SUBPROJECT - A3
A tracer release experiment (POSTRE) to quantify benthic-‐pelagic exchanges in the Peruvian oxygen minimum zone (OMZ) and constraining the water mass ages of the OMZ with transient tracers
This proposed work aims at better understanding of processes affecting oxygen minimum zone (OMZ) oxygen supply and consumption by providing improved quantification of: a) transport of biogeochemically active compounds from the bottom boundary layer to the interior and surface ocean b) horizontal and vertical integrated mixing coefficients for OMZ oxygen supply estimates and c) ventilation rates for estimation of oxygen consumption rates jointly with A4. Specifically three main science questions will be addressed:
1) What are the exchange rates and pathways between the benthic boundary layer and the pelagic ocean in the Peruvian OMZ System? Research efforts conducted during SFB 754 cruises in the Peruvian shelf OMZ region have demonstrated that sediment-‐ocean interface processes are potentially very important for the biogeochemistry of the OMZ and possibly for the development of the OMZ itself. However, the role of diffusive and advective pathways that connect water within the bottom boundary layer (i.e. the water directly affected by sediment exchange processes) to the pelagic ocean and the surface layer by enhanced mixing or whether there is a fast conduit to the OMZ interior, remains poorly known. A targeted tracer release experiment in the Peruvian shelf region (POSTRE) will be started in Nov. 2015 and surveyed and analysed during phase III.
2) What is the CF3SF5 distribution in the Atlantic OMZ 5-‐6 years after OSTRE tracer release in 2012? These estimates are very useful for constraining the horizontal diffusivity and total ventilation of the OMZ in the Northern Tropical Atlantic OMZ region.
3) What are the ventilation ages of the water masses in the Peruvian and Atlantic OMZs? The least well-‐constrained term in the oxygen budget of ETNA OMZ is the consumption term. There are systematic differences in estimates of oxygen utilization rates (OUR) employing water mass renewal time scales and water mass ages. These systematic differences are also found in numerical modelling. This work will be done jointly between A3 (focus on transient tracer analysis) and A4 (focus on oxygen analysis).
These questions will be addressed by analysing a combination of existing hydrographic data, SFB 754 model results and new data from four targeted field campaigns (+ Pacific tracer release during the end of phase II), both in the Pacific and Atlantic Ocean.
References
Banyte, D., M. Visbeck, T. Tanhua, T. Fischer, G. Krahmann and J. Karstensen (2013) Lateral diffusivity from tracer release experiments in the tropical North Atlantic thermocline. J. Geophys. Res., 118, 1-‐15, doi: 10.1002/jgrc.20211
Banyte, D., T. Tanhua, M. Visbeck, D.W.R. Wallace, J. Karstensen, G. Krahmann, A. Schneider and L. Stramma (2012) Diapycnal Diffusivity at the upper boundary of the North Atlantic oxygen minimum zone. J. Geophys. Res., 117, C09016, doi: 10.1029/2011JC007762
Brandt, P., V. Hormann, A. Körtzinger, M. Visbeck, G. Krahmann, L. Stramma, R. Lumpkin and C. Schmid (2010) Changes in the Ventilation of the Oxygen Minimum Zone of the Tropical North Atlantic. J. Phys. Oceanogr., 40(8), 1784-‐1801, doi: 10.1175/2010JPO4301.1
Brandt, P., D. Banyte, M. Dengler, S.-H. Didwischus, T. Fischer, R.J. Greatbatch, J. Hahn, T. Kanzow, J. Karstensen, A. Körtzinger, G. Krahmann, S. Schmidtko, L. Stramma, T. Tanhua and M. Visbeck (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, doi:10.5194/bg-12-489-2015
Contact:
Dr. Toste Tanhua Prof. Martin Visbeck
Tel.: +49 431 600 4219 Tel.: 0431 600 4100
ttanhua(a)geomar.de mvisbeck(a)geomar.de
