Arctic – Atlantic Exchange of the Dissolved Micronutrients Iron, Manganese, Cobalt, Nickel, Copper and Zinc With a Focus on Fram Strait

Abstract

The Arctic Ocean is considered a source of micronutrients to the Nordic Seas and the North Atlantic Ocean through the gateway of Fram Strait (FS). However, there is a paucity of trace element data from across the Arctic Ocean gateways, and so it remains unclear how Arctic and North Atlantic exchange shapes micronutrient availability in the two ocean basins. In 2015 and 2016, GEOTRACES cruises sampled the Barents Sea Opening (GN04, 2015) and FS (GN05, 2016) for dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn). Together with the most recent synopsis of Arctic-Atlantic volume fluxes, the observed trace element distributions suggest that FS is the most important gateway for Arctic-Atlantic dissolved micronutrient exchange as a consequence of Intermediate and Deep Water transport. Combining fluxes from FS and the Barents Sea Opening with estimates for Davis Strait (GN02, 2015) suggests an annual net southward flux of 2.7 ± 2.4 Gg•a −1 dFe, 0.3 ± 0.3 Gg•a −1 dCo, 15.0 ± 12.5 Gg•a −1 dNi and 14.2 ± 6.9 Gg•a −1 dCu from the Arctic toward the North Atlantic Ocean. Arctic-Atlantic exchange of dMn and dZn were more balanced, with a net southbound flux of 2.8 ± 4.7 Gg•a −1 dMn and a net northbound flux of 3.0 ± 7.3 Gg•a −1 dZn. Our results suggest that ongoing changes to shelf inputs and sea ice dynamics in the Arctic, especially in Siberian shelf regions, affect micronutrient availability in FS and the high latitude North Atlantic Ocean. Plain Language SummaryRecent studies have proposed that the Arctic Ocean is a source of micronutrients such as dissolved iron (dFe), manganese (dMn), cobalt (dCo), nickel (dNi), copper (dCu) and zinc (dZn) to the North Atlantic Ocean. However, data at the Arctic Ocean gateways including Fram Strait and the Barents Sea Opening have been missing to date and so the extent of Arctic micronutrient transport toward the Atlantic Ocean remains unquantified. Here, we show that Fram Strait is the most important gateway for Arctic-Atlantic micronutrient exchange which is a result of deep water transport at depths >500 m. Combined with a flux estimate for Davis Strait, this study suggests that the Arctic Ocean is a net source of dFe, dNi and dCu, and possibly also dCo, toward the North Atlantic Ocean. Arctic-Atlantic dMn and dZn exchange seems more balanced. Properties in the East Greenland Current showed substantial similarities to observations in the upstream Central Arctic Ocean, indicating that Fram Strait may export micronutrients from Siberian riverine discharge and shelf sediments >3,000 km away. Increasing Arctic river discharge, permafrost thaw and coastal erosion, all consequences of ongoing climate change, may therefore alter future Arctic Ocean micronutrient transport to the North Atlantic Ocean.

Quantifying Ice‐Sheet Derived Lead (Pb) Fluxes to the Ocean; A Case Study at Nioghalvfjerdsbræ

“…Surface dPb concentrations near the Greenland continental shelf break (3.5 ± 0.7 pM at <50 m, stations 6, 8 and 13) matched observations from the Transpolar Drift in the Central Arctic (3.5 ± 0.8 pM at <50 m depth (stations 81, 87, 96 and 99 as per Gerringa et al, 2021)) and suggest a strong influence of Arctic Ocean outflow on the distribution of dPb in surface waters of the outer NEGS. A similar trend is also evident in the distribution of many other dissolved trace elements including Fe (dFe), Mn (dMn) and Co (dCo) (Krisch et al, 2022). In contrast, advection of Atlantic Water, enriched in dPb (Schlosser & Garbe-Schönberg, 2019), into Norske Trough (Schaffer et al, 2017) is likely the main source contributing to elevated dPb concentrations in AIW near the southern shelf break (10.0 ± 0.2 pM at 200-303 m, station 8, Figure 1).…”

Spatial Complexity in Dissolved Organic Matter and Trace Elements Driven by Hydrography and Freshwater Input Across the Arctic Ocean During 2015 Arctic GEOTRACES Expeditions

“…Sediment-derived DOM did not appear to facilitate the long-range spreading of dFe into the UHC in the Canada Basin. On the other hand, tDOM molecules were found to be strong ligands for dFe, dNi, and dCu, facilitating their long-range transport from the Eurasian shelves to the central Arctic Ocean via the TPD system and eventually the East Greenland Current and the North Atlantic as suggested by the distribution of terrigenous CDOM in these waters (Amon et al, 2003) and a recent study in the Fram Strait (Krisch et al, 2022). Qualitative DOMstudies, for example, nuclear magnetic resonance, coupled with hydrography and trace metal distributions are necessary to further constrain biological utilization and growth as well as physical processes, such as freezing/thawing, advection, and particle scavenging.…”

“…Sediment‐derived DOM did not appear to facilitate the long‐range spreading of dFe into the UHC in the Canada Basin. On the other hand, tDOM molecules were found to be strong ligands for dFe, dNi, and dCu, facilitating their long‐range transport from the Eurasian shelves to the central Arctic Ocean via the TPD system and eventually the East Greenland Current and the North Atlantic as suggested by the distribution of terrigenous CDOM in these waters (Amon et al., 2003) and a recent study in the Fram Strait (Krisch et al., 2022).…”

Dissolved, Labile, and Total Particulate Trace Metal Dynamics on the Northeast Greenland Shelf

“…The significant negative correlation between 228 Ra/ 226 Ra and salinity (Figure 5) and the surface enrichment of 228 Ra close to the shelf break (Figure 1) should therefore mostly reflect the intrusion of Arctic surface waters. The significant positive correlations between dTMs (dCo, dCu, dFe, dMn, and dNi) and 228 Ra/ 226 Ra (Figure 5), therefore, suggest that these dTMs on the NE Greenland shelf should be mostly controlled by southward flowing Arctic surface waters carried by the TPD rather than local signals from Greenlandic glaciers (Ardiningsih et al., 2020; Krisch, Hopwood, et al., 2022).…”

“…Whilst nitrate is thought to be the main limiting nutrient for phytoplankton growth across most of the Arctic, Arctic surface waters may function as a source of TMs to other ocean basins, particularly the high latitude North Atlantic (Charette et al., 2020; Krisch, Hopwood, et al., 2022). After substantial estuarine removal (J. Zhang, 1995; Sholkovitz, 1978) followed by biological drawdown and scavenging during lateral transportation, TMs originating from the Siberian shelf are carried into the North Atlantic Ocean via the Transpolar Drift (TPD) through the Fram Strait (Charette et al., 2020; Krisch, Hopwood, et al., 2022). This Arctic Ocean outflow, characterized by low salinity and high dTM content, occupies the surface water layer on the outer parts of the Northeast (NE) Greenland shelf and may influence primary production in this region (Krisch et al., 2020; Tuerena et al., 2021), with potential consequences for TM availability in the downstream East Greenland Current (EGC; Krisch, Hopwood, et al., 2022; Tonnard et al., 2020).…”