the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Warm tropical oceans and ENSO flavours behind the late Holocene change in hydroclimates in northern South America
Juan Mauricio Bedoya
Maria I. Velez
German Poveda
Abstract. At about 4,000 years ago the earth’s global climate underwent significant transformations resulting from changes in solar insolation. Manifestations of this change are relatively well known in higher latitudes, however, in the American tropics these are still not fully identified or understood. Recent paleo-environmental reconstructions based on paleolimnological and vegetational histories of two Colombian Andean sites suggest that between ~4,150 and 2,500 yr BP the Eastern Cordillera (EC) witness wetter anomalies, while the Western Cordillera (WC) suffered from drier anomalies between ~3,700 and 1,750 yr BP. Results from analyses of modern precipitation series from weather stations close to the study sites indicate that the long-term mean annual cycle of precipitation in both sites is out-of-phase and that precipitation anomalies on the western (eastern) site are negatively (positively) correlated with sea surface temperatures in the tropical Pacific (Tropical Atlantic). Hence that we propose that both oceans warmed up during the late Holocene, likely from a more active ENSO and ENSO flavours. With the current global rise in atmospheric temperature and the warming of tropical oceans, this study sheds light on possible anomalous effects on precipitation over the northern Andes.
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Juan Mauricio Bedoya et al.
Status: open (until 06 Jul 2023)
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RC1: 'Comment on egusphere-2022-1428', Anonymous Referee #1, 07 Apr 2023
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Title: Warm tropical oceans and ENSO flavours behind the late Holocene change in hydroclimates in northern South America
Author(s): Juan Mauricio Bedoya et al.
MS No.: egusphere-2022-1428
MS type: Research article
This manuscript aims to describe the ENSO-related climate variability during the late Holocene in both the western and eastern cordilleras of Colombia. This description is based on the present-day ENSO effects over precipitation and pollen records obtained from two sites: one located on the western branch of the Colombian Andes (Mistrató and Medellincito) and a kind of mirroring site on the eastern branch (Berlin and San Turbán). Present-day precipitation anomalies in the western (eastern) location are negatively (positively) correlated with the sea surface in Tropical Pacific (Tropical Atlantic). The authors propose that the late Holocene had an opposite warming structure in the tropical Atlantic and Pacific oceans by comparing it to today’s climate in these sites.
I have carefully reviewed the manuscript. While I appreciate the time and effort the authors put into their work and thank you for taking me into account to review this manuscript, I regret to inform you that I cannot recommend acceptance of this manuscript for publication in Climate of the Past at this time. My assessment is based on the major concerns I explain below.
Northern South America, specifically Colombia, is characterized by a large spatial variability in precipitation regimes and a very heterogeneous composition of moisture sources becoming rainfall. The interaction of local factors such as the stepped orography, regional circulation, global variability, and external forcing produce a complex spatio-temporal structure of regional rainfall variability. Despite the authors present the general context of climate variability in Colombia (Sec. 2), the line of argument related to the work done oversimplifies this complexity, reaching huge conclusions from some weak coincidences. This argumentative line is maintained throughout the manuscript as follows:
- In lines 99-104, the authors imply that the conclusions derived from these couple of sites could be directly extended to all corresponding western/eastern Colombia. Why are these two places expected to be representative of western/eastern Colombia's climate variability? What does western/eastern Colombia refer to? What about altitude/latitude effects? A deeper discussion is needed.
- In the same sense, Figure 1 shows the main mechanism of moisture transport but only referred to LLJs. I agree these structures are important mechanisms of moisture transport but only represent a portion of the entire atmospheric transport and these systems are seasonally active. In the framework of ENSO-related variability of Colombia rainfall, it is well known that regional circulation, length of deep convection, and the accumulated hydrological response (related to moisture recycling that accounts for more than 50% of total atmospheric moisture) are the main transport mechanisms underlying in the rainfall variability under ENSO stages.
- In lines 299-326 the ms explains Figures 4 and 5 that show the correlation maps between precipitation trend from Mistratró and Berlin and global SST from two datasets. For Mistrató the correlation maps contain a lot of information, showing positive and negative correlated areas along the globe, not only TP and TNA. Even, the two datasets (HADISST and ERA5) have noticeably different spatial structures (nothing is said about it in the ms). For Berlin, the correlation maps look quite different. In both cases, the conclusion derived from maps is quite similar, the ms only refers to TP and TNA and immediately to ENSO (see lines 303-305 and 319-321). What does a globally connected precipitation mean? What does a lack of these connections mean? What about the role of regional, terrestrial, and recycling effects over precipitation?
- Figure 6 introduces a new dataset (NCEP/NCAR Reanalysis I) and shows three Lagrangian trajectories at 700 mb for each site during a wet anomalous season in 2010. Is this a kind of example? How representative of an ensemble of anomalous behavior is it? Why this specific level? Why only three trajectories? Why this dataset? 6A looks to be not properly cropped at the north edge. Here again, a strong statement is derived from this very reduced picture of transport processes, see lines 333-335.
- Spectral power analysis is quite interesting and shows a mix of time-scales of CP SST (Niño 3.4 index) and TA SST (TNA index) influencing precipitation in Mistrató and Berlin. However, the power spectrum intensity scale is different in each panel (Figures 8b, 8c, 9b, and 9c) and it must be unified in order to do a real comparison and avoid misleading. Also, the zero must be clearly shown. The time units must be also specified in these figures. In the text, the time scale signal of El Niño 3.4 influencing Mistrató is explained in months (lines 352-360), for Berlin is in years (lines 360-364). The TNA time scales influencing both Mistrató and Berlin are explained in years (lines 364-373). These couple of indices describe the interannual variability of tropical Pacific and tropical North Atlantic SST. Is there a mistake in the power time scale description? Despite the great variability and information displayed in power spectrum analysis (Figure 8 and 9), the take-home message is summarized in the text as follows: “At interdecadal timescales, an increase in SST in the Central Pacific is associated with negative rainfall anomalies at Mistrató and positive rainfall anomalies at Berlin / Positive anomalies in the TNA index are associated with negative rainfall anomalies at Mistrató and positive anomalies at Berlin”. In my opinion, this analysis deserves a deeper exploration including some dynamical explanations, for instance, what are the dynamical mechanisms underlying in the strengthening/weakening of rainfall in the sampling points due to the heating/cooling of SST in tropical Pacific and Atlantic oceans?
- The first paragraph of the Discussion says precisely contrary to the ms presented in spectral analysis (lines 356 to 373). Please review, there may be a mistake in the use of parentheses for text simplification in this section or there is a mistake in the interpretation of power spectrum analysis. It could be useful to do a cross-spectra analysis between the El Niño 3.4 index and the TNA index.
- The discussion (and conclusion) is based on the idea that today's climate in western/eastern Colombia is comprehensively explained by the SST anomalies in the tropical Pacific and Atlantic oceans and so, the late Holocene Colombia’s climate, opposite to today's configuration (wet in the high elevations of the EC and dry in the WC) was caused by the increase in SST in the TNA and TP. I see several problems with this proposal. Just to illustrate: First, today's climate variability in Colombia is more complex than the SST anomalies in the tropical Pacific and Atlantic oceans explain. Second, today's time scale variability explored in the ms is in the range of interannual variability and the paleo records expand several orders of magnitude. How are the different time scales (dis)aggregated? The authors do not provide any dynamical explanation suitable to integrate the climate dynamics in today's-interannual variability.
Finally, these issues could be addressed through further revisions and additional work for a new submission. I encourage you to consider my feedback and revise the manuscript accordingly.
Citation: https://doi.org/10.5194/egusphere-2022-1428-RC1 -
AC1: 'Reply on RC1', Maria Velez, 21 Apr 2023
reply
We want to thank the Reviewer for very insinghful comments. We are currently addressing these in detail.
Citation: https://doi.org/10.5194/egusphere-2022-1428-AC1
Juan Mauricio Bedoya et al.
Juan Mauricio Bedoya et al.
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