Stable isotope (δ13C and δ15N) composition of particulate organic matter, nutrients and dissolved organic matter during spring ice retreat at Terra Nova Bay

Abstract

AbstractConcentration and isotope composition of particulate organic matter were analysed from five coastal sites 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 the unconsolidated platelet layer, linked with a large accumulation of nutrients and dissolved organic matter. Isotope POM composition in ice habitats was highly varied (δ13CPOC: -30.7 to -15.0‰, δ15NPON: 1.8–9.9‰). Constant negative δ13CPOC (> -29.3‰) and positive δ15NPON (< 9.4‰) values characterized the upper ice horizons, indicating the prevalence of aged detritus in these assemblages. By contrast, isotope composition (δ13CPOC: -15.0 to -29.7‰, δ15NPON: 1.8–9.6‰) and POC/PON ratios (6.2–12.6) changed markedly in bottom ice and interstitial water, even on short time scales, because of the combined effects of internal growth and mixing among freshly produced biomass. Sea ice breakout caused a large settling of particulates in the water column. It changed δ13CPOC (from 7.9 to 1.8‰) and δ15NPON (7.9–1.8‰) values in suspended particulate matter, indicating that inputs from fast ice strongly affect the isotopic signature of the particulate assemblage Antarctic coastal waters.