Table of Contents

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

Submitted for publication to Global Biogeochemical Cycles (Table S2):
Oldham, V.E., Chmiel, R., Hansel, C.M., DiTullio, G.R., Rao, D., and Saito, M.

Location: Ross Sea Polynya

Sampling

Ten stations in the Ross Sea polynya, including stations in in the western Ross Sea and Terra Nova Bay, were sampled during the NBP-1801 expedition aboard the RV/IB N.B. Palmer from February-March 2018. Stations numbers for Mn sampling were less frequent than expedition stations and were numbered sequentially and correspond to expedition stations as described in Table S1 (Stations Mn-1 to Mn-10). Measurements were made for soluble phase Mn speciation using a 12-bottle (X-Niskin bottles) trace metal clean CTD (Conductivity, Temperature and Depth) rosette sampling system equipped with SeaBird equipment for salinity, temperature, dissolved oxygen, conductivity and fluorometry. Sampling depths were selected based on the down-cast profile of salinity, fluorescence and dissolved oxygen. For most stations, 8 depths were selected for soluble Mn speciation. Upon retrieval, Niskin bottles were transported with gloved hands to a trace metal clean van and sampled into acid-washed 1 L PTFE bottles. Bottles were triple rinsed before filling and were overflowed to prevent oxygen contamination. The seawater was immediately filtered in the main laboratory through 0.2 µm PES Millipore filters using acid washed Savillex vacuum-filtration rigs. One 10 mL volume of filtrate was immediately amended with 1 µM hydroxylamine hydrochloride for total MnT (over 10 times excess predicted total dMn concentration), and one volume was immediately analyzed for soluble Mn(II) + Mn(III)-Lw

Shipboard Mn speciation and concentrations

Speciation of soluble Mn(II) and Mn(III)-L was carried out using the spectrophotometric competitive ligand assay first described by Madison et al. (2011) and modified for low-level analysis by Oldham et al. (2017). In brief, a meso-soluble porphyrin ligand α, β, γ, δ-tetrakis(4-carboxyphenyl) porphine (T(4-CP)P) is added to the sample, complexes Mn(II), and rapidly oxidizes to form Mn(III)-T(4-CP)P in the presence of oxygen. This complex is quantified spectrophotometrically at 468 nm. For complete determination of Mn speciation, a separate sample aliquot is completely reduced to Mn(II) by addition of hydroxylamine and quantified similarly. The difference in these two parallel measurements permits determination of total Mn, Mn(II) and strongly bound Mn(III)-L by difference (Oldham et al., 2017).

Filtered samples were immediately analyzed for Mn speciation shipboard using UV/Vis spectrophotometry. One aliquot of sample was amended with 1 µM hydroxylamine and allowed to react overnight at 4 ⁰C before analysis (total dissolved Mn [dMn]). A second aliquot was analyzed immediately; the unreduced fraction represents Mn(II), but as the reaction proceeds for over an hour, it is likely that this fraction also contained some weakly bound Mn(III)-L complexes (Mn(III)-Lw), so our reported Mn(III)-L is a conservative estimate. Samples were added to a solution containing T(4-CP)P, CdCl2 (which complexes T(4-CP)P, opening its ring structure), and imidazole tetraborate buffer (pH=8.2) at a 1:12 dilution factor to avoid chloride interference (Madison et al., 2011). The samples were then heated for 60 minutes in a 90 ⁰C hot water bath, cooled to room temperature, then injected by syringe into the spectrophotometric setup. The analytical setup uses a 100 cm liquid waveguide capillary cell (World Precision Instruments) coupled with an Ocean Optics UV/Vis spectrophotometer in which a mini deuterium halogen light source (DT-Mini-2-GS) is coupled with a USB2000+ fiber optic spectrometer, controlled with SpectraSuite software. The Mn(III)-T(4-CP)P complex is measured at its absorbance maximum against appropriate reagent blanks. The detection limit for this method is 0.5 nM.

BCO-DMO data manager processing notes:
* Imported two sheets from Excel file BCODMO_Mn_Data.xlsx.  The first one was the Mn speciation data (geochemsitry) which is the main dataset served from this page.  The second was a station list which I attached as a supplemental file.
* Joined the station list with geochemistry data on key station ID to add sample date and bottom depth to the dataset.
* Renamed columns to fit the BCO-DMO naming convention (only underscores, aZ0-9).
* Converted date to ISO 8601 yyyy-mm-dd
* Switched column names for Lat and Long since they were switched.

NSF Abstract:

Mercury (Hg) is a toxic trace element that bioaccumulates into marine food webs, imposing a health threat to humans through the consumption of seafood. However, controls on the cycling of Hg in the ocean are poorly understood. Most research to date has focused on sun-lit and/or Hg-laden environments, where light-induced chemical and mercury resistance reactions, respectively, have been identified as dominant pathways for Hg cycling. The paradigm that dark Hg reactions are irrelevant is fading and it is now apparent that dark redox reactions, both reduction and oxidation, are important in the cycling of Hg. In this study, researchers at the Woods Hole Oceanographic Institution and Colorado School of Mines will obtain a better understanding of the biogeochemical reactions responsible for dark redox transformations of mercury (Hg) in marine systems. The researchers will explore the relationship between microbial activity, reactive oxygen species, and Hg speciation in a series of laboratory- and field-based investigations to obtain a mechanistic understanding of dark Hg cycling. By identifying new controls on the redox cycling of Hg in the ocean, this research will help inform global and ecosystem models used to predict Hg bioavailability.

Broader Impacts: The proponents plan to educate high school teachers from Boston Green Academy in South Boston on mercury biogeochemistry and have one teacher participate in the summer research cruises, as well as develop science curricula to engage the underrepresented students at the school in science. One postdoc and one graduate student from Woods Hole Oceanographic Institution and one graduate student from the Colorado School of Mines would be supported and trained as part of this project. It is anticipated that undergraduate students would have the opportunity to participate in the study as summer interns.

NSF abstract:
Phytoplankton blooms in the coastal waters of the Ross Sea, Antarctica are typically dominated by either diatoms or Phaeocystis Antarctica (a flagellated algae that often can form large colonies in a gelatinous matrix). The project seeks to determine if an association of bacterial populations with Phaeocystis antarctica colonies can directly supply Phaeocystis with Vitamin B12, which can be an important co-limiting micronutrient in the Ross Sea. The supply of an essential vitamin coupled with the ability to grow at lower iron concentrations may put Phaeocystis at a competitive advantage over diatoms. Because Phaeocystis cells can fix more carbon than diatoms and Phaeocystis are not grazed as efficiently as diatoms, the project will help in refining understanding of carbon dynamics in the region as well as the basis of the food web webs. Such understanding also has the potential to help refine predictive ecological models for the region. The project will conduct public outreach activities and will contribute to undergraduate and graduate research. Engagement of underrepresented students will occur during summer student internships. A collaboration with Italian Antarctic researchers, who have been studying the Terra Nova Bay ecosystem since the 1980s, aims to enhance the project and promote international scientific collaborations.

The study will test whether a mutualistic symbioses between attached bacteria and Phaeocystis provides colonial cells a mechanism for alleviating chronic Vitamin B12 co-limitation effects thereby conferring them with a competitive advantage over diatom communities. The use of drifters in a time series study will provide the opportunity to track in both space and time a developing algal bloom in Terra Nova Bay and to determine community structure and the physiological nutrient status of microbial populations. A combination of flow cytometry, proteomics, metatranscriptomics, radioisotopic and stable isotopic labeling experiments will determine carbon and nutrient uptake rates and the role of bacteria in mitigating potential vitamin B12 and iron limitation. Membrane inlet and proton transfer reaction mass spectrometry will also be used to estimate net community production and release of volatile organic carbon compounds that are climatically active. Understanding how environmental parameters can influence microbial community dynamics in Antarctic coastal waters will advance an understanding of how changes in ocean stratification and chemistry could impact the biogeochemistry and food web dynamics of Southern Ocean ecosystems.