TracIng Monsoon, Ocean currents and diagenetic carbon Redistribution

Registration deadline: 31 January 2022

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    Vienna, Austria

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The TIMOR workshop aims to develop an IODP mission-specific platform (MSP) proposal to study two separate but complementary topics in a single expedition: (1) the early diagenetic redistribution of carbon via the microbially driven oxidation of organic carbon, the dissolution of aragonite and the precipitation of calcite, and (2) the palaeoclimatic and palaeoceanographic impacts of Quaternary Monsoon and Indonesian Throughflow variability in the Timor Sea. We encourage both experienced and early career researchers to join us.

 

Location: The workshop will take place at the University of Vienna from the 31 March – 2 April 2022.


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Rationale

Palaeoclimate. Today, the Australian summer monsoon eases aridity in northwest Australia and is driven by continental heating, with moisture provided by warm Indonesian and western Pacific waters(1). Recent IODP drilling on the northwest shelf of Australia (Exp. 356, U1463) and off the margin of northwest Australia (Exp. 363, U1482 & U1483) revealed that important shifts in Australian monsoonal intensity seem temporally decoupled from changes in northern hemisphere monsoonal systems(2-3). This observation underlines the need for an in-depth study of the southern hemisphere monsoonal system, as its dynamics were apparently governed by autonomous drivers. This need is most urgent in the Pleistocene and Holocene, as understanding rapid changes on sub-orbital timescales is key to constraining future regional climate. Currently, our understanding of the mechanisms driving the Australian Monsoon on sub-orbital timescales is limited by the absence of extended, continuous climate archives on land. This is a major motivation to drill marine sediment archives on the northern rim of Australia, which hold the potential to robustly constrain the timing and intensity of past Australian monsoon variability. The paleoclimate objective is, thus, to obtain a Pleistocene to Holocene tropical continental hydroclimate archive that can be used to chart Australian monsoon variability via terrestrial runoff at centennial- to millennial-scale resolution. Such an archive would serve as the basis to test the hypothesis that Australian Monsoon intensity was driven by local insolation forcing, superimposed on longer-timescale modulators such as polar ice volume, latitudinal and zonal thermal gradients, and greenhouse gases.

Palaeoceanography. The Indonesian Throughflow (ITF) is the sole tropical connection between the Pacific and Indian Oceans with its main outlet through the Timor Strait(4-6). The Timor Sea is also the perfect place to study the northernmost branch of the Leeuwin Current, which is dynamically linked to the ITF. The Leeuwin Current is the only southward flowing eastern boundary current in the Southern Hemisphere, transporting warm, low-salinity, nutrient-deficient ITF waters southward to subtropical latitudes along the western coast of Australia(7-8). The Leeuwin Current allows tropical and subtropical reef development along its pathway. Drilling in the Timor Sea will enable us to determine and provide a long-term perspective on how coral reefs in the eastern Indian Ocean developed under variable climate boundary conditions. Another crucial challenge is understanding the drivers of Leeuwin Current intensity in response to global climate change. The palaeoceanographic objective is, thus, to determine the Pleistocene to Holocene variability of the northernmost branch of the Leeuwin Current, which is fed by the ITF, and is highly sensitive to changes in eustatic sea-level and zonal atmospheric circulation (Indian Ocean Dipole and El Niño Southern Oscillation). This reconstruction will serve as the basis to test the hypothesis that the Leeuwin Current and the ITF exert a primary control on Indian Ocean thermal gradients, as well as on carbonate and reef deposition along its pathway.

Sedimentology, diagenesis and microbiology. Carbonate rocks play a key role in lithospheric carbon storage(9), and the burial of carbon-bearing material on the ocean floor represents one of the key feedbacks regulating Earth’s climate system over geological time scales(10-11). Observations from the rock record support the hypothesis that early diagenetic aragonite dissolution and its reprecipitation as calcite is the underlying mechanism for the early lithification of individual beds(12). A key control on sediment composition and grain size is the biological carbonate production and the disintegrative processes acting on aragonitic and calcitic shells in the taphonomic active zone (the top 1-50 cm), below which chemical dissolution and authigenic precipitation take over as the dominant processes. The upper centimetres to metres of the modern marine sediment column are characterised by a sequence of microbial communities which oxidise organic carbon using a variety of electron acceptors(13-16). These biochemical reactions are a major control on the saturation state of calcium carbonate through their impact on pore fluid pH and the production of dissolved inorganic carbon(17-18). These microbial zones result in chemical gradients, which likely cause areas of aragonite dissolution and calcite precipitation. However, there is a dispute regarding in which of the distinct redox zones these processes occur(19-21). Investigating these processes in situ was hitherto not possible since applied drilling techniques failed to sample the early lithified beds and associated pore-water. Furthermore, geochemical data are biased by contact with sea water during core retrieval. In addition to the depth and nature of redox zones, calcareous sediment production plays a key role in the early diagenetic carbon redistribution. Key questions in this respect are how strongly the living calcifying fauna is represented in the sediment, whether the composition of the sediment-producing fauna has changed through time, and how strongly the composition of the preserved fossil fauna is biased by aragonite dissolution(19, 22). Therefore, there are multiple unanswered questions about the extent of carbon redistribution, the redox zones involved, its impact on geochemical proxies, its contribution to the global carbon budget, and its impact on the preservation of calcareous fossils. The main objective for carbonate sedimentology, diagenesis and microbiology is to detect the effects of and influences on microbial zones on carbonate sediments, geochemical proxies and the global carbon budget. A better understanding of where and when the transformation of aragonite into stable calcite occurs in the sediment column will help elucidate the role of tropical shallow water carbonate shelves in carbon storage and release and thus links to our understanding of the Earth and climate system.

Study area. The Timor Sea is bordered by the Australian continent to the south, the island of Timor to the north and the Banda/Arafura Seas to the east. The Timor Sea is located at the southern limit of the seasonal (austral summer) displacement of the Intertropical Convergence Zone (ITCZ) and is intensely affected by the Australasian monsoon system. The latitudinal displacement of the ITCZ has changed considerably over Pleistocene glacial-interglacial cycles and the intensity of monsoonal rainfall, wind and cyclone activity over Western Australia varied substantially in relation to millennial, glacial-interglacial and precessional-scale interhemispheric temperature fluctuations(23-24). Western Australia’s climate is additionally influenced by the ITF, which transfers surface and intermediate waters from the Pacific Ocean, thus regulating the heat and freshwater budgets of tropical water masses and impacting regional and global climate(25). The combination of fine-grained sediment (both calcareous and siliciclastic), high terrestrial input by rivers and monsoon discharge, and high variability of depositional setting and water depth within a small range provides optimal conditions for investigating the influence of external factors. The region targeted in this proposed workshop represents a key area to better understand the processes driving the temporal variability of the Australian Monsoon and the ITF within the framework of global climate evolution. There is already a wealth of information available about sediment distribution on the northwest shelf of Australia from commercial and IODP drilling (Exp. 356 2) as well as large diameter piston coring in the middle to lower bathyal zone (R/V Sonne cruises SO185 and SO257 26-27; IODP Exp. 363 3). IODP Exp. 356 also encountered lithified beds within the top 50m of several boreholes, suggesting that early lithification of calcareous sediments is relatively widespread over the shelf. However, the shelf sites could not be completely cored due to technical limitations of the drilling employed. The TIMOR workshop will actively explore MSP-drilling options to allow for scientific drilling at shallow water depths (120 - 500m), while at the same time ensuring good recovery throughout a wide variety of carbonate platform sediments (alternating soft and lithified lithologies). The targeted sediments offer a unique opportunity to integrate multidisciplinary research objectives and to advance understanding of the Southern Hemisphere palaeoclimatic, palaeoceanographic and sedimentological history.

List of keynote speakers:

Name
Institution (Country)
 
Ahm, Anne-Sofie
currently Princeton (USA); from 1st of April 2022: University of Victoria (Canada)
 
Biddle, Jennifer
University of Delaware (USA)
 
Gallagher, Stephen
Marlow, Jeff
University of Melbourne (Australia)
Boston University (USA)
 
Opdyke, Brad
Australian National University (Australia)
 
Schaap, Allison
National Oceanography Centre (UK)
 
Tomašových, Adam
Earth Science Institute Bratislava (Slovakia)
 
Westphal, Hildegard
Zentrum für Marine Tropenforschung (Germany)
 
Wright, Paul
National Museum of Wales (UK)
 
2 staff from the ECORD Science Operators (ESO)
ESO (various European countries)
 

Organising committee:

Name
Institution (Country)
 
Balthasar, Uwe
University of Plymouth (UK)
 
Biddle, Jennifer
University of Delaware (USA)
 
Bolton, Clara
CEREGE (France)
 
Bradbury, Hal
University of Cambridge (UK)
 
De Vleeschouwer, David
Marum (Germany)
 
Holbourn, Ann
University of Kiel (Germany)
 
Kuhnt, Wolfgang
University of Kiel (Germany)
 
Munnecke, Axel
University of Erlangen (Germany)
 
Nohl, Theresa
University of Erlangen (Germany)
 
Wright, Kirstie
Consultant Geoscientist
 
Zuschin, Martin
University of Vienna (Austria)
 

References

[1] Suppiah, R., 1992. The Australian summer Monsoon: A review. Progress in Physical Geography, 16(3),283-318.

[2] Gallagher, S. J., Fulthorpe, C. S., Bogus, K., & the Expedition 356 Scientists, 2017. The Indonesian Through flow. Proceedings of the International Ocean Discovery Program, 356,doi:10.14379/iodp.proc.356.105.2017.

[3] Rosenthal, Y., Holbourn, A.,Kulhanek, D. K. & the Expedition 363 Scientists, 2018. Western Pacific Warm Pool. Proceedings of the International Ocean Discovery Program, 363, doi:10.14379/iodp.proc.363.2018.

[4] Gordon, A. L., Susanto, R. D.,& Vranes, K. 2003. Cool Indonesian through flow as a consequence of restricted surface layer flow. Nature, 425,824 828.

[5] Gordon, A. L. 2005. The Indonesian Seas: oceanography of the Indonesian Seas and their Through flow. Oceanography, 18, 14–27.

[6] Sprintall, J., Wijffels, S. E., Molcard, R., & Jaya, I., 2009,Direct estimates of the Indonesian Through flow entering the Indian Ocean:2004-2006. Journal of Geophysical Research – Oceans, 114, C07001;DOI: 10.1029/2008JC005257.

[7] Feng, M., Meyers, G., Pearce,A., & Wijffels, S., 2003. Annual and inter annual variations of the Leeuwin Current at 32°S. Journal of Geophysical Research - Oceans, 108, 3355.DOI: 10.1029/2002JC001763.

[8] Ridgway, K. R.,& Godfrey, J. S., 2015. The source of the Leeuwin Current seasonality. Journal of Geophysical Research - Oceans,120(10), 6843–6864.https://doi.org/10.1002/2015JC011049.

[9] Milliman, J. D.,1993. Production and accumulation of calcium carbonate in the ocean: budget of a non steady state. Global Biogeochemical cycles, 7, 927-957.

[10] Berner, R. A.,Lasaga, A. C. & Garrels, R. M., 1983, The carbonate-silica cycle and its effect on atmospheric carbon-dioxide over the past 100 million years. American Journal of Science, 283(7), 641-683.

[11] Ridgwell, A. &Zeebe, R. E., 2005. The role of the global carbonate cycle in the regulation and evolution of the Earth system. Earth and Planetary Science Letters, 234,299-315.

[12] Westphal, H.,2006. Limestone–marl alternations as environmental archives and the role of early diagenesis: a critical review. International Journal of Earth Sciences, 95,947-961.

[13] Froelich P. N.,Klinkhammer G. P., Bender M. L., Luedtke N. A., Heath G. R., Cullen D., DauphinP., Hammond D., Hartman B. and Maynard V. 1979. Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxicdiagenesis. Geochimica et Cosmochimica Acta 43, 1075–1090.

[14] Berner, R. A.,1980. Early Diagenesis. Princeton Series in Geochemistry, 1, 243pp., https://doi.org/10.1515/9780691209401.

[15] Bowles, M.W., Mogollón, J.M., Kasten, S., Zabel, M., and Hinrichs, K.-U., 2014.Global rates of marine sulfate reduction and implications for sub-sea-floor metabolic activities. Science, 344, 889-891.

[16] Wurgaft, E., Findlay, A.J., Vigderovich, H., Herut, B., Sivan, O., 2019.Sulfate reduction rates in the sediments of the Mediterranean continental shelf inferred from combined dissolved inorganic carbon and total alkalinity profiles. Marine Chemistry, 211, 64-74,https://doi.org/10.1016/j.marchem.2019.03.004.

[17] Soetaert K., Hofmann A. F., Middelburg J. J., Meysman F. J. R. and Greenwood J.2007. The effect of biogeochemical processes on pH. Marine Chemistry 105,30–51.

[18] Turchyn A. V.,Bradbury H. J., Walker K. and Sun X. 2021. Controls on the Precipitation of Carbonate Minerals Within Marine Sediments. Front. Earth Sci. 9.

[19] Cherns, L. &Wright, V. P., 2009. Quantifying the impacts of early diagenetic aragonite dissolution on the fossil-record. Palaios,24: 756-771.

[20] Wheeley, J.R.,2006. Taphonomy, sedimentology and palaeoenvironmental interpretation of Middle Ordovician Limestones, Jämtland, Sweden [Ph.D. thesis]: Cardiff, Cardiff University, 204 p.

[21] Munnecke. A. & Samtleben, C., 1996. The formation of micritic limestones and the development of limestone-marl alternations in the Silurian of Gotland, Sweden. Facies, 34: 159-176.

[22] James, N. P.,Bone, Y., & Kyser, K., 2005. Where has all the aragonite gone? Mineralogy of Holocene neritic cool-water carbonates, Southern Australia. Journal of Sedimentary Research, 75: 454-463.

[23] Kuhnt, W., Holbourn, A., Xu, J., Opdyke, B., DeDeckker, P., Röhl, U., & Mudelsee, M., 2015. Southern Hemisphere control on Australian monsoon variability during the late deglaciation and Holocene. Nature Communications, 6. https://doi.org/10.1038/ncomms6916.

[24] Pei, R., Kuhnt, W., Holbourn, A., Hingst, J. Koppe,M., Schultz, J. Kopetz, P. Zhang, P., & Andersen, N., 2021. Monitoring Australian Monsoon variability over the past four glacial cycles. Palaeogeography, Palaeoclimatology, Palaeoecology, 568, 110280,doi:10.1016/j.palaeo.2021.110280.

[25] Hu, S.,Zhang, Y., Feng, M., Du, Y., Sprintall, J., Wang, F., et al., 2019. Interannualto decadal variability of upper-ocean salinity in the southern Indian Ocean and the role of the Indonesian Through flow. Journal of Climate, 32(19),6403–6421, https://doi.org/10.1175/JCLI-D-19-0056.1.

[26] Kuhnt, W.et al., 2006. Cruise Report SO185, Vital – Variability of the Indonesian through flow and Australasian climate history of the last 150000 years,Darwin-Jakarta, September 15 2005 – October 06 2005, doi.org/10.2312/cr_so185.

[27] Kuhnt, W., Holbourn, A., Schönfeld, J. et al.,2018. Cruise report Sonne 257 [SO257], WACHEIO - Western Australian Climate History from Eastern Indian Ocean Sediment Archives, Darwin -Fremantle, May 12, 2017 - June 04, 2017, doi:10.2312/cr_so257.

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