Day 33, Station 57 – I got up at 4 am before sunrise, getting ready for our 9th sampling station, or the 57th of the Atlantic Meridional Transect (AMT)-27 cruise. We have already spent over a month at sea since leaving NOCS, having passed Azores, crossed the Equator, traversing some of the bluest waters on the planet (due to low productivity, lack of ‘green lives’ at the surface), as well as low-oxygen waters linked to productive regions in both hemispheres, now we are arriving at the 40ºS ‘frontal zone’ where cold nutrient-rich water from the south meets the warm water from the north, resulting in turbulences yet extraordinarily high productivity. The waters at these latitudes are dubbed the ‘Roaring Forties’ – for its infamous high seas that we could totally attest now. The wind has been blowing strong in the past two days, with significantly cooler temperatures especially compared to the sunny tropics we passed under a week ago. We could see, and feel, the sea surface heaving up and down.
I was very anxious to know whether we could actually proceed with our sampling today. Our project, Shortcut in the Oceanic Nitrogen Cycle (SONiC), has been funded to add extra days to the existing AMT cruise, to conduct our research. I was therefore given choices on when to do our sampling, and we aim to cover as many ocean biogeochemical provinces as possible, in order to check how widespread the phenomena we are investigating really are. I’d like to go to the very centre of this frontal zone, as it should be the most representative. The marine and weather forecasts, however, predicted up to 6m of swells and strong winds. So even if I opted to do our sampling on this day, there was a good chance that it would not happen for safety reasons.
Thankfully, we got the go-ahead from the captain, the cruise’s principal scientist and technical officers. Our first task was to deploy an array of four standalone pumps to filter hundreds of litres of water in situ at discrete depths down to 1000m, as we need to concentrate sufficient materials for protein analyses. The night before, I prepared filters and secured them inside designated compartments of these pumps. As we brought these awkwardly heavy pumps onto the deck for deployment, the deck engineers were already working hard changing wires on the 3-storey high winch. Although they had done the same many times before, the rough sea and wind chill made it rather challenging for today. While waiting and peering through the white caps at the sea surface, we spotted several moving black shades: a group of minke whales were just swimming by. Then followed a big tail fin rising up from the horizon against the beautiful, red-lit sky. Two humpbacks greeted us with their famous bridging posts only 100 m off the ship’s railings. At this point, we were just putting our last pump into the water, and the glowing red sun has just risen. What a way to start our day!
The rest of the day went very smoothly – water sampling with the CTD (Conductivity-Temperature-Depth)-Niskin-rosette, with which we sampled hundreds of litres of water that were distributed into fifty 4L bottles for our various incubation experiments. We subsampled each into numerous small tubes for various measurements a few times over 2 days, then we terminated the experiments by preserving materials, both water and particles, for various chemical and molecular analyses. After a lot of bottle-washing on the 3rd day, our cycle would begin again on the 4th.
Routine it may sound, no two days are exactly the same onboard ship: we are greeted by changing weather and sea conditions, while the organisms living underneath differ from one place and time to another. No matter how prepared we think we are, we never know for certain what awaits us when we start our day.
 Ocean biogeochemical provinces – oceanic regions of common chemical and biological characteristics, e.g. biological productivity shaped by the availability of essential nutrients (e.g. nitrogen, phosphorus, iron) that might in turn be regulated by physical parameters like ocean circulation. Examples include oligotrophic subtropical gyres, equatorial upwelling.
Dr. Phyllis Lam[i]
Associate Professor in Microbial Biogeochemistry
Ocean and Earth Science
[i] Dr. Phyllis Lam has been at sea onboard the RRS Discovery since 23rd September, 2017. After the AMT cruise that sailed from Southampton to Port Stanley via Azores and South Georgia, she is currently on a second cruise working on the project COMICS (Control over Mesopelagic Interior Carbon Storage) in the Scotia Sea, Southern Ocean, until 21st December, 2017.
To find out more about Phyllis ‘s research view her publications.