Physiological characteristics of open ocean and coastal phytoplankton communities of Western Antarctic Peninsula and Drake Passage waters

Photophysiological processes as well as uptake characteristics of iron and inorganic carbon were studied in inshore phytoplankton assemblages of the Western Antarctic Peninsula (WAP) and offshore assemblages of the Drake Passage. Chlorophyll a concentrations and primary productivity decreased from in- to offshore waters. The inverse relationship between low maximum quantum yields of photochemistry in PSII (F-v/F-m) and large sizes of functional absorption cross sections (sigma(PSII)) in offshore communities indicated iron-limitation. Congruently, the negative correlation between F-v/F-m values and iron uptake rates across our sampling locations suggest an overall better iron uptake capacity in iron-limited pelagic phytoplanlcton communities. Highest iron uptake capacities could be related to relative abundances of the haptophyte Phaeocystis antarctica. As chlorophyll a-specific concentrations of humic-like substances were similarly high in offshore and inshore stations, we suggest humic-like substances may play an important role in iron chemistry in both coastal and pelagic phytoplankton assemblages. Regarding inorganic carbon uptake kinetics, the measured maximum short-term uptake rates (V-max(CO2)) and apparent half-saturation constants (K-1/2(CO2)) did not differ between offshore and inshore phytoplankton. Moreover, V-max(CO2) and K-1/2(CO2) did not exhibit any CO2-dependent trend over the natural pCO(2) range from 237 to 507 mu atm. K-1/2(CO2) strongly varied among the sampled phytoplankton communities, ranging between 3.5 and 35.3 mu mol L-1 CO2. While in many of the sampled phytoplanlcton communities, the operation of carbon-concentrating mechanisms (CCMs) was indicated by low K-1/2(CO2) values relative to ambient CO2 concentrations, some coastal sites exhibited higher values, suggesting down-regulated CCMs. Overall, our results demonstrate a complex interplay between photophysiological processes, iron and carbon uptake of phytoplankton communities of the WAP and the Drake Passage. (C) 2015 The Authors. Published by Elsevier Ltd.