SOES 6047 Global Climate Cycles SOES 6047 Global

SOES 6047 - Global Climate Cycles SOES 6047 Global Climate Cycles L 19: Research Themes: Sapropels and organic carbon burial Dr. Heiko Pälike heiko@noc. soton. ac. uk Ext. 23638, Rm. 164/34

SOES 6047 - Global Climate Cycles � Chemical proxies. . . � Overview of chemical proxy tool box � What proxies to use to quantify different aspects of the global Earth and climate system of the past � Focus on stable isotope systems (oxygen & carbon), and on nutrient tracers � Complications that affect stable isotope preservation and measurements � More examples that proxy systems should not be used in an isolated way but combined � Sample calculations L 19 Themes: Sapropels and organic carbon burial Last “proxy” lecture: 2

SOES 6047 - Global Climate Cycles �Orbital forcing and sea level changes �The geological history is characterised by frequent glacial events �new records show that for the Oligocene these were significant (~60 m in sea-level change), and periodically re-occurring �previously identified oxygen isotope extremes (the Mi- and Oievents) have been shown to consist of multiple events, driven at least partly by astronomical variations �Glacio-eustatic sea-level events appear to be more readily achieved during times of low obliquity variations �When obliquity is low, they are paced by 400 kyr cycles �What is the mechanism that connects the orbital evolution with the inception of glacial cycles? cold summers ? �link between sea-level curves of Haq et al. and high-resolution d 18 O records? Maybe L 19 Themes: Sapropels and organic carbon burial Last “themes” lecture: 3

SOES 6047 - Global Climate Cycles � learn about “Sapropels”: what are they, how do they form, why are they important, and what do they tell us? � focus on Mediterranean record of sapropels, but be aware of link with “Cretaceous black shales” � What can sapropels tell us about the palaeoceanographic evolution of the Mediterranean basin (anoxia, salinity. . ) � Why are sapropels important in the context of orbital forcing studies? � How do sapropels relate to the history of organic carbon burial and preservation? L 19 Themes: Sapropels and organic carbon burial Objectives & learning outcomes 4

SOES 6047 - Global Climate Cycles � Introduction � What are sapropels � Aside: Insolation control on Monsoon � What do sapropels tell us from a geochemical point of view � How do sapropels relate to palaeoceanographic changes � Sapropels and organic carbon burial L 19 Themes: Sapropels and organic carbon burial Lecture outline 5

SOES 6047 - Global Climate Cycles � Sapropels are marine sediments very rich in organic carbon. � Found in marine sediments around the Mediterranean � Hydrocarbon content often exceeds that of peat � Rich in sulphur (smelly!) and heavy & trace metals � Formation theories: � Preservation in anaerobic conditions � Formed during high bioproductivity � Linked to Monsoon variations that affect Mediterranean fresh water supply and water column stratification � C 14 dated sapropels coincide with N. H. insolation maxima (climatic precession minima) � Genetically similar to Cretaceous shales Reprinted by permission from Macmillan Publishers Ltd: Sancetta, C. , The Mystery of the Sapropels, Nature, v. 398, p 27 -28. copyright (1999) Not under CC licence L 19 Themes: Sapropels and organic carbon burial What are sapropels?

SOES 6047 - Global Climate Cycles � Sapropels contain high concentrations of heavy and trace metals, sometimes exceeding levels considered poisonous in sewage/soil � High concentrations suggest that these metals were re-supplied from Atlantic in-flow � Sapropels are industrially mined as “ecologically friendly” fertilisers! Element Sapropels Sewage limits Soil limits medium maximum Arsenic (As) 52 260 n. a. 50 Cadmium (Cd) 13 50 10 20 Chrome (Cr) 114 450 900 800 Cobalt (Co) 64 400 n. a. 300 Copper (Cu) 139 600 800 500 Nickel (Ni) 236 970 200 500 Molybdenum (Mo) 111 730 n. a. 200 Zink (Zn) 102 values are in mg/kg dry matter 1600 2500 3000 Data sourced from: Wehausen, R. , Warning, B. , Brumsack, H. J. , Die Klima - und Umweltgeschichte des Mitterleeres, Ergebnisse des internationalen, Tiefseebohrpogramms. Institut fur Chemie und Biologie des Meeres. Carl-von-Ossietzky-Universitat D-26111 Oldenburg L 19 Themes: Sapropels and organic carbon burial Sapropel trace-metals

SOES 6047 - Global Climate Cycles Courtesy of IODP L 19 Themes: Sapropels and organic carbon burial Succession of dark sapropel layers in sediment cores

SOES 6047 - Global Climate Cycles � The ORBITAL MONSOON HYPOTHESIS (Rossignol-Strick, 1985) � modern monsoon strength is related to summer insolation � past solar variation : 12%, in lower latitudes mostly climatic precession Modified from: Ruddiman, W. F. , Earths Climate: Past and Future. 2002, W. H. freeman and Company. New York L 19 Themes: Sapropels and organic carbon burial Insolation control on Monsoon 9

SOES 6047 - Global Climate Cycles � Higher solar radiation during summer should intensify the wet summer monsoon and increase precipitation � stronger inflow of moist ocean air, more rainfall � During winter, lower solar radiation intensifies dry conditions � enhanced cooling of the land surface, stronger down-and-out winter monsoon � Only summer monsoon controls annual precipitation over land Modified from: Ruddiman, W. F. , Earths Climate: Past and Future. 2002, W. H. freeman and Company. New York L 19 Themes: Sapropels and organic carbon burial Insolation control on Monsoon 10

SOES 6047 - Global Climate Cycles � Climatic precession causes major variations in June insolation at 30°N (also remember Short et al. , 1991). � Today’s insolation during June relatively low � During last 140, 000 years was higher by 10% --->> higher rainfall � stronger monsoon -------> higher lake levels Modified from: Ruddiman, W. F. , Earths Climate: Past and Future. 2002, W. H. freeman and Company. New York L 19 Themes: Sapropels and organic carbon burial Insolation control on Monsoon 11

SOES 6047 - Global Climate Cycles Elevation Courtesy of University Pavia: http: //www-3. unipv. it/cibra/ L 19 Themes: Sapropels and organic carbon burial The Mediterranean Sea

13 SOES 6047 - Global Climate Cycles � Evidence for much higher lake levels in North Africa ca. 10000 b. p. � lake levels were high Courtesy of GSA: Trauth, M. H. , Deino, A. , Strecker, M. R. , (2001), Response of the East African climate to orbital forcing during the last interglacial (130 -117 ka) and the early last glacial (117 -60 ka), Geology. v. 29, no. 6, p. 499 -502. � relatively fresh water, as evidenced by freshwater DIATOMS Courtesy, Bjorg Stabell, Univ. Oslo L 19 Themes: Sapropels and organic carbon burial Insolation control on Monsoons

14 SOES 6047 - Global Climate Cycles � minimum insolation: lake levels decline � higher salinity � other fossil assemblages � authigenic minerals (silicates) � lakes might dry up completely, and release diatomaceous dust into atmosphere Courtesy of GSA: Response of the East African climate to orbital forcing during the last interglacial (130 -117 ka) and the early last glacial (117 -60 ka) Trauth, M. H. , Deino, A. , Strecker, MR Geology [Geology]. Vol. 29, no. 6, pp. 499 -502. Jun 2001. L 19 Themes: Sapropels and organic carbon burial Insolation control on Monsoons

SOES 6047 - Global Climate Cycles Correlation of East African high lake levels and equatorial insolation changes during late Pleistocene. Courtesy of GSA: Trauth, M. H. , Deino, A. , Strecker, M. R. , (2001), Response of the East African climate to orbital forcing during the last interglacial (130 -117 ka) and the early last glacial (117 -60 ka), Geology. v. 29, no. 6, p. 499 -502. L 19 Themes: Sapropels and organic carbon burial Insolation control on Monsoons 15

SOES 6047 - Global Climate Cycles The role of diatoms in sapropel formation Sapropel formation takes place during enhanced supply of nutrients to the photic zone. Linked to occurrence of massive “algal” diatom mats Coaggulated mats can sink rapidly, carry organic carbon, and further deplete available oxygen during oxidation of organic matter Annual laminations? Different diatom species part of layers (Kemp et al. , 1999) • • • Courtesy, Bjorg Stabell, Univ. Oslo Coutesy of the University of Berkley, Department of Geography Transmitted light Microscope image of a Semaforo A 5 sapropel. Scale = 1 cm Modified from: Ruddiman, W. F. , Earths Climate: Past and Future. 2002, W. H. freeman and Company. New York � North African lakes filled by strong monsoon rains, later dried and exposed to wind erosion. Lake muds containing Diatoms were later deposited in the tropical Atlantic by winds L 19 Themes: Sapropels and organic carbon burial •

SOES 6047 - Global Climate Cycles � Most recent sapropel in eastern Mediterranean dates 8 -10 ky. During this time African lakes were high and African summer monsoon was strong. (N. H. insolation maximum) � African summer monsoon connected to Mediterranean through the Nile River. higher sum. insolation -> strengthened monsoon expanded north- and eastward, bringing much heavier rainfall. Modified from: Ruddiman, W. F. , Earths Climate: Past and Future. 2002, W. H. freeman and Company. New York Radar observations have also uncovered “hidden” riverbeds, now covered by sand, that carried heavier precipitation during insolation maxima. L 19 Themes: Sapropels and organic carbon burial Monsoon variations

SOES 6047 - Global Climate Cycles � Africa was much wetter around 9, 0006, 000 years ago. � Most of Saharan Desert vegetated! © NASA Courtesy of Peter B. de. Menocal � Wetland animal fossils (such as hippo & crocodile) found in the Saharan desert. L 19 Themes: Sapropels and organic carbon burial The Most Recent African Humid Period

Sapropels (geochemical evidence) � Sapropel formation during times of SOES 6047 - Global Climate Cycles Courtesy of Carl-von-Ossietzky-Universitat: Wehausen, R. , Warning, B. , Brumsack, H. J. , Die Klima - und Umweltgeschichte des Mitterleeres, Ergebnisse des internationalen, Tiefseebohrpogramms. Institut fur Chemie und Biologie des Meeres. Carl-von-Ossietzky-Universitat D-26111 Oldenburg L 19 Themes: Sapropels and organic carbon burial � Insolation maxima � Dust flux minima (more humid) � Nile discharge maxima � High biological productivity (high nutrient supply)

SOES 6047 - Global Climate Cycles � Sediment cores from the equatorial Atlantic Ocean show alternating abundances of warm- and cold- water plankton at cycles of 23, 000 years suggesting a connection to the North African monsoon. Courtesy of Institut Geologie: Duplessy, J-C (1982): Stable carbon and oxygen isotope ratios of foraminifera from North Atlantic sediments. doi: 10. 1594/PANGAEA. 726217, Supplement to: Duplessy, Jean-Claude (1982): North Atlantic deep water circulation during the last climate cycle. Bull. Inst. Geol. Bassin d'Aquitaine, 31, 379 -391 L 19 Themes: Sapropels and organic carbon burial Monsoon teleconnections? 20

21 SOES 6047 - Global Climate Cycles � The Nile drains runoff from Northeast Africa. Nile River Basin � Wetter conditions = more runoff to the eastern Mediterranean Sea. � African Humid Periods lead to a fresh water “lid” which stagnates the deep Mediterranean Sea. © United Nations (2000) L 19 Themes: Sapropels and organic carbon burial Nile River and the Mediterranean Sea

SOES 6047 - Global Climate Cycles � Changes in freshwater supply from Nile (and other “extinct” rivers? ) lead to changes in stratification � Stratification changes lead to sequence of events related to sapropel formation. . . Modified from: Ruddiman, W. F. , Earths Climate: Past and Future. 2002, W. H. freeman and Company. New York L 19 Themes: Sapropels and organic carbon burial Changes in oxygenation 22

SOES 6047 - Global Climate Cycles Courtesy of Carl-von-Ossietzky-Universitat: Wehausen, R. , Warning, B. , Brumsack, H. J. , Die Klima - und Umweltgeschichte des Mitterleeres, Ergebnisse des internationalen, Tiefseebohrpogramms. Institut fur Chemie und Biologie des Meeres. Carl-von-Ossietzky-Universitat D-26111 Oldenburg L 19 Themes: Sapropels and organic carbon burial Mediterranean bathymetry & salinity

SOES 6047 - Global Climate Cycles Today � Two competing models to explain formation of sapropels during times with higher freshwater input: stagnation vs. fresh-water outflow to Atlantic at surface Stagnation model Reversed circ. model Courtesy of Carl-von-Ossietzky-Universitat: Wehausen, R. , Warning, B. , Brumsack, H. J. , Die Klima - und Umweltgeschichte des Mitterleeres, Ergebnisse des internationalen, Tiefseebohrpogramms. Institut fur Chemie und Biologie des Meeres. Carl-von-Ossietzky-Universitat D-26111 Oldenburg L 19 Themes: Sapropels and organic carbon burial Circulation models for the eastern Mediterranean

SOES 6047 - Global Climate Cycles Courtesy of: Frits Hilgen Late Miocene L 19 Themes: Sapropels and organic carbon burial Mediterranean Sapropels (Sicily)

SOES 6047 - Global Climate Cycles • • Mediterranean sapropel cycle Ca. CO 3 maxima (smoothed) can be matched to 100 kyr and 400 kyr eccentricity minima Detailed time-control from correlation of sapropel cycles to insolation maxima Follow link to see matching Link to Article: The Rossello composite; a Mediterranean and global reference section for the early to early late Pliocene Langereis, C G; Hilgen, F J. Earth and Planetary Science Letters, vol. 104, no. 24, pp. 211 -225, Jun 1991 L 19 Themes: Sapropels and organic carbon burial Sapropels and Ca. CO 3 variations

SOES 6047 - Global Climate Cycles Follow link to see stratigraphy Link to Article: The Rossello composite; a Mediterranean and global reference section for the early to early late Pliocene Langereis, C G; Hilgen, F J. Earth and Planetary Science Letters, vol. 104, no. 24, pp. 211 -225, Jun 1991 L 19 Themes: Sapropels and organic carbon burial Detailed sapropel stratigraphy

SOES 6047 - Global Climate Cycles Cretaceous shale in Morocco Courtesy of Christopher Scotese http: //www. scotese. com/ L 19 Themes: Sapropels and organic carbon burial Are extensive Cretaceous Black Shales analogue to Sapropels?

SOES 6047 - Global Climate Cycles �Sapropels give us a detailed insight into the workings of a well confined basin in the past �Record stretches from very recent past into the Miocene �Dramatic changes in Mediterranean water circulation, productivity, and oxygenation �Detailed correlation of sapropels to insolation maxima has resulted in an accurate astronomical time calibration for the Neogene, that agrees well with estimates from oceanic sediments. �Timing of sapropels give us clues as to phase relationship between orbital forcing and response (wait for Lect. 21!) L 19 Themes: Sapropels and organic carbon burial Key point summary 29

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