The study presents experimental and theoretical estimates of bimolecular rate constants (k₂) for cytochrome b₅ self-exchange electron transfer (ET) as a function of ionic strength (μ). The extended-Hückel approach for electronic coupling is parameter-dependent. Recent experimental and theoretical findings suggest that multiple tunneling regimes influence biological ET kinetics. Water molecules mediate ET between protein-protein interfaces, enhancing rates. Structured water between donor and acceptor cofactors significantly boosts ET rates. Aqueous tunneling pathways remain a key open issue in biological ET. Single-exponential decay models fail to describe water-mediated ET reactions. The structured water coupling regime may facilitate ET in critical near-contact distances. Water acts as a strong tunneling mediator when sterically constrained between redox cofactors. Further research is needed to explore how water-mediated coupling varies with protein-protein shape, surface charge, and dynamics. The study also reports a 650,000-year record of atmospheric CO₂ concentrations from the EPICA Dome C ice core, extending the Vostok record. CO₂ concentrations varied between 180 and 280 ppmv during glacial and interglacial periods. The record shows stable CO₂ variations over six glacial cycles, with a stable relationship between CO₂ and Antarctic climate. The Dome C CO₂ record (mean resolution of 731 years) is plotted alongside δD (Antarctic temperature proxy), benthic δ¹⁸O records, and a high-resolution benthic δ¹⁸O record from ODP site 980. The correlation between δD and benthic δ¹⁸O is strong, indicating global ice volume changes. The CO₂ record shows a stable 251.5 ± 1.9 ppmv during MIS 15.1, suggesting a stable carbon cycle for millennia. The study confirms the strong coupling between CO₂ and Antarctic temperature, supporting the role of the Southern Ocean in CO₂ variations. The lag between CO₂ and δD is consistent with previous observations, with a lag of 1900 years for the best correlation. The study also reports a composite CO₂ record over six and a half ice age cycles, showing that atmospheric CO₂ did not exceed 300 ppmv for the last 650,000 years before the preindustrial era. The study highlights the stable coupling between climate and the carbon cycle during the late Pleistocene.The study presents experimental and theoretical estimates of bimolecular rate constants (k₂) for cytochrome b₅ self-exchange electron transfer (ET) as a function of ionic strength (μ). The extended-Hückel approach for electronic coupling is parameter-dependent. Recent experimental and theoretical findings suggest that multiple tunneling regimes influence biological ET kinetics. Water molecules mediate ET between protein-protein interfaces, enhancing rates. Structured water between donor and acceptor cofactors significantly boosts ET rates. Aqueous tunneling pathways remain a key open issue in biological ET. Single-exponential decay models fail to describe water-mediated ET reactions. The structured water coupling regime may facilitate ET in critical near-contact distances. Water acts as a strong tunneling mediator when sterically constrained between redox cofactors. Further research is needed to explore how water-mediated coupling varies with protein-protein shape, surface charge, and dynamics. The study also reports a 650,000-year record of atmospheric CO₂ concentrations from the EPICA Dome C ice core, extending the Vostok record. CO₂ concentrations varied between 180 and 280 ppmv during glacial and interglacial periods. The record shows stable CO₂ variations over six glacial cycles, with a stable relationship between CO₂ and Antarctic climate. The Dome C CO₂ record (mean resolution of 731 years) is plotted alongside δD (Antarctic temperature proxy), benthic δ¹⁸O records, and a high-resolution benthic δ¹⁸O record from ODP site 980. The correlation between δD and benthic δ¹⁸O is strong, indicating global ice volume changes. The CO₂ record shows a stable 251.5 ± 1.9 ppmv during MIS 15.1, suggesting a stable carbon cycle for millennia. The study confirms the strong coupling between CO₂ and Antarctic temperature, supporting the role of the Southern Ocean in CO₂ variations. The lag between CO₂ and δD is consistent with previous observations, with a lag of 1900 years for the best correlation. The study also reports a composite CO₂ record over six and a half ice age cycles, showing that atmospheric CO₂ did not exceed 300 ppmv for the last 650,000 years before the preindustrial era. The study highlights the stable coupling between climate and the carbon cycle during the late Pleistocene.