ALBERT

Description: Here we demonstrate enhanced natural community APase activity following iron amendment within the low zinc and moderately low iron Western North Atlantic. In contrast we find no evidence for trace metal limitation of APase activity beneath the Saharan dust plume in the Eastern Atlantic. Such intermittent iron limitation of microbial phosphorus acquisition provides an additional facet in the argument for iron controlling the coupling between oceanic nitrogen and phosphorus cycles.

Description: Iron (Fe), cobalt (Co), and vitamin B12 addition experiments were performed in the eastern Equatorial Pacific/Peruvian upwelling zone during the 2015 El Niño event. Near the Peruvian coastline, apparent photosystem II photochemical efficiencies (Fv/Fm) were unchanged by nutrient addition and chlorophyll-a tripled in untreated controls over two days, indicating nutrient replete conditions. Conversely, Fe amendment further away from the coastline in the high nitrate, low Fe zone significantly increased Fv/Fm and chlorophyll-a concentrations. Mean chlorophyll-a was further enhanced following supply of Fe+Co and Fe+B12 relative to Fe alone, but this was not statistically significant; further offshore, reported Co depletion relative to Fe could enhance responses. The persistence of Fe limitation in this system under a developing El Niño, as previously demonstrated under non-El Niño conditions, suggests that diminished upwelled Fe is likely an important factor driving reductions in offshore phytoplankton productivity during these events.

Description: Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean1. The extensive boundaries of the oligotrophic sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones1,2,3,4. Here we present the results of full-factorial nutrient amendment experiments conducted at the eastern boundary of the South Atlantic gyre. We find extensive regions in which the addition of nitrogen or iron individually resulted in no significant phytoplankton growth over 48 hours. However, the addition of both nitrogen and iron increased concentrations of chlorophyll a by up to approximately 40-fold, led to diatom proliferation, and reduced community diversity. Once nitrogen–iron co-limitation had been alleviated, the addition of cobalt or cobalt-containing vitamin B12 could further enhance chlorophyll a yields by up to threefold. Our results suggest that nitrogen–iron co-limitation is pervasive in the ocean, with other micronutrients also approaching co-deficiency. Such multi-nutrient limitations potentially increase phytoplankton community diversity.

Description: Biogeochemical parameters collected on RRS Discovery cruise DY080 in June 2017 through two mid-high latitude North Atlantic eddies. Includes macronutrient concentrations, dissolved iron and dissolved manganese, phytoplankton chlorophyll-a, particulate organic carbon and nitrogen, biogenic silicate, flow cytometry cell counts, temperature and salinity.

Description: Current velocities of the upper water column along the cruise track of R/V Meteor III cruise MET187 were collected by a vessel-mounted 75 kHz RDI Workhorse Long Ranger ADCP. The ADCP transducer was located at 5.0 m below the water line. The instrument was operated in broadband mode (WM1) with two different configurations: (1 - corresponding to met_187_vmadcp_75khz_01.nc) bin size: 5.0 m, blanking distance: 2.0 m, number of bins: 128, vertical range: 12.0 m - 647.0 m; (2 - corresponding to met_187_vmadcp_75khz_0[2,3].nc) bin size: 8.0 m, blanking distance: 4.0 m, number of bins: 100, vertical range: 17.0 - 809.0 m. Heading, pitch and roll data from the ship's motion reference unit and the navigation data from the Global Positioning systems were used by the data acquisition software VmDAS internally to convert ADCP velocities into earth coordinates. Single-ping data / ping ensembles were screened for bottom signals and, where appropriate, a bottom mask was manually processed. The ship's velocity was calculated from position fixes obtained by the Global Positioning System (GPS). Accuracy of the ADCP velocities mainly depends on the quality of the position fixes and the ship's heading data. Further errors stem from a misalignment of the transducer with the ship's centerline. For technical reasons, the transducer was lifted from the moonpool on February 18th, 2023. Therefore, two separate calibrations were carried out: Data post-processing included water track calibration of the misalignment angle and scale factor of the Ocean Surveyor signal. For technical reasons, the transducer was lifted from the moonpool on February 18th, 2023. Therefore, two separate calibrations were carried out: prior February 18th, 2023 (corresponding to met_187_vmadcp_75khz_0[1,2].nc): misalignment angle of -41.8717° +/- 0.4333° (0.5755°), scale factor of 1.0001 +/- 0.0064 (0.0079); after February 18th, 2023 (corresponding to met_187_vmadcp_75khz_03.nc): misalignment angle of -41.8071° +/- 0.5600°, scale factor of 0.9971 +/- 0.0074. The velocity data were averaged in time using an average interval of 60 s. Velocity quality flagging is based on following threshold criteria: abs(UC) or abs(VC) 〉 1.5 m/s, rms(UC_z) or rms(VC_z) 〉 0.3.

Description: Underway temperature and salinity data was collected along the cruise track with two autonomous thermosalinograph (TSG) systems, each consisting of a SBE21 TSG together with a SBE38 Thermometer. Both systems worked independent from each other throughout the cruise. While temperature is taken at the water inlet in about 5 m depth, salinity is estimated within the interior TSG from conductivity and interior temperature. No correction against independent data was performed for temperature. Salinity was calibrated against independent water samples. Finally, TSG1 was chosen for publication. For details to all processing steps see Data Processing Report.