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Soil CO₂ efflux (F_s) plays an important role in forest carbon cycling yet estimates of F_s can remain unconstrained in many systems due to the difficulty in measuring F_s over long time scales in natural systems. It is important to quantify seasonal patterns in F_s through long-term datasets because individual years may show patterns that are not reflective of long-term averages. Additionally, determining predictability of net patterns in soil carbon flux based on environmental factors, such as moisture and temperature, is critical for appropriately modeling forest carbon flux. Ecosystems in moderate climates may have strong CO₂ efflux even during winter, and so continuous quantification of annual variability is especially important. Here, we used a 2008–2023 dataset in a lowland temperate forest ecosystem to address two main questions: (1) What are the seasonal patterns in F_s in a highly productive temperate rainforest? (2) How is average F_s across our study area predicted by average coincident temperature, soil moisture and precipitation totals? Data showed clear seasonality where F_s values are higher in summer. We also find F_s across our measurement network was predicted by variation in abiotic factors, but the interaction between precipitation/moisture and temperature resulted in greater complexity. Specifically, in spring a relatively strong relationship between air temperature and F_s was present, while in summer the relationship between temperature and F_s was flat. Winter and autumn seasons showed weak positive relationships. Meanwhile, a negative relationship between precipitation and Fs was present in only some seasons because most precipitation falls outside the normal growing season in our study system. Our data help constrain estimates of soil CO₂ fluxes in a temperate rainforest ecosystem at ~14–20 kg C ha⁻¹ day⁻¹ in summer and autumn, and 6.5–10.5 kg C ha⁻¹ day⁻¹ in winter and spring seasons. Together, estimates suggest this highly productive temperate rainforest has annual soil-to-atmosphere fluxes of CO₂ that amount to greater than 4.5 Mg C ha⁻¹ year⁻¹. Sensitivity of such fluxes to regional climate change will depend on the balance of F_s determined by autotrophic phenological responses versus heterotrophic temperature and moisture sensitivity. Relatively strong seasonal variation coupled with comparatively weak responses to abiotic variables suggest F_s may be driven largely by seasonal trends in autotrophic respiration. Accordingly, plant and tree responses to climate may have a stronger effect on F_s in the context of climate change than temperature or moisture changes alone.