Organic-walled microfossils from the north-west Weddell Sea, Antarctica: records from surface sediments after the collapse of the Larsen-A and Prince Gustav Channel ice shelves

Surface sediments from six box cores along the north-eastern Antarctic Peninsula document the dinoflagellate cyst (=dinocyst) and other non-pollen palynomorph (NPP) content soon after overlying ice shelves collapsed. Prince Gustav Channel (PGC) and Larsen-A (LA) areas exhibited markedly different dinocyst abundances, concentrations being low in LA (0-20 cysts g(-1)) and high in PGC (2600-9100 cysts g(-1), average: c. 3800 cysts g(-1)). Since similar water masses impact both areas, differences may be due to low biological productivity, limited sediment accumulation, and/or restricted fine-grain deposition at Larsen-A. Islandinium minutum (Harland & Reid in Harland et al.) Head et al. dominated dinocyst assemblages, occurring as both excysted and encysted forms (lesser abundance). Other taxa (Echinidinium cf. transparantum Zonneveld, Impagidinium pallidum Bujak, Bitectatodinium tepikiense Wilson, Operculodinium centrocarpum Wall & Dale, Brigantedinium spp., Selenopemphix antarctica Marret & de Vernal, Polykrikos? sp. A, and Polykrikos schwartzii Butschli) were rare. Such assemblage composition is unusual compared to previously published Southern Ocean data, but may be specific to ice shelf and/or recently ice-free environments. Alternatively, it may be attributable to excessive production facilitated by environmental factors and/or abundant food, or similar cyst morphologies produced by different dinoflagellates. Accompanying NPPs included zooplankton remains, acritarchs, and freshwater algae. Tintinnid loricae were most abundant (max. 800 g(-1)), followed by foraminiferal linings (max. 320 g(-1)), and the acritarch Palaeostomocystis fritilla (Bujak) Roncaglia (max. 150 g(-1)). Collectively, NPPs were more abundant in PGC compared to LA samples.