Reconstruction of the Neogene current system in the area of the Eirik Drift, SW Greenland
During Leg MSM 12/2 with RV Maria S. Merian in June/July 2009 both the palaeo as well as the recent sedimentation processes and oceanographic conditions in the area of the Eirik Drift were studied. Proxies determined at recent and sub-recent samples will enable a better interpretation of IODP data and hence lead to a better reconstruction of the long-term development of sedimentation processes, the glacial history, and oceanographic conditions during the Neogene and Quaternary. We have aimed to solve the following questions:
- What is the detailed structure of the Eirik Drift? Can we distinguish between contouritic and turbiditic deposition? Do the turbiditic deposits lead to information on the extension (frequency and dimension) of the Greenland ice shield? To answer those questions we needed to gather seismic data across the entire Eirik Drift from the shallower parts into the deep sea. The profiles further had to cover the locations of ODP and IODP sites.
- Can we reconstruct the development of the Western Boundary Undercurrent (WBUC) in this region? Have modifications in the current system been documented in the sediment transport? In what way did those oceanographic modifications affect the sedimentary sequences? Why did the build-up of the Eirik Drift start with a delay of about 1.1 my relative to the oceanographic modifications (i.e. 4.5 Ma)?
- Can we identify analogies to the build-up and the creation of sediment drifts on the southern hemisphere? Do chronological matches exist between the Eirik Drift and Drift 7 at the Antarctic Peninsula or the Agulhas Drift in the Transkei Basin? Can we identify global climatic and oceanographic events in those drift systems?
- Can we detect short-term variations of oceanic currents (NADW), sea-ice extent, surface water productivity, and terrigenous input within the upper 15 m of the sedimentary column (Milankovich and sub-Milankovic cycles)? How do those parameters correlate with instabilities of the Greenland ice shield?
The project comprised geophysical and marin-geological operations in the area of the Eirik Drift. Streamer, airguns, gravity corer, giant box corer, as well as PARASOUND and multi-beam systems were used. Seismic reflection profiles were gathered in order to study the sedimentary distribution in relation to the tectonic and oceanographic evolution. Those profiles cover the whole Eirik Drift with the transition into the deep sea. Furthermore, the profiles cover the locations of ODP Leg 105 Site 646 and IODP Expedition 303 Sites 1305, 1306, and 1307.
The marin-geological programme concentrated on sampling the near-surface sediments (0-15 m) using giant box corer and gravity corer. Undisturbed sediments not affected by e.g. turbidity currents were sampled. Sample locations were picked based on PARASOUND recordings, which were gathered parallel to the seismic profiling. This saved on ship time. The cores were opened already during the cruise, described and sampled.
A new set of high-resolution seismic reflection data has been interpreted with respect to the build-up of the Eirik Drift. We have refined the seismostratigraphic concept of Arthur et al. (1989) adding horizons A1 (0.8 Ma), A2 (1.4 Ma) and A3 (17–19 Ma) and dating horizon R5 (10–12 Ma). Our study suggests that the onset of drift building was instigated in the early Miocene (17–19 Ma), which contrasts with the hypotheses by Arthur et al. (1989) and Wold (1994), who inferred a drift build-up after ~4.5 Ma and after ~7– 8 Ma, respectively.Our proposed history of sedimentation within the Miocene seismic unit SUIV at the Eirik Drift is as follows:
• Until 19–17 Ma sedimentation at the Eirik Drift was not deepcurrent controlled; deposition of subunit SUIV-c took place in a tranquil and stable environment.
• Horizon A3 is identified as the basal erosional unconformity of the Eirik Drift and is dated 19–17 Ma, when initiation of strong NCW fluxes occurred, as is documented in several erosional unconformities and drifts in the northern North Atlantic. Horizon A3 presumably represents also a sedimentary hiatus due to enhanced erosion. This onset of strong NCW fluxes follows the development of the Faroe Conduit in early Miocene and the onset of deepwater exchange at the Fram Strait.
• Onset of drift building is documented by deposition of unit SUIV-b under the influence of strong NCW fluxes, which were inhibited between 15 and 12.5 Ma.
• Changes in the deep-current velocity presumably formed the highamplitude reflection-band surrounding horizon R5 at 12–10 Ma along with a renewed onset of NCW flow. At that time (~13–11 Ma) the first significant overflows at the Iceland–Faroe-Ridge were observed.
• Drift elongation and progradation to theWSWunder the influence of shallower NCW flow is suggested by the sedimentary record of unit SUIV-a.
• Reflection doublet R3/R4 (7.5 Ma) and the medium- to high amplitude reflections found below this horizon are ascribed to the minor interruptions of NCWflow at 7 and 9 Ma. Presumably, the suggested onset of overflows over the Denmark Strait (~7 Ma) is documented by horizon R3.
In this study, we concentrated on the development of the Eirik Drift during the Miocene to show that drift building at the Eirik Drift started much earlier than previously thought. The refined seismostratigraphic concept will be used in further studies to define a model for the development of pathways and intensity of the NCW flow over the Erik Drift during Neogene and Quaternary.
This project is funded by the Deutsche Forschungsgemeinschaft under contracts No MSM 12 and Ue 49/12.
Müller-Michaelis, A. and Uenzelmann-Neben, G. (2014)
Development of the Western Boundary Undercurrent at Eirik Drift related to changing climate since the early Miocene , Deep Sea Research I: Oceanographic Research Papers, 93 , pp. 21-34 . doi:10.1016/j.dsr.2014.07.010
Müller-Michaelis, A. , Uenzelmann-Neben, G. and Stein, R. (2013)
A revised Early Miocene age for the instigation of the Eirik Drift, offshore southern Greenland: Evidence from high-resolution seismic reflection data, Marine Geology, ELSEVIER SCIENCE BV, 340, pp. 1-15. doi:10.1016/j.margeo.2013.04.012
Uenzelmann-Neben, G. (2009)
The expedition of the research vessel "Maria S. Merian" to the Labrador Sea in 2009 (MSM 12/2) Reykjavik - Reykjavik 17. June - 13. July 2009 / Ed. by Gabriele Uenzelmann-Neben with contributions of the participants. Berichte zur Polar- und Meeresforschung (Reports on Polar and Marine Research), 599 , 91 p., ISSN: 1866-3192 .
Uenzelmann-Neben, G., Schmidt, D., Niessen, F. and Stein, R. (2012)
Intraplate volcanism off South Greenland: Caused by glacial rebound? Geophysical Journal International, WILEY-BLACKWELL PUBLISHING, ISSN: 0956-540X . doi:10.1111/j.1365-246X.2012.05468.x