The Scottish shelf break is not a significant source of iron to North Atlantic surface waters

A high resolution survey of the distribution of dissolved iron (dFe) over the Hebridean (Scottish) shelf break was conducted as part of the U.K. Shelf Sea Biogeochemistry programme, a GEOTRACES process study (GApr04). Despite the close proximity to shelf sediments, which are known to supply large quantities of dFe to overlying water column, the results revealed surprisingly low concentrations of dFe (<0.1 nM) in surface waters overlying the shelf break. Birchill and colleagues (2019, see reference below) relate this to the prevailing physical circulation of the region, which limits off shelf transport in surface waters, and conclude that this shelf system is not a significant source dFe to high latitude North Atlantic surface waters. It is therefore suggested that the conditions leading to seasonal iron limitation of phytoplankton in the Iceland and Irminger basins extend much further eastwards than previously identified.

19 Birchill

Figure: (A) Map of the survey region with sampling locations. (B) Example of cross shelf transect of dFe distribution, detailing the contrast between shelf waters with high dFe concentrations (>2 nM) and surface oceanic waters with remarkably low dFe concentrations (<0.1 nM). (C) Depth profile of dFe: NO3, oceanic stations close to Hebridean shelf have similar values to those previously reported for the seasonally iron limited Icelandic Basin. Dashed line denotes 0.05 dFe:NO3 (nM:μM), the lower limit observed in Fe replete cultured phytoplankton. Click here to view the figure larger.

Reference:

Birchill, A. J., Hartner, N. T., Kunde, K., Siemering, B., Daniels, C., González-Santana, D., Milne, A. Ussher, S. J., Worsfold, P. J., Leopold, K., Painter, S. C., Lohan, M. C. (2019). The eastern extent of seasonal iron limitation in the high latitude North Atlantic Ocean. Scientific Reports, 9(1), 1435. DOI: http://doi.org/10.1038/s41598-018-37436-3

Latest highlights

Science Highlights

Thorium-Protactinium fate across the tropical Atlantic Ocean: what reveals the water column-sediment coupling

Twenty seawater profiles and twenty core-top 231-protactinium and 230-thorium analyses were realised by Ng and colleagues along five depth transects across the northern tropical Atlantic open ocean.

18.01.2021

Science Highlights

Constraining Oceanic Copper Cycling through Artificial Intelligence and Ocean Circulation Inverse Model

Using available observations of dissolved copper, artificial neural networks, and an ocean circulation inverse model, authors calculated a global estimate of the 3-dimensional distribution and cycling of dissolved copper in the ocean

15.01.2021

Science Highlights

Particulate rare earth elements distributions, processes and characterisation of nepheloids in the North Atlantic

Lagarde et al. realised the first basin scale section of particulate rare earth elements concentrations across the North Atlantic Ocean.

06.01.2021

Science Highlights

Isopycnal mixing controls protactinium and thorium distributions in the Pacific Southern Ocean

Pavia and co-workers determined the physical and chemical speciation as well as the vertical distribution of Protactinium-231 and Thorium-230 at 12 stations across the Southern Pacific Antarctic Circumpolar Current…

13.12.2020

Rechercher