ALBERT

Description: This dataset contains measured labile particulate and total particulate trace element concentrations (Al, Ti, V, P, Fe, Mn, Co, Ni, Cu, and Cd) of water bottle samples collected during GEOTRACES expedition GN05 (PS100) between 21 July and 1 September 2016 on Northeast Greenland Shelf. Samples were collected using the ultra-clean CTD rosette, equipped with 24 × 12 L GoFlo bottles following GEOTRACES sampling protocols (Cutter et al., 2017; https://www.geotraces.org). Particulate TM samples were collected onto pre-acid leached Polyethersulfone (PES) Membrane filters (0.2 µm, Sartorius) with 1.2 - 4.1 L of seawater filtered per sample. Labile particulates were determined after applying a weak acid leach with a mild reducing agent and a short heating step with a total leach time of 2 h. Total particulates were then analyzed following a 15 h reflux digest at 150 °C using a mixture of hydrofluoric acid and nitric acid. The validation of labile and total particulate trace metal analyses was monitored by reference materials BCR-414 and PACS-3. Information on the analytical procedure including reference materials and limits of detection can be found in related published manuscripts. The concentrations reflect the mean and the corresponding uncertainty is calculated as the standard deviation to replicate measurements. Uncertainty is calculated as one standard deviation (1σ, STD) to replicate measurements via ICP-MS. Use of quality flags (QF) according to GEOTRACES policy (https://www.geotraces.org/geotraces-quality-flag-policy/).

Description: The file contains Labile (L-pTM), Refractory (R-pTM), and Total (T-pTM) particulate trace metal concentrations of Molybdenum (Mo), Chromium (Cr), Barium (Ba), Tungsten (W), Thorium (Th), and Uranium (U) for marine particle samples collected from the water column of the shelf section and 3-degree latitudinal transect of the GEOTRACES GA08 (R/V Meteor - M121) in the Southwest African shelf region (following Cutter et al., 2010; http://dx.doi.org/10.25607/OBP-2). Particles were collected by filtering seawater through 0.2 µm-pore polyethersulfone (PES) filters in a containerized cleanroom aboard the ship in the field, between the 22nd November - 27th December 2015. Marine particle samples were sequentially leached (following the method of Al-Hashem et al., 2022; https://doi.org/10.1029/2022GB007453, adapted from Berger et al., 2008; https://doi.org/10.1029/2007JC004703), and digested using a strong acid mixture for refractory material (using a method adapted from Cullen and Sherrell, 1999; https://doi.org/10.1016/S0304-4203(99)00060-2) in a land-based clean laboratory at GEOMAR between July 2018- January 2019. Total particulate trace metal concentrations that are reported are the summed concentrations of labile and refractory fractions. Trace metal concentrations were measured by ICP-MS and quantified using external multi-element calibration with standards prepared in a sample-matched matrix (following Cullen et al., 2001; https://doi.org/10.1039/b104398f) between September 2018 - February 2020.

Description: The file contains Labile (L-pTM), Refractory (R-pTM), and Total (T-pTM) particulate trace metal concentrations of Iron (Fe), Aluminum (Al), Titanium (Ti), Manganese (Mn), Cobalt (Co), Zinc (Zn), Nickel (Ni), Copper (Cu), Cadmium (Cd), Lead (Pb), Vanadium (V), and Phosphorus (P) for marine particle samples collected from the water column of the shelf section and 3-degree latitudinal transect of the GEOTRACES GA08 (R/V Meteor - M121) in the Southwest African shelf region (following Cutter et al., 2010; http://dx.doi.org/10.25607/OBP-2). Particles were collected by filtering seawater through 0.2 µm-pore polyethersulfone (PES) filters in a containerized cleanroom aboard the ship in the field, between the 22nd November - 27th December 2015. Marine particle samples were sequentially leached (following the method of Berger et al., 2008; https://doi.org/10.1029/2007JC004703), and digested using a strong acid mixture for refractory material (using a method adapted from Cullen and Sherrell, 1999; https://doi.org/10.1016/S0304-4203(99)00060-2) in a land-based clean laboratory at GEOMAR between July 2018- January 2019. Total particulate trace metal concentrations that are reported are the summed concentrations of labile and refractory fractions. Trace metal concentrations were measured by ICP-MS and quantified using external multi-element calibration with standards prepared in a sample-matched matrix (following Cullen et al., 2001; https://doi.org/10.1039/b104398f) between September 2018 - February 2020.

Description: The duration and magnitude of the North Atlantic spring bloom impacts both higher trophic levels and oceanic carbon sequestration. Nutrient exhaustion offers a general explanation for bloom termination, but detail on which nutrients and their relative influence on phytoplankton productivity, community structure, and physiology is lacking. Here, we address this using nutrient addition bioassay experiments conducted across the midlatitude North Atlantic in June 2017 (late spring). In four out of six experiments, phytoplankton accumulated over 48–72 h following individual additions of either iron (Fe) or nitrogen (N). In the remaining two experiments, Fe and N were serially limiting, that is, their combined addition sequentially enhanced phytoplankton accumulation. Silicic acid (Si) added in combination with N + Fe led to further chlorophyll a (Chl a) enhancement at two sites. Conversely, addition of zinc, manganese, cobalt, vitamin B12, or phosphate in combination with N + Fe did not. At two sites, the simultaneous supply of all six nutrients, in combination with N + Fe, also led to no further Chl a enhancement, but did result in an additional 30–60% particulate carbon accumulation. This particulate carbon accumulation was not matched by a Redfield equivalent of particulate N, characteristic of high C:N organic exudates that enhance cell aggregation and sinking. Our results suggest that growth rates of larger phytoplankton were primarily limited by Fe and/or N, making the availability of these nutrients the main bottom-up factors contributing to spring bloom termination. In addition, the simultaneous availability of other nutrients could modify bloom characteristics and carbon export efficiency.

Description: The duration and magnitude of the North Atlantic spring bloom impacts both higher trophic levels and oceanic carbon sequestration. Nutrient exhaustion offers a general explanation for bloom termination, but detail on which nutrients and their relative influence on phytoplankton productivity, community structure, and physiology is lacking. Here, we address this using nutrient addition bioassay experiments conducted across the midlatitude North Atlantic in June 2017 (late spring). In four out of six experiments, phytoplankton accumulated over 48–72 h following individual additions of either iron (Fe) or nitrogen (N). In the remaining two experiments, Fe and N were serially limiting, that is, their combined addition sequentially enhanced phytoplankton accumulation. Silicic acid (Si) added in combination with N + Fe led to further chlorophyll a (Chl a) enhancement at two sites. Conversely, addition of zinc, manganese, cobalt, vitamin B12, or phosphate in combination with N + Fe did not. At two sites, the simultaneous supply of all six nutrients, in combination with N + Fe, also led to no further Chl a enhancement, but did result in an additional 30–60% particulate carbon accumulation. This particulate carbon accumulation was not matched by a Redfield equivalent of particulate N, characteristic of high C:N organic exudates that enhance cell aggregation and sinking. Our results suggest that growth rates of larger phytoplankton were primarily limited by Fe and/or N, making the availability of these nutrients the main bottom‐up factors contributing to spring bloom termination. In addition, the simultaneous availability of other nutrients could modify bloom characteristics and carbon export efficiency.

Description: Cyclonic ocean eddies drive upwelling of deep waters enhanced in nutrients, which can elevate phytoplankton productivity. At mid‐latitudes in the North Atlantic, satellite images show enhanced chlorophyll‐a associated with eddies. However, surface macronutrient concentrations are often not fully depleted in this region, implying enhanced macronutrient supply is not the primary control. We conducted high resolution sampling through two mid‐latitude Atlantic eddies in late spring, located 800 and 350 km east of the Newfoundland Grand Banks. Waters outside of both eddies had unused residual macronutrients, low dissolved iron, and iron‐stressed phytoplankton. Inside both eddies, plankton biomass was higher and macronutrient concentrations lower. However, full macronutrient drawdown and an absence of iron stress were only present in the eddy nearer the continental shelf. From these two examples, iron supply and proximity to shelf iron sources appear to be important factors regulating productivity and macronutrient utilization in mid‐latitude North Atlantic cyclonic eddies.

Description: Highlights • Oceanic nutrient supply from seabird guano is poorly constrained by field observations. • This was assessed for guano from caught-and-released North Atlantic seabirds. • Guano released nutrients and relieved in situ phytoplankton nutrient limitation. • Guano was modelled to potentially be a major nutrient supply term in summer. • Declining pelagic seabird populations will impact this function. Abstract Nutrients supplied via seabird guano increase primary production in some coastal ecosystems. A similar process may occur in the open ocean. To investigate this directly, we first measured bulk and leachable nutrient concentrations in guano sampled in the North Atlantic. We found that guano was strongly enriched in phosphorus, which was released as phosphate in solution. Nitrogen release was dominated by reduced forms (ammonium and urea) whilst release of nitrate was relatively low. A range of trace elements, including the micronutrient iron, were released. Using in-situ bioassays, we then showed that supply of fresh guano to ambient seawater increases phytoplankton biomass and photochemical efficiencies. Based on these results, modelled seabird distributions, and known defecation rates, we estimate that on annual scales guano is a minor source of nutrients for the surface North Atlantic. However, on shorter timescales in late spring/summer it could be much more important: Estimates of upper-level depositions of phosphorus by seabirds were three orders of magnitude higher than modelled aerosol deposition and comparable to diffusion from deeper waters.

Description: We present labile (L-pTM) and refractory (R-pTM) particulate trace metal distributions of Fe, Mn, Al, Ti, Co, Zn, Cd, Ni, Pb, Cu, and P for a transect along the southwest African shelf and an off-shore section at 3°S of the GEOTRACES GA08 section cruise. Particle sources and biogeochemical cycling processes are inferred using particle-type proxies and elemental ratios. Enhanced concentrations of bio-essential L-pTMs (Zn, Cu, Ni, Cd, Co, and P) were observed in the Benguela upwelling region, attributed to enhanced primary production. Bio-essential pTM stoichiometric ratios (normalized to pP) were consistent with phytoplankton biomass across the transect, except for Fe and Mn, which included adsorbed and labile oxide phases. Low pP lability (∼41%) suggests a potential refractory biogenic source on the Benguela shelf. Variable labilities observed between stations along the transect indicated potentially different biogenic pP labilities among different plankton groups. Benthic resuspension was prevalent in (near-)bottom waters along the transect and formed an important source of Fe and Mn oxides. Lithogenic particles along the entire shelf were Mn deficient and particles on the Benguela shelf were enriched in Fe, consistent with regional sediment compositions. Enhanced available-Fe (dissolved + labile particulate Fe) concentrations (up to 39.6 nM) were observed in oxygen-deficient (near-)bottom waters of the Benguela shelf coinciding with low L-pMn. This was attributed to the faster oxidation kinetics of Fe, allowing Fe-oxide precipitation and retention on the shelf, while Mn oxidation was slower. Enhanced L-pFe in the Congo River plume, which comprised as much as 93% of the available-Fe pool, was attributed to increased scavenging and formation of Fe oxides. Increased scavenging of other particle-reactive trace metals (TMs) (Mn, Al, and Pb) was also apparent in Congo-influenced waters. However, particles did not play a significant role in transporting TMs off-shelf within Congo plume waters. Key Points: • Different oxidation kinetics lead to decoupled Fe and Mn oxide redox cycling within oxygen-depleted waters on the Benguela Shelf • Lower lability of particulate phosphorus (∼41%) indicate potential refractory biogenic source on Benguela shelf • Nepheloid particles formed important sources of Fe and Mn oxides that adsorb trace metals (TMs), and serve as potential TM sources from shelf to open ocean