Periodic Reporting for period 1 - DEstiNi (Investigation of the Dynamic Estuarine and Marine cycling of Nickel)
Reporting period: 2019-09-01 to 2021-08-31
This project addresses a long-standing problem with the marine mass- and isotopic budgets of the trace metal nickel (Ni). At present, there is an enormous imbalance between the known sources and sinks of Ni to and from the ocean. The biological, chemical and physical processes that exert a fundamental control on seawater Ni supply, cycling and removal, must be constrained before Ni isotopes in geological archives can be studied in any meaningful way in terms of tracing past shifts in Earth surface or deep processes. This project focusses on a potential ‘missing source’ of Ni to the ocean – the release of Ni from the surface of riverine sediments as it desorbs during estuarine cycling, and the potential sinks of Ni during formation of Fe-oxides in marine sediments.
The principle aim of this project is to amend the global mass- and isotopic budgets of Ni in the ocean. This will be achieved by answering the following key questions:
I. Does solute-particle interaction and desorption of Ni from particle surfaces in estuarine environments account for the missing flux of Ni to the ocean?
II. What is the isotopic composition of the desorbed Ni pool and what are the effects on the oceanic Ni isotopic budget?
III. How do sediment redox conditions affect the Ni isotopic composition of the dissolved marine pool?
The results of the project greatly modifies trace metal concentrations from the Hooghly estuary, and subsequent flux to the ocean. The results of the project show that continental riverine fluxes are in fact amended by desorption of metals from suspended sediment particles as they reach the salinity gradient within the estuary. However, the new robust analytical techniques developed during the project reveal that the fluxes from this desorption process may be considerably smaller than previous publications suggest, as previously published data often report grossly inflated metal concentrations due to measurement of isobaric interferences in the salinity gradient.
The results of the project are important in order to understand biogeochemical cycling of Ni and other trace metals. Ni isotopes are increasingly used as a biogeochemical tracer, but before they can be used to trace past shifts in environmental conditions, or the existence of ancient or extraterrestrial life, the fundamental knowledge of Ni cycling in the present day needs to be better understood.
The principle aim of this project is to amend the global mass- and isotopic budgets of Ni in the ocean. This will be achieved by answering the following key questions:
I. Does solute-particle interaction and desorption of Ni from particle surfaces in estuarine environments account for the missing flux of Ni to the ocean?
II. What is the isotopic composition of the desorbed Ni pool and what are the effects on the oceanic Ni isotopic budget?
III. How do sediment redox conditions affect the Ni isotopic composition of the dissolved marine pool?
The results of the project greatly modifies trace metal concentrations from the Hooghly estuary, and subsequent flux to the ocean. The results of the project show that continental riverine fluxes are in fact amended by desorption of metals from suspended sediment particles as they reach the salinity gradient within the estuary. However, the new robust analytical techniques developed during the project reveal that the fluxes from this desorption process may be considerably smaller than previous publications suggest, as previously published data often report grossly inflated metal concentrations due to measurement of isobaric interferences in the salinity gradient.
The results of the project are important in order to understand biogeochemical cycling of Ni and other trace metals. Ni isotopes are increasingly used as a biogeochemical tracer, but before they can be used to trace past shifts in environmental conditions, or the existence of ancient or extraterrestrial life, the fundamental knowledge of Ni cycling in the present day needs to be better understood.
Work on the project included:
* Two field campaigns to the Hooghly estuary (India) during pre-monsoon and monsoon seasons.
* Estuary water, suspended sediment and bed load sediment samples were collected along a 120 km transect along the estuary, targeting a wide range in salinity and pH.
* Developing several analytical protocols (adapted to unique sample matrices) for sample treatment and preparation, Ni column chromatography and Ni isotope analysis using a double spike technique
* The methodology was successfully transferred from the initial laboratory at the Institute for Planetary Materials at Okayama University, Japan, to the national infrastructure facility at the Museum of Natural History in Stockholm, Sweden
* Developing robust analytical technique for measurement of trace metal concentrations in estuarine waters, a notoriously challenging sample matrix
* Setting up batch reaction experiments to investigate the behaviour of Ni and Ni isotopes during ferrihydrite formation (coprecipitation and adsorption experiments) mimicking pelagic sedimentation on the seafloor
* 250 samples were collected from 125 separate experimental conditions testing effect of varying concentrations of Ni and other elements, pH and equilibration time
* This work package has already resulted in one publication, and a minimum of one more is expected within the next year.
* Results show that coprecipitation yields the same Ni isotopic fractionation regardless of Si concentration in the solution (Figure 1 attached), whereas adsorption is highly sensitive to Si content. This has implications for the Ni sink in the marine environment where the presence os Si varies greatly with hydrothermal vent input.
* Sample processing and analysis: the project has resulted in over ten thousand data points for Ni isotopes, major-, minor-, and trace element compositions, TEM-, Raman-, IR-, and XRD spectra in a large variety of geological sample matrices (fresh waters, estuary waters, seawaters, suspended sediments, bedload sediments, iron oxides).
The results are currently being synthesised and prepared for publications in peer reviewed journals, and have been presented at two conferences.
* Two field campaigns to the Hooghly estuary (India) during pre-monsoon and monsoon seasons.
* Estuary water, suspended sediment and bed load sediment samples were collected along a 120 km transect along the estuary, targeting a wide range in salinity and pH.
* Developing several analytical protocols (adapted to unique sample matrices) for sample treatment and preparation, Ni column chromatography and Ni isotope analysis using a double spike technique
* The methodology was successfully transferred from the initial laboratory at the Institute for Planetary Materials at Okayama University, Japan, to the national infrastructure facility at the Museum of Natural History in Stockholm, Sweden
* Developing robust analytical technique for measurement of trace metal concentrations in estuarine waters, a notoriously challenging sample matrix
* Setting up batch reaction experiments to investigate the behaviour of Ni and Ni isotopes during ferrihydrite formation (coprecipitation and adsorption experiments) mimicking pelagic sedimentation on the seafloor
* 250 samples were collected from 125 separate experimental conditions testing effect of varying concentrations of Ni and other elements, pH and equilibration time
* This work package has already resulted in one publication, and a minimum of one more is expected within the next year.
* Results show that coprecipitation yields the same Ni isotopic fractionation regardless of Si concentration in the solution (Figure 1 attached), whereas adsorption is highly sensitive to Si content. This has implications for the Ni sink in the marine environment where the presence os Si varies greatly with hydrothermal vent input.
* Sample processing and analysis: the project has resulted in over ten thousand data points for Ni isotopes, major-, minor-, and trace element compositions, TEM-, Raman-, IR-, and XRD spectra in a large variety of geological sample matrices (fresh waters, estuary waters, seawaters, suspended sediments, bedload sediments, iron oxides).
The results are currently being synthesised and prepared for publications in peer reviewed journals, and have been presented at two conferences.
The method development has resulted in several improvements on analytical methods for Ni isotopes. Also the measurements of Ni and other trace metals in estuarine waters which are notoriously challenging to analyse, due to isobaric interferences with seawater matrix elements. The results from the project highlight that previous publications grossly overestimate trace and heavy metal concentrations in the Hooghly (and possibly other estuaries) due to these interferences, leading to inflated heavy metal concentrations with possible ineffective use of funding for metal remediation as a consequence.
The results are expected to increase our understanding of Ni cycling in the surface environment. The data from the experimental work package greatly helps interpretation of the natural data set. An additional 2-3 scientific articles will be published within the coming year .
The results are expected to increase our understanding of Ni cycling in the surface environment. The data from the experimental work package greatly helps interpretation of the natural data set. An additional 2-3 scientific articles will be published within the coming year .