Supply of organic matter to oxygen minimum zones

The aim of this subproject is to better constrain the supply of organic matter to oxygen minimum zones (OMZs), including transfer of dissolved organic matter (DOM) and rates of vertical export of particulate organic matter (POM). In addition we aim to investigate effects of anoxia on particle remineralisation rates, elemental stoichiometry, and on patterns of organic geochemical tracer changes during particle degradation processes. The overall hypothesis to be tested is that remineralization of sinking POM is quantitatively the most important contributor to oxygen consumption in OMZs, and that the remineralisation rates in OMZs are lower than in oxygenated waters.

We will undertake observations in the Peruvian OMZ, and conduct data synthesis for the Peruvian and Mauretanian OMZs using data obtained during SFB 754 phases II, III. This subproject will provide important qualitative and quantitative information on DOM transfer, particle export, and carbon, nitrogen, phosphorus and iron cycling in OMZs.
We will use a combination of approaches to determine transfer of DOM and export fluxes of POM. Water column DOM measurements and high resolution glider observations of coloured DOM (CDOM), nutrients, oxygen, chlorophyll, and turbidity, as well as hydrography and currents, will be used to unravel the transfer and behaviour of DOM, with a specific emphasis on regions with strong gradients (OMZ boundaries, mesoscale eddies and coastal upwelling fronts). Surface tethered drifting sediment traps and large volume pumps (LVPs) will be positioned at different depths in the OMZ region off Peru to capture the export flux and its attenuation with depth, i.e. from just below the mixed layer down to below the OMZ. In addition, the 234Th technique will be used as an alternative approach to quantify vertical fluxes of C, N, P and Fe. Material from the traps and LVPs will be used for elemental analysis and organic geochemical measurements.
Si isotope analysis of species-specific diatoms from material collected by traps and LVP at different depths will be conducted by A5. A variety of biomarkers, such as amino acids, carbohydrates, and pigments will be used to determine diagenetic processes such as microbial degradation. Process studies on particle degradation and organic matter diagenesis will be conducted using incubations with and without oxygen in close collaboration with B4 and B8. In order to understand the development of high gradient zones, the interpretation of the observational data will be advanced by analysis of high- resolution numerical model data (A2, B1).

Engel, A., L. Abramson, J. Szlosek, Z. Liu, G. Stewart, D. Hirschberg and C. Lee (2009) Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi: II: Decomposition of particulate organic matter Deep-Sea Research Part II-Topical Studies in Oceanography, 56(18). 1408-1419. doi: 10.1016/j.dsr2.2008.11.028

Engel, A., J. Szlosek, L. Abramson, Z. Liu and C. Lee (2009) Investigating the effect of ballasting by CaCO3 in Emiliania huxleyi: I. Formation, settling velocities and physical properties of aggregates Deep-Sea Res. Part II, 56(18), 1396-1407. doi: 10.1016/j.dsr2.2008.11.027

Karstensen, J., B. Fiedler, F. Schütte, P. Brandt, A. Körtzinger, G. Fischer, R. Zantopp, J. Hahn, M. Visbeck and D. Wallace (2014) Open ocean dead-zone in the tropical North Atlantic Ocean, Biogeosci. Discuss., 11, 17391-17411, doi: 10.5194/bgd-11-17391-2014

Karstensen, J., T. Liblik, J. Fischer, K. Bumke and G. Krahmann (2014) Summer upwelling at the Boknis Eck time-series station (1982 to 2012) – a combined glider and wind data analysis. Biogeosciences, 11, 3603-3617, doi: 10.5194/bg-11-3603-2014

Karstensen, J., L. Stramma and M. Visbeck (2008) Oxygen minimum zones in the eastern tropical Atlantic and Pacific oceans. Prog. Oceanogr., 77(4), 331-350, doi: 10.1016/j.pocean.2007.05.009

Kreus, M., M. Schartau, A. Engel, M. Nausch and M. Voss, (2014) Variations in the elemental ratio of organic matter in the central Baltic Sea: Part I — Linking primary production to remineralization Continental Shelf Research. doi: 10.1016/j.csr.2014.06.015

Le Moigne, F.A.C., C.M.M. Moore, R. Sanders, M. Villa, S. Steigenberger and E.P. Achterberg (2014) Sequestration efficiency in the iron limited North Atlantic: Implications for iron supply mode to fertilized blooms. Geophys. Res. Lett., 06/2014, doi: 10.1002/2014GL060308

Marsay, C.M., R.J. Sanders, S.S. Henson, K. Pabortsave, E.P. Achterberg and R.S. Lampitt (2015) Attenuation of sinking particulate organic carbon flux through the mesopelagic ocean. Proc. Natl. Acad. Sci. U.S.A., 112, 4, 1089-1094, doi: 10.1073/ pnas.1415311112

Riley J.S., R. Sanders, C. Marsay, F.A.C., Le Moigne, E.P. Achterberg, A.J. Poulton (2012) The contribution of fast and slow sinking particles to ocean carbon export. Glob. Biogeochem. Cy., 26, doi: 10.1029/2011GB004085

Schneider, B., A. Engel and R. Schlitzer (2004) Effects of depth- and CO2-dependent C:N ratios of particulate organic matter (POM) on the marine carbon cycle. Glob. Biogeochem. Cy., 18(2), doi: 10.1029/2003GB002184



Prof. Anja Engel                                 Prof. Eric Achterberg                      Dr. Johannes Karstensen
Tel.: +49 431 600 1510                      Tel.: +49 431 600 1299                   Tel.: +49 431 600 4156   
aengel(a)                           eachterberg(a)