Megabenthic standing stocks and organic carbon demand in a warming Arctic

Abstract. The contributions of micro-, nano-, and picoplankton to particle export were estimated from measurements of size-fractionated particulate 234Th, organic carbon, and phytoplankton indicator pigments obtained during five cruises between 2010 and 2012 along Line P in the subarctic northeast Pacific Ocean. Sinking fluxes of particulate organic carbon (POC) and indicator pigments were calculated from 234Th–238U disequilibria and, during two cruises, measured by a sediment trap at Ocean Station Papa. POC fluxes at 100 m ranged from 0.65 to 7.95 mmol m−2 d−1, similar in magnitude to previous results at Line P. Microplankton pigments dominate indicator pigment fluxes (averaging 69 ± 19% of total pigment flux), while nanoplankton pigments comprised the majority of pigment standing stocks (averaging 64 ± 23% of total pigment standing stocks). Indicator pigment loss rates (the ratio of pigment export flux to pigment standing stocks) point to preferential export of larger microplankton relative to smaller nano- and picoplankton. However, indicator pigments do not quantitatively trace particle export resulting from zooplankton grazing, which may be an important pathway for the export of small phytoplankton. These results have important implications for understanding the magnitude and mechanisms controlling the biological pump at Line P in particular, and more generally in oligotrophic gyres and high-nutrient, low-chlorophyll (HNLC) regions where small phytoplankton represent a major component of the autotrophic community.

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Summertime Chlorophyll a and Particulate Organic Carbon Standing Stocks in Surface Waters of the Fram Strait and the Arctic Ocean (1991–2015)

Frontiers in Marine Science ◽

10.3389/fmars.2020.00350 ◽

2020 ◽

Vol 7 ◽

Author(s):

Eva-Maria Nöthig ◽

Simon Ramondenc ◽

Antonie Haas ◽

Laura Hehemann ◽

Andreas Walter ◽

...

Keyword(s):

Organic Carbon ◽

Arctic Ocean ◽

Particulate Organic Carbon ◽

Chlorophyll A ◽

Surface Waters ◽

The Arctic ◽

Fram Strait ◽

The Arctic Ocean ◽

Standing Stocks

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Bacterial dissolved organic carbon demand in McMurdo Dry Valley lakes, Antarctica

Limnology and Oceanography ◽

10.4319/lo.2001.46.5.1189 ◽

2001 ◽

Vol 46 (5) ◽

pp. 1189-1194 ◽

Cited By ~ 39

Author(s):

Cristina D. Takacs ◽

John C. Priscu ◽

Diane M. McKnight

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

Carbon Demand ◽

Dry Valley

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The Seasonal Flux and Fate of Dissolved Organic Carbon Through Bacterioplankton in the Western North Atlantic

Frontiers in Microbiology ◽

10.3389/fmicb.2021.669883 ◽

2021 ◽

Vol 12 ◽

Author(s):

Nicholas Baetge ◽

Michael J. Behrenfeld ◽

James Fox ◽

Kimberly H. Halsey ◽

Kristina D. A. Mojica ◽

...

Keyword(s):

Organic Carbon ◽

Dissolved Organic Carbon ◽

North Atlantic ◽

Phytoplankton Bloom ◽

North Atlantic Ocean ◽

Net Primary Production ◽

Deep Ocean ◽

Carbon Demand ◽

Carbon Pump ◽

Biological Carbon Pump

The oceans teem with heterotrophic bacterioplankton that play an appreciable role in the uptake of dissolved organic carbon (DOC) derived from phytoplankton net primary production (NPP). As such, bacterioplankton carbon demand (BCD), or gross heterotrophic production, represents a major carbon pathway that influences the seasonal accumulation of DOC in the surface ocean and, subsequently, the potential vertical or horizontal export of seasonally accumulated DOC. Here, we examine the contributions of bacterioplankton and DOM to ecological and biogeochemical carbon flow pathways, including those of the microbial loop and the biological carbon pump, in the Western North Atlantic Ocean (∼39–54°N along ∼40°W) over a composite annual phytoplankton bloom cycle. Combining field observations with data collected from corresponding DOC remineralization experiments, we estimate the efficiency at which bacterioplankton utilize DOC, demonstrate seasonality in the fraction of NPP that supports BCD, and provide evidence for shifts in the bioavailability and persistence of the seasonally accumulated DOC. Our results indicate that while the portion of DOC flux through bacterioplankton relative to NPP increased as seasons transitioned from high to low productivity, there was a fraction of the DOM production that accumulated and persisted. This persistent DOM is potentially an important pool of organic carbon available for export to the deep ocean via convective mixing, thus representing an important export term of the biological carbon pump.

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Dynamics of N<sub>2</sub> fixation and fate of diazotroph-derived nitrogen in a low nutrient low chlorophyll ecosystem: results from the VAHINE mesocosm experiment (New Caledonia)

Biogeosciences Discussions ◽

10.5194/bgd-12-19579-2015 ◽

2015 ◽

Vol 12 (23) ◽

pp. 19579-19626 ◽

Cited By ~ 10

Author(s):

S. Bonnet ◽

H. Berthelot ◽

K. Turk-Kubo ◽

S. Fawcett ◽

E. Rahav ◽

...

Keyword(s):

Organic Carbon ◽

Primary Production ◽

Particulate Organic Carbon ◽

N2 Fixation ◽

Bacterial Production ◽

New Caledonia ◽

Seawater Temperature ◽

Global Ocean ◽

Nitrogen And Phosphorus ◽

Standing Stocks

Abstract. N2 fixation rates were measured daily in large (~ 50 m3) mesocosms deployed in the tropical South West Pacific coastal ocean (New Caledonia) to investigate the spatial and temporal dynamics of diazotrophy and the fate of diazotroph-derived nitrogen (DDN) in a low nutrient, low chlorophyll ecosystem. The mesocosms were intentionally fertilized with ~ 0.8 μM dissolved inorganic phosphorus (DIP) to stimulate diazotrophy. Bulk N2 fixation rates were replicable between the three mesocosms, averaged 18.5 ± 1.1 nmol N L−1 d−1 over the 23 days, and increased by a factor of two during the second half of the experiment (days 15 to 23) to reach 27.3 ± 1.0 nmol N L−1 d−1. These rates are higher than the upper range reported for the global ocean, indicating that the waters surrounding New Caledonia are particularly favourable for N2 fixation. During the 23 days of the experiment, N2 fixation rates were positively correlated with seawater temperature, primary production, bacterial production, standing stocks of particulate organic carbon, nitrogen and phosphorus, and alkaline phosphatase activity, and negatively correlated with DIP concentrations, DIP turnover time, nitrate, and dissolved organic nitrogen and phosphorus concentrations. The fate of DDN was investigated during the bloom of the unicellular diazotroph, UCYN-C, that occurred during the second half of the experiment. Quantification of diazotrophs in the sediment traps indicates that ~ 10 % of UCYN-C from the water column were exported daily to the traps, representing as much as 22.4 ± 5.5 % of the total POC exported at the height of the UCYN-C bloom. This export was mainly due to the aggregation of small (5.7 ± 0.8 μm) UCYN-C cells into large (100–500 μm) aggregates. During the same time period, a DDN transfer experiment based on high-resolution nanometer scale secondary ion mass spectrometry (nanoSIMS) coupled with 15N2 isotopic labelling revealed that 16 ± 6 % of the DDN was released to the dissolved pool and 21 ± 4 % was transferred to non-diazotrophic plankton, mainly picoplankton (18 ± 4 %) followed by diatoms (3 ± 2 %) within 24 h of incubation. This is consistent with the observed dramatic increase in picoplankton and diatom abundances, primary production, bacterial production and standing stocks of particulate organic carbon, nitrogen and phosphorus during the second half of the experiment in the mesocosms. These results offer insights into the fate of DDN during a bloom of UCYN-C in low nutrient, low chlorophyll ecosystems.

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Microbial diversity-informed modelling of polar marine ecosystem functions

10.5194/bg-2020-302 ◽

2020 ◽

Author(s):

Hyewon Heather Kim ◽

Jeff S. Bowman ◽

Ya-Wei Luo ◽

Hugh W. Ducklow ◽

Oscar M. Schofield ◽

...

Keyword(s):

Nucleic Acid ◽

Organic Carbon ◽

Microbial Diversity ◽

Net Primary Production ◽

Marine Ecosystem ◽

Ecosystem Model ◽

Ecosystem Functions ◽

Climate Conditions ◽

Carbon Demand ◽

Particle Export

Abstract. Heterotrophic marine bacteria utilize organic carbon for growth and biomass synthesis. Thus, their variability is key to the balance between the production and consumption of organic matter and ultimately particle export in the ocean. Here we investigate a potential link between bacterial traits and ecosystem functions in a rapidly changing polar marine ecosystem based on a bacteria-oriented ecosystem model. Using a data-assimilation scheme we utilize the observations of bacterial groups with different physiological states to constrain the group-specific bacterial ecosystem functions. We also investigate the association of the modelled bacterial and other ecosystem functions with eight recurrent modes representative of different bacterial taxonomic traits. High nucleic acid (HNA) bacteria show relatively high cell-specific bacterial production, respiration, and utilization of the semi-labile dissolved organic carbon pool compared to low nucleic acid (LNA) bacteria. Both taxonomy and physiological states of the bacteria are strong predictors of bacterial carbon demand, net primary production, and particle export. Numerical experiments under perturbed climate conditions show overall increased bacterial activity and a potential shift from LNA- to HNA-dominated bacterial communities in a warming ocean. Microbial diversity via different taxonomic and physiological traits informs our ecosystem model, providing insights into key bacterial and ecosystem functions in a changing environment.

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Significance of non-sinking particulate organic carbon and dark CO2fixation to heterotrophic carbon demand in the mesopelagic northeast Atlantic

Geophysical Research Letters ◽

10.1029/2010gl043105 ◽

2010 ◽

Vol 37 (9) ◽

pp. n/a-n/a ◽

Cited By ~ 29

Author(s):

Federico Baltar ◽

Javier Arístegui ◽

Eva Sintes ◽

Josep M. Gasol ◽

Thomas Reinthaler ◽

...

Keyword(s):

Organic Carbon ◽

Particulate Organic Carbon ◽

Northeast Atlantic ◽

Carbon Demand

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Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment

Biogeosciences ◽

10.5194/bg-13-6081-2016 ◽

2016 ◽

Vol 13 (21) ◽

pp. 6081-6093 ◽

Cited By ~ 13

Author(s):

Kristian Spilling ◽

Kai G. Schulz ◽

Allanah J. Paul ◽

Tim Boxhammer ◽

Eric P. Achterberg ◽

...

Keyword(s):

Organic Carbon ◽

Primary Production ◽

Ocean Acidification ◽

Bacterial Production ◽

Co2 Concentration ◽

Carbon Fluxes ◽

Co2 Levels ◽

Standing Stocks ◽

Co2 Treatment ◽

Ambient Co2

Abstract. About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans, decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient ( ∼  370 µatm) to high ( ∼  1200 µatm), were set up in mesocosm bags ( ∼  55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export), and biological rate measurements of primary production, bacterial production, and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0–t16; II: t17–t30; III: t31–t43). Pools of TPC, DOC, and DIC were approximately 420, 7200, and 25 200 mmol C m−2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ∼  7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During phase I the estimated gross primary production (GPP) was ∼  100 mmol C m−2 day−1, from which 75–95 % was respired, ∼  1 % ended up in the TPC (including export), and 5–25 % was added to the DOC pool. During phase II, the respiration loss increased to ∼  100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85–95 % of GPP) in the highest CO2 treatment. Bacterial production was ∼  30 % lower, on average, at the highest CO2 concentration than in the controls during phases II and III. This resulted in a higher accumulation of DOC and lower reduction in the TPC pool in the elevated CO2 treatments at the end of phase II extending throughout phase III. The “extra” organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transfer into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on the carbon budget and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools than ambient CO2 concentration. These results highlight the importance of addressing not only net changes in carbon standing stocks but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.

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Carbon Export in the Seasonal Sea Ice Zone North of Svalbard From Winter to Late Summer

Frontiers in Marine Science ◽

10.3389/fmars.2020.525800 ◽

2021 ◽

Vol 7 ◽

Author(s):

Christine Dybwad ◽

Philipp Assmy ◽

Lasse M. Olsen ◽

Ilka Peeken ◽

Anna Nikolopoulos ◽

...

Keyword(s):

Organic Carbon ◽

Sea Ice ◽

Late Summer ◽

Ice Cover ◽

Atlantic Water ◽

Arctic Sea Ice ◽

The Arctic ◽

Phytoplankton Blooms ◽

Carbon Export ◽

Standing Stocks

Phytoplankton blooms in the Arctic Ocean's seasonal sea ice zone are expected to start earlier and occur further north with retreating and thinning sea ice cover. The current study is the first compilation of phytoplankton bloom development and fate in the seasonally variable sea ice zone north of Svalbard from winter to late summer, using short-term sediment trap deployments. Clear seasonal patterns were discovered, with low winter and pre-bloom phytoplankton standing stocks and export fluxes, a short and intense productive season in May and June, and low Chl a standing stocks but moderate carbon export fluxes in the autumn post-bloom conditions. We observed intense phytoplankton blooms with Chl a standing stocks of >350 mg m−2 below consolidated sea ice cover, dominated by the prymnesiophyte Phaeocystis pouchetii. The largest vertical organic carbon export fluxes to 100 m, of up to 513 mg C m−2 day−1, were recorded at stations dominated by diatoms, while those dominated by P. pouchetii recorded carbon export fluxes up to 310 mg C m−2 day−1. Fecal pellets from krill and copepods contributed a substantial fraction to carbon export in certain areas, especially where blooms of P. pouchetii dominated and Atlantic water advection was prominent. The interplay between the taxonomic composition of protist assemblages, large grazers, distance to open water, and Atlantic water advection was found to be crucial in determining the fate of the blooms and the magnitude of organic carbon exported out of the surface water column. Previously, the marginal ice zone was considered the most productive region in the area, but our study reveals intense blooms and high export events in ice-covered waters. This is the first comprehensive study on carbon export fluxes for under-ice phytoplankton blooms, a phenomenon suggested to have increased in importance under the new Arctic sea ice regime.

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Effects of ocean acidification on pelagic carbon fluxes in a mesocosm experiment

10.5194/bg-2016-56 ◽

2016 ◽

Cited By ~ 1

Author(s):

Kristian Spilling ◽

Kai G. Schulz ◽

Allanah J. Paul ◽

Tim Boxhammer ◽

Eric P. Achterberg ◽

...

Keyword(s):

Organic Carbon ◽

Primary Production ◽

Ocean Acidification ◽

Bacterial Production ◽

Co2 Concentration ◽

Carbon Fluxes ◽

Co2 Levels ◽

Standing Stocks ◽

Co2 Treatment ◽

Ambient Co2

Abstract. About a quarter of anthropogenic CO2 emissions are currently taken up by the oceans decreasing seawater pH. We performed a mesocosm experiment in the Baltic Sea in order to investigate the consequences of increasing CO2 levels on pelagic carbon fluxes. A gradient of different CO2 scenarios, ranging from ambient (~ 370 µatm) to high (~ 1200 µatm), were set up in mesocosm bags (~ 55 m3). We determined standing stocks and temporal changes of total particulate carbon (TPC), dissolved organic (DOC), dissolved inorganic (DIC) and particulate organic carbon (POC) of specific plankton groups. We also measured carbon flux via CO2 exchange with the atmosphere and sedimentation (export); and biological rate measurements of primary production, bacterial production and total respiration. The experiment lasted for 44 days and was divided into three different phases (I: t0–t16; II: t17–t30; III: t31–t43). Pools of TPC, DOC and DIC were approximately 420, 7200 and 25 200 mmol C m−2 at the start of the experiment, and the initial CO2 additions increased the DIC pool by ~ 7 % in the highest CO2 treatment. Overall, there was a decrease in TPC and increase of DOC over the course of the experiment. The decrease in TPC was lower, and increase in DOC higher, in treatments with added CO2. During Phase I the estimated gross primary production (GPP) was ~ 100 mmol C fixed m−2 d−1; from which 75–95 % were respired, ~ 1 % ended up in the TPC (including export) and 5–25 % added to the DOC pool. During Phase II, the respiration loss increased to ~ 100 % of GPP at the ambient CO2 concentration, whereas respiration was lower (85–95 % of GPP) in the highest CO2 treatment. Bacterial production was ~ 30 % lower, on average, at the highest CO2 concentration compared with the controls during Phases II and III. This resulted in a higher accumulation DOC standing stock and lower reduction in TPC in the elevated CO2 treatments at the end of Phase II extending throughout Phase III. The "extra" organic carbon at high CO2 remained fixed in an increasing biomass of small-sized plankton and in the DOC pool, and did not transferred into large, sinking aggregates. Our results revealed a clear effect of increasing CO2 on carbon production and mineralization, in particular under nutrient limited conditions. Lower carbon loss processes (respiration and bacterial remineralization) at elevated CO2 levels resulted in higher TPC and DOC pools compared with the ambient CO2 concentration. These results highlight the importance to address not only net changes in carbon standing stocks, but also carbon fluxes and budgets to better disentangle the effects of ocean acidification.

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