North Atlantic Aerosols and Marine Ecosystems Study

The NAAMES project also investigated the quantity, size, and composition of aerosols generated by primary production in order to understand how bloom cycles affect cloud formations and climate.

When the surface mixed layer becomes shallower than the critical depth, initiation of the seasonal bloom occurs due to phytoplankton growth exceeding loss.

Studies conducted in the region via a network of Argo floats and model simulations created through satellite data have shown cases of the opposite phenomena.

Relevant to NAAMES are the emissions from industry and urban environments in eastern North America, which emit substantial quantities of sulfates, black carbon, and aromatic compounds.

Aerosols are very small, solid particles or liquid droplets suspended in the atmosphere or inside another gas and are formed through natural processes or by human actions.

The direct effect occurs when aerosol particles scatter, absorb, or exhibit a combination of these two optical properties when interacting with incoming solar and infrared radiation in the atmosphere.

Within this category, the range of particles that accumulate in the atmosphere (due to low volatility or condensation growth of nuclei) are from 0.1-1 μm, and are usually removed from the air through wet deposition.

[38] The mechanism by which this occurs starts with the generation of air bubbles in breaking waves, which then rise to the atmosphere and burst into hundreds of ultra-fine droplets ranging from 0.1-1.0 μm in diameter.

The freezing of organic matter in these aerosols promotes the formation of clouds in warmer and drier environments than where they would otherwise form,[47] especially at high latitudes such as the North Atlantic Ocean.

[48] Primary marine aerosols created through bubble-bursting emission have been measured in the North Atlantic during spring 2008 by the International Chemistry Experiment in the Arctic Lower Troposphere (ICEALOT).

This research cruise measured clean, or background, areas and found them to be mostly composed of primary marine aerosols containing hydroxyl (58% ±13) and alkene (21% ±9) functional groups,[49] indicating the importance of chemical compounds in the air with biological origin.

Nonetheless, the small temporal scale of these measurements, plus the inability to determine the exact source of these particles, justifies the scientific need for a better understanding of aerosols over this region.

The Intergovernmental Panel on Climate Change (IPCC), forecasted an increase in global surface ocean temperatures by +1.3 to +2.8 degrees Celsius over the next century, which will cause spatial and seasonal shifts in North Atlantic phytoplankton blooms.

[50] For example, in the eastern North Atlantic during the spring 2002 bloom, high phytoplankton activity was marked more by organic carbon (both soluble and insoluble species) than by sea-salts.

Those data provided early empirical evidence of this emission phenomena, while also showing that organic matter from ocean biota can enhance cloud droplet concentrations by as much as 100%.

[50] There is growing evidence describing how oceanic phytoplankton affect cloud albedo and climate through the biogeochemical cycle of sulfur, as originally proposed in the late 1980s.

[66][67] The CLAW hypothesis conceptualizes and tries to quantify the mechanisms by which phytoplankton can alter global cloud cover and provide planetary-scale radiation balance or homeostasis regulation.

[68] The NAAMES campaign sought to provide an empirical understanding of the effects of marine bioaerosols on cloud formation and global radiation balance by quantifying the mechanisms underlying the CLAW hypothesis.

The biological, chemical, and physical processes occurring here may be some of the most important anywhere on Earth, and this thin layer experiences the first exposure to climatic changes such as heat, trace gases, winds, precipitation, and also wastes such as nanomaterials and plastics.

NAAMES conducted multiple campaigns that occurred during the various phases of the cycle in order to capture the important transitory features of the annual bloom for a comprehensive view.

This objective addressed this gap by using combined measurement methods to understand the contribution of various aerosols to cloud formation produced during each major phase of the annual phytoplankton cycle.

Airplane-based measurements were designed to run at precisely the same time as the research vessel cruises so that scientists could link ocean-level processes with those in the lower atmosphere.

[1] Satellite data also provided mean surface chlorophyll concentrations via NASA’s Moderate Resolution Imaging Spectroradiometer (MODIS), as a proxy for primary productivity.

[7] One publication from NAAMES found the winter mixed layer depth to be positively correlated with spring chlorophyll concentrations in the Labrador Sea.

[5] A NAAMES study determined the photoacclimation responses of multiple taxonomic groups during a 4-day storm event that caused deep mixing and re-stratification in the subarctic Atlantic ocean.

[8] One of the most recent results of the NAAMES campaign includes a better understanding of how biology helps draw atmospheric carbon dioxide down into the water column.

Specifically, the impact of zooplankton vertical migration on carbon export to the deep sea via the Biological Pump was parametrized and modeled for the first time.

[75] These empirical measurements by seasonality will help improve the accuracy of climate models that simulate warming or cooling effects of marine bioaerosols.

For example, sorting flow cytometry combined with bioluminescent detection of ATP and NADH provides relatively precise determination of phytoplankton net primary productivity, growth rate, and biomass.

Zhang et al. provided atmospheric corrections for the hyperspectral geostationary coastal and air pollution events airborne simulator (GCAS) instrument using both vicarious[14] and cloud shadow approaches.

The North Atlantic Aerosols and Marine Ecosystems Study (NAAMES) project logo. Image courtesy of NASA.
Competing scientific hypothesis of plankton variability. Figure adapted from. [ 19 ] Courtesy of NASA.gov
Aerosol size distribution and their associated modes of accumulation or removal from the atmosphere. Original diagram by, [ 34 ] and adapted by. [ 35 ]
Representation of the direct and first indirect effect of aerosols on the albedo of clouds and therefore Earth's radiative balance. [ 39 ]
Contribution of aerosols and gases in the atmosphere of to the Earth's radiative forcing. This is Figure 8.17 of  Working Group 1 Firth Assessment (AR5) report by the Intergovernmental Panel on Climate Change (IPCC) [ 45 ] Note the net cooling effect of sulphates.
Phytoplankton booms are important sources for biogenic aerosols that provide cloud condensation nuclei
Schematic of the diverse sampling strategies for NAAMES research campaigns, including satellite sensors, vessel measurements and deployments and aircraft remote sensing. It also depicts key processes, such as phytoplankton booms and aerosol emission and dispersion.
Area of study for NAAMES depicting routes of research vessels and deployment of autonomous profiling floats. Image courtesy of NASA.
The Autonomous ARGOS floats collects Conductivity, Temperature, and Depth (CTD) measurements. It adjusts its hydraulics to ascend and descend in the water.
Illustration of sources of aerosols found during NAAMES cruises [ 75 ]