scholarly journals Quantification of the lithogenic carbon pump following a simulated dust-deposition event in large mesocosms

2014 ◽  
Vol 11 (4) ◽  
pp. 1007-1020 ◽  
Author(s):  
M. Bressac ◽  
C. Guieu ◽  
D. Doxaran ◽  
F. Bourrin ◽  
K. Desboeufs ◽  
...  
Keyword(s):  
Quantitative Estimation ◽  
Linear Regression Analysis ◽  
Deep Ocean ◽  
Biological Pump ◽  
Dust Deposition ◽  
Poc Flux ◽  
Poc Export ◽  
Carbon Pump ◽  
Fertilization Effect ◽  
Dust Events

Abstract. Lithogenic particles, such as desert dust, have been postulated to influence particulate organic carbon (POC) export to the deep ocean by acting as mineral ballasts. However, an accurate understanding and quantification of the POC–dust association that occurs within the upper ocean is required in order to refine the "ballast hypothesis". In the framework of the DUNE (a DUst experiment in a low-Nutrient, low-chlorophyll Ecosystem) project, two artificial seedings were performed seven days apart within large mesocosms. A suite of optical and biogeochemical measurements were used to quantify surface POC export following simulated dust events within a low-nutrient, low-chlorophyll ecosystem. The two successive seedings led to a 2.3–6.7-fold higher POC flux than the POC flux observed in controlled mesocosms. A simple linear regression analysis revealed that the lithogenic fluxes explained more than 85% of the variance in POC fluxes. On the scale of a dust-deposition event, we estimated that 42–50% of POC fluxes were strictly associated with lithogenic particles (through aggregation and most probably sorption processes). Lithogenic ballasting also likely impacted the remaining POC fraction which resulted from the fertilization effect. The observations support the "ballast hypothesis" and provide a quantitative estimation of the surface POC export abiotically triggered by dust deposition. In this work, we demonstrate that the strength of such a "lithogenic carbon pump" depends on the biogeochemical conditions of the water column at the time of deposition. Based on these observations, we suggest that this lithogenic carbon pump could represent a major component of the biological pump in oceanic areas subjected to intense atmospheric forcing.

scholarly journals Quantification of the lithogenic carbon pump following a dust deposition event

2013 ◽  
Vol 10 (8) ◽  
pp. 13639-13677 ◽  
Author(s):  
M. Bressac ◽  
C. Guieu ◽  
D. Doxaran ◽  
F. Bourrin ◽  
K. Desboeufs ◽  
...  
Keyword(s):  
Quantitative Estimation ◽  
Linear Regression Analysis ◽  
Deep Ocean ◽  
Biological Pump ◽  
Dust Deposition ◽  
Poc Flux ◽  
Poc Export ◽  
Carbon Pump ◽  
Fertilization Effect ◽  
Dust Events

Abstract. Lithogenic particles, such as desert dust, have been postulated to influence particulate organic carbon (POC) export to the deep ocean by acting as mineral ballasts. However, an accurate understanding and quantification of the POC-dust association that occurs within the upper ocean is required in order to affine the "ballast hypothesis". In the framework of the DUNE project, two artificial seedings were performed seven days apart within large mesocosms. A suite of optical and biogeochemical measurements were used to quantify surface POC export following simulated dust events within a low-nutrient low-chlorophyll ecosystem. The two successive seedings led to a 2.3–6.7 fold higher POC flux as compared to the POC flux observed in controlled mesocosms. A simple linear regression analysis revealed that the lithogenic fluxes explained more than 85% of the variance in POC fluxes. At the scale of a dust deposition event, we estimated that 42–50% of POC fluxes were strictly associated with lithogenic particles through an aggregation process. Lithogenic ballasting also likely impacted the remaining POC fraction which resulted from the fertilization effect. The observations support the "ballast hypothesis" and provide a quantitative estimation of the surface POC export abiotically triggered by dust deposition. In this work, we demonstrate that the strength of such a "lithogenic carbon pump" depends on the biogeochemical conditions of the water column at the time of deposition. Based on these observations, we suggest that this "lithogenic carbon pump" could represent a major component of the biological pump in oceanic areas subjected to intense atmospheric forcing.

scholarly journals Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

2015 ◽  
Vol 12 (13) ◽  
pp. 3953-3971 ◽  
Author(s):  
S. Z. Rosengard ◽  
P. J. Lam ◽  
W. M. Balch ◽  
M. E. Auro ◽  
S. Pike ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
Euphotic Zone ◽  
Biological Pump ◽  
Carbon Export ◽  
Mesopelagic Zone ◽  
Poc Flux ◽  
Phytoplankton Communities ◽  
Poc Export ◽  
Particulate Inorganic Carbon

Abstract. Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize, and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of > 51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition, and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-rich communities produce large and labile POC aggregates, which not only generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

scholarly journals Carbon export and transfer to depth across the Southern Ocean Great Calcite Belt

2015 ◽  
Vol 12 (3) ◽  
pp. 2843-2896
Author(s):  
S. Z. Rosengard ◽  
P. J. Lam ◽  
W. M. Balch ◽  
M. E. Auro ◽  
S. Pike ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Deep Ocean ◽  
Euphotic Zone ◽  
Biological Pump ◽  
Carbon Export ◽  
Mesopelagic Zone ◽  
Poc Flux ◽  
Phytoplankton Communities ◽  
Poc Export ◽  
Particulate Inorganic Carbon

Abstract. Sequestration of carbon by the marine biological pump depends on the processes that alter, remineralize and preserve particulate organic carbon (POC) during transit to the deep ocean. Here, we present data collected from the Great Calcite Belt, a calcite-rich band across the Southern Ocean surface, to compare the transformation of POC in the euphotic and mesopelagic zones of the water column. The 234Th-derived export fluxes and size-fractionated concentrations of POC, particulate inorganic carbon (PIC), and biogenic silica (BSi) were measured from the upper 1000 m of 27 stations across the Atlantic and Indian sectors of the Great Calcite Belt. POC export out of the euphotic zone was correlated with BSi export. PIC export was not, but did correlate positively with POC flux transfer efficiency. Moreover, regions of high BSi concentrations, which corresponded to regions with proportionally larger particles, exhibited higher attenuation of >51 μm POC concentrations in the mesopelagic zone. The interplay among POC size partitioning, mineral composition and POC attenuation suggests a more fundamental driver of POC transfer through both depth regimes in the Great Calcite Belt. In particular, we argue that diatom-dominated communities produce large and labile POC aggregates, which generate high export fluxes but also drive more remineralization in the mesopelagic zone. We observe the opposite in communities with smaller calcifying phytoplankton, such as coccolithophores. We hypothesize that these differences are influenced by inherent differences in the lability of POC exported by different phytoplankton communities.

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.

scholarly journals Impact of dust deposition on the albedo of Vatnajökull ice cap, Iceland

2017 ◽  
Vol 11 (2) ◽  
pp. 741-754 ◽  
Author(s):  
Monika Wittmann ◽  
Christine Dorothea Groot Zwaaftink ◽  
Louise Steffensen Schmidt ◽  
Sverrir Guðmundsson ◽  
Finnur Pálsson ◽  
...  
Keyword(s):  
Mass Balance ◽  
Radiative Forcing ◽  
Climate Model ◽  
Dispersion Model ◽  
Dust Deposition ◽  
Glacier Surface ◽  
Outlet Glacier ◽  
Ice Cap ◽  
Weather Stations ◽  
Dust Events

Abstract. Deposition of small amounts of airborne dust on glaciers causes positive radiative forcing and enhanced melting due to the reduction of surface albedo. To study the effects of dust deposition on the mass balance of Brúarjökull, an outlet glacier of the largest ice cap in Iceland, Vatnajökull, a study of dust deposition events in the year 2012 was carried out. The dust-mobilisation module FLEXDUST was used to calculate spatio-temporally resolved dust emissions from Iceland and the dispersion model FLEXPART was used to simulate atmospheric dust dispersion and deposition. We used albedo measurements at two automatic weather stations on Brúarjökull to evaluate the dust impacts. Both stations are situated in the accumulation area of the glacier, but the lower station is close to the equilibrium line. For this site ( ∼  1210 m a.s.l.), the dispersion model produced 10 major dust deposition events and a total annual deposition of 20.5 g m−2. At the station located higher on the glacier ( ∼  1525 m a.s.l.), the model produced nine dust events, with one single event causing  ∼  5 g m−2 of dust deposition and a total deposition of  ∼  10 g m−2 yr−1. The main dust source was found to be the Dyngjusandur floodplain north of Vatnajökull; northerly winds prevailed 80 % of the time at the lower station when dust events occurred. In all of the simulated dust events, a corresponding albedo drop was observed at the weather stations. The influence of the dust on the albedo was estimated using the regional climate model HIRHAM5 to simulate the albedo of a clean glacier surface without dust. By comparing the measured albedo to the modelled albedo, we determine the influence of dust events on the snow albedo and the surface energy balance. We estimate that the dust deposition caused an additional 1.1 m w.e. (water equivalent) of snowmelt (or 42 % of the 2.8 m w.e. total melt) compared to a hypothetical clean glacier surface at the lower station, and 0.6 m w.e. more melt (or 38 % of the 1.6 m w.e. melt in total) at the station located further upglacier. Our findings show that dust has a strong influence on the mass balance of glaciers in Iceland.

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;

Deep ocean fluxes and their link to surface ocean processes and the biological pump

2005 ◽  
Vol 65 (2-4) ◽  
pp. 240-259 ◽  
Author(s):  
T. Rixen ◽  
M.V.S. Guptha ◽  
V. Ittekkot
Keyword(s):  
Deep Ocean ◽  
Biological Pump ◽  
Surface Ocean ◽  
Ocean Processes

scholarly journals Response of export production and dissolved oxygen concentrations in oxygen minimum zones to <i>p</i>CO<sub>2</sub> and temperature stabilization scenarios in the biogeochemical model HAMOCC 2.0

2017 ◽  
Vol 14 (4) ◽  
pp. 781-797 ◽  
Author(s):  
Teresa Beaty ◽  
Christoph Heinze ◽  
Taylor Hughlett ◽  
Arne M. E. Winguth
Keyword(s):  
Pacific Ocean ◽  
Organic Carbon ◽  
Dissolved Oxygen ◽  
Radiative Forcing ◽  
The Pacific ◽  
Poc Flux ◽  
Poc Export ◽  
The Pacific Ocean ◽  
Do Concentration ◽  
Oxygen Minimum

Abstract. Dissolved oxygen (DO) concentration in the ocean is an important component of marine biogeochemical cycles and will be greatly altered as climate change persists. In this study a global oceanic carbon cycle model (HAMOCC 2.0) is used to address how mechanisms of oxygen minimum zone (OMZ) expansion respond to changes in CO2 radiative forcing. Atmospheric pCO2 is increased at a rate of 1 % annually and the model is stabilized at 2 ×, 4 ×, 6  ×, and 8 × preindustrial pCO2 levels. With an increase in CO2 radiative forcing, the OMZ in the Pacific Ocean is controlled largely by changes in particulate organic carbon (POC) export, resulting in increased remineralization and thus expanding the OMZs within the tropical Pacific Ocean. A potential decline in primary producers in the future as a result of environmental stress due to ocean warming and acidification could lead to a substantial reduction in POC export production, vertical POC flux, and thus increased DO concentration particularly in the Pacific Ocean at a depth of 600–800 m. In contrast, the vertical expansion of the OMZs within the Atlantic is linked to increases POC flux as well as changes in oxygen solubility with increasing seawater temperature. Changes in total organic carbon and increase sea surface temperature (SST) also lead to the formation of a new OMZ in the western subtropical Pacific Ocean. The development of the new OMZ results in dissolved oxygen concentration of  ≤  50 µmol kg−1 throughout the equatorial Pacific Ocean at 4 times preindustrial pCO2. Total ocean volume with dissolved oxygen concentrations of  ≤  50 µmol kg−1 increases by 2.4, 5.0, and 10.5 % for the 2 ×, 4 ×, and 8 × CO2 simulations, respectively.

scholarly journals BPOP-v1 model: exploring the impact of changes in the biological pump on the shelf sea and ocean nutrient and redox state

2019 ◽  
Author(s):  
Elisa Lovecchio ◽  
Timothy M. Lenton
Keyword(s):  
Organic Matter ◽  
Deep Ocean ◽  
Biological Pump ◽  
Promising Tool ◽  
Biogeochemical Fluxes ◽  
Structure Changes ◽  
Large Particles ◽  
Shelf Sea ◽  
Slope Sediment ◽  
The Impact

Abstract. The ocean’s biological pump has changed over Earth history from one dominated by prokaryotes, to one involving a mixture of prokaryotes and eukaryotes with trophic structure. Changes in the biological pump are in turn hypothesised to have caused important changes in the ocean’s nutrient and redox properties. To explore these hypotheses, we present here a new box model including oxygen (O), phosphorus (P) and a dynamical biological pump. Our Biological Pump, Oxygen and Phosphorus (BPOP) model accounts for two – small and large – organic matter species generated by production and coagulation, respectively. Export and burial of these particles are regulated by a remineralization length (zrem) scheme. We independently vary zrem of small and large particles in order to study how changes in sinking speeds and remineralization rates affect the major biogeochemical fluxes, and O and P ocean concentrations. Modelled O and P budgets and fluxes lay close to present estimates for zrem in the range of currently measured values. Our results highlight that relatively small changes in zrem of the large particles can have important impacts on the O and P ocean availability and support the idea that an early ocean dominated by small particles was nutrient rich due to inefficient removal to sediments. The results also highlight that shelf ocean anoxia can coexist with an oxygenated deep open ocean for realistic values of zrem, especially for large values of the small particle zrem. This could challenge conventional interpretations that the Proterozoic deep ocean was anoxic, which are derived from shelf and slope sediment redox data. This simple and computationally inexpensive model is a promising tool to investigate the impact of changes in the organic matter sinking and remineralization rates as well as changes in physical processes coupled to the biological pump in a variety of case studies.

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