Modelling Mediterranean ocean biogeochemistry of the Last Glacial Maximum
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Published:2024-08-12
Issue:8
Volume:20
Page:1785-1816
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ISSN:1814-9332
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Container-title:Climate of the Past
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language:en
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Short-container-title:Clim. Past
Author:
Six Katharina D.ORCID, Mikolajewicz Uwe, Schmiedl Gerhard
Abstract
Abstract. We present results of simulations performed with a physical–biogeochemical ocean model of the Mediterranean Sea for the Last Glacial Maximum (LGM) and analyse the differences in physical and biochemical states between the historical period and the LGM. Long-term simulations with an Earth system model based on ice sheet reconstructions provide the necessary atmospheric forcing data, oceanic boundary conditions at the entrance to the Mediterranean Sea, and river discharge to the entire basin. Our regional model accounts for changes in bathymetry due to ice sheet volume changes, reduction in atmospheric CO2 concentration, and an adjusted aeolian dust and iron deposition. The physical ocean state of the Mediterranean during the LGM shows a reduced baroclinic water exchange at the Strait of Gibraltar, a more sluggish zonal overturning circulation, and the relocation of intermediate and deep-water-formation areas – all in line with estimates from palaeo-sediment records or previous modelling efforts. Most striking features of the biogeochemical realm are a reduction in the net primary production, an accumulation of nutrients below the euphotic zone, and an increase in the organic matter deposition at the seafloor. This seeming contradiction of increased organic matter deposition and decreased net primary production challenges our view of possible changes in surface biological processes during the LGM. We attribute the origin of a reduced net primary production to the interplay of increased stability of the upper water column, changed zonal water transport at intermediate depths, and lower water temperatures, which slow down all biological processes during the LGM. Cold water temperatures also affect the remineralisation rates of organic material, which explains the simulated increase in the organic matter deposition, which is in good agreement with sediment proxy records. In addition, we discuss changes in an artificial tracer which captures the surface ocean temperature signal during organic matter production. A shifted seasonality of the biological production in the LGM leads to a difference in the recording of the climate signal by this artificial tracer of up to 1 K. This could be of relevance for the interpretation of proxy records like, e.g., alkenones. Our study not only provides the first consistent insights into the biogeochemistry of the glacial Mediterranean Sea but will also serve as the starting point for transient simulations of the last deglaciation.
Funder
Deutsche Forschungsgemeinschaft
Publisher
Copernicus GmbH
Reference102 articles.
1. Abu-Zied, R. H., Rohling, E. J., Jorissen, F. J., Fontanier, C., Casford, J. S., and Cooke, S.: Benthic foraminiferal response to changes in bottom-water oxygenation and organic carbon flux in the eastern Mediterranean during LGM to Recent times, Mar. Micropaleontol., 67, 46–68, https://doi.org/10.1016/j.marmicro.2007.08.006, 2008. a, b 2. Adloff, F., Mikolajewicz, U., Kučera, M., Grimm, R., Maier-Reimer, E., Schmiedl, G., and Emeis, K.-C.: Upper ocean climate of the Eastern Mediterranean Sea during the Holocene Insolation Maximum – a model study, Clim. Past, 7, 1103–1122, https://doi.org/10.5194/cp-7-1103-2011, 2011. a, b 3. Aksu, A., Yaşar, D., and Mudie, P.: Origin of late glacial–Holocene hemipelagic sediments in the Aegean Sea: clay mineralogy and carbonate cementation, Mar. Geol., 123, 33–59, https://doi.org/10.1016/0025-3227(95)80003-t, 1995. a, b 4. Albani, S., Mahowald, N. M., Murphy, L. N., Raiswell, R., Moore, J. K., Anderson, R. F., McGee, D., Bradtmiller, L. I., Delmonte, B., Hesse, P. P., and Mayewski, P. A.: Paleodust variability since the Last Glacial Maximum and implications for iron inputs to the ocean, Geophys. Res. Lett., 43, 3944–3954, https://doi.org/10.1002/2016gl067911, 2016. a, b 5. Allen, J. R. M., Brandt, U., Brauer, A., Hubberten, H.-W., Huntley, B., Keller, J., Kraml, M., Mackensen, A., Mingram, J., Negendank, J. F. W., Nowaczyk, N. R., Oberhänsli, H., Watts, W. A., Wulf, S., and Zolitschka, B.: Rapid environmental changes in southern Europe during the last glacial period, Nature, 400, 740–743, https://doi.org/10.1038/23432, 1999. a
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