Aerosol and Cloud condensation nuclei (CCN) measurement (Texas A&M)

by Peter Deng [Texas A&M University]

I am so happy I finally made it to the cruise after two months preparation with a strong support from my advisor Sarah Brooks and my research group members in atmospheric sciences department. After two days of struggling in the ship, I got my sea legs, which is much faster than I have expected during the period of suffering. I can now focus on my particle measurement and carry on data treatment instead of fighting with sleepiness.

Aerosol denotes to the solid particles or liquid droplets suspended in the atmosphere. It is also named particulate matter (PM) by US EPA (Environmental protection agency) as an air quality criterion. Aerosol has its importance of research in two aspects: air pollution sources (health effect) and a factor influencing global climate. Since we are purely measuring marine aerosols in the cruise, we will pay attention to the climate factor rather than the health effect, which is a key focus for continental aerosols. Due to the large coverage of earth surface by the ocean, marine aerosol is believed to be a very important factor of influencing climate. The scenario of the influence, which is complicated and to state in a simple way, is to interfere the light transfer from the solar inward radiation (short wave) and the earth outward radiation (long wave). The influence could be made by either the aerosol particle itself or the cloud droplet to which it grows in a water vapor-supersaturated environment.

Our goal in the cruise is to measure both the aerosol concentration and the CCN concentration under a specified supersaturation (SS) level. In a supersaturated environment, water vapor is able to condense onto the surface of a particle. Aerosol particles which are able to grow to a certain size (approx. 1 micron) are considered as CCN. We vary the SS levels by a preprogrammed table to control the instrument (CCN counter) to achieve the wanted level. The SS levels are cycling with values defined in the table continuously, so the CCN number concentration based on different SS levels is available sequentially. Meanwhile we use a different instrument called condensation particle counter (CPC) to measure total particle concentration within the size range of 3-1000 nm. The ratio of CCN concentration and total particle concentration is then the efficiency of cloud activation for a specified SS level. We will be able to get this information along the track of the cruise. We then want to correlate the efficiency with the phytoplankton levels to investigate the mechanism of marine aerosol activation as cloud nuclei.

I also collect field samples on filters for chemical analyses after the cruise using Raman microspectroscopy (Raman) in our lab at Texas A&M. Raman is capable of single particle measurement in terms of its chemical composition. We would like to know what kinds of source are there for secondary aerosol formation except those from DMS. Ocean surface borne surfactants has been our hypothesis and we will use the filter sample to verify that.

Everyone in the cruise is super friendly and the food is wonderful. I look forward to learn more from the science party and enjoy three weeks’ great life on the ocean.

What are the smallest things in the ocean?

- Phil Bresnahan [Scripps Institution of Oceanography]

When many people think of oceanography, they picture the whales, sharks, waves, coral reefs, and submarines. Most think of the large things, whether they're organisms, phenomena, or machines associated with the water. Many of us learn about the microscopic plankton that live in the ocean in our early school years, but those things are, at least for most of us, the smallest that are out there.

We're on this trip, however, to study things even smaller: the chemicals in the ocean and those in the air just above the ocean as well as the forces that cause them to move back and forth between the two. My own research involves inorganic carbon--basically carbon dioxide gas that has dissolved into ocean water. There are two main things that we can learn from studying dissolved inorganic carbon: 1) there was always a certain amount of inorganic carbon in the water but a very large quantity of the carbon dioxide that humans have emitted has dissolved (and is dissolving) in the oceans; we can use dissolved inorganic carbon measurements to help determine where and how quickly the CO2 is entering the ocean (it doesn't occur at equal rates at different places across the globe). 2) Just as humans & other land heterotrophs (things that eat stuff, quite simply--like a hippopotamus, for example) respire by intaking oxygen and releasing carbon dioxide and plants & other land photoautotrophs (things that make energy from sunlight--like dandelions) produce oxygen and capture carbon dioxide, so to do ocean creatures capture carbon dioxide (phytoplankton) or release it (zooplankton, fish, etc.); we can estimate rates of respiration and production with our measurements.


My type of oceanography is unique. I don't watch or listen for whales or collect samples of water from the ship. Instead, I let the water come to me. Oceanographic ships (as well as many other ships, named volunteer observing ships) have small intake pumps on the hull at the bow of the ship which deliver water directly to instruments inside the ships' labs. In this picture, you can see that there is quite a bit of sophisticated equipment; all of it is inside the Knorr's lab and will never need to leave its location since the ocean water is coming directly to it.

If you look closely, you might notice that every piece of equipment is meticulously tied down. While the conditions we've seen so far have been quite mild, the ocean is a powerful (and potentially destructive force). It's better for us to be prepared well in advance of any bad weather that could suddenly arise. We aren't searching for storms out here but it would certainly be interesting to see the changing chemistry during violent weather patterns!

Air-sea CO2 Exchange (SUNY Albany)

- Scott Miller [SUNY Albany]

The oceans currently take up a considerable fraction (roughly 25%) of the carbon dioxide emitted by human activities. Thus, at the global scale there is a net transport (or 'flux') of CO2 across the air-sea interface from the atmosphere to the ocean. One of our main goals is to directly measure CO2 flux using a technique called eddy covariance (http://en.wikipedia.org/wiki/Eddy_covariance). While the net global CO2 flux is large, the per-unit-area flux that we measure is actually very small; i.e., the global flux is large because the oceans are very big. The smallness of the local flux we are trying to measure provides many challenges at sea.

R/V Knorr mast

Our setup involves mounting sensors on the ship's bow mast to measure the turbulent wind and CO2 concentrations. We want to be at the most forward location of the ship to minimize flow disturbance and contamination of air samples due to the ship's exhaust. The bow mast was heavily instrumented in port, with the mast lowered to a horizontal position above the main deck. Before leaving port, the mast was raised to the vertical position and secured.

mast lowered to install equipment

Ideally, we would not need to access the sensors after leaving port; however, at sea instruments rarely behave ideally, and at times we need to service the instruments when the ship is on station (not underway) and the environmental conditions permit.

Accessing sensors on station.

Further Information:

Miller, S.D., C.A. Marandino C.A., and E.S. Saltzman (2010) Ship-based Measurement of Air-Sea CO2 Exchange by Eddy Covariance, J. Geophys. Res., 115, D02304

Bloom hunting

- Tom Bell [UC Irvine]

Now that you’ve been introduced to the science party, it seems logical to introduce what we are trying to achieve on this cruise (or, as the French call it, Research Mission, which is far cooler). The primary focus of these few weeks at sea is to make measurements of the movement of gas between the ocean and atmosphere and the various factors that affect this process. The gases we are focusing on are carbon dioxide (CO₂) and DMS (a sulphur compound that is thought to play some role in the reflectance of incoming solar radiation away from the earth surface). Many measurements of concentrations of CO₂ and DMS have previously been made in the atmosphere and ocean and some estimation can be made of the sea-air flux from these. However, a number of assumptions have to be made in order to do this.

Measuring the flux directly - our current experimental method - avoids these assumptions, but requires that we make very rapid (10 times a second) measurements of the concentration in the atmosphere while recording the vertical dynamics of the wind, water vapour and temperature.

Almost all of our sampling takes place from a mast on the bow at the front of the ship. I’m currently reading Moby Dick, which contains a pertinent quote as to why we have to measure from there:

“The Commodore on the quarter-deck gets his atmosphere at second hand from the sailors on the forecastle. He thinks he breathes it first, but not so.”

When measuring the flux of any gas, we have to ‘breathe’ it first, before the gusts of wind are physically and chemically disturbed and the signal lost.

Currently we are steaming North and East away from the North American seaboard - our ultimate destination is the waters close to Iceland. Why go so far away from land to make our measurements? Every year, the waters in the North Atlantic light up with the green colour of chlorophyll.

The oceanic phytoplankton (algae) grow quickly as they make the most of available light and nutrients in the summer months. In the waters to the South and West of Iceland, the annual bloom is consistently dominated by a group of phytoplankton called coccolithophores. These are known to produce large amounts of DMS and, during a previous research cruise, strong flux signals were observed. We hope to try to find similar conditions this time round.

Further information:

Marandino C.A., W.J. DeBruyn, S.D. Miller, and E.S. Saltzman (2008): DMS air/sea flux and gas transfer coefficients from the North Atlantic summertime coccolithophore bloom. Geophys. Res. Lett. 35, L23812

The life aquatic

A safety drill was organized to introduce the science crew to the many risks that life at sea presents.

The science team

Here are the members of the scientific team. Please feel free to contact us if you have questions about our scientific goals during our cruise or life on a research vessel.

Who is onboard?

The science party includes researchers from the State University of New York at Albany, University of California at Irvine, National University of Ireland Galway, Scripps Institution of Oceanography, Texas A&M, the University of Sao Paulo, and the Brazilian Space Agency (INPE).  A range of research backgrounds are represented, including meteorology, atmospheric chemistry, physics, and physical and biological oceanography.  In following blog posts these research groups will provide more specific details about their activities on Knorr.
In addition to the science team, the R/V Knorr has a professional staff of 26 onboard who operate the ship, including maintaining the mechanical functioning (engines, electrical generators, communication, navigation) to assisting with deck operations (CTD casts, instrument deployments) to providing excellent food for everyone onboard.  Included in the ship’s staff are marine technicians who work with the science team to help them carry out their research.
This cruise is the result of a long planning process (over a year) that requires close coordination between the science team and the ship’s personnel so that specific needs of research projects can be met.  Between several weeks to a month before departure, science equipment was shipped from our home institutions to the ship in Woods Hole.  The science team convened in Woods Hole June 18^th to begin loading gear onto the ship and set up equipment for sampling.  The six days of setup time in port is long compared to most oceanographic cruises due to the complexity of the instrumentation used to measure air-sea gas exchange. 

The Research Vessel (R/V) Knorr

R/V Knorr is a 280 ft global class research vessel, owned by the U.S. Navy and operated by Woods Hole Oceanographic Institution in Massachusetts.  Click the link to the Knorr's website to see lots of information about the ship.  (Photo courtesy of Woods Hole Oceanographic Institution).