Exploring the southwest Atlantic – RRS Discovery cruise DY087

Ocean research brings together scientists from all around the world from a variety of backgrounds. Earlier this year, scientists from the University of Southampton, British Antarctic Survey, University of Exeter, University of Birmingham, University of Nebraska Lincoln and University of Padova came together to participate in RRS Discovery cruise DY087 to the South Georgia Basin and Maurice Ewing Bank. We had palaeoceanographers, geophysicists, sedimentologists, oceanographers and biostratigraphers onboard, working closely alongside a dedicated team of marine technicians, engineers and ship crew to investigate Paleogene (66-23 million years ago) climate and deep-water evolution in the Southwest Atlantic.

Why do we care about the climate and deep-water evolution that far back in Earth’s history?
At the beginning of the Paleogene the Earth was a very different and much warmer place. The continents had a slightly different configuration, the ocean current system was different and arguably most notably there was no ice at the poles. However, around 34 million years ago across an interval known as the Eocene-Oligocene Transition (EOT) the Earth rapidly transitioned from a ‘greenhouse’ state to the ‘icehouse’ climate we have today, marked by the growth of the East Antarctic ice sheet. The EOT represents one of the most pivotal tipping points in the development of the modern climate system. Understanding how, why and when the Antarctic ice sheet developed for the first time and how the Earth system responded both in a greenhouse climate and during the early icehouse is crucial if we are to better understand and predict how the climate is changing today and the implications of a melting Antarctic ice sheet for the wider climate system.

Why is it important to investigate deep-water evolution in the Southwest Atlantic?
Model reconstructions show that declining atmospheric carbon dioxide levels throughout the Eocene drove the cooling trend but deep-water evolution also played an important role through heat transport and the thermal isolation of Antarctic, collectively allowing the development and established of the Antarctic ice sheet. The development of the Antarctic Circumpolar Current (ACC) was very important in all this and could only happen when gateways opened in the Southern Ocean. One such gateway was the Tasman gateway but we know comparatively much less about the opening and deepening of the Drake Passage. In the present-day, the Drake Passage is a very important oceanographic region connecting the Pacific and Atlantic ocean basins. This communication of both surface and deep-water between the Pacific and Atlantic Oceans via the Drake Passage plays a crucial role in the global overturning circulation. Investigating when the ACC started and the Drake Passage opened to help facilitate global transport of heat, salt and nutrients, will have important implications for our understanding of the inception of Antarctic glaciation and the Atlantic Meridional Overturning Circulation (AMOC) which is a fundamental component of the modern climate system.

How do we investigate this at sea?
The main aims of our cruise with regards to data collection was to collect a suite of geophysical data to image the seafloor and look at changes in sedimentation (which relate to the inception and strength of ocean currents) and find areas where we could safely recover long sediment cores. You can read more about the geophysical data collection here: https://seafaringscientists.wordpress.com/2018/02/19/marine-geophysics-at-work/
To supplement the geophysical data we collected marine sediment cores to (i) help us date the seismic lines (ii) to allow us to generate downcore palaeoclimate proxy records.The retrieved sediment cores will be used by many scientists over the coming years to piece together a picture of what the southwest Atlantic was like millions of years ago.

To hear about what we got up to day-to-day on the cruise and how science at sea works check out our cruise blog.

For many of the PhD students aboard it was our first research cruise experience. Before setting sail some of us answered three simple questions to capture how we were feeling about the cruise:

Keep an eye out on @pip_penguin (twitter) and/or www.seafaringscientists.wordpress.com to see us answer the same questions post-cruise and follow what happens now we are back in Southampton with the data and samples we collected while at sea.