ALBERT

Description: Key Points: - Glacier-derived particles release 2–46% of labile particulate lead (Pb) upon mixing with seawater - Pb dynamics in glacier fjords are characterized by a rapid release of dissolved Pb followed by readsorption on a timescale of hours-to-days - Dissolved Pb release from the Greenland Ice Sheet is likely within the range 0.2–1 Mmol yr−1 Higher than expected concentrations of dissolved lead (dPb) have been consistently observed along glaciated coastlines and it is widely hypothesized that there is a net release of dPb from glacier-derived sediments. Here we further corroborate that dPb concentrations in diverse locations around west Greenland (3.2–252 pM) and the Western Antarctic Peninsula (7.7–107 pM) appear to be generally higher than can be explained by addition of dPb from glacier-derived freshwater. The distribution of dPb across the salinity gradient is unlike any other commonly studied trace element (e.g., Fe, Co, Ni, Cu, Mn, and Al) implying a dynamic, reversible exchange between dissolved and labile particulate Pb. Incubating a selection of glacier-derived particles from SW Greenland (Ameralik and Nuup Kangerlua) and Svalbard (Kongsfjorden), with a range of labile particulate Pb (LpPb) content (11–113 nmol g−1), the equivalent of 2–46% LpPb was released as dPb within 24 hr of addition to Atlantic seawater. Over longer time periods, the majority of this dPb was typically readsorbed. Sediment loading was the dominant factor influencing the net release of dPb into seawater, with a pronounced decline in net dPb release efficiency when sediment load increased from 20 to 500 mg L−1. Yet temperature also had some effect with 68 ± 22% higher dPb release at 11°C compared to 4°C. Future regional changes in dPb dynamics may therefore be more sensitive to short-term suspended sediment dynamics, and potentially temperature changes, than to changing interannual runoff volume.

Description: Atmospheric aerosol deposition into the low latitude oligotrophic ocean is an important source of new nutrients for primary production. However, the resultant phytoplankton responses to aerosol deposition events, both in magnitude and changes in community composition, are poorly constrained. Here, we investigated this with 19 d of field and satellite observations for a site in the subtropical North Atlantic. During the observation period, surface dissolved aluminum concentrations alongside satellite-derived aerosol and precipitation data demonstrated the occurrence of both a dry deposition event associated with a dust storm and a wet deposition event associated with strong rainfall. The dry deposition event did not lead to any observable phytoplankton response, whereas the wet deposition event led to an approximate doubling of chlorophyll a, with Prochlorococcus becoming more dominant at the expense of Synechococcus. Bioassay experiments showed that phytoplankton were nitrogen limited, suggesting that the wet deposition event likely provided substantial aerosol-derived nitrogen, thereby alleviating the prevalent nutrient limitation and leading to the rapid observed phytoplankton response. These findings highlight the important role of wet deposition in driving rapid responses in both ocean productivity and phytoplankton community composition.