Drilling the seabed for climate secrets
Early in March 2009 scientists from an international project known as the Integrated Ocean Drilling Program (IODP) set sail from Honolulu on a mission aimed at drilling sediments from the sea-bed from a sites that once lay on the equator.
The expedition is part of the Pacific Equatorial Age Transect (PEAT) programme. Researchers will use the sediment samples to reconstruct the Pacific Ocean's climate history over the last 55 million years.
Map of the locations at which the JOIDES Resolution will drill - click on image to enlarge.
A better understanding of how the climate system has switched between warm and cold and back again through this time should in turn aid prediction of future climate change.
The mission will draw on the capabilities of the US drillship JOIDES Resolution (pictured), which will float unanchored and drill into the seabed kilometres below.
Doing so is an extraordinary feat of marine engineering - it has been compared to standing at the top of the Empire State Building and attempting to drill into the pavement at street level using a drill as thick as a piece of spaghetti.
Natural Environment Research Council-funded scientists are on the JOIDES Resolution, and they'll be providing updates on life on board and on scientific discoveries as they happen. Watch this space for updates.
We are finally back on land at the end of our expedition, after two months at sea. During that time, we collected sediment cores from beneath the ocean floor measuring over 3.5 km in total, from six separate sites that tracked the position of the Equator through around 40 million years of Earth history.
We have worked the cumulative equivalent of over 10 years of normal work hours to describe, measure, image and age date these sedimentary successions, but this is just the beginning of our task. The cores are like the pages of a book that, centimetre by centimetre, describe millions of years of Earth history, but so far our work on the ship has revealed only the timescale and broadest of plot lines.
The British contingent at the end of the expedition.
When we return to our home university laboratories, we will start to translate this book by disecting the cores and using fossils, chemical analyses, and tens of thousands of physical property measurements. This will eventually provide us with a detailed climate history through a period of Earth time when the planet switched from very warm climates to the cooler and polar-ice-dominated climate that we live in today.
The hints we have had on the ship of the story are extremely exciting and the cores that we recovered have met the drilling objectives we originally set out with. The most visually striking of these preliminary findings is the record of ocean de-acidification, which accompanied the rapid build up of ice on Antarctica around 34 million years ago.
Welcoming Honolulu harbour after 2 months at sea.
The ocean floor sediments are largely composed of the shells of dead plankton, and in particular silica from radiolarians and diatoms and calcite from coccolithophores and foraminifera. Decreased acidity of deep-ocean water resulted in a switch from dark brown silica-rich ooze to white carbonate-rich sediments at this time, reflecting major shifts in the global carbon cycle (including declining atmospheric carbon dioxide, and influenced by increased weathering and sea-level fall).
One of our hard-working drill bits.
Detailing the precise way in which the climate-ocean system operated through this profound climate shift, and the response of the oceanic ecosystem, will be just one of many projects which we plan to work on over the next few years. Actually, this expedition is far from over. IODP Expedition 321 has just left Honolulu with 26 different scientists, and they will drill a further three sites over the next six weeks that will complete the Pacific Equatorial Age Transect.
The joint science party will meet again in several months' time to finalise the preliminary publications, sample the cores and plan research collaborations. Around two years after that, a research meeting will be held and completed results presented. However, just now I think we all deserve some time to recover from what was a tiring, but exhilarating, inspiring and successful, scientific expedition that we will never forget! Aloha from Hawai'i!
Posted on 11 May 2009 | Comments (0)
I am currently a 4th year PhD student at the University of Leicester. My PhD research is investigating the variability (or heterogeneities) in the rock properties (petrophysics) of limestone oil and gas reservoirs, and in turn relating this to fluid flow and storage properties.
Sailing as a physical properties specialist on IODP Expedition 320 has provided me with a fantastic opportunity to investigate rock properties from a completely different geological setting, and also to be involved in the actual measurement and initial processing of this data - not to mention living on a ship in the middle of the Pacific for eight weeks.
Life on ship has become strangely normal: rarely walking in straight lines, greeting people with "good morning" throughout the day as different shifts begin, eating breakfast at midnight, the sound of "core on deck!"...
My job on the JOIDES Resolution is as a physical properties specialist - we drill a borehole into the ocean floor and then various measurements are made on the sediments (core) which we bring back up onto the ship. When the core arrives on deck we run it through a series of scanners that measure the following properties:
- Bulk density of the sediment: a function of the rock type/mineralogy, pore space and fluid content.
- Magnetic susceptibility: the presence and amount of magnetic grains.
- Sound wave velocity through the sediment: generally the more compact, rigid, and dense the sediment then the faster sound waves can pass through it.
- Resistivity: how well the rock, and any fluid present, can conduct electrical currents.
- Gamma radiation - the decay of naturally occurring radioactive particles within the sediment depends upon the lithology and mineralogy (typically the presence of mudstone with uranium, thorium and potassium particles).
Once the cores have been run through the various scanners we then measure the thermal conductivity, which can be used to investigate heat flow in the sediments, by comparing them with temperatures measured down in the borehole itself.
Peter Fitch making p-wave velocity measurements.
Next the core sections are cut in half: one half goes to the sedimentologists and palaeomagnetists for further measurements, detailed descriptions and archiving, and the other half is used for discrete sampling. Along with the geochemists and palaeontologists we take one sample per 1.5 metre section. Our sample is then weighed, dried for 24 hours at 105oC, re-weighed and then put into a pycnometer to measure the volume.
From these measurements we can calculate various rock properties such as the grain density (indicative of mineralogy) and porosity. Weighing a sample at sea is not an easy task, because with every rise and fall of the boat, the weight will change slightly (sometimes up to 30%!). To combat this we have similar equipment to that used in space research where these forces can be measured and compensated for.
Before the working half of the core is sealed away we measure discrete sound wave velocity, or compressional P-wave, in 3 directions (the x-, y-, and z- axes) by inserting sets of transducers and contact probes into the core. This allows us to investigate how properties change in different directions through the core (known as anisotropy).
Scanner equipment known as the 'Whole Round Multi-Sensor Logger' which measures non-contact resistivity, P-wave velocity, magnetic susceptibility, bulk density and natural gamma radiation.
Once all these measurements have been completed for each hole, we then check the data quality and filter where necessary. When a site is completed (normally three holes per site) we can then download the data and make graphs and plots (or wiggles!) of the various data types.
This is when we can compare our discrete measurements with the scanner measurements, allowing us to confirm and calibrate the different data types. The last task for each site is to write a site report detailing methods, data trends and any initial findings in relation to the other shipboard research groups.
So we are all kept fairly busy through our 12 hour shifts! It is really amazing how much data we have collected over the past seven weeks, and completing five reports in the same time... imagine if all research could occur at similar rates!
Core with moisture and density samples about to be taken.
On ship, our core measurements of physical properties are used to help calibrate the well logs measurements (devices run down the borehole itself), and are used by the stratigraphic correlators to check we are drilling and coring the correct depths, so that adjustments can be made in the second and third holes drilled at the site to ensure complete coverage (the overarching aim of the expedition is to recover a complete section through these Cenozoic sediments to allow for detailed investigations of climate change).
Our physical property measurements also provide information which can be integrated with the sedimentologists core descriptions to aid our understanding of changes in the sediment composition, porosity and also geochemistry. Most of the sediments that we are seeing on this expedition are carbonate-rich ooze, radiolarian-dominated ooze and clays.
These three lithologies have specific properties which we can be identified and used to track them down the borehole, across sharp and gradational boundaries. For example, the density measurements can be combined with geochemical analysis of calcium carbonate content to interpret the rates at which this sediment was deposited through time, which is dependant on a range of factors including the productivity of the oceanic micro-beasties and the amount of dissolution at the sea floor!
My PhD has used lots of well log and core data provided by my industrial sponsor, so to have been part of this team taking measurements and seeing the actual sediments these values come from has been a real eye opener, which I hope will feed directly into my current research.
As well as providing a great opportunity to investigate different sediment types with different physical properties, sailing on the JOIDES Resolution has provided a fascinating opportunity to discuss science findings with a very diverse group of geologists, palaeoceanographers and technicians, allowing me to explore where my current knowledge and understanding can fit into this massive and important research topic of climate change, which is quite different to my normal oil and gas exploration focus!
Posted on 5 May 2009 | Comments (0)
We have just arrived at the last coring Site for this Integrated Ocean Drilling Program Expedition ("PEAT-6C", from today also know as Site U1335), with three more planned as part of this science programme for our colleagues on the next Expedition. It is amazing how much we have already done, and even though it feels as if we have been on the ship forever, time seems to have passed incredibly quickly; a conflicting feeling shared by many here on the ship.
Having been involved in the planning of this project, I thought I'd share some of the amazement I feel when we try to find the best place in the ocean for coring, so we can answer specific questions about Earth history. When we then finally get to that specific spot in the huge Pacific Ocean my excitement of true exploration is huge: we get the first cores on deck, which tell us whether all our planning, predictions, and sometimes "educated guesses" are confirmed by reality.
Pacific sunset from the Joides Resolution.
We are trying to get sediments from special time periods of Earth's history, for example from the switch in the Earth's climate state from a "Greenhouse" world to the current "Icehouse" world, which is a more imaginative way of identifying when huge ice-sheets first grew near the poles of the planet.
The sediments we are coring work almost like a history book, where each layer of sediment corresponds to another page, written by Earth's oceans, climate, and living creatures. If one was to take each centimeter of sediment (Tom, Kirsty and Paul already described what one can find in these) as a page of this book, it would correspond to about 500 to 2000 years of time. Each page of sediment, sometimes with riddles and puzzles, can tell us about what happened in the ocean above, as well as the Earth as a whole.
We are trying to target these specific time periods of Earth's history for the last 53 million years, and for us to be successful and achieve our aims, we need to plan where exactly on the planet we need to take our temporary home, the JOIDES Resolution, to give us sediments of the right age.
This is where the title of this Blog comes into play. The oceanic plates, on top of which the sediments are deposited, are constantly on the move. For example, London and New York move apart by about the same length that fingernails grow: about a couple of centimeters per year. While this sounds small, it amounts to a fair distance over millions of years of Earth's history.
All of our drill sites were estimated to have been located at the Equator during the time when our main sediment targets were deposited. The Pacific plate, however, is moving through time, and you can see this directly from the trend of the Hawaiian island chain, spread out from southeast to northwest. The Pacific oceanic plate has been moving towards the north-west for the last 40 million years or so. The Hawaiian volcano has not moved very much, and is actually fed from underneath the oceanic crust, leaving a signature volcanic island on top of the plate, almost like a bunsen burner (you might know from chemistry lessons) leaving its mark.
Sediments lying on ocean crust basalt (basement). The right hand core has basalt and limestone, and those to the left are younger carbonate sediments. The microfossils in these sediments let us date the age of the ocean crust formation at this site.
Each site moves towards the north and away from the Equator by about 2.5 degrees latitude every 10 million years: that's almost 300 km, or a little bit less than the distance between Southampton and Leeds, each 10 million years. That's why our first drill site, PEAT-1C, is now actually at 12 degrees latitude, as it was first "born" on ocean crust of about 50 million years age. PEAT-6C, the site we have just arrived at, is a meagre 5 degrees north of the Equator, and is only about 26 million years old. All of our sites share the fact that they were on the Equator when they first formed!
The amazing thing is, then, that after all this planning, and detailed calculation, we arrive at a new coring site, and Paul and Kirsty and Tom analyse the microfossil shells in the sediments from each core, and can tell us their age ... and once we hit "basement", or the top of the hard basaltic rocks underneath a few hundred meters of sediment, we can see whether our predictions for the age and position of each site was correct or not.
For me, that is one of the most exciting, and also the most fascinating moments on the ship. We are using theories of plate tectonics that were only first formulated in 1912 by Alfred Wegener, and much refined even later by the British scientists Vince and Matthews in 1963, to decide where we need to take the ship to get the right sediments for our work. So far, it has worked each time for the previous four drill sites - we'll find out in a couple of day's time whether plate tectonics worked again!
Posted on 15 April 2009 | Comments (0)
After five days on site, today we finished drilling at Site 2 (PEAT-2) and are now on our way to Site 3, about 48 km south of our current position. The transit provides us with a brief respite from the organised chaos of coring.
We can now confirm our initial findings and write our science reports about the material that we recovered at Site 2. Like Paul and Tom, I am sailing on this expedition as a micropalaeontologist and am part of the team working to determine the age of the deep sea sediments that we are drilling as they are brought up onto the deck of the ship. More specifically, I specialise in planktic foraminifera which are microscopic marine plankton that produce calcite shells and live in the surface ocean.
Kirsty Edgar collecting the core catcher sediment sample from the catwalk and on the way back to the micropalaontology lab to start processing the sample.
To give you an idea of the everyday life of a micropaleontologist on board the JOIDES Resolution, our twelve-hour shift usually starts with a crossover meeting with our micropalaeontological counterparts whereby we are updated on what has happened during the previous shift and what is happening next.
When we are on site and in the process of drilling, ~9.5 metre long sediment cores are brought up to the deck from the seafloor about every hour or so. When the drill crew announce "core on deck" over the ship's speaker system, one of the micropalaeontologists on shift (there are three of us on the day shift and four on the night shift) will don a hard hat and safety glasses and dash out to the catwalk to get our first glimpse of the new core and collect our samples (see picture).
This can be very exciting as we are often the first scientists to see the core. The micropalaeontology samples are taken from the core-catcher, a 50 cm long stainless steel cylinder with teeth at the bottom (to stop the sediment inside the core liner falling out!), which is attached to the bottom of the 9.5 m core barrel.
Sediment being removed from the core catcher.
From this single sample we divide the material into three and each of the micropalaeontologists dealing with one of the three microfossil groups studied onboard, nannofossils, foraminifera and radiolarians, starts to process the sample using different preparatory techniques and then race to be the first to date the core and write it up in the lab for the rest of the science team to see. We then just hope that the rest of the ages estimated using the other microfossil groups agree (they usually do!).
At Site 3, as at the two previous sites, we will drill three separate, closely spaced holes to recover deep-sea sediments deposited between 46 and 35 million years ago (hopefully!). These sediments will enable us to detail the Earth's transition from a 'greenhouse' world characterised by high atmospheric carbon dioxide levels and only small or no ice sheets, to the onset of the 'icehouse' world and the development of the first large ice sheets on Antarctica.
Investigation of this climate transition is critical to enable us to answer questions that have relevance to many of the climate change issues facing us today. To keep track of our progress at Site 3 watch this space!
Posted on 3 April 2009 | Comments (0)
Tom Dunkley Jones
Tom Dunkley Jones
One of the effects of being on board ship - especially for those on the night shift, midnight to noon, who breakfast one day (11.45pm) and turn up to work the next (midnight) - is a lost sense of days, dates and weeks.
To get today's date I had to check a homemade calendar on the other side of the lab, with the days listed in rows from bottom (today) to top (our due date back in Honolulu, 5 May) - each day another date is torn off the bottom.
The JOIDES Resolution's drilling rig floor as a section of core is brought up to the surface.
It also has key expedition milestones: birthdays, Easter, Passover, phases of the moon, Lyrid's meteor shower and "hump" day (the half-way point, where its all down hill from then on). Like Paul, I'm one of the micropaleontologists who are examining microscopic fossils to determine the age of the sediment cores in "real time" as we drill them.
When we get back to the UK we'll be using the same fossils to understand the evolution, ecology and environment of these microscopic organisms that lived in the surface waters of the Pacific tens of millions of years ago.
Yesterday we finished the first of our three holes at this our second study site (PEAT 2C). As Paul mentioned we have five sites in total, at each of which we will drill three nearby holes (~20 m apart) to ensure we get a complete section through the sea floor sediments at each location. The five site locations stretch in a line extending east-southeast towards the equator from our first site (PEAT 1C), which was 1000 miles from Hawaii. This second site is ~80 miles, or 8 hours sailing time, from PEAT 1C.
For the micropalaeontologists and climate scientists on board it's been exciting to observe the regular variations between sediments that contain both calcareous and siliceous microfossils (made from calcium carbonate and silica respectively), and those that only contain siliceous microfossils. Paul and I study the remains of single-celled photosynthetic algae, the coccolithophores, which produce calcareous protective plates, or coccoliths, around their cells (see the Nannotax website, in the external links section to the right, for pictures of fossil coccoliths!)
The palaeontology lab in action - note Tom Dunkley Jones hard at work at the back.
Although some of the sediments we have drilled are almost entirely made of coccoliths, similar to the white chalk of southern England, in other intervals there are no coccoliths at all. This was not because coccolithphores weren't living in the surface ocean when these sediments were deposited, but because calcium carbonate becomes more under-saturated, and hence more likely to dissolve, in deeper waters.
One of the key parameters in the ocean-climate system is the depth in the ocean at which calcium carbonate becomes under-saturated and sinking particles of calcium carbonate, mostly the remains of surface living micro-organisms, start to dissolve; this is called the "Carbonate Compensation Depth" (CCD). This CCD is intimately related to climatic variables such as the concentration of atmospheric carbon dioxide and the input rate of dissolved minerals from rivers into the oceans.
The regular changes in sediment colour and microfossil assemblages that we see in our cores are largely controlled by major fluctuations in the depth of the CCD in the Pacific Ocean. By accurately recording the composition of the sediments we recover from the sea floor we hope to reconstruct a detailed history of both Pacific Ocean chemistry and the Earth's natural climate variability over millions of years.
Back to life on board ship - Hawaii and the Equatorial Pacific might suggest days of clear skies and baking sun; although its not been too rough yet, most days have an autumnal North Atlantic feel to them, with a persistent NE wind and churning swell. If the sun is out while we're not on shift we have to dash out and make the most of it. Even then reading outside is a battle with the wind.
One of the amazing capabilities of this ship is that it can hold itself absolutely still in these conditions - it rides up and down with the waves (the "heave" of the ship) but the twelve "thrusters" Paul mentioned before are constantly adjusting to avoid the slightest movement sideways, backward or forwards for days on end. The drilling operation is equally amazing as the drill rig automatically compensates for the heave of the ship, keeping the drilling pipe absolutely steady in the vertical whilst drilling with centimetre accuracy 5km below us.
It's a strange site seeing this pipe, which goes through a hole in the bottom of the ship (!), appear to bounce steadily up and down, when actually its stationary and we're the ones on the move. Well I had better sign off for the moment, it's been a quiet night shift so far but I need to get back to those fossils!
Posted on 26 March 2009 | Comments (0)
We have just completed the drilling at our first site (Site U1331). It's taken us a week and we've drilled three separate holes, just to make sure we have a complete record.
I've looked at tens of thousands of fossils from over 100 small samples of sea-floor 'mud' and used them to give ages to the 188 metres of sediment that we've cored. It looks like a really interesting section but there were some surprises along the way, as there almost always are when you go to places that have never been studied before.
Heiko Pälike and Kirsty Edgar examine a core sample.
It's been a long week! We are drilling these sea-floor sediments because they preserve a detailed record of long periods of Earth history - provided you know how to read them. How long-term? Well, the 188 metres of sediment at Site U1331 represent a period of time from 27 to 53 million years ago!
It's a particularly fascinating period of time, because the Earth's climate switched from very warm, with little or no ice in the polar region, to much colder, with major ice sheets over Antarctica. Why, when and how this happened are some of the questions we'd like to answer.
These sea floor sediments are good recorders of the Earth's history because out in the middle of the ocean they are made up mainly of small shells of marine plankton, which accumulate in this relatively undisturbed environment.
Co-chief scientist Heiko Pälike with a length of core.
Each layer of sediment represents a different interval of time, getting older and older, the deeper we drill. The ocean plankton usually live in the sunlit upper part of the oceans and they build their shells out of calcium carbonate (usually calcite) and silica. They are microscopic in size - less than a millimetre at most, but often much smaller and measured in thousandths of millimetres.
After death, these shells sink to the sea floor and pile up to produce sediments (there is a smaller, wind-blown dust contribution to these sediment as well). Think White Cliffs of Dover and you'll have some idea of the kind of sediments we are coring - but those sediments are mainly built from the fossil shells of Cretaceous plankton.
A length of core resting on the catwalk where it will be cut up into 1.5-metre sections.
Because these planktic creatures live close to the ocean surface they are influenced by climate, e.g. the temperature of the water and the strength of the winds. By looking at the types and number of plankton fossils we find we can reconstruct the environments in which they lived.
The chemistry of the shells of these creatures also varies with changes in environment, especially temperature and the amount of food available (nutrients), and so by adding all this information together we can reconstruct climate and ocean history for these long-past periods of time.
The plankton also evolved through time, with new species appearing and others becoming extinct, and so every period of time is characterised by a unique set of species, which allows us to provide the age dates that I mentioned earlier.
I am just one of seven palaeontologists working on these cores, and then there are many other types of sediment description and analyses happening, 24 hours a day, 7 days a week. It's amazing how much information we have produced in just this one week, and now we have to write our reports, and get ready for the next site, 8 hours' sailing away!
Posted on 21 March 2009 | Comments (0)
After five days of sailing through relatively calm seas and good weather we have finally arrived at the location of our first drill site (12 degrees North of the Equator). We've spent a lot of time working out how everything works on the new ship and had plenty of meetings to discuss what we're all planning to do while we're out here.
The JOIDES Resolution in dock at Honolulu.
We've also been moving to our new shifts that are either midday to midnight or midnight to midday, because the ship works 24 hours a day and all of the jobs need to be covered during that time. It's slightly disorientating and it takes a bit of getting used to, especially working out which meal times to aim for - with food served at 6 am, midday, 6 pm and 11pm!
This first drill site will be called PEAT 1C (the Pacific Equatorial Age Transect is the name of our expedition) and the seafloor is over five kilometres below the ship here.
You can imagine that's a lot of drill pipe to put together before we even reach the sea floor. The drill pipe comes in 9.5 m lengths and each piece is moved around, lifted and screwed to the next piece using powerful machinery.
While all this is happening the ship has to remain stationary above the drill site itself and does so by using 12 extra engines (called thrusters) which are lowered into the water through the hull - the precise position is maintained using satellite positioning equipment. It will take our crew around 24 hours to reach the sea floor with the drill pipe and then the coring can begin - 9.5 m at a time!
I think we're all itching to get our hands on a piece of the sea floor so we can start working! It will take about an hour to pull each piece of core back up through 5 km of pipe so we'll hopefully have enough time to look at our microfossils and provide an age date by the time the next core is up - we're planning on drilling through 188m of sediment at this site.
That's the theory anyway, we'll see how it works out in practise, and I'll update you in the next blog!
Posted on 15 March 2009 | Comments (0)
Integrated Ocean Drilling Program Expedition 320 set sail yesterday from Honolulu, Hawaii at 3 pm. Our objective is to drill five long sediment cores from the Pacific Ocean sea-floor, each around 200 metre in depth.
These will provide us with a continuous record of the climate, oceanography and marine life through the last 52 million years. These sediment cores will be recovered using the JOIDES Resolution drill ship, which is staffed by 30 scientists, 22 technicians and 68 crew and drillers. We will be onboard for two months and will return to Honolulu on May 5th (seems a long way off just now).
Most of the UK participants on the PEAT expedition.
The research party is a truly international team, and includes participants from 11 different countries. The six UK-based participants will contribute to this blog over the next two months, and they comprise Paul Bown (myself) and Tom Dunkley Jones from University College London, Heiko Pälike, Paul Wilson and Kirsty Edgar from the National Oceanography Centre, Southampton and Peter Fitch from the University of Leicester.
I will get them to introduce themselves along the way, and they will let you know what they're doing on board, but briefy, Tom, Kirsty and I will look at the microfossils from the sea floor in order to date the sediments, Paul will be describing the sediment cores, Peter will be measuring the physical properties of the sediments and Heiko is the 'co-chief' who leads the scientific operations.
In the team picture from left to right, starting with the back row, you can see Heiko, Peter, me, Tom and Kirsty; in the front row are Trevor Williams and Helen Evans, who are both logging staff scientists on the expedition from Lamont-Doherty Earth Observatory, USA.
It will take us several days to reach our first drill site (we'll probably arrive on Saturday 14th March) and you can follow our route on the JOIDES Resolution website. Although much of the science will be carried out once we're back in our universities, the coring of the sediments and initial description and results of what we find is a pretty exciting process, so hopefully you'll enjoy it!
There are several other ways to keep up with our activities and progress - see the links to the right for pictures and daily updates.
Posted on 10 March 2009 | Comments (0)