General comments

By focussing on interglacial forests during TV, the authors are looking for explaining reasons for low CO₂before the MBE. The combination of three steps (new data, data compilation and modelling) makes for an interesting manuscript, deserving publication.

The grain size of pollen is nor clay but silt and fine sand (line 94).

Lines 94-96: explain briefly why it reflects more the Guadalquivir? Is it a question of current? The paper you mention is not available yet at the time of this review.

Despite the justification proposed, the sum of 100 terrestrial pollen grains remains very low, and I cannot see how your % are stable with such a low sum. I would recommend that you increase your counts and reach a total terrestrial sum of 300, and a sum without Pinus of 150-200. Please provide clearly the sums used for terrestrial pollen for each sample, and also the sums without Pinus. So the reader can estimate himself/herself the quality of your data.

You should anyway delete the sentence “the more pollen counted, the better the concentration estimates are” as you do not seem to follow this recommendation.

Is the “200 grains” of Rull without Pinus?

Although this manuscript is on TV, adding a few more samples at the top of the diagram until the start of the following glacial (thus covering all types of forests), would provide you with the end of the interglacial and give you a more complete and satisfying view of MIS11 forests. This is only a suggestion.

Table 1: “fern spores” are unexpected proxy for forest. Please explain the rationale. ODP 658 is in front of the Sahara that was already developed in TV.

Section 3.1: is there a change in lithology at the transition between pollen zones 1 and 2? Could this be the reason for the high amount of oxidation-resistant Taraxacum?

Figure 2: add a lithological log to the left of the diagram. Line 93 suggests that it has changed over time over the whole core. What is the case for the portion of the core you studied?

Line 351: “Forests are reliable proxies for terrestrial biosphere”. Please develop here. How much is this group better than swamps or other groups? provide figures/numbers if possible.

The text needs to be improved as it feels at times like a literal translation of French. It also contains with quite a few typos. Some of them were corrected in the annotated manuscript.

Throughout the manuscript I would recommend being more restrictive with the use of the word “event”, and keeping it only for very brief changes. In many instances, it could be replaced by, for example, “period”.

Points of details

Pollen/cm³: add superscript (eg lines 230, 271).

In section 2 besides fig.1, in most cases, it is not necessary to call to figures. This will facilitate figures calling in a logical order, later on.

Fig. 5a and 5b should be reversed. First the map, then the records.

Line 301: explain briefly here what SINES is (i.e. a forest phase …).

In the text: the family names of plants should not be in italics, e.g. Cupressaceae, Poaceae. Moreover check their spelling.

Add the position of TV on figures 2, 3, and S2.

The reference format for the main text and the SI needs to be homogenised and adapted to the journal requirements.

See the annotated manuscript for further comments.

In this manuscript Hes et al. studied the pollen as a proxy for forest development and paleoclimate from the 433-405 kyr time span from a deep-sea marine sediment core from the Gulf of Cadiz (IODP Site U1386). This study then deals with a very interesting period in Earth history during the mid-Bruhnes transition: Termination V - the transition from Marine Iso­tope Stage MIS12 to MIS11, which was characterized by the largest de­glaciation of the late Pleistocene, and by one of the warmest and longest interglacials of the Pleistocene, MIS11.  

Another particular feature of MIS 11 is that an early CO₂ peak, usually associated to the deglaciation in response to increasing temperatures, fails to be detected. Therefore, all these questions make this study of great interest to researchers working on paleoclimate and modelers forecasting future climate scenarios.   

From all this, I think this is an interesting study but I have major concerns that should be dealt before publication:

1. My main concern is the overinterpretation of the data. This study is too ambitious and the conclusions obtained about the CO₂ mitigation by high-latitude forests are barely justified by the scarce data available for this time-span. In particular, only two records including the one studied here are available for the Mediterranean forest group and the resolution (and thus accuracy) of the pollen analyses are not that great either (700-yr in this study and even lower in site U1385). The statement about that Mediterranean forest development wasn’t thus important in the CO₂ mitigation is in my opinion very risky. More discussion about this should be added and/or the language should be toned down.
2. Regarding the site groupings done for the different pollen sites covering the selected time span, it looks to me that it was done with a very loose criterium. For example, in the “Euroasian” group, records from all over this area were chosen including records characterized by very distinct climate requirements such as Chinese records very conditioned by monsoon or other climate patterns. Also, the taxa used to represent the pollen record are very random; sometimes using single species and other times using group of taxa.

In this respect, why the two Mediterranean sites were separated from the Eurasian group? Aren’t they also located in Euroasia?

Tropical and South African records show very ambiguous signals during the deglaciation with maxima around 430 kyr (see Fig. 5) – could they also be involved in the CO₂ mitigation during TV?   

3. The authors focus on Termination V (TV, see for example manuscript title), however in reality the authors not only focus on that deglaciation that should have occurred relatively fast - I read in other papers between 427-424 kyr; see for example Hodell et al., 2003 - but also on MIS11 (see Fig. 3 also picturing MIS11e, d and c) and fail to give a clear picture of the time period that they are really focusing on in this study. Therefore, a clear definition of the TV period should be given and should also be shown in the different figures.
4. Sometimes it is confusing where the authors are placing the beginning of MIS11 interglacial in their pollen record and should be clarified. In Fig. 3 it is placed when the “ubiquist” group enhanced but in Fig. 2 it is placed when the Mediterranean taxa increased (pollen zone 2b). Please be consistent.

By the way, what is SINES? The definition should be added to the text and figures.

5. It is interesting to see that the “warm foraminifera” are also delayed with respect to the isotopic data. Does this also mean that the marine environment in this area didn’t react to this climate change that fast either?
6. Where is the dashed black line in fig. 8?
7. The resolution is too low to resolve submillennial-scale changes (see conclusions).
8. The pollen records studied here suggest a moderate warming during MIS11, disagreeing with the statement in the conclusions “The strong warming at the onset of MIS11…” Please add more discussion about this.

Hes et al. present new palynological data from the Iberian Margin (IODP Site U1386) spanning Termination V (TV; i.e., MIS 12/11 transition) and evaluate the effect of terrestrial biosphere on the atmospheric CO₂ concentrations using model simulations in which they include other available, globally distributed pollen records from this interval. This is an important dataset that fills in a critical gap in the palynological records off Iberia, and hence it merits publication. On the other hand, however, there are important methodological caveats related to set up of the study that preclude publication of the manuscript in its current form. As it currently stands, I find the interpretation of the results premature, and hence, I refrain from commenting on it before the points below are addressed by the authors in a revised version.

Study interval

The focus of the manuscript is on TV, which according to the authors it spans the period between 433 and 404 kyr BP (line 39). This is wrong (e.g., see the duration of glacial terminations in the Chinese speleothem record by Cheng et al., 2016). What the authors consider as TV actually spans almost the entire MIS 11c interglacial. If the authors decide to consider the entire period 433-404 kyrs, then they should also include several other palynological records that span MIS 11c, and re-run the model simulations. Please also note that there is at least one more model study that focuses on terrestrial biome simulations for MIS 11­–12 (Kleinen et al. 2011), which the authors should consider and elaborate on in a revised manuscript.

Pollen records database

In contrast to the authors’ argument (line 174), there exist many more pollen records that span TV and aren’t included in this work. For instance, Ioannina (Tzedakis 1994), Heqing (Xiao et al. 2010, An et al. 2011), Lake Baikal (Prokopenko et al. 2010), Lake Biwa (Tarasov et al. 2011), Praclaux (de Beaulieu et al. 2001) and Valles Caldera (Fawcett et al. 2011) among others. In addition, higher temporal resolution data exist for some of the pollen records included in this manuscript (e.g. Lake Ohrid ­– Kousis et al. 2018, Koutsodendris et al. 2019, and Tenaghi Philippon – Ardenghi et al. 2019); these should be also included in the analysis. Moreover, the study by Dupont et al. (2011) included in Table 1 doesn’t span MIS11/12; do the authors refer to Dupont et al. (2019)?

Lithology and pollen concentration

The authors explain that the study samples are taken from a core interval that comprises a ‘unique contourite’ affected by the Mediterranean Outflow Water (MOW) (lines 91-92). The question that arises is to what extent the changes in the MOW strength influence the transport and deposition of pollen grains at the study location. To convincingly show that the palynological results aren’t affected by ocean dynamics, the pollen sums and concentrations should be directly compared with the grain size and XRF data from Site U1386 that record the MOW variability. Only then it will be possible to conclude that even pollen sums of 100 grains can provide reliable insights on terrestrial vegetation at the study site.

Pollen groups

Please explain in a more concise way which pollen taxa are included in each group (lines 140-143 are very confusing). Is it correct that Betula is included in two groups, i.e., Mediterranean and Pioneer forests? Please explain. Also, shouldn’t Populus and Salix be included in the Pioneer Forest group? Which taxa are included in the Ubiquist group?

Other comments:

• Please carefully check and correct the spelling of the pollen taxa names (several taxa e.g., Helianthemum, Hippophaë, and Cupressaceae are misspelled many times in the text).
• Consider the latest, higher resolution CO₂ data from the EDC ice cores for the interval 330-450 kyr BP (Nehrbass-Ahles et al. 2020).

References

An, Z., et al., 2011. Glacial-interglacial Indian summer monsoon dynamics. Science 333, 719-723.

Ardenghi, N., et al., 2019. Temperature and moisture variability in the eastern Mediterranean region during Marine Isotope Stages 11–10 based on biomarker analysis of the Tenaghi Philippon peat deposit. Quaternary Science Reviews 225, 105977.

Cheng, H., et al., 2016. The Asian monsoon over the past 640,000 years and ice age terminations. Nature 534, 640-646.

de Beaulieu, J.L., et al., 2001. An attempt at correlation between the Velay pollen sequence and the Middle Pleistocene stratigraphy from central Europe. Quaternary Science Reviews 20, 1593–1602.

Dupont, L.M., et al., 2019. Effects of atmospheric CO₂ variability of the past 800 kyr on the biomes of southeast Africa. Climate of the Past 15, 1083-1097.

Fawcett, P.J., et al., 2011. Extended megadroughts in the southwestern United States during Pleistocene interglacials. Nature 470, 518-521.

Kleinen, T., et al., 2014. The climate and vegetation of Marine Isotope Stage 11 – Model results and proxy-based reconstructions at global and regional scale. Quaternary International 348, 247-265.

Nehrbass-Ahles, C., et al., 2020. Abrupt CO₂ release to the atmosphere under glacial and early interglacial climate conditions. Science 369, 1000-1005.

Kousis, I., et al., 2018. Centennial-scale vegetation dynamics and climate variability in SE Europe during Marine Isotope Stage 11 based on a pollen record from Lake Ohrid. Quaternary Science Reviews 190, 20-38.

Koutsodendris, A., et al., 2019. The Marine Isotope Stage 12 pollen record from Lake Ohrid (SE Europe): Investigating short-term climate change under extreme glacial conditions. Quaternary Science Reviews 221, 105873.

Prokopenko, A.A., et al., 2010. Climate in continental interior Asia during the longest interglacial of the past 500 000 years: the new MIS 11 records from Lake Baikal, SE Siberia. Climate of the Past 6, 31-48.

Tarasov, P.E., et al., 2011. Progress in the reconstruction of Quaternary climate dynamics in the Northwest Pacific: A new modern analogue reference dataset and its application to the 430-kyr pollen record from Lake Biwa. Earth-Science Reviews 108, 64-79.

Tzedakis, P.C., 1994. Vegetation change through glacial-interglacial cycles: a long pollen sequence perspective. Philosophical Transactions B Society London 345, 403-432.

Xiao, X., et al., 2010. The variation of the southwest monsoon from the high resolution pollen record in Heqing Basin, Yunnan Province, China for the last 2.78 Ma. Palaeogeography, Palaeoclimatology, Palaeoecology 287, 45-57.