Abstract
Iron (Fe) is an essential micronutrient for marine microbial organisms, and low supply controls productivity in large parts of the world’s ocean. The high latitude North Atlantic is seasonally Fe limited, but Fe distributions and source strengths are poorly constrained. Surface ocean dissolved Fe (DFe) concentrations were low in the study region (<0.1 nM) in summer 2010, with significant perturbations during spring 2010 in the Iceland Basin as a result of an eruption of the Eyjafjallajökull volcano (up to 2.5 nM DFe near Iceland) with biogeochemical consequences. Deep water concentrations in the vicinity of the Reykjanes Ridge system were influenced by pronounced sediment resuspension, with indications for additional inputs by hydrothermal vents, with subsequent lateral transport of Fe and manganese plumes of up to 250–300 km. Particulate Fe formed the dominant pool, as evidenced by 4–17 fold higher total dissolvable Fe compared with DFe concentrations, and a dynamic exchange between the fractions appeared to buffer deep water DFe. Here we show that Fe supply associated with deep winter mixing (up to 103 nmol m−2 d−1) was at least ca. 4–10 times higher than atmospheric deposition, diffusive fluxes at the base of the summer mixed layer, and horizontal surface ocean fluxes.
Highlights
Primary productivity, species composition and trophic structure of planktonic communities are controlled in many ocean regions by the availability of light and macronutrients, i.e. nitrogen (N), phosphorus (P) and silicon (Si)[1,2,3]
The sampling was conducted in the high latitude North Atlantic Ocean, including the Iceland Basin (IB) and Irminger Basin (IRB), the Reykjanes Ridge and Rockall Trough regions and the Hatton-Rockall Plateau (Fig. 1)
The North Atlantic sub-polar gyre flows through the IB and IRB, and has a cyclonic circulation
Summary
There is overwhelming evidence that the availability of the micronutrient iron (Fe) plays a critical role in regulating phytoplankton primary productivity and microbial diversity in the major High Nitrate Low Chlorophyll (HNLC) regions of the sub-Arctic and equatorial Pacific[4,5] and Southern Ocean[6,7]. These regions account for 40% of the world’s ocean and are replete with macronutrients but have low productivity as a result of a limited supply of Fe, intensified by a low solubility of the thermodynamically favoured Fe(III) redox state[8]. This study is part of the Irminger Basin Iron Study (IBIS) and presents the distribution of dissolved and total dissolvable Fe and the quantification of their various sources to the surface ocean of the high latitude North Atlantic
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