Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

The experiment was conducted onboard the RV Seward Johnson II, from June 20 to July 4, 2005, with water collected at 57 deg 58" N, 15 deg 32" W. Four treatments were used with 6 replicates each: (1) 12 deg C and 390 ppm CO₂ (LTLC), (2) 12 deg C and 690 ppm CO₂ (LTHC), (3) 16 deg C and 390 ppm CO₂ (HTLC), and (4) 16 deg C and 690 ppm CO₂ (HTHC). Sea surface temperature at this location was 12°C at the time of water collection. Experiments were run using a seawater continuous culture system, termed an ‘Ecostat’ (Hutchins et al. 2003, Hare et al. 2005, 2007). Briefly, whole seawater was collected from 5 to 10 m depth using a trace-metal-clean, towed-intake Teflon pump system (Hutchins et al. 2003), prefiltered through 200 um Nitex mesh to remove mesozooplankton and incubated in twenty-four 2.7 l trace-metal-clean, clear polycarbonate bottles. Bottles were placed in racks in a temperature-controlled deck incubator with recirculating water and shaded to 30 percent of surface irradiance (I0) using a neutral-density shade screen. Temperatures in the 16 deg C incubator were gradually increased over a period of 24 h to avoid heat-shocking the plankton. Bottles were bubbled with either air or a commercially prepared air/CO2 mixture with 750 ppm CO2 using an inflow tube through the cap and an airstone to maximize gas transfer to the liquid phase. The gases used for bubbling were filtered through a 0.2 um HEPA filter to avoid contamination of experimental bottles by trace metals (Hare et al. 2005). The system was run in batch mode for 3 days prior to turning on the pumps, in order to stimulate phytoplankton growth and prevent wash-out of slower growing species. After this batch growth period, whole seawater in each incubation bottle was slowly diluted at a continuous rate using seawater collected at the initial site. This seawater medium was filtered through a 0.2 um inline capsule filter initially, then re-filtered through a second 0.2 um inline capsule filter immediately prior to use as a diluent. The medium was stored in trace-metal-clean, 50 l carboys in the dark. Initial in situ nutrient concentrations were low (0.32 umol nitrate l^–1, 0.12 umol phosphate l^–1, 0.7 umol silicate l^–1), so the medium and the whole water in the incubation bottles were amended with 5 and 0.31 umol l^–1 (final concentration) of nitrate and phosphate. The dilution rate of 0.5 d^–1 was controlled in each incubation bottle using a peristaltic pump and calibrated daily to ensure constant flow rate. This flow rate constituted a 50 percent dilution of the experimental bottle volume daily. Incubation bottles were mixed by inverting the rack 120 degrees every 5 to 15 min using a compressed-air-driven system. Diluted seawater flowed out of the incubation bottles at a continuous rate and into 2.7 l polycarbonate bottles stored in the dark, which were used as outflow collection vessels. Seawater carbonate system measurements were performed as described in Feng et al. (2009).

References:
Feng, Y., C.E. Hare, K. Leblanc, G.R. DiTullio, P.A. Lee, S.W. Wilhelm, J. Sun, J.M. Rose, N. Nemcek, I. Benner, and D.A. Hutchins. 2009. The effects of increased pCO2 and temperature on the North Atlantic Spring Bloom: I. The phytoplankton community and biogeochemical response. Marine Ecology Progress Series 388: 13-25.

Hare, C.E., G.R. DiTullio, C.G. Trick, S.W. Wilhelm, K.W. Bruland, E.L. Rue, and D.A. Hutchins. 2005. Phytoplankton community structure changes following simulated upwelled iron inputs in the Peru upwelling region. Aquatic Microbial Ecology 38: 269-282.

Hare, C.E., K. Leblanc, G.R. DiTullio, R.M. Kudela, Y. Zhang, P.A. Lee, S.F. Riseman, and D.A. Hutchins. 2007. Consequences of increased temperature and CO2 for phytoplankton community structure in the Bering Sea. Marine Ecology Progress Series 352: 9-16.

Hutchins, D.A., F. Pustizzi, C.E. Hare, and G.R. DiTullio. 2003. A shipboard natural community continuous culture system for ecologically relevant low-level nutrient enrichment experiments. Limnology and Oceanography: Methods 1: 82-91.

Related files and references:
Rose, J.M., Y. Feng, C.J. Gobler, R. Gutierrez, C.E. Hare, K. Leblanc, and D.A. Hutchins. 2009. The effects of increased pCO2 and temperature on the North Atlantic Spring Bloom. II. Microzooplankton abundance and grazing. Marine Ecology Progress Series 388: 27-40.

Additional parameters measured during these experiments are described in: Feng, Y., C.E. Hare, K. Leblanc, G.R. DiTullio, P.A. Lee, S.W. Wilhelm, J. Sun, J.M. Rose, N. Nemcek, I. Benner, and D.A. Hutchins. 2009. The effects of increased pCO2 and temperature on the North Atlantic Spring Bloom: I. The phytoplankton community and biogeochemical response. Marine Ecology Progress Series 388: 13-25.

Lee, P.A., J.R. Rudisill, A.R. Neeley, D.A. Hutchins, Y. Feng, C.E. Hare, K. Leblanc, J.M. Rose, S.W. Wilhelm, J.M. Rowe, and G.R. DiTullio. 2009. The effects of increased pCO2 and temperature on the North Atlantic Spring Bloom: III. Dimethylsulfoniopropionate. Marine Ecology Progress Series 388: 41-49.

Microzooplankton abundance and community composition determined by light microscopy
Samples for enumeration of microzooplankton were removed from outflow collection bottles on Days 4, 9, and 14 of the experiment. Triplicate samples were counted on the initial day. Duplicate samples on Days 4 and 9 were mixed to obtain enough volume for accurate counts, yielding 3 replicates per treatment on these days. All 6 replicates were counted on the final day of the experiment. All samples were preserved with 10% acid Lugols solution and stored at room temperature in the dark until enumeration of microzooplankton in the laboratory (Throndsen 1978). Then, 100 ml of sample was settled for at least 18 h into Utermohl chambers before before counting using an inverted Zeiss Axiovert S100 microscope at 200× magnification (Utermohl 1958). Microzooplankton were identified to genus level when possible. The use of Lugol fixative obscured chl a fluorescence and rendered the distinction between phototrophic and heterotrophic dinoflagellates based on autofluorescence impossible. However, certain heterotrophic dinoflagellates such as Protoperidinium and Gyrodinium were identified based on morphology, and were thus included in the counts.

References:
Throndsen, J. 1978. Preservation and storage. In Phytoplankton manual, ed. A. Sournia, 69-74. Paris: UNESCO.

Utermohl, H. 1958. Zur Vervollkommung der quantitativen phytoplankton-methodik. Mitteilungen der Internationalen Vereinigung fur Limnologie 9: 1-38.

BCO-DMO Processing Notes:

- File was sorted by treatment
- Added lat,lon values of original water sampling location to file
- Added BCO-DMO header lines
- Parameter names were edited to conform with BCO-DMO convention
- File was transposed to serve data by taxon and abundance in columns
- In data values representing mixed sampling bottles, plus signs (+) were edited to underscores(_)

Climate-related shifts in phytoplankton assemblages may have profound implications for oceanic feedbacks on the atmosphere, and for human use of marine resources. Particular algal groups are largely responsible for crucial processes like vertical carbon export, biogenic calcification and silicification, production of climatically active gases like dimethylsulfide (DMS), and for sustaining food webs that lead to economically valuable higher trophic levels. The North Atlantic Spring Bloom 2005 (NASB 2005) research program was designed to investigate potential climate change impacts on algal community structure and biogeochemistry during the North Atlantic Spring Bloom, a regime that is ideal for determining how changing ocean conditions may affect both calcareous and siliceous algae.

The research was coordinated with CarboOcean, a major European Union funded activity led by investigators from the Alfred Wegener Institute.

The investigator will examine to what extent rising climatic temperatures impact antarctic microzooplankton growth and grazing, and to what extent such an impact would modulate top-down control of phytoplankton growth in cold waters. The experimental part of the proposed work would take place in the Ross Sea, a permanently cold ecosystem, and the location of annual large-scale blooms of both diatoms and Phaeocystis antarctica. Changing climate regimes may alter current microzooplankton grazing rates on these blooms either directly through temperature increases or indirectly through algal community shifts. Complementary laboratory experiments on cultures of Antarctic microzooplankton will be conducted to determine the individual and combined effects of temperature and carbon dioxide levels on growth and grazing.