Description: Autonomous systems measuring the partial pressure of CO2 (pCO2) in surface waters on commercial carrier ships (Voluntary Observing Ship, VOS), which allows for high spatiotemporal data coverage, are a major component of the Ocean Thematic Centre (OTC) data stream. Currently, ICOS operates lines in the Atlantic, North Sea and the Baltic. All lines are determining pCO2 by measuring CO2 in air that has been equilibrated with seawater. As part of the European H2020 project RINGO (https://www.icos-ri.eu/ringo), we are evaluating the possibility of using VOS to expand the atmospheric network. We will provide technical solutions for three different settings and approaches, and assess the added value for the atmospheric observation network. Two systems are designed as stand-alone modules for continuous atmospheric CO2 and CH4 measurements, following the technological requirements defined by the ATC, and will be operated in the Baltic (high anthropogenic influence) and on a line between France and Brazil (clean marine air, large temperature and humidity gradient). A second approach is using the existing instrumentation for seawater measurements (North Atlantic), which we aim to improve in order to make these measurements usable for the atmospheric research community. This is an effort that connects the ocean research community with the Central Analytical Laboratories (CAL; testing an extended range of standard gases, providing flask sampling opportunity), the Atmospheric Thematic Centre (ATC; work on data streams that can be digested by the ATC system), and the modelling community (identifying useful sampling strategies). Here we present a status update of the ongoing work, which is a joined effort of the atmospheric and ocean community within ICOS and relying on the expertise of both fields.

Description: Understanding the dynamics and fate of methane (CH 4 ) release from oceanic seepages on margins and shelves into the water column, and quantifying the budget of its total discharge at different spatial and temporal scales, currently represents a major scientific undertaking. Previous works on the fate of methane escaping from the seafloor underlined the challenge in both, estimating its concentration distribution and identifying gradients. In April 2019, the Envri Methane Cruise has been conducted onboard the R/V Mare Nigrum in the Western Black Sea to investigate two shallow methane seep sites at ∼120 m and ∼55 m water depth. Dissolved CH 4 measurements were conducted with two continuous in-situ sensors: a membrane inlet laser spectrometer (MILS) and a commercial methane sensor (METS) from Franatech GmbH. Additionally, discrete water samples were collected from CTD-Rosette deployment and standard laboratory methane analysis was performed by gas chromatography coupled with either purge-and-trap or headspace techniques. The resulting vertical profiles (from both in situ and discrete water sample measurements) of dissolved methane concentration follow an expected exponential dissolution function at both sites. At the deeper site, high dissolved methane concentrations are detected up to ∼45 m from the seabed, while at the sea surface dissolved methane was in equilibrium with the atmospheric concentration. At the shallower site, sea surface CH 4 concentrations were four times higher than the expected equilibrium value. Our results seem to support that methane may be transferred from the sea to the atmosphere, depending on local water depths. In accordance with previous studies, the shallower the water, the more likely is a sea-to-atmosphere transport of methane. High spatial resolution surface data also support this hypothesis. Well localized methane enriched waters were found near the surface at both sites, but their locations appear to be decoupled with the ones of the seafloor seepages. This highlights the need of better understanding the processes responsible for the transport and transformation of the dissolved methane in the water column, especially in stratified water masses like in the Black Sea.

Description: During 7–12 July 2012, extreme moist and warm conditions occurred over Greenland, leading to widespread surface melt. To investigate the physical processes during the atmospheric moisture transport of this event, we study the water vapor isotopic composition using surface in situ observations in Bermuda Island, South Greenland coast (Ivittuut), and northwest Greenland ice sheet (NEEM), as well as remote sensing observations (Infrared Atmospheric Sounding Interferometer (IASI) instrument on board MetOp-A), depicting propagation of similar surface and midtropospheric humidity and