Nitrogen fixation, the microbial conversion of dinitrogen gas to ammonia, is a key nitrogen source and critical for sustaining marine productivity. We investigated the diversity and activity of nitrogen‐fixers in surface waters of the North Sea and Norwegian coast during July 2023. We detected, for the first time, the presence of Braarudosphaera /UCYN‐A (up to 10 4 nifH copies L −1 ) and measurable nitrogen fixation rates (up...

Net primary production in the Southern Ocean plays a critical role in governing ecosystem production, the biological carbon pump, and global biogeochemical cycles. Recent work has advanced our understanding of novel factors regulating Southern Ocean net primary production and the regional physiological adaptations employed by Southern Ocean phytoplankton in terms of their photosynthetic strategies and resource acquisition. Her...

The international GEOTRACES program was developed to enhance knowledge about the distribution of trace elements and their isotopes (TEIs) in the ocean and to reduce the uncertainty about their sources, sinks, and internal cycling. Recognizing the importance of intercalibration from the outset, GEOTRACES implemented intercalibration efforts early in the program, and consensus materials were generated that included the full rang...

Chromium (Cr) is a redox-sensitive element and because Cr isotopes are fractionated by redox and/or biological processes, the Cr isotopic composition of ancient marine sediments may be used to infer changes in past seawater oxygenation or biological productivity. While there appears to be a ‘global correlation’ between the dissolved Cr concentration and Cr isotopic composition of seawater, there is ongoing debate about the rel...

The offshore Gulf of Alaska—in the northeastern subarctic Pacific—is a high-nitrate, low-chlorophyll (HNLC) oceanic region where concentrations of dissolved iron (DFe) and zinc (DZn) are of the order ~0.1 nmol kg −1 in surface waters. At the average winter mixed layer depth of ~120 m, DFe and DZn are of the orders ~0.1–0.2 nmol kg −1 and ~1–2 nmol kg −1 , respectively. Vertical supply of Fe to surface waters is therefore limit...

Continental margins are disproportionally important for global primary production, fisheries and CO 2 uptake. However, across the Northeast Atlantic shelves, there has been an ongoing summertime decline of key biota—large diatoms, dinoflagellates and copepods—that traditionally fuel higher tropic levels such as fish, sea birds and marine mammals. Here, we combine multiple time series with in situ process studies to link these...

In the northern Gulf of Alaska, mesoscale, anticyclonic eddies have been implicated as a mechanism of the cross‐shelf exchange of iron (Fe)‐replete coastal waters with Fe‐deplete subarctic Alaskan gyre waters. Based on existing hydrography and macronutrient distributions, a Sitka eddy sampled during August 2007 is divided into a surface eddy core, a shallow subsurface eddy core, and a deeper subsurface eddy core. The distribut...

Primary production in the Ross Sea, one of the most productive areas in the Southern Ocean, has previously been shown to be seasonally limited by iron. In two of three bottle incubation experiments conducted in the austral summer, significantly higher chlorophyll a (Chl a ) concentrations were measured upon the addition of iron and B 12 , relative to iron additions alone. Initial bacterial abundances were significantly lower i...

Dissolved iron (Fe) speciation in the Columbia River plume, the San Francisco Bay plume, and the Columbia River estuary was investigated using competitive ligand exchange‐adsorptive cathodic stripping voltammetry (CLE‐ACSV) with the added ligand salicylaldoxime. A stronger L 1 ‐type Fe‐binding ligand class was measured in all surface samples, and in the Columbia River estuary. A weaker L 2 ‐type ligand class was present in the...