Unraveling the choice of the north Atlantic subpolar gyre index

Koul, Vimal; Tesdal, Jan‐Erik; Bersch, Manfred; Hátún, Hjálmar; Brune, Sebastian; Borchert, Leonard; Haak, Helmuth; Schrum, Corinna; Baehr, Johanna

doi:10.1038/s41598-020-57790-5

Cited by 40 publications

(63 citation statements)

References 36 publications

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“…are more skillful than uninitialized ones both inside and outside the polar cap domain, except the Pacific Arctic and the sea ice outflows from the central Basin) is seen to benefit more from the initialization than the east side of SPG. Such a zonally asymmetric pattern is consistent with the leading mode of observed sea surface height (SSH) variability in the North Atlantic (Koul et al, 2020), suggesting large scale atmospheric response to ocean initialization. The added skill by sea ice initialization represented by RMSESS of AI2/AI0 appears also prominent in the landward vicinity of the Barents Sea and the E. Siberian Sea.…”

Section: Ai2supporting

confidence: 73%

Benefits of sea ice thickness initialization for the Arctic decadal climate prediction skill in EC-Earth3

Tian¹,

Yang²,

Karami³

et al. 2020

Preprint

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Abstract. A substantial part of Arctic climate predictability at interannual time scales stems from the knowledge of the initial sea ice conditions. Among all the variables characterizing sea ice, sea ice volume, being a product of sea ice area/concentration (SIC) and thickness (SIT), is the most sensitive parameter for climate change. However, the majority of climate prediction systems are only assimilating the observed SIC due to lack of long-term reliable global observation of SIT. In this study the EC-Earth3 Climate Prediction System with anomaly initialization to ocean, SIC and SIT states is developed. In order to evaluate the benefits of specific initialized variables at regional scales, three sets of retrospective ensemble prediction experiments are performed with different initialization strategies: ocean-only; ocean plus SIC; and ocean plus SIC and SIT initialization. The increased skill from ocean plus SIC initialization is small in most regions, compared to ocean-only initialization. In the marginal ice zone covered by seasonal ice, skills regarding winter SIC are mainly gained from the initial ocean temperature anomalies. Consistent with previous studies, the Arctic sea ice volume anomalies are found to play a dominant role for the prediction skill of September Arctic sea ice extent. Winter preconditioning of SIT for the perennial ice in the central Arctic Ocean results in increased skill of SIC in the adjacent Arctic coastal waters (e.g. the Laptev/East Siberian/Chukchi Seas) for lead time up to a decade. This highlights the importance of initializing SIT for predictions of decadal time scale in regional Arctic sea ice. Our results suggest that as the climate warming continues and the central Arctic Ocean might become seasonal ice free in the future, the controlling mechanism for decadal predictability may thus shift from being the sea ice volume playing the major role to a more ocean-related processes.

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Section: Ai2supporting

confidence: 73%

Benefits of sea ice thickness initialization for the Arctic decadal climate prediction skill in EC-Earth3

Tian¹,

Yang²,

Karami³

et al. 2020

Preprint

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“…The freshwater tendencies due to changes in advection derived from ECCOv4 show significant positive correlation with both NAO and AO (

r = 0.36

, 0.48, respectively), while the heat tendencies show significant negative correlation (

r = - 0.43

, −0.56, respectively). The SPNA freshwater and heat advection convergence also show correlation with the Subpolar Gyre Index (SPGI; Figure S17) which is associated with the strength and size of the North Atlantic SPG (Häkkinen & Rhines, 2004; updated by Hátún & Chafik, 2018; Koul et al, 2020). The SPGI is correlated positively with freshwater convergence (

r = 0.54

) and negatively with heat convergence (

r = - 0.44

).…”

Section: Discussionmentioning

confidence: 98%

“…The daily fields were selected for the relevant period (2004–2015) and averaged to monthly mean fields. The Subpolar Gyre Index is defined as the principal component of the second Empirical Orthogonal Function (Koul et al, 2020) but here is derived using monthly anomalies of ADT over the North Atlantic (20–70°N, 0–80°W).…”

Section: Methodsmentioning

confidence: 99%

Dominant Terms in the Freshwater and Heat Budgets of the Subpolar North Atlantic Ocean and Nordic Seas From 1992 to 2015

Tesdal

Haine

2020

JGR Oceans

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The Arctic and subarctic oceans exhibit distinct decadal variations in freshwater and heat content. We describe freshwater and heat budgets with the ECCOv4 reanalysis product and compare budget variability and mechanisms within the subpolar North Atlantic Ocean, Nordic Seas, and Labrador Sea from 1992 to 2015. For all regions, changes in freshwater content are largely anticorrelated with changes in heat content. Since 1995, the subpolar North Atlantic Ocean has undergone a decade of warming and salinification followed by ongoing cooling and freshening. The recent increase in freshwater content and the reduction in heat in the subpolar North Atlantic can largely be attributed to anomalous circulation of mean salinity and temperature, respectively. Interannual variability in heat and freshwater mostly corresponds to boundary fluxes from the subtropics. Meanwhile, the Nordic Seas have undergone an overall warming and salinification from the mid-1990s to 2015. Salinification is primarily driven by reduced sea ice flux through Fram Strait, while warming is due to changes in both sea surface heating and advective flux. In the last 5 years, Labrador Sea freshwater convergence remained unchanged, as increased inflow via the Baffin Island Current is balanced by increased outflow via the Labrador Current. Hence, the observed freshening of the Arctic Ocean is expected to be an increasingly important source of future freshwater increases in the subpolar North Atlantic. This stands in contrast to variability in freshwater flux from the subtropical North Atlantic, which is associated with variability in the Atlantic Meridional Overturning Circulation.

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“…1), overlying the relatively warm Atlantic-source subsurface water masses 23 . The influx of both the Atlantic and Polar water masses to the Labrador Sea is linked to the strength and position of the North Atlantic SPG 24 , with the present day advection of warm and saline WGIW being at maximum strength with highest temperatures, salinities and velocities during winter, when also the transport of Atlantic-sourced water via the Irminger Current is at a maximum 25 . Current strength in the study region may however vary significantly due to local or regional topographic effects 26 .…”

Section: N N N N Ne E E E E E E E E E E E E Ea a A A A A A A A A A A mentioning

confidence: 99%

Evidence for influx of Atlantic water masses to the Labrador Sea during the Last Glacial Maximum

Seidenkrantz

Kuijpers

Aagaard-Sørensen

et al. 2021

Sci Rep

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The Last Glacial Maximum (LGM, 23–19,000 year BP) designates a period of extensive glacial extent and very cold conditions on the Northern Hemisphere. The strength of ocean circulation during this period has been highly debated. Based on investigations of two marine sediment cores from the Davis Strait (1033 m water depth) and the northern Labrador Sea (2381 m), we demonstrate a significant influx of Atlantic-sourced water at both subsurface and intermediate depths during the LGM. Although surface-water conditions were cold and sea-ice loaded, the lower strata of the (proto) West Greenland Current carried a significant Atlantic (Irminger Sea-derived) Water signal, while at the deeper site the sea floor was swept by a water mass comparable with present Northeast Atlantic Deep Water. The persistent influx of these Atlantic-sourced waters entrained by boundary currents off SW Greenland demonstrates an active Atlantic Meridional Overturning Circulation during the LGM. Immediately after the LGM, deglaciation was characterized by a prominent deep-water ventilation event and potentially Labrador Sea Water formation, presumably related to brine formation and/or hyperpycnal meltwater flows. This was followed by a major re-arrangement of deep-water masses most likely linked to increased overflow at the Greenland-Scotland Ridge after ca 15 kyr BP.

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Unraveling the choice of the north Atlantic subpolar gyre index

Cited by 40 publications

References 36 publications

Benefits of sea ice thickness initialization for the Arctic decadal climate prediction skill in EC-Earth3

Benefits of sea ice thickness initialization for the Arctic decadal climate prediction skill in EC-Earth3

Dominant Terms in the Freshwater and Heat Budgets of the Subpolar North Atlantic Ocean and Nordic Seas From 1992 to 2015

Evidence for influx of Atlantic water masses to the Labrador Sea during the Last Glacial Maximum

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