Distinct Phytoplankton Responses to Dust in the Chinese Marginal Seas: Role of Synoptic Circulation and Air&ndash;Sea Heat Exchange

Hu, Jiehua; Tian, Rong; Yan, Jinpei; Zhang, Xiaoke; Wang, Shanshan; Sun, Heng; Xu, Hanyue; Shen, Shiyu; Zeng, Qisheng

doi:10.5194/egusphere-2026-2018

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https://doi.org/10.5194/egusphere-2026-2018

Preprints

18 May 2026

| 18 May 2026

Distinct Phytoplankton Responses to Dust in the Chinese Marginal Seas: Role of Synoptic Circulation and Air–Sea Heat Exchange

Jiehua Hu, Rong Tian, Jinpei Yan, Xiaoke Zhang, Shanshan Wang, Heng Sun, Hanyue Xu, Shiyu Shen, and Qisheng Zeng

Abstract. East Asian dust outbreaks are accompanied by pronounced synoptic circulation anomalies, yet their influence on phytoplankton variability through atmospheric forcing remains poorly understood. Here we investigate the response of chlorophyll-a (Chl-a) to spring dust optical depth (DOD) in the Chinese marginal seas during 2003–2023 using daily anomalies from reanalysis products and a reconstructed Chl-a dataset. We find contrasting Chl-a responses to DOD between the Northern and Southern Chinese marginal seas. The Northern Region exhibits an initial Chl-a suppression followed by a positive anomaly persisting for about one week, while the south shows an immediate positive response that gradually weakens. These distinct patterns are associated with ocean mixed-layer depth (MLD) adjustments driven by dust-related synoptic circulation. Over the northern seas, Mongolian cyclones produce positive air–sea temperature and humidity gradients through anomalous southerly winds, thus reducing upward latent and sensible heat fluxes and promoting net ocean heat gain and initial mixed-layer shoaling before subsequent deepening. In contrast, southern dust events are associated with migrating anticyclones that drive strong northeasterly winds, generating negative air–sea thermal and moisture gradients and intensified upward latent heat flux, thereby promoting net ocean heat loss and mixed-layer deepening. Net surface heat flux exhibit the strongest negative correlation with MLD at a one-day lag in both regions, and surface heat loss-driven mixed-layer deepening generally coincides with elevated Chl-a anomalies. These results highlight synoptic-scale atmospheric forcing and air–sea heat exchange as important physical pathways linking dust variability to short-term Chl-a changes in the Chinese marginal seas.

Received: 09 Apr 2026 – Discussion started: 18 May 2026

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Journal article(s) based on this preprint

20 Aug 2026

Distinct phytoplankton responses to dust in the Chinese marginal seas: role of synoptic circulation and air–sea heat exchange

Jiehua Hu, Rong Tian, Jinpei Yan, Xiaoke Zhang, Shanshan Wang, Heng Sun, Hanyue Xu, Shiyu Shen, and Qisheng Zeng

Biogeosciences, 23, 5697–5714, https://doi.org/10.5194/bg-23-5697-2026,https://doi.org/10.5194/bg-23-5697-2026, 2026

Short summary

Jiehua Hu, Rong Tian, Jinpei Yan, Xiaoke Zhang, Shanshan Wang, Heng Sun, Hanyue Xu, Shiyu Shen, and Qisheng Zeng

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2026-2018', Anonymous Referee #1, 02 Jun 2026
The manuscript investigates the contrasting chlorophyll-a responses to spring dust events in the Chinese marginal seas and highlights the potential role of dust-related synoptic circulation and air–sea heat exchange. The topic is interesting and relevant to both atmospheric and marine biogeochemical communities. The manuscript is generally well organized, and the analyses provide useful insights into the coupling between synoptic forcing, upper-ocean mixing, and phytoplankton variability. However, there are several issues that require the author to provide detailed explanations or clarifications. The manuscript is recommended for publication after the following revisions and clarifications are addressed.
Major Comments:
The applicability and uncertainty of the OCNET reconstructed Chl-a dataset should be described in more detail. Although the manuscript provides the overall reconstruction accuracy (R²=0.93), additional information regarding the methodology and data sources of the OCNET product would help improve the clarity of the dataset and its suitability for this study. In particular, since the OCNET framework incorporates multiple environmental variables and reanalysis fields as predictors, it would be useful to further clarify which variables and datasets were used in the reconstruction process and to discuss the potential uncertainties associated with applying such a reconstructed product to synoptic-scale analyses. A brief discussion and more details in the Data and Methods or Discussion section would strengthen the robustness of the study. If possible, an additional comparison with satellite products or validation results within the study regional area would further support the robustness of the findings.

The role of dust versus dust-related synoptic circulation should be clarified. The manuscript primarily emphasizes synoptic-scale atmospheric circulation anomalies, air–sea heat exchange, and mixed-layer responses associated with dust outbreaks. In this regard, some of the phrasing in the manuscript may benefit from placing more emphasis on the role of dust-related synoptic forcing, rather than the direct physical and chemical effects of dust aerosols. A clearer description of how the observed Chl-a anomalies are linked to the accompanying synoptic conditions during dust events, rather than solely to dust aerosol loading itself, would help strengthen the overall conceptual clarity of the study, particularly in the Abstract, Introduction, and Conclusions sections. Some related wording and phrasing are also provided in the minor comments below.

Clarification of statistical significance testing for daily correlations. Some parts of the manuscript (e.g., Fig. 2) present daily lag correlations between DOD and Chl-a anomalies. Since daily atmospheric and oceanic variables often exhibit temporal autocorrelation, the significance testing should consider the effect of reduced effective degrees of freedom. Was the autocorrelation-adjusted significance test taken into account? A clarification of statistical significance testing for daily correlations should be included to enhance the robustness of the statistical analysis.

Minor Comments:
Line 11: “Here we investigate the response of chlorophyll-a (Chl-a) to spring dust optical depth (DOD)” suggest to be revised to “investigate the response of chlorophyll-a (Chl-a) to spring dust events, characterized by dust optical depth (DOD),” since DOD is primarily a metric rather than the forcing itself.

Line 13: “We find contrasting Chl-a responses to DOD” may place too much emphasis on DOD itself as the direct driver. Consider revising to “We find contrasting Chl-a responses to dust synoptic events” or “We find contrasting relationships between Chl-a anomalies and DOD”.

Line 21: “Net surface heat flux exhibit the strongest negative correlation” should be revised to “Net surface heat flux exhibits the strongest negative correlation.”

Line 57: “though the response vary depending on” should be revised to “though the response varies depending on.”

Line 62: Consider revising “In addition to the direct nutrient supply associated with dust deposition...” to “Beyond the direct biogeochemical pathway of nutrient supply...” to improve the transition from biogeochemical effects to physical mechanisms.

Lines 74–75: “This study examines the response of Chl-a to spring dust variability” may be revised to “This study examines the response of Chl-a to synoptic atmospheric forcing associated with spring dust events.”

Line 94: The sentence “The net surface heat flux (Qnet) was calculated as the sum of these four components and is defined as positive downward” contains inconsistent tense usage. Consider revising to “The net surface heat flux (Qnet) is calculated as the sum of these four components and is defined as positive downward.”

Line 129, Figure 2: Please check and clarify whether temporal autocorrelation was considered in the significance testing.

Line 133: Terms such as “Northern Region/northern region” and “Southern Region/southern region” appear inconsistently capitalized throughout the manuscript. Please check and revise the formatting.

Line 175: “These contrasting temporal patterns suggest that the Chl-a response to dust differ substantially between the two regions” should be revised to “the Chl-a response to dust differs substantially between the two regions.”

Line 98: Consider including some references that have applied this product (GMEMS) in MLD studies, particularly over marginal seas.

Line 230: The term “dust onset” may not be fully appropriate, especially for multi-day dust events. Since lag 0 appears to correspond more closely to the DOD peak day rather than the actual initiation of the event, please consider using terms such as “dust-event day”, “peak dust day” for improved clarity and precision.

Line 382, Figure 10: The manuscript uses the 95% significance level in most analyses, whereas Figure 10 adopts the 99% significance level. Please consider using consistent significance criteria throughout the manuscript, or clarify the reason for using different thresholds. In addition, please check and clarify whether the significance testing accounts for the potential influence of temporal autocorrelation.

Line 368: “deeper mixing facilitates upward nutrient entrainment and promotes phytoplankton growth”, suggest revising to "promotes phytoplankton biomass accumulation" or “favors elevated Chl-a concentrations”, since the analysis is of Chl-a anomaly variability.

Lines 386–387: “This study examines how spring dust events influence daily Chl-a anomalies” may be revised to “This study examines how synoptic atmospheric forcing accompanying spring dust events influences daily Chl-a anomalies.”

Line 395: “These findings highlight the role of dust-associated atmospheric forcing in modulating short-term phytoplankton variability through air–sea heat exchange and upper-ocean mixing, and provides an insight into ecosystem responses” should be revised to “and provide an insight into ecosystem responses.”

Several abbreviations are defined more than once in the manuscript. For example, DOD, MLD and SST are defined in the Abstract, Data and Methods section but re-defined in the Results section. Please ensure each abbreviation is defined only at its first occurrence and used consistently thereafter.
Citation: https://doi.org/10.5194/egusphere-2026-2018-RC1
- AC1: 'Reply on RC1', Rong Tian, 09 Jul 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2018/egusphere-2026-2018-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2026-2018-AC1
RC2:
'Comment on egusphere-2026-2018', Anonymous Referee #2, 30 Jun 2026

attached

Citation: https://doi.org/10.5194/egusphere-2026-2018-RC2
- AC2: 'Reply on RC2', Rong Tian, 09 Jul 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2018/egusphere-2026-2018-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2026-2018-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Submit a revised manuscript (13 Jul 2026) by Emilio Marañón

AR by Rong Tian on behalf of the Authors (14 Jul 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (21 Jul 2026) by Emilio Marañón

RR by Anonymous Referee #2 (24 Jul 2026)

RR by Anonymous Referee #1 (30 Jul 2026)

ED: Publish as is (04 Aug 2026) by Emilio Marañón

AR by Rong Tian on behalf of the Authors (10 Aug 2026) Manuscript

Interactive discussion

Status: closed

RC1:
'Comment on egusphere-2026-2018', Anonymous Referee #1, 02 Jun 2026
The manuscript investigates the contrasting chlorophyll-a responses to spring dust events in the Chinese marginal seas and highlights the potential role of dust-related synoptic circulation and air–sea heat exchange. The topic is interesting and relevant to both atmospheric and marine biogeochemical communities. The manuscript is generally well organized, and the analyses provide useful insights into the coupling between synoptic forcing, upper-ocean mixing, and phytoplankton variability. However, there are several issues that require the author to provide detailed explanations or clarifications. The manuscript is recommended for publication after the following revisions and clarifications are addressed.
Major Comments:
The applicability and uncertainty of the OCNET reconstructed Chl-a dataset should be described in more detail. Although the manuscript provides the overall reconstruction accuracy (R²=0.93), additional information regarding the methodology and data sources of the OCNET product would help improve the clarity of the dataset and its suitability for this study. In particular, since the OCNET framework incorporates multiple environmental variables and reanalysis fields as predictors, it would be useful to further clarify which variables and datasets were used in the reconstruction process and to discuss the potential uncertainties associated with applying such a reconstructed product to synoptic-scale analyses. A brief discussion and more details in the Data and Methods or Discussion section would strengthen the robustness of the study. If possible, an additional comparison with satellite products or validation results within the study regional area would further support the robustness of the findings.

The role of dust versus dust-related synoptic circulation should be clarified. The manuscript primarily emphasizes synoptic-scale atmospheric circulation anomalies, air–sea heat exchange, and mixed-layer responses associated with dust outbreaks. In this regard, some of the phrasing in the manuscript may benefit from placing more emphasis on the role of dust-related synoptic forcing, rather than the direct physical and chemical effects of dust aerosols. A clearer description of how the observed Chl-a anomalies are linked to the accompanying synoptic conditions during dust events, rather than solely to dust aerosol loading itself, would help strengthen the overall conceptual clarity of the study, particularly in the Abstract, Introduction, and Conclusions sections. Some related wording and phrasing are also provided in the minor comments below.

Clarification of statistical significance testing for daily correlations. Some parts of the manuscript (e.g., Fig. 2) present daily lag correlations between DOD and Chl-a anomalies. Since daily atmospheric and oceanic variables often exhibit temporal autocorrelation, the significance testing should consider the effect of reduced effective degrees of freedom. Was the autocorrelation-adjusted significance test taken into account? A clarification of statistical significance testing for daily correlations should be included to enhance the robustness of the statistical analysis.

Minor Comments:
Line 11: “Here we investigate the response of chlorophyll-a (Chl-a) to spring dust optical depth (DOD)” suggest to be revised to “investigate the response of chlorophyll-a (Chl-a) to spring dust events, characterized by dust optical depth (DOD),” since DOD is primarily a metric rather than the forcing itself.

Line 13: “We find contrasting Chl-a responses to DOD” may place too much emphasis on DOD itself as the direct driver. Consider revising to “We find contrasting Chl-a responses to dust synoptic events” or “We find contrasting relationships between Chl-a anomalies and DOD”.

Line 21: “Net surface heat flux exhibit the strongest negative correlation” should be revised to “Net surface heat flux exhibits the strongest negative correlation.”

Line 57: “though the response vary depending on” should be revised to “though the response varies depending on.”

Line 62: Consider revising “In addition to the direct nutrient supply associated with dust deposition...” to “Beyond the direct biogeochemical pathway of nutrient supply...” to improve the transition from biogeochemical effects to physical mechanisms.

Lines 74–75: “This study examines the response of Chl-a to spring dust variability” may be revised to “This study examines the response of Chl-a to synoptic atmospheric forcing associated with spring dust events.”

Line 94: The sentence “The net surface heat flux (Qnet) was calculated as the sum of these four components and is defined as positive downward” contains inconsistent tense usage. Consider revising to “The net surface heat flux (Qnet) is calculated as the sum of these four components and is defined as positive downward.”

Line 129, Figure 2: Please check and clarify whether temporal autocorrelation was considered in the significance testing.

Line 133: Terms such as “Northern Region/northern region” and “Southern Region/southern region” appear inconsistently capitalized throughout the manuscript. Please check and revise the formatting.

Line 175: “These contrasting temporal patterns suggest that the Chl-a response to dust differ substantially between the two regions” should be revised to “the Chl-a response to dust differs substantially between the two regions.”

Line 98: Consider including some references that have applied this product (GMEMS) in MLD studies, particularly over marginal seas.

Line 230: The term “dust onset” may not be fully appropriate, especially for multi-day dust events. Since lag 0 appears to correspond more closely to the DOD peak day rather than the actual initiation of the event, please consider using terms such as “dust-event day”, “peak dust day” for improved clarity and precision.

Line 382, Figure 10: The manuscript uses the 95% significance level in most analyses, whereas Figure 10 adopts the 99% significance level. Please consider using consistent significance criteria throughout the manuscript, or clarify the reason for using different thresholds. In addition, please check and clarify whether the significance testing accounts for the potential influence of temporal autocorrelation.

Line 368: “deeper mixing facilitates upward nutrient entrainment and promotes phytoplankton growth”, suggest revising to "promotes phytoplankton biomass accumulation" or “favors elevated Chl-a concentrations”, since the analysis is of Chl-a anomaly variability.

Lines 386–387: “This study examines how spring dust events influence daily Chl-a anomalies” may be revised to “This study examines how synoptic atmospheric forcing accompanying spring dust events influences daily Chl-a anomalies.”

Line 395: “These findings highlight the role of dust-associated atmospheric forcing in modulating short-term phytoplankton variability through air–sea heat exchange and upper-ocean mixing, and provides an insight into ecosystem responses” should be revised to “and provide an insight into ecosystem responses.”

Several abbreviations are defined more than once in the manuscript. For example, DOD, MLD and SST are defined in the Abstract, Data and Methods section but re-defined in the Results section. Please ensure each abbreviation is defined only at its first occurrence and used consistently thereafter.
Citation: https://doi.org/10.5194/egusphere-2026-2018-RC1
- AC1: 'Reply on RC1', Rong Tian, 09 Jul 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2018/egusphere-2026-2018-AC1-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2026-2018-AC1
RC2:
'Comment on egusphere-2026-2018', Anonymous Referee #2, 30 Jun 2026

attached

Citation: https://doi.org/10.5194/egusphere-2026-2018-RC2
- AC2: 'Reply on RC2', Rong Tian, 09 Jul 2026
  
  The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2026/egusphere-2026-2018/egusphere-2026-2018-AC2-supplement.pdf
  
  Citation: https://doi.org/10.5194/egusphere-2026-2018-AC2

Peer review completion

AR – Author's response | RR – Referee report | ED – Editor decision | EF – Editorial file upload

ED: Submit a revised manuscript (13 Jul 2026) by Emilio Marañón

AR by Rong Tian on behalf of the Authors (14 Jul 2026) Author's response Author's tracked changes Manuscript

ED: Referee Nomination & Report Request started (21 Jul 2026) by Emilio Marañón

RR by Anonymous Referee #2 (24 Jul 2026)

RR by Anonymous Referee #1 (30 Jul 2026)

ED: Publish as is (04 Aug 2026) by Emilio Marañón

AR by Rong Tian on behalf of the Authors (10 Aug 2026) Manuscript

Journal article(s) based on this preprint

20 Aug 2026

Distinct phytoplankton responses to dust in the Chinese marginal seas: role of synoptic circulation and air–sea heat exchange

Jiehua Hu, Rong Tian, Jinpei Yan, Xiaoke Zhang, Shanshan Wang, Heng Sun, Hanyue Xu, Shiyu Shen, and Qisheng Zeng

Biogeosciences, 23, 5697–5714, https://doi.org/10.5194/bg-23-5697-2026,https://doi.org/10.5194/bg-23-5697-2026, 2026

Short summary

Jiehua Hu, Rong Tian, Jinpei Yan, Xiaoke Zhang, Shanshan Wang, Heng Sun, Hanyue Xu, Shiyu Shen, and Qisheng Zeng

Data sets

MERRA-2 Aerosol Optical Depth Analysis Global Modeling and Assimilation Office (GMAO), NASA https://gmao.gsfc.nasa.gov/reanalysis/MERRA-2/

The daily chlorophyll-a concentration dataset with a 0.25° × 0.25° resolution Zhongkun Hong et al. https://doi.org/10.5281/zenodo.14691522

Jiehua Hu, Rong Tian, Jinpei Yan, Xiaoke Zhang, Shanshan Wang, Heng Sun, Hanyue Xu, Shiyu Shen, and Qisheng Zeng

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We study the response of Chl-a to spring dust variability in the Chinese marginal seas over 2003–2023, revealing contrasting regional responses driven by distinct synoptic circulation patterns. Mongolian cyclones in the north and anticyclones in the south drive opposing air–sea heat flux anomalies and MLD adjustments that regulate Chl-a on daily timescales. Our study highlights synoptic-scale atmospheric forcing and air–sea heat exchange as key pathways linking dust to phytoplankton variability.


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