Distributions, sources, and dynamics of particulate Ba, Cr, Sr, Zn, Mo, W, Th, and U on the Northeast Greenland Shelf

We present distributions of labile and refractory particulate barium (Ba), chromium (Cr), strontium (Sr), zinc (Zn), molybdenum (Mo), tungsten (W), thorium (Th), and uranium (U) along a transect on the Northeast (NE) Greenland shelf obtained during the GEOTRACES GN05 cruise. The cruise traversed the outflow of Nioghalvfjerdsbræ (79NG), Greenland's largest floating glacier ice tongue. Particulate metal concentrations ranged from 10⁻³ to 10³ pM, exhibiting strong spatial variations but no consistent vertical variations with depth. The average labile fractions (labile/total particulate metal×100 %) of particulate Sr were greater than 90 %; Ba, Cr, Zn, Mo, and U ranged from around 20 % to 65 %; and W and Th were below 10 %. A low labile fraction was observed for phosphorus (P, 29.2 ± 10.8 %). All particulate metals were associated with lithogenic particles as indicated by their strong positive relationships (R² on average > 0.95) with refractory particulate Ti. Particulate Th and U showed coherent behaviors on the NE Greenland shelf. Conversely, biogenic particles, represented by labile particulate P, played a crucial role in the cycling of particulate Sr, Zn, and Cr. Particulate Mo and W were additionally controlled by the formation of manganese (Mn) oxides and variations in lithogenic sources. Distributions of particulate metals on the shelf were predominantly controlled by the mixing between Arctic Ocean Polar Surface Water and Atlantic Intermediate Water, with localized peaks of particulate metals resulting from the re-suspension of glacier cavity sediments. Additionally, Greenland runoff provided an important source of particulate metals (2–10 times enrichment for labile and/or refractory particulate Ba, Cr, Sr, Zn, Mo, and Th) to the shelf. The lithogenic metals were mainly removed from the water column by the sinking and aggregation of particles. Refractory particulate metals discharged to the shelf from the 79NG cavity were rapidly removed from the water column with a sinking rate of 6.5×10⁻⁵ kg·ng⁻¹·km⁻¹. In summary, particulate metal distributions on the NE Greenland shelf were influenced by a combination of basal and surface glacier melt, and intrusion of Arctic surface waters, in addition to the more general biological and shelf-sediment processes that commonly occur in other shelf regions. With ongoing oceanic warming, both retreat and eventual loss of the 79NG ice tongue, and changes in Arctic Ocean outflow via the Transpolar Drift, may alter particulate metal distributions on the Greenland shelf.