[1] Sea ice is a key component in the global carbon cycle and climate system. In the traditional view, the sole effect of expanded sea ice coverage is to reduce the atmospheric pCO 2 by inhibiting air-sea gas exchange. However, this view neglects the effect that sea ice capping has on the biological production. By limiting light for photosynthesis, larger sea ice coverage would reduce the strength of the biological pump and therefore increase atmospheric pCO 2 . Recently, Kurahashi-Nakamura et al. (2007) suggested that the opposing impact of biology on atmospheric pCO 2 will more than offset the gas exchange effect, such that atmospheric pCO 2 will actually increase with larger sea ice coverage. In an effort to resolve this controversy, we use an intermediate-complexity, global model of biogeochemistry and climate to determine the sensitivity of atmospheric CO 2 concentration to changes in the sea ice coverage, driven by prescribed changes in sea ice albedo. When sea ice in our model is increased by 34% globally relative to the control run, gas solubility, ice capping effect and stratification increase, while biological production decreases; overall atmospheric pCO 2 is reduced by 9.4 ppmv. Our results broadly support the notion that the biological response of sea ice capping is as important as its physical response. Furthermore, we show that the overall change in atmospheric pCO 2 is indeed inversely related to sea ice coverage, but it is not because sea ice caps off gas exchange but because gas solubility is increased by lower temperatures that accompany sea ice expansion in our model simulations.Citation: Sun, X., and K. Matsumoto (2010), Effects of sea ice on atmospheric pCO 2 : A revised view and implications for glacial and future climates,

Consensus on the cause of recent midlatitude circulation changes toward a wavier manner in the Northern Hemisphere has not been reached, albeit a number of studies collectively suggest that this phenomenon is driven by global warming and associated Arctic amplification. Here, through a fingerprint analysis of various global simulations and a tropical heating-imposed experiment, we suggest that the suppression of tropical convection along the Inter Tropical Convergence Zone induced by sea surface temperature (SST) cooling trends over the tropical Eastern Pacific contributed to the increased summertime midlatitude waviness in the past 40 years through the generation of a Rossby-wave-train propagating within the jet waveguide and the reduced north-south temperature gradient. This perspective indicates less of an influence from the Arctic amplification on the observed mid-latitude wave amplification than what was previously estimated. This study also emphasizes the need to better predict the tropical Pacific SST variability in order to project the summer jet waviness and consequent weather extremes.