RESEARCH: Eastern Tropical South Pacific (ETSP)

Work in the ETSP included cruises during the austral summers of 2010 and 2011 to quantify carbon and N₂ fixation using as many tools as possible. N₂ fixation was evaluated using geochemical tools ("δ¹⁵N budgets"), traditional ¹⁵N₂ uptake assays, as well as molecular tools. Results revealed extremely low rates of N₂ fixation, likely carried out by hetertrophic dizaotrophs, and their contribution of nitrogen played a minor role in supporting regional export production. Studies of DON also showed novel evidence of photosynthetic production and consumption with an isotope effect in the upper 50 m. DON consumption may also contribute to regional observations of very low ratios of net to gross productivity.

Carbon fixation and export was documented using floating and moored sediment traps, with bottle incubations of carbon fixation, with ²³⁴Th deficits, with O₂/Ar supersaturation ratios, with triple oxygen isotopic measurements.

Additionally, constraints were placed on sulfur cycling, rates of upwelling were quantified using new ⁷Be techniques, and trace metal concentrations were measured.

Publications

Knapp, A.N., K.L. Casciotti, and M.G. Prokopenko, Dissolved organic nitrogen production and consumption in eastern tropical South Pacific surface waters, 2018, Global Biogeochemial Cycles, 32, doi:10.1029/2017GB005875

Haskell, W.Z., M.G. Prokopenko, R.H.R. Stanley, and A.N. Knapp, Estimates of vertical turbulent mixing used to determine a vertical gradient in net and gross oxygen production in the oligotrophic South Pacific Gyre, 2016, Geophysical Research Letters, 43, doi:10.1002/2016GL069523

Knapp, A.N., K.L. Casciotti, W.M. Berelson, M.G. Prokopenko, and D.G. Capone, Low rates of nitrogen fixation in the eastern tropical South Pacific surface waters, 2016, Proceedings of the National Academy of Sciences, 113, 4398-4403, doi:10.1073/pnas.1515641113

Letscher, R.T., A.N. Knapp, A.K. James, C.A. Carlson, A.E. Santoro, and D.A. Hansell, 2015, Microbial community composition and nitrogen availability influence DOC remineralization in the South Pacific Gyre, Marine Chemistry, 177, 325-334, doi:10.1016/j.marchem.2015.06.024

Berelson, W.M., W. Haskell, M.G. Prokopenko, A.N. Knapp, D. Hammond, N. Rollins, D.G. Capone, 2015, Biogenic rain and benthic remineralization in the Eastern Tropical South Pacific, Deep-Sea Research I, 99, 23-34, doi:10.1016/j.dsr.2014.12.006.

Haskell, W.Z., D. Kadko, D.E. Hammond, A.N. Knapp, M.G. Prokopenko, W.M. Berelson, and D.G. Capone, 2015, Upwelling velocity and eddy diffusivity from 7Be measurements used to compare vertical nutrient flux to export POC flux in the Eastern Tropical South Pacific, Marine Chemistry, 168, 140-150, doi: 10.1016/j.marchem.2014.10.004

Johnston, D.T., B.C. Gill, A. Masterson, E. Beirne, K.L. Casciotti, A.N. Knapp, and W. Berelson, 2014, Placing an upper limit on cryptic sulphur cycling, Nature, 513, 530-533, doi:10.1038/nature13698

Jacquot, J.E., Y. Kondo, A.N. Knapp, and J.W. Moffett, 2013, The speciation of copper across active gradients in nitrogen-cycle processes in the eastern tropical South Pacific, Limnology & Oceanography, 58, 1387-1394

Capone, D.G., and A.N. Knapp, 2007, A marine nitrogen cycle fix?, Nature, 445, 159-160

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