The large-scale oceanic distribution of trace elements: disentangling preformed contributions, regenerative processes, subsurface sources and sinks

Lead Research Organisation: University of Oxford
Department Name: Earth Sciences

Abstract

Elements present in seawater in quantities so small that they do not affect salinity are called "trace elements". In spite of their low abundances, trace metals can play disproportionally large roles in controlling the dynamics of marine ecosystems. This is because some are necessary for the proper functioning of important enzymes and proteins and must thus be supplied in sufficient quantities to maintain phytoplankton populations. There are regions in the ocean where key metals, particularly iron (Fe), are lacking in proportion to the other nutrients, what limits biological productivity. Why some micronutrients are lacking in some region and not others is not fully understood; the processes that govern the natural cycles of these metals are not well known. This gap in understanding is partly due to the difficulty of measuring trace metals in the ocean: trace metals are present in very small quantities and water samples are taken from metallic research ships, making measurements prone to contamination. Reliable techniques to routinely measure trace metals in seawater have only been recently developed. Thanks to them, the accuracy of the data and data coverage over the oceans have improved dramatically over the last few years. With this project, I aim to improve the general understanding of the cycling of trace metals, particularly the micronutrients, by analyzing the newest and most complete trace metal databases available.

The difficulty when trying to interpret measurements of dissolved trace metal concentrations, or other nutrients, in the deep sea is that one cannot easily distinguish between the amount that is present because it has been transported to the point of sampling from somewhere else and the amount that has been added or removed due to local, internal processes. Yet, one must be able to isolate that later component to quantify and interpret the influence of subsurface biogeochemical processes on trace metal cycles. Without this ability, one's interpretation of the measured concentration field could be wrong, mistaking transport phenomena for internal cycling mechanisms. This work will directly address this issue by applying statistical deconvolution techniques to explicitly quantify the amount that is transported. By taking the difference between the measured concentrations and the calculated transported component, it is possible to quantify the fraction that is due to biogeochemical processes and map these residual quantities.

One of the most important processes influencing the distribution of trace metals in the sea is "scavenging"; that is the propensity for dissolved metals to stick to particles and sink along with them. Scavenging affects metals more than other nutrients. It is an important process because it is omnipresent (particles are everywhere) and can redistribute the metals within the ocean interior. It is hypothesized that if scavenging is strong, or operating for a long time, the scavenging process can fractionate metals relative to the other nutrients. When layers that are affected strongly by this process are transported back to the surface, they will bring with them waters that are depleted in the metal relative to the other nutrients. If the metal abundance is too low, this will limit surface productivity. Preliminary modeling experiments support the view that scavenging exerts a first order control on the distribution of some metals, such as thorium, beryllium, the rare earth elements and aluminium. It is, however, not clear how much micronutrient metals scavenge and if this effect is able to explain the distribution and characteristics of micronutrient-limited regions. This project will test this hypothesis. First, the statistical deconvolution results from the data will inform on the degree of fractionation imposed by scavenging on each metal. Secondly, models will be used to simulate scavenging and the fractionation process and quantify the influence on surface ecosystems.

Planned Impact

The benefits of this work will extend beyond advances in academic research. The following areas will be particularly concerned.

i. Environment and climate change: problems and remediation strategies
a. Iron fertilization: Iron addition was proposed as a geo-engineering solution to pump carbon out of the atmosphere into the ocean. It is not clear how to quantify the benefits of such schemes and how to weight the negative aspects, such as the possible development of anoxic conditions and their influence on sea life. This project will provide a better understanding of iron remineralization on large scales, on interior iron transport and on the relationships between iron and other metals.

b. Acidification: Changing seawater pH affects metal speciation and bioavailability. pH and redox conditions also control sedimentary metal cycling and the dissolution of carbonates. Acidification changes the lysocline depth and can influence sediment-water column metal exchange. This project will provide a baseline assessment of current relationships between pH-gradients in the sea and ocean interior metal cycling.

c. Ecosystems: Micronutrients such as Fe, Zn, Cd, Mn and Ni are important to maintain phytoplankton growth and thus to support the marine ecosystem. By analysing the large-scale subsurface signature of these metals, the project will provide a new understanding of the supply of micronutrients to the surface ocean. A better understanding of ecosystems will help better manage fisheries and international marine resources.

ii. Deep-sea resource exploitation and management
a. Deep-sea mining: It has been known for decades that marine deposits are rich in valuable metals. About 30 years ago, deep-sea mining was deemed not profitable; it was cheaper to exploit land-based resources. Today, our economies rely on access to critical metals. With prices going up and the risk that some might use metal supply as geopolitical leverage in international negotiations, countries and corporations are looking again in the potential of deep-sea mining. The results from this project will provide a large-scale picture of the processes controlling the deep-sea distribution of metals, information that will help identify, evaluate and, in time, mitigate the influence of deep-sea mining on ecosystems and on the metal budget of the ocean.

iii. Earth system modeling and forecasting
a. Carbon export: The flux of particulate carbon is a critical quantity to assess the strength of the biological pump and its role in the global carbon cycle. It is, however, a difficult quantity to observe and model. No model currently simulates the dynamics of marine particles with any confidence. Since some metals scavenge on particles, tracing the interior distribution of metals helps constrain particles dynamics, the particle flux and its spatial pattern, provided the role of transport on concentrations can be quantified. This work will explicitly quantify the role of advection. By focusing on modeling the distribution of metals better, one will achieve a better understanding and representation of carbon export and ultimately of the fate of atmospheric CO2 and of the functioning of ecosystems. This will be pursued through Oxford's relationship with the Met-Office.

b. Ocean interactions with its boundaries: Our understanding of the interactions between submerged landmasses (continental shelves, mid-ocean ridges, seamounts, bottom boundary layer) and the ocean is generally poor. Our ability to model these interactions is commensurate with our understanding of these processes. This work will estimate of the fraction of trace elements that cannot be explained by advection. It will then be possible to interpret this "residual" fraction using a combination of trace metals and ancillary isotopic data. By investigating the spatial gradient of these residuals, the project will contribute a much greater understanding of these land-ocean interactions.

Related Projects

Project Reference Relationship Related To Start End Award Value
NE/M017826/1 01/06/2015 30/06/2018 £501,472
NE/M017826/2 Transfer NE/M017826/1 01/07/2018 31/05/2020 £196,895
 
Description 1) The amount of any chemical present in a sewater sample is affected by a suite of processes, chiefly transport from upstream, and local biological or chemical processing. By applying end-member mixing ideas to the ocean, we are now able to quantify and separate the amount that is due to transport from that due to other processes. This technique was applied to data from the Sout Atlantic as a proof a study. More work constructing on this success is underway.
2) Using the global rare earth element dataset, we can now link the rare earth patterns from formaminiferal shells to the deep water rare earth patterns, moving closer to using rare earth element patterns from forams as a paleoproxy.
Exploitation Route 1) The end-member analysis technique developed can be readily used to study the transport and biogeochemical cycles of other metals in the ocean.
2) the formaminifer to seawater REE relationship can be exploited to study past climates. 3) Have Rare earth elements gain mainstream acceptance by the broader oceanographic community as valuable tracers and people can now attempt to move them up the priority lists of global sampling programme, from Level 3 to Level 2.
Sectors Aerospace, Defence and Marine,Chemicals,Creative Economy,Energy,Environment,Financial Services, and Management Consultancy

 
Description John Fell OUP Research Fund
Amount £7,500 (GBP)
Funding ID 161/059 
Organisation Oxford University Press 
Sector Private
Country United Kingdom
Start 01/2017 
End 01/2018
 
Description Met Office Academic Partnership - Modeling the transient evolution and atmospheric transport of Pb emissions in the past 100 years
Amount £3,000 (GBP)
Organisation Meteorological Office UK 
Sector Public
Country United Kingdom
Start 07/2017 
End 08/2017
 
Description Met Office Academic Partnership - the subtropical circulations of biogeochemically active tracers in the Atlantic
Amount £3,000 (GBP)
Organisation Meteorological Office UK 
Sector Public
Country United Kingdom
Start 07/2017 
End 08/2017
 
Description Oxford Met Office Academic Partnership Internship Programme (Pb project)
Amount £2,500 (GBP)
Organisation Meteorological Office UK 
Sector Public
Country United Kingdom
Start 06/2016 
End 08/2016
 
Description Oxford Met Office Academic Partnership Internship Programme (UKESM project)
Amount £2,500 (GBP)
Organisation Meteorological Office UK 
Sector Public
Country United Kingdom
Start 06/2016 
End 08/2016
 
Title A global database of Pb and Pb isotopes 
Description Collection of Pb and Pb isotopes measurements made in the ocean. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? No  
Impact Versions of this database were used to substantiate 2 (failed) bids for NERC funding (standard grant) and 2 master theses. Research is ongoing. 
 
Title A global database of eNd and REE in rivers 
Description Global database of Rare earth elements and neodymium isotopes in the world's rivers. 
Type Of Material Database/Collection of data 
Year Produced 2018 
Provided To Others? No  
Impact Database formed the basis for 1 master's thesis. Further resarch ongoing. 
 
Title A steady state model of metals in seawater by TMM 
Description This is a model written in Matlab that can be used to efficiently calculate the steady state distribution of metals in the global ocean. 
Type Of Material Computer model/algorithm 
Year Produced 2015 
Provided To Others? Yes  
Impact So far, aside from me, this model has served as the basis for 2 undergraduate student project and it is now being used by other researchers in Imperial College, Lamont Doherty Earth Laboratory and ETH Zurich. 
 
Title Global 10Be database 
Description Database of published 10Be measurements in the ocean. 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Putting this database together is part of a student project I am advising. This database has so far served to train a student and it is being used to write a scientific paper. The results will be presented by the student in April 2016 during the European Geophysical Union meeting in Vienna. 
 
Title Global 230Th and 232Th database 
Description Global collection of Th230, Th232 and Pa231 measurements in seawater. 
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
Impact I am currently using the Th230 and Th232 data to constrain a model used to evaluate the value of the Th230-Th232 isotopic couple to reconstruct dust fluxes over the ocean. The Th230 data are also used by a colleague in Lamont-Doherty Earth Observatory New York to test ideas about the value of the Pa231/Th230 method of estimating paleocirculation. Part of this database was presented in Goldschmidt 2015 (Henderson et al.) in a keynote address and will be presented in February 2016 in the Ocean Sciences Meeting in New Orelans (USA) and also in Goldschmidt Paris 2017 (Plancherel et al.) and AGU San Francisco 2016 (Plancherel et al.). 
 
Title Global distribution of rare earth elements in the ocean 
Description Global collection of all previously published REE measurements in seawater. 
Type Of Material Database/Collection of data 
Year Produced 2015 
Provided To Others? Yes  
Impact Multiple papeers were published in collaboration with colleagues in Kiel/GEOMAR, CEREGE (France) and Cambridge (UK). This database is now being used to constrain global biogeochemical models and was used to motivate new observational programmes (i.e. GOSHIP P18, S04P cruises). 
URL http://www.bodc.ac.uk/geotraces/data/historical/
 
Description GOSHIP SO4P 
Organisation National Science Foundation (NSF)
Country United States 
Sector Public 
PI Contribution I participated in a 69 days research expedition in the Southern Ocean (SO4P) linking Tasmania with Punta Arenas, via the Ross Sea. As part of this expedition, I took >1200 samples to be measured for rare earth element concentration. This will be the first and only high-resolution section of REEs in the whole Southern Ocean. This section complements a previous sampling expedition (P18).
Collaborator Contribution The partner organized the whole expedition and provided the entire logistic and funding for the cruise (except shipping of my samples).
Impact Samples are now back in the UK. They will be analyzed as soon as I can find funding to pay for the analysis.
Start Year 2018
 
Description Global analysis of Nd and Nd isotopes 
Organisation European Centre for Research and Teaching of Environmental Geosciences (CEREGE)
Country France 
Sector Academic/University 
PI Contribution I provided statistical expertise and a data compilation of Rare Earth Elements dissolved in seawater.
Collaborator Contribution My partner (K. Tachikawa from CEREGE) provided a global dataset of dissolved Neodymium (Nd) and Nd isotopes. Dr. Tachikawa also drafted a manuscript on this collaborative work which is currently under review.
Impact A manuscript was submitted to Chemical Geology and is currently under review.
Start Year 2016
 
Description Rare Earth Element cycling in rivers and estuaries 
Organisation University of Cambridge
Department Department of Earth Sciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Intellectual contribution for defining the research question and logistical contribution by starting an observational time-series programme on the Severn River which the project partner now contributes to also.
Collaborator Contribution Partner provided samples from multiple locations, including Greenland and Myanmar. The partner now also performs major cations and anions analysis on the samples collected.
Impact Training of a Master's student in Oxford, triggered discussion with the Enviromental Agency targeted towards further collaborations. Projects under discussions. New funding was awarded to the project partner to go back to Greenland in Summer 2018 to continue the work there.
Start Year 2017
 
Description Rare Earth Elements on GOSHIP cruise S04P 
Organisation Imperial College London
Department Department of Earth Science & Engineering
Country United Kingdom 
Sector Academic/University 
PI Contribution I am participating in cruise S04P (67 days, between Hobart Tasmania and Punta Arenas Chile) to take rare earth elements samples to be analyzed at a later date in the lab. I also contribute to the collection of other samples, including Helium and Noble Gases, a project lead by colleagues in Scripps Institution of Oceanography (Nicholas Beaird, Fiamma Straneo) and Woods Hole Oceanographic Institute (Kevin Cahill) and Neodymium Isotopes for Prof Tina van de Flierdt (Imperial College London). These rare earth elements samples will increase the data coverage in the Pacific sector of the Southern Ocean by 2 orders of magnitude, from a few tens of samples to over 1000.
Collaborator Contribution The GOSHIP organization provides berthing abord the ship (R/V Nathaniel B. Palmer), a US NSF vessel, the opportunity to take the samples and all the logistics from the cruise, all of it, free of charge to me.
Impact The cruise will depart from Hobart on March 9th and return to Punta Arenas on May 19th 2018. Outputs will only occur after the cruise is completed.
Start Year 2017
 
Description Rare Earth Elements on GOSHIP cruise S04P 
Organisation University of California, San Diego (UCSD)
Department Scripps Institution of Oceanography
Country United States 
Sector Academic/University 
PI Contribution I am participating in cruise S04P (67 days, between Hobart Tasmania and Punta Arenas Chile) to take rare earth elements samples to be analyzed at a later date in the lab. I also contribute to the collection of other samples, including Helium and Noble Gases, a project lead by colleagues in Scripps Institution of Oceanography (Nicholas Beaird, Fiamma Straneo) and Woods Hole Oceanographic Institute (Kevin Cahill) and Neodymium Isotopes for Prof Tina van de Flierdt (Imperial College London). These rare earth elements samples will increase the data coverage in the Pacific sector of the Southern Ocean by 2 orders of magnitude, from a few tens of samples to over 1000.
Collaborator Contribution The GOSHIP organization provides berthing abord the ship (R/V Nathaniel B. Palmer), a US NSF vessel, the opportunity to take the samples and all the logistics from the cruise, all of it, free of charge to me.
Impact The cruise will depart from Hobart on March 9th and return to Punta Arenas on May 19th 2018. Outputs will only occur after the cruise is completed.
Start Year 2017
 
Description Using Rare Earth Elements to trace upwelled deep waters in the Southern Ocean 
Organisation Helmholtz Association of German Research Centres
Department Helmholtz Centre for Ocean Research Kiel
Country Germany 
Sector Public 
PI Contribution I have contributed the intellectual premise, i.e. the rationale, for this study and initiated the collaboration. The hypothesis underlying this study builds on my efforts to build a global dataset of rare earth element measurements, on results from my global biogeochemical model used to simulate the distribution of rare earth elements in seawater, and from my expertise about the distribution and relevance of ocean water masses. Aside from the motivation for the study, I have also contributed funding to purchase sampling equipment, salary time to go to sea and perform the sampling and funds to cover the cost of my travel to and from the ship and to ship the samples. I have also developed the sampling plan and organized the collaboration between the different parties. In time, I will be advising a student and paying for some of the laboratory supplies and analyses. This will directly help me expand my research portfolio. Participating in the P18 cruise has now established a collaboration between me and the GO-SHIP programme which can be leveraged in the future to access samples and participate in future cruises.
Collaborator Contribution GEOMAR will be providing laboratory supplies and will perform part of the analyses to measure rare earth element concentrations in seawater and possibly a Masters' student (pending sample availability). NOAA/PMEL ran/organized/paid for the research cruise (nearly 3 months at sea in total - Nov 2016 to Feb 2017) and provided personel and logistical support to take the samples during leg1 of the P18 cruise.
Impact Direct outcomes so far involve my visit to Kiel/GEOMAR between 12-14 November 2015. Plans have been made for my Kiel/GEOMAR colleagues to come visit Oxford and help us setup the SeaFAST method for measuring rare earth elements locally in summer 2017. Nearly 1200 samples (60 ml) have been collected as part of the P18 repeath hydrography GO-SHIP (www.go-ship.org) cruise. About 500 samples have been shipped to Kiel and 700 samples are now in Oxford waiting to be analyzed. A studenship (Master's level) has now been advertised in Oxford to recruit a student to perform the REE analyses. Using the NERC grant, it was possible to guarantee participation in the expedition and as such seek and secure additional funding. The additional funding came in the form of the Oxford University John Fell Fund award and amounts to 7500 pounds. This additional grant will largely cover the cost of the analyses and provided additional resources to pay for sample shipping.
Start Year 2015
 
Description Using Rare Earth Elements to trace upwelled deep waters in the Southern Ocean 
Organisation National Oceanic And Atmospheric Administration
Country United States 
Sector Public 
PI Contribution I have contributed the intellectual premise, i.e. the rationale, for this study and initiated the collaboration. The hypothesis underlying this study builds on my efforts to build a global dataset of rare earth element measurements, on results from my global biogeochemical model used to simulate the distribution of rare earth elements in seawater, and from my expertise about the distribution and relevance of ocean water masses. Aside from the motivation for the study, I have also contributed funding to purchase sampling equipment, salary time to go to sea and perform the sampling and funds to cover the cost of my travel to and from the ship and to ship the samples. I have also developed the sampling plan and organized the collaboration between the different parties. In time, I will be advising a student and paying for some of the laboratory supplies and analyses. This will directly help me expand my research portfolio. Participating in the P18 cruise has now established a collaboration between me and the GO-SHIP programme which can be leveraged in the future to access samples and participate in future cruises.
Collaborator Contribution GEOMAR will be providing laboratory supplies and will perform part of the analyses to measure rare earth element concentrations in seawater and possibly a Masters' student (pending sample availability). NOAA/PMEL ran/organized/paid for the research cruise (nearly 3 months at sea in total - Nov 2016 to Feb 2017) and provided personel and logistical support to take the samples during leg1 of the P18 cruise.
Impact Direct outcomes so far involve my visit to Kiel/GEOMAR between 12-14 November 2015. Plans have been made for my Kiel/GEOMAR colleagues to come visit Oxford and help us setup the SeaFAST method for measuring rare earth elements locally in summer 2017. Nearly 1200 samples (60 ml) have been collected as part of the P18 repeath hydrography GO-SHIP (www.go-ship.org) cruise. About 500 samples have been shipped to Kiel and 700 samples are now in Oxford waiting to be analyzed. A studenship (Master's level) has now been advertised in Oxford to recruit a student to perform the REE analyses. Using the NERC grant, it was possible to guarantee participation in the expedition and as such seek and secure additional funding. The additional funding came in the form of the Oxford University John Fell Fund award and amounts to 7500 pounds. This additional grant will largely cover the cost of the analyses and provided additional resources to pay for sample shipping.
Start Year 2015
 
Description Elements of Planetary Climate 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Local
Primary Audience Schools
Results and Impact STEM enrichment programme for Years 11-13 at the Matthew Arnold school, Oxford. The goal is to give students a flavour for current research to try to motivate them to pursue a career in science.
Year(s) Of Engagement Activity 2017
 
Description Energy and the Environment: An Earth Sciences Perspective 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach Regional
Primary Audience Schools
Results and Impact "Looking Forward Event" organized by the Oxford Mathematical Institute. Weeklong science conference aiming to motivate Year 10 girls to pursue science A-levels, about 50 students in attendence, and many school teachers.
Year(s) Of Engagement Activity 2017
 
Description Portugal Biogeochemistry Summer School 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Postgraduate students
Results and Impact This course provided students (Ms and PhD) and young Researchers, with an opportunity to gain a better understanding of the marine biogeochemical cycles and large-scale distribution of biological utilized elements and/ or tracers of oceanographic processes. In light of society's pressing needs to prepare for the future consequences of global warming, it is of major importance for the next generation of young marine researchers to grasp the basic biogeochemical concepts and gain the capacity to use the acquired knowledge in their future work. Invited professors were researchers working in the field of Biogeochemistry. The assembled group of experts, joined for the first time, allowed for a unique training opportunity that is not available in any other institution. The course covered: (1) the modern ocean distributions and biogeochemical cycles of the elements that regulate marine ecosystem dynamics; (2) the distribution of elements, which can be important tracers for oceanographic processes both via conceptual and numerical modeling; and (3) the use of such elements and their isotopes as proxies for reconstruction of past conditions. Also included were free form / brainstorming evening discussions covering communicating science, proposal and paper writing and presentations by the students. The course took place in Faro - Algarve, a touristic region of Portugal, served by an international airport with cheap flight options. In June, accommodation is reasonable, meaning that the event can be very affordable both to students and researchers alike. Given thte success of this first course, another course is being planned for 2020.
Year(s) Of Engagement Activity 2018
URL https://www.ccmar.ualg.pt/activity/att-marine-biogeochemistry-training-school-biogeochemical-and-eco...