Summary 

This study focusses on understanding the seasonal cycle of Sea Surface Temperature (SST) in the tropical Angolan Upwelling System and in particular look at the processes responsible for an increased cross-shore SST gradient in winter. To do so, the authors analyse the seasonal mixed layer heat budget using satellites and reanalysis datasets in two boxes: at the coast and offshore. By comparing the temperature rate of change to the surface heat fluxes, horizontal advection and residual, they found (1) a strong contribution of the surface heat fluxes that sets the seasonal cycle counterbalance by (2) a significant contribution of the residual; (3) The contribution of the horizontal advection is shown to be minor. Interestingly, the cooling contribution of the residual is larger near the coast than offshore suggesting a key role of the residual in driving the increased SST cross-shore gradient in winter. Turbulent heat fluxes estimated from shipboard measurements show a strong cooling effect of turbulent mixing, which is particularly strong at the coast. This process might explain the increased cross-shore SST gradient.  

This is an important topic, and the paper is well-structured and clear. I do have reservations about the large uncertainties that might exist due to the use of various datasets, the gaps between data resolutions and the contribution of the other processes included in the residual but the major points are well discussed in the discussion and the main conclusions of the paper are still valid. There are a few general remarks and minor corrections of the text that I feel that the authors should address, but overall, it is a substantive piece of work of good quality and worthy of publication. 

General Remarks 

Introduction: L30-35. When reading the introduction, I will have found it nice to see a plot with the seasonal cross-shore SST gradient and primary productivity (the paper's main motivation). Maybe, as a last subplot of Fig. 1?  

Introduction: L45 to 61. In this part of the introduction, you describe the SST seasonal cycle, emphasizing that the latter cannot be explained by the upwelling-favourable winds. What about the net heat flux that I guess is a major contributor to the seasonal cycle SST in the tAUS?  

L160-163: Why did you decide to interpolate variables with coarser resolution onto a higher resolution grid? Usually, the inverse is done to prevent the generation of fake information. How much do you think this might affect the contribution of mean horizontal advection?  

L254 – It is interesting that the SW is higher in the coastal box than in the offshore box. I will have thought the contrary due to the important cloud cover along the coast. Do you think that the bias in the SW could be more important along the coast?  

Figure8: From the figure, it seems that the rate of change in winter is more negative offshore than inshore (except for April maybe). Should not be the cooling stronger at the coast, resulting in an increased SST cross-shore gradient in winter. Could you provide a plot showing the difference of heat content change in the two boxes?  

Discussion: L494 onward: What about the other processes constrained in the residual (entrainment, vertical temperature velocity covariance)? They also represent an uncertainty for the contribution of the turbulent heat to the net budget that is not discussed here. In literature, are there studies that have shown that their contribution could be neglected?  

Also, I wonder how much the contribution of the mean advection is smoothed (due to their low spatial and temporal resolution) compared to the turbulent heat loss derived using high resolution data. Are the terms comparable?

Overall document: In overall, I suggest to re-check the punctuation and the various acronyms in the text. For example, I found several times the term mixed layer instead of “ML”. 

Line by Line Comments 

L40, 53 Same sometime to define acronym you use capital letters, sometime no. To me it is better to do, one or the other 

L8 – remove “the” before strongest 

L17 - “This turbulent cooling, strongest in shallow shelf regions, can explain the observed negative cross-shore temperature gradient.” 

L66 – Acronym not defined – it is defined later at L78. 

L21- southeast to be consistent with the rest of the draft 

L26 – “extent” instead of “extend” 

Figure1 – Please add the arrow length on the figure 

L65 – AC instead of Angola Current 

L66, 67: Maybe here you want to use the acronyms you defined (SSS/SST) 

L76- shows 

L77-helps to reduce errors. 

L89 – sections 

L118 – mentioned 

L120- radiations 

L123 - fluxes 

L128 – SST analyses are 

L131 – decide if you prefer near-surface or near surface for consistency 

L135 – remove coma 

L140 – remove “the” 

L160 – extent instead of extend 

L161 – resolutions 

L169 - ‘by’ applying 

L172 - parts 

L173 - exponentials 

L173 – MLD 

L189 - provided 

L190 – are used to 

L215 – is calculated instead of are calculated 

L217 – level 

L220 – The arrow  

L228 – impacting 

L229 - analysis 

L236 – The black line shows or Black lines show 

L240 – Surface heat fluxes show 

L251- increased wind speed away from the … leads 

L255 – dampen 

L257 – in the coastal 

L261 – decreases 

L268 – is generally weak 

L271 – AC 

L274 – centered 

L275 – annually averaged 

L288-290 - , microstructure profiles available in this study (section 2.1) indicate instead of “the microstructure profiles available to this study (section 2.1) indicates” 

L297 – to the coast 

L299 - “close to” or “at the surface” 

L318 – “Results in Fig. 7 clearly show” instead of “The results in Fig. 7 clearly shows” 

L321 - exhibits 

L327 – strengths 

L331 – contributes 

L339 – In shallow water, fluxes … 

L343-345: Here the sentence could be reformulated 

L347 – exhibit 

L349 – a possible explanation 

L365 - and is only 

L383-384 – Microstructure profiles suggest 

L388 – revealed large differences in monthly averaged .. 

L404/405 – As the warming [...], the resulting 

L406 – dampen 

L407 – Do you mean Austral winter? 

L408- The mean […] to the warming  

L413 – to the coast 

L417 – twice as large as in the offshore box 

L436 - exhibits 

L447 – acts to dampen 

L454 – suggest 

L464 - show 

L466 – the breaking 

L467 – values 

L477 – suggests 

L479 – in this context are  

L494 – Results […] show 

L496 – represents 

L511 – datasets 

Figure A. 2: Correct the title of sensible heat flux; Be consistent in the paper for shortwave / longwave  

L532, 534, 535, 538 – exhibits, reveals, shows, differs 

L547 – in better agreement with 

L559 – “than” instead of “then” 

L564 – PIRATA-SEE instead of TropFlux 

Figure A.3 - In the legend of the figure add a description of the Net flux. 

L570 – The smallest 

L578 – A minimum southward velocity 

L605 – the institute