the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Aug 2026
A paired marine-fluvial modern pollen dataset from the Bohai Sea and its inflowing rivers, China
Abstract. Modern marine pollen records can be interpreted reliably only when the main source-to-sink processes between terrestrial vegetation, rivers, and marine depocentres are documented by comparable modern data. Here, we present and quality-assess a paired marine-fluvial pollen dataset for the Bohai Sea, China, consisting of 430 marine surface-sediment samples and 104 fluvial surface-sediment samples from 16 major inflowing rivers. The dataset includes sample coordinates, water depth for marine stations, river and regional identifiers, pollen and spore counts, pollen concentrations, and grain-size parameters. In total, 104 pollen and spore morphotypes were identified. Marine assemblages are dominated by arboreal pollen, especially Pinus (mean 59 %), whereas nearshore and river-influenced settings contain higher proportions of herbaceous taxa, particularly Chenopodiaceae/Amaranthaceae-type (mean 14 %), Artemisia, and Poaceae. Redundancy analysis after variance-inflation-factor screening indicates that water depth is the strongest retained predictor of marine pollen composition (λ1/λ2 = 0.303), followed by geographic position and sediment texture. In river samples, geographic position, water discharge, and pollen concentration together explain 20.53 % of the compositional variance. Along the 0–35 m depth interval, arboreal pollen and Pinus increase with water depth, whereas herbaceous taxa decrease, providing an internally consistent modern analogue for distinguishing nearshore fluvial influence from more distal aeolian influence. The dataset is intended primarily as a reusable calibration and quality-assessment resource for palaeoenvironmental studies in the Bohai-Yellow Sea region. The archived data are available at the National Tibetan Plateau Data Center (TPDC; Li et al., 2026; https://doi.org/10.11888/Paleoenv.tpdc.303516).
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RC1: 'Comment on essd-2026-504', Anonymous Referee #1, 23 Aug 2026
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AC1: 'Reply on RC1', Shixiong Yang, 07 Sep 2026
The manuscript by Li et al., submitted to Earth System Science Data (ESSD), presents a very interesting and relevant study that contributes to improving the interpretation of marine pollen sedimentary sequences. The main conclusions highlight the importance of core location, particularly in shallow marginal seas such as the study area, for reliably interpreting the pollen signal.
Pollen records from shallow marginal seas can provide information about changes in water depth rather than solely reflecting changes in terrestrial vegetation. This is because both pollen sources and sediment recruitment mechanisms differ between fluvial and near-shore environments and more offshore settings, where pollen transport by wind may become increasingly important. The study provides a very useful paired marine–fluvial pollen dataset that, in my opinion, deserves publication in ESSD after some minor revisions, which I list below.
We thank the reviewer for the positive and constructive assessment of our manuscript and for recognizing the value of the paired marine–fluvial pollen dataset. We have carefully addressed all the comments point by point below and revised the manuscript accordingly. All changes are indicated in the revised manuscript.
Lines 18–19 – Could you also mention pollen and spore percentages?
Thanks for your thoroughness. We have added pollen and spore percentages to the list of archived variables in the Abstract, which now reads "pollen and spore counts and percentages, pollen concentrations, and grain-size parameters".
Lines 26–27 – Do you refer specifically to an increase in pollen percentage or to an increase in pollen concentration?
Thanks for requesting this clarification. The increases and decreases along the 0–35 m depth interval refer to pollen percentages (relative abundance), not concentrations. We have revised the Abstract to state "percentages" explicitly.
Line 37 – Please add “and surface and deeper oceanic currents”.
We agree and have added "surface and deeper oceanic currents" to the list of processes integrated by marginal-sea sediments in the Introduction.
Lines 59–66 – Are there no previous studies in the Bohai Sea region comparing terrestrial pollen sequences with marine pollen sequences? Such comparisons would provide another way to improve the interpretation of the marine pollen records from the Bohai Sea.
Thanks for this observation. While marine surface-sediment pollen (Yang et al., 2016a,b,c, 2019a, 2021) and alluvial pollen around the Bohai Sea (Yang et al., 2019b) have been published, they were released separately and lack a unified taxonomic framework or consistent processing protocol. The distinct value of our dataset lies in its integration of both marine and fluvial records into a single, harmonized, quality-assured, paired dataset. We have accordingly revised the Introduction to state this explicitly.
Figure 1 legend – Please explain the abbreviations used for the “Marine samples”.
Thanks for this suggestion. We have added additional explanations in the caption in Figure 1.
Table 1 – Please enlarge the characters, as they are currently too small to read comfortably.
We have enlarged the font size of Table 1 to improve its readability.
Lines 171–173 – Were the samples mounted in a mobile medium that allows the pollen grains to rotate, thereby facilitating their identification?
We thank the reviewer for this methodological point. Samples were mounted in glycerine jelly, a mobile medium that permits pollen grains to be rotated and examined from multiple orientations, which is essential for the reliable identification of pollen taxa, such as bisaccate taxa Pinus. We have added this detail to Section 3.2.
Lines 251–253 – Please add the reference to Naughton et al. (2007)*. This study also shows a decrease in pollen concentration from the coast towards the sea.
Naughton, F., Sanchez Goñi, M.F., Desprat, S., Turon, J.-L., Duprat, J., Malaizé, B., Joli, C., Cortijo, E., Drago,T., Freitas, M.C. (2007) Present-day and past (last 25,000 years) marine pollen signal off western Iberia. Marine Micropaleontology 62, 91-114.
We thank the reviewer for this suggestion. The recommended reference (Naughton et al., 2007) is highly relevant to our study, as it documents a similar coast-to-sea decrease in pollen concentration off western Iberia. We have incorporated it into the main text and the reference list accordingly.
Figure 4 – The characters in the legends are too small. Please enlarge them.
We have enlarged the legend fonts in Figure 4.
Line 376 – Please replace “Within this interval, AP and Pinus percentages increase significantly with water depth, whereas…” with “Pinus percentages increase significantly with water depth, whereas…”. The AP pollen percentages are strongly dominated by the Pinus pollen percentages, as shown by the statistical analyses. In contrast, Quercus and Betulaceae pollen percentages, which represent the two other most dominant arboreal taxa, decrease with water depth.
We thank the reviewer for this careful statistical observation. Since the arboreal pollen sum is overwhelmingly dominated by Pinus, reporting "AP and Pinus" together is redundant and potentially misleading—particularly because the other two main arboreal taxa, Quercus and Betulaceae, actually show a decreasing trend with water depth. We have therefore revised the sentence to report Pinus alone, and we now explicitly clarify that the overall arboreal increase is driven primarily by an increase in Pinus pollen, whereas Quercus and Betulaceae decline with depth.
Lines 419–422 – Please define the abbreviations “P/A” and “PB” in “PB/NAP”.
Agree. We have defined the abbreviations at their first occurrence: P/A is the Pinus/Artemisia ratio and PB/NAP is the ratio of bisaccate pollen to non-arboreal pollen.
Line 427 – MIS 2 includes the Last Glacial Maximum. Please rephrase this sentence to make this point clear.
We thank the reviewer for this correction. We have rephrased the sentence to clarify that the Last Glacial Maximum falls within MIS 2.
Line 428 – Please replace “MD982194” with “MD98-2194”.
We have replaced "MD982194" with the standard core designation "MD98-2194" throughout the manuscript.
Lines 425–432 – At what distance from the shore and at what water depth are cores DGKS9602 and MD98-2194 located? If these cores are from considerably deeper locations than 35 m, and if the river mouths remained relatively far from the cores during periods of low sea level, it would be difficult to interpret the statement that “ In core DGKS9602, P/A and PB/NAP ratios were used to infer changing shoreline distance, with lower ratios during MIS 2 and the Last Glacial Maximum and higher ratios during warmer high-sea-level intervals (Zheng et al., 2011). The MD982194 record similarly shows negative relationships between herbaceous pollen, freshwater algae, and sea level, whereas bisaccate taxa such as Pinus and Tsuga increase during interglacial or interstadial stages (Zheng et al., 2013).”
This relationship could instead reflect changes in terrestrial vegetation associated with cold and warm climatic conditions. Indeed, cold climates, low sea-level stands, and an increased contribution of herbaceous vegetation are generally closely coupled and may therefore produce similar pollen signals. Please provide additional information on the locations and water depths of the cores and discuss whether changes in terrestrial vegetation/climate could explain the observed pollen patterns.
We thank the reviewer for this insightful and important comment. We agree that pollen assemblages reflect the coupling signal of climate, sea-level stands, and vegetation changes. To further substantiate our viewpoint“Although the variation in pollen signals across different sea regions reflects the distinct sediment source contributions and depositional settings specific to each area, common and universal pollen signals and patterns still persist”, we have modified this paragraph accordingly.
Pollen records from the Okinawa Trough show that pollen assemblages exhibit regular alternating patterns between glacial and interglacial periods. During interglacials, saccate conifer pollen, represented by Pinus and Tsuga, overwhelmingly dominates. This high abundance corresponds to high sea‑level stands, when pollen is primarily derived from distant landmasses and transported over long distances by wind. In glacial stages, the contents of herbaceous pollen (e.g., Artemisia, Cyperaceae, Poaceae) and freshwater algae increase markedly. Particularly during the Last Glacial Maximum, when the shelf was largely exposed and the coastline retreated substantially, rivers could no longer supply sediment directly to the Okinawa Trough. Instead, the grassland and meadow vegetation developed on the exposed shelf became an important pollen source for the trough during glacial periods, leading to a significant increase in herbaceous pollen such as Artemisia and Chenopodiaceae in the trough sediments—a pattern that shows a strong negative correlation with sea‑level changes (Zheng et al., 2011, 2013). on glacial–interglacial timescales, the primary factor governing changes in sedimentary pollen assemblages and provenance in the Okinawa Trough or deep‑sea basins is shoreline migration caused by sea‑level fluctuations, and its signal intensity even exceeds that of climatic changes in the source areas themselves. Therefore, the P/A and PB/NAP variations in these cores therefore can be interpreted as an inferred measure of shoreline distance.
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AC1: 'Reply on RC1', Shixiong Yang, 07 Sep 2026
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RC2: 'Comment on essd-2026-504', Anonymous Referee #2, 02 Sep 2026
This manuscript by Jie Li and co-authors presents an extensive dataset of pollen samples from surface sediments in the Bohai Sea and the rivers that feed into it, investigating changes in pollen assemblages across these environments. The dataset is impressive, comprising more than 400 marine samples and over 100 river samples, and I applaud the authors for undertaking this thorough work.
The authors state that the primary application of this dataset is for paleoenvironmental studies in the Bohai-Yellow Sea region. However, this dataset provides valuable information on pollen transport from rivers to marine environments and will be of interest to marine palynologists globally. Overall, the manuscript is well written and I offer only a few minor comments below and in the annotated PDF that the authors may wish to consider to further strengthen the manuscript.
General comments:
- In Section 3.2, the authors state that a minimum of 200 terrestrial pollen grains were counted. Line 226 indicates that the number of grains counted per sample ranged from 59 to 1530, which is in contrast to the 200 grains stated in Section 2.3. Consider adding a sentence to the Methods describing why substantially more than 200 grains were counted in some samples.
- In Figure 2, the white circles represent the number of pollen grains counted. It would be more informative and conventional to present pollen concentrations as grains/g of sediment, particularly because sample weights varied by as much as 10 g.
- Consider writing more abbreviations in full. This would improve the manuscript's readability, especially in sentences containing several abbreviations, such as line 419: "lower AP/NAP, P/A, and PB/NAP ratios."
- The manuscript interprets the marine samples as being influenced by aeolian pollen transport, accounting for their higher proportions of Pinus and other arboreal pollen. Although wind likely is transporting pollen to the marine sites, the increase in Pinus and other saccate pollen also reflects their hydrodynamic transport efficiency relative to herbaceous taxa. Herbaceous pollen is more likely to settle from suspension near the coast, whereas Pinus and other saccate pollen may remain suspended in water and be transported farther offshore. The manuscript should therefore acknowledge that increased Pinus abundance does not necessarily indicate an exclusively aeolian source and may also result from fluvial and marine transport processes.
- Consider adding an additional figure/map that just has the names of the rivers and different bays in the Bohai Sea. For example, on line 274, “northern Liaodong Bay and Laizhou Bay”, the location of these bays is not shown on any map. Additionally, an overview map could be used to show the location of cores DGKS9602 and MD982194, which are mentioned in the text.
Comments on Figures:
Figure 1:
- The colour schemes for the bathymetry and vegetation are very intense. I would consider picking a less vibrant yellow for the cultivated vegetation in particular.
- The bathymetry transitioning to black between 50–300 m water depth is very abrupt, and the black colour is quite intense. Some of the samples fall within this bathymetric range, so the legend indicates that these could be anywhere between 50 and 300 m water depth. Consider using a colour scheme with a more consistent gradient across the full bathymetric range.
- Write the marine sample name abbreviations in full.
Figure 2:
- Change river names to white text to make it easier to read.
- Add a white background to the upper left corner plot and make the axes black to increase readability.
Figure 4:
- Text is too small and very blurry so I can not read this plot.
Figure 5:
- Make all heading text size the same.
- Increase text size for readability.
- Very blurry, although this may just be an issue with the PDF.
Figure 6:
- The pink and blue bars require axes or a brief description explaining what they represent.
- Increase the font size where possible. Alternatively, consider arranging the figure as two plots wide by three plots long so that it occupies approximately two-thirds of a page, which would improve readability.
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AC2: 'Reply on RC2', Shixiong Yang, 07 Sep 2026
This manuscript by Jie Li and co-authors presents an extensive dataset of pollen samples from surface sediments in the Bohai Sea and the rivers that feed into it, investigating changes in pollen assemblages across these environments. The dataset is impressive, comprising more than 400 marine samples and over 100 river samples, and I applaud the authors for undertaking this thorough work.
The authors state that the primary application of this dataset is for paleoenvironmental studies in the Bohai-Yellow Sea region. However, this dataset provides valuable information on pollen transport from rivers to marine environments and will be of interest to marine palynologists globally. Overall, the manuscript is well written and I offer only a few minor comments below and in the annotated PDF that the authors may wish to consider to further strengthen the manuscript.
We thank the reviewer for the careful and constructive evaluation of our manuscript and for the positive assessment of the dataset and its broader significance for marine palynology. We have revised the manuscript in response to every comment. Our point-by-point responses are given below; the reviewer's comments are reproduced in italic type and our responses follow each comment.
General comments:
In Section 3.2, the authors state that a minimum of 200 terrestrial pollen grains were counted. Line 226 indicates that the number of grains counted per sample ranged from 59 to 1530, which is in contrast to the 200 grains stated in Section 2.3. Consider adding a sentence to the Methods describing why substantially more than 200 grains were counted in some samples.
We thank the reviewer for this observation. Sorry for our imprecise descriptions. The 200-grain count is generally a minimum counting threshold of terrestrial pollen and spore, not an upper limit. For pollen-spore-rich samples, counting was extended beyond this threshold to stabilize percentage estimates of less abundant taxa and to reduce counting errors in pollen concentration estimates derived from the added Lycopodium spores. Samples that did not reach 200 grains were retained and flagged as low-count samples, as described in Section 4.1. We have accordingly added a clarifying sentence to Section 3.2 to make this explicit.
In Figure 2, the white circles represent the number of pollen grains counted. It would be more informative and conventional to present pollen concentrations as grains/g of sediment, particularly because sample weights varied by as much as 10 g.
We agree. Pollen concentration is normalized to sediment mass and is therefore directly comparable among samples, whereas raw counts are sensitive to the variable mass of sediment processed (10 to 20 g). We have redrawn Figure 2 to display pollen concentration (grains g−1 dry sediment) as the primary mapped variable.
The frequency distribution of pollen sums is retained as the inset histogram so that the counting effort and data quality remain documented, and the caption has been updated accordingly.
Consider writing more abbreviations in full. This would improve the manuscript's readability, especially in sentences containing several abbreviations, such as line 419: "lower AP/NAP, P/A, and PB/NAP ratios."
We have expanded all abbreviations at first use and simplified sentences that carried several abbreviations. In particular, AP (arboreal pollen), NAP (non-arboreal pollen), P/A (Pinus/Artemisia ratio) and PB/NAP (pollen with bladders / non-arboreal pollen ratio) are now defined at first use in Section 5.2, and the sentence in question has been rewritten for clarity.
The manuscript interprets the marine samples as being influenced by aeolian pollen transport, accounting for their higher proportions of Pinus and other arboreal pollen. Although wind likely is transporting pollen to the marine sites, the increase in Pinus and other saccate pollen also reflects their hydrodynamic transport efficiency relative to herbaceous taxa. Herbaceous pollen is more likely to settle from suspension near the coast, whereas Pinus and other saccate pollen may remain suspended in water and be transported farther offshore. The manuscript should therefore acknowledge that increased Pinus abundance does not necessarily indicate an exclusively aeolian source and may also result from fluvial and marine transport processes.
We thank the reviewer for raising this important point. We agree that the offshore enrichment of saccate grains such as Pinus is not solely attributable to aeolian input, but rather reflects the combined effects of atmospheric transport and hydrodynamic sorting (fluvial and marine), whereby buoyant grains are preferentially transported farther offshore than herbaceous taxa, which settle more readily near the coast. To clarify this, we have revised the Abstract, Sections 4.2, 4.3.2, and 5.1 to emphasize this dual-transport mechanism.
Consider adding an additional figure/map that just has the names of the rivers and different bays in the Bohai Sea. For example, on line 274, “northern Liaodong Bay and Laizhou Bay”, the location of these bays is not shown on any map. Additionally, an overview map could be used to show the location of cores DGKS9602 and MD982194, which are mentioned in the text.
We agree that a dedicated locator map enhances readability. Accordingly, we have revised Figure 1 in two ways. First, we have labeled the three bays (Liaodong, Bohai, and Laizhou), the Central Basin, and the Bohai Strait, along with the names of the sixteen inflowing rivers. Second, we have added an inset overview map that situates the Bohai Sea within the broader Bohai, Yellow Sea, and East China Sea region, and also indicates the locations of cores DGKS9602 and MD982194 from the Okinawa Trough.
L144“The main limitations of the dataset are that surface sediments integrate different time spans across settings”True but I don't think this is a major limitation! The oldest surface sample would only go back a few decades (I assume) and the local vegetation wouldn't have changed much in this time.
We apologize that our sedimentological information was is not rigorous enough. Although surface sediments in the Bohai Sea are dominated by modern fluvial input, small-scale relict deposits (late Pleistocene sediments) are distributed in the eastern Bohai.
Comments on Figures:
Figure 1:
- The colour schemes for the bathymetry and vegetation are very intense. I would consider picking a less vibrant yellow for the cultivated vegetation in particular.
- The bathymetry transitioning to black between 50–300 m water depth is very abrupt, and the black colour is quite intense. Some of the samples fall within this bathymetric range, so the legend indicates that these could be anywhere between 50 and 300 m water depth. Consider using a colour scheme with a more consistent gradient across the full bathymetric range.
- Write the marine sample name abbreviations in full.
We agree that a dedicated locator map improves readability. We have revised Figure 1 to label the three bays (Liaodong Bay, Bohai Bay, Laizhou Bay), the Central Basin and the Bohai Strait, together with the names of the sixteen inflowing rivers.
We have also added an inset overview map showing the Bohai Sea within the wider Bohai, Yellow Sea and East China Sea region, including the positions of the Okinawa Trough cores DGKS9602 and MD982194 cited in the text.
However, since the original data employ region‑specific sample point numbers that serve only to distinguish samples from different areas and carry no substantive meaning, we have clarified this in the figure caption and have omitted the full names.
Figure 2:
- Change river names to white text to make it easier to read.
- Add a white background to the upper left corner plot and make the axes black to increase readability.
We have changed the river name labels to white text against the map background for better contrast, and have given the upper-left inset a white background with black axes. As noted in our response to Comment 2, the main panel now displays pollen concentration, while the pollen-sum frequency distribution has been retained in the inset.
Figure 4:
- Text is too small and very blurry so I can not read this plot.
We have increased the font size throughout Figure 4 and exported it at a higher resolution to ensure that all taxon labels and axis text are clearly legible.
Figure 5:
- Make all heading text size the same.
- Increase text size for readability.
- Very blurry, although this may just be an issue with the PDF.
We have standardized the font size for all panel headings, increased the label sizes throughout to improve readability, and re-exported the figure at a higher resolution to eliminate blurring.
Figure 6:
- The pink and blue bars require axes or a brief description explaining what they represent.
- Increase the font size where possible. Alternatively, consider arranging the figure as two plots wide by three plots long so that it occupies approximately two-thirds of a page, which would improve readability.
We have added explicit axis labels and a legend to clarify the meaning of the pink and blue bars, enlarged the font size for better readability, and rearranged the six panels into a two-column by three-row layout. This configuration allows the figure to occupy approximately two-thirds of a page while maintaining clear legibility.
Was some sediment just scooped from your original sample bags? Was the sediment homogenized prior to sub-sampling? Consider explaining this a bit more.
We thank the reviewer for this comment. The sub-samples used for pollen and grain-size analyses were not scooped directly from the original storage bags. After field collection, each sample was kept in a sealed, labelled bag and returned to the laboratory, where the entire sample was homogenised by thorough mixing before sub-sampling. Representative aliquots were then withdrawn for pollen analysis (10 to 20 g dry weight) and grain-size analysis, so that the two measurements derive from the same homogenised material rather than from different portions of the bag. We have added a sentence to Section 3.2 to make this procedure explicit.
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The manuscript by Li et al., submitted to Earth System Science Data (ESSD), presents a very interesting and relevant study that contributes to improving the interpretation of marine pollen sedimentary sequences. The main conclusions highlight the importance of core location, particularly in shallow marginal seas such as the study area, for reliably interpreting the pollen signal.
Pollen records from shallow marginal seas can provide information about changes in water depth rather than solely reflecting changes in terrestrial vegetation. This is because both pollen sources and sediment recruitment mechanisms differ between fluvial and near-shore environments and more offshore settings, where pollen transport by wind may become increasingly important. The study provides a very useful paired marine–fluvial pollen dataset that, in my opinion, deserves publication in ESSD after some minor revisions, which I list below.
Lines 18–19 – Could you also mention pollen and spore percentages?
Lines 26–27 – Do you refer specifically to an increase in pollen percentage or to an increase in pollen concentration?
Line 37 – Please add “and surface and deeper oceanic currents”.
Lines 59–66 – Are there no previous studies in the Bohai Sea region comparing terrestrial pollen sequences with marine pollen sequences? Such comparisons would provide another way to improve the interpretation of the marine pollen records from the Bohai Sea.
Figure 1 legend – Please explain the abbreviations used for the “Marine samples”.
Table 1 – Please enlarge the characters, as they are currently too small to read comfortably.
Lines 171–173 – Were the samples mounted in a mobile medium that allows the pollen grains to rotate, thereby facilitating their identification?
Lines 251–253 – Please add the reference to Naughton et al. (2007)*. This study also shows a decrease in pollen concentration from the coast towards the sea.
Figure 4 – The characters in the legends are too small. Please enlarge them.
Line 376 – Please replace “Within this interval, AP and Pinus percentages increase significantly with water depth, whereas…” with “Pinus percentages increase significantly with water depth, whereas…”. The AP pollen percentages are strongly dominated by the Pinus pollen percentages, as shown by the statistical analyses. In contrast, Quercus and Betulaceae pollen percentages, which represent the two other most dominant arboreal taxa, decrease with water depth.
Lines 419–422 – Please define the abbreviations “P/A” and “PB” in “PB/NAP”.
Line 427 – MIS 2 includes the Last Glacial Maximum. Please rephrase this sentence to make this point clear.
Line 428 – Please replace “MD982194” with “MD98-2194”.
Lines 425–432 – At what distance from the shore and at what water depth are cores DGKS9602 and MD98-2194 located? If these cores are from considerably deeper locations than 35 m, and if the river mouths remained relatively far from the cores during periods of low sea level, it would be difficult to interpret the statement that “ In core DGKS9602, P/A and PB/NAP ratios were used to infer changing shoreline distance, with lower ratios during MIS 2 and the Last Glacial Maximum and higher ratios during warmer high-sea-level intervals (Zheng et al., 2011). The MD982194 record similarly shows negative relationships between herbaceous pollen, freshwater algae, and sea level, whereas bisaccate taxa such as Pinus and Tsuga increase during interglacial or interstadial stages (Zheng et al., 2013)..”
This relationship could instead reflect changes in terrestrial vegetation associated with cold and warm climatic conditions. Indeed, cold climates, low sea-level stands, and an increased contribution of herbaceous vegetation are generally closely coupled and may therefore produce similar pollen signals. Please provide additional information on the locations and water depths of the cores and discuss whether changes in terrestrial vegetation/climate could explain the observed pollen patterns.