Almost Home, with Another 7 Million Years of Climate History

Science at sea isn’t easy, but the benefits are huge, writes Sidney Hemming in her final post from a two-month expedition that collected millions of years of climate history in the deep-sea sediment from off southern Africa.

Sidney Hemming
March 25, 2016
Expedition 361's scientists near the end of an exciting and successful two-month expedition. Photo: Tim Fulton/IODP
Expedition 361’s scientists aboard the JOIDES Resolution, near the end of a successful two-month expedition. Photo: Tim Fulton/IODP

Read Sidney Hemming’s first post to learn more about the goals of her two-month research cruise off southern Africa and its focus on the Agulhas Current and collecting climate records for the past 5 million years.

We reached our last site yesterday morning, off Cape Town, South Africa, and the first core was on deck at 11:15 a.m. It was pretty stiff at the bottom, and its microfossils indicated it was more than 250,000 years at 1 meter. We decided to start again, and ended up with 6 meters in the first core of the B hole, with further indications of a very low sediment accumulation rate of approximately 1.5 cm per thousand years. The next few cores gave us troubles with shattered liners and low recovery, so Ian and I went back to the data from the alternative sites to consider moving. Luckily we decided not to, because things really started looking up.

We just completed the first hole with 300 meters of sediment and a base age of more than 7 million years, and with a quite pleasing accumulation rate below the very top part. We still don’t have quite enough information to evaluate the situation in the upper 1 million years, but it seems very clear that the rest of the site will be excellent. The sediment composition is very similar from top to bottom and very rich in carbonate (so called nannofossil ooze). The gamma ray (measures radioactivity and thus is a sensitive measure of clay) and color measurements give a very nice signal and are varying in concert with each other. The weather has gotten nicer since the beginning of the first hole, and we are hoping the conditions hold and that the sea conditions were the reason for the troubles at the beginning of our first hole. Meanwhile, we have just enough time to complete the triple coring of this site back to 7 million, with maybe enough time for logging of the final hole.

Crew members retrieve the beacon. (Credit: Jens Gruetzner, Alfred-Wegener-Institut for Polar and Marine Research)
Crew members retrieve the beacon. Photo: Jens Gruetzner, Alfred-Wegener-Institut for Polar and Marine Research

So, the good fortune continues. Each site on this cruise has provided real prize material, and the team members are very eager to get started on the work back at home. We have been burning the midnight oil (or midday, depending on your shift), meeting about the various plans for post-cruise science. There remain a couple of conflicts to resolve, but overall it looks like there will be plenty of great science for each participant, and plenty of opportunities to develop career-long collaborations.

It has been a great privilege to be part of this, and it really makes you realize how powerful these huge efforts, that require the cooperation of so many countries and their scientists, are. It is a very different way of doing science, and not always convenient for the individual, but overall the benefits are huge.

Meanwhile, this is my last post for this cruise. We are less than a week from arriving at our dock in Cape Town, and there is no question that we are all quite eager to get there. The JOIDES Resolution is amazing and the (multiple) staffs of the ship company, catering service, and IODP are truly remarkable. They are friendly, professional and very eager to help us to get the best we can out of this amazing scientific discovery process.

Sidney Hemming is a geochemist and professor of Earth and Environmental Sciences at Lamont-Doherty Earth Observatory. She uses the records in sediments and sedimentary rocks to document aspects of Earth’s history.

The crew and scientists of Expedition 361. Photo: Tim Fulton/IODP
The crew and scientists of Expedition 361. Photo: Tim Fulton/IODP