Award Abstract # 1433710
Collaborative Research: Isotopic insights to mercury in marine food webs and how it varies with ocean biogeochemistry

NSF Org: OCE
Division Of Ocean Sciences
Recipient: REGENTS OF THE UNIVERSITY OF MICHIGAN
Initial Amendment Date: July 21, 2014
Latest Amendment Date: June 4, 2019
Award Number: 1433710
Award Instrument: Standard Grant
Program Manager: Henrietta Edmonds
hedmonds@nsf.gov
 (703)292-7427
OCE
 Division Of Ocean Sciences
GEO
 Directorate For Geosciences
Start Date: August 1, 2014
End Date: July 31, 2020 (Estimated)
Total Intended Award Amount: $358,982.00
Total Awarded Amount to Date: $358,982.00
Funds Obligated to Date: FY 2014 = $358,982.00
History of Investigator:
  • Joel Blum (Principal Investigator)
    jdblum@umich.edu
Recipient Sponsored Research Office: Regents of the University of Michigan - Ann Arbor
1109 GEDDES AVE, SUITE 3300
ANN ARBOR
MI  US  48109-1079
(734)763-6438
Sponsor Congressional District: 06
Primary Place of Performance: University of Michigan Ann Arbor
MI  US  48109-1005
Primary Place of Performance
Congressional District:
06
Unique Entity Identifier (UEI): GNJ7BBP73WE9
Parent UEI:
NSF Program(s): Chemical Oceanography
Primary Program Source: 01001415DB NSF RESEARCH & RELATED ACTIVIT
Program Reference Code(s): 9150, 9156
Program Element Code(s): 1670
Award Agency Code: 4900
Fund Agency Code: 4900
Assistance Listing Number(s): 47.050

ABSTRACT

Mercury is a pervasive trace element that exists in several states in the marine environment, including monomethylmercury (MMHg), a neurotoxin that bioaccumulates in marine organisms and poses a human health threat. Understanding the fate of mercury in the ocean and resulting impacts on ocean food webs requires understanding the mechanisms controlling the depths at which mercury chemical transformations occur. Preliminary mercury analyses on nine species of marine fish from the North Pacific Ocean indicated that intermediate waters are an important entry point for MMHg into open ocean food webs. To elucidate the process controlling this, researchers will examine mercury dynamics in regions with differing vertical dissolved oxygen profiles, which should influence depths of mercury transformation. Results of the study will aid in a better understanding of the pathways by which mercury enters the marine food chain and can ultimately impact humans. This project will provide training for graduate and undergraduate students, and spread awareness on oceanic mercury through public outreach and informal science programs.

Mercury isotopic variations can provide insight into a wide variety of environmental processes. Isotopic compositions of mercury display mass-dependent fractionation (MDF) during most biotic and abiotic chemical reactions and mass-independent fractionation (MIF) during photochemical radical pair reactions. The unusual combination of MDF and MIF can provide information on reaction pathways and the biogeochemical history of mercury. Results from preliminary research provide strong evidence that net MMHg formation occurred below the surface mixed layer in the pycnocline and suggested that MMHg in low oxygen intermediate waters is an important entry point for mercury into open ocean food webs. These findings highlight the critical need to understand how MMHg levels in marine biota will respond to changes in atmospheric mercury emissions, deposition of inorganic mercury to the surface ocean, and hypothesized future expansion of oxygen minimum zones. Using field collections across ecosystems with contrasting biogeochemistry and mercury isotope fractionation experiments researchers will fill key knowledge gaps in mercury biogeochemistry. Results of the proposed research will enable scientists to assess the biogeochemical controls on where in the water column mercury methylation and demethylation likely occur.

PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH

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(Showing: 1 - 10 of 13)
Dana K. Sackett, Jeffrey C. Drazen, C. Anela Choy, Brian Popp, Gerald L. Pitz "Mercury Sources and Trophic Ecology for Hawaiian Bottomfish. Environmental Science and Technology" Environmental Science and Technology , v.49 , 2015 , p.6909 10.1021/acs.est.5b01009
Blum, J.D., Popp, B.N., Drazen, J.C., Choy, C.A. and Johnson, M.W. "Evidence for methylmercury production below the mixed layer in the North Pacific Ocean." Nature Geoscience , 2013 , p.879 10.1038/ngeo1918
Kwon SY, Blum JD, Madigan DJ, Block BA, Popp BN. "Quantifying mercury isotope dynamics in a captive pelagic fish, Pacific bluefin tuna (Thunnus orientalis)." Elementa , v.4 , 2016 10.12952/journal.elementa.000088
Kwon SY, Blum JD, Madigan DJ, Block BA, Popp BN "Quantifying mercury isotope dynamics in a captive pelagic fish, Pacific bluefin tuna (Thunnus orientalis)." Elementa , v.4 , 2017 10.12952
Sackett, D.K., Drazen, J.C., Popp, B.N., Choy, C.A., Blum, J.D., Johnson, M.W., "Seasonal dynamics of midwater zooplankton and relation to particle cycling in the North Pacific Subtropical Gyre." Environmental Science & Technology , v.51 , 2017 , p.13976
Archer DE and Blum JD. "A model of mercury cycling and isotopic fractionation in the ocean." Biogeosciences , 2018
Sackett, D.K., Drazen, J.C., Popp, B.N., Choy, C.A., Blum, J.D., Johnson, M.W., "Seasonal dynamics of midwater zooplankton and relation to particle cycling in the North Pacific Subtropical Gyre." Environmental Science & Technology , v.51 , 2017
Motta LC, Blum JD, Johnson MW, Washburn SJ, Popp BN, Close H, Umhau B, Benitez-Nelson C, and Hannides C. "Hg cycling in the North Pacific Subtropical Gyre as revealed by Hg isotopes." Global Biogeochemical Cycles , v.6 , 2019 , p.777
Archer DE and Blum JD. "A model of mercury cycling and isotopic fractionation in the ocean." Biogeosciences , v.15 , 2018 , p.6297
Blaire Umhau, Hilary Close, Cecelia Hannides,Laura Motta*, Brian Popp, Joel Blum, Jeffrey Drazen, Claudia Benitez-Nelson. "Seasonal and spatial changes in carbon and nitrogen fluxes estimated using 234Th:238U disequilibria in the North Pacific Subtropical Gyre" Marine Chemistry , 2019
Motta LC, Blum JD, Popp BN, Drazen JC, and Close HG. "Mercury Stable Isotopes in Flying Fish as a Monitor of Photochemical Degradation of Methylmercury in the Atlantic and Pacific Oceans" Marine Chemistry , 2020
(Showing: 1 - 10 of 13)

PROJECT OUTCOMES REPORT

Disclaimer

This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.

Project Outcomes Report

Award Title: Collaborative Research: Isotopic insights to mercury in marine food webs and how it varies with ocean biogeochemistry 

Federal Award ID: 1433710 

Report Submission Period: 08/01/2021 to 07/31/2022

Mercury is a pervasive element that exists in the marine environment in several different chemical forms. The Monomethylmercury (MMHg) form of mercury is an organic, carbon-containing, neuorotoxin. It bioaccumulates in commonly harvested marine organisms, which can pose a human health threat. Knowledge of where and how mercury changes its chemical form allows us to understand the impacts of mercury on ocean food webs. Previous work examined mercury concentrations in nine species of marine fishes from the North Pacific Ocean and found that MMHg appears to enter open ocean food webs at waters depths of 200—600 m. At these depths, dissolved oxygen concentrations are much lower than in surface waters. Thus, we hypothesized that oxygen influences the depth where mercury transformations occur. To study how mercury enters the marine food chain, we analyzed mercury in rainfall, marine organic particles, zooplankton and micronekton (small fishes, squid and shrimp) from the surface ocean to 1500 meters depth on four research expeditions in the Pacific Ocean.

Intellectual Merit
Mercury deposited to the surface ocean from the atmosphere is quickly adsorbed onto organic particles, which then settle through the ocean and are eventually eaten by organisms. We found distinct nitrogen isotope values of individual amino acid compounds in small (<53 micrometers) and large particles (>53 micrometers). Our analyses suggest that these distinct values are due to a high proportion of amino acids that derive from microbes clinging to the particles or from microbes breaking down particles for their growth. The proportion of amino acids with distinct nitrogen isotope values also increases with depth. This is important to the mercury cycle because the transformation of elemental mercury to toxic MMHg has been associated with microbial metabolism. We can also trace these distinct amino acid nitrogen isotope values into zooplankton and micronekton—indicating whether small or large particles form the base of the food chain at depth. Our study also revealed seasonal and spatial changes in the rates at which small and large particles, and the mercury within those particles, settle out of the surface ocean.

Mercury isotopic variations can provide insight into a wide variety of environmental processes. Mass-dependent processes, which affect mercury isotopic variations, are associated with most biotic and abiotic chemical reactions. On the other hand, mass-independent processes, which occur during photochemical reactions, drive isotopic variations of mercury at the surface where there is abundant sunlight. The unusual combination of mass-dependent and mass-independent processes provided information on reaction pathways and the biogeochemical history of mercury. Our mercury isotopic analyses indicate that the MMHg bioaccumulated in fish is derived primarily from elemental mercury deposited to the surface ocean by rainfall. Our results also indicate that marine particles host the majority of mercury available for the formation and degradation of MMHg, which we found can happen throughout the water column. These particles further transport mercury to deeper waters where it can enter deeper residing fish. Our mercury isotope results indicate that photochemical reactions that break down MMHg are responsible for the low concentrations of mercury in fish living in well-lit surface waters. Combined, these findings highlight the critical need to understand how MMHg levels in marine biota will respond to changes in atmospheric mercury emissions, deposition of inorganic mercury to the surface ocean, and hypothesized future expansion of low oxygen zones in the ocean as the Earth warms.

Broader Impacts

This project trained three graduate students and three undergraduate students, all women and one of native Hawaiian ancestry. We also provided at sea experiences for an additional 6 undergraduate and 7 graduate students exposing them to a diversity of sampling techniques and learning opportunities. This research provided early career opportunities to coPI Hannides.

CoPI Duncan has generated substantial public outreach for the project. We produced eight television episodes of the Telly Award winning series Voice of the Sea. These episodes aired widely in Hawaii and in U.S. Pacific territories and affiliated Pacific regions. In Hawaii alone, our viewership averages 10,000-20,000 viewers per episode (Nielsen Ratings and Marshall Marketing surveys). Audience feedback shows that Voice of the Sea episodes have been effective at increasing viewer knowledge and interest as well as viewer connection to scientists across age groups, from middle school, to college, to adult populations.

We presented our research results at numerous seminars and conferences. We published results of this research and outreach in 10 peer-reviewed papers. We have recently submitted for publication two more manuscripts and have at least three additional manuscripts in preparation for submission.  Our data is publicly available through the Biological and Chemical Oceanography Data Management Office (http://www.bco-dmo.org/project/560580).

 


Last Modified: 09/29/2020
Modified by: Joel D Blum

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