Monday.

I join the Royal Research Ship Discovery in the port of Vigo, Spain. Meet the old and a few new faces in the ship's crew and the other scientists sailing with me. It is a multicultural experience. The research we are about to attempt is funded by the European Union and in total involves 17 partner institutions from nine countries.

Tuesday

We all pitch in to complete the loading of enough scientific stuff to keep us busy for our month-long expedition. Ceri, the chief officer, takes us through the ship's safety equipment. Tony, the principal scientist, takes us through our planned programme of work. It is also a time to get to know your shipmates before the battle against limited science time begins. The captain, who has relaxed but ultimate authority; the bridge officers, who can make Discovery pirouette or stand glued to a satellite-fixed spot; the chief engineer and his merry gang who make it all run; the catering crew, who provide hotel-style service; and the deck crew who get our awkward and expensive equipment into and out of the ocean under the all-seeing eye of the bosun. Dear Michael - Dainty Doris to his very close friends - is a bosun in the traditional pirate mould who has developed a language all of his own. If he tells you that your "doobrey" is loose, this may mean your irreplaceable scientific equipment is rolling around the deck - or that your flies are undone.

Wednesday

Discovery sets sail for the 500-mile steam to our oceanic work site. The trip out takes a little under two days.

Thursday

We are there. Our various doobries have been checked and secured, so it is time for the relentless onslaught of round-the-clock, seven-days-a-week science to begin. Our primary aim is a better understanding of how outputs from the ocean's surface are translated and written into the geological record contained in the muddy sediment that carpets the ocean floor three miles below us. Climate variations generate signals in the biology of the upper ocean which are transmitted as sinking particles. The signal gets weaker (is eaten) as it makes the long drop. Once on the sea floor the signal is further modified (eaten) by the animals (NB no light, no plants).

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Friday

The first order of the day is to recover instruments we left moored here six months ago. We begin to broadcast chirping sounds into what seems to be a very big ocean. These coded chirps wake up sleeping receiver units on the sea floor and command them to let go of their ballast weights. Two hours of pacing the decks later, our moorings bob to the surface. First back aboard is a sediment trap, a big funnel that collects sinking particles in a series of little pots that are motored round under the funnel every week or two during the six-month deployment. Next back is a time-lapse camera that has been photographing a small patch of sea floor ten times a day since we were last here, monitoring the arrival and departure of sinking particles and the daily lives of deep-sea animals. Our first deployment is to be a "benthic lander". By analogy to "lunar lander", this is a free-fall vehicle that lands on the sea floor and carries out a range of programmed experiments before being recalled in the same fashion as our moorings. This lander is designed to enclose a small portion of the sea floor and carefully measure exchanges of chemicals between the sediment and overlying water, such as the take-up of oxygen by animals living in the mud. Benthic lander work proves to be much more satisfying than Mars lander work - we have no trouble detecing alien life-forms.

Saturday

The science programme continues: sometimes high-tech landers, sometimes relatively simple equipment that would be familiar to the pioneering deep-sea scientists who first plumbed these depths 125 years ago. We use trawls to collect fish and the larger invertebrates of the sea floor; a fairly straightforward procedure but you do need seven miles of wire to do it. Just winding all that wire out and back means it can be well over half a day before you see any results. Out here, sea cucumbers of all shapes, sizes, and colours dominate the catch, but we also bring up sponges, corals, anemones, worms various, shrimps, crabs, lobsters, giant sea spiders, starfish and squirts. Invariably we also dredge up human artefacts, occasionally some nice old glass bottle, and always clinker, the residue of burnt coal tipped overboard from steam ships - to some of the animals of the deep-sea floor a welcome home in the vast expanse of mud.

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Sunday

On and on we go, more moorings, more lander deployments, more trawling; we use various corers that collect different sized chunks of seafloor, we photograph particles as they sink through the water column and we photograph animals as they go about their business on the sea floor. Then it is all over, our month is almost up and the ship sets course for Spain. Waiting in Vigo is another party of scientists, ready to join Discovery and tackle another set of oceanographic problems. We'll be back out there again in July, trying to follow life's annual cycle on the deep-sea floor.

Brian Bett

Deep-sea biologist at the Southampton Oceanography Centre.