The Present is the Key to the Past

Trace element and isotope proxies in paleoceanography: A synthesis workshop

3 – 5 December 2018, Aix-Marseille, France

Report by Susan Little

At a workshop in December, scientists from 11 countries and 4 continents converged on Chateauneuf de Rouge, Southern France. With expertise spanning modern and paleoceanography, we gathered to talk biology, ocean circulation, particle fluxes, and models of the present and past oceans…

Why focus on the oceans?

In short, the oceans, and the bugs growing in them, are a vital part of Earth’s climate system.

Microscopic algae in the sunlit upper ocean use carbon (from carbon dioxide, CO₂) to build their cells. After they die, they sink and decay, a process that ‘pumps’ CO₂ from the surface ocean to the deep.

Once in the deep ocean, the CO₂ is trapped for hundreds, or even thousands, of years. This process reduces the level of CO₂ in the atmosphere, and the resultant greenhouse effect, cooling the planet.

The Present is the Key to the Past?

Charles Lyell famously wrote: ‘The Past is the Key to the Present’. Scientists even use the past to help predict what might happen in the future warming world.

But how do we figure out what happened in the past? The past oceans are long gone, so scientists use proxies to reconstruct particular ocean properties.

Interesting properties might include the availability of nutrients that algae need to grow, or the patterns of ocean currents. Past ocean proxies include a spectrum of all kinds of bio/geo/chemical measurements, made in all sorts of seawater archives, from individual microfossils to ancient sediments collected from the seafloor.

To develop proxies, it turns out that the present is the key …

Tuning your Time Machine

A good proxy is a real life Tardis, allowing us to go back in time… But how do we know what, and how well, a proxy is recording an ocean property?

To test and improve a proxy (e.g., Cd/Ca ratios in microfossils as a record of past nutrients) scientists compare modern measurements of the property in seawater (e.g., nutrient concentrations) with the value recorded by the proxy in its modern archive (e.g., in modern microorganisms).

At this workshop, we set out to improve our understanding and application of a range of proxies. We used what we have learned from the modern ocean in the international GEOTRACES program (www.geotraces.org).

The Modern Ocean

Since 2006, GEOTRACES has completed 109 cruises and released two Intermediate Data Products (IDP), in 2014 and in 2017. The IDP2017 includes data from 41 cruises, more than 1866 stations, 470 parameters and 51000 samples…

That’s a lot of data! And it’s all freely available to download here: https://www.bodc.ac.uk/geotraces/data/idp2017/

The Wine Work

The workshop addressed the following questions:

State of the Art

What trace element and isotope proxies are currently being measured and modelled in the ocean?

Challenges

Can we use data from GEOTRACES to improve our understanding of proxies for use by the paleaoceanographic (PAGES, www.pastglobalchanges.org) community?

Perspectives

What future technical developments, modelling approaches, cruises or other activities would help to develop or interpret proxy distributions?

It was a fascinating, stimulating, interdisciplinary three days of discussion. Thanks to everyone who was involved[i]. Watch this space for upcoming workshop products!

[i]More details of the workshop:

https://geotracespages.sciencesconf.org/

Thanks to the Sponsors:

PAGES, GEOTRACES, SCOR, US-NSF, Aix-Marseille Université and John Cantle Scientific