Stacy M Maenner

Chemically rich and diverse submarine hydrothermal plumes of the southern Kermadec volcanic arc (New Zealand)

Abstract The New Zealand American PLUme Mapping Expedition (NZAPLUME) provided the first systematic survey of chemical emissions along a submarine volcanic frontal arc. Chemical plumes emanated from seven of 13 volcanoes that line a 260 km-long section of the southern Kermadec arc northeast of New Zealand. Hydrothermal plumes ranged in depth from <200 to 1500 m and are generally more shallow than plumes over mid-ocean ridges (MORs). The chemical signatures of plumes along the southern Kermadec arc are unusually diverse and have concentration anomalies for CO2, H2S and Fe that can exceed those for MOR settings by 5–10 times, or more. Projected end-member fluid concentrations of carbon and sulphur gases at some volcanoes require a magmatic vapour source, while unusually high Fe concentrations and Fe/Mn values are consistent with venting an iron-rich magmatic brine. Thus, vent-fluid emissions on the Kermadec arc volcanoes often appear as hybrid mixtures of hydrothermally evolved sea water influenced by water-rock reaction with compositionally diverse arc lavas, and exsolved magmatic fluid present as gaseous (CO2 and SO2+H2S) and liquid (Fe-rich brines) components. While rock-buffered fluids in arc settings are expected to vary compositionally from one another and from MOR fluids, it is the magmatic components that clearly differentiate arc emissions as being super-enriched in sulphur gases and ionic metals. These first systematic observations of spatially frequent and chemically robust fluid emissions from southern Kermadec arc forecast arcs as being a potentially important source of chemicals to the oceans.

Intraseasonal variability linked to sampling alias in air‐sea CO2 fluxes in the Southern Ocean

The Southern Ocean (SO) contributes most of the uncertainty in contemporary estimates of the mean annual flux of carbon dioxide CO2 between the ocean and the atmosphere. Attempts to reduce this uncertainty have aimed at resolving the seasonal cycle of the fugacity of CO2 (fCO2). We use hourly CO2 flux and driver observations collected by the combined deployment of ocean gliders to show that resolving the seasonal cycle is not sufficient to reduce the uncertainty of the flux of CO2 to below the threshold required to reveal climatic trends in CO2 fluxes. This was done by iteratively subsampling the hourly CO2 data set at various time intervals. We show that because of storm-linked intraseasonal variability in the spring-late summer, sampling intervals longer than 2 days alias the seasonal mean flux estimate above the required threshold. Moreover, the regional nature and long-term trends in storm characteristics may be an important influence in the future role of the SO in the carbon-climate system.