Five things we’ve learnt about the oceans in the last 25 years

It’s early 1993 and I am sailing across the Atlantic Ocean aboard the Royal Research Ship Charles Darwin on my first deep-sea adventure. The late Harry Elderfield is our chief scientist and we are mapping out the newly discovered hydrothermal vents along the Mid-Atlantic Ridge and sampling the plumes that waft upwards from the hot seafloor vents. We tow our sensors on frames hanging from conducting wires that are kilometres long, gradually building up a picture of the plumes. The data acquisition is slow and the on-board data visualisation was largely paper and pencil.

Jump forward to the end of 2017 and we are here again – over the last decades there have been vast improvements in our analytical capabilities, we can measure our tracers at orders of magnitude lower levels, we can sample without contaminating our water samples, we have a new framework within which to interpret our data and we can plot our data in real time onboard ship. We are here to assess the trace metal and isotope impact of the hydrothermal vents that populate the ridge from the Azores southwards.

Amber Annett, Maeve Lohan and Aly Lough watching the sun set on Christmas Day

This has made me think what we have learnt since the early 1990’s and here is my list:

  1. Hydrothermal vents are almost as common along the slow spreading ridges of the Atlantic as they are along the fast spreading ridges of the Pacific and elsewhere. Contrary to early opinion, the slow spreading ridges host a wide range of vents that mine heat through deep faults on the rocky axial rift-valley. Many of the Atlantic sites are controlled by tectonic processes that cut deep into the crust rather than volcanic processes supplying hot lava to the seafloor.
  2. Hydrothermal vents supply significant iron and other trace metals to the deep ocean – while a lot of metals are precipitated in the chimneys and sediments at the seafloor there is a lot of chemical complexation that happens in the water above the vents that stabilises the metals and off they go into the deep ocean to be transported around the global ocean.

    Red colour shows the high concentrations of dissolved iron associated with ridge crest hydrothermal vents and its dispersion into the deep sea
  3. The vents are all very different and we haven’t by any extent found them all – they occur in the middle of the ridge segments, they occur at the discontinuities between the segments, they occur on-axis, they occur off-axis, they are high temperature, they are low temperature – it is really hard to generalise and we are still in the discovery phase of finding new things in the deep oceans.
  4. If you are careful and consistent and wrap things up carefully in clean plastic it is possible to measure 10 picomoles of reduced iron per litre of seawater on a ship made out of steel using a winch and sampling system that is greasy and grubby.

    Arthur, Shaun, Lise, Wenhao and Travis clean the trace metal cable before we sample
  5. If you put a team of chemists, biologists, physicists, computational scientists, geologists and engineers on a ship for 6 weeks extraordinary things happen – the shipboard environment provides an uninterrupted space for incredible thinking, testing of new ideas and is a key part of the progress of our science from the days of the HMS Challenger Expedition to the modern ocean exploration. The key is the team you choose to take to sea and how you get them to interact once you are there.
    Science Team modelling their cruise t-shirts supplied by Joe Resing, U Washington & PMEL

    We’d love hear what your thoughts are…….

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