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Journal of Geophysical Research Oceans Supporting Information for

Penetration of ultraviolet-B radiation in oligotrophic regions of the oceans during the Malaspina 2010 Expedition

Authors: S. Overmans ^1*, C. M. Duarte ^1,2, C. Sobrino ³, F. Iuculano ⁴, X. A. Álvarez-Salgado ⁵ & S.

Agustí ¹

Affiliations:

1 Red Sea Research Center (RSRC), King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia

2 Computational Biosciences Research Center (CBRC), King Abdullah University of Science and Technology (KAUST), Thuwal, Kingdom of Saudi Arabia

3 Biological Oceanography Group, Department of Ecology and Animal Biology, University of Vigo, Vigo, Spain

4 Global Change Research Group, Department of Oceanography and Global Change, Mediterranean Institute of Advanced Studies (IMEDEA), CSIC UIB, Esporles, Spain

5 Organic Geochemistry Lab, Department of Oceanography, CSIC Instituto de Investigaciones Marinas, Vigo, Spain

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Figures S1 to S8

Figure S1. CDOM absorption coefficients (aCDOM, in m^-1) at UV-B wavelengths 305 nm (top panel), 313 nm (middle panel), and 320 nm (bottom panel) measured during the Malaspina 2010 Expedition.

Figure S2. Results of the Dunn’s tests, that were performed after Kruskal-Wallis tests to identify if aCDOM (top row), ap (middle row) and ap as % of anw (bottom row) at 305 nm (left column), 313 nm (middle column) and 320 nm (right column) varied significantly (p<0.05) between Longhurst

provinces during the Malaspina 2010 Expedition. For a description of the Longhurst province codes, see Fig. 1.

Figure S3. Particulate absorption coefficients (ap, in m^-1) at UV-B wavelengths 305 nm (top panel), 313 nm (middle panel), and 320 nm (bottom panel) measured during the Malaspina Expedition.

Reported values are depth-weighted averages from surface waters (3 m depth) down to the 20% PAR

Figure S4. Downwelling diffuse attenuation coefficients (Kd, in m^-1) for the UV-B wavelengths 305 nm (top panel), 313 nm (middle panel), and 320 nm (bottom panel) measured during the Malaspina 2010 Circumnavigation.

Figure S5. Downwelling diffuse attenuation coefficients (Kd, in m^-1) for the UV-A wavelengths 340

Figure S6. Downwelling diffuse attenuation coefficients (Kd, in m^-1) for the integrated PAR spectrum (400–700 nm) measured during the Malaspina 2010 Expedition.

Figure S7. Results of the Dunn’s tests, that were performed after Kruskal-Wallis tests to identify if the downwelling diffuse attenuation coefficient (Kd) at 305, 313, 320, 340 nm varied significantly (p

<0.05) between Longhurst provinces during the Malaspina 2010 Expedition. For a description of the Longhurst provinces code, see Fig. 1.

Figure S8. Seasonal comparison between cloud fractions in the northern and southern tropics (15.5N to 15.5S) in year 2010. Bars represent monthly averages (mean  SD) of 1 x 1 sector squares between 179.5W and 179.5E (n=5760 per bar). Data were obtained from the publicly available Aqua/MODIS satellite data set curated by NASA’s Earth Observatory

(https://earthobservatory.nasa.gov/global-maps/MODAL2_M_CLD_FR). WIN, SPR, SUM and AUT refer to winter, spring, summer and autumn, respectively. WIN1 represents December for the northern latitudes and June for the southern latitudes. Asterisks indicate instances where the non- paired t-test identified significantly different means at level p <0.01.

Table S1. Slope, correlation, 95% confidence intervals and p-values determined as part of the pairwise correlation analysis with the variables sea surface temperature, Chl-a and Kd(PAR), as well as aCDOM, ap and Kd(λ) at wavelengths 305, 313 and 320 nm. For Chl-a, aCDOM and ap, depth-weighted (3 m to 20% PAR depth) average values were used for the analysis.

Wavelength Variable by Variable Count Slope

Lower 95% CI

Upper

95% CI p-value

305 nm Chl-a Temperature 129 0.007 0.171 -0.002 0.052

aCDOM Temperature 130 0.009 0.277 0.111 0.0014*

aCDOM Chl-a 133 0.377 0.436 0.287 <.0001*

ap Temperature 130 0.001 0.299 0.134 0.0005*

ap Chl-a 133 0.030 0.531 0.396 <.0001*

ap aCDOM 134 0.042 0.645 0.534 <.0001*

Kd(305) Temperature 112 -0.002 -0.084 -0.266 0.378

Kd(305) Chl-a 114 0.393 0.698 0.589 <.0001*

Kd(305) aCDOM 113 0.296 0.479 0.322 <.0001*

Kd(305) ap 113 3.913 0.393 0.225 <.0001*

Kd(PAR) Temperature 112 0.001 0.132 -0.055 0.164

Kd(PAR) Chl-a 114 0.086 0.794 0.714 <.0001*

Kd(PAR) aCDOM 113 0.056 0.471 0.313 <.0001*

Kd(PAR) ap 113 0.715 0.376 0.206 <.0001*

Kd(PAR) Kd(305) 117 0.164 0.780 0.697 <.0001*

313 nm Chl-a Temperature 129 0.007 0.171 -0.002 0.052

aCDOM Temperature 130 0.009 0.294 0.129 0.0007*

aCDOM Chl-a 133 0.335 0.429 0.279 <.0001*

ap Temperature 130 0.001 0.312 0.147 0.0003*

ap Chl-a 133 0.028 0.533 0.399 <.0001*

ap aCDOM 134 0.042 0.635 0.522 <.0001*

Kd(313) Temperature 112 -0.001 -0.039 -0.222 0.686

Kd(313) Chl-a 114 0.313 0.738 0.641 <.0001*

Kd(313) aCDOM 113 0.259 0.502 0.349 <.0001*

Kd(313) ap 113 3.642 0.450 0.289 <.0001*

Kd(PAR) Temperature 112 0.001 0.132 -0.055 0.164

Kd(PAR) Chl-a 114 0.086 0.794 0.714 <.0001*

Kd(PAR) aCDOM 113 0.061 0.460 0.301 <.0001*

Kd(PAR) ap 113 0.793 0.386 0.217 <.0001*

Kd(PAR) Kd(313) 117 0.219 0.797 0.720 <.0001*

320 nm Chl-a Temperature 129 0.007 0.171 -0.002 0.052

aCDOM Temperature 130 0.007 0.242 0.073 0.0055*

a Chl-a 133 0.309 0.412 0.260 <.0001*