Saharan Dust

Saharan dust storm in 2003. We are just south of the frame of this picture

Now that we are nearing the coast of Africa, we have been seeing lots of Saharan dust coming from the continent. Why would anyone care about this dust, you might be asking? The Sahara Desert is the second largest desert in the world (Antarctica is considered the first), and is a vast dry area full of sand and dust. Strong winds often sweep over the continent from Europe, and can carry this dust thousands of miles-it can be seen across the Atlantic Ocean and into the United States. These large dust storms can carry important nutrients, as well as harmful things into the ocean and onto land, and is one of the important sources of nutrients to the ocean that is being studied on this cruise.

Aerosol samplers on the flying bridge with lots of dust!

Some scientists on board from University of Alaska, Fairbanks and from Florida State University, are studying these dust storms and other "aerosols" in the marine environment. Aerosols are tiny particles that are generally made up of some kind of dust or sea salt, and water. They are called aerosols because they are a mixture between a liquid and a solid, and are found floating in the air. Aerosols are comprised of many things, and oceanographers often distinguish between anthropogenic aerosols (aerosols that are human-derived, often forms of smoke/smog and other pollution) and natural aerosols (like those from the Sahara). By measuring the sizes of the aerosols, and the different metals and nutrients in the aerosols, scientists can often distinguish where these particles originated from and how far they have traveled. This is just what scientists on our ship have been doing everyday of the cruise since we left. They have large aerosol samplers on the "flying bridge" of the ship, which is the highest desk on the ship above everything else so that the samples don't get contaminated by any pollution coming from the ship itself.

Red/orange Sahara dust in the medium size range

Black/gray anthropogenic dust in the small size fraction

The dust from the Sahara is visibly orange/red and is generally greater than 1 micron in size. Knowing the size of the dust is helpful, because both the color and size can help scientists distinguish it from other types of dust, like anthropogenic dust, which is generally gray/black in color and in the small size range (0.45-0.95 micron). Each type of dust contains different levels of metals, and when it lands on the ocean it may have different effects on the resident phytoplankton communities.

Sahara dust on the aerosol filters

For example, dust from the Sahara usually has high levels of iron, an important nutrient for phytoplankton, so a dust storm could mean an increase in nutrients that the phytoplankton need. On the other hand, anthropogenic dust from industrialized areas has high levels of toxins such as lead and sometimes mercury, which can be potentially harmful to phytoplankton and other organisms.

The Scientists Take Over the Galley!

Menu items

I think most people would agree that the most difficult job on the ship is the cook and the stewards (other cooks, who help with preparing meals). They have long hours, have to feed up to 60 hungry people 3 times a day, all with different likes/dislikes and diet requirements. They usually get up at 4 am each day to make breakfast, and chop and prepare other items to be used throughout the day. They stay up working until around 7pm, when they have finished cleaning all of the dishes for the day, and have planned meals for the next day. Talk about a tough job!

Melissa and Chief Scientist Greg Cutter preparing the meal

The scientists on the ship felt that the cooks had therefore been working way too hard over the past 30 days, so we asked if we could give them something in return and cook for them and all of the crew. They agreed, so a feast was prepared. The Chief Scientist, Greg Cutter, decided on making his legendary fajitas recipe, and we took the job in shifts in order to make sure we made it on time, and had enough food. Other scientists made some other delicious dishes, including homemade hummus by Chris Measures, salsa and guacamole from some of the other scientists, and desserts by Ana Aguilar-Islas and Rachel Shelley. I helped to serve the meal to all of the crew members and scientists when they came to eat.

Everyone seemed to enjoy themselves, and we definitely had a lot of fun. I think all of the cooks enjoyed the break too, and we definitely appreciate how hard they work everyday! We were in the galley (another name for the kitchen on a ship) from 10am-7pm just for one meal! It was also nice to cook a little bit for those of us who enjoy cooking, because it is usually one of the things that we miss from home when out on these cruises.

Finished product!

We are continuing on in our journey, and are almost done! We pull into port on Sunday morning in Cape Verde, and are currently on station 22 out of 24. The countdown has begun!

Mid-Atlantic Ridge

Relative amount of particles in the water over the Mid-Atlantic Ridge

We just finished a station over the Mid-Atlantic Ridge, a huge plate boundary that runs down the middle of the Atlantic ocean as a long underwater mountain range. Some parts of this mountain range are more than 3000m (about 9000 ft) higher than the surrounding ocean floor. This is only slightly lower than Mt. Whitney in California. This huge mountain range under the sea is a divergent plate boundary, or an area of the Earth's crust where two plates are moving apart from one another. In this case, the Mid-Atlantic Ridge forms the boundary between the North American Plate and the Eurasian Plate. The plates are moving apart at about 2 cm/yr. When the plates move apart, lava and other chemicals are emitted into the water that we can measure. Once the lava hits the seawater, it rapidly cools off since the seawater is colder than the lava, and looks like black smoke when it comes out of the vents. Due to this, these underwater volcanoes are often called "black smokers." Black smokers are interesting for a group of scientists studying metals, because some of these metals are emitted in extremely high concentrations near these hydrothermal vents, or underwater volcanoes. Some of the metals that were found in high concentrations at this sight were iron, and mercury. In order to sample in the plume from the ridge, we first put some sensors into the water, including one that can measure the relative amount of particles in the water at different depths. This is called a transmissometer, and where the measurements rapidly decrease (due to an increase in particles), is generally where the plume should be. We therefore collected samples in the plume, as well as directly above and below it for comparison. We also got our instrument a little too close for comfort to the bottom of the ocean at this station, and had a little bit of a scare that we might have damaged our equipment, but all was well when it came back on board (phew!).