Table of Contents

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

Sampling Plan:
This study was conducted during the California Current Ecosystem Long Term Ecological Research (CCE LTER) Process Cruise P2105 from July 10 to August 8, 2021, on board the R/V Roger Revelle (RR2105) where we sampled two water parcels and a seven station transect. Water parcels were sampled with a Lagrangian-style process study using drifter floats and modeled after previous CCE LTER cruises (Krause et al., 2015; Landry et al., 2009). During these process studies, an upwelled water parcel was identified by satellite temperature and chlorophyll-a concentrations. We followed an upwelled water parcel for 11 days and a water parcel that had already moved to the eastern edge of the oligotrophic gyre for three days. Profiles for dissolved Hg concentrations, including total mercury (THg), dimethylmercury (DMHg), monomethylmercury (MMHg), and elemental mercury (Hg0), were taken every other day during the water parcel studies. A seven station transect from stations S1-S7 was conducted across the California Current water mass to the coast, and profiles for THg, DMHg, and Hg0 were taken for all stations in the transect. A MMHg profile was only taken for Station S4 in the transect. Stations are colored based on their corresponding water mass in Figure 1 of Adams et al. (2024). Profiles for Hg speciation typically covered the upper water column to 200 meters (m), and those data are presented here. One station within the California Undercurrent was sampled to 600 m, and the concentrations of Hg species in the waters deeper than 200 m are used as a reference for upwelled waters in our mass budget model. Benthic Boundary Layer (BBL) stations were selected based on previous work in the region and are locations where the continental shelf drops off and can have high levels of suspended sediments within the water column (Biller and Bruland, 2013). Samples at BBL stations were taken at one depth around 40 to 70 m identified as 5 m above the sea floor (Biller and Bruland, 2013).

Sampling Methods:
Vertical dissolved Hg profiles were sampled using 5-liter (L) X-Niskin bottles (Ocean Test Equipment) mounted on a trace metal rosette (Seabird) deployed on a non-metallic hydroline (Brzezinski et al., 2015; Cutter and Bruland, 2012) and triggered automatically by pressure on upcasts using a Seabird Auto Fire Module. BBL samples were collected using a 30 L Teflon™-coated GO-Flo™ bottle (General Oceanics) deployed on a non-metallic hydroline and triggered with an acid-cleaned Teflon™ messenger (Bruland et al., 1979). The Niskin or GO-Flo™ bottles were transported into a dedicated Class 100 laboratory van under trace metal-clean conditions (Cutter and Bruland, 2012). Samples were pressure-filtered (N2 gas, 99.99%) directly from the Niskin or GO-Flo™ bottles through 0.2 um capsule filters (Acropak 200, Pall Laboratory) into 2 L acid-cleaned Teflon™ bottles.

An aliquot of sample was transferred from the 2 L Teflon™ bottle into 0.25 L pre-cleaned borosilicate glass bottles (I-Chem) for THg analysis and oxidized with 0.04% bromine monochloride at least 12 hours prior to analysis (U.S. Environmental Protection Agency Method 1631, Revision E).

The remainder of the sample in the 2 L Teflon™ bottle was analyzed for gaseous Hg0 and DMHg with a purge-and-trap method (Bowman et al., 2011; Tseng et al., 2004). Samples were purged with Hg-free N2 gas for 60 minutes ;at a rate of 0.5 L per minute. Effluent gas was passed through a soda lime trap to remove water vapor and aerosols, then DMHg was concentrated onto a Carbotrap® (graphitized carbon black, Sigma-Aldrich) matrix downstream of the soda lime trap, and Hg0 was concentrated onto a gold trap downstream of the Carbotrap® (Tseng et al., 2004; Lamborg et al., 2012). DMHg was thermally desorbed from the Carbotrap® and quantified on board via Gas Chromatographic Cold Vapor Atomic Fluorescence Spectrometry (GC-CVAFS) on a Tekran 2500 (Bowman et al., 2011; Baya et al., 2013). The detection limit for DMHg was 2 fM. Hg0 was quantified by dual gold amalgamation Cold Vapor Atomic Fluorescence Spectroscopy (CVAFS) on a Tekran 2600 following thermal desorption from the gold trap (Tseng et al., 2004; Bloom and Fitzgerald, 1988). The method detection limits for Hg0 were 40 fM (n=14). Sample concentrations for DMHg and Hg0 were determined by a calibration curve based on a gaseous Hg0 standard (Tekran 2505 Mercury Vapor Primary Calibration Unit).

Seawater purged of DMHg and Hg0 was transferred into a 0.25 L precleaned amber borosilicate glass bottles (I-Chem) for MMHg analysis, acidified with 1% sulfuric acid (Trace Metal Grade, Fisher Scientific), stored at 4°C, and analyzed at Scripps Institution of Oceanography within 2 months of collection.

THg samples were analyzed following U.S. EPA Method 1631 on board the ship (U.S. Environmental Protection Agency Method 1631, Revision E; Lamborg et al., 2012). Samples were reduced to Hg0 with 20% wt:vol tin (II) chloride solution (ACS grade, Fisher Chemical) in 10% hydrochloric acid (ACS grade, Fisher Chemical). Hg0 was purged onto a gold trap with Hg-free argon gas and thermally desorbed via CVAFS for detection using a Tekran 2600 Automated Mercury Analyzer. Sample concentrations were determined by a calibration curve based on a gaseous Hg0 standard (Tekran 2505 Mercury Vapor Primary Calibration Unit). The method detection limit was 0.22 pM (n=8 blanks) and replicates had an average precision of 6.4% (n = 73).

MMHg samples were analyzed by ascorbic acid-assisted direct ethylation following Munson et al. (2014) and U.S. EPA Method 1630 (U.S. Environmental Protection Agency Method 1630; Munson et al., 2014). Samples were adjusted to a pH of 4.8 using a 2 M acetate/glacial acetic acid buffer (J.T. Baker) in ultrapure water (Milli-Q, 18.2 MW per centimeter) and 8 M potassium hydroxide (J.T. Baker) in ultrapure water (Milli-Q, 18.2 MW per centimeter). 2.5% wt:vol ascorbic acid (J.T. Baker) in ultrapure water (Milli-Q, 18.2 MW per centimeter was added to the samples, then samples were ethylated with sodium tetraethylborate (NaTEB) solution (1% NaTEB in 2% potassium hydroxide, Strem Chemicals) to convert MMHg to volatile methylethylmercury. Ethylation was allowed to proceed for 10 minutes before sample analysis. Samples were analyzed by GC-CVAFS on a Tekran 2700 Automated Methylmercury Analyzer. Concentrations were determined by a calibration curve based on standards prepared from a certified 1000 ppm MMHg (II) chloride standard (Alfa Aesar). The method detection limit was 11.3 fM (n=9 blanks), and ongoing precision and recovery was 98.4 ± 7.9% (n=25). Replicates had an average precision of 9.2% (n=18) and matrix spike recovery was 112 ± 13% (n=15).

- Imported original file "2024-0311-California Current System Dissolved Hg Speciation.xlsx" into the BCO-DMO system.
- Marked "N/A" as a missing data value (missing data are empty/blank in the final CSV file).
- Made corrections in the time column: added "AM" where needed to the times missing them and converted the times that were in 24-hour time to 12-hour AM/PM time.
- Converted the date and time columns into ISO 8601 format in PDT and UTC time zones.
- Renamed fields to comply with BCO-DMO naming conventions.
- Saved final file as "926873_v1_dissolved_hg_speciation_california_current_system.csv".

From ccelter.edu:
The California Current System is a coastal upwelling biome, as found along the eastern margins of all major ocean basins. These are among the most productive ecosystems in the world ocean. The California Current Ecosystem LTER (32.9 degrees North, 120.3 degrees West) is investigating nonlinear transitions in the California Current coastal pelagic ecosystem, with particular attention to long-term forcing by a secular warming trend, the Pacific Decadal Oscillation, and El Nino in altering the structure and dynamics of the pelagic ecosystem. The California Current sustains active fisheries for a variety of finfish and marine invertebrates, modulates weather patterns and the hydrologic cycle of much of the western United States, and plays a vital role in the economy of myriad coastal communities.

LTER Data:
The California Current Ecosystem (CCE) LTER data are managed by and available directly from the CCE project data site URL shown above. If there are any datasets listed below, they are data sets that were collected at or near the CCE LTER sampling locations, and funded by NSF OCE as ancillary projects related to the CCE LTER core research themes.

NSF Award Abstract (OCE-2224726):
Coastal upwelling regions are found along the eastern boundaries of all ocean basins and are some of the most productive ecosystems in the ocean. This award is supporting the California Current Ecosystem Long Term Ecological Research (CCE LTER) site in a major upwelling biome. It leverages the 73-year California Cooperative Oceanic Fisheries Investigations (CalCOFI) program which provides essential information characterizing climate variability and change in this system. The CCE LTER addresses two over-arching questions: What are the mechanisms leading to ecological transitions in a coastal pelagic ecosystem? And what is the interplay between changing ocean climate, community structure, and ecosystem dynamics? The investigators are working towards diagnosing mechanisms of ecosystem change and developing a quantitative framework for forecasting future conditions and how these might affect the management of key living marine resources, including numerous fishes, invertebrates, marine mammals, and seabirds. They are training graduate and undergraduate students, as well as providing educational opportunities for teachers. Public programs and outreach efforts in collaboration with the Birch Aquarium at Scripps Institution of Oceanography are increasing public awareness and understanding of climate effects on coastal pelagic communities and connecting the public to cutting-edge ocean research.

This project is adding to understanding of the mechanisms underlying abrupt ecological transitions with three interrelated foci: (1) investigation of marine heatwaves and resultant multiple stressors on organisms and communities, (2) elucidation of ecological stoichiometry and the response of multiple trophic levels to altered elemental ratios of source nutrients, and (3) analysis of top-down pressures mediated by a diverse suite of organisms. It is sustaining multi-scale measurements of five core LTER variables and responses to ocean warming, increased stratification, acidification, deoxygenation, and altered nutrient stoichiometry in the Northeast Pacific. The investigators are using long-term, spatially-resolved time series at multiple spatial scales to evaluate community shifts at multiple temporal scales, with new measurements allowing interrogation at finer taxonomic levels. They are conducting in situ multi-factorial experiments (temperature, macronutrients, micronutrients, light, grazing) in combination with genomic and transcriptomic analyses. These will complement time series measurements, inform next-generation biogeochemical models, and test hypotheses related to ecological stoichiometry and marine heatwaves. The team is also using a suite of imaging techniques, molecular and morphological methods, and active and passive acoustic approaches to quantify vertical structure and cooccurrence of organisms across trophic levels and test hypotheses about top-down control of the ecosystem.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

This project is supported by continuing grants with name variations:

• LTER: Nonlinear transitions in the California Current Coastal Pelagic Ecosystem
• Ecological Transitions in the California Current Ecosystem: CCE-LTER Phase II
• LTER: CCE-LTER Phase III: Ecological Transitions in an Eastern Boundary Current Upwelling Ecosystem
• LTER: Ecosystem controls and multiple stressors in a coastal upwelling system - CCE IV

NSF Award Abstract
This project will study how dimethylmercury is formed and removed in the oceans. Dimethylmercury is a naturally occurring compound. It is thought to be formed when man-made mercury is converted into monomethylmercury, a toxin that accumulates in fish. Despite representing a large fraction of mercury in the oceans, the origin and fate of dimethylmercury is not known. This research will use state-of-the-art analytical, genomic and modeling tools to address this information gap. It will also train graduate and undergraduate students to use field, experimental, and modeling methods. The results will be used in predictive models to forecast future trends in the oceanic mercury cycle. These models are needed to evaluate the effectiveness of international actions that seek to reverse increasing trends in the bioaccumulation of monomethylmercury in fish.

Methylated mercury species in the ocean are formed in sediment and the water column from inorganic divalent mercury delivered from the atmosphere and rivers. The putative mechanism is a two-step process during which monomethylmercury is formed first, followed by slow methylation into dimethylmercury. The first step, biomethylation of divalent mercury into monomethylmercury, is relatively well-studied in sediment and known to be driven by sulfate- and iron-reducing bacteria and methanogens. The mechanism for monomethylmercury formation in the water column is less well understood, and the process of dimethylmercury formation in sediment or seawater is essentially unknown. Until recently, it was assumed that dimethylmercury represented a small enough fraction of the methylated and total mercury (the sum of all mercury species) pools to be insignificant in the global mercury cycle. Recent measurements, however, show that dimethylmercury levels in seawater can be in the same range as the other mercury species. This project will identify the biological and chemical methylating agents involved in the formation of dimethylmercury. Further, it will test the impact of varying biogeochemical conditions on dimethylmercury production. Results will be used to update the mercury module of the MIT General Circulation Model (MITgcm, a global biogeochemical model, and analyze the impacts of dimethylmercury production and degradation on monomethylmercury concentrations.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.

adapted from http://www.lternet.edu/

The National Science Foundation established the LTER program in 1980 to support research on long-term ecological phenomena in the United States. The Long Term Ecological Research (LTER) Network is a collaborative effort involving more than 1800 scientists and students investigating ecological processes over long temporal and broad spatial scales. The LTER Network promotes synthesis and comparative research across sites and ecosystems and among other related national and international research programs. The LTER research sites represent diverse ecosystems with emphasis on different research themes, and cross-site communication, network publications, and research-planning activities are coordinated through the LTER Network Office.

2017 LTER research site map obtained from https://lternet.edu/site/lter-network/