Marine cold-spells (MCSs), the cold ocean temperature extremes as the counterpart to marine heatwaves (MHWs), may have brutal impacts on marine ecosystems and fisheries. However, recent MCS-related researches mainly focused on the ocean surface, while the character of bottom MCSs (BMCSs) remains unclear. Here, we provide an analogous assessment of BMCSs and surface MCSs (SMCSs) over the continental shelf of China based on a 1/12° ocean reanalysis dataset during period of 1993–2023. We found that the duration and cumulative intensity of BMCSs can be longer and more intense than SMCSs, up to 20 d and ‒20 °C days, respectively. The mean and cumulative intensities of BMCSs and SMCSs increased in most regions, reaching 0.2 °C–0.4 °C/10a and 20 °C–40 °C days/10a, respectively. In contrast, there are no clear trends in the area-averaged time series of BMCS/SMCS metrics over the period 1993–2023. In terms of category and seasonal variations, BMCS generally has longer days than SMCS in the Moderate and Strong categories, persists longer than SMCS in summer and autumn (ranging from 2–6 d), and is more intense than SMCS in autumn and winter (ranging from 1 °C–2 °C). There are clear differences in category and seasonal changes between BMCS and SMCS. Furthermore, annual BMCS days are positively correlated with bottom depth, while mean intensity is negatively correlated. In addition, BMCS and SMCS often co-occur over shallow areas where the mixed layer depth can extend to the bottom.

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