1Supporting Information for

23Fast Response of the Tropics to an Abrupt Loss of Arctic Sea Ice via Ocean Dynamics

45Kun Wang1,2,3, Clara Deser*1, Lantao Sun4 and Robert A. Tomas1

671 National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 USA

82 Laboratory for Climate and Ocean-Atmosphere Studies, Department of Atmospheric and

9Oceanic Sciences, School of Physics, Peking University, Beijing, China

103 Department of Aviation Meteorology, College of Air Traffic Management, Civil Aviation

11University of China, Tianjin, China

124 Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder

13and NOAA Earth System Research Laboratory, Boulder CO 80305, USA

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16Jan 27, 201817

Submitted to GRL

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Revised March 31, 201819
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*Corresponding author address: Dr. Clara Deser, Climate and Global Dynamics Division,

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National Center for Atmospheric Research, P.O. Box 3000, Boulder, CO 80307 USA. Email:22

cdeser@ucar.edu Tel: 303-497-1359; Fax: 303-497-1333.

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Contents of this file24

Text S1

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Figures S1 to S926
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Text S1

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We compute the heat budget for the upper 100m of the eastern equatorial Pacific region (10°S-2910°N, 90°W-150°W) using the following equation:30

𝜌# 𝐶% ∫+, ') 𝑑𝑧 = −𝜌# 𝐶% ∫+, 𝛻 ∙ (𝑼𝑇)𝑑𝑧 − 𝜌# 𝐶% ∫+, 𝛻 ∙ 𝑲𝑑𝑧 + 𝑄:;) (1)31

where 𝜌# is the reference density of seawater, 𝐶% the specific heat of seawater, T is temperature,32

H=100m, U is the three-dimensional velocity, K is the diffusive temperature flux resulting from33

diapycnal diffusion and parameterized isopycnal diffusion, and 𝑄:;) is the net air-sea heat flux.

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The anomalous temperature tendency (TEND in Fig. 4a) is given by the sum of the advection term

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(first term on right hand side; ADV in Fig. 4a), the diffusion term (second term on right hand side;

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DIFF in Figs. 4a and 4b) and 𝑄:;) . The advection term can be divided into horizontal (ADVh) and37

vertical (ADVw) components as follows:

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𝐴𝐷𝑉ℎ = −𝜌# 𝐶% ∫+, @𝑢B 'C + 𝑢 'C + 𝑢B 'C + 𝑣 B 'F + 𝑣 'F + 𝑣′ 'F H 𝑑𝑧

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𝐴𝐷𝑉𝑤 = −𝜌# 𝐶% ∫+, @𝑤 B 'J + 𝑤 'J + 𝑤′ 'J H 𝑑𝑧

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where primed variables are anomalies and overbar variables are the climatology.

4142In Fig. 4c, the first, second and third terms on the right-hand side of Eqn. (3) are denoted 𝑊′𝑇L,

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M 𝑇′, and 𝑊′𝑇′ for short, respectively.
𝑊

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With equation (2) and (3), equation (1) can be changed into

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TEND-DIFF-Qnet = ADVh+ADVw (4)* '(**'(*'(*'( D'( D'( D'( D'( D'('( D(2)

(3)

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Note that the right-hand side of Eqn. (4) includes the decomposition terms

47(𝑢B 'C + 𝑢 'C + 𝑢B 'C + 𝑣 B 'F + 𝑣 'F + 𝑣 B 'F +'('( D'( D'('( D'( D'('( D'( D𝑤 B 'J + 𝑤 'J + 𝑤′ 'J ).

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Figure S1. Meridional streamfunction response (color shading; 10-9 kg s-1) to an abrupt loss ofArctic sea ice in FOM and SOM averaged over years (a, b) 6-25, (c, d) 41-60 and (e, f) 81-100.
Contours show the late 20th century climatology (contour interval = 2 x 10-9 kg s-1; zero contour isthickened).

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Figure S2. Pressure vertical velocity (omega; Pa s ) response across the Pacific averaged over5°N-5°S (color shading) to an abrupt loss of Arctic sea ice in FOM and SOM averaged over years(a, b) 6-25, (c, d) 41-60 and (e, f) 81-100. Contours show the late 20 century climatology (contourinterval = 0.01 Pa s ; negative values dashed). Positive (negative) values indicate downward(upward) motion.
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th-1

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Figure S3. Evolution of Pacific zonal-mean (a, b) SST (°C) and surface wind (m s-1) and (c, d)precipitation (mm d-1) responses to an abrupt loss of Arctic sea ice in FOM and SOM. (e)Climatological Pacific zonal-mean precipitation (mm d-1). Note the different wind vector scales in(a) and (b). The tropical (30N-30S) Pacific mean SST response at each time step has been removed
for clarity in (a) and (b).

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Figure S4. SST (°C) and surface wind (m s-1) responses to an abrupt loss of Arctic sea ice in FOM
averaged over years (a) 6-25, (b) 41-60 and (c) 81-100.

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Figure S5. Heat budget decomposition for temperature averaged over the layer 200-400m (T; °C)
in the region [10°S-10°N, 150°W-90°W] from FOM. The terms are defined as follows in units of°C s-1: (a) ADV = total advection, DIFF = diffusion; (b) ADVw = vertical advection, ADVu =zonal advection, ADVv = meridional advection; (c) VprTbr = meridional advection due to theanomalous meridional current acting on the mean meridional temperature gradient, VbrTpr =meridional advection due to the mean meridional current acting on the anomalous meridionaltemperature gradient, VprTpr = meridional advection due to the anomalous meridional current
acting on the anomalous meridional temperature gradient; (d) WprTbr = vertical advection due tothe anomalous vertical motion acting on the mean vertical temperature gradient, WbrTpr = verticaladvection due to the mean vertical motion acting on the anomalous vertical temperature gradient,WprTpr = vertical advection due to the anomalous vertical motion acting on the anomalous verticaltemperature gradient.

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Figure S6. Depth-latitude sections of the temperature response (color shading; °C) superimposed
upon climatological mean isopycnals (contours; kg m-3) averaged over the longitude band (150°W90°W) to an abrupt loss of Arctic sea ice in FOM, averaged over years: (a) 6-25, (b) 21-40, (c) 4160, (d) 61-80 and (e) 81-100.

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Figure S7. Heat budget decomposition for temperature averaged over the layer 200-400m (T; °C)
in the region [30°S-10°S, 150°W-90°W] in FOM. The terms are defined as follows, in units of °C
s-1: (a) ADV = total advection, DIFF = diffusion; (b) ADVw = vertical advection, ADVu = zonaladvection, ADVv = meridional advection; (c) WprTbr = vertical advection due to the anomalous
vertical motion acting on the mean vertical temperature gradient, WbrTpr = vertical advection due
to the mean vertical motion acting on the anomalous vertical temperature gradient, WprTpr =vertical advection due to the anomalous vertical motion acting on the anomalous verticaltemperature gradient, We = Ekman pumping computed from the wind stress curl (10 cm s-1).
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Figure S8. Evolution of the AMOC response (Sv) to an abrupt loss of Arctic sea ice in FOM.
AMOC is defined as the maximum meridional overturning streamfunction in the Atlantic sector.

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Figure S9. Demonstration that the heat budget decomposition for temperature averaged over theupper 100m in the region [10°S-10°S, 150°W-90°W] closes. Red curve shows the sum of the termson the left-hand side of Eqn. (4) in Text S1 (TEND – DIFF - Qnet); blue curve shows the sum ofthe terms on the right-hand side of Eqn. (4) in Text S1 (ADVh + ADVw). The close match between
the red and blue curves indicates that our heat budget decomposition closes to a high degree ofaccuracy.

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