Short-term variability of sea ice and surface-water characteristics in the Late Neogene North Atlantic Ocean: A biomarker approach (IODP Leg 303 and 306)
Understanding the mechanisms and causes of the abrupt climate change is one of the major challenges in global climate change research today. In this context, the determination of the long-term evolution of millennial-scale variability in surface temperature, ice sheet stability as source for meltwater discharge, and thermohaline circulation can provide clues to the mechanisms responsible for abrupt climate change, which are still poorly understood in detail.
To shed more light on these topics, the North Atlantic Ocean was visited by scientific drilling ship Joides Resolution during Integrated Ocean Drilling Program (IODP) Expedition 306 in March–April 2005. The main goal of Expedition 306 — as was the main goal of Expedition 303 — was to generate a continuous high-resolution chronology spanning the last ~5 million years (late Neogene–Quaternary), using North Atlantic climate proxies collected from layers of ocean sediments. Using a range of stratigraphic tools, including stable isotopes and relative (geomagnetic) paleointensity (Channell et al., 2006; Channell, Kanamatsu, Sato, Stein, Alvarez-Zarikian, Malone, et al., 2006; Stein et al., 2006), these records will be correlated at scales much smaller than the Milankovitch cycles of eccentricity (100,000 years), obliquity (41,000 years), and precession (23,000 years), which are known to externally govern climate changes. For this specific research program, nine holes were drilled to a depth of several hundred meters below the seafloor at three sites in the central North Atlantic between 40° and 56°N in water depth between 2800 and 3400 meters, using the advanced piston coring (APC) system (Fig. 1; Sites U1312, U1313, and U1314).
At Site U1313 (a reoccupation of the famous DSDP Site 607), for example, an upper Miocene to Holocene sequence of nannofossil ooze with varying amounts of foraminifers and clay- to gravel-sized terrigenous components. The detrital components become much more important and variable in the upper Pliocene-Pleistocene interval of the sequence, as indicated by the magnetic susceptibility record as well as the records of carbonate, natural gamma radiation (NGR), and lightness (L*) from color reflectance measurements (Fig. 2; Channell, Kanamatsu, Sato, Stein, Alvarez-Zarikian, Malone, et al., 2006; Stein et al., 2006), probably reflecting increased Northern Hemisphere ice sheet instability.
Within our own 306 Project Study, we will concentrate on detailed studies of organic carbon and biomarker records as tools for high-resolution reconstruction of sea-ice cover, sea-surface temperature, sea-surface salinity, and sea-surface productivity, to be done within this project. The project is composed of two subprojects especially focussing on two aspects:
(1) The determination of paleosalinity records and their correlation with Heinrich Events and related IRD and meltwater pulses. Within IRD-/Heinrich-type intervals, specific terrigenous biomarkers indicative for IRD sources will be quantified.
(2) The high-resolution reconstruction of biomarker-based paleotemperature and its relationships to environmental change.
Applied methods include elemental analyses (TOC, C/N), Rock-Eval pyrolysis, biomarker studies using GC and GC/MS techniques, and compound-specific stable carbon and hydrogen isotopes.
Fig. 1: Location map of sites drilling during Expeditions 303 and 306.
Fig. 2: (a) A preliminary low-resolution carbonate record of hole U1313A (black) and a high-resolution carbonate record of DSDP Site 607 (orange) (Ruddiman et al., 1989). (b) Linear correlation of logging natural gamma radiation (using HSGR) (black) from hole U1313B and benthic oxygen isotope stack (red) over past 5.3 million years (Lisiecki and Raymo, 2005). The blue-shaded interval between 0.6 and 0.9 Ma marks the Mid-Pleistocene climate shift, where obliquity periodicity transitions from a dominant 41,000-year cycle to a dominant 100,000-year cycle (e.g., Mudelsee and Schulz, 1997). The brown bar marks the occurrence of gravel-sized dropstones (from Stein et al., 2006).
AWI Participants
External collaborators
Jens Grützner (Bremen University)
Members of the 303/306 Science Party
Funding
DFG and AWI
Related Publications
Channell, J.E.T., Sato, T., Kanamatsu, T., Stein, R., Malone, M., Alvarez-Zarikian, C., and the IODP Expeditions 303 and 306 Scientists, 2006. IODP Expeditions 303 and 306 monitor Miocene-Quaternary climate in the North Atlantic. Scientific Drilling 2, 4-10.
Channell, J.E.T., Kanamatsu, T., Sato, T., Stein, R., Alvarez Zarikian, C.A., Malone, M.J., and the Expedition 303/306 Scientists, 2006. Proceedings of the Intergrated Ocean Drilling Program, Vol 303/306 Expeditions Report, North Atlantic Climate, doi: 10.2204/iodp.proc.303306.2006.
Lisiecki, L. E., and M. E. Raymo, 2005. A Pliocene-Pleistocene stack of 57 globally distributed benthic d18O records. Paleoceanography 20, PA1003, doi:10.1029/2004PA001071.
Mudelsee, M., and Schulz, M., 1997. The Mid-Pleistocene climate transition: Onset of 100 ka cycle lags ice-volume build-up by 280 ka. Earth Planet. Sci. Lett. 151, 117–123.
Ruddiman, W. F., Raymo, M.E., Martinson, D.G., Clement, and Backman, J., 1989. Pleistocene evolution: Northern Hemisphere ice sheets and North Atlantic Ocean. Paleoceanography 4(4), 353–412.
Stein, R., Kanamatsu, T., Alvarez-Zarikian, C., S.M. Higgins, Channell, J.E.T., and the IODP Expedition 306 scientists, 2006. Ocean Drilling Expedition Explores North Atlantic Paleoceanography. EOS 87, p. 129, 133.