The eastern extent of seasonal iron limitation in the high latitude North Atlantic Ocean

A. J. Birchill*, N. T. Hartner, K. Kunde, B. Siemering, C. Daniels, D. González-Santana, A. Milne, S. J. Ussher, P. J. Worsfold, K. Leopold, S. C. Painter, M. C. Lohan

*Corresponding author for this work

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Abstract

The availability of iron (Fe) can seasonally limit phytoplankton growth in the High Latitude North Atlantic (HLNA), greatly reducing the efficiency of the biological carbon pump. However, the spatial extent of seasonal iron limitation is not yet known. We present autumn nutrient and dissolved Fe measurements, combined with microphytoplankton distribution, of waters overlying the Hebridean (Scottish) shelf break. A distinct biogeochemical divide was observed, with Fe deficient surface waters present beyond the shelf break, much further eastwards than previously recognised. Due to along and on-shelf circulation, the Hebridean shelf represents a much-localised source of Fe, which does not fertilise the wider HLNA. Shelf sediments are generally thought to supply large quantities of Fe to overlying waters. However, for this Fe to influence upper-ocean biogeochemical cycling, efficient off-shelf transport mechanisms are required. This work challenges the view that the oceanic surface waters in close proximity to continental margins are iron replete with respect to marine primary production demands.

Original languageEnglish
Article number1435
Number of pages12
JournalScientific Reports
Volume9
Issue number1
Early online date5 Feb 2019
DOIs
Publication statusPublished - 1 Dec 2019

Keywords

  • UKRI
  • NERC
  • NE/L501840/1
  • NE/K001779/1
  • NE/ K001884/1
  • NE/K001701/1

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