We are still steaming at low speed to spare the machines. We are not sampling anymore but the work continues, particularly for Martine who is in charge of the chemistry and the analysis of phytoplankton.

One of the experiences conducted onboard consists in estimating the primary production, that is the quantity of matter (carbon in this case) that is absorbed by the phytoplankton. Phytoplankton is made of micro-algae which are at the base of the food web and which are consumed by herbivores and omnivores of the zooplankton. Knowing the quantity of carbon absorbed by the micro-algae is important to determine if the area is rich and if an important food web could develop where large quantities of fish could be found. Moreover, areas where a lot of carbon is absorbed by the phytoplankton contribute to decrease the quantity of carbon in the atmosphere and mitigate climate change.

We measure the absorption of carbon during 24 hours by the micro-algae of the phytoplankton. We collect surface water that contains micro-algae and transfer it into 2 litre bottles. We inject labelled carbon and labelled gaseous nitrogen, using a syringe. The bottles are then placed into an aquarium covered with a blue screen that simulates the light present at 5 m depth. After 24 hours in the incubator the water is filtered, this stops the growth of the phytoplankton. Filters will then be analysed in the lab to measure the quantity of labelled carbon absorbed by the micro-algae. By measuring the labelled nitrogen absorbed, we will know the growth of a very specific type of micro-algae, the diazotrophs, which are unique because they can absorb the nitrogen from the air dissolved in the water. This type of nitrogen is always abundant while all the other micro-algae require nitrogen incorporated in molecules of ammonium or nitrates which can be in low concentration in the water and then limit the growth of the micro-algae.

Elodie injects labeled carbon and gazeous nitrogen in surface water samples containing phytoplankton to measure its growth, or primary production.

At the front Martine shakes the bottles injected before putting them in the incubator

The incubator where bottles are stored for primary production measurement

After the third sampling station conducted yesterday afternoon in the middle of an anticyclonic eddy, we steamed all night to arrive at station 4 in the same eddy, this morning at 6am. We are lucky because the weather is perfect, no swell no wind. The visibility in the water is exceptional and we can see many gelatinous organisms including some jellyfish. However this good news is impaired by a pessimistic report from the mechanics. Indeed there is an important problem that could require to end the cruise prematurely. While they continue investigating the problem and communicate with the base, we start our experiments with the hope that they will be able to solve the problem.

A splendid weather this morning

Hauling the net

We start with 2 CTD casts to determine vertical profiles of temperature and to collect water, then a first trawl at 520m depth which contains a few hatchetfish and jellyfish.

Jellyfish

However while we haul the net, the conclusion of the investigation by the mechanics arrive, we have to end the cruise and come back to Noumea to proceed with repairs that will require to take the boat out of the water. Everybody is really sorry but there is no alternative. We are steaming towards Noumea at low speed and it will take us about 2 days to come back. We hope we will be able to organise a new Nectalis cruise soon to complete the work.

As planned we arrived around midnight at the second station and we started with two micronekton trawls in the surface water as most of the organisms that are deep during the day migrate towards the surface during the night. The first net was trawled at 100m depth and caught a lot of Myctophidae (lantern fish) and less gelatinous organisms than during daytime trawls. The second net was trawled at 25m and we caught less organisms but with surprising creatures, particularly 2 magnificent Argonauts of 6cm each. Argonauts are cephalopods in the same family as octopus and they live in the water column. Females produce a thin translucent shell where they lay their eggs. The 2 specimens we caught were alive and we kept them in a small aquarium for a photo shoot before releasing them in the sea. We also observed a few fish we rarely see such as a small scorpionfish.

After the various technical problems we faced during the first sampling station which nearly lasted 24 hours, the station 2 went very smoothly and we managed to conduct all the measurements and sampling in less than 6 hours.

Two female argonauts measuring around 6cm, caught in the net at 25m depth and released alive.

A small fish, probably of the scorpionfish family, with black spots on its pectoral fins.

Finally, last night, after 5 hours in the water, instead of 30 minutes, we managed to retrieve the net. After so much time, including the period when organisms from the depth come to the surface at night, the net contained a large quantity of micronecton, mainly Myctophidae or lanternfish that are small black fish with numerous photophores. We also collected interesting squids and small shrimps. It took us nearly 3 hours to sort the catch and we went to bed after midnight. Meanwhile the team of mechanics were trying to resolve the problem.

Catch of the second trawl showing a lot of Myctophidae and gelatinous organisms.

This morning the hydraulic system was working and we proceeded with the rest of the measurements which includes 2 casts of CTD down to 600 m depth to provide vertical profiles of temperature, salinity and fluorescence (indicative of the quantity of phytoplankton), and which allow to collect water at different depths. This water is filtered to collect chlorophyll pigments among others and particulate organic matter.

Finally after 24h spent on this station we are steaming north towards our next station that we should reach around midnight.

Cast carrying the CTD probe (not visible on the picture) and the bottles to collect water.

Martine preparing water samples for filtration

The swell and the wind have decreased. It makes our life onboard and our work much more easier. Our chef prepared some strawberry tartelettes to celebrate.

Jacques, our chef, prepared mouth-watering strawberry tartelettes for lunch.

We arrived at our first sampling station around 1:30 pm and we started with 2 micronekton net trawls at 550 m where the acoustic signal was the strongest and at 190 m depth where the acoustic signal is null. During the day it is classical to observe no micronekton between 100 m and 400 m depth. Unfortunately we had a problem with the hydraulic winch and we had to stop the hauling of the net. The mechanics are working on the case and the net is still in the water. We will have to wait for them to repair the problem to retrieve the net and to continue the work.

SIMRAD EK60 echosounder signal for 2 different frequencies (38kHz, top and 70kHz, bottom) showing, during the day, that most of the micronekton is located between 500 and 600 m depth ; a weaker signal is observed within the first 100 m and nothing is observed between 100 and 500 m.

Catch of the first trawl at 550 m

Yesterday afternoon we left the sheltered area of Sainte Marie bay to reach our first sampling station. We made the most of the quiet waters of the lagoon to proceed with an evacuation exercise. When the alarm rings 6 short and 1 long bip, we all have to grab our safety jacket and our immersion suit and gather at the back of the boat. While on the deck we were very lucky to observe a Humpback whale and at the same time a large cruise ship passed behind us to leave the lagoon through the Dumbéa pass. We stayed in the lagoon for diner and we then had to leave through the pass with a large swell and strong trade winds. We soon realised it would not be possible to proceed with our first sampling station with a high risk to break some gears while lowering it in the water. We decided to steam towards our second sampling station which is at the south-west corner of our sampling area, 38 hours of steaming away. Today we steamed with still a strong swell.

Considering the bad weather and under the threat of a tropical storm in the south-eastern part of New Caledonia, we had to change the cruise plan. We decided to target 2 eddies in the south western part of the economic zone. We will sample the 2 eddies and the frontal zone located between them.

After one hour of steaming in the quiet waters of the lagoon, we throw the anchor in Sainte Marie bay sheltered by the islands to proceed with the calibration of the SIMRAD EK60 echosounder. We need to make sure that the setting of the echosounder has not drifted since the latest calibration and that the echosounder gives us accurate information. With small winches linked to motor located on each side of the boat, a tungsten ball, the size of a golf ball, is lowered down below the boat to go through the beam of the echosounder.

David and Christophe working on the echosounder calibration

Elodie and Guillaume preparing vials for the samples

Nectalis 4, last but not least.

Nectalis the fourth is probably the last cruise of this fantastic adventure which explored the deep and surface offshore waters of New Caledonia. After three successful cruises in the northern and southern western part of the EEZ, we are completing our spatial exploration of the pelagic waters of New Caledonia by heading towards the south-eastern part of the EEZ. Our goal this time, on top of extending the spatial coverage of our work, is to specifically target eddies to try and understand their influence of the physical, chemical and biological components of the ecosystem.

Eddies are sections of moving water that swirl off from the main current and loop back on themselves, forming something like whirlpools. The topography of the ocean floor, such as seamounts or islands, by disrupting the flow of the current can help eddies to form in the lee of the obstacle. These eddies consist of water that is of different temperature than the water that surrounds them. They are usually around 100-200 km wide; they can last several weeks and will typically travel at the speed of 1m/s (3.6 km/h or 86 km in a day). We believe that, in certain conditions, eddies can bring nutrients at the surface and then create an environment favourable for higher development of phytoplankton, zooplankton and micronekton. This enhanced ecosystem could attract tuna and other large pelagic predators or seabirds. The scientific literature provides contradictory information about eddies impact on the ecosystem so we thought we should better go and check what is really happening there.

Our goal is to target two eddies, one cyclonic eddy (turning clockwise) and one anticyclonic eddy (turning counter clockwise). Another very interesting area is the frontal zone between the 2 types of eddies where currents are meeting and create a lot of turbulences which usually have a positive impact on the phytoplankton production and, through a cascading effect, on the rest of the food web.

Recent maps of the sea level indicate the presence of a large cyclonic eddy east of the southern part of Grande Terre of New Caledonia (in blue on the sea level map below) which is characterised by colder waters. We are planning to investigate all the physical, chemical and biological parameters of this eddy and of the adjacent anticyclonic eddy, as well as the frontal zone between the 2 where chlorophyll concentration appears to be higher according to the satellite image.

Along the cruise track we will stop for several hours to collect a series of data and samples. Sampling station are planned on the edge of the eddies, at the centre and outside the eddies. Continuous variables will also be recorded along the cruise track.

As for the previous Nectalis cruise we will collect oceanographic physical and chemical data:

• sea surface temperature and salinity along the track of the cruise with TS probes,
• at each sampling station we will lower a CTD probe (Conductivity, temperature, depth) down to 600 m
• with the CTD probe we have 9 water bottles that will be closed at different depth. Nitrates, Silicates and Phosphates will be measured at each depth using the water samples.

For the biological parameters, at each sampling station,

• using the water samples the particulate organic matter (including phytoplankton) will be measured and collected for stable isotope analysis,
• several phytoplankton pigments will be measured such as Chlorophyll and Phycoerythrin,
• the number of bacteria and phytoplankton cells of different size will be counted,
• using a zooplankton net we will collect zooplankton at different depths between 200 m depth and the surface, to identify the organisms, estimate their quantities and measure isotope and mercury concentration,
• using an acoustic device called the TAPS that is lowered down to 200 m we will be able to estimate the amount of zooplankton in the water column,
• using a micronekton net we will collect small squids, crustaceans and fish (2-20 cm long) at depth between 550 m and the surface; we will identify them, count them and conduct some analyses on them (bar coding, stable isotope, mercury)
• finally, along the track of the cruise we will record the acoustic signal of the micronekton using a SIMRAD EK60 echosounder to estimate their quantities and their spatial distribution.

A new experiment will be conducted during this cruise: environmental DNA (eDNA). By collecting and filtering water samples, we will collect and analyse DNA fragments left behind by the living organisms that shade scales or mucus. By comparing our results to a DNA database we will identify organisms that were in the water without the need to collect the organism themselves. This technique is very promising but still in development so our goal is to try and prove that the method works.

The Nectalis 4 cruise will depart on the 19th of October 2015 and our scientific team of SPC and IRD staff will be at sea for 2 weeks of hard work. We wish them all the best for this adventure, especially considering the strong trade winds blowing in New Caledonia at the moment, and we are looking forward to hear about their fascinating discoveries.

The Nectalis 4 cruise received the financial support of IRD, SPC and AAMP (French Agency of Marine Protected Areas).