The Glacial North Atlantic “Capacitor” effect controlled by seasonal sea ice change

doi:10.13745/j.esf.sf.2021.9.57

Abstract

Abstract:

Millennium-scale climate fluctuations, known as Dansgaard-Oeschger (D-O) events during the last glacial cycle, have been a hot topic in paleoclimatology research. Previous modeling studies show that during the cold DO-stadials the amplitude of interannual-interdecadal climate variability in the subpolar North Atlantic is greater than during the warm DO-interstadials. This phenomenon provides valuable implications for interpreting temperature proxies during D-O events, yet its dynamic mechanism remains unclear. Here, via simulation of a typical D-O event during marine isotope stage 3 (MIS 3) using a fully coupled atmosphere-ocean general circulation model, we explore the mechanism behind the amplitude change in interannual-interdecadal climate variability. We find that subpolar seasonal sea-ice in the northern North Atlantic plays an important role by regulating atmosphere-ocean heat exchange. During stadials, sea subsurface gradually warms up due to the northward transport of tropical warm water masses, weakening the density stratification between sea surface and subsurface, which eventually leads to upwelling of the subsurface warm water masses, promoting sea ice melting and sea surface warming. In turn, the sea level pressure lowers and the associated cyclonic wind stress anomaly accelerates the vertical mixing by Ekman suction, which further promote local upwelling. This positive feedback mechanism results in the rapid release of sea subsurface heat and rapid sea surface warming. As the heat release gradually ceases, surface warming is deaccelerated and even paused, allowing sea ice to regrow. This weakens the low-pressure system and stimulates anti-cyclonic wind anomaly, which in turn reduces the vertical mixing. Consequently, sea temperature drops quickly, meanwhile heat starts accumulating in sea subsurface until the vertical stratification is broken again. During interstadials, with the disappearing of seasonal sea ice in the key convection sites of the North Atlantic, the atmosphere-ocean heat exchange is no longer affected by sea ice. This enables a quasi-static heat exchange between the sea subsurface layer and atmosphere. Our results suggest that the existence of seasonal sea ice effectively regulates sea subsurface heat accumulation and release (as termed sea-ice driven “capacitor” effect) in the subpolar North Atlantic, shining a light on our understanding of the glacial amplification of interannual-interdecadal climate variability.

Key words: interannual-decadal climate variability, glacial amplification, air-sea-sea ice interaction, Dansgaard-Oeschger Event

CLC Number:

ZHANG Xu, ZHANG Weichen, WANG Zhenqian, ZHENG Kai, DENG Fengfei. The Glacial North Atlantic “Capacitor” effect controlled by seasonal sea ice change[J]. Earth Science Frontiers, 2022, 29(5): 334-341.

Figures/Tables 7

Fig.1 Time series of Atlantic Meridional Overturning Circulation (AMOC) Index. Gray lines represent the original outputs, and black line is its 30-year running mean

Fig.2 Spatial distribution of standard deviations of different variables in the northern North Atlantic

Fig.3 Climatology annual mean of different climate variables in the northern North Atlantic during cold stadial (model year 1600-1800) and warm interstadial (model year 2200-2400) periods

Fig.4 Time series of climate variables in south of Iceland and southern Nordic Sea

Fig.5 Annual mean composite anomaly of different variables based on SAT variation in the south of Iceland during the cold stadial

Fig.6 Cross-correlations of climate variables in different AMOC states and histogram of SST and SIC variability of the cold stadial in south of Iceland

Fig.7 Histogram of (a) SST and (b) SIC variability during stadial in south of Iceland

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