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- **D020 (purple dashed curve)** is similar to D018, except that the SST is restored to the mean climatology increased by 5°C;
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**Results** show that:
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- Fig. 1: the mean Atlantic OHT increases north of 60N and decreases south of 60N compared to the control run in the experiments where the SST restoring is imposed in the North Atlantic and northern North Atlantic (no clear change with the restoring occurring only at the BSO); the OHT increase north of 60N is logical as the SST is getting warmer; the reason for the decrease south of 60N is probably linked to a weakening of the ocean circulation at latitudes lower than 60N following the increase in SST (so decrease in density) (see Fig. 7);
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- Fig. 1: the mean Atlantic OHT increases north of 60N and decreases south of 60N compared to the control run in the experiments where the SST restoring is imposed in the North Atlantic and northern North Atlantic (no clear change with the restoring occurring only at the BSO); the OHT increase north of 60N is logical as the SST is getting warmer; the reason for the decrease south of 60N is probably linked to a weakening of the ocean circulation at latitudes lower than 60N following the increase in SST (so decrease in density) (see Fig. 8);
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- Fig. 2: the total OHT to the Arctic through all Arctic straits (BSO, Fram, Bering, Davis) clearly increases with increasing SST; the strength of the increase in OHT increases with higher SST increase and is clearly higher with the North Atlantic domain compared to the 2 other domains; with the BSO domain, the OHT increase is relatively small; so the higher the domain for the SST increase, the higher the resulting OHT increase;
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- Fig. 3: this is the OHT through the BSO, which is the most important OHT contributor to the Arctic; results are broadly consistent with Fig. 2, except that the increase in OHT does not linearly increase with the increase in SST when the BSO domain (smallest domain) is considered;
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- Fig. 4: there is an OHT increase at Fram Strait with SST when using the 2 first (larger) domains and not really when using the BSO domain; however, the strength of the OHT increase is much lower than for the OHT through the BSO;
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- the OHT at the Bering Strait also increases with increasing SST for all 3 domains, but the strength of the
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increase is much lower compared to BSO and Fram; amd the changes in OHT at Davis Strait are very small in all experiments (not shown);
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- Fig. 5: the total Arctic-sea ice area (SIA) and volume (SIV) decrease in all experiments with SST increase, in agreement with the OHT increase; the strength of the SIA decrease is higher with increased SST for the 2 first domains, but not for the BSO domain (where the strength of the SIA decrease is relatively similar between the 3 experiments);
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- Fig. 6: the spatial extent of the SST increase follows the domain used for the SST restoring, with a larger spatial extent in the SST increase with the larger domain;
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- Fig. 7: the mixed layer depth in the Labrador and Greenland-Iceland-Norway (GIN) Seas decreases with SST increase for the 2 larger domains (North Atlantic and northern North Atlantic); this probably explains the OHT decreases south of 60N, following a weakening of the overturning circulation.
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- Figs. 5 and 6: the total Arctic-sea ice area (SIA) and volume (SIV) decrease in all experiments with SST increase, in agreement with the OHT increase; the strength of the SIA decrease is higher with increased SST for the 2 first domains, but not for the BSO domain (where the strength of the SIA decrease is relatively similar between the 3 experiments);
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- Fig. 7: the spatial extent of the SST increase follows the domain used for the SST restoring, with a larger spatial extent in the SST increase with the larger domain;
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- Fig. 8: the mixed layer depth in the Labrador and Greenland-Iceland-Norway (GIN) Seas decreases with SST increase for the 2 larger domains (North Atlantic and northern North Atlantic); this probably explains the OHT decreases south of 60N, following a weakening of the overturning circulation.
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**Fig. 1: Latitudinal transect of mean Atlantic OHT averaged over 50 years (except 2000-2014 for the CMIP6 r1 member to compare to TF2017); OHT estimates from Trenberth and Fasullo (TF2017) and hydrographic measurements (as in Grist et al., 2018) are plotted for reference; the number in brackets is the difference in mean OHT between the experiment and the control (CTRL)**
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**Fig. 4: Time series of annual mean OHT at the Fram Strait; the number in brackets is the difference in mean OHT between the experiment and the control (CTRL)**
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**Fig. 5: Mean seasonal cycle of Arctic sea-ice area averaged over 50 years for the control run and sensitivity experiments and over 1979-2014 fof the CMIP6 r1 member and satellite observations; the numbers in brackets are the differences in mean March and September Arctic sea-ice areas between the experiment and the control (CTRL)**
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**Fig. 5: Mean seasonal cycle of Arctic sea-ice area averaged over 50 years for the control run and sensitivity experiments and over 1979-2014 for the CMIP6 r1 member and satellite observations; the numbers in brackets are the differences in mean March and September Arctic sea-ice areas between the experiment and the control (CTRL)**
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**Fig. 6: Mean seasonal cycle of Arctic sea-ice volume averaged over 50 years for the control run and sensitivity experiments and over 1979-2014 for the CMIP6 r1 member and PIOMAS reanalysis; the numbers in brackets are the differences in mean March and September Arctic sea-ice volumes between the experiment and the control (CTRL)**
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**Fig. 6: Maps of difference in mean March SST between the different sensitivity experiments and the control run, averaged over 50 years**
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**Fig. 7: Maps of difference in mean March SST between the different sensitivity experiments and the control run, averaged over 50 years**
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**Fig. 7: Maps of difference in mean March mixed layer depth between the control run and the different sensitivity experiments, averaged over 50 years**
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**Fig. 8: Maps of difference in mean March mixed layer depth between the control run and the different sensitivity experiments, averaged over 50 years**
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Important note: These figures were produced by D. Docquier and constitute preliminary results (not published in papers). |
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