The biogeochemical composition and spatial distribution of suspended particulate organic carbon (POC), its stable carbon isotope (δ13C-POC), and suspended total particulate nitrogen (PN) were investigated during the austral summer of 2020 in the Gerlache Strait, a productive coastal area of the Northern Antarctic Peninsula. This study addressed the distribution patterns relative to sea ice meltwater inputs, phytoplankton community composition, and water masses distribution, aiming to identify the primary drivers of particle composition and δ13C-POC signatures in the water column. The results showed that distinct physical-biological processes influenced the biogeochemical dynamics of POC, PN and δ13C-POC across the surface and mesopelagic layers (100–800 m) in the Gerlache Strait. Surface suspended particles indicated an autotrophic production and has been accumulated due the seasonal organic matter production and shallow stratification (<20 m). Higher surface concentrations of POC (>10 μmol L−1), PN (>2 μmol L−1) and chlorophyll-a (>2 mg m−3) were found at low salinity conditions emphasising the role of meltwater input on organic matter production. Additionally, our findings suggested the influence of phytoplankton community composition on shaping surface δ13C-POC signatures and POC/PN ratios, consistent with differences in cell size and geometry. At the mesopelagic layer, particle composition variations were associated with the distribution of the water masses in the studied region. Intrusions of old modified-Circumpolar Deep Water contributed to increase the δ13C-POC and POC/PN ratios, due to preferential remineralisation of the lighter carbon isotope (12C) and nitrogen. Conversely, High Salinity Shelf Water – a water mass recently ventilated and advected from the Weddell Sea continental shelf to the northeast sector of the Gerlache Strait – showed a particle chemical composition like that observed in the surface waters.
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