fixation ◽  
Particulate Material ◽  
Taxonomic Composition ◽  
Small Cells ◽  
Carbon Export ◽  
Surface Ocean ◽  
Carbon Pump ◽  
Small Phytoplankton ◽  
Production Research

Carbon fixation by phytoplankton near the surface and the sinking of this particulate material to deeper waters are key components of the biological carbon pump. The efficiency of the biological pump is influenced by the size and taxonomic composition of the phytoplankton community. Large, heavily ballasted taxa such as diatoms sink quickly and thus efficiently remove fixed carbon from the upper ocean. Smaller, nonballasted species such as picoplanktonic cyanobacteria are usually thought to contribute little to export production. Research in the past decade, however, has shed new light on the potential importance of small phytoplankton to carbon export, especially in oligotrophic oceans, where small cells dominate primary productivity. Here, I examine the mechanisms and pathways through which small-phytoplankton carbon is exported from the surface ocean and the role of small phytoplankton in food webs of a variety of ocean ecosystems.

Insights into the ocean’s biological carbon pump: What makes marine snow falling into the deep ocean?

2021 ◽  
Author(s):  
Frederic Le Moigne
Keyword(s):  
Carbon Cycle ◽  
Global Analysis ◽  
Deep Ocean ◽  
Ecosystem Structure ◽  
Faecal Pellets ◽  
Surface Ocean ◽  
Mesopelagic Zone ◽  
Carbon Pump ◽  
Biological Carbon Pump

&lt;p&gt;The oceanic biological carbon pump (BCP) regulates the Earth carbon cycle by transporting part of the photosynthetically fixed CO&lt;sub&gt;2&lt;/sub&gt; into the deep ocean. Suppressing this mechanism would result in an important increase of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; level. The BCP occurs mainly in the form of organic carbon particles (POC) sinking out the surface ocean. Various types of particles are produced in surface ocean. They all differ in production, sinking and decomposition rates, vertically and horizontally. The amount of POC transported to depths via these various export pathways as well as their decomposition pathways all have different ecological origins and therefore may response differently to climate change. Here I will briefly review some of the processes driving both particle export out of the euphotic zone (0-100m) as well as particles transport within the mesopelagic zone (100-1000m). In the early 2000s, strong correlations between POC and mineral (calcite an opal) fluxes observed in the deep ocean have inspired the inclusion of &amp;#8220;ballast effect&amp;#8221; parameterizations in carbon cycle models. These relationships were first considered as being universal. However global analysis of POC and mineral ballast fluxes showed that mineral ballasting is important in regions like the high-latitude North Atlantic but that in most places (some of which efficiently exporting) the unballasted fraction often dominates the export flux. In such regions, we later showed that zooplankton-mediated export (presence of faecal pellets) and surface microbial abundance were important drivers of the efficiency of particles export. Similar trends were found globally by including bacteria and zooplankton abundances to a global reanalysis of the global variations of the POC export efficiency. This implies that the whole ecosystem structure from bacteria to fishes, rather than just the phytoplankton community, is important in setting the strength of the biological carbon pump. Further down in the water column (mesopelagic zone), processes impacting the transport of particles are less clear. Sinking particles experience a number of biotic and abiotic transformations during their descent. These includes solubilization, remineralisation, fragmentation, ingestion/active transport, breakdown among others. While some potential factors such as O&lt;sub&gt;2&lt;/sub&gt; concentration and temperature have been proposed as powerful controls, global evidences are often inconsistent. In the award talk, I will review current challenges related to the role of particles consumption by zooplankton and fishes as well as the role of particles attached prokaryotes (bacteria and archaea) in setting the efficiency of the carbon transport in the mesopelagic zone.&lt;/p&gt;

scholarly journals Impact of hydrothermalism on the ocean iron cycle

2016 ◽  
Vol 374 (2081) ◽  
pp. 20150291 ◽  
Author(s):  
Alessandro Tagliabue ◽  
Joseph Resing
Keyword(s):  
Southern Ocean ◽  
Oxidation Kinetics ◽  
State Of The Art ◽  
Section Data ◽  
Trace Element Chemistry ◽  
Carbon Pump ◽  
Climatic Impacts ◽  
The Impact ◽  
Biological Carbon Pump

As the iron supplied from hydrothermalism is ultimately ventilated in the iron-limited Southern Ocean, it plays an important role in the ocean biological carbon pump. We deploy a set of focused sensitivity experiments with a state of the art global model of the ocean to examine the processes that regulate the lifetime of hydrothermal iron and the role of different ridge systems in governing the hydrothermal impact on the Southern Ocean biological carbon pump. Using GEOTRACES section data, we find that stabilization of hydrothermal iron is important in some, but not all regions. The impact on the Southern Ocean biological carbon pump is dominated by poorly explored southern ridge systems, highlighting the need for future exploration in this region. We find inter-basin differences in the isopycnal layer onto which hydrothermal Fe is supplied between the Atlantic and Pacific basins, which when combined with the inter-basin contrasts in oxidation kinetics suggests a muted influence of Atlantic ridges on the Southern Ocean biological carbon pump. Ultimately, we present a range of processes, operating at distinct scales, that must be better constrained to improve our understanding of how hydrothermalism affects the ocean cycling of iron and carbon. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

scholarly journals Continuous moulting by Antarctic krill drives major pulses of carbon export in the north Scotia Sea, Southern Ocean

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
C. Manno ◽  
S. Fielding ◽  
G. Stowasser ◽  
E. J. Murphy ◽  
S. E. Thorpe ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Antarctic Krill ◽  
Deep Ocean ◽  
Carbon Export ◽  
Scotia Sea ◽  
Faecal Pellets ◽  
The North ◽  
Poc Flux ◽  
Moulting Cycle

AbstractAntarctic krill play an important role in biogeochemical cycles and can potentially generate high-particulate organic carbon (POC) fluxes to the deep ocean. They also have an unusual trait of moulting continuously throughout their life-cycle. We determine the krill seasonal contribution to POC flux in terms of faecal pellets (FP), exuviae and carcasses from sediment trap samples collected in the Southern Ocean. We found that krill moulting generated an exuviae flux of similar order to that of FP, together accounting for 87% of an annual POC flux (22.8 g m−2 y−1). Using an inverse modelling approach, we determined the krill population size necessary to generate this flux peaked at 261 g m−2. This study shows the important role of krill exuviae as a vector for POC flux. Since krill moulting cycle depends on temperature, our results highlight the sensitivity of POC flux to rapid regional environmental change.

scholarly journals Sinking Diatom Assemblages as a Key Driver for Deep Carbon and Silicon Export in the Scotia Sea (Southern Ocean)

2021 ◽  
Vol 9 ◽  
Author(s):  
D. Zúñiga ◽  
A. Sanchez-Vidal ◽  
M. M. Flexas ◽  
D. Carroll ◽  
M. M. Rufino ◽  
...  
Keyword(s):  
Carbon Sequestration ◽  
Southern Ocean ◽  
Sea Ice ◽  
Environmental Conditions ◽  
Model Simulation ◽  
Deep Ocean ◽  
Global Ocean ◽  
Carbon Export ◽  
Scotia Sea

Physical and biogeochemical processes in the Southern Ocean are fundamental for modulating global climate. In this context, a process-based understanding of how Antarctic diatoms control primary production and carbon export, and hence global-ocean carbon sequestration, has been identified as a scientific priority. Here we use novel sediment trap observations in combination with a data-assimilative ocean biogeochemistry model (ECCO-Darwin) to understand how environmental conditions trigger diatom ecology in the iron-fertilized southern Scotia Sea. We unravel the role of diatoms assemblage in controlling the biogeochemistry of sinking material escaping from the euphotic zone, and discuss the link between changes in upper-ocean environmental conditions and the composition of settling material exported from the surface to 1,000 m depth from March 2012 to January 2013. The combined analysis of in situ observations and model simulation suggests that an anomalous sea-ice episode in early summer 2012–2013 favored (via restratification due to sea-ice melt) an early massive bloom of Corethron pennatum that rapidly sank to depth. This event drove high biogenic silicon to organic carbon export ratios, while modulating the carbon and nitrogen isotopic signals of sinking organic matter reaching the deep ocean. Our findings highlight the role of diatom ecology in modulating silicon vs. carbon sequestration efficiency, a critical factor for determining the stoichiometric relationship of limiting nutrients in the Southern Ocean.

Abyssal Ocean Warming and Salinification after Weddell Polynyas in the GFDL CM2G Coupled Climate Model

2015 ◽  
Vol 45 (11) ◽  
pp. 2755-2772 ◽  
Author(s):  
Hannah Zanowski ◽  
Robert Hallberg ◽  
Jorge L. Sarmiento
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Deep Ocean ◽  
Weddell Sea ◽  
Coupled Climate Model ◽  
Composite Event ◽  
Recent Warming ◽  
Time Period ◽  
Ocean Properties

AbstractThe role of Weddell Sea polynyas in establishing deep-ocean properties is explored in the NOAA Geophysical Fluid Dynamics Laboratory’s (GFDL) coupled climate model CM2G. Using statistical composite analysis of over 30 polynya events that occur in a 2000-yr-long preindustrial control run, the temperature, salinity, and water mass changes associated with the composite event are quantified. For the time period following the composite polynya cessation, termed the “recovery,” warming between 0.002° and 0.019°C decade−1 occurs below 4200 m in the Southern Ocean basins. Temperature and salinity changes are strongest in the Southern Ocean and the South Atlantic near the polynya formation region. Comparison of the model results with abyssal temperature observations reveals that the 1970s Weddell Polynya recovery could account for 10% ± 8% of the recent warming in the abyssal Southern Ocean. For individual Southern Ocean basins, this percentage is as little as 6% ± 11% or as much as 34% ± 13%.

scholarly journals On the Southern Ocean CO 2 uptake and the role of the biological carbon pump in the 21st century

2015 ◽  
Vol 29 (9) ◽  
pp. 1451-1470 ◽  
Author(s):  
J. Hauck ◽  
C. Völker ◽  
D. A. Wolf‐Gladrow ◽  
C. Laufkötter ◽  
M. Vogt ◽  
...  
Keyword(s):  
Southern Ocean ◽  
21St Century ◽  
Carbon Pump ◽  
Biological Carbon Pump

scholarly journals Glacial CO<sub>2</sub> decrease and deep-water deoxygenation by iron fertilization from glaciogenic dust

2019 ◽  
Vol 15 (3) ◽  
pp. 981-996 ◽  
Author(s):  
Akitomo Yamamoto ◽  
Ayako Abe-Ouchi ◽  
Rumi Ohgaito ◽  
Akinori Ito ◽  
Akira Oka
Keyword(s):  
Southern Ocean ◽  
Deep Water ◽  
Large Scale ◽  
Deep Ocean ◽  
Carbon Accumulation ◽  
Oxygen Solubility ◽  
Biological Pump ◽  
Iron Fertilization ◽  
Carbon Pump ◽  
Water Deoxygenation

Abstract. Increased accumulation of respired carbon in the deep ocean associated with enhanced efficiency of the biological carbon pump is thought to be a key mechanism of glacial CO2 drawdown. Despite greater oxygen solubility due to seawater cooling, recent quantitative and qualitative proxy data show glacial deep-water deoxygenation, reflecting increased respired carbon accumulation. However, the mechanisms of deep-water deoxygenation and contribution from the biological pump to glacial CO2 drawdown have remained unclear. In this study, we report the significance of iron fertilization from glaciogenic dust in glacial CO2 decrease and deep-water deoxygenation using our numerical simulation, which successfully reproduces the magnitude and large-scale pattern of the observed oxygen changes from the present to the Last Glacial Maximum. Sensitivity experiments show that physical changes contribute to only one-half of all glacial deep deoxygenation, whereas the other one-half is driven by iron fertilization and an increase in the whole ocean nutrient inventory. We find that iron input from glaciogenic dust with higher iron solubility is the most significant factor in enhancing the biological pump and deep-water deoxygenation. Glacial deep-water deoxygenation expands the hypoxic waters in the deep Pacific and Indian oceans. The simulated global volume of hypoxic waters is nearly double the present value, suggesting that glacial deep water was a more severe environment for benthic animals than that of the modern oceans. Our model underestimates the deoxygenation in the deep Southern Ocean because of enhanced ventilation. The model–proxy comparison of oxygen change suggests that a stratified Southern Ocean is required for reproducing the oxygen decrease in the deep Southern Ocean. Iron fertilization and a global nutrient increase contribute to a decrease in glacial CO2 of more than 30 ppm, which is supported by the model–proxy agreement of oxygen change. Our findings confirm the significance of the biological pump in glacial CO2 drawdown and deoxygenation.

Controls over the export flux of marine snow into the deep ocean

2020 ◽  
Author(s):  
Frederic Le Moigne
Keyword(s):  
Carbon Cycle ◽  
Global Analysis ◽  
Deep Ocean ◽  
Ecosystem Structure ◽  
Export Flux ◽  
Surface Ocean ◽  
Mesopelagic Zone ◽  
Carbon Pump ◽  
Biological Carbon Pump

&lt;p&gt;The oceanic biological carbon pump (BCP) regulates the Earth carbon cycle by transporting part of the photosynthetically fixed CO&lt;sub&gt;2&lt;/sub&gt; into the deep ocean. Suppressing this mechanism would result in an important increase of atmospheric CO&lt;sub&gt;2&lt;/sub&gt; level. The BCP occurs mainly in the form of organic carbon particles (POC) sinking out the surface ocean. Various types of particles are produced in surface ocean. They all differ in production, sinking and decomposition rates, vertically and horizontally. The amount of POC transported to depths via these various export pathways as well as their decomposition pathways all have different ecological origins and therefore may response differently to climate change. Here I will briefly review some of the processes driving both particle export out of the euphotic zone (0-100m) as well as particles transport within the mesopelagic zone (100-1000m). In the early 2000s, strong correlations between POC and mineral (calcite an opal) fluxes observed in the deep ocean have inspired the inclusion of &amp;#8220;ballast effect&amp;#8221; parameterizations in carbon cycle models. These relationships were first considered as being universal. However global analysis of POC and mineral ballast fluxes showed that mineral ballasting is important in regions like the high-latitude North Atlantic but that in most places (some of which efficiently exporting) the unballasted fraction often dominates the export flux. In such regions, we later on showed that zooplankton-mediated export (presence of faecal pellets) and surface microbial abundance were important drivers of the efficiency of particles export. Similar trends were found globally by including bacteria and zooplankton abundances to a global reanalysis of the global variations of the POC export efficiency. This implies that the whole ecosystem structure, rather than just the phytoplankton community, is important in setting the strength of the biological carbon pump. Further down in the water column (mesopelagic zone), processes impacting the transport of particles are less clear. Sinking particles experience a number of biotic and abiotic transformations during their descent. These includes solubilization, remineralisation, fragmentation, ingestion/active transport, break down among others. While some potential factors such as O&lt;sub&gt;2&lt;/sub&gt; concentration and temperature have been proposed as powerful controls, globally evidences are often inconsistent. Current challenges related to the role of particles consumption by zooplankton and fishes as well as the role of particles attached prokaryotes (bacteria and archaea) in setting the efficiency of the carbon transport in the mesopelagic zone will be discussed.&lt;/p&gt;

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