Status: this preprint is open for discussion and under review for Climate of the Past (CP).
Atlantic water intrusions onto the Scotian Shelf during the past 8.6 ka BP
Henriette M. Kolling,Markus Kienast,Peter Matzerath,Julia Gottschalk,Stephanie Kienast,Daniel A. Frick,Felix Gross,Jack Wharton,David Thornalley,and Ralph R. Schneider
Editorial note: the leadership of Climate of the Past has been alerted that the authors of the paper "Atlantic Water Intrusions onto the Scotian Shelf during the Past 8.6 ka BP" are making extensive use of unpublished data and ideas from a student's PhD thesis. Although the authors correctly cite the thesis in numerous places to support new ideas, they are presenting these ideas for the first time. Kolling et al. as preprint authors, the former PhD student, their supervisor, the Climate of the Past leadership, the handling editor, and Copernicus have decided that the manuscript currently under assessment should be edited to include the PhD student and their supervisor as co-authors. Jack Wharton and David Thornalley were added as co-authors on 25 February 2026.
Abstract. The Scotian Shelf lies at the confluence of warm Gulf Stream (GS) waters and the cold Labrador Current (LC), making it highly sensitive to large- and small-scale climate variability. Modern observations show rapid regional warming accelerated by episodic GS-derived intrusions, yet Holocene paleoceanographic reconstructions from this margin are sparse and often conflicting with respect to the frequency and extent of intrusion events. Here, we present high-resolution Mg/Ca-derived sea-surface temperature (SST) and planktonic δ¹⁸O records from St. Anns Basin on the north-eastern Scotian Shelf that provide new insights into the hydrographic surface-ocean variability of the past 8.5 ka calibrated Before Present (cal BP). While the SST record does not capture the 8.2 ka event, this event is evident in the δ¹⁸O and Ca/Sr records, indicating that its freshwater signal reached the Scotian Shelf. Reconstructed SSTs are generally cold from ~8.5 to ~6.2 cal ka BP, followed by a gradual increase in mean SSTs punctuated by multiple short-lived warm and saline events beginning around 6 cal ka BP, at 6.0–5.8, 5.5–5.4, 5.1–4.9, 3.2–3.1, 2.5–2.2 and 1.05–0.8 cal ka BP, which we interpret as intrusions of GS-sourced slope waters. We attribute these events to basin-scale reorganizations of the GS-LC system, consistent with the minimum/maximum modal state framework of Pickart et al. (1999). Minimum modal state circulation, characterized by a strong onshore LC and an intensified Deep Western Boundary Current (DWBC), which is dominated by Denmark Strait Overflow water, creates a sharp front which restricts intrusions of warm water onto the Scotian Shelf. Maximum modal state conditions feature a weakened LC and increased Labrador Sea Water (LSW) contribution to the DWBC, and reduce cross-slope temperature and salinity gradients that permit GS-derived waters to penetrate the shelf. Overall, our results indicate that warm-water intrusions occurred regularly throughout the past 6.5 ka BP with magnitudes of 6.7 °C and 1.5 psu comparable to those observed today.
Received: 10 Feb 2026 – Discussion started: 17 Feb 2026
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this paper. While Copernicus Publications makes every effort to include appropriate place names, the final responsibility lies with the authors. Views expressed in the text are those of the authors and do not necessarily reflect the views of the publisher.
Henriette M. Kolling,Markus Kienast,Peter Matzerath,Julia Gottschalk,Stephanie Kienast,Daniel A. Frick,Felix Gross,Jack Wharton,David Thornalley,and Ralph R. Schneider
Editorial note: the leadership of Climate of the Past has been alerted that the authors of the paper "Atlantic Water Intrusions onto the Scotian Shelf during the Past 8.6 ka BP" are making extensive use of unpublished data and ideas from a student's PhD thesis. Although the authors correctly cite the thesis in numerous places to support new ideas, they are presenting these ideas for the first time. Kolling et al. as preprint authors, the former PhD student, their supervisor, the Climate of the Past leadership, the handling editor, and Copernicus have decided that the manuscript currently under assessment should be edited to include the PhD student and their supervisor as co-authors. Jack Wharton and David Thornalley were added as co-authors on 25 February 2026.
Status: open (until 02 May 2026)
Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor
| : Report abuse
The paper presents a new and fairly high resolution reconstruction (of Holocene SST, salinity and elements including calcite) from the Scotian Shelf and identifies several abrupt and short-lived warm episodes within the Holocene, interpreted as being incursions of gulf stream water onto the shelf. The introduction, study area, methods and results are concise and well written, and the comments below related to these sections are minor. The data-set is really interesting!
I recommend below that the discussion is in places restructured/re-written to provide a more succinct and clear explanation, because some ideas and interpretations are spread over different paragraphs and sections. I also have some questions about some of the interpretations (particularly on the argument that the NAO would not have been an influence), although I agree with most of the authors interpretations (e.g. the gulf stream being the source of the shelf variability, the early Holocene influence of melt water).
Abstract:
Sentence at line 17-19 - mention within this sentence that salinity is reconstructed
Line 20 - 'and Ca/Sr records' - first mention of these - say that this proxy has been developed in preceding sentence
line 28 - 'and reduce cross-slope' - reword to 'which reduces cross-slope...' perhaps
line 29 - 'warm-water', given the rest of the sentence you should say here warm, saline water...'
Introduction:
Line 38-39 - how much of a warming trend has there been? A detail highlighting the scale would be good here. In addition detail about the temperatures achieved during the warm intrusions compared to the average trend, as well as the duration of the intrusions would be good. For example saying ‘GS intrusions since 2011 have increased SST's from X to X for periods of X weeks’.
Line 48 - think this should be 'from' rather than 'on'
Line 65 - 'additional freshwater reconstruction', the wording here is unusual. Do you mean a salinity reconstruction?
Study Area:
Line 92 - do you mean 'during the last 50 years'? rather than 'for more than 50 years'?
Materials and Methods:
Methods - the descriptions of what you did is well written and thorough. Through the methods I would like to see a bit more explanation of why certain methods are being done. For example sentences at the start of the subsections saying e.g.' XRD analysis was applied to determine X, Y, and Z which are proxies for X (+ references)'. It otherwise assumes that the reader is familiar with what different proxies are used for and doesn’t give any context of previous studies that have led to these methods being used.
Line 103-104 - What was the sieving for? Its not clear here currently, link it to the proxies.
line 155 – typo - specimens
Results:
line 207 - typo ' complete'
Line 212 - it should read 'range between 0.7 and 2.8' I think
line 230 - the wording here is unclear. Not clear if the decreasing trend is through the whole record, and if this is the case why mention 6ka? I think you mean it gradually decreases until 6 ka and then a steeper decrease occurs towards the core top?
Discussion:
Line 236 - the warming trend is not clear at all from looking at the figure. Is it significant and worth mentioning? I would almost say it was warmer between 6 and 2 ka BP but cooler before and after, but with no longterm trend.
Line 238 - do you mean the long term trends differ or the presence/timing of warm anomalies differ?
line 241 - warming trend or warm period? please clarify
Lines 244-247 - could another explanation be a stronger GS associated with a stronger SPG circulation and greater cold water transported southwards along the LC?
Line 249 - the first 2 paragraphs are quite confusing, jumping between proxy explanations, physical explanations, warming/cooling trends in different areas... consider if these could be restructured or clarifying sentences added to guide the discussion
line 255 - rather than 'here' say scotian shelf, otherwise could mean this paper
line 257 - 'in contrast' - do you mean in contrast to the suggestion of Osman about frontal migration? Perhaps say that 'In contrast, other studies of alkenone records highlight'
Line 261 - I am not an expert in the proxies, but wonder if changes in seasonal SST's were influencing the alkenone records how do you know that seasonal SST shifts are not having an influence on your record?
Line 266 - this paragraph doesn’t fit well here. I think this point should have been made before the above discussion of the SST reconstruction at the start of this section
Line 272 - in this paragraph your record shows stable but cool SSTs at 8.5-6.5, and you go on to say this is the same as records with cooling trends? Please be clear in your description whether you mean these other records had cooler temperatures during this period or cooling trends, as these are not the same thing
Line 279 - here you say your record shows a cooling, not stable temperatures which is a contradiction
Line 288-289 - while the final sentence here leads into the next section I don’t think it is needed here. I would include it (if necessary) at the start of the next section
Line 318 - could the move to deeper waters have also isolated the foraminifera from atmospheric changes in temperature, resulting in the lack of a signal?
Line 324 - this should be part of the above paragraph I think.
Line 329 - This paragraph seems to be a summary of the above discussion. If that is the case then it should be highlighted (e.g. In summary, between...' Otherwise I would remove this paragraph as a bit repetitive of the above section
Line 350 - 'this interpretation contrasts with...' I am not sure there is a contradiction here, as you would expect conditions on the shelf to be influenced by different conditions to the NW Atlantic, which covers a much larger area of open ocean. Instead of implying there is a disagreement or debate here you could highlight the shelf and open ocean conditions differed, and then say the warm signal is fairly muted in your record.
Line 360 - do you mean re-expansion or just expansion?
Line 361 - as strong stratification has not been directly measured by your study I would suggest making this statement more cautious. '...strong stratification that likely characterized...'
Line 363 - the separate section on the GS intrusions below was unexpected as I considered that the short term variability in the record was discussed in this section. Perhaps add some signposts for the reader, such as highlighting at the start of section 4.3 that this section is looking at the broad oceanography over time and milllennial changes and the following section is more local or centennial oceanography. Such signposts would provide some justification for discussing the variability in section 4.3 and 4.4. An alternative would be to combine sections 4.3 and 4.4.
Line 368-369 - the results of Levac are not inconsistent with yours, they support yours as summer SST's were low?
Line 423-428 - looking at figure 5 the Shuman drought periods described here do not align with the warm or cold periods in your SST reconstruction. I am also not sure that the mechanisms here support or bring much to your description of the mechanisms, but perhaps it is just that more explanation is needed. Are you suggesting that atmospheric changes were driving the gulf stream incursions? Or that the GS incursions contributed to the drought/wet phases in America?
Line 435 - 'reflects wintertime atmospheric variability...operated on interannual to decadal timescales', I am not sure that this is the case and that the influence of the NAO should be disregarded for these reasons. The observations we have show just annual/decadal changes because they are short, palaeoclimate reconstructions of the NAO (e.g. Trouet et al. 2009; Olsen et al., 2012) show centennial variations. There is also literature on the NAO influence on GS strength and position. While the NAO is a winter phenomenon the influence of wind forcing on ocean circulation continues through the year. Similarly winter atmospheric temperature anomalies could influence sea ice thickness, persistence and thus spring/summer conditions.
Line 457 - I disagree as above that the impacts of the NAO are only felt in winter and have no impact on spring and summer conditions. The SPG and AMOC strength you have highlighted as important controls, and these are driven by wind stress and changes in winter deepwater formation. These therefore provide several ways that NAO variability can have an influence on the ocean year around - winter temperatures, wind and rainfall over the deepwater formation regions (influenced at least in part by the NAO state) would control NADW formation rates and thus the AMOC strength. Winter wind stress over the Atlantic would control the surface currents and SPG. These responses would not just be during winter, so would influence the GS intrusions onto the scotian shelf.
Line 468 – have ‘Bond Events’ been solely linked to solar variability? Is it not also linked to internal ocean variability? If there is debate about this I would not highlight it as a proxy for solar variability in Figure 5.
Line 473 - I would suggest merging this section on spectral analysis with the above discussion on the drivers of the GS intrusions. While the discussion here stems from the cycles identified, it is providing a more in depth discussion of the processing that were started in the above section. Combining it with the above section, and just mentioning the spectral results there, would strengthen the explanation I feel.
Line 486 - I am not sure what the resolution is of the record, but if it is over 100 years I would caution against reading too much into the 200-300 year cycles here.
Conclusions:
Line 512 - mention the other proxies, calcite and sea surface salinity as well perhaps?
Figure 4 - it is not clear from the plot or the caption which is which in plot D (the Wharton and Sachs records)
Figure 5 - the event around 4.7 ka BP does not have a shaded bar, its similar magnitude to other events.
Please see the attached PDF for a summary of planned additions to the manuscript, including updates to the age model, Emerald Basin record, and associated figures, following the recent update to the author list.
Henriette M. Kolling,Markus Kienast,Peter Matzerath,Julia Gottschalk,Stephanie Kienast,Daniel A. Frick,Felix Gross,Jack Wharton,David Thornalley,and Ralph R. Schneider
Editorial note: the leadership of Climate of the Past has been alerted that the authors of the paper "Atlantic Water Intrusions onto the Scotian Shelf during the Past 8.6 ka BP" are making extensive use of unpublished data and ideas from a student's PhD thesis. Although the authors correctly cite the thesis in numerous places to support new ideas, they are presenting these ideas for the first time. Kolling et al. as preprint authors, the former PhD student, their supervisor, the Climate of the Past leadership, the handling editor, and Copernicus have decided that the manuscript currently under assessment should be edited to include the PhD student and their supervisor as co-authors. Jack Wharton and David Thornalley were added as co-authors on 25 February 2026.
Henriette M. Kolling,Markus Kienast,Peter Matzerath,Julia Gottschalk,Stephanie Kienast,Daniel A. Frick,Felix Gross,Jack Wharton,David Thornalley,and Ralph R. Schneider
Editorial note: the leadership of Climate of the Past has been alerted that the authors of the paper "Atlantic Water Intrusions onto the Scotian Shelf during the Past 8.6 ka BP" are making extensive use of unpublished data and ideas from a student's PhD thesis. Although the authors correctly cite the thesis in numerous places to support new ideas, they are presenting these ideas for the first time. Kolling et al. as preprint authors, the former PhD student, their supervisor, the Climate of the Past leadership, the handling editor, and Copernicus have decided that the manuscript currently under assessment should be edited to include the PhD student and their supervisor as co-authors. Jack Wharton and David Thornalley were added as co-authors on 25 February 2026.
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We studied past ocean conditions on the Scotian Shelf to understand how warm Gulf Stream waters reached this region in the past. Using chemical signals preserved in microscopic shells from seafloor sediments, we reconstructed sea surface temperature and salinity over the last 8,500 years. We found repeated warm-water intrusions during the mid to late Holocene, similar in strength to those observed today, providing important context for modern ocean warming.
We studied past ocean conditions on the Scotian Shelf to understand how warm Gulf Stream waters...
The paper presents a new and fairly high resolution reconstruction (of Holocene SST, salinity and elements including calcite) from the Scotian Shelf and identifies several abrupt and short-lived warm episodes within the Holocene, interpreted as being incursions of gulf stream water onto the shelf. The introduction, study area, methods and results are concise and well written, and the comments below related to these sections are minor. The data-set is really interesting!
I recommend below that the discussion is in places restructured/re-written to provide a more succinct and clear explanation, because some ideas and interpretations are spread over different paragraphs and sections. I also have some questions about some of the interpretations (particularly on the argument that the NAO would not have been an influence), although I agree with most of the authors interpretations (e.g. the gulf stream being the source of the shelf variability, the early Holocene influence of melt water).
Abstract:
Sentence at line 17-19 - mention within this sentence that salinity is reconstructed
Line 20 - 'and Ca/Sr records' - first mention of these - say that this proxy has been developed in preceding sentence
line 28 - 'and reduce cross-slope' - reword to 'which reduces cross-slope...' perhaps
line 29 - 'warm-water', given the rest of the sentence you should say here warm, saline water...'
Introduction:
Line 38-39 - how much of a warming trend has there been? A detail highlighting the scale would be good here. In addition detail about the temperatures achieved during the warm intrusions compared to the average trend, as well as the duration of the intrusions would be good. For example saying ‘GS intrusions since 2011 have increased SST's from X to X for periods of X weeks’.
Line 48 - think this should be 'from' rather than 'on'
Line 65 - 'additional freshwater reconstruction', the wording here is unusual. Do you mean a salinity reconstruction?
Study Area:
Line 92 - do you mean 'during the last 50 years'? rather than 'for more than 50 years'?
Materials and Methods:
Methods - the descriptions of what you did is well written and thorough. Through the methods I would like to see a bit more explanation of why certain methods are being done. For example sentences at the start of the subsections saying e.g.' XRD analysis was applied to determine X, Y, and Z which are proxies for X (+ references)'. It otherwise assumes that the reader is familiar with what different proxies are used for and doesn’t give any context of previous studies that have led to these methods being used.
Line 103-104 - What was the sieving for? Its not clear here currently, link it to the proxies.
line 155 – typo - specimens
Results:
line 207 - typo ' complete'
Line 212 - it should read 'range between 0.7 and 2.8' I think
line 230 - the wording here is unclear. Not clear if the decreasing trend is through the whole record, and if this is the case why mention 6ka? I think you mean it gradually decreases until 6 ka and then a steeper decrease occurs towards the core top?
Discussion:
Line 236 - the warming trend is not clear at all from looking at the figure. Is it significant and worth mentioning? I would almost say it was warmer between 6 and 2 ka BP but cooler before and after, but with no longterm trend.
Line 238 - do you mean the long term trends differ or the presence/timing of warm anomalies differ?
line 241 - warming trend or warm period? please clarify
Lines 244-247 - could another explanation be a stronger GS associated with a stronger SPG circulation and greater cold water transported southwards along the LC?
Line 249 - the first 2 paragraphs are quite confusing, jumping between proxy explanations, physical explanations, warming/cooling trends in different areas... consider if these could be restructured or clarifying sentences added to guide the discussion
line 255 - rather than 'here' say scotian shelf, otherwise could mean this paper
line 257 - 'in contrast' - do you mean in contrast to the suggestion of Osman about frontal migration? Perhaps say that 'In contrast, other studies of alkenone records highlight'
Line 261 - I am not an expert in the proxies, but wonder if changes in seasonal SST's were influencing the alkenone records how do you know that seasonal SST shifts are not having an influence on your record?
Line 266 - this paragraph doesn’t fit well here. I think this point should have been made before the above discussion of the SST reconstruction at the start of this section
Line 272 - in this paragraph your record shows stable but cool SSTs at 8.5-6.5, and you go on to say this is the same as records with cooling trends? Please be clear in your description whether you mean these other records had cooler temperatures during this period or cooling trends, as these are not the same thing
Line 279 - here you say your record shows a cooling, not stable temperatures which is a contradiction
Line 288-289 - while the final sentence here leads into the next section I don’t think it is needed here. I would include it (if necessary) at the start of the next section
Line 318 - could the move to deeper waters have also isolated the foraminifera from atmospheric changes in temperature, resulting in the lack of a signal?
Line 324 - this should be part of the above paragraph I think.
Line 329 - This paragraph seems to be a summary of the above discussion. If that is the case then it should be highlighted (e.g. In summary, between...' Otherwise I would remove this paragraph as a bit repetitive of the above section
Line 350 - 'this interpretation contrasts with...' I am not sure there is a contradiction here, as you would expect conditions on the shelf to be influenced by different conditions to the NW Atlantic, which covers a much larger area of open ocean. Instead of implying there is a disagreement or debate here you could highlight the shelf and open ocean conditions differed, and then say the warm signal is fairly muted in your record.
Line 360 - do you mean re-expansion or just expansion?
Line 361 - as strong stratification has not been directly measured by your study I would suggest making this statement more cautious. '...strong stratification that likely characterized...'
Line 363 - the separate section on the GS intrusions below was unexpected as I considered that the short term variability in the record was discussed in this section. Perhaps add some signposts for the reader, such as highlighting at the start of section 4.3 that this section is looking at the broad oceanography over time and milllennial changes and the following section is more local or centennial oceanography. Such signposts would provide some justification for discussing the variability in section 4.3 and 4.4. An alternative would be to combine sections 4.3 and 4.4.
Line 368-369 - the results of Levac are not inconsistent with yours, they support yours as summer SST's were low?
Line 423-428 - looking at figure 5 the Shuman drought periods described here do not align with the warm or cold periods in your SST reconstruction. I am also not sure that the mechanisms here support or bring much to your description of the mechanisms, but perhaps it is just that more explanation is needed. Are you suggesting that atmospheric changes were driving the gulf stream incursions? Or that the GS incursions contributed to the drought/wet phases in America?
Line 435 - 'reflects wintertime atmospheric variability...operated on interannual to decadal timescales', I am not sure that this is the case and that the influence of the NAO should be disregarded for these reasons. The observations we have show just annual/decadal changes because they are short, palaeoclimate reconstructions of the NAO (e.g. Trouet et al. 2009; Olsen et al., 2012) show centennial variations. There is also literature on the NAO influence on GS strength and position. While the NAO is a winter phenomenon the influence of wind forcing on ocean circulation continues through the year. Similarly winter atmospheric temperature anomalies could influence sea ice thickness, persistence and thus spring/summer conditions.
Line 457 - I disagree as above that the impacts of the NAO are only felt in winter and have no impact on spring and summer conditions. The SPG and AMOC strength you have highlighted as important controls, and these are driven by wind stress and changes in winter deepwater formation. These therefore provide several ways that NAO variability can have an influence on the ocean year around - winter temperatures, wind and rainfall over the deepwater formation regions (influenced at least in part by the NAO state) would control NADW formation rates and thus the AMOC strength. Winter wind stress over the Atlantic would control the surface currents and SPG. These responses would not just be during winter, so would influence the GS intrusions onto the scotian shelf.
Line 468 – have ‘Bond Events’ been solely linked to solar variability? Is it not also linked to internal ocean variability? If there is debate about this I would not highlight it as a proxy for solar variability in Figure 5.
Line 473 - I would suggest merging this section on spectral analysis with the above discussion on the drivers of the GS intrusions. While the discussion here stems from the cycles identified, it is providing a more in depth discussion of the processing that were started in the above section. Combining it with the above section, and just mentioning the spectral results there, would strengthen the explanation I feel.
Line 486 - I am not sure what the resolution is of the record, but if it is over 100 years I would caution against reading too much into the 200-300 year cycles here.
Conclusions:
Line 512 - mention the other proxies, calcite and sea surface salinity as well perhaps?
Figure 4 - it is not clear from the plot or the caption which is which in plot D (the Wharton and Sachs records)
Figure 5 - the event around 4.7 ka BP does not have a shaded bar, its similar magnitude to other events.