Hydro-climatic variability in the southwestern Indian Ocean between 6000 and 3000 years ago

Abstract

Abstract. The “4.2 ka event” is frequently described as a major global climate anomaly between 4.2 and 3.9 ka, which defines the beginning of the current Meghalayan age in the Holocene epoch. The “event” has been disproportionately reported from proxy records from the Northern Hemisphere, but its climatic manifestation remains much less clear in the Southern Hemisphere. Here, we present highly resolved and chronologically well-constrained speleothem oxygen and carbon isotopes records between ∼6 and 3 ka from Rodrigues Island in the southwestern subtropical Indian Ocean, located ∼600 km east of Mauritius. Our records show that the 4.2 ka event did not manifest itself as a period of major climate change at Rodrigues Island in the context of our record's length. Instead, we find evidence for a multi-centennial drought that occurred near-continuously between 3.9 and 3.5 ka and temporally coincided with climate change throughout the Southern Hemisphere.

A multimillennial climatic context for the megafaunal extinctions in Madagascar and Mascarene Islands

“…In addition, the LAVI-4  18 O record also exhibits a high degree of replication with the PATA-1  18 O record from the nearby Patate cave between ~3000 and 6000 yr B.P. (37). Second, the theoretical range of calcite  18 O values [e.g., (54)…”

“…The IsoGSM has been widely used for both modern and past climate simulations and has been shown to be in good agreement with the  18 O p observations from GNIP stations globally (38). The model-simulated  18 water vapor sources with substantially different isotopic compositions (37). Consequently, we have used these observations to interpret temporal variations in speleothem  18 O from Rodrigues in terms of hydroclimate variability over the SWIO.…”

“…The DJF precipitation composites for La Niña minus El Niño years suggest a rather modest increase in precipitation over northern Madagascar and Rodrigues during the El Niño events and vice versa ( fig. S4E) (37).…”

Mid–late Holocene event registered in organo-siliciclastic sediments of Lagoa Salgada carbonate system, southeast Brazil

“…Silva et al (2013) identified 21 species of cyanobacteria in stromatolites of the Lagoa Salgada, with the most representative being Microcoleus chthonoplastes and Lyngbya aestuarii, which are diazotrophic cyanobacteria present in coastal microbial mats. In hypersaline lakes, such as Lagoa Salgada, microbial mats precipitate CaCO 3 as a by-product of CO 2 capture through photosynthesis by cyanobacteria (Jonkers et al, 2003;Ludwig et al, 2005). The precipitation of CaCO 3 that generated the lithification of the microbial mats in the lake are caused by cyanobacteria that increase the pH through photosynthesis in a CaCO 3 supersaturated system (Decho and Kawaguchi, 2003).…”

How Far North Did the African Monsoon Fringe Expand During the African Humid Period? Insights From Southwest Moroccan Speleothems

“…Between 9 and 4 Kyr BP, the climate signal from the WIN record is synchronous to the persistent northward position of the ITCZ (Figure 2c), which likely triggered or amplified the expansion of the WASM further northward during the AHP. Interestingly, synchronous growth hiatuses in two WIN2 and WIN3 records suggest a period of drought initiating around 4 Kyr BP (Figure 2a), coincident with the timing of several abrupt climate change events identified in many Holocene records around the world (e.g., Bond et al, 2001;Li et al, 2018;Marchant & Hooghiemstra, 2004;Mayewski et al, 2004;Roland et al, 2014). This abrupt climate event has indeed been linked to collapse of ancient civilizations in Northern Hemisphere subtropical regions, including Mesopotamia, Egypt, and the Indus Civilization [e.g., Staubwasser & Weiss, 2006;Weiss, 2016].…”