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Anfang

Anfang. Ocean Variability, Productivity and Sediment Record Prof. Dr. Karin Lochte Alfred-Wegener-Institut für Polar- und Meeresforschung in der Helmholtz-Gemeinschaft. LINKS ANALYSING THE LINKS BETWEEN PRESENT OCEANIC PROCESSES AND PALEO-RECORDS. Foto: L. Tadday.

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Anfang

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  1. Anfang Ocean Variability, Productivity and Sediment Record Prof. Dr. Karin Lochte Alfred-Wegener-Institut für Polar- und Meeresforschung in der Helmholtz-Gemeinschaft LINKS ANALYSING THE LINKS BETWEEN PRESENT OCEANIC PROCESSES AND PALEO-RECORDS Foto: L. Tadday 50th Anniversary of SCOR, Woods Hole, 19-21 October 2008

  2. The Rain Rate Hypothesis (RRH) Archer and Maier-Reimer (1994) - 3D circulation model: A 40% reduction in theexport rain ratio RCXPis sufficienttoproduce a 90 ppm reduction in atmospheric CO2. Rain Ratio: R = fluxof CaCO3 (mol C) / fluxofCorg (mol C) R increaseswithdepthbecauseof fast remineralization ofCorgandnoorslowdissolution CaCO3 Source: Dieter Wolf-Gladrow 2007

  3. % CaCO3 in core-top sediments CSH CTZtop CTZbottom CCD LGM Today Catubig et al. (1998) Munhoven (2007)

  4. Big question: Didit happen in thepast ? • A peakreductionoftheCarb-C/Org-C rain ratioby40% atthe LGM was foundtoproduce a netatmospheric CO2 reductionof 40 ppm, on top of a 55 ppm reduction due tochangingshelfcarbonateaccumulationratesandcontinentalweatheringinputs. The overall 90–95 ppm oscillationcompares well withtheobserveddata. However, theeffect on the model sedimentaryrecordisatoddswithactualsedimentrecords • Munhoven (2007): II) Whathascausedthechange in RCXP?

  5. T High relative CaCO3 flux High POC/Mineral flux In the present ocean most POC sedimentation is linked to CaCO3 flux. To change the Rain Ratio would need an extremely large increase in opal flux. However, the POC export efficiency for opal is determined in iron limited areas (that have a very high Si:POC ratio). * (Archer et al. 2000) CaCO3 flux (mg m-2d-1) POC flux (mg m-2 d-1) High relative Opal flux Low POC/Mineral flux in iron-limited areas Klaas & Archer [2002] SiO2 flux (mg m-2d-1)

  6. The Dust-Nitrogen Fixation Hypothesis Increasing iron inputs (via dust) could lead to increasing primary productivity and nitrogen fixation and hence to draw down of CO2 (Falkowski 1997). Such a feedback is assumed to have contributed to the transition from interglacial to glacial periods.

  7. Dusty periods recorded ice cores (in both hemispheres) and by Arabian Sea sediments have similar patterns. They are periods of reduced denitrification in the Arabian Sea as shown by Sediment cores from the Arabian – Somali Margin. The Last Glacial Period (LGM; roughly 12 kyr to 24 kyr) , the Younger Dryas (YD) and Henrich Events (H1-6; Ice rafting in N. Atlantic) are marked by lower denitrification periods in the Arabian Sea and high dust inputs in the ice cores. This would not be the case if dust input would lead to higher productivity and export and thus question the dust-nitrogen-fixation hypothesis.

  8. The ocean‘s oxygen minimum zones (OMZs) Model results (Deutsch et al. 2007) imply that the majority of nitrogen fixation is supported by denitrification through lowered N/P ratios and increased Fe availability and that a variable portion is fuelled by additional iron input from atmospheric depositions. Thus the relative roles of iron supply from upwelling and from dust depositions for oceanic productivity and nitrogen fixation may change over time. Oxygen 50m water depth Source: NOAA NODC World Ocean Atlas 1998

  9. In order toprogresswiththeunderstandingofthevariabilityoftheocean… • weneedtoknowmoreaboutspeciesandtheirlife style ->Whatprovidestheconditionsfordominanceofopalorcarbonateor N-fixingplanktonspeciesoverothers?

  10. N fixation in Hemiaulus bloom can supply > 85% of N requirement (Carpenter et al. 1999) sed. accum. rates Eastern Mediterranean Sapropel flux Hemiaulushauckii - typical of Mediterranean sparse summer flora - but abundant in sapropels 1999, 398, 57-61 Source: Kemp et al. 1999

  11. Time Series Observations in the Northern North Atlantic Source: Klages es al.

  12. Recommendations • In order toprogresswiththeunderstandingofthevariabilityoftheocean… • Weneedtoknowmoreaboutspeciesandtheirlife style. ->Whatprovidestheconditionsfordominanceofopalorcarbonateor N-fixingplanktonspeciesoverothers? • Weneedto understand processes in themeso-pelagiczoneandtheirfeedbacktosurfacewater. ->Atthesedimentweonlyseethe end resultoftheseinterlinkedprocesses. • Andofcourse: Weneedproxiesfor N-fixation

  13. Thank you and thanks to the LINKS Group Marie-Alexandrine Sicre , Frank Dehairs, Roger Francois, Raja S. Ganeshram, Alan Kemp, Carina Lange, Renate Scharek, Dieter Wolf-Gladrow …….. and the associated members

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