1. SOES6047 - Global Climate Cycles SOES 6047 Global Climate Cycles L22: Research Themes: Southern Ocean history and climate Dr. Heiko Pälike heiko@noc.soton.ac.uk Ext. 23638, Rm. 164/34

2. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 2 Last “themes” lecture: ๏ Sapropels and Monsoon changes ๏ 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!) ๏ Sapropels and Monsoon changes ๏ 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!)

3. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 3 Objectives & learning outcomes ๏ learn about the Southern Ocean ๏ appreciate that it occupies a central and crucial role in the mixing of oceanic currents and renewed deep water formation ๏ learn about the mechanisms that connects atmospheric pCO 2 concentrations and processes north and south of the polar front ๏ learn that there are conflicting lines of evidence from nutrient utilisation proxies about glacial-interglacial changes in the Southern Ocean ๏ learn about the Southern Ocean ๏ appreciate that it occupies a central and crucial role in the mixing of oceanic currents and renewed deep water formation ๏ learn about the mechanisms that connects atmospheric pCO 2 concentrations and processes north and south of the polar front ๏ learn that there are conflicting lines of evidence from nutrient utilisation proxies about glacial-interglacial changes in the Southern Ocean

4. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 4 Lecture outline ๏ General introduction to setting of Southern Ocean ๏ Nutrient concentrations in the Southern Ocean ๏ The role of the Southern ocean as hub between the Pacific, Atlantic, and Indian Ocean ๏ The potential importance of the Southern Ocean for regulating pCO 2 ๏ Proxy estimates for glacial-interglacial changes of proxies for nutrient utilisation ๏ General introduction to setting of Southern Ocean ๏ Nutrient concentrations in the Southern Ocean ๏ The role of the Southern ocean as hub between the Pacific, Atlantic, and Indian Ocean ๏ The potential importance of the Southern Ocean for regulating pCO 2 ๏ Proxy estimates for glacial-interglacial changes of proxies for nutrient utilisation

5. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 5 Armand, L. K. (2000), ‘An Ocean of Ice – Advances in the Estimation of Past Sea Ice in the Southern Ocean’, GSA Today 10. Berger, W., ‘Global maps of ocean productivity’, Productivity in the ocean: Present and Past. Dahlem Workshop Reports LS44, W. Berger, V. Smetacek, & G. Wefer, eds. (Wiley & Sons, 1989), 429–456. De La Rocha, C. L., et al. (1998), ‘Silicon-isotope composition of diatoms as an indicator of past oceanic change’, Nature 395, 680–683. Elderfield, H. & Rickaby, R. E. M. (2000), ‘Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean’, Nature 405, 305–310. Falkowski, P. G. (1997), ‘Evolution of the nitrogen cycle and its influence on the biological sequestration of CO2 in the ocean’, Nature 387. François, R. et al. (1997), ‘Contribution of Southern Ocean surface-water stratification to low atmospheric CO2 concentrations during the last glacial period’, Nature 389, 929–935. Hodell, D. A., Gersonde, R., & Blum, P., ‘Leg 177 Synthesis: Insights into the Southern Ocean Paleoceanography on tectonic to millenial timescales’, Proc. ODP, Sci. Res. 177, R. Gersonde & P. Hodell, D. A. Blum, eds. (2002), 1–54. Kumar, N., et al. (1995), ‘Increased biological productivity and export production in the glacial Southern Ocean’, Nature 378, 675–680. Marchitto, T. M., Oppo, D. W., & Curry, W. B. (2002), ‘Paired benthic foraminiferal Cd/Ca and Zn/Ca evidence for a greatly increased presence of Southern Ocean Water in the glacial North Atlantic’, Paleoceanography 17, 1038. Open University Course Team, Ocean Circulation (Open University, Pergamon Press, Oxford, 1989). Rosenthal, Y., Dahan, M., & Shemesh, A. (2000), ‘Southern Ocean contributions to glacial-interglacial changes of atmospheric pCO2: An assessment of carbon isotope records in diatoms’, Paleoceanography 15, 65. Sarmiento, J. L. & Toggweiler, J. R. (1984), ‘A new model for the role of the oceans in determining atmospheric pCO2’, Nature 308, 621– 624. Schmitz, W. J. (1996), ‘One the World Ocean Circulation: Volume II. The Pacific and Indian Oceans A global update’, Technical Report WHOI-96-08, Woods Hole Oceanographic Institution. 241 pp. Siegenthaler, U. & Sarmiento, J. L. (1993), ‘Atmospheric carbon dioxide and the ocean’, Nature 365, 119–125. Sigman, D. M. et al. (1999), ‘The isotopic composition of diatom-bound nitrogen in Southern Ocean sediments’, Paleoceanography 14, 118–134. Sullivan, C. W., et al. (1993), ‘Distributions of Phytoplankton Blooms in the Southern Ocean’, Science 262, 1832–1837. Takahashi, T., et al. (1997), ‘Global air-sea flux of CO2: An estimate based on measurements of sea-air pCO2 difference’, Proc. Natl. Acad. Sci. USA 97, 8292–8299. Toggweiler, J. R. & Sarmiento, J. L. (1985), ‘Glacial to interglacial changes in atmospheric carbon dioxide: the critical role of ocean surface water in high latitudes’, Geophys. Monogr. Ser. AGU 32. Some references

6. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 6 Introduction ๏ What is the “Southern Ocean”? ๏ legally, water mass poleward of 60°S, approximated by the Polar Front (Antarctic Convergence) ๏ palaeoceanographically, polewards of ~50°S, with deep water formation ๏ Why is the SO important (particularly to explain glacial-interglacial ∆CO 2 ) ? ๏ Due to ocean circulation patterns, the SO is the window through which much of the deep oceans “see” the atmosphere (Siegenthaler & Sarmiento, 1993) ๏ SO globally has largest wave height and wind speeds: CO 2 exchange at a maximum at around 50°S ๏ SO accounts for >+20% of NET CO2 flux into the ocean (Takahashi, 1997) ๏ SO nutrient limited? At present efficient biological pump, coupled with tendency of cold salty waters to sink ๏ What is the “Southern Ocean”? ๏ legally, water mass poleward of 60°S, approximated by the Polar Front (Antarctic Convergence) ๏ palaeoceanographically, polewards of ~50°S, with deep water formation ๏ Why is the SO important (particularly to explain glacial-interglacial ∆CO 2 ) ? ๏ Due to ocean circulation patterns, the SO is the window through which much of the deep oceans “see” the atmosphere (Siegenthaler & Sarmiento, 1993) ๏ SO globally has largest wave height and wind speeds: CO 2 exchange at a maximum at around 50°S ๏ SO accounts for >+20% of NET CO2 flux into the ocean (Takahashi, 1997) ๏ SO nutrient limited? At present efficient biological pump, coupled with tendency of cold salty waters to sink

7. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 7 The Southern Ocean ๏ Today, the Southern Ocean is the primary site for intermediate, deep- and bottom-water formation. ๏ Almost 2/3 of ocean floor is bathed by Antarctic Bottom Water (AABW), originating in the Weddell Sea ๏ AABW depresses the temperature of ca. 55-60% of the world’s ocean volume below 2°C ๏ The Southern Ocean connects the three large oceans, and has significant importance in mixing different water masses. ๏ Today, the Southern Ocean is the primary site for intermediate, deep- and bottom-water formation. ๏ Almost 2/3 of ocean floor is bathed by Antarctic Bottom Water (AABW), originating in the Weddell Sea ๏ AABW depresses the temperature of ca. 55-60% of the world’s ocean volume below 2°C ๏ The Southern Ocean connects the three large oceans, and has significant importance in mixing different water masses. Reprinted by permission from Macmillan Publishers Ltd: Charles, C.D., Fairbanks, R.G.,Nature Evidence from Southern Ocean sediments for the effect of North Atlantic deep- water flux on climate. (London), v. 355, no. 6359, p. 416-419, Copyright (1992) Not under CC licenceCharles, C.D., Fairbanks, R.G.,Nature Evidence from Southern Ocean sediments for the effect of North Atlantic deep- water flux on climate. (London), v. 355, no. 6359, p. 416-419,

8. L6 Themes: Quaternary glacial-interglacial cycles SOES6047 - Global Climate Cycles 8 RECAP G-IG changes in CO 2 Despite best efforts, still need to explain 110 ppm residual!

9. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 9 Ocean Carbon Budget (present) ๏ Total anthropogenic CO2 emissions7.1 ±1.1 GtC/yr ๏ Partitioning between reservoirs ๏ atmospheric storage3.3±0.2GtC/yr ๏ sum of terrestrial sinks1.8±2.0 GtC/yr ๏ ocean uptake 2.0±0.8GtC/yr ๏ Southern Ocean ๏ 0.8±0.4 GtC/yr ๏ slightly different numbers than in figure, but highlight important role of Southern Ocean ๏ Total anthropogenic CO2 emissions7.1 ±1.1 GtC/yr ๏ Partitioning between reservoirs ๏ atmospheric storage3.3±0.2GtC/yr ๏ sum of terrestrial sinks1.8±2.0 GtC/yr ๏ ocean uptake 2.0±0.8GtC/yr ๏ Southern Ocean ๏ 0.8±0.4 GtC/yr ๏ slightly different numbers than in figure, but highlight important role of Southern Ocean Courtesy of the University of Michigan: http://sitemaker.umich.edu/section2group4/the_link__human_influences_on_storm_intensity

10. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 10 SO Primary Productivity ๏ The Southern Ocean is also a region of high primary production and a region with potential for even higher productivity. ๏ The only oceanic region with large reserves of unutilized nutrients in surface waters (HNLC). ๏ What limits production? Light, clouds, ice, deep mixing, micronutrients (Fe, Mn, Zn), grazing, but not, apparently, macronutrients (N,P) ๏ The Southern Ocean is also a region of high primary production and a region with potential for even higher productivity. ๏ The only oceanic region with large reserves of unutilized nutrients in surface waters (HNLC). ๏ What limits production? Light, clouds, ice, deep mixing, micronutrients (Fe, Mn, Zn), grazing, but not, apparently, macronutrients (N,P) Courtesy of NASA: SeaWiFS project

11. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 11 Productivity (II) ๏ Another view of Primary Production in the Southern Ocean, ๏ This one makes use of colour data from the CZCS satellite ๏ Is Fe input from the continent and seabed features important? OR is Fe the biolimiting nutrient? ๏ Another view of Primary Production in the Southern Ocean, ๏ This one makes use of colour data from the CZCS satellite ๏ Is Fe input from the continent and seabed features important? OR is Fe the biolimiting nutrient? From: Sullivan, C.W., Arrigo, K.R., McClain, C.R., Comiso, J.C., Firestone, J., (1993) Distributions of Phytoplankton Blooms in the Southern Ocean, Science, v. 262, p. 1832–1837. Reprinted with permission from AAAS. This figure may be used for non-commercial, classroom purposes only. Any other uses requires the prior written permission from AAAS.Sullivan, C.W., Arrigo, K.R., McClain, C.R., Comiso, J.C., Firestone, J., (1993) Distributions of Phytoplankton Blooms in the Southern Ocean, Science, v. 262, p. 1832–1837

12. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 12 ๏ The Southern Ocean has high surface water concentrations of both P and N, which are used up almost everywhere else ๏ What is actually biolimiting? N can be produced by bio-fixation, P cannot. But what about other elements? ๏ The Southern Ocean has high surface water concentrations of both P and N, which are used up almost everywhere else ๏ What is actually biolimiting? N can be produced by bio-fixation, P cannot. But what about other elements? Biolimiting nutrients? Courtesy of Ocean Data View: Conkright, M. E., Locarnini, R. A., Garcia, H. E., O'Brien, T. D., Boyer, T. P., Stephens, C., Antonov. J. I., World Ocean Atlas 2001

13. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 13 Southern Ocean Phosphate Courtesy of Ocean Data View: M. E. Conkright, R. A. Locarnini, H. E. Garcia, T. D. O'Brien, T. P. Boyer, C. Stephens, J. I. Antonov. World Ocean Atlas 2001 Courtesy of Ocean Data View: Conkright, M. E., Locarnini, R. A., Garcia, H. E., O'Brien, T. D., Boyer, T. P., Stephens, C., Antonov. J. I., World Ocean Atlas 2001

14. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 14 Southern Ocean Nitrate Courtesy of Ocean Data View: Conkright, M. E., Locarnini, R. A., Garcia, H. E., O'Brien, T. D., Boyer, T. P., Stephens, C., Antonov. J. I., World Ocean Atlas 2001

15. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 15 Iron fertilisation? © NOAA 1994

16. L6 Themes: Quaternary glacial-interglacial cycles SOES6047 - Global Climate Cycles 16 Southern Ocean water masses Schematic block diagram showing the surface currents and the vertical motion of water masses in the Atlantic Ocean poleward of about 40 o S. North Atlantic Deep Water (NADW) becomes Antarctic Circumpolar Water (ACW) and rises to the surface at the Antarctic Divergence. Surface water flowing northwards from the Antarctic Divergence sinks at the Antarctic Polar Frontal Zone (as AAIM, while that flowing southwards may become AABW. The contours show isotherms in o C; this schematic diagram should be compared with the actual temperature and salinity distribution measured in the Drake Passage between 56 o and 62 o S. From Open University (1989)

17. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 17 Southern Ocean circulation ๏ The role of the Southern Ocean as the “hub” of ocean circulation ๏ complicate, buoyancy driven upwelling, mixing and downwelling ๏ interaction with polar frontal systems ๏ The role of the Southern Ocean as the “hub” of ocean circulation ๏ complicate, buoyancy driven upwelling, mixing and downwelling ๏ interaction with polar frontal systems Courtesy WHOI: Schmitz, W.J. (1996), ‘One the World Ocean Circulation: Volume II. The Pacific and Indian Oceans A global update’, Technical Report. WHOI-96-08, Woods Hole Oceanographic Institution. 241 pp. 3D global overturning diagram

18. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 18 Present-day snapshot Courtesy of the American Meterological Survey: Speer, K., Rintoul, S.R., Sloyan, B., (2000) The Diabatic Deacon Cell., Journal of Physical Oceanography, v. 30, no. 12, p. 3212–3222. Schematic Diagram of the overturning circulation in the Southern Ocean

19. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 19 ๏ During LGM, equatorward shift of sea-ice edges, fronts, isotherms, and iceberg tracks Last Glacial Sea-ice Snapshot Courtesy of GSA: Armand, L.K. (2000), ‘An Ocean of Ice – Advances in the Estimation of Past Sea Ice in the Southern Ocean’, GSA Today, v. 10.

20. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 20 Southern Ocean nutrient concentrations ๏ The interaction of ocean circulation affects the concentration of nutrients such as silicic acid, and nitrate ๏ Concept of “pre-formed” nutrients: Preformed nutrients are those initially present in seawater at the time of downwelling ๏ The interaction of ocean circulation affects the concentration of nutrients such as silicic acid, and nitrate ๏ Concept of “pre-formed” nutrients: Preformed nutrients are those initially present in seawater at the time of downwelling Reprinted by permission from Macmillan Publishers Ltd: Sarmiento, J.L., Gruber, N., Brzezinski, M.A., Dunne, J.P., High-latitude control of thermocline nutrients and low latitude biological productivity. Nature (London), v. 427, no. 6969, p. 56-60. Copyright (2004). Not under CC licenceSarmiento, J.L., Gruber, N., Brzezinski, M.A., Dunne, J.P., High-latitude control of thermocline nutrients and low latitude biological productivity. Nature (London), v. 427, no. 6969, p. 56-60.

21. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 21 Changes in SO properties ๏ The response of the Southern Ocean to changing environmental conditions due to warming is crucial, due to its role in the carbon cycle ๏ Major processes: ๏ Increased stratification after warming? ๏ Sea-ice extent ๏ Change in upwelling patterns, nutrient supply from upwelling (Fe?) ๏ Changes in major biogeochemical fluxes due to changes in both primary and export production? ๏ The response of the Southern Ocean to changing environmental conditions due to warming is crucial, due to its role in the carbon cycle ๏ Major processes: ๏ Increased stratification after warming? ๏ Sea-ice extent ๏ Change in upwelling patterns, nutrient supply from upwelling (Fe?) ๏ Changes in major biogeochemical fluxes due to changes in both primary and export production?

22. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 22 Nutrient changes and CO 2 ๏ Upwelling of deep, nutrient-rich water in the Southern Ocean results in nearly 1/3 of TOTAL marine productivity (Berger, 1989) ๏ 2/3 of silica supplied to annually to the ocean is removed as hard parts of planktonic siliceous micro-organisms in the Southern Ocean ๏ -> high accumulation rates of biogenic opal, and formation of a circum-Antarctic biogenic silica belt (between the Polar Frontal Zone and the northern seasonally sea-ice covered Antarctic zone of the A counter current) ๏ Due to productivity, and importance for air-sea gas exchange, most palaeogeochemical models of pCO2 are highly sensitive to changes in nutrient utilisation and/or alkalinity of Antarctic surface waters ๏ Hence, variations in the export of organic matter from the Southern Ocean has been associated with drawdown of pCO 2 ๏ Upwelling of deep, nutrient-rich water in the Southern Ocean results in nearly 1/3 of TOTAL marine productivity (Berger, 1989) ๏ 2/3 of silica supplied to annually to the ocean is removed as hard parts of planktonic siliceous micro-organisms in the Southern Ocean ๏ -> high accumulation rates of biogenic opal, and formation of a circum-Antarctic biogenic silica belt (between the Polar Frontal Zone and the northern seasonally sea-ice covered Antarctic zone of the A counter current) ๏ Due to productivity, and importance for air-sea gas exchange, most palaeogeochemical models of pCO2 are highly sensitive to changes in nutrient utilisation and/or alkalinity of Antarctic surface waters ๏ Hence, variations in the export of organic matter from the Southern Ocean has been associated with drawdown of pCO 2

23. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 23 Evidence from the LGM ๏ During the LGM, palaeorecords from the Southern Ocean suggest that the gradient between middepth and deep d13C values was dramatically higher than today ๏ separates low-CO 2 middepth waters above from high-CO 2 deep water below ๏ During the LGM, palaeorecords from the Southern Ocean suggest that the gradient between middepth and deep d13C values was dramatically higher than today ๏ separates low-CO 2 middepth waters above from high-CO 2 deep water below Courtesy of IODP: Hodell, D.A., Gersonde, R., & Blum, P., ‘Leg 177 Synthesis: Insights into the Southern Ocean Paleoceanography on tectonic to millenial timescales’, Proc. ODP, Sci. Res. 177, R.Gersonde & P.Hodell, D. A.Blum, eds. (2002), p. 1–54.

24. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 24 Evidence from the LGM Courtesy of IODP: Hodell, D.A., Gersonde, R., & Blum, P., ‘Leg 177 Synthesis: Insights into the Southern Ocean Paleoceanography on tectonic to millenial timescales’, Proc. ODP, Sci. Res. 177, R.Gersonde & P.Hodell, D. A.Blum, eds. (2002), p. 1–54.

25. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 25 ๏ COMPLICATED... ๏ Due to its potential importance for glacial interglacial changes in pCO2, many attempts have been made to quantify this change, for both north and south of the polar front ๏ Examples: δ 15 N isotope systematics (Kumar, 1995;Sigman 1999) find little glacial-interglacial change in nutrient utilisation north of polar front, but a glacial-interglacial decrease on the Antarctic side ๏ supported by Cd/Ca data (Elderfield & Rickaby, 2000) -> ๏ δ 30 Si (de la Rocha et al., 1998) and Cd/Ca suggest INCREASE in nutrient utilisation from glacial to interglacial south of polar front, opposite to δ 15 N ๏ COMPLICATED... ๏ Due to its potential importance for glacial interglacial changes in pCO2, many attempts have been made to quantify this change, for both north and south of the polar front ๏ Examples: δ 15 N isotope systematics (Kumar, 1995;Sigman 1999) find little glacial-interglacial change in nutrient utilisation north of polar front, but a glacial-interglacial decrease on the Antarctic side ๏ supported by Cd/Ca data (Elderfield & Rickaby, 2000) -> ๏ δ 30 Si (de la Rocha et al., 1998) and Cd/Ca suggest INCREASE in nutrient utilisation from glacial to interglacial south of polar front, opposite to δ 15 N Conflicting paleonutrient proxies Reprinted by permission from Macmillan Publishers Ltd: Elderfield, H. & Rickaby, R. E.M. ‘Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean’, Nature, v. 405, p. 305–310. Copyright (2000). Not under CC licence.Elderfield, H. & Rickaby, R. E.M. ‘Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean’, Nature, v. 405, p. 305–310.

26. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 26 ๏ To reconcile the conflicting proxy evidence for higher, lower, or equal nutrient utilisation in the Southern Ocean between glacial-interglacial time, Elderfield & Rickaby (2000) suggest sea-ice is the answer: ๏ If sea-ice cover in SO during glacial times is high, then higher PO 4 (less utilisation) south of polar front could be reducing productivity..... can also explain δ 15 N signal ๏ Their interpretation: increased glacial sea-ice cover acts as a barrier to air-sea exchange, preventing loss of CO 2 from surface oceans: “Sea-ice hindered productivity in the Southern Ocean, leading to high surface water nutrients with concomitent enrichment in δ 15 N or organic matter, but, ironically, trapped the excess carbon in the deep ocean, thus lowering atmospheric CO 2 at glacial times ๏ To reconcile the conflicting proxy evidence for higher, lower, or equal nutrient utilisation in the Southern Ocean between glacial-interglacial time, Elderfield & Rickaby (2000) suggest sea-ice is the answer: ๏ If sea-ice cover in SO during glacial times is high, then higher PO 4 (less utilisation) south of polar front could be reducing productivity..... can also explain δ 15 N signal ๏ Their interpretation: increased glacial sea-ice cover acts as a barrier to air-sea exchange, preventing loss of CO 2 from surface oceans: “Sea-ice hindered productivity in the Southern Ocean, leading to high surface water nutrients with concomitent enrichment in δ 15 N or organic matter, but, ironically, trapped the excess carbon in the deep ocean, thus lowering atmospheric CO 2 at glacial times How to re-concile data.... Reprinted by permission from Macmillan Publishers Ltd: Elderfield, H. & Rickaby, R. E.M. ‘Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean’, Nature, v. 405, p. 305–310. Copyright (2000). Not under CC licence.Elderfield, H. & Rickaby, R. E.M. ‘Oceanic Cd/P ratio and nutrient utilization in the glacial Southern Ocean’, Nature, v. 405, p. 305–310.

27. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 27 Key point summary ๏ The Southern Ocean occupies a central role as the “mixing tap” of oceanic currents between the Atlantic, Pacific and Indian Ocean ๏ It plays a central role in deepwater formation, and the upwelling and distribution of nutrients to the world’s oceans ๏ It acts as the main connection between deep waters and the atmosphere, and has vigorous air-sea gas exchange ๏ Therefore, it has a potentially large role in explaining the glacial-interglacial “remaining” pCO 2 difference of ~110ppm ๏ two main theories for glacial-interglacial change: palaeoproductivity and/or stratification ๏ Proxy records disagree ๏ Some researchers think they can explain and reconcile the evidence by invoking dramatic changes in sea-ice cover ๏ The Southern Ocean occupies a central role as the “mixing tap” of oceanic currents between the Atlantic, Pacific and Indian Ocean ๏ It plays a central role in deepwater formation, and the upwelling and distribution of nutrients to the world’s oceans ๏ It acts as the main connection between deep waters and the atmosphere, and has vigorous air-sea gas exchange ๏ Therefore, it has a potentially large role in explaining the glacial-interglacial “remaining” pCO 2 difference of ~110ppm ๏ two main theories for glacial-interglacial change: palaeoproductivity and/or stratification ๏ Proxy records disagree ๏ Some researchers think they can explain and reconcile the evidence by invoking dramatic changes in sea-ice cover

28. L22 Themes: Southern Ocean history & climate SOES6047 - Global Climate Cycles 28 ๏ This resource was created by the University of Southampton and released as an open educational resource through the 'C-change in GEES' project exploring the open licensing of climate change and sustainability resources in the Geography, Earth and Environmental Sciences. The C-change in GEES project was funded by HEFCE as part of the JISC/HE Academy UKOER programme and coordinated by the GEES Subject Centre. ๏ This resource is licensed under the terms of the Attribution-Non-Commercial-Share Alike 2.0 UK: England & Wales license (http://creativecommons.org/licenses/by-nc-sa/2.0/uk/).http://creativecommons.org/licenses/by-nc-sa/2.0/uk/ ๏ However the resource, where specified below, contains other 3rd party materials under their own licenses. The licenses and attributions are outlined below: ๏ The University of Southampton and the National Oceanography Centre, Southampton and its logos are registered trade marks of the University. The University reserves all rights to these items beyond their inclusion in these CC resources. ๏ The JISC logo, the C-change logo and the logo of the Higher Education Academy Subject Centre for the Geography, Earth and Environmental Sciences are licensed under the terms of the Creative Commons Attribution -non-commercial-No Derivative Works 2.0 UK England & Wales license. All reproductions must comply with the terms of that license. ๏ All content reproduced from copyrighted material of the American Geophysical Union (AGU) are subject to the terms and conditions as published at: http://www.agu.org/pubs/authors/usage_permissions.shtml AGU content may be reproduced and modified for non-commercial and classroom use only. Any other use requires the prror written permission from AGU. http://www.agu.org/pubs/authors/usage_permissions.shtml ๏ All content reproduced from the American Association for the Advancement of Science (AAAS) may be reproduced for non commercial classroom purposes only, any other uses requires the prior written permission from AAAS. ๏ All content reproduced from Macmillan Publishers Ltd remains the copyright of Macmillan Publishers Ltd. Reproduction of copyrighted material is permitted for non-commercial personal and/or classroom use only. Any other use requires the prior written permission of Macmillan Publishers Ltd ๏ All content reproduced from the Wood’s Hole Oceanographic Institute (WHOI) is intended for non-commercial scientific and scholarly purposes only WHOI retains all rights. Any other use other than those stated requires the prior written permission of WHOI. ๏ Content reproduced from the American Meteorological Society (AMS) may be used under the "fair use" policy under Section 107 or that satisfies the conditions specified in Section 108 of the U.S. Copyright Law (17 USC, as revised by P.L. 94-553). Other uses requires the prior written permission from AMS ๏ Use of World Ocean Atlas material is allowed for non-commercial personal and educational use. No alteration of this material is permitted. Copyright statement