Featured image: a large group gathers below the bridge to enjoy the sights as the R/V Investigator departed Sydney 3 weeks ago. Image credit: Amaranta Focardi
Hard to believe but our time on the R/V Investigator for voyage IN2016_V04 is coming to an end! Today marks the end of the science operations as we need to be at the meeting location to pick up our pilot by tomorrow at 8am. When the on board science stops its time to clean up and pack up- we have Friday to off load (demobilize). We’re spent 3 weeks in an extremely dynamic, productive region of the ocean at the location where the warm waters of the EAC enter the cool Tasman Sea. In this time we’ve been sampling the water, the sediment, the air, and the rain! So much science, so little time! But now to look back and prepare to head home. Demobilization has to be a quick project, there is little time between voyages and we have to be off before the next group can get on! But, it also means an opportunity to run through some of the highlights from the various groups on board! So here it goes, the highlight reel:
During the voyage we were able to see several different communities of plankton as we transited various water masses. The coastal nutrient rich waters had high phytoplankton diversity and a large variety of diatoms. The cold core eddy in contrast had a single dominant species of colony forming phytoplankton (nicknamed “green slime”- see below). In the EAC, we saw mainly (prokaryotic) cyano-bacteria and very few (eukaryotic) phytoplankton with only the occasional diatom. This is because the EAC is warm and nutrient depleted (iron, nitrate, and silicate limitations)– however, add in the limiting factor (like one of our on-board incubations experiments did) and you can end up with a lot of diatoms.
The highlight here was probably the sperm whale (named Moby according to the white board outside the mess) given that sightings are rare. Fun fact: the blow of a sperm whale comes out at an angle, its one of the characteristics scientists can look at to identify the whale from a distance.
But the two humpbacks that came right up to the ship to check us out during the CTD in the first part of the voyage were also very cool!
A little more on the marine mammal survey itself… the main goal is to create a spatial model of the distribution of cetaceans (includes whales and dolphins) and take advantage of the EK60 data on zooplankton to make a link between food source (zooplankton) and whale presence and behavior. To do so, Gary and Ricardo are constantly scanning the horizon for whales, dolphins, birds, and seals anytime the ship is underway in daylight hours. They’ve sighted almost 500 cetaceans on this voyage! Over 100 of these sightings (mostly humpbacks) were on the transit north from Sydney. In addition, the ship hydrophones are providing passive acoustic monitoring to listen for the whale presence. The visual data will be compared with the acoustics to evaluate the efficiency and limitations of each method. The species can be identified by a specific acoustic signature. For instance, the Antarctic Blue whale’s (not seen on this voyage) call appears like a Z on a frequency versus time (very clear high pitch followed by lower pitch) plot thus called the “zed call.”
We saw a lot of green slime throughout the voyage. Including it as a “highlight” might be an over statement, rather this particular phytoplankton stinks (trust us on this one!) and clogs up the nets. Furthermore, nothing seems to be eating it.
Throughout the voyage we were always watching sea surface temperature to identify the location of currents and eddies, but to actually trace a water mass we tossed in these fairly small floats- the idea is they float with the currents and emit a signal that the ship can then follow. Several were deployed during the trip at points of interest, such as where we thought was the source of warm water for the large warm core eddy just off Sydney. These drifters really came into play for our drift study, when we followed them for 3 days moving >200 km to the south of where we began the drift (just off Coffs Harbor).
We spent a lot of time looking at eddies this trip, so a quote from Lewis Fry Richardson: “Big whirls have little whirls, that feed on their velocity. And little whirls have lesser whirls, and so on to viscosity”
You’ve heard a lot about our coring already (see Into the mud!), but in summary: 3 successful sites at water depths of 150 m, 1600 m, and 2600 m!!! And we got a lot of pore water out of them! So back in lab we’ll be getting started in analysis again! (see Pore water)
So small, we can’t see them.. but are microbes the smallest part or the largest part of the food web? On an individual basis, they’re tiny. For that matter, until recently we didn’t really know just how many were in seawater. It wasn’t until 1988 that the single celled phytoplankton Prochlorococcus (only 1600 genes) was discovered. A single cell but very numerous, these small marine organisms have 4000x the total biomass of all whales in the ocean. Even the first DNA stain of seawater, showing us just how numerous bacteria and viruses are there (in just 1 mL of seawater= 10^6 bacteria, 10^7 viruses, probably on the order of 20,000 microbial species) wasn’t taken until almost a decade after man walked on the moon.
What are they doing? Who are they? What processes are the participating in? Turnover of microbes in the ocean is estimated to be just 6 days- they must be very active!! The in-situ pumps on this voyage have filtered over 6000 liters of water! That’s an awful lot of filtering! But what it means: not only can the microbiologists look at the DNA (who is present), but the large sample size allows them to see how and what that community is doing! (Check out marine microbes project of Bioplatforms here to see some of the results!)
The underway systems allows further examination of productivity. The fluorescence on the underway system has several ‘color’ of LED, allowing scientists on board to look at how many plankton are present, how the community is doing (nutrient stress etc), and who is doing most of the production in a given location.
This is a cool piece of equipment, and despite intentions to write about it many times-here the Triaxus finally makes an appearance! Built from carbon fiber, the Triaxus is tethered and towed behind the ship (up to 3 km of cable between it and us!). Why is the Triaxus special? First of all, its a lot of data, and a lot of data in real time! The Triaxus measures temperature, salinity, and chlorophyll among others. And has a camera which can attract curious dolphins (check out the video clip at https://blog.csiro.au/voyage-meaning-life-ocean-microbes/). Ok, so we get most of these measurements from the underway system (see Dolphins, and squid, and cups- oh my!) so why do we need the Triaxus? Well, a major advantage of the Triaxus is that it ‘flies’ at multiple depths- typically we’ll have it going in a pattern from 0 to 200m repeatedly to characterize the surface mixed layer instead of just the very surface. This pattern takes ~0.5km resulting in a high resolution record of the upper 200 m and can help inform where we put the CTD stations.
Luvia was interested in studying larval lobster (phyllosoma). In this case, it is all luck of the catch! Even got one on the salinity sensor of the Triaxus. There were several phyllosoma-less nets but they did manage to get 21 lobster larvae (5 on the last night of net tows!!!). Other than the last night, the phyllosoma were largely concentrated in offshore cyclonic eddies including the cold core eddy off of Seal Rocks (about 100 nautical miles).
Some other highlights from around the ship:
- Great coverage of the different water masses in the area- including below the EAC. The focus is often on the EAC itself, but having samples from the far side of the EAC, below the EAC, and the Australian shelf side of the EAC helps contextualize the samples
- Watching the EK60 at sun rise or sun set
- Food: While all delicious, the general consensus is the mango cheesecake won hands down
- From the nets: Octopi, Dave the dragon fish, Spike the squid & flying fish!