the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 07 Mar 2024
Distinct seasonal changes and precession forcing of surface and subsurface temperatures in the mid-latitudinal North Atlantic during the onset of the Late Pliocene
Abstract. The Late Pliocene marks the intensification of Northern Hemisphere Glaciation, offering a unique opportunity to study climate evolution and ice-sheet related feedback mechanisms. In this study, we present high-resolution Mg/Ca-based sea surface (SST) and subsurface temperatures (SubT) derived from foraminiferal species Globigerinoides ruber and Globorotalia hirsuta, respectively, at the Integrated Ocean Drilling Project (IODP) Expedition 306 Site U1313 in the mid-latitudinal North Atlantic during the early Late Pliocene, 3.65 – 3.37 million years ago (Ma). We find distinct differences between our new G. ruber Mg/Ca-based SST record and previously published alkenone-based SST record from the same location. These discrepancies in both absolute values and variations highlight distinct seasonal influences. The G. ruber Mg/Ca-based SST data, reflecting summer temperatures, were primarily influenced by local summer insolation, showing a dominant precession cycle. Conversely, the variations in alkenone-based SST are found to be more indicative of cold season changes, despite previous interpretations of these records as reflecting annual mean temperatures. A simultaneous decline in Mg/Ca-based SST and SubT records from 3.65 to 3.5 Ma suggests a diminished poleward oceanic heat transport, implying a weakening of the North Atlantic Current. A comparison with early Pleistocene G. ruber Mg/Ca-based SST records shows a shift in the dominant climatic cycle from precession to obliquity, alongside a marked increase in amplitude, indicating an enhanced influence of obliquity cycles correlated with the expansion of Northern Hemisphere ice sheets.
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Notice on discussion status
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-603', Heather L. Ford, 15 Apr 2024
In this manuscript, the authors use the Mg/Ca values of a surface dwelling and subsurface dwelling foraminifera to investigate climate in the North Atlantic during the early Late Pliocene. They find spectral and temperature differences from the existing alkenone-based record highlighting the seasonality in surface foraminifera and alkenones and the related climatological interpretations. I found the use of the subsurface dwelling records to reconstruct the North Atlantic current and poleward heat transporting compelling. I found the study well executed and the manuscript well-written. I have a few minor comments and suggestions to improve the clarify of the manuscript.
Line 122-123: write out abbreviations to full names
Figure 1: Avoid rainbow color palette on figures. You can use BlueRed or Viridis in ODV
Figure 2: Update to ProbStack instead of LR04
Figure 3c: 100 peak blocked by 100 label – adjust position slightly
Line 185: In the last sentence I would reiterative the precession cycle is absent from the 2.4 to 2.8 period, i.e. “The results indicate that the 2.4 to 2.8 Ma records are all dominated by obliquity, with a notable absence of a significant precession cycle after iNHG in comparison to the oNHG (3.3 to 3.7 Ma records)”. The first time I read it and then looked at the figure I was confused so I would just be more specific.
Line 235-240: Do you mean 2000 AD? I would re-write this as “For our study interval (3.65 to 3.37 Ma), the reconstructed CenCO2PIP CO2 concentration averaged around 300 ppm with a maximum value generally not exceeding 360 ppm (Fig. 4c). This is similar to the high-resolution reconstruction for 3.35-3.15 Ma, i.e. immediately following our study period (de la Vega et al., 2020). For comparison, the modern CO2 value in 2000 was 360 ppm. Considering the reconstructed SSTs are warmer than the modern average temperature from 2000 to 2015 (Fig. 1d), the relatively higher CO2 could not be the primary cause of the warmer temperature during the late Pliocene.”
Citation: https://doi.org/10.5194/egusphere-2024-603-RC1 -
AC1: 'Reply on RC1', Xiaolei Pang, 09 Jun 2024
We thank Dr. Heather Ford for her valuable comments and detailed suggestions, which have helped us improve the quality of the manuscript.
Our detailed point-by-point responses to her comments and the corresponding manuscript revisions are outlined in the attached document.
On behave of all co-authors,
Xiaolei Pang
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AC1: 'Reply on RC1', Xiaolei Pang, 09 Jun 2024
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RC2: 'Comment on egusphere-2024-603', Anonymous Referee #2, 08 May 2024
Pang et al. present interesting new high-resolution foraminiferal Mg/Ca based SST and subsurface temperatures from the North Atlantic Site U1313 for the late Pliocene (3.65-3.4 Ma). The authors compare their data with previously published alkenone derived SST from the same Site and discover a different development. Especially, during 3.65-3.5 Ma, when alkenone derived SST showed a warming, their study suggests SST and subsurface cooling. They argue that this supports a previous study that suggested a weakening of the NAC during this time, which might have preconditioned the Northern Hemisphere Glaciation. The authors explain the differences between foraminiferal Mg/Ca based SST and alkenone derived SST due to representations of different seasons. They further argue that Mg/Ca derived SST experienced a marked change from precession dominated during the late Pliocene towards obliquity dominated during the Pleistocene. In contrast, alkenone SST were always driven by obliquity changes. I think the presented data is of interest in terms of a proxy comparison from an important core location when the Northern Hemisphere Glaciation begun. It is also a nice extension of previous published SST records in this region. The manuscript text needs some revisions at several locations when interpreting the results. Figures look good. In the following are my comments that should be addressed before publication:
- The authors explain the close similarity of alkenone SST from Site U1313 and global benthic d18O due to “ice-related albedo effects”. However, the mechanisms are not sufficiently explained. Is a regional albedo effect meant? How does the albedo effect affect the temperature gradient at ~40ºN?
- The authors argue that “summer” SST from G. ruber Mg/Ca in combination with subsurface temperature reconstructions are better suited to infer changes in NAC than “spring” SST from alkenones. However, I think the authors should also look at possible seasonal changes in NAC. Further, the connection between gyre circulation at 400 m water depth and NAC strength could be better explained.
- As mentioned above, subsurface Mg/Ca temperatures were used to support the surface temperatures, especially during 3.65-3.5 Ma. However, in the method section the authors show an error in subsurface temperatures of about ±5°C, and further it is argued that this does not affect the results as the record is not used for comparison. I suggest revising this, better describing how subsurface temperatures can support SST.
More detailed comments in the manuscript:
Title: It might be better to focus on the differences between SST derived from foraminiferal Mg/Ca and alkenones. Why not mention the “onset of Northern Hemisphere Glaciation”?
Line 24: Please include the influence of obliquity
Lines 31: Is “Cool-house climate” needed here? Maybe delete it as it may confuse the reader.
Lines 85-87: This needs to be better described.
Line 112: Reference are needed for “is widely used”.
Lines 117-119: Please make two sentences out of this.
Lines 121-124: There is unnecessary information and repetition. Please shorten.
Line 136: Also provide absolute error.
Line 145: Please provide the reader with the difference between uncorrected and corrected Mg/Ca derived SST.
Line 160: Capital letter after a full stop.
Line 162: Provide latitudes and longitudes of the sites.
Lines 174-176: Please indicate how much temperatures decrease
Line 188: Indicate the time period.
Line 193: Give more information how the smooth was calculated
Line 206: Please provide the reference for the alkenones
Line 235: Shorten the phrase. Is there something available with higher resolution?
Line 251: The authors argue that alkenone derived SST indicate spring temperatures why mention here “mean or spring conditions”? This is confusing.
Line 284: Define which depths are meant.
Lines 287-288: Unclear. Please better describe.
Line 322: Replace “was” for “were”.
Line 325: Better explain. See also main comment above.
Line 331: Replace “decreasing” for “increasing”
Lines 331-333: Better explain. See also main comment above.
Lines 343-346: Split sentence or shorten.
Lines 347-358: I suggest condensing this paragraph.
Line 355: Please indicate a value for “slightly higher”
Lines 374-375. Please see main comments. The same mechanism is mentioned several times but not explained once in detail.
Citation: https://doi.org/10.5194/egusphere-2024-603-RC2 -
AC2: 'Reply on RC2', Xiaolei Pang, 09 Jun 2024
We thank the reviewer for their valuable comments and insights. Addressing these concerns has significantly improved the quality and clarity of the paper.
Our detailed point-by-point responses to their comments and the corresponding manuscript revisions are outlined in the attached document.
On behave of all co-authors,
Xiaolei Pang
Interactive discussion
Status: closed
-
RC1: 'Comment on egusphere-2024-603', Heather L. Ford, 15 Apr 2024
In this manuscript, the authors use the Mg/Ca values of a surface dwelling and subsurface dwelling foraminifera to investigate climate in the North Atlantic during the early Late Pliocene. They find spectral and temperature differences from the existing alkenone-based record highlighting the seasonality in surface foraminifera and alkenones and the related climatological interpretations. I found the use of the subsurface dwelling records to reconstruct the North Atlantic current and poleward heat transporting compelling. I found the study well executed and the manuscript well-written. I have a few minor comments and suggestions to improve the clarify of the manuscript.
Line 122-123: write out abbreviations to full names
Figure 1: Avoid rainbow color palette on figures. You can use BlueRed or Viridis in ODV
Figure 2: Update to ProbStack instead of LR04
Figure 3c: 100 peak blocked by 100 label – adjust position slightly
Line 185: In the last sentence I would reiterative the precession cycle is absent from the 2.4 to 2.8 period, i.e. “The results indicate that the 2.4 to 2.8 Ma records are all dominated by obliquity, with a notable absence of a significant precession cycle after iNHG in comparison to the oNHG (3.3 to 3.7 Ma records)”. The first time I read it and then looked at the figure I was confused so I would just be more specific.
Line 235-240: Do you mean 2000 AD? I would re-write this as “For our study interval (3.65 to 3.37 Ma), the reconstructed CenCO2PIP CO2 concentration averaged around 300 ppm with a maximum value generally not exceeding 360 ppm (Fig. 4c). This is similar to the high-resolution reconstruction for 3.35-3.15 Ma, i.e. immediately following our study period (de la Vega et al., 2020). For comparison, the modern CO2 value in 2000 was 360 ppm. Considering the reconstructed SSTs are warmer than the modern average temperature from 2000 to 2015 (Fig. 1d), the relatively higher CO2 could not be the primary cause of the warmer temperature during the late Pliocene.”
Citation: https://doi.org/10.5194/egusphere-2024-603-RC1 -
AC1: 'Reply on RC1', Xiaolei Pang, 09 Jun 2024
We thank Dr. Heather Ford for her valuable comments and detailed suggestions, which have helped us improve the quality of the manuscript.
Our detailed point-by-point responses to her comments and the corresponding manuscript revisions are outlined in the attached document.
On behave of all co-authors,
Xiaolei Pang
-
AC1: 'Reply on RC1', Xiaolei Pang, 09 Jun 2024
-
RC2: 'Comment on egusphere-2024-603', Anonymous Referee #2, 08 May 2024
Pang et al. present interesting new high-resolution foraminiferal Mg/Ca based SST and subsurface temperatures from the North Atlantic Site U1313 for the late Pliocene (3.65-3.4 Ma). The authors compare their data with previously published alkenone derived SST from the same Site and discover a different development. Especially, during 3.65-3.5 Ma, when alkenone derived SST showed a warming, their study suggests SST and subsurface cooling. They argue that this supports a previous study that suggested a weakening of the NAC during this time, which might have preconditioned the Northern Hemisphere Glaciation. The authors explain the differences between foraminiferal Mg/Ca based SST and alkenone derived SST due to representations of different seasons. They further argue that Mg/Ca derived SST experienced a marked change from precession dominated during the late Pliocene towards obliquity dominated during the Pleistocene. In contrast, alkenone SST were always driven by obliquity changes. I think the presented data is of interest in terms of a proxy comparison from an important core location when the Northern Hemisphere Glaciation begun. It is also a nice extension of previous published SST records in this region. The manuscript text needs some revisions at several locations when interpreting the results. Figures look good. In the following are my comments that should be addressed before publication:
- The authors explain the close similarity of alkenone SST from Site U1313 and global benthic d18O due to “ice-related albedo effects”. However, the mechanisms are not sufficiently explained. Is a regional albedo effect meant? How does the albedo effect affect the temperature gradient at ~40ºN?
- The authors argue that “summer” SST from G. ruber Mg/Ca in combination with subsurface temperature reconstructions are better suited to infer changes in NAC than “spring” SST from alkenones. However, I think the authors should also look at possible seasonal changes in NAC. Further, the connection between gyre circulation at 400 m water depth and NAC strength could be better explained.
- As mentioned above, subsurface Mg/Ca temperatures were used to support the surface temperatures, especially during 3.65-3.5 Ma. However, in the method section the authors show an error in subsurface temperatures of about ±5°C, and further it is argued that this does not affect the results as the record is not used for comparison. I suggest revising this, better describing how subsurface temperatures can support SST.
More detailed comments in the manuscript:
Title: It might be better to focus on the differences between SST derived from foraminiferal Mg/Ca and alkenones. Why not mention the “onset of Northern Hemisphere Glaciation”?
Line 24: Please include the influence of obliquity
Lines 31: Is “Cool-house climate” needed here? Maybe delete it as it may confuse the reader.
Lines 85-87: This needs to be better described.
Line 112: Reference are needed for “is widely used”.
Lines 117-119: Please make two sentences out of this.
Lines 121-124: There is unnecessary information and repetition. Please shorten.
Line 136: Also provide absolute error.
Line 145: Please provide the reader with the difference between uncorrected and corrected Mg/Ca derived SST.
Line 160: Capital letter after a full stop.
Line 162: Provide latitudes and longitudes of the sites.
Lines 174-176: Please indicate how much temperatures decrease
Line 188: Indicate the time period.
Line 193: Give more information how the smooth was calculated
Line 206: Please provide the reference for the alkenones
Line 235: Shorten the phrase. Is there something available with higher resolution?
Line 251: The authors argue that alkenone derived SST indicate spring temperatures why mention here “mean or spring conditions”? This is confusing.
Line 284: Define which depths are meant.
Lines 287-288: Unclear. Please better describe.
Line 322: Replace “was” for “were”.
Line 325: Better explain. See also main comment above.
Line 331: Replace “decreasing” for “increasing”
Lines 331-333: Better explain. See also main comment above.
Lines 343-346: Split sentence or shorten.
Lines 347-358: I suggest condensing this paragraph.
Line 355: Please indicate a value for “slightly higher”
Lines 374-375. Please see main comments. The same mechanism is mentioned several times but not explained once in detail.
Citation: https://doi.org/10.5194/egusphere-2024-603-RC2 -
AC2: 'Reply on RC2', Xiaolei Pang, 09 Jun 2024
We thank the reviewer for their valuable comments and insights. Addressing these concerns has significantly improved the quality and clarity of the paper.
Our detailed point-by-point responses to their comments and the corresponding manuscript revisions are outlined in the attached document.
On behave of all co-authors,
Xiaolei Pang
Peer review completion
Journal article(s) based on this preprint
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Xiaolei Pang
Antje Helga Luise Voelker
Sihua Lu
Xuan Ding
The requested preprint has a corresponding peer-reviewed final revised paper. You are encouraged to refer to the final revised version.
- Preprint
(5115 KB) - Metadata XML
-
Supplement
(1301 KB) - BibTeX
- EndNote
- Final revised paper