Spatiotemporal ITCZ dynamics during the last three millennia in Northeastern Brazil and related impacts in modern human history
Abstract. Changes in tropical precipitation over the past millennia have usually been associated with latitudinal displacements of the Intertropical Convergence Zone (ITCZ). Recent studies provide new evidence that contraction and expansion of the tropical rainbelt may also have contributed to ITCZ variability on centennial time scales. Over tropical South America few records point to a similar interpretation, which prevents a clear diagnosis of ITCZ changes in the region. In order to improve our understanding of the equatorial rainbelt variability, our study presents a reconstruction of precipitation for the last 3200 years from the Northeast Brazil (NEB) region, an area solely influenced by ITCZ precipitation. We analyze oxygen isotopes in speleothems that serve as a faithful proxy for the past location of the southern margin of the ITCZ. Our results, in comparison with other ITCZ proxies, indicate that the range of seasonal migration, contraction and expansion of the ITCZ was not symmetrical around the equator. A new NEB ITCZ pattern emerged based on the comparison between two distinct proxies that characterize the ITCZ behavior during the last 2500 years, with an ITCZ zonal pattern between NEB and the eastern Amazon. In NEB, the period related to the Medieval Climate Anomaly (MCA) was characterized by an abrupt transition from wet to dry conditions. These drier conditions persisted until the onset of the period corresponding to the Little Ice Age (LIA), representing the longest dry period over the last 3200 years in NEB. The ITCZ was apparently forced by teleconnections between Atlantic Multidecadal Variability and Pacific Decadal Variability that controlled the position, intensity and width of Walker cell over South America changing the ITCZ zonally, and sea surface temperature changes in both the Pacific and Atlantic, stretching/weaking the ITCZ-related rainfall meridionally over NEB. Wetter conditions started around 1500 CE in NEB. During the last 500 years, our speleothems document the occurrence of some of the strongest drought events for the last millennia, which drastically affected population and environment of NEB during the Portuguese colonial period. The historical droughts were able to affect the karst system, and led to significant impacts over the entire NEB region.
Giselle Utida et al.
Status: open (until 13 Apr 2023)
- CC1: 'Comment on cp-2023-2', Alessandro Mauceri, 13 Mar 2023 reply
- RC1: 'Comment on cp-2023-2', Anonymous Referee #1, 18 Mar 2023 reply
- RC2: 'Comment on cp-2023-2', Anonymous Referee #2, 21 Mar 2023 reply
Giselle Utida et al.
Giselle Utida et al.
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Comments on “Spatiotemporal ITCZ dynamics during the last three millennia in Northeastern Brazil and related impacts in modern human history.”
Authors: Giselle Utida, Francisco William Cruz, Mathias Vuille, Angela Ampuero, Valdir F. Novello, Jelena Maksic, Gilvan Sampaio, Hai Cheng, Haiwei Zhang, Fabio Ramos Dias de Andrade, and R. Lawrence Edwards
This is an interesting study that uses speleothem δ18O and δ13C records to characterize the nuanced behavior of the ITCZ/tropical rain belt and its impact on the regional hydroclimate (i.e., precipitation variability) of Nordeste and eastern Amazona during the late Holocene. The main objective of this study is to improve the interpretation of late Holocene ITCZ dynamics in the South American tropics, which may help to better our understanding of past SASM variability. Additionally, their interpretation of RN δ18O as a recorder of extreme dry events during the last 500 years has archeological and societal implications. This manuscript presents several thought-provoking and novel ideas pertaining to Atlantic and Pacific impacts on ITCZ-related precipitation during the late Holocene, which have the potential to reconcile paleoclimate records from Nordeste and Amazonia. Overall, this study also has the potential to be an excellent contribution to the field of South American paleoclimatology. However, I find that the manuscript (in its present state) has several major issues, which require further consideration, detail, and development before it should be accepted for publication. As such, I would recommend major revisions of the manuscript before final acceptance.
Details are provided in the attached file.