DFG-Leibniz Center for Surface Process and Climate Studies

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Short-term variability of surface-water characteristics in the Late Neogene North Atlantic Ocean:
A biomarker approach (IODP Leg 303 and 306)

Funding:
Starting date:

Gerald Haug, David Naafs (AWI and Universität Potsdam)

Collaborating researchers (PI’s only)

Ruediger Stein (AWI), Jens Hefter (AWI), Jens Grützner (Bremen University), Members of the 303/306 Science Party

Description

Understanding the mechanisms and causes of 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, Integrated Ocean Drilling Program (IODP) Expeditions 303 and 306 were undertaken to generate a continuous high-resolution chronology spanning the last ~6 million years (late Neogene), using North Atlantic climate proxies collected from ocean sediments.  This study focuses on the usage of organic carbon and biomarkers to reconstruct high-resolution sea surface temperature (SST) and productivity records and their relationships to environmental change in the North Atlantic for the last 6 Myr.

We are especially interested

  1. in the longer-term evolution of the SST during the last 6 Ma,
  2. in the period of onset of major Northern Hemisphere Glaciation between 3.5 and 2.4 Ma, and
  3. in the high-resolution variability during the last about 1 Ma. To reconstruct SST we will make use of the alkenone unsaturation index Uk’37 (e.g., Brassell et al.,1986; Prahl and Wakeham, 1987; Müller et al., 1998; Lawrence et al., 2006), while total alkenone abundance will be used as an indicator for surface productivity (e.g. Villanueva et al. 2001).

Of first priority is the reconstruction of a high resolution (~ 3 kyr) SST and productivity record over the last 6 Myr using samples from Site U1313. Site U1313, a reoccupation of the famous DSDP Site 607, consists of a complete upper Miocene to Holocene sequence and is located on the southern edge of the IRD belt (Ruddiman, 1977), making it ideal to study (sub-) milankovitch climate variability. For certain key intervals (e.g. the mid-Pleistocene climate transition, NHG) even higher resolution (± 0.5 kyr) SST and productivity records will be obtained to identify millennial-scale climate variability. Secondly, for these same key intervals a North-South transect using IODP Site U1313, U1308 and U1314 will be made to reconstruct the position of the polar front (Pflaumann et al., 2003).

Based on our high-resolution study of alkenone SST in sites 1313, 1308 and 1314 (across the LGM Polar Front area), we would like to answer the following five major questions related to long- as well as short-term changes in SST:

  1. Is the long-term SST cooling trend of the Pacific starting near 4.3 Ma (Lawrence et al., 2006) also reflected in the North Atlantic records?
  2. How is the relationship between the onset of major Northern Hemisphere Glaciation and the North Atlantic SST records?
  3. How has the SST gradient between 40 and 60°N (i.e., the location of the Polar Front) changed on long- and short-term time scales?
  4. How does the SST change between glacial and interglacials and on a millennial time scale?
  5. How is the (anti-) phasing between IRD (Heinrich-type) Events and SST? Has it changed during late Neogene-Quaternary times?

 

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