Surface salinity under transitioning ice cover in the Canada Basin: Climate model biases linked to vertical 2 distribution of freshwater

Rosenblum, Erica; Fajber, Robert; Stroeve, Julienne; Gille, Sarah T.; Tremblay, Bruno; Carmack, Eddy C.

doi:10.1002/essoar.10507260.1

Cited by 2 publications

(4 citation statements)

References 43 publications

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“…These findings are consistent with Rosenblum, Fajber, et al. (2021), who show that the model bias can be partly attributed to unrealistic vertical mixing rather than sea ice melt. It appears that the two opposing effects of increased ice melt with warming and surface mixing by faster moving sea ice (and increased surface stress) lead to a more stable stratification in the real world (Peralta‐Ferriz & Woodgate, 2015) and a less stable stratification in the CESM1‐LE in May.…”

Section: Resultssupporting

confidence: 92%

“…While we find that CESM1‐LE does simulate increases in both sea ice melt and surface stress (Figure 8), the model instead simulates a deepening in the mixed layer. This points to a problem in vertical mixing in the CESM1‐LE, consistent with previous studies (Holloway et al., 2007; Ilıcak et al., 2016; Rosenblum, Fajber, et al., 2021).…”

Section: Discussionsupporting

confidence: 89%

“…In models, a proper representation of the halocline requires accurate brine rejection and vertical mixing parameterizations (Large et al., 1994; Nguyen et al., 2009), and high vertical resolution to resolve the sharp gradient in temperature and salt present at the base of the mixed layer. These processes are still poorly (or not at all) represented in climate models (Holloway et al., 2007; Ilıcak et al., 2016; Rosenblum, Fajber, et al., 2021). A detailed comparison of simulated and observed upper ocean stratification is therefore crucial before analyzing the vertical heat transport in a model.…”

Section: Introductionmentioning

confidence: 99%

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Pacific Waters Pathways and Vertical Mixing in the CESM1‐LE: Implication for Mixed Layer Depth Evolution and Sea Ice Mass Balance in the Canada Basin

2022

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We compare the vertical hydrography of the Community Earth System Model Large Ensemble (CESM1‐LE) with observations from two specific periods: the Arctic Ice Dynamics Joint Experiment (AIDJEX; 1975–1976) and Ice‐Tethered Profilers (ITP; 2004–2018). A comparison between simulated and observed salinity and potential temperature profiles highlights two key model biases in all ensemble members: (a) an absence of Pacific Waters in the water column and (b) a slight deepening of the May mixed layer contrary to observations, which show a large reduction in the mixed‐layer depth and an increase in stratification over the same time period. We examine processes controlling the sea ice mass balance using a one‐dimensional vertical heat budget in the light of the model limitations implied by these two biases. Results indicate that remnant solar heat trapped beneath the halocline is mostly ventilated to the surface by mixing before the following melt season. Furthermore, we find that vertical advection associated with Ekman pumping has only a small effect on the vertical heat transport, even in early fall when the winds are strong and the pack ice is weak. Lastly, we estimate the impact of the missing Pacific Waters at 0.40 m of reduced winter ice growth.

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Section: Resultssupporting

confidence: 92%

Section: Discussionsupporting

confidence: 89%

Section: Introductionmentioning

confidence: 99%

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Pacific Waters Pathways and Vertical Mixing in the CESM1‐LE: Implication for Mixed Layer Depth Evolution and Sea Ice Mass Balance in the Canada Basin

2022

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“…Rosenblum et al. (2021) found that some coupled models tend to simulate an unrealistic vertical mixing in the upper Arctic Ocean and accordingly fail to capture the observed freshwater change in recent years.…”

Section: Resultsmentioning

confidence: 99%

Arctic Ocean Freshwater in CMIP6 Coupled Models

Wang

et al. 2022

Earth's Future

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In this study we assessed the representation of the sea surface salinity (SSS) and liquid freshwater content (LFWC) of the Arctic Ocean in the historical simulation of 31 CMIP6 models with comparison to 39 Coupled Model Intercomparison Project phase 5 (CMIP5) models, and investigated the projected changes in Arctic liquid and solid freshwater content and freshwater budget in scenarios with two different shared socioeconomic pathways (SSP2‐4.5 and SSP5‐8.5). No significant improvement was found in the SSS and LFWC simulation from CMIP5 to CMIP6, given the large model spreads in both CMIP phases. The overestimation of LFWC continues to be a common bias in CMIP6. In the historical simulation, the multi‐model mean river runoff, net precipitation, Bering Strait and Barents Sea Opening (BSO) freshwater transports are 2,928 ± 1,068, 1,839 ± 3,424, 2,538 ± 1,009, and −636 ± 553 km3/year, respectively. In the last decade of the 21st century, CMIP6 MMM projects these budget terms to rise to 4,346 ± 1,484 km3/year (3,678 ± 1,255 km3/year), 3,866 ± 2,935 km3/year (3,145 ± 2,651 km3/year), 2,631 ± 1,119 km3/year (2,649 ± 1,141 km3/year) and 1,033 ± 1,496 km3/year (449 ± 1,222 km3/year) under SSP5‐8.5 (SSP2‐4.5). Arctic sea ice is expected to continue declining in the future, and sea ice meltwater flux is likely to decrease to about zero in the mid‐21st century under both SSP2‐4.5 and SSP5‐8.5 scenarios. Liquid freshwater exiting Fram and Davis straits will be higher in the future, and the Fram Strait export will remain larger. The Arctic Ocean is projected to hold a total of 160,300 ± 62,330 km3 (141,590 ± 50,310 km3) liquid freshwater under SSP5‐8.5 (SSP2‐4.5) by 2100, about 60% (40%) more than its historical climatology.

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Surface salinity under transitioning ice cover in the Canada Basin: Climate model biases linked to vertical 2 distribution of freshwater

Abstract: The models distribute fresh water over an unrealistically large depth range in recent years, which contributes to the surface salinity bias.

Cited by 2 publications

References 43 publications

Pacific Waters Pathways and Vertical Mixing in the CESM1‐LE: Implication for Mixed Layer Depth Evolution and Sea Ice Mass Balance in the Canada Basin

Pacific Waters Pathways and Vertical Mixing in the CESM1‐LE: Implication for Mixed Layer Depth Evolution and Sea Ice Mass Balance in the Canada Basin

Arctic Ocean Freshwater in CMIP6 Coupled Models

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