The influence of Arctic Fe and Atlantic fixed N on summertime primary production in Fram Strait, North Greenland Sea

Abstract

Climate change has led to a ~ 40% reduction in summer Arctic sea-ice cover extent since the 1970s. Resultant increases in light availability may enhance phytoplankton production. Direct evidence for factors currently constraining summertime phytoplankton growth in the Arctic region is however lacking. GEOTRACES cruise GN05 conducted a Fram Strait transect from Svalbard to the NE Greenland Shelf in summer 2016, sampling for bioessential trace metals (Fe, Co, Zn, Mn) and macronutrients (N, Si, P) at ~ 79°N. Five bioassay experiments were conducted to establish phytoplankton responses to additions of Fe, N, Fe + N and volcanic dust. Ambient nutrient concentrations suggested N and Fe were deficient in surface seawater relative to typical phytoplankton requirements. A west-to-east trend in the relative deficiency of N and Fe was apparent, with N becoming more deficient towards Greenland and Fe more deficient towards Svalbard. This aligned with phytoplankton responses in bioassay experiments, which showed greatest chlorophyll-a increases in + N treatment near Greenland and + N + Fe near Svalbard. Collectively these results suggest primary N limitation of phytoplankton growth throughout the study region, with conditions potentially approaching secondary Fe limitation in the eastern Fram Strait. We suggest that the supply of Atlantic-derived N and Arctic-derived Fe exerts a strong control on summertime nutrient stoichiometry and resultant limitation patterns across the Fram Strait region.

The 79°N Glacier cavity modulates subglacial iron export to the NE Greenland Shelf

“…Other stations from the same cruise, not discussed herein, are marked for completion (see ref. 44 for an overview). The black thin line from S1 to S7 highlights the section from which depth profiles are discussed in Figs.…”

Iron Speciation in Fram Strait and Over the Northeast Greenland Shelf: An Inter-Comparison Study of Voltammetric Methods

“…Sampling and sample-handling were done following GEOTRACES sampling procedures for trace elements (Cutter et al, 2010). The detailed sample collection for DFe was reported by Kanzow (2017); (Krisch et al, 2020), and for dissolved Fe-binding organic ligands by Ardiningsih et al (2020). Right after recovery of the trace metal clean rosette and the GO-FLO bottles were carried into a trace metal clean container for filtration.…”

“…Figure was made using the software Ocean Data View (Schlitzer, 2018). coupled plasma-mass spectrometry (HR-ICP-MS, Thermo Fisher Element XR) after pre-concentration (Rapp et al, 2017), the detailed procedure is described elsewhere (Krisch et al, 2020). Subsamples for a second DFe determination from the ligand bottles, was analyzed using HR-ICP-MS (Thermo Fisher Element XR) after pre-concentration using an automated SeaFAST system (SC-4 DX SeaFAST pico; ESI), and the quantification was done via standard additions.…”

“…From results from the same expedition where our samples were taken we know that probably phytoplankton is limited by Fe and N in Fram strait. These deficiencies have geographical east west gradients with N being more deficient in the west near Greenland and Fe in the east (Krisch et al, 2020). This region provides an ideal hydrographic setting for comparing different CLE-AdCSV methods with different ALs.…”

“…Concentrations of organic ligands in the vicinity of the 79N Glacier terminus were high, but those ligands were relatively weak compared to organic ligands in Fram Strait and Norske Trough. In addition, it appears that the characteristics of organic ligands control the glacial DFe export from the northeast Greenland continental shelf to the Fram Strait (Ardiningsih et al, 2020;Krisch et al, 2020). Therefore, it is of interest to study whether the different methods will give the same information on ligand presence and environmental Fe transport in this region.…”