Water mass structure in the eastern tropical Pacific Ocean: Relationship to oxygen variability and geochemical properties

In A5 the joint hydrographic and geochemical tracer study of the tropical oceans with focus on the Pacific Ocean will be continued and finalized. A comprehensive synthesis of the changes and trends of hydrography and oxygenation and their relationships to climate indices (El Nino etc.) from spatial scales of eddies to the entire Pacific Basin will be generated for the last 50 years. New combined measurements of hydrographic parameters and of the dissolved and particulate Si and N isotope compositions together with macronutrients and micronutrients such as Fe (B10) will be performed in the water column of the upwelling area off Peru and during the planned mesocosm experiment (B2). These investigations will lead to a better understanding and a synthesis of the impact of the advective supply of nutrients on diatom productivity and nutrient utilisation.

The goal of the hydrographic measurements including oxygen and nutrient concentrations is the understanding of the factors controlling their long-term trends of the past 50 years and the superimposed temporal variability linked to climate indices. These include the Interdecadal Pacific Oscillation/Pacific Decadal Oscillation and El Nino modes, as well as changes in the Pacific subtropical cell that will be compared to the time series data in close cooperation with the modelling efforts in A9 and A2. Hence these investigations will contribute to resolving the SFB 754 overarching questions on the reasons for temporal variability in oxygen concentration and to distinguish trends from fluctuations. The measurements and results will help to better evaluate future observations in the tropical Pacific. The main biogeochemical question of A5 is how the utilisation of the nutrients silicate and nitrate by different diatom species and their remineralisation in the water column is influenced by changes in advective macro- and micronutrient supply and how the fractionation of silicate is influenced by micronutrient availability (B10). This will improve our quantitative understanding of the factors controlling diatom productivity and nutrient utilisation today and will allow a more reliable reconstruction of the biogeochemical cycles of Si and N in the Peruvian upwelling system in the past based on records obtained from the sediments of the past 20,000 years generated in B7 and A6 during phases I and II of the SFB 754. Hence these investigations add to resolving the SFB 754 overarching questions on the impact of past changes in import/export rates of oxygen and nutrients and will lead to a synthesis of both, the present day and past biogeochemical results obtained within SFB 754. 

Ehlert, C., P. Grasse and M. Frank (2013) Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum – insights from silicon and neodymium isotopes. Quaternary Sci. Rev., 72, 18-35, doi: 10.1016/j.quascirev.2013.04.013

Ehlert, C., P. Grasse, E. Mollier-Vogel, T. Böschen, J. Franz, G.F. de Souza, B.C. Reynolds, L. Stramma and M. Frank (2012) Factors controlling the silicon isotope distribution in waters and surface sediments of the Peruvian coastal upwelling. Geochim. Cosmochim. Acta, 99, 128-145, doi: 10.1016/j.gca.2012.09.038

Grasse, P., C. Ehlert and M. Frank (2013) The influence of water mass mixing on the dissolved silicon isotope composition of the eastern Equatorial Pacific. Earth Planet. Sc. Lett., 380, 60-71., doi: 10.1016/j.epsl.2013.07.033

Grasse, P., T. Stichel, R. Stumpf, L. Stramma and M. Frank (2012) The distribution of neodymium isotopes and concentrations in the eastern equatorial Pacific: Water mass advection versus particle exchange. Earth Planet. Sc. Lett., 353-354, 198-207, doi: 10.1016/j.epsl.2012.07.044

Hathorne, E.C., B.A. Haley, T. Stichel, P. Grasse, M. Zieringer and M. Frank (2012) Online preconcentration ICP-MS analysis of rare earth elements in seawater. Geochem., Geophy., Geosy., 13, Q01020, doi: 10.1029/2011GC003907

Kalvelage, T., G. Lavik, P. Lam, S. Contreras, L. Artega, C. Löscher, A. Oschlies, A. Paulmier, L. Stramma and M.M.M Kuypers (2013) Nitrogen cycling driven by organic matter export in the South Pacific oxygen minimum zone. Nat. Geosci., 6, 228-234, doi: 10.1038/NGEO1739

Stramma, L., R.A. Weller, R. Czeschel and S. Bigorre (2014) Eddies and an extreme water mass anomaly observed in the eastern south Pacific at the Stratus mooring. J. Geophys. Res. Oceans, 119, 1068-1083, doi: 10.1002/2013JC009470

Stramma, L., H.W. Bange, R. Czeschel, A. Lorenzo and M. Frank (2013) On the role of mesoscale eddies for the biological productivity and biogeochemistry in the eastern tropical Pacific Ocean off Peru. Biogeosciences, 10, 7293-7306, doi: 10.5194/bg-10-7293-2013

Stramma, L., A. Oschlies and S. Schmidtko (2013) Mismatch between observed and modeled trends in dissolved upper-ocean oxygen over the last 50 yr. Biogeosciences, 9, 4045-4057, doi: 10.5194/bg-9-4045-2012

Stramma, L., E.D. Prince, S. Schmidtko, J. Luo, J.P. Hoolihan, M. Visbeck, D.W.R. Wallace, P. Brandt and A. Körtzinger (2012) Expansion of oxygen minimum zones may reduce available habitat for tropical pelagic fishes. Nat. Clim. Change, 2, 33-37. doi: 10.1038/NCLIMATE1304


Dr. Lothar Stramma                     Prof. Martin Frank
Tel.: +49 431 600 4103                Tel.: +49 431 600 2218
lstramma(a)                mfrank(a)