Archive for March, 2010

March 11, 2010

11 March, 2010

The cruise is coming to a close and we are on our final transit back to Fortaleza, Brazil.  The very last core was taken at 11pm last night in 2800 meters of water, and we have been disassembling and packing our gear all day today.  We did a total of 90 deployments (including box cores, gravity cores, multicores, piston cores, in situ pumps and CTDs) during our 3-week cruise and surveyed much of the Amazon outflow region.  Overall we were very successful in obtaining oceanic sediment core and water samples, and are looking forward to getting back to the lab where we will be able to analyze the material in greater detail.  At this point we don’t know how far back in time a 50 meters of sediment represents.  We will have to radiocarbon date calcium carbonate microfossils (i.e. Foraminifera) in order to determine the age of our core material.

The science party of Leg 179-4 congregates on the deck for one final sunset

The RV Knorr arrives at the Port of Fortaleza early Friday morning. We can’t wait to get to the beach in Brazil, since we have been surrounded by sunshine and tropical waters for weeks now, but have not been able to go swimming!  There is still a lot of work to do though.  We have over 14,000 lbs of sediment cores that need to be loaded into a refrigerated shipping container on Saturday, so that they will be safely stored, until their journey back to the United States.

It ‘s all about calibration!

March 10, 2010

Your climate reconstructions are only as good as your calibrations!

One of the most important goals of our research expedition is to reconstruct climate and hydrological conditions on the South American continent over the past 60,000 years. To reconstruct the past climate, we measure specific chemical components in sediments that record climate conditions. In order to be sure our climate reconstructions are accurate we are always testing or calibrating our chemical tools in the modern environment. To calibrate means that we relate modern conditions to the variation in our measured chemical components measured from modern water column and surface sediment samples. In this way we develop a mathematical relationship between temperature and variations in our chemical components that can, in turn be used to reconstruct past temperature when layers of the sediment are analyzed for the specific chemical components.

The red points indicate the sampling points of the transect north and south of the main Amazon river out flow.

The new method that we want to apply will help us to understand continental temperature. To learn about the temperature of the continents the out flow of the Amazon River from the South American continent is a perfect study site, because the river transports particles from all over the Amazon basin into the ocean. To extensively study the transport of the particles into the ocean we took samples during two transect from deep water sites on the continental slope at 3100 m to very shallow water sites on the continental shelf at 35 m. One transect was north and one transect was south of Amazon River.

So how can we deduce the temperature of the continent from river water and sediment?

Some of the molecules that are transported from the land into the sea, contain the secret in their chemical structure. The molecules are membrane lipids (called branched glycerol dialkyl glycerol tetraether or short GDGT) from soil bacteria. All bacteria have a cell wall and a membrane that protect them.

Like we are putting more cloth on when it is colder, bacteria are also able to adapt to temperature. They do this by changing the chemical structure of their membrane lipids. The structure changes so that the membranes are tighter when it is warmer and looser when it is cold.

Scheme of a bacterial cell

Once a method is calibrated and tested in several environments it can be used to determine the temperatures of the past times by looking at deeper sediment layers. Utilizing our calibration study from the water column and surface sediments we will be able to accurately reconstruct South American land temperatures over the past 60,000 years.

Example of a branched GDGT

No pain no gain

March 9, 2010

Deep-sea coring is not a simple oceanographic operation by any means. The long core itself is about 25 thousand pounds, and can generate a load of more than 60 thousand pounds when it’s being recovered from the mud. Such a difficult operation requires high-tech hydraulics and electronics, and a team of experts specialized in very specific tasks ready to troubleshoot any problem at any time. During the last 24 hours we’ve been trying to core on the edge of the continental platform without much success. The release mechanism that drops the core into the sediments has not been working. This system is triggered by an acoustic signal that travels from the ship down the water column and tells the release to ‘let go’ the core when it is a few meters above the ocean floor, so it can penetrate deep enough into the mud. This issue has caused three failed deployments, and considering that coring at 3,200 m takes about 4-5 hours it’s pretty frustrating recovering a spotless barrel filled just with seawater. Apparently the release mechanism is being affected by high pressure, which at 3,200 m is more than 310 atm. The release system has been replaced and the long core is now ready for a new deployment. But just now we heard that the winch controller is not working, so stay tuned.

Going for the top!

March 8, 2010

8 March, 2010

Yesterday we came across a remarkable ocean feature – a seamount. Seamounts are common in the world’s oceans, and their origin is diverse. The seamount we mapped yesterday is a part of a submersed ridge (North Brazilian Ridge) of tectonic and volcanic origin.

We spent several hours mapping the seamount, which was located in approximately 3,500 meters of water. Mapping the ocean floor is a long process; the ship’s equipped with a Seabeam, which can ‘see’ at that depth about 6 kilometers on each side. That means that with each transect, the Seabeam covers an approximate footprint of 12km. We also use a high resolution sub-bottom profiler, which allows us to determine how the bottom sediments are, whether they are soft and layered, or made of harder rock. In order to cover the entire seamount (24 km wide, 48 km long) we spent approximately 12 hours. However long, mapping the ocean floor is a fundamental necessity of coring – without knowing what’s down there we cannot make an asserted decision of where to take ocean floor samples. There is also the added risk of sending our instrumentation against hard rock, which would probably damage it irreparably.

After the mapping was completed, two coring locations were chosen and a gravity core was taken at each (see map). A box core was also taken at the second location. We were quite surprised at the sediment we recovered in the box core – there appeared to be three distinct layers – an upper one of calcareous sand, a second one of consolidated calcareous silts of light brown color, and a third one of compacted mud of a darker shade of brown. Our expert geophysicist Cleverson pointed out that the seamounts in this area are thought not to receive much material from the continental shelf, as they are relatively isolated, and the majority of the sediment from the shelf reaches the deepest portions of the ocean floor via slumping, or mass wasting. The sand and silts we observed in the core were likely of pelagic origin, raining down and accumulating on the seamount from the water column above it. It provides an ideal location to understand what processes have occurred in the water column, away from the coast, in the past few hundred years.

Life at sea aboard a research vessel

March 6, 2010

Laura and Kara on deck awaiting the rosette at 0400 during our 'round the clock sampling

Living aboard a working research vessel like the R/V Knorr is very different from being on a cruise liner or even a small pleasure craft.  While 21 days at sea may seem to be a long time, we must work constantly around the clock to accomplish our goals of finding and collecting enough good water and sediment samples to bring home with us to study Amazon climate.  This means that there are always scientists up in the middle of the night either coring sediments, filtering water samples or looking at seismic data to find new sampling sites for the days ahead.  Sometimes we will work all night long and sleep during the day, or vise versa.

This is the main science lab, where we have science meetings, work on our computers, and analyze core sections for magnetic susceptibility

Most of our work is done either out on deck or in the main laboratory.  Sediment cores are brought up on deck where they are capped and brought into the main laboratory to be labeled.  Small samples are stored in freezers in the main laboratory while large cores are held in a large walk in freezer on the ships deck.

Claudia takes a turn showing off her skills on the Hula Hoop

Laura gets some work done out on deck

Although we are working long days, there is always time for some fun and relaxing on the ship!  The ships crew and scientists all enjoy watching evening sunsets after diner, playing cards, sunbathing and even hula hooping!  The R/V Knorr also has a great library of books, movies and even an entertainment room with a flat screen TV!  There is even a small gym aboard that includes two tread mills, a stationary bike, elliptical machine and some weights.

Claudia and Kara catch up on some reading on the "steal beach" during transit

Of course, one of the best parts about being on a scientific research cruise is the food!  The galley is open for breakfast, lunch and dinner everyday day, serving a wide variety of delicious meals like homemade granola, fresh fruit salad, lamb chops, eggplant casserole, and sesame encrusted sea scallops just to name a few.  For those who work late night shifts, meals are set aside and snacks/desserts are left out for anyone who wants a midnight snack!

Dale entertains us in the science lab with his ukulele during a survey

After a long day (or night) of work, we are always happy to return to our staterooms for some rest.  Most scientist stay in rooms with 2 bunks and a bathroom that is shared by an adjoining room. Staterooms are generally very simple, but have plenty of room to store all of our personal gear and belongings.  Sheets, blankets and towels are all provided by the ship and laundry facilities are available for everyone to use.

The science crew takes a view of the water from the top deck

Today marks the start of our last week on the R/V Knorr.  So far, we have deployed and collected over 50 sediment cores and water casts combined!  While we are excited to return back to USF to begin analyzing all of our data, we’ll miss the fun and excitement of living and working aboard the Knorr.

The scientists and crew enjoy dinner in the mess

11+ cubic meters of very clean seawater

March 5, 2010

We are also deploying two in situ filtration devices, or instruments that pump very large volumes of water through a fine filter, to collect particles directly from the water column. We are talking about ~340 liters of water pumped by each instrument during one-hour deployments. We’ve made 16 deployments so far, which make a total of 11.2 cubic meters of filtered seawater (quite a bit). The pumps are attached to a wire that lowers them to target depths; in this case we are chasing the chlorophyll maximum (the depth with the highest concentration of chlorophyll, the most abundant pigment in phytoplankton) and near the ocean floor. We can tell exactly where the chlorophyll max is using data from a fluorometer installed on the rosette. This instrument measures the specific optical response of particles when they are exposed to light of known wavelength emitted by the fluorometer; and in oceanography it is widely used for detecting chlorophyll in seawater. Why do we care about the chlorophyll max? Because particles from the phytoplankton community will allow us to get information about type of organisms present in it, as well as detect specific molecules that carry information about the origin of these particles and the environmental conditions in which they were formed. Particles collected near the ocean floor will provide information about the level of degradation and chemical transformation of settling material that was originally formed near the surface. The chemical composition of these particles captured in the water column will be compared to that of the sediments collected with the box core, to connect modern environmental conditions with those present several hundred and thousands of years ago, with the aim of unraveling the history of climate in this region of the Atlantic Basin. Simple.

How do we know where to take a sediment core?

March 5, 2010

Cleverson Silva, our resident geophysics expert, keeps watch over the Seabeam and Chirp systems

5  March, 2010

It’s another slow day of surveying on the RV Knorr, but that doesn’t mean that we’re not accomplishing anything.  As the ship moves along a preplanned survey track, it is continuously collecting bathymetric data that can show us what the seafloor looks like.  High resolution mapping of this area is one of the objectives of this cruise.  The main objective, however, is to find a sediment sequence that can give us a continuous, undisturbed paleoclimate record of the past 30, 000-60, 0000 years.

In order to find an ideal location that is likely to have such a sedimentary record, we use the Seabeam and Chirp systems to collect information about the geometry of the surface and sub-surface sediments.  We are looking for a site with flat, horizontal deposition that is not subject to slumping or faulting, or any sedimentary process that would disturb sediments once they have been deposited.

Bathymetric map of seafloor while "mowing the lawn", or making a zig-zag ship track

The Sea Beam system is a multibeam echo sounder that produces high resolution bathymetric contour charts of swaths the seafloor, like the one seen here from one of our first surveys. The swaths of map track the path of the ship.

Bottom profile as recorded by the SeaBeam system

Sediment Profile in 1,175 meters water depth

The Sea Beam system also produces gray-scale swath maps (side scan sonar maps) of the seafloor terrain that can help us determine the bottom roughness and the nature of the bottom sediments.

Finally, the Chirp system is a single-channel, high frequency seismic system. It collects information about the sub-bottom sedimentary sequence. The output is in the form of a cross section of the sediments below the seafloor, showing bottom topography and the large-scale internal structure of the strata.

Put on your galoshes…We’re in the ITCZ!!!

March 2, 2010

The Inter-tropical convergence zone (ITCZ) migrates annually from its northern position in the northern hemisphere summer to its southern position in the winter.

2 March, 2010

We had a full 24 hours of transit yesterday before arriving on site at 11pm for a night of long coring, gravity coring and box coring. We are now sitting within the Intertropical Convergence Zone (ITCZ), which is the band of convection that circles the globe near the equator and occurs where the trade winds from north and south of the equator converge.  The ITCZ migrates northward in the Northern Hemisphere summer, and southward in the winter, and is responsible for the wet and dry seasons experienced in the tropics.  Right now we are positioned at  2º 51.5575′ North latitude, and are surrounded by impressive thunderclouds.

Large thunderclouds associated with the ITCZ off our starboard bow.

One of the major objectives of this cruise is to investigate the effects of the ITCZ position on Amazon Basin climate.  We know from previous studies that the mean position of ITCZ  has changed on glacial to interglacial periods (100,000 year cycles).  However, researchers are interested in learning more about the detailed movements of the ITCZ on shorter timescales as well (i.e. during the Little Ice Age and Medieval Warm Periods, 100-200 year timescales).

Kara and Carlie "sunbathing" on the steel beach. Hopefully they make it down the 5 flights of stairs to the main deck before the rain.