How old are our samples?

After splitting the cores, collecting the sediment samples, and label, weight, and dry them, the moment has come to investigate their age. To do this we applied a Radiocarbon Dating method. This radiometric dating method uses the naturally occurring radioisotope 14C to estimate the age in those materials that contain carbon (e.g. organic matter, textiles, carbonates, wood). This method, however, can only be applied to date materials that are less than ~55-60 thousand years old, after this period the radioactive decay (the rate in which 14C decays into a non radiometric carbon isotope) is such that there is not enough 14C in the materials to calculate an age.

Radiocarbon measurements are traditionally performed by counting the radioactive decay of individual carbon atoms via gas proportional counting or via liquid scintillation counting. However, for small samples decay counting is relatively insensitive and subject to large statistical uncertainties.

In our case, as we dated samples of biogenic carbonate from the planktic foraminifera collected from the sediments, and as foraminifera are very small and their shells don’t weight much (in addition that only ~12% of calcium carbonate corresponds to carbon atoms) we can’t use proportional counting or liquid scintillation. Thus, we applied a technique called Accelerator Mass Spectrometry (AMS). This technique detects and counts the 14C atoms directly.  How? Samples for radiocarbon AMS measurements are incinerated. The resulting C02 is collected and reduce to a solid carbon (graphite) target for sputtering atomic carbon ions into a mass spectrometer, which allows dating samples containing only a few milligrams of carbon.

Cruise participant: Antoon Kuijpers

Antoon Kuijpers is a marine geologist specialised in marine sediment transport processes and late Quaternary (paleo)oceanography/climatology. Presently, his research focus is the Labrador Sea and adjacent Greenland waters, the Baltic Sea and the Caribbean. Previously, he also worked in the Barents Sea, North Sea, Northeastern and (sub)tropical Atlantic, and Indian Ocean.

Freeze drying samples

For some analyses (e.g. micropaleontological, compositional, etc.) it’s essential to freeze dry the sediment rather than oven-dry it.

Freeze-drying it’s preferable to oven drying because it removes the water content without greatly altering the physical structure of the sediment. As a result, sediments containing clay are much easier to handle (they remain friable) and diatom or foraminifera breakage, resulting from contraction of the sediment during drying, is greatly reduced. Furthermore, the formation of carbonate aggregates on the surface of calcareous microfossils due to carbonate re-precipitation, which may change their isotopic composition, is also prevented.

Cruise participant: Christof Pearce

I am a Ph.D. student at the Centre for Past Climate Studies of the Department of Geosciences at Aarhus University in Denmark. My research is on the reconstruction of past sea-surface conditions (temperature and sea-ice variability) in the North Atlantic Subpolar gyre region. For this I am using sedimentological, geochemical and micropalaeontological data with the main focus on diatom analysis.

Diatoms are unicellular algae and are generally the main constituents of the phytoplankton. As primary producers in the upper layers of the ocean, they play a vital role in the marine food web. The cell walls of diatoms have characteristic shapes and ornamentations depending on the species and are made up of silica, resulting usually in excellent preservation in the sediments. Because of the wide variety in species, all with their own ecological preferences (e.g. temperature, salinity, nutrient availability), diatom remains in sediments are ideal indicators of past sea-surface condition.  

At the moment I am studying a gravity core from offshore Newfoundland, that encompasses the Late Glacial to Early Holocene time period (from 12500 to 9500 years ago). In the core, the transition from glacial times to the current Holocene epoch is not smooth and is associated with numerous big climatic fluctuations such as the Younger Dryas, a cold interval when temperatures dropped almost back to glacial levels.

The diatom assemblages clearly reflect these changes as variations in sea-surface temperatures and sea ice presence.The results will be combined with analysis of benthic foraminifera and geochemical parameters to achieve a more comprehensive record. The study of these fluctuations is important to improve our understanding of past and present natural climate variability and will contribute to better future predictions.

Sampling the cores

After the cores arrived to the CORESTORE laboratory we split them longwise. Then we packed, labeled and deposited them in the cold room.

All the working halves* were taken to the GEOLOGICAL WELL SAMPLE LABORATORY. Here, with the help of Sebastian a Geology and Geography undergrad student working in the lab, we sliced each half section every 1 cm.

Dark gray layer: volcanic ashes?

The sediment composing the cores is high in carbonate content, hence the light color, however on the cores’ surface it was possible to distinguish some darker layers that we think are volcanic ashes. Some of these layers appear gray while others look greenish. The analysis of the elemental composition of the sediments will tell us why the difference in color and will confirm if those are, in fact,  pyroclastic particles.

Sebastian showing a slice of the core sediment

We use a CD to slice the cores. The physical and chemical characteristics of the polymer plastic use to produce CDs prevents the sticking of the sediment to   the CD surface, making the slicing process (that is already time consuming and a little tedious) much easier than when using aluminium or regular plastic cutters.

Each of the sample-slices was divided in 3, and each of these subsamples will be used for something different:

1. Elemental analysis (composition of the sediment) and magnetic susceptibility

2. Planktic and benthic foraminifera (assemblage changes, stable isotopes, etc)

3. Sediment characteristics (granulometric analysis)

At the end, the linning is empty and we have 265 x 3 little bags full of mud.

The end of the core, finally!!!

*The half of the core that is used for all the analyses is commonly referred as the Working half. The half that is keep intact and preserved in the cold room is the Archive.

A little more about our project

Cruise rute from Tuxpan (Mexico) to the Yucatan Strait

The cruise's focal objective was to obtain sediment samples—by gravity and box core retrieval—from depths between 500 and 2000m along the Yucatán Strait,which is an ocean channel extending for 217 km between Cabo Catoche (Mexico) and Cabo San Antonio (Cuba). This strait represents the boundary between the Caribbean Sea and the Gulf of Mexico.

Oceanographically speaking, this is a very interesting area, where water masses advecting from the Caribbean Current, derived from the North and South Equatorial Current, enter the Gulf of Mexico to form the Loop Current, outlining the foundation of the Gulf Stream. Thus, sediments from the Strait of Yucatan may contain a record of the past oceanographic variability that affected the strength and characteristics of the Gulf Stream in previous times.

With sediment from our cores, we are working towards generating a multi-proxy record of high resolution to reconstruct past climate and oceanographic variability in this region.

Finalcial support from this cruise was provided by the Dansk Center for Havforskning (Danish Center for Marine Research)  in their 2010 applicatuion for ship-time funding.

NEWS

After some months without any updates on the blog it's time to start posting again. We've started the analyses of the recovered cores and it's now time to tell you about it. Also,  we have made some changes to the blog:

1. To make it easier for everybody to understand what we did during the cruise, we've decided to translate all entries regarding the trip to English (you can still find the original version, in Danish, German or Spanish, as a comment to each particular entry) .

2. We are also starting a series of notes about each one of the participants. Once a week I'll post some info about one researcher or student, telling you about them, what they do and where are they now.

3. You will also find new pictures from before, during and after the cruise. We plan to change this pictures at least one a month.

The adventure is finished

A nice view of Tuxpan from the B.O. Justo Sierra

We arrived back in Tuxpan at midnight of March 29th.

Next morning all the equipment was load back in the container and we started to say goodbye to the crew, to our other fellow students and scientits and to the warm weather.

I hope the container will arrived in Denmark without delays or problems and we´ll have samples to work on for a long time.

y nos dieron las 10 y las 11... y a las 12, llegamos a puerto.

The Justo Sierra just after our arrival

Finally here... back in Tuxpan

Y las muestras, estuvieron a bordo...

In the last station, at which we arrived last night, it was possible to obtain very good samples from both the box and the gravity corers.

Once the work was finished we had much time to spare before arriving to the port of Tuxpan, thus the whole research group gathered for a photo shoot ...

Status pt

We're now traveling back to Tuxpan with a lot of CTD profiles and one good gravity core + a small piece recovered from a 2000 m depth. I must admit, though it probably sounds a little nerdy, I’m a bit in awe of that little lump of clay.

We’re now sailing with the current (instead of against it) and there is not more sea surface chaos, so sailing it’s definitively a greater pleasure. The water is blue and the sun shines, and a part of me wants to go on deck to enjoy the sun and the fresh breeze much more than during the way over.  At 9:00 pm we’ll arrive at our last station, and here we bring all the guns to get as many samples as possible. Both the gravity core, box core, CTD' and perhaps even de Van Veen excavating will be sent out. We wait in excitement and hope for a lot of mud! :)

el recuento de los daños

Coring at night

Since in previous stations the Reineck (box) corer was launched several times but it was not possible to obtain cores =( we have changed our ways and now the strategy to follow is to sample two much shallower sites to obtain sediment from an area where the carbonated province converges with the  terrigenous one in the south Gulf of Mexico.

Preventing the return of seasickness

Note: this blog had not been updated because I was out of circulation for the past 2 days due to a major collapse ... the cause... SEASICKNESS ... snif snif ...

A cultural breviary:

According to nautical nomenclature...

Singladura: to the dictionary of the Royal Spanish Academy, this word refers to the distance traveled by a ship in 24 hours which ordinarily begins from 12:00 hrs. However in the B / O Justo Sierra, are counted starting from 0:00 hours  

The first samples with The Gravity Corer

The first core sampled with the Gravity Corer measured almost 3 meters.

Launching the gravity corer

Extracting the lining full with sediment from the corer tube

Labeling each of the core sections

Den første nattevagt

Waiting for the end of the night shift

So the first night watch is over. It was long and very lonely. It seem as if only Kathrine and I were onboard the ship. I must admit that there have been times when life on board has been more inspiring, sigh. But it is now over and we’ve started our second morning shift, which has to be something more rewarding than the former.

We collected two gravity cores from stations three and four, whereas none were retrived at stations one and two.

The situation is a little disappointing, but at least now we have something to take home.

We are moving towards the last station. It is on the way back.

Say hallo to our dolphin friends...

Seawater - deep blue and full of life

One minor study during the cruise is filtring of sea water. Sieves of 50 micrometer catch everthing which live and floate in water, i.e. mud particles, diatoms, dinoflagellate cysts, coccoliths and foraminifera. We will take water samples of 5 liter in different detphs, starting close to the sea surface and ending close to the sea floor in the 'bottom nepheloid layer'.

The results give information about the amount of turbidity in the water column, living planktonic micro-fauna and much more.

Let's see what it brings...

Sampling and processing meiofauna

Meiofauna will be sorted out of sediment samples from both the Van Veen grab and the box corer. The top layer of the sediment from the box corer is scooped of and put into a bucket with seawater and the Van Veen grab is emptied into another bucket with seawater. Meiofauna often have adhesive features, so to make sure we get most of the organisms out of the sediment we will add an isotonic MgCl2 solution to half of the samples. This will anesthetize the organisms and thereby prevent them from sticking to the sediment. By stirring the sample, both with or without MgCl2, we can now force the living organisms out of the sediment and into the surface water. The surface water is then decanted through a 30µm or 60µm sieve and the meiofauna captured in the net can now be sorted out using an dissecting microscope. Further tales of my experience with using the microscope while sailing will probably come. But as the waves are now I'm happy that I brought pills to prevent seasickness...

Somebody received airmail to day...

A package with a nice surprise (a pair of repaired sunglases) was delivered via flying balloon

Shit happens

This morning we got some visitors. Three Frigatebirds decided to join us for the trip.

Guess what...

Filtern von Wasserproben

Before we can start with the filters we need water samples. That we’ll obtain by using the CTD (Conductivity Temperature Depth) and rosette system. Inside the CTD there are measuring sensors for water temperature, salinity and water density. Outside, on the frame, there are 10 water sampling bottles arranged in a rosette.

The entire device is lowered into the water to take measurements and water samples at different depths. Each individual container is open to let water in. At the selected depths, a radio signal will release the bottle lid and the water from that deep will be trap inside.  After the operation is complete, the CTD keeps moving through the water column until a new depth is selected and a new bottle is signaled to get a new sample. Typically, the first water sample is taken near surface and the last one close to the sea bed. The other depths are selected according with the needs of each study. Then, after having taken all the water samples and measurements, the CTD is pull back on deck where we take a 5 liters sample from each bottle.

In our case, three layers are particularly important: (a) near surface, (b) near the sea bed and (c) the layer of maximum change in temperature. Then 5 liters from the individual containers are filter.

Each filter runs as follows:

- We clean the unit with fresh water or alcohol

- Closed the faucets below the filter

- Weigh the filter (approx. 10 mg)

- Set the filter below the funnel in the appropriate ring.

- Then, we pour the sampled water in the funnel, open the faucets and turn on the pump.

- By suction, the water moves from the funnels through the filter and out to the sink while the particles suspended in it are retained in each filter.

-After all the water has drained, the filter is removed, well packaged, labeled and we clean the unit again.
-Then, the filters are dried and weighed again, so we can calculated how many particles are in a liter of water (mg / l).

-Later, the filters are evaluated under an ERM (electron scanning microscope)

The Gravity Corer

This tool allows us to retrieve sediment cores from the ocean floor using a very straightforward method. Consisting of nothing but a large weight (approx. 1 metric ton) attached on top of a long tube, the corer is lowered from the ship into the water using a powerful winch and kilometers of cable. Once it hits the bottom, the weigth drives the corer several meters deep into the sediment, hence the name gravity corer. After the core is retrieved, i.e. raised back up on deck, it gets cut up into 1 meter sections for the ease of handling and transportation. It is now ready for scientifical analysis.

Depending on the local sedimentation rate at the sampling site, several meters of core can correspond to thousands of years of sediment accumulation on the sea floor. Using radiocarbon dating on a number of samples throughout the core, an age-depth relationship is established.

Samples at certain intervals, depending on the desired resolution in time, are studied for microfossil content and geochemical parameters, allowing researchers to reconstruct oceanographic and climatic conditions of the past. This study of past climatic variability contributes to the understanding of our complex climate system and plays a crucial role in making reliable predictions for the future.

In conclusion, despite its apparent simplicity, the use of the gravity corer will provide us with some of the most important information to be obtained during this cruise.

CTD

At every station we are going to measure different fysical and chemical parameters in the sea, from the surface to the bottom. For this purpose we use the CTD Rosette system. The CTD measures Conductivity, Temperature and Depth. On the CTD there is also an oxygen electrode, a fluorometer, turbidity sensor and a lightmeasurer. The flourometer measures the amount of chlorophyll in the water.
From all the different parameters a profile is made, which are real time shown on the computer. From this profile it's decided at which water depths samples should be taken.

On the CTD there are 12 bottles attached. When the CTD is decending the watercolumn all the bottles are open. The bottles are controlled with a remote, and can be closed in different depths. In that way water samples can be obtained down through the water column at the wanted depths.

Retriving the CTD

As we do not have much time at each station, we only take around 3 water samples. One in the top layer, one in the chlorofyll maximum and one in the bottom layer. If there is further stratification in the water column, more samples will probably be taken. As the area we are going to is unexplored everything is still unknown and everything (well, in parts.. ) will be revealed. :)

The water samples is to be analysed for algeas. In this way it is posible to compare the algae in the bottom sediment with the algeas in the water samples. For further information about this, see Marikas text.

The Van Veen Grab

A more scientific assignment was given to us students this morning. We are to describe the different types of equipment on board. My task is to describe the Van Veen grab.

The grab is send to the bottom of the sea to check the type of sediment at the given station before descending the boxcorer and the gravity corer (these will be described in other blogs). The reason why this is done is to make sure that the sediment at the given station is of such quality that it won't damage the two later corers. These (box- and gravity corer) are more sensitive to hard sediment.

The sediment samples from the Van Veen are used for a project on foraminifers made by myself and the lovely Kathrine. A more elaborate report on the subject will be available later this June.

La mar en calma...

Calm at sea. Now, Neptune has become an unbeatable host while Eolos takes a well deserved nap.

For changes on the schedule, in search of better sampling sites, it will take a little longer to reach the long-awaited first season…

good thing Christof found the best place to run the story (see attached picture =)...

Hej landkrabber!

So there is little news from the Gulf of Mexico.

A good way to pass the time: playing in an improvise ping pong table

The voyage started out with some people getting seasick. Some of us had to spend most of a day in recovery from an unbalanced balance nerve. We are now on our way to the first of six sampling stations and we expect (as you may have read) to be there by Saturday morning between 5-6 hrs local time. Here, the first of our three  teams (shifts) will take action to collect the first samples. Until then, we use our time eating delicious food prepared by our amazing on-board chef, watching movies, or just enjoying the view.

The trip has been incredibly beautiful. Here, there is no one around other than us and some dolphins.


Until next time...

Twelve hours to station

Cruise kick off meeting

We're calculating to reach the first station at about 5:00 hrs tomorrow. Hopefully the weather will be as nice as now and the first samples will come with no trouble.
Few students were sea sick, as well as I was, but we all recovered now.

Del Golfo de México al Canal de Yucatán....

After a long wait ... the container finally arrived yesterday just before dawn and the crew was ready to move and secured all the equipment above the ship.

Now nothing more than to sail (finally) towards the Yucatan Channel ...

Venter og venter

We should have been sailing by now...

Still waiting...

a little delay on the start...
The container with the equipment is not yet here. We hope it'll arrive soon and then we'll be ready to leave but for now we have to endure horrible sunsets by the river ^.^

The night before....

We are all excited and getting ready to start the cruise.

Howeverm we need to wait for the container with the equipment and after it arrives in Tuxpan, we'll need to load everything on the vessel.