The bridge phone gave its peculiar chirp and Roger Goodison, the skipper, answered it. “OK, we’ll keep an eye out for it,” he said, and hung up. “That was the boys from the Netherlands. They’ve just given the release signal to the lander and it’s on its way up.” He gave a tight grin. We had just been discussing whether conditions would allow us to recover the instrument. The wind was howling at 30 knots and rising fast. Darkness had fallen an hour before, rain was sluicing almost horizontally and the sea was ugly. Our vessel, the 70 m research ship Tangaroa, was rearing and plunging through large swells. Trying to recover the lander, a delicate package of instruments weighing 750 kg and worth half a million dollars, was going to be far from easy.
For the past day-and-a-half the lander had been sitting on the seafloor 450 m below, accumulating information about that alien universe. Now its masters above had sent a signal commanding it to drop the heavy steel weight that held it on the bottom, and as a result it was heading towards the surface at 50 m per minute. It was coming whether we were ready or not.
Ten minutes later the bridge detected a radio signal indicating that the lander had broken the surface. After a few more minutes, Goodison thought he caught a glimmer from its distant strobe—a tiny fleck of light, its flashes briefer than the blink of an eye and visible only when the lander was on the crest of a wave.
Over the next 10 minutes the flashes became definite and more regular as we steamed slowly towards them. Somehow, Goodison had to get the lander close in against our starboard side without running over the top of it. At 100 m he fixed it in a spotlight beam and suddenly we were upon it.
Two hastily thrown grapples fell short, but one crewman landed his over the very end of the float line attached to the lander. The crew tried to haul it in, but the seas were too strong. As the rope between ship and lander pinged taut, the steel grappling hook straightened, let go and whistled back to smash into the side of the ship. Half a metre higher and it would have struck a crewman.
Now the lander was away, disappearing into the dark and foam two or three hundred metres astern. Goodison didn’t seem unduly perturbed, and I heard him mutter something about letting us drift down on it. This idea seemed to me about as feasible as using a bulldozer to catch a runaway horse. Yet somehow Tangaroa started to keep pace with the flashing light and then creep up on it. Ten minutes later the lander fetched up docilely against the hull of the ship directly below the crane that was to lift it out. Within minutes the crew had hoisted it from the water and secured it safely on the deck.
The landers—there were two of them—were the centrepieces of this expedition. Developed by the Netherlands Institute for Sea Research (NIOZ), they had been shipped here with a team of five scientists. Battery-powered and capable of performing an assortment of sophisticated tests and then storing the results, they can be lowered into any depth of water. They represent a revolution in biological oceanography. Hitherto, when scientists wanted to study the seafloor, they procured a bit and studied it in their labs—which can never mimic deep-sea conditions. On this trip there was still plenty of that traditional activity going on, but the landers offered a new approach: doing the tests on the actual seafloor and just bringing up the results. This trip was the first time they had been tested in the Pacific, and their performance was being carefully scrutinised by our shipload of biologists.
But why embark on such a project at all? What relevance does the distant ocean and its depths have to mankind and the problems we face? Keith Probert and Conrad Pilditch, from Otago and Waikato Universities respectively, enlightened me. They said that the deep ocean may well provide clues to understanding one of the most vexing of contemporary issues: enhanced global warming associated with greenhouse gas emissions.
The ocean covers 71 per cent of the surface of the Earth, and has an average depth of 3800 m, making deep-ocean seafloor the most abundant ecosystem on the planet. Carbon dioxide is the major greenhouse gas, and ocean phytoplankton is one of the great biological engines for converting carbon dioxide into the complex carbon molecules of life. But what happens to the phytoplankton and its vast load of carbon when it dies? Is it quickly recycled into zooplankton, fish and eventually humans? Or does it sink to the floor of the deep ocean, where it may take hundreds or even thousands of years to re-enter general circulation (since the floor of the deep ocean is such a stable repository)? Understanding the role of the deep ocean in the carbon balance of the planet may be crucial for accurate prediction of climate change over the next few decades.
Finding out how carbon (in the form of biomass) is produced and cycled through the ocean from top to bottom was central to this expedition. Twenty-five scientists and technicians were looking at a whole range of phenomena, from the growth of plankton in the upper layers of the ocean to oxygen consumption and the range of creatures inhabiting the seafloor.
The area being studied—between the South Island and the Chatham Islands—was in itself significant. Running from Canterbury out to the Chatham Islands and beyond is a high, broad, undersea ridge, the Chatham Rise. Ocean to the north and south of the ridge is about 3000 in deep, but over the crest of the ridge it is a mere 350 m, so the ridge can be thought of as a mountain range 2500 m high, in length equivalent to the distance from Taupo to Invercargill and as wide as the South Island.
Above the ridge lies an important ocean feature: the Subtropical Front, where cold water of subantarctic origin meets warm water from the subtropics.
This front girdles the entire southern hemisphere and is a zone of unusual richness, combining the abundant oxygen and nutrients of cool subantarctic water with the warmth of subtropical water. Around most of the globe the subtropical convergence occurs in very deep water, and its location tends to move with the seasons. The waters east of the South Island provide an opportunity to study this important ocean phenomenon at an unusually stable site and an accessible depth.
To make the study as comprehensive as possible, a series of nine stations were sampled from 3000 m-deep subtropical waters off Castlepoint in the Wairarapa to a similar depth far off the south-eastern corner of the South Island and well into the subantarctic water mass. The stations followed the line of longitude at 178° 30′ east—very close to the longitude of East Cape—running due south. No land was visible for the 15 days of the voyage.
Scott Nodder of the National Institute of Water and Atmospheric Research (NIWA) had organised this expedition. From conception to realisation, the process had taken four years. Yet so tight was the sailing schedule of Tangaroa that the previous research cruise arrived back in Wellington the very day our cruise was to depart.
Unloading the gear and samples from that trip and loading supplies and equipment for our own was a hectic rush. Three shipping containers holding small laboratories were lifted aboard by a dockside crane and welded in place—and that was probably the easiest part of the process. There are no lifts on Tangaroa, and lugging computer monitors and bulky items of delicate scientific equipment along narrow companionways and down steep stairs by hand has little to commend it. The gangplank—a narrow, rickety affair buttressed with safety nets—appeared to have sprung from the same stable as the wire-rope bridges that are favoured for use on back-country rivers. It was hauled aboard at 8 A.M. the next day, and we set out for our first and northernmost station, the rather grandly titled “northern biophysical mooring,” or NBM, 115 nautical miles off the Wairarapa coast, where the bottom was three kilometres down. We arrived at 11 o’clock that night.
I had imagined an impressive buoy would mark our destination, but daylight revealed the ocean to be just as empty here as elsewhere. The mooring consisted of a 680 kg weight on the seafloor and a cable that terminated in four scarlet floats some 40 m below the surface.
I asked Alex Morrice, the first mate, how we went about finding it. “Ah, well, we send out a signal and get a response indicating how far away we are, but no direction,” he replied in a broad Scots brogue, well laced with contemporary (and expurgated) expletives. “We move around, and when the distance is 3100 m, we are right above it. Then we send a signal that causes the cable to release the weight.”
It took a while for the floats to pop to the surface, about three-quarters of a kilometre away, and we cruised over and started to winch the cable aboard. At intervals were floats and instruments for measuring temperature and current direction and speed. Near the bottom was a large plastic cone that intercepted falling material and directed it into collecting jars.
Black plastic covered the galvanized steel core of the cable to reduce corrosion. Bill Main, who supervised the hauling-aboard, ran his hands along the smooth coating and pointed out damage to the sheath. “Those are shark bites. The cable vibrates in the water, and sharks are attracted and attack it.”
Before we left the site a new weight would be attached and the whole array returned to the arms of Neptune for another four months.
At this station, the expedition’s research programme got under way very smartly. No sooner had we arrived than attempts to secure core samples from the bottom were launched. The multicorer device uses weight to stab 10 cm-diameter clear plastic cylinders into the seafloor. Lids then snap into place, securing the mud. The multicorer, which weighs half a tonne, is then winched back to the surface, where the mud, or more precisely the creatures it contains, becomes the raw material for a whole cottage industry of analyses and experiments. If all goes well, eight cores are obtained per drop, and, to satisfy various demands, about five drops are needed from each station.
“You have to love dirt, cold, wet and tedium to be a benthic biologist,” Kerstin Kroeger, a mud-splattered siever with blue-chilled fingers from Victoria University, told me. Benthic biologists study organisms that live on the seafloor, and Krbeger is investigating the bed of Wellington Harbour for her PhD. But at the moment she was free from that millstone and able to enjoy the dubious delight of sieving mud from the deep.
It was a particularly fine and glutinous sediment, so I asked why she didn’t use a more forceful jet than the pathetic drizzle she was employing to coax the ooze through the sieve. “You have to be very gentle or else you run the risk of breaking up the delicate sand tubes and small worms that live in the mud,” she said. “They can be very fragile. Once they are in bits, they are almost impossible to identify.”
The excruciatingly fine sieve she was using didn’t expedite matters, either. Keith Probert, manning another sieve, explained that they were interested in both the macrofauna animals more than 500 microns (0.5 mm) in length—and the meiofauna, creatures from 500 microns down to 64 microns. The finest sieve they were using here was 500 microns. Very, very gently all mud was rinsed away and whatever was retained in the sieve was carefully washed into jars, to be sorted and identified later under a microscope.
To examine the meiofauna, scientists take large syringefuls of mud from the top 5 cm of a core, where life is concentrated, and add a fixative to kill and preserve the animals. Back on shore, the mud is put through a 64-micron sieve, and a special high-density liquid is used to float off the organisms. They are then examined under microscopes and a calculation of their total biomass is made. “Out here in deep water, where the macrofauna is sparse, the meiofauna can weigh as much as the macrofauna,” Probert told me.
And what were the main organisms they were finding?
“In the macrofauna, polychaete worms [marine relatives of earthworms, bearing prominent bristles] are dominant, followed by small crustaceans such as isopods and amphipods. In the meiofauna, free-living nematodes [roundworms in the same phylum as those that infect farm animals] usually make up 80 per cent of the individuals, followed by very small crustaceans such as copepods. But there are a few really weird things that have their own phyla and never occur in sizes larger than the meiofaunal range.”
Sieving multicore samples was such a chore that at times half the scientific staff on the cruise were assigned to one of two 12-hour shifts to handle the task, and the trickle of muddy water that flowed along the deck from the operation became a greasy stream.
But sieving was only one of the possible fates awaiting bottom samples snared by the multicorer. Conrad Pilditch took some, incubating them at whatever the bottom temperature was, and then measuring how much oxygen the organisms within consumed over the next 24-36 hours.
Julie Hall added radioactively labelled thymidine—a constituent of DNA—to small cultures of the mud so that dividing bacteria, an important component of the biomass, would take up the label and could be quantified. Since other bacteria might be quiescent, she also added a dye that colours all live organisms.
Nodder and Rob Witbaard took cores to X-ray ashore for animal burrows, and also to perform analyses for carbon and breakdown products of chlorophyll, to gain an indication of how much phytoplankton might be raining down upon the seafloor.
Another instrument central to oceanography that was quickly pressed into service at the northern biophysical mooring that first night was the CTD (standing for conductivity, temperature, depth). Shortly after four in the morning it was hoisted over the side and lowered almost to the bottom at 60 m a minute before being reeled back in. This ritual was performed every day, often at an even less congenial hour. Darkness was important, I was told, because the diatoms coming up from the shallower depths (where light is in reasonable supply) might otherwise burst into some uncharacteristic activity that could undermine the veracity of growth experiments aboard Tangaroa.
Dick Singleton, an oceanographer since 1962 and affectionately described as “the oldest man in the world” by the predominantly youthful biologists on board, was the CTD guru. He rose every morning at 3 o’clock to watch over its early foray to the bottom of the sea. The CTD, unlike the multicorer, was connected to the ship by a cable that was smart as well as strong. Messages flowed up and down the cable between Singleton’s computer and the suite of instruments in the CTD unit. Many times a second, these instruments sent up readings of pressure (an indicator of depth), water temperature, oxygen level, salinity, light levels and chlorophyll concentration in the water.
“Chlorophyll concentration is a measure of the numbers of phytoplankton in the water,” Singleton explained, “and we use the ratio between salinity and temperature as a kind of fingerprint to help characterise different water masses.”
On his computer was a complex graph showing how all these measurements varied with depth. Chlorophyll was abundant in a thin layer close to the surface, but diminished sharply with increasing depth so that there was no signal at all below 300 m (the limit of light penetration). Temperature was about 12°C at the surface but fell, by no means evenly, to a mere 1.3°C at the bottom. Light levels diminished quickly with increasing depth, but salinity seemed to follow no steady course.
CTD data were the backbone of the expedition in the sense that explanations for biological observations were often sought in the physical measurements. The CTD apparatus carried a cargo of long cylindrical bottles, and Singleton could trigger these from his computer to seal off at any desired depth. See an anomalously deep layer of phytoplankton? Take a water sample. Spot an abrupt temperature change? Fire off another bottle. Some mornings, if the demand for deep-sea water was high, the CTD made several trips.
Where did all this water go? Marieke van Kooten was a heavy user. She passed her days filtering large volumes to trap plankton and other particulate matter on very fine filters, to be analysed later in NIWA’s Hamilton lab for chlorophyll and nutrients.
Stu Pickmere assayed small samples of the filtered water on an elaborate auto-analyser for plant nutrients: ammonia, nitrate, phosphate and silicate. Julia Hall and Andrea Cumming used another very sophisticated analyser to determine numbers of different types of phytoplankton and bacteria at various water depths, and also measured bacterial growth. Then Karl Safi and Liza deLizo attempted to work out how rapidly phytoplankton in surface waters were growing and being eaten by microscopic animals. They cultured their samples in large baths darkened by filters and shade cloth on deck. Isotopes were again used to label growing cells in these experiments. And all this was only a fraction of what was going on scientifically.
Living at sea was the other side of the voyage. Out here, the horizon was identical and flat in every direction. The “ground” beneath constantly tilted, and books loosely packed on the library shelves shushed gently from side to side. Stairs sometimes became much steeper or almost disappeared in mid flight. Every item of equipment was tied down, and even laptop computers were Velcroed to the tables.
Food was excellent, plentiful and so punctually ready that it served as the daily clock. No TV reached us, and only occasionally did news filter through from the radio on the bridge—and then it seemed strangely irrelevant.
Apart from two windblown sparrows, the birds we encountered were albatross, mollymawks, petrels, shearwaters and Cape pigeons. After cruising all night, I found each new destination indistinguishable from the last. Only the depth sounder and the GPS indicated we had moved. One night we saw the lights of a single trawler—the only concrete sign of a human realm beyond the steel hull of our ship.
The world of the ship assumed a curious timelessness, and all that had been before or was to come took on a measure of unreality. That the only part of the world with which we were concerned was an invisible piece of terra firma kilometres below and the fluid ephemera between there and us contributed to the unreality.
Although our days followed a largely unchanging routine, each brought its own surprises and frustrations. Deploying a heavy dredge with a video camera at its mouth proved problematic. The dredge had been designed for a ship with an entirely different set-up of winches and pulleys from that on Tangaroa. The crew managed to concoct a way of getting it over the side, and on the second evening 3.85 km of Tangaroa’s heaviest wire was run out, dredge attached, with great anticipation. I flopped into my bunk about 11 P.M., rising blearily an hourand-a-half later to catch the dredge’s arrival back on deck. To my annoyance, it was already there and showed every sign of having been for a while. One of the Dutch team told me it had failed to reach the bottom—the wire was too short.
An elaborate sled bearing eight 6 m-long plankton nets was successfully launched the following day. A motor on the sled opens and closes each of the nets on command from the ship via a smart cable, and the sled can also let the operator know its depth and how much water has passed through each net.
I went below to have a look at the array of jars of plankton Lisa Northcote and Bridget Alexander were processing. Northcote explained that the nets had a 200-micron mesh and that the samples were all zooplankton. Phytoplankton, which are usually smaller, pass through the mesh. The water in all the jars had a reddish tinge, and while there were a few 4 cm fish, the bulk of the material was small shrimps and crustaceans a few millimetres long. One sample had been collected with a net open all the way from the surface down to 800 m, and it contained perhaps 600 ml of thick zooplankton soup. But once you appreciated that was all the zooplankton from 1600 cubic metres of water, you realised it wasn’t that much. The greatest concentration was at 500 to 600 m depth.
Zooplankton are known to swim up and down, depending on the time of day, so a second trawl was carried out that night. It produced twice as much as the daylight haul and included a few deep-red 3 cm-long shrimps.
Sam McClatchie, an American, and Nick Cockroft, an Australian who has spent 10 years on submarines, determined zooplankton and fish abundance in a completely different way. “If you send out sound waves underwater, when they hit something solid they are reflected back and you can learn something about the objects and their distance from the pattern of the returning echoes,” McClatchie explained. “A fish with a swim bladder gives an especially strong echo, but you can also detect fish without swim bladders and aggregations of plankton. This acoustic approach has been used for a number of years in measuring the abundance of deep-water fish, most species of which congregate in breeding masses at certain times of the year, but the technique can be adapted to look at the distribution of smaller organisms.”
Most nights on the voyage, McClatchie and Cockroft did an acoustic run for three or four hours, starting somewhere between 10 P.M. and 1 A.M. Tangaroa carries a sophisticated array of fish-finding and echo-sounding gear (she is used part time for fisheries research), and the pair obtained useful information from that source, but they also put out an instrument frame with their own echo-sounder and video camera, towing it at depths of 25 to 400 m behind the ship.
The three frequencies they use most are 12 kHz, 38 kHz and 70 kHz, which can be used to distinguish different target organisms. Small mesopelagic fish (those that live in the upper 1000 m of the ocean, migrating up to 500 m vertically each day) possess swim bladders despite being only 5 cm long, and show up very clearly with 12 kHz sound. These fish are an important component of what is known as the deep scattering layer. Krill, only 1 cm long in these more northern waters (they grow much larger in the Southern Ocean), lack swim bladders but are detectable at 38 kHz if sufficiently dense. Higher-frequency signals are better at detecting small objects, but don’t penetrate as well as lower frequencies.
On their computer monitor, a strong band of organisms was visible at about 50 m and another at about 500 m. “Two of the things we are particularly interested in are regional differences in the deep scattering layer and determining target strengths—the size of the echo from individual fish and krill,” McClatchie told me.
Dick Singleton explained that years ago, when underwater physics and acoustics were in their infancy, there used to be a lot of talk about that deep scattering layer. It was thought to be of biological origin, but nobody was sure what caused the effect. They tried dragging nets through it, but they came up empty. Then someone had a good Kiwi idea: try blowing it up and see what floated to the surface.
“We had these primitive triggering devices that you could drop down a line to cause a net to open or close, so someone suggested that we could just lower a hand grenade on a string to the deep scattering layer, drop a trigger that would release the pin and whacko! I’ve never been more frightened in my life than seeing a line pulled in with a live grenade on the end, and noticing that the pin was gone as it came over the side. None of them ever went off, fortunately. Water must have got into the primers or somewhere pretty quickly.”
Given the large “Safety First” slogan emblazoned across the A frame on the back of Tangaroa, NIWA is unlikely to reactivate this indigenous approach to biological sampling.
Our next station was at a depth of 2300 m, far to the east of Kaikoura. From the chart, it looked as if you could squeeze two South Islands widthwise between us and the coast. The sea was calm and there was no wind when we awoke. Albatrosses were sitting on the water like ducks. Flying without wind is difficult for these heavy gliders.
The colour of the ocean was mesmerising. Viewed obliquely, it was a reflected blue-grey from the sky, but stare straight down from the superstructure and it was entirely different, more a light black (if such a shade be possible) with tints of maroon and grey. Yet with bubbles through it, such as where waves sloshed in the stern ramp of the ship, it was a rich turquoise.
CTDs, multicores, acoustics, a lander launching—much of the sampling we had initiated at the previous site was repeated here, but there was one notable addition. The big dredge finally made it all the way to the (shallower) bottom and, three hours after being launched, was hauled up the stern ramp trailing a slight smear of mud. However, to the disappointment of the horde of onlookers, the vast bag was almost empty, containing only a single bucketful of debris you wouldn’t have wasted a second glance on had you not known its origin.
The multicore had already discovered that the bottom was soft mud. Could this meagre haul have been the only residue after a mass of mud was sluiced away on the journey up? It contained a dozen fish, ranging in length from 10 to 30 cm, all dark and eel-like in appearance with large gaping mouths. There were a dozen heart urchins, most of them damaged, and dark fragments of long-dead heart urchin tests (shells) dominated the material.
Fragile pink brittle stars were the commonest species, and there were a few starfish and sea cucumbers, all being types of echinoderm (as are heart urchins). A few plump sipunculid worms, several annelid worms, a couple of salps, small anemones, one leathery white sponge, the odd fragment of dead coral, two or three shrimps and hermit crabs, two handfuls of what looked like stiff maroon-dyed hair and three or four flat dirty white objects closely resembling potato peelings completed the catch.
At the next station, now stepping up the northern side of the rise to only 1000 m, the dredge brought in a slightly larger haul. Fifty small fish, including a young orange roughy, made up the vertebrates, but there was a greater range of invertebrates. Echinoderms were still dominant, but less so. There was a bucketful of sea cucumbers, large as salamis, some blunt-spined sea urchins, a smattering of starfish, and another type of large heart urchin. In addition there were 20 species of mollusc, a curious coral, some hermit crabs, a very long-legged sea spider and a few more salps. And there was a bonus. A little baited cage trap Marc Lavaleye had set up on the lander at this station produced some relatives of the common intertidal sandhopper—except these were 4 cm long and brilliant red.
Next morning I quizzed Lavaleye, a member of the Dutch team who does two or three of these trips a year, about the types of deep-sea organisms he sees. Were they all similar? “Yes, pretty much,” he said. “Rattails [a type of fish] are in the deep Atlantic and they are here. Those big red amphipods are everywhere in deep water, except in the Arctic and Antarctic, where they come right up into 30 m of water.
“Videos changed my idea of the deep sea, and you need to see the ones from the lander and the dredge. Once we got a whole load of crinoids [feather stars] in the dredge, but there were none on the video except for the last few metres around a break in the seafloor. One year, south of Ireland in 4 km of water, I saw a dark green layer 5 or 6 mm thick and lots of great big sea cucumbers grazing on it. Next year there was no green stuff and no sea cucumbers. We don’t know how animals sense such temporary movable feasts or how they get there. Sea cucumbers are usually fat and heavy with sand as they eat their way through it, extracting goodness from the detritus. But I think if they emptied their guts they would be much lighter and perhaps waft around on undersea currents.”
Taking his advice, I watched one of the videos shot from a lander at 1000 m, showing fish attacking a baitfish which had been wired on to a stalk at the base of the lander. Smallish black sharks with white eyes had a pretty good go at the bait first. They were followed by a variety of eel-like fish with wide jaws like those we had seen in the dredge. Some were black, others silver or bronze. When the sharks reappeared they became a bit more circumspect, but they persisted even when only the head of the bait remained.
Also interesting was the current. Every fragment of fish drifted smartly away, and the sand the fish stirred up was also borne off. The video changed my thinking of the deep seafloor, too. It was far from still and sluggish.
At our shallowest station-350 m, the crest of the Chatham Rise—the dredge haul was different, but still meagre in quantity. Echinoderms were pushed out of their position as top dogs, to be replaced by crustaceans. Large colourful (and edible) scampi, numerous smaller shrimps and long-limbed deep-sea crabs were common. For the first time there were a few burrowing bivalves, and brachiopods and fish were also more plentiful. There were several flatfish and stargazer types—fish that are flat dorso-ventrally, rather than laterally as at the deeper stations. To the delight of Steve O’Shea, our invertebrate taxonomist with a special passion for octopus and squid, there were a couple of small dead octopus also.
You could tell that there was something in the net at our next station when the dredge came up from 450 m on the south side of the rise. Unlike on all previous hauls, this time the back of the net hung down so you couldn’t see what was in there. But we found out soon enough: mud and rocks for the most part. There were a couple of 100 kg boulders, a binful or two of more manageable stones and lots of marble-sized pebbles. Everything was covered in mud. It took half a day for four people to wash out the mud and retrieve the animals.
But it wasn’t just the animals that were of interest. While most of the rocks and pebbles were black, there were also granite boulders, densely banded red sedimentary rocks and some chalky limestone, deeply gouged by boring bivalves.
“The black rock is phosphorite, very rich in phosphate as its name suggests. Millions of tons of it lie out here on the Chatham Rise and there has been interest in mining it,” Keith Probert told me. Scott Nodder thought the rest of the miscellany was from Antarctica: “When temperatures were cooler, 20,000 years ago, glaciers carved out rocks, became icebergs, and floated north. Eventually the icebergs melted and the rocks fell to the seafloor.” Not many icebergs make it this far north now, but they were seen as recently as 1950.
The animals in this haul included about 20 species of mollusc, most of them carnivorous gastropods. The flat shrimp Munida was common, but there were few crabs and no scampi. Quill worms, a type of polychaete which lives in a 10 cm-long tube indistinguishable from the quill of a large feather, were the most abundant organisms. Among the five or six species of sea urchin was one with bright orange spines and test, another that was large and white, and a third, smaller variety which sheltered its young under toadstool-like structures, probably modified spines, on the outside of its test.
At this site there were unexpected problems with the multicorer. On the previous day, several sets of cores had been collected from the bottom without difficulty. But at 2 A.M. the corer came up with only water, and so it continued for another four attempts. Was a harder bottom to blame? It was impossible to know. But now we were hours behind in our sampling programme, so we headed south to 750 m, our next station.
Things went no better with the multicores, but the dredge had better luck. None of the rocks of yesterday, none of the mud, hardly a single stone. Dominating the catch was a handsome species of large sea urchin, similar in size and overall appearance to the common intertidal species, but with a pinkish-white test and spines. Many gastropods were present, most common a large carnivorous triton, but there was a smattering of seldom-seen deep-water volutes as well, many still alive.
The contents of the dredge hauls were of widespread interest to those aboard Tangaroa. Although you could argue that phytoplankton were much more important than anything the dredge brought up, they are invisible without a microscope. In the dredge were oddities which could be poked and handled; slimy and spiky creatures plucked straight from the world of darkness far beneath our feet.
The dredge haul at 1200 m depth south of the Chatham Rise looked extraordinarily boring. Ninety-nine of every 100 animals was a large orange ophiuroid—a thin-armed type of seastar—but most of them had lost their arms. There were a few other starfish, a couple of collapsed bag urchins, a skate, a few other fish, a handful of gastropods, several very leggy sea spiders and that was it. About 10 barrow-loads of it.
Would ophiuroids feature in next day’s seafood chowder, I wondered?
It was time to head south to our last station, the southern biophysical mooring (SBM), in 2700 m of water not far from the Bounty Islands. Down here, the mixture of sand and mud that came up in the multicores operating again, but on a reduced number of tubes-was a whitish grey, like finely ground pumice, and slightly gritty to tile touch. Our earlier muds had all been finer, softer, oozier.
Once the water hoses had done their work, in the bottom of the sieves lay hundreds of minute white shells. Most were wheel-shaped but some looked like traffic cones. “They are the shells of foraminifera, a type of protozoan,” Lisa Northcote explained. “We think tile whole sediment here is almost pure foram shells and coccoliths. Coccoliths are far smaller again than forams. They are calcareous plates made within the cells of certain phytoplankton, and then secreted and fixed around the outside of the organism like an array of shields. You need an electron microscope to examine them. Some forams live on the sea bottom, others in the plankton. The difficulty we have is that it’s very hard to tell whether they are dead or alive, so we don’t know whether to consider them part of the biomass or not.”
At 8 P.M. the last dredgeload came up. Four-centimetre khaki-coloured sea urchins were the commonest organisms, but rocks in the dredge bag had crushed most of them. Even the few that were mostly intact had lost all their coarse purplish spines. Besides the usual few fish were a couple of 20 cm-long sea cucumbers, a number of semitransparent scallops which looked like fish scales and a dozen chunky white anemones. Each must have weighed at least half a kilogram, and they were contracted into hard blocks of flesh, looking for all the world like glistening West Coast quartz beach stones.
Our last activities at the SBM site were to redeploy the mooring, with its associated instruments, and drop off a lander which would remain gathering data on the seafloor for a year or more.
On the way back to port I watched more of the videos taken by the underwater cameras belonging to the Dutch team. One was taken from the front of the dredge at 2700 m. Although a smallish sea urchin had been the most common animal in the dredge bag, the video showed that these were sparsely distributed, with specimens 5 or 10 m apart. Most of the bottom was bare grey sand with few organisms present, although many animal tracks were visible.
Next was a video shot from a lander as it sat at 2700 m for 24 hours. A skate-like fish swam very sedately through the field, and a few of the usual rattails also appeared, but none took much interest in the bait. Then a half-metre-long snake-like creature rose from the sand and glided slowly away. It was a sea cucumber, a realisation of Marc Lavaleye’s suggestion that these creatures could swim. Lavaleye was excited, for this behaviour had never been seen before.
Less dramatic, but surprising to me, was the amount of particulate matter swirling through the water and how rapidly it was moving. Lavaleye told me that the currents were associated with tide movements—still strong even that far from the coast and that deep.
We steamed north for 30 hours, clawing our way back up the side of the globe to the NBM, and there we dropped the other lander for its year-long vigil on the seabed.
Science entails a lot of tedious piecing together of evidence, so I waited a few weeks after our return before asking Scott Nodder and Julie Hall, the cruise leaders, about preliminary results from the trip. “The most exciting finding was evidence that a fresh plankton bloom had sunk to the seafloor in 750 m of water south of the rise. It was still full of chlorophyll, so it was pretty recent. Water analyses showed nutrients in the area were depleted—most likely consumed by growing plankton. And we have been able to go back through satellite photos and find evidence of a plankton bloom in the surface waters a couple of weeks before we arrived.
“Analysis of records from the instruments retrieved at the SBM showed that last December there was an even higher chlorophyll content in the water than was seen from either the ship or satellite.
“Instrument packages left in place for a long time—the moorings and the landers—clearly have a lot of potential for collecting information about infrequent but important events. We’ve got plans to put carbon dioxide sensors on the southern biophysical mooring. We are finding much more carbon dioxide in the sea than we would expect—probably driven by phytoplankton growth. Regarding the carbon dioxide/global warming issue, we think that the ocean is a sink for carbon dioxide, especially if a lot of the surface phytoplankton blooms end up on the bottom as we have seen this trip.
“The Subtropical Front seems to be just on the south side of the rise and it is biologically the richest area, but the water is shallower, too, and shallower waters are typically more productive. It will be very interesting to see how the lander’s oxygen, metabolism and chlorophyll measurements pan out over the next year.”
I wondered if Nodder and Hall would they be going back to help retrieve these, but then I realised I already knew the answer to that question. Wild horses wouldn’t keep them away!