|Review of revised manuscript “Signals of Holocene climate transition amplified by anthropogenic land-use changes in the Westerly-Indian Monsoon realm” by Burdanowitz et al.. The main thrust of this manuscript is to use high-resolution proxy records from the NE-Arabian Sea reflecting various aspects of Holocene monsoonal changes in the region. The main new data series include Uk37 based SST estimates, alongside a number of proxy time series (Ti/Al, endmember modelled aeolian input and lithogenics mass accumulation rates) reflecting lithogenic input in the region with the latter being of central importance. Based on these data the authors conclude that the Arabian Sea region around 4.6-3kaBP be- came more sensitive to changes in the tropical westerly jet controlling climate in the region. In addition, early agricultural activities in the region, may be reflected in the data. Compared to the initial version of the manuscript, there are areas of improvement in the revised manuscript. There are, however, still a number of issues which prevent recommending publication at this stage. Below there is a list of comments related to specific sections of the manuscript (line referencing based on version with track changes being highlighted). More generally, there are still too many occasions where the aspects focussed on the discussion are not properly described in the results sections and there seems to be some randomness with regard which events to discuss, despite the undiscussed events being of the same size. The results section should be expanded (including all the purely descriptive elements from the discussion). Also, the entire ENSO angle is rather unconvincing. It may help, in a revised version to remove this link and focus more on the change in vegetation. |
The list below is in random order or importance/gravity:
Lines 40-42 Can any of these things be proven. WD disturbances on which time scale do they occur? Can this be resolved in the existing data. How exactly are, probably short term changes in the STWJ affecting the ISM? This should be better explained.
Lines 130-131: It is not clear how this is supposed to work. First, what is the average and best resolution of the record. Second, there needs to be a much better explanation why it is justified (if it is) to "invent" data in a part of the record that does not have any measured data?
Line 143: 93 grain size classes between 10 and 3 mm??? - are there no small size classes in the sediments as would need to be expected in this region of the world ocean?
Line151-152: “High SSTs were registered between 8.1 and 5.2 ka BP during the Mid-Holocene.” This is not correct. There is a short term cool period centred at ~7.8 Ka BP. Also, how is the averaging done. Is this just, as stated, a five point moving average (without any time control) or a time controlled filtering (it should be the latter).
Lines 217-220 The link between the 8.2ka event and the G. ruber isotope data is unclear. Also, the Ti/Al ratio change is small and not quite in phase (it seems). This sections would benefit from a rewording.
line 245 “indicated by...” The end of this sentence does not make sense.
lines 248-250 The entire discussion surrounding SST/d18O-data is based on marginally significant data (i.e. most of the signal in either the Uk37 and the d18O ruber data is within the uncertainties for either method). There is some change in those records, but the discussion should also reflect that this is based on a small signal.
Line 253 It is unclear how a climate change in one direction leads to a two (opposite) changes in the early civilizations. Better to remove the link from the study or explain better (interpret jointly with other data in a section on anthropogenic change?).
Line 257 The statement is not correct. The LitMar data over the last 3ka are generally low with some superimposed spikes.
Lines 278 and following: The entire argument surrounding cross-equatorial insolation gradient as a driver for short term change in the record is weak. As the authors noted with regard to summer insolation, smooth changes in the latter are very unlikely to be the main cause for short term change. The gradient records are equally smooth and it is therefore not clear how these help to explain short term change in core SO90-63KA.
Lines 313-317 It is unclear which period is being referred to. In the first sentence a change between 4.2 and 3.5 ka is introduced. Thereafter, suddenly there is a reference to the period 7.5-3.5 kaBP -which is it?
Lines 338-354 This, again, is an unconvincing section. My understanding is that the authors try to discuss a non-finding, i.e. that there is not signal in the data that matches the ENSO signal. It would be better to remove the ENSO link entirely. First, in modern climate the link between ENSO and the ISM strength is complicated and not linear. Second, the change happens on times scales beyond the scope of the study and thirdly, the data of core SO90-63KA do not support a link. It therefore does not seem to make much sense to include a rather long discussion surrounding ENSO in the manuscript.
As indicated above, the manuscript has improved but it is still not in a state supporting publication at this stage. A further revision is recommended.