Outstanding high-resolution chronicle of Cenozoic climatic and oceanographic changes in the southern Indian Ocean
Located in a key region in the southern Indian Ocean the complex topography of the Kerguelen Plateau, one of the world’s largest Large Igneous Provinces, has a strong influence on pathways of water masses within the Antarctic Circumpolar Current (ACC) and the Antarctic Bottom Water (AABW). Topographic highs like the Williams Ridge at the Kerguelen Plateau reduce the flow of water masses leading to the deposition of thick sediment packages. Gaps and narrow passages in contrast lead to erosion and non-deposition. In the Cenozoic era significant modifications in pathways and intensity of those water masses have been caused by the tectonic development of the Kerguelen Plateau as well as the opening of the Tasman Gateway, the Drake Passage and major global climatic changes. In the Kerguelen Plateau region all of these changes are explicitly well documented in the formation of sedimentary structures, e.g. sediment drifts, supposedly at very high resolution.
To complement the seismic studies and provide ages of the outcropping sediment geological samples were retrieved at 11 locations using a gravity corer and multi-corer. Both datasets will form the base for an IODP proposal.
Onset and modifications in intensity and pathways of water mass exchange between the Southeast Pacific and the South Atlantic: A focus on the Falkland Plateau
The opening of Drake Passage and the Scotia Sea, the gateway between South America and Antarctica, enabled the exchange of water masses between the southern Pacific and the South Atlantic. In this way heat and energy could be transferred between the two oceans. Together with the opening of the Tasman Gateway this allowed the establishment of the Antarctic Circumpolar Current (ACC) thermally isolating Antarctica, which has been considered as one of the major causes for the onset of widespread glaciation. Both tectonic movements within Drake Passage and the Scotia Sea as well as modifications in climate have led to changes in intensity and pathway of the ACC and the water masses flowing within it. The onset of the ACC and those changes have been documented in sedimentary structures deposited on the Falkland Plateau.
The deep and bottom water masses flowing within the ACC (Antarctic Bottom Water (AABW), WSDW, SPDW, LCDW, UCDW) are steered by the complex topography of the Drake Passage and the Scotia Sea. Rounding topographic highs the water masses reduce their speed and hence deposit sediment. In gaps and passages their speed is increased leading to erosion and non-deposition. In this way the aforementioned water masses shape sediment drifts, which in their structure (geometry, internal unconformities, reflection characteristics) document the modifications in the flow paths and intensities of the water masses. The tectonic development of both the Drake Passage and the Scotia Sea during the Cenozoic have led to strong modifications in the flow paths, which, when studying sediment drifts, can be deciphered. Additionally, the ACC fronts are assumed to have been subject to relocations during glacial-interglacial cycles. This again has led to relocations in depocentres, which can be identified via seismic profiles. So far, research here has concentrated on the area south of the Falkland Islands towards South America but the flow of water masses across the plateau has not been studied. Results of DSDP Legs 36 and 71 suggest intensified bottom currents as early as the Eocene, which led to the discussion of an early Tertiary water mass exchange between the Pacific and the Atlantic oceans . Numerical simulations also suggest a weak ACC for the late Cretaceous but no overturning circulation.
RV Marian S Merian cruise MSM 81
Cruise Leg MSM81 with RV Maria S. Merian, leaving Valparaiso, Chile, on February 2 2019, returning to Montevideo, Uruguay, on March 15 2019, comprised seismic reflection studies of the Falkland Plateau, the westernmost part of the Agulhas-Falkland Fracture Zone in the South Atlantic. The Falkland Plateau rises up 1500 m above the surrounding seafloor and hence forms an obstacle for the exchange of water masses between high and lower latitudes. A water mass exchange between the Pacific and Atlantic oceans has been enabled with the opening of Drake Passage. In this way heat and energy could be transferred between the two oceans. A detailed study and analysis of the structure of the Falkland Plateau and channel in the south via seismic data and a correlation with results from DSDP Leg 36 Sites 327, 329, and 330 as well as Leg 71 Site 511 was needed to supply information on the Cretaceous and Tertiary development of the Falkland Plateau and its influence on the path of the Antarctic Circumpolar Current, Upper and Lower Circumpolar Deepwater, South Pacific Deepwater, and Weddell Sea Deepwater. Seismic profiles were gathered, which capture the structure of the Falkland Plateau to basement and possible sediment drifts. In total ~5200 km of high resolution seismic reflection data were recorded. Bathymetric and Parasound data were recorded parallel to the seismic profiling.
To complement the seismic studies SVP and XSV measurements at 6 locations and ADCP measurements across the whole working area were carried out. The overaching goal of the cruise was to study variations in flow paths and intensities of deep and bottom water masses in response to a) tectonic movements, and b) climate variability.
In particular, we intend to answer the following questions:
When and how did the onset of the ACC and the deep and bottom water masses flowing within the ACC affect sedimentation at the Falkland Plateau area?
When can we recognise the first overspill of UCDW and LCDW over the Falkland Plateau indicating transport of cold water masses into the South Atlantic?
What are the variations of the pathways and intensity of overspill and the location of the ACC fronts in relation to a) tectonic movements, and b) modifications in climate (e.g. Mid-Miocene Climatic Optimum and Transition, Pliocene warming, onset of widespread glaciation on the Northern Hemisphere)?
The Labrador shelf, located off the eastern Canadian coast, is a key area for paleoclimate and paleoceanographic research. The Canadian hinterland was covered by the so-called Laurentide Ice Sheet during glacials. During phases of ice melt at the transition from glacials to interglacials, large amounts of fresh water were released into the Labrador Sea and North Atlantic Ocean. This release of fresh water occurred through fjords and adjacent troughs that were excavated by ice streams during the glacials.
These fresh water pulses have a profound influence on the strength of the Atlantic meridional overturning circulation, which in turn significantly influences the climate of the Northern Hemisphere. The major drainage system, Hudson Bay in the northernmost part of the Labrador coast, is well investigated as are the areas around Newfoundland and Nova Scotia. Large parts of the Labrador shelf, however, remain rather unexplored.
So far, the dynamics of the Laurentide Ice Sheet were reconstructed based on marine sediment cores that were taken mostly far offshore from the North Atlantic. This area was never directly covered by the Laurentide Ice Sheet. Direct evidence from glacial features on the shelf is largely missing.
Therefore, scientists of expedition MSM84 will investigate the glacial history of the Labrador shelf and hence the glacial history of the eastern part of the Laurentide Ice Sheet. In addition to the Labrador shelf, we will also investigate Lake Melville, a small inlet into the eastern Canadian coast. Scientists will use a wide variety of scientific methods:
- Geophysicists (cooperation between AWI, University of Kiel, Germany, and Université Laval, Québec, Canada) will use hydro- and geoacoustic methods. With bathymetry, the morphology of the sea floor will be scanned in high resolution. We will investigate glacially generated sea floor features such as moraines and iceberg scours that help us to reconstruct the extent and decay of the ice sheet. We will also use sediment echo sounding and seismics to image the deeper sedimentary layers where we will identify signs of older glacials.
- Geologists (cooperation between AWI, University of Bremen, University of Kiel, Université du Québec à Montreal + à Rimouski) will retrieve sediment cores from the shelf and from the lake. They will investigate the sediment cores for their physical properties and carry out geochemical measurements. This helps to reconstruct the changing paleoclimate and paleoenvironmental conditions, e.g. between glacials and interglacials. Some cores will be specifically taken from glacial features (moraines, iceberg scours...) in order to date these and to establish a chronology of the decay of the Laurentide Ice Sheet at the end of the last glacial.
Expedition MSM84 will take place from mid June to mid July 2019 onboard of the German research vessel Maria S. Merian.
