Iron stress in the Pacific region of the Southern Ocean:evidence from enrichment bioassays

Abstract

The effect of iron on phytoplankton physiology in a scarcely investigated part of the Pacific region of the Southern Ocean was studied during an expedition aboard RV 'Polarstern' Physiological effects of iron enrichments were studied during short-term bottle experiments (72 h) in highnutrient, low-chlorophyll (HNLC) water samples. Throughout the expedition (March to May 1995), surface water nitrate concentrations were high (21 to 27 pM) and surface water silicate concentrations varied considerably north (<3.5 pM) and south ( > l 3 pM) of the Polar Front, whereas low chlorophyll a concentrations (<0.2 pg I-') were measured in the research area. Small-sized cells (<S pm) dominated the phytopianicton communiiy; & d i ~l l l b w e l e observed only occasionci!:Y north G! thc Po!ar Prent.