Description: Global Drifter Program (GDP) drifter data and Argo float data from 2006 to 2013 are used to provide quantitative description and comparison of the mean near-surface (15 m) and 1000 m velocity fields in the New Zealand region. These fields are estimated both from bin-averaging the drifter/float velocities and by fitting non-divergent streamfunctions to the velocities. At both levels, our velocity fields are broadly consistent with previous drifter/float estimates, but provide more detail on the local structure of the mean fields. North of the Subantarctic Front there are large differences between the surface and 1000 m flows, with the Tasman Front being largely absent at 1000 m. South of the Subantarctic Front, where the flow is expected to be more barotropic, there is a closer correspondence between the flows at both levels. Several previously undocumented eddies in the mean flows at both levels are described.

Description: Hydrothermal vents are a source of many trace metals to the oceans. Compared to mid-ocean ridges, hydrothermal vent systems at arcs occur in shallower water depth and are much more diverse in fluid composition, resulting in highly variable water column trace metal concentrations. However, only few studies have focused on trace metal dynamics in hydrothermal plumes at volcanic arcs. During R/V Sonne cruise SO253 in 2016/2017, hydrothermal plumes from two hydrothermally active submarine volcanoes along the Kermadec arc in the Southwest Pacific Ocean were sampled: (1) Macauley, a magmatic dominated vent site located in water depths between 300 and 680 m, and (2) Brothers, located between 1,200 and 1,600 m water depth, where hydrothermalism influenced by water rock interactions and magmatically influenced vent sites occur near each other. Surface currents estimated from satellite-altimeter derived currents and direct measurements at the sites using lowered acoustic Doppler current profilers indicate the oceanic regime is dominated by mesoscale eddies. At both volcanoes, results indicated strong plumes of dissolved trace metals, notably Mn, Fe, Co, Ni, Cu, Zn, Cd, La, and Pb, some of which are essential micronutrients. Dissolved metal concentrations commonly decreased with distance from the vents, as to be expected, however, certain element/Fe ratios increased, suggesting a higher solubility of these elements and/or their stronger stabilization (e.g., for Zn compared to Fe). Our data indicate that at the magmatically influenced Macauley and Brothers cone sites, the transport of trace metals is strongly controlled by sulfide nanoparticles, while at the Brothers NW caldera wall site iron oxyhydroxides seem to dominate the trace metal transport over sulfides. Solution stabilization of trace metals by organic complexation appears to compete with particle adsorption processes. As well as extending the generally sparse data set for hydrothermal plumes at volcanic arc systems, our study presents the first data on several dissolved trace metals in the Macauley system, and extends the existing plume dataset of Brothers volcano. Our data further indicate that chemical signatures and processes at arc volcanoes are highly diverse, even on small scales.

Description: Highlights • Dissolved iron limits primary production in offshore South Pacific surface waters. • Phytoplankton is elevated in high-iron filaments in mesoscale eddies east of New Zealand. • Iron in these eddies is due to entrainment of high-iron coastal water into offshore water. • The resultant eddy-driven flux of iron supports production in the Subtropical Front. Abstract Subtropical and subantarctic waters either side of the southern hemisphere Subtropical Front are considered iron-limited, suggesting production within the front is dependent on a supply of iron from atmospheric deposition, zonal advection of coastal water, or upwelling. We present the results from a one-day biogeochemical survey in Subtropical Water east of the North Island, New Zealand, in a region where mesoscale cyclonic and anticyclonic eddies entrain chlorophyll in filaments around the eddies. There was no significant relationship between upper mixed layer chlorophyll and any physical or macronutrient quantity. However, chlorophyll was significantly positively correlated with dissolved iron. A simple model suggests that while vertical entrainment of iron into the upper mixed layer occurred, most of the dissolved iron in the eddy was due to entrainment of high-iron coastal water into low-iron offshore Subtropical Water, and that this iron supports primary production in otherwise iron-deficient water. We suggest that a significant component of the total primary production within the Subtropical Front may be determined by mesoscale eddy induced lateral advection of iron.