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Microorganisms play a key role in the carbon (C) cycle through soil organic matter (SOM). The rate of SOM mineralization, the influence of abiotic factors on this rate and the potential behaviour of SOM are of particular interest in the northern Antarctic Peninsula and offshore islands. This is one of the most rapidly warming regions on Earth with numerous ice-free areas, some with abundant wildlife and with the greatest known soil organic carbon (SOC) storage in Antarctica. The latter implies extended Antarctic summer conditions promote increased terrestrial plant growth and soil microbial activity (SMA). SMA, determined by respirometry, is a measure of ecosystem function, and depends on microclimatic conditions and soil environmental properties. SMA and the effect of abiotic variables have been analysed in locations with different soil types, on Cierva Point (Antarctic Peninsula), Deception Island and Fildes Peninsula (King George Island). Soil microbial biomass carbon (SMBC) ranged from 5.66 to 196.6 mg SMBC kg -1 and basal respiration (BR) from 2.86 to 160.67 mg CO 2 kg -1 d -1 . SMBC and BR values were higher in Cierva Point, followed by Fildes Peninsula and Deception Island, showing the same trend of SOM abundance . Except for Cierva Point, low nitrogen, phosphorus and C concentrations were observed. SMBC/total organic carbon (TOC) levels indicated that SOC was recalcitrant and SOM content was closely related to the extent of vegetation cover observed in situ. High metabolic quotient values obtained at Cierva Point and Deception Island (median values 7.27 and 6.53 mg C-CO 2 g SMBC -1  h -1 ) and low SMBC/TOC in Cierva Point suggest a poor efficiency of the microbial populations in the consumption of the SOC. High SMBC/TOC values obtained in Deception Island indicates that SMBC may influence SOM stabilization. Mineralization rates were very low (negligible values to 1.44%) and sites with the lowest values had the highest SOM., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)