Seasonal and spatial dynamics of iron availability in the Scotia Sea

• Published in: Marine Chemistry
• Main Authors: Nielsdóttir, Maria C., Bibby, Thomas S., Moore, C. Mark, Hinz, Daria J., Sanders, Richard, Whitehouse, Michael, Korb, Rebecca, Achterberg, Eric P.
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Elsevier 2012
• Subjects: Marine Sciences; Chemistry; Southern Ocean; Austral; Scotia Sea; South Orkney Islands; Sea ice
• Online Access: http://nora.nerc.ac.uk/id/eprint/17950/; http://www.sciencedirect.com/science/article/pii/S0304420311001320

The Southern Ocean is the world's largest high nutrient low chlorophyll (HNLC) region. However, satellite images highlight several areas associated with island chains and shallow topographic features which display high phytoplankton biomass. Here we present the first study of seasonal variations in phytoplankton biomass and ironavailability in the ScotiaSea over both austral spring and summer seasons. Based on dissolved iron (dFe) and Chlorophyll a (Chl a) concentrations, the study area is be divided into three regions: North of South Georgia, south of South Georgia and the vicinity of South Orkney Islands. The ScotiaSea to the south of South Georgia exhibited low dFe concentrations (< 0.027–0.05 nM) in surface waters during both the spring and summer seasons. Nevertheless, nitrate concentrations were considerably lower in spring compared to summer (difference ~ 8 μM). Summer Chl a concentrations were ~ 1.4 mg m− 3 and in situ phytoplankton populations displayed evidence of iron stress, suggesting the development of seasonaliron limitation. Surface water dFe concentrations in the South Georgia bloom waters (north of the islands) were elevated and slightly lower during spring than summer (0.20 nM compared to 0.31 nM, P > 0.05). Nitrate concentrations were 16 μM lower in summer compared to spring, whilst Chl a standing stocks remained high. Enhanced dFe (~ 0.25 nM) and Chl a concentrations were furthermore observed in the vicinity of the South Orkney Islands, located in the southern ScotiaSea. Iron addition experiments showed that in situ phytoplankton were iron replete spring and summer north of South Georgia and in the vicinity of South Orkney Islands during summer. We thus suggest that increased iron supply in high productivity areas including the area north of South Georgia and the South Orkney Islands, was sustained by a continuous benthic supply from their shelf systems, with a potential additional input from seasonally retreating sea ice in the South Orkney system.