Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Data Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

The Central Baltic Air-Sea Exchange Experiment (CenBASE) was conducted from June to July 2022 on board the R/V Elisabeth Mann Borgese (research cruise EMB295), in an area of the central Baltic Sea east of Gotland, Sweden.

On 6 July 2022, ³He and SF₆ were injected at approximately 7 meters (m) depth in a hexagonal spiral pattern with a diameter of about 1 kilometer (km), centered ​​at 57.263°N, 20.147°E over the course of 40 minutes. After the injection, discrete samples were taken approximately every 12 hours in the water column near the center of the SF₆ patch using a rosette with a conductivity, temperature, and depth (CTD) sonde and 13 5-liter (L) Niskin bottles. 250-milliliter (mL) syringes were used to obtain discrete SF₆ samples from the Niskin bottles. For discrete ³He samples, about 40 mL of seawater were collected in copper tubes placed in aluminum channels. Stainless steel clamps were used to seal the tubes at both ends for later shore-based measurements.

SF₆ concentrations were measured onboard using a purge-and-trap SF₆ analysis system (Bullister and Weiss, 1988; Gerke et al., 2024). This system separated SF₆ from other gases and measured its concentration by a gas chromatograph equipped with an electron capture detector (GC-ECD). Approximately 200 mL of the water sample were injected into a purge-and-trap unit. Nitrogen served as the carrier gas to purge the samples, and the gases were trapped on a 70-centimeter (cm) column filled with Heysep D (60/80 mesh). The trap was maintained at a temperature of approximately −70 degrees Celsius (°C) by suspending it over liquid nitrogen. The trapped analytes were then desorbed by heating the trap to 100°C. Separation was achieved using a 90-cm pre-column filled ⅓ with Porasil C and ⅔ with Molsieve 5A, and a 220-cm main column, packed 90% with Carbograph 1AC and 10% with Molsieve 5A.

The ³He samples were shipped to the laboratory at the Institute of Environmental Physics at the University of Bremen for analysis. In the laboratory, after being removed from the copper tube, the samples were released into glass bulbs. From there, they were transferred into glass ampoules, which were then sealed for analysis with a helium isotope mass spectrometer (MAP 215-50). δ³He precision for ocean samples is usually better than 0.5% (Sültenfuß et al., 2009).

³He in excess of the solubility was calculated by the following equation:

[³He]exc = [⁴He]s (Rs − Ra) + [⁴He]eqRa(1 − a),

where:

[³He]exc is ³He in excess of solubility equilibrium

[⁴He]s is the measured ⁴He concentration of the sample;

[⁴He]eq is the atmospheric equilibrium concentration of ⁴He (Weiss, 1971);

Rs is the measured ³He/⁴He ratio (ratio of sample);

Ra is the ³He/⁴He ratio in the atmosphere (1.386 × 10^^-6 (Clarke et al. 1976));

From (1 - a), a is the solubility isotope effect (0.983 (Benson and Krause, 1980)).

- Imported original file "CenBASE_data_submission.txt" into the BCO-DMO system.
- Converted the date-time column to ISO 8601 format.
- Renamed fields to comply with BCO-DMO naming conventions.
- Saved the final file as "988658_v1_cenbase_3he_sf6.csv".

NSF Abstract:

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

The process that controls the exchange of gases between the atmosphere and the ocean plays an important role in regulating global climate, since it influences the amount of atmospheric greenhouse gases and aerosol precursors. Once in the atmosphere, these substances influence global and regional climate. Over the past 30 years, significant advances have been made in understanding this process in the open ocean away from the coasts, and how wind speed controls this process. These advances are mainly due to improvements in experimental techniques, and a number of successful scientific experiments in the open ocean. However, it is not clear if the same understanding applies to inland seas like the Baltic Sea. There, the presence of surfactants, which are biological and chemical substances that concentrate at the sea surface, and the lower salinity, could influence how wind affects this process in a different way than in the open ocean. In this project, a team of investigators will conduct an experiment that aims to assess these processes in the Baltic and compare them to previous experiments in the open ocean.

The Central Baltic Sea Air-Sea Exchange Experiment (CenBASE) is a collaboration between scientists from the US, UK, and Germany to measure gas exchange rates in the central Baltic Sea on the German research vessel Elisabeth Mann Borgeseat. This proposal will provide funding to US scientists to make measurements of two gas tracers used to determine the gas exchange rate. German scientists are independently funded to measure surfactants, and make direct flux measurements of carbon dioxide and dimethyl sulfide, as well as make continuous measurements of pCO2, CH4, N2O, O2, and CO in the sea surface, and discrete measurements of dissolved inorganic carbon, total alkalinity, and pH in the water column. A UK colleague will make measurements of bubble size distribution. The ultimate goals of CenBASE are to determine whether the relationship between wind speed and gas exchange in the open ocean also applies to inland seas like the Baltic, shed new light on the effect of natural surfactants on gas exchange, and examine whether different techniques for measuring gas exchange are in agreement.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.

The Surface Ocean Lower Atmosphere Study (SOLAS) program is designed to enable researchers from different disciplines to interact and investigate the multitude of processes and interactions between the coupled ocean and atmosphere.

Oceanographers and atmospheric scientists are working together to improve understanding of the fate, transport, and feedbacks of climate relevant compounds, and also weather and hazards that are affected by processes at the surface ocean.

Oceanographers and atmospheric scientists are working together to improve understanding of the fate, transport, and feedbacks of climate relevant compounds.

Physical, chemical, and biological research near the ocean-atmosphere interface must be performed in synergy to extend our current knowledge to adequately understand and forecast changes on short and long time frames and over local and global spatial scales.

The findings obtained from SOLAS are used to improve knowledge at process scale that will lead to better quantification of fluxes of climate relevant compounds such as CO2, sulfur and nitrogen compounds, hydrocarbons and halocarbons, as well as dust, energy and momentum. This activity facilitates a fundamental understanding to assist the societal needs for climate change, environmental health, weather prediction, and national security.

The US SOLAS program is a component of the International SOLAS program where collaborations are forged with investigators around the world to examine SOLAS issues ubiquitous to the world's oceans and atmosphere.

» International SOLAS Web site

Science Implementation Strategy Reports

US-SOLAS (4 MB PDF file)
Other SOLAS reports are available for download from the US SOLAS Web site