Table of Contents

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

Chlorophyll and phaeopigment concentrations from incubation experiments performed with amended Southern Drake Passage waters on cruise NBP 16-08.

Incubation 1: Chlorophyll and phaeopigment samples were collected from an incubation experiment set up with near-surface waters (35 - 25 meters depth) collected using the TMC CTD at -62.332N, -64.6485E over three casts with each cast homogenized in 50 L carboys. Incubation setup occurred in a TMC van and treatments were incubated in 4L polycarbonate bottles in a temperature controlled (2 °C) lighted incubator van with 24hr light. Sampling occurred in a TMC bubble.Treatment identifiers are as follows:

Cast = Homogenized carboy sample at T0 for individual casts.
A = control
B = +1 nM 57FeCl3
C = +4 nM Fe 57FeCl3
D = +10 nM Fe 57FeCl3
E = +600 pM Vitamin B12
F = +4 nM 57FeCl3/+600 pM Vitamin B12
G = Dark control
H = Dark +1 nM 57FeCl3
I = Dark +4 nM Fe 57FeCl3
J = Dark +10 nM Fe 57FeCl3
K = Dark +600 pM Vitamin B12
L = Dark +4 nM 57FeCl3/+600 pM Vitamin B12

Incubation 2: Chlorophyll and phaeopigment samples were collected from an incubation experiment set up with near-surface waters (35 - 25 meters depth) collected using the TMC CTD at -62.46N, -59.565E over two casts with each cast homogenized in 50 L carboys. Incubation setup occurred in a TMC van, treatments were incubated in 4L polycarbonate bottles in a temperature controlled (2 °C) lighted incubator van with 24hr light. Sampling occurred in a TMC bubble. Treatment identifiers are as follows:

Cast = Homogenized carboy sample at T0 for individual casts.
M = control
N = +4 nM Fe 57FeCl3
O = +600 pM Vitamin B12
S = Dark control
T = Dark +4 nM Fe 57FeCl3
U = Dark +600 pM Vitamin B12

Incubation 3: Chlorophyll and phaeopigment samples were collected from an incubation experiment set up with near-surface waters (35 - 25 meters depth) collected using the TMC CTD at -62.332N, -64.6485E over a single cast where waters were homogenized in 50 L carboys. The only amendment included adding 50% of 0.2 um filtered near surface (35 – 25 meters depth) waters collected at -62.46N, -59.565E. Incubation setup occurred in a TMC van and treatments were incubated in 4L polycarbonate bottles in a temperature controlled (2 °C) lighted incubator van with 24hr light. Sampling occurred in a TMC bubble. Treatment identifiers are as follows:

Cast = Homogenized carboy sample at T0 for individual casts.
Q = control (unfiltered water from -62.332N, -64.6485E)
R = 50% unfiltered water from -62.332,N -64.6485E with 50% 0.2 um filtered waters from -62.46N, -59.565E

For each sampling timepoint, samples of 50-100 mL were filtered onto 25 mm GFF filters and extracted using the protocol of:
Jespersen, A.M. and Christoffersen, K. (1987) Measurements of Chlorophyll-a from phytoplankton using ethanol as extraction solvent. Arch. Hydrobiol. 109 (3) 445-454, as updated in:
Morison, F. and Menden-Deuer, S. (2015) Early spring phytoplankton dynamics in the sub polar North Atlantic: The influence of protistan herbivory. Limnol. Oceanogr. 60(4) 1298-1313.

Analyses were performed by Ms. Zuzanna Abdala (ODU) and Ms. Alexa Sterling (URI).

At the start of the cruise, Turner 10-AU Fluorometer was calibrated using Chla Standard Stock Solution (SSS) from Anacystis nidulans algae (#C-5753) following the protocol by Kirk Ireson & Karen Baker (PDF).

Calibration was performed by Dr. Randelle Bundy (UW) and Dr. Bethany Jenkins (URI).

BCO-DMO Processing:
- changed date format from m/dd/yyyy to yyyy-mm-dd;
- combined 3 separate files into one dataset.

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.