ALBERT

Description: We mapped, sampled, and quantified gas emissions at the continental margin west of Svalbard during R/V Heincke cruise He-387 in late summer 2012. Hydroacoustic mapping revealed that gas emissions were not limited to a zone just above 396 m below sea level (m b.s.l.). Flares from this depth gained significant attention in the scientific community in recent years because they may be caused by bottom water-warming induced hydrate dissolution in the course of global warming and/or by recurring seasonal hydrate formation and decay. We found that gas emissions occurred widespread between about 80 and 415 m b.s.l. which indicates that hydrate dissolution might only be one of several triggers for active hydrocarbon seepage in that area. Gas emissions were remarkably intensive at the main ridge of the forlandet moraine complex in 80 to 90 m water depths, and may be related to thawing permafrost. Focused seafloor investigations were performed with the remotely operated vehicle (ROV) "Cherokee". Geochemical analyses of gas bubbles sampled at about 240 m b.s.l. as well as at the 396 m gas emission sites revealed that the vent gas is primarily composed of methane (〉 99.70%) of microbial origin (average d13C = -55.7 per mil V-PDB). Estimates of the regional gas bubble flux from the seafloor to the water column in the area of possible hydrate decomposition were achieved by combining flare mapping using multibeam and single beam echosounder data, bubble stream mapping using a ROV-mounted horizontally-looking sonar, and quantification of individual bubble streams using ROV imagery and bubble counting. We estimated that about 53 × 10**6 mol methane were annually emitted at the two areas and allow a large range of uncertainty due to our method (9 to 118 × 10**6 mol yr**-1). These amounts, first, show that gas emissions at the continental margin west of Svalbard were in the same order of magnitude as bubble emissions at other geological settings, and second, may be used to calibrate models predicting hydrate dissolution at present and in the future, third, may serve as baseline (year 2012) estimate of the bubble flux that will potentially increase in future due to ever-increasing global-warming induced bottom water-warming and hydrate dissolution.

Description: Upward transport and/or mixing of trace gas-enriched subsurface waters fosters the exchange of nitrous oxide (N2O) and methane (CH4) with the atmosphere in the Eastern-South Atlantic (ESA). To date, it is, however, unclear whether this source is maintained by local production or advection of trace-gas enriched water masses. So, the meridional and zonal variability of N2O and CH4 in the ESA were investigated to constrain the contributions of the major regional water masses to the overall budget of N2O and CH4. The fieldwork took place during the cruises M99 (July 31st - August 23rd, 2013) and M120 (October 17th - November 18th, 2015) onboard the R/V METEOR, which encompassed close-coastal and open ocean regions off Angola and Namibia. To investigate the regional concentration gradients of N2O and CH4 and corresponding sea-air fluxes, seven hydrographic sections (six zonal transects and one alongshore transect) were conducted between ~10°S and 26°S. Concentrations of dissolved N2O and CH4 in surface waters were continuously measured by using the Mobile Equilibrator Sensor System. To evaluate, the oceanic-atmospheric trace gas exchange, the atmospheric N2O and CH4 in ambient air were measured at several sporadic locations, with an inlet installed at 35 m height. The data were quality controlled by comparing with the data generated by NOAA in the nearest atmospheric sampling station (23.58° S, 15.03°E, Station NMB (Gobabeb, Namibia)). Also, to better understand the underlying patterns of the trace gas in the ESA, the vertical profiles were investigated by measuring discrete samples of N2O using the dynamic headspace method on M99. N2O and CH4 concentrations were also measured using a purge and trap system during M120 expedition.

Description: The Surface Ocean CO2 Atlas (SOCAT) is a synthesis activity by the international marine carbon research community (〉100 contributors). SOCAT version 6 has 23.4 million quality-controlled, surface ocean fCO2 (fugacity of carbon dioxide) observations from 1957 to 2017 for the global oceans and coastal seas. Calibrated sensor data are also available. Automation allows annual, public releases. SOCAT data is discoverable, accessible and citable. SOCAT enables quantification of the ocean carbon sink and ocean acidification and evaluation of ocean biogeochemical models. SOCAT represents a milestone in biogeochemical and climate research and in informing policy.

Description: The Surface Ocean CO2 Atlas (SOCAT) is a synthesis activity by the international marine carbon research community (〉100 contributors). SOCATv2019 has 25.7 million quality-controlled, surface ocean fCO2 (fugacity of carbon dioxide) observations from 1957 to 2019 for the global oceans and coastal seas. Calibrated sensor data are also available. Automation allows annual, public releases. SOCAT data is discoverable, accessible and citable. SOCAT enables quantification of the ocean carbon sink and ocean acidification and evaluation of ocean biogeochemical models. SOCAT represents a milestone in biogeochemical and climate research and in informing policy. This publication contains the individual cruise files that are new or updated from SOCATv6, with cruise QC flags A-E and all fCO2 WOCE flags. The synthesis file hosted in NOAA NCEI (see other version) contains A-D cruises and WOCE flag 2 (good) data. To download the SOCATv2019 data product in other formats or subsets, please go to www.socat.info.

Description: The Surface Ocean CO2 Atlas (SOCAT) is a synthesis activity by the international marine carbon research community (〉100 contributors). SOCAT version 5 has 21.5 million quality-controlled, surface ocean fCO2 (fugacity of carbon dioxide) observations from 1957 to 2017 for the global oceans and coastal seas. Calibrated sensor data are also available. Automation allows annual, public releases. SOCAT data is discoverable, accessible and citable. SOCAT enables quantification of the ocean carbon sink and ocean acidification and evaluation of ocean biogeochemical models. SOCAT, which celebrates its 10th anniversary in 2017, represents a milestone in biogeochemical and climate research and in informing policy.

Description: The high surface productivity triggered by nutrient-rich Benguela upwelled waters results in significant enrichment of organic carbon in the sub-surface waters due to enhanced mineralization in the water column and benthic fluxes. Hence, microbial O2-consuming processes are promoted, driving oxygen depletion that favors trace gases i.e. methane (CH4) and nitrous oxide (N2O) production at relatively shallow depths. During upwelling, gas-rich subsurface waters are also transported towards the surface waters, enhancing trace gas sea-air fluxes. We investigate the variability of these fluxes on seasonal and shorter timescales to understand the intensity of the Benguela upwelling system in gas emissions. The data might serve as a base for projections under a changing climate. The fieldwork took place during the cruise M157 (August 4th – September 16th, 2019) onboard the R/V METEOR, which encompassed close-coastal and open ocean regions between Mindelo (Cape Verde) and Walvis Bay. The main transect lines around 18, 23 and 25°S represents the Angola-Benguela frontal zone, Walvis Bay and Lüderitz upwelling cells respectively, which are suggested to represent some regional hotspots of trace gas emissions to the atmosphere, in particular in the vicinity of the upwelling cells. The partial pressures of CH4, N2O, and CO2 as well as oxygen saturation in surface water were determined using IOW's self-built Mobile Equilibrator Sensor System (MESS). The system was described in details elsewhere (Sabbaghzadeh et al., 2021) but in brief, it consists of a custom-built equilibrator (combined shower-head/bubble type) with a water flow rate of about 5 l min-1 and an airflow rate of ~ 4 l min-1, which is linked to two off-axis integrated cavity output laser spectrometers (oa-ICOS, Los Gatos Instruments) for the detection of CH4 / CO2 and N2O / CO. Seawater was supplied by a pump installed at a water depth of about 6 m in the moon pool on board of RV METEOR. oa-ICOS sensors combine a highly specific infrared band laser with a set of reflective mirrors and achieve an effective absorption path length of several kilometers. This enables the detection of the trace gases with high accuracy. Three standard gases, provided by the central calibration lab of the European Integrated Carbon Observation System Research Infrastructure (ICOS RI) were used to calibrate the sensors almost daily throughout the entire expedition. To estimate sea-air gas fluxes, the atmospheric concentration of trace gases was also measured at several positions during the cruise using a tube with the inlet positioned to minimize ship contamination. All other ancillary parameters out of the MESS system were synchronized with D-ship data with a simultaneous data reduction to one-minute intervals.