Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Nitrate-nitrite, Phosphate, Silicate, Nitrite

Samples were collected from a trace-metal clean towed-fish system (Bruland et al., 2001) (transects), from teflon-coated Go-Flos on a non-metal line, and from the ship's rosette. Samples were analyzed shortly after collection at sea using standard spectrophotometric methods (Parsons 1984) on a Lachat QuickChem 8000 Flow Injection Analysis System.

Dissolved trace metals

Depth profiles were taken using individual teflon-coated GoFlo bottles on a non-metal line, which were sampled in a trace metal clean van at sea. Surface samples for transects were sampled using a tow-fish system (Bruland et al., 2001). Samples were filtered directly from the GoFlo through 0.2 μm Acropak Supor membrane capsule filters into pre-cleaned LDPE bottles. The acropaks were pre-cleaned and flushed with at least 250 mL of sample before sampling. Sample bottles were pre-cleaned cleaned rigorously as per the GEOTRACES cookbook (Cutter et al., 2014), and were rinsed with sample three times before filling. Samples were acidified at sea to a pH of ~1.7 with quartz-distilled 6 M HCl (4 mL per liter) and stored for analysis post-cruise. Samples were analyzed for trace metals after the cruise with the method of Biller and Bruland (2012), with modifications as described in Parker et al. (2016). Briefly, this involves buffering the seawater to pH 6.0 ± 0.2 immediately before pre-concentrating on PA1 resin. The resin was extracted with 1 N optima nitric acid with rhodium as an internal standard. Extracts were analyzed on the Thermo Fisher Element 2 extended range ICP-MS at UC Santa Cruz. 

Iron was additionally analyzed shipboard with a flow injection analysis method published in Lohan et al. (2006) with modifications as described in Biller et al. (2013). Briefly, this method involves pre-concentrating the iron on a toyopearl column at pH 2, eluting it into a buffered (pH ~5.7) reaction stream that contains DPD, a molecule that turns pink when oxidized by iron. H2O2 is also in the reaction stream, which re-oxidizes the iron, so that each iron molecule can react with multiple DPD molecules, another mechanism to increase the iron signal. The reaction stream absorbance is measured with a flow through spectrophotometer. 

Generally, the measurements from these two methods for Fe agreed well; where there was a problem with one or the other dataset, we only report one dataset. 
 

For the surface transect data, we did not have nutrient data and trace metal data taken from exactly the same moment. In order to directly compare the two datasets, the nutrient data was interpolated based on time to align with the trace metal data. 

- Imported original file "IRNBRU TM and macronutrient surface data.xlsx" into the BCO-DMO system.
- Converted "DATE TIME (GMT)" from %Y-%m-%dT%H:%M:%S to ISO format %Y-%m-%dT%H:%M:%SZ and changed parameter name to "ISO_DateTime_UTC"
- Renamed fields to comply with BCO-DMO naming conventions, removing special characters and spaces
- Saved the final file as "943015_v1_iron_limitation_surface.csv"

NSF Award Abstract:
Eastern boundary upwelling systems have long been recognized for their high phytoplankton productivity. Carr and Kearns (2003), in a detailed comparison of eastern boundary current systems, reported that biomass sustained by a given macronutrient concentration in Atlantic eastern boundary current systems was twice as large as those systems in the Pacific. The authors concluded "It is not clear whether the apparent difference in biomass supported by available nutrients is due to differences in the efficiency of the phytoplankton community, perhaps related to the availability of iron, or to grazing pressure." They suggested that the width of the shelf might be considered a proxy for the benthic availability of iron. The lowest biomass for a given macronutrient concentration was in the Peru-Humboldt Current and in the northern California region of the California Current System, both areas with low dust inputs and a relatively narrow shelf.

In this Accomplishment Based Renewal project, a marine trace metal geochemist at the University of California - Santa Cruz and his students and colleagues will continue a decades-old quest to understand the role of iron in the central California Current System (cCCS). Field efforts will combine continuous underway iron and nutrient data in surface waters and a series of vertical profiles. The focus will include three regions within the cCCS: a variety of active Fe-replete and Fe-deplete coastal upwelling regimes, the eddy-rich California Current transition zone that is Fe-limited and has elevated nitrate but relatively low and uniform chlorophyll concentrations, and the offshore, oligotrophic California Current. They will map surface and depth distributions of Fe and other micro- and macronutrients. There are four specific goals dealing with characterizing the organic Fe(III)-binding organic ligands, determining Fe(II) and Fe(III) concentrations in hypoxic waters over the shelf, examining the exchange between particulate and dissolved forms of Fe, and studying the roles of eddies in the eddy-rich transition waters of the cCCS.

Broader Impacts

Direct Benefits to Science: There is a great deal of interest in the CCS because of its importance in terms of phytoplankton productivity and the support of higher trophic levels. Until now, the emphasis in studies of the CCS has been on relationships between physics and biology. This study will insert the important role of micronutrient chemistry into the picture. It will also serve an important role in securing ship time in advance and providing logistical support for other collaborative studies. This is extremely valuable and cost effective for collaborating scientists since with the hydrography, nutrient and trace metal data provided, they can focus on their complimentary research efforts.

Outreach and Education: The project will provide funding for two current graduate students at UCSC, where they will also receive course training in a curriculum that includes i) scientific communication, ii) careers in marine science, and iii) grant writing. A broader impact goal of this project is to facilitate teaching and learning on marine science-related topics through translating research objectives into widely distributed educational materials for classroom use. To accomplish this, the team will partner with the Seymour Discovery Center at the Long Marine Lab, UCSC. The Discovery Center receives 14,000 visitors each year, and the project will provide funds to develop an interactive display on limiting nutrients and phytoplankton bloom development in the CCS.