Table of Contents

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

Dissolved macronutrient concentrations from NBP16-08 depth profiles.

Sampling and analytical procedures:
Depth profile samples were collected in September and October 2016 aboard the R/V/I/B Nathanial B. Palmer using a SeaBird GEOTRACES style SBE32 rosette system deployed on a conducting Kevlar line with OceanTestEquipment, Inc. X-Niskin samplers modified for trace element sampling. Samples for macronutrients were filtered through 0.2 um Pall Acropak membrane filter capsules and collected in 50 mL Falcon tubes that had been rinsed with distilled water (DIW), soaked overnight in 10% hydrocholoric acid (HCl, Fisher, Trace Metal Grade), rinsed three times with DIW again, dried and rinsed three times with sample prior to filling. Samples were analyzed shipboard, typically within 24 hours, for nitrate+nitrite, phosphate, silicate, and occasionally nitrite. Until analyzed shipboard, samples were stored sealed at 4 ºC in the dark and, following analyses, samples were frozen at -20 ºC and shipped back to the University of South Florida for laboratory-based analyses of nitrite, ammonium, and in some cases nitrate+nitrite, phosphate and silicate again.

Analytical methodology was based on established methods (Parsons 1984; Gordon et al. 1993) as described for the Lachat 8500 QuickChem in the Lachat QuickChem methods manuals and for the Technicon AAII in the CARIACO methods manual. All labware were either glass or high density polyethylene and were cleaned by an initial distilled water (DIW) rinse, followed by an overnight 10% hydrochloric acid (Fisher, Trace Metal Grade) soak, then rinsed three times with DIW and three times with solvent, analyte or sample prior to fill. Dedicated glassware was used for reagents and standards to avoid cross contamination issues. All reagents were made in high purity Milli-Q (>18 MΩ cm) water.

An artificial seawater matrix was used as the carrier for the analyses on the Lachat QuickChem 8500 at sea and on the Technicon AAII in the lab. 4L batches of artificial seawater were made by dissolving pre-weighed salts (128.50 g NaCl, 28.50 g MgSO4*7H2O, 0.6714 g NaHCO3) in Milli-Q to match Southern Ocean seawater salinity and adjusted to match Southern Ocean seawater pH with 10% hydrochloric acid.

Five-point standard curves were analyzed in duplicate at the beginning and end of each run with duplicate reagent blanks, and quality control checks every seventh sample. Quality control check consisted of either an international reference sample or a quality control sample. The certified nutrient reference samples used, lots CC and CD, were purchased from Kanso Technos in Osaka, Japan. The quality control sample was made from a 20-L homogenized surface Southern Ocean filtered and autoclaved seawater sample. The midpoint standard from the calibration curve was also analyzed every fourteenth sample to check for drift during the runs.

Detection limits for all five parameters on the two instruments used were determined from three times the standard deviation of replicate artificial seawater blanks (n>6). On the Lachat QuickChem 8500, limits of detection were 0.01 uM for nitrate+nitrite, 0.02 uM for phosphate, 0.03 uM for silicate, 0.05 uM for nitrite and 0.5 uM for ammonium. On the Technicon AAII, limits of detection were 0.06 uM for nitrate+nitrite, 0.02 uM for phosphate, 0.2 uM for silicate, 0.01 uM for nitrite, and 0.05 uM for ammonium.

Sample analyses for macronutrients were performed by William Abbott (USF).

Gordon, L.I., Jennings, J., J.C., Ross, A.A. and Krest, J.M., 1993. A suggested protocol for continuous flow automated analysis of seawater nutrients (phosphate, nitrate, nitrite and silicic acid) in the WOCE Hydrographic Program and the Joint Global Ocean Fluxes Study, Methods Manual WHPO 91-1. WOCE Hydrographic Program Office.

Parsons, T.R., Maita, Y. and Lalli, C.M., 1984. A manual of chemical and biological methods for seawater analysis. Pergammon Press, Oxford, 173 pp.

Data were processed using Omnion 4.2 software.

BCO-DMO Processing:
 - changed date format from m/dd/yyyy to yyyy-mm-dd;
- changed time format to HH:MM (some were H:MM);
- replaced % with "pcnt" in param names;
- replaced blanks (missing data/no data) with "nd";
- replaced spaces with underscores in platform column 
- created ISO_DateTime column.

This project focuses on an important group of photosynthetic algae in the Southern Ocean (SO), diatoms, and the roles associated bacterial communities play in modulating their growth. Diatom growth fuels the SO food web and balances atmospheric carbon dioxide by sequestering the carbon used for growth to the deep ocean on long time scales as cells sink below the surface. The diatom growth is limited by the available iron in the seawater, most of which is not freely available to the diatoms but instead is tightly bound to other compounds. The nature of these compounds and how phytoplankton acquire iron from them is critical to understanding productivity in this region and globally. The investigators will conduct experiments to characterize the relationship between diatoms, their associated bacteria, and iron in open ocean and inshore waters. Experiments will involve supplying nutrients at varying nutrient ratios to natural phytoplankton assemblages to determine how diatoms and their associated bacteria respond to different conditions. This will provide valuable data that can be used by climate and food web modelers and it will help us better understand the relationship between iron, a key nutrient in the ocean, and the organisms at the base of the food web that use iron for photosynthetic growth and carbon uptake. The project will also further the NSF goals of training new generations of scientists and of making scientific discoveries available to the general public. The project supports early career senior investigators and the training of graduate and undergraduate students as well as outreach activities with middle school Girl Scouts in Rhode Island, inner city middle and high school age girls in Virginia, and middle school girls in Florida.

The project combines trace metal biogeochemistry, phytoplankton cultivation, and molecular biology to address questions regarding the production of iron-binding compounds and the role of diatom-bacterial interactions in this iron-limited region. Iron is an essential micronutrient for marine phytoplankton. Phytoplankton growth in the SO is limited by a lack of sufficient iron, with important consequences for carbon cycling and climate in this high latitude regime. Some of the major outstanding questions in iron biogeochemistry relate to the organic compounds that bind >99.9% of dissolved iron in surface oceans. The investigators' prior research in this region suggests that production of strong iron-binding compounds in the SO is linked to diatom blooms in waters with high nitrate to iron ratios. The sources of these compounds are unknown but the investigators hypothesize that they may be from bacteria, which are known to produce such compounds for their own use. The project will test three hypotheses concerning the production of these iron-binding compounds, limitations on the biological availability of iron even if present in high concentrations, and the roles of diatom-associated bacteria in these processes. Results from this project will provide fundamental information about the biogeochemical trigger, and biological sources and function, of natural strong iron-binding compound production in the SO, where iron plays a critical role in phytoplankton productivity, carbon cycling, and climate regulation.