Sea-ice algal primary production and nitrogen uptake rates off East Antarctica

• Published in: Deep Sea Research Part II: Topical Studies in Oceanography
• Main Authors: Roukaerts, A, Cavagna, A-J, Fripiat, F, Lannuzel, D, Meiners, KM, Dehairs, F
• Format: Article in Journal/Newspaper
• Language: English
• Published: Pergamon-Elsevier Science Ltd 2015
• Subjects: Earth Sciences; Oceanography; Chemical Oceanography; Antarctic; Austral; East Antarctica; Antarc*; Antarctica; Sea ice
• Online Access: https://doi.org/10.1016/j.dsr2.2015.08.007; http://ecite.utas.edu.au/104046

Antarctic pack ice comprises about 90% of the sea ice in the southern hemisphere and plays an important structuring role in Antarctic marine ecosystems, yet measurements of ice algal primary production and nitrogen uptake rates remain scarce. During the early austral spring of 2012, measurements for primary production rates and uptake of two nitrogen substrates (nitrate and ammonium) were conducted at 5 stations in the East Antarctic pack ice (6366S, 115125E). Carbon uptake was low (3.52mgCm −2 d −1 ) but a trend of increased production was observed towards the end of the voyage suggesting pre-bloom conditions. Significant snow covers reaching, up to 0.8m, induced strong light limitation. Two different regimes were observed in the ice with primarily nitrate based new production ( f -ratio: 0.800.95) at the bottom of the ice cover, due to nutrient-replete conditions at the icewater interface, and common for pre-bloom conditions. In the sea-ice interior, POC:PN ratios (2070) and higher POC:Chl a ratios suggested the presence of large amounts of detrital material trapped in the ice and here ammonium was the prevailing nitrogen substrate. This suggests that most primary production in the sea-ice interior was regenerated and supported by a microbial food web, recycling detritus.