ALBERT

Description: During the 13 day Southern Ocean Iron RE-lease Experiment (SOIREE), dissolved iron concentrations decreased rapidly following each of three iron-enrichments, but remained high (〉1 nM, up to 80% as FeII) after the fourth and final enrichment on day 8. The former trend was mainly due to dilution (spreading of iron-fertilized waters) and particle scavenging. The latter may only be explained by a joint production-maintenance mechanism; photoreduction is the only candidate process able to produce sufficiently high FeII, but as such levels persisted overnight (8 hr dark period) -ten times the half-life for this species- a maintenance mechanism (complexation of FeII) is required, and is supported by evidence of increased ligand concentrations on day 12. The source of these ligands and their affinity for FeII is not known. This retention of iron probably permitted the longevity of this bloom raising fundamental questions about iron cycling in HNLC (High Nitrate Low Chlorophyll) Polar waters.

Description: The growth of populations is known to be influenced by dispersal, which has often been described as purely diffusive (Kierstead and Slobodkin, 1953; Okubo, 1980). In the open ocean, however, the tendrils and filaments of phytoplankton populations provide evidence for dispersal by stirring (Gower et al., 1980, doi:10.1038/288157a0; Holligan et al., 1993, doi:10.1029/93GB01731). Despite the apparent importance of horizontal stirring for plankton ecology, this process remains poorly characterized. Here we investigate the development of a discrete phytoplankton bloom, which was initiated by the iron fertilization of a patch of water (7 km in diameter) in the Southern Ocean (Boyd et al., 2000, doi:10.1038/35037500). Satellite images show a striking, 150-km-long bloom near the experimental site, six weeks after the initial fertilization. We argue that the ribbon-like bloom was produced from the fertilized patch through stirring, growth and diffusion, and we derive an estimate of the stirring rate. In this case, stirring acts as an important control on bloom development, mixing phytoplankton and iron out of the patch, but also entraining silicate. This may have prevented the onset of silicate limitation, and so allowed the bloom to continue for as long as there was sufficient iron. Stirring in the ocean is likely to be variable, so blooms that are initially similar may develop very differently.

Description: The database includes measurements of the trace gases carbonyl sulfide (OCS) and carbon disulfide (CS2) in seawater (in picomol per liter) and the marine boundary layer (parts per trillion, ppt). It consists of individual datasets compiled from published original data, digitalization from publications (pdf documents) and unpublished data. Only shipborne measurements or measurements from time series stations with a dominant marine signal are included. The database contains mainly surface ocean measurements, but few available profiles down to 〉1000 m are included as well. Temporal resolution ranges from 12 minutes to hourly or monthly intervals. The database includes the following metadata (if available): latitude, longitude, depth, time of sampling, meteorological and physical parameters, main reference, method, contributor(s). The database is intended to facilitate model evaluation and the identification of global patterns. Data in excel and txt-files are identical.

Description: At the end of the two year incubation of a subantarctic E. huxleyi culture (2015-11-20 to 2017-12-01), a temperature response experiment was performed using the Now (Day 747) and Future (Day 725) populations. Now and Future populations were grown in triplicate 28 ml Nalgene Oak Ridge-style centrifuge tubes (Sigma) in Now or Future medium, respectively. The tubes were held in an aluminium temperature gradient block similar to Thomas et al. (1963), that was heated at one end and cooled at the other using water maintained at constant temperature by refrigerated circulators (Julabo GmbH). The temperature regime resulted in a range of 10 temperatures along the length of the block from 6.2°C at one end to 16.5°C at the other, with a range within replicates at each temperature of 0.1 – 0.2°C. The block was lit from below which achieved a light level of 62 +/- 7 μmol m⁻² s⁻¹ at the bottom of the tubes in a 12 hour: 12 hour light: dark cycle. To ensure uniform light each replicate was manually rotated through the row holes at the set temperature during the incubation period. Measurements of in vivo chl-a were made daily and growth rates calculated from the least squares regression of the natural logarithm of in vivo fluorescence, versus time.

Description: During a two year incubation of a subantarctic E. huxleyi culture (2015-11-20 to 2017-12-01), at the final cross-over point (Day 670) an additional suite of measurements were performed with cells from Now (11°C and pH 8.1) and Future (14°C and pH 7.8) cultures, and also the crossover experiments - Future cells inoculated into Now medium and incubated under Now conditions (Future in Now), and Now cells incubated in Future medium under Future conditions (Now in Future). For in vitro chlorophyll a (chl-a) measurement, chl-a was extracted from the cells for 20 hours in 90 % acetone and the fluorescence, before and after acidification, measured using a Turner 10-AU fluorometer (Parsons et al. 1984; Welschmeyer 1994). Particulate organic carbon (POC) and particulate organic nitrogen (PON) cell content was determined in cells collected on pre-ashed GF/F (Whatman) filters with particulate inorganic carbon (PIC) removed by flooding the filter with 0.1N sulphuric acid on the filtration manifold (Kennedy et al. 2005). Dried filters were packed in tin capsules before analysis using a ThermoFlash 2000 CHN Elemental Analyser by the Campbell Microanalytical Laboratory, University of Otago. PIC was determined by measuring total carbon in a similar way to POC, and then subtracting the POC. Particulate organic phosphorus (POP) content was measured according to the methods of Solorzano and Sharp (1980). Cell counts of 1% glutaraldehyde subsamples were made under an Olympus IX70 inverted microscope after mounting in a nanoplankton chamber (Phycotech). Uptake rates of dissolved inorganic carbon (DIC) into POC (photosynthetic rates) were measured using C-14 labelled sodium bicarbonate (Perkin Elmer; Parsons et al. 1984; Knap et al. 1996). Unlabelled DIC was measured in subsamples of culture fixed with saturated mercury dichloride (HgCl2) that had been stored in glass vials with rubber sealed caps until analysis using an Airica micro DIC system (Marianda, Germany). Calcium (Ca) uptake rate was measured using Ca-45 (Perkin Elmer) as a tracer for total Ca uptake. Briefly, Ca-45 (0.5 – 1 x 10-4 mg) was added to 10 ml culture subsamples and incubated for 6 to 7 hours in the light. Cells were then collected on GF/F filters and the radioactive label counted by scintillation counter (Perkin Elmer) after the addition of Hi-Safe II scintillant (Perkin Elmer). The total calcium uptake was calculated in a similar manner to that for inorganic carbon uptake using C-14 tracer (Knap et al. 1996). The unlabelled calcium content in the culture medium required for this calculation was measured by inductively coupled plasma mass spectrometry in the Trace Element Centre, University of Otago. In a previous experiment measuring Ca-45 only, it was determined that 97% of the Ca-45 taken up by the cells was incorporated into coccoliths (Satoh et al. 2009). Assuming there is no fractionation within the cell then 97% of the total Ca uptake would be used for calcification.

Description: On four occasions during the two year incubation of a subantarctic E. huxleyi culture (2015-11-20 to 2017-12-01), from Day 309 onwards, cell size of the cultures was measured at cross-over points, after 7 – 8 generations while still in exponential growth phase. Cells from Now (11°C and pH 8.1) and Future (14°C and pH 7.8) cultures, and also the crossover experiments - Future cells inoculated into Now medium and incubated under Now conditions (Future in Now), and Now cells incubated in Future medium under Future conditions (Now in Future) were fixed in 1 % glutaraldehyde. Subsamples were mounted in a nanoplankton chamber (Phytotech) and measured with a calibrated eye-piece graticule under an Olympus IX70 inverted microscope. As the fixation process caused coccoliths to separate, the cell size measurements were for the cell body only, which allows more accurate determinations of cell volume (Buitenhuis et al., 2008). Cell volume was calculated assuming that the cells were spherical.

Description: Lower pH and elevated temperature alter phytoplankton growth and biomass in short-term incubations, but longer-term responses and adaptation potential are less well-studied. To determine the future of the coccolithophore Emiliania huxleyi, in subantarctic waters, a mixed genotype culture was incubated for two years. E. huxleyi was isolated from subantarctic waters at the end of the Munida Transect (Currie et al. 2011) east of New Zealand (-45.829 171.532) on 3rd June 2014. The coccolithophore was isolated in Aquil medium but then maintained in a 10-fold dilution of the recommended addition of Guillards f/2 (Sigma G0154) to natural seawater supplemented with additional nutrients to nitrate 96 μM and phosphate 6 μM (f/20). In this medium, the strain continued to calcify throughout the experiment after treatment with the antibiotics penicillin, streptomycin and neomycin (Sigma P4083) at the recommended dosage to remove bacteria prior to the start of the incubation (20th November 2015). E. huxleyi was incubated for two years under present-day summer temperature and pH (11°C and pH 8.1; Now), and also projected future conditions by the year 2100 (14°C and pH 7.8; Future; Law et al. 2018). The pH of the medium was amended by bubbling with 10% CO₂ prior to cells being added. Special air mixes (21% oxygen in nitrogen, with 380 ppm CO₂ for Now cultures and 750 ppm CO₂ for Future cultures; BOC Gas NZ) were passed through an inlet into the culture bottle headspace via a 0.22 μm syringe filter (Millipore) to maintain target pH with an exhaust with 0.22μm filter attached to relieve pressure. The cultures were maintained at 60 µmol m⁻² s⁻¹ in a 12 hour: 12 hour light: dark cycle. Cultures were grown in a semi-batch style to ensure the cells remained in exponential growth, with cell concentration maintained at low levels (〈80000 cells ml⁻¹) to maintain pH at the target value. Growth rates of each population were measured throughout the experiment (20th November 2015 - 1st December 2017) and calculated by least squares regression of the natural logarithm of in vivo fluorescence versus time during exponential growth. At five time points, some cells from the Now culture were moved to Future conditions (Now in Future) and vice versa (Future in Now) with growth rates and cell sizes being determined in the Now, Future, Now in Future and Future in Now cultures. At the final cross-over, additional measurements were made - cell chlorophyll, inorganic carbon and organic carbon, nitrogen and phosphorus contents. From these measurements cell ratios were calculated. In addition, the uptake of inorganic carbon (C-14) and calcium (Ca-45) were measured to indicate primary production and calcification rates. At the end of the incubation a temperature response experiment was performed with the Now and Future populations measuring the cell growth rates at a range of temperatures covering current and projected conditions in the subantarctic waters. The experiments were carried out in the Department of Chemistry, University of Otago, New Zealand.

Description: On five occasions during the two year incubation of a subantarctic E. huxleyi culture (2015-11-20 to 2017-12-01), triplicate cultures of Now (11°C and pH 8.1) and Future (14°C and pH 7.8) cells, and also the crossover experiments - Future cells inoculated into Now medium and incubated under Now conditions (Future in Now), and Now cells incubated in Future medium under Future conditions (Now in Future) were prepared. Growth rates of each culture were monitored by measuring the in vivo chl-a of subsamples daily with a Turner 10AU fluorometer and calculating the least squares regression of the natural logarithm of in vivo fluorescence, versus time during exponential growth.