Stable isotope (delta13C and delta15N) composition of particulate organic matter, nutrients and dissolved organic matter during spring ice retreat at Terra Nova Bay.

Concentration and isotope composition of particulate organic matter were analysed in five coastal sites placed on the annual fast ice and in the underlying water column at Terra Nova Bay. The highest increases of POC (< 2767 µM C) and PON (< 420 µM N) were reached in bottom ice and unconsolidated platelet layer, in connection with a large accumulation of nutrients and dissolved organic matter. Isotope POM composition highly varied in ice habitats (?13CPOC: -30.7 to -15.0?, ?15NPON: 1.8 to 9.9?). Constant negative ?13CPOC (down to -29.3?) and positive ?15NPON (up to 9.4?) values characterised the upper ice horizons, indicating the prevalence of aged detritus in these assemblages. By contrast, isotope composition (?13CPOC: -15.0 to -29.7?, ?15NPON: 1.8 to 9.6?) and POC/PON ratios (6.2 to 12.6) markedly changed in bottom ice and interstitial water, even on short temporal scales, because of the combined effects of internal growth and mixing among freshly produced biomasses. Sea ice breakout caused a large settling of particulate in the water column. It changed ?13CPOC (-27.8 to -22.8?) and ?15NPON (7.9 to 1.8?) values in suspended particulate matter, indicating that inputs from fast ice strongly affect the isotopic signature of particulate in Antarctic coastal waters.