Controls on the spatial variability of δ13CDIC along the Bransfield Strait during austral summer

Bransfield Strait has been identified as a climate hotspot for understanding regional environmental changes with global impact. This study focuses on enhancing the understanding of carbon cycle dynamics and its interactions with hydrographic variables in Bransfield Strait, located on the northern Antarctic Peninsula. The stable carbon isotopes of dissolved inorganic carbon (δ13CDIC) were investigated in the study region during comprehensive sampling in 2023 along the major ocean basins. Bransfield Strait is influenced by two main source water masses: the Circumpolar Deep Water (CDW), which intrudes into the region from the Antarctic Circumpolar Current meander, and Dense Shelf Water (DSW), which is advected by coastal currents from the Weddell Sea continental shelf. The study reveals CDW’s dominant role in 2023, accounting for ~60% of the water mass mixture in the region and limiting the highest contribution of DSW to the deep layer of the central basin. The spatial variation of δ13CDIC signatures showed that biogeochemical processes predominantly shape the δ13CDIC distribution along the water column. Photosynthesis enriched the surface waters with the heavier carbon isotope, with signatures ranging from 2 to 1.5‰, while organic matter remineralization depleted it below the mixed layer (ranging from 0 to − 2‰). Horizontally, δ13CDIC distribution was influenced by the higher contribution of each source water mass. Thermodynamic fractionation contributed to the enrichment of δ13CDIC (~ 1 to 1.5‰) in the CDW layer in Bransfield Strait. Conversely, the predominance of younger and colder DSW exhibited a depletion of δ13CDIC (− 1 to − 2‰). Therefore, δ13CDIC is identified as an additional tracer to provide new insights into the biogeochemical and hydrodynamic processes of Bransfield Strait.