Coastal saltmarshes are dynamic, intertidal ecosystems which are increasingly being recognised for their contributions to ecosystem services, including carbon (C) accumulation and storage. The survival of saltmarshes and their capacity to store C under rising sea levels, however, is partially reliant upon surface sedimentation rates and influenced by a combination of physical and biological factors. In this study, we use several complementary methods to assess short-term (days) deposition and medium-term (months) accretion dynamics within three saltmarsh vegetation types common throughout southeast (SE) Australia. We found that surface accretion varies among vegetation assemblages, with medium-term (19 month) bulk accretion rates in the upper marsh rush ( Juncus ) assemblage (1.74 ± 0.13 mm y −1 ) consistently in excess of estimated local sea level rise (1.15 mm y −1 ). Accretion was lower and less consistent in both the succulent ( Sarcocornia ) (0.78 ± 0.18 mm y −1 ) and grass ( Sporobolus ) (0.88 ± 0.22 mm y −1 ) assemblages located lower in the tidal frame. Short-term (6 d) experiments showed deposition within Juncus plots to be dominated by autochthonous organic inputs with C deposition rates ranging from 0.41 ± 0.15 g C cm −2 y −1 (neap tidal period) to 0.87 ± 0.16 g C cm −2 y −1 (spring tidal period), while minerogenic inputs and lower C deposition dominated Sarcocornia (0.03 ± 0.01 to 0.23 ± 0.03 g C cm −2 y −1 ) and Sporobolus (0.06 ± 0.01 to 0.15 ± 0.03 g C cm −2 y −1 ) assemblages. Elemental (C : N), isotopic (δ 13 C), mid infrared (MIR) and 13 C NMR analyses revealed little difference in either the source or character of materials being deposited among neap versus spring tidal periods. Instead, these analyses point to substantial redistribution of materials within the Sarcocornia and Sporobolus assemblages, compared to high retention and preservation of organic inputs in the Juncus assemblage. By combining medium-term accretion quantification with short-term deposition measurements and chemical analyses we have gained novel insights into biophysical processes responsible for regional differences in surface dynamics among key saltmarsh vegetation assemblages. Our results suggest that unless belowground processes (e.g. root production) make substantial contributions to surface elevation gain, then Sarcocornia and Sporobolus assemblages may be particularly susceptible to changes in sea level, with implications for the future structure and function of these saltmarsh areas.