Brief description
We dissect the spokes of the ferrous wheel associated with Fe demand by quantifying the uptake rates of heterotrophic bacteria and phytoplankton in the subantarctic Southern Ocean during summer and situate these findings within a seasonal context. To do so, we conducted bioassays in which the effects of light on Fe photochemistry and uptake physiology were studied by comparing light and dark incubations, and the effects of DOC supply and competition between phytoplankton and heterotrophic bacteria were examined by isolating bacteria from the larger members of the ferrous wheel by pre-incubation size fractionation.Lineage
Progress Code: completed
Maintenance and Update Frequency: notPlanned
Statement: Net primary productivity (i.e. inorganic C uptake) and Fe uptake rates were determined for water column samples collected at four to six depths between 0 and 70 m with the trace metal rosette. Water samples were collected pre-dawn at sampling depths determined from in situ PAR depth profiles obtained during midday CTD casts the day prior to collection. Samples were dispensed into 300 mL acid-washed polycarbonate bottles (ThermoScientific Nalgene, Waltham, MA, USA) and spiked with 16-20 μCi of sodium 14C-bicarbonate (NaH14CO3; specific activity 1.85 GBq mmol−1; PerkinElmer, Waltham, MA, USA) and 0.2 nmol L−1 of an acidified 55Fe solution (55FeCl3 in 0.1 M Ultrapure HCl; specific activity 30 MBq mmol−1; PerkinElmer). Six samples (five light and one “dark correction” bottle per irradiance) were incubated for 24h in a temperature-controlled deckboard incubator under natural sunlight at four to six light intensities (ranging from 67 to 1.0% of incident PAR). Light attenuation was adjusted by varying the layers of neutral density mesh and measured with a Biospherical Instruments QSL2101 Quantum Scalar PAR Sensor (San Diego, CA, USA). The incubation temperatures were 9, 10 and 12 ± 0.2°C for the spring, summer and fall experiments, respectively.
After 24h of incubation, four replicate samples were serially vacuum-filtered (<10 mm Hg) through 20, 2.0, and 0.2 μm porosity polycarbonate filters (47 mm diameter; Poretics, Waltham, MA, USA) separated by 200 μm nylon mesh spacers to determine size-fractionated Fe uptake rates and NPP. Two size-fractionated samples were washed with Titanium (III) EDTA—citrate reagent for 5 min to remove extracellular Fe and rinsed three times with 15 mL of 0.2 μm-filtered seawater, and the other two size-fractionated samples were rinsed only with 0.2 μm-filtered seawater. In addition, two samples were filtered through 0.2 μm filters: an unfractionated light measurement and a dark correction bottle. The dark correction was 1.6 ± 1.4% of the C uptake rates measured in the light over multiple voyages, depths, and years (N=11). Data for the dark-corrected, size-fractionated samples rinsed with the Ti(III) EDTA— citrate reagent are reported here (i.e. intracellular Fe and C uptake) (N=2). The one exception to this protocol was for the size-fractionated depth profile samples collected from 19 m in summer 2020 that were performed in triplicate and incubated in parallel with the ferrous wheel experiment (N=3). Samples were counted on a liquid scintillation counter (PerkinElmer Tri-Carb 2910 TR) as described previously..
Notes
CreditAustralian Research Council Special Research Initiative (Project Number SR200100008 (ACEAS) and ASCI000002 (AAPP)
Issued: 29 01 2025
Data time period: 2018-03-03 to 2021-01-16
text: westlimit=139.884; southlimit=-47.80; eastlimit=142.884; northlimit=-45.80
text: uplimit=70; downlimit=0
Subjects
AQUATIC ECOSYSTEMS |
BACTERIA/ARCHAEA |
BIOGEOCHEMICAL CYCLES |
BIOLOGICAL CLASSIFICATION |
BIOSPHERE |
EARTH SCIENCE |
ECOLOGICAL DYNAMICS |
ECOSYSTEM FUNCTIONS |
Global / Oceans | Global / Oceans | Southern Ocean |
Investigator |
Iron |
NUTRIENT CYCLING |
NUTRIENTS |
OCEAN CHEMISTRY |
OCEANS |
PHYTOPLANKTON |
PLANKTON |
SPECIES COMPETITION |
SPECIES/POPULATION INTERACTIONS |
Southern Ocean |
carbon |
competition |
ferrous wheel |
heterotrophic bacteria |
light |
microbes |
oceans |
phytoplankton |
picoeukaryote |
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Other Information
(DATA ACCESS - Southern Ocean Fe uptake rates [.xlsx])
Strzepek RF, Latour P, Ellwood MJ, Shaked Y, Boyd PW (2025). Microbial competition for iron determines its availability to the ferrous wheel. The ISME Journal. doi:10.1093/ismejo/wraf015 (ASSOCIATED PUBLICATION)
Identifiers
- DOI : 10.25959/9G97-VH65
- global : d0a1067d-4348-467d-a8e7-7d8f57e24bab
