Spatial and inter-annual variability of net community productivity in the western Antarctica Peninsula region
The distribution of net community production (NCP) and gross primary production (GPP) in the western shelf of the Antarctic Peninsula (WAP) has been studied during cruises in 4 consecutive Januaries (2008-2011). NCP and GPP are derived from measurements of [O2]/[Ar] ratios, and triple oxygen isotopic compositions of dissolved O2 in the mixed layer water. This study shows large spatial and inter-annual variability of NCP and GPP, and indicates persistently a negative correlation between NCP, GPP and the mixed layer depth (MLD) in the shelf and coastal waters where there is no significant iron limitation. This relationship suggests that light availability may be the key factor regulating NCP and GPP in the inshore WAP, and highlights importance of various physical processes that strengthen upper water column stratification and relieve light limitation. This is especially observed in the southern part of the study region for Jan. 2011, where low wind, high surface photosynthetically active radiation (PAR) and freshening of the surface water by ice melting acted together to facilitate anomalously high NCP and GPP in the warm and well-stratified water.