Disentangling seasonal and annual precipitation signals in the tropics over the Holocene : Insights from δD, alkanes and GDGTs
Hällberg, Petter L. (Stockholm University. Department of Geological Sciences)
Smittenberg, Rienk (Stockholm University. Department of Geological Sciences)
Kylander, Malin E. (Stockholm University. Department of Geological Sciences)
Villanueva, Joan (Universitat Autònoma de Barcelona. Institut de Ciència i Tecnologia Ambientals)
Davtian, Nina (Universitat Autònoma de Barcelona. Institut de Ciència i Tecnologia Ambientals)
Hapsari, Anggi (University of Göttingen)
Sjöström, Jenny K. (Stockholm University. Department of Geological Sciences)
Axelsson, Josefine (Stockholm University. Department of Physical Geography)
Jarne-Bueno, Guillermo (Stockholm University. Department of Geological Sciences)
Yamoah, Kweku (University of York. Department of Archaeology)
Rifai, Hamdi (Universitas Negeri Padang. Department of Physics)
Schenk, Frederik (Stockholm University. Department of Geological Sciences)

Data:	2024
Descripció:	17 pàg.
Resum:	Rainfall seasonality in the tropics has a substantial impact on both ecosystems and human livelihoods. Yet, reconstructions of past rainfall variability have so far generally been unable to differentiate between annual and seasonal precipitation changes. Past variations in seasonality are therefore largely unknown. Here, we disentangle hydrogen isotopic (δD) signals from terrestrial leaf waxes and algae in an 8000-year peat core from Sumatra, which reflect annual versus wet season rainfall signals, respectively. We validate these results using lipid biomarkers by reconstructing vegetation dynamics via n-alkane distributions and peatland hydrological conditions using glycerol dialkyl glycerol tetraethers (GDGTs), as well as biomass burning using levoglucosan concentrations in the core. Finally, we compare our proxy results to a transient climate model simulation (MPI-ESM1. 2) to identify the mechanism for seasonality changes. We find that algal δD indicates stronger Indonesian-Australian Summer Monsoon (IASM) precipitation in the Mid-Holocene, between 8 and 4. 2 cal ka BP. A period of alternating flooding, droughts and wildfires is reconstructed between 6 and 4. 2 cal ka BP, implicating very strong monsoonal precipitation and drying out and burning during a longer and intensified dry season. We attribute this strong rainfall seasonality in the Mid-Holocene mainly to orbitally forced insolation seasonality and a strengthened IASM, consistent with the modeling results. In terms of annual rainfall, terrestrial plant δD, vegetation composition and GDGTs all indicate wetter conditions peaking between 3 and 4. 5 cal ka BP, preceded by drier conditions, followed by drastic and rapid drying in the late Holocene from around 2. 8 cal ka BP. Our multiproxy annual precipitation reconstruction thereby indicates the wettest overall conditions approximately 1500-2000 years later than a nearby speleothem δ18O record, which instead follows the seasonally biased algal δD in our record. We, therefore, hypothesize that speleothem reconstructions over the Holocene in parts of the tropics with low but significant seasonality may carry a stronger seasonal component than previously suggested. The data presented here contribute with new insights on how isotopic rainfall proxies in the tropics can be interpreted. Our findings resolve the seasonal versus annual components of Holocene rainfall variability in the Indo-Pacific Warm Pool region, highlighting the importance of considering seasonality in rainfall reconstructions.
Nota:	Unidad de excelencia María de Maeztu CEX2019-000940-M
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Biomarkers ; Indo-Pacific warm pool (IPWP) ; Leaf waxes ; Organic geochemistry ; Paleoclimatology ; Southeast Asia ; Stable isotopes ; SDG 13 - Climate Action ; SDG 15 - Life on Land
Publicat a:	Quaternary Science Reviews, Vol. 344 (November 2024) , art. 108948, ISSN 0277-3791

DOI: 10.1016/j.quascirev.2024.108948

17 p, 9.4 MB

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