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 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

Southern control of interhemispheric synergy on marine carbon sequestration during glacial cycles   

2021 ◽  
Author(s):  
Jinlong Du ◽  
Xu Zhang ◽  
Ying Ye ◽  
Christoph Völker ◽  
Jun Tian
Keyword(s):  
Carbon Sequestration ◽  
Southern Ocean ◽  
Sea Ice ◽  
North Atlantic ◽  
Glacial Cycles ◽  
The North ◽  
Carbon Pump ◽  
The North Atlantic ◽  
The Impact ◽  
Biological Carbon Pump

<p>The mechanisms of atmospheric CO2 draw-down by ~90 ppm during glacial cycles have been one of the most contentious questions in the past several decades. Processes in the Southern Ocean (SO) have been suggested to be at the heart, while the North Atlantic (NA) is recently proposed to be critical during glacial periods as well. However, in a full course of glacial cycles, the individual and synergic roles of these two regions remain enigmatic. Using a state-of-the-art biogeochemical model (MITgcm-REcoM2) associated with an interactive CO<sub>2</sub> module, we examined the impact of the onset of individual mechanisms and combinations of them on atmospheric CO<sub>2</sub>. Here we show that SO controls carbon sequestration in both hemispheres. In sensitivity runs with respect to mechanisms happening during glacial inceptions, cooling in SO contributes to a larger portion of CO<sub>2</sub> draw-down than cooling in NA, by shortening the surface water exposure time, while the early sea ice expansion tends to weaken the carbon uptake. The efficiency of surface carbon storage in the North Atlantic depends on the volume of Antarctic bottom water and reaches its maximum when the glacial stratification is well developed during glacial maxima.  SO cooling and sea ice expansion strongly promote the formation of AABW and the full development of the glacial stratification. Furthermore, increased dust deposition during the glacial maxima raises the contribution of the Southern Ocean in the global biological carbon pump, leading to a higher efficiency of the biological carbon pump. And the maximal expanded sea ice suppresses local carbon leakage.</p><p> </p><p> </p><p> </p>

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

<p>The oceanic biological carbon pump (BCP) regulates the Earth carbon cycle by transporting part of the photosynthetically fixed CO<sub>2</sub> into the deep ocean. Suppressing this mechanism would result in an important increase of atmospheric CO<sub>2</sub> 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 “ballast effect” 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<sub>2</sub> 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.</p>

scholarly journals An examination of the role of particles in oceanic mercury cycling

2016 ◽  
Vol 374 (2081) ◽  
pp. 20150297 ◽  
Author(s):  
Carl H. Lamborg ◽  
Chad R. Hammerschmidt ◽  
Katlin L. Bowman
Keyword(s):  
Deep Water ◽  
Oceanic Water ◽  
Deep Water Formation ◽  
Mercury Cycling ◽  
Trace Element Chemistry ◽  
Sinking Particles ◽  
Water Formation ◽  
Climatic Impacts ◽  
Using Data

Recent models of global mercury (Hg) cycling have identified the downward flux of sinking particles in the ocean as a prominent Hg removal process from the ocean. At least one of these models estimates the amount of anthropogenic Hg in the ocean to be about 400 Mmol, with deep water formation and sinking fluxes representing the largest vectors by which pollutant Hg is able to penetrate the ocean interior. Using data from recent cruises to the Atlantic, we examined the dissolved and particulate partitioning of Hg in the oceanic water column as a cross-check on the hypothesis that sinking particle fluxes are important. Interestingly, these new data suggest particle-dissolved partitioning ( K d ) that is approximately 20× greater than previous estimates, which thereby challenges certain assumptions about the scavenging and active partitioning of Hg in the ocean used in earlier models. For example, the new particle data suggest that regenerative scavenging is the most likely mechanism by which the association of Hg and particles occurs. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

scholarly journals Microstructure and composition of marine aggregates as co-determinants for vertical particulate organic carbon transfer in the global ocean

2020 ◽  
Vol 17 (7) ◽  
pp. 1765-1803 ◽  
Author(s):  
Joeran Maerz ◽  
Katharina D. Six ◽  
Irene Stemmler ◽  
Soeren Ahmerkamp ◽  
Tatiana Ilyina
Keyword(s):  
Organic Carbon ◽  
Particulate Organic Carbon ◽  
Global Ocean ◽  
Co2 Uptake ◽  
Diatom Frustule ◽  
Marine Aggregates ◽  
Carbon Pump ◽  
The Impact ◽  
Biological Carbon Pump ◽  
Sinking Velocity

Abstract. Marine aggregates are the vector for biogenically bound carbon and nutrients from the euphotic zone to the interior of the oceans. To improve the representation of this biological carbon pump in the global biogeochemical HAMburg Ocean Carbon Cycle (HAMOCC) model, we implemented a novel Microstructure, Multiscale, Mechanistic, Marine Aggregates in the Global Ocean (M4AGO) sinking scheme. M4AGO explicitly represents the size, microstructure, heterogeneous composition, density and porosity of aggregates and ties ballasting mineral and particulate organic carbon (POC) fluxes together. Additionally, we incorporated temperature-dependent remineralization of POC. We compare M4AGO with the standard HAMOCC version, where POC fluxes follow a Martin curve approach with (i) linearly increasing sinking velocity with depth and (ii) temperature-independent remineralization. Minerals descend separately with a constant speed. In contrast to the standard HAMOCC, M4AGO reproduces the latitudinal pattern of POC transfer efficiency, as recently constrained by Weber et al. (2016). High latitudes show transfer efficiencies of ≈0.25±0.04, and the subtropical gyres show lower values of about 0.10±0.03. In addition to temperature as a driving factor for remineralization, diatom frustule size co-determines POC fluxes in silicifier-dominated ocean regions, while calcium carbonate enhances the aggregate excess density and thus sinking velocity in subtropical gyres. Prescribing rising carbon dioxide (CO2) concentrations in stand-alone runs (without climate feedback), M4AGO alters the regional ocean atmosphere CO2 fluxes compared to the standard model. M4AGO exhibits higher CO2 uptake in the Southern Ocean compared to the standard run, while in subtropical gyres, less CO2 is taken up. Overall, the global oceanic CO2 uptake remains the same. With the explicit representation of measurable aggregate properties, M4AGO can serve as a test bed for evaluating the impact of aggregate-associated processes on global biogeochemical cycles and, in particular, on the biological carbon pump.

scholarly journals Southern Ocean biological iron cycling in the pre-whaling and present ecosystems

2016 ◽  
Vol 374 (2081) ◽  
pp. 20150292 ◽  
Author(s):  
Maria T. Maldonado ◽  
Szymon Surma ◽  
Evgeny A. Pakhomov
Keyword(s):  
Southern Ocean ◽  
Future Research ◽  
Iron Cycling ◽  
Baleen Whales ◽  
Marine Food Webs ◽  
Trace Element Chemistry ◽  
Fe Content ◽  
Plankton Biomass ◽  
Climatic Impacts ◽  
Wet Weight

This study aimed to create the first model of biological iron (Fe) cycling in the Southern Ocean food web. Two biomass mass-balanced Ecopath models were built to represent pre- and post-whaling ecosystem states (1900 and 2008). Functional group biomasses (tonnes wet weight km −2 ) were converted to biogenic Fe pools (kg Fe km −2 ) using published Fe content ranges. In both models, biogenic Fe pools and consumption in the pelagic Southern Ocean were highest for plankton and small nektonic groups. The production of plankton biomass, particularly unicellular groups, accounted for the highest annual Fe demand. Microzooplankton contributed most to biological Fe recycling, followed by carnivorous zooplankton and krill. Biological Fe recycling matched previous estimates, and, under most conditions, could entirely meet the Fe demand of bacterioplankton and phytoplankton. Iron recycling by large baleen whales was reduced 10-fold by whaling between 1900 and 2008. However, even under the 1900 scenario, the contribution of whales to biological Fe recycling was negligible compared with that of planktonic consumers. These models are a first step in examining oceanic-scale biological Fe cycling, highlighting gaps in our present knowledge and key questions for future research on the role of marine food webs in the cycling of trace elements in the sea. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.

scholarly journals Role of zooplankton in determining the efficiency of the biological carbon pump

2017 ◽  
Vol 14 (1) ◽  
pp. 177-186 ◽  
Author(s):  
Emma L. Cavan ◽  
Stephanie A. Henson ◽  
Anna Belcher ◽  
Richard Sanders
Keyword(s):  
Biogeochemical Model ◽  
Atlantic Sector ◽  
Mesopelagic Zone ◽  
Carbon Pump ◽  
Minimum Zone ◽  
Direct Contrast ◽  
Particle Export ◽  
Biological Carbon Pump

Abstract. The efficiency of the ocean's biological carbon pump (BCPeff – here the product of particle export and transfer efficiencies) plays a key role in the air–sea partitioning of CO2. Despite its importance in the global carbon cycle, the biological processes that control BCPeff are poorly known. We investigate the potential role that zooplankton play in the biological carbon pump using both in situ observations and model output. Observed and modelled estimates of fast, slow, and total sinking fluxes are presented from three oceanic sites: the Atlantic sector of the Southern Ocean, the temperate North Atlantic, and the equatorial Pacific oxygen minimum zone (OMZ). We find that observed particle export efficiency is inversely related to primary production likely due to zooplankton grazing, in direct contrast to the model estimates. The model and observations show strongest agreement in remineralization coefficients and BCPeff at the OMZ site where zooplankton processing of particles in the mesopelagic zone is thought to be low. As the model has limited representation of zooplankton-mediated remineralization processes, we suggest that these results point to the importance of zooplankton in setting BCPeff, including particle grazing and fragmentation, and the effect of diel vertical migration. We suggest that improving parameterizations of zooplankton processes may increase the fidelity of biogeochemical model estimates of the biological carbon pump. Future changes in climate such as the expansion of OMZs may decrease the role of zooplankton in the biological carbon pump globally, hence increasing its efficiency.

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.

scholarly journals Role of zooplankton in determining the efficiency of the biological carbon pump

2016 ◽  
Author(s):  
Emma L. Cavan ◽  
Stephanie A. Henson ◽  
Anna Belcher ◽  
Richard Sanders
Keyword(s):  
Biogeochemical Model ◽  
Atlantic Sector ◽  
Mesopelagic Zone ◽  
Carbon Pump ◽  
Minimum Zone ◽  
Direct Contrast ◽  
Particle Export ◽  
Biological Carbon Pump

Abstract. The efficiency of the ocean’s biological carbon pump (BCPeff – here the product of particle export and transfer efficiencies) plays a key role in the air-sea partitioning of CO2. Despite its importance in the global carbon cycle, the biological processes that control BCPeff are poorly known. We investigate the potential role that zooplankton play in the biological carbon pump using both in situ observations and model output. Observed and modelled estimates of fast, slow and total sinking fluxes are presented from three oceanic sites: the Atlantic sector of the Southern Ocean, the temperate North Atlantic and the equatorial Pacific oxygen minimum zone (OMZ). We find that observed particle export efficiency is inversely related to primary production likely due to zooplankton grazing, in direct contrast to the model estimates. The model and observations show strongest agreement in remineralization coefficients and BCPeff at the OMZ site where zooplankton processing of particles in the mesopelagic zone is thought to be low. As the model has limited representation of zooplankton-mediated remineralization processes, we suggest that these results point to the importance of zooplankton in setting BCPeff, including particle grazing and fragmentation, and the effect of diel vertical migration. We suggest that improving parameterizations of zooplankton processes may increase the fidelity of biogeochemical model estimates of the biological carbon pump. Future changes in climate such as the expansion of OMZs may decrease the role of zooplankton in the biological carbon pump globally, hence increasing its efficiency.

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