nanoSIMS; nutrient cycling; ocean chemistry; isotopes; trace metals
Little S., Vance D., McManus J., Severmann S., Lyons T. (2017), Copper isotope signatures in modern marine sediments, in Geochimica et Cosmochimica Acta
, 212, 263-273.
Vance D., Little S., de Souza G., Khatiwala S., Lohan M., Middag R. (2017), Silicon and zinc biogeochemical cycles coupled through the Southern Ocean, in Nature Geoscience
, 10, 202-206.
Moynier F., Vance D., Fujii T., Savage P. (2017), The isotope geochemistry of zinc and copper, in Reviews in Mineralogy and Geochemistry
, 82, 543-600.
Little S., Vance D., Lyons T.W., McManus J. (2016), Key role of continental margin sediments in the oceanic mass balance of Zn and Zn isotopes, in Geology
, 44, 207-210.
Conway T.M., John S.G. (2015), Biogeochemical cycling of cadmium isotopes along a high-resolution section through the North Atlantic, in Geochimica et Cosmochimca Acta
, 148, 269-283.
Conway T.M., Wolff E.W., Rothlisberger R., Mulvaney R., Elderfield H.E. (2015), Constraints on soluble aerosol Fe flux to the Southern Ocean at the Last Glacial Maximum, in Nature Communications
, 6, 7850.
Little S.H., Vance D., Lyons T.W., McManus J. (2015), Controls on trave metal authigenic enrichment in reducing sediments: insights from modern oxygen-deficient settings, in American Journal of Science
, 316, 77-119.
Middag R., Sefarian R., Conway T.M., John S.G., Bruland K.W., de Baar H.J.W. (2015), GEOTRACES Intercomparison of Dissolved Trace Elements at the Bermuda Atlantic Time Series Station., in Marine Chemistry
, 177, 476-489.
Sherman D.M., Little S.H., Vance D. (2015), Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts, reply to comment by Manceau and Nagy, in Earth and Planetary Science letters
, 411, 313-315.
Conway T.M., John S.G. (2015), The cycling of iron, zinc and cadmium in the North East Pacific Ocean - insights from stable isotopes, in Geochimica et Cosmochimica Acta
, 164, 262-283.
Revels B.N., Ohnemus D.C., Lam P.J., Conway T.M., John S.G. (2015), The isotopic signature and distribution of particulate iron in the North Atlantic Ocean, in Deep Sea Research II
, 116, 321-331.
Andersen M.B., Romaniello S., Vance D., Little S.H., Herdman R., Lyons T.W. (2014), Amodern framework for the interpretation of 238U/235U studies in ancient redox, in Earth and Planetary Science Letters
, 400, 184-194.
Little S.H., Sherman D.M., Vance D. (2014), Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts, in Earth and Planetary Science Letters
, 396, 213-222.
Andersen M.B., Vance D., Morford J.L., Bura-Nakic E., Breitenbach S.F.M., Och L., Closing in on the marine 238U/235U budget, in Chemical Geology
The supply of nutrients to the euphotic zone of the oceans controls phytoplankton growth and, to a large extent, the partitioning of carbon between the atmosphere and the oceans. Though the biogeochemical cycling of the major nutrients (C, P, N, Si) has been an area of very active research for many years, our understanding of the oceanic cycling of another set of biologically-important elements, the trace metal micronutrients, is still in its infancy. It is becoming clear, however, that these trace metals limit, or co-limit, algal growth in key oceanic settings, and thus carbon partitioning between the surface ocean and atmosphere now and in the past. The supply of nutrients to the euphotic zone is controlled both by their whole ocean budgets, as well as their internal oceanic biogeochemical cycling. There are critical gaps in our understanding of both these aspects of the ocean chemistry of the trace metals. We propose two linked sub-projects that are aimed at a better understanding of the sources of trace metals to the oceans, their intra-oceanic cycling, and ultimately their outputs from the dissolved pool to sediment. We propose to use a variety of sample sets and tools, but key among the latter are the new isotopic systems of these elements.Sub-Project A: Emerging constraints on the oceanic budgets of trace metals, including the two that are the focus here (Zn and Ni), suggest that we do cannot currently be closed. A significant new constraint comes from isotopic data for these metals in the oceanic realm, a pursuit that the proponent’s lab has been leading. Particularly for Ni, but also for Zn, one likely solution to these budgetary problems is the existence of an as yet un-quantified sedimentary source. Scarce pore water data suggest that these metals are mobilised by reductive dissolution of Mn and Fe oxides, and that there is a diffusive benthic source to the deep ocean. A similar source is well known for Fe, and isotopic studies have been instrumental in both identifying it and quantifying its magnitude. In this sub-project we seek to quantify this source for Ni and Zn, and to measure its isotopic composition. We will do this through the collection and analysis of pore water and sediment samples from key redox settings, and use mass balance and Earth System models to scale up to a global flux.Sub-Project B: Though it is clear that both Zn and Ni are intensely cycled in the oceans by biology, we currently know very little about the exact process by which this occurs. For example, the extreme removal of Zn from the photic zone has been variously attributed to uptake into cells for enzymatic use, uptake into diatom opal, uptake onto extra-cellular organic material associated with diatoms, and passive scavenging onto marine biological particulates. The precise process controls the timescale on which these biologically-important metals are recycled back to the photic zone after re-mobilisation in the deep ocean, and the extent to which trace metals control carbon sequestration in the modern and past surface ocean. These processes are often associated with distinctive isotopic fractionations. New isotopic data for both Zn and Ni from the dissolved phase can identify and quantify these different pathways for biological uptake, and have led the proponent to new hypotheses for the oceanic cycling of trace metals in general. However, these hypotheses need to be tested. One crucial missing piece of information concerns the size and isotopic composition of different pools of metals within oceanic phytoplankton. We aim here to begin to undertake these tests through analysis of biological particulates from the modern ocean.