Table of Contents

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

The complete dataset for the ships underway system includes the following parameters: BOTTOM_DEPTH, TRUE_WIND_SPEED, BAROM_PRES, PAR, CORR_SST, CORR_SALINITY, FLUORESCENCE. This dataset is available via the Rolling Deck to  Repository: rvdata.us/search/cruise/MV1405

Diatom 18S Amplicon Sequencing from California Current System Mesoscale Eddies. Available from: NCBI:BioProject: PRJNA743307

OCE-1259776 is credited since it generated the metal and nutrient data that are part of this dataset.

Sampling location: California Current System 38 N -126 E depth of sampling ~2m

Nitrate-nitrite, Phosphate, Silicate: Samples were collected from a trace-metal clean towed-fish system (Bruland et al 2005), filtered through an acid-cleaned, seawater flushed 0.2 um Acropak filter capsule (Pall 500) and analyzed shortly after collection at sea using standard spectrophotometric methods (Parsons 1984) on a Lachat QuickChem 8000 Flow Injection Analysis System.

Dissolved iron and manganese samples were collected from a trace-metal clean towed-fish system (Bruland et al., 2005), filtered through an acid-cleaned, seawater flushed 0.2 um Acropak Supor 200 filter capsule (Pall), acidified at sea to pH 1.7-1.8 with quartz-distilled HCl and stored at room temperature until analysis. Once in the lab, samples were buffered to pH 6.0 +/- 0.2 with ammonium acetate and immediately pre-concentrated using Nobias-chelate PA1 chelating resin (concentration factor ~24). Extracts were analyzed on an Element XR High-Resolution Inductively Coupled Plasma Mass Spectrometer (HR ICP-MS) using techniques described initially in Biller and Bruland (2012) with adaptations listed in Parker et al. (2016).

Diatom Amplicon Sequencing: Whole seawater was collected from a trace-metal clean towed-fish system (Bruland et al 2005) and filtered onto 3 um polyester filters using a peristaltic pump system. Filters were preserved in RLTPlus buffer and immediately frozen in liquid nitrogen.  For long term storage samples were maintained at -80 degrees celsius until extraction.  DNA extraction, PCR amplification, and analysis followed that of Chappell et al. 2016 with modification listed in Oliver et al. 2021. Briefly, DNA and RNA were co-extracted using a Qiagen Allprep RNA/DNA mini kit. Diatom 18S was amplified from the DNA using diatom-specific primers modified for Illumina indexing.  PCR products were purified, multiplexed using Illumina indices, and sequenced on an Illumina MiSeq desktop sequencer.

Processing of original SBE-45 data included interpolation between data points and identification of data where flow rate for sensors dropped below 1L/min (indicative of a filter clog or shipboard maintenance).

BCO-DMO Processing Notes:
* Added ISO formatted DateTime column

This project focuses on an important group of photosynthetic algae, the diatoms, and how iron availability modulates their growth. Diatoms are important organisms at the base of the marine food web. Iron is required for the structure and function of proteins essential to diatom growth. Iron concentrations can be low in many areas of the ocean and exists in different forms classified by size and chemical characteristics. Recent efforts have increased understanding of the distribution of these different iron forms, but which forms individual phytoplankton can access remains unclear. The investigator will conduct experiments with important diatom species to develop and use assays that can assess whether iron provided in different forms or from different sources can be accessed by those species to alleviate iron stress. These data will help us understand the relationship between iron and an important group of organisms at the base of the food web, which will prove valuable to climate and food web modelers. This project will further the NSF goals of training new generations of scientists and making scientific discoveries available to the general public. The project supports the research of an early-career scientist, the training of undergraduate and high school students, including inner city middle and high school girls.

The project combines trace metal biogeochemistry, phytoplankton cultivation, and molecular biology to address questions about the bioavailability of various iron forms to environmentally relevant diatoms. Iron is an essential micronutrient for marine phytoplankton. While knowledge of the distribution of iron has increased significantly as a result of the ongoing GEOTRACES program, a mechanistic and quantitative understanding of the bioavailability of various forms of iron remains illusive. Previously, the investigator developed a calibrated molecular bioassay capable of indicating when a specific oceanic diatom was experiencing iron stress. It has been used to evaluate iron stress in oceanic field samples and in incubation samples in response to additions of different iron fractions. The goal of this proposal is to develop additional calibrated molecular assays for iron stress in other environmentally relevant diatoms from both coastal and oceanic habitats and use them to asses the biological availability of iron from varying sources. The experimental plan includes culture experiments monitoring growth, photosynthetic physiology, and gene expression of iron stress response genes. The molecular assays will then be used to test whether iron from a variety of sources can alleviate iron stress in the different species. Results from this project will provide tools to answer fundamental questions about the bioavailability of various forms of iron to important phytoplankton. As such, this research will provide valuable information for biogeochemical modelers, increasing their ability to use the data generated from the GEOTRACES program to accurately predict future changes in ocean productivity.

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.