SFB 754: Climate - Biogeochemistry Interactions in the Tropical Ocean
Biology
Medicine
Final Report Abstract
The overall goal of the SFB 754 was to understand the coupling of tropical ocean circulation and climate variability with the ocean’s oxygen and nutrient budgets, to quantitatively evaluate the functioning of oxygen-sensitive microbial processes and their impact on biogeochemical cycles, and to assess potential consequences for the ocean’s future. Oxygen dissolved in seawater was the central chemical element of the project. It is not only essential for higher forms of marine life, but it also controls remineralisation processes and thereby interacts with major nutrient cycles in the ocean and Earth system. This is most prominent in so-called - (OMZs) where low oxygen levels act as “switch” from aerobic to anaerobic processes, such as denitrification and associated loss of fixed nitrogen from the ocean, or the release of the nutrients phosphate and iron from sediments and the associated gain of these nutritive elements upon sediments turning anoxic. OMZs are located in the tropical oceans. The SFB 754 targeted two contrasting regions, the generally anoxic OMZ off Peru and the OMZ off Mauretania, where oxygen concentrations are low, but generally well above the thresholds for switches from aerobic to anaerobic processes. Major scientific findings of the SFB 754 include the identification and detailed quantitative understanding of oxygen supply by small-scale physical processes, in particular temporally varying zonal current bands that transport oxygen to the tropical OMZs. Coarse-resolution climate models cannot resolve these small-scale features and thus tend to systematically underestimate the oxygen supply – and hence overestimate the volume of OMZs. New high-resolution biogeochemical models and parameterizations developed for coarse-resolution models developed within the SFB 754 have helped to considerably improve the representation of OMZs in state-of-the-art climate models. An unexpected finding of the dedicated field work was the discovery of anoxic eddies in the tropical Atlantic. These form regularly in the Cape Verde region and for their many month long lifetime provide stable environments for anoxic microbial processes and special food webs that were not previously thought to occur in the North Atlantic. Novel biogeochemical processes for cycling nutrients in the sediments and in the water column were identified in the quasi-permanent low-oxygen conditions off Peru, and their often substantial role in the nutrient budgets of the OMZs and the overlying productive surface waters was quantified to derive, for the first time, a closed nitrogen budget. Some processes drive feedbacks that may accelerate marine oxygen loss under climate change, and, via the production of greenhouse gases such as nitrous oxide, may also accelerate climate change under expanding anoxia. Parameterisations of these processes were developed and employed in climate models to yield realistic representations of past oceanic anoxic events in Earth’s history. These models also suggest that positive oxygen-climate feedbacks for expected future warming are relatively small compared to uncertainties in other components of current climate models. Perhaps the single most surprising finding of the SFB 754 was the identification of the rapid decline of the marine oxygen inventory, called ocean deoxygenation, a term coined by the SFB 754 and now widely used in science and environmental assessments. Interestingly, our estimate of a 2 % oxygen decline during the past 50 years is 2 to 3 times larger than simulated by current climate models. This discrepancy between observational estimates and model results poses a major challenge for both modellers and observationalists, which is now addressed by a number of research groups worldwide. The comprehensive data set of oxygen and additional biogeochemical and physical parameters obtained by the SFB 754 will continue to help the international scientific community in better understanding the processes and consequences of ocean deoxygenation.
Publications
- (2008) Expanding oxygen-minimum zones in the Tropical oceans. Science, 320, 655-658
Stramma, L., Johnson, G. C., Sprintall, J. and Mohrholz, V.
(See online at https://doi.org/10.1126/science.1153847) - (2008) Simulated 21st century’s increase in oceanic suboxia by CO2-enhanced biological carbon export. Global Biogeochem. Cycles, 22(4), GB4008
Oschlies, A., Schulz, K. G., Riebesell, U. and Schmittner, A.
(See online at https://doi.org/10.1029/2007GB003147) - (2010) Changes in the ventilation of the oxygen minimum zone of the tropical North Atlantic, J. Phys. Oceanogr., 40, 1784-1801
Brandt, P., Hormann, V., Körtzinger, A., Visbeck, M., Krahmann, G., Stramma, L., Lumpkin, R. and Schmid, C.
(See online at https://doi.org/10.1175/2010JPO4301.1) - (2011) Benthic nitrogen cycling traversing the Peruvian oxygen minimum zone. Geochim. Cosmochim. Acta 75, 6094-6111
Bohlen, L., Dale, A. W., Sommer, S., Mosch, T., Hensen, C., Noffke, A., Scholz, F. and Wallmann, K.
(See online at https://doi.org/10.1016/j.gca.2011.08.010) - (2011) Sensitivity of simulated extent and future evolution of marine suboxia to mixing intensity. Geophysical Research Letters, 38 (6). L06607
Duteil, O. and Oschlies, A.
(See online at https://doi.org/10.1029/2011GL046877) - (2011) Simulating the biogeochemical effects of volcanic CO2 degassing on the oxygen-state of the deep ocean during the Cenomanian/Turonian Anoxic Event (OAE2). Earth Planet. Sci. Lett., 305 (3-4), 371-384
Flögel, S., Wallmann, K., Poulsen, C. J., Zhou, J., Oschlies, A., Voigt, S. and Kuhnt, W.
(See online at https://doi.org/10.1016/j.epsl.2011.03.018) - (2012) Benthic iron and phosphorus fluxes across the Peruvian oxygen minimum zone. Limnology and Oceanography, 57 (3), pp. 851-867
Noffke, A., Hensen, C., Sommer, S., Scholz, F., Bohlen, L., Mosch, T., Graco, M. and Wallmann, K.
(See online at https://doi.org/10.4319/lo.2012.57.3.0851) - (2012) Diapycnal oxygen supply to the Tropical North Atlantic oxygen minimum zone. Biogeosciences, 10, 5079-5093
Fischer, T., Banyte, D., Brandt, P., Dengler, M., Krahmann, G., Tanhua, T. and Visbeck, M.
(See online at https://doi.org/10.5194/bg-10-5079-2013) - (2012) Doubling of marine dinitrogen-fixation rates based on direct measurements. Nature 488(7411): 361-364
Großkopf, T., Mohr, W., Baustian, T., Schunck, H., Gill, D., Kuypers, M. M. M., Lavik, G., Schmitz, R. A., Wallace, D. W. R. and LaRoche, J.
(See online at https://doi.org/10.1038/nature11338) - (2012) Dynamics and stoichiometry of nutrients and phytoplankton in waters influenced by the oxygen minimum zone in the tropical South East Pacific. Deep-Sea ResearchPart I, 62, 20-31
Franz, J., Krahmann, G., Lavik, G., Grasse, P., Dittmar, T. and Riebesell, U.
(See online at https://doi.org/10.1016/j.dsr.2011.12.004) - (2012) Production of oceanic nitrous oxide by ammonia-oxidizing archaea. Biogeosciences, 9, 2419-2429
Löscher, C. R., Kock, A., Könneke, M., LaRoche, J., Bange, H. W. and Schmitz, R. A.
(See online at https://doi.org/10.5194/bg-9-2419-2012) - (2012) The distribution of neodymium isotopes and concentrations in the Eastern Equatorial Pacific: Water mass advection versus particle exchange. Earth and Planetary Science Letters, 353-354, 198-207
Grasse, P., Stichel, T., Stumpf, R., Stramma, L. and Frank, M.
(See online at https://doi.org/10.1016/j.epsl.2012.07.044) - (2013) Changes in silicate utilisation and upwelling intensity off Peru since the Last Glacial Maximum – insights from silicon and neodymium isotopes. Quaternary Science Reviews 72, 18-35
Ehlert, C., Grasse, P. and Frank, M.
(See online at https://doi.org/10.1016/j.quascirev.2013.04.013) - (2013) The influence of water mass mixing on the dissolved Si isotope composition in the Eastern Equatorial Pacific. Earth and Planetary Science Letters, 380, 60-71
Grasse, P., Ehlert, C. and Frank, M.
(See online at https://doi.org/10.1016/j.epsl.2013.07.033) - (2014) Facets of diazotrophy in the oxygen minimum zone waters off Peru. ISME Journal 8(11): 2180-92
Löscher, C. R., Großkopf, T., Desai, F. D., Gill, D., Schunck, H., Croot, P. L., Schlosser, C., Neulinger, S. C., Pinnow, N., Lavik, G., Kuypers, M. M. M., LaRoche, J. and Schmitz, R. A.
(See online at https://doi.org/10.1038/ismej.2014.71) - (2014) Major role of the equatorial current system in setting oxygen levels in the eastern tropical Atlantic Ocean: A high-resolution model study. Geophys. Res. Lett., 41, 2033-2040
Duteil, O., Schwarzkopf, F. U., Böning, C. W. and Oschlies, A.
(See online at https://doi.org/10.1002/2013GL058888) - (2014) The impact of ocean deoxygenation on iron release from continental margin sediments. Nat. Geosci. 7, 433-437
Scholz F., McManus, J., Mix, A. C., Hensen, C. and Schneider, R. R.
(See online at https://doi.org/10.1038/ngeo2162) - (2015) A revised global estimate of dissolved iron fluxes from marine sediments. Glob. Biogeochem. Cy. 29
Dale, A.W., Nickelsen, L., Scholz, F., Hensen, C., Oschlies, A. and Wallmann, K.
(See online at https://doi.org/10.1002/2014GB005017) - (2015) Hidden biosphere in an oxygendeficient Atlantic open ocean eddy: future implications of ocean deoxygenation on primary production in the eastern tropical North Atlantic. Biogeosciences, 12, 7467-7482
Löscher, C. R., Fischer, M. A., Neulinger, S. C., Fiedler, B., Philippi, M., Schütte, F., Singh, A., Hauss, H., Karstensen, J., Körtzinger, A., Künzel, S. and Schmitz, R. A.
(See online at https://doi.org/10.5194/bg-12-7467-2015) - (2015) Massive nitrous oxide emissions from the tropical South Pacific Ocean. Nature Geoscience, 8, 530-533
Arévalo-Martínez, D. L., Kock, A., Löscher, C. R., Schmitz, R. A. and Bange, H. W.
(See online at https://doi.org/10.1038/ngeo2469) - (2015) Organic carbon production, mineralization and preservation on the Peruvian margin. Biogeosciences 12, 1537-1559
Dale, A. W., Sommer, S., Lomnitz, U., Montes, I., Treude, T., Gier, J., Hensen, C., Dengler, M., Stolpovsky, K., Bryant, L. D. and Wallmann, K.
(See online at https://doi.org/10.5194/bg-12-1537-2015) - (2015) Oxygen minimum zone variations in the tropical Pacific during the Holocene. Geophysical Research Letters, 42, 8530-8537
Xu, X., Segschneider, J., Schneider, B., Park, W. and Latif, M.
(See online at https://doi.org/10.1002/2015GL064680) - 2015) On the role of circulation and mixing in the ventilation of oxygen minimum zones with a focus on the eastern tropical North Atlantic. Biogeosciences, 12, 489-512
Brandt, P., Bange, H. W., Banyte, D., Dengler, M., Didwischus, S.-H., Fischer, T., Greatbatch, R. J., Hahn, J., Kanzow, T., Karstensen, J., Körtzinger, A., Krahmann, G., Schmidtko, S., Stramma, L., Tanhua, T. and Visbeck, M.
(See online at https://doi.org/10.5194/bg-12-489-2015) - (2016) Centennial to millennial-scale changes in oxygenation and productivity in the Eastern Tropical South Pacific during the last 25 000 years. Quaternary Science Reviews, 131, 102-117
Salvatteci, R., Gutierrez, D., Sifeddine, A., Ortlieb, L., Druffel, E., Boussafir, M. and Schneider, R.
(See online at https://doi.org/10.1016/j.quascirev.2015.10.044) - (2016) Dead zone or oasis in the open ocean? Zooplankton distribution and migration in low-oxygen modewater eddies. Biogeosciences, 13:1977- 1989
Hauss, H., Christiansen, S., Schütte, F., Kiko, R., Edvam Lima, M., Rodrigues, E., Karstensen, J., Löscher, C. R., Körtzinger, A. and Fiedler, B.
(See online at https://doi.org/10.5194/bg-13-1977-2016) - (2016) Depletion of oxygen, nitrate and nitrite in the Peruvian oxygen minimum zone cause an imbalance of benthic nitrogen fluxes. Deep-Sea Research, 112, 113-122,
Sommer, S., Gier, J., Treude, T., Lomnitz, U., Dengler, M., Cardich, J. and Dale, A. W.
(See online at https://doi.org/10.1016/j.dsr.2016.03.001) - (2016) Nitrate-dependent iron oxidation limits iron transport in anoxic ocean regions. Earth and Planetary Science Letters, 454, pp. 272-281
Scholz, F., Löscher, C. R., Fiskal, A., Sommer, S., Hensen, C., Lomnitz, U., Wuttig, K., Göttlicher, J., Kossel, E., Steininger, R. and Canfield, D. E.
(See online at https://doi.org/10.1016/j.epsl.2016.09.025) - (2016) Occurrence and characteristics of mesoscale eddies in the tropical northeastern Atlantic Ocean. Ocean Science, 12, 663-685
Schütte, F., Brandt, P. and Karstensen, J.
(See online at https://doi.org/10.5194/os-12-663-2016) - (2017) Biological and physical influences on marine snowfall at the equator. Nature Geoscience, 10(11), 852-858
Kiko, R., Biastoch, A., Brandt, P., Cravatte, S., Hauss, H., Hummels, R., Kriest, I., Marin, F., McDonnell, A. M. P., Oschlies, A., Picheral, M., Schwarzkopf, F. U., Thurnherr, A. M. and Stemmann, L.
(See online at https://doi.org/10.1038/ngeo3042) - (2017) Calibrating a global three-dimensional biogeochemical ocean model (MOPS-1.0). Geosci. Model Dev., 10, 127-154
Kriest, I., Sauerland, V., Khatiwala, S., Srivastav, A. and Oschlies, A.
(See online at https://doi.org/10.5194/gmd-10-127-2017) - (2017) Decline in global oxygen content during the past five decades. Nature, 542, 335-339
Schmidtko, S., Stramma, L. and Visbeck, M.
(See online at https://doi.org/10.1038/nature21399) - (2017) Nutrient co-limitation at the boundary of an oceanic gyre. Nature 551(7679): 242-24
Browning, T. J., Achterberg, E. P., Rapp, I., Engel, A., Bertrand, E. M., Tagliabue, A. and Moore, M.
(See online at https://doi.org/10.1038/nature24063) - (2017) Patterns of deoxygenation – sensitivity to natural and anthropogenic drivers. Phil. Trans. R. Soc. A, 375
Oschlies, A., Duteil, O., Getzlaff, J., Koeve, W., Landolfi, A. and Schmidtko, S.
(See online at https://doi.org/10.1098/rsta.2016.0325) - (2017) Unraveling the onset of Cretaceous Oceanic Anoxic Event 2 in an extended sediment archive from the Tarfaya-Laayoune Basin, Morocco. Paleoceanography, 32(8), 923-946
Kuhnt, W., Holbourn, A. E., Beil, S., Aquit, M., Krawczyk, T., Flögel, S., Chellai, E. H. and Jabour, H.
(See online at https://doi.org/10.1002/2017PA003146) - (2018) A novel eukaryotic denitrification pathway in foraminifera. Current Biology, 28, 2536-2543
Woehle, C., Roy, A.-S., Glock, N., Wein, T., Weissenbach, J., Rosenstiel, P., Hiebenthal, C., Michels, J., Schönfeld, J. and Dagan, T.
(See online at https://doi.org/10.1016/j.cub.2018.06.027) - (2018) Coupling of oceanic carbon and nitrogen cycling facilitates spatially resolved quantitative reconstruction of nitrate inventories. Nature Communications, 9, 1217
Glock, N., Erdem, Z., Wallmann, K., Somes, C., Liebetrau, V., Schönfeld, J., Gorb, S. and Eisenhauer, A.
(See online at https://doi.org/10.1038/s41467-018-03647-5) - (2018) Drivers and mechanisms of ocean deoxygenation. Nat. Geosci., 11, 467-473
Oschlies, A., Brandt, P., Stramma, L. and Schmidtko, S.
(See online at https://doi.org/10.1038/s41561-018-0152-2) - (2019) Diapycnal dissolved organic matter supply into the upper Peruvian oxycline. Biogeosciences, 16, 2033-2047
Loginova, A. N., Thomsen, S., Dengler, M., Lüdke, J. and Engel, A.
(See online at https://doi.org/10.5194/bg-16-2033-2019) - (2019) Interannual variability of the Atlantic North Equatorial Undercurrent and its impact on oxygen. Journal of Geophysical Research: Oceans, 124 (4). pp. 2348-2373
Burmeister, K., Lübbecke, J. F., Brandt, P. and Duteil, O.
(See online at https://doi.org/10.1029/2018JC014760) - (2019) Metabolic preference of nitrate over oxygen as electron acceptor in Foraminifera from the Peruvian oxygen minimum. PNAS, 116 (8), 2860-2865
Glock, N., Roy, A.-S., Romero, D., Wein, T., Weissenbach, J., Revsbech, N.-P., Høgslund, S., Clemens, D., Sommer, S. and Dagan, T.
(See online at https://doi.org/10.1073/pnas.1813887116)
