Low dissolved Fe and the absence of diatom blooms in remote Pacific waters of the Southern Ocean

• Published in: Marine Chemistry
• Main Authors: de Baar, Hein J.W., de Jong, Jeroen T.M., Nolting, Rob F., Timmermans, Klaas R., van Leeuwe, Maria A., Bathmann, U., Rutgers van der Loeff, Michiel, Sildam, Jüri
• Format: Article in Journal/Newspaper
• Language: English
• Published: 1999
• Subjects: diatom; dissolved Fe; Southern Ocean; ANTARCTIC CIRCUMPOLAR CURRENT; NORTHERN NORTH-ATLANTIC; WEDDELL SEA; PHYTOPLANKTON COMMUNITIES; ELEMENTAL COMPOSITION; MARINE-PHYTOPLANKTON; BELLINGSHAUSEN SEA; IRON DISTRIBUTIONS; SURFACE WATERS; INDIAN-OCEAN; Antarctic; Austral; Bakker; Bellingshausen Sea; Drake Passage; Indian; Pacific; The Antarctic; Weddell; Weddell Sea; Antarc*; North Atlantic
• Online Access: https://hdl.handle.net/11370/ef63525a-8ba8-4ecd-89e8-e90016c4c0b8; https://research.rug.nl/en/publications/ef63525a-8ba8-4ecd-89e8-e90016c4c0b8; https://doi.org/10.1016/S0304-4203(99)00022-5; https://pure.rug.nl/ws/files/10515216/1999MarChemdeBaar.pdf

The remote waters of the Pacific region of the Southern Ocean are the furthest away from any upstream and upwind continental Fe sources. This prime area for expecting Fe limitation of the plankton ecosystem was studied (March-April 1995) along a north-south transect at similar to 89 degrees W. At the end of the austral summer the upper wind-mixed layers were in the order of similar to 100 m deep, thus mixing the algae down into the dimly lit part of the euphotic zone where photosynthesis is severely restricted. The dissolved Fe was found at low concentrations ranging from 0.05 nM near the surface to 0.5 nM in deeper waters. Along the transect (52 degrees S-69 degrees S), the dissolved iron was enhanced in the Polar Front, as well as near the Antarctic continental margin (0.6-1.0 nM). In between, the southern ACC branch was depleted with iron; here the concentrations in surface waters were quite uniform at about 0.21 nM. This is only somewhat lower than the 0.49 nM (October 1992) and 0.31 nM (November 1992) averages in early spring in the southern ACC part of Atlantic 6 degrees W sections [de Baar, H.J.W., de Jong, J.T.M., Bakker, D.C.E. Loscher, B.M., Veth, C., Bathmann, U., Smetacek, V., 1995. Importance of iron for phytoplankton spring blooms and CO2 drawdown in the Southern Ocean. Nature 373, 412-415; Loscher, B.M., de Jong, J.T.M., de Baar, H.J.W., Veth, C., Dehairs, F., 1997. The distribution of iron in the Antarctic Circumpolar Current. Deep-Sea Research II 44, 143-188.]. First, the lower similar to 0.21 nM in March-April 1995 may partly be due to continuation of the seasonal trend where the phytoplankton growth, albeit modest, was removing Fe from the surface waters. Secondly, the 89 degrees W Pacific stations are further downstream continental or seafloor sources than the Atlantic 6 degrees W section. In the latter case, the ACC water had passed through the Drake Passage and also over the Sandwich Plateau. Indeed for Drake Passage, intermediate Fe concentrations have been reported by others. The ...