the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 04 Oct 2022
The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales
Abstract. Analyses of observational data (from year 1870 AD) show that Sea Surface Temperature (SST) anomalies along the pathway of Atlantic Water transport in the North Atlantic, the Norwegian Sea and the Iceland Sea are in-phase at multidecadal time scales. In-phase SST anomaly relationships are also observed over hundreds of thousands of years during parts of the Pliocene (5.23–5.03, 4.63–4.43 and 4.33–4.03 Ma). However, when investigating CMIP6 SSP126 future scenario runs (next century) and Pliocene reconstructions (5.23–3.13 Ma), three additional phase relations emerge: 1) The Norwegian Sea is out of phase with the North Atlantic and the Iceland Sea (Pliocene; 4.93-4.73 and 3.93–3.63 Ma); 2) The Iceland Sea is out of phase with the North Atlantic and the Norwegian Sea (Pliocene; 3.43–3.23 Ma); 3) The North Atlantic is out of phase with the Norwegian and Iceland Seas (future trend). Hence, out of phase relationships seem to be possible in equilibrium climates (Pliocene) as well as in response to transient forcing (CMIP6 SSP 126 low-emission future scenario). Since buoyancy is a key forcing for inflow of Atlantic Water to the Norwegian Sea, we investigate the impacts of buoyancy forcing on the phase relation between SST anomalies in the North Atlantic, Norwegian and Iceland Seas. This is done by performing a range of idealized experiments using the Massachusetts Institute of Technology general circulation model (MITgcm). Through these idealized experiments we can reproduce three out of four of the documented phase relations: in-phase relationships under weak to intermediate fresh water forcing over the Nordic Seas; the Iceland Sea out of phase with the North Atlantic and the Norwegian Sea under weak atmospheric warming over the Nordic Seas; and the North Atlantic out of phase with the Norwegian and Iceland Seas under strong atmospheric warming over the Nordic Seas. We suggest that the unexplained phase relation, when the Norwegian Sea SSTs are out of phase with the North Atlantic and the Iceland Sea, may reflect a response to a weakened Norwegian Atlantic Current compensated by a strong Irminger current, or an expanded East Greenland Current.
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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.
- Preprint
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Supplement
(3296 KB) - BibTeX
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- Final revised paper
Journal article(s) based on this preprint
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-959', Pepijn Bakker, 31 Oct 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-959/egusphere-2022-959-RC1-supplement.pdf
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AC1: 'Reply on RC1', Bjørg Risebrobakken, 23 Jan 2023
Attached you will find our responses to Pepijn Bakker’s review of our manuscript “The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales”, egusphere-2022-959. His comments are provided in blue while our responses are shown in black, directly following the individual reviewer comments.
We appreciate his positive view on the overall goal of the paper and his very thorough, constructive, and useful feedback that clearly will help improve the manuscript. We acknowledge the main points about coherence, terminology etc. of the manuscript and will put major efforts into clarifying these.
Best regards,
Bjørg Risebrobakken, on behalf of all co-authors
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AC1: 'Reply on RC1', Bjørg Risebrobakken, 23 Jan 2023
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RC2: 'Comment on egusphere-2022-959', Anonymous Referee #2, 04 Dec 2022
Review of the manuscript “The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales” by Risebrobakken et al.
This manuscript presents an excellent combination of observational data, paleoclimate data and modeling. The authors tried to provide an explanation for the different scenarios observed in the Pliocene data (from sedimentary records), and, also, to understand the mechanisms that may bring different scenarios in the future. This manuscript illustrates perfectly how the paleoclimate data may be extremely useful to obtain a better understanding of the climate forcings and to predict future scenarios, as stressed in the last IPCC report.
The manuscript is well written and can be easily followed. Figures and tables are clear and illustrate the text clarifying some of the descriptions. I particularly liked figure 11 and Table 2, which summarize the main results of the experiments.
I am not an expert in modeling, and, therefore, I cannot evaluate if there are any flaws in the modeling experiments performed. From my perspective the manuscript presents a set of experiments that allowed the authors to assess the role of buoyancy forcing on different scenarios. According to the observations of the Pliocene data, the authors investigated the main drivers of the phase relationships observed between the sea surface temperatures in the North Atlantic, Norwegian Sea and Iceland Sea. It is very interesting that those experiments investigating the role of buoyancy forcing in different scenarios, only provided a robust explanation for 3 of the 4 scenarios. For the scenario in which the Norwegian Sea is out phase the authors propose 2 alternative changes in ocean circulation and/or in water column stratification. Since the experiments are only evaluating the role of buoyancy forcing, I wonder if there are other mechanisms that could affect the SST during those intervals. If so, could you just mention what other factors may be causing that kind of phasing? I understand that you will probably need a new set of experiments to evaluate those other factors, but it will be nice to acknowledge that maybe buoyancy forcing is not the only forcing. Also, maybe a sketch with the 2 alternative explanations for the Norwegian Sea out of phase will clarify the proposed hypothesis.
Minor comments:
Figure 1. The figure caption indicates a, b and c panels but those are not indicated in the figure, please add the letters in each panel.
Line 593: Have not reached
Citation: https://doi.org/10.5194/egusphere-2022-959-RC2 -
AC2: 'Reply on RC2', Bjørg Risebrobakken, 23 Jan 2023
Attached you will find our responses to the second review of our manuscript “The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales”, egusphere-2022-959. The reviewer comments are provided in blue while our responses are shown in black, directly following the individual reviewer comments. We acknowledge how addressing the reviewers’ comments will help us to improve the manuscript.
Best regards,
Bjørg Risebrobakken, on behalf of all co-authors
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AC2: 'Reply on RC2', Bjørg Risebrobakken, 23 Jan 2023
Interactive discussion
Status: closed
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RC1: 'Comment on egusphere-2022-959', Pepijn Bakker, 31 Oct 2022
The comment was uploaded in the form of a supplement: https://egusphere.copernicus.org/preprints/2022/egusphere-2022-959/egusphere-2022-959-RC1-supplement.pdf
-
AC1: 'Reply on RC1', Bjørg Risebrobakken, 23 Jan 2023
Attached you will find our responses to Pepijn Bakker’s review of our manuscript “The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales”, egusphere-2022-959. His comments are provided in blue while our responses are shown in black, directly following the individual reviewer comments.
We appreciate his positive view on the overall goal of the paper and his very thorough, constructive, and useful feedback that clearly will help improve the manuscript. We acknowledge the main points about coherence, terminology etc. of the manuscript and will put major efforts into clarifying these.
Best regards,
Bjørg Risebrobakken, on behalf of all co-authors
-
AC1: 'Reply on RC1', Bjørg Risebrobakken, 23 Jan 2023
-
RC2: 'Comment on egusphere-2022-959', Anonymous Referee #2, 04 Dec 2022
Review of the manuscript “The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales” by Risebrobakken et al.
This manuscript presents an excellent combination of observational data, paleoclimate data and modeling. The authors tried to provide an explanation for the different scenarios observed in the Pliocene data (from sedimentary records), and, also, to understand the mechanisms that may bring different scenarios in the future. This manuscript illustrates perfectly how the paleoclimate data may be extremely useful to obtain a better understanding of the climate forcings and to predict future scenarios, as stressed in the last IPCC report.
The manuscript is well written and can be easily followed. Figures and tables are clear and illustrate the text clarifying some of the descriptions. I particularly liked figure 11 and Table 2, which summarize the main results of the experiments.
I am not an expert in modeling, and, therefore, I cannot evaluate if there are any flaws in the modeling experiments performed. From my perspective the manuscript presents a set of experiments that allowed the authors to assess the role of buoyancy forcing on different scenarios. According to the observations of the Pliocene data, the authors investigated the main drivers of the phase relationships observed between the sea surface temperatures in the North Atlantic, Norwegian Sea and Iceland Sea. It is very interesting that those experiments investigating the role of buoyancy forcing in different scenarios, only provided a robust explanation for 3 of the 4 scenarios. For the scenario in which the Norwegian Sea is out phase the authors propose 2 alternative changes in ocean circulation and/or in water column stratification. Since the experiments are only evaluating the role of buoyancy forcing, I wonder if there are other mechanisms that could affect the SST during those intervals. If so, could you just mention what other factors may be causing that kind of phasing? I understand that you will probably need a new set of experiments to evaluate those other factors, but it will be nice to acknowledge that maybe buoyancy forcing is not the only forcing. Also, maybe a sketch with the 2 alternative explanations for the Norwegian Sea out of phase will clarify the proposed hypothesis.
Minor comments:
Figure 1. The figure caption indicates a, b and c panels but those are not indicated in the figure, please add the letters in each panel.
Line 593: Have not reached
Citation: https://doi.org/10.5194/egusphere-2022-959-RC2 -
AC2: 'Reply on RC2', Bjørg Risebrobakken, 23 Jan 2023
Attached you will find our responses to the second review of our manuscript “The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales”, egusphere-2022-959. The reviewer comments are provided in blue while our responses are shown in black, directly following the individual reviewer comments. We acknowledge how addressing the reviewers’ comments will help us to improve the manuscript.
Best regards,
Bjørg Risebrobakken, on behalf of all co-authors
-
AC2: 'Reply on RC2', Bjørg Risebrobakken, 23 Jan 2023
Peer review completion
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Bjørg Risebrobakken
Mari F. Jensen
Helene R. Langehaug
Tor Eldevik
Anne Britt Sandø
Camille Li
Andreas Born
Erin L. McClymont
Ulrich Salzmann
Stijn De Schepper
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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