Brief description
Here, we hypothesize that Fe uptake rates by sea-ice algae and under-ice phytoplankton are higher than the rates reported for open ocean phytoplankton in the SO. We performed 55Fe and carbon (14C) short-term uptake field measurements in, on and under Antarctic sea ice. We collected under ice seawater, melted snow and sea-ice cores. We then spiked them with 14C or 55Fe radiotracers to measure Fe and C uptake rates by sea-ice algae. Samples were then filtered, and residual radioactivity on the filters measured liquid scintillation counter (Packard).Lineage
Maintenance and Update Frequency: none-planned
Statement: Sampling of seawater, brine, slush and sea ice
All labware used for sampling and incubation was cleaned following trace metal clean procedures. To obtain samples for uptake experiments, sea-ice cores of 14 cm diameter were collected 20 cm apart on Days 6, 21, 29 and 32 using the trace-metal clean techniques described in Lannuzel et al. (2006). The cores were then transported to the ship, placed in a polyethylene (PE) lathe under class-100 laminar flow, and 1cm thick slices were cut along the cores using titanium (Ti) chisels and blades.
Bottom slices were collected from the cores dedicated to 55Fe and 14C uptake experiments and transferred into acid-washed PC dishes of 14 cm diameter. Samples of surface-ice slush and under-ice seawater were also collected for uptake experiments. Slush was collected on Day 22 at the snow/ice interface, using an acid-clean PE shovel, and transferred into trace-metal clean 250 mL PC bottles. Seawater was sampled on Day 23 at the ice/water interface, using an acid-cleaned braided PVC flexible tube and portable peristaltic pump (Cole-Parmer, Masterflex E/P) with acid-cleaned C-flex pump tubing, and collected into trace-metal clean 250 mL and 400 mL PC bottles.
Filtered seawater was also collected from 30 m below sea ice using an acid-cleaned braided PVC flexible tube and a portable peristaltic pump (Cole-Parmer, Masterflex E/P) with acid-cleaned C-flex pump tubing connected to an acid-cleaned 0.2 μm cartridge filter (Sartorius Sartroban® 300) and transferred into 20 L acid-clean PC carboys. The carboys were stored shipboard in the dark at 4 °C until needed. This filtered seawater was used for two procedural purposes: 1/to melt the incubated sea-ice sections at a 4:1 (v:v) ratio to avoid cell damage, and 2/as a spike solution for the slush incubation (see below).
Sea-ice brines were drained in-situ at 0.6 m depth in the ice cover, using the sack-hole technique, and collected using the same equipment as for seawater (Tison et al. 2008). The 0.2 μm filtered brines were collected into trace-metal clean 250 mL LDPE bottles previously rinsed with the collected brines. The brines were stored shipboard in the dark at 4 °C until needed for the bottom-ice experiments, when filtered brine was used as a spike solution for the bottom-ice incubations (see below).
The PC dishes containing the sea-ice sections and the PC bottles containing the slush and seawater samples were stored for 4 hours in the dark in the culture room set at −1°C. The in-situ DFe concentrations in the samples (Table 3) were estimated from the DFe concentration measured by Lannuzel et al. (2008) and corrected for the background DFe concentration in the 3 mL spike solution (brine DFe = 9.6 nmol L−1 and 30 m seawater = 1.2 nmol L−1). The average in-situ dissolved inorganic carbon (DIC) concentration was 2,100 µmol L–1. Methods for DIC analysis are described in (Delille et al. 2014).
Methods for 55Fe and 14C uptake experiments
Sea ice
The 1 cm thick ice was spiked with 3 mL of pre-filtered brine (0.2 µm) with 17 µL of 55FeCl3 stock solution (266 µCi mL−1, Perkin Elmer). The final 55Fe concentrations in the sea-ice samples ranged from 0.7 to 1.4 nmol L-1, depending on the sea-ice brine volume fraction. Another 1 cm thick slice from a nearby core was spiked with 3 mL pre-filtered brine (0.2 µm) with 20 µL of 14C source solution (NaH14CO3, 1 mCi mL−1, specific activity 50-60 mCi mmol−1, Amersham Biosciences). The Petri dishes were sealed in a zip-lock bag and re-inserted at their original depth together with the remaining ice core sections. The reconstructed ice cores were then transferred into a triple-layered transparent plastic bag and returned to the original core hole (Fig. 1b). The core holes were covered with snow to the original snow thickness (11 cm on Day 21 and 6 cm Day 32). This moment marked the start of the in-situ incubation period. In-situ sea-ice incubations were performed for 5-6 hours during ISPOL on two separate occasions (Day 21 and Day 32). Short-term incubations of 5-6 hours were also performed shipboard with 1 cm thick slices of bottom sea ice in the ship’s culture room under set temperature (-1 ± 1°C) and light (50 µmol m−2 s−1) conditions on two separate occasions (Day 6 and Day 29) to mimic general in-situ conditions.
Slush and under-ice seawater
The 250 mL PC bottles filled with slush were spiked with 3 mL of pre-filtered seawater (0.2 µm) with 1.5 µL of the 55FeCl3 source solution. The final 55Fe concentration in the amended slush was about 0.03 nmol L-1 of 55Fe. Another 250 mL PC bottle filled with slush was spiked with 3 mL pre-filtered seawater (0.2 µm) with 25 µL of 14C source solution.
For the seawater incubation, 2.5 µL of 55Fe source was added directly to a 400 mL PC bottles containing the seawater sample (final 55Fe concentration 0.05 nmol L−1). Another 250 mL PC bottle filled with seawater was spiked directly with 25 µL of 14C source solution. The PC bottles were sealed in a zip-lock bag and incubated for 5-6 hours in the shipboard culture room.
Filtration procedures
At the end of the incubation period, the ice cores were removed from the ice floe, immediately covered with black plastic bags, and transported to the laboratory of the RV Polarstern. The sea-ice sections were left to melt in filtered seawater in the dark at ambient temperature of the laboratory (melting time 1 hour), taking care to filter the samples as soon as the last piece of ice was melted (sample still close to 0°C), according to (Rintala et al. 2014).
The 55Fe samples contained in PC bottles and LDPE melting containers were split and filtered onto 0.8 µm and 10 µm Nuclepore PC membranes to distinguish Fe uptake by large organisms (> 10 µm) from uptake by small (0.8 - 10 µm) organisms. Total and intracellular 55Fe were counted on separate filters for each size fraction. For total Fe measurements, cells collected on the filters were rinsed once with 5 mL of 0.2 µm filtered seawater. For 55Fe intracellular measurements, cells collected on the filters were rinsed with a freshly prepared Ti-citrate-EDTA wash solution Tang and Morel (2006) to eliminate non-incorporated 55Fe (extracellular and abiotic adsorption on filter). The washing solution was applied directly on the filters for 2 min, followed by a rinse for 2 min with 5 mL of filtered seawater (Hudson and Morel 1989; Hassler and Schoemann 2009b).
The 14C samples in PC bottles and LDPE melting containers were filtered onto 25 mm GF/F membranes (0.7 µm pore size, Whatman). The filters were then rinsed with filtered seawater to reduce the background 14C-DIC and allowed to dry in a desiccator for 1 hour under a fume hood. Filters were dried and 200 µl of HCl 0.1 N was added onto each filter to allow the inorganic C to evaporate overnight, therefore leaving only organic C on the filter. Note that the GF/F filters used for the filtrations from the 14C incubations tend to retain more organic carbon (and associated Fe) than the PC filters used for the 55Fe incubations (Morán et al. 1999).
Finally, filters were transferred into scintillation vials and 10 mL of scintillation cocktail (Ready SafeTM, Perkin Elmer) was added. After vortex agitation, the radioactivity on filter (55Fe or 14C) was counted by liquid scintillation counter (Packard). Counts per minute (cpm) were then converted into disintegration per minute using 55Fe and 14C custom quench curves.
The Fetot uptake rates of the cells rinsed with filtered seawater represent whole-cell Fe contents, while the ratios of Ti-rinsed cells provide an indication of internal Fe contents (Feintra). Feintra by small algae (0.8 - 10 µm) was estimated by calculating the difference between Feintra of the whole community (> 0.8 µm) and the Feintra by large algae (> 10 µm). Extracellular Fe uptake rates were calculated as the difference between Fetot and Feintra uptake rates. Molar uptake rates of C were estimated by the following equations: C uptake = (naturally occurring DIC x 14C-POC x 1.05)/(14C-DIC added), with the naturally occurring concentration of DIC = 2,100 µmol L−1 and 1.05 the correction for the preferential uptake of light isotopes (Welschmeyer and Lorenzen 1984).
Validation of the experimental set-up
No parallel incubations were carried out in-situ and in the ship’s culture room, instead in-situ (Day 26 and 32) and shipboard (Day 6 and 29) incubations were alternated during ISPOL. The temperature and light intensity in the ship’s culture room were controlled and purposefully set to mimic in-situ conditions to ensure the same growing conditions were met. The temperature of the culture room was set at −1 ± 1 °C. In-situ temperatures in bottom sea ice measured using a Testo thermometer varied from −1.4 to −1.9 °C (see Tison et al. (2008) for detail). In-situ light of 0.5 to 40 µmol m−2 s−1 was measured at the ice/water interface using a LiCOR sensor positioned at different angles to capture in-situ irradiance. Using the same sensor, light measured in the ship’s culture room varied between 12 and 43 µmol m−2 s−1 depending on the distance of the radio-labelled petri dish from the light source.
All labware used for sampling and incubation was cleaned following trace metal clean procedures. To obtain samples for uptake experiments, sea-ice cores of 14 cm diameter were collected 20 cm apart on Days 6, 21, 29 and 32 using the trace-metal clean techniques described in Lannuzel et al. (2006). The cores were then transported to the ship, placed in a polyethylene (PE) lathe under class-100 laminar flow, and 1cm thick slices were cut along the cores using titanium (Ti) chisels and blades.
Bottom slices were collected from the cores dedicated to 55Fe and 14C uptake experiments and transferred into acid-washed PC dishes of 14 cm diameter. Samples of surface-ice slush and under-ice seawater were also collected for uptake experiments. Slush was collected on Day 22 at the snow/ice interface, using an acid-clean PE shovel, and transferred into trace-metal clean 250 mL PC bottles. Seawater was sampled on Day 23 at the ice/water interface, using an acid-cleaned braided PVC flexible tube and portable peristaltic pump (Cole-Parmer, Masterflex E/P) with acid-cleaned C-flex pump tubing, and collected into trace-metal clean 250 mL and 400 mL PC bottles.
Filtered seawater was also collected from 30 m below sea ice using an acid-cleaned braided PVC flexible tube and a portable peristaltic pump (Cole-Parmer, Masterflex E/P) with acid-cleaned C-flex pump tubing connected to an acid-cleaned 0.2 μm cartridge filter (Sartorius Sartroban® 300) and transferred into 20 L acid-clean PC carboys. The carboys were stored shipboard in the dark at 4 °C until needed. This filtered seawater was used for two procedural purposes: 1/to melt the incubated sea-ice sections at a 4:1 (v:v) ratio to avoid cell damage, and 2/as a spike solution for the slush incubation (see below).
Sea-ice brines were drained in-situ at 0.6 m depth in the ice cover, using the sack-hole technique, and collected using the same equipment as for seawater (Tison et al. 2008). The 0.2 μm filtered brines were collected into trace-metal clean 250 mL LDPE bottles previously rinsed with the collected brines. The brines were stored shipboard in the dark at 4 °C until needed for the bottom-ice experiments, when filtered brine was used as a spike solution for the bottom-ice incubations (see below).
The PC dishes containing the sea-ice sections and the PC bottles containing the slush and seawater samples were stored for 4 hours in the dark in the culture room set at −1°C. The in-situ DFe concentrations in the samples (Table 3) were estimated from the DFe concentration measured by Lannuzel et al. (2008) and corrected for the background DFe concentration in the 3 mL spike solution (brine DFe = 9.6 nmol L−1 and 30 m seawater = 1.2 nmol L−1). The average in-situ dissolved inorganic carbon (DIC) concentration was 2,100 µmol L–1. Methods for DIC analysis are described in (Delille et al. 2014).
Methods for 55Fe and 14C uptake experiments
Sea ice
The 1 cm thick ice was spiked with 3 mL of pre-filtered brine (0.2 µm) with 17 µL of 55FeCl3 stock solution (266 µCi mL−1, Perkin Elmer). The final 55Fe concentrations in the sea-ice samples ranged from 0.7 to 1.4 nmol L-1, depending on the sea-ice brine volume fraction. Another 1 cm thick slice from a nearby core was spiked with 3 mL pre-filtered brine (0.2 µm) with 20 µL of 14C source solution (NaH14CO3, 1 mCi mL−1, specific activity 50-60 mCi mmol−1, Amersham Biosciences). The Petri dishes were sealed in a zip-lock bag and re-inserted at their original depth together with the remaining ice core sections. The reconstructed ice cores were then transferred into a triple-layered transparent plastic bag and returned to the original core hole (Fig. 1b). The core holes were covered with snow to the original snow thickness (11 cm on Day 21 and 6 cm Day 32). This moment marked the start of the in-situ incubation period. In-situ sea-ice incubations were performed for 5-6 hours during ISPOL on two separate occasions (Day 21 and Day 32). Short-term incubations of 5-6 hours were also performed shipboard with 1 cm thick slices of bottom sea ice in the ship’s culture room under set temperature (-1 ± 1°C) and light (50 µmol m−2 s−1) conditions on two separate occasions (Day 6 and Day 29) to mimic general in-situ conditions.
Slush and under-ice seawater
The 250 mL PC bottles filled with slush were spiked with 3 mL of pre-filtered seawater (0.2 µm) with 1.5 µL of the 55FeCl3 source solution. The final 55Fe concentration in the amended slush was about 0.03 nmol L-1 of 55Fe. Another 250 mL PC bottle filled with slush was spiked with 3 mL pre-filtered seawater (0.2 µm) with 25 µL of 14C source solution.
For the seawater incubation, 2.5 µL of 55Fe source was added directly to a 400 mL PC bottles containing the seawater sample (final 55Fe concentration 0.05 nmol L−1). Another 250 mL PC bottle filled with seawater was spiked directly with 25 µL of 14C source solution. The PC bottles were sealed in a zip-lock bag and incubated for 5-6 hours in the shipboard culture room.
Filtration procedures
At the end of the incubation period, the ice cores were removed from the ice floe, immediately covered with black plastic bags, and transported to the laboratory of the RV Polarstern. The sea-ice sections were left to melt in filtered seawater in the dark at ambient temperature of the laboratory (melting time 1 hour), taking care to filter the samples as soon as the last piece of ice was melted (sample still close to 0°C), according to (Rintala et al. 2014).
The 55Fe samples contained in PC bottles and LDPE melting containers were split and filtered onto 0.8 µm and 10 µm Nuclepore PC membranes to distinguish Fe uptake by large organisms (> 10 µm) from uptake by small (0.8 - 10 µm) organisms. Total and intracellular 55Fe were counted on separate filters for each size fraction. For total Fe measurements, cells collected on the filters were rinsed once with 5 mL of 0.2 µm filtered seawater. For 55Fe intracellular measurements, cells collected on the filters were rinsed with a freshly prepared Ti-citrate-EDTA wash solution Tang and Morel (2006) to eliminate non-incorporated 55Fe (extracellular and abiotic adsorption on filter). The washing solution was applied directly on the filters for 2 min, followed by a rinse for 2 min with 5 mL of filtered seawater (Hudson and Morel 1989; Hassler and Schoemann 2009b).
The 14C samples in PC bottles and LDPE melting containers were filtered onto 25 mm GF/F membranes (0.7 µm pore size, Whatman). The filters were then rinsed with filtered seawater to reduce the background 14C-DIC and allowed to dry in a desiccator for 1 hour under a fume hood. Filters were dried and 200 µl of HCl 0.1 N was added onto each filter to allow the inorganic C to evaporate overnight, therefore leaving only organic C on the filter. Note that the GF/F filters used for the filtrations from the 14C incubations tend to retain more organic carbon (and associated Fe) than the PC filters used for the 55Fe incubations (Morán et al. 1999).
Finally, filters were transferred into scintillation vials and 10 mL of scintillation cocktail (Ready SafeTM, Perkin Elmer) was added. After vortex agitation, the radioactivity on filter (55Fe or 14C) was counted by liquid scintillation counter (Packard). Counts per minute (cpm) were then converted into disintegration per minute using 55Fe and 14C custom quench curves.
The Fetot uptake rates of the cells rinsed with filtered seawater represent whole-cell Fe contents, while the ratios of Ti-rinsed cells provide an indication of internal Fe contents (Feintra). Feintra by small algae (0.8 - 10 µm) was estimated by calculating the difference between Feintra of the whole community (> 0.8 µm) and the Feintra by large algae (> 10 µm). Extracellular Fe uptake rates were calculated as the difference between Fetot and Feintra uptake rates. Molar uptake rates of C were estimated by the following equations: C uptake = (naturally occurring DIC x 14C-POC x 1.05)/(14C-DIC added), with the naturally occurring concentration of DIC = 2,100 µmol L−1 and 1.05 the correction for the preferential uptake of light isotopes (Welschmeyer and Lorenzen 1984).
Validation of the experimental set-up
No parallel incubations were carried out in-situ and in the ship’s culture room, instead in-situ (Day 26 and 32) and shipboard (Day 6 and 29) incubations were alternated during ISPOL. The temperature and light intensity in the ship’s culture room were controlled and purposefully set to mimic in-situ conditions to ensure the same growing conditions were met. The temperature of the culture room was set at −1 ± 1 °C. In-situ temperatures in bottom sea ice measured using a Testo thermometer varied from −1.4 to −1.9 °C (see Tison et al. (2008) for detail). In-situ light of 0.5 to 40 µmol m−2 s−1 was measured at the ice/water interface using a LiCOR sensor positioned at different angles to capture in-situ irradiance. Using the same sensor, light measured in the ship’s culture room varied between 12 and 43 µmol m−2 s−1 depending on the distance of the radio-labelled petri dish from the light source.
Notes
CreditThis work was carried out in the framework of the Belgian research program Action de Recherche Concertée “-Biogeochemistry in a CLIMate change perspective” financed by the Belgian French Community under contract n°ARC-02/7-318287. This is also a contribution to the European Network of Excellence EUR–OCEANS (contract n°511106-2) and to the BELCANTO (contracts SD/CA/03A&B) and BIGSOUTH (contract N° SD/CA/05A) projects financed by the Belgian Federal Science Policy Office. DL was funded by the Australian Research Council (FT190100688). This work was supported by the Australian Government’s Cooperative Research Centre Program through the Antarctic Climate and Ecosystems Cooperative Research Centre (ACE CRC) and through the Australian Antarctic Science grant #4291.
Data time period: 2004-11-29 to 2004-12-31
text: westlimit=-55.34000000000001; southlimit=-68.06700000000001; eastlimit=-54.519999999999996; northlimit=-67.29
Subjects
BIOLOGICAL CLASSIFICATION |
Biological Oceanography |
Chemical Oceanography |
EARTH SCIENCE |
Earth Sciences |
Fe:C ratio |
Oceanography |
PHYTOPLANKTON |
PLANKTON |
PROTISTS |
Sea ice |
algae |
biota |
oceans |
phytoplankton |
update rates |
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Other Information
(DATA ACCESS - Fe C ISPOL [direct download])
uri :
https://data.imas.utas.edu.au/attachments/279aa69a-861e-4453-ba52-30e044048f19/data_Fe_C_ISPOL.xlsx
Identifiers
- global : 279aa69a-861e-4453-ba52-30e044048f19
