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Interannual climate changes and increasing atmospheric CO2 (AtmCO2) have significantly altered sea surface partial pressure of CO2 (pCO2) in the Beaufort Sea (BS). Yet, their decadal variability and underlying mechanisms remain inadequately understood. Using observational data and the Regional Arctic System Model (RASM), a decreasing trend transition of the BS summer surface pCO2 was identified at around 2010–2012. Sensitivity cases reveal that the decadal trend transition in surface pCO2 (early: 4.12 ± 0.80 μatm/yr, p < 0.05 and late: 1.23 ± 2.22 μatm/yr, p > 0.05) is driven by interannual climate changes. While the long-term increase in AtmCO2 does not directly drive surface pCO2 trend transition, it reduces its magnitude. The sensitivity experiment with no interannual AtmCO2 changes from 1990 reveals that the statistically significant contributor of the decadal trend transition in surface pCO2 is the concurrent transition in sea ice concentration (SIC, early: −0.0120 ± 0.0037/yr, p < 0.05 and late: 0.0101 ± 0.0063/yr, p > 0.05). The decadal trend transitions in the subsurface and deep layer pCO2 are negligible compared to that in the sea surface pCO2 due to the insignificant influence of interannual climate changes on subsurface and deep layer pCO2. The surface pCO2 decadal trend transition is significantly correlated with a trend transition of CO2 sink. On seasonal timescales, the effects of SIC on the decadal trend transition of pCO2 occur primarily within the duration of open-water (DOW), and align with the decadal trend transitions in the open-water start day, end day, and DOW. The magnitude of sea surface pCO2 trend transition increases as the magnitude of the DOW trend transition increases.

What are the main findings? * A decadal trend transition in sea surface pCO[sub.2] in the Beaufort Sea was found around 2010–2012 both by observation and via a numerical model. * The sea surface pCO[sub.2] trend transition was driven by a concurrent trend transition in sea ice cover through changing the seasonal duration of open-water. A decadal trend transition in sea surface pCO[sub.2] in the Beaufort Sea was found around 2010–2012 both by observation and via a numerical model. The sea surface pCO[sub.2] trend transition was driven by a concurrent trend transition in sea ice cover through changing the seasonal duration of open-water. What are the implications of the main findings? * This finding improves our understanding of the decadal-scale response of the Arctic Ocean carbon cycle to climate changes. * This finding advances our understanding of the influence of seasonal sea ice variabilities on decadal trends in the carbon cycle. This finding improves our understanding of the decadal-scale response of the Arctic Ocean carbon cycle to climate changes. This finding advances our understanding of the influence of seasonal sea ice variabilities on decadal trends in the carbon cycle. Interannual climate changes and increasing atmospheric CO[sub.2] (AtmCO[sub.2]) have significantly altered sea surface partial pressure of CO[sub.2] (pCO[sub.2]) in the Beaufort Sea (BS). Yet, their decadal variability and underlying mechanisms remain inadequately understood. Using observational data and the Regional Arctic System Model (RASM), a decreasing trend transition of the BS summer surface pCO[sub.2] was identified at around 2010–2012. Sensitivity cases reveal that the decadal trend transition in surface pCO[sub.2] (early: 4.12 ± 0.80 μatm/yr, p < 0.05 and late: 1.23 ± 2.22 μatm/yr, p > 0.05) is driven by interannual climate changes. While the long-term increase in AtmCO[sub.2] does not directly drive surface pCO[sub.2] trend transition, it reduces its magnitude. The sensitivity experiment with no interannual AtmCO[sub.2] changes from 1990 reveals that the statistically significant contributor of the decadal trend transition in surface pCO[sub.2] is the concurrent transition in sea ice concentration (SIC, early: −0.0120 ± 0.0037/yr, p < 0.05 and late: 0.0101 ± 0.0063/yr, p > 0.05). The decadal trend transitions in the subsurface and deep layer pCO[sub.2] are negligible compared to that in the sea surface pCO[sub.2] due to the insignificant influence of interannual climate changes on subsurface and deep layer pCO[sub.2]. The surface pCO[sub.2] decadal trend transition is significantly correlated with a trend transition of CO[sub.2] sink. On seasonal timescales, the effects of SIC on the decadal trend transition of pCO[sub.2] occur primarily within the duration of open-water (DOW), and align with the decadal trend transitions in the open-water start day, end day, and DOW. The magnitude of sea surface pCO[sub.2] trend transition increases as the magnitude of the DOW trend transition increases.

The magnetic fields and dynamical processes in the solar polar regions play a crucial role in the solar magnetic cycle and in supplying mass and energy to the fast solar wind, ultimately being vital in controlling solar activities and driving space weather. Despite numerous efforts to explore these regions, to date no imaging observations of the Sun's poles have been achieved from vantage points out of the ecliptic plane, leaving their behavior and evolution poorly understood. This observation gap has left three top-level scientific questions unanswered, 1) How does the solar dynamo work and drive the solar magnetic cycle? 2) What drives the fast solar wind? 3) How do space weather processes globally originate from the Sun and propagate throughout the solar system? The Solar Polar-orbit Observatory (SPO) mission, a solar polar exploration spacecraft, is proposed to address these three unanswered scientific questions by imaging the Sun's poles from high heliolatitudes. In order to achieve its scientific goals, SPO will carry six remote-sensing and four in-situ instruments to measure the vector magnetic fields and Doppler velocity fields in the photosphere, to observed the Sun in the extreme ultraviolet, X-ray, and radio wavelengths, to image the corona and the heliosphere up to 45 \\(R_\\), and to perform in-situ detection of magnetic fields, and low- and high-energy particles in the solar wind.