Part of the Radiation Budget, pulled from the IPCC Fourth Assessment Report. Source: Kiehl and Trenberth (1997).

Aerosols have different properties depending on what they are made of. Some of those properties that are important are roughness, color, and size. These properties affect what happens to solar radiation as it reacts with the particle such as whether it will scatter or absorb. For example, a particle of black carbon (left over after burning of a fossil fuel let’s say) is going to be much more effective at absorbing solar radiation than a piece of salt that has a much lighter color as well as a shinier surface (shiner, brighter surfaces reflect radiation better). It is also important how they are distributed spatially around the globe and how long they stay in the atmosphere. To think more about the spatial distribution, at the South Pole, we have no vegetation, dirt, salt water, or large sources of combustion anywhere close to us (aside from our own station which is downwind from where we sample). We have extremely low concentrations of aerosols in the air here compared to a sand desert or near a volcanic eruption. The time that they spend in the atmosphere can depend on many things. If it is a large particle, it may settle back to the surface quicker. If it rains, the aerosol may get collected by the raindrops and land back on the surface. Depending on the hygroscopic (the ability for a surface to become wetted or have water stick to it) properties of the aerosol, water can also condense on them to make cloud droplets.

Speaking of cloud droplets, aerosols can indirectly affect solar radiation by being an ingredient for clouds to form. Water likes particular sizes and types of aerosols to condense upon. The name this particular type are Cloud Condensation Nuclei. If there are no Cloud Condensation Nuclei present, the water has nothing to condense onto and there will be no cloud. The size and type of aerosol affect the physical properties of the cloud as well. Therefore a change of aerosols in a region can change the type of cloud, thus changing its radiative properties. This dependency on Condensation Nuclei brings up yet another complicated variable that can affect the radiation budget.

So that explains a little bit why we are so interested about the “dust” in the air. Aerosols have a significant influence on climate processes. Now let’s take a look at the instruments that deal with aerosols at the South Pole.

The Condensation Nucleus Counter (CNC) does basically what its name says. It uses butyl alcohol to create a cloud by cooling the flow of the air through the instrument. Inside is a particle counter that counts how many droplets there are.

The Nephelometer measures the radiation scattering ability of the aerosols. By running air through the instrument and shining a light through the air, we can detect how much of that light is getting scattered with a photomultiplier tube (PMT). There are filters in front of the PMT in order to detect several specific wavelengths of light. If we know the output of light initially, and subtract what is detected, then we know how much light is scattered by the aerosols.

The Aethalometer is an instrument that we use to measure radiation absorbing aerosols. For this instrument, air is passed through a filter where the aerosols will deposit onto. The filter is illuminated by a lamp and there are two photocells that sense the light. One is a reference sensor on a spot of the filter with no aerosols, and the other is sensing where the aerosols where deposited. The difference between these 2 sensors is the amount of light absorbed.

Here I am using the Pollack which is an older instrument that is used to compare to the CNC. It creates a cloud by depressurizing a chamber which causes the air to cool and form a cloud. There is a PMT that detects light and I watch an ammeter to see how much the current goes down when the cloud forms.

Not pictured is the Water-Based Condensation Particle Counter which is very similar to the Condensation Nuclei Counter that is shown above. The laser inside broke during the summer and we were not able to send it to the lab, get it fixed, and get it back to the Pole before station closing.

So that is how we measure aerosol concentrations and their scattering/absorbing properties at the South Pole. The next process that we measure at the South Pole will be the Carbon Cycle and Greenhouse Gas (CCGG) group. We’ll take a look at the CO2 analyzer and the role that greenhouse gases play in the climate.

ABOARD THE RVIB N. B. PALMER, ON THE SOUTHERN OCEAN– Not only do we want to know about what type of phytoplankton grow close to icebergs but we also want to know how well they grow. Primary production, or the rate of inorganic carbon taken up by cells is one of the methods used on this cruise to determine productivity. Diane Chakos takes the water collected by the Niskin bottles in CTD rosette (see previous dispatch) and incubates them for 24 hours under sunlight to estimate daily organic carbon production.

Diane Chakos in the lab preparing samples for a 24-hour incubation under sunlight.

Based on underwater light levels we sample water from surface and at depth corresponding to 50%, 25%, 10%, 5% and 1% of surface light. Within the layer defined by 100% and 1% surface light most of the primary production occurs. Biomass, light intensity and abundance of nutrients, including inorganic carbon, all contribute to production. During austral fall in Antarctic waters we are experiencing only 12-h day light, plenty of nutrients and phytoplankton biomass equivalent to 0.5 milligrams per cubic meter results in about 5-10 milligrams carbon produced per cubic meter per day.

Karie Sines filtering cultures to estimate phytoplankton abundance in productivity experiments by chlorophyll concentration.

ABOARD THE RVIB N. B. PALMER, ON THE SOUTHERN OCEAN– We are all used to thinking of the ocean as blue. Sometimes greenish, if close to the coast, or brownish if a lot of sediments are delivered at a river’s mouth, but mostly it is blue; a clear blue close to coral reefs, a dark blue when seen from space or a grayish blue during a storm. Why is the ocean blue?

During this cruise we measured the underwater light to better understand how icebergs affect the phytoplankton growth environment. All of the colors that make the white light are sensed and measured from surface to 100 m. The first color to disappear is the red, as it is absorbed by water. A few meters under the surface the light loses the red. On the other side of the visible spectrum, ultraviolet light is also rapidly absorbed. By 20 meters depth we are left with purple, blue, green and orange light. As we go deeper only green and blue remain until only blue light is available to plants.

Transmission of different light colors (wavelengths) as taken with a Profiling Radiometer. Each line represents a different wavelength: red is absorbed first (flatter line) and it becomes background at 10 m. Grey lines represent ultraviolet light (below the visible range at less than 400 nm) and each color refers to each corresponding wavelength. The blue line, on the right, with less steepness indicates higher transmission, reaching deeper in the water column.

Phytoplankton use this light to photosynthesize and make new organic carbon, food for animals. All colors of light are usable. As might be expected, phytoplankton absorb blue light very effectively. Light absorbed but not used to drive the biochemical machinery is emitted as fluorescence, as red light.

Underwater light next to the iceberg at 30 m depth. Photo by Robert Sherlock taken with a camera mounted on the Remote Operating Vehicle (ROV).

The transmission and scattering of blue light in the water turns the ocean blue to our eyes. A sense of the underwater blueness can be seen in the picture taken from the ROV camera at 30 m depth. It is great to see the water so blue when outside the sky is overcast and grey dominates.

Sky conditions next to iceberg C18A during most of our stay in the Weddell Sea.

MCMURDO STATION, ANTARCTICA– After our full day of sea ice training, we headed back to McMurdo Station, with a steaming Mt. Erebus looming above us amid a picturesque swirling wispy sky. Yet what was in store was the highlight of the day. We found out that our next destination was an ice cave.

I knew this was going to be amazing as soon as I jumped out of the Hagglund and saw the ice cave entrance in the distance.

The ice cave entrance in the distance.

As we approached, the scene quickly became other-worldly, like nothing I had ever laid eyes on before. We were at the very edge of the Erebus Glacier Tongue, and about to walk into the glacier. This is where the Erebus Glacier, spilling off from the Mt. Erebus, goes out to sea. And here, at this location, the sea ice afforded an ideal location to walk right up to it. The icescape became an uplifted, gnarled jumble, very different than the relative flatness of the sea ice we had spent the day out on.

The view surrounding the ice cave entrance.

As I slid through the narrow entrance to the ice cave and down the slippery corridor drawing me deeper in, I began to wonder if I was still on Planet Earth.

Entering the ice cave.

Wow! Am I really seeing this? Am I really here? Is this really real? Stalactite spikes of ice were hanging from the ceiling of the corridor leading to the inner cave chambers. The light became not like the bright sun-splashed scene out where we had just been. It was starting to become a greenish-blue as light was filtered through the overhanging snow and ice. The corridor was steep and slick, but I had to go further inside this natural wonder.

Easing down the corridor, going deeper into the ice cave.

Inside the cave, away from the influence of unfiltered sunlight, a crystal palace started taking shape, draped in an ethereal blue light that only deepened as I went in further. The ice took on new shapes and character, and I was astonished as I ventured further into the main chamber.

Ethereal blue light in the crystal palace.

The ceiling, walls, and internal structures of the ice cave were formed from the glacial ice tongue. If melted, you could drink the fresh water. The floor is sea ice, which is salty from the frozen ocean water. The main chamber was the most magnificent of the whole with a large twisting spine leading up to a recessed area capped by skylights to the outside world, a world I felt a million miles away from at the moment.

The main chamber.

Further along, moving deeper within the ice cave, a rear chamber could be seen. The ice bridge over the entrance seemed to bar the way, but a peek back revealed a narrow chasm lit from above with ice crystals of various shapes and dimension all around.

Looking toward the back chamber.

I turned and walked back the way I came, feeling energized and exhilarated by this adventure. Gazing out the entrance I was reminded of where I was. I was floating over McMurdo Sound on a vast and dynamic layer of ice; from one other-worldly place to another. What a wonderful treat. What a special place.

Gazing out the ice cave entrance to the vast sea ice.

We decided to have a little fun while waiting for others to fully enjoy their own experience in the ice cave. Yup, that’s me, hanging from an ice axe over Mt. Erebus!

Dangling from an ice axe above Mt. Erebus.

Reality soon set in hard, bringing all of us back for our time in the ice cave. As we gathered the group back into the Hagglund to drive back to McMurdo Station, not long into our ride, we ran out of gas.

The Hagglund out of gas.

A little bit of patience, and reserve fuel, we were on our way, and back in time for dinner.